Method of manufacturing semiconductor device using top antireflection film

A method of manufacturing a semiconductor device for patterning a semiconductor substrate by photolithography, the semiconductor substrate having a transparent or semitransparent layer having a high transmissivity at an exposure wavelength .lambda., and the transparent or semitransparent layer being formed on an underlying structure with a surface having a high reflectivity at the exposure wavelength .lambda.. The method comprises the steps of: forming a resist layer having a refractive index n.sub.r and a thickness d.sub.r on the transparent or semitransparent layer; forming a top antireflection film having a refractive index n.sub.a and a thickness d.sub.a on the resist layer; selectively exposing the resist layer via the top antireflection film with light having the exposure wavelength .lambda.; removing the top antireflection film; and developing a latent image in the resist layer to form a resist pattern, wherein an optical thickness n.sub.a d.sub.a of the top antireflection film and an optical thickness n.sub.r d.sub.r of the resist layer are selected so that a size change in the resist pattern becomes small even if the thickness of the transparent or semitransparent layer changes. This method provides an excellent size precision in patterning a transparent or semitransparent layer formed on a high reflectivity surface.

BACKGROUND OF THE INVENTION 
a) Field of the Invention 
The present invention relates to a method of manufacturing a semiconductor 
device, and more particularly to a method of manufacturing a semiconductor 
device including an exposure process of a resist layer covered with a top 
antireflection coating or film. 
b) Description of the Related Art 
Highly integrated semiconductor devices have necessarily fine semiconductor 
elements formed therein. For improving resolution, an exposure wavelength 
used for photolithography patterning is becoming shorter. If the layer 
under a resist layer has a high reflectivity, the intensity of exposure 
light being incident on and reflected from the underlying layer during 
photolithography becomes high and the intensity of light internally 
reflected when it reaches the resist layer surface is also not negligible. 
If there are many kinds of light (incident light, reflected light, 
multi-reflected light) in a resist layer, this layer is exposed in 
accordance with the intensity distribution of composite light of all light 
components. 
If an underlying substrate has a step structure, the thickness of a resist 
layer formed thereon changes so that the phase and intensity of reflected 
light in the resist layer vary. The distribution of amplitudes of standing 
waves in the resist layer therefore varies and the precision of resist 
pattern size lowers. 
If the thickness of a resist film changes because of an uneven surface of 
the underlying substrate, the amplitudes of standing waves in the resist 
layer varies and the resist pattern precision lowers. In such a case, if 
reflection at the resist layer surface is reduced, the intensities of 
standing waves in the resist layer may be made uniform. 
Basing upon this concept, techniques of forming an antireflection film on 
the surface of a resist film have been proposed. Such an antireflection 
film is called a top antireflection coating or film. For example, the top 
antireflection film is formed on the surface of a resist layer to a 
thickness of (.lambda./4n.sub.a) by using material having a refractive 
index n.sub.a lower than the refractive index n.sub.r of the resist layer. 
This layer having a thickness of (.lambda./4n.sub.a) is a .lambda./4 plate 
having an optical length of .lambda./4 in the thickness direction (in this 
specification, an optical length may also be called an optical thickness). 
The .lambda./4 plate is used as a single layer antireflection film, and 
shows the maximum effects of antireflection at n.sub.a =(n.sub.r).sup.1/2. 
Studies made by the present inventors indicate that even if a top 
antireflection film is formed on a resist layer to an optical thickness of 
.lambda./4 by using material having a refractive index smaller than that 
of the resist layer, the resist pattern size precision is not necessarily 
improved, but it may lower in some cases. If the underlying layer of the 
resist film is a transparent film in particular, the resist pattern size 
precision becomes likely to be worsened. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a method of 
manufacturing a semiconductor device capable of providing an excellent 
patterning size precision of a resist layer formed on the surface of a 
transparent or semitransparent layer on a high reflectivity surface of a 
semiconductor substrate. 
