Note: Descriptions are shown in the official language in which they were submitted.
,rl
IN ~HE UNITED STATES PATENT AND ~RADEMARR OFFICE
APPLICATION FO~ PATENT
InYentors: Jesse D. Wol~e
~braham ~elkind
Ronald E. Laird
s This application i8 a con~inuation-in-part o~
Serial No. 522,266, filed ~ay 10, 1990, ~nd has a ~ommon
assignee.
~ackqxou~d Q~_~hQ Inven~ion
This ~nvention relates generally to visibly
transparent infrared reflecting interference filters,
and more particularly, to a durable low-emissivity
filter.
The use of transparent panels in buildings,
~ehicles and other structures ~or controlling solar
radiation i8 quite prevalent today. The goal of ~olar
control is to transmit liqht while excluding much of the
solar energy, thus decreasing the ~mount of air
condition or cooling required, and conserving energy.
In nddition, modified glass as ~ ~tructural ~aterial
prov$de~ the color flexibility architects desire.
Various process0s have been employed to ~lter
the optical propert~e~ of these panels, lncl~ding
coating glas~ or plastic ~ubstrates by various
techniques such as electrolysi~, ~hemical vapor
deposition and physical vapor deposition, including
~putterin~ with planar ~agnetrons. For instance, thin
metal films have ~een deposited on glass or plastic to
increase the reflectance of ~olar radiation. Windows
deposited with a multi-layer dielectric-metal-dielectric
2 ~
coating that exhibits h$gh visible transmittance, ~nd
high reflectivity and low ~missivity in the infrared
ran~e, are ~ven Dora energy ~fficient. The index of
refraction of the dielectr~c layer i8 prefer~bly 2.0 or
greater in order to minimize the visible reflectance and
~nhance the visible tr~nsmittance o~ the window. This
dielectric layer which often con~ists o~ ~etal oxide
coating also offers additional protection to the fragile
metal ~l~s. The optical properties o~ panels can also
be modified by altering the composition o~ the substr~te
~aterial. Nevertheless, ~nter~erence ~ilter panels
manufactured by the above-described methods have ~een
only partially successful in reflecting ~olar radiation
to the degree required ~or signi~icant energy
lS conservation. For example, Apfel et ~1., U.S. Patent
3,682,528, issued August 8, 1972, described an ~nfra-red
interference filter with visible light transmission of
only approximately 72% and with ~n~ra-red transmission
of approximat~ly 8%.
..
Summary_Qf the Invention
It is a primary object of the present
invention to provide a durable, thin-~ilm $nterference
f~lter which transmits v~sible light while reflecting
infrared radiation.
It i~ another ob~ect o~ the present invention
to provide an inter~erance ~lter that i8 userul in
~rchitectural panels which give~ l~ss reflected color of
visible light over ~ wide band.
~hese and additional objects ~re accomplished
by the present invention which provides a durable, thin-
$ilm interference ~ilter which comprises a substrate
onto which is deposited a dielectric layer, followed by
~etal nnd dielectric layers. In between each of the
dielectric and ~etal layers is deposited a "nucleation"
or glue layer that promotes adhesion between the
3 1
dielectric to the metal. In one pre~erred e~bodimen~ of
the invention, the interference filter comprises a glass
6ubstrate onto which is depo~ited a thin-film desiqn
consisting of ~ive layers, n~ely: titaniuD oxide,
nickel-chromiu~ alloy, ~ilver, nickel-chromium alloy,
and ~ilicon nitride.
Another pre~erred ~mbodiment of the
~nter~erence filter comprises of a ~ive layer ~tructure
where$n on~ or both Or the dielectric layers is for~ed
of a composite material containing zirconium nitride and
silicon nitride. It was found that mixing zircGnium
nitride with silicon nitride create~ a composite layer
that has a high refractive index ~nd excellent
tr~nsparency in the vlsible region. Moreover, ~e
optical properties o~ thi3 co~posite l~yer ~an be
~djusted by varying the rel~tiv~ amounts of zirconium
nitrid~ and ~ilicon ~itride.
