Method of manufacturing SOI semiconductor device

A method of manufacturing an SOI device having a conductive impurity layer;

• said method comprising the steps of:
• (a) forming a non-single crystal silicon layer on the exterior of a first single crystal wafer and an insulating film on the exterior of a second single crystal wafer and thereafter bonding these first and second single crystal wafers with each other through said non-single crystal silicon layer and said insulating film;
• (b) removing by polishing a part of said non-single crystal silicon layer and a part of said first single crystal wafer from an end surface on a side of said first single crystal wafer, leaving a part of said first single crystal wafer as an element forming layer having an interface with said non-single crystal silicon layer;
• (c) selectively introducing impurity atoms into said element forming layer to provide a conductive impurity region at a first impurity concentration reaching said non-single crystal silicon layer;
• (d) forming a conductive impurity diffused region, having a second concentration lower than the first concentration, in said element forming layer and substantially extending to the interface between said element forming layer and said non-single crystal silicon layer, said conductive impurity diffused region formed by impurity diffusion from said conductive impurity region through said non-single crystal silicon layer at least, by using heat treatment;
• and
• (e) forming a transistor in a region between an exterior surface of said element forming layer and said conductive impurity diffused region.