JPH0572747A - Pattern formation method - Google Patents

Abstract

(57) [Summary] (Modified) [Objective] To provide a chemically amplified resist pattern forming method capable of stably obtaining a highly accurate pattern. [Structure] A step of forming a photosensitive resin film on a substrate, a step of pattern-exposing the photosensitive resin film, a step of performing a post-exposure bake, and a step of developing the photosensitive resin film using an alkali developing solution. After this post-exposure bake, the substrate is cooled while controlling the temperature history of the photoresist film to be uniform within the surface of the substrate and the same between the substrates, and then the development is performed. I do. Post-exposure bake after exposure Exposure of photosensitive resin film to water vapor atmosphere prior to or after exposure Chemically amplified resist is exposed to light after exposure post-exposure bake or exposure of photosensitive resin film to solvent atmosphere Post-exposure of resist Jabake is performed in a reduced pressure atmosphere or an inert gas atmosphere.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pattern forming method, and more particularly to a resist pattern forming method in lithography in a semiconductor device manufacturing process.

[0002]

2. Description of the Related Art In the manufacture of semiconductor integrated circuits, a method is known in which a fine pattern is formed on a film to be processed such as a semiconductor thin film and the film is etched using the pattern as a mask.

The process of forming this pattern is usually constituted by the following operations.

That is, first, a solution containing a resin and a photosensitizer is applied onto a film to be processed such as a semiconductor thin film and dried to form a resist film (photosensitive resin film).

Next, the resist film is subjected to an exposure treatment for selectively irradiating an energy ray such as light.

After that, a mask pattern (resist pattern) is formed on the substrate by a developing process.

In forming such a pattern, a resist material using a phenol resin which is excellent in sensitivity to exposure light and dry etching resistance is often used.

By the way, at present, the degree of integration of semiconductor integrated circuits has been increased at a speed of 4 times in 2 to 3 years.
Along with this, the dimensions of the pattern of the circuit element are becoming finer year by year, and thus strict dimensional accuracy control is required.

At present, a positive resist composed of, for example, a novolac resin and an O-quinonediazide compound is often used as a resist of a phenolic resin, but recently, from the viewpoint of demand for high dimensional accuracy and improvement of sensitivity, an acid catalytic reaction is used. Expectations are increasing for chemically amplified resists (especially negative resists). This chemically amplified negative resist material is composed of a resin, a cross-linking agent, and an acid generator (PAG: Photo Acid Generator). When this resist is exposed to light, an acid is generated from PAG, and this acid diffuses in the resist and acts as a catalyst on the cross-linking agent to create active sites therein. The cross-linking of the resin proceeds through the active points, and as a result, the cross-linked region becomes insoluble in the developer and forms a pattern.

In this chemically amplified negative type resist, the amount of acid generated by exposure does not much depend on the amount of exposure, so that even a portion with a small amount of exposure becomes slightly soluble.
Therefore, as compared with a conventional positive resist material in which a pattern is formed largely depending on the exposure amount, there is an advantage that a pattern with excellent vertical dimension of side walls and excellent dimensional accuracy can be easily formed.

As described above, in the chemically amplified resist, the acid generated by exposure diffuses in the resist matrix to form active points, and this diffusion rate is a heat treatment after exposure called post exposure bake. Is in control. Therefore, strict control of post exposure bake is extremely important for pattern formation and its dimensional control.

It should be noted that, for example, the time from exposure to post-exposure bake is controlled to be constant. And the post exposure bake has a high temperature,
The longer the time, the higher the sensitivity.

However, it is extremely difficult to control the conditions of the post-exposure bake, which is a process using heat, to be constant, and it is difficult to accurately process a fine pattern due to variations in resolution. .. in this way,
Particularly in the case of a chemically amplified resist, it was difficult to control the line width of the pattern.

Further, the lithography process using a resist such as a chemically amplified negative type resist has the following problems.

First, there is a problem that the resist characteristics are easily influenced by the surrounding environment, particularly temperature and humidity, and the finished size of the resist pattern changes according to the change of the environment.

