JPH03282549A - Photosensitive resin - Google Patents

Abstract

PURPOSE:To obtain patterns of a rectangular shape in lithography using far UV light by consisting the above resin of the polycondensate of 2-diazomalonic acid and bisphenol. CONSTITUTION:This photosensitive resin is constituted of the polycondensate of the 2-diazomalonic acid and the bisphenol and, therefore, the reaction that the 2-diazo-1, 3-dicarbonyl structural part changes to beta ketocarboxylic acid takes place in the part of this resin irradiated with the far UV light. The part of the photosensitive resin irradiated with the UV rays is, therefore, soluble in an alkaline developer and the light absorbing characteristic of 250mm wave length decreases. The bisphenol has the structure similar to the structure of p-substd. phenol is much smaller in the absorption of the far UV light than cresol novolak resin, etc. The exposing light arrives sufficiently at the bottom of the film in the part of the photosensitive resin irradiated with the far UV light and, therefore, the resist pattern having the shape approximate to the rectangular shape is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention is directed to photosensitive resins used for manufacturing semiconductor devices M and the like.

(Prior Art) In recent years, the integration of LSIs has been increasing more and more. In the production of such RLSIs, phosphorography technology plays an extremely important role, because the degree of integration of LSIs depends on the resolution of lithography and alignment precision. ! This is due to the fact that it depends on the technical level of LSI, etc., and that phosphorography is used repeatedly more than 10 times during LSI manufacturing.

Therefore, improvements to the conventional lithographic 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 proposed resolution R of the reduction projection exposure method is R=
Since it is expressed as 0.6λ/NA (where λ is the exposure wavelength and NA is the numerical aperture of the optical system), it can be improved by increasing the NA.

For this reason, the 9-ray (wavelength 436n) of the conventional mercury lamp
In the exposure method using m), 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, in LSIs whose surfaces have complex irregularities due to multilayer wiring and integration of various types of elements, it is difficult to form submicron-level patterns on the surfaces.

So, the latest cedar exposure system! , it is being considered to set the NA to a value that can ensure a standard depth of focus (for example, about 2 um in a range) and to shorten the exposure wavelength. Specifically, i-line (wavelength 365 nm), KrF
The exposure light is an excimer laser (248.5 nm) and far ultraviolet light with a wavelength of around 25 Onm. In particular, the second
0.0.
It can also resolve fine patterns of 5 μm or less. Note that far ultraviolet light herein refers to light with a wavelength of 200 to 300 nm. Same below.

On the other hand, photoresist (sometimes referred to as resist) plays an extremely important role in improving the resolution of lithography technology.

The diazonaphthoquinone/novolak-based positive photoresist is 91j! It is known that a high-resolution resist pattern can be obtained when a light source (more specifically, i-line) is used as a light source. 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 novolak resin (formula below, sometimes abbreviated as substance ■) and naphthoquinone sulfonic acid ester of trihydroxyhenzophenone (formula below, below). , sometimes abbreviated as substance ■). However, n in the formula (■) indicates the degree of polymerization (the same applies to n in the various structural formulas below), and DN in the 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 the substance (2) 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.

When this type of photoresist is exposed to 9-line or 1-line light, the partial structure (2) of substance (2) changes into an alkali-soluble indenecarboxylic acid derivative (substance (3) below) in the exposed area, which inhibits the alkali dissolution of substance (2). lose. Therefore, the exposed portions of the photoresist are dissolved in the developer, resulting in a positive pattern.

In addition, the wavelengths of this photoresist are 436 nm and 365 nm.
The multi-light absorbing property of m 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) no longer absorbs light at wavelengths of 436 nm and 365 nm. KJ, photobleaching occurs. For this reason, the exposure light (in this case, 9-line or i-line) reaches the bottom of the photoresist layer, and the exposed portion is dissolved down to the bottom by the developer, resulting in a resist pattern having a rectangular cross section.

However, in this photoresist, when it is exposed to deep ultraviolet light, a change occurs in the part of the substance (2) except for the partial structure (2), so photobleaching hardly occurs.
The exposure light (KrF excimer laser far 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. This results in a large reduction in film thickness.

In order to solve this problem, it is necessary to reduce the absorption of deep ultraviolet light by the photoresist. Specifically, it is important that the material exhibits photobleaching when exposed to deep 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
ptical InstrumentationEnc
+1neers) Vol, 771. pp, 2-10
(1987)).

