JPH0455323B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an etching method, and more particularly to an etching method using photolithography, which is useful for microfabrication in the production of semiconductor devices, magnetic valve devices, and the like.

[Background of the invention]

When forming a pattern using a photoresist film, light causes multiple interference within the photoresist film.
This causes pattern dimensions to vary as the photoresist film thickness changes. In order to reduce this effect, there is a method of reducing multiple interference using an antireflection film. However, since conventional anti-reflection films are formed on the substrate surface, when mask alignment is performed using light of the same wavelength as that for exposure, the mask alignment detection signal is also weakened by the anti-reflection film, which prevents reflection. When the effect was increased, there was a drawback that mask matching was not possible. Furthermore, it was necessary to accurately transfer the photoresist pattern to the antireflection film, and it was also necessary to remove the antireflection film formed on the substrate without affecting the elements. Therefore, the number of steps increases, and it cannot necessarily be applied to all substrate processing.

[Purpose of the invention]

An object of the present invention is to solve the above-mentioned conventional problems and to provide a method that can form fine and highly accurate patterns using a simple method.

[Summary of the invention]

In order to achieve the above object, the present invention involves forming a light-transmissive antireflection film on a photoresist film and then exposing the film to light. The anti-reflection film reduces optical multiple interference within the resist film, and since a light-transmissive anti-reflection film is used, the mask alignment detection signal is also improved.

The gist of the present invention is to form a photoresist film on an object to be processed, and to irradiate light onto the photoresist film using a mask using a projection exposure method to form a predetermined photoresist film pattern. The etching method for etching the object to be processed based on a film pattern includes the step of forming a first film on the photoresist film, the first film having a property of transmitting the light, The light incident on the first film and the photoresist film is reflected as a first reflected light on the surface of the workpiece, and a part of the first reflected light is transmitted between the photoresist film and the first reflected light. The light that is reflected at the first interface with the photoresist film and the other part of the first reflected light is reflected between the first film and the outside of the first film. When light that is reflected at a second boundary surface, passes through the first film, and enters the photoresist film is defined as second reflected light, the second reflected light is reflected within the photoresist film. The etching method is characterized in that the first film is configured so that the intensity of the second reflected light is made weaker than before the interference occurs by causing the interference.

[Embodiments of the invention]

Among optical multiple interferences within a photoresist film, a factor that affects pattern dimensional accuracy is interference between lights traveling in the same direction within the photoresist film. For example, when a photoresist pattern is formed on a Si substrate, as shown in FIG. 1, a dimensional variation of about 0.3 μm occurs due to a change in the resist film thickness. Therefore, by reducing the reflected light from the upper surface of the photoresist, the reflected light traveling in the same direction as the incident light is reduced, and the amount of pattern dimension variation due to this multiple interference is reduced. In order to ensure that the mask detection signal strength is sufficient and the exposure time is not too long, the antireflection film on the photoresist film is a film with a sufficiently small absorption coefficient that transmits enough exposure light, and the interference effect is used to reduce reflection. .

That is, as shown in FIG. 2, the reflected light 4 from the substrate 1 is made to interfere with the reflected light 5 from the photoresist/antireflection film surface 3a and the reflected light 6 from the antireflection film/atmospheric surface 3b to form a composite light. Make it small enough. If the refractive index of the photoresist film is n and the wavelength of the exposure light is λ, then the refractive index n' of the anti-reflection film is √, and the closer the film thickness is to an odd multiple of λ/4n', the more the reflectance (amplitude) of this anti-reflection film ratio) is reduced as shown in FIG. By reducing the reflection in this way, the dimensional accuracy of the resist pattern is improved. Furthermore, since this anti-reflection condition is a condition that allows light to pass through, the addition of this anti-reflection film does not weaken the mask detection signal.

By the way, Japanese Patent Publication No. 56-12011 describes that incident light is reflected by the substrate and becomes reflected light, and this incident light and reflected light cause interference and generate standing waves within the resist film. has been done.

