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  • 1
    Electronic Resource
    Electronic Resource
    Real time spectroellipsometry characterization of optical gap profiles in compositionally-graded semiconductor structures: Applications to bandgap engineering in amorphous silicon-carbon alloy solar cells (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 2420-2429 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have applied a real time spectroellipsometry data analysis procedure developed previously [S. Kim and R. W. Collins, Appl. Phys. Lett. 67, 3010 (1995)] to characterize depth profiles in the optical gap for compositionally-graded semiconductor alloy thin films prepared by plasma enhanced chemical vapor deposition. The analysis procedure employs a two-layer (four-medium) optical model consisting of the ambient, a thin surface roughness layer and outer-layer (5–15 A(ring)) whose properties are to be determined, and a pseudo-substrate that contains the past history of the graded-layer deposition. The ellipsometric spectra (2.3–4.0 eV) are analyzed to provide, not only the depth-profile of the optical gap and alloy composition for the graded layer, but also the instantaneous deposition rate and the surface roughness layer thickness versus time or accumulated layer thickness. To apply the previous analysis approach, it was necessary to (i) parameterize the dielectric function of the alloys as a continuous function of composition over the desired alloy range and (ii) express the optical gap as an accurate function of alloy composition. As an example, we have applied the extended analysis to obtain the depth-profile of the optical gap and alloy composition with 〈15 A(ring) resolution for a hydrogenated amorphous silicon-carbon alloy (a-Si1−xCx:H) film prepared by continuously varying the gas flow ratio z=[CH4]/{[CH4]+[SiH4]}. In order to demonstrate the technological importance of such structures, the graded layer has been incorporated at the p/i interface of widegap a-Si1−xCx:H p-i-n solar cells, and improvements in open-circuit voltage have been observed. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363077
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  • 2
    Electronic Resource
    Electronic Resource
    Real time spectroellipsometry for optimization of diamond film growth by microwave plasma-enhanced chemical vapor deposition from CO/H2 mixtures (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 6489-6495 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Real time spectroellipsometry has been applied to determine the deposition rate and thickness evolution of the nondiamond (sp2-bonded) carbon volume fraction in very thin (〈1000 A(ring)), but fully coalesced, nanocrystalline diamond films prepared on Si substrates by microwave plasma-enhanced chemical vapor deposition from gas mixtures of CO and H2. At a substrate temperature of ∼800 °C, high quality diamond films can be obtained over two orders of magnitude in the CO/H2 gas flow ratio, from 0.04, the lowest value explored, to ∼5. A well-defined minimum in the sp2 C volume fraction (0.03 in a 600 A(ring) film) is observed for a CO/H2 ratio of 0.2, corresponding to the C–H–O diamond-growth phase-diagram coordinate XH/Σ=[H]/{[H]+[C]} of 0.9. Under these conditions, the deposition rate increases with increasing temperature over the range of ∼400–800 °C with an activation energy of 8 kcal/mol, behavior identical to that observed for diamond film growth from a CH4/H2 ratio of 0.01. This observation shows that the dominant film precursors in the diamond growth process from CO/H2=0.2 are hydrocarbons whose flux at the growing film surface is controlled through the reaction of excited CO with H or H2 in the plasma. A broad subsidiary minimum in the sp2 C content is observed, centered near a CO/H2 ratio of 2, corresponding to an XH/Σ value of ∼0.5. Under these gas flow conditions, the deposition rate is a complicated function of temperature, exhibiting a peak near 550 °C. This peak shifts to lower temperature with further increases in the CO/H2 ratio above 2, suggesting a nonhydrocarbon precursor and a different growth mechanism for diamond prepared at high CO/H2 ratio and low temperature. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363668
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  • 3
    Electronic Resource
    Electronic Resource
