Improving wafer temperature uniformity for etch applications

Wafer temperature uniformity is one of the major factors affecting etch performance at elevated temperatures. Several factors influence temperature uniformity. In order to achieve the desired temperature uniformity on the surface of the wafer, it is essential to understand the thermal behavior of the various components of the metal etching system. Experimental data for this study was obtained by the De-coupled Plasma Source (DPSII) system, which is an etch process chamber that uses two independent RF power subsystems namely source RF and bias RF.

Knowledge of heat transfer between the wafer and the electrostatic chuck is essential for the design of thermal management of the DPSII system and for maintaining uniform wafer temperature. In this study, a comprehensive research was conducted on heat transfer in rarefied gases. The experimental data obtained from laboratory tests were compared to theoretical values in literature.

After determining the thermal characteristics of the system, a simplified two-dimensional axisymmetric thermal model of the High Temperature Cathode and DPSII chamber was developed using a commercially available finite element method (FEM) code in order to determine the factors that affect the temperature uniformity on the wafer. Simulation of temperature distribution in High Temperature Cathode chamber considers process and design parameters such as plasma load, heater power, chuck temperature, and backside helium. This thermal model involves heat transfer by conduction, convection, and radiation. Model results were validated experimentally by measuring the wafer temperature under various conditions. Necessary design changes were performed to improve wafer temperature distribution. This research was carried out in order to understand the role of each factor and how the factors are interconnected on the wafer temperature uniformity.