Rapid Thermal Chemical Vapor Deposition Process Research Articles

Nucleation and growth dynamics of graphene on oxygen exposed copper substrate

We study the nucleation and growth dynamics of graphene grown on Cu and CuO substrates in a cold wall rapid thermal chemical vapor deposition (RTCVD) system under low pressure. Through image processing and analysis, we quantitatively characterize the RTCVD process. Larger and more compact graphene grains are found on CuO substrate. Furthermore, contrary to the hot wall CVD which exhibit instantaneous nucleation characteristics, our system exhibit substrate dependent non-constant nucleation rates. The coverage evolution can be well described by Johnson-Mehl-Avrami-Kolmogorov (JMAK) model, with the exponent varies from 3.9 to 2.1 for Cu and CuO substrate, respectively. Putting the measured fractal dimensions into the JMAK model, we find exponents related to non-equilibrium nucleation rates that qualitatively agree with observations. Our analysis suggests that new nucleation centers are more efficiently suppressed on CuO substrate during the RTCVD process.

Thin Multi-Walled Carbon Nanotubes Synthesized by Rapid Thermal Chemical Vapor Deposition and Their Field Emission Properties

Thin multi-walled carbon nanotubes (MWCNTs) were successfully synthesized by a rapid thermal chemical vapor deposition (RTCVD) method using a liquid catalyst. The growth of the thin MWCNTs was achieved by decomposition of C2H2 over Fe-Mo/MgO/citric acid directly at 700 degrees C for 30 min. Most thin MWCNTs, which had about 6 approximately 8 graphene layers, showed high purity (approximately 90%) and good crystallinity. Moreover, they showed homogenous morphology and uniform diameters. The average outer diameter of the thin MWCNTs was about 8 nm. The uniform diameter and good homogeneity of thin MWCNTs were mainly attributed to prevention of catalyst agglomeration at high temperature due to a short reaction time, and the high purity of thin MWCNTs was caused by suppression of the residual CNT growth after finishing a reaction in RTCVD process. Field emission properties of the thin MWCNTs were measured in a vacuum chamber at a pressure of less than 2 x 10(-7) Torr. The turn-on field was about 3.35 V/microm at the emission current density of 0.1 microA/cm2, and the emission current density was 2.5 mA/cm2 at an applied field of 6.7 V/microm. Particularly, the thin MWCNTs showed strong emission stability at emission current density of 0.8 mA/cm2 for 20 h.

Nanostructural Silicon Films Prepared by Metal-Induced Growth Using an RTCVD System

Nanostructural (grain size of 35–80 nm) silicon films had been prepared by a metal-induced growth (MIG) technique with a rapid thermal chemical vapor deposition (RTCVD) system. A low-temperature (550°C) RTCVD process was presented to deposit these nanostructural silicon films onto a Ni-prelayer substrate. The influences of various thickness of Ni prelayer, hydrogen flow rate, and growth temperatures on the nanostructural silicon films were investigated in this study. It is shown that thicker Ni films (≧15 nm) could result in uniform nanograin silicon films, while for the thinner ones (≦10 nm), larger whisker crystals and some nanocrystalline grains were found distributed randomly on a smooth amorphous film. More flow rate retards the formation of compound and thus offers nanocrystalline silicon films. The lower growth temperature (≦500°C) has the same results. All these examinations were demonstrated by X-ray diffraction, scanning electron microscopy, Raman spectra, and atomic force microscopy analysis. The mechanism of MIG by the RTCVD system was explained from a result of Auger depth profiles. © 2004 The Electrochemical Society. All rights reserved.

Nucleation and growth of hemispherical-grained Si by rapid thermal CVD

Hemispherical-grained Si (HSG) coating was deposited on an amorphous Si layer by using a rapid thermal chemical vapor deposition (RTCVD) process. The formation of the HSG coating consists of “seeding” and subsequent isothermal annealing stages. The microstructure and surface morphology of the HSG coating was studied after various stages of its formation by TEM and HRSEM techniques. The “seeding” process results in formation of nanometer size Si crystals on the substrate. Each Si crystal is covered with a thin amorphous Si film which forms a hemisphere shape. The annealing process results in growth and crystallization of polycrystaline Si hemispheres. The RTCVD process enables high control of the size and crystallinity of the Si hemispheres. The mechanism of formation and growth of the HSG coating is discussed and compared with other fabrication methods.

