Schematic of the outgassing measurement experimental apparatus during a 400 °C bake showing the chamber, SRG, isolation valve, and pumps. For bakes at lower temperature, the first isolation valve, the ion pump, and the RGA were within the oven.
Representative rate-of-rise data at four room temperatures. These data were obtained using the SS1 stainless steel chamber, and correspond to outgassing rates between 1.4 × 10−13 and 5.5 × 10−13 Torr L s−1 cm−2 following a 150 °C bake (third in the series noted in Table I ). A least-square linear fit was used for each data set to calculate outgassing rates.
Outgassing rates for the bare stainless steel (SS1) chamber as a function of inverse room temperature, with each data set obtained following a bake at the temperature noted in the legend. The error bars for statistical and systematic errors are smaller than the data points for these data. The slope yields the temperature dependent activation energy as described in thetext.
Outgassing rates for the a-Si and the SS1:a-Si chambers as a function of inverse room temperature, with each data set obtained following a bake at the temperature noted in the legend. The low outgassing rate of the heat treated SS1 chamber (solid stars) was largely preserved following coating the chamber with a-Si and baking. The error bars for statistical and systematic error are comparable in size to the data points shown for these data.
Outgassing rates for the TiN-coated stainless steel chamber as a function of inverse room temperature, with each data set obtained following a bake at the temperature noted in the legend. The best outgassing rate for the SS1 bare stainless steel chamber is plotted for reference. Systematic and statistical errors, though small at larger outgassing rates, become significant at the lowest measured outgassing rates.
EDS and SEM data show coating composition and morphology for (a) bare stainless steel, showing expected composition and morphology, (b)a-Si on stainless steel, with a Si peak evident in conjunction with the steel substrate, and (c) TiN coating with approximately 1:1 atomic ratio of Ti and N, but obvious particulate matter and pores visible across the surface. Inset SEM images each show an120 × 80 μm area.
Outgassing rates for each chamber are plotted vs the Fourier number, . The straight line represents the calculated outgassing rate for the systems using Fick's law, disregarding surface effects. For the steel chambers, the transition from diffusion limited reduction in outgassing rate to recombination limited behavior occurs near = 1, with the outgassing rates vs in close agreement with Fick's law at low (see inset), and diverging from Fick's law toward recombination limited behavior at higher values. The a-Si chambers have outgassing rate largely independent of , suggesting that the surface effects of the system dominate the outgassing, and diffusion of hydrogen from the material during bakes is not significant. The steep slope of the TiN indicates either an excellent diffusion barrier or a slight pumping speed in the coating that increases with additional heat treatment. Note: data labeled SS2 is from previously published data (Ref. 2 ).
Uncoated chamber (SS1) bake history and corresponding outgassing rate at 20 °C.
Amorphous silicon coated (a-Si) chamber bake history and corresponding outgassing rates at 20 °C.
Chamber coated with amorphous silicon following heat treatment (SS1:a-Si) bake history and corresponding outgassing rate at 20 °C. The outgassing rate of SS1 prior to coating with a-Si was 1 × 10−13 Torr L s−1 cm−2.
Titanium nitride coated chamber (TiN) bake history and corresponding outgassing rate at 20 °C. Outgassing rates may be artificially low if there is any pump speed in the system, and the inhomogeneity found in the EDS analysis suggests the presence of some elemental Ti.
Coating thickness and RMS roughness values for bare steel, TiN coated and a-Si coated test samples.
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