Temperature cycling and control system for photosensitive materials processing

Abstract

A temperature processing module and control system is presented for the thermal cycling of substrates such as semiconductor wafers and/or quartz photomasks. The module consists of a multizone etched foil heater adhered to the surface of a fluid heat exchanger. The heat exchanger is designed with aluminum foam that enables an angularly uniform temperature distribution on the heat exchanger surface as heat is transferred to it from the fluid. A temperature control algorithm is employed to manipulate the multizone surface heater to compensate for wafer temperature nonuniformities during the thermal cycle. The performance specifications for the thermal technology are: 30 s ramp-up time, 35 s ramp-down time, 3.5 °C peak nonuniformity during ramp up, 1 °C steady-state nonuniformity, and 3 °C peak nonuniformity during ramp down for a 200 mm wafer. The control results are achieved at the expense of significant energy expenditure. The total energy for the thermal cycle exceeded 10 kW compared to a theoretical minimum of a few hundred watts for 200 or 300 mm wafers. The axial temperature gradients in the module plate also induce thermal stresses that lead to a transient mechanical deformation of the heat exchanger that can be as large as 15 mil (380 μm) during the ramp up. We conclude that the proposed technology is more appropriate for operations with low throughput applications, such as photomask or large substrate processing, that benefit from thermal cycling.