L. Rubin

Diffusion of ion implanted boron in preamorphized silicon

Transient enhanced diffusion of boron in preamorphized and subsequently regrown Si was studied by secondary ion mass spectrometry (SIMS) and transmission electron microscopy (TEM). A comparison of 4 keV, 1× 1014/cm2 boron implants into crystalline and Ge+ preamorphized silicon was undertaken. Upon annealing the B+ implant into crystalline material exhibited the well‐known transient enhanced diffusion (TED). In this case the peak of the boron distribution was relatively immobile and only B in the tail showed TED. In the second set of samples, the surface was first preamorphized by a 180 keV, 1×1015/cm2 Ge+ implant which produced an amorphous layer 2300 A deep, which then was implanted with boron. After implantation the tail of the B distribution extended to only 700 A. Upon annealing, TED of the boron in the regrown Si was also observed, but the diffusion profile was very different. In this case the peak showed no clustering, so the entire profile diffused. The time for the TED to decay was around 15 min a...

Effect of implant temperature on transient enhanced diffusion of boron in regrown silicon after amorphization by Si+ or Ge+ implantation

Si wafers were preamorphized by either Si+ or Ge+ ions at temperatures between 5 and 40u2009°C. The diffusion of low energy (4 keV) B+ implants into the preamorphized Si was studied in order to monitor the flux of interstitials from the end of range (EOR) region toward the surface. Transient enhanced diffusion (TED) in the regrown silicon was observed for all implants. Increasing the implantation temperature of the Si+ implant by as little as 15u2009°C can result in a marked decrease in the magnitude of the interstitial flux flowing from the EOR region toward the surface. This sensitivity to implant temperature appears to be even greater for Ge+ implants. In order to better understand this effect, detailed transmission electron microscopy (TEM) studies were conducted. As-implanted cross-sectional TEM micrographs indicate a measurable decrease in the thickness of the amorphous layer (up to 300 A) occurs when the implantation temperature increases from 5 to 40u2009°C as a result of ion beam induced epitaxial recrystall...

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 750u200a°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.

The effect of boron implant energy on transient enhanced diffusion in silicon

Transient enhanced diffusion (TED) of boron in silica after low energy boron implantation and annealing was investigated using boron-doping superlattices (DSLs) grown by low temperature molecular beam epitaxy. Boron ions were implanted at 5, 10, 20, and 40 keV at a constant dose of 2×1014/cm2. Subsequent annealing was performed at 750u2009°C for times of 3 min, 15 min, and 2 h in a nitrogen ambient. The broadening of the boron spikes was measured by secondary ion mass spectroscopy and simulated. Boron diffusivity enhancement was quantified as a function of implant energy. Transmission electron microscopy results show that 〈311〉 defects are only seen for implant energies ⩾10 keV at this dose and that the density increases with energy. DSL studies indicate the point defect concentration in the background decays much slower when 〈311〉 defects are present. These results imply there are at least two sources of TED for boron implants (B-I): short time component that decays rapidly consistent with nonvisible B-I pai...

Transient enhanced diffusion and defect microstructure in high dose, low energy As+ implanted Si

(001) CZ silicon wafers were implanted with As+ at 100 keV to a dose of 1×1015/cm2 in order to produce a continuous amorphous layer to a depth of about 120 nm. Furthermore, the implant condition was such that the peak arsenic concentration was below the arsenic clustering threshold. Subsequently, a second As+ or Ge+ implant was performed at 30 keV to doses of 2×1015/cm2,u20095×1015/cm2 and 1×1016/cm2, respectively, into the as-implanted samples. All of the samples were annealed at 800u2009°C for 1 h. The second implant was designed to be contained within the amorphous region created by the initial implant. The second As+ implant was also designed to provide the additional arsenic needed to exceed the critical concentration for clustering at the projected range. Of the three samples with the dual As+ implant the clustering threshold was exceeded for the two lower doses while the SiAs precipitation threshold was exceeded at the highest dose. In the case of the dual As+/Ge+ implants the clustering and precipitation ...

