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Buried Contact Formation By Electrochemical Means

IP.com Disclosure Number: IPCOM000044693D
Original Publication Date: 1984-Feb-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Spencer, OS: AUTHOR

Abstract

During the course of formation of a depletion mode FET load device in polycrystalline silicon gate technology, a polycrystalline silicon buried contact must be formed in order to establish a connection between the age of the depletion load device and its source. A problem which has arisen is that during the process for removal of the photoresist layer which is employed to define the buried contact opening through the thin oxide layer a very thin layer of silicon dioxide (approximately 20-30 angstroms in thickness) forms on the silicon surface. This inadvertent formation of oxide layer prevents the penetration of phosphorous ions during a subsequent solid diffusion step, thereby preventing the formation of a necessary doped region in the silicon substrate beneath the intended location of the buried contact.

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Buried Contact Formation By Electrochemical Means

During the course of formation of a depletion mode FET load device in polycrystalline silicon gate technology, a polycrystalline silicon buried contact must be formed in order to establish a connection between the age of the depletion load device and its source. A problem which has arisen is that during the process for removal of the photoresist layer which is employed to define the buried contact opening through the thin oxide layer a very thin layer of silicon dioxide (approximately 20-30 angstroms in thickness) forms on the silicon surface. This inadvertent formation of oxide layer prevents the penetration of phosphorous ions during a subsequent solid diffusion step, thereby preventing the formation of a necessary doped region in the silicon substrate beneath the intended location of the buried contact.

The solution to this problem is that while the photoresist layer is still on the chip, immerse the chip in a solution of hydrochloric acid and As2O3 and apply a potential difference between the solution and the chip, thereby imposing anelectro-diffusion of the arsenic atoms through the native silicon dioxidelayer (having a thickness of approximately 10-15 angstroms) into the silicon substrate beneath the intended location of the buried contact. Thereafter, the photoresist layer can be removed by conventional steps and the doped polycrystalline silicon contact applied over the 30 angstroms thick silicon dioxide l...