Aqueous developing solution and its use in developing positive-working photoresist composition

An aqueous developing solution useful in developing positive-working photoresists comprising: ______________________________________ A. Soluble Alkali Metal Phosphate 1.50-3.00% by weight B. Soluble Alkali Metal Silicate 1.00-2.00% by weight C. Mono (lower alkanol) amine 0.40-5.00% by weight D. Soluble Alkylene Glycol 0.25-3.00% by weight E. Lower Alkanol 0.05-1.00% by weight F. Water Balance to 100% by weight ______________________________________

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an aqueous developing solution and its use 
in providing improved development of positive-working photoresist 
compositions. 
2. Description of Related Art 
Photoresist compositions are used in microlithography processes for making 
miniaturized electronic components such as in the fabrication of 
integrated circuits and printed wiring board circuitry. Generally, in 
these processes, a thin coating or film of a photoresist composition is 
first applied to a substrate material, such as silicon wafers used for 
making integrated circuits or aluminum lithographic printing plates or 
copper plates of printed wiring boards. The coated substrate is then baked 
to evaporate any solvent in the photoresist composition and to fix the 
coating onto the substrate. The baked coated surface of the substrate is 
next subjected to an imagewise exposure of radiation. This radiation 
exposure causes a chemical transformation in the exposed areas of the 
coated surface. Visible light, ultraviolet (UV) light, electron beam and 
X-ray radiant energy are radiation types commonly used today in 
microlithographic processes. After this imagewise exposure, the coated 
substrate is treated with a developer solution to dissolve and remove 
either the radiation-exposed or the unexposed areas of the coated surface 
of the substrate. 
There are two types of photoresist compositions--negative-working and 
positive-working. When negative-working photoresist compositions are 
exposed imagewise to radiation, the areas of the resist composition 
exposed to the radiation become less soluble to a developer solution (e.g. 
a cross-linking reaction occurs) while the unexposed areas of the 
photoresist coating remain relatively soluble to a developing solution. 
Thus, treatment of an exposed negative-working resist with a developer 
causes removal of the non-expsed areas of the resist coating and the 
creation of a negative image in the photoresist coating, and thereby 
uncovering a desired portion of the underlying substrate surface on which 
the photoresist composition was deposited. On the other hand, when 
positive-working photoresist compositions are exposed imagewise to 
radiation, those areas of the resist composition exposed to the radiation 
become more soluble to the developer solution (e.g. a rearrangement 
reaction occurs) while those areas not exposed remain relatively insoluble 
to the developer solution. Thus, treatment of an exposed positive-working 
resist with the developer causes removal of the exposed areas of the 
resist coating and the creation of a positive image in the photoresist 
coating. Again, a desired portion of the underlying substrate surface is 
uncovered. 
After this development operation, the now partially unprotected substrate 
may be treated with a substrate-etchant solution or plasma gases and the 
like. This etchant solution or plasma gases etch the portion of the 
substrate where the photoresist coating was removed during development. 
The areas of the substrate where the photoresist coating still remains are 
protected and, thus, an etched pattern is created in the substrate 
material which corresponds to the photomask used for the imagewise 
exposure of the radiation. Later, the remaining areas of the photoresist 
coating may be removed during a stripping operation, leaving a clean 
etched substrate surface. In some instances, it is desirable to heat treat 
the remaining resist layer after the development step and before the 
etching step to increase its adhesion to the underlying substrate and its 
resistance to etching solutions. 
Positive-working photoresist compositions are currently favored over 
negative-working resists because the former generally have better 
resolution capabilities and pattern transfer characteristics. 
Photoresist resolution is defined as the smallest feature which the resist 
composition can transfer from the photomask to the substrate with a high 
degree of image edge acuity after exposure and development. In many 
manufacturing applications today, resist resolution on the order of one 
micron or less are necessary. 
In addition, it is generally desirable that the developed photoresist wall 
profiles be near vertical relative to the substrate and no resist residue 
be present on the substrate surface on the exposed and developed areas. 
