In Temperature Preparation Of Polycrystalline Silicon Thin Film And Related Theoretical Issues

The wide use of solar cell exhibits important role to solve the resource crisis and environmental crisis. There exists a huge contradiction between the production and needs in the high developing period of our country. The rich Solar energy and huge market give a very good opportunity to solar cell.The development of solar cells is showing a tendency to improve efficiency and reduce cost. The material price, pollution and cell efficiency were analyzed. Polycrystalline silicon thin film possesses the excellences of both crystalline silicon and amorphous thin film silicon. It not only is compatible with the existing solar cell technology but also promise cheap and excellent material for solar cell. The fabricating procession was divided into three kinds: low temperature, middle temperature and high temperatures according to the process temperature. Because the glass material has good transmission, suitable soft point, cheap, aesthetic and integrated with building easily, middle temperature procession was considered a suitable direction. Fabricating polycrystalline silicon thin films with large grain size is the key technique to increase cell efficiency. To achieve this aim, polycrystalline silicon thin films at middle temperature were focused in this thesis.A better parameters to fabricating polycrystalline silicon thin films at middle temperature by conventional furnace annealing were studied. Different annealing temperature and time were found to be connected in 550°C-1000°C. The high annealing temperature was corresponding short time, the low annealing temperature was corresponding long time in the procession of getting the same crystalline effect. It was found that there existed a series of critical point in the procession, for example, annealed at 940℃for 1h, annealed at 850℃for 3h, et. al. The crystalline effect was dependent on the deposit condition too.The performance of annealing procession by rapid thermal annealing was investigated, annealing temperature and time were connected too. There existed a series of critical point in the procession, for example, annealed at 850℃for 5 min, annealed at 750℃for 8min, et. al. and there exists a start crystalline temperature point between 700℃and 750℃, it is difficult to be crystallized beyond the temperature, however, it is easy to be crystallized above the temperature.It was found that the poly-silicon thin film fabricated by FA were roughness and requires very long annealing times compared with RTA. The similar size of poly-silicon thin film so is obtain; the thin film made by pulsed rapid thermal method is smoothly and perfect structure. The effect of deposit temperature was investigated. The amorphous silicon thin film deposited at 30℃, 350℃and 450℃, annealed at same condition, it was found that the poly-silicon deposited at 350℃had bigger grain size that those at other temperatures. This was not coincident with the old idea: the lower depositing temperature, the bigger grain size of the poly-silicon.The decay of amorphous silicon deposited by PECVD was studied. The decay was found in nature, so the delay in the procession should be avoided. The match of polycrystalline silicon thin films and glass substrate was studied too. It was found that there was separation between silicon thin films and glass substrate, and choose glass with suitable soft point could avoid the separation phenomena.Draw a conclusion, a better parameters was found in fabrication of polycrystalline silicon thin film on glass at middle temperature: amorphous silicon film to be annealed were deposited at a certain temperature on glass substrate and fused quartz by plasma enhanced chemical vapor deposition (PECVD) method, using SiH₄, H₂ mixture. The gas flow ratios was 2%, the chamber pressure 1 Torr, substrate temperatures 350℃and the radio-frequency power 50W. Then the a-Si thin films are crystallized in a rapid thermal processor, the time-temperature budget of the process is 850℃-5min.Finally, it was found that the critical point phenomena was shown between polycrystalline silicon size and the annealing temperature and time in the solid phase crystallize procession. The phenomena was investigated at the angle of the micro quantum state, according to which the principle of equal energy driving was put up and the rapid thermal procession was calculated, the result was corresponding to the experiment.