| 摘要 |
The invention relates to the manufacture of a so-called double poly bipolar transistor. In a layer structure of a first insulating layer (4), a polycrystalline layer (5) of silicon and a second insulating layer (6), an opening (7) is formed which extends to a monocrystalline part of the semiconductor body (10), a third insulating layer (8) being provided on the bottom of the opening (7). Via the opening (7) at least a part (1A) of the base (1) is formed. By means of a further opening (9) in the third insulating layer (8), the emitter (3) is formed. A drawback of the known method resides in that the transistors obtained by means of said method exhibit a relatively great spread in electrical characteristics, such as a base current which is not ideal and demonstrates a spread. In a method in accordance with the invention, the doping atoms are provided prior to the provision of the third insulating layer (8), the third insulating layer (8) is formed by means of deposition, and the semiconductor body (10) is heated, after the provision of the third insulating layer (8), in an ambient comprising a gaseous compound (40) including oxygen. By directly providing the doping atoms, preferably from the gas phase, a very shallow and steep base (1) is obtained, resulting in an improved spread in electrical characteristics. This improvement is partly made possible by providing the third electrically insulating layer (8) at a later stage by means of CVD. The thermal treatment in an oxygen compound (40)-containing ambient averts the occurrence of a high base current as a result of the use of a CVD-deposited third insulating layer (8). Preferably use is made, for this purpose, of a short-cycle annealing step in a N2O or NO-containing ambient.
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