Such demarcations between developed and undeveloped areas of the resist 
coating translate into accurate pattern transfer onto the substrate. 
The formation of a latent image on the photoresist coating by the imagewise 
exposure of the coating with radiant energy and the conversion of this 
latent image to a suitable relief image on the coating by the developer 
solution may be dependent upon several processing variables, including: 
1. Photoresist coating thickness 
2. Photoresist soft baking temperature 
3. Radiant Energy Type (e.g., UV light or electron beam current) 
4. Radiant Energy Amount 
5. Developer Type 
6. Developer Concentration 
7. Development Temperature 
8. Development Time 
9. Development Mode (e.g., immersion or spray or both) 
These parameters are frequently played against each other to balance the 
sometimes-conflicting goals of the overall microlithographic operation 
(e.g. amount of throughput, degree of image dimension control and 
resolution desired as well as process latitude). This parameter balancing 
may be aided in the case of positive-working photoresist coating if a 
developer solution is selected which has a rapid dissolution rate of the 
exposed areas of the resist coating while relatively unaffecting the 
unexposed areas of the resist as well as also providing good image 
quality, developed image dimension (DID) control and process latitude. 
In the past, numerous aqueous developing solutions have been known in the 
photoresist art for use with positive-working resist coatings. Generally, 
there are three classes of these developing solutions. They are 
metal-containing developers, metal ion-free developers and organic solvent 
developers. 
Known metal-containing developers include aqueous solutions of alkali metal 
salts such as alkali metal hydroxides, alkali metal phosphates, and alkali 
metal silicates and mixtures thereof. One known metal-containing developer 
contains the combination of trisodium phosphate sodium metasilicate in 
water. Known metal ion-free developers include aqueous solutions of 
quaternary ammonium hydroxides such as tetramethylammonium hydroxide. 
Known alkaline organic solvent developers include solutions of alkaline 
organic solvents such as mono lower alkanol amines, alkylene glycols and 
the lower alkyl alcohols. One known alkaline organic solvent-containing 
developer is made up of the combination of monoethanolamine, ethylene 
glycol and isopropyl alcohol. 
Organic solvent developers are not favored over the two other developer 
types for most applications because they are very sensitive to temperature 
changes, thereby causing inconsistent lithographic performance. However, 
alkali-metal containing developers, while very stable under most 
processing conditions and providing relatively high resolution, have the 
disadvantage of leaving alkali metal ion residues which may be detrimental 
in some processes. Metal ion-free developers have the disadvantage of 
being too aggressive, thus not obtaining high resolution for certain 
applications. 
In electron beam exposure processes and some UV light exposure processes, 
an aggressive development with high selectivity is needed. None of these 
known type developers meet this need. Accordingly, the present invention 
is a solution to this need. 
BRIEF SUMMARY OF THE INVENTION 
Accordingly, the present invention is directed at an aqueous developing 
solution comprising: 
______________________________________ 
A. Soluble Alkali Metal Phosphate 
1.50-3.00% by weight 
B. Soluble Alkali Metal Silicate 
1.00-2.00% by weight 
C. Mono (lower alkanol) amine 
0.40-5.00% by weight 
D. Soluble Alkylene Glycol 
0.25-3.00% by weight 
E. Lower Alkanol 0.05-1.00% by weight 
F. Water Balance to 100% by 
weight 
______________________________________ 
The present invention is also directed to a method of developing an 
imagewise-exposed layer of positive-working photoresist composition 
(preferably comprising a novolak-type resin and a diazoketone 
photosensitive agent), which comprises: 
contacting said layer with an aqueous developing solution comprising the 
above formulation. 
The use of developer solutions of the present invention with lithographic 
applications such as with optical/UV light sources or high energy sources, 
e.g., electron beam current, have shown improved photospeed/sensitivity, 
high developer selectivity, low film loss of the unexposed areas, very 
good image quality and wide process latitude. 
