Surface Roughness of LPCVD Polysilicon and Its Influence on Overlying Electroless Plated Nickel

The surface roughness and adhesion of electroless plated nickel to underlying polysilicon layers are investigated in order to develop a surface micromachining process with nickel as the structural and polysilicon as the sacrificial layers. Surface roughness of undoped polysilicon increases with film thickness (i.e., in the range of 1 to 5 μm); this effect is attributed to the increasing dominance of {110}‐oriented grains with increasing polysilicon film thickness. Electroless plating is used to deposit nickel on polysilicon; surface roughness of the underlying polysilicon directly correlates with that of the plated nickel surface. A short pretreatment etch of the thicker (e.g., 3 to 5 μm) polysilicon films prior to electroless plating, causes the polysilicon surface to become porous, providing suitable mechanical bonding sites for adhesion of nickel to polysilicon. Adhesion of the electroless nickel film to polysilicon improves with surface roughness of the polysilicon underlayer.