According to one aspect of the present invention, there is provided a 
method of manufacturing a semiconductor device for patterning a 
semiconductor substrate by photolithography, the semiconductor substrate 
having a transparent or semitransparent layer having a high transmissivity 
relative to an exposure wavelength .lambda., and the transparent or 
semitransparent layer being formed on an underlying structure with a 
surface having a high reflectivity relative to the exposure wavelength 
.lambda., the method comprising the steps of: forming a resist layer 
having a refractive index n.sub.r and a thickness d.sub.r on the 
transparent or semitransparent layer; forming a top antireflection film 
having a refractive index n.sub.a and a thickness d.sub.a on the resist 
layer; selectively exposing the resist layer via the top antireflection 
film with light having the exposure wavelength .lambda.; removing the top 
antireflection film; and developing a latent image in the resist layer to 
form a resist pattern, wherein an optical thickness n.sub.a d.sub.a of the 
top antireflection film and an optical thickness n.sub.r d.sub.r of the 
resist layer are selected so that a size change in the resist pattern 
becomes small even if the thickness of the transparent or semitransparent 
layer changes. The method of manufacturing a semiconductor device provides 
an excellent size precision in patterning a semiconductor substrate having 
a transparent or semitransparent layer formed on a high reflectivity 
surface. 
A resist layer is formed on a transparent or semitransparent layer formed 
on the surface of a semiconductor substrate, and a top antireflection film 
is formed on the resist layer. In this case, even if the optical thickness 
of the top antireflection film is set to .lambda./4, good results of 
exposure may not be obtained. However, if a sum of the optical thicknesses 
of the top antireflection film and resist layer is set in a range around a 
center value of (.lambda./2)N+(constant), good results are obtained. This 
fact was confirmed by experiments. The constant is N.multidot.p+127 under 
some conditions, where N is a positive integer or 0 and p=(.lambda./2). 
This constant may be expressed as N.multidot.p+127=N.multidot.p+90n.sub.a 
=N.multidot.p+0.35.lambda.. 
It is therefore possible to improve the size precision of photolithography 
of a semiconductor substrate having a transparent or semitransparent layer 
on the surface thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Consider first the structure such as shown in FIG. 1A. In this example, on 
the surface of a high reflectivity substrate 1 having a step, a 
transparent layer 2 with a flat surface is formed. A high reflectivity 
substrate means a substrate having a high reflectivity surface of 0.2 or 
higher. The transparent layer 2 is, for example, a CVD oxide film formed 
by chemical vapor deposition (CVD). The surface of the transparent layer 2 
is usually planarized. It is assumed that the high reflectivity substrate 
1 has an irregular surface (step). On the surface of such a semiconductor 
substrate, a resist layer 3 is coated and a top antireflection film 4 is 
formed on the resist layer 3. The transparent layer 2 is not required to 
be a perfectly transparent body of light absorption-free. A transparent or 
semitransparent layer having a transmittance of 0.2 or higher in the total 
film thickness is called a transparent layer in this specification. 
The top antireflection film 4 prevents reflection at the surface of the 
resist layer 3. According to conventional techniques, it is said that if 
the optical thickness of the top antireflection film 4 is set to 1/4 the 
exposure wavelength (.lambda./4), reflection at the surface of the resist 
layer 3 can be lowered and the standing waves in the resist layer 3 are 
reduced. 
However, the present inventors have found that if the transparent layer 2 
is formed under the resist layer 3 as shown in FIG. 1A, good results are 
not always obtained even if the optical thickness of the top 
antireflection film 4 is set to (.lambda./4). In order to examine this 
reason, the inventors performed the experiments and simulations described 
in the following. 
FIG. 2A shows the structure of samples used in the experiments. On the 
surface of a high reflectivity substrate 1 made of a bare silicon wafer, a 
CVD oxide film 2 was formed. On the surface of the CVD oxide film 2, a 
resist film 3 was coated, on which a top antireflection film 4 was formed. 
CVD oxide films 2 of different thicknesses were prepared. If the pattern 
size of the resist layer changes with a thickness of the CVD oxide film 2 
formed on a substrate having a transparent layer with uneven thickness, 
the size precision of photolithography worsens. 
The refractive index of the CVD oxide film 2 was n.sub.t =1.47. The resist 
layer 3 was made of positive resist (PFI-32 manufactured by Sumitomo 
Chemical Co. Ltd., Japan). The refractive index of the resist layer 3 was 
n.sub.r =1.65, and its extinction coefficient was k.sub.r =0.029. The top 
antireflection film 4 was made of AZ AQUATAR (tradename, available from 
Cloriant, Japan) having a refractive-index n.sub.a =1.41. 
AZ AQUATAR is transparent material made of at least one type of 
polysaccharide selected from a group consisting of alginate salt, sodium 
alginate salt, potassium alginate salt, tetraethylammonium alginate salt, 
tetramethylammonium alginate salt, soluble starch, amylose, lichenin, 
glycogen, and Pullulan. 
