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Chapter 15: Modeling Surface Chemistry

This tutorial is divided into the following sections:

15.1.Introduction

15.2.Prerequisites

15.3.Problem Description

15.4.Setup and Solution

15.5.Summary

15.6.Further Improvements

15.1. Introduction

In chemically reacting laminar flows, such as those encountered in chemical vapor deposition (CVD) applications, accurate modeling of time-dependent hydrodynamics, heat and mass transfer, and chemical reactions (including wall surface reactions) is important.

In this tutorial, surface reactions are considered. Modeling the reactions taking place at gas-solid interfaces is complex and involves several elementary physicochemical processes like adsorption of gas-phase species on the surface, chemical reactions occurring on the surface, and desorption of gases from the surface back to the gas phase.

This tutorial demonstrates how to do the following:

•Create new materials and set the mixture properties.

•Model surface reactions involving site species.

•Enable physical models and define boundary conditions for a chemically reacting laminar flow involving wall surface reactions.

•Calculate the deposition solution using the pressure-based solver.

•Examine the flow results using graphics.

15.2. Prerequisites

This tutorial is written with the assumption that you have completed one or more of the introductory tutorial Fluid Flow and Heat Transfer in a Mixing Elbow (p. 35) found in this manual and that you are familiar with the ANSYS Fluent tree and ribbon structure. Some steps in the setup and solution procedure will not be shown explicitly.

Before beginning with this tutorial, see the Fluent User's Guide for more information about species transport, chemically reacting flows, wall surface reaction modeling, and chemical vapor deposition. In particular, you should be familiar with the Arrhenius rate equation, as this equation is used for the surface reactions modeled in this tutorial.

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15.3. Problem Description

A rotating disk CVD reactor for the growth of Gallium Arsenide (GaAs) shown in Figure 15.1: Schematic of the Reactor Configuration (p. 504) will be modeled.

Figure 15.1: Schematic of the Reactor Configuration

The process gases, Trimethyl Gallium ( ) and Arsine () enter the reactor at 293 K through the inlet at the top. These gases flow over the hot, spinning disk depositing thin layers of gallium and arsenide on it in a uniform, repeatable manner. The disk rotation generates a radially pumping effect, which forces the gases to flow in a laminar manner down to the growth surface, outward across the disk, and finally to be discharged from the reactor.

The semiconductor materials Ga(s) and As(s) are deposited on the heated surface governed by the following surface reactions.

(15.1)

(15.2)

The inlet gas is a mixture of Trimethyl Gallium, which has a mass fraction of 0.15, and Arsine, which has a mass fraction of 0.4, the remainder is hydrogen. The mixture velocity at the inlet is 0.02189 m/s. The

disk rotates at 80 rad/sec. The top wall (wall-1) is heated to 473 K and the sidewalls (wall-2) of the reactor are maintained at 343 K. The susceptor (wall-4) is heated to a uniform temperature of 1023 K and the bottom wall (wall-6) is at 303 K. These CVD reactors are typically known as cold-wall reactors, where

only the wafer surface is heated to higher temperatures, while the remaining reactor walls are maintained at low temperatures.

In this tutorial, simultaneous deposition of Ga and As is simulated and examined. The mixture properties and the mass diffusivity are determined based on kinetic theory. Detailed surface reactions with multiple

	Release 2019 R1 - © ANSYS,Inc.All rights reserved.- Contains proprietary and confidential information
504	of ANSYS, Inc. and its subsidiaries and affiliates.