Integrated Bake/Chill Module With In Situ Temperature Measurement for Photoresist Processing

Abstract

Thermal processing of photoresist are critical steps in the microlithography sequence. The postexpose bake (PEB) steps for current DUV chemically amplified resists is especially sensitive to temperature variations. The problem is complicated with increasing wafer size and decreasing feature size. Conventional thermal systems are no longer able to meet these stringent requirements. The reason is that the large thermal mass of conventional hot plates prevents rapid movements in substrate temperature to compensate for real-time errors during transients. The implementation of advanced control systems with conventional technology cannot overcome the inherent operating limitation. An integrated bake/chill module with in situ temperature measurement capability has been developed for the baking of 300-mm silicon wafers. The system provides in situ sensing of the substrate temperature. Real-time closed-loop control of the substrate temperature is thus possible as oppose to conventional open-loop control of the substrate temperature. Experimental results are provided to demonstrate a complete thermal cycle.Index Terms-300-mm wafer processing, in situ temperature measurement, lithography, photoresist processing.

Modeling and Real-Time Control of Multizone Thermal Processing System for Photoresist Processing

“…It can be seen that the agreement between of the wafer temperatures from simulation and experimental results is excellent, thereby verifying the effectiveness of the proposed 15,17 for temperature measurement. The wafer is dropped onto the bake plate by aligning the major flat surface of the wafer with the proximity pins.…”

“…The experimental setup for the baking of 200 mm wafer is shown in Figure . Resistance temperature detectors (RTDs) are attached to the wafer , for temperature measurement. The wafer is dropped onto the bake plate by aligning the major flat surface of the wafer with the proximity pins.…”

A lamp thermoelectricity based integrated bake/chill system for photoresist processing

“…Efforts in addressing some of these issues have been ongoing by our collaborators and us [14][15][16][17][18]. A fluid-heatexchanger based thermal cycling module was developed earlier [14,15].…”

“…In addition, all of the above approaches lack the capability to conduct real-time temperature control on the substrate. A notable exception is our recent work [18] featuring a thermal cycling module integrated with in situ measurement of substrate temperature.…”

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

“…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. Tay et al [13,18] developed an integrated bake/chill module with in situ temperature measurement capability for the baking of 300 mm silicon wafers, which gives better control over the substrate temperature. Three dimensional numerical simulation studies and experimental verification on a combination bake-chill station were done by Narasimhan et al [19] and Narasimhan and Ramanan [9], addressing the thermal agility capability of disc heaters to reach and maintain the wafer at different T SET values (for triggering various combinations of photo-resists on the wafer surface) and bring the temperature back to clean room temperature (by chilling/cooling process) within the prescribed bakechill cycle time of 150 s. Temperature uniformity of the heater surface was addressed only marginally.…”