Characterization of thin Chemical/Native Oxides on Si (100) by Auger and Angle-Resolved XPS
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EDDIE D. PYLANT*+, CAROLYN F. HOENER*, MARK F. ARENDT AND BOB WITOWSKI*# *SEMATECH, 2706 Montopolis Drive, Austin, TX 78741 "**Universityof Texas Department of Chemistry, Austin, TX 78712 + Present Address: University of Texas Department of Chemistry, Austin, TX 78712 # Present Address: Motorola, Advanced Products Research and Development Lab, 3501 Ed Bluestein Blvd., Austin, TX 78721
ABSTRACT Chemical/native oxides grown on Si(100) after several standard wet cleans are characterized by Angle-resolved X-ray Photoelectron Spectroscopy (ARXPS), and Auger Electron Spectroscopy using sputter depth profiles. Target Factor Analysis (TFA) was used to separate the Si LVV Auger peak into three components identified by their lineshapes and positions as Si, SiO2, and SiOx. Auger depth profiles were used to quantify the thickness of the oxides, the depth distribution, and amount of SiOx in the interface region. ARXPS was used to study the chemical state distribution in the native oxides as a function of depth. The depth distribution function from the Auger data was converted to an angle-resolved format for direct comparison to the angle-resolved XPS data. With this comparison, the SiOx lineshape is correlated to a 3:1 mixture of Si 3+ and Si 2+ oxidation states.
INTRODUCTION Wafer cleaning plays an important role in the manufacturing of silicon devices. Wet cleaning has long been an essential step in semiconductor device manufacturing. Wet cleaning of the wafer surface is used at many locations in the device fabrication sequence; however, we will focus on the wet cleans used prior to gate oxidation. The chemical cleaning used in this step typically leaves a thin native oxide on the wafer's surface. As device complexity increases and the corresponding critical gate oxide thickness decreases, the native chemical oxide thickness begins to become a significant portion of the total gate oxide thickness. Consequently, knowledge of native oxides grown on silicon, and the nature of the SiO2/Si interface produced by various wet cleans is essential [1-7]. The interface between native oxides and silicon has received considerable attention. Analytical techniques such as Fourier-transform infrared spectroscopy (FTIR)[8], XPS [9-12] and Auger [13-17] have been used to study this interface. Since device feature sizes are shrinking, the need exists for an analytical technique with the ability to analyze small features. The study of native oxides by small-spot Auger is advantageous because of its sampling size relative to XPS and FTIR. In fact, the spatial resolution capabilities of Auger have kept pace with the decrease in device feature size. Several commercially available Field Emission-Auger systems can obtain spot sizes below 200 A in diameter. Auger depth profiles are usually analyzed by examining the peak-to-peak heights of their derivative spectra. This method is inadequate for cases where Auger peaks of differing elements overlap, or where peaks indicative of different chemical states for the same element overlap. It is
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