Silicon wafers were preamorphized with 70 keV Si+ at a dose of 1×1015 atoms/cm2, generating a deep amorphous layer of 1800 Å. Implants of 500 eV B+11, with and without 6 keV F+, followed at doses of 1×1015 atoms/cm2 and 2×1015 atoms/cm2, respectively. After annealing at 550 °C, secondary ion mass spectroscopy determined that the diffusivity of boron in amorphous silicon is significantly enhanced in the presence of fluorine. Ellipsometry and cross-sectional transmission electron microscopy indicate the enhanced diffusion only occurs in the amorphous layer. Fluorine increases the boron diffusivity by approximately five orders of magnitude at 550 °C. It is proposed that the ability of fluorine to reduce the dangling bond concentration in amorphous silicon may reduce the formation energy for mobile boron, enhancing its diffusivity.

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High-power arc lamp design has enabled ultrahigh-temperature ͑UHT͒ annealing as an alternative to conventional rapid thermal processing ͑RTP͒ for ultrashallow junction formation. The time duration of the UHT annealing technique is significantly reduced from those obtained through conventional RTP. This difference in time may offer the ability to maintain a highly activated ultrashallow junction without being subjected to transient enhanced diffusion ͑TED͒, which is typically observed during postimplant thermal processing. In this study, two 200-mm ͑100͒ n-type Czochralski-grown Si wafers were preamorphized with either a 48-or a 5-keV Ge + implant to 5 ϫ 10 14 cm 2 , and subsequently implanted with 3-keV BF 2 + molecular ions to 6 ϫ 10 14 cm 2 . The wafers were sectioned and annealed under various conditions in order to investigate the effects of the UHT annealing technique on the resulting junction characteristics. The main point of the paper is to show that the UHT annealing technique is capable of producing a highly activated p-type source/drain extension without being subjected to TED only when the preamorphization implant is sufficiently deep.

Low temperature molecular beam epitaxy was used to grow boron doping superlattices DSLs in Si, with peak boron concentrations of 110 18 /cm 3 , and spike widths of 10 nm. Amorphization of these DSLs was achieved using a series of Si implants of 30 and 112 keV, each at a dose of 1 10 15 /cm 2 , which placed the amorphous to crystalline interface between the first and second doping spikes. The dose rate of the Si implants was varied from 0.13 to 1.13 mA/cm 2. Post-implantation anneals were performed in a rapid thermal annealing furnace at 800°C, for times varying from 5 s to 3 min. Secondary ion mass spectrometry was used to monitor the dopant diffusion after annealing. Increasing the implant dose rate appears to increase the amount interstitial flux toward the surface but has no observable effect on the flux into the crystal. Transmission electron microscopy was used to study the end of range defect evolution. Increasing dose rate was observed to decrease the end of range defect density. These observations are consistent with previous findings that indicate the amount of backflow toward the surface decreases as the end of range loop density increases.

Fluorine and boron co-implantation within amorphous silicon has been studied in order to meet the process challenges regarding p+ ultra-shallow junction formation. Previous experiments have shown that fluorine can reduce boron TED (Transient Enhanced Diffusion), enhance boron solubility and reduce sheet resistance. In this study, boron diffusion characteristics prior to solid phase epitaxial regrowth (SPER) of the amorphous layer in the presence of fluorine are addressed. Samples were pre-amorphized with Si+ at a dose of 1x1015 ions/cm2 and energy of 70 keV, leading to a deep continuous amorphous surface of approximately 1500 Å. After pre-amorphization, B+ was implanted at a dose of 1x1015 ions/cm2 and energy of 500 eV, while F+ was implanted at a dose of 2x1015 ions/cm2 and energies ranging from 3 keV to 9 keV. Subsequent furnace anneals for the F+ implant energy of 6 keV were conducted at 550°C, for times ranging from 5 minutes to 260 minutes. During annealing, the boron in samples co-implanted with fluorine exhibited significant enhanced diffusion within amorphous silicon. After recrystallization, the boron diffusivity was dramatically reduced. Boron in samples with no fluorine did not diffuse during SPER. Prior to annealing, SIMS profiles demonstrated that boron concentration tails broadened with increasing fluorine implant energy. Enhanced dopant motion in as-implanted samples is presumably attributed to implant knock-on or recoil effects.