Depth Profiling of SiC Lattice Damage Using Micro-Raman Spectroscopy
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Depth Profiling of SiC Lattice Damage Using Micro-Raman Spectroscopy Iulia C. Muntele, Daryush Ila, Claudiu I. Muntele, David B. Poker1, Dale K. Hensley1 Center for Irradiation of Materials, Alabama A&M University, Normal, AL – 35762, U. S. A. 1 Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN, U. S. A. ABSTRACT Depth profiling for the amount of lattice damage using a Confocal Micro-Raman (CMR) spectrometer is demonstrated in this paper. Samples of n-type silicon carbide were implanted with 2 MeV He and O ions at both room temperature and 500 °C, and fluences between 1015 and 1017 ions/cm2. Post-implantation annealing at 1000 °C was also performed in order to study the damage evolution. Optical Absorption Spectrophotometry (OAS) was used for establishing the opacity (and therefore the probing depth) of the damaged layer to the 632.8 nm wavelength of the He-Ne laser used for CMR throughout this study. The methodology used and the results obtained are presented herein. Total dissipation of amorphous carbon islands was observed even at low annealing temperatures of the RT implanted samples, along with an increase in the size of the amorphous silicon islands. INTRODUCTION In device fabrication the ion implantation is usually the doping method of choice because it offers precise control over the spatial distribution and doping level using conventional masking techniques. Hot implantation of silicon carbide is a common practice aimed at reducing the damages incurred during the passage of ions through the material, reducing the needs for postimplantation annealing for crystalline lattice recovery. Although literature mentions that strong dynamical recovery has been achieved at temperatures as low as 200 °C, an annealing temperature up to 1700 °C is still necessary for an acceptable degree of lattice recovery, especially for Al-doped p-type silicon carbide. In order to predict a certain type of behavior of an electronic device, it is important to know the depth distribution of the residual damage present in the crystalline lattice. This is necessary because the carrier trapping levels introduced in the band gap by lattice damages (vacancies, interstitials, substitutionals etc.) can significantly change the electric behavior. Techniques like Positron Annihilation Spectroscopy [5,6] and Rutherford Backscattering/Channeling Spectrometry [7] have been reported in the literature as good tools for this type of investigation. This paper is intended to present an all-optical approach of this problem, using a CMR spectrometer for depth monitoring of the 400 – 600 cm-1 (amorphous silicon) and 1250 – 1450 cm-1 (amorphous carbon) spectral regions. Also, an UV/Vis (200 – 980 nm wavelength range) spectrophotometer was used for optical absorption measurements aimed at establishing the probing depth of the He-Ne laser (632.8 nm wavelength) used by the CMR spectrometer. The SRIM computer code was used as well, for establishing the ranges of the He and O ions into silicon carbide, and to provide a depth profile for the numb
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