Ion Implanted p + /n 4H-SiC Junctions: effect of the Heating Rate during Post Implantation Annealing
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0911-B11-01
Ion Implanted p+/n 4H-SiC Junctions: effect of the Heating Rate during Post Implantation Annealing Roberta Nipoti1, Alberto Carnera2, Fabio Bergamini1, Mariaconcetta Canino3, Antonella Poggi1, Sandro Solmi1, and Mara Passini1 1 IMM, CNR, via Gobetti 101, Bologna, 40129, Italy 2 Dipartimento di Fisica G. Galilei, Università di Padova, via Marzolo 8, Padova, 35131, Italy 3 Dipartimento di Fisica, Università di Bologna, viale Berti Pichat 6/2, Bologna, 40127, Italy
ABSTRACT Structural, morphological and electrical characteristics of Al-implanted p+/n 4H-SiC diodes are compared for the same implantation process and post implantation annealing with identical stationary and cooling cycles but different heating rate. Al+ ions were implanted at 400°C, with energies in the range 250-350 keV and 1.2 × 1015 cm-2 fluence. Post implantation annealing processes were done at 1600°C for 30 min with a constant heating rate in the range 7-40°C/s and an abrupt cooling cycle. Gas in the annealing ambient was high purity Ar. The Al depth profile of annealed and as implanted samples were equal except for concentrations below 1017 cm-3 where the former profiles showed a diffusion tail. With the increase of the heating rate of the post implantation annealing process, the sheet resistance of the Al implanted layer and diode leakage current decrease while the surface roughness increases. INTRODUCTION Selective doping of SiC is obtained by ion implantation. However, this process introduces a high density of crystal defects that must be removed by a post implantation annealing treatment at high temperature for an efficient electrical activation of the implanted species. Annealing parameters like heating ramp, temperature, time and cooling ramp, can influence the morphological and electrical characteristics of the implanted layer and must be well controlled to optimise the electrical performance of implanted p/n junctions. In the case of SiC, during the post implantation annealing surface roughening can occur [1-2] with less significant intensity the shorter the annealing time is [3]. The effects of the annealing temperature and of the thermal cycle both on the SiC surface roughness and on the electrical activation of the implanted layer have been reported [4-7] but often samples were treated in dissimilar heating systems like lamp, laser and inductive furnace [6-8]. So far, experimental data showing a relationship between the annealing parameters and the electrical characteristics of the p/n junction are not reported. This paper presents experimental results that evidence the relevance of the heating kinetics on the structural, morphological and electrical characteristics of Al+ implanted p+/n junctions. EXPERIMENTAL DETAILS A 3 inches n-type 8° off-axis 4H-SiC epitaxial wafer [9] was used for this study. The epilayer was 5 µm thick and doped 3 × 1015 cm-3. Via a photolithographic process selected areas of dimension < 1 × 10-3 cm2 were implanted with Al+ ions through a silicon dioxide film 420 nm thick. Implantation temperature,
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