An exposure system having a numerical aperture of NA=0.57, a light source 
size of (.sigma.) S=0.4 and an i-line with a wavelength of 365 nm was used 
to form a hole having a diameter of 0.36 .mu.m in the resist layer. The 
resist layers 3 having thicknesses of 0.76 .mu.m and 0.82 .mu.m were 
prepared, some of them were formed with the top antireflection film 4 of 
65 nm thick, and others were not formed with the top antireflection film. 
FIG. 2B is a graph showing the diameters of holes formed in the resist 
layer 3 at various thicknesses of the transparent layer made of a CVD 
oxide film as the underlying layer of the resist layer. The abscissa 
represents the thickness of the transparent layer in the unit of nm, and 
the ordinate represents a hole diameter in the unit of .mu.m. 
A curve h1 shows the experiment results using the resist layer having a 
thickness of d.sub.r =0.76 .mu.m without the top antireflection film. A 
curve h2 shows the experiment results using the resist layer having a 
thickness of d.sub.r =0.76 .mu.m with the top antireflection film of 65 nm 
thick. A curve h3 shows the experiment results using the resist layer 
having a thickness of d.sub.r =0.82 .mu.m without the top antireflection 
film. A curve h4 shows the experiment results using the resist layer 
having a thickness of d.sub.r =0.82 .mu.m with the top antireflection film 
of 65 nm thick. 
The thickness of 65 nm of the top antireflection film corresponds to an 
optical thickness of about 91.7 nm and is about .lambda./4 of the exposure 
wavelength of 365 nm. 
It is seen from this graph that all the curves change as a function of the 
transparent film thickness. Namely, if the transparent layer is present 
under the resist layer, the photolithography precision depends on this 
transparent layer. 
With the top antireflection film 4 formed on the resist layer having a 
thickness d.sub.r of 0.76 .mu.m, a change in the curve h2 was more than 
that in the curve h1 without the top antireflection film. Namely, 
provision of the top antireflection film worsened the size precision of 
photolithography. 
With the top antireflection film 4 formed on the resist layer having a 
thickness d.sub.r of 0.82 .mu.m, a change in the curve h4 was less than 
that in the curve h3 without the top antireflection film. Namely, 
provision of the top antireflection film having an optical thickness of 
.lambda./4 worked effectively for the resist film having a thickness of 
0.82 .mu.m. 
The experiment results of FIG. 2B indicate that provision of the top 
antireflection film having an optical thickness of .lambda./4 on the 
surface of the resist layer over the transparent layer improves the 
precision of photolithography in some cases and worsens in other cases. 
The experiment results of FIG. 2B may have some errors. For example, the 
thickness of the top antireflection film is determined on the assumption 
that the expected thickness is the same as that when a film of the same 
material is formed on a bare silicon wafer. However, it is not certain 
whether the expected film thickness is actually obtained if the top 
antireflection film is formed on the resist layer. In order to check this 
point, computer simulations were made under the same conditions. 
FIG. 3 is a graph showing the results of computer simulations made under 
the same conditions given in FIG. 2B. Similar to FIG. 2B, the abscissa 
represents the thickness of the transparent layer in the unit of nm, and 
the ordinate represents a hole diameter in the unit of .mu.m. 
A curve s1 shows the simulation results using the resist layer having a 
thickness of d.sub.r =0.76 .mu.m without the top antireflection film. A 
curve s2 shows the simulation results using the resist layer having a 
thickness of d.sub.r =0.76 .mu.m with the top antireflection film of 65 nm 
thick. A curve s3 shows the experiment results using the resist layer 
having a thickness of d.sub.r =0.82 .mu.m without the top antireflection 
film. A curve s4 shows the experiment results using the resist layer 
having a thickness of d.sub.r =0.82 .mu.m with the top antireflection film 
of 65 nm thick. The curves s1 to s4 correspond to the curves h1 to h4 
shown in FIG. 2B. 
From the comparison of the simulation results shown in FIG. 3 with the 
experiment results shown in FIG. 2B, it is understood that there is very 
good coincidence therebetween from the qualitative point of view. Namely, 
with the top antireflection film formed on the resist layer having a 
thickness d.sub.r of 0.76 .mu.m, a change in the curve s2 was not improved 
but rather worsened compared to that in the curve s1 without the top 
antireflection film. However, with the top antireflection film formed on 
the resist layer having a thickness d.sub.r of 0.82 .mu.m, a change in the 
curve s4 was less than that in the curve s3 without the top antireflection 
film, and the photolithography precision was improved. 
