JPH02257624A - Formation of resist pattern - Google Patents

Abstract

PURPOSE:To enhance a high resolution property and a dry-etching-resistant property by a method wherein, after a pattern has been exposed and a resist composition pattern has been formed, high-energy radiant rays are irradiated and a resist pattern whose surface is covered with a polymer film containing an aromatic ring is formed. CONSTITUTION:A nitrocellulose thin film 2 is formed on the surface of a silicon substrate 1; the thin film 2 is irradiated with an argon fluoride excimer laser beam 4; nitrocellulose in a part irradiated with the laser is decomposed and removed; a pattern 2 of the nitrocellulose thin film is formed. Then, the substrate 1 is irradiated with an electron beam 5 in the air; an active radical 6 which can start addition polymerization is generated on the pattern 2, coupled with oxygen in the air and transformed into a hydroperoxide and a diperoxide which are comparatively stable at room temperature. After that, a styrene monomer gas 7 is introduced and heated; a graft polymerization reaction is caused; a graft polymer film 8 of styrene is formed on the pattern. Since an aromatic ring is introduced in this manner, a dry-ecthing-resistant property is enhanced sharply; when a resist pattern is formed, high resolution can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Field of Application) The present invention relates to a resist pattern forming method, and particularly to improving the resolution and dry etching resistance of a resist pattern.

(Prior Art) As the density of semiconductor integrated circuits increases, and as elements and interconnections become increasingly finer, even higher resolution is required when forming resist patterns.

Currently, when forming fine patterns, it has become essential to adopt a projection exposure method, but the resolution obtained by such a method is conveniently calculated as: resolution curve m x wavelength of exposure light / numerical aperture of projection lens.・
It is given by (Formula) (where m is a constant determined by the properties of the resist composition itself and the controllability of the process).

For this reason, in the field of lithography, the development of excimer laser lithography, which uses excimer laser light with a short wavelength and high light intensity as exposure light, is actively progressing as a means of achieving high resolution of layers. It is being

By the way, in the manufacturing process of semiconductor integrated circuits, it is necessary for the resist pattern itself to fulfill its original function as a mask when dry etching the underlying substrate. In addition to such high resolution, high resistance to dry etching is also required.

For example, when the underlying material to be processed is a silicon-based substrate, CF4 and C are usually used as the etching gas.
Although HF3-based gas is used, it is empirically known that resist pattern compositions containing a large number of aromatic rings have high dry etching properties with respect to such gases.

Main chain cleavage type resist compositions such as polymethyl methacrylate and polymethyl glutarimide, which have already been improved in resolution, have extremely good pattern accuracy as resist patterns, but both Since it does not contain an aromatic ring, it has poor dry etching resistance and cannot be put to practical use.

On the other hand, resist compositions containing aromatic rings inherently have a drawback of extremely low transmittance to exposure light having a short wavelength of 260 ns or less.

Therefore, in order to improve the precision of the resist pattern, when a positive resist pattern composition made of a novolac resin is pattern-exposed with krypton fluoride (KrF) excimer laser light (wavelength 248 nm), the As a result, the pattern obtained after development is triangular in shape. A resist pattern having such a shape causes a significant decrease in processing accuracy in the subsequent dry etching process.

Thus, at present, no resist composition has been found that maintains high dry etching resistance and has sufficient transmittance for short wavelength exposure light.

Against this background, a completely new pattern forming method using graft polymerization has been attracting attention in recent years. A graft polymer has a structural formula in which a second polymer, which serves as a branch, is grafted from the middle of a first polymer, and has properties that combine the properties of both the first and second polymers. This shows that.

Taking advantage of this property, graft polymers are beginning to be used in the formation of resist patterns.

One method is to irradiate a polymer film that is easily etched with high-energy rays in a pattern to form active points that can initiate graft polymerization, and then form a graft polymer film that is difficult to etch into a pattern around these active points. A pattern forming method has been proposed in which after forming a graft polymer film, the underlying polymer film is etched using the graft polymer film as a mask (
(Patent Application No. 184495/1982).

However, with this method, the difference in etching rate between the graft polymer film and the underlying polymer film was not sufficient.
It is not possible to obtain a high selectivity, and as a result, when the resist film thickness is increased, there is a problem in that the resolution decreases.

