JPH03200968A - Positive type photosensitive resin composition - Google Patents

Abstract

PURPOSE:To obtain a rectangular pattern by lithography with far UV rays by incorporating styrene resin and maleimide. CONSTITUTION:This positive type photosensitive resin compsn. contains styrene resin and maleimide. When this compsn. is irradiated with far UV rays, the maleimide is added to the styrene resin e.g. polystyrene as shown by equation I to form an adduct. Hydrogen of each imido group of the adduct is abstracted by hydroxyl ions in an alkali developing soln. such as 5% tetramethylammonium hydroxide soln. by contact with the developing soln. and the exposed part of the compsn. is made soluble in the developing soln. In the unexposed part, the maleimide acts as a dissolution inhibitor for the styrene resin and the unexposed part does not dissolve in the developing soln. A rectangular resist pattern can be obtd. by lithography with far UV rays.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to positive photosensitive resin compositions (prior art) In recent years, the integration of LSIs has been increasing more and more. In the manufacture of such LSIs, lithography technology plays an extremely important role.This is because the degree of integration of LSIs depends on the technology level such as the resolution and alignment accuracy of the lithography, and when manufacturing LSIs, the lithography technology plays an extremely important role. is 10
This is due to repeated use several times or more.

Therefore, improvements to the conventional lithography technology, in particular,
Research has been conducted to improve resolution, and exposure devices have been developed and put into practical use as described below.

As is well known, the practical resolution 0 of the reduction projection exposure method is R=
Since it is expressed as 0.6λ/NA (wherein is the exposure wavelength and NA is the numerical aperture of the optical system), it can be improved by increasing NA.

For this reason, the 9!1 (wavelength 436
In the exposure method using 3 nm), the resolution was improved by increasing the NA.

However, as is well known, the depth of focus DOF of an exposure device is
Since it is expressed as DOF=0.5λ/NA2, high N
It becomes shallower as it becomes A. Therefore, it is difficult to form submicron-level patterns on the surface of an LSI whose surface has complex irregularities due to multilayer wiring or the integration of various types of elements.

Therefore, in recent projection exposure drawings, consideration has been given to setting the NA to a value that can ensure a practical depth of focus (for example, about 2 um in a range) and shortening the exposure wavelength. Specifically, i-line (wavelength 365 nm), KrF
Excimer laser (248.5 nm) and far ultraviolet light with a wavelength of around 250 nm are used as exposure light. Especially the latter two
0.5, since those with shorter wavelengths can greatly benefit from shorter wavelengths.
It is also possible to resolve fine patterns smaller than um. Note that far ultraviolet light herein refers to light with a wavelength of 200 to 300 nm. Same below.

On the other hand, photosensitive resin compositions (hereinafter sometimes referred to as photoresists or resists) play an extremely important role in improving the resolution of lithography techniques.

Diazonaphthoquinone/novolak-based positive photoresists are known to provide a high-resolution resist pattern when a 9-line (or even i-line) light source is used. However, this cannot be used when the above-mentioned KrF excimer laser or far ultraviolet light is used as a light source for the reasons explained below.

Diazonaphthoquinone/novolak-based positive photoresists are generally made of, for example, a novolac resin (the following formula, hereinafter sometimes abbreviated as substance ■) and a naphthoquinone sulfosic acid ester of trihydroxybenzophenone (the following formula ■, hereinafter sometimes referred to as substance ■). , sometimes abbreviated as substance■). However, n in formula 0 indicates the degree of polymerization (same as n in various structural formulas below), and DN in formula
Q is the diazonaphthoquinone sulfonic acid moiety of substance ■ and is represented by the following formula ■ (hereinafter, partial structure of substance ■
It is sometimes abbreviated as. ), and substance (1) is not only a photosensitizer but also a dissolution inhibitor having the property of inhibiting the dissolution of substance (2) in an alkaline aqueous solution.

The substance (2) loses its ability to inhibit alkali dissolution.Therefore, the exposed portion of the photoresist dissolves in the developer, resulting in a positive pattern.

