# Patent

## Title
Photoresist formulation for high aspect ratio plating

## Abstract

SU-8 photoresist compositions are modified to improve their adhesion properties by adding 1% to 6% of an adhesion promoter selected from the group consisting of glycidoxypropanetrimethoxysilane, mercaptopropyltrimethoxysilane, and aminopropyltrimethoxysilane. SU-8 photoresist compositions are modified to improve their resistance to cracking and film stress by adding 0.5% to 3% of a plasticizer selected from the group consisting of dialkylphthalates, dialkylmalonates, dialkylsebacates, dialkyladipates, and diglycidyl hexahydrophthalates. The improvements can be obtained simultaneously by adding both the adhesion promoter and the plasticizer to SU-8 photoresist compositions.

## Background
FIELD OF THE INVENTION
The present invention relates generally to photoresist masks for high aspect ratio plating on semiconductor circuit boards, and more particularly to improvements in negative photoresist masks made from octafunctional epoxidized novolac resins such as SU-8.
BACKGROUND OF THE INVENTION
Negative photoresist masks are commonly employed in lithographic processes used to build integrated circuit boards. As is known in the art, lithography is a process by which geometric shapes are transferred from a mask onto the surface of a substrate. These geometric shapes, when transferred onto the surface of a silicon wafer, make up the parts of the circuit, such as gate electrodes, contact windows, probe electrodes, switches, metal interconnections, and the like.
The steps of the lithographic process are generally as follows. First, a base semiconductor (e.g., silicon) substrate is provided, and a second material layer, such as an oxide layer, is formed thereon. Next, a photosensitive polymer film or photoresist layer is deposited on the wafer, evenly covering the second material layer. Then, the photoresist layer is selectively fixed to produce a desired pattern thereon. This is done by selectively exposing the photoresist layer with ultraviolet light or other radiation, with the selective exposure defining the desired pattern.
Then, the unfixed portions of the photoresist layer are removed by a solvent rinse. (The unfixed portions may be either the exposed or non-exposed areas of the photoresist layer depending upon the type of polymer used.) At this point the surface of the wafer is covered by a substrate and a second material layer, with a desired design “masked” thereon.
The next step is to etch away the exposed second material layer while leaving the fixed portions of the photoresist layer intact. This is typically done by etching with an etchant that attacks the second material layer but not the photoresist layer, such as by hydrofluoric acid (HF), etching the exposed silicon dioxide (SiO2) while leaving the HF-resistant polymer photoresist layer intact. Excess etchant is rinsed away after the etching step, followed by a chemical removal of the photoresist layer with a solvent solution. The wafer is then rinsed to remove excess solvent and is now ready for the next photoresist step to occur.
A typical IC device requires between about five and 30 lithographic deposition layers, more if the device is fairly complex. Each of those layers corresponds to a separate type of device in the circuit, such as gate electrodes, contact windows, probe electrodes, switches, metal interconnections, and the like.
It can be seen from the above that the photoresist masking material must adhere firmly to the substrate, and must maintain planarity to very high tolerance levels.
One group of commonly used photoresist materials are those based on octafunctional epoxidized novolac resins, and particularly those based on the SU-8 family of photoresists made from Shell Chemical's EPON® SU-8 epoxy resin. The SU-8 photoresist materials are negative, epoxy-type, near-UV photoresist materials. The SU-8 family of photoresist materials is popular because it can provide relatively thick-film (2 mm or larger) photoresist films having aspect ratios greater than 20 at relatively low costs. In addition to being a relatively thick-film photoresist material, SU-8 is well suited for acting as a mold for electroplating because of its relatively high thermal stability (Tg greater than 200 degrees C. for the cross-linked or post-exposure photoresist material).
While the SU-8 family of photoresist materials enjoys relatively wide use and positive results as a photoresist in IC lithography, its utility is somewhat limited for use with silicon wafers greater than three or four inches in diameter. As with most polymer photoresists, the SU-8 family of photoresist materials is prone to delamination and via cracking arising from high film stress when used with relatively large silicon wafers.
Another problem with the SU-8 family of photoresists arises from adhesion problems with certain substrate materials. For example, SU-8 does not adhere as readily to metallic copper as it does to copper oxide.
The IC device industry is constantly demanding larger and/or more complex devices. As the size and complexity of the demanded IC devices increase, the need arises for a photoresist material having reduced film stress and increased adhesion properties for use in the lithography process to make such devices. The present invention addresses that need.
SUMMARY OF THE INVENTION
Briefly describing one aspect of the present invention, there is provided a photoresist composition for high aspect ratio lithography. The composition comprises an octafunctional epoxidized novolac resin such as SU-8, an organic solvent, a photopolymerization initiator, a plasticizer, and an adhesion promoter. The adhesion promoter is effective for improving the adhesion of the mask, particularly onto copper-based substrates. The plasticizer reduces delamination and via cracking between the photoresist film and the substrate, making larger wafers commercially viable.
One object of the present invention is to provide an improved photoresist composition for lithographic processes.
Further aspects and advantages of the present invention will be apparent from the following description.


