1. Damaged abrasive discs inevitably produce damage layers of more than 10 microns; the damage caused by sandblasting may be greater! These damages can lead to the fragility of silicon wafers and the formation of diffusion channels. For larger mechanical damage, not only can it not be eliminated in the corrosion process, but it will be expanded and the surface pressure resistance will be greatly reduced. Cutting damage has a great impact on chip voltage. The damage layer on the surface of cut silicon wafer includes mosaic layer and stress layer. The surface of wafer is mosaic layer, and the lower layer is damage layer and stress layer with serious damage. Their thickness ranges from 15 to 25 microns, which is the average for the whole section.

2. Sources of stress: friction and extrusion between silicon wafers, clamping of metal tweezers, thermal mismatch between silicon wafers and quartz boats, rapid temperature rise and fall resulting in faster temperature change at the edge of silicon wafers than at the center, high temperature generated during corrosion, mismatch of atomic diameter when heavily doped, different thermal expansion coefficients of chips and plates... Stress can easily lead to breakage and warpage of silicon wafers.

3. Heavy metal impurities will greatly reduce minority carrier lifetime. They will cause large leakage current in PN junctions, and even make the voltage drop to zero. Heavy metals accumulate in the tail of single crystal and can be removed. In addition, after diffusion, phosphorus silica glass or borosilicate glass can be used to absorb at 950 - 1050 C for one hour, but the absorption has little effect on alkali metal (sodium, potassium) and alkaline earth metal (calcium, magnesium).

4. Because of the high concentration of phosphorus diffusion, large dislocations will occur in silicon at high temperature, and the dislocations of silicon single crystal itself will make phosphorus expand deeper along the places where dislocations are larger or more concentrated. Local penetration is easy to form when space charge region is widened. So the concentration of phosphorus diffusion should not be too high. It is necessary to prevent the diffusion of phosphorus and boron to produce alloy points, which will narrow the width of the base zone.

5. If the avalanche breakdown occurs in a small part of the PN junction, the rapidly increasing current will be concentrated in this area, which will be burned down due to the concentration of heat. This destructive breakdown is called thermal breakdown, which is irreversible. This is mostly due to the uneven surface or residual mechanical damage of PN junctions.

6. Surface ions contaminate negative charges and repel electrons to attract holes, forming P-type inverted layer channels, thus increasing leakage current; while positive charges attract electrons to repel holes, which is equivalent to reducing surface resistivity, narrowing surface space charge region and forming low breakdown on PN junction surface.

7. When the surface of PN junction only produces the effect of current, the waveform is still avalanche breakdown, and VB is basically unchanged. Generating current I = qGXmS, S is the surface area of PN junction. Therefore, inadequate corrosion, rough surface, a large number of composite centers, make the surface leakage current larger.