JPS5949691B2 - Manufacturing method of semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a semiconductor device, and particularly to the manufacturing of a highly reliable semiconductor device having high-speed switching characteristics.

Generally, lattice defects are formed in a semiconductor substrate by radiation irradiation, and carrier recombination centers are created in the forbidden band of the semiconductor substrate. Methods of improving the switching characteristics of devices are widely known.

In particular, the method using electron beam irradiation has a smaller leakage current than the conventional gold diffusion method, and is an effective means for manufacturing high-speed semiconductor devices without changing other electrical characteristics. However, in the conventional radiation irradiation, the generated recombination centers begin to disappear in a short time at relatively low temperatures, and this is known as the annealing effect. The present inventors have succeeded in improving this point based on several experimental results regarding research on electron beam irradiation to semiconductor substrates.

For example, when a semiconductor device with a metal thin film of nickel (Ni) attached is irradiated with an electron beam and then heat treated in air at 400°C for 2 hours, the carrier life of the diode is 1000 hours when stored at a high temperature of 250°C. The results showed that it was stable. Further detailed research has shown that it has high-speed switching characteristics through electron beam irradiation and heat treatment in the temperature range of 300℃ to 500℃, and has a practical use temperature of 250℃.
A semiconductor device with a stable carrier life time in the temperature range below .degree. C. was obtained. Embodiments of the present invention will be described in detail below with reference to the drawings.

As shown in FIG. 1, nickel (Ni) plating 4 with a thickness of 2 to 5 μm is formed on both main surfaces of a diode wafer with a PIN structure consisting of a P-type region 3, an N-type region 1, and an N-type region 2. , acceleration voltage 1.5 MeV, total electron flux 2×1013θ/
The electron beam 5 is irradiated under the conditions of d~2×10 15 Θ/Cd. After that, we stored the diode at a high temperature of 250℃ in nitrogen gas and investigated the change in the carrier life of the diode.
As shown in the figure. As can be seen from FIG. 2, it is confirmed that the carrier life begins to change after about 200 hours. Next, the diodes irradiated under the above conditions were heated at 250°C, 350°C, and 45°C.
FIG. 3 shows the results of heat treatment at 0° C. in a nitrogen atmosphere and measuring the change in carrier lifetime over time. These results show that the carrier lifetime, which is controlled by recombination centers formed by electron beam irradiation, changes in stages during constant heat treatment, and its change with temperature is shorter at high temperatures than at low temperatures. It turned out to be progressing. The above phenomenon is explained as follows. In other words, the recombination centers in a semiconductor substrate caused by electron beam irradiation consist of defects corresponding to various activation energies, and the carrier life time changes over time due to storage at a constant temperature due to defects with low activation energy. This is a process in which crystal defects disappear in order. It is known that the number of crystal defects with a single activation energy changes at temperature T according to the following equation. −Kt N(t)=N(0)θ− ・・・・・・・
... (1) K-TexO (-E/RT) ...
...(2) N(t): Number of crystal defects at time t Based on the results of the above experiments and their considerations, the present invention is extremely effective for manufacturing semiconductor devices with high-speed switching characteristics by electron beam irradiation. provide a method.

That is, the semiconductor substrate after electron beam irradiation is heated at 300°C to 50°C.
By performing heat treatment at 0° C. for several tens of minutes to several hours, only crystal defects with low activation energy can be completely eliminated.

Furthermore, when nickel is used as a metal thin film, it becomes possible to promote the disappearance of crystal defects with low activation energy through interaction with recombination centers formed by electron beams. Therefore, after this heat treatment, only crystal defects with high activation energy remain in the silicon, and it is possible to obtain a device with sufficiently stable switching characteristics in the temperature range of 250°C or less under the actual operating conditions of the device. An example is shown below. The irradiation diode was heat treated in a nitrogen atmosphere at 400 DEG C. for 2 hours, and subjected to a high temperature storage test at 250 DEG C. to examine changes in carrier life over time. The results are shown in FIG. According to this, no change in carrier life was observed even after 1000 hours had passed. Incidentally, the acceleration energy of the electron beam, the total electron beam flux, and the heat treatment temperature are factors that are selected according to design needs in order to obtain the specified characteristics.If the heat treatment time is determined according to the heat treatment temperature, practical use is possible. A sufficiently stable carrier life can be obtained within the temperature range.

Although in the embodiment the nickel layer was deposited by plating, it can also be done by other methods such as vapor deposition, sputtering, etc.

Further, since this nickel layer is used to promote the disappearance of crystal defects having low activation energy, it is not necessarily necessary to use a pure nickel layer, and a metal layer containing nickel in its composition is also effective. Further, this nickel layer or a metal layer containing nickel in its composition is effective if used as an electrode layer or a part of an electrode layer of a semiconductor device.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing one embodiment of the present invention. FIG. 2 is a graph showing the relationship between the lifetime and storage time of a semiconductor device produced by a conventional manufacturing method. FIG. 3 is a graph showing the relationship between lifetime and heat treatment time in one embodiment of the present invention, and FIG. 4 is a graph showing the relationship between lifetime and storage time in a semiconductor device manufactured by the manufacturing method of one embodiment of the present invention. This is a graph showing. In the figure, 1
...N type region, 2...N+ type region, 3
...P-type region, 4...Nickel layer, 5
...It's an electron beam.

Claims (1)

[Claims] 1. A step of attaching a nickel layer or a metal layer containing nickel in its composition to the main surface of a semiconductor wafer, a step of irradiating the semiconductor wafer with radiation, and heat-treating the semiconductor wafer at a temperature range of 300° C. or higher and 500° C. or lower. A method for manufacturing a semiconductor device, comprising the steps of: