Effect of low thermal budget annealing on surface passivation of silicon by ALD based aluminum oxide films

Abstract

Thermal ALD deposited Al 2 O 3 films on silicon show a marked difference in surface passivation quality as a function of annealing time (using a rapid thermal process). An effective and quality passivation is realized in short anneal duration (B100 s) in nitrogen ambient which is reflected in the low surface recombination velocity (SRV o10 cm s À1 ). The deduced values are close to the best reported SRV obtained by the high thermal budget process (with annealing time between 10-30 min), conventionally used for improved surface passivation. Both as-deposited and low thermal budget annealed films show the presence of positive fixed charges and this is never been reported in the literature before. The role of field and chemical passivation is investigated in terms of fixed charge and interface defect densities.Further, the importance of the annealing step sequence in the MIS structure fabrication protocol is also investigated from the view point of its effect on the nature of fixed charges.

Influence of deposition temperature of thermal ALD deposited Al2O3 films on silicon surface passivation

“…films show high quality surface passivation for both n-and p-Si. [5][6][7]9 Al 2 O 3 , a dielectric, has large band gap (8.8 eV) and its films have excellent thermal and chemical stability and good adhesion with silicon. [14][15][16] Al 2 O 3 films can be deposited by several techniques such as molecular beam epitaxy (MBE), 17 chemical vapor deposition (CVD), [18][19][20] plasma enhanced chemical vapor deposition (PECVD), 21,22 sputtering 23 and atomic layer deposition (ALD).…”

“…However, literature in low thermal budget annealing process using RTP with less annealing time is very few. 9,26 In this paper, a systematic study is made wherein Al 2 O3 films are deposited using thermal ALD process at different deposition temperature. The influence of T dep on silicon surface passivation properties is investigated.…”

“…The first strategy is based on the reduction of the density of electronic states at the surface and the second is based on significant reduction of one type of charge (electron/hole) carrier from the surface by an internal electric field. [4][5][6][7][8][9][10] The interface defect density can be reduced by chemical route where atomic hydrogen or a halogen atom is, generally, attached with the unsaturated Si (dangling) bonds. Consequently surface is passivated 11 and this process is referred as chemical passivation.…”

“…[14][15][16] Al 2 O 3 films can be deposited by several techniques such as molecular beam epitaxy (MBE), 17 chemical vapor deposition (CVD), [18][19][20] plasma enhanced chemical vapor deposition (PECVD), 21,22 sputtering 23 and atomic layer deposition (ALD). [4][5][6][7]9,24 ALD being a conformal deposition process provides high-quality thin films with precise control over the thickness. 9,25 The best reported SRV values for Al 2 O 3 films deposited by ALD process are made by suitable combination of deposition temperature; T dep ≥ 200…”

“…[4][5][6][7]9,24 ALD being a conformal deposition process provides high-quality thin films with precise control over the thickness. 9,25 The best reported SRV values for Al 2 O 3 films deposited by ALD process are made by suitable combination of deposition temperature; T dep ≥ 200…”