From the above results, it can be seen that the photolithography precision 
cannot be expected to be improved if the thickness of the top 
antireflection film 4 on the resist layer 3 formed on a thickness changing 
transparent layer 2 is simply set to 1/4 the exposure wavelength .lambda.. 
Further simulations were conducted for clarifying how conditions are to be 
selected in order to ensure stable effects of the top antireflection film. 
FIG. 4 shows simulation results of hole diameters in a resist layer having 
a fixed thickness of d.sub.r =0.76 .mu.m on which a top antireflection 
film having a different film thickness is formed. A curve s11 shows the 
simulation results using the top antireflection film having a thickness 
d.sub.a =0 nm (without the top antireflection film). A curve s12 shows the 
simulation results using the top antireflection film having a thickness 
d.sub.a =65 nm. Similarly, curves s13 to s19 show the simulation results 
using top antireflection films with their thicknesses d.sub.a being 
changed from 75 nm to 135 nm at an increment step of 10 nm. 
With the top antireflection film whose thickness is set to 65 nm 
corresponding to (.lambda./4), a change in the hole diameter is large and 
the effects of the top antireflection film are not provided. However, as 
the top antireflection film is increased in its thickness, a change in the 
hole diameter reduces. The curve s15 at the thickness d.sub.a =95 nm of 
the antireflection film shows only a very small change in the hole. 
diameter. The thickness of the top antireflection film is therefore 
preferably set to d.sub.a =95 nm for the resist layer having a thickness 
d.sub.r =0.76 .mu.m. 
FIG. 5 shows simulation results of hole diameters in a resist layer having 
a thickness of d.sub.r =0.82 .mu.m. A curve s21 shows the simulation 
results without using the top antireflection film (d.sub.a =0 nm). Curves 
s22 to s28 show the simulation results using top antireflection films with 
their thicknesses d.sub.a being changed from 35 nm to 95 nm at an 
increment step of 10 nm. In this case, the curve s23 at the thickness 
d.sub.a =45 nm of the antireflection film has the smallest change in the 
hole diameter. Namely, it is most preferable to form a top antireflection 
film having a thickness of about 45 nm on the resist layer having a 
thickness d.sub.r =0.82 .mu.m. 
FIG. 6 is a graph showing a change in the standing wave ratio in a resist 
layer relative to a change in a top antireflection film thickness, the 
graph being obtained through simulations and the resist layer thickness 
d.sub.r being used as a parameter. The abscissa represents a top 
antireflection film thickness in the unit of nm and the ordinate 
represents a standing wave ratio, which is the quotient obtained by 
dividing the (maximum-minimum) of the standing wave upon variation of the 
SiO.sub.2 film thickness of more than one period by the central value of 
the standing wave. The thickness of the resist layer was changed from 0.70 
.mu.m to 0.82 .mu.m at an increment step of 0.02 .mu.m. Curves s41 to s47 
show the simulation results using the resist layers whose thicknesses 
being changed from d.sub.r =0.70 .mu.m to 0.82 .mu.m at an increment step 
of 0.02 .mu.m. 
The curve s44 for the resist layer thickness d.sub.r =0.76 .mu.m shows the 
minimum standing wave ratio at the top antireflection film thickness of 
0.95 nm, which coincides with the results shown in FIG. 4. Similarly, the 
curve s47 for the resist layer thickness d.sub.r =0.82 .mu.m shows the 
minimum standing wave ratio at the top antireflection film thickness of 
about 0.45 nm, which also coincides with the results shown in FIG. 5. It 
can be understood that the smaller the standing wave ratio, the smaller 
the size change in photolithography. 
As the resist layer thickness d.sub.r changes, the top antireflection film 
thickness showing the minimum standing wave ratio changes with the 
underlying transparent layer thickness. It can be known from the results 
shown in FIG. 6 that the thickness of the top antireflection film must be 
determined from the relation to the thickness of the underlying resist 
layer. 
Optimum values of the top antireflection film were obtained for resist 
layers having different thicknesses. 
FIG. 1B is a graph showing optimum thicknesses of a top antireflection film 
relative to resist layers having different thicknesses. The abscissa 
represents a resist layer thickness in the unit of nm and the ordinate 
represents an optimum top antireflection film thickness in the unit of nm. 
In FIG. 1B, the area under solid straight lines y1 and y2 corresponds to 
the area verified also by the experiments, and the areas indicated by 
broken lines and dot lines correspond to the areas obtained through 
computer simulations. 