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 1×1015u200acm2. The Si+ implants produced a 2400 A deep amorphous layer, which was then implanted with 4 keV 1×1014/cm2u200aB+. Postimplantation anneals were performed in a tube furnace at 750u200a°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 Siu2009+ 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 Siu2009+ implants was varied from 0.13 to 1.13u2002mA/cm2. Post-implantation anneals were performed in a rapid thermal annealing furnace at 800u2009°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...

Enhanced Boron Diffusion in Amorphous Silicon

In prior works, we demonstrated the phenomenon of fluorine-enhanced boron diffusion within self-amorphized silicon. Present studies address the process dependencies of low temperature boron motion within ion implanted materials utilizing a germanium amorphization. Silicon wafers were preamorphized with either 60 keV or 80 keV Ge + at a dose of 1×10 15 atoms/cm 2 . Subsequent 500 eV, 1×10 15 atoms/cm 2 11 B + implants, as well as 6 keV F + implants with doses ranging from 1×10 14 atoms/cm 2 to 5×10 15 atoms/cm 2 were also done. Furnace anneals were conducted at 550°C for 10 minutes under an inert N 2 ambient. Secondary Ion Mass Spectroscopy (SIMS) was utilized to characterize the occurrence of boron diffusion within amorphous silicon at room temperature, as well as during the Solid Phase Epitaxial Regrowth (SPER) process. Amorphous layer depths were verified through Cross-Sectional Transmission Electron Microscopy (XTEM) and Variable Angle Spectroscopic Ellipsometry (VASE). Boron motion within as-implanted samples is observed at fluorine concentrations greater than 1×10 20 atoms/cm 3 . The magnitude of the boron motion scales with increasing fluorine dose and concentration. During the initial stages of SPER, boron was observed to diffuse irrespective of the co-implanted fluorine dose. Fluorine enhanced diffusion at room temperature does not appear to follow the same process as the enhanced diffusion observed during the regrowth process.

Influence of low temperature preanneals on dopant and defect behavior for low energy Ge preamorphized silicon

The hold temperature of an anneal plays a crucial role in controlling the final activation and diffusion of dopants. A study on the influence of a variety of low temperature preanneals on the behavior of dopants and defects for low energy germanium preamorphization is conducted. Si wafers are preamorphized with 1×1015u2009cm−2 Ge+ at energies of 10, 12, 15, 20, and 30 keV and implanted with 1×1015u2009cm−2, 1 keV B+. Furnace preanneals are performed at 450, 550, 650, and 750u200a°C; the samples are subsequently subjected to a spike RTA at 950u200a°C. Defect analyses indicate an energy threshold above which the preanneal has an effect on the defect density. Further experiments are conducted on the 10 keV Ge+ preamorphizing implant in which the second anneal step is conducted at 750u200a°C for various times. An analysis of the defect evolution with time reveals that the evolution does not follow previously reported Ostwald ripening-type behavior. The microstructure is populated with very small dot-like defects, which simply di...

The effect of end of range loops on transient enhanced diffusion in Si

In the Si IC industry today all highly doped, ion implanted regions were amorphized at one point. Upon annealing, it has generally been believed that dopant in the regrown silicon does not show any enhanced diffusion. The accepted model was that the end of range (EOR) dislocation loop density was sufficient to prevent the back flow of interstitials toward the surface by acting as a blocking layer. In this paper it is shown that conditions exist where significant transient enhanced diffusion (TED) of dopants in regrown silicon can occur for amorphizing implants of Si and Ge. The effect of implantation temperature and species on the amount of TED in the regrown silicon is studied. Comparison of SIMS and TEM results indicates the end of range damage is the source of the TED not defects grown in during the solid phase epitaxial regrowth process. In particular the dissolution of <311> defects in the EOR damage appears to account for a significant amount of the TED. Comparison of the magnitude of the back flow from several different experiments is presented. There appears to be an exponential dependence of the amount of back flow on the dislocation loop density in the EOR layer. Increasing loop density results in a decreasing back flow.