JPS61265835A - Formation of metallic pattern - Google Patents

Abstract

PURPOSE:To make it possible to perform minute patterning of metal, by using a photoresist mask, which is formed on a polycrystalline semiconductor film that is formed on a metal film to a specified thickness, as a mask, and performing dry etching of the metal film. CONSTITUTION:A metal film 14 is formed on an insulating film 12 on a semiconductor substrate 10. On the film 14, a polysilicon film 16 is formed as a polycrystalline semiconductor film so that the reflectivity with respect to the exposure wavelength becomes approximately minimum. On the film 16, a photoresist film 18 corresponding to a desired wiring pattern is formed by a photolithography technology. At this time, the light reflection from the lower layer of the photoresist is suppressed in photoresist exposure. Thus, the photoresist pattern characterized by less dispersion in size and shape is obtained. With the photoresist film 18 as a mask, dry etching is performed, and a metal film 14A and a polysilicon film 16A are obtained. Thus, the metal film 14A, which has excellent fidelity to the wiring pattern, can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a metal pattern forming method suitable for use in forming fine wiring in semiconductor devices such as LSIs.

[Summary of the Invention] This invention involves forming a polysilicon film on the surface of a high reflectivity metal film such as AI or A1 alloy to a thickness that makes the reflectance at an exposure wavelength almost minimum, and then applying photolithography technology on the polysilicon film. By forming a photoresist film and performing dry etching using this photoresist film as a mask, fine patterning of metal becomes possible.

[Prior Art] Conventionally, when forming fine wiring for LSI etc., after depositing a metal film such as AI or A1 alloy on the upper surface of a semiconductor wafer,
A method is known in which a photoresist film corresponding to a desired wiring pattern is formed on this metal film by photolithography technology, and the metal film is dry-etched using this photoresist film as a mask.

According to this method, when the wiring pattern is transferred to the photoresist by exposure, because the reflectance of AI or A1 alloy, which is the material of the metal film, is high, the scattered reflected light from the steps on the wafer, etc., reaches undesired parts of the photoresist. In many cases, the photoresist pattern was exposed to light, resulting in variations in the dimensions and shape of the photoresist pattern. For this reason, individual wiring becomes thicker or thinner.

This was a cause of decreased reliability.

As a way to deal with such problems, (a) AI
Or a method in which a high melting point metal film with low reflectance is applied to the surface of a high reflectance metal film such as A1 alloy (for example, JP-A No. 5 El-1)
54027), (b) a light-absorbing organic insulating film (for example, BREWER5CIE) on the surface of the high reflectance metal film.
Some are known, such as those coated with RARCl (sold under the name rARCl by NCE INC.).

[Problems to be Solved by the Invention] According to the conventional method (a) above, there are few metals that can be used that have sufficiently lower reflectance than AI etc., so a large antireflection effect cannot be expected.

Further, according to the conventional method (b) above, a considerable antireflection effect can be expected, but it is difficult to realize a narrow wiring width with a simple process. That is, for example, 0.5[
If there is a step difference of μml, if an organic insulating film is applied at a thickness of 0.2 [μm] or more at the top of the step to obtain a sufficient antireflection effect, the thickness of the organic insulating film at the bottom of the step will be 0.5 [μm1].
Normally, this type of organic insulating film is selectively etched with a photoresist developer during development of the photoresist, and the etch process during development creates an isotropic side etch in the area directly below the photoresist. receive. Therefore, when an organic insulating film is formed to a thickness of 0.5 [lLm] at the bottom of the step, a total of 1
There will be a side etch of 1 [gm].
] It is not possible to realize the following wiring width.

In order to realize such a fine wiring width, AI or A1
It is possible to secure a film thickness of about 0.2 [ILm] over the entire surface of the sea urchin by adding a planarization process before forming the alloy metal film, but this would significantly complicate the process. cannot be avoided.

[Means for Solving the Problems] This invention has been made to solve the above-mentioned problems, and its purpose is to enable fine buttering of metal in a simple process. be.

That is, in the metal pattern forming method according to the present invention, after forming a metal film such as A1 or A1 alloy on a substrate, the metal film is covered with a polycrystalline semiconductor film such as polysilicon, which has an almost minimum reflectance at the exposure wavelength. A photoresist film corresponding to a desired pattern is formed on this polycrystalline semiconductor film using photolithography technology, and the polycrystalline semiconductor film and metal film are dry-etched using this photoresist film as a mask. This is what I did.

In this invention, the thickness of the polycrystalline semiconductor film formed on the metal film is limited to a thickness at which the reflectance at the exposure wavelength is almost minimal.The reason for this is to form a thin film on the metal film that transmits light. In this case, as shown in FIG. 5, the reflectance periodically shows a maximum or minimum as the thickness changes. Such periodic changes in reflectance are caused by standing wave phenomena in thin films, and are already known for photoresist films. In this invention, by forming a polycrystalline semiconductor film on a metal film at a thickness such as t+, tz, tz, and ta where the reflectance is minimum, or a thickness close to any of these, it is possible to obtain a fog light wavelength. In contrast, it has a surface with low reflectance.

