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86 Electrical characteristics of Pt Schottky contacts on sulfide-treated n-type ZnO
Author(s): Sang-Ho Kim (Affiliation: Dept. of Mater. Sci. & Eng., Gwangju Inst. of Sci. & Technol., South Korea), Han-Ki Kim, Tae-Yeon Seong
Journal: Appl. Phys. Lett. (USA), vol.86, no.2, p.22101-1-3 (10 Jan. 2005)
Publisher: AIP, USA
Language: English
ISSN: 0003-6951, Full text
Document type: Journal article
Abstract: We have investigated the effect of sulfide treatment on the electrical characteristics of Pt contacts on (000-1) ntype ZnO (~5×1015cm-3) single crystals. The Pt contact on conventionally cleaned ZnO surface shows an ohmic behavior. However, the contact produces a Schottky behavior, when the ZnO surface is etched in a boiling (NH4)2Sx solution. Measurements show that the Schottky barrier height, ideality factor, and leakage current at -5 V of the Pt contact on the sulfide-treated ZnO are 0.79 eV, 1.51, and 3.75×10-10 A, respectively. Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS) examinations indicate the formation of ZnS phase at the Pt/ZnO interface. Based on the capacitance-voltage, AES, and XPS results, a possible mechanism for the formation of good Schottky contacts is given (25 refs.)
Inspec No.: 8247184
87 Surface roughness in XeF2 etching of a-Si/c-Si (100)
Author(s): A.A.E. Stevens, H.C.W. Beijerinck (Affiliation: Phys. Dept., Eindhoven Univ. of Technol., Netherlands)
Journal: J. Vac. Sci. Technol. A, Vac. Surf. Films (USA), vol.23, no.1, p.126-36 (Jan. 2005)
Publisher: AIP for American Vacuum Soc, USA
Language: English
ISSN: 0734-2101, Full text
Document type: Journal article
Abstract: Single wavelength ellipsometry and atomic force microscopy (AFM) have been applied in a well-calibrated beam-etching experiment to characterize the dynamics of surface roughening induced by chemical etching of a ~12 nm amorphous silicon (a-Si) top layer and the underlying crystalline silicon (c-Si) bulk. In both the initial and final phase of etching, where either only a-Si or only c-Si is exposed to the XeF2 flux, we observe a similar evolution of the surface roughness as a function of the XeF2 dose proportional to D (XeF2)â with ¦Â¡Ö0.2. In the transition region from the pure amorphous to the pure crystalline silicon layer, we observe a strong anomalous increase of the surface roughness proportional to D(XeF2)â with ¦Â¡Ö1.5. Not only the growth rate of the roughness increases sharply in this phase, also the surface morphology temporarily changes to a structure that suggests a cusplike shape. Both features suggest that the remaining a-Si patches on the surface act effectively as a capping layer which causes the growth of deep trenches in the c-Si. The ellipsometry data on the roughness are corroborated by the AFM results, by equating the thickness of the rough layer to 6 ó, with ó the root-mean-square variation of the AFM's distribution function of height differences. In the AFM data, the anomalous behavior is reflected in a too small value of ó which again suggests narrow and deep surface features that cannot be tracked by the AFM tip. The final phase morphology is characterized by an effective increase in surface area by a factor of two, as derived from a simple bilayer model of the reaction layer, using the experimental etch rate as input. We obtain a local reaction layer thickness of 1.5 monolayer consistent with the 1.7 ML value of Lo et al. [Lo et al., Phys. Rev. B 47, 648 (1993)] that is also independent of surface roughness (33 refs.)