Secondly, in the heat treatment performed after the exposure, the crosslinking reaction is more likely to proceed in the bottom portion than in the vicinity of the surface of the resist film. However, the resist remains undeveloped, and a sufficient resolution cannot be obtained. This problem becomes particularly serious when forming a hole pattern that connects wirings via an interlayer insulating film, and if a hole pattern is formed using a chemically amplified negative resist material, a high resolution excimer is expected. In reality, even if a laser is used as an exposure light source, only a resolution of about 0.5 μm can be obtained.

Further, in the chemically amplified positive resist process, there is a problem that the eaves are formed in the pattern when the elapsed time from the exposure to the post-exposure bake becomes long, and the resolution is remarkably lowered. As a result, although the time depends on the material composition of the resist, in the case of the positive resist, it is a short time of about 1 hour or less, which is a factor difficult to control in the process.

[0018]

As described above, in the pattern formation using the chemically amplified resist, the latent image is formed by two steps of exposure and post exposure bake. Particularly, the post exposure bake is controlled by heat. Since difficult energy is used, there is a problem in that this process control is difficult, variations in sensitivity and resolution occur, and a highly accurate pattern cannot be stably obtained.

Further, the resist characteristics are easily affected by temperature and humidity, and the finished size of the resist pattern changes according to changes in the environment, or the cross-linking reaction proceeds more easily at the bottom than in the vicinity of the surface of the resist film. Therefore, there is a problem that a sufficient resolution cannot be obtained.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a resist pattern forming method capable of stably obtaining a highly accurate pattern.

[0021]

Therefore, in the first aspect of the present invention, a step of forming a photosensitive resin film on a substrate, a step of pattern-exposing this photosensitive resin film, and a step of performing a post-exposure bake. And a step of developing the photosensitive resin film to form a pattern, and controlling the temperature history of the photoresist film to be uniform within the surface of the substrate and the same between the substrates after the post-exposure bake. While the substrate is cooled, development is performed after this.

In the second aspect of the present invention, the photosensitive resin film is exposed to a water vapor atmosphere before the post-exposure bake after exposure, or the photosensitive resin film is exposed to a water vapor atmosphere during the post-exposure bake. There is.

Further, in the third aspect of the present invention, the photosensitive resin film is exposed to a solvent atmosphere after the chemically amplified resist is exposed and prior to the post exposure bake, or the photosensitive resin film is exposed to a solvent atmosphere during the post exposure bake. I try to expose it inside.

Furthermore, in the fourth aspect of the present invention, post exposure bake is performed in a reduced pressure atmosphere or an inert gas atmosphere.

[0025]

According to the first method of the present invention, after the photoresist is coated on the substrate, the temperature history of the resist film of the substrate is uniform after the exposure and post exposure bake, and even between the substrates. Since the resist pattern is formed by cooling while controlling the temperature to be the same and then performing development processing to form a resist pattern, it is possible to stably obtain a highly accurate pattern.

Here, examples of the substrate include a wafer, those obtained by coating various semiconductor films, insulating films, or metal films on the wafer, or mask substrates. As the resist, a photosensitive resin (particularly a chemically amplified material) which is sensitive to ultraviolet light, deep ultraviolet light, vacuum ultraviolet light, X-ray, electron beam, or ion beam can be used. Furthermore, it is desirable to start the cooling control immediately after the end of post exposure bake. This is because if natural cooling is allowed to proceed by leaving it for a period of time, variations in sensitivity within the plane of the substrate and between the substrates may occur due to it. Furthermore, as a coolant used for cooling the substrate, a gas that does not substantially dissolve or react with the resist can be, for example, nitrogen gas at an arbitrary set temperature. When bringing the substrate into contact with or close to the control plate with a larger heat capacity,
There is a method in which the plate is cooled and maintained at a predetermined temperature by using a coolant such as cooling water or Fluorinert.

