Elsevier

Thin Solid Films

Volume 520, Issue 8, 1 February 2012, Pages 3190-3194
Thin Solid Films

Gas phase particle formation and elimination on Si (100) in low temperature reduced pressure chemical vapor deposition silicon-based epitaxial layers

https://doi.org/10.1016/j.tsf.2011.10.165Get rights and content

Abstract

Gas phase particle formation and elimination in silicon epitaxial layers grown on Si (100) substrates using reduced pressure chemical vapor deposition at low temperatures (< 600 °C) are investigated. High-order silane precursors (SinH2n + 2; n = 3, n > 3) are useful for high growth rate epitaxy at low temperature. However, particulates are observed on the surface of the epitaxial layers grown with high-order silanes. These particulates are attributed to gas phase particles. As atomically smooth epitaxial films are desired, the elimination of gas phase particles is required. Cyclical deposition and etch process and/or low pressure deposition enables atomically smooth SiCP epitaxial films with a high-order silane.

Introduction

Low temperature silicon-based epitaxial process is required for 22 nm-node Complimentary Metal Oxide Semiconductor (CMOS) technology applications. High boron concentration (3-6E20 cm 3) and high Ge fraction (60%) pseudomorphic SiGeB layers are desirable for future P type MOS technology for future device performance enhancement via source/drain stressors. For N type MOS technology, highly Phosphorous-doped (3-5E20 cm 3) pseudomorphic meta-stable Si:C layers with fully substitutional C levels in excess of 2% are desired. In order to achieve such high carbon fractions high-growth rates and low temperatures (< 600 °C) are required [[1], [2], [3]]. These non-equilibrium deposition conditions also allow for dopant levels exceeding solid solubility for B, P, and As. Several researchers have investigated various high-order silane precursors for the deposition of Si:C and SiCP for embedded CMOS stressors [4], [5]. Traditional silicon precursors, (e.g. silane (SiH4)), have high dissociation energies (EH–Si 318 kJ/mol) resulting in low growth rates (< 1 nm/min) at low process temperature (< 600 °C). High-order silanes, (e.g. trisilane (Si3H8)), are highly reactive molecules with low dissociation energies (ESi–Si 226 kJ/mol), resulting in higher growth rates for the same deposition temperature and partial pressure when compared with silane and disilane [6].

However, it has been reported that the non-chlorinated silane(s), silane (SiH4), disilane (Si2H6) and trisilane (Si3H8) can create gas-phase particles. To suppress the total amount of gas-phase particles, lower precursor partial pressure deposition is used [[6], [7], [8]]. This reduction in partial pressure leads to a reduction in growth rate [8]. To maintain a high-growth rate (> 10 nm/min) while suppressing gas phase particles on the surface, a high-order silane (SinH2n + 2 where n > 3) with lower partial pressure and cyclic deposition and etch (CDE) cycles is used in this work.

In particular, for recessed source-drain deposition on SiCP, it has been shown that CDE is required to remove (110) sidewall defects [5], but no mention is made for removing gas-phase particles on the (100) growth interface. In this paper, particulates on the surface of epitaxial layers were observed by atomic force microscopy (AFM) and cross-sectional transmission electron microscopy (TEM) analysis. These particulates are associated to defects caused by gas-phase reactions (i.e. gas-phase defects). Techniques to reduce and to eliminate gas phase particles are demonstrated using both CDE and a reduced pressure process.

Section snippets

Experimental details

Silicon epitaxial layers were deposited using a 300 mm single-wafer industrial reduced pressure chemical vapor deposition (RPCVD) Tool. The silicon precursors examined in our experiments are dichlorosilane (SiCl2H2), silane (SiH4), trisilane (Si3H8) and a high-order silane (SinH2n + 2 where n > 3). SiCP epitaxial layers were grown using a high-order silane in conjunction with mono-methylsilane (SiH3CH3) and phosphine (PH3). SiGe epitaxial layers were grown using a high-order silane and germane (GeH4

Results and discussion

In high-volume manufacturing production for low temperature silicon-based epitaxial process, high growth rate and low temperature are required for high throughput and low thermal budget. Dichlorosilane precursor is widely used as a selective silicon precursor to deposit silicon-based layers at temperatures between 650 °C and 850 °C. To reduce the thermal budget while maintaining the same growth rates, silane-based low pressure chemical vapor deposition was developed [10]. It has been shown with

Conclusion

Silicon epitaxial growth surface using several silicon precursors (SiCl2H2, SiH4, Si3H8 and a high-order (n) silane (n > 3)) has been investigated. Gas phase particles are observed when the silicon precursor used is Si3H8 or a high-order silane. For the same growth rate and thickness, fewer particles are observed when a high-order silane is used as the silicon precursor. CDE and/or the reduction of deposition pressure suppresses gas-phase reactions which allows for particle free silicon-based

Acknowledgment

The authors would like thank Professor Robert Geer and YunFei Wang of the College of Nano Science and Engineering (CNSE) of the University of Albany for tool support of atomic force microscopy.

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