Growth and Stress Characterization of LPCVD SiC Films Deposited on Bare, Carbonized and Oxidized Si(001) Substrates
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away during device processing to obtain free-standing membranes. Moreover, the final stress of these films can be controlled through deposition parameters. This is of crucial importance for micromachining purposes and for membranes fabrication. Concerning single-crystalline 3C-SiC, the large lattice mismatch between SiC and Si is better accommodated when a buffer layer is prepared on the Si substrate surface by a carbonization process [1]. The quality of the buffer layer is a key parameter to the growth of low defect single-crystalline films [2]. Ultra high vacuum-MBE is the most appropriate method to grow the first carbonized layer due to both better process control and the very clean growth ambient [3,4]. On the other hand, LPCVD provides a convenient technique to achieve rapid growth of the SiC film [6] while keeping a low defect density. In this report we describe the influence of different substrates (bare, oxidized Si and carbonized Si) and deposition conditions on the crystalline quality and mode of growth of 3CSiC films grown in a simple LPCVD reactor. The early stages of nucleation and growth and the final stress of the films are also investigated. The best LPCVD-SiC film quality was achieved when depositing on smooth single-crystalline carbonized substrates. EXPERIMENTAL PROCEDURE The experimental setup used for the low pressure chemical vapor deposition (LPCVD) of SiC films is a hot-wall horizontal reactor heated by a 4-zone conventional furnace. An 173 Mat. Res. Soc. Symp. Proc. Vol. 555 01999 Materials Research Society
ultimate base pressure of 10i3 Torr is achieved with a mechanical booster pump followed by a Rotary pump. As our pumping system is not efficient to achieve low enough background pressure compared to UHVCVD systems, special attention has been paid to the cleanliness of the reactor and gas lines. We have used a leak-tight system design together with a high hydrogen flow during the high temperature pre-bake. The loading of the wafers is performed at 500°C with a constant purge of N2. After wafer loading the system is evacuated to its minimum pressure and the pre-bake removes the native oxide and cleans the reactor from residual oxygen or moisture. The deposition proceeds by pyrolisis of tetramethylsilane, Si(CH3) 4, an organometallic molecule, with a relatively high vapour pressure and a low decomposition temperature. To preclude any free C codeposition a high flow of hydrogen is used as a carrier gas. A typical LPCVD process routine started with a surface cleaning which included a degrease step, an oxidizing step with a mixture of H 2 0 2 and H 2 S0 4 and the oxide removal by HF. After rinsing the wafers in deionized water and drying, they were introduced in the LPCVD reactor at 5000C. Temperature was then raised up to about 1100IC. In-situ etching was performed with an H2 flow of 4 slm. The total pressure inside the reactor tube was kept at 30 torr. The etch process was done while increasing the temperature to the growth temperature, normally 1170 0C, for 5 min. Then, the total pressure
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