JPH03225340A - Resist material - Google Patents

Abstract

PURPOSE:To enhance sensitivity to far ultraviolet rays and to revolve fine patterns with good rectangularity by synthesizing a novolak resin in the presence of excess formalin and combining a diazo compound with the hydroxyl groups. CONSTITUTION:The novolak resin is synthesized in the presence of excess formaline, resulting in forming branched structure as shown on the right, and greatly enhancing dissolution velocity in an aqueous solution of alkali, and extremely facilitating development. The diazo compound, such as naphthoquinone-diazido derivatives, is chemically combined with the hydroxyl groups present in the novolak resin to cause them to function as photosensitive agents, thus permitting high sensitivity and high resolution to be ensured, and ultrafine patterns, for example, <= 0.5 mum to be resolved with good rectangularity.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a resist material suitable for forming fine patterns, which is applied to the manufacture of semiconductor integrated circuits, magnetic bubble memory elements, etc. This relates to a positive resist material that is dissolved by an alkaline solution.

[Summary of the invention]

The present invention has developed a resist material mainly composed of novolac resin synthesized from cresol and formalin, by increasing the ratio of formalin and introducing a divided structure, and by chemically bonding a diazo compound directly to the novolac resin. The present invention aims to provide a resist material that is highly sensitive to ultraviolet light and has high resolution.

[Conventional technology]

BACKGROUND OF THE INVENTION As semiconductor integrated circuits, magnetic bubble memories, and the like become highly integrated, there is a demand for the formation of even finer patterns, and the wavelength of light sources used in photolithography is becoming shorter. In addition, in response to the miniaturization of patterns, dry etching using oxygen or the like has been used instead of conventional wet etching in order to accurately transfer resist patterns onto substrates.

Therefore, there is a need for a resist material that is sensitive to the far ultraviolet wavelength range of 200 to 300 ns and has high dry etching resistance.

As resist materials sensitive to the deep ultraviolet wavelength range, positive type resists such as polymethyl methacrylate resists and novolac type resists, and negative type resists such as chloromethylated styrene type resists and polyglycidyl methacrylate type resists have already been proposed. has been done.

However, regarding polymethyl methacrylate-based resists and polyglycidyl methacrylate-based resists,
It has poor dry etching resistance and extremely low sensitivity, making it impractical.

In addition, chloromethylated styrene resists, such as K
An rF laser requires 1 to 2 J/c4, and poor sensitivity is a problem.

On the other hand, novolac resists have etching resistance against chlorine gases and fluorine gases, and have the highest sensitivity among the resists mentioned above, but they still have a resistance of 200 to 300 mJ.
/d is necessary, but cannot be said to be sufficient.Furthermore, the novolak resist contains a large amount of components that absorb deep ultraviolet light, and the resist shape after exposure tends to be triangular in cross section. It is in. Therefore, when a short wavelength light source is used, it is difficult to obtain a fine pattern with good rectangularity.

[Problem to be solved by the invention]

As described above, there are many dissatisfaction with conventionally proposed resist materials in terms of sensitivity in the deep ultraviolet region and furthermore in terms of resolution, and improvements are desired.

Therefore, the present invention was proposed in view of the conventional situation, and an object of the present invention is to provide a resist material that has high sensitivity in the far ultraviolet region and is capable of resolving fine patterns with good rectangularity. shall be.

[Means to solve the problem]

The inventors of the present invention have conducted intensive research over a long period of time in order to achieve the above-mentioned purpose. As a result, they have found that when synthesizing novolac resin, they use excessive formalin, and by introducing a branched structure into the resin, they can use a developing solution (alkaline solution). As a result, the resist sensitivity and γ characteristics are improved, and by chemically bonding the photosensitive agent and novolac resin, sensitivity can be secured with less photosensitive agent, resulting in improved transmittance. It was found that the resist shape was improved.

The present invention was proposed based on these findings, and the molar ratio of cresol and formalin is set to 1:1 to 1:1.
It is mainly composed of a novolak resin synthesized as No. 4, and is characterized in that a diazo compound is chemically bonded to the phenolic hydroxyl group of the novolak resin.

The resist material of the present invention is mainly composed of a novolak resin synthesized from cresol and formalin, but a divided structure is introduced by making the molar ratio of cresol and formalin excessive in formalin during synthesis. There is.

Therefore, during synthesis, cresol:formalin was mixed in a ratio of 1:1.
-1:4, and preferably 1F1.5 to 1:2. If the molar ratio of formalin to cresol (formalin/cresol) is less than 1, a branched structure will not be introduced and the sensitivity will be No effect can be expected in terms of γ properties, etc. However, if the molar ratio exceeds 4, the novolac resin will gel and become difficult to handle.

A diazo compound that reacts with light of around 249 ns is further chemically bonded to the novolac resin, and this diazo compound is a compound having a diazo group and functioning as a photosensitizer, such as a naphthoquinone diazide derivative, a cyclic or Examples include linear 1,3-diketone-2-diazo compounds (Meldrum's acid diazo compounds).

To illustrate, etc.

Note that these diazo compounds contain a functional group [for example, a sulfonic acid group, -3o!] that chemically bonds to the phenolic hydroxyl group of the novolak resin. X, -COX (X is halogen, etc.)], and therefore, the following compounds are exemplified as the compounds used.

If the diazo compound has, for example, a -3O,C1 group, it will be chemically bonded to the hydroxyl group of the novolak resin through a sulfonic acid ester bond.

