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Masking Process for Base and Isolation Diffusion

IP.com Disclosure Number: IPCOM000075660D
Original Publication Date: 1971-Oct-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 67K

Publishing Venue

IBM

Related People

Berger, H: AUTHOR [+3]

Abstract

This method permits base and isolation zone diffusion to be separately adjusted in bipolar processes, although the mask windows determining the spacing of the two zones are arranged on a common mask. Thus, the adjusting tolerance required in the case of two masks is eliminated. This leads to substantial area savings, since it is possible to adjust the minimum permissible distance between base and isolation zone.

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Masking Process for Base and Isolation Diffusion

This method permits base and isolation zone diffusion to be separately adjusted in bipolar processes, although the mask windows determining the spacing of the two zones are arranged on a common mask. Thus, the adjusting tolerance required in the case of two masks is eliminated. This leads to substantial area savings, since it is possible to adjust the minimum permissible distance between base and isolation zone.

In step 1, an oxide layer 4, serving as a mask, is generated on an N- epitaxial layer 2 grown on P substrate 1 with N+ subcollector 3. Simultaneously, windows 5 and 6 for the isolation diffusion and window 7 for the base diffusion are etched.

In step 2, reoxidation to about half the thickness of the original oxide layer is carried out, so that windows 5, 6 and 7 are again filled by oxide layer 8.

By an etching mask which does not cover windows 5 and 6 for the isolation zones and which has apertures whose width is increased by the adjusting tolerance, etching, in step 3, is carried out until the surface of N- epitaxial layer 2 in the area of the original windows 5 and 6 has been freed. Subsequently P+ isolation zones 9 and 10 are diffused.

In step 4 original window 7 for the base zone is etched. Finally, P base zone 11 is diffused. During this diffusion process the P+ isolation zones remain unaffected, not considering the outdiffusion connected with the additional temperature cycle.

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