According to the second aspect of the present invention, the resist film formed on the substrate to be processed is exposed to a water vapor atmosphere after pattern exposure, prior to or during post exposure bake. A stable latent image can be formed without being affected by the surrounding environment. In particular, even when a chemically amplified resist material that is easily affected by the surrounding environment is used, the finished pattern size after development can be kept constant by using this method. In particular, if the chemically amplified resist film is exposed to an atmosphere such as water vapor before or during heating, the crosslinking reaction at the time of heating can be promoted only near the surface of the resist film. That is, it is possible to reduce the difference in dissolution rate in the developing solution between the vicinity of the resist film surface and the vicinity of the bottom portion, and when a chemically amplified negative resist material is used, the resist near the bottom portion of the pattern remains undeveloped and the resolution is improved. It is possible to solve the problem that the price does not rise as expected.

According to the third aspect of the present invention, the chemically amplified resist film is exposed to an atmosphere of a predetermined solvent vapor such as alcohol in the reaction vessel before or during heating. In this case, the crosslinking reaction at the time of heating can be promoted only near the surface of the resist film. That is, it is possible to reduce the difference in dissolution rate in the developing solution between the vicinity of the resist film surface and the vicinity of the bottom portion, and when a chemically amplified negative resist material is used, the resist near the bottom portion of the pattern remains undeveloped and the resolution is improved. It is possible to solve the problem that the price does not rise as expected. Furthermore, in the case of a positive type resist, the surface layer is treated with a solvent vapor to increase the solubility in a developing solution, whereby the unique eaves shape can be eliminated.

Further, according to the fourth aspect of the present invention, if the post-exposure step of the resist film is carried out under reduced pressure or in an inert gas atmosphere, changes in the surrounding environment,
In particular, it becomes possible to extremely eliminate the influence of moisture in the air, and it becomes possible to obtain high resolution.

[0030]

Embodiments of the pattern forming method according to the present invention will be described below in detail with reference to the drawings. Example 1 FIG. 1 is a process sectional view showing an example of a pattern forming method of the present invention.

The surface of the silicon substrate 1 on which a predetermined element region is formed is oxidized to form a silicon oxide film 2 having a thickness of 0.8 μm.
To form. Next, Shipley negative resist SAL
-601ER7 was spin-coated and pre-baked by hot plate treatment at 85 ° C for 60 seconds to give a thickness of 0.5μ.
m resist film 3 was formed.

Next, a silicon substrate 1 was formed by a reduction projection exposure apparatus using an excimer laser 248.4 nm oscillation line using a mixed gas of krypton, fluorine and helium.
Pattern exposure is performed on the upper resist film 3 through the mask 4. The energy intensity at this time is 50 to 100 mJ / cm ²
Met.

Immediately thereafter, on a hot plate at 110 ° C. for 9
After the post-exposure bake for 0 seconds, after completion of this post-exposure bake, the plate was set at 15 ° C. and cooled, and 1 minute later, the metal-free developer MF-312 of Shipley Co. was removed as an alkaline developer. Development was performed by a dipping method for 100 seconds using a developing solution (concentration 0.27N) diluted 1: 1 with ionized water. When the dimensional variation between the wafers when 24 sheets were processed continuously was measured, the 0.4 μmL / S pattern was ± 0.
It was possible to control the thickness to 02 μm or less.

Comparative Example 1 After the post-exposure bake, the same process as in Example 1 was carried out except for the step of allowing the plate set at 15 ° C. to cool naturally without contacting it. ± 0.03μ in 0.4μmL / S pattern
m, and the dimensional accuracy was significantly inferior to the results of Example 1 of the present invention.

Example 2 In the above example, after the post exposure bake was completed,
The plate was cooled by bringing it into contact with a plate set at 15 ° C., but in this example, low temperature nitrogen gas is blown to forcibly cool the plate.

First, SAL601 was formed by spin coating on a glass substrate on a rotary table on which chromium was vapor-deposited.
-ER7 was applied to 0.5 μm, prebaked at 85 ° C. for 2 minutes, and then selectively irradiated with an electron beam at an acceleration voltage of 20 kV,
After that, post exposure bake at 100 ℃,
A low temperature nitrogen gas was blown to force cooling.

After that, development processing is performed with an alkali developing solution,
When the in-plane uniformity of the obtained pattern was examined, a highly accurate pattern with a maximum deviation value of 0.1 μm or less could be obtained.

