Thermal management in ion implantation

Thermal management is defined as the maintenance of a necessary balance between heat energy delivered to the workpieces, fixtures and chamber walls by the incident ion beam and heat removal from these by a combination of physically inevitable (passive) and designed-in (active) cooling mechanisms. This balance must be such that the surface temperature of the workpieces never exceed a specified temperature. This paper discusses the problem as studied on the Westinghouse ion implantation facility. Most of the heat to the chamber and fixtures can be removed by simple water or freon cooling. However, most of the workpieces can only be gripped gently in continuously rotating fixtures. The thermal contact resistance in vacuum is a function of contact pressure and the details of the microdimensional details of the contact boundary layer. With contact pressures of a few hundred psi, interface conductances of 3.5 W/cm/sup 2/-0C can be achieved. Unloaded clean contacts in vacuum can have conductances as low as 0.1W/cm/sup 2/-0C. The heat transfer across moving bearings in vacuum is of particular interest. It can be measured while a workpiece is being implanted. The authors compare the measured heat transfer in the bearings to estimates based on the literature