Note: Descriptions are shown in the official language in which they were submitted.
~25897~
TITLE OF THE INVENTION:
OPTICAL RECORDING MEDIUM AND PROCESS FOR PRODUCING
THE SAME
~AL~ D:~o ~ IE TlV NTION: -
The present invention relates to an optical re-
cording medium and a process for producing the same. More
in detail, the present invention relates to an optical re-
cording medium produced by irradiating a laser beam on a
recording layer to heat locally for forming an ablative hole
or a depression in the thus heated part, thereby recording
informations, and to a reliable process for well-reproduc-
tively producing the optical recording medium.
As an optical recording medium produced by ir-
radiating a laser beam to a thin recording layer formed on
a substrate~ thereby for~ing a hole, a depression or a
protuberance thereon, it has been hitherto known to use thin
Te films. Since Te is large in the light absorption coef-
ficient, melts at a low temperature and is low thermal
conductivity, Te shows a high sensitivity in the recording
by the above-mentioned methodO However, there is a problem
that Te films tends to be oxidized rapidly in air, the
degradation of the light absorption efficiency by oxidation
results the degradation of recording sensitivity.
As the medium in which the degradation resistance
~, ~
,
125~3~74
of Te films has been improved, those using an alloy contain-
ing Se other than Te, those using lower oxides of Te, those
using an organic polymer layer in which Te is dispersed,
etc. have been known [for instance, refer to Japanese Patent
Applications ~aid-Open (KOKAI) No. 53-31104(1978), No. 58-
54338(19~3) and No. 57-98394(1982)].
Although, the above-mentioned recording medium is
produced by a vacuum evaporation method or an ion-plating
method, a sputtering method is preferably adopted because
of the favorable controlability during the deposition of
films.
As a result of the present inventors' studies on
the films produced by sputtering of the Te or Te based
materials using pure argon gas, it was found by X-ray dif-
fraction, electron diffraction and the transmission electron
microscopy that the large crystal grains of a size of from
several thousands A to several ~m are observed in the whole
area of these films, and that the flatness, the shape of
pits and the recording sensitivity are poor and a large
amount of noise is generated in a readout signal. In addi-
tion, it has been made clear that the polycrystalline
structure of the deposited films is unstable and accordingly,
since the ref].ectance increases nearly to 1.3 times as
compared to the initial reflectance within 24 hours in the
accelerated test at a temperature of 65C and a relative
,.
. . .
~2~
humidity of 80%, the stability of such a recording medium
in the course of time is extremely poor.
For solving the above-mentioned problem, -there is
a method by which the film of recording layer has non-
crystalline or microcrystalline structure and the tempera-
ture at which the above-mentioned micro-structures are
transformed into the polycrystalline structure of larger
grain size, that is the crystallization temperature, is made
to be higher, thereby stabilizing the micro-structure of the
films at room temperature. Concretely, it may be exemplified
that a thin recording layer of a Te based alloy containing
Ge, Pb, Sn, etc. it used [refer to Japanese Patent Publica-
tion No. 59-35356(1984)].
Furthermore, it is proposed that the same efect
as above is obtained even by dispersing Te in an organic
substance through the reactive sputtering [refer to Japanese
Patent Applications Laid-Open (KOKAI) No. 57-165292(1982)
and No. 57-78394(1982)].
However, even in the produced medium by the above-
mentioned process, the change in reflectance (transmission)
of the medium in the course of time occurs with the change
of the micro-structure and the degradation of the medium by
the long-term irradiation of readout laser light. Namely,
it has been difficult to maintain the micro-structure of
the recording layer in a stable state for a long-time period
~5~3~
in the case of using a Te based alloy films as the recording
layer.
On the other hand, in the optical recording medium
wherein the ablative holes or the depression are formed as
the pits for recording the informations, not only the
recording layer but also the state of the interface between
the recording layer and the substrate or the underlayer is
important as the primary factor which determines the laser
beam power required for forming the pit, namely, the record-
ing sensitivity and the forms of pits.
In order to form the pits in the thin layer of the
recording medium comprising the above-mentioned substrate
and the thin recording layer by the laser beam, it is
necessary that the materials of the recording layer which
is melted locally by laser heating removed from the substrate
while ovércoming the work'of'adh'esion of the film to the
substrate. For the purpose of reducing the adhesion and of
improving the recording sensitivity, a disposition of an
underlayer comprising a thin layer of fluorocarbon polymer
between the recording layer and the substrate has been
examined [refer to Japanese Patent Application Laid-Open
(KOKAI) No. 59-90246(1984)]. The factors contributing to
the adhesion of the films to the substrate are the surface
tensions of the recording layer and the substrates thereof,
the molecular weight and the degree of crosslinking of the
r~ ~
1~58'~37~
surface layer of the substrate, etc. As the work of adhesion
of the recording layer to the substrate is smaller, the pit
can be formed in a shorter pulse width by a smaller laser
beam power; The above-mentioned fact means the improvement
of the recording sensitivity, and therefore the recording
of high speed and the use o a cheap semiconductor laser
diode of a low output power become possible~ However, in
order to perorm a recording of a higher quality, it is
required that the sensitivity is improved but also that not
only recorded pits have sharp and well-defined edges are
uniform.
On the other hand, to the optical recording medium,
it is required that the storage capacity is large, namely
that a recording of high density is possible, in addition
to the above-mentioned specific properties. In order to
improve the storage capacity of the optical recording medium
of the perforating type, it is required that the minimum
size of the pit is as small as possible. In the case where
due to the large heat conductivity of the recording layer,
the region to be melted and removed by irradiation of laser
beam becomes too large and in the case where due to the
smallness of the adhesion of the recording layer to the
underlayer, the amount of the substance to be removed becomes
too large and the size of the pit is apt to be enlarged, and
accordingly ln such a case, high density storage is impossible.
~L~,5~3~7~
Furthermore, in the above-mentioned media, since
there is a tendency that the size of the pit changes
sensitively by the slight chanye of the laser beam power,
the stable and accurate recording of the digital signals is
difficult.
In the case where a thin film of fluorocarbon
polymer is provided as the underlayer, it is relatively easy
to improve the recording sensitivity, however, there still
remains problems concerning the above-mentioned shape and
size of a pit. In Japanese Patent Application Laid-Open
(KOKAI) No. 59-90246(1984), any method for dissolving the
above-mentioned problem concerning the pit shape has not
been given.
Furthermore, in addition to the problem concerning
the above-mentioned pit shape, in the case of recording by
the laser beam of short pulse width or in the case where
the disk is rotated at a high constant angle velocity, since
particularly in the outer region of the disk, the energy
density of the laser beam focused on the unit area of the
surface of the optical recording medium is small, the laser
beam output necessary for forming a pit is larger, an~ the
requirement for the improvement of the sensitivity to the
optical recording medium is more severe than that of the
inner region.
In order to fulfil the above-mentioned requirements,
~ .
~5~37~
the combination of the material of the recording layer and
that of the substrate or the underlayer becomes an extremely
important factor. Namely, in order to shorten the length
of the minimum size of pit, it is desirable that the adhesion
is larger, and on the other hand, in order to improve the
sensitivity, it is desirable that the adhesion is smaller.
In other words, the two requirements which mutually con-
tradict at a glance must be fulfilled. In order to cvercome
the above-mentioned contradiction, for instance, a method
of utilizing an organic compound which decomposes and/or
sublimes at a low temperature while having a high adhesion
(nitrocellulose, guanine and pigments such as phthalocyanine)
may be mentioned (refer to the Proceeding of XXXII Combined
Recture Meeting of Applied Physics, p. 115, Spring in 1985).
However, by such a method, a sufficient sensitivity and
.. . .
stability of the optical recording medium have not necessarily
obtained. Furthermore, the physical properties of these
existing organic compounds (decomposition temperature, sub-
limation temperature and adhesion) are specific to each of
them, and it is impossible to optimize the properties of
those compounds easily and flexibly corresponding to the
combination of the various recording layers and the driving
system.
Moreover, the above-mentioned sublimative pigments
cannot be formed into a thin layer by the sputtering method
~S~397~
and the plasma polymerization method and accordingly the
constitution of a consistent dry process with forming that
of the recording layer while using the sputtering method is
impossible.
