JPH042181B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a positive photoresist composition with improved resolution, that is, the γ value described below. A photosensitive resin composition containing a compound having a quinonediazide group such as a naphthoquinonediazide group or a benzoquinonediazide group changes from an alkali-insoluble state to an alkali-soluble state by decomposing the quinonediazide group and producing a carboxyl group when irradiated with light of 300 to 500 μm. It is used in positive photoresists to take advantage of this fact. In this case, novolac resins are usually used in combination. Novolac resins are important in obtaining uniform and durable resist coatings. This positive type photoresist has a feature of significantly superior resolution compared to a negative type photoresist. Taking advantage of this high resolution, it is used as an etching protection film for photolithography when manufacturing integrated circuits such as copper-clad laminates for printed wiring and ICs and LSIs. Among these, integrated circuits are becoming increasingly finer as they become more highly integrated, and pattern formation with a width of 1 μm is now required. Conventionally, a mask contact method has been used to mold integrated circuits, but
This method is said to have a limit of 2 μm, and as an alternative, reduced projection exposure methods are attracting attention. This method is a method in which the pattern of a master mask (reticle) is reduced and projected using a lens system for exposure.
Resolution is possible down to approximately 1 μm. On the other hand, as equipment improves, resists are also required to have higher performance. One of the important items is improving the γ value. As a definition of the γ value, when the exposure amount changes from E ₁ to E ₂ and the development speed of the exposed area changes from R ₁ to R ₂ , γ = (logR ₂ - logR ₁ ) / (logE ₂ −
The value is expressed as _logE1 ). The γ value is an index corresponding to resolution, and the larger the value, the greater the change in development speed with respect to the change in exposure amount, and the sharper the pattern. Until now, there have been only a few positive photoresist compositions with improved γ values and methods for producing the same that involve improving quinonediazide, and these are not sufficient to meet the recent demands for high resolution. . Therefore, the inventors of the present application focused on improving the γ value by improving novolac resins, which had been neglected until now. By the way, this novolac resin has been well known for a long time as a resin for general molding materials, and although various attempts have been made to improve it, there is a difference between its use as a general molding material and its use as a positive photoresist. The difference is quite significant, and the resin for the former use cannot be used as is for the latter use. For example, looking at the molecular weight of the resin, the weight average molecular weight (Mw) for the former application is less than 2000, but for photoresist use it is required to be at least 3000. This is because the selection criteria for other raw material phenols are also significantly different. be. West German Patent No. 1022005 relates to technology related to this novolak resin for general molding materials.
No. 1, which describes a method for producing a novolak resin using an organic acid salt of a divalent metal, which has a greater tendency to ionize than hydrogen, as a catalyst. This novolak resin has more ortho-ortho bonds than novolak resins synthesized using acid catalysts, and is called a high-ortho novolak resin. When mixed with an amine curing agent and molded, the curing speed is faster than resins synthesized with acid catalysts. It is said to have the advantage of being fast. However, the curing speed itself is not necessarily a desirable attribute for positive type photoresists, and this publication does not contain any description or suggestion regarding positive type photoresists. Against this background, the inventors of the present application have made intensive improvements to novolac resins, and as a result, they have developed a resin that can be synthesized from specially selected phenols using an organic acid salt of a divalent metal that is more electropositive than hydrogen as a catalyst. When a novolak resin is combined with a quinone diazide compound and used in a positive type photoresist, the inventors surprisingly found that the γ value, which is an important basic performance of a resist, was greatly improved, and the present invention was completed. That is, the present invention is based on the general formula

A mixture of one or more compounds represented by the formula (R is hydrogen or an alkyl group having 1 to 4 carbon atoms), and the average number of substituent carbon atoms per phenol skeleton is 0.5 to 0.
