Adhesion of Ni-structures on Al2O3 ceramic substrates used for the sacrificial layer technique

This study presents an investigation of the adhesion properties of a chromi um-gold-titanium layer system, which is used in the LIGA process to create moveable microstructures. The main purpose has been the improvement of the process parameters to increase yield reliability. Three mechanisms affecting the adhesion have been identified. As a conseque nce of humidity adsorbed H2O reacts with Al2O3 to AlO(OH) (aluminum meta hy drates), which does not bond to the sputtered chromium layer. Thus the hydr ate must be removed by cleaning the surface with Ar+-ions. Tight layers wit hout pores could be realized by optimization pressure and temperature durin g sputtering of chromium and gold. Thus, diffusion of chromium or penetrati on of etchants into the gold layer as well as impact or diffusion of titani um into the gold layer could be prevented. In addition, a copper layer was introduced as a further intermediate layer by electroforming to improve the formation of stable nickel alloys at the interface between the sputtered g old and the electroplated nickel. These measures resulted in an improvement of the adhesion, so that full fun ctional acceleration sensors were produced with a high yield.