Application of atomic layer deposited dopant sources for ultra‐shallow doping of silicon

Abstract

The advanced silicon semiconductor technology requires doping methods for production of ultra‐shallow junctions with sufficiently low sheet resistance. Furthermore, advanced 3‐dimensional topologies may require controlled local doping that cannot be achieved by ionimplantation. Here, the application of the atomic layer deposition (ALD) method for pre‐deposition of dopant sources is presented. Antimony oxide and boron oxide were investigated for such application. Ozone‐based ALD was carried out on silicon wafers by using triethylantimony or tris‐(dimethylamido)borane. Very homogeneous Sb2O5 deposition could be achieved on flat silicon wafers and in trench structures. The thermal stability of antimony oxide layers was investigated by rapid thermal annealing experiments. The layers were not stable above 750 °C. Therefore, this material failed to act as dopant source so far. In contrast, ultra‐shallow boron doping of silicon from ALD grown boron oxide films was successful. However, pure B2O3 films were highly unstable after exposure to ambient air. The boron oxide films could be protected by thin Sb2O5 or Al2O3 films that were in‐situ grown by ALD. Low temperature ALD of Al2O3 at 50 °C from trimethylaluminium (TMA) and ozone was investigated in detail with respect of its protective effect on boron oxide. Interestingly, it was observed that already one ALD cycle of TMA and O3 resulted in significant increase in stability of the boron oxide in air. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Diffusion of Phosphorus and Boron from Atomic Layer Deposition Oxides into Silicon

“…Due to the instability of B 2 O 3 and P 2 O 5 films in air, [25,27] they were capped in situ with ALD-grown Sb 2 O 5 layers for ex situ investigation. [23] The temperature of the Si substrate during growth was 200 C. Halogen-free precursors were used for the deposition processes, tris(dimethylamido)borane (B(NMe 2 ) 3 ) for boron oxides, tris(dimethylamido) antimony (Sb(NMe 2 ) 3 ) for antimony oxides, and tris(dimethylamido)phosphine (P(NMe 2 ) 3 ) for phosphorus oxides.…”

“…Phosphorus oxide (P 2 O 5 ) and boron oxide (B 2 O 3 ) films with different thicknesses were grown on the crystalline silicon by ALD. Due to the instability of B 2 O 3 and P 2 O 5 films in air, they were capped in situ with ALD‐grown Sb 2 O 5 layers for ex situ investigation . The temperature of the Si substrate during growth was 200 °C.…”

“…ALD is one of the most promising candidates compared with CVD techniques due to its already demonstrated conformity, uniformity, controllability over material thickness and composition, low impurity contamination, low growth temperature (<350 °C), and radiation‐free processing . The use of ALD‐grown boron‐ and phosphorus‐doped dopant sources has been demonstrated already for the shallow doping of silicon . In order to be able to optimize the doping processing conditions and control dopant diffusion according to the requirements of advanced 3D nanostructered devices, it is necessary to understand the mechanisms governing dopant diffusion in silicon as well as in covering oxides.…”

“…[19,21,22] The use of ALD-grown boron-and phosphorusdoped dopant sources has been demonstrated already for the shallow doping of silicon. [23][24][25][26][27] In order to be able to optimize the doping processing conditions and control dopant diffusion according to the requirements of advanced 3D nanostructered devices, it is necessary to understand the mechanisms governing dopant diffusion in silicon as well as in covering oxides.…”

Use of B2O3 films grown by plasma-assisted atomic layer deposition for shallow boron doping in silicon

“…The doping technology for such structures is challenging, and conventional doping methods need to be adapted or replaced. 7,9 Growth could be observed from room temperature up to 100 C, but growth per cycle decreased significantly with increasing temperature. Alternatives like plasma doping 1 were investigated in order to overcome limitations of conventional implantation, but problematic damage-related phenomena as transient enhanced diffusion during dopant activation and shadowing effects due to showers of directed species cannot be fully avoided.…”