DETAILED DESCRIPTION 
It is believed that any conventional positive-working photoresist 
formulation may be developed with the above-noted developer formulation of 
the present invention. Generally, photoresist formulations are made up of 
an alkali-soluble resin component and a photosensitive agent component, 
both dissolved in a compatible solvent. 
One preferred type of alkali-soluble resin for positive-working 
photoresists is a novolak-type resin such as cresol-formaldehyde novolaks 
or phenolformaldehyde novolaks. Particularly preferred are mixed isomer 
cresol-formaldehyde novolaks. An example of such a resin is described in 
U.S. Pat. No. 4,377,631 (Toukhy), which is incorporated herein by 
reference in its entirety. 
The preferred class of photosensitive agents is diazoketones which are 
relatively insoluble in aqueous alkaline solutions and sensitive to 
radiation in the ultraviolet region of the light spectrum or to electron 
beam or x-ray radiation and forming, when exposed to such radiation, 
decomposition products which are relatively soluble in aqueous alkaline 
solutions. Diazoketone compounds which are particularly suitable for the 
practice of the present invention include naphthoquinone diazides such as 
naphthoquinone-1,2-diazide-5-sulfonic acid esters of 
trihydroxybenzophenones. 
The most preferred photoresist compositions are formed by adding the 
novolak-type resin and the diazoketone photosensitive agent to a solvent 
in which all of the components of the photoresist are readily soluble. The 
order of addition to the solvent is generally not critical. The solvent 
may be any of the solvents conventionally used to dissolve photoresist 
compositions for coating purposes. These include ethyl lactate, aliphatic 
alkylene glycol alkyl ethyl esters, cyclohexanone, methyl cellosolve 
acetate, ethyl cellosolve acetate, butyl acetate, xylene and mixtures 
thereof. A particularly preferred solvent is ethyl lactate or a mixture of 
ethyl cellosolve acetate, butyl acetate and xylene. The choice of solvent 
will depend on the specific novolak-type resin and specific diazoketone 
employed. 
The solids content (i.e., non-solvent ingredients) of the photoresist 
formulation before coating may vary broadly, but it is preferable to have 
a total solids content in the range of from about 10 to about 55 percent 
by weight, based on the total photoresist weight. The resin component is 
preferably from about 60 to about 95 percent by weight of the total solids 
content. The photosensitive agent component is preferably from about 30 to 
about 5 percent by weight of the total solids content. 
After the novolak-type resin and diazoketone have been added to the 
solvent, the mixture is agitated until all solids are dissolved. The 
resultant photoresist solution is microfiltered, preferably using a 
microfiltration system under a nitrogen, or other inert, oxygen-free 
atmosphere. 
Conventional photoresist additives such as dyes, anti-striation agents, 
plasticizers, adhesion promoters, speed enhancers and non-ionic 
surfactants in individual quantities up to about 5% by weight each may 
preferably be added to the photoresist formulation before it is filtered. 
The filtered photoresist composition can be applied to a suitable substrate 
or support by any conventional method known to those skilled in the art, 
including dipping, spraying, whirling and spin coating. The coated 
substrate or support can then be imagewise-exposed to radiation (e.g. UV 
or electron beam or other high energy light sources) in any known manner. 
The exposed, photoresist coated substrate is then contacted with an aqueous 
alkaline developing solution of the present invention. This method of 
contacting is preferably carried out by immersing the coated substrate in 
a bath of the developing solution, for example, a Teflon tank until all of 
the photoresist coating has been dissolved from the imagewise-exposed 
areas. The solution preferably agitated, for example, by nitrogen burst 
agitation. 
Alternative developing modes such as spray, puddle or mechanical agitation 
development may be employed instead. The specific development process 
parameters (e.g. development time and temperature) will depend upon the 
specific type of photoresist employed, specific developer concentrations 
and particular mode of development employed. Development temperatures in 
the range of about 20.degree. C. to 30.degree. C. and development times 
from about 60 seconds to 840 seconds are suitable for most immersion 
applications. 