As seen from FIG. 1B, the thickness of the top antireflection film showing 
the minimum standing wave ratio appears at a constant period at the same 
resist layer thickness. This period of the top antireflection film 
thickness is about 130 nm. It can be expected that the optimum resist 
layer thickness also appears periodically at the same top antireflection 
film thickness. The period of the resist layer thickness is about 110 nm. 
As described earlier, the refractive index of the resist layer is n.sub.r 
=1.65 and that of the top antireflection film is n.sub.a =1.41. The period 
or pitch of the optimum values of the top antireflection film is given by 
using the optical thickness as: 
EQU n.sub.a .times.d.sub.a =1.41.times.130.congruent.183 (nm) 
The period or pitch of the optimum values of the resist layer is given as: 
EQU n.sub.r .times.d.sub.r =1.65.times.110.congruent.182 (nm) 
Representation by the optical thickness leads to a conclusion that the 
pitch of appearance of the optimum values of resist layer thicknesses is 
equal to the pitch of appearance of the optimum values of top 
antireflection film thicknesses. This pitch of about 182 (183) nm is about 
a half of the exposure wavelength of 365 nm. Namely, the optimum values 
appear every .lambda./2 of the optical thickness of the resist layer and 
top antireflection film. A pitch of the optical thickness p representing 
both the resist layer and top antireflection film is therefore equal to 
(.lambda./2). 
The straight lines y1 to y5 shown in FIG. 1B can be expressed by: 
EQU n.sub.a d.sub.a =-n.sub.r d.sub.r +N.multidot.p+127 (nm) 
where N is a positive integer or 0. Substituting the refractive index 
n.sub.a =1.41 of the top antireflection film and the exposure wavelength 
n.sub.a =365 nm into the above equation, we obtain: 
EQU n.sub.a d.sub.a =-n.sub.r d.sub.r +N.multidot.p+90n.sub.a 
EQU =-n.sub.r d.sub.r +N.multidot.p+0.35.lambda. (nm) 
The optimum values of the thicknesses of the resist layer and top 
antireflection film are given by the above equation. However, other values 
slightly different from these optimum values can also provide the effects 
of the top antireflection film, as expected from the above-described 
experiment and simulation results. This range covers upper and lower 
ranges, each of about 1/4 of the optimum value period. Therefore, the 
effects of the top antireflection film can be expected if the thicknesses 
of the resist layer and top antireflection film are selected in the range 
between: 
EQU (n.sub.a d.sub.a +n.sub.r d.sub.r)=(.lambda./2)N+90n.sub.a +/-(.lambda./8) 
EQU =(.lambda./2)N+0.35.lambda.+/-(.lambda./8) 
where N is a positive integer or 0. Preferably, the (.lambda./8) is 
replaced with (.lambda./16), or more preferably it is replaced with 
(.lambda./32). 
In the above experiments and simulations, the exposure wavelength of 365 nm 
was used. The experiment and simulation results may not vary even if the 
wavelength is changed so long as the optical property of a lamination 
structure does not change. 
In the above experiments and simulations, the refractive index of the top 
antireflection film was n.sub.a =1.41, that of the resist layer was 
n.sub.r =1.65, and that of the transparent or semitransparent layer was 
n.sub.t =1.47. Similar experiment and simulation results may be expected 
at different refractive indices if the relationship between them is 
maintained. For example, the refractive index n.sub.a of the top 
antireflection film may be 1.35 to 1.45, the index n.sub.r of the resist 
layer may be 1.60 to 1.70, and the index n.sub.t of the transparent or 
semitransparent layer may be 1.45 to 1.55. 
If refractive indices are very different from those used for the above 
experiments and simulations although the above relationship is maintained, 
it is preferable to perform experiments and simulations again. With these 
experiments and simulations, the new optimum relationship between the 
optical thickness n.sub.a d.sub.a of a top antireflection film and the 
optical thickness n.sub.r d.sub.r of a resist layer is obtained while 
changing the thickness of a transparent or semitransparent film. In 
accordance with this relationship ensuring the good size precision of 
photolithography, the thicknesses of the top antireflection film and 
resist layer are determined. 
Namely, in order to determine this new optimum relationship, samples are 
prepared by forming a transparent or semitransparent film on a high 
reflectivity surface and forming a resist layer and a top antireflection 
film thereon, while changing the thicknesses of these films and layer. 