Comparative Example 2 For comparison, the same in-plane uniformity of the pattern was obtained as in Example 2 except that the substrate was naturally cooled after post-exposure bake. The deviation value was 0.3 μm, which was clearly inferior to that of Example 2. Third Embodiment Next, as a third embodiment of the present invention, a method of performing post exposure bake in steam will be described.

FIG. 2 is a process sectional view showing an embodiment of a method of forming a resist pattern according to the present invention, and FIG. 3 shows a sectional structure of a reaction vessel having a built-in hot plate and having a gas supply and exhaust mechanism. It is a figure.

First, as shown in FIG. 2A, a CV is formed on the surface of the silicon substrate 11 on which a predetermined element region is formed.
A silicon oxide film (interlayer insulating film) 12 having a film thickness of 1200 nm is deposited by using the D method.

Then, a chemically amplified negative resist containing poly-p-hydroxystyrene (base polymer), a photoacid generator and a cross-linking agent was spin-coated on this, and heated at 100 ° C. for 60 seconds on a hot plate. A treatment (prebaking) was performed to form a resist film 13 having a film thickness of 1000 nm (FIG. 2 (b)).

Next, pattern exposure was performed on this resist film through a mask 15 using a reduction projection exposure apparatus using a 248.4 nm oscillation line 14 of a krypton fluoride excimer laser as a light source (FIG. 2 (c)). The exposure energy at this time was 30 to 50 mJ.

After that, heat treatment (post-exposure bake) at 125 ° C. for 60 seconds on a hot plate open to the atmosphere (conventional method) and a reaction vessel shown in FIG. Heat treatment (post-exposure bake) at 125 ° C. for 60 seconds while passing the solution at a flow rate of / min (post-exposure bake) was 1.2.
Immersion development was performed for 90 seconds in a wt% tetramethylammonium hydroxide aqueous solution (FIG. 2 (d)).

This reaction vessel is equipped with a gas introducing joint portion 16
Cylinder 1 designated by the cylinder support 18 from
The substrate to be processed 21 placed on the hot plate 24 is post-exposure baked while the gas is supplied from the gas supply nozzle 20 into the region covered by the chamber sealing cover 19 via the gas supply nozzle 7. Here, 22 is a substrate supporting portion, 23 is an exhaust hole, 25 is an O-ring for sealing the inside of the container, and 26 is an exhaust joint portion.

FIG. 4 shows a resist pattern (hole diameter 0.4 μm) when heat treatment is performed by the conventional method and the method of the present invention.
(m hole pattern). As shown in FIG. 4 (b), in the conventional method, the resist 1 on the bottom of the pattern is
No. 3 is left undeveloped, whereas in the method of the present invention, as shown in FIG. 4 (a), a hole pattern having a hole diameter of 0.4 .mu.m is formed to the bottom of the pattern with high dimensional accuracy.

In the method of the present invention, a hole diameter of 0.
It was possible to resolve up to a hole pattern of 35 μm. The optimum exposure energy at this time was 40 mJ in the conventional method and 34 mJ in the method of the present invention.

As described above, in the patterning of the chemically amplified negative resist using the method of the present invention, not only the resolution is significantly improved as compared with the conventional method, but also the sensitivity is increased. It becomes possible.

Example 4 In Example 3, a method of performing post-exposure bake in water vapor was described. Here, post-exposure bake was carried out after introducing ethyl cellosolve acetate solvent vapor using nitrogen as a carrier gas into the reaction vessel. A method of baking will be described.

First, by the same method as in the third embodiment,
A chemically amplified negative resist film having a film thickness of 1000 nm was formed on the surface of the substrate to be treated with the silicon oxide film.

Next, pattern exposure was performed on the resist film through a mask using a reduction projection exposure apparatus using a 248.4 nm oscillation line of a krypton fluoride excimer laser as a light source. The exposure energy at this time is 30 to 50 m.
It was J.

Then, the substrate to be treated was placed in a reaction vessel similar to that used in Example 3, and an ethyl cellosolve acetate solvent vapor containing nitrogen as a carrier gas was introduced into the reaction vessel at room temperature for 2 liters / min. After being introduced at a flow rate of 30 seconds for 30 seconds, a heat treatment (post exposure bake) at 125 ° C. for 60 seconds was performed on the hot plate built in the reaction vessel.