Any alkali metal phosphate salt which is soluble in an aqueous alkaline 
developer solution may be used. The preferred alkali metals are sodium and 
potassium. The most preferred soluble alkali metal phosphate is sodium 
triphosphate. 
Any alkali metal silicate which is soluble in an aqueous alkaline 
developing solution may be used. The preferred alkali metals are again 
sodium and potassium. The most preferred soluble alkali metal silicate is 
sodium metasilicate. 
Any mono (lower alkanol) amine which is soluble in an aqueous alkaline 
developer solution may be used. The term lower alkanol is used to mean any 
alcohols having 1-4 carbon atoms. The most preferred mono (lower alkanol) 
amine is monoethanolamine. 
Any alkylene glycol which is soluble in an aqueous alkaline developer 
solution may be used. The most preferred alkylene glycol is ethylene 
glycol. 
Any lower alkanol which is soluble in an aqueous alkaline developing 
solution may be used. The term lower alkanol is used to mean any alcohols 
having 1-4 carbon atoms. The most preferred lower alkanol is isopropyl 
alcohol. 
The preferred concentration of each developer ingredient of the present 
invention will depend on the particular ingredient used, the process 
parameters employed and the particular type and thickness of photoresist 
used. For many development operations, the preferred ranges of the 
above-noted most preferred ingredients are as follows: 
______________________________________ 
A. Trisodium phosphate 
1.8-2.50% by weight 
B. Sodium Metasilicate 
1.2-1.8% by weight 
C. Monoethanolamine 
1.50-3.50% by weight 
D. Ethylene Glycol 1.00-2.25% by weight 
E. Isopropyl Alcohol 
0.20-0.70% by weight 
F. Water Balance to 100% by weight 
______________________________________ 
The aqueous alkaline developing solution can optionally contain various 
other standard developer ingredients that are known to those having 
ordinary skill in this art. For example, the developing solution may also 
include stabilizers such as disodium ethylenediamine tetraacetic acid 
(Na.sub.2 EDTA) in amounts of less than about 0.2% by weight or an 
alkaline-soluble antioxidant in amounts of less than 0.1% by weight, based 
on the total weight of the developing solution. Another optional 
ingredient is phloroglucinol which may be present in amounts less than 
about 0.1% by weight of the total developer solution. 
It also should be apparent to those skilled in the art that an aqueous 
concentrate of the developing solution of the present invention can be 
prepared which can be diluted with more water prior to use as the 
developing solution. This concentrate may be advantageous in that it would 
reduce the amount of water which must be stored or shipped. 
By employing the above-noted combination of developing ingredients on an 
aqueous solution, the exposed areas of the positive-working photoresist 
composition are removed by the aqueous developing composition while the 
unexposed areas are relatively unaffected. Thus, the exposed areas of the 
photoresist may be removed without leaving a residue between the edges or 
surfaces of the unexposed areas and the substrate.

The following examples are provided to illustrate the invention. All parts 
and percentages are by weight unless otherwise noted. 
EXAMPLES 
The following procedure was followed in each of the examples and 
comparative examples with the use of two types of exposure systems: a 
broad band UV light source and a 10KV and 20KV electron beam current. 
In all of the following examples and comparative examples, the photoresist 
compositions that were employed are commercially available under the 
designations "HPR-204" and "HEBR-214" from Olin Hunt Specialty Products, 
Inc., West Paterson, N.J., and both contain a mixed isomer 
cresol-formaldehyde novolak resin and, as a photosensitive agent, a 
naphthoquinone-1,2-diazide-5-sulfonic acid ester of a 
trihydroxybenzophenone. 
