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Browse Prior Art Database

METHOD FOR STABILIZING A Pd2Si-Si CONTACT

IP.com Disclosure Number: IPCOM000047350D
Original Publication Date: 1983-Nov-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Reith, TM: AUTHOR [+2]

Abstract

A method for stabilizing a Pd2Si-Si contact against degradation by Al diffusion from an overlying metal interconnect is disclosed. Pd2Si, the equilibrium reaction product between Pd and Si, is used to make low resistance, reproducible ohmic contacts to Si. However, Pd2Si and Al-based alloys (such as Al-Cu-Si) readily interdiffuse at temperatures greater than 300ŒC, forming reaction products which can degrade specific contact resistance in VLSI device structures. While thermally stable diffusion barriers, such as sputtered TiW, can completely eliminate Pd2Si interdiffusion with Al, their implementation is expensive and can lead to lithographic complexity. The method disclosed here involves placing a discrete, thin layer of Cu between the Pd2Si layer and the Al-based alloy, thereby forming a sacrificial diffusion barrier.

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METHOD FOR STABILIZING A Pd2Si-Si CONTACT

A method for stabilizing a Pd2Si-Si contact against degradation by Al diffusion from an overlying metal interconnect is disclosed. Pd2Si, the equilibrium reaction product between Pd and Si, is used to make low resistance, reproducible ohmic contacts to Si. However, Pd2Si and Al-based alloys (such as Al-Cu-Si) readily interdiffuse at temperatures greater than 300OEC, forming reaction products which can degrade specific contact resistance in VLSI device structures. While thermally stable diffusion barriers, such as sputtered TiW, can completely eliminate Pd2Si interdiffusion with Al, their implementation is expensive and can lead to lithographic complexity. The method disclosed here involves placing a discrete, thin layer of Cu between the Pd2Si layer and the Al-based alloy, thereby forming a sacrificial diffusion barrier. A Pd-rich layer known to exist on the Pd2Si surface reacts preferentially with Cu to form an intermetallic compound which delays further Pd2Si-Al interaction as a function of time at an elevated temperature. Since Cu is required in the Al metallization for electromigration resistance, its use as a discrete layer beneath the Al presents only a minor increase in the process complexity. Because only a few percent of Cu is required in Al for electromigration control and because Cu readily diffuses through Al, the discrete Cu layer thickness can be adjusted to supply enough Cu to the Al layer while still formi...