Fishing – trapping – and vermin destroying
Patent
1994-02-28
1995-10-03
Hearn, Brian E.
Fishing, trapping, and vermin destroying
437 59, 437 76, 437 70, 148DIG9, H01L 21265
Patent
active
054551897
ABSTRACT:
In a bipolar or BiCMOS process, a heavily doped buried layer of a first conductivity type and a heavily doped channel stop region of a second conductivity type are formed in a lightly doped substrate of the second conductivity type. A lightly doped epitaxial layer of the first conductivity type is grown. An implant of the first conductivity type creates a guard ring around the bipolar transistor active region and also creates a higher-doped collector region inside the active region. In the BiCMOS process, during the formation of CMOS wells, a silicon nitride mask over the bipolar transistor inhibits oxidation of the epitaxial layer and the oxidation-enhanced diffusion of the buried layer. As a result, the epitaxial layer can be made thinner, reducing the collector resistance. The MOS transistor wells can be formed without an underlying buried layer, simplifying the process and decoupling the bipolar and MOS transistor characteristics from each other. A heavy implant of the second conductivity type creates a field implant region around each transistor. Around the bipolar transistor, the field implant region meets the channel stop region. Field oxide is grown over the field implant region by LOCOS process. A base region is formed inside the guard ring. Other features and embodiments are described in the specification, the drawings and the claims.
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Hearn Brian E.
National Semiconductor Corporation
Nelson H. Donald
Nguyen Tuan
Robinson Stephen R.
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