Sputtering refers to the transfer of energy and momentum from an impinging energetic particle to a target material. If the energy transfer is high enough to overcome the binding energy of the atoms in the target, the target atom or atom will be ejected. The ejected target atoms are then free to be transported to a workpiece. Sputtering is typically used for thin-film deposition in high-tech applications such as in fabrication of semiconductor wafers, solar cells, and electrochromic windows. For example, sputtering may be used to deposit or otherwise incorporate target material in a stack of material layers on a glass or otherwise transparent substrate to form electrochromic devices used to make electrochromic windows. Many of these high-tech applications required highly uniform deposition in order to make their devices perform well. In addition, as technology advances, coatings in some devices become thinner and thinner, and thus uniformity of the layers making up such coatings must be commensurately higher. Some electrochromic devices are fabricated by a process that includes deposition of lithium on a partially fabricated device. Frequently, the deposition is by sputtering.
In conventional sputtering processes, argon plasma or other inert gas plasma is used to sputter material from the target. Conventional physical vapor deposition sputtering typically has a noble gas dominated environment during sputtering of the target atoms. In this environment, interactions with the target can be more prevalent by noble gas ions than with the target ions. For some target materials such as lithium, this may lead to various problems such as poor deposition rates and/or non-uniformity of the deposited material.