JPH0669123A - Antireflection film and formation of resist pattern employing it - Google Patents

Abstract

PURPOSE:To suppress effect of light reflected on an underlying layer at the time of exposure further than the case where alpha-Si film or TiN film is employed as an antireflection film by composing the antireflection film of at least one material selected from carbon and materials containing carbon. CONSTITUTION:A thin film 21 of Al-Si-Cu alloy is formed, as an underlying layer having high reflectance, by 500nm thick on a BPSG film through DC magnetron sputtering. A thin film of carbon of predetermined thickness is then formed, as an antireflection film 23, continuously thereon through the same method. A resist layer 17 is subsequently formed on the thin carbon film of a sample and selectively exposed through a photomask. The resist layer 17 is then developed to obtain a stabilized resist pattern 17a having a reduced notch. This method provides a desired resist pattern using a thin film having high reflectance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antireflection film and a method for forming a resist pattern by photolithography using the antireflection film.

[0002]

2. Description of the Related Art Photolithography technology has become an indispensable technology for manufacturing semiconductor devices and fine parts.
When forming a wiring pattern of a semiconductor device using this photolithography technique, the following procedure is generally taken. 2 (A) to 2 (C) are process diagrams of main parts used for the description. However, an example using a positive resist is shown. Further, in all of the drawings, the sample is shown by a sectional view taken along the thickness direction of the semiconductor substrate (the same applies to FIG. 3 below).

First, an intermediate insulating film 13, a wiring forming thin film 15, and a resist layer 17 are formed in this order on a semiconductor substrate 11 having a semiconductor element (not shown) formed therein. Next, the resist layer 17 is selectively exposed through the photomask 19 whose predetermined portion is the light shielding portion 19a (FIG. 2).
(A)). Next, the resist layer 17 is developed to form a resist pattern 17a (FIG. 2 (B)). next,
A portion of the wiring forming thin film 15 which is not covered with the resist pattern 17a is removed by an etching technique to obtain the wiring pattern 15a (FIG. 2C).

However, when the underlayer on which the resist pattern is to be formed (the wiring forming thin film 15 in the above example) has a high reflectance, the exposure light is reflected from the underlayer when the resist layer is exposed. Since the light largely affects the exposure light, a notch occurs in the resist pattern. For example, when a thin film of Al or an Al-based alloy, for example, an Al-Si-based alloy is used as the wiring forming thin film 15, the above-described notch is likely to occur because this has a high reflectance. When the notch is formed, the resist pattern does not have a desired shape, so that a desired wiring pattern or the like cannot be obtained. Therefore, it is necessary to take measures against it.

Therefore, an antireflection film has been used when a resist pattern is formed on a base having a high reflectance by a photolithography technique. This will be described with reference to an example of forming an Al-Si alloy wiring. FIG. 3 (A)-
(C) is a principal part process drawing provided for the description.

First, an intermediate insulating film 13, an Al--Si alloy thin film 21, an antireflection film 23, and a resist layer 17 are formed in this order on a semiconductor substrate 11 having a semiconductor element (not shown) formed therein. . Conventionally, as the antireflection film 23, α-
Si films and TiN films have been used. Next, exposure is performed through the photomask 19 (FIG. 3 (B)). Next, the resist layer 17 is developed to form a resist pattern 17a (FIG. 3 (B)). After that, the same processing as that described with reference to FIG.
Is obtained (FIG. 3 (C)). The wiring pattern 21a
The upper antireflection film 21 may be removed or may remain.

[0007]

However, in order to form a finer resist pattern in order to respond to higher integration of semiconductor devices, it is necessary to further reduce the influence of light reflected from the base during exposure. Α- as a protective film
The conventional method using the Si film or the TiN film has its limits.

This application has been made in view of the above circumstances, and therefore an object of the present invention is to provide an antireflection film capable of further reducing the reflection from the underlayer and a resist pattern forming method using the same. Especially.

[0009]

In order to achieve this object, according to the antireflection film of the first invention of this application, at least one material selected from carbon and a material containing carbon is used. Characterize. Here, the material containing carbon in the first invention may be, for example, a carbide. Specific examples of the carbide include silicon carbide (the same applies in the second invention).

