Is surface potential measurement (SPM) a useful charging damage measurement method

Recently, there has been strong interest in using the surface potential measurement (SPM) method to monitor plasma charging damage. This method is also called contact potential measurement (CPM). The appeal of this method is obvious, in that it is fast, inexpensive and simple to use. More than one commercial system is available for this measurement. Given the importance of plasma-charging damage in advanced VLSI manufacturing, the use of this method is spreading quickly. However, the data presented in this paper shows that this method does not always work. The SPM method produces a voltage map that does not always correlate with damage. Since a highly nonuniform or high value SPM map does not imply damage, nor does a uniform and low value map imply no damage, it cannot be used as a damage monitor directly. Until it is understood how and where the residual charges are created, the relation between SPM and plasma damage cannot be established. Although we provide a possible explanation for the residual charge distribution for a specific case, it cannot be generalized to all situations.