M. A. Sahiner

Modeling of boron and phosphorus implantation into (100) Germanium

Boron and phosphorus implants into germanium and silicon with energies from 20 to 320 keV and ion doses from 5/spl times/10/sup 13/ to 5/spl times/10/sup 16/ cm/sup -2/ were characterized using secondary ion mass spectrometry. The first four moments of all implants were calculated from the experimental data. Both the phosphorus and boron implants were found to be shallower in the germanium than in the silicon for the same implant parameters and high hole concentrations, as high as 2/spl times/10/sup 20/ cm/sup -3/, were detected by spreading resistance profiling immediately after boron implants without subsequent annealing. Channeling experiments using nuclear reaction analysis also indicated high substitutional fractions (/spl sim/19%) even in the highest dose case immediately after implant. A greater straggle (second moment) is, however, observed in the boron implants in the germanium than in the silicon despite having a shorter projected range in the germanium. Implant profiles predicted by Monte Carlo simulations and Lindhard-Scharff-Schiott theory were calculated to help clarify the implant behavior. Finally, the experimentally obtained moments were used to calculate Pearson distribution fits to the boron and phosphorus implants for rapid simulation of nonamorphizing doses over the entire energy range examined.

Implantation and activation of high concentrations of boron in Germanium

There is renewed interest in the development of Ge-based devices. Implantation and dopant activation are critical process steps for future Ge devices fabrication. Boron is a common p-type dopant, which remarkably is active immediately after implantation in Ge at low doses. This paper examines the effect of increasing dose (i.e., 5/spl times/10/sup 13/-5/spl times/10/sup 16/ cm/sup -2/) and subsequent annealing (400/spl deg/C-800/spl deg/C for 3 h in nitrogen) on activation and diffusion of boron in Ge. Secondary ion mass spectrometry (SIMS), spreading resistance profiling (SRP), high resolution X-ray diffraction (HRXRD), Rutherford backscattering spectrometry (RBS), and nuclear reaction analysis (NRA) are used to characterize the implants before and after annealing. It is found that very high fractions of the boron dose (/spl sim/5%-55%) can be incorporated substitutionally immediately after implantation leading to very high hole concentrations, /spl ges/2/spl times/10/sup 20/ cm/sup -3/, deduced from SRP. Small increases in activation after annealing are observed, however, 100% activation is not indicated by either SRP or NRA. Negligible diffusion after annealing at either 400/spl deg/C or 600/spl deg/C for 3 h was, furthermore, observed.

Correlation of local structure and electrical activation in arsenic ultrashallow junctions in silicon

The understanding of the behavior of arsenic in highly doped near surface silicon layers is of crucial importance for the formation of N-type ultrashallow junctions in current and future very large scale integrated technology. This is of particular relevance when studying recently developed implantation and annealing methods. Past theoretical as well as experimental investigations have suggested that the increase in As concentration, and therefore the reciprocal proximity of several As atoms, leads to a drastic increase in electrically inactive defects giving only marginal reduction in sheet resistance. Monoclinic SiAs aggregates as well as various arsenic-vacancy clusters contribute to the deactivation of arsenic. This study aims to correlate between the results of electrical activation measurements and x-ray absorption fine structure measurements. Samples were doped with a nominal fluence of 1×1015–3×1015 atoms/cm2, implanted at 2 keV, and annealed by rapid thermal treatments, laser submelt treatments, ...

Windowless CdSe/CdTe solar cells with differentiated back contacts: J-V, EQE, and photocurrent mapping.

This study presents windowless CdSe/CdTe thin film photovoltaic devices with in-plane patterning at a submicrometer length scale. The photovoltaic cells are fabricated upon two interdigitated comb electrodes prepatterned at micrometer length scale on an insulating substrate. CdSe is electrodeposited on one electrode, and CdTe is deposited by pulsed laser deposition over the entire surface of the resulting structure. Previous studies of symmetric devices are extended in this study. Specifically, device performance is explored with asymmetric devices having fixed CdTe contact width and a range of CdSe contact widths, and the devices are fabricated with improved dimensional tolerance. Scanning photocurrent microscopy (also known as laser beam induced current mapping) is used to examine local current collection efficiency, providing information on the spatial variation of performance that complements current-voltage and external quantum efficiency measurements of overall device performance. Modeling of carrier transport and recombination indicates consistency of experimental results for local and blanket illumination. Performance under simulated air mass 1.5 illumination exceeds 5% for all dimensions examined, and the best-performing device achieved 5.9% efficiency.

Deactivation of submelt laser annealed arsenic ultrashallow junctions in silicon during subsequent thermal treatment

The use of nonequilibrium annealing approaches can produce very high levels of arsenic electrical activation in Si. However, subsequent thermal treatments between 500 and 800°C easily deactivate the dopant to a level one order of magnitude below the solid solubility. In this work, the authors study the deactivation of laser annealed (LA) ultrashallow arsenic distributions in silicon using Hall effect measurements, extended x-ray absorption fine structure spectroscopy, and secondary ion mass spectrometry. Single crystal Si (100) wafers implanted with As ions at 2keV energy and different doses were activated with a millisecond LA at 1300°C using a scanning diode laser annealing system under nonmelt conditions. The samples were then thermally treated in a furnace at 300–900°C in a N2 atmosphere for 10min. Electrical deactivation has been observed for all the implanted doses but for the lowest one. In particular, it was observed that the higher the As dose the easier the deactivation, in particular, after the...

