| 摘要 |
PURPOSE:To increase dielectric strength with a double negative bevel obtained by causing a step by control of an etching velocity along the depthwise derection by controlling the SiO2 mask width and window width used for forming a mesa slot in an Si substrate. CONSTITUTION:In the both faces of a thyristor wafer having a PNPN construction, no film is provided in a portion 5 to become a central portion of a mesa slot after an etching while an oxidized film 10 is provided in the circumferential portions to leave the film partially. Subsequently, an etching is effected by utilizing the mixed solution of nitric acid and fluoric acid, a mesa slot similar to a double negative bevel is formed by utilizing a difference of the etching speed in the depthwise direction between the portions 5 and 6. That is, the depth of a shallow mesa portion caused in the circumferential portion of the mesa slot is measured less than the PN-junction disposed between the layer 3 and layer 2 or 4, and the central portion of the mesa slot is formed deeper than the PN junction. Thereafter, the slot is filled with a glass 9 and others to form a thyristor with a high dielectric strength. |