DESCRIPTION OF THE PREFERRED EMBODIMENTS
For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the preferred embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, with such alterations and further modifications of the described embodiments being contemplated as would normally occur to one skilled in the art to which the invention relates.
As indicated above, one aspect of the present invention is an improved negative photoresist composition. In one preferred embodiment the composition comprises an octafunctional epoxidized novolac resin, an organic solvent, a photopolymerization initiator, a plasticizer, and an adhesion promoter. The inventive photoresist masking composition has improved adhesion on copper-based substrates, and resists cracking and other film stresses so that larger MEMS wafers can be made.
Referring first to the components of the preferred composition, the photoresist composition of the present invention comprises an octafunctional epoxidized novolac resin appropriate for building high-aspect ratio masks for MEMS lithography. The preferred resin is EPON® SU-8 epoxy resin, available from the Shell Chemical Company. That resin is described by the formula:




In the inventive masking compositions the resin is preferably present in an amount ranging from about 50% to about 75%. More preferably, the resin comprises between about 60% and 65% of the masking composition, with 62% to 63% resin being most preferred.
As is known to the art, a solvent is typically used to make epoxy-resin based masking compositions. In the preferred embodiment the solvent is an organic solvent with a boiling point of between about 160° C. and 260° C. More preferably the solvent has a boiling point of between about 190° C. and 220° C. The most preferred solvent is γ-butyrolactone, with a boiling point of about 205° C.
The solvent is preferably present in an amount ranging from about 15% to about 45%. In the more preferred embodiments about 20-30% solvent is used, with about 25% solvent being used in the most preferred embodiment.
The photoresist composition also includes a photopolymerization initiator. As is known to the art, the photopolymerization initiator is a material that promotes cross-linking of the resin when exposed to optical radiation. The cross-inking makes the resin insoluble to the developing solution used to pattern the semiconductor device.
One class of photopolymerization initiator (hereinafter alternatively referred to as either a photoinitiator or a cationic initiator) useful for the present invention is the class of triaryl sulphonium SbF6 salts. For example, Cyracure® 6974, available from the Union Carbide Corp., is particularly preferred.
The photoinitiator is preferably present in an amount ranging from about 3% to about 10%. More preferably the initiator is present in an amount ranging from about 5% to about 8%, with about 6% to about 7% photoinitiator being most preferred.
An adhesion promoter is preferably added to the masking compositions to improve its adhesion characteristics (i.e., increase the relative tackiness of the composition and/or increase the scope of materials to which the composition significantly adheres). The adhesion promoter is preferably a member selected from the group consisting of glycidoxypropanetrimethoxysilane, mercaptopropyltrimethoxysilane, and aminopropyltrimethoxysilane.
In the most preferred embodiment the adhesion promoter is glycidoxypropane-trimethoxysilane (GPTMS). In other preferred embodiments the adhesion promoter is another silicone containing adhesion promoter, such as mercaptopropyltrimethoxysilane (MPTMS) or aminopropyltrimethoxysilane (APTMS). Any of these adhesion promoters, or others, may be use alone or in combination as desired to tailor the adhesion characteristics of the mask. For example, MPTMS is particularly useful as an adhesion promoter when the composition is desired to adhere to gold.
The adhesion promoter is preferably added in concentrations of between about 1 and about 6 weight percent Concentrations of between about 3% and about 4% are more preferred in testing to date. Since the adhesion promoter can affect the viscosity of the composition (hampering deposition of the composition as a film) and/or promote phase separation of the composition (resulting in an inhomogeneous film with inhomogeneous physical, chemical, and/or mechanical properties), those factors should be taken into account when selecting adhesion promoter concentration levels.
A plasticizer is preferably added to the masking composition to reduce film stresses and allow the manufacture of larger (e.g., 8′′) wafers. The plasticizer is preferably a member selected from the group consisting of dialkylphthalates, dialkylmalonates, dialkylsebacates, dialkyladipates, and diglycidyl hexahydrophthalates.
In the most preferred embodiment the plasticizer is dioctylphthalate (DOP). Other preferred plasticizers include the dialkyl esters of dicarboxylic acids, wherein the dicarboxylic acids are between 1 and 18 carbon atoms in length (such as, for example, dialkylphthalates, dialkylsebacates, dialkylmalonates, dialkyladipates and the like). Epoxy-containing plasticizers such as diglycidyl hexahydrophthalate may be also used.
