JP2994501B2 - Pattern formation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art In the manufacture of a semiconductor integrated circuit, a method of forming a fine pattern on a film to be processed such as a semiconductor thin film and etching the film to be processed using this pattern as a mask is used.

[0003] This pattern forming step is usually constituted by the following operation.

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

Next, an exposure process for selectively irradiating the resist film with energy rays such as light is performed.

Thereafter, a mask pattern (resist pattern) is formed on the substrate by a development process.

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

At present, the degree of integration of semiconductor integrated circuits is increasing at a rate of four times in two to three years.
Along with this, the dimensions of circuit element patterns have become smaller year by year, and thus strict control of dimensional accuracy has been required.

At present, a positive resist composed of, for example, a novolak resin and an O-quinonediazide compound is often used as a phenolic resin resist. Recently, however, acid catalysis has been used in view of the demand for high dimensional accuracy and improvement of sensitivity. Expectations for chemically amplified resists (especially negative resists) have become stronger. This chemically amplified negative resist material is composed of a resin, a crosslinking agent and an acid generator (PAG: photoacid generator). When the resist is exposed to light, an acid is generated from the PAG, and the acid diffuses through the resist and acts as a catalyst for the crosslinking agent to create an active site therein. Crosslinking of the resin proceeds through these active points, and as a result, the crosslinked region becomes hardly soluble in the developer and forms a pattern.

[0010] In this chemically amplified negative resist, the amount of acid generated by exposure does not depend much on the amount of exposure, so that even a portion where the amount of exposure is small progresses insolubilization to some extent.
Therefore, as compared with a conventional positive resist material in which a pattern is formed largely depending on the amount of exposure, there is an advantage that a pattern with good verticality of a side wall and excellent dimensional accuracy can be easily formed.

As described above, in a chemically amplified resist, an acid generated by exposure diffuses in a resist matrix to form active sites. The diffusion rate is determined by a post-exposure bake called post-exposure bake. Is dominating. Therefore, strict control of post-exposure bake is extremely important for pattern formation and dimensional control thereof.

It should be noted that, for example, the time from exposure to post-exposure bake is kept constant. And the post exposure bake is hot,
The longer the time, the higher the sensitivity.

However, it is extremely difficult to control the conditions of post-exposure bake, which is a process using heat, at a constant level, and it is difficult to precisely 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.

The lithography process using a resist such as a chemically amplified negative resist has the following problems.

The first problem is that the resist characteristics are easily affected by the surrounding environment, especially temperature and humidity, and the finished size of the resist pattern fluctuates according to changes in the environment.

Second, the cross-linking reaction proceeds more easily at the bottom of the resist film than in the vicinity of the surface of the resist film during the heat treatment performed after the exposure. Is left undeveloped, and a sufficient resolution cannot be obtained. This problem is particularly serious when forming a hole pattern that connects wirings via an interlayer insulating film.If an attempt is made to form a hole pattern using a chemically amplified negative resist material, an excimer that is expected to have high resolution is expected. Even if a laser is used as an exposure light source, a resolution of only about 0.5 μm can be obtained at most.

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

[0018]

As described above, in the pattern formation using a chemically amplified resist, the formation of a latent image is performed in two steps of exposure and post-exposure bake. In particular, post-exposure bake is controlled by heat. Since difficult energy is used, this process management is difficult, and there is a problem that sensitivity and resolution vary, and a high-precision pattern cannot be stably obtained.

In addition, the resist characteristics are easily affected by temperature and humidity, and the finished dimensions of the resist pattern fluctuate in accordance with 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 has as its object to provide a method of forming a resist pattern capable of stably obtaining a highly accurate pattern.

[0021]

[0022]

[Means for Solving the Problems] Therefore, the first of the present invention
Is a chemically amplified type containing a photoacid generator on the substrate to be processed
A photosensitive resin film coating step of applying a photosensitive resin film of
Pattern exposure of the photosensitive resin film and prior to heating
And heating the photosensitive resin film by exposing it to a water vapor atmosphere.
Heating or heating the photosensitive resin film in a steam atmosphere
Exposure bake to expose and heat
Process and developing the photosensitive resin film to form a pattern
And a developing step.