EXPOSURE TO UV LIGHT SOURCE 
Several 4 inch diameter silicon wafers which had a 6000.ANG. silicon 
oxidized surface layer and had hexamethyldisilazane (HMDS) applied thereto 
were employed herein. Each of these wafers were spin coated with HPR-204 
positive-working photoresist to provide a film thickness of 1 micron. The 
coated wafers were then softbaked at 100.degree. C.-105.degree. C. for 30 
minutes in a BLUE M convection oven. The soft-baked wafers were then 
exposed through a focus wedge photomask on a Perkin Elmer Micralign 340 
broad band exposure system (at UV 4 mode). These imagewise exposed wafers 
were developed for 60 seconds each at 22.degree. C..+-.1.degree. C. by an 
immersion process with different aqueous developer solutions as shown 
below as Examples 1, 2, 4 and 5 and Comparisons 1-5. After developing, the 
wafers were inspected and analyzed as indicated below. 
EXPOSURE TO ELECTRON BEAM CURRENT 
Several 4-inch diameter silicon wafers which had a 6000.ANG. silicon oxide 
surface layer and had HMDS applied thereto and several 4-inch square 
photomasks (made of low expansion glass with 950.ANG. of oxidized chromium 
surface film thereon) were employed in these experiments. The silicon 
wafers were first spin coated wih 1.0-micron layer of HEBR-214 
positive-working photoresist and the photomasks were each spin coated with 
a 0.5 micron layer of HEBR-214 photoresist. The coated wafers and 
photomasks were then soft baked at 100.degree. C..+-.5.degree. C. for 30 
minutes in a BLUE M convection oven. The softbaked wafer and photomasks 
were then separately exposed to an electron beam current in JEOL E-Beam 
system. The beam current for the wafers was 20KV and the beam current for 
the photomasks was 10KV. A relief image was produced on both the wafers 
and photomask of predefined patterns. These imagewise exposed wafers and 
photomasks were individually developed for 240 seconds at 22.degree. 
C..+-.1.degree. C. by an immersion process with different developer 
solutions as shown below as Examples 1-5 and Comparsons 1, 2 and 4. After 
developing, the wafers and photomasks were inspected and analyzed as 
indicated below. 
EXAMPLE 1 
______________________________________ 
Amount 
Developer Ingredient 
% by Weight 
______________________________________ 
Trisodium Phosphate 
2.14 
Sodium Metasilicate 
1.53 
Na.sub.2 EDTA 0.09 
Monoethanolamine 1.73 
Ethylene Glycol 1.13 
Isopropyl Alcohol 
0.30 
Water 93.08 
100.00 
______________________________________ 
EXAMPLE 2 
______________________________________ 
Amount 
Developer Ingredient 
% by Weight 
______________________________________ 
Trisodium Phosphate 
2.00 
Sodium Metasilicate 
1.43 
Na.sub.2 EDTA 0.08 
Monoethanolamine 3.24 
Ethylene Glycol 2.12 
Isopropyl Alcohol 
0.57 
Water 90.56 
100.00 
______________________________________ 
EXAMPLE 3 
______________________________________ 
Amount 
Developer Ingredient 
% by Weight 
______________________________________ 
Trisodium Phosphate 
2.00 
Sodium Metasilicate 
1.43 
Na.sub.2 EDTA 0.08 
Monoethanolamine 3.24 
Ethylene Glycol 2.12 
Isopropyl Alcohol 0.57 
Phloroglucinol 0.013 
Alkaline-soluble antioxidant 
0.003 
Water 90.544 
100.000 
______________________________________ 
EXAMPLE 4 
______________________________________ 
Amount 
Developer Ingredient 
% by Weight 
______________________________________ 
Trisodium Phosphate 
2.25 
Sodium Metasilicate 
1.61 
Monoethanolamine 0.49 
Ethylene Glycol 0.32 
Isopropyl Alcohol 
0.09 
Na.sub.2 EDTA 0.09 
Water 95.15 
100.00 
______________________________________ 
EXAMPLE 5 
______________________________________ 
Amount 
Developer Ingredient 
% by Weight 
______________________________________ 
Trisodium Phosphate 
2.22 
Sodium Metasilicate 
1.58 
Monoethanolamine 0.84 
Ethylene Glycol 0.55 
Isopropyl Alcohol 
0.14 
Na.sub.2 EDTA 0.09 
Water 94.58 
100.00 
______________________________________ 
COMISON 1 