    Effect of deposition conditions on the nucleation and growth of glow-discharge a-Si:H (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 1869-1882 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In situ ellipsometry experiments have been used to study the initial nucleation and growth of glow-discharge hydrogenated amorphous silicon (a-Si:H) deposited on c-Si substrates under different conditions. The substrate temperature (Ts), dc bias, and silane concentration in both hydrogen and inert gas diluents were varied. In the first ∼30–60 A(ring) of film growth, deviations of the in situ ellipsometry data from models assuming thickness independent dielectric functions are observed for a-Si:H prepared under conditions that lead to a low density of electronic defects. The form of the deviations in the in situ data appear to be consistent with the development and convergence of densely packed clusters with a lateral extent of ∼20–30 A(ring), not with a well-dispersed distribution. The deviations disappear for Ts less than ∼200 °C and for flow ratios less than 1:20 (SiH4):(diluent). The low Ts effect is attributed to the lack of development of the initial growth microstructure caused by (1) the low mobility and desorption rate of surface radicals and/or (2) the low average coordination number due to ineffective hydrogen elimination. The low SiH4:diluent ratio effect is attributed to the lack of effective convergence of the initial growth microstructure since film formation may be limited, not by hydrogen elimination and surface reaction, but by radical flux arriving at the surface. The effect of deposition parameters on the bulk bonding density, surface roughness, and the interface structure is also presented. At very low SiH4:diluent ratios, it has been instructive to consider the damage mechanisms induced by the pure diluent plasmas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.338032
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  • 4
    Electronic Resource
    Electronic Resource
    Dual rotating-compensator multichannel ellipsometer: Instrument development for high-speed Mueller matrix spectroscopy of surfaces and thin films (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 1742-1754 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A multichannel ellipsometer in the dual rotating-compensator configuration has been developed for applications in real time Mueller matrix spectroscopy of anisotropic surfaces and thin films. The sequence of optical elements for this instrument configuration can be denoted PC1r(5ω)SC2r(3ω)A, where P, S, and A represent the polarizer, sample, and analyzer. In this sequence, C1r and C2r represent the first and second compensators, rotating with angular frequencies of 5ω and 3ω, respectively, where ω=π/TC is the base angular frequency (corresponding to 2 Hz) and TC=0.25 s is the fundamental optical period. The instrument can provide 170 point spectra over the wavelength range from 235 nm (5.3 eV) to 735 nm (1.7 eV) in all 16 elements of the unnormalized Mueller matrix with minimum acquisition and repetition times of TC=0.25 s. In this study, instrumentation calibration procedures are demonstrated in the transmission geometry without a sample, including (i) alignment of the two MgF2 zero-order biplate compensators, (ii) determination of the retardance and phase spectra for the compensators, (iii) determination of the offset angles for the optical elements, and (iv) characterization of the spectral response function of the ellipsometer. Calibration procedure (iv) allows the (1,1) element of the transmission Mueller matrix to be determined; thus the unnormalized Mueller matrix can be obtained. The dual rotating-compensator multichannel ellipsometer is assessed with respect to its performance in transmission without a sample, and is then applied in the transmission geometry to study anisotropy, depolarization, and light scattering effects for a MgF2 helicoidally sculptured thin film on a glass substrate. Numerous future applications of this instrument are anticipated for real time analysis of complex surfaces and thin films in the reflection geometry as well. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1347969
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  • 5
    Electronic Resource
    Electronic Resource
    Multichannel ellipsometer for real time spectroscopy of thin film deposition from 1.5 to 6.5 eV (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3451-3460 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A rotating polarizer multichannel ellipsometer has been optimized for operation well into the ultraviolet (UV) spectral range. With this instrument, 132 spectral points in the ellipsometric parameters (ψ, Δ) over the photon energy range from 1.5 eV (827 nm) to 6.5 eV (191 nm) can be collected in a minimum acquisition time of 24.5 ms, corresponding to one optical cycle of the rotating polarizer. Averages over two and 80 optical cycles (obtained in 49 ms and 1.96 s, respectively) give standard deviations in (ψ, Δ) of less than (0.04°, 0.08°) and (0.007°, 0.015°), respectively, for the energy range from 3.5 to 6.0 eV, as determined from successive measurements of a stable thermally oxidized silicon wafer. Key modifications to previous instrument designs include: (i) a tandem in-line Xe/D2 source configuration for usable spectral output from 1.5 to 6.5 eV; (ii) MgF2 Rochon polarizers for high transmission in the UV without the need for optical activity corrections; (iii) a spectrograph with a grating blazed at 250 nm and two stages of internally mounted order-sorting filters; and (iv) nonuniform grouping of the pixels of the photodiode array detector for a more uniform spectral resolution versus photon energy, with energy spreads per pixel group ranging from 0.02 eV at 1.6 eV to 0.05 eV at 5.1 eV. As an example of the application of this instrument, results of real time spectroscopic ellipsometry studies are reported for the deposition of an amorphous silicon nitride thin film by radio-frequency magnetron sputtering onto a silicon wafer substrate. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1288260
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  • 6
    Electronic Resource
    Electronic Resource
    Rotating-compensator multichannel ellipsometry: Applications for real time Stokes vector spectroscopy of thin film growth (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 1800-1810 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A multichannel spectroscopic ellipsometer based on the rotating-compensator principle was developed and applied to measure the time evolution of spectra (1.5–4.0 eV) in the normalized Stokes vector of the light beam reflected from the surface of a growing film. With this instrument, a time resolution of 32 ms for full spectra is possible. Several advantages of the rotating-compensator multichannel ellipsometer design over the simpler rotating-polarizer design are demonstrated here. These include the ability to: (i) determine the sign of the p-s wave phase-shift difference Δ, (ii) obtain accurate Δ values for low ellipticity polarization states, and (iii) deduce spectra in the degree of polarization of the light beam reflected from the sample. We have demonstrated the use of the latter spectra to characterize instrument errors such as stray light inside the spectrograph attached to the multichannel detector. The degree of polarization of the reflected beam has also been applied to characterize the time evolution of light scattering during the nucleation of thin film diamond by plasma-enhanced chemical vapor deposition, as well as the time evolution of thickness nonuniformities over the probed area of the growing diamond film. In this article, a detailed description of calibration and data reduction for the new instrument is provided. Future applications of this instrument are expected for real time characterization of film growth and etching on patterned surfaces for microelectronics and on thick transparent substrates for large area displays and photovoltaics. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148844
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  • 7
    Electronic Resource
    Electronic Resource
    Spectroscopic ellipsometry on the millisecond time scale for real-time investigations of thin-film and surface phenomena (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 3842-3848 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Submonolayer sensitivity to thin-film nucleation and growth in real time on the millisecond scale has been achieved with a unique rotating polarizer multichannel ellipsometer. Continuous spectra in the ellipsometry angles {ψ(hv),Δ(hv)} consisting of ∼50 points from hv=1.5 to 4.3 eV have been obtained with acquisition and repetition times as short as 16 and 32 ms, respectively. As an example of the instrument capabilities, we present results for hydrogenated amorphous silicon (a-Si:H) growth on c-Si by plasma-enhanced chemical vapor deposition at a rate of 400 A(ring)/min. In this example, the acquisition and repetition times are both 64 ms, and at this speed a precision in (ψ,Δ) of ∼0.02–0.03° is obtained under optimum conditions. We observe a-Si:H nucleation in the first 2 s of deposition, and detect relaxation of nucleation-induced surface roughness with submonolayer sensitivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143280
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  • 8
    Electronic Resource
    Electronic Resource
