I am using microfabrication techniques to make chemical sensors to detect
sugars and amino acids in a solution. The detection of sugars and amino acids
calls for the use of copper as the sensor material on a silicon substrate.
Evaporation is my only available way of depositing a copper film on silicon.
However, the adhesion of copper evaporated on silicon is very poor. I have
attempted to use an intermediate chromium layer between copper and silicon to
improve its adhesion. The adhesion of chromium evaporated on silicon is very
good when done alone. If I break vacuum, to change evaporation sources, and
evaporate a copper layer on top of the chromium layer, the copper will adhere
very poorly to chromium. But if I evaporate a chromium layer and then a copper
layer without breaking vacuum, the chromium adheres very poorly to silicon,
while the chromium and copper layers adhere to each other very well. I have
only attempted to evaporate a 1 micron copper layer onto a .04 micron chromium
layer, while not breaking vacuum in between evaporation of the two layers.
Would increasing the chromium layer thickness improve adhesion of the copper
and chromium to silicon? I would apprecitate any suggestions.

e-mail: dtjohn01@starbase.spd.louisville.edu
Darren Johnson
University of Louisville
Louisville, Ky