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Browse Prior Art Database

Protection of Porous Silicon from Oxidation and Impurities

IP.com Disclosure Number: IPCOM000082273D
Original Publication Date: 1974-Nov-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 53K

Publishing Venue

IBM

Related People

Dockerty, RC: AUTHOR [+3]

Abstract

A known technique for forming deep recessed oxide regions in a monocrystalline silicon wafer is to mask the wafer, anodize the exposed areas to form porous Si, and oxidize the porous Si to form SiO(2). In some cases, the oxide that forms causes internal wafer stress, which is undesirable.

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Protection of Porous Silicon from Oxidation and Impurities

A known technique for forming deep recessed oxide regions in a monocrystalline silicon wafer is to mask the wafer, anodize the exposed areas to form porous Si, and oxidize the porous Si to form SiO(2). In some cases, the oxide that forms causes internal wafer stress, which is undesirable.

Thermal oxidation of porous silicon is extremely rapid, quickly oxidizing through the whole thickness of a porous silicon slab, which causes an enormous amount of elastic stress that far exceeds any thermal stress that can occur during silicon wafer processing. For instance, compare the stress levels due to thermal expansion of composite material, temperature gradient (or inhomogeneity) and oxidation of porous silicon, which are respectively:

(Image Omitted)

This proposed technique is to form porous silicon regions in the wafer to relieve the stresses, and to cap the regions to protect against contamination and oxidation. Fig. 1 is a sketch of a wafer cross-section with a stress relief of a porous silicon ring. Fig. 2 is a sketch of a wafer in cross-section, illustrating a structure embodying a sealed porous silicon volume.

In this method, a silicon wafer 10 is masked on top and bottom leaving the peripheral areas exposed. If desired, other central areas could be left exposed to form internal porous regions. The resultant masked wafer is anodized in an aqueous hydrofluoric solution forming annular porous region 12. A sea...