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 do not have an aromatic ring, or even if they do have an aromatic ring, the aromatic ring remains conjugated with other unsaturated groups, and that they undergo photorearrangement to form a 2-carboxylactam structure (
It has a structure that produces the following formula (2). As such diazoketones, specifically, diazobieridinediones as shown by the following formulas (1), (2), or (0) have been used.

h The photoreaction of diazobiveridine sion is The above substances To explain using the example of (2), it is as shown in the following equation.

■ 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 36M photograph in the document, the obtained positive pattern was 1.0u.
For the line pattern of m, the taper angle of the side wall of the resist button (the angle formed between the side! and the substrate surface) is at least 7.
0/I or more, and furthermore, since the upper surface is flat, it can be seen that the film loss is extremely small. Therefore, the photoresist of the above-mentioned document is superior to novolac/diazonaphthon-based resists as a resist for deep ultraviolet rays.

(The problem that the invention seeks to solve!!!i) However,
With the conventional photoresist disclosed in the above-mentioned literature, the resulting pattern is not a perfect rectangle but has a taper. Therefore, when forming a submicron level pattern using this photoresist, the incident light intensity is Coupled with the decrease in contrast, the taper becomes even larger, 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 (the difference between the resist pattern dimension and the etching depth) depends on the etching selectivity of the resist and workpiece materials. (difference with pattern size).

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 will be only 0.5 mil when processing at the 0.5 um level.
To achieve this, it is necessary to have a resist pattern whose sidewalls are perpendicular to the substrate surface, but conventional photoresists have not been technically satisfactory in this respect.

Here, the main causes of deterioration of the pattern shape are (a)...The photoresist's photobleaching property is not sufficient, so the exposure amount also absorbs the exposure light, and (b)...necessary for pattern formation. Since the decomposition of the photosensitizer in the photoresist is not completed at a certain amount of exposure, it is thought that this also causes absorption of the exposure light.

The above phenomenon (a) is mainly caused by the absorption of exposure light by the aromatic rings in the Hess resin (novolac resin in the conventional example). Therefore, it is possible to solve the problem (a) by making the Hess resin itself transparent to far ultraviolet light.

In particular, a completely rectangular resist pattern can be formed by using a methacrylic acid polymer such as Boa (methyl methacrylate), so-called PMMA. However, methacrylic acid-based polymers cannot be used in current microfabrication processes because of their low dry etching resistance. Therefore, this countermeasure is not an essential solution at present.

The present invention has been made in view of these points, and therefore, an object of the present invention is to provide a photosensitive resin that can obtain a rectangular pattern in phosphorography using deep ultraviolet light.

(Means for solving Section! ija) In order to achieve this objective, the photosensitive resin of this invention is
It is characterized by being composed of a polycondensate of 2-diazomalonic acid and bisphenol.

In carrying out the present invention, the above-mentioned polycondensate is represented by the following general formula (1) and has a weight average molecular weight within the range of 2,000 to 100,000(7)ffi,
Alternatively, it is preferably composed of a compound represented by the following general formula (■) and a weight average molecular weight within the range of 2.000 to 10o, ooo (however, day 1 and day 2 are hydrogen, They are an alkyl group or a fluorinated alkyl group, and may be the same or different. Also, R3 is a methyl group, an ethyl group, or a tertiary-butyl group. The reason why polycondensates with a weight average molecular weight of 2,000 to 100,000 are preferable is that if the weight average molecular weight is less than 2.000, the last film formed using the polycondensate is too soft for exposure. This may cause problems such as problems with adhesion to the mask or the development speed being too fast, making it difficult to control the development time.
This is because if it is too large than 00000, problems such as difficulty in filtering the resist solution and formation of striations (radial wrinkles) on the coating film will occur.

Further, the polycondensate represented by the formula 0 can be synthesized by acid-catalyzed transesterification between a 2-diazomalonic acid alkyl ester represented by the following formula 0 and a bisphenol represented by the following formula 0.

That is, a mixture of equimolar amounts of 2-diazomalonic acid alkyl ester and bisphenol and a catalytic amount of acid is heated, or these are heated in a high boiling point solvent such as xylene or chlorobenzene, and during heating, compound formation occurs. It can be obtained by distilling off the alcohol (represented by R30H) and then reacting.

The alkyl residue of the 2-diazomalonic acid alkyl ester is preferably a methyl group, ethyl group, or tert-butyl group to facilitate acid-catalyzed transesterification.

The raw material for the 2-diazomalonic acid alkyl ester, malonic acid ester represented by the following formula 0, is commercially available, and this raw material is used by known diazotization methods (for example, in the literature (Chem, Ber., 9th edition). , 3128 (1966
)) can be easily obtained by the method disclosed in )).