______________________________________ 
Amount 
Developer Ingredient 
% by Weight 
______________________________________ 
Monoethanolamine 24.80 
Ethylene Glycol 16.28 
Isopropyl Alcohol 
4.40 
Water 54.52 
100.00 
______________________________________ 
COMISON 2 
______________________________________ 
Amount 
Developer Ingredient 
% by Weight 
______________________________________ 
Trisodium Phosphate 
4.60 
Sodium Metasilicate 
3.28 
Na.sub.2 EDTA 0.19 
Water 91.93 
100.00 
______________________________________ 
COMISON 3 
______________________________________ 
Amount 
Developer Ingredient 
% by Weight 
______________________________________ 
Trisodium Phosphate 
4.44 
Sodium Metasilicate 
3.17 
Monoethanolamine 3.38 
Na.sub.2 EDTA 0.18 
Water 88.83 
100.00 
______________________________________ 
COMISON 4 
______________________________________ 
Amount 
Developer Ingredient 
% by Weight 
______________________________________ 
Trisodium Phosphate 
4.38 
Sodium Metasilicate 
3.12 
Monoethanolamine 4.76 
Na.sub.2 EDTA 0.18 
Water 87.56 
100.00 
______________________________________ 
COMISON 5 
______________________________________ 
Amount 
Developer Ingredient 
% by Weight 
______________________________________ 
Trisodium Phosphate 
4.18 
Sodium Metasilicate 
2.98 
Monoethanolamine 9.09 
Na.sub.2 EDTA 0.17 
Water 83.58 
100.00 
______________________________________ 
The developed wafers and photomasks of the above experiments were measured 
for film loss, photospeed and in some instances resolution. The image 
quality of the developed photoresist layers on both the wafers and 
photomasks were observed and these observations are given. 
To measure film loss, the photoresist film (e.g. the unexposed portion) was 
measured after the softbake step and after development. The difference in 
the two values is the film loss. The lower the film loss, the higher the 
contrast between exposed and unexposed images. To measure the film loss in 
UV light exposure experiments, a Dektak II A surface profilometer (with 
12.5 grams of stylus weight) was used. To measure the film loss in 
electron beam exposure experiments, a Rudolph film thickness monitor (at 
1.63 resist refractive index) was used. The results of these film loss 
measurements are given in Table I. 
TABLE I 
______________________________________ 
Film Loss Measurement 
Developer 
Example or 
UV Exposure Electron Beam Exosure 
Comparison 
Film Loss (.ANG.) 
Film Loss (.ANG.) 
______________________________________ 
1 -93 -250 
2 +197 -400 
3 -- -600 
4 +270 -800 
5 +187 -600 
C-1 -10000 -10000 
C-2 0 -2000 
C-3 -108 -- 
C-4 -356 -1800 
C-5 -1000 -- 
______________________________________ 
The data in the UV exposure column of Table 1 indicates that the developers 
of Examples 1, 2, 4 and 5 all have a very low and acceptable film loss 
(i.e., less than 10% of the original film, 1.0 micron or 10,000 
Angstroms). Please note the accuracy of the instrument was .+-.200.ANG.. 
The organic solvent developer of Comparison 1 was overly aggressive and 
caused a complete removal of all original film (i.e., in both exposed and 
non-exposed areas). The metal-containing aqueous developer of Comparison 2 
showed no film loss. Comparisons 3-5 show that increasing concentrations 
of monoethanolamine (MEA) increase the film loss until the film loss is 
unacceptable (i.e., 10% of the original film or 1000.ANG.). 
The data in the Electron Beam Column of Table 1 shows that the developers 
of Examples 1, 2, 4 and 5 all have very low and acceptable film loss for 
the photoresist coating on the wafers (i.e., less than 10% of the original 
film--1.0 micron or 10000.ANG.). The developers of Examples 1, 2, 4 and 5 
also have a very low and acceptable film loss for the photomask coating 
(i.e., less than 20% of the original coating--0.5 micron or 5000.ANG.). In 
contrast, the developers of Comparisons 1, 2 and 4 are unacceptable for 
both wafer and photomask developing. 