Thereafter, the resist film was immersion developed in a 1.2 wt% tetramethylammonium hydroxide aqueous solution for 90 seconds.

Also in this case, as in the case of the third embodiment, a hole pattern having a hole diameter of 0.35 μm can be formed with high dimensional accuracy, and the resolution is greatly improved as compared with the conventional method.

Fifth Embodiment Next, as a fifth embodiment of the present invention, a method of using ethanol to remove the “visor” from the chemically amplified positive resist will be described.

First, a chemically amplified positive type resist is applied on a silicon substrate so as to have a film thickness of 1 μm, and the temperature is kept at 90 ° C. for 6 hours.
A heat treatment for 0 seconds was performed. After that, this resist film was pattern-exposed through a mask using a reduction projection exposure apparatus using a 248.4 nm oscillation line of a krypton fluoride excimer laser as a light source.

The exposure energy at this time is 24 mJ / cm ²
Met.

Next, the substrate to be processed was exposed to a reaction vessel in an ethanol atmosphere for 60 seconds, and then heat-treated (post exposure bake) at 95 ° C. for 90 seconds on a hot plate open to the atmosphere. 2.
Immersion development was performed for 120 seconds in a 0% aqueous solution of tetramethylammonium hydroxide.

By carrying out this treatment, as shown by the ethanol atmosphere treatment in FIG. 5, the "peaks" are removed and the shape is improved. For comparison, "eaves" remain, as untreated is shown as untreated.

Furthermore, regarding the exposure energy,
Exposure energy is 33 mJ / cm ² for untreated
Whereas it was necessary, it was found that the one treated with ethanol only required 24 mJ / cm ² as described above, and the sensitivity was extremely high.

Example 6 In this example, a method of performing post exposure bake under reduced pressure will be described.

First, the film thickness of 1000 nm was formed on the surface of the substrate to be treated with the silicon oxide film by the same method as in the third embodiment.
A chemically amplified positive resist film was formed.

Next, 2 of the krypton fluoride excimer laser is used.
Pattern exposure was performed on the resist film through a mask using a reduction projection exposure apparatus using an oscillation line of 48.4 nm as a light source. The exposure energy at this time was 36 mJ.

Then, the substrate to be treated was placed in a reaction vessel similar to that used in Example 3, and the pressure in the reaction vessel was reduced to 30 Torr and heat treatment at 100 ° C. for 60 seconds (post-exposure) was performed. Each of those subjected to a heat treatment (post-exposure bake) at 100 ° C. for 60 seconds (conventional method) on a hot plate open to the atmosphere, respectively. 38t
% Tetramethylammonium hydroxide aqueous solution for 90 seconds. Since chemically amplified positive resists are more susceptible to the surrounding environment than negative resists, it is necessary to pay particular attention to changes in environmental temperature and humidity during post exposure bake.

The above-described treatment was continuously performed 20 times daily for 7 days in a clean room in which the temperature and humidity were controlled, and the influence of changes in the surrounding environment on the finished size of the resist pattern was measured by the method of the present invention. Each conventional method was investigated. In addition, as for the fluctuation amount of temperature and humidity in the clean room during these 7 days, the temperature is set to 24
± 0.5 ° C for ℃ and ± 30% for humidity
It was 2.4%.

FIG. 6 shows the result of plotting the average value and the variation of the resist finish dimension of the hole pattern having the design dimension of 0.5 μm for each date. As is clear from this figure, in the method of the present invention, the variation in the finished dimension per day is about ± 0.01 μm, and the dimensional variation over 7 days is 0.02 μm or less, whereas According to the method, the variation in finished dimensions per day is ±
0.02μm, 0.04μ dimensional variation over 7 days
It was m. From this result, it was demonstrated that the method of the present invention significantly improves the dimensional controllability of the resist pattern as compared with the conventional method.