Phenols and formaldehyde in which the proportion of compounds having a substituent in the ortho or para position relative to the hydroxyl group is 50 mol% or less, and organic acid salts of divalent metals that are more electropositive than hydrogen. A positive photoresist composition characterized by containing a novolac resin and a quinonediazide compound obtained by an addition condensation reaction under conditions of PH4 to 7 (hereinafter referred to as a one-step method) using a catalyst, and as described above. Using the metal organic acid salt as a catalyst, PH4
After partial addition condensation reaction under the conditions of ~7,
A positive photoresist composition characterized by containing a novolac resin and a quinonediazide compound obtained by further carrying out an addition condensation reaction using an acid as a catalyst under conditions of pH below 4 (hereinafter referred to as a two-step method). It is. The present invention will be described in more detail below. First, the novolak resin will be explained. The general formula for phenols used as raw materials is

One type of compound or a mixture of two or more types of compounds represented by the formula is used. In the general formula, R represents hydrogen or an alkyl group having 1 to 4 carbon atoms, and R may be bonded to the hydroxyl group at any of the ortho, meta, and para positions. Such compounds include phenol, o-cresol, m-cresol, p-cresol, o-ethylphenol, m-cresol,
Examples include isomers of -ethylphenol, p-ethylphenol, propylphenol, and isomers of butylphenol. One type or a mixture of two or more of these compounds is used, and in that case, the average number of substituent carbon atoms per phenol skeleton is 0.5 to 1.5, and the substituent is substituted in the ortho or para position with respect to the hydroxyl group. It is selected and used so as to satisfy the condition that the proportion of the group-containing compound is 50 mol% or less. For the conditions, the average number of substituent carbons per phenol skeleton is 0.5
If the average number of substituent carbon atoms exceeds 1.5, the novolak resin will dissolve too quickly in the developer (alkaline aqueous solution), resulting in a decrease in the remaining film rate in the unexposed areas. However, there arises a problem that the rate at which the novolac resin dissolves in the developer becomes slow, and it takes time to develop the exposed areas. Therefore, the average number of substituent carbon atoms is selected to be 0.5 to 1.5. In addition, if the proportion of the compound having a substituent at the ortho or para position with respect to the hydroxyl group exceeds 50 mol%, the target of the present invention is γ.
This is not preferable because the effect of improving the value becomes small. Therefore, this proportion is selected to be 50 mol% or less. These conditions will be explained below using specific examples. For example, m-cresol and p-
When using a mixture of cresols, the average number of substituent carbon atoms per phenol skeleton is 1, and the following condition is satisfied, so the ratio of compounds having a substituent at the ortho or para position to the hydroxyl group is Under the condition that m-cresol/p-cresol is 50 mol% or less, it is preferable to use the mixture in the range of m-cresol/p-cresol≧1. Next, when using a mixture of phenol and m-ethylphenol, the phenol skeleton is The average number of carbon atoms per substituent is
From the condition of 0.5 to 1.5, 1/3≦phenol/m
- Ethylphenol may be used within the range of 3 (molar ratio). In addition, as another example, when using a mixture of phenol and p-ethylphenol, from the condition, 1/3≦phenol/p-ethylphenol≦3 (molar ratio), and from the condition, phenol/p-ethylphenol≧ 1, so
It may be used within the range of 1≦phenol/p-ethylphenol≦3 (molar ratio), including the following conditions. In particular, when only one type of compound is selected as the phenol, m-cresol is the only one selected from the following conditions. Above, specific examples of phenols have been described, but various other combinations and combinations of three or more types are possible.In that case, the mixing ratio should be selected from the conditions of , as in the case of the specific examples above. use Among these, phenols containing 95 mol % or more of m-cresol are particularly suitable. That is, m-cresol at 95
% or more of phenols is similar to m-cresol alone, and the addition condensation reaction with formaldehyde can be precisely controlled, resulting in a novolak resin with very stable quality, and as a result, a positive-working photo film with very little variation between lots. It has a great advantage in that it provides a resist composition. Next, formaldehyde to be subjected to an addition condensation reaction with phenols will be explained. As the formaldehyde, an aqueous formaldehyde solution (formalin) and paraformaldehyde, which is an oligomer of formaldehyde, can be used. In particular, 37% formalin is produced industrially in large quantities and is convenient. Next, an organic acid salt of a divalent metal that is more electropositive than hydrogen and used as a catalyst will be explained. The order of magnitude of the tendency of metals to emit electrons and become ionized is known as an ionization series, and Kyoritsu Shuppan's Chemistry Dictionary lists K> as an example.
