Lance S. Robertson

The Effect of Impurities on Diffusion and Activation of ion Implanted Boron in Silicon

The interaction between boron and silicon interstitials caused by ion implant damage is a physical process which hinders the formation of ultra-shallow, low resistivity junctions. The possibility of mitigating the effective interstitial point defect population via introduction of nonmetallic impurities in ion implanted silicon has been investigated. Amorphization of a n-type Czochralski wafer was achieved using a series of Si+ implants of 40 keV and 150 keV, each at a dose of 1×10 15 /cm 2 . The Si + implants produced a 2800A deep amorphous layer, which was then implanted with 8 keV 1×10 14 /cm 2 B + . The samples were then implanted with high doses of either carbon, oxygen, sulfur, chlorine, selenium, or bromine. The implant energies of the impurities were chosen such that the damage and ion profiles of the impurity were contained within the amorphous layer. This allowed for the chemical species effect to be studied independent of the implant damage caused by the impurity implant. Post-implantation anneals were performed in a tube furnace at 750° C. Secondary ion mass spectrometry was used to monitor the dopant diffusion after annealing. Hall effect measurements were used to study the dopant activation. Transmission electron microscopy (TEM) was used to study the end-of-range defect evolution. The addition of carbon and chlorine appear to reduce the boron diffusion enhancement compared to the boron control. Carbon and chlorine also appear to prevent boron out-diffusion during annealing compared to the control, which exhibited 20% dose loss following annealing.

Fluorine-enhanced boron diffusion in amorphous silicon

Silicon wafers were preamorphized with 70 keV Si+ at a dose of 1×1015 atoms/cm2, generating a deep amorphous layer of 1800 A. Implants of 500 eV 11B+, 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.

Annealing kinetics of {311} defects and dislocation loops in the end-of-range damage region of ion implanted silicon

The evolution of both {311} defects and dislocation loops in the end-of-range (EOR) damage region in silicon amorphized by ion implantation was studied by ex situ transmission electron microscopy (TEM). The amorphization of a (100) n-type Czochralski wafer was achieved with a 20 keV 1×1015/cm2 Si+ ion implantation. The post-implantation anneals were performed in a furnace at 750 °C for times ranging from 10 to 370 min. After annealing the specimen for 10 min, the microstructure showed a collection of both {311} defects and small dislocation loops. The evolution of a specific group of defects was studied by repeated imaging of the same region after additional annealing. Quantitative TEM showed that {311} defects followed one of two possible evolutionary pathways as annealing times progressed; unfaulting to form dislocation loops or dissolving and releasing interstitials. Results indicate that in this temperature regime, {311} defects are the preferential site for dislocation loop nucleation.

Correlation of End-of-Range Damage Evolution and Transient Enhanced Diffusion of Boron in Regrown Silicon

Amorphization of a n-type Czochralski wafer was achieved using a series of Si+ implants of 30 and 120 keV, each at a dose of 1×1015 cm2. The Si+ implants produced a 2400 A deep amorphous layer, which was then implanted with 4 keV 1×1014/cm2 B+. Postimplantation anneals were performed in a tube furnace at 750 °C, for times ranging from 15 min to 6 h. Secondary ion mass spectrometry was used to monitor the dopant diffusion after annealing. Transmission electron microscopy (TEM) was used to study the EOR defect evolution. Upon annealing, the boron peak showed no clustering, and TED was observed in the entire boron profile. TEM results show that both {311} defects and dislocation loops were present in the EOR damage region. The majority of the {311} defects dissolved in the interval between 15 min and 2 h. Results indicate that {311} defects release interstitials during the time that boron exhibits TED. These results show that there is a strong correlation between {311} dissolution in the EOR and TED in the r...

The effect of dose rate on interstitial release from the end-of-range implant damage region in silicon

Low temperature molecular beam epitaxy was used to grow boron doping superlattices DSLs in Si, with peak boron concentrations of 1×1018/cm3, 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 1×1015/cm2, 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/cm2. 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 ar...

