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Modified Triple Diffused Power Transistor Process

IP.com Disclosure Number: IPCOM000086691D
Original Publication Date: 1976-Oct-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Anantha, NG: AUTHOR [+3]

Abstract

Two processes for fabricating power transistors are well-known: (a) the double-diffused process involving growth of an N/-/-type epitaxial silicon layer on an N/+/-type wafer and (b) the triple-diffused process involving a very deep N/+/ diffusion in the backside of an N/-/-type wafer.

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Modified Triple Diffused Power Transistor Process

Two processes for fabricating power transistors are well-known: (a) the double-diffused process involving growth of an N/-/-type epitaxial silicon layer on an N/+/-type wafer and (b) the triple-diffused process involving a very deep N/+/ diffusion in the backside of an N/-/-type wafer.

Each of the above two processes has shortcomings. In the first process, it is difficult to obtain good, defect free epitaxial silicon with thickness in the neighborhood of 80 mu m. In the second process an N/+/ diffusion as deep as 4 mils is required. Typically, this deep diffusion requires a heat cycle spanning several days. Further, the long heat cycle can create stresses and warpage of the wafers.

The modified triple-diffused process given below avoids these problems: (1) Start with 35 omega-cm N/-/ wafer with any thickness (typically 12-16 mils). (2) Diffuse base and emitter impurities using proper masking. (3) Open base and emitter contact areas. (4) Deposit, etch and anneal front-side metal. (5) Deposit quartz, etch via-holes and deposit Cr/Cu/Au. (6) Reduce wafer to the desirable thickness from the backside, typically 80-100 mu m. (7) Ion implant a skin layer of N/+/ impurity on the backside of the wafer (low-energy and high-dosage) to facilitate ohmic contact. (8) Deposit about 1 mu m thick layer of a refractory metal on the backside of the wafer. (9) Anneal the wafer at about 600-700 degrees C and complete fabrication throu...