JPH0515300B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates to an improved method for thermally stabilizing positive photoresist patterns. More specifically, the present invention has good thermal stability and is suitable for manufacturing semiconductor devices such as ICs and VLSIs.
The present invention relates to a thermal stabilization method for obtaining a positive photoresist pattern that does not generate wrinkles on the surface and has extremely high reproducibility.

Conventional technology In recent years, the manufacturing of semiconductor devices has become more dense and highly integrated, and with this, submicron-order microfabrication is required for forming micropatterns using photolithography processes. . For this reason, negative photoresists have been mainly used for pattern formation in the manufacture of semiconductor devices, but instead of negative photoresists, high-resolution positive photoresists that can produce pattern widths of 1 to 2 μm are being used. is becoming mainstream.

On the other hand, in the manufacture of semiconductor devices, a substrate is usually subjected to photolithography and etching processes multiple times, so that the substrate has steps. When forming a pattern on such a substrate using a positive photoresist, the difference in level of the substrate causes scattering of actinic rays and a shift in focus, resulting in a problem that the desired resolution cannot be obtained. .

As a means to solve such problems, a method is known in which conventionally, a positive type photoresist containing an ultraviolet absorber is used to eliminate halation from the substrate. However, in order to form fine patterns on the submicron order, it is necessary to improve the positive photoresist used as described above to eliminate halation from the substrate and to improve the thermal strength of the photoresist film. come. This is because the thermal strength of the photoresist greatly affects the etching, lift-off, and other processes performed after pattern formation.

By the way, in the photolithography process when a positive photoresist is used in the manufacture of semiconductor devices, a positive photoresist is first applied onto a substrate and dried to form a photosensitive layer, and then actinic rays are applied to the photosensitive layer. After selectively irradiating to form an image, development is performed to form a resist pattern. This resist pattern is usually subjected to a heat treatment in order to improve its thermal strength, and then transferred to an etching process.

In this etching process, in recent years, with the trend toward finer patterns, dry etching methods such as plasma etching and reactive ion etching have been used.Furthermore, with the miniaturization of resist patterns, extremely thin lines can be produced. Etching processing is required. Therefore, in order to meet such demands, there is a strong desire for a resist pattern with excellent thermal strength.

However, there is a limit to the ability to improve the thermal strength of a resist pattern only by the conventional heat treatment after development, and it is difficult to meet the above requirements. Therefore, various methods have been proposed for the purpose of further improving the thermal strength of the resist pattern. For example, the resist pattern after development has a UV ray of 200~
A method has been proposed in which UV light in the 300 nm wavelength range is irradiated for several seconds. This ultraviolet irradiation treatment crosslinks the resin component of the photoresist by the action of ultraviolet rays, increases the softening point of the photoresist itself, and increases the heat treatment temperature to obtain a resist pattern with improved thermal strength. It is.

However, in this processing method, the surface layer of the resist pattern layer is mainly crosslinked, so although the surface layer and the inside of the resist pattern layer are continuous, the degree of crosslinking is different, and the resulting stress As a result, wrinkles occur on the surface of the resist pattern and the shape changes.
Dimensional accuracy inevitably deteriorates.

Therefore, this processing method cannot be said to be a practical method in a field where high precision is required, such as the manufacture of semiconductor devices.

In addition, as another method to improve the thermal strength of the resist pattern, the resist pattern can be
A method has been proposed in which a resist pattern with less wrinkles and improved thermal strength is obtained by irradiating the entire surface of the pattern with ultraviolet rays while heating the pattern to a temperature of Publication No. 135943). This method reduces the internal stress of the resist pattern by cross-linking the surface layer of the resist pattern using ultraviolet rays while heating it at 80 to 150°C, thereby increasing the thermal strength while preventing the occurrence of wrinkles. This is a way to improve.

However, although this method shows the effect of preventing wrinkles to some extent, the heating temperature,
It is necessary to control many conditions such as time and amount of ultraviolet irradiation, but these adjustments are difficult, and in the manufacturing of semiconductor devices, which requires high precision reproducibility, defective products often occur and yields decrease. There is a problem with doing so. Moreover, the resist pattern layer after development processing contains water, solvent, etc. as evaporable components, and even if these components are tried to volatilize from within the resist pattern, crosslinking of the surface of the resist pattern due to ultraviolet irradiation occurs at the same time. for,
It is trapped inside the resist pattern, resulting in problems such as inhibiting improvement in the thermal strength of the pattern and impairing reproducibility. Therefore, this method is still not fully practical in the semiconductor industry.