Ca＞Na＞Mg＞Zn＞Fe＞Co＞Pb＞H＞Cu＞Ag
They are listed in the order of >Hg>Au. As the organic acid salt of a metal used in the present invention, an organic acid salt of a divalent metal that is on the left side of hydrogen in this ionization series, that is, has a larger ionization tendency than hydrogen, and is divalent.
Examples of such metals include barium, strontium, calcium, magnesium, manganese, zinc, cadmium, cobalt, lead, and the like.
Among these, magnesium, manganese, zinc, cadmium, cobalt, and lead are particularly preferred. In addition, iron, chromium, nickel, and tin can also be used, but these divalent metals have poor stability and are therefore less useful. As the catalyst of the present invention, a salt of the above divalent metal and an organic acid is used. As the organic salt of the divalent metal, one is used that is soluble in the reaction mixture and has a pH of 4 to 7. Specific examples of such salts include acetic acid, formic acid, lactic acid,
Examples include salts such as benzoic acid. Among these, acetate is particularly preferred. The appropriate amount of the divalent metal salt used as the catalyst is 0.1 to 5% by weight based on the phenol. If it is less than 0.1% by weight, the catalytic effect will not be sufficient, and if it exceeds 5% by weight, the effect will reach a plateau.
This is uneconomical and undesirable. The above-described addition condensation reaction between phenols and formaldehyde using the divalent metal salt as a catalyst can be carried out according to a known method, but the reaction rate varies depending on the type of phenol and the type of catalyst. Therefore, it is necessary to select appropriate conditions depending on the reaction system. In particular, the pH of the reaction system is important, and in order to obtain the novolak resin of the present invention, the pH is set at 4 to 7. Further, the reaction can be carried out either in bulk or by using a suitable solvent. Next, a method will be described in which a phenol and formaldehyde are subjected to a partial addition-condensation reaction using the above divalent metal salt as a catalyst, and then further subjected to an addition-condensation reaction using an acid as a catalyst. In this case, the partial addition condensation using the divalent metal salt as a catalyst in the first stage may be carried out in the same manner as the above-mentioned method. For the subsequent addition condensation reaction, an acid is used as a catalyst, and the acid used here may be either an inorganic acid or an organic acid. Specific examples include hydrochloric acid, sulfuric acid, phosphoric acid, p-toluenesulfonic acid, oxalic acid, and trichloroacetic acid. The reaction is carried out by carrying out an addition condensation reaction using a divalent metal salt for a predetermined period of time, and then adding an acid to the reaction system. By adjusting the ratio between the reaction time in the first stage and the reaction time in the second stage, the γ value of the resist can be controlled. If the reaction time in the first stage is increased, the γ value increases, but the sensitivity tends to decrease. Therefore, by adjusting this ratio, a well-balanced novolak resin with an improved γ value and good sensitivity can be obtained. PH after adding acid is 4
Adjust so that it is less than The lower the PH, the faster the reaction rate, but since the reaction rate varies depending on the type of phenol, select an appropriate catalyst and PH. Further, the reaction can be carried out either in bulk or by using a suitable solvent. Next, regarding the molecular weight of novolak resin, the optimum range differs depending on the type of phenol, the type of catalyst, and the reaction conditions, but when using only a divalent metal salt as a catalyst, the GPC
It is appropriate that the weight average molecular weight Mw determined by this method is 3000 to 8000. In addition, when using a divalent metal salt in the first stage and an acid in the second stage as a catalyst, it is generally determined by GPC.
Mw of 3000 to 20000 is appropriate. Molecular weight is controlled by changing the ratio of formaldehyde to phenols. The Mw shown here is a value calculated from a GPC chromatogram using a calibration curve obtained using monodisperse polystyrene, and the GPC chromatogram was measured using an LC-08 preparative liquid chromatograph manufactured by Nippon Analytical Kogyo. Using the equipment, the column was JAIGEL, LS255 manufactured by Nippon Analytical Industry Co., Ltd.
