The Influence of Surface Oxides on Whiskering

Some mechanistic models of tin (Sn) whisker growth presume that surface oxidation plays an important role in whisker formation. The notion is that Sn whiskers grow through weak spots in the Sn oxide, which is cracked during whisker growth and propagation. It is often implied that a surface oxide is necessary for whisker growth. However, the premise of a surface oxide requirement for whiskering is clearly questionable. Not only have there been anecdotal reports of Au whiskers, but studies by Moon, Handwerker, et al. [31] and our laboratory show that Sn whiskers can grow from atomically clean surfaces and/or surfaces having extremely low amounts of oxygen. This paper reports a definitive test of the surface oxidation hypothesis by attempting to grow whiskers from surfaces having no native oxide (Au). The results show that high aspect ratio Au whiskers can be grown within a few weeks from intrinsically (compressively) stressed thin films of sputtered Au on silicon.