Byungyou Hong

Effects of processing conditions on the growth of nanocrystalline diamond thin films: real time spectroscopic ellipsometry studies

Abstract Real time spectroscopic ellipsometry has been applied to characterize the preparation of ∼2000-A thick nanocrystalline diamond films on Si substrates by microwave plasma-enhanced chemical vapor deposition. Diamond films prepared under different conditions, including variations in the substrate temperature and CH4+H2+O2 gas mixture, have been studied. In addition to providing accurate Si substrate surface temperatures for diamond film growth via an ellipsometry-based calibration, the real time approach yields information on the following processes: (i) generation of initial substrate damage by the seeding process used to enhance diamond nucleation, (ii) annealing of the seeding damage that occurs upon heating the substrate to the deposition temperature, and (iii) the structural evolution of the diamond film throughout the nucleation and bulk film growth regimes. In the nucleation regime, the following information on the diamond film can be extracted: (i) the diamond mass thickness evolution with time, (ii) the sp2 C and void volume fractions in the nucleating layer, and (iii) the thickness at which nuclei make contact, the latter providing an estimate of the nucleation density. In the bulk layer growth regime, the time evolution of the following information can be extracted: (i) the bulk layer thickness, (ii) the surface roughness layer thickness, (iii) the mass thickness of sp2 C in the bulk layer, and (iv) the void volume fraction in the bulk layer. In the nucleation regime, we find that high quality diamond nanocrystals form under a wide range of gas compositions for substrate temperatures above 700°C. It is proposed that nucleation is controlled by a disordered carbon phase embedded in the substrate surface during the seeding process, in which the Si wafer is abraded with diamond powder. Above 700°C, the disordered C at the substrate surface is believed to recrystallize in the diamond phase upon exposure to an initial H2 plasma prior to diamond film growth. A common feature of diamond growth under all deposition conditions is the incorporation of a large concentration of sp2 C when diamond nuclei coalesce (typically after a thickness of 200–400 A). The maximum concentration occurs under conditions for which poorer quality bulk films are obtained, including low substrate temperatures ( 0.02). The sp2 C is trapped within ∼300 A of the substrate interface, but under optimum conditions of growth (i.e., the diamond growth region of the Cue5f8Hue5f8O gas phase diagram), little additional sp2 C forms with continued growth after the first 300 A. The formation of sp2 C in the coalescence stage has been attributed to shadowing effects that lead to a reduction of atomic H relative to C-containing precursors arriving at shadowed surfaces. For the nanocrystalline diamond films studied here, it is found that films having the lowest volume fraction of sp2 C at the end of the 2000 A deposition also exhibit the lowest void volume fraction and the smoothest surfaces.

Nucleation and bulk film growth kinetics of nanocrystalline diamond prepared by microwave plasma‐enhanced chemical vapor deposition on silicon substrates

Real time spectroscopic ellipsometry has been applied to characterize the substrate temperature (T) dependence of the deposition rates for nanocrystalline diamond thin films prepared by microwave plasma‐enhanced chemical vapor deposition on seeded Si substrates. With the real time capability, it is possible to determine the rates at which the diamond mass thickness (i.e., volume per area) increases during the early nucleation and bulk film growth regimes. The increases in the nucleating and bulk diamond growth rates with T for 400<T<800u2009°C are consistent with activation energies of ∼17 and 8 kcal/mol, respectively. The results reported here provide insights into the nature of the low‐T growth rate limitations for diamond films on nondiamond substrates.

Real-time spectroscopic ellipsometry studies of diamond film growth by microwave plasma-enhanced chemical vapour deposition

Abstract We have applied real-time spectroscopic ellipsometry to monitor the growth of highly uniform, nanocrystalline diamond films by microwave plasma-enhanced chemical vapour deposition. In this study, a unique multichannel instrument is employed to collect full ellipsometric spectra from 1.5 to 4.0 eV. Here we focus on two capabilities. First, we will describe a method to calibrate the true temperature of the top 200Aof the Si substrate under diamond growth conditions. Second, we describe the full microstructural evolution of the diamond films. The parameters derived include the time evolution of the void and optically absorbing, non-diamond (sp 2 ) carbon volume fractions in the film. In addition, the nuclei, bulk and surface roughness layer thicknesses during the nucleation, coalescence and bulk growth regimes are determined. These results reveal reproducible and remarkably internally consistent behaviour that provides new insights into the growth mechanisms for nanocrystalline diamond. We find that in the coalescence process, a large volume fraction of sp 2 carbon is trapped in the grain boundaries under all conditions of growth. After coalescence is complete, further generation of sp 2 carbon is impeded under optimum conditions.

Selective formation of a latticed nanostructure with the precise alignment of DNA-templated gold nanowires.

A very efficient method is introduced to selectively align and uniformly separate λ-DNA molecules and thus DNA-templated gold nanowires (AuNWs) using a combination of molecular combing and surface-patterning techniques. By the method presented in this work, it is possible to obtain parallel and latticed nanostructures consisting of DNA molecules and thus DNA-templated AuNWs aligned at 400 nm intervals. DNA-templated AuNWs are uniformly formed with an average height of 2.5 nm. This method is expected to hold potential for the integration of nanosized building blocks applicable to nanodevice construction.

