P doping control during SiGe:C epitaxy

Phosphorus (P) doping during SiGe:C epitaxy by using reduced pressure chemical vapor deposition (RPCVD) was investigated with the aim to prevent non-intended doping and to create steep doping profiles. We found that P diffusion during cap SiGe:C growth is not a major cause for P autodoping. The source of P autodoping is not the reactor but the wafer itself. By unloading the wafer at < 200 °C in H2 HF dip treatment after P-doped SiGe:C layer deposition, P autodoping was drastically suppressed. This means that the source layer for P autodoping was partly removed by the HF treatment. We also found that this layer could not be removed by in-situ HCl dry etching after P-doped SiGe:C layer deposition. Lowering growth rate of nondoped cap SiGe:C layer without changing temperature improves the P autodoping at high P concentration. By reducing growth temperature from 600 to 550 °C for nondoped SiGe:C cap layer keeping same growth rate, steepness of P autodoping was improved from 20.9 nm/dec to 8.7 nm/dec. By reducing growth temperature further to 500 °C, steepness of P autodoping is drastically improved to 3.4 nm/dec. The impact of the growth temperature is indicating segregation as the main factor for autodoping and profile steepness. Therefore, by reducing growth temperature for SiGe cap layer deposition, non-intended P doping could be suppressed resulting in very steep P profiles applicable for devices with critical doping profile requirements.