JPS6210024B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of forming a metal pattern such as a metal electrode, particularly an aluminum electrode, on a semiconductor substrate, and relates to a method of forming the pattern by dry etching.

BACKGROUND OF THE INVENTION Aluminum or aluminum alloys are widely used as materials for semiconductor devices, such as electrodes of planar transistors or electrodes including interconnection wiring of semiconductor integrated circuits. By the way, when forming electrodes, it is necessary to perform an etching process to form a predetermined pattern on the aluminum film formed by adhering these materials, but it is necessary to make the pattern finer, make the manufacturing process dryer, or make it non-polluting. For the purpose of improving etching, the etching method is being switched from the conventional wet etching method using an aqueous solution to a so-called dry etching method using a plasma reaction or the like.

By the way, although such a dry etching method is superior to a wet etching method in terms of pattern miniaturization, depending on the composition of the metal film to be etched, the side etching becomes large and it becomes difficult to form a fine pattern. There are cases.

For example, selective diffusion regions formed using a SiO ₂ film as a mask, such as the source and drain regions of MOS type large-scale integrated circuits (MOSLSI) or the emitter regions of high-frequency, high-output transistors with a multi-divided emitter structure. , if the diffusion depth is selected to be shallow, the p-n junction formed by building these regions
The distance from the pn junction end located on the surface of the silicon substrate directly under the SiO ₂ film to the edge of the opening of the impurity diffusion window formed in the SiO ₂ film becomes shorter. When aluminum is used as the electrode material of such a semiconductor device, and the electrode formation region is the entire surface portion of the diffusion region located within the window, the alloy layer formed between the aluminum electrode and the silicon substrate forms the p-n junction edge. There is a risk that the p-n junction may be short-circuited by this alloy layer. In order to eliminate this inconvenience, approximately 2% of the electrode metal
Aluminum alloys containing a certain amount of silicon have come into use.

However, when gas plasma etching is applied to the electrode layer made of this aluminum alloy to form an electrode pattern, side etching becomes large and the etching progresses to the lower part of the resist film that serves as a mask during gas plasma etching.
As a result, the formed electrode becomes thinner, making it difficult to form an electrode that is faithful to the resist pattern.
Alternatively, this may cause inconveniences such as wire breakage accidents becoming more likely to occur.

The present invention was made in consideration of these problems, and when performing dry etching using a halogen-based gas, a metal containing a metal whose vapor pressure is lower as a halide than the main component metal is used as an electrode metal. By using an alloy, it is possible to suppress side etching and form electrodes that are faithful to the mask pattern.

Next, embodiments of the present invention will be described with reference to the drawings.

Using a normal method, 2% Si and Cu are applied to the entire surface of the silicon substrate where a predetermined area has been formed.
After forming an aluminum alloy film containing 1.5% and further forming a photoresist pattern on this film, the film was transferred to a reaction chamber having a parallel plate electrode structure, and carbon tetrachloride with a gas partial pressure of 0.2 torr,
Gas plasma etching is performed for 5 minutes in a helium mixed gas of 0.15 torr. After this, the photoresist is removed and the electrode formation is completed.

In the aluminum electrode formed in this way, the amount of side etching during dry etching is significantly reduced compared to when a conventional metal layer is used.
The electrode pattern shape is faithful to the mask pattern.

That is, in etching with halogen-based gas, Al, which is the main component metal, is removed as Al halide. At this time, according to the present invention
Since other metals having a lower vapor pressure as halides than Al are added, etching becomes difficult and the amount of side etching is thought to be reduced.

Next, the results of experimental measurements of the relationship between side etching amount (vertical axis a) and etching depth (horizontal axis b) for electrode metals with different compositions are shown in the drawings. Line A is a normal Al-Si alloy containing 2% Si by weight, B is pure Al, C is an Al-Si-Cu alloy containing 0.3% Si and 0.2% Cu by weight, D is weight Contains 2% Si and 1.5% Cu
This indicates an Al--Si--Cu alloy, and shows that the smaller the slope of the straight line, a/b, is, the less side etching occurs. these 4
As is clear from the two straight lines, the addition of Si tends to increase side etching, while
Addition of Cu tends to reduce side etching. Although this tendency differs somewhat depending on the etching conditions, it shows the same tendency across the board, and when halogen compounds such as Si and gold (hereinafter referred to as Au) are mixed in, which has a higher vapor pressure than Al, etching is reduced. This is because halogen compounds with low vapor pressure such as Cu, zinc (Zn), (calcium (Ca),) magnesium (Mg), beryllium, iron, and nickel are difficult to be etched by halogen gases. It is believed that there is.

Therefore, if it is necessary to increase the content of Si, Au, etc., these will work in the direction of increasing the amount of side etching, so increase the amount of added Cu, etc. to suppress side etching, etc. as necessary. The relationship between side etching amount and depth can be easily adjusted.

Regarding the amount of metals with low vapor pressure such as halides such as Cu, it is appropriate to keep the weight ratio at 3% or less; if it exceeds 5%, the etching rate will drop significantly and workability will be affected. cause

In addition, the main component metal is Al as shown in the example.
Not limited to, tungsten (W),
The same can be said for molybdenum (MO) (and other metals).

As explained above, according to the method of the present invention, a fine electrode pattern with a line width of about 2 to 3 μm can be formed accurately and faithfully to a mask pattern.
This will greatly contribute to the production of high-density semiconductor devices.

[Brief explanation of the drawing]

The figure shows the change in the relationship between side etching amount and etching depth when the composition of the electrode metal is changed.

Claims (1)

[Claims] 1. A first metal containing silicon or gold in aluminum, tungsten, or molybdenum on the surface of a semiconductor substrate formed in a predetermined region has a vapor pressure higher than that of the first metal as a halide. Forming a metal layer containing a second metal consisting of at least one of copper, beryllium, magnesium, iron, nickel and zinc with a small content of the second metal of 3% by weight or less A method for forming a metal pattern on a semiconductor substrate, characterized in that, after this, a dry etching process is performed using a halogen-based gas to form a metal pattern made of the metal layer.