As a result of the inventors' further studies, it
has been found that by carrying out a reactive sputtering
in gaseous mixture of a selenium fluoride gas and argon gas
while using an alloy containing Te and Se as a taryet
material, the obtained optical recording medium is excellent
in the recording sensitivity, the pit shape, the smoothness
of the surace of the recording layer thereof, the archival
stability etc. and shows the low readout noise, and based
on the finding, the present invention has been attained.
SUM~1ARY OF THE INVENTION:
In a first aspect of the present invention, there
is provided an optical recording medium for recording
informations by irradiating che optical recording medium
with a laser beam to form a hole or a deformed part thereon,
said optical recording medium comprising a substrate and a
recording layer containing at least Te, Se and F in the
amounts of from 35 to 94.9 atomic% of Te, from 5 to 25 atomic
~ of Se and from 0.l to 40 atomic~ of F, produced by a
reactive sputtering, said Se being derived from selenium
fluoride and a sputtering target of Te or a sputtering target
~ . ... .
37~
comprising Te-Se-alloy.
In a second aspect of the present invention, there
is provided a process for producing an optical recording
medium, comprising the step of carrying out a reactive
sputtering in a gaseous mixture of a selenium fluoride gas
and argon gas while using Te or an alloy con-taining Te and
Se as the target material, thereby forming a deposited layer
containing from 35 to 94.9 atomicP6 of Te, from 5 to 25 atomic%
of Se and from 0.1 to 40 atomic% of F, on a substrate.
The object of the present invention is to provide
an optical recording medium excellent in the recording
performance such as high recording sensitivity, the good
shape of the pit, the uniformaty of the microstructure of
the recording layer thereof, the archival stability, etc.,
since the recording layer is non-crystalline or crystalline
having a microcrystalline structure and an underlayer
comprising a fluorocarbon polymer is disposed between the
recording layer and the substrate, and to provide a reliable
process for producing the above-mentioned optical recording
medium well-reproducibly.
BRI~F DESCRIPTION OF THE DRAWINGS:
Fig. 1 shows a longitudinal cross sectional view
of an e~ample of the optical recording media according to
the present invention, Fig. 2 shows an apparatus for producing
,
~2S8~7~
the optical recording medium according to the present inven-
tion, Fig. 3 shows a pattern of the temperature change to
the transmission of the recording medium obtained in
Example 4, Fig. 4 shows the dependency of the C/N ratio of
the recording medium obtained in Example ll on the recording
laser power and Fig. 5 shows the dependency of the C/N ratio
of the recording medium ob-tained in Example 12 on the record-
ing laser power.
DETAILED DESCRIPTION OF THE INVENTION:
. ~
As a substrate of a recording medium according to
the present invention, a plastic material such as acrylic
resin, polycarbonate resin, etc., a metal such as aluminum,
or glass as well as a material made by applying a thermo-
setting resin or photosetting resin on the above-mentioned
substrate mày be me~tioned. Particularly, the plastic
substrate have a merit of being cheap in price, easy in
processing and excellent in the optical properties.
In the optical signals readout system wherein a
laser beam is irradiated through the transparent substrate
on the recording medium and the reflected light from record-
ing medium is detected as is usually carried out, thereby
carring out the readout of the signals, the birefringence
change of the substrate in the course of time is unfavorable,
because the birefringence of the substrate becomes the
-- 10 --
s ~ .
97~
considerable factor of the fluctuation of the readout light
intensity.
In the recording medium according to the present
inventlon, a cheap plastic substrate is available since the
birefringence change thereof is small, and is stabilized by
annealing the recording medium of a high quality and a high
cost-performance can be offered.
According to the present invention, a recording
layer containing Te, Se and F is deposited onto the above-
mentioned substrate by a reactive sputtering method. Namely,
in the process according to the present invention, the
recording layer containing Te, Se and F is deposited onto
the substrate by providing a glow discharge in a vacuum
chamber into which a gaseous mixture comprising argon gas
and a selenium fluoride gas has been introduced while using
an target material comprising Te or Te and Se, thereby
providing the reactive sputtering.
The thickness of the deposited recording layer made
by sputtering is 150 to 1000 A, preferably 200 to 1000 A.
In the case where the thickness thereof is less than 150 A,
a satisfactory readout signal can not be obtained since a
reflection from the recording layer is low, and in the case
where the thickness thereof is more than 1000 A, the record-
ing sensitivity of the optical recording medium becomes poor.
Te which is a component of the recording layer has
~. .
~ S~3~
been clerived from the target material, and F which is also
a component thereof has been derived from the fluoride gas,
Se which is also a component thereof has been derived from
the target material containing Te and Se or the selenium
fluoride gas.
Conventional RF sputtering or DC sputtering methods
are utilized to carried out the reactive sputtering.
It is necessary to maintain the temperature of the
substrate at a temperature of an extent of from a room
temperature to a sufficient lower temperature than the
softening point of the substrate during deposition, for
instance, at a temperature of an extent of from 40 to 50C,
in the case of using polycarbonate substrate. The above-
mentioned temperature of the substrate is easily achieved
even without cooling the substrate by a conventional magnetron-
sputtering method.
As the target material, Te alone, an alloy com-
prising Te and Se, and an alloy comprising Te and Se as the
main component and further containing Pb, Sb, Sn, In, Ge,
etc. may be exemplified.
In the case where the target made of Te alone is
used, there is a case that the surface of such a target is
oxidized even if the target is preserved in a vacuum, and as
a result, there are cases that the sputtering rate of Te
fluctuates and an abnormal electric discharge is caused.
- 12 -
~5~7~
As the means of removing the oxidized layer on
the surface of a target, pre-sputtering by an inert gas is
generally carried out. However, since the conditions of
electric discharge at the time of carrying out the pre-
sputtering and the time period thereof depend on the oxidized
state of the surface of the target, it is necessary to care-
fully carrying out the pre-sputtering.
sy using the alloy containing Te and Se according
to the present invention as the target, the fluctuation of
the sputtering rate owing to the oxidation of the surface of
the target can be prevented, and as a result, there is an
effect in preventing the fluctuation of the composition of
the deposited films on the above-mentioned reactive sputtering.
The alloy target containing Te and Se is easily
prepared by an ordinary sintering method or melting method.
The deposition of the recording layer of the
optical recording rnedium is carried out by a conventional
sputtering apparatus of radio frequency or direct current
discharge while using the above-mentioned target. The effect
of making the recording medium of Te contain Se is to prevent
the degradation of the recording medium itself by oxidation.
For attaining such an object, in the case of using the alloy
target the content of Se in the target is preferably made
to be from 5 to 30 atomic~. However, since the surface
tenslon of the recording medium at the time of melting thereof
".,
~5~379~
is reduced by containing of Se in the film materials, it is
not favorable to make the target contain Se in an amount
over 30 atomic~ in the case of forming the pits by deforming
the part locally irradiated by a laser beam while utilizing
the surface tension of the film material. Particularly, in
the case where the reduction of the surface tension of the
recording layer hecomes a problem, the amount of Se in the
target is preferably made to be from 1 to 5 atomic%, and
even by such a content of Se, there is an effect in prevent-
ing the oxidation of the surface of the target.
On the other hand, as a method of making the
recording medium contain another element in addition to Te,
Se and F, a method of adding the objective element into
target of Te alone or the alloy target containing Te and Se
may be mentioned. For instance, by addition of Pb, Sb, Sn,
In, Ge, etc. into the target containing Te and Se, if desired,
the specific properties of the medium for recording can be
controlled.
Although Se2F2, SeF4 and SeF6 are mentioned as a
selenium fluoride gas, SeF6 is generally used, and the ratio
of the selenium fluoride gas in the gaseous mixture is
selected in the range of from 0.1 to 50% by volume.
It is preferable that from 35 to 94.9 atomic~ of
Te atoms, from 5 to 25 atomic% of Se atoms and from 0.1 to
40 atomic~ of F atoms are contained in the deposited recording
- 14 -
,
3974
layer. In -the case where other fourth component is contained
in the deposited recording layer, the amount of such a
fourth component is preferably l to 20 atomic%.
In the case where Se is contained in an amount of
less than 5 atomic%, the oxida-tion resistance of the above-
mentioned recording layer is poor and the stability thereof
in the course of time becomes poor. On the other hand, in
the case where the content of Se is more than 25 atomic%,
the energy which is necessary for forming the holes parts
is raised. Namely, the recording sensitivity becomes poor.
In the case where the content of F in the deposited
layer is less than 1 atomic%, the films do no-t take the non-
crystalline structure, and in the case where the content of
F is more than 40 atomic%, the substrate is apt to be damaged
and moreover, the recording sensitivity becomes poor.