Even when light is made incident on a resist film to expose the resist film as in the present invention, standing waves exist because reflected light is generated with respect to the incident light.

However, methods are currently known for reducing the influence of standing waves to such an extent that there are no practical problems.

This is a method in which a pattern is exposed on a resist, heat treatment is performed, and then a phenomenon is performed. To explain this in more detail, when a resist is exposed, a standing wave is generated, and exposure unevenness occurs along the thickness direction of the resist. (There are differences in the degree of Then, when an appropriate heat treatment is performed after exposure, the photosensitive material is diffused in the film thickness direction within the resist, and the difference in the degree of deterioration of the photosensitive material is alleviated.

By the subsequent phenomenon, it is possible to form a resist pattern in which the influence of standing waves is sufficiently reduced.

Therefore, even when using the present invention, by using this known method in combination, the influence of standing waves can be ignored.

Note that while the invention described in Japanese Patent Publication No. 56-12011 deals with the existence of standing waves existing in the photoresist film, in the present invention The problem is interference with light reflected at the interface between the two. Therefore, I would like to point out that the two are separate matters.

The present invention will be explained below using examples.

Example 1 First, as shown in FIG. 4a, a Si substrate 7 with a step is prepared.
A photoresist 8 is formed on the photoresist 8 by a conventional method, and then polysiloxane 9 (refractive index of about 1.4) is coated on the photoresist 8 as an antireflection film to a thickness of about 60 to 100 nm, as shown in FIG. 4b. did. The absorption coefficient of polysiloxane is 10 ^-2 or less at the wavelength of exposure light of 436 nm, and it can sufficiently transmit light. Thereafter, normal exposure was carried out using light having a wavelength of 436 nm, as shown in FIG. 4c. When mask alignment was performed using light with the same wavelength as that for exposure, the intensity of the alignment pattern detection signal was as good as in the case of only photoresist without this anti-reflection film, indicating the influence of multiple interference within the resist film. The waveform was better than that with only photoresist because the amount of irradiation was reduced. Thereafter, polysiloxane 9 was removed using xylene as shown in FIG. 4d. Not only xylene but also chlorobenzene can be used, as long as the antireflection film can be removed without deteriorating the photoresist to the extent that pattern formation is difficult. Thereafter, a conventional process was carried out to form a photoresist pattern 8' on the Si substrate as shown in FIG. 4e. Anti-reflection film 9
The pattern dimensional accuracy without was approximately ±0.15μm, but with the above process, the dimensional accuracy has decreased to ±0.08μm.
Si
could be formed on the substrate.

In this example, the anti-reflection film is made of polysiloxane, but is not limited to polysiloxane. For example, it can be made of polyvinyl alcohol, etc., which reduces reflection based on the above-mentioned anti-reflection principle, and which sufficiently transmits the exposed light. In addition, any material may be used as long as it does not alter the quality of the photoresist.

Example 2 In Example 1 above, an intermediate layer was formed between the photoresist 8 and the polysiloxane 9 so that the antireflection film and its removal did not affect the photoresist at all. The film thickness is approximately 10 to 50 nm as an intermediate layer.
Polyvinyl alcohol was used. After that, following the same process as in Example 1 above, even the polysiloxane was removed, and then washed with water or MF312
A photoresist pattern was formed by adding a step of removing polyvinyl alcohol using a phenomenon liquid (manufactured by Shipley). By using polyvinyl alcohol in the intermediate layer, it was possible to form a pattern that was completely unaffected by the reduction in film thickness caused by xylene or the insolubilization of the photoresist surface caused by chlorobenzene. Furthermore, by using an intermediate layer, it was possible to use materials such as OCD (manufactured by Tokyo Ohka Co., Ltd.), which react with photoresists and alter the quality of the photoresists, as an antireflection film.

Although polyvinyl alcohol was used for the intermediate layer in this example, it is not limited to polyvinyl alcohol; any material may be used as long as it transmits light, does not mix with the photoresist and antireflection film, and can be removed without changing the quality of the photoresist. .

