Prediction of residual clamping force for Coulomb type and Johnsen–Rahbek type of bipolar electrostatic chucks

Abstract

As a key component in semiconductor manufacturing equipment, electrostatic chuck is conventionally divided into Coulomb type and J–R type depending on the generating mechanism of clamping force. After supply voltage is cut off, residual clamping force usually remains and becomes a serious issue for production efficiency and process reliability. Hence, it is significant to propose a general prediction model and reveal changing laws of residual force with time for both types. This paper establishes an equivalent circuit model for a bipolar electrostatic chuck containing distributed embosses on dielectric layer surface, and deduces a unified form of mathematical expression describing decaying force, which can cover the two types. The obtained equations can also predict steady force in working state. Furthermore, an experimental method for measuring clamping force and de-clamping time is presented. The results indicate relative deviations tend to decrease as voltages rise. It is found that prediction precision for J–R type is lower than that for Coulomb type. Main reasons are explained and relevant mechanisms are discussed. Overall, the calculations coincide with the measurements within an acceptable error range. The comparisons suggest the theoretical model is effective for simulating the characteristics of residual clamping force for both types of electrostatic chucks.