[0066]

As described above, according to the first aspect of the present invention, the substrate is controlled while controlling the temperature history of the photoresist film after post-exposure bake to be uniform within the surface of the substrate and the same between the substrates. Since it is cooled and the post-development is performed, it is possible to overcome the sensitivity change due to the post-exposure bake treatment, which is a drawback of the chemically amplified process, resulting in uniform and dimensional accuracy. It becomes possible to form a high pattern.

Further, according to the second aspect of the present invention, the chemical amplification resist material which is easily affected by the surrounding environment is used because it is exposed to water vapor before or during post exposure baking. Even when it is used, the finished pattern size after development can always be kept constant, and the resolution of the resist pattern is significantly improved as compared with the conventional method.

According to the third aspect of the present invention, by exposing the chemically amplified resist film to the atmosphere of a predetermined solvent vapor such as alcohol in the reaction vessel before or while heating the resist film, Similar to the second aspect of the present invention, the resolution is significantly improved.

Furthermore, according to the fourth aspect of the present invention, if the post-exposure step of the resist film is carried out under reduced pressure or in an inert gas atmosphere, changes in the surrounding environment, especially the influence of moisture in the air, can be extremely suppressed. Therefore, it is possible to obtain high resolution.

[Brief description of drawings]

FIG. 1 is a process sectional view showing an embodiment of a pattern forming method according to the present invention.

FIG. 2 is a process sectional view showing a method of forming a resist pattern according to a third embodiment of the invention.

FIG. 3 is a diagram showing a cross-sectional structure of a reaction container having a hot plate built therein and having a gas supply and exhaust mechanism.

FIG. 4 is a diagram showing a cross-sectional shape of a resist pattern (hole pattern having a hole diameter of 0.4 μm) when heat treatment is performed by the conventional method and the method of the present invention.

FIG. 5 is a comparative view of a pattern formed by the method of the fifth embodiment of the present invention and a pattern formed by the conventional method.

FIG. 6 is a diagram in which the average value and variation of the resist finish dimension of a hole pattern having a design dimension of 0.5 μm are plotted for each date.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Silicon substrate 2 ... Silicon oxide film 3 ... Resist film 4 ... Mask 3a ... Exposed part 11 ... Silicon processed substrate 12 ... Silicon oxide film 13 ... Resist film 14 ... Excimer laser 15 ... Mask 16 ... Gas introduction joint part 17 ... Cylinder 18 ... Cylinder support 19 ... Chamber sealing cover 20 ... Gas supply nozzle 22 ... Substrate support 23 ... Exhaust hole 24 ... Hot plate 25 ... O-ring 26 ... Exhaust joint

Claims (4)

[Claims] 1. A photosensitive resin film applying step of applying a photosensitive resin film on a substrate to be processed, a step of pattern exposing the photosensitive resin film, and a post-exposure bake to the photosensitive resin film. A cooling step of cooling the substrate while controlling the temperature history of the photoresist film to be uniform in the plane of the substrate and the same between the substrates, and a developing step of developing the photosensitive resin film to form a pattern And a pattern forming method comprising: 2. A photosensitive resin film coating step of coating a photosensitive resin film on a substrate to be processed, a step of pattern exposing the photosensitive resin film, and the photosensitive resin film in a water vapor atmosphere prior to heating. A step of performing a post-exposure bake of exposing and heating or exposing the photosensitive resin film to a steam atmosphere during heating, and a developing step of developing the photosensitive resin film to form a pattern A pattern forming method characterized by the above. 3. A photosensitive resin film coating step of coating a chemically amplified photosensitive resin film on a substrate to be processed, a step of pattern exposing the photosensitive resin film, and the photosensitive resin film prior to heating. A step of performing a post-exposure bake of exposing the photosensitive resin film to a predetermined solvent vapor atmosphere for heating, or exposing the photosensitive resin film to a predetermined solvent vapor atmosphere for heating, and developing the photosensitive resin film. And a developing step of forming a pattern. 4. A photosensitive resin film applying step of applying a photosensitive resin film on a substrate to be processed; a step of pattern exposing the photosensitive resin film; and a step of depressurizing the photosensitive resin film or using an inert gas. A pattern forming method comprising: a step of performing a post-exposure bake of heating in an atmosphere; and a developing step of developing the photosensitive resin film to form a pattern.