Chemical Vapor Deposition of Silicon from Silane Pyrolysis

The four basic elements in the chemical vapor deposition (CVD) of silicon from silane are analytically treated from a kinetic standpoint. These elements are mass transport of silane, pyrolysis of silane, nucleation of silicon, and silicon crystal growth. Rate expressions that describe the various steps involved in the chemical vapor deposition of silicon were derived from elementary principles. Applications of the rate expressions for modeling and simulation of the silicon CVD are discussed

Modeling and Simulation of a Tungsten Chemical Vapor Deposition Reactor

Chemical vapor deposition (CVD) processes are widely used in semiconductor device fabrication to deposit thin films of electronic materials. Physically based CVD modeling and simulation methods have been adopted for reactor design and process optimization applications to satisfy the increasingly strigent processing requirements. In this research, an ULVAC ERA-1000 selective tungsten chemical vapor deposition system located at the University of Maryland was studied where a temperature difference as large as 120 oC between the system wafer temperature reading and the thermocoupled instrumented wafer measurement was found during the manual processing mode. The goal of this research was to develop a simplified, but accurate, three-dimensional transport model that is capable of describing the observed reactor behavior.A hybrid approach combining experimental and simulation studies was used for model development. Several sets of experiments were conducted to investigate the effects of process parameters on wafer temperature. A three-dimensional gas flow and temperature model was developed and used to compute the energy transferred across the gas/wafer interface. System dependent heat transfer parameters were formulated as a nonlinear parameter estimation problem and identified using experimental measurements. Good agreement was found between the steady-state wafer temperature predictions and experimental data at various gas compositions, and the wafer temperature dynamics were successfully predicted using a temperature model considering the energy exchanges between the thermocouple, wafer, and showerhead

DEVELOPMENT OF AN OBJECT-ORIENTED FRAMEWORK FOR MODULAR CHEMICAL PROCESS SIMULATION WITH SEMICONDUCTOR MANUFACTURING APPLICATIONS

Chemical Vapor Deposition (CVD) processes constitute an important unit operation for micro electronic device fabrication in the semiconductor industry. Simulators of the deposition process are powerful tools for understanding the transport and reaction conditions inside the deposition chamber and can be used to optimize and control the deposition process. This thesis discusses the development of a set of object-oriented modular simulation tools for solving lumped and spatially distributed models generated from chemical process design and simulation problems. The application of object-oriented design and modular approach greatly reduces the software development cycle time associated with designing process systems and improves the overall efficiency of the simulation process. The framework facilitates an evolutionary approach to simulator development, starting with a simple process description and building model complexity and testing modeling hypothesis in a step-by-step manner. Modularized components can be easily assembled to form a modeling system for a desired process. The framework also brings a fresh approach to many traditional scientific computing procedures to make a greater range of computational tools available for solving engineering problems. Two examples of tungsten chemical vapor deposition simulation are presented to illustrate the capability of the tools developed to facilitate an evolutionary simulation approach. The first example demonstrates how the framework is applied for solving systems assembled from separate modules by simulating a tungsten CVD deposition process occurring in a single wafer LPCVD system both at steady-state and dynamically over a true processing cycle. The second example considers the development of a multi-segment simulator describing the gas concentration profiles in the newly designed Programmable CVD reactor system. The simulation model is validated by deposition experiments conducted in the three-segment prototype. To facilitate the CVD system design, experimental data archiving, and distributed simulation, a three-tier Java and XML-based integrated information technology system has also been developed

Pattern formation during the evaporation of a colloidal nanoliter drop: a numerical and experimental study

An efficient way to precisely pattern particles on solid surfaces is to dispense and evaporate colloidal drops, as for bioassays. The dried deposits often exhibit complex structures exemplified by the coffee ring pattern, where most particles have accumulated at the periphery of the deposit. In this work, the formation of deposits during the drying of nanoliter colloidal drops on a flat substrate is investigated numerically and experimentally. A finite-element numerical model is developed that solves the Navier-Stokes, heat and mass transport equations in a Lagrangian framework. The diffusion of vapor in the atmosphere is solved numerically, providing an exact boundary condition for the evaporative flux at the droplet-air interface. Laplace stresses and thermal Marangoni stresses are accounted for. The particle concentration is tracked by solving a continuum advection-diffusion equation. Wetting line motion and the interaction of the free surface of the drop with the growing deposit are modeled based on criteria on wetting angles. Numerical results for evaporation times and flow field are in very good agreement with published experimental and theoretical results. We also performed transient visualization experiments of water and isopropanol drops loaded with polystyrene microsphere evaporating on respectively glass and polydimethylsiloxane substrates. Measured evaporation times, deposit shape and sizes, and flow fields are in very good agreement with the numerical results. Different flow patterns caused by the competition of Marangoni loops and radial flow are shown to determine the deposit shape to be either a ring-like pattern or a homogeneous bump

Chemical vapor deposition modeling: An assessment of current status

The shortcomings of earlier approaches that assumed thermochemical equilibrium and used chemical vapor deposition (CVD) phase diagrams are pointed out. Significant advancements in predictive capabilities due to recent computational developments, especially those for deposition rates controlled by gas phase mass transport, are demonstrated. The importance of using the proper boundary conditions is stressed, and the availability and reliability of gas phase and surface chemical kinetic information are emphasized as the most limiting factors. Future directions for CVD are proposed on the basis of current needs for efficient and effective progress in CVD process design and optimization

CVD of solid oxides in porous substrates for ceramic membrane modification

The deposition of yttria-doped zirconia has been experimented systematically in various types of porous ceramic substrates by a modified chemical vapor deposition (CVD) process operating in an opposing reactant geometry using water vapor and corresponding metal chloride vapors as reactants. The effects of substrate pore dimension and structure, bulk-phase reactant concentration, reactant diffusivity in substrate pores and deposition temperature are experimentally studied and explained qualitatively by a theoretical modeling analysis. The experimental and theoretical results suggest a reaction mechanism which depends on water vapor and chloride vapor concentrations. Consequently, the diffusivity, bulk-phase reactant concentration, and substrate pore dimension are important in the CVD process. Effects of deposition temperature on the deposition results and narrow deposition zone compared to the substrate thickness also suggest a Langmuir-Hinshelwood reaction mechanism involved in the CVD process with a very fast CVD reaction rate. Gas permeation data indicate that whether deposition of solid in substrate pores could result in the pore-size reduction depends strongly on the initial pore-size distribution of the substrate