Recently, the underlying polymer film has been constructed with a two-layer structure consisting of a silicone resin layer and an organic polymer layer. After forming the combined film, the silicone resin layer was first etched with CF4 gas using this graft polymer film as a mask, and the organic polymer film at the bottom layer was etched with oxygen gas using the remaining silicone resin layer as a mask. A resist pattern forming method has also been proposed (Japanese Patent Publication No. 33737/1983).

Although this method improves the etching selectivity compared to the above method, it requires two dry etching steps to obtain the desired resist pattern, making the process complicated and impractical for mass production purposes. It was not suitable.

In addition, in both of the above two pattern forming methods, it is necessary to irradiate high-energy radiation such as an electron beam in a pattern in order to create active sites that can initiate graft polymerization.
This also caused a reduction in processing capacity.

(Problems to be Solved by the Invention) As described above, a resist pattern composition that can be put to practical use in excimer laser lithography using short wavelength exposure light has not yet been found, and it is difficult to use conventional graft polymerization. The pattern forming method has problems such as a decrease in resolution due to an increase in film thickness and a decrease in throughput due to the complexity of the process.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a method for forming a resist pattern that can achieve both high resolution and high dry etching resistance.

[Structure of the invention]

(Means for Solving the Problems) Therefore, in the present invention, a graftable resist composition is applied, and this resist composition is pattern-exposed using energy rays such as short wavelength ultraviolet light as exposure light. After forming a pattern, the pattern is irradiated with high-energy radiation to create active points capable of initiating graft polymerization, and the pattern is graft-polymerized around these active points to form a graft polymer film containing aromatic rings. A resist pattern is formed.

When forming active sites, active sites that can initiate graft polymerization are captured in the form of peroxide groups by irradiation with high-energy radiation in an oxygen atmosphere, and after removing excess oxygen, heating is performed to activate the active sites. The points may be regenerated and then graft polymerized.

(Function) Therefore, in the present invention, first, a pattern is formed using a main chain cleavage type resist composition that does not contain aromatic rings and has high resolution, and then a graft polymerization reaction is caused to this pattern to remove the aromatic rings. Since this method allows for the introduction of the oxide, the dry etching resistance can be greatly improved.

In addition, since pattern formation and generation of active sites for initiating graft polymerization can be performed using different types of light or high-energy radiation, short-wavelength ultraviolet light, which can provide high resolution, can be used to form resist patterns. It becomes possible to apply batch pattern transfer using light. On the other hand, when generating active sites for initiating graft polymerization, it is sufficient to irradiate the entire surface of the resist pattern with high-energy radiation, and the problem of high-energy radiation irradiation itself, such as difficulty in transferring the negative pattern, is also solved.

In addition, high-energy radiation is irradiated in an oxygen atmosphere to temporarily capture active sites capable of initiating graft polymerization in the form of peroxide groups, and after removing excess oxygen, the active sites are regenerated by heating. If the graft polymerization is then carried out, the irradiation with high-energy radiation can be performed in the air, which improves the throughput.

Furthermore, according to the method of the present invention, if a self-developing resist that is decomposed and removed by exposure is used as a pattern-forming resist, the solution development step can also be omitted, which greatly reduces the processing steps. It can be simplified to

(Example) Hereinafter, a method for forming a resist pattern according to an example of the present invention will be described in detail with reference to the drawings.

First, as shown in FIG. 1(a), a silicon substrate is used as the substrate to be processed 1, and a 10 weight percent amyl acetate solution of nitrocellulose having a weight average molecular weight of about 50,000 and containing 15 weight percent of nitrogen is applied to the surface of the silicon substrate. Spin coating using a spinner with a rotation ff14000 rpa+,
80°C on a hot plate.

Prebaking is performed for 20 minutes to form a nitrocellulose thin film 2 with a thickness of 1 μl.

As shown in FIG. 1(b), a wavelength of 193 nw was applied to this nitrocellulose thin film through a photomask 3.
Argon fluoride excimer laser beam with pulse width Ions 4
By collectively transferring the desired mask pattern using an exposure device using a light source, the nitrocellulose in the laser irradiated area is decomposed and removed, as shown in FIG. 1(c).
A pattern 2 of a nitrocellulose thin film having a minimum line width of 0.35 μm is formed.

The exposure amount at this time was 120 sJ/clf.

Next, as shown in FIG. 1(d), this substrate is irradiated with an electron beam 5 at 3 μC/cd in air to generate active radicals 6 capable of initiating addition polymerization in the pattern 2'. At this time, the generated active radicals quickly combined with oxygen in the air and changed into hydroperoxide and shiver oxide, which are relatively stable at room temperature.