When a photoresist of this type is exposed to 9-ray or i-ray, the partial structure (2) of the substance (2) in the exposed area changes to an alkali-soluble indenecarboxylic acid-induced (436nm and 365nm) wavelength.
The property of m to absorb each light was based on the diazocarbonyl of the partial structure (2) of the substance (2). Therefore, when the partial structure (2) of substance (2) changes to substance (2) due to exposure to light, substance (2) ceases to absorb light at wavelengths of 436 nm and 365 nm. That is, photobleaching occurs. For this reason, the exposure light (in this case, the 9-line or i-line) reaches the bottom of the photoresist layer, so the exposed area is dissolved by the developer to the bottom, so that
A resist pattern having a rectangular cross section is obtained.

However, in this photoresist, when it is exposed to deep ultraviolet light, no change occurs in the part of the substance (1) except for the partial structure (2), so photobleaching hardly occurs. For this reason,
Exposure light (KrF excimer laser or deep ultraviolet light) is absorbed only in the upper part of the photoresist layer, and only an extremely insufficient amount of light reaches the lower part. As a result, the resulting resist pattern has a large taper angle and a large amount of film loss.

In order to solve this problem, it is necessary to reduce the absorption of far ultraviolet light by the photoresist. Specifically, it is important that the material exhibits photobleaching property against far ultraviolet light.

To achieve this, it was necessary to devise the chemical structure of the base resin and photosensitizer that make up the photoresist. As an example, for example, the literature (SPI
IE:The 5ociety of Photo-O
pticalInstrumentationEnqi
neers) Vol, 771. pp, 2-10 (1
There was a photoresist disclosed in 987)).

In this document, various new diazoketones are investigated in place of the conventional substance (1) as a dissolution inhibitor (photosensitizer) to be included in a photoresist.

The characteristics of these diazoketones are that they either do not have an aromatic ring, or even if they do have an aromatic ring, they are conjugated with other unsaturated groups, and that they undergo photorearrangement to form a 2-carboxylactam structure (
It has a structure that makes the following formula (see formula (2) below) more than 1. As such diazoketones, specifically, diazobiberidine ions represented by the following formulas (1), (2), or (2) have been used.

h The photoreaction of diazobiveridine sion is explained using the example of the above substance (①) as shown in the following formula.

■ ■ In other words, the substance (■) changes into the alkali-soluble substance (■).

Therefore, the ability of substance (1) to inhibit dissolution of the base resin in an alkaline solution is lost, thereby making it possible to pattern the resist.

According to the above-mentioned literature, a photoresist containing a novolac resin and the above-mentioned substance (■)! A resist pattern is formed by exposure with a KrF excimer laser. Judging from the SEM photograph of the document, the obtained positive pattern is 1. Ou
m line pattern, the taper angle of the side wall of the resist pattern (the angle formed between the side wall and the substrate surface) is at least 7.
It can be seen that since the upper surface is roughly flat, the film loss is extremely small. Therefore, the photoresist of the above-mentioned document is superior to a novolak/diazonaphthoquinone resist as a resist for deep ultraviolet rays.

(Problems to be Solved by the Invention) However, with the conventional photosensitive resin compositions disclosed in the above-mentioned documents, the resulting pattern is not a perfect rectangle but has a taper. When a submicron-level pattern is formed using a resin composition, the taper becomes even larger due to a decrease in the contrast of the intensity of incident light, and the shape of the resulting pattern becomes closer to a triangle than a rectangle.

Therefore, when dry etching a workpiece, such as a substrate, using a resist pattern with such a shape as a mask, the dimensional conversion difference (resist pattern dimension and pattern after etching) depends on the etching selectivity of the resist and workpiece materials. (difference with the size) will occur.

If we consider that the allowable dimensional conversion difference in microfabrication is 10% of the resist pattern dimension, the dimensional regression of the resist pattern is only 0.5 gm level machining.
The resist pattern must be kept within 0.05 um, and for this purpose, a resist pattern with side walls perpendicular to the substrate surface is required, but in this respect, conventional photosensitive resin compositions are not technically satisfactory. Ta.

Here, the main causes of deterioration of pattern shape are: 1. The photobleaching property of the photosensitive resin composition is not sufficient, so the exposure light is still absorbed even after exposure, and 2. Necessary for pattern formation. Since the decomposition of the photosensitizer in the photosensitive resin composition is not completed at such an exposure amount, it is thought that this also causes absorption of the exposure light.