In implementing the first invention, it is preferable that the film thickness of the antireflection film is within a predetermined range including the film thickness at which the reflectance of the antireflection film with respect to the light to be reflected is minimized. Is. However, the reflectance of the antireflection film changes as the film thickness is changed, and has a minimum value at some film thicknesses.
Which of these thicknesses is selected can be determined according to the design. Considering the throughput at the time of film formation and the step reduction at the time of etching, it is preferable that the film thickness be the thinnest among the several film thicknesses at which the reflectance is minimized.
The film thickness dependence of the reflectance of the antireflection film can be examined by an experiment, and the refractive index of the antireflection film, each refractive index of the medium above and below the antireflection film, the film thickness of the antireflection film, and the light to be reflected Based on the wavelength of the light source, for example, reference (I: "Optical Measurement Handbook", Toshiharu Tayuki, Asakura Shoten (1981.7.25)
According to the theory disclosed in)), it is also possible to investigate by obtaining the reflectance with the film thickness of the antireflection film as a parameter. In the case where the inventor according to this application provides the above-mentioned antireflection film on the upper side of an aluminum-based underlayer (including only Al, including Al as the main component and alloying with other substances) and the reflection target light is i-line. When an experiment was conducted for a certain case, the film thickness of the antireflection film was 15 to 30 nm, preferably 20 nm.
It is known that the reflectance becomes the smallest when the value is set to the vicinity.

Further, according to the second invention of this application, in a resist pattern forming method using an antireflection film when forming a resist pattern by a photolithography technique, the antireflection film is selected from carbon and a material containing carbon. A film made of at least one material is used.

In carrying out the second invention, the antireflection film is a base having a high reflectance (however, the base is, for example, a substrate having a high reflectance (not limited to a semiconductor substrate. (Including the case)) or an insulating film, a thin film such as a wiring forming thin film described in the section of the prior art, etc.) and a resist layer. It should be provided. Therefore,
Not only the most basic stacking order of base-antireflection film-resist layer, but also the stacking order of base-third film-antireflection film-resist layer, and base-antireflection film-third film. -Of course, the order of lamination such as a resist layer is also acceptable. Here, the third film is not so high in reflectance as to the exposure light itself, but it is relatively transparent to the exposure light and may allow the exposure light reflected by the underlayer to pass through the resist layer side. It is a film that needs to be provided on a base having a high reflectance in manufacturing the device (for example, an intermediate insulating film of two-layer wiring). The present invention also includes the case where the third film has a plurality of layers.

Further, in implementing the second invention, it is preferable that the film thickness of the antireflection film is set to a value within a predetermined range including the film thickness at which the reflectance of the antireflection film with respect to the exposure light is minimized. Such a film thickness can be determined by the same method as in the first invention.

In the first and second inventions, the antireflection film made of at least one material selected from carbon and carbon-containing materials is, for example, DC magnetron sputtering method, RF sputtering method, plasma CVD (Ch
It can be formed by various methods such as various film forming methods such as an emical vapor deposition method, a thermal CVD method, a photo CVD method, a glow discharge vapor deposition method, and a coating method using a coater. Among these methods, the sputtering method has an advantage that throughput can be made higher than other methods. In addition, each CVD method
It has an advantage that it is excellent in step coverage as compared with other methods. Further, the plasma CVD method has an advantage that a film can be formed at a low temperature, and the photo CVD method has an advantage that a film can be formed at a low temperature and an antireflection film with low damage can be obtained. Further, the glow discharge vapor deposition method has an advantage that the degree of contamination is lower than other methods. However, in forming the antireflection film, when the lower layer of the antireflection film is a thin film, it is preferable to continuously form the thin film and the antireflection film by a film forming method of the thin film. That is, the lower layer is, for example, Al-S.
When a thin film of an i-based alloy is formed by, for example, a sputtering method, the antireflection film is also formed by the sputtering method, and the thin film of the Al--Si alloy is continuously formed without taking out the sample from the film forming chamber. It is better to do it. By doing so, it is possible to improve the throughput and prevent contamination of the lower layer. In particular, a material whose lower layer has a high hygroscopic property (for example, ozone TEOS BPSG (O ₃ -TEOS BP
SG), or NSG, etc.),
The above continuous film formation is useful in preventing moisture absorption of the lower layer.

