Improvement Of LTPS Process By Monitoring Minority Carrier Life Time

With the development of science and technology as well as the increasing requirement of visual enjoyment, AMOLED is expected to be a brilliant star in the display industry of next generation for its fast response, high fresh rates, less power consumption, higher PPI, super high color gamut and contrast. In this study, the relations between minority carrier lifetime of low temperature polycrystalline silicon(LTPS) film extensively employed in AMOLED display, TFT performance, grain size of polycrystalline silicon, excimer laser crystallization(ELC) process and AMOLED device have been investigated based on the microwave photoconductivity decay method. Consequently, a new technique route has been developed which is low-cost, environment-friendly and capable of getting a quick feedback on production issues.(1) The minority carrier lifetime measurement system was analyzed for LTPS film according to the statistical principle. Its feasibility, existing issues and solutions compared with other characterization methods were elucidated theoretically.(2) The corresponding experiment scheme was designed from the theoretical calculation analysis results. LTPS film was prepared using ELC method under different process conditions. Then the minority carrier lifetime, grain size, carrier mobility, threshold voltage and subthreshold swing of TFT made from polycrystalline silicon film were studied. Moreover, the impacts of minority carrier lifetime under different conditions on the respective semiconductor parameters were analyzed. As for the characterization of the sample phase, microscopic morphology, grain size and its distribution, herein AFM, SEM and semiconductor analyzer were employed.(3) This study indicates that the minority carrier lifetime analysis can be effectively used to characterize the uniformity of LTPS TFT performance and AMOLED device and further direct and control the ELC process. After the discussion of the influence of grain size and AFM results under distinct conditions, the optimum ELC process condition falls in the laser energy density range of 460-500 mJ/cm2 while the microwave reflection signal is stabilized at around 500 mV with the minimum fluctuation, which finally provides experimental data and theoretical basis for the feedback and correction system research on the industrialized, full automatic mass production.