Further, a second aspect of the present invention is that a substrate to be processed is
Applying photosensitive resin film to apply chemically amplified photosensitive resin film
And a step of pattern-exposing the photosensitive resin film,
Prior to heating, the photosensitive resin film is heated in a predetermined solvent vapor atmosphere.
Exposure during heating or during heating the photosensitive resin
A post that heats the film by exposing it to a specified solvent vapor atmosphere
Performing an exposure bake, and the photosensitive resin film
And a developing step of forming a pattern
It is characterized by.

[0024]

[0025]

Here, examples of the substrate include a wafer or a substrate in which various semiconductor films, insulating films, or metal films are coated on the wafer, or a mask substrate. Examples of the resist include a photosensitive resin (particularly, a chemically amplified material) that is sensitive to ultraviolet light, deep ultraviolet light, vacuum ultraviolet light, X-ray, electron beam, or ion beam. Further, it is desirable to start the cooling control immediately after the end of the post-exposure bake. This is because if the natural cooling is allowed to proceed for a while, the sensitivity of the substrate may vary within the surface and between the substrates. Further, as a coolant used for cooling the substrate, a gas that does not substantially dissolve or react with the resist can be, for example, a nitrogen gas at an arbitrary set temperature. When contacting or approaching the substrate to a 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 first aspect of the present invention, a chemically amplified photosensitive resin film containing a photo-acid generator formed on a substrate to be processed is subjected to pattern exposure and then to post-exposure baking or post-exposure baking. During the baking, a stable latent image can be formed without being affected by the surrounding environment because the apparatus is exposed to a water vapor atmosphere. 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 always 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 during heating can be promoted only in the vicinity of the resist film surface. In other words, the dissolution rate difference in the developing solution between the vicinity of the resist film surface and the vicinity of the bottom can be reduced. It can solve the problem of not going up as expected.

Further, according to the second aspect of the present invention, the chemical amplification type resist film is exposed to an atmosphere of a predetermined solvent vapor, for example, alcohol in the reaction vessel before or during the heating. By doing so, the crosslinking reaction during heating can be promoted only in the vicinity of the resist film surface. That is, the dissolution rate difference in the developing solution between the vicinity of the surface of the resist film and the vicinity of the bottom can be reduced. When a chemically amplified negative resist material is used, the resist near the bottom of the pattern remains without being developed, and the resolution is low. It can solve the problem of not going up as expected. Further, in the case of a positive resist, the eaves shape peculiar to the eaves can be eliminated by treating the surface layer with a solvent vapor and increasing the solubility in a developing solution.

[0029]

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the pattern forming method according to the present invention will be described below in detail with reference to the drawings. Embodiment 1 FIG. 1 is a process sectional view showing an embodiment of the 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 0.8 μm thick silicon oxide film 2.
To form Next, Shipley negative resist SAL
-601ER7 is spin-coated, pre-baked by hot plate treatment at 85 ° C for 60 seconds, and has a thickness of 0.5μ.
m of the resist film 3 was formed.

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

Immediately afterwards, at 110 ° C. on a hot plate, 9
After a 0 second post-exposure bake, after the post-exposure bake was completed, it was brought into contact with a plate set at 15 ° C. and cooled, and after 1 minute, a metal-free developer MF-312 of Shipley was removed as an alkaline developer. Development was carried out by a dipping method for 100 seconds using a developing solution (concentration: 0.27 N) diluted 1: 1 with ion water. When the dimensional variation between wafers when 24 consecutive wafers were processed was measured, it was found that the 0.4 μmL / S pattern was extremely accurately ± 0.4.
It could be controlled to not more than 02 μm.

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

Embodiment 2 In the above embodiment, after the end of the post-exposure bake,
The plate is set at 15 ° C. and cooled by contact with the plate. In this example, a low-temperature nitrogen gas is blown to forcibly cool the plate.

First, a SAL601 was spin-coated on a chromium-deposited glass substrate placed on a turntable.
-Apply ER7 to a thickness of 0.5 μm, and selectively irradiate an electron beam at an acceleration voltage of 20 kV after pre-baking at 85 ° C. for 2 minutes,
After baking at 100 ° C,
Cooling was performed by blowing low-temperature nitrogen gas.

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

Comparative Example 2 For comparison, the in-plane uniformity of the pattern was the same as in Example 2 above, except that the substrate was allowed to cool naturally after the post-exposure bake. The deviation was 0.3 μm, which was clearly inferior to Example 2. Embodiment 3 Next, as a third embodiment of the present invention, a method of performing post-exposure baking in steam will be described.