Output Feedback Control of Parabolic PDE Systems with Nonlinear Spatial Differential Operators

This article focuses on nonlinear static (direct) output feedback control of parabolic partial differential equations (PDE) systems with nonlinear spatial differential operators with application to a rapid thermal chemical vapor deposition (RTCVD) process. Initially, a detailed mathematical model is presented for the RTCVD process, which consists of a nonlinear parabolic PDE that describes the spatiotemporal evolution of the wafer temperature, coupled with a set of nonlinear ordinary differential equations (ODEs) that describes the time evolution of the chamber temperature and the concentrations of the various species. Then, a systematic methodology is presented for the synthesis of nonlinear static output feedback controllers for parabolic PDE systems with nonlinear spatial differential operators. Initially, the Karhunen−Loéve expansion is used to derive empirical eigenfunctions of the nonlinear parabolic PDE system, then the empirical eigenfunctions are used as basis functions within a Galerkin model reduction framework to derive low-order ODE systems that accurately describe the dominant dynamics of the PDE system, and finally, these ODE systems are used for the synthesis of nonlinear static output feedback controllers that guarantee stability and enforce output tracking in the closed-loop system. The proposed control method is employed to synthesize a nonlinear easy-to-implement controller for the RTCVD process that uses measurements of wafer temperature at five locations to manipulate the power of the top lamps in order to achieve uniform temperature and, thus, uniform deposition of a thin film on the wafer over the entire process cycle. The performance of the developed nonlinear output feedback controller is successfully tested through simulations and is shown to be superior to the one of a linear control scheme.

Atomic force microscopy and ellipsometry study of the nucleation and growth mechanism of polycrystalline silicon films on silicon dioxide

The primary purpose of this research was to elucidate the mechanism of Si nucleation on SiO2 in a rapid thermal chemical vapor deposition (RTCVD) environment. To this end a combination of in situ real time ellipsometry and atomic force microscopy (AFM) to follow the RTCVD process in real time and measure key nucleation parameters was used. Real time ellipsometry data, in terms of Δ versus time, show significant changes as the deposition evolves from critical nuclei through coalescence to continuous film growth. From these data nuclei parameters such as the incubation time (tinc), coalescence point, nuclei density, and nuclei size are obtained from nucleation models. From the AFM images, nuclei parameters such as nuclei height, radius, and density were collected and compared across processing temperatures. It was found that kinetics rather than thermodynamics controls nuclei growth, and the mechanism depended upon the temperature regime (pressure not varied) due to the higher activation energy (212 kJ/mol) for vertical growth relative to lateral growth (167 kJ/mol). A transition temperature (∼600 °C) was identified where the size, shape, and density of the nuclei abruptly change from small numerous nuclei at temperatures less than 660 °C to large, sparse, disklike nuclei for temperatures greater than 660 °C. The temperature regime also affected the shape of the nuclei during growth with low temperature nuclei becoming flatter with time as the adatoms attached to the nuclei circumference, whereas high temperature nuclei grew taller with time. It is demonstrated that the RTCVD temperature regime dictates both the initial nuclei size and the nuclei growth mechanism with high temperature processes (i.e., highest adatom mobility), yielding the lowest nuclei density, largest nuclei, and roughest final Si film.

Integrated dynamic simulation of rapid thermal chemical vapor deposition of polysilicon

A physically-based dynamic simulator has been constructed to investigate the time-dependent behavior of equipment, process, sensor, and control systems for rapid thermal chemical vapor deposition (RTCVD) of polysilicon from SiH/sub 4/. The simulator captures the essential physics and chemistry of mass transport, heat transfer, and chemical kinetics of the RTCVD process as embodied in equipment. In order to complete the system-level description, reduced-order models are also employed to represent processes involving high complexity of physics. Integration of individual simulator elements for equipment, process, sensors, and control systems enables the evaluation of not only the deposition rate and film thickness, but also of a broad range of dynamic system properties such as equipment performance, gas flow conditions, wafer temperature variation, wafer optical properties (absorptivity/emissivity), reaction gas composition, total process cycle time, consumables volume, and reactant utilization. This makes the simulator directly applicable to the optimization of process recipes and equipment design, to process control strategy, and to fault classification. This case study of polysilicon RTCVD demonstrates (1) that integrated dynamic simulation is a versatile tool for representing system-level dynamics and (2) that such representation is pivotal in successful applications of modeling and simulation for manufacturing optimization and control.