Furthermore, various bisphenols represented by formula 0 are easily available. For example, it is known whether 1 and R2 in the formula 0 are both methyl groups, R1 and R2 are both n-propyl groups, R1 and R2 are both fluorinated alkyl groups, etc. In addition, spirohexyl bisphenol with a structure having a cyclohexyl group (instead of 12 days 2) is also well known. Spirohexyl bisphenol,
A polycondensate represented by formula 0 can be synthesized by acid-catalyzed transesterification with an alkyl 2-diazomalonic acid ester.

In addition, in acid-catalyzed transesterification of 2-diazomalonic acid alkyl ester and bisphenol, p
- Good results are obtained by using strong organic acids such as toluenesulfonic acid, camphorsulfonic acid, etc.

(Function) The above-mentioned polycondensate constituting the photosensitive resin of this invention has 2
-Diazo-1,3-dicarbonyl structure and p-substituted phenol ester structure.

Since this 2-diazo-1,3-dicarbonyl structure changes to β-ketocarboxylic acid when exposed to deep ultraviolet light, the portion of the photosensitive resin irradiated with deep ultraviolet light becomes soluble in an alkaline developer. As a result, patterning becomes possible.

In general, since β-ketocarboxylic acid has a smaller light absorption characteristic at a wavelength of 250 nm than 2-diazo 1,3-dicarbonyl, significant photobleaching occurs in the portions of the photosensitive resin that are irradiated with deep ultraviolet light.

Furthermore, since the pm[converted phenol ester structure has reactive gas plasma resistance, the reactive gas plasma resistance of the photosensitive resin is ensured. In general, the PM-converted phenol ester structure can absorb light at a wavelength of 250 nm to a lesser extent than cresol novolac resins.

(Example) Examples of the photosensitive resin of the present invention will be described below.

In addition, the names of the chemicals used, molecular weight,
It should be understood that the numerical conditions such as mixing amount, temperature, film thickness, and time are merely preferred examples within the scope of the present invention.

As Example 1, a photosensitive resin composed of a polycondensate of di-t(tertiary)-butyl 2-diazomalonate and bisphenol (where day 1 = day 2 = CH3
, R3=t-butyl. Hereinafter, this will be referred to as the photosensitive resin of Example 1. ) will be explained.

<Synthesis Example> First, the photosensitive resin of Example 1 is synthesized as described below.

24.2 q of di-t-butyl 2-diazomalonate, 22.89 q of bisphenol A, and 1.
29 into a reactor, and while reducing the pressure inside the reactor to 50 mmHg, heat the reactor and maintain the temperature at 120°C.

After reacting in this state for 18 hours, the temperature of the reactor was returned to room temperature.

Next, the contents were dissolved in Hensen 500mff, and this solution was washed sequentially with sodium bicarbonate and water, and then
Dry with sodium sulfate.

Next, Hensen was distilled off from the dried solution and the entire volume was reduced to 115
This is poured into 500 mff of methanol. This causes a precipitate to form in the methanol. After the precipitate was collected by filtration, it was vacuum dried overnight to obtain photosensitive resin 329 of Example 1.

The weight average molecular weight Mw of the photosensitive resin of Example 1 is 7.60
It was 0.

Further, when the absorption spectrum of the photosensitive resin of Example] in the ultraviolet-visible region was measured using a spectrophotometer, it was found that the maximum absorption wavelength λ, II8 was 280,278 nm.

Also, in the TR spectrum, the wave number is 2170 cm-'
Absorption of a diazo group was observed at a wave number of 1650 cm-', and absorption of a carbonyl group was observed at a wave number of 1650 cm-'.

<Buttering experience> 2.09% of the photosensitive resin of Example 1 was mixed with methoxyethyl acetate (
After dissolving in 8 mu of MCA), this solution is filtered through a Teflon filter to prepare a coating solution of the photosensitive resin of Example 1.

Next, the above-mentioned coating solution was applied to a silicon wafer that had been subjected to hydrophobization treatment using hexamethyldisilazane at a rotation speed of 25.
Coating is performed by a spin coating method at a rate of 0.00 min.

Next, using a hot plate, this silicon wafer was
Hake for 1 minute at a temperature of °C.

Next, a quartz mask having a line-and-space pattern (chrome pattern) 8 of various dimensions is densely wrapped on the scratched silicon wafer, and then this sample is coated with Xe-Hg
Expose with a lamp.

After exposure, the sample is immersed in 0.11N tetramethylammonium hydroxide (TMAH) in the dark for 50 seconds for development, and then rinsed with pure water for 30 seconds.