The above phenomenon (2) mainly occurs due to absorption of exposure light by aromatic rings in the base resin (novolak resin in the conventional example). Therefore, one possible solution to the problem (2) is to make the base resin itself transparent to far ultraviolet light. In fact, methacrylic acid-based polymers such as poly(methyl methacrylate) so-called PMMj! By using In, a completely rectangular resist pattern can be formed. However, methacrylic acid-based polymers cannot be used in current microfabrication processes due to their low dry etching resistance.
Therefore, this countermeasure is not an essential solution at present.

The present invention has been made in view of the above points, and therefore, an object of the present invention is to provide a positive photosensitive resin composition capable of obtaining a rectangular pattern using deep ultraviolet light or lithography. It is in.

(Means for Solving the Problem) In order to achieve this objective, the inventor of this application has conducted various studies. As a result, as a countermeasure for the above problem (2), it was thought that it would be good to give the photosensitive resin composition a physical property that changes so that upon exposure, the aromatic ring portion of the base resin ceases to absorb deep ultraviolet light.

In addition, as a countermeasure for the above-mentioned problem (2), we thought that it would be better to use a photosensitizer that has photobleaching properties.

In addition, in any of the measures, the smaller the absorption of exposure light by the photosensitive resin composition itself, the smaller the absorption after exposure.
I thought it was preferable because it was possible.

As a result of studying such a configuration, we applied the photoaddition of maleimide (substance ■ in the following formula) to benzene (substance 0 in the following formula) to a photosensitive resin composition, as shown in the following formula. I planned something.

According to this photoreaction, the unsaturated bonds that were conjugated in the substance [phase] and the substance (1), respectively, become isolated in the substance (@). Roughly speaking, since the absorption of unsaturated bonds in a substance is at a wavelength of 220 nm or less, the substance is substantially transparent to far ultraviolet light. Therefore, it is considered possible to achieve the object of the present invention.

Therefore, the positive photosensitive resin composition of the present invention is characterized by containing a styrene resin and maleimide.

In carrying out this invention, poly(styrene) represented by the following formula 0 and the following [phase] are used as the styrene resin.
It is preferable to use one or both of poly(α-methylstyrene) represented by the formula.

In addition, if the molecular weight of the styrene resin is less than 2.000, the film of the photosensitive resin composition formed using the styrene resin will be too soft, causing problems in adhesion to the exposure mask, or the development speed will be too fast, resulting in a short development time. Styrene-based It is preferable to use a resin having a molecular weight of 2,000 to 100,000.

In addition, if the amount of maleimide is less than 10 parts by weight per 100 parts by weight of the styrene resin, problems such as the exposed areas of the photosensitive resin composition not being dissolved in an alkaline developer will occur, while if it is more than 40 parts by weight, the photosensitive resin composition will not be dissolved in the alkaline developer. The amount of maleimide in the photosensitive resin composition is determined by the amount of maleimide in the photosensitive resin composition. The content is preferably 10 parts by weight or more and less than 40 parts by weight per 100 parts by weight of the styrene resin.

(Function) According to such a configuration, when the positive photosensitive resin composition of the present invention is irradiated with far ultraviolet light, as shown in the following formula,
Maleimide■ is a styrenic resin such as poly(styrene)
Addition to ■ gives adduct ■.

■ ■ ■ Rarani,
The imide hydrogen of this adduct (①) is prepared using an alkaline developer such as 5
% tetramethylammonium hydroxide (TMAH), it is extracted by hydroxide ions in an alkaline developer (see the formula below). Therefore, the exposed area becomes soluble in the alkaline developer.

+\--~/ On the other hand, in the unexposed areas of the photosensitive resin composition of the present invention, maleimide acts as a dissolution inhibitor for the styrene resin, so the unexposed areas do not dissolve in the developer.

As a result, there is a difference in the solubility of the exposed and unexposed areas in the developing solution, making it possible to process the exposed area and the unexposed area.

Furthermore, the transmittance of light near the wavelength of KrF excimer laser light (including this light, hereinafter the same) of the portion of the positive photosensitive resin composition of the present invention exposed by KrF excimer laser light is clear from the experimental results described below. As shown, the K of the base resin contained in this positive photosensitive resin composition is
Since the transmittance is higher than the transmittance of light near the wavelength of rF excimer laser light, a sufficient amount of exposure light reaches the lower part of the exposure section.

