JPS61265836A - Formation of metallic pattern - Google Patents

Abstract

PURPOSE:To make it possible to perform minute patterning of metal, by forming a photoresist film on an inorganic insulating film, which is formed on a metal film to a specified thickness, and performing dry etching of the metal film with the photoresist film as a mask. CONSTITUTION:A metal film 14 is formed on an insulating film 12 on a semiconductor substrate 10. On the film 14, a silicon nitride film 16 is formed as an inorganic insulating film to a thickness (t) so that reflectivity with respect to the exposure wavelength is approximately minimum. On the film 16, a photoresist film 18 corresponding to the desired wiring patterns is formed by the photolithgraphy technology. At this time, the light reflection from the lower layer of the photoresist is suppressed when the photoresist is exposed. 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 silicon nitride film 16A are obtained. Thus the metal film 14A, whose fidelity to the wiring pattern in very excellent, 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 of semiconductor devices such as LSIs.

[Summary of the Invention] This invention involves forming a silicon nitride film on the surface of a high-reflectance 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 on the silicon nitride film. This technology enables fine patterning of metal by forming a photoresist film and performing dry etching using this photoresist film as a mask.

[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 transferring a wiring pattern to a photoresist by exposure, AI or A1, which is the metal film material V),
Because the alloy has a high reflectance, scattered reflected light from steps on the wafer, etc., exposes undesired portions of the photoresist, often causing variations in the size and shape of the photoresist pattern. As a result, individual wiring becomes thicker or thinner, which is a factor in reducing 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. 511-1
54027), (b) a light-absorbing organic insulating film (for example, BREWER5CIE) on the surface of the high reflectance metal film.
Some of the known products include those sold under the name rARCJ 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 pml level difference, if the organic insulating film is applied at a thickness of 0.2 [μm] or more to obtain a sufficient antireflection effect at the top of the step, it will be 0.5 [μm] at the bottom of the step.
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, if an organic insulating film is formed to a thickness of 0.5 [pm] at the bottom of the step, then at the top of the five steps, a film of 0.5 [g, m] from both sides will be deposited directly under the photoresist for a total of 1 [
There will be a side etch of pml, + [pm
It is not possible to realize a wiring width of 1 or less.

In order to realize such a fine wiring width, A1 or A1
It is possible to secure a film thickness of about 0.2 [pm1] 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. I can't escape it.

[Means for Solving the Problems] This invention was made to solve the above problems, and its purpose is to enable fine patterning of metal with a simple process. .

That is, in the metal pattern forming method according to the present invention, after forming a metal film such as AI or A1 alloy on a substrate, the metal film is covered with an inorganic insulating film such as silicon nitride, which has an almost minimal reflectance to the exposure wavelength. A photoresist film corresponding to a desired pattern is formed on this inorganic insulating film using photolithography technology, and the inorganic insulating film and metal film are dry-etched using this photoresist film as a mask. It is.

In this invention, the thickness of the inorganic insulating film formed on the metal film is limited to a thickness at which the reflectance to the exposure wavelength is almost minimum, because a thin film that transmits light is formed on the metal film. In this case, as shown in FIG. 5, the reflectance periodically shows a maximum or minimum as the film 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, the reflectance is minimized at tl, t2. t3. By forming an inorganic insulating film on a metal film with a thickness of ta or a thickness close to either of these, a surface with low reflectance at the exposure wavelength is realized.

[Function] According to the configuration of the present invention, even if the metal film is made of a material having a high reflectance such as AI or A1 alloy, by forming an inorganic insulating film on top of it with the above-mentioned thickness. The reflectance can be reduced to about half or less compared to the case without the film (the case where the film thickness is zero in FIG. 5). For this reason,
When exposure treatment is performed after depositing a photoresist on an inorganic insulating film, the light reflected from the lower layer of the photoresist is weak, so
The photoresist is no longer exposed in undesired areas, allowing accurate pattern transfer. In other words, variations in the dimensions and shape of the photoresist pattern due to non-uniform Rn light can be suppressed, and when forming fine wiring, it is possible to reduce the thickness and thinning of each wiring.

[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 a vacuum evaporation method or a sputtering method. On the metal film 14, silicon nitride [16] is deposited as an inorganic insulating film by a CVD (Chemical Coating Deposition) method or the like.

In this case, the thickness t of the silicon nitride film 16 is t=30+110Xm±20[nm] when the exposure wavelength is 438 [nm] and mI:o or a positive integer such as 1.2... It can be selected according to the following formula. In other words, the reflectance becomes almost minimum at a thickness that satisfies this equation.

(2) Next, a photoresist is deposited on the silicon nitride film 16 according to a conventional method, and then a desired wiring pattern is transferred by exposure and further developed to form a photoresist film 18 corresponding to the wiring pattern. Form. In this case, since the silicon nitride film 16 was formed on the metal lAl4 with the above thickness, light reflection from the lower layer of the photoresist was suppressed during photoresist exposure, and variations in size and shape were reduced. A photoresist pattern is obtained.

(3) Next, by performing dry etching such as plasma etching using the photoresist film 18 as a mask, the metal film 14A and silicon nitride 11!116A corresponding to the wiring pattern are obtained.In this case, the silicon nitride film 16A is , hardly side-etched and acts as an etching mask for the metal [14]. Therefore, the metal film 14A has extremely good fidelity to the pattern (wiring pattern) of the photoresist film 18.

(4) Thereafter, an insulating film 20 is formed by CVD or the like, covering the metal film 14A and the silicon nitride film 16A. This insulating film 20 serves as a surface protection film or an interlayer insulating film. Note that the silicon nitride film 16
A may be removed prior to the formation of the insulation [20,
Leaving it in place is beneficial because hillock growth in Al-5i or the like can be suppressed.

[Effects of the Invention] As described above, according to the present invention, an inorganic insulating film is formed on a metal crotch to a thickness that makes the reflectance to the exposure wavelength almost minimum, and then a desired pattern is formed thereon using photolithography technology. Since a photoresist film is formed and the inorganic insulating 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 inorganic insulating film is hardly side-etched during dry etching, high etching accuracy can be obtained. That is, the metal pattern does not taper due to side etching, which occurs in the case of conventional anti-reflection organic insulating films, and therefore it is possible to realize a wiring width of 1 hr or less.

(3) The use of conventional organic insulating films for antireflection 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 an insulating 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...Silicon nitride film (inorganic insulating film), 18...Photoresist film.

Claims (1)

[Scope of Claims] (a) A step of forming a metal film on a substrate; (b) A step of forming an inorganic insulating 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 inorganic insulating film by photolithography; and (d) dry etching the inorganic insulating film and the metal film using the photoresist film as a mask. A metal pattern forming method including.