The dielectric layers of the inventive
inter~erences ~ilters can ~e reactively ~puttered by a
rotatable cylindrical ~agnetron. Composite layers can
be formed by cosputtering from dual cathode targets or
~ro~ one or ~ore alloy targets. A feature of the
inventive process i8 that by reducing the intrinsic
6tress o~ the ~econd dielectric layer, an extremely hard
and chemically resi~tant thin fil~ coating is produced.
In sputtering illcon nitride a~ the second dielectric
layer, lt wa~ de~onstrated that the intrinsic stre~s o~
this layer can be reduced by orienting tbe ~agnetic
assembly of the cathode at an ncute angle v~s~ is the
substrate.
Additional ob~ects, ~dvantages and features of
the present invention will become apparent from the
~ollowing det~iled exemplary description, wbich
description should be taken in conjunction with the
accompanying drawings.
Brie~_Pescription of the Drawinqs
- Figure la is a cross-sect~onal view of a five
layer design thin-f~ nterference ilter produced in
accordance wit~ t~is invention.
Figure lb is ~ graph illustrating the spectral
transmittancs ~nd ~eflectanco o~ ~ thin-fil~
interferencQ ~ilter.
Figure 2 i3 ~ cross-sectional view of
~athode asse~bly.
Figure 3 ~8 a graph illustr~ting the spectral
tr nsmission ~n the visible light region for a composite
rilm.
Figure 4 i~ a graph illustrating the spectral
reflection in tha visible light reg~on for a compos~te
~llm.
Figure 5 is a graph illustrating the spectral
adsorption in the visible light region for a composite
~ilm.
~esc~ipti~n of the Preferred Embodiments
~0 A thin-film interference filter incorporat$ng
the present invent~on is hown in Figure la. As shown
therein, the filter consists o~ a transparent substrate
2 which i provided with two planar parallel surfaces 4
and 6, ~n which ~urface 4 ~ exposed to the medium ~nd
~urface 6 i8 coated. The sub~trate c~n be formed of any
6ultabla transparent material; however, the substrate is
preferably a ~aterial which ~as ~uperior ~tructural
properties and ~in~mum absorpt~on in the visible and
~ear-infrared ~pectra regi~ns where the solar energy $s
concentrated. Crystalline quartz, fused silica, soda-
lime silicate glass, and plastics 6uch as polycarbonates
and ~crylates, are ~11 preferre~ substrate materials.
Depos~ted onto the ubstrate surface 6 is a
first dielectric layer 8 that is preferably made of a
material having an index of refraction of greater than
,d ~
about 2.0, and most preferably between 2.4 and 2.7.
Suitable dielectric layer material~ include metal oxides
such as titanium oxide, tln oxidQ, zinc oxide, indium
oxide (optionally doped with tin oxide), bismuth oxide,
and zirconium oxide. See Hart, U.S. Patent 4,462,883,
issued July 31, 1~84, Which i~ ineorporated herein by
ref~rence. Yet another ~uita~le ~aterial ~ sil~con
n$trlde. A particularly su~table dielectrio material
compri6es a thin composite ~ilm containing zirconium
nitride ~nd ~ilicon nitride (collectively referred to
herein as ~SiZrN") that i~ fabricated by cosputtering
from dual targets or from a ~ingle alloy target of ~ dc
cylindrical magnetro~, as described herein.
Zirconium nitride is an electrically
conductiv~ material which ~as very good optical
reflectance in the infrared 6pectru~; however, this
materi~ very absorbing in the visible portion of the
Qpectrum and cannot be u~ed on device~ requiring high
transparency. Silicon nitride, on the other hand, is
very transparent ln the near W through the near IR
spectrum (350 nm, 2.0 microns). It was discovered that
~ixing z~rconium nitride with the ~ilicon nitride
creates a composite film that has ~ high index of
refraction (22.10) and excellent transparency in the
vis~ble ~pectrum. ~h~ film also demonstr~tes good
chemic~l and mechanical ~urability. FurtherDore, by
employing co~puttering with dual cathode targets, the
~ndex of refraction of the film can be adjusted by
vsrying the ~mount of power to c~ch cathode ~nd/or the
gases used in the process. The index of refraction of
the film 80 fabricated ranges ~rom approximately 2.00 to
2.45.