It has been confirmed by X-ray and electron beam
diffraction method that the film according to the present
invention takes an uniform non-crystalline structure. In
contrary to the polycrystalline structure of the deposited
layer prepared by a simple vacuum evaporation method or a
sputtering method only with argon gas, the reason why the
deposited film according to the present invention takes a
non-crystalline s-tructure has not necessarily been clear,
however, it is considered that since the molecules of the
reactive gas according to the present invention contain
- 15 -
, . . .
9'7~
fluorine atom(s), fluoride ions, fluorine radicals, and Se
and Te fluorides are formed in the glow discharge plasma,
these fluorides impinge onto the substrate together with
the atoms of Te atom and Se atom, and at the same time,
etching of the glowing surface of the films occur, resulting
in the prevention of the growth of the large grain.
Furthermore, the etching of the surface of the
substrate slightly by the above-mentioned fluoride ions or
fluorine radicals has also an effect of uniformalizing the
adherence between the substrate and the deposited film.
Since in the above-mentioned non-crystalline film,
grains and grain boundaries are almost negligibly small, in
the case where such films are used as the recording medium,
it is possible to uniformize the recording sensitivity and
the shape of pits, and moreover, it is possible to reduce
the readout noise in a low level due to no fluctuation of
the readout light at the time of reading-out of signals by
the laser beam. Accordingly, a high C/N ratio (carrier to
noise ratio) can be obtained.
In addition, due to the fact that the deposited
layer contains Se other than Te, the oxidation-resistance
which cannot be obtained by Te alone can be obtained and the
reflectivity of the above-mentioned recording medlum does
not change at all even after beeing exposed to an accelerated
test for 30 days at a temperature of 70C and at a relative
- 16 -
1~:5~397~
humidity of 85%.
By heating the above-mentioned recording layer to
a suitable temperature, that is, by subjecting the recording
medium to annealing, the micro-structure of the films is
changed and as a result, it is able to increase the stability
of the crystal, the recording sensitivity, the pit form, etc.
in the course of time.
The recording medium before annealing according
to the present invention shows a uniform non-crystalline
structure, and even after the annealing, it shows a stable
polycrystalline structure of grain of less than 1000 A in
the diameter. Particularly, it is possible to make the
grain size to not more than several hundred A, and the
recording medium of the just-mentioned grain size does not
cause any bad influence such as the occurrence of noise to
the readout signal and the disorder of the shape of pits
form at all.
In addition, the non-crystalline structure mentioned
in the present invention means the micro-structure showing
the pattern of the usual X ray diffraction method, in which
~attern any clear crystal line peak cannot be obserbed, and
further means the structure in which so-called micro-crystal-
line of the grain diameter of several tens A are present~
Further, the polycrystalline structure of the grain size of
less than 1000 A means all the micro-structures in which the
- 17 -
^,. :
~'~ S ~ 7 ~
largest grain size is less than 1000 A, and therefore
includes the non-crystalline structure, the microcrystalline
structure, the polycrystalline structure and the hetero-
structure as the mixture of the above-mentioned three struc-
tures~ Such a structure can be confirmed accurately by
observing the transmission image, the diffraction pattern or
the lattice image of the deposited films with a transmission
electron-microscopy.
The annealing may be carried out in a vacuum, a
dried air on a nitrogen atmosphere, however, in order to
maintain the atmosphere in a uniform state t the dxied air
or a nitrogen atmosphere is preferable. The annealing is
carried out in the atmosphere maintained at a temperature of
higher than 60C to less than 130C, preferably 60C to
100C and more preferably 60C to 90C. In the case of using
a plastic substrate, it is preferable that the temperature
of the annealing is sufficiently lower than the softening
point of the plastic substrate, and for instance, a tempera-
ture of lower than 90C is preferable in the case of
annealing a substrate made of a polycarbonate resin.
Although it is necessary to carry out the annealing
until the micro-structure in the film is no more change,
about 10 min is sufficient as the time of the annealing to
the recording medium according to the present invention.
However, in order to remove a garlic-like odor which is
- 18 -
~5~37~
specific -to the Te based recording medium, it is effective
to carry out the annealing for about one hour.
Al-though the annealing may be carried out in
succession after finishing the sputtering at a higher tem-
perature than that during deposition of the films, the
treated substrate is usually taken out once from the sput-
tering vacuum system to be cooled to room temperature and
then subjected to the annealing.
Although the fluorine content in the deposited
film decreases by the anneàling, in order to obtain the
above-mentioned stable and micro-structure after the anneal-
ing, since the fluorine atom effectively terminates dangling
bond of Te, the fluorine content contained in the films is
from 0.1 to 30 atomic% after the annealing. It is preferable
that the above-mentioned fluorine content is from 1 to 20
atomic%, and there is a tendency in which the grain diameter
of the crystals is apt to be larger than 1000 A after the
annealing in the case where the fluorine content is below
0.1 atomic~O. Moreover, in the case where the fluorine
content is more than 30 atomic%, the shapes of pits have
serious irregularities and such a high content is not pref-
erable. Still mor~, in the case where the fluorine content
is more than 20 atomic%, there is a tendency of raising the
crystallization temperature.
It is preferable that the micro-structure in the
19
:~L25~3~
above-mentioned recording layer is sufficiently stabilized
by the annealing at a temperature of from not less than 60C
to less than 100C, particularly at a temperature of not
more than 90C. By controlling the mixing ratio of the
selenium fluoride gas and argon gas, it is possible to
control the amorphous-to-crystalline transition temperature
of the recording medium according to the presen-t invention
within the above-mentioned range.
According to the present invention, it ls possible
to stabilize the birefringence value of the above-mentioned
plastic substrate by carrying out the annealing. Particularly,
in the case of using a plastic substrate in which the
birefringence in the parpendicular direction to the surface
of the substrate after the annealing is not more than 30 nm,
the noise due to the fluctuation of the readout signals
derived from birefringènce in a method of detecting the
readout llght through the substrate is reduced to the
negligible extent.
Although in the recording medium according to the
present invention, the recording layer has been diposited
directly on the substrate as has been described above, it
is also available to provide an underlayer between the
substrate and the recording layer for the purposes of improv-
ing the recording sensitivity and the shape of pits, etc.,
and further, it is available to provide a protective layer
- 20
12~ 7~
on the above-mentioned recording medium for the protection
of the recording medium. Particularly, it is effective to
use an underlayer made of a fluorocarbon polymerO
As the underlayer of a fluorocarbon polymer,
various kind are considered corresponding to the performance
required to the optical recording medium which is to be
obtained.
A dry-process in vacuum is fa~orable for producing
the underlayer from the viewpoint of the uniformity of the
layer, the decrease of pin-holes and the constitution of
in-line process with the recording layer, and in the con-
crete, a plasma polymerized film of a fluorocarbon, a
sputtered film of a polyfluorocarbon, a vacuum evaporated
film of a polyfluorocarbon, etc. is exemplified. As the
fluorocarbon, a perfluoroalkane such as CF4, C2F6, etc., a
perfluoroalkene such as CF3CFCF2, perfluorohexane, per-
fluorobenzene, etc. may be exemplified. Namely, any fluoro-
carbon may be used even if it is a yas or a liquid at normal
temperature, provided that the fluorocarbon has an adequately
high vapour pressure, glow discharge can be sustained in a
vacuum chamber after filling the chamber with the vapour of
the fluorocarbon at a pressure of the order of higher than
10 3~Torr and the fluorocarbon has a high degree of sub-
stitution by fluorine. The~plasma polymerized film of
fluorocarbon can be formed by using the above-mentioned
- 21 ~
r
" ,i .~
~5B97~
fluorocarbon as the monomer and using a capacitively coupled
electric discharge or inductively coupled electric discharge.
Moreover, as another method, the films may be deposited by
the sputtering of polytetrafluoroethylene, copolymer of
tetrafluoroethylene and hexafluoropropylene, copolymer of
tetrafluoroe-thylene and perfluoroalkoxyethylene, etc. in the
gasous region such as argon gas, a gaseous mixture of the
inert gas and the above-mentioned monomer, etc.
Still more, it is available to carry out a vacuum
evaporation, of a polyfluorocarbon, however, deposition rate
of the film is generally slower than the above-mentioned
two methodsO
The thickness of the underlayer of the fluorocarbon
polymer is ordinally 100 to 1000 A.
