Although all areas of semiconductor manufacturing have experienced the reality of miniaturization, this review is intended to highlight the key materials and processing parameters for successful high aspect ratio contacts (HARCs) in the tungsten plug process. Seven fundamental points of interest are highlighted: (1) dopant levels, (2) cleans, (3) contact layer, (4) barrier layer, (5) Ti-TiN anneal, (6) tungsten fill, and (7) tungsten etchback. Several of these factors-residual native oxides, Ti thickness at the bottom of the contact, and anneal temperature-toggle the amount of silicidation at the bottom of the contact in an interactive way and need to be optimized accordingly along with the W seed layer to minimize TiFx, formation during tungsten deposition. Other detrimental contact-related defects are discussed with emphasis on their source. Ti cusping and grain growth as well as TiN and W film conformality are shown to be first order factors in forming W keyholes. Collimation has been a means of minimizing cusping and achieving sufficient Ti at the bottom of the contact, but the logistics of increasing collimation for that required for 5:1 HARCs and beyond (deposition rates and collimator changes) may provide an opportunity for one of the newer technologies. TiN has been shown to act as a barrier to W wormholes. Two means of depositing TiN are presented with their inherent advantages and disadvantages. Sputter-deposited TiN is a low resistance form of TiN, but does not deposit on the sidewalls of the contact. The more conformal chemical vapor deposited (CVD) TiN process provides a more complete barrier with better sidewall coverage, but has higher sheet resistance. Tungsten planarization can be accomplished by dry etch or chemical-mechanical polishing (CMP). Dry etch is effective in removing W but ineffective in removing the large W defects that are often associated with the deposition process. CMP more readily planarizes the larger defects, but is more likely to scratch the oxide. Optimization of each is required. (C) 1997 Elsevier Science S.A.

CuInSe2 photoanodes can be optimized for use in electrochemical photovoltaic cells, containing aqueous polyiodide as the electrolyte, by wet chemical etching in Br2MeOH and subsequent thermal treatment (air oxidation). Surface analyses show the formation of a rather clean, Cu-depleted surface with some adsorbed oxygen after Br2/MeOH etch, and the formation of indium-oxygen bonds after thermal treatment, in accordance with previous studies that show indium oxides to be the native ones on this semiconductor. Samples that underwent photoanodic decomposition in the iodide electrolyte and those that were purposely decomposed in acetonitrile showed severe to near-total Cu depletion near their surface and the presence of lower valent Se. These data complement those from solution analyses and from electrochemical studies, to characterize the preferred decomposition path of CuInSe2 sufficiently to stabilize this type of photoelectrochemical cell. Our conclusions are based on the use of Auger parameters and, to a lesser extent, on empirical comparison of x-ray induced Auger electron line shapes, because of the difficulty in extracting unambiguous conclusions from x-ray photoelectron binding energies only.

X-ray photoelectron spectroscopy (XPS) is used in both a qualitative and quantitative fashion to study the AlxGa1−xAs alloy. Gallium and aluminum atoms are always bonded to the arsenic atom. As the concentration of Al increases, a notable shift in the As-3d level could be expected as Ga and Al both have different electronegativities. Spectra taken on molecular beam epitaxially grown samples do not show this shift in the As-3d core level. The composition of the films have been measured with an electron probe, and these results agree very well with the XPS quantitative data. Standard spectra are presented for films with x=0.16, 0.23, 0.32, 0.46, and 0.65.

n-CuInSe2, n-CuInS2 and n-CuIn5S8 were used as photoanodes in electrochemical photovoltaic solar cells, using aqueous polysulfide electrolyte. CuIn5S8 was found to be less stable than CuInS2. Because of kinetic limitations of polysulfide-based systems, the CuInSe2/aqueous polyiodide cell was studied and optimized to yield stable, near 12% AM1 conversion efficiency. The strategy used to achieve this is described. (Photo)electrochemical methods were used to characterize the semiconductor materials and a photoelectrochemical test was developed to gauge the photovoltaic activity of p-CuInSe2 layers used in solid state cells. Solid-state chemical studies on the (Cu2X)2-(In2X3)(X=S,Se) system, and the use of photoelectrochemistry in them, are briefly described.

The efficiency and operational characteristics of the (CdZn)S/CuInSe2 heterojunction solar cell are significantly improved as a result of a postfabrication heat treatment in an oxygen containing environment. The effects of this critical annealing process on the microchemical and microelectrical properties of the various cell layers and interfaces are investigated. Time-resolved EBIC and laser scanning techniques are correlated with cell performance data to identify two separate mechanisms that affect cell response. High resolution SIMS is used to evaluate compositional changes and interdiffusion effects, showing that penetration of the Cu-ternary layer by the oxygen is minimal. Light and dark current–voltage characteristics and diagnostic spectral response data are used to explain changes in cell operation.

Photoelectrochemistry has been employed to characterize the p-CuInSe/sub 2/ component of the CdS/CuInSe/sub 2/ photovoltaic cell. Using the junction between CuInSe/sub 2/ on-metal and a nonaqueous electrolyte containing a redox couple not specifically adsorbed onto the semiconductor, one can test the films for photovoltaic activity and obtain effective electronic properties of them, before CdS deposition, in a nondestructive manner. Electrochemical decomposition of CuInSe/sub 2/ was investigated in acetonitrile solutions to determine the mechanism of decomposition (n and p) in the dark and under illumination. Electrochemical, solution chemical and surface analyses confirmed at the light-assisted decomposition of CuInSe/sub 2/ resulted in metal ions and elemental chalcogen. On the basis of the results from the electrochemical decomposition, and studies on the solid state chemistry of the (Cu/sub 2/Se) /SUB x/ (In/sub 2/Se/sub 3/) /SUB 1-x/ system and surface analyses, the CuInSe/sub 2//polyiodide interface was stabilized and up to 11.7% conversion efficiencies were obtained.

