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Masking Process for Base and Isolation Diffusion

IP.com Disclosure Number: IPCOM000076220D
Original Publication Date: 1972-Jan-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 37K

Publishing Venue

IBM

Related People

Berger, HH: AUTHOR [+3]

Abstract

The 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

The 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 less than 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.

In step 3, base window 7 is covered with a positive photoresist 12, using the subcollector mask which was previously employed for diffusing subcollector 3. Etching 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 process the p+ isolation zones remain unaffected, not considering the out-diffusion connected with the additional temperature cycle.

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