Auger Electron Spectroscopy of Cleanup‐Related Contamination on Silicon Surfaces

Abstract

Auger electron spectroscopy has been used to evaluate the chemical state of silicon (111) surfaces cleaned by various liquid reagents, ion sputtering, and plasma treatment. The two most common impurities observed were carbon and oxygen. Results indicated that liquid reagent cleaning produced surfaces which were heavily contaminated with carbon, and that when oxidizing reagents were used, carbon contamination could be kept to a minimum. Sputtering was toured to be an unsatisfactory method of cleaning because slices became activated after sputtering and adsorbed impurities from the atmosphere when removed from the vacuum system. Plasma treatment was the most effective of the three types of cleanups used, producing surfaces with the lowest carbon concentrations. One exception was CF4 plasma which was shown to deposit carbon on the surface.A large number of processes are used by the semiconductor industry for the cleaning of silicon prior to process steps such as oxidation, diffusion, and metal deposition. The chemical state of the surface after cleanup has not been systematically investigated, resuiting in wasteful consumption of chemicals and the use of "overkill" in slice cleanup. We have investigated the effect of eight liquid reagent cleaning sequences, six plasma cleanups, argon sputtering, and deionized water rinsing on silicon surfaces.Auger electron spectroscopy (AES) has been shown to be a useful and highly sensitive tool for the study of etched silicon (i) and chemically cleaned germanium surfaces (2), particularly for the determination of the effects of carbon contamination (3), and has been chosen for this study. The principles of AES have been described in the literature (4-6).In this work carbon was found to be one of the major contaminants, along with oxygen, on chemically cleaned silicon surfaces and the effectiveness of various chemicals, plasma, and sputtering for the removal of carbon have been examined. ExperimentalThe samples used were 0.76 mm thick mechanically polished 10 ohm-cm boron-doped silicon (111) slices. The slices were cut from the same boule in order to minimize the effect of the bulk material on the surface contamination. Strips from the slices were then subjected to liquid cleaning, argon ion bombardment, or plasma cleaning All reagents used were (ACS) Low Mobile Ion Grade and the deionized water used for rinsing had a resistivity of 18 megohms.Details of the process sequences used to prepare the samples are given in Tables I (liquid reagent), II (argon ion sputter), and III (plasma).Argon ion bombardment was performed with a Varian ion gun (Model 981-1045) at 5 X 10 -5 Torr argon (Matheson, Research Grade) pressure, which produced a 12 mm diameter ion beam at 600 eV energy. Samples could be heated inside the Varian Cylindrical Mirror Analyzer system (Model 981-2607) by conduction from radlatively heated stainless steel blocks on which they were mounted for analysis. Chromel-Alumel thermocouples, spot welded on stainless steel retaining strips used to press the samples to

Etch rates for micromachining processing

“…Notes: Piranha has been in use for wafer cleaning for decades [l], [39], [40]. The term refers to a hot solution of HzSO4 and HzOz mixed in any ratio [39], [40].…”

“…The term refers to a hot solution of HzSO4 and HzOz mixed in any ratio [39], [40]. In lower ratios of HzSO4 to HzO2 (e.g., 5:1), the solution is noticeably self-heating (no external heat source is needed).…”

Laboratory intercomparison of marine particulate digestions including Piranha: a novel chemical method for dissolution of polyethersulfone filters

“…Piranha solution-typically a 3:1 v/v mixture of concentrated sulfuric acid and hydrogen peroxide-is a strong oxidizing agent typically used to clean organics from substrates such as silicon wafers and laboratory glassware (Yang et al 1975). We describe a procedure that utilizes Piranha solution to dissolve the PES matrix.…”

Preparation and characterization of Si sheets by renewed SSP technique

“…From Fig. 6, it can be seen that the upper surface has been slightly oxidized, because there exists a peak at 76 eV, meanwhile, at the lower energy side (o76 eV), a set of weak peaks appear which is different from the standard pattern of pure silicon sample; moreover, the intensity of KLL peak of O at 503 eV increases remarkably; all these are the characteristics of SiO 2 [13]. Besides, the strong LMM peak of Si at 92 eV, the KLL peak of C at 272 eV, the KLL peak of N at 379 eV and the KLL peak of O at 503 eV are also found in all the spectra measured at the three test spots, which strongly suggests that there are C, N and O impurities in the as-prepared SSP ribbons.…”