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Silicon Coating Speed Calibrating
We have tentatively tried to operate a RF sputtering machine[1] to deposit a thin layer of silicon onto the surface of an optical window made of BK7 glass. This machine generates a powerful (>100 Watt) RF electric field to ionize the Argon gas in the chamber. This ionized argon gas will then bombard the sputtering targets (silicon in this case), and the sputtered atoms from the targets will in turn form the deposition layer on the substrate.
The deposition rate (how fast does the layer grow, usually in nm/s) depends not only on the input RF power, but is also related to the distance between the sputtering targets and the substrate sample as well as the surface area of the sample. This deposition rate needs to be measured as accurate as possible to ensure correct layer thickness.
We took an optical method approach by observing the change in transmission spectrum for different deposition time (which should translate to different thickness if a constant deposition rate is assumed). We deposited a few different thin-film samples, with deposition time of 6000s, 8000s, 10000s, 12000s. The transmission spectrum of each sample is measured with a spectrophotometers. From the measured spectra we roughly estimated a deposition rate of 0.034nm/s (2.05nm/min).