[Function] According to the structure of the present invention, even if the metal film is made of a material having a high reflectance such as AI or A1 alloy, a polycrystalline semiconductor film can be formed on the metal film with the above-mentioned thickness. The reflectance is calculated without the film (in the case of zero film thickness in Figure 5).
can be reduced to about half or less compared to For this reason, when exposure processing is performed after depositing a photoresist on a polycrystalline semiconductor film, the light reflected from the lower layer of the photoresist is weak, so the photoresist is not exposed in undesired areas, and an accurate pattern can be created. In other words, variations in the size and shape of the photoresist pattern due to non-uniform exposure can be suppressed, and when forming fine wiring, the thickening and thinning of individual wiring can be reduced. I can do it.

[Example] FIGS. 1 to 4 show a wiring forming process according to an example of the present invention, and the process (1) corresponding to each figure number is
- (4) will be explained in order.

(1) After forming an insulating film 12 made of silicon oxide or the like on the surface of a semiconductor substrate 10 made of silicon, for example, the insulating film 12 is coated with AI or A1 alloy (e.g. Al-9i).
) is formed by any method such as vacuum evaporation or sputtering. On the metal film 14, polysilicon 1li16 is deposited as a polycrystalline semiconductor film by a CVD (chemical φ paper deposition) method or the like.

In this case, the thickness t of the polysilicon film 16 is selected according to the formula: t=8+48Xm±10[nml], where the exposure wavelength is 436[nml] and a positive integer such as mlO or l, 2... be able to. In other words, the reflectance becomes almost minimum at a thickness that satisfies this formula.

(2) Next, 5, after depositing a photoresist on the polysilicon film 16 according to a conventional method, a desired wiring pattern is transferred by exposure and further developed to form a photoresist (818) corresponding to the wiring pattern. Form.

In this case, since the polysilicon film 16 is formed on the metal film 14 with the above thickness, light reflection from the lower layer of the photoresist is suppressed during photoresist exposure, and variations in size and shape are reduced. A photoresist pattern is obtained.

(3) Next, by performing dry etching such as plasma etching using the photoresist film 18 as a mask, a metal film 14A and a polysilicon film 16A corresponding to the wiring pattern are obtained. In this case, the polysilicon [18A is hardly side etched and acts as an etching mask for the metal Ifi 14. Therefore, the metal film 14A
Therefore, a photoresist film 18 with extremely good fidelity to the pattern (wiring pattern) can be obtained.

(4) After this, the metal film 14A and the polysilicon film 16A
An insulating film 20 is formed by covering it by a CVD method or the like. This insulating film 20 serves as a surface protection film or a living room insulating film. Note that the polysilicon film 16A is similar to the insulating film 20.
may be removed prior to the formation of A, but if left,
This is advantageous because hillock growth in I or Al-9i, etc. can be suppressed.

[Effects of the Invention] As described above, according to the present invention, after forming a polycrystalline semiconductor film on a metal film to a thickness that makes the reflectance at the exposure wavelength almost minimum, Since a photoresist film with a desired pattern is formed and the polycrystalline semiconductor film and metal film are dry-etched using this photoresist film as a mask, the following excellent effects can be obtained.

(1) Since light reflection from the lower layer of the photoresist is suppressed during exposure processing, it is possible to obtain a photoresist pattern with less variation in size and shape. Since dry etching is performed using this photoresist pattern as a mask, LSI It is possible to prevent local thickening or thinning from occurring in fine metal patterns such as wiring.

(2) Since the polycrystalline semiconductor film is hardly side-etched during dry etching, high etching accuracy can be obtained. In other words, the metal pattern does not have the extremely thin side etch that occurs in the case of conventional anti-reflection organic insulating films, and therefore it is possible to realize a wiring width of 1 [ti-rn] or less. It is.

(3) Using conventional anti-reflection *mechanical insulating films requires processes such as coating, baking, simultaneous development with photoresist, and removal after etching, but the method of this invention It is only necessary to deposit a polycrystalline semiconductor film, and there is no need to necessarily remove it after etching, making the process extremely simple.

[Brief explanation of the drawing]

1 to 4 are cross-sectional views of a substrate showing a wiring forming process according to an embodiment of the present invention, and FIG. 5 is a graph showing the relationship between film thickness and reflectance for a thin film formed on a metal film. be. 10... Semiconductor substrate, 12.20... Insulating film, 14
. . . Metal film, 16 . . . Polysilicon film (polycrystalline semiconductor film), 18 . . . Photoresist film.

Claims (1)

[Claims] (a) A step of forming a metal film on a substrate; (b) A step of forming a polycrystalline semiconductor film covering the metal film to a thickness such that the reflectance to the exposure wavelength is almost minimum. (c) forming a photoresist film corresponding to a desired pattern on the polycrystalline semiconductor film by photolithography; (d) drying the polycrystalline semiconductor film and the metal film using the photoresist film as a mask; A metal pattern forming method comprising the step of etching.