The amount of these diazo compounds introduced is preferably 3 to 30% by weight based on the novolac resin. If the amount of diazo compounds introduced is too small, sensitivity cannot be ensured, and conversely, if it is too large, However, the transmittance decreases and the sensitivity actually decreases.

The above-mentioned novolak resin is dissolved in a solvent to obtain a resist material, but the type of solvent used is not limited as long as it can dissolve the novolak resin.
It may be selected as appropriate depending on the purpose.

Furthermore, as a light source for exposing the resist material of the present invention, one suitable for irradiating light with a wavelength of 300 nm or less is suitable, and various deep ultraviolet light sources can be used. It is possible to use

During development, an alkaline solution is used, but an alkaline solution with a lower concentration than that of conventional resist materials may be used, and an alkaline aqueous solution with an alkali concentration of 0.6 to 0.8% by weight is preferred.

[Effect]

When synthesizing a novolak resin, by adding too much formalin, a split structure is introduced into the resin, as shown in FIG. This branched part of cresol easily reacts with alkali, and therefore, the novolak resin into which a branched structure has been introduced is extremely easy to develop.

In addition, if a diazo compound, which is a photosensitizer, is chemically bonded to the novolak resin, sufficient characteristics can be obtained with a small amount.
Decrease in sensitivity due to decrease in transmittance.

Deterioration of resist shape is eliminated.

〔Example〕

The present invention will be explained below based on specific experimental results.

Phase J [lll sucking Acquired 25g of tacresol, 24.3g of formalin.

180 mg of oxalic acid was weighed out and reacted in ethyl cellosolve acetate by heating and stirring at 120°C for 5 hours.

This was reprecipitated in water, unreacted formalin was removed, and dried under reduced pressure. The weight average molecular weight of the obtained resin was approximately 2,000.

Above, the molar ratio (cresol/formalin) is 1/1.3
As an example, by changing the amount of preparation, cresol/
Formalin-1/1.1/1.1.1/1.5.1/2
．． 1/3 of the novolac resin was synthesized. By adjusting the polymerization time, the weight average molecular weights of all of these were made to be approximately 2,000.

When the synthesized novolac resin was confirmed by NMR spectroscopy, it was found that the molar ratio was 1/1.3 and the number of bonds was about 1.1/1.5, whereas the number of bonds was about 1.1/1.5 for 5 bonds. In the case of 1/2, branching occurred at a ratio of about 1 to 3 bonds.

Diazo A 9 g of each novolac resin synthesized above and 0.63 g of naphthoquinone diazide-4-sulfonyl chloride (7% by weight based on the resin) were dissolved in dioxane, and 0.33 M1 of triethylamine was added dropwise to form naphthoquinone diazide-4.
- Sulfonyl chloride was ester bonded to novolak resin.

This was reprecipitated in an aqueous hydrochloric acid solution to remove the amine salt.

Finally, it is dissolved in ethyl cellosolve acetate and the pore size is 0.
A photoresist was prepared by filtering through a 2 μm filter.

The T value, sensitivity, and resin dissolution rate of each of these resists are
Shown in the table.

Table 1 It can be seen from Table 1 that as the formalin ratio increases, the sensitivity improves and the resin dissolution rate increases.

Pano: ≦ Yo L Among the synthesized photoresists, each sample with cresol/formalin = 1/1.3.1/1.5.1/2 was spin-coated to a film thickness of 1 μm. , baked at 90°C for 90 seconds.

Next, it was exposed with a KrF excimer stepper (NA=0.42) and developed with a tetramethylammonium hydroxide aqueous solution (6 seconds).

When the cross section of the formed resist pattern was observed with a scanning electron microscope, it was found that in each sample, a pattern of 0.35 μmL/S, which is close to the resolution limit of an excimer stepper, was resolved with good shape.

Table 2 shows the sidewall angle of the resist pattern for each sample and the concentration of the alkaline solution (tetramethylammonium hydroxide aqueous solution) used.

Table 2 As is clear from Table 2, changing the molar ratio of cresol and formalin increases the dissolution rate of the resin.
As a result, it was confirmed that the resist sensitivity was improved and the shape was improved.

In addition, when similar measurements were performed and compared with commercially available resists, novolak resists with high resolution, the resist sensitivity was 200 to 460 sJ/C-1 resolution was 0.
The sidewall angle of 4 to 0.5 μm was 60 to 70°, and it was found that the resist sensitivity, resolution, and resist shape were significantly inferior to the resist material to which the present invention was applied.

〔Effect of the invention〕

As is clear from the above description, in the resist material of the present invention, formalin is added in excess when synthesizing the novolak resin and a split structure is introduced, so that the dissolution rate in an aqueous alkaline solution can be significantly increased. Furthermore, since a diazo compound sensitive to deep ultraviolet light is chemically bonded, high sensitivity and high resolution can be achieved. For example, by exposing and developing with excimer laser light, fine particles of 0.5 μm or less can be produced. It is possible to resolve a pattern with good rectangularity.

Therefore, if applied to the manufacture of semiconductor integrated circuits, for example, it will lead to miniaturization of semiconductor elements and improvement in yield, and has very high industrial value.

[Brief explanation of drawings]

FIG. 1 is a structural formula showing the branched structure of novolak resin.

Claims (1)

[Scope of Claims] Mainly composed of a novolak resin synthesized with a molar ratio of cresol and formalin of 1:1 to 1:4, and characterized in that a diazo compound is chemically bonded to the phenolic hydroxyl group of the novolac resin. resist material.