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

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

Then, a chemically amplified negative resist containing a poly-p-hydroxystyrene (base polymer), a photoacid generator and a crosslinking agent is spin-coated thereon, and heated on a hot plate at 100 ° C. for 60 seconds. A process (pre-bake) was performed to form a 1000 nm-thick resist film 13 (FIG. 2B).

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

Thereafter, a heat treatment (post-exposure bake) at 125 ° C. for 60 seconds on a hot plate open to the atmosphere (post-exposure bake) was performed, and steam was supplied at a flow rate of 2 liters in a reaction vessel shown in FIG. (Post-exposure bake) at 125 ° C. for 60 seconds (method of the present invention) while passing at a rate of 1.2 min / min.
It was immersed and developed in a wt% aqueous solution of tetramethylammonium hydroxide for 90 seconds (FIG. 2 (d)).

The reaction vessel is provided with a gas introducing joint 16.
From the cylinder 1 indicated by the cylinder support 18
The substrate to be processed 21 placed on the hot plate 24 is subjected to post-exposure baking while supplying gas from the gas supply nozzle 20 into the area covered by the chamber sealing cover 19 through the substrate 7. Here, 22 is a substrate support, 23 is an exhaust hole, 25 is an O-ring for sealing the inside of the container, and 26 is an exhaust joint.

FIG. 4 shows a resist pattern (having a hole diameter of 0.4 μm) when heat treatment was performed by the conventional method and the method of the present invention.
m hole pattern). As shown in FIG. 4B, in the conventional method, the resist 1 at the bottom of the pattern is used.
While No. 3 remains without being developed, in the method of the present invention, as shown in FIG. 4A, a hole pattern having a hole diameter of 0.4 μm is formed with good dimensional accuracy to the bottom of the pattern.

In the method of the present invention, the hole diameter is further increased to 0.1 mm.
It was possible to resolve 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 greatly improved as compared with the conventional method, but also the sensitivity is increased. It becomes possible.

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

First, by the same method as in the third embodiment,
A 1000-nm-thick chemically amplified negative resist film was formed on the surface of the silicon oxide film-treated substrate.

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
J.

Next, the substrate to be processed was placed in the same reaction vessel as that used in Example 3, and a vapor of ethyl cellosolve acetate using nitrogen as a carrier gas was supplied into the reaction vessel at room temperature for 2 liter / min. Then, a heat treatment (post-exposure bake) was performed at 125 ° C. for 60 seconds on a hot plate built in the reaction vessel.

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

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

Embodiment 5 Next, as a fifth embodiment of the present invention, a method of removing "eaves" from a chemically amplified positive resist using ethanol will be described.

First, a chemically amplified positive resist is applied on a silicon substrate so as to have a thickness of 1 μm.
A heat treatment for 0 seconds was performed. Thereafter, the resist film was subjected to pattern exposure 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 was 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 subjected to a heat treatment (post-exposure bake) at 95 ° C. for 90 seconds on a hot plate open to the atmosphere. To 2.
It was immersed and developed in a 0% aqueous solution of tetramethylammonium hydroxide for 120 seconds.

By performing this processing, as shown in FIG. 5 as an ethanol atmosphere processing, "eaves" are removed and the shape is improved. For the sake of comparison, "eaves" remain so that unprocessed ones are shown as unprocessed.

Further, regarding the exposure energy,
Exposure energy is 33 mJ / cm ² for untreated
In contrast to the necessity, it was only 24 mJ / cm ² in the case of ethanol treatment as described above, indicating that the sensitivity was extremely high.

Embodiment 6 In this embodiment, a method of performing post-exposure bake under reduced pressure will be described.

First, a film having a thickness of 1000 nm
The chemically amplified positive resist film was formed.

Next, the krypton fluoride excimer laser 2
The resist film was subjected to pattern exposure through a mask using a reduction projection exposure apparatus using a 48.4 nm oscillation line as a light source. At this time, the exposure energy was 36 mJ.

