Very Low Temperature (Cyclic) Deposition / Etch of In Situ Boron-Doped SiGe Raised Sources and Drains

Abstract

We have developed an innovative 500°C process for the selective deposition of SiGe:B Raised Sources and Drains (RSDs). We have first of all studied on blanket Si wafers the in-situ boron doping of SiGe with Si2H6, GeH4 and B2H6. A growth rate increase by a factor higher than 4 together with a Ge concentration decrease from 45% down to 28% occurred as the diborane mass-flow increased (at 500°C, 20 Torr). Very high substitutional boron concentrations were achieved (∼5 × 1020 cm−3) in layers that were single crystalline and flat. Adding large amounts of HCl to the gaseous mixture did not yield the selectivity aimed for on SiO2-covered Si wafers, however. To that end, we have thus benchmarked various 500°C Cyclic Deposition / Etch (CDE) processes. 12 cycles CDE processes were characterized by HCl etch rates of poly-SiGe:B that were too low to be of any practical use or yielded 3 dimensional SiGe:B layers on Si(001). Straightforward Deposition / Etch (DE) processes, with the HCl selective etch of poly-SiGe:B carried out at 740 Torr (i.e. atmospheric pressure), enabled us by contrast to achieve selectivity on SiO2 while retaining single crystalline and slightly rough SiGe:B layers. Those DE processes were tested on patterned Silicon-On-Insulator substrates with gate stacks. Longer HCl etch times than the ones identified on blanket wafers were key in getting rid of poly-SiGe:B on top of dielectrics covered surfaces; rather smooth, facetted SiGe:B RSDs were obtained in the end.

Selective epitaxial growth of stepwise SiGe:B at the recessed sources and drains: A growth kinetics and strain distribution study

“…18 It was previously reported that in-situ doping of boron compensated for the compressive strain in the SiGe layer, and the Ge concentration calculated from the XRD results was lower than the actual quantity of Ge atoms. 19 In the present study, however, the SiGe peak shift from the undoped SiGe sample to the in-situ B-doped SiGe sample was 0.01 • . Thus, the effect of compensation was excluded from further discussions.…”

Area-Selective Deposition: Fundamentals, Applications, and Future Outlook

“…In addition, the advantages of incorporating an etching component into the deposition process were also demonstrated in early SEG research . More recently the advantages of cyclical deposition and etch processes for SEG have been demonstrated …”

“…109 More recently the advantages of cyclical deposition and etch processes for SEG have been demonstrated. 110 In its current form, SEG is an essential process in the formation of leading-edge metal oxide semiconducting field effect transistors (MOSFETs). 111 SEG is utilized in forming the source and drain of both N-type and P-type MOSFETs within the complementary MOS process flows used for advanced logic devices and SRAM memory.…”

Epitaxial growth of Si and SiGe at temperatures lower than 500°C with disilane and germane

“…Disilane is however intrinsically non-selective versus dielectrics commonly used as spacer (Si 3 N 4 ) or isolation (SiO 2 ). This drawback can however be overcome with the addition of gaseous hydrochloric acid (or Cl 2 ) or the use of advanced (cyclic) deposition/etch (CDE) processes [9][10][11]. …”