Incidentally, the above-mentioned positive photoresists containing ultraviolet absorbers are attracting attention as they can cope with the further miniaturization of patterns that is expected to progress in the future. Therefore, a resist pattern stabilization method that is effective even for such positive photoresists is extremely important, and its development is strongly desired.

Problems to be solved by the invention In response to such demands, the present invention
Provides a method for thermally stabilizing a positive photoresist pattern suitable for manufacturing semiconductor devices such as LSI, which has high thermal strength, no wrinkles on the surface, and extremely high reproducibility. It was done for the purpose of

Means for Solving the Problems As a result of various studies on stabilizing positive photoresist patterns, the present inventors found that by heat-treating the resist pattern after development under reduced pressure while irradiating it with ultraviolet rays, Based on this finding, we discovered that water, solvent, etc. in the resist pattern layer evaporate, and crosslinking of the resist pattern due to ultraviolet irradiation progresses uniformly to the inside of the resist pattern, resulting in a pattern with good thermal stability. As a result, the present invention was completed.

That is, in the present invention, after selectively exposing a photosensitive layer made of a positive photoresist, a developing treatment is performed to form a resist pattern, and then a heat treatment is performed under reduced pressure while irradiating the entire surface of the resist pattern with ultraviolet rays. The present invention provides a method for thermally stabilizing a positive photoresist pattern.

Although there are no particular limitations on the positive photoresist used in the method of the present invention, a preferred positive photoresist is a positive photoresist whose main components are a photosensitive substance and a film-forming substance. This photosensitive material is prepared by partially or completely esterifying a quinonediazide group-containing compound, for example, a sulfonic acid of a quinonediazide such as orthobenzoquinonediazide, orthonaphthoquinonediazide, orthoanthraquinonediazide, and a compound having a phenolic hydroxyl group or an amino group, or Examples include partially or completely amidated ones.

Examples of compounds having a phenolic hydroxyl group or amino group include polyhydroxybenzophenones such as 2,3,4-trihydroxybenzophenone and 2,2',4,4'-tetrahydroxybenzophenone, or gallic acid. Alkyl gallate, phenol, p-methoxyphenol, dimethylphenol, hydroquinone, bisphenol A, naphthol, pyrocatechol, pyrogallol, pyrogallol monomethyl ether, pyrogallol-1,3-dimethyl ether, gallic acid, with some hydroxyl groups remaining Examples include esterified or etherified gallic acid, aniline, p-aminodiphenylamine, and the like.

On the other hand, film-forming substances include, for example, novolak resins obtained from phenol, cresol, etc. and aldehydes, acrylic resins, polyvinyl alcohol, polyvinyl alkyl ethers, copolymers of styrene and acrylic acid, hydroxystyrene polymers, polyvinyl Examples include alkali-soluble resins such as hydroxybenzoate and polyvinylhydroxybenzal.

The positive photoresist used in the present invention is advantageously used in the form of a solution by dissolving the photosensitive material and film-forming material in a suitable solvent.

Examples of such solvents include ketones such as acetone, methyl ethyl ketone, cyclohexanone, isoamyl ketone; monomethyl ether, monoethyl ether of ethylene glycol, ethylene glycol monoacetate, diethylene glycol or diethylene glycol monoacetate;
Mention may be made of polyhydric alcohols and their derivatives such as monopropyl ether, monobutyl ether or monophenyl ether; cyclic ethers such as dioxane; and esters such as methyl acetate, ethyl acetate and butyl acetate. These may be used alone or in combination of two or more.

In the method of the present invention, the positive photoresist containing an ultraviolet absorber may be used. As this ultraviolet absorber, azo dyes, quinoline dyes, aminoketone dyes, anthraquinone dyes, etc. can be used, but a particularly preferable ultraviolet absorber is, for example, 4-N,N-dimethylamino-4'-ethoxyazobenzene. , 4-hydroxy-4'-dimethylaminoazobenzene, 2,4
-dihydroxy-4'-diethylaminoazobenzene, 2,4-dihydroxyazobenzene, 2,4
-dihydroxy-4'-nitroazobenzene, 4-
(3-methoxy-4-hydroxybenzylidene)
Aminoazobenzene, 2-hydroxynaphthalene-1-azobenzene, 8-hydroxynaphthalene-1-azo (2'-methylbenzene), 8-hydroxynaphthalene-1-azo (2',4'-dimethylbenzene), 1-[ Examples include 4'-(2-methyl-1-phenylazo)-2'-methylphenylazo]-2-hydroxybenzene and 1-(4'-phenylazo-1'-phenylazo)-2-hydroxynaphthalene. These ultraviolet absorbers may be used alone or in combination of two or more, and the amount thereof is usually 0.1 to 20% by weight, preferably 0.1 to 20% by weight, based on the solid weight of the positive photoresist.
Selected in the range of 15% by weight. This amount is 0.1% by weight
If it is less than 20% by weight, the effect of preventing halation will not be effectively exhibited, and if it exceeds 20% by weight, crystals of the ultraviolet absorber will tend to precipitate in the photoresist film and form a heterogeneous phase, which is not preferable.

