| 摘要 |
PURPOSE:To obtain a maximum withstand voltage at all times by a method wherein the steps (d1, d2 from the inside) between the depletion layers widened when the counter bias is applied from an N type substrate P layer and a P type protective ring in the outside and the inside, are set at a predetermined position, the surface is removed over the region from the inner circumference of the P layer to the outside protective ring and further the surface is covered with a stable protective film. CONSTITUTION:A P type protective ring is provided being apart at the distance M1 and M2 from a P layer 2 on the surface of an N type Si substrate 1. The substrate surface is removed over the region from a main junction 2 to the outside of an outer protective ring junction 7 to eliminate a crystal distortion of the surface and the influence due to the widening of a depletion layer and further be covered with SiO2 4', 4''. Therefore, the influence is restricted only to the surfacial charge density of SiO2. When the steps d1, d2 are formed by widening the depletion layers of width W respectively, and by applying a counter bias to electrodes 5 and 6 added, a protective ring is arranged so that the following relations are set; 2mum<=d1<=4mum, d1<= d2<=4d1. A curvature of the depletion layer being subject to the influence of unevenness of the distance M based on the lack of the uniformity in the most uneven transverse diffusion can be improved and consequently a maximum counter withstand voltage can be obtained. |
