JPH0416781B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a microfabrication method, and more particularly:
This invention relates to a pattern forming method using a novel radiation-sensitive polymer material.

Conventional microfabrication methods involve coating a photosensitive resin (photoresist) on a substrate, forming a pattern by exposing and developing it, and then wet-etching the substrate other than the patterned area. . However, this method is not suitable for microfabrication of 1 μm or less because there is a limit in resolution due to the diffraction effect of light, and wet etching is affected by side etching and impurities in the etchant. Therefore, with the recent demand for higher density semiconductor integrated circuits, high-energy radiation such as X-rays with shorter wavelengths, electron beams, gamma rays, neutron beams, and ion beams are being used instead of light. A shift is being made to a method of forming a pattern with good resolution and performing highly accurate microfabrication using a dry etching method using plasma gas, reactive sputtering, ion milling, etc. instead of wet etching.

In such microfabrication methods, patterns are formed using radiation, and the polymer film used for dry etching not only reacts with high sensitivity to radiation, but also reacts with plasma gas, reactive sputtering,
It is necessary to have high resistance to ion milling. To date, many resist materials have been considered for this purpose. However, this type of resist currently has low sensitivity. For example, polystyrene, polyvinylnaphthalene, etc. have been reported, but their sensitivity to electron beams is low and they cannot meet current requirements as they are.

An object of the present invention is to provide a pattern forming method using a novel radiation-sensitive polymer material having high sensitivity in a microfabrication method using ionizing radiation such as X-rays, electron beams, and γ-rays.

According to the present invention, as a radiation-sensitive polymer, the general formula: (However, R represents a lower alkyl group.) 4-alkyl-3,5,8- which can be represented by
trioxabicyclo[2,2,2]octo-1-
A pattern forming method using a polymer containing ylmethoxymethylstyrene as a structural unit is obtained.

That is, in the present invention, 4-alkyl-3,5,8-
trioxabicyclo[2,2,2]octo-1-
The one with 4 mol% of ylmethoxymethyl group introduced is 7 times; the one with 20 mol% introduced is 13 times, 45 mol%
The one introduced showed a 16.5-fold increase in sensitivity. An increase in sensitivity means that a smaller amount of exposure is required in inverse proportion to the increase in sensitivity, so it is possible to shorten the exposure time, which is often a problem with electron beam exposure.

As mentioned above, even if the introduction rate of functional groups is increased, the sensitivity does not increase proportionally, as shown in FIG. 1. In order to improve the sensitivity of polystyrene, which is a low-sensitivity material, it is desirable that the introduction rate of the above-mentioned substituents be 4 mol % or more.

In addition, sensitivity to ionizing radiation such as electron beams and X-rays increases as the molecular weight increases;
If it is less than 10,000, the sensitivity will be insufficient, while if it is more than 1,000,000, the resolution will decrease and the dissolution and coating properties will decrease, so the molecular weight of the copolymer is preferably 10,000 to 1,000,000. The user can select the most suitable substitution rate and molecular weight within the above range, taking into consideration the required sensitivity and resolution. Furthermore, polystyrene is known as a material with good dry etching resistance, but even in materials with the above substituents introduced, the main chain structure is composed of polystyrene, so the dry etching resistance decreases only slightly (about 10%). However, it maintains high resistance and has properties suitable for application to the dry etching process essential for microfabrication. It goes without saying that a polymer obtained by introducing a substituent having a bicyclo group into polystyrene is equivalent to a copolymer of a styrene substituted product having the above-mentioned substituent and styrene.

The present invention attempts to form fine patterns using such new materials.

Example 1 1-ethyl-4-bitroxylmethyl=2,6
-7 trioxabicyclo[2,2,2]octane
Dissolve 0.9g and 10ml of dehydrated tetrahydrofuran in a flask, and add sodium hydride (50ml) at room temperature.
% oil suspension) was added and reacted for 2 hours at 30°C in a nitrogen stream. A solution containing 1.94 g of narrowly dispersed chloromethylated polystyrene (weight average molecular weight 100,000, degree of chloromethylation 20%) was added dropwise to the resulting reaction solution, and the mixture was reacted at 35°C for 3 hours.
I left it undisturbed overnight. The product is tetrahydrofuran-h
- White solid after repeated precipitation purification with hexane
Obtained 2.0g. As a result of NMR analysis of this product, it was found that all chloromethyl groups were substituted with bicyclo groups, and 0.2 moles of bicyclo groups were introduced per mole of monomer. This obtained polymer was dissolved in xylene (Xylene) at 12% by weight and passed through a 0.2 μm filter to obtain a resist solution. This was applied onto a silicon wafer using a spinner (2000 rpm) and dried by heating at 80°C for 30 minutes to obtain a uniform coating film of 0.6 μm. Patterns were drawn on this resist film by electron beam irradiation at various exposure doses, developed with N,N-dimethylformamide for 90 seconds, and rinsed with isopropanol for 30 seconds to obtain resist patterns. The sensitivity curve of this resist is shown as curve a in FIG. For comparative reference, the sensitivity curve of conventional polystyrene having the same molecular weight is shown as curve e in the figure. The exposure amount at the gel point of polystyrene is 5 x 10 ^-5 c/cm ² , while this copolymer has an exposure dose of 3.8 x 10 ^-6 c/cm ² , meaning that the sensitivity is 13 times higher. I understand. The resulting pattern showed that fine lines of 1 μm or less were well formed. Also, the argon milling speed of this material is |72Å|
There is almost no deterioration at |83Å|min compared to min.

