JPS5942452B2 - Manufacturing method of semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a silicon semiconductor device having a multilayer electrode containing gold.

Multilayer electrodes containing gold (hereinafter referred to as gold multilayer electrodes) are used for the purpose of improving the corrosion resistance of electrode metals. Further, in order to further improve the protection and corrosion resistance of this electrode, the entire surface of the semiconductor device including this electrode is coated with a silicon oxide film. In such an electrode structure, the first layer from the ohmic junction with silicon is made of a metal (hereinafter referred to as barrier metal) for preventing gold from diffusing into silicon, for example, a titanium-tungsten alloy; The second layer is made of gold, and the third layer has a multilayer structure made of a metal that has good adhesion to the silicon oxide film coated after the electrode metal is formed, such as a titanium-tungsten alloy. Figures 1 and 2 show an example of the conventional manufacturing process of this type of seed gold multilayer electrode. After a titanium-tungsten alloy and a gold film are deposited on the entire surface, the portions left as electrodes are etched. 1 shows a cross section of a semiconductor element covered with photoresist. In the figure, 1 is an emitter diffusion region, 2 is a base diffusion region, 3 is a silicon oxide film, 4 and 6 are titanium-tungsten alloys, 5 is gold,
T is photoresist, 8 is emitter contact hole,
9 indicates a base contact hole. In such a gold multilayer electrode, as shown in the figure, after drilling holes in the silicon oxide film 3 in the necessary electrode parts, for example, titanium-tungsten alloy 4, gold 5, titanium-tungsten alloy 4, etc.
After each tungsten alloy 6 is vacuum-deposited, a photoresist 7 is deposited by photolithography on the portion left as an electrode in the etching process. Thereafter, each electrode layer is sequentially etched to form an electrode as shown in FIG.
However, in such a conventional electrode structure, 10
As shown in FIG. 2, undercuts in the first titanium-tungsten alloy layer tend to appear, and at the same time, undercuts in the third titanium-tungsten layer are also likely to occur. This is believed to be due to local cell formation due to the difference in standard electrode potential between gold, titanium, and tungsten. In the case of the first layer of titanium-tungsten alloy, there is a strong possibility that the problems caused by these undercuts may be caused by contact between gold and silicon at the undercuts. As is well known, gold and silicon tend to diffuse into each other, and when gold and silicon come into contact, gold will diffuse into the silicon layer during subsequent die-bonding processes, causing increased leakage current and destruction of functional parts. There is a possibility that this may occur. Furthermore, gold is directly exposed at the undercut portion of the third layer of titanium-tungsten alloy and on the side surfaces of the metal, resulting in unfavorable results for the following reasons.

As is well known, gold has poor adhesion to SiO2, Si3O4, etc., so in such conventional electrode structures, gold is exposed in these parts, and if it is covered with a protective film such as a silicon oxide film, it will be removed. Adhesive strength is low, and properties deteriorate due to intrusion of moisture, etc. This invention was made to improve the above-mentioned disadvantages, and the above-mentioned disadvantages were eliminated by covering the gold with another metal or alloy.

An embodiment of the present invention will be described below with reference to the drawings. First, as with conventional products, holes are made in the silicon oxide film in the areas that will become electrodes, then titanium-tungsten alloy and gold are vacuum-deposited, and the remaining areas are covered with photoresist as shown in Figure 3. Mask with. After this, the gold is etched, but as an etching liquid,
For example, use Aurostrip (trade name) and increase the etching time to create a slight undercut. After this, the photoresist was removed as shown in Figure 4, the same metal as the first layer was vacuum deposited, and then the photoresist was selectively deposited using the same procedure as shown in Figure 5.・Perform etching of tungsten alloy.
For example, 30% hydrogen peroxide is used as the etching solution. In this case, the product after removing the photoresist becomes as shown in Figure 6, where gold 5 is replaced by titanium-tungsten alloy 4.
Since there is no local battery formation mentioned above, undercuts are also reduced. The above has shown an example of the method for forming an electrode structure according to the present invention, but as mentioned in the example, since the gold 4 is completely covered with titanium and tungsten, the contact between the gold and silicon is perfect. Since gold is not exposed on the top and side surfaces of the electrode,
A protective film such as a silicon oxide film is also sufficiently deposited, contributing to improving the electrical and physical characteristics of the semiconductor device.

In this invention, titanium-tungsten alloy is used as an example of the first and third layer metals, but other metals may also be used which are effective as barrier metals and have sufficient adhesion to the silicon oxide film and gold, for example. , Ti, MO,
Ti-MO and the like can also be used.

In addition, in the above examples, the photomask for selectively etching gold and the photomask for etching barrier metal were the same, but two types of masks with different dimensions were used. It also has the same effect.

[Brief explanation of drawings]

Figures 1 and 2 are cross-sectional views for explaining the method of forming a semiconductor element having a gold multilayer electrode using a conventional method. FIG. 3 to 6 are cross-sectional views of a semiconductor device at each stage showing the process of forming a gold multilayer electrode according to the present invention. In the figure,
1 is an emitter diffusion region, 2 is a base diffusion region, 3 is a silicon oxide film, 4 and 6 are a titanium-tungsten alloy,
5 is gold, 7 is photoresist, 8 is emitter contact hole, 9 is base contact hole, 10 is titanium.
A tungsten alloy undercut is shown.

Claims (1)

[Claims] 1. After drilling a hole in the silicon oxide film in the area where the electrode will be formed of the semiconductor element coated with the silicon oxide film, a barrier metal selected from titanium-tungsten alloy, titanium, molybdenum, and titanium-molybdenum alloy is vacuum-deposited. vacuum evaporating gold onto the barrier metal; etching the gold layer so as to create a slight undercut by masking the portion of the gold layer that remains after etching; After removing the mask, vacuum evaporating the barrier metal again;
A method of manufacturing a semiconductor device, comprising the step of selectively applying the mask again and etching the barrier metal layer to form an electrode.