Phase Analysis for Single Crystalline Silicon Scratched by Spherical Diamond TIP
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PHASE ANALYSIS FOR SINGLE CRYSTALLINE SILICON SCRATCHED BY SPHERICAL DIAMOND TIP Seong-Min Jeong, Han-Seog Oh, Sung-Eun Park, Hyun-Ho Kim and Hong-Lim Lee Department of Ceramic Engineering, Yonsei University 134 Shinchon-Dong, Seodaemoon-Gu, Seoul, 120-749, Korea * On leave from MEMC Korea. Co. ABSTRACT The mechanical properties of silicon crystals are important from the viewpoint of wafer and device fabrication processes. It is now widely recognized that silicon undergoes a series of phase transformations when subjected to high pressures, using conventional high pressure devices, such as diamond anvils or hydrostatic pressure cells, or under indentation. Scratching on a silicon surface in the various conditions introduces various kinds of mechanical damage and stressed states. Micro-Raman spectroscopy was used to observe the phase transition of single crystal silicon. Several different phases were observed depending on scratching speed and scratched locations.
INTRODUCTION It is well known that silicon undergoes a series of phase transformations when subjected to high pressures, such as under diamond anvils or indentations[1-3]. Diamond cubic Si(Si-I) transforms to a metallic β-tin phase(Si-II) at high pressure. In some indentation tests, the metallic phase of Si was converted to amorphous(Si-I’) or body centered cubic structure(Si-III) during unloading. Pressure induced mechanical properties on silicon have also been studied using scratching tests. The load applied during scratching test is gradually increased from 0 to maximum load unlikely in turning test. To compensate for this, Leung et. al. adapted an increasing-depth cutting method to turning test[4]. They observed that three distinct regimes(elastic, ductile and brittle regime) could be distinguished along the groove with an increasing depth of plunging. In this study, the (100) planes of single crystalline silicon wafer were scratched by an evaporated film tester with a spherical diamond tip(R=200µm) and analyzed with micro Raman spectroscopy to examine the pressure induced phase transformation during machining. The effects of scratching direction and scratching speed were studied as well. EXPERIMENT A commercial 8 inch, B doped, (100) oriented, Czochralski grown wafer (MEMC Korea) was cut into 2 x 2 cm squares. The scratches were made by evaporated film tester(CSEM revetest) with a spherical type diamond tip(radius=200µm). The chosen scratching directions were and directions. The maximum load and the measuring time were 30N and 1min, respectively. As scratching speed is considered to be important factor to machining of brittle materials, scratching was done in fast and slow scratching speeds, 10 mm/min and 1 mm/min, respectively. In the slow scratching along direction, scratching was carried out P8.5.1
up to a point just after first crack occurred to avoid the failure of silicon sample. The scratch grooves were analyzed by optical microscopy and micro Raman spectroscopy. The latter was used for its non-destructive character, simplicity of the equipment
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