| 摘要 |
PURPOSE:To detect the charges of a surface protective film by reverse-biasing a p-n junction, measuring the extension of a depletion layer in the vicinity of the surface of a substrate by using optical response and collating the relationship of a bias and the quantity of extension with known relationship. CONSTITUTION:When reverse bias voltage VA is selected in the avalanche breakdown voltage or less of the p-n junction, the extension of the depletion layer 12 in the vicinity of the surface is determined by VA and the quantity of charges in the surface protective film. Large photocurrents flow when a light spot 10 is irradiated into a depletion layer region, and only small leakage currents flow when the light spot is irradiated into other regions. The change of the photocurrents Ip is obtained as that of a position, and the width L of the depletion layer can be acquired. When VA is altered and the change of the width L is plotted, the quantity of charges Q in the surface protective film prepared previously is used as a parameter and characteristics agreeing with measurement best are selected, the quantity of charges is decided. Calculation value prepared previously can be obtained by solving a Poisson formula from the size of the element, the depth of a p layer and the quantity of diffusion, the concentration of a m layer, the quantity of charges Q in the surface protective film and bias voltage VA. In the constitution, special structure is unnecessitated completely. |
