Method of fabricating bipolar transistor having a guard ring

US5580798A · kind A · utility

Assignee

• NATIONAL SEMICONDUCTOR CORPORATION · US

Inventor

• Michael J. Grubisich · San Jose, US

Key dates

• Filing date: Dec 12, 1994
• Grant date: Dec 3, 1996
• Expiry date: Dec 12, 2014

Classification

• Technology area (CPC Y): Emerging Cross-Sectional Technologies
• CPC primary: Y10S148/01

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 r…