Selective and non-selective rapid thermal epitaxy of Si/Si1-xGex heterojunction bipolar transistors

We report a novel Si/Si0.7Ge0.3 heterojunction bipolar transistor (HBT) structure which incorporates a thin (18 nm) heavily boron doped base using a combination of selective and non-selective growth. We grew each layer in-situ with rapid thermal epitaxy (RTE) using the limited reaction processing mode of growth. The collector was grown in two stages. First, we used selective epitaxial growth (SEG) using dichlorosilane (DCS), and HCl. The second non-selective growth stage used SiH4 as the source gas. The strained alloy base grew with DCS and GeH4 source gases while the lightly doped emitter was grown with DCS. evaluated the material structure of devices with transmission electron microscopy (TEM). In addition, we utilized Rutherford backscattering spectrometry (RES), secondary ion mass spectrometry (SIMS), and electrical device measurements to assess the quality of epitaxial layers. Devices with an oxide sidewall oriented along a {100} plane exhibited much lower reverse collector-base leakage currents than devices with {110} oriented sidewalls. These electrical measurements correlate with the TEM observation that the {100} oriented sidewall is defect-free compared with the {110} sidewall. Facetting of the crystalline layers grown outside of the oxide window is also less severe for {100} versus {110} oriented sidewalls. High frequency measurements of fabricated devices displayed cutoff frequencies of 54 GHz.