(Examples) Examples of the positive photosensitive resin composition of the present invention will be described below. It should be understood that the names of the chemicals used and the numerical conditions such as molecular weight, mixing amount, temperature, film thickness, and time described in the following description are only preferred examples within the scope of the present invention.

Monodisperse poly(styrene) (manufactured by Tosoh) 109 whose weight average molecular weight j1M- is 50,000 and the ratio Mw/M* of Mw to number average molecular weight MN is 1°02
And maleimide 29! After dissolving in 100rr+j7 of cyclohexanone, this solution is filtered through a Medibrene filter having pores of 0.2 um in diameter to prepare a coating solution of the positive photosensitive resin composition of Example 1.

Next, the photosensitive resin composition of Example 1 is applied to a film thickness of lum using a spin coater onto a silicon wafer that has been subjected to hydrophobization treatment with hexamethyldisilazane.

Next, use a hot plate to make this silicon wafer! 10
Bake for 1 minute at a temperature of 0°C.

Next, a quartz mask having a line-and-space pattern (chrome pattern) of various dimensions is closely attached to the surface of the photosensitive resin composition side of the baked silicon wafer, and then this sample is exposed to light using a KrF simmer laser. Note that this exposure is performed using Lambda physics.
KrF excimer laser device manufactured by Physik)
The exposure was carried out at a dose of 18400 mJ/cm2L+ using an apparatus (H) which can perform exposure of 2 mJ/cm' per pulse and generates pulses at a cycle of 50 Hz.

Sample 1 & 5% TMA after exposure with KrF laser
Development is performed by immersing the film in a H aqueous solution in the dark for 300 seconds, and then rinsing with pure water.

When the obtained pattern was observed using a scanning electron microscope (SEM), it was found that although it was a 0.5 um line-and-space pattern, its cross section was nearly perfectly rectangular, that is, the pattern sidewall was substantially at an angle of 90 degrees to the silicon wafer surface. It turns out that a pattern can be obtained.

Moreover, apart from the above-mentioned buttering experiment, the absorption spectrum of the photosensitive resin composition of Example 1 in the ultraviolet-visible region was measured as described below.

The film thickness of the photosensitive resin composition of Example 1 on the quartz substrate was lu
Next, the absorption spectrum of this film in the ultraviolet-visible region is measured using a spectrophotometer.Then, the above-mentioned KrF laser device is used for this film at a dose of 400 mJ/c. Exposure is performed under conditions of m 2 , and then the absorption spectrum in the ultraviolet-visible region is measured again.

According to this measurement, the transmittance of the above film to light near the wavelength of KrF laser light before exposure to the KrF laser was 61%, and the transmittance after exposure to the KrF laser was 95%. It was found that exposure to light improves transmittance. Further, when the transmittance of a film made only of poly(styrene) with the same lum as the photosensitive resin composition of the example was measured for light near the wavelength of KrF laser light, the film thickness was 90%.

As is clear from these transmittance measurement results, the positive photosensitive resin composition of the present invention not only has low absorption of light in the vicinity of the wavelength of KrF excimer laser light, but also has low absorption after exposure. It was found that the absorbance was smaller than that of the base resin alone. Therefore, since the exposed portion is fogged with a predetermined exposure amount down to the lower part, the predetermined portion can be accurately dissolved by the developer. Therefore, a rectangular resist pattern is obtained.

East 11 Gloss 2 A coating solution of the photosensitive resin composition of Example 2 is prepared in exactly the same manner as in Example 1 except that 19 is changed to maleimide.

Next, in the same manner as in Example 1, a 1 um thick film of the photosensitive resin composition of Example 2 is formed on a silicon wafer.

Next, after baking is performed in the same manner as in Example 1, exposure with a KrF laser is performed under the same conditions as in Example 1 except that the dose amount is 650 mJ/cm 2 .

Next, the film was developed with a 5% TMAH aqueous solution for 450 seconds, and rinsed with pure water.

The resulting pattern! When observed by SEM, 0.
It was found that a 5 um line and space pattern was resolved. It was found that the cross-sectional shape was roughly a completely rectangular shape similar to Example 1.

