Note: Descriptions are shown in the official language in which they were submitted.
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PHD. 74-130.
104~6~ff
The invention relates to a method of structur-
ing thin layers in which the layer to be structured is
- . .
provided on a substrate masked locally by a layer of
photolacquer and is removed again partly by removing
the layer of photolacquer.
Such methods are already known and are used
in thin-layer-technology, for example, in manufacturing
maska for integrated circuits.
It is already known to manufacture SiO2 masks
on a semiconductor substrate in such manner that a
photolacquer mask is formed on the substrate by means
of photolithographic processes and a layer of silicon
oxide or silicon nitride is provided by means of cathode
sputtering in a gas discharge both on the photolacquer
ma~k and on the surfaces of the semiconductor substrate
not covered with lacquer. The substrate is then treated
w1th a solvent which attacks the lacquer mask; the
photolacquer mask swells up and the parts of the layer
of silicon oxide or silicon nitride present thereon are
removed by chipping off. After removing the photo-
lacquer mask, the desired silicon oxide or silicon nitride
mask remains on the semiconductor substrate a~ a negative
~l of the pattern of the photolacquer mask.
It has been found that this known method ex-
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PHD. 74.130~ ~
~046~4t3
hibits drawbacks in the cases in which very finely struc-
tured layers having layer thicknesses of more than 1
are to be formed on a substrate. According to the kncwn
method, structured layers of this type cannot be manu-
factured with the desired reproducibility. In other w~rds:
the yield of fully, accurately proportioned and perfectly
structured layers on a substrate in ccmparison wi$h the
pattern of the mask is not high enough. "Full" structuring
is to be understoad to mean that all the surfaces on the
substrate to be exposed are exposed indeed in a repro-
ducible manner, while the "perfect" structuring relates
in particular to the quality of the edges of the profile
formed in the layer to be structured. It is of importance
; especially with a view to series pr~duction to be able
to manufacture layers of the said kind with always the
same quality and with a great precision. Inaccuracies in
the profile, for example, have a particularly disadvan-
tageous effect in forming structured m~lt;l~yers.
The invention is based on the reoognition that
the reproducibility and the yield, respectively, depend
on the quality of the surface on which the layer of photo-
I laoquer is provided and on which the layer to be struk-
! tured is provided in the places not covered with laoquer:
' this surface should be such that the photolacquer has
only a small adhesive capacity with respect to that.
The invention is furthermDre based on the re-
cDgnitiQn tbat the chipping off Erocess of the parts of
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PHD. 74.130.
104~8
the layer to be structured present on the photolacquer
can be stimulated by vDlume variations of the layer o~
photolaoquer which can be obtained, for example, by temr
perature influen oes.
It is thus an cbject of the invention to pro-
vide an Lmprov3d method of Qbtaining very fine structures
in thin layers of different materials.
The methcd of the kind mentioned in the prea~ble
is therefore characteri æd acoDrding to the invention in - -
that a layer is provid~d directly on the substrate (1)
as a supporting layer (2) for the layer of photolaoquer
~3) and for the layer (4) to be structured with respect
to which photolaoquer, in the subs~quent thermal treat- ~ -
ment, has only a small adheslve capacity and that the
substrate, after providing the layer to be structured,
is heated in ~uch a temperature range that the chemical
I reaction capacity of the phstolaoquer is just not yet
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detr$mentally influew ed and the photolaoquer is remaved.
e advantages resulting fram the use of the
iDvEntion consist in particular in that fully, accurately
¦ proportioned, structured layers having a good profile
qu~lity with respect to the mas;k can be abtained in a
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readily reproducible yield~ The layer thicknesses of the
;~ layers to be structured are preferably in the rang fr~m
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~ 25 approxlmately 1 to 3 /um; however, they may also be larger.
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e layer thicknesses of the layers to be structured are
Iimdted m the first instance by the possibility of
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PHD. 74.130.