When such processing was carried out with various exposure jl and the samples were observed after development to check the sensitivity (the amount of exposure at which the amount of residual film on the exposed part of the photosensitive resin became O), it was found to be 45.
It turns out that it is 0mJ/cm2. Also,
It was found that even line and space patterns of 0.5 um could be resolved. Further, when the cross section of the pattern was observed using an SEM, it was found that the Tevar angle of the side wall of the resist pattern was about 80', and the cross section of the pattern was quite rectangular.

<Photobleaching property> In addition to the patterning experiment described above, the photobleaching property of the photosensitive resin of Example was measured as described below.

A film of the photosensitive resin of Example 1 having a thickness of 1 LIm is formed on a quartz substrate. Next, the absorption coefficient of this film for light with a wavelength of 250 nm is measured. The result is 3.2um
-' was. Next, this film is irradiated with far ultraviolet light using an Xe-Hg lamp at an exposure dose of 500 mJ/cm 2 , and then the absorption coefficient of this film for light with a wavelength of 250 nrn is measured again. The result is 0.9um
Met. It can be seen that the photosensitive resin of Example 1 has remarkable photobleaching properties.

Next, as Example 2, a polycondensate of di-t-butyl 2-diazomalonate and 1,1-bis(4-hydroxyphenyl)cyclohexane, that is, sudrocyclohexylbisphenol was used. Photosensitive resin (in 0 formula, day 3 =
Corresponds to t-butyl. Hereinafter, this will be referred to as the photosensitive resin of Example 2. ) will be explained.

The photosensitive resin of Example 2 was prepared in exactly the same manner as the synthesis method of Example 1, except that sudrocyclohexylbisphenol 26.89 was used in place of bisphenol A used in the synthesis example of Example 1. Synthesize S. The yield was 339.

The weight average molecular weight M of the photosensitive resin of Example 2 is 6.80
It was 0.

Further, it was found that the maximum absorption wavelength λ□ax of the photosensitive resin of Example 2 in the ultraviolet-visible region was 260,279 nm.

Also, in the TR spectrum, the wave number is 2170 cm −
1 is the absorption of diazo group, and the wave number is 1650 crrV'
Absorption of carbonyl groups was observed in .

In addition, the photosensitive resin 2.09 of Example 2 was added to MCA8rrl
A coating solution was prepared in the same manner as in [Example], and then,
A patterning experiment is conducted in the same manner as in Example 1, and the absorption coefficient for light with a wavelength of 250 nm is determined.

As a result, the sensitivity of the photosensitive resin of Example 2 was 400 m
It was found that the resolution was J/cm2 and 0.5 um. In addition, it was found that the pattern obtained had a taper angle of approximately 80" on the side wall of the pattern, and the cross section was approximately rectangular, as in Example 1.
The absorption coefficient was 3°0 um-' before exposure, and decreased to almost the same level as that of Example 1 after exposure.

(Effects of the Invention) As is clear from the above explanation, the photosensitive resin of the present invention is composed of a polycondensate of 2-diazomalonic acid and bisphenol, and therefore the photosensitive resin is resistant to far ultraviolet light. In the irradiated area, a reaction occurs in which the 2-diazo-1,3-dicarbonyl structure changes into B-ketocarboxylic acid. Therefore, the portion of the photosensitive resin irradiated with deep ultraviolet light becomes soluble in an alkaline developer, and its light absorption characteristic at a wavelength of 250 nm becomes small (shows photobleaching property).

Furthermore, hisphenol has a structure similar to that of p-ff1-converted phenol, and its absorption of far ultraviolet light is much lower than that of cresol novolak resin and the like.

Therefore, in the part of the photosensitive resin of this invention that is irradiated with far-infrared light, the exposure light sufficiently reaches the bottom of the film, resulting in a nearly rectangular resist that could not be achieved with conventional far-infrared positive resists. Patterns can be formed.

Claims (3)

[Claims] (1) A photosensitive resin comprising a polycondensate of 2-diazomalonic acid and hisphenol. (2) The polycondensate is represented by the following general formula (1) and has a weight average molecular weight of 2,000 to 100,000.
The photosensitive resin according to claim 1, wherein R^1 and R^2 are hydrogen, an alkyl group or a fluorinated alkyl group, and may be the same or different.
Moreover, R^3 is a methyl group, an ethyl group, or a tertiary butyl group. ) ▲There are mathematical formulas, chemical formulas, tables, etc.▼・・・■ (3) The polycondensate is represented by the following general formula (1) and has a weight average molecular weight of 2,000 to 100,000.
The photosensitive resin according to claim 1, which is within the range of (provided that R^3 is a methyl group, ethyl group, or tertiary butyl group) ▲There are mathematical formulas, chemical formulas, tables, etc.▼... ■