Method of manufacturing semiconductor substrate dielectric isolating structure

A method of manufacturing a semiconductor substrate having a dielectric isolating structure, comprising the steps of:

• mirror-polishing a surface of each of first and second semiconductor substrates of a predetermined conductivity type;
• forming a dielectric film on one of said mirror-polished surfaces obtained in said polishing step;
• opposing said mirror-polished surfaces through said dielectric film to join said first and second semiconductor substrates therebetween;
• reducing a one of said first and second semiconductor substrates to a predetermined thickness using mechanical means;
• selectively doping a first impurity in a first region of the one of the semiconductor substrates reduced in the reducing step, at a time when the one of the semiconductor substrates has the predetermined thickness to form a first high-concentration impurity region;
• selectively doping a second impurity in a second region of the one of the semiconductor substrates reduced in the reducing step, at a time when the one of the semiconductor substrates has the predetermined thickness, the second region being laterally offset from the first region to form a second high-concentration impurity region;
• and
• forming a low-concentration impurity semiconductor layer on surfaces of said first and second high-concentration impurity regions, respectively.