The amount of Tayu m two-dimensional maleimide was set as 59.309 and 409, and the exposure amount by KrF laser and 5% TMA were adjusted to correspond to these amounts.
The photosensitive resin compositions of Examples 3 to 5 were prepared and used in the same manner as in Example 1, except that the development time with the H aqueous solution was changed as shown in Table 1. Perform a buttering experiment.

Table 1 also shows the maleimide content, exposure amount, etc. of the photosensitive resin compositions of the first and second examples.

Further, the degree of film thinning of the photosensitive resin composition of each example before and after development is shown as a value (%) determined from film thickness before and after 100X development/film thickness before development.

As is clear from Table 1, if the amount of maleimide is less than 5 parts by weight per 100 parts by weight of the styrene resin, problems such as the exposed areas of the photosensitive resin composition not being dissolved in the alkaline developer occur. If the amount is 40 parts by weight or more, the film loss in the unexposed areas of the photosensitive resin composition will be 10% or more, which will cause problems such as precipitation of maleimide from the film of the photosensitive resin composition. The amount of maleimide in the styrene resin composition is in the range of more than 5 parts by weight and 40 parts by weight, preferably 10 parts by weight or more and 40 parts by weight, based on 100 parts by weight of the styrene resin.
It is found that it is best to keep the amount by weight within the range of 10% by weight.

In the above, examples of the positive photosensitive resin composition of the present invention have been described, but the present invention is not limited only to these examples, and various changes as described below can be made. .

In the above examples, the Mw of the styrene resin is so, o.
oo and M*/M Poly(styrene) with N of 1.02 was used, but poly(styrene) that can be used is not limited to those with such a molecular weight. Poly(styrene) with Mw of 2 If it is smaller than .000, the film of the photosensitive resin composition formed using the photosensitive resin composition will be too soft, which will cause problems in adhesion to the exposure mask, or the development speed will be too fast, making it difficult to control the development time. arise, 10
If the molecular weight is too large than o or ooo, problems such as difficulty in filtering the resist solution or formation of striations on the coating will occur, but if the molecular weight is 2.000 to 10o or ooo, the same effect as in the example will be obtained. can be expected. This suitable range of molecular weight can be similarly considered when using styrene resins other than poly(styrene).

Furthermore, the styrene resin is not limited to poly(styrene), and other styrene resins such as poly(α-methylstyrene) may also be used, and depending on the design, A mixture of two or more styrene resins may be used.

Furthermore, it is clear that the positive photosensitive resin composition of the present invention may contain other substances in addition to the styrene resin and maleimide in order to improve the properties of the positive photosensitive resin composition. .

Further, in the above-mentioned examples, cyclohexanone was used as a solvent for preparing a coating solution of a positive photosensitive resin silk composition. However, instead of this, ketone solvents such as methyl isobutyl ketone, methyl ethyl ketone, etc.
Cyclohexanone is also a ketone solvent. ), dimethylformamide, dimethylacetamide, etc., and ether solvents such as tetrahydrofuran can also be used to obtain the same effects as in the examples.

(Effects of the Invention) As is clear from the above description, the positive photosensitive resin composition of the present invention has a structure containing a styrene system, a resin, and maleimide, so it is difficult to resist exposure to deep ultraviolet light. Due to the photosensitive principle of photo-addition of maleimide to the aromatic ring of the styrene resin, the light absorption after exposure is smaller than the light absorption of the base resin itself, providing unprecedented photobleaching properties. Therefore, a rectangular resist pattern similar to that of PMMA can be obtained in phosphorography using deep ultraviolet light.

Claims (4)

[Claims] (1) A positive photosensitive resin composition comprising a styrene resin and maleimide. (2) The positive photosensitive resin composition according to claim 1, wherein the styrenic resin is one or both of poly(styrene) and poly(α-methylstyrene). (3) The styrene resin has a molecular weight of 2,000 to 10
3. The positive photosensitive resin composition according to claim 1, wherein the positive photosensitive resin composition has a molecular weight of 0,000. (4) The content of maleimide is 10% of the styrene resin.
The positive photosensitive resin composition according to claim 1, wherein the amount is in the range of 10 parts by weight or more and less than 40 parts by weight relative to 0 parts by weight.