JAIGEL, 2H connected one by one in series,
Tetrahydrofuran was used as a carrier solvent at a flow rate of about 2.5 ml/min. Next, the quinonediazide compound, which is a photosensitive component, will be described. A quinonediazide compound can be obtained by condensing naphthoquinonediazide sulfonic acid chloride or benzoquinonediazide sulfonic acid chloride with a compound having a hydroxyl group in the presence of a weak alkali. Examples of compounds with hydroxyl groups include hydroquinone, resorcinol,
Examples include phloroglucin, 2,4-dihydroxybenzophenone, 2,3,4-trihydroxybenzophenone, gallic acid alkyl ester, and the like. The mixing ratio of the quinonediazide compound and the novolac resin is preferably in the range of 1:1 to 1:6. The resist solution is prepared by mixing and dissolving a quinonediazide compound and a novolak resin in a solvent. The solvent used here is preferably one that provides a uniform and smooth coating film after the solvent evaporates at an appropriate drying rate. Such substances include ethyl cellosolve acetate, methyl cellosolve acetate, ethyl cellosolve, methyl cellosolve, butyl acetate, methyl isobutyl ketone, xylene, and the like. The positive photoresist composition described above may further contain small amounts of additional resins, plasticizers, dyes, etc. as additional additives. Among these, epoxy resin is particularly suitable as the additional resin. Adhesion is improved by adding epoxy resin. Epoxy resins are low-molecular or high-molecular compounds having two or more epoxy groups in one molecule, and those having a molecular weight of 200 to 20,000 are preferred. Industrially, there are two types: one synthesized from epichlorohydrin and an active hydrogen compound, and one based on oxidation of olefin, both of which can be used. Examples of the former include a reaction product of bisphenol A and epichlorohydrin, a reaction product of tetrabromobisphenol A and epichlorohydrin, a reaction product of resorcinol and epichlorohydrin, a reaction product of phenol-formaldehyde novolak resin and epichlorohydrin,
Examples include a reaction product of cresol-formaldehyde novolac resin and epichlorohydrin, a reaction product of p-aminophenol and epichlorohydrin, and a reaction product of aniline and epichlorohydrin. Examples of the latter include epoxidized polybutadiene and epoxidized soybean oil. The amount of this epoxy resin added is preferably within a range that does not significantly change the photosensitive characteristics of the resist, and will vary depending on the type and molecular weight of the epoxy resin.
It is preferably used in an amount of 1 to 20 wt% based on the total of the novolac resin and the quinonediazide compound. EXAMPLES Next, the present invention will be specifically explained with reference to Examples, but the present invention is not limited to these Examples. Reference Example 1 (One-stage method) Into a 500 ml separable flask, 66.3 g of m-cresol (purity 99.4%), 42.5 g of formalin (37.0% aqueous solution), and 0.66 g of zinc acetate dihydrate were charged (the pH of the reaction system was approximately 6). ), heated and stirred in a 115°C oil bath for 4 hours to react, neutralized, washed with water, and dried under reduced pressure to obtain a novolak resin. The weight average molecular weight determined by GPC chromatography was 4420. Reference Examples 2 and 3 (Two-step method) 66.3 g of m-cresol (purity 99.4%) and formalin (37% aqueous solution) in a 500 ml separable flask.
After charging 47.3 g of zinc acetate dihydrate and 0.66 g of zinc acetate dihydrate (PH of the reaction system is about 6), heating and stirring in an oil bath at 115°C for 30 minutes to react, add 1.02 g of oxalic acid dihydrate and 6 g of ion-exchanged water.
g, and 60 g of ethyl cellosolve acetate were charged (PH of the reaction system was about 1), and the mixture was heated and stirred for further X hours to react, neutralized, washed with water, and dehydrated to obtain a solution of novolac resin in ethyl cellosolve acetate. The weight average molecular weight determined by GPC chromatography was as follows.

[Table] Reference Example 4 (Two-step method) Charge 66.3% m-cresol (purity 99.4%), 0.66 g of zinc acetate dihydrate, and 6.6 g of ion-exchanged water into a 500 ml separable flask, and heat in an oil bath at 115°C. While heating and stirring, add 45.0 g of formalin (37.0%) aqueous solution.
Dropped over 40 minutes, then further heated for 2 hours.