Simultaneous determination of ultra-shallow junction depth and abruptness using thermal wave technique

Thermal wave (TW) studies of ultra-shallow junctions (USJ) formed by ion implantation into a semiconductor wafer followed by rapid thermal annealing (RTP) are described. It is shown that using the TW technique allows for a simultaneous determination of the most important USJ parameters—depth and profile abruptness. In a TW-based system, the USJ depth is obtained using the quadrature component of the TW signal while determination of USJ profile abruptness is based on the analysis of the TW quadrature and in-phase components measured at two different pump-probe beam offsets. Experimental results for junction depth and abruptness obtained on a set of B+-implanted, RTP-annealed USJ samples show better than 0.99 correlations to the corresponding secondary ion mass spectroscopy data.

Effect of Fluorine on the Diffusion of Boron in Amorphous Silicon

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 1x10 15 ions/cm 2 and energy of 70 keV, leading to a deep continuous amorphous surface of approximately 1500 A. After pre-amorphization, B + was implanted at a dose of 1x10 15 ions/cm 2 and energy of 500 eV, while F + was implanted at a dose of 2x10 15 ions/cm 2 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.

The effect of preamorphization energy on ultrashallow junction formation following ultrahigh-temperature annealing of ion-implanted silicon

High-power arc lamp design has enabled ultrahigh-temperature (UHT) annealing as an alternative to conventional rapid thermal processing (RTP) 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 (TED), which is typically observed during postimplant thermal processing. In this study, two 200‐mm (100) n-type Czochralski-grown Si wafers were preamorphized with either a 48- or a 5‐keV Ge+ implant to 5×1014cm2, and subsequently implanted with 3‐keV BF2+ molecular ions to 6×1014cm2. 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 ...

The role of fluorine on reducing TED in boron implanted silicon

Recently, it was shown that fluorine limits the transient enhanced diffusion of the boron in the regrown silicon by a chemical species by implanting BF/sup 2+/ and B/sup +/ into pre-amorphized silicon. However, it remained unclear from these studies whether the fluorine was interacting with the boron or the excess silicon interstitials from the EOR damage. In order to answer this question, a series of experiments have been performed. Amorphization of a n-type Czochralski wafer was achieved with a 70 keV Si/sup +/ implantation at a dose of 1/spl times/10/sup 15//cm/sup 2/ The Si/sup +/ implant produced a 1500 /spl Aring/ deep amorphous layer, which was then implanted with 1.12 keV 1/spl times/10/sup 15//cm/sup 2/ B/sup +/ The samples were then implanted with a dose of 2/spl times/10/sup 15//cm/sup 2/F/sup +/ at various energies ranging from 2 keV to 36 keV. By varying the F/sup +/ energy it was possible to change the position and concentration of the fluorine relative to the boron and the end-of-range interstitial source. After annealing at 750/spl deg/C and 1050/spl deg/C the wafers were analyzed by secondary ion mass spectrometry (SIMS), transmission electron microscopy (TEM), and Hall effect. The results suggest the fluorine is reducing the TED of the boron by interacting with the boron more than the excess interstitials.

Fluorine-enhanced boron diffusion in germanium-preamorphized silicon

Silicon wafers were preamorphized with 60 keV Ge+ or 70 keV Si+ at a dose of 1×1015 atoms∕cm2. F+ was then implanted into some samples at 6 keV at doses ranging from 1×1014 to 5×1015 atoms∕cm2, followed by B+11 implants at 500 eV, 1×1015atoms∕cm2. Secondary-ion-mass spectrometry confirmed that fluorine enhances boron motion in germanium-preamorphized materials in the absence of annealing. The magnitude of boron diffusion scales with increasing fluorine dose. Boron motion in as-implanted samples occurs when fluorine is concentrated above 1×1020atoms∕cm3. Boron atoms are mobile in as-implanted, amorphous material at concentrations up to 1×1019atoms∕cm3. Fluorine directly influences boron motion only prior to activation annealing. During the solid-phase epitaxial regrowth process, fluorine does not directly influence boron motion, it simply alters the recrystallization rate of the silicon substrate. Boron atoms can diffuse in germanium-amorphized silicon during recrystallization at elevated temperatures with...