Tem and Hrem Study of mGH-Temperature Aluminum Ion Implantation to 6H-SiC
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a region containing aluminum precipitates and below there is a region without precipitates. Defects below the precipitates are referred to as end of range (EOR) damage. Fig. lb shows an example of the two regions of a damaged layer resulting from implantation at a temperature of 1700 0C at a high dose of 1.5 x 1016 cnm2. The thickness of the damaged layer is 150 nm. From the experimental data described above it is seen that the dose parameters strongly influence on morphology of the implanted layer. With increasing implantation dose, the thickness of the implanted layer increase and the layer is more defective.
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Fig. 1. Cross-sectional TEM image of 6H-SiC sample implanted at 1700 0C a) at a low dose of 1.5 x 1014 cm"2 and b) at a high dose of 1.5 x 1016 cm"2. Now, we will consider detailed studies of the defect structure observed in 6H-SiC after high-temperature implantation to a low and a high dose. Low-Dose Implantation Fig.2a shows a TEM bright-field image taken along the [0001] 6H-SiC direction for a sample implanted at 1700°C at a low dose (1.5 x 1014 cm 2). The formation of dislocation loops is observed. To investigate the size distribution of the dislocation loops, the number of loops was counted and their sizes were measured along their longest axis. Because the conventional two-or weak-beam imaging technique is unable to reveal simultaneously all the dislocation loops having different habit planes and Burgers vectors, we used a symmetrical bright-field technique to image all of them. The result of the size distribution measurements is shown on Fig.2b. It was found that the average size of the loops was about 16 nm. The density of dislocation loops was estimated to be n = 1.1 x 1010 cm 2 .
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Using a conventional diffraction and trace analyses, dislocation loops were characterized. The dislocation loops have a (0001} habit plane and are of the interstitial type. The Burgers vector b- 1/6[0001] and the (0001 ) habit planes of the dislocation loops were confirmed by high resolution study. Fig.3 provides an example of HREM an image of the dislocation loops.
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Fig.2b. Loop size stack histogram built from plan-view image.
Fig.2a. Plan-view image of a low-dose implanted 6H-SiC sample (g-l 12 0).
Fig.3. HREM of interstitial dislocation loops lying on the basal (0001) plane.
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High-Dose implantation The presence of aluminum precipitates in 6H-SiC was found in the case of high-temperature implantation to high doses. The planview image shown in Fig. 4 was obtained from sample implanted at 1500°C to a high dose of 1.5 x 10's cm"2 . Aluminum precipitates reveal a Moire fringe contrast which confirm the crystalline nature of the particles. The Moire fringe distances agree within the margin of error with those of hexagonal Al as previously published [5]. The orientation relationship of the aluminum precipitates with the matrix was derived from selected area diffraction patterns Sand HREM
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