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Increasing the Yield in the Manufacture of Semiconductor Components

IP.com Disclosure Number: IPCOM000092617D
Original Publication Date: 1966-Dec-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 31K

Publishing Venue

IBM

Related People

Statz, H: AUTHOR

Abstract

Where transistors are fabricated out of III-V compounds, especially GaAs, the base must be extremely thin in order to achieve a useful current gain. That is due to the short life of the carriers. In the process of diffusing successive zones, it can happen that the emitter diffusion time is selected too short resulting in a too thick base zone as in drawing A. This results in the necessity of repeating the emitter diffusion step. It can also happen that the emitter diffusion time is too long. This results in the emitter diffusing through the base into the collector as in drawing B. Thus the component becomes useless.

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Increasing the Yield in the Manufacture of Semiconductor Components

Where transistors are fabricated out of III-V compounds, especially GaAs, the base must be extremely thin in order to achieve a useful current gain. That is due to the short life of the carriers. In the process of diffusing successive zones, it can happen that the emitter diffusion time is selected too short resulting in a too thick base zone as in drawing A. This results in the necessity of repeating the emitter diffusion step. It can also happen that the emitter diffusion time is too long. This results in the emitter diffusing through the base into the collector as in drawing B. Thus the component becomes useless.

In the last mentioned case, however, it is possible to restore the operability of the component under the following conditions. The doping substance for the base must have a higher diffusion coefficient than that for the emitter. Then it is possible by a tempering step conducted after the diffusion processes to cause the base front to catch up with the emitter front. Such results in a thin, operable base zone as in drawing C.

As an example, in a GaAs transistor the base is produced by the diffusion of Zn and the emitter is produced by the diffusion of Sn. The diffusion coefficient of Zn is higher in GaAs than that of Sn. The tempering step for removing a diffused emitter zone can, e. g., be performed at a temperature of 900 degrees C for a duration of three hours.

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