Position and Orientation Control of Si Thin-Film Crystal Grain Using Nano-Imprint Technology

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This research work was carried out aiming at developing a innovative technology that can control the position and crystal orientation of Si thin-film grains on an amorphous substrate. The followings summarize this work.(1) We have developed a method to enhance crystal nucleation at desired position of amorphous silicon by transferring very small amount of metal form a tip array, which was prepared by anisotropic etching of single crystal silicon covered with a metal film, to nano-meter sized area at the surface of amorphous silicon film. The chemistry involved is the metal induced crystallization of silicon. The crystal enhanced crystal nucleation is observed at crystallization temperatures as low as 450 degree C. Ni was found to be most effective metal species for this phenomenon. Analysis of crystal orientation using electron backscattering pattern analysis has revealed that the crystal orientation of thus prepared crystal grains are (111) orientation.(2) Melting and recrystallizatio … More n of thus prepared silicon film by irradiating an excimer laser light pulse have been found to result in the growth of silicon grains whose diameter is as large as 3 micrometers owing to the grain growth from the crystal nucleus formed by the above mentioned metal induced crystallization. The grain size was found to be increased by reducing the reflection of the laser light by forming an antireflective coating of silicon dioxide film.(3) By forming an array of pit at the surface of the amorphous substrate before deposition of amorphous silicon, the silicon film was found to start recrysatallization upon irradiation of excimer laser annealing. As the result, an array of silicon grains having the diameter of about 2 micrometers are formed.(4) By combining the grain positioning using the pit formation at the substrate surface and the preferred orientation of the metal induced lateral crystallization of amorphous silicon, it is able to prepare silicon crystal grains whose position and orientation are controlled.(5) The filtering effect of lateral crystal orientation appears when the amorphous silicon film was patterned prior to the metal induced lateral crystallization. This effect was found to be effective to further improve the crystalline quality of silicon grains. Less