Besides SiZrN, composite fil~s comprising
titanium nitride and silicon nitride (collectively
3S re~erred to ~erein as "SiTiN") or comprising hafnium
nitride and ~ilicon nitride (collectively referred to
2 ~ 3 3 ~
herein ~ "SiHfN~) can ~l~o be used. SiTiN and SiHfN
composite films ~re ~160 prepared by cosputtering from
dual or ~ingle targets. Finally, ~ composite film
comprising ~ mixtur~ of silicon nitride, zirconium
nitride, titanium nitride, and/or hafniu~ nitride can be
used ~s th~ first dielectric layer. As ~ill be
descri~ed further below, th~ re~racti~ index o~ She
composite film~ will VAry depending on the relative
amounts of th~ di~ferent nitrides that comprise each
film.
It has been found ~hat when 8ili~0n nitride i8
used a~ the first dielectric layer, the visible light
transmission of the inventive filtQr is slightly less
than the trans~ission when titan~u~ oxide or a composite
fil~ is used.
~ he th~ckness of the rirst dielectric layer
ranges from approximately 200 to 500 A, and more
preferably ~rom approximately 300 to 350 ~
A3 shown in Fig. la, the inventi~e ~ilter next
comprises of a ~irst metal precoat 10 that is deposited
over t~e first dielectric layer. Precoat layer 10 ~8
preferably maintained a~ thin AS possible ~o that it
will have very little, lf nny, ~dver~e effect upon the
optical characteri tics of the ~lter or the ~ubseguent
metal layer. Pr~coat layer3 with thicknesses ranging
rrom approxi~ately 5 to 20 A h~ve been 6atisfactory;
~ore prefer~bly, the thickness 1~ between approximately
8 to 16 A. Thi~ thin precoat layer can be formed ~rom
any number of ~etals. It has been gound that nickel-
chromium alloy comprising ~pproximately 1 to 80 percent~ickel and approxi~ately 1 to 20 percent chromium can be
used ~s a precoat; more preferably, the alloy content is
- approxi~ately 80 percent nicXel and 20 percent chromiuffl.
Other metals and alloys thereof that can be used as a
preooat include nickel, chromiu~, rhodium, platinum,
tung~ten, molybdenum, and tantalum. See Hart, U.S.
r~
Patent 4,462,883, issued July 31, 1984. The precoat
layer apparently acts a~ a glue or nucleat~on layer and
as a stress reducing l~yer. It is believed that while
the precoat layer is thin enough not to adversely affect
th~ optical propertieC Or the ~ilter, it causes the
metal.~ 12 :t~ behAve. a~ -if ~t werc a homogeneous
~e~aL.sl~b~
Next, a partially x~flective metal layer 12 is
deposited onto the first precoat layer. ~he metal layer
reflects infrared-radiation, yet ~llows for ~uficient
visible light tra~s~ission. ~hc metal layer can be
formed fro~ ~ number of ~aterials, with ~ilver being
particularly ~atlsfactory. Other ~etal~ which also ca~
~.util~zed: include gold, copper and platinum. The
thickness of the metal layer ranges from approximately
40 to l5o A, and more preferably, from approximately 90
to llo ~.
In ~hi~ preferred embodi~ent, ~ 6econd ~etal
precoat layer 14 i8 then deposited onto the metal layer
which i~ followed by the ~inal dielectric layer 16.
