| 摘要 |
PURPOSE:To enable elements to be isolated without using the photolithography by a method wherein, after forming an oxide film thickly on the surface of one MOS transistor forming region while thinly on the surface of the other MOS transistor forming region, an impurity is ion-implanted and after removing the thin oxide film, another impurity is ion-implanted. CONSTITUTION:After covering each element region part with each mask layer 23, one of the two MOS transistor forming regions is implanted with an impurity 26 with a conductivity opposite to that of substrate. After heat treatment, a well layer 27 with conductive type reverse to that of substrate is formed by diffusing said impurity 26 simultaneously forming oxide films 28, 29 thickly on the surface excluding the element region part of well layer 27 while thinly on the surface excluding the element region part of the other MOS transistor forming region. Next, after implanting another impurity 30 with conductive type reverse to that of substrate through the intermediary of the oxide films 28, 29, the oxide film 29 is removed using the difference in film thickness to implant the other impurity 31 with conductive type similar to that of substrate. Later, any residual oxide film 28 is removed; the substrate is thermal-oxidized to form the other oxide film 32 for element isolation; simultaneously diffused layers 33, 34 for element isolation are formed in the substrate below the film 32 by diffusing said impurities 30, 31. |