After this, as shown in FIG. 1(e), the substrate to be processed is
Placed in a reaction vessel of Torr 17, pressure 10T.

"Styrene monomer gas 7 is introduced at r, and the temperature is
It is heated at 20° C. for 30 minutes to cause a graft polymerization reaction and form a styrene graft polymer film 8 on the pattern.

When the graft polymerization is completed in this way, excess styrene monomer gas is removed under reduced pressure, and a resist pattern having a uniform graft polymer H8 with a film thickness of 0.2 μI is formed as shown in FIG. 1(f). I was able to get R.

Using the resist pattern R thus formed as a mask, the silicon substrate was selectively etched away by a plasma etching method using CF4 gas, and the etching resistance of the resist pattern when forming, for example, a trench was measured.

This method is applicable, for example, to a trench-type DRAM in which a trench is formed on the substrate surface and a capacitor is formed within the trench.
This is a method often used in the formation of

The etching conditions are 13. Under high vacuum conditions with a high frequency electric field of 56 Ml1z applied, the pressure was 1°2 T.
orr, and the gas flow rate was 33 CCM.

FIG. 2 shows the dependence of the etching selectivity between the resist pattern and the silicon substrate (etching rate of the silicon substrate/etching rate of the resist pattern) on the thickness of the graft polymer film.

As can be seen from these results, it was confirmed that the styrene graft polymer film formed on the resist pattern of the nitrocellulose thin film was thicker (I see, the etching selectivity was improved).

Further, in the case of a graft polymer film having a film thickness of 0.2 μm, the etching selectivity was about 10.

As described above, the resist pattern formed by the method of the present invention has high precision and high dry etching resistance.

In this example, a self-developing resist that can be decomposed and removed by exposure was used.
It goes without saying that a normal resist that dissolves unnecessary portions of the resist in the post-exposure development process may be used.

Next, a second embodiment of the present invention will be described.

First, in the same manner as in the previous example, a silicon substrate was used as the substrate to be processed, and a thin film of polymethyl vinyl ketone (PMVK) having a weight average molecular weight of about 90,000 was coated on the surface to a thickness of 0.8 μm.
Apply it on top and heat it on a hot plate at 80℃ for 2 hours.
Pre-bake for 0 minutes.

For this polymethyl vinyl ketone thin film, an accelerating voltage of 2K
An eV argon ion beam is irradiated in a pattern to decompose and remove the polymethyl vinyl ketone thin film in the irradiated area, forming a pattern with a minimum line width of 0.4 μm. The irradiation energy at this time was 1O-6C/cd.

Thereafter, a styrene graft polymer film is formed in the same manner as in the previous example. The graft polymerization conditions at this time were as follows: 1. It was placed in an OTorr reaction vessel, and styrene monomer gas was introduced at a pressure of 10 Torr.
It is heated at 1.0° C. for 40 minutes to cause a graft polymerization reaction and form a styrene graft polymer film on the pattern.

The thickness of the graft polymer film thus formed was about 0.15 .mu.-.

When the underlying silicon substrate is etched using the resist pattern thus formed as a mask, the etching selectivity is approximately 7.5, and the etching resistance is sufficient for practical use. I understand.

In addition, in the above two examples, when causing the graft polymerization reaction (-, the resist pattern that can be grafted is irradiated with an electron beam in the air to generate active radicals that can initiate addition polymerization on the pattern). As a result, the active radicals quickly combine with oxygen in the air and change into hydroperoxide and siber oxide, which are relatively stable at room temperature, and when heated, the oxide groups are cleaved and a graft polymerization reaction occurs. The pattern is irradiated with an electron beam in a vacuum to generate active radicals capable of initiating addition polymerization on the pattern, and is heated to cause a graft polymerization reaction to form a graft polymer film on the top of the pattern. You can do it like this.

In this way, when performing a graft polymerization reaction in vacuum,
This will be explained as a third embodiment of the present invention.

A pattern 2 of a nitrocellulose thin film is formed in the same manner as in the first embodiment.

Next, this substrate was placed in a reaction vessel and heated at 3 μC in vacuum.
The pattern 2 is irradiated with an electron beam 5 at /cd to generate active radicals 6 capable of initiating addition polymerization.

After that, styrene monomer gas is introduced into the reaction vessel at a pressure of 10 Torr, and heated at 40°C to 120°C for 30 minutes to cause a graft polymerization reaction, and a styrene graft polymer film 8 is formed on the top of the pattern. Form.