Thi~ second metal precoat layer can be ~ormed from the
same material and ~n the ~ame thicknesR range as precoat
layer 10. ~he second dielectric layer can be made of
~ilicon nitrid2 that i8 ~ormed by reactive sputtering a
cylindrical magnetron. This layer has a thickness from
~pproximately 350 to 500 A, and moro prefera~ly from
approximately 4so to 475 A. The above re~erenced
composite films can also be used although the relative
proportion o~ ~ilicon nitr~de ~n each film is ad~usted
30 fiO that the re~r~ctive index ranges preferably ~rom
~pproxi~ately 2.04 to 2.10. When a composite film is
used, its thickness should be from approximately 300 to
500 A, preferably 350 to 375 ~. However, whether
~ilicon nitride or a composite substance is used as the
second dielectric layer, the layer ~ost preferably
exhibits low intrinsic stress as described further
2i~`?3~
~elow. A suitable composite f ilm is SiZrN comprising
~pproximately 80-83% by weight silicon nitride ~nd the
balance zlrconiu~ nitride. This particulAr ~ilm has a
refr~ctlv~ index o~ approxiBately 1. 85 to 2.2. A
preferred SiZrN composite ~il~ has 2 refractivQ index o~
about 2.08. A3 will be described below, the inventive
~ilters offer excellent ~echanical and corrosion
resistance.
- T~e precoat ~nd ~etal layers were deposited
with ~ D.C. planar ~agnetron. Other technigues
including E-beam evaporation could have also been
employed. The dielectric layers of the inventive filter
~ere prep~red by DC-re~ctive Eputtering with a rotating
~ylindrical DagnetrOn- The ~agnetron reactive
~puttering technique iB particularly useful for
depo~iting dielectric films. While there are other
technigues for depositing the dielectric layers ~uch as
thermal oxidation and LPCVD (low pr~ssure chemical vapor
deposition), these method3 ~uffer fro~, a~ong other
things, 810w depos$tion rates. Moreover, RF planar
~agnetron 6puttering ~or depositing dielectric material
~6 impr~Gtical for l~rge-scale industrial applications
bec~use o~ the enormous power reguire~ents and RF
radi~tion hazards. A description of n cylindrical
magnetron suitable for deposit~ng eubstrates with th~
di~lectric ~ateri~ 8 ~ound ln Wolfe et ~1., U.S.
Patent S,047,131, i~sued Septomber 10, 1991,
incorporated herein by reference. To provide additional
protection to the lnventive filter, a plastic laminate
can be applied to the filter of Fig. la. See Young et
al., U.S. P~tent 4,965,121, issued October 23, 1990
incorporated herein by reference.
In ~abricating the lnventive filter, it was
~ound that by reducing the intrinsic ~tress of the
~econd dielectric layer 16~ an extremely hard and
che~ically resistant thin ~ilm coating is produced.
Stress i8 an important Yariable that i8 inherent in each
layer of ~- thin film stac~. There are generally two
stres~ states; ~1). compressive, where the film i~
tryi~g to ~xpand on th~ substrate ~nd, ~2) tensile,
S where the.film ~.trying to contract. In ~a~netron
~yste~s, the pressure o~:the vacuum depositing chamber
i8 ~n impQrt~nt ~ctor which influences stress. It is
beli~ed that ~t ~ufficiently low pres~ures, sputtered
atoms and reflected neutral gas ~toms lmpinge on the
film at nearly normal ~ncidence with high energy because
at lower pressure thers are ~ewer.collisions within the
plasma (larger ~ean fre~ path). This mechanism, as
reported by Hoffman and ~horton in Thin solid F~lms, ~0,
3~5 ~1977), ~ ~nown aS ~atomic peening", ~nd is
lS believed to cause compression i~ ~ilms.
At higher worX~ng pressures, the sputtered
atoms collide with atoms in the plas~a more frequently.