To give an example of a preferred method for forming a resist pattern in the method of the present invention, first, the positive photoresist is coated on a substrate, and after drying, a low pressure mercury lamp, a high pressure mercury lamp, an ultra-high pressure mercury lamp, an arc lamp, a xenon lamp, etc. This method is used to selectively irradiate actinic light through a desired mask, or to irradiate scanning electron beams. Next, a developer,
For example, sodium hydroxide aqueous solution, tetramethylammonium hydroxide aqueous solution, trimethyl (2
-Hydroxyethyl) A resist pattern is formed on the substrate by dissolving and removing the portion solubilized by irradiation with actinic light using a weakly alkaline aqueous solution such as an aqueous solution of ammonium hydroxide.

In the present invention, after forming a resist pattern on a substrate in this manner, it is necessary to heat-process the resist pattern under reduced pressure while irradiating the entire surface of the resist pattern with ultraviolet rays. There are no particular restrictions on the degree of pressure reduction during heat treatment, but if the pressure is too high, the evaporated components in the photoresist will not be sufficiently volatilized and the effects of the present invention will not be effectively exhibited, so it is usually 100 Torr or less, preferably 30 Torr. It is desirable to process under the following reduced pressure.

The processing temperature may be appropriately selected depending on the type of positive photoresist used, film thickness, etc., and is not particularly limited, but the processing temperature is usually in the range of 40 to 130°C. Generally, if the resist pattern is processed at a temperature exceeding 130°C, the resist pattern will melt and sag, and the edges of the pattern will become rounded, which is undesirable. Components cannot be removed sufficiently.

On the other hand, the method of this heat treatment is not particularly limited as long as it is a method that can heat the resist pattern layer, and for example, a hot plate method, a far-infrared lamp method, etc. can be used.

Further, examples of the ultraviolet generating lamp used for irradiating ultraviolet rays include a low pressure mercury lamp, a high pressure mercury lamp, an ultra-high pressure mercury lamp, a xenon lamp, and the like. The amount of ultraviolet rays irradiated to the resist pattern varies depending on the type of resist used, but in order to crosslink to the inside of the resist pattern, for example,
When using 253.7 nm ultraviolet light, the irradiation dose should be at least 150 mJ/cm ² to the resist pattern.
It is desirable to do more than that.

In the present invention, heating, reduced pressure, and ultraviolet irradiation may be performed simultaneously, or ultraviolet irradiation may be performed after reduced pressure heat treatment, but a method of reducing pressure, heating, and ultraviolet irradiation is preferred.
Also effective is a method of irradiating ultraviolet light while gradually increasing the heating temperature under reduced pressure.

Effects of the Invention The method for thermally stabilizing a positive photoresist pattern of the present invention is a method in which a developed resist pattern is heat-treated under reduced pressure and the entire surface of the resist pattern is irradiated with ultraviolet rays. Then, the water, solvent, etc. in the resist pattern layer evaporates, and crosslinking of the resist pattern due to ultraviolet irradiation progresses uniformly to the inside of the resist pattern, so thermal stability is significantly improved and no wrinkles occur on the surface. A positive photoresist pattern with extremely high reproducibility can be formed thereon. Therefore, the method of the present invention is particularly suitable for manufacturing semiconductor devices such as VLSI.

Examples Next, the present invention will be explained in more detail with reference to Examples.

Example 1 A positive photoresist TSMR-8800 (manufactured by Tokyo Ohka Kogyo Co., Ltd.), which is a combination of a photosensitive material having a naphthoquinone diazide group and a novolac resin as a film-forming material, was applied onto a silicon wafer having a 4-inch thermal oxidation film. After coating using a TR-5111 type resist coater (manufactured by Tatsumo Co., Ltd.),
It was dried for seconds to form a coating film with a thickness of 2.0 μm. Next, use the wafer stepper DSW-4800 through a test chart mask (manufactured by Dai Nippon Printing Co., Ltd.).
After exposure using a mold (manufactured by GCA), development was performed using a 2.38% by weight tetramethylammonium hydroxide aqueous solution, followed by rinsing at 23°C for 1 minute to form a resist pattern on the wafer. Ta.