Determining the Ratio of the Precipitated versus Substituted Arsenic by XAFS and SIMS in Heavy Dose Arsenic Implants in Silicon

Doping silicon with arsenic by ion implantation above the solid solubility level leads to As clusters and/or precipitates in the form of monoclinic SiAs causing electrical deactivation of the dopant. Information on the local structure around the As atom, and the As concentration depth profiles is important for the implantation and annealing process in order to reduce the precipitated As and maximize the electrically activated As. In this study, we determined the local As structure and the precipitated versus substituted As for As implants in CZ (001) Si wafers, with implant energies between 20 keV and 100 keV, and implant doses ranging from 1 × 10 15 /cm 2 to 1 × 10 18 /cm 2 . The samples were subjected to different thermal annealing conditions. We used secondary ion mass spectrometry (SIMS) and UT- MARLOWE simulations to determine the region where the As-concentration is above the solid solubility level. By x-ray absorption fine structure spectroscopy (XAFS), we probed the structure of the local environment around As. XAFS being capable of probing the short-range order in crystalline and amorphous materials provides information on the number, distance and chemical identity of the neighbors of the main absorbing atom. Using Fourier analysis, the coordination numbers (N) and the nearest-neighbor distances (R) to As atoms in the first shell were extracted from the XAFS data. When As precipitates as monoclinic SiAs, the nearest-neighbor distances and coordination numbers are ∼2.37 A and ∼3, as opposed to ∼2.40 A and ∼4 when As is substitutional. Based on this information, the critical implant dose where the precipitation/clustering of As starts, and the ratio of the substitutional versus cluster/precipitate form As in the samples were determined.

Spectroscopic analysis of Al and N diffusion in HfO2

X-ray photoelectron core level spectroscopy, secondary ion mass spectroscopy, spectroscopic ellipsometry, and extended x-ray absorption fine structure measurements have been employed to distinguish the effects of Al and N diffusion on the local bonding and microstructure of HfO2 and its interface with the Si substrate in (001)Si/SiOx/2 nm HfO2/1 nm AlOx film structures. The diffusion of Al from the thin AlOx cap layer deposited on both annealed and unannealed HfO2 has been observed following anneal in N2 and NH3 ambient. Both N2 and NH3 subsequent anneals were performed to decouple incorporated nitrogen from thermal reactions alone. Causal variations in the HfO2 microstructure combined with the dependence of Al and N diffusion on initial HfO2 conditions are presented with respect to anneal temperature and ambient.

Formation of arsenic rich silicon oxide under plasma immersion ion implantation and laser annealing

Samples produced by plasma immersion ion implantation of Arsenic in Silicon using a non-pulsed plasma source and subsequent laser annealing were investigated with respect to As depth distribution, oxide thickness, and As local order using SIMS, XPS, INAA and EXAFS analysis. A surface layer (∼10 nm), was identified as an As-rich Si oxide formed after implantation. The thickness of this layer was found to be larger for samples annealed using a low thermal budget up to a threshold where probably melting occurred. Dopant depth profile was re-distributed whereas the final oxide film of these samples showed thicknesses of a few nm. The retained As dose exhibited an apparent drastic increase. A hypothesis for the processes involved is presented based on experimental evidence.

Subtle local structural variations in oxygen deficient niobium germanate thin film glasses as revealed by x-ray absorption spectroscopy

The local electronic and crystal structure of niobium-lead-germanate, Nb2O5-PbO- GeO2 (NPG), glass thin films on silicon substrates were probed by XANES and EXAFS. NPG glasses are promising candidates for applications in nonlinear optical devices because they exhibit interesting optical characteristics such as high nonlinear third order optical susceptibility. In this work NPG glasses were prepared with pulsed laser deposition method with varying oxygen partial pressure to induce thin films with different oxygen stoichiometry. Previously, it was shown that oxygen stoichiometry has a very important effect to produce unusual high optical susceptibility. Detailed EXAFS and XANES analyses in a series of NPG thin films revealed the subtle variations in the local environment around Nb atoms and the Nb oxidation states caused by oxygen deficiencies.

Synchrotron XPS and EXAFS identification of chemical state and crystal phase changes of HfO 2 films doped with Si, N, Al, and La

The recent industry wide investigation of incorporating various elemental dopant species into HfO2 to achieve higher-k gate dielectric alloy materials in order to maintain the rapid pace of scaling according to Moores Law has been expanded to include enhancement of the SiO/HfO interface dipole to tune the effective work function (EWF) of n and p-type gate electrodes. This work illustrates the value of high resolution synchrotron X-ray photoemission spectroscopy (XPS), X-ray photoabsorption spectroscopy (XAS), and extended X-ray absorption fine structure (EXAFS) techniques to identify changes in chemical state bonding and associated crystalline polymorph transitions as a function of dopant species and anneal parameters. Direct correlation of these spectra with representative device data greatly elucidates critical process optimization pathways.