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USE OF Ni/W CAP ON THE REFRACTORY OHMIC CONTACTS TO GaAs

IP.com Disclosure Number: IPCOM000006985D
Original Publication Date: 1993-Oct-01
Included in the Prior Art Database: 2002-Feb-14
Document File: 1 page(s) / 54K

Publishing Venue

Motorola

Related People

Jaeshin Cho: AUTHOR [+3]

Abstract

The ohmic contact properties of GaAs devices can be improved by using an additional Ni/W cap on the previously known refractory ohmic contacts: Ge/Mo/W Ge/In/W Ni/In/W Ni/Si/W PdfGelW Ni/Ge/W Ge/Ni/WN, etc. The W or WN layer on these contacts is used for a dithrsion barrier, and it must maintain its thickness during subsequent device processing for optimum device performance. How- ever, in actual device processing, the W or WN layer can be easily overetched, when the vias are etched open to the refractory ohmic metals, which results in deterioration of ohmic contact properties. This is because the fluorine-based dry-plasma chemistries have low etch rate selectivity of W or WN metals to dielectric films. The W or WN overetch is an unique problem for refractory ohmic contacts. Gold-based contacts such as NiGeAu have overlying Au layers as good etch stops for dry-plasma etching. The prob- lem of W or WN overetch for refractory ohmic con- tacts can be completely eliminated by employing an additional Ni/W cap on the top of previously known refractory ohmic contact metals.

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MOTOROLA INC. Technical Developments Volume20 October 1993

USE OF Ni/W CAP ON THE REFRACTORY OHMIC CONTACTS TO GaAs

by Jaeshin Cho, Kelly Kyler and Gregory H. Hansell

  The ohmic contact properties of GaAs devices can be improved by using an additional Ni/W cap on the previously known refractory ohmic contacts: Ge/Mo/W Ge/In/W Ni/In/W Ni/Si/W PdfGelW Ni/Ge/W Ge/Ni/WN, etc. The W or WN layer on these contacts is used for a dithrsion barrier, and it must maintain its thickness during subsequent device processing for optimum device performance. How- ever, in actual device processing, the W or WN layer can be easily overetched, when the vias are etched open to the refractory ohmic metals, which results in deterioration of ohmic contact properties. This is because the fluorine-based dry-plasma chemistries have low etch rate selectivity of W or WN metals to dielectric films. The W or WN overetch is an unique problem for refractory ohmic contacts. Gold-based contacts such as NiGeAu have overlying Au layers as good etch stops for dry-plasma etching. The prob- lem of W or WN overetch for refractory ohmic con- tacts can be completely eliminated by employing an additional Ni/W cap on the top of previously

known refractory ohmic contact metals.

  The Ni/W cap (each layer 100-200 8, thick) on the refractory ohmic contacts will provide the fol- lowing advantages:

(a) Since Ni is an excellent etch stop for most fluorine- or chlorine-based dry etch plasmas, the refractory contac...