It should be noted that the phthalates have positional isomers, but these do not substantially affect their effectiveness as plasticizers. Likewise, the alkyl groups may be straight chain, branched chain, aromatic and/or cyclic. These plasticizers may be added, either alone or in combination, to tailor the plasticity of the resultant composition.
The plasticizer is preferably added in an amount sufficient to substantially reduce film stresses in films spun from about 5 to 500 μm thick, but is insufficient to cause excessive softening of the composition to the extent that contact printing difficulties arise. Also, excessive plasticizer can decrease the photo speed of the film. Therefore, plasticizer is added in an amount sufficient to substantially reduce film stress but insufficient to adversely affect film photo speed or contact printability. In the preferred embodiments the plasticizer is present in amounts ranging from 0.5 weight percent to 3.0 weight percent.
As to how to make and use the inventive compositions, the epoxy-based photoresist compositions are preferably prepared by dissolving the epoxy resin in the organic solvent to form a solution. The plasticizer is next added to the solution and the solution is mixed to substantially achieve uniformity. Next, the cationic initiator is separately added to the solution and the solution is again mixed until substantially uniform. Finally, the adhesion promoter is added to the solution and the solution is immediately mixed to result in a substantially uniform or homogeneous solution.
While the additives (i.e., the plasticizer, the adhesion promoter and the cationic initiator) may be added in any convenient order, the above sequence is preferred. Likewise, while mixing the solution after the addition of each of additives is preferred, mixing may be delayed until two or all of the additives have been added to the solution. Thorough and immediate mixing is preferred after the addition of the adhesion promoter to minimize reaction of the adhesion promoter with the remaining ingredients of the solution; delayed or incomplete mixing can result in gel formation.
After mixing, the solution may be milky due to air entrapment during the mixing process, and natural debubbling is preferred by storing the mixture in an amber glass container or the like and/or in a dark environment for a sufficient time for the entrapped gas to escape from the solution.
As discussed above, devices may be built on semiconducting wafers by a series of photolithographic processing steps. In the first photolithographic step, the photoresist film may be applied to a silicon wafer by methods known in the art, such as by spin deposition. The thickness of the film is a function of the coating process (such as the RPM chosen during spin deposition, spin deposition time, and the like), the viscosity of the photoresist composition, the amount of photoresist composition used, and the like. Typically the film is between about 1 micron and about 200 microns thick, with film thicknesses of between about 50 microns and 200 microns commonly being prepared.
After the wafer has been coated with the photoresist film, the wafer is dried to remove excess solvent. Drying may be accelerated by a pre-exposure bake of the wafer. Typically the pre-exposure bake lasts between 3 and 5 hours at a temperature approaching about 80-95 degrees C. The photoresist film is fixed by selectively exposing it to high energy electromagnetic radiation, preferably ultraviolet or near-ultraviolet light, on the order of from about 500 to 2500 mJ. After fixing, the film undergoes a post-exposure bake (PEB) at about 55° C. for a predetermined length of time, typically up to 1 or 2 hours.
Unfixed photoresist film is removed with a solvent and further processing of the wafer such as deposition of material and/or etching of material is done at this time. After these device processing and building steps have been completed, the photolithographic process is then repeated to build the next step in the series.
Reference will now be made to specific examples using the compositions and methods described above. It is to be understood that the examples are provided to more completely describe preferred embodiments, and that no limitation to the scope of the invention is intended thereby.
EXAMPLE 1
Preparation of Unmodified SU-8 Masking Composition
A two-step process is used to produce SU-8 photoresist without adhesion and plasticity modification.
Stock Solution. In a 2 L mixing container equipped with a mechanical stirrer or roller add 624 g of solid Epon SU-8 resin and 262 g of Gama-butyrolactone. The mixture is allowed to soak with occasional agitation until a viscous homogeneous solution is formed. This is a slow dissolution process and may take between 1-5 days to complete, The process can be accelerated by heating to about 60° C. if needed. Make sure the container is properly sealed during the process so that water absorption is kept to a minimum.
The solution then can be filtered through a 5 μm filter at room or elevated temperature to ensure gel-free resin stock solution. The above operation can be performed under normal lighting.
Final mixture. To 886 g of the resin stock solution under yellow light, add 63 g of filtered Cyracure® 6974 and mix with a mechanical stirrer until a uniform solution is fonned (800 rpm for 20 min).