~046~;~8
pmviding correspondingly thick photolacquer layers.
m e invention will now be described in greater
detail with reference to an enbodlment and the accompa- -
~ying drawings, in which:
figs. la - lc are cmss-sectional vie~s of a
substrate in various stages of the method,
fig. 2 is a graph showing the yield of perfectly
and fully struotured layers as a function of the quality of
the surface of the substrate and of the duration of the
thermal treatment.
Figs. 3a - 3f are cross-sectional views of a
substrate having multi-layers in various stages of the
method, and
Fig. 4 shows the yield of perfectly and fully
structured layers and the angle of inclination of the
edges of the layer of photolaoquer as a function of the
baking temperature of the laoquer mask.
, For the exa~ple below is described the manu-
facture of a structured aluminium layer which may be used,
for example, as a layer of oonductor tracks on a substrate,
sald aluminium tracks being 5 /um wide and approximately
!
20 mm long and being present at a distance of 5 /um fr~m
j each other. The thickness of the aluminium tracks should
~ be approximately 1 ~ m. In the same m2nner, layers of a
i~ 25 different quality can also be structured, for example,
titanlun L3ysrs, magnetic layers for mass m2m~ries or
thlr~ yn~ti~ h~bd~ or Layers of oxides and nitrides
_
A PHD 74-130
10466413
which are used as diffusion masks, oxidation masks, dif-
fusion sources, d;electr;cs or passivating layers ;n
planar semiconductor technology.
On a substrate 1 (Fig. l_) a supporting layer
5 2 is provided to which photolacquer does not readily
adhere. SiO2 and aluminium have proved to be particularly
suitable as a material for such layers. In the case of a
silicon substrate, an SiO2 layer can be formed by thermal
oxidation; however, the layers may equally readily be -
l~ formed, for example, by cathode sputtering in the gaseous
phase or by vapour deposition. On the substrate l having
the supporting layer 2 a masking photolacquer layer 3
having steep edges is then provided by means of the known
photolithographic methods, the photolacquer mask being
the negat~ve of the structured layer to be formed. Both
a positive and a negative lacquer may be used for the
~I manufacture of the photolacquer layer 3. For the present
;l embodiment was used the positive photolacquer of Messrs.
1 Shipley (AZ* 135 OH) in a thickness of approximately 3 /um.
! 20 At any rate the th;ckness of the photolacquer layer must
be larger than the thickness of the layer to be structured.
The photolacquer layer 3 after providing and developing,
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may no longer be heated so as not to influence the steep-
ness of the edges dlsadvantageously. After providing the
photolacquer layer, a 1 /um thick layer 4 of aluminium
is provided on the cooled substrate l having the support-
ng layer 2 and the photolacquer layer 3 by means of high
A registered trade mark.
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PHD. 74.130.
~o4~;4~3 :
frequency cathode sputtering in a gas discharge tprefe-
rably in Argon) (Fig. lb). The substrate is then heated
for 30 minutes at 130C. ~-
The practical results have demonstrated that ~'
such a temperature treatment considerably stimulates the
chipping off process of the p æts of the layer to be
structured present on the photolacquer layer. Ihis may
be a result of the fact that due to expansion of the
photolacquer, as a result of thermal expansion or by
giving off of solvent residues still present in the
; lacquer, the cracking or at least the formation of cracks
in the layer to be structured i5 stimulated. The tempe-
rature should be as high as possible and be at any rate
above the flow limit d the photolaoquer but on the other
hand may not be so high that as a result of this a fur-
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ther "cross linking" of the photolaoquer is produced and
hence the solubility thereof in an associated solvent is
reduced.
Bow great the importance of the quality of
the surface of the substrate on which the photolaoquer
layer and the layer to be structured as provided is for
I the yield of perfectly and fully structured layers,
''1 appears fron the following table and from Fig. 2. The ~ '
surface of the substrate should have such a quality that
the phDtoiacquer'layer'does'not readily adhere to it. '
When'an SiO2 layer'was formed on a silicon substrate '~
-1 by thermQl oxidation, the yield was much better than
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PHD. 74.130.
