| 摘要 |
In a bipolar or BiCMOS process, a heavily doped buried layer (140) of a first conductivity type and a heavily doped channel stop region (150) of a second conductivity type are formed in a lightly doped substrate (120) of the second conductivity type. A lightly doped epitaxial layer (210) of the first conductivity type is grown. An implant (250) 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 (310, 520), a silicon nitride mask (230) 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 (840.1) around each transistor. Around the bipolar transistor, the field implant region meets the channel stop region. Field oxide (830) is grown over the field implant region by LOCOS process. A base region (940) is formed inside the guard ring. |
