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Transistor Fabrication

IP.com Disclosure Number: IPCOM000075678D
Original Publication Date: 1971-Oct-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 31K

Publishing Venue

IBM

Related People

Ashar, KG: AUTHOR [+4]

Abstract

In using a mixed source, two opposite type impurities are diffused into a semiconductor 10 through a window 12 in a masking layer 14. One of the impurities has a significantly greater diffusivity than the other impurity and consequently, diffuses downwardly and outwardly under layer 14 to form region 16. The second impurity, having a slower diffusivity, forms region 18.

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Transistor Fabrication

In using a mixed source, two opposite type impurities are diffused into a semiconductor 10 through a window 12 in a masking layer 14. One of the impurities has a significantly greater diffusivity than the other impurity and consequently, diffuses downwardly and outwardly under layer 14 to form region
16. The second impurity, having a slower diffusivity, forms region 18.

During the development of the mixed source, it was found that the vapor pressure of boron is significantly reduced in the presence of arsenic. The boron diffusion can consequently be reduced to the point that the emitter and collector junction are scarcely separated.

Region 16 would be very thin under these conditions. The base width could be increased by providing a higher boron vapor pressure, but this degrades the performance of the resultant device.

In this process the mixed source consists of powdered silicon containing gallium and arsenic impurities. Gallium has a significantly higher vapor pressure then boron in the presence of arsenic. Further, since gallium has a better match to the silicon atom than boron, higher doping levels can be used in the base without producing strain induced defects and consequent breakdown problems.

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