Sputtered mater~al reache~ the ~ubstrate at oblique
~ncidence and with lower energies. The decrease in
~inetic energy of t~e ~ncident atoms ~akes the peening
~echanism inoperative. The decrease in the ~lux o~
atoms ~rriving at normal incidence results in
"shadowing~ -- voids remaining from the nucleation cta~e
of ~ilm growth are not filled ~ecause nucleation ~ites
2~ shadow the obliguely ~rriving atoms. Shadowing and
'competinq ~one growth~ can lead to isolated columnar
grain ~tructures and ~n extensive void network. Messier
and Yehoda, ~. Appl. Phys., 58, 3739 ~1985).
- Whatever the cause o~ internal ~tress in
~puttered fil~s, there ~5~ ~or a given set of system
parameters (e.g., ~agnetro~ geometry, deposit~on rate,
film thickness, gas pressure), ~n abrupt transition from
co~pression to tension at a critical pressure which
depends on the ~tomic ~a~s of the material. (Hoffman
and Thorton, Thin Solid Films, 45, 387 (1977); Hoffman
and Thorton, J. Vac~ Sci. Technol., 20, 35~ ~1982);
~ ~ S ~
i
Hoffman and T~orton, J. Yac. Sc~. Technol., 17, 380
(1980).) Above thi8 critical pressure, tensile stresses
gradually decrease to zero. The relaxat~on o~ 8tre5s
beyond some ~axi~um tensil~ ~tres5 point was reported
for chromium sputtered $n argon and molybdenu~ sputtered
~n- xenon- Shl~ ~t al. f ~Propertie8- of Cr-N Films
Produced by Reactivo Sputtering~, ~. V~c. Sc~. Technol.
A4 (3), May/JunQ 1986, 564-567.
In depositing ~ilicon nitride as the second
lQ dielectric layer wi~h a rotatable cylindrical magnetron,
it was found that the intrinC$~ stress of the ailicon
nitride layer can be reduced by orienting the magnetic
asse~bly of the ca~hode ~t an acute angle. As shown in
Fig. 2, w~ich ~ a cross-~ectional view of cathode 20
and gubstrate 21, the maynetic assembly 18 has a "Wl~
conf~guration with three elongated magnetics 24, 26, and
28. The permanent magnetics used ~ormed an unbalanced
system which i6 typical for rotatable cylindrical
magnetrons. As is ~pparent, the assembly is oriented at
an acute angle ~-o~ ~pproximately 45 ~o as to direct
sputtere~ ~aterial tow~rds the substrate 29 as it enters
the deposit~on chamber. ~ngle ~ can range from
approxi~ately 30 to 80. Silicon nitride layers ~o
deposited have ~pproximately one-fourth the intrinsic
~tress of ~ilicon nitride layer~ produced when tha
aBaembly 15 ~t ~ nor~al ~ngle r~latlve to th~ ~ub~trate.
Experimental Re~ul~
- A low-e~issiv~ty interference filter having
the ~tructure ~5 shown in Fig. la compri~ing a glass
~ub~trate, a titaniu~ oxide first dielectric layer,
nickel-chromium alloy precoat layers, a silver ~etal
layer, and a 6ilicon nitride 6econd dielectric layer was
~abricated ~n an in-line magnetron system manufactured
by Airco Coating Technology, a division of Assignee. It
is known that Tio2 ~s the predominant form o~ titanium
oxide created i~ the 6puttering process. However, it iB
believed that other forms are produced a~ well. Thus,
unless ot~erwise stated, TiO2 will represent all forms
o~ titanium oxide produced. The system comprises of
S five magnetron~ arran~ed in series, with each ~agnetron
depositing one o~ the ~iv~ layers of the filter. The
~econd, third, and ~ourtb are planar magnetrons for
depo~iting th~ first precoat, ~etal, and second precoat
layer~ respectively. The planar magnetrons, each
comprising of a ~odel HRC-3000 unit, were manufactured
by Airco Coating Technology. The first and fifth
magnetrons are cylindrical ~agnetrons to dep~sit the
dielectric layers. The cylindrical magnetrons, each
comprised of a C-Mag~ model 3000 cathode, also
manufactured by Airco Coating Technology.
