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Capsule Diffusion Control Using Multicomponent Source Material

IP.com Disclosure Number: IPCOM000092933D
Original Publication Date: 1967-Mar-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 3 page(s) / 16K

Publishing Venue

IBM

Related People

Carlsen, GS: AUTHOR

Abstract

This diffusion process improves wafer surface concentrations, wafer surface quality, impurity distribution profile and eliminates ragged junctions within the sealed capsule diffusion system. Capsule diffusion can be improved by control of composition, phase, and molar quantity of source powder surface and bulk material within the sealed capsule chamber. Also, control of the composition, phase, and the molar quantity of the wafer surface material is influential in the capsule diffusion process.

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Capsule Diffusion Control Using Multicomponent Source Material

This diffusion process improves wafer surface concentrations, wafer surface quality, impurity distribution profile and eliminates ragged junctions within the sealed capsule diffusion system. Capsule diffusion can be improved by control of composition, phase, and molar quantity of source powder surface and bulk material within the sealed capsule chamber. Also, control of the composition, phase, and the molar quantity of the wafer surface material is influential in the capsule diffusion process.

A reproducible source material for capsule diffusions can be prepared by placing high-purity silicon, germanium, or other semiconductor material in a refractory crucible. The latter is placed in a sealed chamber under high vacuum of approximately 10/-6/ torr. The semiconductor material can be melted by RF induction techniques. When the molten semiconductor material reaches equilibrium at melt temperature, a single elemental impurity or a combination of elemental impurities is added to the molten semiconductor material. Such addition occurs until the amount of dissolved impurities is the maximum amount allowed by the liquid solubility of impurities at the melt temperature and chamber pressure. This liquid solubility limit is determined by the thermodynamic phase diagram for the metallurgical system comprised of bulk semiconductor material and impurities added to the melt. A typical source material preparation is to add either phosphorus, boron, or arsenic to molten silicon at 1425 Degrees C. A second typical source preparation is to add either phosphorus, boron, or arsenic to a molten alloy of silicon and germanium at temperatures from 1000 Degrees to 1500 Degrees C.

Impurity vapor composition and pressure within the sealed chamber can be controlled by the existence of a temperature controlled, condensed phase region within the sealed chamber. An alternate impurity control procedure is to have a dynamic inert gas flow with a controlled pressure passing over the melt when impurities are added to the melt. The physical phenomenon of the liquid solubility limit is used to insure reproducible control of impurity concentrations within the source material. When the source material solidifies, there is a definite concentration distribution of impurities within the source material. Such depends upon melt temperature and the chamber vapor composition and pressure.

After equilibrium is reached with the maximum amount of impurities dissolved into the molten semiconductor material, the molten solution can be cooled down to room temperature at a cooling rate which approximates equilibrium cooling. Solid source material can be removed from the crucible using standard techniques. The solid source material can then be ground to powder with a particle size between 50 and 200 microns.

Since the capsule diffusion chamber is sealed during the diffusion process, various phase transformations can occur...