EXAMPLE 2
Preparation of Modified SU-8 Masking Composition
A two-step mixing process is also used to produce the modified GD41 solution:
Stock Solution. In a 2 L mixing container equipped with a mechanical stirrer or roller add 624 g of solid Epon SU-8 resin, 262 g of Gama-butyrolactone, and a 10 g of dioctyl phthalate (DOP). The mixture is allowed to soak with occasional agitation until a viscous homogeneous solution is formed. This is a slow dissolution process and may take between 1-5 days to complete. The process can be accelerated by heating to about 60° C. if needed. Make sure the container is properly sealed during the process so that water absorption is kept to a minimum. The solution is then filtered through a 5 μm filter at room or elevated temperature to ensure gel-free resin stock solution. The above operation can be performed under normal lighting.
Final mixture. To 896 g of resin stock solution under yellow light, add 64 g of filtered Cyracure® 6974 and mix with a mechanical stirrer until a uniform solution is formed (about 800 rpm for 10 min). Forty grams of filtered glycidoxyproprane-trimethoxysilane (GPTMS) is then added and mixed at about 800 rpm for 20 min. The final blend should be uniformly milky due to air entrapment during mixing and natural debubbling by storing the mixture in an amber glass container in a dark cabinet should be completed within 36 hours. Both Cyracure® 6974 and glycidoxyproprane-trimethoxysilane should be filtered by 1 μm syringe filters prior to addition to the resin stock solution. Since GPTMS in its concentrated form will react with the remaining ingredients to form a gel, it is desirable to minimize the delay between addition and mixing to avoid gel formation.
EXAMPLE 3
Preparation of Alternative Modified SU-8 Masking Composition
A photoresist composition was made by combining the following components with mixing: 62.4% SU-8 resin, 26.3% γ-butyrolactone, 6.3% Cyracure® 6974, 1% DOP, and 4% GPIMS, all on a weight percent basis. The photoresist was prepared under yellow light, stored in an opaque container, and allowed to debubble. The coating was applied to copper seed silicon wafers, was dried, exposed, and submitted to a PEB to provide a photoresist film with superior adhesion and film stress properties.
EXAMPLE 4
Preparation of Alternative Modified SU-8 Masking Composition
A photoresist composition was made by combining the following components with mixing: 60% SU-8 resin, 27% γ-butyrolactone, 6% Cyracure® 6974, 1% percent DOP, and 6% GPTMS, all on a weight percent basis. The photoresist was prepared under yellow light, stored in an opaque container, and allowed to debubble. The coating was applied to copper seed silicon wafers, was dried, exposed, and submitted to a PEB to provide a photoresist film with superior adhesion and film stress properties.
EXAMPLE 5
Preparation of Modified SU-8 Masking Composition without Adhesion Improver
A photoresist composition was made by combining the following components with mixing: 60% SU-8 resin, 30% γ-butyrolactone, 7% Cyracure® 6974, and 3% percent DOP, all on a weight percent basis. The photoresist was prepared under yellow light, stored in an opaque container, and allowed to debubble. The coating was applied to copper seed silicon wafers, was dried, exposed, and submitted to a PEB to provide a photoresist film with superior film stress properties.
EXAMPLE 6
Preparation of Modified SU-8 Masking Composition without Plasticizer
A photoresist composition was made by combining the following components with mixing: 65% SU-8 resin, 23% γ-butyrolactone, 6% Cyracure® 6974, and 6% GPTMS, all on a weight percent basis. The photoresist was prepared under yellow light, stored in an opaque container, and allowed to debubble. The coating was applied to copper seed silicon wafers, was dried, exposed, and submitted to a PEB to provide a photoresist film with superior adhesion properties.
EXAMPLE 7
Verification of Improved Adhesion Properties
Physical tests to measure the difference in adhesion between modified and unmodified SU-8 epoxy resin-based photoresist materials were conducted. The two resins (modified and unmodified) were prepared generally as described above. The modified masking composition comprised about 62.4 weight percent SU-8 resin, 26.3 weight percent γ-butyrolactone, 6.3 percent Cyracure® 6974, 1.0 percent DOP, and 4.0 percent GPTMS. Each composition was applied to an untreated copper seed wafer.
Adhesion was measured by a block shearing method, wherein each block is a 210 micron square with a thickness of approximately 140 microns. Both systematic die site and random walk sampling were taken. The die site is defined by the central 12 by 16 die array with (1, 1) being the lower left corner die. Using die site sampling, the wafer average sheer force for the unmodified SU-8 material was 49.5 grams while the wafer average sheer force for the modified SU-8 material was 63.6 grams, showing a 28 percent improvement over the unmodified SU-8. Likewise, for the random walk testing, the wafer average sheer for the unmodified SU-8 was 51.3 grams while the wafer average for the modified SU-8 was 61.2 grams, showing an improvement of 19 percent.
The Tables below show the results.