[0015]

According to the structure of the first invention of this application, as is clear from the experimental results described later, an antireflection film having a lower reflectance than the α-Si film or the TiN film can be obtained.

Further, according to the structure of the second invention of this application, the resist layer can be exposed in a state in which the reflection of the exposure light from the base is suppressed as compared with the conventional case. The antireflection film may be removed or left after the photolithography is performed. Even if the antireflection film is removed, since the antireflection film is made of carbon (the material may contain carbon), for example, a gas containing O ₂ , a gas containing O ₃ , or both of them. Since it can be easily removed by dry etching using a gas containing, there is an advantage that the antireflection film can be removed at the same time in the oxygen ashing step for removing the resist pattern.

[0017]

Embodiments of the method for forming an antireflection film of the first invention and the resist pattern of the second invention of this application will be described below with reference to the drawings. However, the drawings used for the description are only schematically shown so that the present invention can be understood.

A BPSG (Boro-Phospho S) is used as an insulating film on a semiconductor substrate having a field effect transistor and the like built therein.
An ilicate glass) film is formed by CVD to a film thickness of about 600 nm. Next, reflow by heat treatment is performed to flatten the BPSG film. This heat treatment is performed for 15 minutes at a temperature of 950 ° C. in a nitrogen atmosphere. Next, on the reflowed BPSG film, as a base having a high reflectance, in this case Al
A thin film of —Si—Cu alloy is formed to a thickness of 500 nm by the DC magnetron sputtering method. Further, by the same method, a thin film of carbon as an antireflection film is formed on the Al—Si—Cu alloy thin film to a predetermined thickness. In the sputtering for forming the carbon thin film, a carbon target having a specific resistance of 0.1 Ω-cm or less is used, the argon gas pressure is 5 mTorr, the DC power is 1.0 KW, and the substrate is not heated. A plurality of samples are prepared according to the procedure described above except that the thickness of the carbon thin film is different from several nm to 100 nm (see FIG. 1). Also, as a comparative example, an antireflection film is
A plurality of samples with different thicknesses of the antireflection film for each of -Si and TiN film (see Fig. 1)
Are manufactured respectively. The antireflection film of each comparative example was also formed by the DC magnetron sputtering method.

Next, the reflectance of each sample of the example and each sample of the comparative example with respect to the i-line (light having a wavelength of 365 nm) is measured. FIG. 1 shows the results, in which the horizontal axis represents the film thickness (nm) of the antireflection film and the vertical axis represents the reflectance (%). It is a characteristic view which showed the film thickness dependence of reflectance. Figure 1
In the figure, the white circles are the characteristic diagrams of the examples, and the black circles are T.
A characteristic diagram of the iN film, and a black triangle mark is a characteristic diagram of the α-Si film.

As is clear from FIG. 1, the antireflection film formed of a carbon thin film has a lower reflectance than the α-Si film and the TiN film. Further, when an antireflection coating of a carbon thin film is provided on the Al-based substrate, the thickness of the carbon thin film that can minimize the reflectance for i-line is in the range of 15 to 30 nm, more preferably 20.
It can be seen that it is around nm.

Next, a resist layer is formed on the carbon thin film of the sample, and this resist layer is selectively exposed through a photomask. Then, this resist layer is developed. Thereby, a resist pattern is obtained. The obtained resist pattern was stable with less notches than the conventional one. Next, a portion of the Al—Si—Cu alloy thin film which is not covered with the resist pattern is removed by a known etching technique. Thereby, a desired wiring pattern made of an Al-Si-Cu alloy can be obtained.

Next, O ₂ is used to remove the resist pattern.
Perform ashing. It was found that in this treatment, the carbon thin film remaining under the resist pattern was also removed together with the resist.