It was observed in the film loss measurements of the electron beam 
current-exposed wafers and photomasks with the developers of Examples 1-5 
that the bulk of the film loss in unexposed areas occurred in the first 60 
seconds of the 240 second development time. In contrast, it was observed 
that the developers of the Comparisons 1, 2, and 4 likewise tested showed 
a linear development rate over the whole period. The different development 
modes between the Examples and Comparisons indicate that developing 
solutions of present invention have a greater selectivity between the 
exposed and unexposed areas (this resulting in greater contrast and better 
critical dimension control and image profiles). The minor modifications 
between Examples 1-5 and their corresponding similar film loss results in 
both the UV and electron beam exposure modes indicate that the developers 
of present invention have good development latitude. 
The photospeed values in the UV mode and the sensitivity values in the 
electron beam mode were determined for the developing solutions of the 
above Examples and Comparisons. The results are shown in Table II. 
TABLE II 
______________________________________ 
Developer Photospeed and Sensitivity 
Sensitivity 
Example or Photospeed (uC/cm.sup.2) 
Comparison (mj/cm.sup.2) 
wafer photomask 
______________________________________ 
1 108 16 8 
2 90 14 7 
3 N.T. 12 6 
4 119.6 N.T. N.T. 
5 115.4 N.T. N.T. 
C-1 N.M. N.M. N.M. 
C-2 125 24 12 
C-3 82 N.T. N.T. 
C-4 70.2 N.T. N.T. 
C-5 40 N.T. N.T. 
______________________________________ 
N.M. = Not Measurable 
N.T. = Not Tested 
With photospeed values, the lower the value, the higher the throughput 
(meaning you can process more wafers per hour and the overall operation is 
more economical). It is recognized that the photospeed values of Examples 
1, 2, 4 and 5 are somewhat higher than Comparisons 3-5, yet they are 
within acceptable range for most conventional UV exposure operations. It 
is noted that the Comparison 1 developer could not be measured because the 
developer totally removed the photoresist coating. It is known from 
previous experience that conventional UV photospeeds are related to 
electron beam sensitivities. 
With sensitivity values, again the lower the values, the higher the 
throughput. Thus, electron beam exposure operations desire the lowest 
possible developer sensitivity for both wafers and photomasks. As shown in 
Table II, Examples 1, 2, 3 all have acceptable sensitivities. In 
particular, Example 3 has a very good sensitivity value. It is believed 
that this resulted from the addition of the small amount of phloroglucinol 
to the developer. 
The image quality of the developed coatings were also observed through an 
optical microscope and by a scanning electron microscope. Residue in the 
exposed and developed areas was examined as well as the image profile. 
These observations were graded on a scale from 1-5 with 1 representing a 
photoresist which had much residue in developed areas or unacceptable poor 
image profile; with 2 representing a photoresist with little residue and a 
below average profile (low contrast), and with 3 representing no residue 
and average profile (average contrast); with 4 representing no residue and 
an above average profile (improved contrast); and with 5 representing no 
residue and very high profile (high contrast). The observations for each 
developer are given in Table III. The wafers and photomasks were grouped 
together for each electron beam developer. 
TABLE III 
______________________________________ 
Image Quality Observations 
Examples and UV Electron Beam 
Comparisons Exposure Exposure 
______________________________________ 
1 4 4 
2 4 5 
3 N.T. 4 
4 3 N.T. 
5 3 N.T. 
C-1 N.M. N.M. 
C-2 3 3 
C-3 3 N.T. 
C-4 2 N.T. 
C-5 2 N.T. 
______________________________________ 
N.T. = Not Tested 
N.M. = Not Measurable 
As can be seen from the values in Table III, each of the developers of the 
Examples had above average image quality for both exposure modes. 
The resolution of the wafers exposed with the electron beam system was 
observed. It was seen with the scanning electron microscope that high 
quality, sub-micron features with high aspect ratios are achievable.