The above-mentioned underlayer of the fluorocarbon
polymer exerts an influence or the shape of pits, the
presence or absence of remnants in the plts, the recordlng
sensitivity of the recording medium, etc. according to the
condltions of the interfaee between the above-mentioned
underlayer and the recording layer. Aecordingly, an exaet
evaluation coneernlng the eomposition and the structure of
the underlayer surface of the fluoroearbon polymer, and a
eontrol thereof in the manufaeturing step are important.
As an evaluating method, ESCA method (electron
speetroscopy for chemical analysis) whieh can obtain extremely
- 22 -
~ ;25~3~37~
useful i.nformation is exemplified.
Namely, i.n the present inventicn, the composi-tion
and the structure of the underlayer of fluorocarbon polymer
was evaluated by the ESCA method. According to ESCA method,
-the ki.nds of the elements, their composition and the state
of chemical bond:ing in the vicinity of the surface of the
specimen can be analyzed from the energy spectrum of the
photoelectron turned ou-t of the atoms in the compound of the
specimen by the irradiation of soft x-ray.
In the present invention, the spectrum of the
fluorine lS orbital (FlS) and the spectrum of the carbon lS
orbital (Cls) on the surface of the thin film of fluorocarbon
polymer before forming the recording layer thereon were
determined while using the ESCA spectrometer of the type of
"XSAM-800" trademark made by SPECTROS Company. The spectrum
FlS consists of a single peak having the center in the
vicinity of 688 eV of binding energy, and the Cls spectrum
consists of several peaks having the centers in the region of
from 285 to 294 eV of binding energy. The peaks concerning
the -CF3 group and the >CF2 groups can be discriminated
particularly clearly from the other bi.nding states. In the
present invention, the peaks concerning the CF3 group and
the > CF2 groups may be identified by comparison with
reference chemical shifts according to the method disclosed
in literature (D.T. Clark and D. Shut-tleworth, J. Poly. Sci.,
18(80) page
- 23 -
,
~5~397~
27; K. Nakajima, A.T. sell and M~ Shen, J. Appl. Poly. Sci.,
23(79) page 2627, etc.), the ratio of each integral peak
area intensity to the whole integral intensity of C1s is
calculated and the thus calculated ratios were made to be
"-CF3/C" and ">CF2/C". Namely, "~CF3/C" is the ratio of
carbon atoms forming the -CF3 groups to total carbon atoms
and ">CF2/C" is the ratio of carbon atoms forming the >CF2
groups to total carbon atoms. Furthermore, the ratio of
the number of fluorine atoms to the number of carbon atoms
can be calculated from the peak area ratio of Cls to FlS.
The relationship between the composition and the
structure of the obtained underlayer of fluorocarbon polymer
by the above-mentioned method and the specific properties of
the optical recording medium, and furthermore the controlling
method of the composition and the structure thereof are
explained as follows. Then, it is easily to select the most
suitable composition and structure of the underlayer of the
fluorocarbon polymer along each kind of the recording layer
containing Te, Se and F.
Namely, the relationship between the composition
of the underlayer of fluorocarbon polymer and the specific
property as the optical recording medium are primarily due
to the ratio (F/C) of the number of fluorine atoms to the
number of carbon atoms in the surface of the underlayer
which contacts to the recording layer.
- 24 -
~5~39~4
In the case where the F/C ratio is less than 0.9,
the effec-t of the lmprovement of the sensitivity is scarcely
observed as compared to the case where the recording layer
is deposited directly on the polycarbonate substrate. With
the increase of the F/C ratio from 0.9, the power of the
laser beam necessary for recording decreases monotonously,
namely, the recording sensitivity is improved. The above-
mentioned improvement of the recording sensitivity is
saturated in the F/C ratio of not less than 1.4.
Further, in the case where the F/C ratio is not
less than 1.4, there are no remnants in the pits and the
uniform pits having smooth and well-defined rim are formed
without according to the difference of the process for
producing the underlayer and of the detailed morphology of
the underlayer surface, and a high C/N ratio (Carrier to
Noise Ratio) can be attained. Accordingly, it is suitable
for offering an optical recording medium particularly high
in the sensitivity and the C/N ratio to make the F/C ratio
not less than 1.4.
However, in the case where the F/C ratio is more
than 1.8, since the adhesion between the recording layer
and the underlayer deteriorates, there is a tendency that
the minimum size of the pits is apt to be enlarged in the
case of forming the pits by the same laser power as compared
to the case where the F/C ratio is not more than 1.8.
- 25 -
397~1
Namely, there is a limit of carrying out the recording of
high density.
In order to perform the high density recordiny,
it is necessary to make the size of the pi-ts to be small,
and for that purpose, it is necessary to increase the work
of adhesion between the recording layer and the underlayer
to an extent. In the case where the F/C ratio is not less
than 1.4, the adhesion is nearly constant and there is no
effect of improving. By making the F/C ratio to be less
than 104, the adhesion increase and it is possible to make
the size of the pits small. Accordingly, by making the F/C
ratio of not less than 0.9 to less than 1.4, the recording
of high density can be attained while improving the recording
sensitivity. However, in the case where the F/C ratio is
not less than 0.9 to less than 1.4, there are cases where
the remnants remain in the pits and the shapes of the rim
reveal irregularities under conditions on preparing the layer
of fluorocarbon polymer, and there are cases where a high
C/N ratio can not be obtained in the case where the F/C
ratio is not less than 1.4 cannot be obtained, however, the
C/N ratio in case of the F/C ratio of not less than 0.9 to
less than 1.4 is superior to that in case of using no under-
layer.
In order to overcome the above-mentioned problems
concerning the dlsorder of the pit shape, it is necessary to
- 26 -
97~
control not only the composition ratio of fluorine atom to
carbon atom in the layer o~ fluorocarbon polymer but also
the structure of the layer. Namely, the purpose is attained,
in the Cls spectrum obtained by the ESCA method, by control-
ling the composition of the underlayer so that not less
than 18 atomic% of the total carbon atoms construct the
-CF3 groups and from not less than 18 to less than 40 atomic%
of the total carbon atoms construct the >CF2 groups.
In the case where the amount of the >CF2 group is
too small, the sensitivity is poor, and on the other hand,
in the case where the amount thereof is too large, the size
of the pits becomes too large. Namely, the above-mentioned
these media are not suitable for the recording of high
density. In addition, in the case where the amount of the
-CF3 group is too small, remnants remain in the pits and
the pit shape reveal irregularities. Since the irregularities
are detected as the noise, the C/N ratio (Carrier to Noise
Ratio) is low.
Although a particularly favorable pit shape and
accordingly, a remarkable improving effect of the C/N ratlo
is obtained by applying the above-mentioned conditions to
the thin underlayer of fluorocarbon polymer, particularly,
of the F/C ratio of from not less than 0.4 to less than 1.4.
An lmprovement of the C/N ratio can be obtained, although
in a some degree, by applying the above-mentioned conditions
- 27 -
. . .
37~
to the case where the F/C ratio is not less than 1.4 and not
more than 1.8.
Since the above-mentioned ratio (F/C) of fluorine
atom to carbon atom and the construction concerning the
rate of >CF2 and -CF3 control the interface of the underlayer
of fluorocarbon polymer, which contacts to the recording
layer, it is enough that only the surface region of the
underlayer of fluorocarbon polymer, which contacts to the
recording layer, has the above-mentioned composition, and
it is not necessary to make the whole underlayer of fluoro-
carbon polymer have the above-mentioned composition.
In the case of making the composition and structure
of the underlayer comprising a thin layer of fluorocarbon
polymer most suitable according to the above-mentioned results,
it is necessary to take care of the combination of several
recording layers and the combination with the driving system
which effects the recording and readout. The thin layer of
fluorocarbon polymer can be optimized flexibly by only
changing the raw materials such as the gaseous monomer, the
~puttering target etc. or by controlling the discharge
conditions even in the case of using the same apparatus for
fabricating the layer.
Furthermore, the capacitively coupled plasma
polymerization can be actualized by only exchanging the
target of the sputtering apparatus taking the parallel
- 28 -
. ,
~5~7~
electrode structure with the material which is not subjected
to sputtering such as stainless s-teel, and in the same
sputtering apparatus, the plasma polymerization of a mono-
meric fluorocarbon and the sputtering of polyfluorocarbon
can be carrled out. The above-mentioned method has a merit
of having a large for selecting the process for production
and the raw material. Furthermore, it is also easy to
construct an in-line process including the process for
preparing the recording layer by the reactive sputtering
method.