Controlled gold nanoparticle assembly on DNA molecule as template for nanowire formation

A reducer was used to construct Au nanowires (AuNWs) by the conjugation of 2-aminoethanthiol-capped gold nanoparticles (AET-AuNPs) and the immobilized DNA molecules on 3-aminopropyltriethoxysilane-coated Si wafer. The AuNPs coated with AET monolayer seem to be electrostatically assembled along DNA molecules by careful control of the relative molar quantities of AuNPs and AET. A variety of AuNP sizes (2, 5, and 10nm) was used and also the ratio of AET to AuNP solution was varied to control the interparticle spacing and finally to form the nanowire based on DNA template. The formation of long-range AuNWs and the interparticle spacing were observed with atomic force microscopy.

Structural, electrical, and optical properties of antimony-doped tin oxide films prepared at room temperature by radio frequency magnetron sputtering for transparent electrodes

Antimony-doped tin oxide (ATO) films were prepared on 7059 Corning glass substrate by the radio frequency (rf) magnetron sputtering method using SnO2 target mixed with Sb of 6u2002wtu2009% at room temperature. The working pressure was varied from 0.67 to 2 Pa in steps of 0.67 Pa, and the rf power was varied from 100 to 175 W in steps of 25 W at room temperature. The thickness of the deposited ATO films was about 150 nm. X-ray diffraction (XRD) measurements showed the ATO films to be crystallized with a strong (101) preferred orientation as the rf power is increased. The spectra revealed that the deposited films were polycrystalline, retaining the tetragonal structure. The grain size was estimated from the XRD spectra using the Scherrer equation and found to decrease with a decrease in the working pressure and an increase in the rf power, while the surface roughness was observed to be smoothened. The ATO film that was deposited at a working pressure of 0.67 Pa with rf power of 175 W showed the lowest resistivity o...

Etching characteristics and application of physical-vapor-deposited amorphous carbon for multilevel resist

For the fabrication of a multilevel resist (MLR) based on a very thin, physical-vapor-deposited (PVD) amorphous carbon (a-C) layer, the etching characteristics of the PVD a-C layer with a SiOx hard mask were investigated in a dual-frequency superimposed capacitively coupled plasma etcher by varying the following process parameters in O2∕N2∕Ar plasmas: high-frequency/low-frequency combination (fHF∕fLF), HF/LF power ratio (PHF∕PLF), and O2 and N2 flow rates. The very thin nature of the a-C layer helps to keep the aspect ratio of the etched features low. The etch rate of the PVD a-C layer increased with decreasing fHF∕fLF combination and increasing PLF and was initially increased but then decreased with increasing N2 flow rate in O2∕N2∕Ar plasmas. The application of a 30nm PVD a-C layer in the MLR structure of ArF PR∕BARC∕SiOx∕PVD a-C∕TEOS oxide supported the possibility of using a very thin PVD a-C layer as an etch-mask layer for the TEOS-oxide layer.

Real time spectroellipsometry for optimization of diamond film growth by microwave plasma‐enhanced chemical vapor deposition from CO/H2 mixtures

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), 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 ∼800u2009°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 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 ∼400–800u2009°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...

Application of real-time spectroscopic ellipsometry for the development of low-temperature diamond film growth processes

Abstract Spectroscopic ellipsometry (SE) performed in real time using a multichannel instrument over the range 1.5–4.2 eV has been applied to investigate nanocrystalline diamond film growth by microwave plasma-enhanced chemical vapor deposition on silicon wafer substrates. Using the real-time SE measurement capability, we have established calibration procedures that provide the true near-surface substrate temperature under the actual conditions of diamond growth. In addition, we have developed procedures for the analysis of the real-time SE data that provide the deposition rates and film properties for a series of films prepared on the same substrate under different conditions. These procedures have enabled us to identify a new diamond film growth process based on CO-rich CO/H 2 gas mixtures that yields high deposition rates (2.5 μm/h) at low temperatures (∼500°C).

Simultaneous determination of reflectance spectra along with {ψ(E), Δ(E)} in multichannel ellipsometry: applications to instrument calibration and reduction of real-time data

Abstract We describe applications of the rotating polarizer multichannel ellipsometer for three-parameter spectroscopy (1.4–4.1 eV), in which a full reflectance spectrum is acquired simultaneously with (ψ, Δ), all in a time as short as 16 ms. Because data acquisition requires no significant effort beyond that of spectroscopic ellipsometry, the challenge of three-parameter spectroscopy becomes one of utilizing the third parameter effectively. Here, we demonstrate its utility in measurements either vs. fixed analyzer angular setting A for instrument calibration or vs. time for kinetic studies of nucleating films. In calibration, accurate results for the polarizer phase and analyzer azimuth scale correction can be obtained from measurements of the average reflected irradiance vs. A in the sample measurement configuration, irrespective of the value of Δ for the surface. In the kinetic studies of thin-film nucleation, the reflectance spectrum provides a criterion that allows one to identify the correct thickness and thus extract the evolution of the dielectric function with thickness. This procedure is demonstrated for Ag thin-film nucleation by magnetron sputtering on Si substrates.