The target ~8) for each of the cylindrical
magnetrons was conditioned using an inert ga,
thereafter the process ga~ was added until the desired
partial pressure was reached. The process was operated
at that point until the process was stabilized. The
substrate was then ~ntroduced to the coat zone of the
first cylindrical ~agnetron and the fil~ was applied.
The substrate used wa~ soda lime glass.
Fcr depositing ~ ~irst dielectric layer
comprising o~ titanium oxide, a C-MAG~- rotatable
~agnetron employing a titanium target was used.
Alternatively, ~ planar magnetron can be employed.
Argon was the inert gas and oxygen was the reactant gas.
When depositing ~ilicon nitride in the cylindrical
magnetron, ~rgon was used as an inert gas ~nd nitrogen
was used as the reactant gas. The partial pressure of
the gas was determined ~y the transition fro~ the
nitride mode to the metallic ~ode. Experiments were run
as close to that transition as practicable. The
pressure and flow rate of the sputtering gases were
controlled by conventional devices.
Becaus~ the electrical conductivity of pure
~ilicon i8 80 low that it $~ unsultable for ~puttering
with direct current, the ~ con target was impregnated
or doped with a ~mall amount o~ aluminum in the range of
from 2-4%. Th~ tarqet was prepared by plas~a 6pray.
The sputtering source wa~ connected to ~n appropr~ate
direct curr~nt po~er ~ource ~aving provision for au~o-
~atically malnt~inlng t~e voltage, current or power, as
desired. The ~agnet assembly o~ the single cathode was
oriented at ~n angle of approximately 45~ from nor~al.
With nitrogen a~ the 6puttering ~as, the
coating ~ontained a ~ixture Or ~luminum and ~ilicon
nitrides. All of these ~o~ponents are relatively hard
and form an ~morphou fil~ that acts as a strong
barrier. However, the amount of aluminum in the film
did not interfere with for~ation of the desired silicon
based compound film~. In the course of the experiments,
films were sent out for independent RBS (Rutherford
Back-Scattering) 6ampling to determine the composition
of the compound. The ~ilicon nitride ~easured 42%
Si/57% N, which ~s very close to the theoretical 3:4
ratio for nitride (Si3N~).
Table 1 ~ets forth the process datA for
deposition of ~n inventive filter.
~A~E_1
Flo~- ~lo~- Sub
Th~ck- r-t~ rrte rot- ~ot-n- Pres- trrte
~. ~sca) ssc~) tsca~ tlal Po~r ur- ~o. S~
r ~ tV~ (kl~) tu~ Passes t1n/~nin~
T~02 32r71 0 131 -371 ~0 1.5 ~ r
lI~Cr ~2 1700 0 -U~ 1 3.0 1 15~
A~100 i9 0 0 -552 10 1.5 1 156
3 0II~Cr lZ 1700 O -~4 1 3.0 1 154
5~3N4 Ul 12~0 0 -38r 15~J~2) 5.0 2 31
~ ~ ~?~
The abov~ filter had th~ following optical and
electr$cal characteristics:
82.4 % Transmittance (integrated ~65 ~ource)
6.1 % Reflectanc~ of the film co~ered side
511.5 % Absorbanc~
- - 10.5 n/0 Electric~l ~heet resistance
O.09: E~i siv~ty
The dur~bility o~ thQ inventivQ filter of
Table 1 was tested. The procedures of the chemical and
mechanical tests that were performed are described in
Table 2. The ~nventive fllter passed ~11 the tests.
Curve 1 ~n Fig. lb illustrates the reflectance
of the interferance fllter produc~d under the parameters
set forth in Table 1 as ~ro~ thQ ~ ide. Curve 3 is
the reflectance of the uncoated 6ubstrate slde and curve
S is the transmittance. The measurement~ were performed
with a scanning spectrophotometer.
