研究目的
Investigating the effects of millisecond laser annealing and doping concentration on the chemical bonding states and dopant behaviors of P-doped epitaxial Si layers.
研究成果
The chemical bonding states of highly P-doped epitaxial Si films grown on Si (100) substrates were measured by HR-XPS to understand dopant behaviors at the near-surface region of the films during the laser annealing and the subsequent HF cleaning. The intensities of P 2p1/2 and P 2p3/2 peaks in the Si:P films after the laser annealing are significantly increased compared to those of the as-grown films. In particular, the P 2p peak is clearly observed in the 0.6% Si:P film after the laser annealing, while the peak is not shown in the as-grown film due to the low P concentration. These XPS results indicate that the number of P–Si bonds at the near-surface region of the Si:P film increases during the laser annealing, resulting in dopant pile-up. Surface cleaning by 1% HF solution contributes to the removal of the native oxide layer from the Si:P film, increasing the intensities of the P 2p peaks in the as-grown Si:P films. In contrast, the intensities of P 2p peaks in the laser-annealed films after the HF cleaning are decreased due to the local loss of the dopants diffused into the near-surface region during the laser annealing, diffused P was removed when the native oxide was etched by the HF treatment. Additionally, the P distributions measured by SIMS and AES also show P pile-up and loss near the Si:P film surfaces.
研究不足
The study focuses on the near-surface region of P-doped epitaxial Si films and the effects of millisecond laser annealing and HF cleaning. The limitations include the specific conditions of laser annealing and the concentration range of phosphorus doping.
1：Experimental Design and Method Selection:
Heavily P-doped epitaxial Si films were grown on p-type Si (100) substrates by RPCVD under atmospheric conditions over 100 Torr. Pre-cleaning was performed using 1% HF solution to remove the native oxide. Si:P epitaxial films with high P concentration were obtained by growing the films at 700 °C using dichlorosilane (DCS) and phosphine (PH3) gases. The P concentration (
2：3–1 × 1021 atoms/cm?3) in the Si:
P films was measured by SIMS. After the deposition, ms-laser annealing was performed at 1150°C with a continuous-type yttrium aluminum garnet (YAG) laser (VANTAGE ASTRA DSA system) operating at 810 nm. For surface treatment, the as-grown and laser-annealed films were dipped in a 1% HF solution for 50 s and rinsed with deionized (DI) water. XPS measurements were performed using a K-Alpha XPS System (Thermo Scientific) to investigate the effects of the laser annealing and HF cleaning on the chemical bonding states of the Si:P films. The XPS spectra were measured with monochromated Al Kα X-rays (hν =
3：6 eV) at a base pressure below 8 × 10?9 Torr. A double-focusing hemispherical analyzer was operated at 200 eV and 40 eV to obtain full-range spectra and core-level spectra (P 2s, P 2p, Si 2s, Si 2p, O 1s, and C 1s), respectively. The energy calibration of the XPS spectra was done by adjusting the main peak of Si 2p to 4 eV. Deconvolution of the P 2p core-level spectra into the P 2p1/2, P 2p3/2, and Si plasmon loss peaks was performed using Shirley background subtraction and Gaussian–Lorentzian functions. The P concentration in the Si:
14P films was measured by SIMS (CAMECA IMS 7f magnetic sector). The profile of P concentration was obtained at a low sputtering rate to precisely measure the dopant distribution at the near-surface region as deep as several nanometers. Cs+ primary ions were accelerated to 6 kV and Si+, O+, and P+ secondary ions were collected under an applied bias of 4 kV on the films. During SIMS measurement, oxygen from the native oxide can alter P profiles since it has high electronegativity, and thus AES was used to characterize the P distribution in Si:P films. AES (PHI 700 Xi) was performed with a 10 nA electron beam at 10 keV. Samples were sputtered using a 5 keV Ar+ ion beam at an incident angle of 75°.
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