Experimental Study On Laser Bending Of Thin Silicon Chip

As the development of semiconductor industry and MEMS, the non-flat silicon-girder and silicon-cantilever have been demanded, meanwhile many micro-process also need curving brittle materials (such as ceramic and glass) so as to fabricate micro-actuator and micro-sensor etc. But the conventional process with external force, higher temperature condition during process and contacted loads is easy inducing the broken of brittle materials as well as not easily applied in lab. However etching process not only wastes the material, but the chemical reagent used would also cause the environmental pollution. According to the problem referred, laser bending method of thin silicon chip using pulse Nd: YAG laser is carried out, the following work is done:(1) Experiment of silicon chip bending with millisecond pulse width Nd:YAG laser is done. The energy threshold of silicon bending is given. Meanwhile, the influence of pulse frequency and pulse width on the bending angle using the Nd: YAG long pulse laser is mainly investigated. The pulse duty cycle is used to present the influence of the energy's time distribution on effect of bending. In addition, the relations between numbers of scanning, width of sample and angles are studied.(2) Bending silicon surface properties such as the micro-structure and crystal phase are analyzed. The results indicate that the irradiated surface was distributed to three regions including ambient region, transition region and main irradiated region. Each region character is analyzed and summed up.(3) According to the given single-pulse energy(0.04J), scanning speed(100mm/min) and the dimension of silicon(20mm×l0mm×0.1mm) condition, the temperature simulation is applied to calculate the temperature distribution, and thus the characters of temperature were analyzed. The results of simulation demonstrate that during the process of silicon bending, temperature gradient mechanism (TGM) and buckling mechanism (BM) are co-existent, and the bending relies on appearance of brittle-ductile transformation temperature.(4) Aimed at slip line and stacking fault induced of silicon surface, the dislocation theory is used to analyze the reasons of causing dislocation and stacking fault during the process of bending and study the influence on the laser bending. The analyzed results indicate that the slip line is caused by the dislocation accumulation, and the stacking fault is the results of piled dislocation. Meanwhile influence of the dislocation density and dislocation moving speed on the process of laser bending is analyzed, the changing process of dislocation density and the deceased dislocation moving speed are considered to influence on the phenomena of max-angle degrees.The work of thesis has accomplished the max-bending been up to 30 degrees. So the research work could help to establish foundation of theory and experiment on application of laser bending in MEMS field.