Semiconductor substrate, process for production thereof, and semiconductor device

A process for producing a semiconductor substrate comprising:

• (1) forming, on one side of a first single-crystal silicon substrate of a first conductivity and low impurity content, a polycrystalline silicon layer of said first conductivity and higher impurity content than the impurity content of the first single-crystal silicon substrate, which layer later becomes a lifetime killer of a second-conductivity carrier;
• (2) forming, on one side of a second single crystal silicon substrate of second conductivity and high impurity content, a polycrystalline silicon layer of said second conductivity and high impurity content;
• (3) bonding the two substrates so that the respective polycrystalline silicon layers come in contact with each other;
• (4) subjecting the resulting bonded wafer to a heat treatment to obtain a composite substrate;
• and
• (5) forming a vertical power semiconductor device.

A process for producing a semiconductor substrate comprising:

• (1) forming, on one side of a first single-crystal silicon substrate of first conductivity and low impurity content, a polycrystalline silicon layer of said first conductivity and higher impurity content than the impurity content of the first single-crystal silicon substrate, which layer later becomes a lifetime killer of a second-conductivity carrier;
• (2) forming, on one side of a second single-crystal silicon substrate of second conductivity and high impurity content, an intrinsic polycrystalline silicon layer;
• (3) bonding the two substrates so that the respective polycrystalline silicon layers come in contact with each other;
• (4) subjecting the resulting bonding wafer to a heat treatment to obtain a composite substrate;
• and
• (5) forming a vertical power semiconductor device.