The reaction was stirred. Next, add 60 g of ethyl cellosolve acetate and 12.5 g of 5% oxalic acid aqueous solution.
The reaction mixture was heated and stirred in an oil bath at 115° C. for 7 hours, and then neutralized, washed with water, and dehydrated to obtain an ethyl cellosolve acetate solution of novolak resin. The weight average molecular weight determined by GPC chromatography was 7430. Reference Examples 5 to 7 (Two-step method) Charge 66.3 g of m-cresol (purity 99.4%), 0.66 g of zinc acetate dihydrate, and 6.6 g of ion-exchanged water in a 500 ml separable flask and heat in an oil bath at 115°C. While stirring, add 47.3 g of formalin (37.0%) aqueous solution.
The mixture was added dropwise over a period of 40 minutes, and the reaction was continued with stirring for an additional 40 minutes. Next, add 60g of ethyl cellosolve acetate, followed by 12.5g of 5% oxalic acid aqueous solution.
The mixture was added dropwise over 40 minutes, followed by heating and stirring reaction for X hours, followed by neutralization, washing with water, and dehydration to obtain a solution of novolac resin in ethyl cellosolve acetate.
The weight average molecular weight determined by GPC chromatography was as follows.

[Table] Reference example 8 66.3 g of m-cresol (purity 99.4%) and formalin (37% aqueous solution) in a 500 ml separable flask.
47.3g, oxalic acid dihydrate 1.02g, ion exchange water 6g,
Prepare 60g of ethyl zero solve acetate, 115
The reaction mixture was heated and stirred in an oil bath at 0.degree. C. for 5 hours, neutralized, washed with water, and dehydrated to obtain an ethyl cellosolve acetate solution of novolak resin. The weight average molecular weight by GPC chromatography is
It was 8220. Reference Example 9 (Two-step method) Mixed cresol of m-cresol/p-cresol = 6/4 in a 500 ml separable flask.
66.3 g, formalin (37% aqueous solution) 45.0 g, and zinc acetate dihydrate 0.66 g were heated and stirred in an oil bath at 115°C for 0.5 hours to react, and then oxalic acid dihydrate 1.02 g,
6g of ion exchange water, ethyl cellosolve acetate
60 g of the solution was added, heated and stirred for 3.5 hours to react, and further neutralized, washed with water, and dehydrated to obtain an ethyl cellosolve acetate solution of novolak resin.
The weight average molecular weight by GPC chromatography is
It was 5010. Reference example 10 Mixed cresol of m-cresol/p-cresol = 6/4 in a 500ml separable flask.
66.3g, formalin (37% aqueous solution) 45.0g, oxalic acid dihydrate 1.02g, ion-exchanged water 6g, and ethyl cellosolve acetate 60g were prepared and heated in an oil bath at 115°C.
The mixture was heated and stirred for a period of time to react, neutralized, washed with water, and dehydrated to obtain a solution of novolak resin in ethyl cellosolve acetate. The weight average molecular weight determined by GPC chromatography was 5280. Reference example 11 (Two-step method) Phenol 28.9 in a 500ml separable flask
37.5 g of m-ethylphenol, 45.0 g of formalin (37% aqueous solution), and 0.66 g of zinc acetate dihydrate were heated and stirred in an oil bath at 115°C for 0.5 hours to react, and then 1.02 g of oxalic acid dihydrate was prepared. , 6g of ion exchange water,
60 g of ethyl cellosolve acetate was added, heated and stirred for further 8 hours to react, neutralized, washed with water, and dehydrated to obtain a solution of novolak resin in ethyl cellosolve acetate. The weight average molecular weight by GPC chromatography is
It was 4830. Reference example 12 Phenol 28.9 in a 500ml separable flask
g, m-ethylphenol 37.5g, formalin (37% aqueous solution) 47.5g, oxalic acid dihydrate 1.02g, ion exchange water 6g, ethyl cellosolve acetate 20g
After heating, stirring, and reacting in an oil bath at 115°C for 3 hours, 40 g of ethyl cellosolve acetate was added, and the mixture was heated, stirred, and reacted for an additional 3 hours, and then neutralized.