Next, the wafer with the resist pattern formed thereon is placed on a hot plate in a vacuum processing apparatus equipped with a built-in low-pressure mercury lamp and a hot plate, and the vacuum processing chamber is opened using a vacuum pump.
After reducing the pressure to 0.2 Torr, the temperature of the hot plate was maintained at 60°C and ultraviolet rays were irradiated for 5 minutes. The exposure amount at this time was 253.7 nm and 6 J/cm ² .

Next, the wafer was cut so that the cross section of the resist pattern could be observed, and after being immersed in isoamyl acetate for 5 seconds, the cross section of the resist pattern was observed. There was no change. This indicates that the inside of the resist pattern was crosslinked and became insoluble in isoamyl acetate.

In addition, a wafer that had been similarly heated under reduced pressure and treated with UV irradiation was placed on a hot plate for 170°C.
Although it was heated at .degree. C. for 5 minutes, no change was observed in the shape of the resist pattern.

Furthermore, this was etched using a plasma etching device (OAPM-300 manufactured by Tokyo Ohka Kogyo Co., Ltd.) using a mixed gas of C ₂ F ₆ :He of 1:3 under conditions of a gas pressure of 1.5 Torr and an output of 400 W. When etching _{No. 2} was performed, no change in resist pattern shape or deterioration was observed, and etching with a uniform and anisotropic shape was achieved.

Comparative Example 1 In exactly the same manner as in Example 1, three 4-inch silicon wafers with a resist pattern provided thereon were prepared.

Next, the wafer was placed on a hot plate at normal pressure and irradiated with ultraviolet light using a low-pressure mercury lamp. The irradiation amount at this time was 6J/cm ² for 253.7nm light,
They were 15J/cm ² and 30J/cm ² .

Next, in the same manner as in Example 1, after cutting the resist pattern and immersing it in isoamyl acetate, the cross section of the resist pattern was observed. It was becoming a state of affairs. The state of the cross section at this time is 6J/ ^cm2 ,
Figure 2 a, for 15J/cm ² and 30J/cm ² respectively.
Shown in b and c. As is clear from this figure, even if the amount of ultraviolet irradiation was increased, no resistance was shown to isoamyl acetate, and it can be seen that the portions of the resist pattern crosslinked by ultraviolet irradiation did not reach the interior.

Furthermore, a heat resistance test was conducted on a resist pattern with an ultraviolet irradiation dose of 30 J/cm ² . When the wafer was divided and placed on a hot plate set at each temperature, the pattern on the wafer heated at 150°C for 5 minutes melted and sagged.

Comparative Example 2 A resist pattern was formed on a 4-inch silicon wafer in the same manner as in Example 1, and then ultraviolet rays were irradiated under reduced pressure in the same manner as in Example 1 except that the processing temperature was 25°C. In this case, wrinkles were observed in the 10 μm wide resist pattern when heated to 150°C.

Next, the wafer was cut in the same manner as in Example 1,
When a cross section of the resist pattern was immersed in isoamyl acetate, the inside of the resist pattern with a width of 10 μm was dissolved except for about 0.5 μm of the surface layer, forming a cavity.

Comparative Example 3 In the same manner as in Example 1, a positive photoresist was applied onto a silicon wafer having a thermally oxidized film, dried, and then exposed and developed through a test chart mask. Next, place this wafer on a hot plate.
It was heated to 90°C and irradiated with ultraviolet light.

The oxide film was etched using a plasma etching device (OAPM-300 manufactured by Tokyo Ohka Kogyo Co., Ltd.) using a mixed gas of C ₂ F ₆ :He of 1:3 under the same conditions as in Example 1. During this process, the resist pattern deteriorated due to the rise in wafer surface temperature, and the pattern also sagged, making it impossible to perform good etching.

[Brief explanation of the drawing]

FIGS. 1 and 2 are diagrams showing the cross-sectional shapes of the resist patterns obtained in Examples and Comparative Examples, respectively, after the resist patterns were immersed in isoamyl acetate.

Claims (1)

[Claims] 1. Positive type, which is characterized by selectively exposing a photosensitive layer made of positive type photoresist, performing a development process to form a resist pattern, and then heat-treating the resist pattern while irradiating the entire surface of the resist pattern with ultraviolet rays under reduced pressure. Method for thermal stabilization of photoresist patterns.