The method for controlling the composition and
structure of the thin underlayer of fluorocarbon will be
explained in detail as follows.
The sputtering of polyfluorocarbon (tetrafluoro-
ethylene polymer, copolymer of tetrafluoroethylene and
hexafluoropropylene, copolymer of tetrafluoroethylene and
perfluoroalkoxyethylene, etc.) is carried out by introducing
argon gas under a pressure of from 5 x 10 3 to 1 x 10 Torr
between the parallel electrodes and applying an electric
field of a radio frequency thereon.
The plasma polymerization of a fluorocarbon
(tetrafluoroethylene, hexafluoropropylene, etc.) is carried
out by introducing a monomeric fluorocarbon under a pressure
of from 5 x 10 3 to 1 x 10 2 Torr also between the parallel
electrodes and applying an electric field of a radio fre-
quency thereon.
- 29 -
~L~S~97~
Also, the vacuum evaporation may be carried out
by an electric resistance heating method. The F/C ratio in
the surface layer of fluorocarbon polymer obtained by using
a capacitively coupled plasma polymerization appar~tus
depends on the monomeric gas, the form of the apparatus,
the conditions of electric discharge and particularly, on
the discharge power and the pressure of the gaseous monomer,
and as the F/C ratio, those in the range of from 0.2 to 1.5
are easily available. In the surface of fluorocarbon polymer
layer obtained by sputtering, the F/C ratio is easily
available in the range of from 1.1 to 1.8.
In order to make the ratio of the n~ber of
fluorine atoms to that of carbon atoms in the surface of the
above-mentioned underlayer, which contacts to the recording
layer, to be not less than 0.9, the radicals such as -CF3,
>CF2, etc. are made to be generated in numbers as large as
possible and made to impinge onto the glowing surface of
the films. Or else, there is a method by which the growing
surface of the thin layer of fluorocarbon polymer, which has
once adhered to the substrate, is made not to be e~posed to
high ënergy particles (electrons and ions) in the plasma as
far as possible.
Concretely, in the sputtering method, it is pref-
erable that F/C ratio of the target material is raised, the
distance between the electrodes is also separated and the
- 30 -
~'~5~397~
power of the electrical discharge is raised to increase the
deposition rate of the layer of fluorocarbon polymer.
Still more, F/C ratio can be raised also by mixing
a monomeric fluorocarbon such as CF4, C2F6, etc. with the
inert gas such as argon gas, etc. which is used in the
sputtering~ Furthermore, F/C ratio can be raised by raising
F/C ratio of the evaporated polyfluorocarbon in the vacuum
evaporation method.
On the other hand, in the plasma polymerization
method by the inductively coupled electric discharge, the
substrate is established while avoiding the internal part
of the coil, wherein the density of the plasma is high, and
in the plasma polymerization method by the capacitively
coupled electric discharge, the distance between the parallel
electrodes is separated and the substrate is established on
one of the electrodes, preferably on the electrode in the
earth side.
Also, the rate of the >CF2 group and the -CF3 group
can be relatively increased by using a lower electric power
of discharge, a higher pressure of the gaseous substance
and a higher flow rate of the gaseous substance.
The ratio of the number of fluorine atoms to that
of carbon atoms in the underlayer of fluorocarbon polymer,
which contacts to the recording layer, is 0.9 to 1.8, and
further not less than 18 atomic% of the total carbon atoms
- 31 -
397~
are preferably made -to constitute the -CF3 group and further,
from not less than 18 atomic% to less than 40 atomic% of
the total carbon atoms are preferably made to constitute the
>CF2 group. Namely, it is necessary to control the fine
structure thereof shown by ESCA spectrum.
For this purpose, it is available that the struc-
tures of the plasma polymerized layer of fluorocarbon and
the sputtered layer of fluorocarbon polymer reflect those
of the gaseous monomer and the target material to a certain
extent. In the case where the -CF3 groups are contained in
a large amount in the gaseous monomer or in the case where
the -CF3 groups are rich in the radicals and the ions
generated in the plasma, the -CF3 groups are apt to be taken
into the polymerized layer. For instance, in the case of
using hexafluoropropylene as the monomer, it is possible to
raise the rate o~ the -CF3 groups in the polymerized layer
to a higher extent than in the case of using tetrafluoro-
ethylene as the monomer. Moreover, by mixing carbon tetra-
fluoride with tetra~luoroethylene, the content of the -CF3
group in the polymerized layer can be raised also. Still
more, there is a tendency that a large amount of the >CF2
groups are contained in a deposited layer made from monomer
gas containing the unsaturated bond. The layer deposited by
sputtering of polytetrafluoroethylene also reflects the
structure of the target and contains the ~CF2 group in a
- 32 -
, . . .
5~9t7f~
large amount, however, the ratio of the -CE3 group can be
raised also by carrying out the reactive sputtering with a
gaseous mixture obtained by mixing hexafluoropropylene or
carbon tetrafluoride with argon gas.
Eor example, to the plasma polymerized layer of
hexafluoropropylene according to the presen-t invention, a
structure which fulfills the requisites of the present
invention has been obtained in the conditions of the pressure
of 5 x 10 3 to 1 x 10 2 Torr, the flow rate of the gas of
300 to 500 cc/min (determined by capillary-type flow meter
set up for argon gas) and the electric power of discharge
in the range of from 100 to 200 W.
However, in the plasma polymerization and the
sputtering method, it is well known that the electric dis-
charge conditions depend on the shape and perfo.rmances of
the using apparatus (size and shape of the vacuum chamber,
vent property, introducing method of the reactive gas, and
shape, size and structure of the electrodes). Accordingly,
in the above-mentioned description and Examples, concrete
values of a gas pressure at the electric discharge, flow
rate, electric discharge power, etc. are to be optimalized
according to indi~idual apparatus, and the present invention
is not limited by the above-mentioned concrete values.
Further, in the case of using the apparatus having the same
shape, size, structure and performances, it is easily to have
- 33 -
97~
reproducibility.
In the present invention, a layer of chlorofluoro-
carbon polymer may be used as the underlayer. In such a
case, it is preferable to have the layer wherein the ratio
of the number of fluorine atoms to that of carbon atoms in
the surface of the underlayer, which contacts to the record-
ing layer, is 0.9 to 1.4 and it contains chlorine in an
extent of from 5 to 15 atomic%.
The thin layer of chlorofluorocarbon is available
by the sputtering of polychlorotrifluoroethylene, the re-
active sputtering of polytetrafluoroethylene in a gaseous
mixture of argon gas and a chlorofluorocarbon gas such as
FRON 113 (CC12F - CClF2) or the plasma treatment by chloro-
fluorocarbon of the surface of the deposited layer by
sputtering of polytetrafluoroethylene. Furthermore, the
thin layer of chlorofluorocarbon is available by carrying
out plasma polymerization whi~e using the chlorofluorocarbon
gas as the monomer. The thic~ness of the above-mentioned
layer is generally from 20 to 1000 A.
In the above-mentioned thin layer of fluorocarbon
polymer containing chlorine atoms, since the chlorine atom
terminates dangling bonds of the carbon atoms in the same
manner as in the càse of fluorine atoms, the crosslinking of
carbon atoms has been hindered and accordingly, the layer
has a structure low in the crosslinking degree. Consequently,
- 34 -
1~5~397~
it is considered that the resistance in the case of removing
the melted substances in the recording layer becomes small.
On the other hand, since chlorine atom, in contrast with
fluorine atom, has an effect on increasing the surface
tension of high polymeric substances, the adhesion itself
is raised to a considerable extent. In order to evaluate
the adhesion of the recording layer to the underlayer
according to the present invention by using a simple peeling
method, it has been confirmed that the adhesion of the
underlayer containing chlorine atoms is several times as
large as that of the underlayer not containing chlorine atom,
while both underlayers having the same ratio of F/C.
However, in the case where chlorine atoms are
contained more than 15 atomic~, the adhesion thereof is
reduced on the contrary.
. In the case of the present invention, it is enough
that the composition of the surface of the underlayer, which
contacts to the recording layer, is made to be the above-
mentioned composition and it is not necessary to make the
composition of the whole ~mderlayer to be the above-mentioned
composition.