Test Conditions and Scorina Procedures
~. HuDidity Test Exposures in a humidity cabinet
for: (1) 24 hrs. at 90C and 98% RH
and (23 96 hrs. ~t 60C and 98% RH.
2. Salt ~og Test 20% Salt Fog, 9S-98F for 72 hrs.
3. W Exposure Expo~ure ~or 24 ~r~. with cycles
Test o~ 4 hrs. ~ondensation until
failur~ or 120 hrs.
4. Ammonium Test Samples Are placed upright in
closed container of 50% a D onium
hydroxide solution at room
temperature for 5 hrs.
S. Salt Dot Test A 1% ~alt ~olution is applied to a
filter paper dot placed on the film
with the sample placed in a con-
~tant humidity environment for 24
hrs.
; 5 3 r~
Evaluations o~ the above tests are based on both ~icro-
scopic ~valuation and amissivity measurements. The
detail~ o~ thQ evaluations are:
A. Sample~ ~r~ ~cored for evidence o~ micro-
fiCOpiC eorrosion as seen under 200x magni-
fication on a scale o~ 1 to 10, where 10 is
unaffected and 1 ~8 completely corroded.
B. Measure the change ~n ~missivity due to
corrosion. ~he s~oring i8 based on:
Emissivity Score - 10 (Emi~s. ~e~ore/~miss. ~fter)
C. Recorded scores are an average of 1 and 2
6. Taber Abrasion Samples are subjected to a total o~
SO revolutions on the Taber
abrader, using the standard 500
gra~ weight and CS-lOP wheels.
.
Evaluation is based on the average number of ~cratches
seen under 50x magnification in 4 inch2 areas. Using
the equation below gives a score of o for more than 55
~cratches ~n a ~" ~guare area and 10 for none:
Taber Score ~ 10 - tt~ ~cratches) x ~0.18~]
A~ ~tated above, in other embodiments o~ the
inventive f~lter, one or both o~ the dielectric layers
can comprise of composite ~ilms o~ elther SiZrN, SiTiN,
SiHfN, or mixtures thereof. For each composite, the
relative ~mount o~ ~ilicon nitride ranges from
~pproximat~ly 60-95% by weight depending on whether the
compositQ io used as t~ ~$rst or second dielectric
layer. The index of re~ract~on of the composite ~ilm
correspondingly ranges from approximately 2.4 (60%
silicon nitride) to zpproximately 2.05 (95% silicon
nitride).
One method of depositing composite films is
cosputtering of a cylindrical ~agnetron employing dual
targets with one target being made of silicon ~nd the
other target being made o~ oither zirconium, titanium,
hafnium, or mixtures thereo~. When cosputtering ~ith
dual cathodes with nitrogen ~5 th2 reactant gas, the
angle of th8 ~agnetic assembly of ~ach target can be
~djusted to get ho~ogeneou~ ~omposition distribution.
See Belkind et ~1., U.S. Patent Application Serial No.
~71,360, filad March 19, 1991, of common assignee, and
Belkind et Al., ~Reactiv~ Co-Sputtering of Oxides and
Nitrides using a C-MAG~ Rotabable Cylindrical Cathode,~
Surface ~nd Coating Technology, ~9 (1991), 155-160.
Another ~ethod of depositing composite films
to have one or more ~lloy targetY, ~ach coated with
~ilicon and either zirconium, titanium, hafnium, or a
mixture thereof. A process for fabricating cylindrical
alloy targets involves doping silicon and another metal
(or other metals) to form a conductive silicide. For
instance, doping ~ilicon ~nd zirconium results in
forming ZrSi2, a conductive cilicide that possesse~ a
bulk resistivity oP ~pproximately 160 micro ohm am.
~his material i~ conductive enough to be sputtered ~y a
magnetron. The silicide can ~e synthesized by heating
zirconiu~ and 3ilicon together (hot press technique) to
a sufficient temperature to form ZnSi2. Thereafter, the
sili~ide i~ grounded to a powder and sprayed onto 8
~tainles~ ~teel backing tube to form a ~omogeneous
coating.
