David S. Simons

Secondary ion yield changes in Si and GaAs due to topography changes during O+2 or Cs+ ion bombardment

Changes in secondary ion yields of matrix and dopant species have been correlated with changes in surface topography during O+2 bombardment of Si and GaAs. In Si, profiles were measured in (100) wafers at 6‐ and 8‐keV impact energy. At 6 keV, a yield increase of about 70% occurred for Si+ over a depth range of 2.5 to 3.5 μm, with changes in other species ranging from a decrease of ∼20% for Si+3 to an increase of more than 25% for O+. The development of a rippled surface topography was observed in scanning electron micrographs over the same depth range. Similar effects occurred over a 3–5 μm depth range for 8‐keV ions, and in (111) silicon at a depth of 3 to 4 μm for 6‐keV ions. No differences were noted between p‐ and n‐type silicon, or implanted and unimplanted silicon. In GaAs, profiles were measured in (100) wafers at 2.5‐, 5.5‐, and 8‐keV impact energies. At 8 keV, a yield increase of about 70% was found for GaO+ in the range 0.6–1.0 μm, with smaller changes for other matrix species. At 5.5 keV, simil...

Transient enhanced diffusion without {311} defects in low energy B+‐implanted silicon

Low energy and low dose B+‐implanted Si has been studied using transmission electron microscopy (TEM) and secondary ion mass spectrometry (SIMS). Czochralski‐grown (100) Si wafers were implanted with 4 keV B+ to a dose of 1×1014/cm2. Subsequently, anneals were performed between 700 and 800 °C for times between 15 s and 8 h in an ambient atmosphere of N2. SIMS results show transient enhanced diffusion (TED) of the boron that saturates in less than 15 min for all annealing temperatures studied. TED results in an increase in the junction depth by at least 60 nm at a 1×1016/cm3 concentration. TEM studies show that, even for the shortest times before TED is observed, {311} defects are not detected. These results imply that there may be more than one source of interstitials for TED.

Al and B ion‐implantations in 6H‐ and 3C‐SiC

Low (keV) and high (MeV) energy Al and B implants were performed into n‐type 6H‐ and 3C‐SiC at both room temperature and 850 °C. The material was annealed at 1100, 1200, or 1400 °C for 10 min and characterized by secondary ion mass spectrometry, Rutherford backscattering (RBS), photoluminescence, Hall and capacitance‐voltage measurement techniques. For both Al and B implants, the implant species was gettered at 0.7 Rp (where Rp is the projected range) in samples implanted at 850 °C and annealed at 1400 °C. In the samples that were amorphized by the room temperature implantation, a distinct damage peak remained in the RBS spectrum even after 1400 °C annealing. For the samples implanted at 850 °C, which were not amorphized, the damage peak disappeared after 1400 °C annealing. P‐type conduction is observed only in samples implanted by Al at 850 °C and annealed at 1400 °C in Ar, with 1% dopant electrical activation.

Low-temperature cleaning processes for Si molecular beam epitaxy

Hydrogen‐terminated surface cleaning techniques of silicon substrates were investigated by using x‐ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), and transmission electron microscopy (TEM). Either a 4% HF dip or an HF‐terminated abbreviated Shiraki clean was used as the cleaning technique. Shiraki‐cleaned samples were grown as control samples. XPS was used to measure the C, O, and F remaining on the surface at various stages of the cleaning/growth process, including after a 1 h bake at 200 °C prior to growth. XPS did not detect a significant difference in the adsorbate concentrations between the baked and unbaked samples. From SIMS, the lowest impurity concentrations at the epitaxial/substrate interface were achieved with the abbreviated Shiraki clean, approximately at the same levels as obtained with the standard Shiraki clean, 1.3×1013, 5.4×1012, 1.6×1010, and 4.2×1011/cm2 for C, O, F, and N, respectively. This was achieved without the 850 °C anneal required to desorb the ...

