Study On A PVDF-Based Pressure Detection Method For Immersion Flow Field

Immersion lithography utilizes the filling of highly refractive liquid between the last projection lens and silicon wafer to improve system resolution, allowing the minimum linewidth of optical lithography to be less than 45nm. Because immersion lithography can be achieved by minor modification of the traditional lithography equipment and process, it is time and cost effective, and becomes one of the most advanced integrate circuit manufacturing methods. During the working process of immersion lithography, the pressure fluctuation of immersion flow field is inevitable due to the stepping motion of silicon wafer and vertical position adjustment when focusing, which results in fluctuating stresses on the lower surface of projection lens, leading to the lens positional deviation, deformation and even vibration, and then seriously affecting the exposure precision. Therefore, the research on the dynamic pressure of immersion flow field is significantly important to the optimization of the immersion system and working parameters.According to the characteristics of the immersion flow field, this dissertation presents a PVDF film-based dynamic pressure detection method. Taking advantage of the properties of PVDF film, namely high sensitivity, light in weight, thin and flexible, a low-cost PVDF pressure sensor has been designed and fabricated, which can be easily installed and has little disturbance to the immersion flow field. Moreover, it avoids the problems of big sizes and measuring ranges with common pressure sensors. Detailed work is described as follows:1. An aluminum electrode etching method of the PVDF film is proposed according to the basic principle of lithography process. Then the single-spot and multiple-spot PVDF pressure sensors have been fabricated by using this method.2. A signal processing circuit for the PVDF sensor has been designed, which converts the electric charge to voltage between -5V～5V and eliminates the interference noises.3. A series of experiments have been carried out to study the properties of the PVDF pressure sensor and signal processing circuit. The results indicate that the linearity error and sensitivity of pressure sensor is±2.3% and 1.32mv/Pa, respectively. The measuring circuit almost has no zero-drift, and has a lower cut-off frequency of 0.88Hz and flat amplitude-frequency characteristic between 2-80Hz. 4. The test-bed was set up to measure the dynamic pressure of lithography immersion flow field by using PVDF pressure sensor. Pressure fluctuation of the flow field between last projection lens and silicon wafer was successfully detected. Experiment results indicate that the pressure fluctuation frequency increases with the increase of the flow field thickness. The pressure fluctuation under double-port flow injection is greater than that under single-port flow injection. Besides, the scanning motion of silicon wafer significantly increases the amplitude of pressure fluctuation.