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Browse Prior Art Database

Etching a Transistor Mesa

IP.com Disclosure Number: IPCOM000096990D
Original Publication Date: 1962-Mar-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 38K

Publishing Venue

IBM

Related People

Rideout, AJ: AUTHOR [+2]

Abstract

During the etching of the mesa in a transistor, a mask is employed to protect the regions which are not to be attached by the etchant. Silicon monoxide is an excellent masking material. It is resistant to the CP8 etchant, adheres well to the substrate, can be accurately positioned on it by a simple evaporation procedure, and is readily removed from the substrate surface after the mesa is formed.

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Etching a Transistor Mesa

During the etching of the mesa in a transistor, a mask is employed to protect the regions which are not to be attached by the etchant. Silicon monoxide is an excellent masking material. It is resistant to the CP8 etchant, adheres well to the substrate, can be accurately positioned on it by a simple evaporation procedure, and is readily removed from the substrate surface after the mesa is formed.

A layer 10 of silicon monoxide, having a thickness of about 0.165 mil, is evaporated over the emitter and base regions 11 and 12 and over the metal emitter and base contacts 13 and 14 of transistor 15. The region, beneath the broken lines in the sectional view taken on the line A-A, represents semiconductor material to be removed by the chemical etch CP8 to form mesa
16. Immersion of the unit in the etching solution removes the unwanted material without damaging the protective layer 10 and the regions under it. The layer or mask 10 of silicon monoxide remains on the contacts 13 and 14 when they are alloyed with their semiconductor regions. The mask serves as a confining jacket which prevents the contacts from balling up during alloying and creating unreliable electrical contacts. Mask 10 is removed by boiling the transistor in hydrofluoric acid for several minutes.

Heretofore, wax has been used extensively as an etch resistant mask. It is sprayed or evaporated on the wafer. Then, a plaid pattern of lines is hand- scribed in the wax with a pointed...