Example 2 Example 1 using narrowly dispersed chloromethylated polystyrene with a molecular weight of 100,000 (degree of chloromethylation: 4%)
A 4-ethyl-3,5,8-trioxabicyclo[2,2,2]oct-1-ylmethoxymethyl group was introduced in the same manner as described above. As a result of NMR analysis, 0.04 mol of bicyclo group was introduced per 1 mol of styrene unit. This polymer was used as a resist solution in the same manner as in Example 1. The electron beam sensitivity as a resist is shown by curve b in FIG. The exposure amount at the gel point is
The sensitivity was 7.1×10 ⁻⁶ c/cm ² , which was a seven-fold increase in sensitivity compared to polystyrene of the same molecular weight.

Using this resist, a resist pattern was formed on an Al vapor deposited film (1 μm thick) in the same manner as in Example 1. However, the initial film thickness is 0.9μm and the irradiation dose is 1.5×
The film thickness after development at 10 ^-5 coulombs of 1 cm ² was 0.7 μm.
When this was spat quenched using CCl ₄ gas, a good Al pattern was obtained.
The etching rate ratio to Al was 4 (the etching rate of this resist was 1/4 that of Al).

Example 3 Similar to Examples 1 and 2, using narrowly dispersed polystyrene with a molecular weight of 100,000 as a starting material, 45 mol% of 4-ethyl-3,5,8-trioxabicyclo[2,2,2] was obtained through chloromethylation. A resist into which oct-1-ylmethoxymethyl groups were introduced was prepared. It was found that the sensitivity was improved by 16.5 times when compared with the gel point exposure amount. The sensitivity curve is shown as curve c in FIG.

Example 4 Using narrowly dispersed polystyrene with a molecular weight of 600,000 as a starting material, 4-ethyl-
3,5,8-trioxabicyclo[2,2,2]
A polymer was prepared in which 15 mol% of oct-1-ylmethoxymethyl groups were introduced. When this polymer was evaluated as a resist, the gel point was 7.6×10 ^-7
A material with high sensitivity of c/cm ² was obtained. The sensitivity curve is shown as curve d in FIG.

When we tried patterning, we found that compared to the previous example, there was some moisture in the area of 1 μm or less.
The formation of patterns up to 1 μm was sufficient.

Properties such as etching resistance were not changed at all.

As described above, the present invention enables highly accurate microfabrication and is particularly suitable for dry etching processes, so it provides an excellent method for processes that require high density, such as semiconductor integrated circuits.

[Brief explanation of drawings]

Figure 1 is a diagram showing the correlation between the introduction rate of bicyclo groups and improvement in sensitivity in the organic polymer material used in the present invention, and Figure 2 is a diagram for explaining the present invention. FIG. 2 is a diagram showing a comparison of the electron beam sensitivities of organic polymer materials a, b, c, and d and a conventional material e.

Claims (1)

[Claims] 1. In a pattern forming method in which a radiation-sensitive polymer film is irradiated with ionizing radiation to form a pattern, the general formula (However, R represents a lower alkyl group.) 4-alkyl-3,5,8- which can be represented by
trioxabicyclo[2,2,2]octo-1-
A pattern forming method characterized by using a polymer containing ylmethoxymethylstyrene as a constituent unit as a radiation-sensitive polymer film. 2. The polymer is a copolymer of 4-alkyl-3,5,8-trioxabicyclo[2,2,2]oct-1-ylmethoxymethylstyrene and styrene as described in claim 1. pattern formation method. 3 The copolymer has 4-alkyl-3,5,8-trioxabicyclo[2,2,2]oct-1-ylmethoxymethylstyrene as a monomer unit.
The pattern forming method according to claim 2, wherein the pattern formation method includes mol% or more. 4. The pattern forming method according to claims 1 to 3, wherein the polymer has a molecular weight of 10,000 to 1,000,000.