JPS6227155B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to dry etching technology, and is primarily directed to A wiring processing using plasma etching.

With the increasing integration of semiconductor devices such as LSI and IC,
Dry etching technology using plasma discharge is becoming a major means for microfabrication of interconnects. Dry etching is generally performed through a mask made of photoresist (a photosensitive material resistor). When the material to be etched is A (aluminum), the etching rate ratio (also called etching selection ratio) of photoresist A is 1:2 to 3 times. In order to perform microfabrication, it is necessary to reduce the thickness of the photoresist film, and if the material to be etched is, for example, Al for internal wiring of an LSI, the Al wiring film must also be made thin. However, the wiring material cannot be made thinner than a certain thickness due to limits in allowable current density and wiring resistance. In addition, in LSI, as shown in FIG. 1, there are irregularities 2 on the substrate surface, which are formed to form, for example, an oxide film as a field insulating part, and on the stepped part, a first Al wiring 3 and an interlayer insulating film 4 are formed. When trying to etch a part of the second Al wiring with the photoresist 6 after laminating the second Al wiring 5, etc., the material to be etched (the second Al wiring) becomes thinner at the step part, and the photoresist As the film thickness becomes thinner, etching progresses to a deeper part as shown in FIG. Furthermore, if the viscosity of the photoresist is increased and the film thickness of the photoresist is made thicker as a countermeasure against this problem, the film thickness at the step portion becomes thicker, and there is a possibility that wiring shorts may occur at the step portion.

The present invention has been made to solve the above-mentioned problems, and one purpose thereof is to perform fine processing using dry etching, and another purpose is to realize fine Al wiring processing using a thin photomask.

In order to achieve the above object, according to the aluminum dry etching method of the present invention, a silicon nitride film is formed on the surface of an aluminum layer, and the silicon nitride film is opened by etching through a photosensitive material mask formed thereon. After drilling and scolding,
The method is characterized in that the aluminum is dry-etched using the photosensitive food-resistant mask and the silicon nitride film as masks.

FIGS. 2a to 2c show the essential processes of an embodiment in which the present invention is applied to dry etching of Al wiring.

(a) In the same figure, 1 is the Si substrate, 2 is the stepped part, and 3 is the Si substrate.
is the first layer Al wiring, 4 is the interlayer insulating film, e.g.
A PSG (phosphorus silicate glass) film is formed by CVD (vapor phase chemical reaction deposition), and 5 is the second layer Al wiring which is the material to be etched. A plasma Si ₃ N ₄ film 7 with a thickness of 1500 Å is deposited on the surface of this second layer Al wiring 5.
A photomask 6 is formed by applying a photoresist thereon and performing a well-known exposure process.

(b) Using the above photomask as a mask, the Si ₃ N ₄ film 7 is etched (dry etching or wet etching) to open a hole. (c) Using the above photomask and the opened photomask as a mask, the Al film 5 is dry etched to form the required size.
Obtain the Al wiring pattern. Thereafter, the photomask may be dissolved and removed, leaving the Si ₃ N ₄ film as a surface protective film.

According to the configuration described in the above embodiment, the above object can be achieved for the following reasons.

The selectivity ratio between Si ₃ N ₄ and Al is about 1:7 to 10, and the selectivity ratio between Si ₃ N ₄ and photoresist is about 1:3 to 1:3.
It is about 5. Therefore, by dry etching the thin Si ₃ N ₄ film using the thin photoresist film as a mask, and then dry etching the Al using the photoresist and the Si ₃ N ₄ film as a mask, the etching process was improved compared to the conventional method. and the thickness of the photoresist
It became possible to reduce the size to about 1/2, making it easier to process fine patterns. For example, conventionally, film thickness 2
Using µm photoresist, the film thickness of Al wiring is 2.5
However, according to the method of the present invention, a 7000 Å photoresist is used, the Al wiring thickness is 2.5 μm, the Al wiring width is 6 μm, and the wiring width is 6 μm. Spacing 2μ
Microfabrication of the order of m in size has become possible.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a semiconductor device showing a conventional dry etch process, and FIGS. 2A to 2C are sectional views of a semiconductor device showing each step of the dry etch process according to the present invention. 1... Si substrate, 2... Step portion (oxide film), 3...
...First layer Al wiring, 4... Interlayer insulating film, 5... Second layer Al wiring, 6... Photoresist mask, 7...
... _{Si3N4 film} .

Claims (1)

[Scope of Claims] 1. A silicon nitride film is formed on the surface of the aluminum layer, a hole is formed in the silicon nitride film by etching through a photosensitive material-resistant mask formed thereon, and then the photosensitive material-resistant mask and the above-mentioned A dry etching method for aluminum, characterized in that the dry etching of aluminum is performed using a silicon nitride film as a mask. 2. The method of dry etching aluminum according to claim 1, wherein the silicon nitride film is left as a surface protection film for aluminum after dry etching.