Surface Oxidation Study of Silicon-Doped GaAs Wafers by Ftir Spectroscopy
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Wet chemical cleaning processes can meet the rigorous demands on wafer smoothness and low metal surface contamination in advanced cleaning processes. Widely used wet cleaning procedures in the semiconductor industry are treatments based on the RCA cleaning sequences [1], containing an BF step for oxide removal, an alkaline NH4 OH/H 20 2 (SC1) wet chemical oxidation step and an acid HCI/H 20 2 (SC2) cleaning step. However there are some limitations of wet wafer cleaning processes, such like an incompatibility between wet wafer cleaning operation and process integration, and metallic contaminants plated on silicon surfaces from HF solutions [2]. Also these processes may induce various oxidation reactions on the surface of silicon-doped GaAs wafers [3]. The activation energy of such reactions are relatively low, so that they can proceed at room temperature. These reactions involve oxidation of GaAs, silicon, and oxygen diffusion at various reaction rate constants. Residues from wet cleaning processes must be removed in order to make sure that the Dry cleaning subsequent steps provide accurate electrical and mechanical performance. procedures followed by wet cleaning treatments could eliminate inherent disadvantages brought by wet cleaning processes. Widely used dry cleaning procedures are thermally enhanced, vapor phase, photochemically-enhanced, and plasma-enhanced treatments. Among these, plasma based processes can effectively remove layers of organic contaminant, residual oxide or metallic residue remaining on the wafer surfaces after wet chemical cleaning processes. Several attempts at plasma-enhanced cleaning have been reported [4][5][6]. In the past few years investigations of plasma cleaning techniques were mainly based on argon, ozone, oxygen, or hydrogen 75 Mat. Res. Soc. Symp. Proc. Vol. 448 ©1997 Materials Research Society
atmospheres. Most of the applications are focused on silicon wafers; howeve, few of them have been put into GaAs wafers. In this study, we will identify the products induced by fluorine containing plasma on the GaAs wafer surfaces using FTIR technique in order to understand if the applied cleaning methods could effectively remove oxides that possibly formed after HCi and NH 4OH cleaning. EXPERIMENT A surface study was conducted on 8 three-inch (100)-oriented GaAs wafers. Samples were provided by M/A-COM Microelectronic Division. These wafers were implanted with Si and annealed. Both sides of each wafer were optically flat surfaces. Surface preparation of each wafer is described in Table 1.
Table 1. Surface Preparation of 8 (100)-oriented GaAs Wafers Wafer #1 #2 #3 #4 #5 #6 #7 H8
Surface Preparation None NH4 OH clean HCI clean 45 sec. exposure to fluorine containing plasma 90 sec. exposure to fluorine containing plasma HCI clean and 45 sec. exposure to fluorine containing plasma HCI clean and 90 sec. exposure to fluorine containing plasma NH 4OH clean and 45 sec. exposure to fluorine containing plasma
Measurements were performed by Nicolet Magna-IRTm 550 spectrometer. Experiments were
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