Inspec No.: 8248318
88 Deep dry-etch of silica in a helicon plasma etcher for optical waveguide fabrication
Author(s): W.T. Li, D.A.P. Bulla, J. Love, B. Luther-Davies, C. Charles, R. Boswell (Affiliation: Res. Sch. of Phys. Sci. & Eng., Australian Nat. Univ., Canberra, ACT, Australia)
Journal: J. Vac. Sci. Technol. A, Vac. Surf. Films (USA), vol.23, no.1, p.146-50 (Jan. 2005)
Publisher: AIP for American
Vacuum Soc, USA
Language: English
ISSN: 0734-2101, Full text
Document type: Journal article
Abstract: Dry-etch of SiO2 layers using a CF4 plasma in a helicon plasma etcher for optical waveguide fabrication has been studied. Al2O3 thin films, instead of the conventional materials, such as Cr or photoresist, were employed as the masking materials. The Al2O3 mask layer was obtained by periodically oxidizing the surface of an Al mask in an oxygen plasma during the breaks of the SiO2 etching process. A relatively high SiO2/Al2O3 etching selectivity of ~100:1, compared with a SiO2/Al selectivity of ~15:1, was achieved under certain plasma condition. Such a high etching selectivity greatly reduced the required Al mask thickness from over 500 nm down to ~100 nm for etching over 5-ìm-thick silica, which make it very easy to obtain the mask patterns with near vertical and very smooth sidewalls. Accordingly, silica waveguides with vertical sidewalls whose roughness was as low as 10 nm were achieved. In addition, the mechanism of the profile transformation from a mask to the etched waveguide was analyzed numerically; and it was found that the slope angle of the sidewalls of the mask patterns only needed to be larger than 50° for achieving vertical sidewalls of the waveguides, if the etching selectivity was increased to 100 (12 refs.)
Inspec No.: 8248322
89 Plasma-surface interactions of nanoporous silica during plasma-based pattern transfer using C4F8 and C4F8/Ar gas mixtures
Author(s): Xuefeng Hua (Affiliation: Dept. of Phys., Univ. of Maryland, College Park, MD, USA), C. Stolz, G.S. Oehrlein, P. Lazzeri, N. Coghe, M. Anderle, C.K. Inoki, T.S. Kuan, P. Jiang
Journal: J. Vac. Sci. Technol. A, Vac. Surf. Films (USA), vol.23, no.1, p.151-64 (Jan. 2005)
Publisher: AIP for American Vacuum Soc, USA
Language: English
ISSN: 0734-2101, Full text
Document type: Journal article
Abstract: We have investigated plasma surface interactions of nanoporous silica (NPS) films with porosities up to 50%, and SiO2 with C 4F8/Ar discharges used for plasma etching. The pore size was about 2-3 nm for all films. In highly polymerizing plasmas (e.g., pure C4F8 discharges), the porous structure of NPS material favors surface polymerization over etching and porosity-corrected etching rates (CER) were suppressed and lower than SiO2 etching rate for the same conditions. The etching rates of NPS were dramatically enhanced in ion rich discharges (e.g., C4 F8/90%Ar) and the CER in this case is greater than the SiO2 etching rate. Both x-ray photoelectron spectroscopy (XPS) and static secondary ion mass spectroscopy (static SIMS) show that fairly thick (~2-3 nm) fluorocarbon layers exist on the NPS surface during C4F8 etching. This layer blocks the direct interaction of ions with the NPS surface and results in a low etching rate. For C4F8/90% Ar discharges, little fluorocarbon coverage is observed for NPS surfaces and the direct ion surface interaction is significantly enhanced, explaining the enhancement of CER. We can deduce from analysis of angular resolved XPS data that the surface of NPS materials and SiO2 remain smooth during C4F8 etching. For C4F8/90%Ar etching, the NPS surfaces became rough. The surface roughening is due to angle-dependent ion etching effects. These surface models were directly verified by the transmission electron microscopy. Depth profiling study of NPS partially etched using C4 F8 or C4F8/90%Ar discharges using dynamic SIMS indicates that the plasma induced modification of NPS was enhanced significantly compared with SiO2 due to the porous structure, which allows the plasma attack of the subsurface region. The modified layer thickness is related to the overall porosity and dramatically increases for NPS with an overall porosity of 50%. The distinct etching behavior of high porosity NPS (~50%) in fluorocarbon-based discharges relative to NPS material with lower overall porosity is possibly due to interconnected pores, which allow plasma species to more easily penetrate into the subsurface region (30 refs.)
Inspec No.: 8248323
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