By subjecting the thus obtained underlayer of
fluorocarbon polymer to a plasma treatment by an inert gas
before forming the recording layer on the underlayer, the
adhesion can be improved, the shortest pit length is shortened
- 35 -
.
.
:'
37~
and on the other hand, the hlgh sensitivity and the improve-
ment of the shape of pit can be achieved.
In the case where the plasma treatment is utilized
and the recording layer is an alloy containing Te and Se,
it is more favorable to treat the layer of fluorocarbon
polymer so that the ratio of the number of fluorine atoms to
the number of carbon atoms in the surface of the layer of
fluorocarbon polymer, which contacts to the recording layer,
is from 1.0 to 1.2.
Due to the coming off of fluorine atoms, the surface
tension of the surface of the layer of fluorocarbon polymer
becomes larger, and moreover, due to the crosslinking of
carbon atoms, the density and the molecular weight of the
crosslinked layer in the surface of the layer of fluorocarbon
polymer are raised.
Every one of the above-mentioned changes of the
surface layer has an effect of raising the adhesion between
the recording layer and the underlayer. The thickness and
the degree of crosslinking of the above-mentioned surface
layer can be controlled by the condition of plasma discharge,
particularly by the power of discharge and the time period
of exposure to the plasma and the distance between the
substrate and the electrode, and as a result, it is possible
to control and adhesion of the recording layer to the under-
layer broadly and to set each kind of the recording layer
in the optimum state.
- 36 -
1~5~
The above-mentioned effect of the plasma treatment
of the surface of the thin layer of fluorocarbon polymer has
been confirmed as follows.
At first, a sputtered layer of polytetrafluoro-
ethylene (PTFE) was prepared, and the layer was subjected
to the plasma treatment by argon plasma under a pressure of
5 x 10 3 Torr at a discharge power of 100 W, and thereafter
the contact angle of the layer and the atomic ratio (F/C)
of fluorine atom to carbon atom within 10 nm from the
surface of the layer were measured according to the ESCA
method. The determination of the atomic ratio (F/C) by the
ESCA method was carried out as that described before.
It has been confirmed that the contact angle and
F/C ratio were reduced with the increase of the time period
of the treatment. On the other hand, in the case where a
recording layer of TeSe-SeF6 series was formed on the plasma
treated ~mderlayer of fluorocarbon polymer, and the adhesion
was measured by the simple peeling method, it was foun.d that
the adhesion was increased by several times as compared to
the adhesion measured before subjecting the layer to the
treatment.
In the following, the improving effect in the
recording and reading-out property of the optical informations
storage medium according to the present invention will be
described in detail while referring to the non-limitative
Examples.
.. .
, . .;:
~5~7~
EXAMPLE 1:
Fig. 2 shows one example of the apparata for pro-
ducing the medium for optlcal recording medium according to
the present invention by the reactive sputtering method.
In Fig. 2, (5) is a vacuum chamber, (6) are cathode
and anode electrodes, (7) is a target of an alloy containing
Te and Se, (8) is a substrate, (9) is a gas inlet, (10) is a
shutter and (11) is an exhaust gas outlet.
At first, the vacuum chamber (5) was evacuated to
the back pressure of the order of 10 6 Torr and then, argon
gas was introduced into the chamber ~5) from the gas inlet (9)
to raise the inner pressure of the chamber (5) to 5 x 10 3
Torr. A radio frequency voltage at 13.56 MHz was continuously
applied between the electrodes (6) to cause glow discharge,
and the above-mentioned state was kept for about 10 min to
clean the surface of the target (7). Thereafter, the inner
space of the chamber (5) was evacuated again to the extent of
10 6 Torr, and a gaseous mixture of 90% by volume of argon and
10~ by volume of gaseous SeF6 was introduced into the chamber
(5) from the gas inlet (9) to make the total pressure to
5 x 10 3 Torr. Thereafter, by applying a radio frequency
voltage of 50 W at 13.56 MHz between the anodic electrode (6)
on the side of the substrate and the cathodic electrode (6)
on th~ side of the target (7), thereby a glow discharge was
caused for carrying out the sputtering. As the target, an
alloy of 88 atomic % of Te and 12 atomic % of Se was used, and
- 38 -
~5~7~
a sputtered layer of 40 nm in thickness was deposited on the
substrate. The content of Se in the thus deposited layer was
15 atomic %, and the content of fluorine atom therein was 20
atomic %. Thereafter, the recording and reading-out were
carried out on the thus produced optical recording medium by
a semiconductor laser diode of wave length of 830 nm (pulse
width of 500 n sec). A sensitivity of 4mW and a C/N ratio
(Carrier to noise ratio) of 52 d~ were obtained.
EXAMPLE_ :
After evacuating a vacuum chamber to 3 x 10 Torr,
argon gas was introduced to a pressure of 1 x lO 2 Torr, and
by causing a glow discharge at lO0 W of a high frequency
electric power of 13.56 MHz, a sputtered layer (F/C ratio of
1.6) of about 150 A was made to deposite on a substrate of
polycarbonate resin. Thereafter, the electrode of the side
of the substrate was moved to right over the alloy target made
of 88% of Te and 12% of Se, and after carrying out pre-
sputtering, SeF6 gas was introduced into the chamber in a
volume ratio of 10% to make the total pressure in the chamber
to 5 x lO Torr~ Thereafter, by applying a radio frequency
~oltage of 50 W at 13.56 MHz between the electrode on the side
of the substrate and the electrode on the side of the target,
thereby a glow discharge was caused for carrying out the
sputtering. A sputtering layer of 40 nm in thickness ~as
deposited on the substrate. The content of Se in the thus
deposited layer was 15 atomic ~, and the content of fluorine
- 39 -
1~5~3~74
atom therein was 20 atomic %.
After that, on carrying out the recording and the
reading-out on the thus fabricated optical recording medium
by a semiconductor laser diode of a wave length of 830 nm
(pulse width of 500 n sec), a C/N ratio of 57 dB was obtained.
The recording sensitivity was 2.~ mW.
Fig. 1 shows a longitudinal cross sectional view of
the thus obtained optical recording medium. In Fig. 1, (1)
is a substrate, (2) is an underlayer, (3) is a recording layer
and (4) is a channel for track-servo.
EXAMPLE 3:
By flowing 50 cc/min of monomeric tetrafluoroethylene
(determined by capillary-type flow meter set up for argon gas)
and 15 cc/m of argon gas through a mass-flow controller which
had been calibrated to argon, the vacuum chamber was filled
with the reactive gas at total pressure of 5 x 10 Torr. To
a capacitively coupled radio frequency voltage had been used,
a radio frequency voltage of 13.56 MHz was applied to cause
a glow discharge for 5 min at a discharge power of 100 W,
thereby forming a plasma polymerized layer (F/C ratio of 1.1)
of a thickness of about 150 A. After that, in the same manner
as in Example 2, a deposited layer of Te, Se and F was formed
in a thickness of about 40 nm.
Thereafter, on carrying out the recording and
reading-out on the thus produced optical recording medium
in the same manner as in Example 2, a C/N ratio of 56 dB was
- 40 -
'3-~
obtained. The recording sensitivity was 3.4 mW.
COMPARATIVE E~AMPLE 1:
Af-ter evacuating a vacuum chamber to 3 x 10 6 Torr,
argon gas was introduced into the vacuum chamber and a glow
discharge was caused between the substrate and the target by
a radio frequency voltage of 50 W at 13.56 MHz ~
As the target, an alloy of 85 atomic % of Te and
15 atomic ~ of Se was used, and a Te-Se deposite layer of
400 A in thickness was formed on the substrate. On carrying
out a recording-reading-out test by a semiconductor la~er
diode on the thus obtained optical recording medium, the C/N
ratio was 45 dB. The recording sensitivity was 4.5 mW.
There were local irregularity of recording sensitivity.
Moreover, in the case of forming a deposited layer
of Te and Se by sputtering only with argon gas on the under-
layer comprising a sputtered layer of fluorocarbon polymer
formed in the same manner as in Example 2, the C/N ratio was
only 45 dB~ In addition, the recording sensitivity was 4 mW.
EXAMPLES 4 to 6, COMPARATIVE EXAMPLES 2 and 3:
The vacuum chamber was evacuated to the extent of
10 6 Torr, and then SeF6 gas to argon gas was introduced
thereinto at a flow ratio shown in Table l, and by applying
a high frequency voltage between the electrodes in the same
manner as in Example l, an electric discharge was caused.