TABLE I







Adhesion test of unmodified SU-8 by block shearing on untreated Cu


seed wafers. Each block is a 210 um square with thickness ~140 um.


Both systematic die site and random walk sampling were taken.


Die site is defined by the central 12 × 16 die array with (1, 1) being


the lower-left corner die.


SU-8 on Cu, No ash, Test speed: 50 um/s


Land speed: 250 um/s Shear height: 10 um Overtravel 10 um













Shear (g)

Shear (g)

Shear (g)


Die
n = 20
Die
n = 20
Die
n = 20





1, 1
42.02 (4.44)
1, 6
44.75 (2.80)
1, 12
37.46 (8.79)


8, 1
41.09 (1.81)
8, 6
48.14 (3.10)
8, 12
42.25 (4.03)


16, 1 
64.91 (5.40)
16, 6 
61.49 (3.84)
16, 12 
63.39 (2.99)





Wafer average, 9 die, 49.5 (4.13) g shear force, n = 180


Wafer average, random walk, 51.32 (7.94) g shear force, n = 100













TABLE II







Adhesion test of modified SU-8 according to the present invention by


block shearing on untreated Cu seed wafers. Each block is a 210 um


square with thickness ~140 um. Both systematic die site and random


walk sampling were taken. Die site is defined by the central 12 × 16 die


array with (1, 1) being the lower left-corner die.


Modified SU-8 on Cu, No ash, Test speed: 5-um/s


Land speed: 250 um/s Shear height: 10 um Overtravel: 10 um













Shear (g)

Shear (g)

Shear (g)


Die
n = 20
Die
n = 20
Die
n = 20





1, 1
59.02 (2.15)
1, 6
59.02 (2.15)
1, 12
57.70 (5.05)


8, 1
64.64 (3.61)
8, 6
64.64 (3.61)
8, 12
63.72 (1.58)


16, 1 
66.99 (4.85
16, 6 
66.99 (4.85)
16, 12 
67.45 (6.82)





