Characterization of In Situ Phosphorus‐Doped Polycrystalline Silicon Films Grown by Disilane‐Based Low‐Pressure Chemical Vapor Deposition

Abstract

Low-pressure chemical vapor deposition of in situ phosphorus-doped silicon films using disilane (Si,H,) and phosphine (PH 3 ) has been investigated in the growth temperature range of 415 to 560'C and for doping levels between 10 9 and 1021 cm 3. Regarding the film deposition, no significant difference in apparent activation energy was observed between the undoped and heavily doped deposition process. The electrical and structural properties of the films grown at 480°C have been studied as a function of doping level and post-heat-treatment including furnace and rapid thermal annealings. The observed changes in film resistivity after isochronal annealings for doping levels above 102° cm-3 are interpreted in terms of dopant segregation and supersaturation of carriers. The impact on resulting film properties when replacing disilane with silane (SiH 4 ) in the deposition process has been investigated. The films were grown under identical conditions except for the deposition temperature which was 80°C higher for the silane than for the disilane case. There is no indication of different phosphorus incorporation when comparing electrical properties of crystallized silane-and disilane-based films. However, the disilane layers exhibit larger crystallite grains and lower specific resistivities than the silane layers. In addition, the disilane films demonstrate a strongly preferred <111> texture after crystallization which is absent for the silane films. The observations are attributed to the higher degree of disorder of the as-deposited disilane films compared to the silane films resulting from the difference in deposition temperature.

In situ phosphorus-doped polycrystalline silicon films by low pressure chemical vapor deposition for contact passivation of silicon solar cells

“…Furthermore, importance of post-LPCVD annealing for grain growth and dopant activation i.e., ND,act enhancement was demonstrated (Ahmed and Ahmed, 1992;Mulder et al, 1990). In addition, use of disilane (Si2H6) instead of silane as the Si precursor was investigated as a strategy to enhance rdep of in situ P-doped LPCVD poly-Si films (Grahn et al, 1997;Madsen and Weaver, 1990). Based on this knowledge, this paper addresses the problem concerning the trade-off by targeting the optimal balance between ND,act and rdep specifically for application of the in situ P-doped LPCVD poly-Si films in passivating contacts for Si solar cells.…”

Structures, Energetics, and Transition States of the Silicon−Phosphorus Compounds Si2PHn (n = 7, 5, 3, 1). An ab Initio Molecular Orbital Study

“…It has been suggested by Ahmed et al that this is due to the stronger adsorption of disilane to the surface. An alternative explanation is that silylene, produced along with silane in the decomposition of disilane, can adsorb to the surface with a sticking probability competitive with that of phosphine. , In the gas phase, silylene can easily insert into a phosphine PH bond, with a computed barrier height of less than 2 kcal/mol. , The product of this reaction, silylphosphine, has been observed experimentally in the pyrolysis of a phosphine/disilane mixture . Thus the present theoretical study on Si−P bonding and reactivity could also contribute to our understanding of the gas-phase reactions in the CVD of phosphorus-doped silicon.…”

“…An alternative explanation is that silylene, produced along with silane in the decomposition of disilane, can adsorb to the surface with a sticking probability competitive with that of phosphine. 14,16 In the gas phase, silylene can easily insert into a phosphine PH bond, with a computed barrier height of less than 2 kcal/mol. 17,18 The product of this reaction, silylphosphine, has been observed experimentally in the pyrolysis of a phosphine/disilane mixture.…”