Next, the substrate to be processed was placed in the same reaction vessel as that used in Example 3, and the pressure in the reaction vessel was reduced to 30 Torr and heat treatment was performed at 100 ° C. for 60 seconds (post-exposure). (Bake method) of the present invention (method of the present invention) and heat treatment (post-exposure bake) at 100 ° C. for 60 seconds on a hot plate open to the atmosphere (conventional method). 38t
And immersion development in a 90% aqueous solution of tetramethylammonium hydroxide for 90 seconds. Since the chemically amplified positive resist is more susceptible to the surrounding environment than the negative resist, it is necessary to pay particular attention to the fluctuation of the environmental temperature and the environmental humidity during the post-exposure bake.

The above-described processing is continuously performed 20 times a day for 7 days in a clean room where the temperature and humidity are controlled, and the influence of a change in the surrounding environment on the finished dimensions of the resist pattern is determined by the method of the present invention. Each of the conventional methods was examined. The amount of change in the temperature and humidity of the clean room during the seven days is based on the fact that the temperature is the set value 24.
± 0.5 ° C relative to ° C, humidity ± 30% relative to set value
2.4%.

FIG. 6 shows the result of plotting the average value and the variation of the finished resist size of the hole pattern having the designed size of 0.5 μm for each date. As is apparent from this figure, in the method of the present invention, the variation in finished dimensions per day is about ± 0.01 μm, and the dimensional variation over seven days is 0.02 μm or less, while In the method, variation in finished dimensions per day is ±
0.02μm, dimensional variation over 7 days is 0.04μ
m. From these results, it was demonstrated that the dimensional controllability of the resist pattern was significantly improved by the method of the present invention 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 the post-exposure bake so as to be uniform within the surface of the substrate and to be the same between the substrates. Cooling is performed and development is performed after that, so it is possible to overcome the sensitivity change due to post-exposure bake treatment, which is a drawback in the chemical amplification type process, and as a result, uniformity and dimensional accuracy are achieved. A high pattern can be formed.

Further, according to the second aspect of the present invention, since the wafer is exposed to water vapor before or during post-exposure baking, a chemically amplified resist material which is easily affected by the surrounding environment is used. When used, the finished pattern dimensions after development can always be kept constant, and the resolution of the resist pattern is greatly improved as compared with the conventional method.

According to the third aspect of the present invention, by exposing a chemically amplified resist film to an atmosphere of a predetermined solvent vapor, for example, alcohol in the reaction vessel before or during heating, As in the second aspect of the present invention, the resolution is greatly improved.

Further, according to the fourth aspect of the present invention, if the post-exposure step of the resist film is performed 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 reduced. And high resolution can be obtained.

[Brief description of the 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 for forming a resist pattern according to a third embodiment of the present invention.

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

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

FIG. 5 is a comparison diagram of a pattern formed by a method according to a fifth embodiment of the present invention and a pattern formed by a conventional method.

FIG. 6 is a diagram in which the average value and variation of the finished resist size of a hole pattern having a design size 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 ... Exposure part 11 ... Silicon substrate to be processed 12 ... Silicon oxide film 13 ... Resist film 14 ... Excimer laser 15 ... Mask 16 ... Gas introduction joint 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

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-60-157223 (JP, A) JP-A-3-15849 (JP, A) JP-A-64-86519 (JP, A) JP-A-60-157 157225 (JP, A) JP-A-3-136231 (JP, A) JP-A-2-127646 (JP, A) JP-A-1-157527 (JP, A) JP-B-3-47493 (JP, B2) (58) Field surveyed (Int.Cl. ⁶ , DB name) G03F 7/38 G03F 7/038

Claims (2)

(57) [Claims] 1. A photosensitive resin film coating step of coating a chemically amplified photosensitive resin film containing a photoacid generator on a substrate to be processed, a step of patternwise exposing the photosensitive resin film, and a step of heating. Prior to heating the photosensitive resin film in a steam atmosphere or heating or exposing the photosensitive resin film in a steam atmosphere during heating and performing a post-exposure bake, A developing step of performing development and forming a pattern. 2. A photosensitive resin film coating step of coating a chemically amplified photosensitive resin film on a substrate to be processed, a step of patternwise exposing the photosensitive resin film, and a step of heating the photosensitive resin film prior to heating. Performing a post-exposure bake by exposing the photosensitive resin film to a predetermined solvent vapor atmosphere and heating or exposing the photosensitive resin film to a predetermined solvent vapor atmosphere during heating, and developing the photosensitive resin film. And a developing step of forming a pattern.