Equipment fault detection using spatial signatures

This paper describes a new methodology for equipment fault detection. The key features of this methodology are that it allows for the incorporation of spatial information and that it can be used to detect and diagnose equipment faults simultaneously. This methodology consists of constructing a virtual wafer surface from spatial data and using physically based spatial signature metrics to compare the virtual wafer surface to an established baseline process surface in order to detect equipment faults. Statistical distributional studies of the spatial signature metrics provide the justification of determining the significance of the spatial signature. Data collected from a rapid thermal chemical vapor deposition (RTCVD) process and from a plasma enhanced chemical vapor deposition (PECVD) process are used to illustrate the procedures. This method detected equipment faults for all 11 wafers that were subjected to induced equipment faults in the RTCVD process, and even diagnosed the type of equipment fault for 10 of these wafers. This method also detected 42 of 44 induced equipment faults in the PECVD process.

Polysilicon RTCVD process optimization for environmentally-conscious manufacturing

In the semiconductor manufacturing industry, optimization of advanced equipment and process designs must include both manufacturing metrics (such as cycle time, consumables cost, and product quality) and environmental consequences (such as reactant utilization and by-product emission). We have investigated the optimization of rapid thermal chemical vapor deposition (RTCVD) of polysilicon from SiH/sub 4/ as a function of process parameters using a physically-based dynamic simulation approach. The simulator captures essential time-dependent behaviors of gas flow, heat transfer, reaction chemistry, and sensor and control systems, and is validated by our experimental data. Significant improvements in SiH/sub 4/ utilization (up to 7/spl times/) and process cycle time (up to 3/spl times/) can be achieved by changes in 1) timing for initiating wafer heating relative to starting process gas flow; 2) process temperature (650-750/spl deg/C); and 3) gas flow rate (100-1000 seem). Enhanced gas utilization efficiency and reduced process cycle time provide benefits for both environmental considerations and manufacturing productivity (throughput). Dynamic simulation proves to be a versatile and powerful technique for identifying optimal process parameters and for assessing tradeoffs between various manufacturing and environmental metrics.

Low-temperature plasma-assisted oxidation combined with in situ rapid thermal oxide deposition for stacked-gate Si–SiO2 heterostructures: Integrated processing and device studies

We have fabricated stacked-gate structures with (i) thin Si–SiO2 heterostructures formed by a combination plasma-assisted and rapid thermal processing, and (ii) polysilicon gate electrodes deposited by rapid thermal chemical-vapor deposition (RTCVD). All processing was performed in situ and sequentially in a single chamber reactor, which provided for independent control of the interface formation and oxide deposition steps. The predeposition, low-temperature, 300 °C, remote-plasma-assisted Si-cleaning/passivation/oxidation (i) removed residual C-atom contamination, (ii) created a device-quality Si–SiO2 interface, and (iii) generated ∼0.5–0.6 nm of oxide, which served as a platform for the subsequent SiO2 deposition. Deposition of the SiO2 film, ∼10.0 nm thick, was performed in situ by an 800 °C RTCVD process. This study emphasizes the interface formation process, and its effect on electrical properties of stacked-gate structures in metal–oxide–semiconductor capacitors and field effect transistors.

Effects of oxygen doping on properties of microcrystalline silicon film grown using rapid thermal chemical vapor deposition

An oxygen doped microcrystalline silicon (μc-Si) deposition process is developed by mixing small amounts of nitrous oxide (N2O) with silane (SiH4) in a rapid thermal chemical vapor deposition (RTCVD) reactor. The effects of oxygen doping on the properties of RTCVD μc-Si films are studied. Experimental results show that the RTCVD process provides high deposition rates for μc-Si and polycrystalline silicon (polySi) films at elevated deposition temperatures and pressures. The surface roughness of the RTCVD μc-Si films can be significantly reduced compared to that of conventional LPCVD polySi films. Steep side walls can be realized due to the small grain size of the μc-Si films. The sheet resistance of BF2 doped μc-Si films is slightly higher than that of BF2 doped polySi films, whereas sheet resistances of P and As doped μc-Si films are much higher than those of the corresponding P and As doped polySi films. Measurements of the catastrophic breakdown strength of metal-oxide-semiconductor (MOS) capacitors indicate that the quality of gate electrodes fabricated using μc-Si is improved relative to that of MOS capacitors fabricated using polySi gate electrodes.