USE OF Ni/W CAP ON THE REFRACTORY OHMIC CONTACTS TO GaAs
Original Publication Date: 1993-Oct-01
Included in the Prior Art Database: 2002-Feb-14
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.