In the above, the embodiments of the antireflection film of the first invention and the method of forming the resist pattern of the second invention of the present application are described together, but these inventions are not limited to the above-mentioned embodiments. Absent.

For example, in the above-mentioned embodiment, the Al-Si-Cu alloy thin film is used as the high reflectance base. However, the first and second inventions are not applicable only to the Al-Si-Cu alloy thin film, and when the resist pattern is formed on the upper side of various underlayers that cause trouble in patterning due to high reflectance. , Widely applicable. Further, it is apparent that the present invention can be used not only in the semiconductor device field but also in other fields.

In the above embodiment, the exposure light is i-line. This is because the i-line is currently regarded as a promising light source for high integration. However, the antireflection film of the present invention uses light of other wavelengths such as g-line, which is widely used at present,
Further, it is also useful for deep UV light, which is expected as a future light source. In this case, a suitable film thickness can be determined by experiments or simulations according to the case of the above-mentioned i line.

It should be understood that the sputtering conditions for the carbon thin film in the above-mentioned embodiment are merely examples within the scope of the present invention.

[0027]

As is apparent from the above description, according to the first invention of this application, an antireflection film having a lower reflectance than the α-Si film or the TiN film can be obtained. Further, according to the second invention of this application, since the resist layer can be exposed in a state in which the reflection of the exposure light from the underlayer is suppressed as compared with the conventional case, it is possible to form a resist pattern with less notches than in the conventional case. Therefore, even if a thin film having a high reflectance such as Al-Si alloy is used, a desired resist pattern can be obtained and a desired wiring pattern can be obtained. Further, since this antireflection film is made of carbon (which may be a material containing carbon), for example, by dry etching using a gas containing O ₂ , a gas containing O ₃ , or a gas containing both of them. Since it can be easily removed, there is an advantage that the antireflection film can be removed by utilizing the oxygen ashing process for removing the resist pattern.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing film thickness dependence of reflectance in antireflection films of Examples and Comparative Examples.

FIGS. 2A to 2C are process diagrams for explaining a general photolithography technique.

3A to 3C are process diagrams for explaining a photolithography technique using an antireflection film.

[Explanation of symbols]

11: Semiconductor substrate 13: Intermediate insulating film 15: Wiring forming thin film 15a, 21a: Wiring pattern 17: Resist layer 17a: Resist pattern 19: Photomask 19a: Light shielding part 21: High reflectance is a wiring forming thin film (eg Al- Si-based alloy) 23: Antireflection film

 ─────────────────────────────────────────────────── ─── Continued front page (72) Inventor Yusuke Harada 1-7-12 Toranomon, Minato-ku, Tokyo Oki Electric Industry Co., Ltd.

Claims (7)

[Claims] 1. An antireflection film comprising at least one kind of material selected from carbon and a material containing carbon. 2. The antireflection film according to claim 1, wherein the thickness of the antireflection film is a value in a predetermined range including a thickness at which the reflectance of the antireflection film with respect to light to be reflected is minimized. An antireflection film characterized by the above. 3. The antireflection film according to claim 1 or 2, wherein the antireflection film is provided on an upper side of an aluminum-based base, and the reflection target light is light having an i-line as a main wavelength.
An antireflection film, wherein the film thickness of the antireflection film is 15 to 30 nm. 4. A resist pattern forming method using an antireflection film when forming a resist pattern by a photolithography technique, wherein a film made of at least one material selected from carbon and a material containing carbon is used as the antireflection film. And a resist pattern forming method. 5. The resist pattern forming method according to claim 4, wherein the thickness of the antireflection film is set to a value within a predetermined range including a thickness at which the reflectance of the antireflection film with respect to exposure light is minimized. A method of forming a resist pattern, comprising: 6. The method of forming a resist pattern according to claim 4, wherein when the antireflection film is provided on an upper side of an aluminum-based base and the exposure light is an i-line, the film thickness of the antireflection film. Of 15 to 30 nm. 7. The method for forming a resist pattern according to claim 4, wherein, when forming the antireflection film, a lower layer of the antireflection film is a thin film, the thin film forming method is used. A method of forming a resist pattern, which comprises continuously forming a thin film and the antireflection film.