| Summary: | 碩士 === 國立交通大學 === 工學院碩士在職專班半導體材料與製程設備組 === 98 === The advancement of the computer science and technology has resulted in an increasing demand for memory chips such as dynamic random access memory (DRAM) and flash read-only memory (Flash-ROM) chips, etc. Manufacturers aim to develop chips that have maximum possible memory capacity with minimum chip area while simultaneously reducing the cost. With reference to Moore’s law, many methods can be used to improve IC circuit image resolution; however, the most effective method is to use the increasingly shorter wavelengths, which require weaker light source. By extending exposure time will allow sufficient energy to pass through photoresist, thus enabling the photoacid reaction to proceed; however, this will result in heavy losses, which can produce and expose stability. Hence a more feasible solution by the usage of chemically amplified photoresist (CAPR) process is created. The CAPR process has been said to obtain the energy of the photoresist and can be divided into exposed and baked components. Bake heat-conduction by wafer and hot plate contact control uniformity is unlike light, which is perfect and correct. In addition, contact issues on pre-bake (PB), post-exposure bake (PEB) and direct influence uniformity of the photochemical reaction within CAPR can usually cause yield loss on half of the wafer. Method to guarantee the performance baked by CAPR is an extremely important subject in the semi-conductor manufacturing at the moment.
Generally speaking, the main function of PEB is to support the energy of CAPR H+ continuous catalysis, which is the most direct and important influence on critical dimension (CD). The experimental result has found that regardless of the PB of 248 nm or 193 nm, PB influence is still greater than PEB, thus PB has proven to be more important than PEB. The finding of PB contrary to the direction of PEB impact on CD will also be conducted. For example, if DUV photoresist wafer is 0.5 mm on both PB and PEB plate gap, PB will increase line distance by 94~340Å while PEB will reduce line distance by 61~109Å. Although I-line has little influence on some CDs, the relatively loose specification will not consider the change in CD. We will utilize software to set up a simple and limited element model in three-dimension. The wafer surface temperature predicted by the model and actual T-Map instrument data difference examined by quantity is less than ±2℃. Wafer and instantaneous plate-plate contact temperature drop ΔT, actual plate temperature drop ΔT and ΔT data difference are predicted to reach below ±0.2℃. Impacts will be seen in CD temperature, 248 nm photoresist at PB 0.34 nm/℃, PEB –0.21 nm/℃ in addition to 193 nm photoresist at PB 1.23 nm/℃ and PEB –0.39 nm/℃. The model used to predict CD wafer and temperature to all gaps of contact experiment has proved to possess extreme reliability.
In conclusion, PB/PEB was found capable in representing ongoing photoresist bake plate, which uses drop temperature ΔT parameter in addition to the direct relationship with the one with verified ΔT and CD. This model can be used to assist in the prediction of the standing range for new products or new process conditions.
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