Study on Thermal Contact Conductance in Vacuum

—Evaluation Result under Low Contact Pressure Condition in Free Molecular Flow Region—

Abstract

In most semiconductor manufacturing processes, the wafer is processed in vacuum. It is important to achieve optimal wafer temperature control during fabrication to ensure high precision. Therefore, for optimal thermal design, it is necessary to analyze the characteristics of thermal contact conductance in vacuum. In this study, the characteristics of low contact pressure region (less than 50 kPa) were evaluated with SUS304 stainless steel to simulate typical wafer chucking conditions, such as electrostatic chucks. The thermal contact conductance of direct-contact and gas components were examined separately. The results showed that, except for the low contact pressure region, the thermal contact conductance of the direct-contact component increased linearly with the contact pressure. It is assumed that the direct-contact component was affected by the asperities of the contact surface, particularly in the low contact pressure region. Conversely, in vacuum under the free molecular flow region, the thermal contact conductance of the gas component was not affected by the contact pressure. It is assumed from the results that the robustness of the thermal contact conductance in vacuum can be enhanced by increasing the gas pressure within the free molecular flow region.