Manufacturing method of a semiconductor device

A manufacturing method of a semiconductor device, comprising the steps of:

• (a) forming a semiconductor element and interconnect on the side of a first surface of a first conductivity type semiconductor substrate;
• (b) after covering the semiconductor element and interconnect with a protective film, attaching a reinforcing plate over the protective film;
• (c) implanting first impurity ions of the first conductivity type from the side of a second surface which is on the side opposite to the first surface of the semiconductor substrate;
• (d) irradiating laser to a region into which the first impurity ions have been implanted to form a first semiconductor region having an activation ratio of the first impurity ions of 60% or greater;
• (e) implanting, from the second surface side of the semiconductor substrate, second impurity ions of a second conductivity type which is different from the first conductivity type into a region shallower than the region into which the first impurity ions have been implanted;
• (f) irradiating laser to a region into which the second impurity ions have been implanted to form a second semiconductor region having an activation ratio of the second impurity ions from 1 to 15%;
• and
• (g) peeling off the reinforcing plate from the first surface of the semiconductor substrate.