JPS6353693B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a semiconductor device, and more particularly, to an improvement in a method for manufacturing a semiconductor device having a structure in which a semiconductor element is fixed to a heat dissipating metal substrate. As is well known, in this type of semiconductor device, a semiconductor element consisting of a silicon single crystal semiconductor piece (pellet) and a conductive wire connected to this pellet is fixed to a heat dissipating metal substrate called a heat sink, and these are attached to a support substrate. It has an assembled structure. By the way, the semiconductor device with the above-mentioned structure has conventionally
It is manufactured by the following method. First, a nickel thin film is formed on the silicon pellet of the semiconductor device, and then sintered at a temperature of about 500 to 550°C for about 30 minutes to cause the silicon pellet and nickel thin film to react to form a nickel silicide intermetallic compound layer. let Next, the silicon pellets and the heat dissipating metal substrate are soldered together with a strength of 500° C. or less to manufacture a semiconductor device. However, in the above conventional method, it is difficult to avoid oxidation of the surface of the nickel thin film during the sintering process, resulting in defective semiconductor devices due to poor wetting between the nickel thin film and the solder. Additionally, since sintering is essentially a heat treatment that causes the nickel thin film to react with silicon pellets, unless the sintering conditions are well controlled or the nickel thin film is made sufficiently thick, the nickel thin film will turn into nickel. It becomes a silicide intermetallic compound, and as a result, it becomes difficult to join with solder and strength decreases. Therefore, in the conventional method, the surface is oxidized after sintering, and the thin film converted to nickel silicide must be cleaned with nitric acid, etc., and a nickel thin film must be formed again, which increases the number of work steps and is complicated. This has the disadvantage that it hinders the productivity of semiconductor devices. Furthermore, it is known that when a nickel layer is formed on a silicon substrate, a metal is interposed therebetween (Japanese Patent Publication No. 50-27990). However, since gold reacts with silicon even at room temperature and diffuses into the silicon as gold silicide, the formation of nickel silicide cannot be effectively prevented, making it difficult to bond with solder. The shortcomings of the law have not yet been improved. Therefore, the present inventor interposed a vanadium thin film between the silicon pellet and the nickel thin film, and examined the formation temperature of the nickel silicide intermetallic compound by X-ray analysis and analysis using an ion microanalyzer. As shown in the table, it was found that the nickel silicide metal compound was not formed at a heat treatment temperature of 380°C or lower, and the nickel silicide formation temperature was further substantially raised by the vanadium thin film's barrier effect on silicide formation.

【table】

[Table] However, ○ in the table indicates silicide formation.
× means that silicide is not generated.
Based on the above findings, the inventors of the present invention have conducted extensive research, and as a result, formed a nickel thin film on the silicon pellet of a semiconductor element via a vanadium thin film, and soldered it to a heat dissipating metal substrate by heat treatment at 380°C or less. By bonding, the nickel thin film is not silicided and has sufficient solderability and strength, and a good solder joint can be achieved without complicated purification treatment or re-formation of the nickel thin film, resulting in a sufficient bond. We have discovered a method for manufacturing semiconductor devices with high productivity with high strength. Furthermore, it is possible to manufacture semiconductor devices that can further increase the heat treatment temperature during soldering, expand the types of solder that can be used, improve solder reliability, and speed up the soldering process. I found a way. That is, the present invention coats a semiconductor element with a vanadium thin film, further forms a nickel thin film on this thin film, and then arranges this semiconductor element on a heat dissipation metal substrate such that the nickel thin film side of the element faces the substrate. However, the device is characterized in that these elements and the substrate are soldered together by heat treatment at 380°C or less. As a means for forming a nickel thin film in the present invention, a method of forming a nickel plating thin film by plating, a method of depositing a nickel thin film by sputtering or vapor deposition, etc. can be adopted. In particular, a nickel thin film formed by sputtering is advantageous because it is highly dense and has excellent mechanical strength. The thickness of the nickel thin film in the present invention is 2500 mm from the viewpoint of providing sufficient thermal conductivity and mechanical properties.
(0.25 μt) to 30000 (3 μt) Å is desirable. Further, as a means for forming a vanadium thin film in the present invention, a method of depositing a vanadium thin film by sputter deposition, etc. can be mentioned. In particular, the vanadium thin film formed by sputtering is highly dense and has a high barrier effect for nickel silicide formation, so it is not limited by the thickness of the thin film and has the effect of increasing the silicide formation temperature to 400°C. The thickness of the vanadium thin film in the present invention is
A thickness of 100 Å or more is sufficient to provide a barrier effect for the formation of nickel silicide, but especially if the thickness is 250 Å or more,
If the temperature is Å or more, the silicide formation temperature can be reduced from 380°C.
It is possible to increase the temperature to 400℃, expand the types of solder that can be used, and speed up the soldering process. Next, examples of the present invention will be described. Example 1 Vanadium was vacuum-deposited on the back side of a silicon pellet of a semiconductor device to cover a vanadium thin film with a thickness of 500 Å, and then nickel was vacuum-deposited on this thin film to form a nickel thin film with a thickness of 4000 Å. Next, the back side of the silicon pellet of the above device was placed on a heat-dissipating metal substrate made of copper via a 95Pb-3Sn-2Ag preform solder, and then heated at 350℃ for 1 hour.
After heat treatment for a minute and solder bonding, a semiconductor device was fabricated. It was confirmed that the obtained semiconductor device did not produce a nickel silicide layer, had good solder joints, and had good characteristics in thermal fatigue test results. Example 2 Vanadium was vacuum-deposited onto a silicon pellet of a semiconductor device to cover it with a vanadium thin film with a thickness of 300 Å, and nickel was further vacuum-deposited on top of this to form a thin vanadium film with a thickness of 300 Å.
A nickel thin film of 6000 Å was formed. Next, the back side of the silicon pellet of the semiconductor element was placed on a heat-dissipating metal substrate made of copper via 95Pb-5Sb- preform solder, and then heat treated at 300°C for 2 minutes and soldered together to produce a semiconductor device. It was confirmed that in the obtained semiconductor device, no nickel silicide layer was formed, good solder bonding was achieved, and the results of the thermal fatigue test were also good. As detailed above, according to the present invention, the nickel thin film is not silicided and has sufficient solderability and strength, and good solder joints can be achieved without complicated purification treatment or re-formation of the nickel thin film. This has remarkable effects such as making it possible to manufacture semiconductor devices with sufficient bonding strength with high productivity. Furthermore, according to the present invention, it is possible to further increase the heat treatment temperature during solder bonding, expand the types of solder that can be used, improve solder reliability, and speed up the soldering process. Accordingly, it is possible to provide a method for manufacturing a semiconductor device that can achieve the following.

Claims (1)

[Claims] 1. After coating a semiconductor element with a vanadium thin film and further forming a nickel thin film on this thin film, the semiconductor element is placed on a heat dissipating metal substrate such that the nickel thin film side of the element faces the substrate. 1. A method for manufacturing a semiconductor device, which comprises arranging these elements and soldering them to a substrate by heat treatment at 380°C or less. 2. The method for manufacturing a semiconductor device according to claim 1, wherein the vanadium thin film has a thickness of 250 Å or more.