Wafer average, 9 die, 63.55 (3.54) g shear force, n = 180


Waver average, random walk, 61.21 (8.59) g shear force, n = 100






EXAMPLE 8
Verification of Improved Resistance to Cracking and Film Stress
Physical tests to measure the difference in resistance to cracking and film stress for modified and unmodified SU-8 epoxy resin-based photoresist materials were conducted. The two resins (modified and unmodified) were prepared generally as described above. The modified masking composition comprised about 62.4 weight percent SU-8 resin, 26.3 weight percent γ-butyrolactone, 6.3 percent Cyracure® 6974, 1.0 percent DOP, and 4.0 percent GPTMS.
In the first test, the via cracking frequency for wafers coated with modified and unmodified SU-8 was measured. As is known to the art, via cracking arises from differences in the thermal expansion between the film and the substrate and is measured as a function of ultraviolet exposure dosage and cooling rate after the PEB. The cooling rate is given as either “fast” or “slow”, with “fast” being defined as cooling from 90° C. to about 22° C. in about 4 minutes and “slow” being defined as cooling from 90° C. to about 22° C. in about 20 minutes.
As is apparent from Table III, the modified SU-8 photoresist material trends towards having a substantially lower percentage of via cracking than does the unmodified SU-8 photoresist film material under the same conditions.







TABLE III







Via cracking frequency and photodose/PEB cooling correlation for


photoresist coatings on a wafer substrate. Only circular vias in the


array were counted. Q1, Q2, etc. represent quadrants with Q1 being


upper-left corner with flat facing down, clockwise to Q4. 40 vias


in each quadrant were counted. Fast cooling is defined as a rate


of ~4 min. from 90° C. to 22° C.; slow cooling is defined


as a rate ~20 min. from 90° C. to 22° C.;


NA indicates catastrophic failure of the wafer substrate.












Die position



Photo
PEB
with % via cracking
Die position with %


dose
cool-
(Modified SU-8)
cracking (SU-8)
















MJ/cm2
ing
Q1
Q2
Q3
Q4
Q1
Q2
Q3
Q4



















1200
Fast
100
100
100
100
100
100
100
100


1200
Fast
70
80
100
65
100
100
100
100


1200
Slow
20
40
15
25
NA
NA
NA
NA


1200
Slow
33
30
40
33
NA
NA
NA
NA


1570
Fast
40
33
40
33
100
90
100
80


1570
Fast
75
100
90
85
100
100
100
100


1570
Slow
40
60
50
53
NA
NA
NA
NA


1570
Slow
55
30
55
40
NA
NA
NA
NA


1940
Fast
100
80
90
60
80
100
100
95


1940
Fast
90
85
75
80
100
90
100
85


1940
Slow
42
58
33
53
NA
NA
NA
NA


1940
Slow
60
35
55
40
NA
NA
NA
NA


2310
Fast
60
45
30
40
100
100
90
100


2310
Fast
65
53
75
45
80
90
85
100


2310
Slow
5
10
15
0
30
20
60
28


2310
Slow
5
25
0
15
20
40
23
50









In a second test, real time wafer bow was measured for wafers coated with modified and unmodified SU-8 masks. All wafers were baked at 90° C. for 3 hours, and both after solvent bake bow and after PEB bow were measured after a 30 minute room temperature cooling period.
As can be seen from the data, the modified SU-8 films had substantially less wafer bow than did their unmodified counterparts when tested under the same conditions.







TABLE IV







Real-time wafer bow monitoring for 90 C./3 hour bake.


Both after solvent bake and after PEB bow were measured


after 30 minute room temperature cooling.









Formulation










Modified SU-8
SU-8













Mask
Film
Dot
Dot
Film
Dot
Dot





Bake Temp C./Time (hrs)
90/3
90/3
90/3
90/3
90/3
90/3


Before coat
32
40
NA
25
33
NA


After solvent bake
66
74
74
97
101
108


After expose
44
42
63
55
55
83


After PEB
310
95
98
330
125
132


After Develop
300
39
50
300
45
48









While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.

## Claims

1. A method of making a photoresist masking composition, the method comprising:
providing an organic solvent;
dissolving an octafunctional epoxidized novolac resin in the solvent to form a solution;
adding to the solution a plasticizer selected from the group consisting of dialkylphthalates, dialkylmalonates, dialkylsebacates, and dialkyladipates;
adding to the solution a photopolymerization initiator; and
adding to the solution an adhesion promoter selected from the group consisting of glycidoxypropanetrimethoxysilane, mercaptopropyltrimethoxysilane, and aminopropyltrimethoxysilane.