    Real time spectroscopic ellipsometry studies of the nucleation and growth of p-type microcrystalline silicon films on amorphous silicon using B2H6, B(CH3)3 and BF3 dopant source gases (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 4141-4153 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Real time spectroscopic ellipsometry (RTSE) has been applied to study the nucleation, coalescence, and growth processes for ∼100–200 Å thick microcrystalline silicon (μc-Si:H) p-layers prepared by radio frequency (rf) plasma-enhanced chemical vapor deposition at 200 °C on amorphous silicon (a-Si:H) i-layers in the substrate/(n-i-p) device configuration. Analysis of the RTSE data provides the bulk p-layer dielectric function (2.5–4.3 eV), whose amplitude and shape characterize the void and crystalline Si contents in the p-layer. Among the parameters varied in this study of the deposition processes include the underlying a-Si:H i-layer surface treatment, the p-layer H2-dilution flow ratio, the p-layer dopant source gas and flow ratio, and the p-layer rf plasma power flux. Here we emphasize the differences among p-layer deposition processes using diborane, B2H6, trimethyl boron, B(CH3)3, and boron trifluoride, BF3, dopant source gases. We find that it is easiest to nucleate μc-Si:H p-layers immediately on the i-layer without any surface pretreatment when B2H6 is used as the source gas. In contrast, when B(CH3)3 or BF3 is used, a H2-plasma treatment of the i-layer is necessary for immediate nucleation of Si microcrystals; without pretreatment, the p-layer nucleates and grows as an amorphous film. For H2-plasma-treated i-layers, p-layer microcrystal nucleation at low plasma power is controlled by the catalytic effects of B-containing radicals at the i-layer surface, irrespective of the dopant source, whereas nucleation at higher plasma power is controlled by the bombardment of the i-layer by Si-containing ions. Under high power plasma conditions using BF3, dense single-phase μc-Si:H p-layers can be obtained over a wide range of the dopant gas flow ratio. In contrast, for B2H6 and B(CH3)3, such properties are obtained only over narrow flow ratio ranges owing to the relative ease of dissociation of these gases in the plasma. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370323
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  • 9
    Electronic Resource
    Electronic Resource
    In situ ellipsometry comparison of the nucleation and growth of sputtered and glow-discharge a-Si:H (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 4146-4153 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the results of ellipsometry measurements performed during the growth of hydrogenated amorphous silicon (a-Si:H) thin films on crystalline silicon substrates using ion beam sputtering. The data have been compared to our earlier results for high-quality a-Si:H prepared by glow-discharge decomposition of SiH4, and significant differences in the initial nucleation and microstructural evolution have been deduced for the two types of films. For the glow-discharge a-Si:H, the in situ pseudodielectric function data provided evidence for the convergence of initial growth microstructure in the first ∼50 A(ring), leaving a-Si:H of near bulk Si–Si bond-packing density at the interface to the c-Si substrate. After the nucleation process, growth was found to be nearly layer by layer. The data for the sputtered a-Si:H also reveal the formation of a low-density microstructure in the initial stages of growth. However, in contrast to the glow-discharge films, the microstructure does not converge, and an extensive layer (∼200–400 A(ring)) of bond-packing density lower than the bulk is left at the interface to the substrate. The effect of hydrogen incorporation on this and other aspects of the microstructural evolution of the sputtered films is discussed. Finally, similarities observed between the microstructural evolution of the sputtered films and poorer-quality glow-discharge films provide insights into the growth mechanisms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.339132
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  • 10
    Electronic Resource
    Electronic Resource
    Influence of substrate structure on the growth of hydrogenated amorphous silicon studied by in situ ellipsometry (1986)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 60 (1986), S. 4169-4176 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using in situ ellipsometry as a probe, the effect of substrate microstructure on the growth habit of high-quality hydrogenated amorphous silicon (a-Si:H) has been studied. An understanding of the growth process is important when combining a-Si:H with other materials in thin-film multilayer devices. The present study concentrates on cases where a-Si:H of different microstructure, microcrystalline Si:H (μc-Si:H), and single-crystal Si are used as substrates. The a-Si:H top film is grown under identical conditions on each substrate material and pseudo-dielectric-function trajectories are collected during growth. These trajectories have been applied to characterize the bulk and interface structure and the evolution of surface roughness layers during growth. For the same deposition conditions, a range of growth patterns is observed, depending on the structure of the substrate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.337501
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