The resist layers on these samples are selectively exposed with light 
having a wavelength .lambda. through the top antireflection films. A 
change in the patterns formed in the resist layers is measured. If the 
pattern sizes are uniform even if the thicknesses of the transparent or 
semitransparent films are changed, the relationship obtained in this case 
is judged as the optimum relationship. 
From these measurement results, the relationship between the optical 
thickness n.sub.a d.sub.a of a top antireflection film and the optical 
thickness n.sub.r d.sub.r of a resist layer is obtained, which maintains 
good size precision even if the thicknesses of the transparent or 
semitransparent layers are changed. 
In accordance with the relationship obtained in the above manner, the 
thicknesses of the resist layer and top antireflection film are 
determined. 
By incorporating such a manufacture method, photolithography with good size 
precision can be realized when a transparent or semitransparent layer is 
patterned even if its thickness is not uniform. 
With reference to FIGS. 7A to 7F, a method of manufacturing a semiconductor 
device after the above-described preliminary steps are performed, will be 
described briefly. 
As shown in FIG. 7A, a p-type well 12 and an n-type well 13 are formed in 
the surface layer of a silicon substrate 11 of, for example, a p-type. 
Thereafter, a field oxide film 14 is formed by well known local oxidation 
of silicon to define active regions. Gate oxide films 15 are formed on the 
active regions by thermal oxidation. On these gate oxide films 15, gate 
electrodes Gn and Gp are formed by laminating polysilicon layers 16n and 
16p and silicide layers 17. 
The polysilicon layers 16n and 16p contain respective n- and p-type 
impurities doped by independent ion implantation processes. After the gate 
electrodes Gn and Gp are patterned, shallow diffusion layers of an LDD 
structure are formed by independent ion implantation processes. 
An oxide film is formed on the surface of the substrate by CVD or the like, 
and anisotropic etching is performed to form side spacers 18. Source/drain 
regions 19 and 20 are formed by independent ion implantation processes. 
Heat treatment for the activation of impurities is then performed. When 
the side spacers are formed or after the source/drain regions are formed 
through ion implantation, the gate oxide films in the active regions over 
the source/drain regions may be removed. In the above manner, a basic 
structure of a CMOS semiconductor device is formed. At the same time when 
the gate electrodes are formed, gate wiring patterns W are formed on the 
field oxide film 14. 
After the CMOS structure is formed, an interlevel insulating film 22 of 
PSG, BPSG or the like is formed over the whole surface of the substrate. 
The surface of the interlevel insulating film 22 is planarized by a 
planarizing process such as a reflow process and a chemical mechanical 
polishing (CMP) process. 
As shown in FIG. 7B, a resist layer 23 and a top antireflection film 24 are 
coated on the interlevel insulating film 22. The thicknesses of the resist 
layer 23 and top antireflection film 24 are set so as to have the optimum 
values determined by the above-described measurements. 
At this stage, an exposure process is performed to form a latent image in 
the resist layer 23. Thereafter, the top antireflection film 24 is 
removed. 
As shown in FIG. 7C, the resist layer 23 is developed to form a desired 
hole pattern. This hole pattern corresponds to holes to be formed later in 
the interlevel insulating film 22. 
As shown in FIG. 7D, contact holes H are formed in the interlevel 
insulating film 22 at areas corresponding to the source/drain regions of 
CMOS transistors and the gate wiring W on the field oxide film. 
As shown in FIG. 7E, a conductive layer of tungsten (W), polysilicon, or 
the like is deposited over the whole substrate surface, and the surface of 
the conductive layer is planarized by etch-back, CMP or the like to leave 
conductive plugs P only in the contact holes. 
As shown in FIG. 7F, an upper wiring layer is formed on the substrate 
surface, and patterned by photolithography to form an upper wiring layer 
pattern UW. 
Thereafter, if necessary, an interlevel insulating film covering the upper 
wiring layer pattern is formed, and contact holes are formed, and a wiring 
layer at a higher level is formed. Similar processes are repeated as many 
as the number of necessary wiring layers. 
The present invention has been described in connection with the preferred 
embodiments. The invention is not limited only to the above embodiments. 
For example, the structure of a semiconductor device may be any type 
already known. If the above-described patterning method is used for the 
photolithography of a transparent or semitransparent layer exposed on the 
substrate surface, the patterning precision can be improved. It will be 
apparent to those skilled in the art that various modifications, 
improvements, combinations, and the like can be made.