In Situ Phosphorus Doping during Silicon Epitaxy in an Ultrahigh Vacuum Rapid Thermal Chemical Vapor Deposition Reactor

Abstract

Low temperature silicon epitaxy processes capable of producing ultrathin in situ doped layers have been considered able to overcome some of the challenges in realizing advanced metal oxide semiconductor field effect transistor (MOSFET) devices. As previously demonstrated for complementary metal oxide semiconductor (CMOS), 1 for buried p-channel MOSFET (PMOSFET), 2 and for double-layer epitaxial-channel p-channel MOSFETs, 3 epitaxial deposition in forming channels is a potentially promising technique since it allows independent control of doping and thickness. This is clearly an important advantage over other doping techniques provided that ultrathin layers (Յ300 Å) with abrupt doping transitions can be obtained.Early studies on n-type doping which were performed mostly in atmospheric pressure reactors at temperatures in excess of 1000ЊC revealed several common features unique to doping using PH 3 and arsine (AsH 3 ). Namely, doping incorporation decreased as the deposition temperature increased, 4-7 and the silicon growth rate was dramatically reduced when PH 3 or AsH 3 were added as the dopant source in both polycrystalline deposition and epitaxial silicon growth. 8-11 It was confirmed through surface studies that PH 3 with its very high sticking coefficient adsorbed readily on the silicon surface and hindered SiH 4 adsorption. 12 The pyrolysis of PH 3 at low partial pressures additionally resulted in PH and PH 2 species at high temperatures. At high partial pressures, however, the existence of P 2 and P 4 species made heavy phosphorus doping difficult. 7 Another challenge in phosphorus doping is the formation of retrograde profiles with abrupt transitions desired for novel device applications. 13-15 It has been commonly reported that undoped layers grown following an in situ phosphorus doped layer using PH 3 contain high levels of phosphorus, which was attributed to the high residence time of phosphorus species. 13,16 In this report, we present experimental results on phosphorus incorporation using PH 3 , Si 2 H 6 , and Cl 2 chemistry in a temperature range of 650 to 800ЊC. Effects of phosphine partial pressure and temperature on growth rate as well as phosphorus concentration are determined. Difficulties associated with n-type doping using PH 3 , which do not exist with in situ boron doping using B 2 H 6 , are also addressed in the context of forming epitaxial layers needed for advanced devices.Ultrahigh vacuum rapid thermal chemical vapor deposition (UHV-RTCVD) has been previously introduced by this laboratory to produce ultrathin device quality epitaxial layers for ultralarge scale integration (ULSI) device applications, 17,18 UHV-RTCVD is a singlewafer, cold wall, rapid thermal processing technique that can be incorporated in a cluster tool. In UHV-RTCVD, disilane (Si 2 H 6 ) is used to achieve growth rates compatible with single-wafer manufacturing at low pressures. Epitaxial growth is achieved at 800ЊC with growth rates in excess of 200 nm/min. Selectivity to insulators is maintained with the help of Cl 2...

Disilane-based cyclic deposition/etch of Si, Si:P and Si1−yCy:P layers: I. The elementary process steps

“…The situation is very different when using Si 2 H 6 + PH 3 (at 550 • C) where we have an almost linear increase of the P + ion concentration with the F(PH 3 )/2F(Si 2 H 6 ) MFR, and 1 order of magnitude higher concentrations achieved for high phosphine flows (up to 1.7 × 10 20 cm −3 ). Similar linear increases of [P + ] with the phosphine flow were observed previously in ultra-high vacuum CVD (growth pressure around 10 −4 Torr, no added H 2 ) [14,15]. If we consider that the Si:P layers are Si 1−z P z binary alloys, with z = [P + ] (i.e.…”