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Gas Phase Doping of Semiconductors during Float Zone Crystal Growth

IP.com Disclosure Number: IPCOM000082634D
Original Publication Date: 1975-Jan-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Ciszek, TF: AUTHOR

Abstract

A difficulty in gas phase doping is the reproducible control of low-gas flows, which is required when using premixed dopant/carrier gases that are commercially available in dopant concentrations of 5-5000 parts per million (ppm). One way to control gas flow is to permit it the gas to flow through thin bore (4 mil capacity) precision capillary tubing under modestly accurate pressure, because viscous gas flow in a long, thin tube is inversely proportional to tube length and varies as the fourth power to the tube radius.

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Gas Phase Doping of Semiconductors during Float Zone Crystal Growth

A difficulty in gas phase doping is the reproducible control of low-gas flows, which is required when using premixed dopant/carrier gases that are commercially available in dopant concentrations of 5-5000 parts per million (ppm). One way to control gas flow is to permit it the gas to flow through thin bore (4 mil capacity) precision capillary tubing under modestly accurate pressure, because viscous gas flow in a long, thin tube is inversely proportional to tube length and varies as the fourth power to the tube radius.

For instance, for a tube length L (see Fig. 1), inner radius A and inlet and outlet pressures P2 and P1, respectively, argon flow is viscous if 2A (P1 and P2)/2 >500, where A is in cm and pressure is in microns Hg.

By making A small and L large, a very low flow can be attained. Furthermore, this flow can be effectively controlled through P2 and P1. Fig. 2 shows a cylinder 4 of dopant gas in argon at concentration CO, argon purge 6, a crystal 8, melt 10, feed rod 12, vent 14, and pressure regulators P1 and P2.

It is assumed that the cylinder 4 of dopant gas contains a fractional concentration CO of dopant (diborane, phosphine, etc.) in argon and that a fraction E of these dopant molecules are incorporated in the melt 10 (the rest is lost in the chamber atmosphere or leaves through the vent 14. N(d) is the crystal dopant concentration, D(c) is the crystal meter, and V(c) is the crysta...