Ex Situ and In Situ Methods for Complete Oxygen and Non-Carbidic Carbon Removal from (0001) SI 6H-SiC Surfaces
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Binding Energy (eV) Figure 1. XPS of C Is from (0001)Si 6H-SiC surface after: (a) 5 min. 10:1 HF dip, (b) after thermal annealing at 800°C, and (c) after annealing at 1200"C in UHV.[8] in a 10:1 HF dip (CMOS grade, J.T. Baker). Further cleaning of this surface was then investigated by immersion in other acid/base solutions or by reoxidizing the SiC surface using a UV/0 3 treatment followed by a wet chemical treatment. The UV/O 3 treatments described in this study employed a box in which was positioned a high intensity Hg lamp in close proximity to the SiC wafer. The details of this process have been described previously [15]. The wet chemistries examined included 10:1 HF, 10:1 buffered HF (7:1 NH 4 F:HF), 40% NH 4F, HCI:HF, and NH 3 OH:HF solutions, HNO 3, H2 SO 4, acetic, and lactic acid. Except where noted, after all wet chemical cleans the samples were rinsed in DI water (18 MQ) and blown dry with N2 (UHP). All wet chemicals were of CMOS grade purity (J.T. Baker). The in situ cleaning and the surface analyses of the samples subjected to ex situ and in situ cleaning were conducted in a unique ultra-high vacuum (UHV) system consisting of a 36 ft. long UHV transfer line to which were connected several surface analysis and thin film deposition units. The details of each and the transfer line have been described elsewhere [15]. Surfaces prepared in the above manner were then subsequently mounted to a molybdenum sample holder and loaded into the loadlock for subsequent analysis by AES, XPS, EELS, and LEED. XPS analysis was performed using the Al anode (hu = 1486.6 eV) at 20 mA and 10kV. AES spectra were obtained using a beam voltage of 3 keV and an emission current of 1 mA. LEED was performed using rear view optics, a beam voltage of approximately 100 eV, and an emission current of 1 mA. Calibration of the XPS binding energy scale was performed by measuring the position of the Au 4f7/ and shifting the spectra such that the peak position occurred at 83.98 eV. All sample temperatures quoted here were measured using an optical pyrometer and an emissivity of 0.5.
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Binding Energy (eV) Figure 2. XPS of 0 Is from (a) (OOO)si 6H-SiC and (b) Si (111) wafers after dipping in 10:1 LF for 5 min.[12] RESULTS Si and SiC wetting experiments. As previously mentioned, oxide removal from (0001) 6H-SiC surfaces using HF leaves a hydrophilic surface containing significant amounts of oxide surface (see Fig. 3a). To determine a wet chemistry which produces a more hydrophobic SiC surface, several (0001)si 6H-SiC wafers were dipped in HF, NH4F, NH 3OH, HCI, HNO 3, H 20 2, H 2SO 4 , acetic acid, and lactic acid and the wetting characteristics of these surfaces in these acids and bases and de-ionized water monitored visually. For comparison purposes, Si (111) and Si (100) wafers were also dipped simultaneously in each acid with the SiC wafer. All wafers (Si or SiC) were initially dipped in 10% HF to remove any native oxides fr
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