| AVS 54th International Symposium | |
| Thin Film | Thursday Sessions |
| Session TF-ThP |
| Session: | Aspects of Thin Films Poster Session |
| Presenter: | F.W. DelRio, University of California Berkeley |
| Authors: | F.W. DelRio, University of California Berkeley J. Lai, University of California Berkeley T.-J. King Liu, University of California Berkeley R. Maboudian, University of California Berkeley |
| Correspondent: | Click to Email |
In the manufacture of very large scale integrated circuits and microelectromechanical systems, polycrystalline silicon (polysilicon) thin films are typically formed directly by low-pressure chemical vapor deposition at temperatures above 600 °C, using silane as the precursor gas. Such a high process temperature makes this approach unsuitable for formation of polysilicon films on low-cost glass substrates and on substrates with completed CMOS integrated circuits. To lower the thermal budget, aluminum-induced crystallization (AIC) can be used to crystallize an amorphous silicon (a-Si) film deposited at low temperature. The formation of polysilicon by AIC of non-hydrogenated a-Si relies heavily on the layer exchange of the adjacent Si and Al films. Several factors affect the exchange of the Al and Si layers, and consequently, have an impact on the characteristics of the polysilicon film. In this paper, we study the effect of silicon doping on AIC of non-hydrogenated a-Si. In particular, Al-2%Si is examined, which is commonly used in microelectronics to prevent junction spiking, hillocks, and electromigration. A series of Al-2%Si/a-Si samples are prepared in a sputtering system with multiple process chambers and annealed in vacuum at temperatures in the range of 250 to 375 °C. The silicon doping is found to enhance the crystallization process, thereby reducing the initial crystallization temperature by ~50 °C. The enhancement is attributed to the presence of Si precipitates in the Al-2%Si film, which act as nucleation sites for Si grain growth. As with the Al/a-Si system, adjacent Al-2%Si and a-Si films undergo a layer exchange during isothermal annealing, resulting in a continuous polycrystalline silicon film with good physical and electrical properties. The observed decrease in the Si2p binding energy is consistent with p-type doping of the Si layer, attributed to the presence of Al in the crystallized film. Assuming an Arrhenius-type behavior for the crystallization, the activation energy for the process is found to be 0.97±0.09 eV. This value is in good agreement with the activation energy for Si diffusion in evaporated Al films, indicating that the crystallization is a diffusion-limited process.