The mixture was washed with water and dehydrated to obtain a solution of novolak resin in ethyl cellosolve acetate. The weight average molecular weight determined by GPC chromatography was 5570. Reference Examples 13 to 19 (One-stage method) 66.3 g of m-cresol (purity 99.4%), 42.5 g of formalin (37.0% aqueous solution), and 0.66 g of the following metal salts were placed in a 500 ml separable flask (the pH of the reaction system (also falls within the range of 4 to 7), the reaction is heated and stirred in an oil bath at 115° C. for 4 hours, neutralized, washed with water, and dried under reduced pressure to obtain a novolak resin.

[Table] Examples 1 to 9, Comparative Examples 1 to 8 As shown in Table 1, the novolac resins shown in Reference Examples 1 to 12 were mixed with ethyl cellosolve acetate/n-butyl acetate/n-butyl acetate/photosensitive agent, epoxy resin, and dye, respectively. A resist solution was prepared by dissolving it in a solvent with a mixing ratio of xylene = 8/1/1 (the amount of solvent was adjusted to 1.25 μm under the coating conditions shown below). These compositions were filtered through a filter with a pore size of 0.2 μm to remove foreign particles. This was applied to a silicon wafer that had been cleaned using a conventional method using a spin coating machine.
It was applied at 4000r.pm. This silicon wafer was then placed in a clean oven at 900°C and baked for 20 minutes. Thereafter, using a contact aligner using a 350 W ultra-high pressure mercury lamp as a light source, exposure was performed for 5 seconds through a step tablet mask with stepwise changing optical transmittance. Then an aqueous solution of tetramethylammonium hydroxide (2.38
%) for 75 seconds. After rinsing and drying, the development speed and exposure amount at each step were plotted to determine the γ value. The results are shown in Table 1. As is clear from the table, the γ values of Examples 1 to 9 were significantly improved compared to Comparative Examples 1 to 3.

【table】

[Table] Examples 13 to 19 17 parts of the novolac resin shown in Reference Examples 13 to 19, 7 parts of the same photosensitizer used in Example 1, 2.0 parts of the same epoxy resin used in Example 1, and 2.0 parts of the same epoxy resin used in Example 1. A resist solution is prepared by dissolving 0.15 parts of the same dye in a solvent with a mixing ratio of ethyl cellosolve acetate/n-butyl acetate=7/3. (The amount of solvent is
Adjusted to 1.25μm by spin coating at 4000rpm). These compositions were filtered in the same manner as in Example 1,
After coating the silicon wafer, baking, exposing, developing, rinsing, and drying, the development speed and exposure amount for each step are plotted to determine the γ value. As shown in Table 2, the γ value was significantly improved in all cases.

【table】

Claims (1)

[Scope of Claims] 1 A mixture of one or more compounds represented by the general formula [Formula] (R is hydrogen or an alkyl group having 1 to 4 carbon atoms), which has a phenol skeleton 1
Barium, strontium, Calcium, magnesium, manganese, zinc, cadmium, cobalt,
Contains a novolak resin and a quinone diazide compound obtained by addition condensation reaction under conditions of PH4 to 7 using an organic acid salt of at least one divalent metal selected from lead, iron, chromium, nickel, and tin as a catalyst. A positive photoresist composition characterized by: 2 A mixture of one or more compounds represented by the general formula [Formula] (R is hydrogen or an alkyl group having 1 to 4 carbon atoms), which has a phenol skeleton 1
Barium, strontium, Calcium, magnesium, manganese, zinc, cadmium, cobalt,
Using an organic acid salt of at least one divalent metal selected from lead, iron, chromium, nickel, and tin as a catalyst, a partial addition condensation reaction is carried out under conditions of PH4 to 7, and then an acid is used as a catalyst. 1. A positive photoresist composition comprising a novolak resin and a quinone diazide compound obtained by further addition-condensation reaction under conditions of pH below 4. 3. The positive photoresist composition according to claim 1, wherein the phenol is a phenol containing 95 mol% or more of m-cresol. 4. The positive photoresist composition according to claim 2, wherein the phenol is cresol containing 95 mol% or more of m-cresol.