Basic study of selective deposition by using excimer laser

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Spatially selective deposition of thin films is one of key issues for future VLSI process technology. Laser-induced chemical vapor deposition (laser CVD) technique enables us to grow thin films on the specific area irradiated with laser light passing through a metal mask. The purpose of the present project is to develop direct pattern projection CVD technique by using an ArF excimer laser. In the experiment the laser beam was projected onto a quartz substrate through a free-standing metal mask with 100 <micro> m stripe pattern. The quartz substrate is exposed to a low pressure disilane ( <Si_2> <H_6> ) gas. Photochemical decomposition of adsorbed <Si_2> <H_6> occurs on the irradiated quartz surface. Hence initial silicon nuclei are produced on the surface and are strongly excited by incident photons. This results in rapid growth of the nuclei and thin layer deposition proceeds on the irradiated region. Consequently very clear pattern projection of silicon film is achieved on a quartz substrate. The spatial resolution of the pattern projection CVD is estimated to be better than 3 <micro> m by calculating the interference fringes measured as thickness fluctuations of the deposited silicon film. This newly developed CVD technique is based on purely photochemical process without involving any significant contribution of thermal reaction to deposition. This is the first experimental success in silicon selective deposition by photochemical process.