10466~8
whRn, for example , a chrcmiunrnickel layer was provided
on the substrate as a supporting layer for the photo-
lacquer layer and the layer to be structured. -
The fav~urable effects when using an SiO2 layer
as a supporting layer also beoome apparent from the
Example in which a chromium~nickel layer on the substrate
was covered with a further SiO2 layer which in turn then
farmEd the supportin~ layer for the photolaoquer layer and
the layer to be structured. -~
Surface of the substrate Yield (%)
silioon substrate having SiO2
supp~rting layer 98
silioon substrate having chromiumr
;I nickel supporting layer (0.1 /um) 45
silicon substrate having a chrcmiumr
nickel intermediate layer (0.1 ~ )
and an SiO2 supporting layer (0.1 ~ ) 96.
¦ After the temperature treatment of the substrate
1 having the photolaoquer layer 3 and the layer 4 to be
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~;j 20 structured, the substrate is dipped in a solvent which dis-
,
} solve~ the photolaoquer. Su~h a solvent may be, for
example, acetone. As a result of diffusion through the
layer 4 to be structured, the solvent dissolves the phctD-
lacquer present below the layer and causes it to ~well up.
The treatment can be acaelerated by ultrasanic effects.
e swelling phL~olacquer 3 causes the parts of the
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~. 74.130. '~ -
~04664t3
the layer 4 to be structured present thereon to be re~
maved, the renaining parts of the layer 4 to be struc*ured ''
remaining on the substrate l having the supporting layer 2
after the ccmplete re val of the photolacquer (Fig. lc).
According to the principle described, multi-
layers can also be structured which are built up from
layers of different materials, for example, an insulating
material and a material for oanductor trac~s. Such multi-
layers are of importance, for exa~ple, for the oonstruc-
' 10 tion of integrated magnetic mem~ries.
Fig. 3a is a cross-sectional view of a sub-
strate 1 having a supporting layer 2, in this case in
the fonm of a magnetic layer of FeSi, a photolacquer
layer 3 covering the supporting layer 2 partly, an SiO2 ~ '
layer 4 provided by cathode sputtering and an alumLnium
'~ layer S provided on said SiO2 layer 4 by cathode sputter-
ing. After removing the photolaoquer layer 3, the sub- ;~
~ strate l covered with a double layer having the sueport-
;1 ing layer 2, the SiO2 layer'4 and the aluminium layer 5
is obtained as is shown in Fig. 3b. These suocessive
' layers shown in Fig. 3b can now be provided again with
an insulating layer and a layer'of conductor tradks; the
stage shcwn in Fig. 3c is then'obtained, in which on
the'substrate l with the first layer structure 4 and 5
25' a further pb~tolacqyer layer 33 is provided and a further
SiO2 layer'44 and a ~urthe~'aluminium layer 55 are pro,
vided by cathode sFuttering. After removing the photo~
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PHD. 74.130.
~0466~8
laoquer layer 33 the substrate 1 with the supporting
layer 2 and the double layer structures 4,5 and 44, 55
is obtained as is shcwn in Fig. 3d. A third SiO2-layer
444 as an insulating layer (Fig. 3e) may be pr~vided on
said m~ltiple-structured successive layers in a further
process step by cathode sputtering, which insulating
layer may then be provided, for exa~ple by electroless
plating, with a magnetic c wering layer, for example,
of nickel-iron (Fig. 3f). The magnetic coupling between
the magnetic supporting layer 2 and the magnetic covering
layer 6 is not shcwn in the fig~res.
The steepness of the edges of the structured
photolacquer layer is of great importance in the me*hDd
described; in addition the photolaoquer layer should show
sides w~ich are rounded off as little as possible. For
`1 example, a thermal treat~.ent of a photolaoquer layer .
prior to providing the layer to be structured results
in flattening of the angle of inclination of the edges
and in rounding of the sides.
I 20 Fig. 4 shows the yield of perfectly and fully
structured thin layers, (solid line) and the angle of
I the edges as a function of the baking temperature of
.~ the lacquer mask (broken line).
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