ZnSiN compositQ fllms were formed by ~o-
sputtering a C-MAG rotatable magnetron ~ystem
~anufactured by Airco Coating ~echnology. The system
employed dual cathode targets wherein the angle the
magnetic assembly o~ each target was 6et at approxi-
mately 45~ relative to normal ~o ~s to focus the ZrN and
Si3N~ ~olecul~s onto the glass 6ubstrates. It is
believed that ZrN is the predomin~nt form of zirconium
nitride created in the sputtering process, although
other forms may be produced as well. Thus, unless
otherwise ~tated, ZrN will represent all forms o~
zirconium nitride ~uttered.
- With dual target~, tho relative amounts o~
reactively ~puttered material deposited frc~ each target
can be regulated, in.partj ~y-ad~usting th~ power to
e~ch target. Employin~ thi~ technique, three di~ferent
ZrSiN co~posit~ films were depo~ited.~. The first ~ilm
comprised o~ approximat~ly 60% Si~N~ and 40~ ZrN (60/40),
the second comprised of approxi~ately 72% si~N~ and 28%
Zr~, and the third comprised of approximately 83% Si3N~
and 17% ZrN (83/17).
- Curves 30 and 32 ~n F~g. 3 illustrate the
percentage transmission in the visible llght region for
fil~s one-(60/40) ~nd three ~83~17), respectively;
15curves 40 and 42 in Fig. 4 illustrate the percentage
re~lection in the visible light region for f~lms one
(60/40) and three ~3/17), respect~vely; and curves 50
and 52 in Fig. 5 illustrate the percentage absorption
for films one (60/50) ~nd three (83/1~), respectively.
20Table-3 sets forth the refractlve index (n)
and extinction ccefficient (~) values versus wavelength
or the first composite film (6~ Si3N~, 40% ZrN),
~nd Table 4 ~ets forth the optical values versus
wavelength for the second composite film (72% Si3N~, 28~
2S ZrN). (The optical v~lues were measured ~y ~n
ellip~o~eter.)
2~ r~ 3~
.: . ; .
a . _ n k
: i80 - 2.600 0.0500
^ . 40Q. 2.566 - 0.0500
s . 420 2.55~ . 0.0400
-- -44~ -- . 2.54z 0.0350
. . 460.. . .2.521 : . 0.0300
480 2.500 0~0250
~ - 500 - 2.472 0.0200
lo - - 520 . . 2.463 0.0150
s40 2.44g 0.0150
-` 560 - 2.436 0.0150
580 2.424 0.0100
600 2.412 0.~110
620 2.404 o.ooso
640 . . 2.396 0.0080
660 2.389 0.0070
680 2.382 0.0060
700 2~376 0.0060
720 2.371 0.0060
- 740 2.366 0.0060
760 2.361 0.0050
780 2.356 0.0040
800 2.353 0.0030
. 820 2.349 0.0030
840 2.347 0.0001
860 2.344 0.0000
~80 2.341 0.0000
900 2.338 o~oooo
, 920 2.337 0.0000
940 ~.335 o.oooo
960 2.332 0.0000
980 2.332 0.0000
looo 2.329 0.0000
2000 2.300 0.0000
2~
TABLE 4
~ . n k
300 2.4972 0.1768
350 2.3298 0.0718
4002 . 2752 0 . 0400
4502 . 2298 0 . 0156
5002 . 2122 0. 0071
5502 . 195~ 0. 000
6002 . 1886 0 . 0028
6502 . 1813 0. 0051
700 2.1779 0.0060
800 - 2.1724 0.0070
1000 2.1673 0.0070
2000 2.1500 0.0070
As is apparent, refractive index in the visible region
was higher for the f~rst composite film which ~as less
Si3N~.
Although the invention has been described wit~
respect to ~ts preferred ~mbodi~ents, it will be
understood tbat the invention is to be protected within
the full ~cope of the appended claims.
