8. Cleaning treatment before and after diffusion and cleanliness of diffusion system itself have great influence on voltage. Soft properties are related to the entry of harmful impurities into the body, so all kinds of contamination should be avoided.

9. Control of junction depth: A breakdown voltage requires the base region to exceed the width of the maximum space charge region; deep junction is easy to manufacture high-voltage device B current capacity requirements, VF can not exceed the standard C switching speed requirements. The wider the base area, the slower the speed.

10. The decrease of minority carrier lifetime is mainly caused by heavy metal impurities (copper, iron, nickel, lead, zinc, etc.) forming strong recombination centers. In addition to the silicon wafer itself, process operation, chemical reagents and utensils will bring heavy metal impurities. In addition, diffusion furnace tube wall is also an important, sometimes even the most important source. There are also a lot of alkali metals, alkaline earth metals and some excessive rare earth elements in the tube wall. They can penetrate the quartz tube wall and enter the tube from the quartz crystal gap. They not only pollute the silicon wafer, but also disintegrate the quartz tube (from transparency to whitening, crispening, peeling!).

11. At room temperature, the maximum surface field intensity is located in the N region of low concentration, while at 80 C, the maximum surface field intensity shifts to the N+-N junction. Therefore, although this device exhibits a beautiful avalanche ionization breakdown at room temperature, its breakdown voltage begins to decrease at high temperature. This is a typical surface breakdown feature.

12. Leakage current is another important parameter to characterize high voltage devices. The high temperature characteristics of devices with room temperature soft characteristics are certainly not good. Only devices with avalanche breakdown characteristics at room temperature can have good high temperature characteristics, but not necessarily. Some devices are still hard at room temperature or even up to 80 degrees Celsius, but at high temperature (diode 150 degrees Celsius), they become soft, resulting in low stability and reliability. This can be divided into two cases: A. Room temperature is a hard characteristic, but the starting current is large, that is, the diffusion current is large, which is commonly referred to as the "back chair". One of the common reasons for this is that

The protective material is impervious to solidification, and the surface channel is induced by the high density negative surface charge, which forms a large initial current. This phenomenon can be eliminated by improving the curing process and eliminating the channel. B. Room temperature is also a hard characteristic, but it produces a large current, that is, leakage current increases rapidly with the increase of voltage. The reason is that the surface damage layer caused by cutting or grinding is contaminated by heavy metals, and there are at least two impurity levels, which improves the recombination probability. Deep corrosion process can reduce the large leakage current after removing the damaged layer and contamination and eliminating surface contamination.