The discharge power and the pressure within the
vacuum chamber were the same as shown in Table l. Further,
- 41 -
.. .
., .
~5~397~
glass substrates of a thickness of 12 mm were used. The
thickness of each of the deposited layer by sputtering was
from 300 to 400 A. The fluorine content (shown by atomic %)
of the layer after annealing was the same as that shown in
Table 1. In order to evaluate the annealing temperature
necessary for stabilizing the crystal structure of the
deposited layer by sputtering, the dependencies of the
transmission of recording layer on temperature were measured.
As an example of the pattern of the temperature change of the
transmission, the pattern of a specimen of Example 4 in Table
1 in the case of raising a temperature at 13C/min is shown
in Fig. 3. It has been confirmed by the X-ray and electron
beam diffraction and the transmission electron microscopic
image that the rapid change of the transmissivity in the narrow
temperature range as that shown in Fig. 3 is due to the change
of micro-structure of the layer, that is, the growth of the
crystalline and then the saturation of reflectivity means
stabilization on the micro-structure. Table 1 shows the
temperature at which the transmission changes, that is, the
crystallization temperature of the layer (corresponding to the
point on the dotted line of Fig. 3) in the case of raising a
temperature at 13C/min and the maximum value of the grain
size after crystallization.
The medium for recording of Examples 4 and 5 and
Comparative Example 2 and 3 was formed on the disk-shaped
substrate of polycarbonate resin, wherein a hexafluoropropylene
- 42 -
~ ;25~3~374
polymer as an underlayer was formed on the disk-shaped
substrate of polycarbonate resin, and the change of the
specific properties of the disk was examined before and
after annealing, which was carried out in the air at 80C
for one hour.
With the formation of the polycrystalline by the
annealing, the reflectivity of the medium for recording
became about 1.1 times of the initial value, and the thus
raised value was stabilized at that level. By the above-
mentioned procedure, it was possible to raise the intensity
of carrier signals without increasing the noise of the readout
signal.
In Examples 4 to 5, a stabilized and uniform micro-
structure was formed by annealing, and it does not give any
unfavorable effects such as noises in the readout signal.
Further, there was no local irregularity of the sensitivity
and the uniform pits were formed. As a result, an improve-
ment of from 2 to 3 dB of C/N ratio (carrier to noise ratio)
was effected.
As comparative examples 2 and 3, the case where the
selenium fluoride gas was not used and the case where carbon
disulfide gas instead of a selenium fluoride gas were shown.
In the cases of Comparative Examples 2 and 3, since the grain
size thereof was large, the noise of the readout signal was
high and the shape of the pits was also irregular.
- 43 -
~2 ~3~3~
As are seen in -the above-mentioned Examples, the
grain size of the polycrystalline of the recording medium
according to the present invention was externally small, and
it was possible to control the crystallization temperature,
particularly to not less than 90C.
Further, the optical specific properties were quite
stable in the accelerated test at 65C and 80% RH. Also, on
examining the change in quality of the recording medium due
to the repeated irradiation on the same track by the readout
light, the degradation in quality of the medium before
annealing began by the power of readout laser beam of 1.3 mW
and the accurate readout was impossible, however, on the
other hand, the quality of the medium was quite stable after
the annealing.
Accordingly, it was clearly seen that the stabiliza-
tion of the micro-structure of the recording medium had been
sufficiently attained by the annealing.
In Example 6, the annealing at a temperature of not
less than 90C was necessary in order to obtain the same
effect as above, and such medium was not suitable for use of
the substrate of polycarbonate resin, wherein a hexafluoro-
propylene polymer as an underlayer was formed on the disk-
shaped substrate of polycarbonate resin.
- 44 -
1~5~
Z^ ~ '
In U~ In ~ U~
C~
.
o o
_ o o o o o
o~ o o o o o
a~ o In U~ O Ln
~ N ~1 ~`I
V V V 11 V
.~ ,_ I ~:
r~ o
~1~ o o o 0 a~l o
O O co cn ~ ~ ~ h ~d co
U) rl ~ a) -1 ~n ~ o o
~ ~ E~ S~ ~1 N ~1 ~:
C) N ~) ~ C,) ~1 ~ ,a
_ _
a)
O
. .
Lf U~
~0 0 ,_1 t'`l
04~ 00\o
'1 ~ - _
S-l ~ l l l l
tl7 ~ h O o o O o
a~ 5-, o ~1 ~t ~1 ~, ,_,
S~ X X X X X
P~ U~-- U~ U~ U~ ~ Lr
_ .
~^
,1 ~3
1:~1 t~ o o o o o
~ ~ 5~ o o o o Ln
U~ ~ ~ ~ r~
a Q.
.__ ~ . .. ~ . ,
3 ~ ~ a) ~ g ~ :
o ~ a) ~ ~I ~ ~ ~ r~
~ ~ ~ O
1~ h ~ 7 u~ Lt~ ~ o In
. . _ _
I
t) C) ~D ~D
~n E4 ~ ~ I
a) a) u~
U~ Cl~ U~ C.)
_ . o _ . ,
rl 4
u~ O ~J a) a
O ~ U~ U~
o oo
O S~ ~ a~
o,l ~ a~
J ~ I i
a) ~ I d) I
~1 ~ ~ 5~ ~ 5
a) ~ ~ a
Z ~ ~ ~ ~ ~:~ Ei ~ ~ ~
X X X O.IJ X 0~ X
C~ ~a ~ C) ~ ~
_ _
_ 45 _
;,~
:
t37~
EXAMPLES 7 to lO and COMPARAI'IVE EXAMPL~S 4 to 8:
Each of several underlayers of fluo.rocarbon polymer
shown in Table 2 was provided on a substrate (130 mm in dia-
meter and 1.2 mm in thickness) of pol~carbonate resin by the
sputtering method or the plasma polymerization method~
The sputtering by the fluorocarbon polymer (tetra-
fluoroethylene resin, copolymer of tetrafluoroethylene and
hexafluoropropylene or copolymer of tetrafluoroethylene and
perfluoroalkoxyethylene) was carried out by introducing argon
gas under a pressure range of from 5 x 10 to l x lO Torr
between the parallel electrodes and applying a radio fre-
quency voltage of from 50 to 200 W at 13.56 MHz.
The plasma polymerization of the fluorocarbon
(tetrafluoroethylene or hexafluoropropylene) was carried out
by also introducing the gaseous monomer under a pressure
range of from 5 x 10 3 to 1 x 10 2 Torr between the parallel
electrodes and applying a radio frequency voltage of from
100 to 600 W at 13.56 MHz.
The reactive sputtering was carried out on the
underlayer while using an alloy target con3isting of 88% of
Te and 12% of Se and introducing SeF6 gas and argon gas in
the same manner as in Example 1, thereby a recording layer
of a thickness of about 400 A was formed. (The composition
of the thus obtained layers is the same as that of Example l)
- 46 -
~2~397~
F/C, CF3/C, CF2/C, the presence or absence of the
remnants in -the pits and the recording sensitivity of the
thus obtained recording media were measured, the results
being shown in Table 2.
- 47 -
~25~397
o~ I
~1 X ~ m ~r o ~r
Z~ ~ ~ ~ u~ ~n
\ ~ ~ 5
_
O rl .V ~ Lr~
X ~ ~ ~ ~ .
.
...._._
~: ~ ~ O O
S:
~,1 Q, . . .
\
~ ~ o~ ~o
_ __
C~
~1
~1
I . _ . . ._ _ ___
E~ ~ u~ er ~ ~
~ ,i ,i ~ ~
. _ .. ___ ~ ~ .
a) a) ~: ~
e ~ a) e ~^
. ~ ~0 ~ ~o ~3
O O ~:4 O ~X O
~ ~ a) ~ p~c o ~ o O
.,1O ~ ~ ~ 0~ ~ O~X~
~~ 5) ~ o ~ o a) ~ ~ t) a) ~
S~ ~1 3 Q 3 O O O ~ ~H
O~1 ~ ~:) (~ 4~ h ~ o ~ ~1 0 0
41O ~1 ~ o O O O O O O h
~1 ~~ O a) ~ ~ ~ ~ o~ a)
~0 t~ o O ~ 40 ~ ~ ~ 3
,,~ O ~ e ,~ ~ x h ~
a~ ~ ~ s I o ~ o ~ a~ ~ a)--
~3 ~ u~ 3 ~ $s~ 3 ~$
,io ~ O ~ ~ O
::~Q. S~ ~ o ~ ~ ~ 4
u~ ~ cn o ~_ u~ O
a) h ,_1 ~1 ~i
O e~r~ ~ e
Z ~X 0'~ ~X X
~ C) ~ ~ F~
.. . __ . . __
_ 48 ~
- - - - -
x ~ m
z ~ r~
~_ o o co
. _ ..
O ~,q.V ~ ~r ~r ~ ~ o
~r
~ .. __
~ a) u~l ~ u~ O ~ u~
~s~ ~ ~ ~ ~o
4 .
O A O ~`1 li ) ~ l
~I
~ ~ In ~1 ~1 ~
~ I _ . .__ .. . .
E~ ~ ~ ~ ~ ~ ~ I
~ ~ ~1 O ~
_ _ .
~ 0 ~ 0 ~ 0 ~ ~
a ~ ~ ~ E ~ 51 ~:
E o ~ ~ ~ o O ,~ O
X ~ 0 ~ .~
O ,~ ~ e ~ a) ~n ~ ~ o
.c: ~ ~ ~ 30 ~ ~ o ~ 30 ~ ~ X S
~:)P~ ~0 ~ P~ ~0 ~4 S ~ P~ Q S S 5
_ _
h ~1 ~ ~ ~1 ~1
X e0 o 0 ~D ~ X S~ 0~
_ u 0 ~ ~ C) ~ ~ U (a Ç~
-- 49 --
5~t~
~ he recording and reading-out was carried out by
a semiconductor laser beam while using the above-mentioned
optical recording medium prepared on a disk-shaped substrate
of polycarbonate resin of 130 mm in diameter. The power of
the laser beam necessary for writing was taken as the
recording sensitivity. In addition, the shapes of the thus
formed pits were obser~ed by a scanning electron microscopy
(SEM) and the presence or absence of the remnants in the pit.
In the case where the remnants were absent, the rim
of the pit was well-defined without any irregularity and the
C/N ratio of the optical recording medium was improved by a
few dB as compared to the case where the remnants were
present.
EXAMPLE 11:
By carrying out a sputtering on a disk-shaped
substrate (diameter of 130 mm and thickness of 1.2 mm) of
polycarbonate resin while using polychlorotrifluoroethylene
as the target under a pressure of argon gas of 1 x 10 2 Torr
at discharge power of 100 W, an underlayer of a thickness of
about 150 A was formed. On measuring the composition of the
surface of the thus formed underlayer by the ESCA method,
the ratio of the number of fluorine atoms to the number of
carbon atoms was l.l and the underlayer contained 12 atomic%
of chlorine.
By sputtering Te88Sel2 as the recording layer on
the thus formed underlayer in a gaseous mixture of argon
-- 50 --
~2~74
and SeF6, a medium of TeSe-SeF6 series (consisting of 15
atomic% of Se, 20 atomic % of F and the balance of Te and
having a thickness of 400 A) was prepared. On the thus
prepared optical recording medium, the evaluation of the
writing and reading-out properties was carried out under the
following conditions.
Namely, the disk-shaped substrate was rotated at
1800 rpm, and the recording and reading-out were carried out
on the tracks of the radius of about 30 mm from the rotating
axis by a semiconductor laser diode of a wave length of 830 nm.
The recording was carried out by a pulse light of 1.0 MHz and
duty of 50 %.
The dependency of C/N ratio (carrier to noise ratio)
on the recording power is shown in Fig. 4 (a). The C/N ratio
was larger than 55 dB and showed a stable specific property
within a broad range of the recording power. On carrying out
the SEM observation, any remnant could scarcely be found in
the pits.
COMPARATIVE EXAMPLE 9:
, In Fig. 4, (b) and (c) respectively show the de-
pendency of C/N ratio on the recording power in the cases of
forming the same recording layer as in Example 2 on the
underlayer of polytetrafluororethylene by sputtering wherein
the ratio of the number of fluorine atoms to the number of
carbon atoms was 1.5 [in the case of (b)] and 1.25 [in the
case of (c)]. Also in Fig. 4, (d) shows the case where the
recording layer was directly formed on the substrate of
polycarbonate without using an underlayer.
~5~397~
Further, (e) in Fig. 4 shows the case wherein a
reactive sputtering of polychlorotrifluoroethylene was carried
out in a gaseous mixture of argon gas and CC12F-CClF2 to form
a layer in which the ratio of the number of fluorine a-toms to
the number of carbon atoms was 0.85 and which contains 19
atomic % of chlorine, as the underlayer.
In the case of (b) wherein the ratio of the number
of fluorine atoms to the number of carbon atoms was high, if
the content of chlorine was too large as in the case of (e),
the C/N ratio is rapidly reduced with the increase of the
recording power. It has been understood as the result of the
SEM observation that the above-mentioned fact is due to the
rapid increase of pit size with the increase of the recording
power. On the other hand, although the pit size is stable in
the cases of (c) and (d), the amount of the remnants in the
pits was large and there was much irregularity in the shape
of the pits and accordingly, only a low C/N ratio was obtained
in a wide range of recording power.
EXAMPLE 12.
.
A sputtering of polytetrafluoroethylene (PTFE) was
carried out under a pressure of argon gas of 1 x 10 Torr
and at a discharge power of 200 W to form a thin layer of a
thickness of about 200 A on a disk-shaped substrate of poly-
carbonate resin. Thereafter, the thus prepared material was
subjected to plasma treatment under a pressure of argon gas
of 5 x 10 3 Torr at a discharge power of 50W for 30 sec.
- 52 -
~L~5~97~
On the above-mentioned underlayer which had been
treated, as a comparison the underlayer which had not been
treated and the substrate without having any underlayer,
reactive sputtering of Te88Sel2 was carried out in a gaseous
mixture of SeF6 and argon gas, thereby forming a thin layer
of a thickness of about 400 A which contains Te and Se in
the same manner as Example 1.
Eig. 5 shows the dependency of C/N ratio on the
recording power. ~n Fig. 5, al shows the case of the
underlayer which has not been treated in the plasma, bl shows
the case of the plasma treated underlayer and cl shows the
case of without having the underlayer. The sensitivity of
the medium bl was more improved than the sensitivity of the
medium cl, and on the other hand, C/N ratio of the medium of
bl was larger than C/N ratio of the medium of al by from
2 to 3 dB, and the dependency of C/N ratio of the medium of
bl on the recording power is smaller than that of the medium
of al. It was found as the result of observation of SEM
that the above-mentioned facts were due to the relatively
slight increase of the pit size in the medium of bl in
contrast to the rapid increase of the pit size in the medium
of al with the increase of the recording power.
Furthermore, the amount of the remnants in the pits
was smaller in bl than in cl, and a uniform rim was formed
bl .
- 53 ~
~5~ 7~
The plasma treating conditions for obtaining the
optimized property as bl can be decided by the ESCA method.
Namely, it is desirable to decide the treating
conditions and the treating time period so that the ratio
of the number of fluorine atoms to the number of carbon
atoms in the layer within 10 nm from the treated surface is
from 1.0 to 1.2.
E~AMPLE 13:
A substrate of polymethyl methacrylate resin (PMMA)
or polycarbonate resin (PC) which had been preliminarily
washed was set in a vacuum room, and after evacuating to
about 1 x 10 5 Torr, 20 cc/min of argon (determined by
capillary-type flow meter) and 5 cc/min of SeF6 (determined
by capillary-type flow meter set up for argon) were introduced
into the room to raise the inner pressure thereof to about
5 x 10 3 Torr. As a target material, Te was used. On
carrying out the reactive sputtering while using a high
frequency power of 50 W for 15 sec between the electrodes of
a distance of 80 mm, a deposited layer of about 250 A in
thickness was obtained.
In the case of recording the thus obtained layer
(recording layer) by using a semiconductor laser diode of an
output of 4 mW at 830 nm, on recording the layer deposited
on the PMMA substrate, the pits were formed by the pulse
width of 200 nsec, and on the layer deposited on the PC
substrate, the pits were formed by the pulse width of 250 nsec.
- 54 -
~ .
~Z5~97~
Further, after preserving the thus prepared
specimens in an accelerating atmosphere of 60C and 80% RH
for one month, the light reflectivity (in the extent of 30~)
at 830 nm did not show any change before and after the
acceleration.
- 55 -
