Improved cooling on the Varian VIISta series ion implanters

Increased beam power densities on the VIISta series ion implanters allow for increased throughput, while maintaining the advantages of single wafer processing. In order to absorb elevated beam power while maintaining acceptable wafer temperatures, a new electrostatic platen was developed. The new platen utilizes a gas, introduced between the platen surface and the wafer, as a cooling medium. Control of this gas is critical to balance such important factors as dose uniformity, photoresist temperature, contamination, and wafer security. In order to achieve necessary cooling rates, the gas must be delivered to the platen-wafer interface as quickly as possible after wafer loading, to allow for the required pressure buildup and thermal conductivity through the gas. The new platen has microscopic surface structures that maximize heat conductance in several ways. High surface area increases the effective area over which heat can be absorbed. At the same time, the shape of the microstructure allows rapid conductance of the gas, and hence rapid gas pressure buildup. The surface coating itself is highly efficient at heat transfer, and increases beam power dissipation capability even without the presence of a cooling gas. Multiple factors were finely balanced to produce the most effective electrostatic platen for the next generation of ion implantation tools