JPH0481343B

Epitaxial npn transistors are built up on a heavily n-doped substrate (1) which may contain p-doping impurities, especially boron. The emitter and base zones (3, 4) are driven in at high temperatures which simultaneously expel the impurities from the substrate (1). Consequently, either a p-doped intermediate layer is formed between transistor and substrate or a high-resistance intermediate layer is produced by counterdoping. This results either in an undesirable thyristor effect, which may lead to the destruction of the devices, or in an increase in the spreading resistance. To avoid these effects, an n-doped intermediate layer (9) whose doping exceeds that of the epitaxial layer by a factor of 2 to 100 is laid down between the substrate and the transistor.