Comparison and Reproducibility of H-Passivation of Si(100) with HF in Methanol, Ethanol, Isopropanol and Water by IBA, T
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SiO 2 + HF => Si-F
(1)
Substitution ofF by H
Si-F + HF = Si-H
(2)
lSupported by SEMATECH under contract # 740 86276. Supported by NSF grant # DMR-9200055 for Research Education for Undergraduate (REU).
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Mat. Res. Soc. Symp. Proc. Vol. 477 01997 Materials Research Society
H-passivated surfaces are stable at low temperatures and hydrogen can be desorbed between 200'C and 600'C [11]. Treatment of Si surfaces in HF/alcohol solutions is more effective in producing H-terminated surfaces than HF/water solutions [12]. HF/water solutions tend to be more oxidizing and lead to oxygen adsorption. Light alcohols have more affinity for Si surfaces and help in forming H-terminated surfaces due to their ease of evaporation [13]. The rate of evaporation decreases with the increase in the molecular weight of alcohol used [14]. Alcohols can avoid the haze seen during aqueous HF processing [15]. In this work, a cleaning sequence typically referred to as "RCA-type cleaning" removes Three different HF:alcohol solutions, impurities from Si(100) prior to H-passivation. HF/methanol, HF/ethanol and HF/isopropanol are used to passivate Si(100) and compared using as a reference Si(100) passivated by a standard aqueous HF: solution (1:98 parts of HF: H 2 0).. Passivated Si(100) is then analyzed by Ion Beam Analysis (IBA) to determine the absolute surface coverage of C, 0 and H. Accurate surface coverage of C and 0 is measured with a high signal to noise (S/N) ratio by using ion channeling in combination with nuclear resonance at 3.05 MeV for 0 and 4.265 MeV for C. Ion channeling improves the S/N by a factor 30, the 3.05 MeV resonance improves it further by a factor 10 for 0 and the 4.265 MeV resonance by a factor 128 for C [16]. H is measured by elastic recoil detection (ERD), also forward recoil elastic spectrometry (FRES) using a calibration standard of known H concentration [16]. Chemical species present on the surface are identified by Fourier Transform Infrared Spectroscopy (FTIR) in the Attenuated Total Reflection (ATR) mode [ 17]. The root-mean -square (rms) surface roughness is measured by Tapping Mode Atomic Force Microscope (TMAFM) [18]. Seven experiments (Table I) are conducted to test the reproducibility of the measurement of H, C and 0 coverages and to compare the different HF solutions studied. EXPERIMENTAL PROCEDURE Samples are prepared in a chemical laminar hood, constructed of polypropylene, in a class 100 clean room located in the Combined Ion and Molecular beam Deposition (CIMD) laboratory. The CIMD laboratory clean-room itself is located inside the Ion Beam Analysis for Materials facility (IBM) at Arizona State University, Tempe, AZ which minimizes contamination of samples during transfer. The 100 mm. diameter B-doped Si(100) wafers with a resistivity of 10 - 14 ficm were donated by Motorola Inc. [19]. The ppb grade chemicals are classified as "Class 10" [20].
Table I. EXPERIMENTAL GOALS Expt. # ASI AS2 AS3 AS5 AS6 AS7 AS9
Goal of the experiment Comparison of three different HF:alcohol solutions by IBA Compar
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