Although a Si substrate was used in this embodiment, the present invention is applicable to all substrates, not just Si substrates. Further, in this embodiment, the case where the substrate has a step difference has been described, but the present invention is also effective when the substrate has no step difference. When the photoresist film thickness changes within a wafer, between wafers, or between lots, the state of multiple interference within the resist film changes and pattern dimension variations occur. We were able to reduce this.

Although the exposure wavelength was set to 436 nm in this example, it is not limited to this wavelength, and may be any wavelength as long as the antireflection film satisfies the above-mentioned antireflection conditions.

As shown in this embodiment, the present invention is a simple process that requires only 2 to 4 steps added to the normal photoresist pattern forming process, and each added processing time is 1 to 2 minutes, so the throughput is high.

〔Effect of the invention〕

As described above, according to the present invention, a highly accurate photoresist pattern can be formed by a simple method, and the mask alignment detection signal is also good.

Furthermore, since this anti-reflection film is formed on the top surface of the resist, it can be applied regardless of the substrate material, and will not affect the device.

[Brief explanation of the drawing]

Figure 1 is a diagram showing dimensional fluctuations due to multiple interference within a resist film, Figure 2 is a diagram to explain the principle of an anti-reflection film, Figure 3 is a diagram showing the effect of an anti-reflection film, and Figure 4 is a diagram showing the effect of the anti-reflection film. FIG. 2 is a process diagram showing one embodiment of the invention. 1...Si substrate, 2...Photoresist, 3...Anti-reflective film, 3a...Anti-reflective film/photoresist interface, 3b...Air/anti-reflective film interface, 4...Reflected light from the substrate toward the anti-reflective film , 5...Reflected light from the antireflection film/photoresist interface toward the substrate,
6...Reflected light from the atmosphere/antireflection film interface toward the substrate, 7...Si substrate, 8...Photoresist, 8'
...Photoresist pattern, 9...Polysiloxane.

Claims (1)

[Scope of Claims] 1. A photoresist film is formed on an object to be processed, and a predetermined photoresist film pattern is formed by irradiating light onto the photoresist film using a mask using a projection exposure method. The etching method for etching the object to be processed based on a resist film pattern includes the step of forming a first film on the photoresist film, and the first film has a property of transmitting the light. , the light incident on the first film and the photoresist film is reflected as a first reflected light on the surface of the workpiece, and a part of the first reflected light is reflected between the photoresist film and the photoresist film. The light reflected at the first interface with the first film and incident on the photoresist film, and the other part of the first reflected light are outside the first film and the first film. When the light reflected at the second interface with the photoresist film passes through the first film and enters the photoresist film as second reflected light, the second reflected light is reflected at the photoresist film. An etching method characterized in that the first film is configured such that the intensity of the second reflected light is made weaker than before the interference occurs by causing interference within the first film. 2. The light has a substantially single wavelength, and when the wavelength of the light is λ, the refractive index of the photoresist film is n, and the refractive index of the first film is n', the first The film is made of a material in which the value of n' is substantially equal to the value of √, and the film thickness of the first film is substantially a value in the vicinity of an odd multiple of λ/4n'. An etching method according to claim 1, characterized in that: 3. The etching method according to claim 1 or 2, wherein the object to be processed is a substrate. 4. By forming the first film on the photoresist film, the first film and the photoresist film come into contact, thereby causing a chemical change to the photoresist film based on the first film. Claims 1, 2 or 3, characterized in that a second film is provided between the photoresist film and the first film to prevent the photoresist film from being damaged. The etching method described in Section 3. 5. The etching method according to claim 1, 2 or 3, wherein the material constituting the first film is polysiloxane or polyvinyl alcohol. 6. Claim 1, characterized in that means for aligning the object to be processed and a photomask is formed on the object to be processed.
The etching method according to item 2, item 4, or item 5. 7. Claims 1, 2, and 3, wherein the light for exposing the photoresist film is light of substantially a single wavelength.
The etching method according to item 4, 5 or 6.