The influence of hydrofluoric acid concentration on electroless copper deposition onto silicon

Abstract

Electroless metal plating is widely used in a variety of applications in the electronic and semiconductor industries such as selectively depositing on patterned substrates [1,2], making ohmic contacts [3-81, filling contact holes and vias in microelectronic devices [9,101, and delineating semiconductor junctions [ll-131. Some of the advantages of electroless deposition over conventional vacuum deposition techniques are its ease of use and low cost. Hence much research has gone into improving and utilizing this plating process. In contrast to the large number of papers dealing with electroless metal deposition on metal surfaces, relatively few papers have been written dealing with electroless metal deposition onto semiconductor surfaces, especially during the initial stages of formation. The advent of scanning probe microscopy, such as scanning tunneling microscopy WI&I) 1141 and atomic force microscopy (AFM) [15], enables the investigation of such processes to be performed simply on the nanometer scale. For example, Osaka and co-workers [16-181 have used STM to study the electroless plating process of magnetic materials (e.g. NiP and CoNiReP) on highly oriented pyrolytic graphite (HOPG). Moffatt Kennedy et al. [19] observed the growth of electroless copper films on Pd-activated HOPG and printed circuit boards. Phaner et al. [20] have reported STM observation of 100-200 nm thick electroless gold deposits on Pd-activated n-GaAs. In the case of electroless metal deposition onto Si, HF solution is occasionally used in the plating bath in place of a reducing agent in order to induce deposition onto the surface. The HF removes any residual oxide on the surface and more importantly aids in metal deposition through direct displacement of the silicon [9,21]. In this note, we