Processing chemically amplified resists on advanced photomasks using a thermal array

An inverse heat transfer method to provide near-isothermal surface for disc heaters used in microlithography

“…The present problem can also be solved in a steady state domain for the following reasons. Although transient effects could affect the CD uniformity to an extent [11,12], the photo-chemistry and hence the CD accuracy is more sensitive only after the wafer reaches the amplification threshold of T SET [10]. Hence the 120 s baking process is done in two phases.…”

“…1(a)) of larger thermal mass [10,6]. This is true only when the natural convection effect from the top and side of the wafer substrate considered in [11][12][13] are eliminated. This can be done by providing a sealed container with proper size within which the baking is carried out.…”

“…Hence, the requirement of a cost-effective method from the semiconductor industry, to minimize the heater surface DT, while baking the wafer at a T SET led to a lot of research in this field in the past few years. For instance, Ho et al [12,16] proposed an optimal control scheme to maintain the steady state wafer surface temperature at the set-point temperature. Tan and Li [17] described a method for in situ estimation of the temperature sensor parameters, and proposed an algorithm for post-processing the sensor output to improve temperature measurement accuracy, to maintain stringent temperature conditions.…”

Integrated bake/chill system for across-wafer temperature uniformity control in photoresist processing

“…[3][4][5][6] Typically the temperature nonuniformity during transient can be as large as 9 and 0.7°C during steady-state. 4 Most of the reported improvements [7][8][9][10][11] are the simulation results involving a preset heater temperature to achieve uniform wafer temperature. Schaper et al, 7 ElAwady et al, 12 and Tiffany and Cohen 2 reported improvements with temperature nonuniformity during the thermal cycle between 3 and 3.5°C.…”

“…4 Most of the reported improvements [7][8][9][10][11] are the simulation results involving a preset heater temperature to achieve uniform wafer temperature. Schaper et al, 7 ElAwady et al, 12 and Tiffany and Cohen 2 reported improvements with temperature nonuniformity during the thermal cycle between 3 and 3.5°C. In most of these systems, the difficulties in achieving uniform temperature control are primarily due to the hardware systems, most of these are of large thermal mass, and/or involving separate bake/chill units with limited number of heating zones.…”