CuInSe2 has emerged as an important photovoltaic semiconductor. The critical importance of stoichiometry changes, interfacial chemical reactions, and compositional variations on cell performance has made the acquisition of reliable quantitative data by surface analysis methods mandatory. In this study, single crystals of CuInSe2 were cleaved in UHV, exposing the (110) plane which is representative of the bulk material. Quantitative AES analysis was performed using both N(E) and dN(E)/dE data, yielding concentration results within 2 at. % of stoichiometric values. The method developed is based upon an independent evaluation of matrix effects using elemental standards and actual density considerations. The effects of Ar+ ion sputtering were investigated for beam energies 0.1

AES, XPS, and SIMS analysis of the plasma grown oxyfluorides on GaAs are presented. These data indicate that the films are composed of three basic layers. Region 1 is a mixed As2O3, Ga2O3 glass with low concentrations of fluorine. In the second region, fluorine concentrations increase and a shoulder on the As-3d and Ga-3d peaks are observed. As2O3 and Ga2O3 are still the major constituents of the film. At the interface between the oxyfluoride glass and the substrate is a thin metallic As region. The difference between pure oxides and this oxyfluoride is the incorporation of fluorine in the films and lower concentrations of metallic As at the interface.

The optical properties of CuInSe2 thin films and single crystals are reported. The wavelength dependence of the refractive index and extinction coefficient is measured using multiple angle-of-incidence ellipsometry. Absorption coefficients as high as 6×105/cm are reported—the highest for any semiconductor. CuInSe2 is confirmed to have a room temperature, direct-bandgap transition near 0.96 eV for the single crystals, and 1.02 for the thin films. The difference is proposed to be due to nonuniformity in composition of the polycrystalline material. Additional absorption in the low absorption-coefficient regime is likely due to transitions associated with phonon absorptions for the single crystals. The effects of heat treatments in Ar, N, and O are shown to improve the optical properties of the thin films due to improvement in film compositional uniformity. Heating in high vacuum causes Se desorption near the film surface, causing a related degradation in the absorption characteristics.

Fundamental properties of interface formation in the CdS and Cd(Zn)S/CuInSe/sub 2/ solar cell are investigated using surface analysis and microelectrical characterizations. The formation of a binary semiconductor transition layer during the initial stages of heterojunction growth is reported. The effects of annealing on the integrity of the various device interfaces and the performance of the cells are discussed. The evaluation of heterojunction and electrical response at other internal interfaces is studied using high resolution EBIC on fractured cell cross-sections. The importance and effects of post-deposition oxygen heat-treatments on the cell performance are discussed.

The initial formation and subsequent development of the CdS/CuInSe2 interface are studied. XPS depth-compositional data are used to identify the composition of a interfacial reacted region between the CdS and Cu-ternary layers. Angular-resolved XPS confirm the existence of this transition layer which is a mixed Cu2S–Cu2S binary. Auger transitions in the XPS spectra are used to resolve those compounds. Differences in EELS spectra as a function of CdS growth are also ascribed to the existence of the interface region. The effects of annealing on the integrity of this interface and photovoltaic performance of the device are also presented. Three distinct regimes are identified: (1) T<150 °C. Device and interface properties are stable; (2) 200

The correlations between the electrical and compositional properties of grain boundaries in polycrystalline Si are examined in detail. High-resolution surface analysis techniques (AES, SIMS, XPS, EELS) and microelectrical (SAM, EBIC, minority-carrier lifetime) characterization methods are used. The direct evidence for impurity segregation to the intergrain regions is presented. Effect of illumination on the grain boundary electrical characteristics are correlated with impurity compositions. Finally, the interrelationships among heat-treatment, oxygen segregation and grain boundary electrical activity are discussed.

Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation L. L. Kazmerski, P. J. Ireland, O. Jamjoum, R. A. Mickelsen, W. Chen, A. H. Clark; Summary Abstract: Annealing and interface effects in Cds–CuInSe2 solar cells. J. Vac. Sci. Technol. 1 March 1982; 20 (3): 308–309. https://doi.org/10.1116/1.571289 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAVS: Science & Technology of Materials Interfaces and ProcessingJournal of Vacuum Science and Technology Search Advanced Search |Citation Search

Native oxides and oxyfluorides were grown on GaAs by a glow discharge plasma process. Analysis of metal-insulator-semiconductor structures based on oxyfluoride dielectrics indicated vastly different interface properties compared to pure oxide dielectrics. Whereas oxide structures showed high densities of fast surface states, oxyfluorides showed no evidence of such effects.

A glow discharge technique is used to grow native oxides and oxyfluorides on GaAs. The capacitance-voltage and conductance-voltage measurements of the resulting metal/insulator/semiconductor structures show vastly different properties. Specifically, the density of interface states in the d.c.-to-5 MHz range appears to be much lower at the oxyfluoride interface than at the oxide interface. Secondary ion mass spectroscopy analyses indicate that some fluorine ions are mobile and the fluorine concentration is reduced by about an order of magnitude after a thermal anneal at 450°C. X-ray photoemission studies indicate that the glass is a mixture of GaF 3 and AsOF 3 molecules.