2. The method of claim 1, wherein said plasticizer is a dialkylphthalates.

3. The method of claim 1, wherein said plasticizer is a dialkylmalonates.

4. The method of claim 1, wherein said plasticizer is a dialkylsebacates.

5. The method of claim 1, wherein said plasticizer is a dialkyladipates.

6. The method of claim 1, wherein said adhesion promoter is a glycidoxypropanetrimethoxysilane.

7. The method of claim 1, wherein said adhesion promoter is a mercaptopropyltrimethoxysilane.

8. The method of claim 1, wherein said adhesion promoter is a aminopropyltrimethoxysilane.

9. The method of claim 1, wherein said octafunctional epoxidized novolac resin is of the formula:

10. The method of claim 1, wherein said solvent is present in an amount ranging between about 15% and about 45% by weight.

11. The method of claim 1, wherein said solvent is present in an amount ranging between about 20% and about 30% by weight.

12. The method of claim 1, wherein said solvent is present in an amount of about 25% by weight.

13. The method of claim 1, wherein said photopolymerization initiator is present in an amount ranging between about 3% and about 10% by weight.

14. The method of claim 1, wherein said photopolymerization initiator is present in an amount ranging between about 5% and about 8% by weight.

15. The method of claim 1, wherein said photopolymerization initiator is present in an amount ranging between about 6% and about 7% by weight.

16. The method of claim 1, wherein said photopolymerization initiator is a triaryl suiphonium SbF6 salt.

17. The method of claim 1, wherein said plasticizer is present in an amount ranging between about 0.5% and about 3% by weight.

18. The method of claim 1, wherein said plasticizer is present in an amount of about 2% by weight.

19. The method of claim 1, wherein said adhesion promoter is present in an amount ranging between about 1% and about 6% by weight.

20. The method of claim 1, wherein said adhesion promoter is present in an amount ranging between about 3% and about 4% by weight.

21. The method of claim 1, further comprising mixing the solution to substantially achieve uniformity.

22. The method of claim 1, wherein the steps of providing the solvent, dissolving the resin in the solvent, adding the plasticizer, adding the initiator, and adding the adhesion promoter are performed in that order.

23. The method of claim 1, wherein the initiator is added to the solution separately from the plasticizer.

24. The method of claim 1, wherein the solution is immediately mixed after the adhesion promoter is added.

25. The method of claim 1, further comprising debubbling the solution.

26. A method of making a photoresist masking composition, the method comprising:
providing an organic solvent having a boiling point of between 160° C. and 260° C.;
dissolving an octafunctional epoxidized novolac resin in the solvent to form a solution;
adding to the solution a plasticizer selected from the group dialkylphthalates, dialkylmalonates, dialkylsebacates, dialkyladipates, and diglycidyl hexahydrophthalates;
adding to the solution a photopolymerization initiator; and
adding to the solution an adhesion promoter selected from the group consisting of glycidoxypropanetrimethoxysilane, mercaptopropyltrimethoxysilane, and aminopropyltrimethoxysilane.

27. The method of claim 26, wherein said solvent has a boiling point of between 190° C. and 220° C.

28. A photoresist masking material according to claim 26 wherein said solvent has a boiling point of between 200° C. and 210° C.

29. A method of making a photoresist masking composition, the method comprising:
providing an organic solvent comprising gamma butyrolactone;
dissolving an octafunctional epoxidized novolac resin in the solvent to form a solution;
adding to the solution a plasticizer selected from the group dialkylphthalates, dialkylmalonates, dialkylsebacates, dialkyladipates, and diglycidyl hexahydrophthalates;
adding to the solution a photopolymerization initiator; and
adding to the solution an adhesion promoter selected from the group consisting of glycidoxypropanetrimethoxysilane, mercaptopropyltrimethoxysilane, and aminopropyltrimethoxysilane.

30. A method of making a photoresist masking composition, the method comprising:
providing 15% to 45% by weight of an organic solvent;
dissolving an octafunctional epoxidized novolac resin in the solvent to form a solution, the resin being 50% to 75% by weight and of the formula:




adding to the solution 0.5% to 3% by weight of a plasticizer selected from the group consisting of dialkylphthalates, dialkylmalonates, dialkylsebacates, and dialkyladipates;
adding to the solution 3% to 7% by weight a photopolymerization initiator; and
adding to the solution 1% to 6% by weight of an adhesion promoter selected from the group consisting of glycidoxypropanetrimethoxysilane, mercaptopropyltrimethoxysilane, and aminopropyltrimethoxysilane.