When the graft polymerization is completed in this way, excess styrene monomer gas is removed under reduced pressure, and a uniform graft polymer film 8 with a thickness of 0.2 μι is formed as in the first embodiment. Resist pattern R with excellent etching resistance
was able to obtain.

In this method, after electron beam irradiation under vacuum, styrene monomer gas must be introduced without exposure to air and heated to cause a graft polymerization reaction.

In the above embodiments, excimer laser light and ion beams are used as exposure light for pattern formation, but the exposure light is not limited to these, and high-resolution pattern formation such as X-rays from synchrotron radiation can also be used. It goes without saying that other energy rays that can perform this may also be used.

Further, when generating active sites capable of initiating addition polymerization by irradiation with radiation, it is not limited to electron beams, and β-rays or other high-energy radiations may be used.

Also, the types of active points and 1. However, species other than radicals, ie, ionic species such as anions and cations, may be used as long as they can initiate addition polymerization. In this case, oxygen may be present during high-energy radiation irradiation.

Furthermore, although styrene monomer gas was used as the monomer to be graft-polymerized, it is not necessary to use a gas, and the monomer can be appropriately selected from compounds containing aromatic rings such as 4-hydroxystyrene and vinyl cinnamate. It is possible. Especially 4
When hydroxystyrene is used, a hydrogen bond system due to hydroxyl groups is easily generated in the graft polymer film, and this suppresses the main chain scission reaction of the polymer, so the resist pattern that is finally obtained is higher than that when styrene is used. It has high dry etching resistance.

In addition, when vinyl cinnamate is used, the resist pattern after the graft polymerization film is formed is irradiated with ultraviolet light to cause a dimerization reaction of cinnamic acid, which improves not only dry etching resistance but also heat resistance. It is also possible to significantly improve performance.

In addition, graft polymerization of the pattern 1. As the compound containing an aromatic ring for binding, not only the monomers used in the examples, but also dimers, trimers, etc. may be used.

〔Effect of the invention〕

As explained above, according to the method of the present invention, when forming a resist pattern, a film made of a graftable resist composition is first formed on a substrate, and pattern exposure is performed to form a resist composition pattern. After that, this resist composition pattern is irradiated with high-energy radiation to form active points capable of initiating addition polymerization. Since a resist pattern whose surface is covered with a polymer film containing aromatic rings is formed, it is possible to improve high resolution and dry etching resistance.

[Brief explanation of drawings]

1(a) to 1(f) are diagrams showing the process of forming a resist pattern by the method of the first embodiment of the present invention, and FIG. 2 is a resist pattern formed by the method shown in FIG. 1. FIG. 3 is a diagram showing the dependence of the etching selectivity between the silicon substrate and the graft polymer film on the thickness of the graft polymer film. DESCRIPTION OF SYMBOLS 1... Silicon substrate, 2... Nitrocellulose thin film 3... Photomask, 4... Excimer laser light, 5
...Electron beam, 6...Active radical, 7...Styrene monomer gas, 8...Graft polymer film. To 100' also intersects ≦7

Claims (2)

[Claims] (1) A resist coating step in which a graftable resist composition is applied to the surface of the substrate to be processed, and this resist composition is subjected to pattern exposure using energy rays such as short wavelength ultraviolet light as exposure light. a pattern exposure step of forming a resist composition pattern; a radiation irradiation step of irradiating the resist composition pattern with high-energy radiation to form active points capable of initiating graft polymerization; and forming a resist composition around the active points. 1. A method for forming a resist pattern, comprising a graft polymerization step of graft polymerizing an aromatic compound onto an aromatic pattern to form a resist pattern made of a graft polymer film containing an aromatic ring. (2) A resist coating step in which a graftable resist composition is applied to the surface of the substrate to be processed, and this resist composition is subjected to pattern exposure using energy rays such as short-wavelength ultraviolet light as exposure light. a pattern exposure step for forming a resist composition pattern; irradiating the resist composition pattern with high-energy radiation in the presence of oxygen to form active sites capable of initiating graft polymerization and converting the active sites into peroxide group forms; a heating step in which oxygen is removed and then heated to decompose the peroxide groups and regenerate active sites capable of initiating graft polymerization; and an aromatic compound is introduced and the resist is A method for forming a resist pattern, comprising the step of graft polymerizing a composition pattern to form a resist pattern made of a graft polymer film containing an aromatic ring.