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Purifying Semiconductor Crystals from Rapidly Diffusing Contaminations

IP.com Disclosure Number: IPCOM000085843D
Original Publication Date: 1976-Jun-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 29K

Publishing Venue

IBM

Related People

Bohg, A: AUTHOR

Abstract

Semiconductor crystals, for example, of silicon, are purified by being exposed to propagating temperature gradients transferring the rapidly diffusing contaminations distributed throughout the crystal to a predetermined area, from where they can be removed chemically or mechanically. The method can be combined with high-temperature processes, such as diffusions, provided that each part of the wafer is subjected to the same mean heat cycle.

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Purifying Semiconductor Crystals from Rapidly Diffusing Contaminations

Semiconductor crystals, for example, of silicon, are purified by being exposed to propagating temperature gradients transferring the rapidly diffusing contaminations distributed throughout the crystal to a predetermined area, from where they can be removed chemically or mechanically. The method can be combined with high-temperature processes, such as diffusions, provided that each part of the wafer is subjected to the same mean heat cycle.

The principle of the purification method is shown in the drawing by a circular semiconductor wafer. The successive figures show the wafer cross section at different times. In the example chosen, zones of the same temperature form concentric circles. By focussed heat radiation, for example, wafer 1 is heated in two concentric rings 2 to a suitable temperature of say 700 degrees C. The remaining regions are kept at a lower temperature as a result of radiation.

As shown in the figures, the hot zones are then permitted to move from the inside to the outside, whereby the rings disappearing towards the outside are replaced by zone 3 which is newly formed in the center. Irrespective of whether the contamination collects in the hot or cold zones, it is transferred to the periphery of the wafer where it can be left or from where it can be removed by etching, grinding, etc.

By suitable sinks, such as crystal defects, the contamination can also be permanently trapped i...