Diffusion barrier cladding in Si/SiGe resonant interband tunneling diodes and their patterned growth on PMOS source/drain regions

Si/SiGe resonant interband tunnel diodes (RITDs) employing /spl delta/-doping spikes that demonstrate negative differential resistance (NDR) at room temperature are presented. Efforts have focused on improving the tunnel diode peak-to-valley current ratio (PVCR) figure-of-merit, as well as addressing issues of manufacturability and CMOS integration. Thin SiGe layers sandwiching the B /spl delta/-doping spike used to suppress B out-diffusion are discussed. A room-temperature PVCR of 3.6 was measured with a peak current density of 0.3 kA/cm/sup 2/. Results clearly show that by introducing SiGe layers to clad the B /spl delta/-doping layer, B diffusion is suppressed during post-growth annealing, which raises the thermal budget. A higher RTA temperature appears to be more effective in reducing defects and results in a lower valley current and higher PVCR. RITDs grown by selective area molecular beam epitaxy (MBE) have been realized inside of low-temperature oxide openings, with performance comparable with RITDs grown on bulk substrates.

Isotopic analysis with the laser microprobe mass analyzer

Abstract The capability of the laser microprobe mass analyzer (LAMMA) to perform isotopic ratio measurements has been investigated. The dynamic range is limited by the 8-bit resolution of the transient waveform recorder, but can be increased by using independent recording channels operated at different input sensitivities. An abundance sensitivity for uranium of 0.1% was measured on the low-mass side of the major peak. Measurement precision is limited by the finite number of ions in a pulse and by the dynamic bit resolution of the transient recorder. The major limitation for isotopic accuracy is a decrease in gain of the electron multiplier as the output pulse amplitude increases. This effect can be quantified using a calibration procedure. Isotopic ratio measurements were made on nanogram quantities of osmium with non-natural isotopic abundances. Relative accuracies better than 3% (1σ) were obtained for ratios larger than 0.2. These results give confidence that the LAMMA can be used to determine directly the radioactive decay constant of 187 Re by measuring the ingrowth of 187 Os.

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...

Surface segregation and structure of Sb-doped Si(100) films grown at low temperature by molecular beam epitaxy

Abstract Sb surface segregation and doping during Si(100) molecular beam epitaxy were studied for growth temperatures of 320–500°C. Surface segregation was analyzed by depth profiling with secondary ion mass spectrometry and the results indicate the existence of several distinct dopant concentration- and temperature-dependent surface segregation regimes: (1) For dilute Sb surface concentrations the measurements reveal a region where bulk and surface concentrations are linearly related, and the surface segregation is described by a constant. However, the experimentally determined temperature dependence of the segregation does not follow simple kinetics theory, and appreciable surface segregation is observed at temperatures ≤ 400°C. (2) At temperatures ≥ 350°C, the surface segregation reaches a maximum for Sb surface concentrations of 0.5 monolayers. (3) For surface concentrations near 1 monolayer, the surface segregation decreases with increasing surface Sb coverage due to dopant interaction within surface and subsurface layers. In cases where films were grown under very high dopant fluxes, we have identified cone-like defects and stacking faults that are the result of the apparent surface concentration exceeding 1 monolayer.

PN junction formation in 6HSiC by acceptor implantation into n-type substrate

Abstract A1 and B implantations were performed into n-type 6H-bulk SiC and epitaxial layers at both room temperature and 850°C. Annealings were performed in the temperature range of 1100–1650°C in a SiC crucible. For single-energy implants, the implant gettered to the 0.7Rp location for annealing temperatures ≥1400°C. For the 850°C implanted samples the RBS yield in the annealed material is comparable to the yield in the as-grown material, indicating a good lattice recovery. A maximum activation of 18% for Al-implanted samples was observed. PN junction diodes were made using Al-implanted material.

Doping of gallium nitride using disilane

The silicon doping of n-type GaN using disilane has been demonstrated for films grown on sapphire substrates by low pressure organometallic vapor phase epitaxy. The binding energy of an exciton bound to a neutral Si donor has been determined from low temperature (6K) photoluminescence spectra to be 8.6 meV. Nearly complete activation of the Si impurity atom in the GaN lattice has been observed.