Abstract:
The aim of the growth of Oxide on Silicon Experiment is to make an oxidation layer on a silicon wafer. There are two factors that affect the thickness and quality of the silicon dioxide layer: growth time and growth temperature. The silicon substrate oxidized easily at a high temperature. The heating temperatures were typically in the range from 800°C to 1200°C. When oxygen arrived at the silicon surface, oxygen was combined with silicon to become silicon dioxide. The chemical reaction that took place was Si (s) + O2 (g) → SiO2 (s). This experiment explored whether the thickness of the oxide layer changed with the oxidation time and setting temperature. When the growth time was longer, the thickness of silicon oxide layer became greater. A higher temperature produced better quality oxide.
Introduction:
There are different ways to grow oxide on a silicon wafer, such as through vapor-phase, a plasma reaction, and thermal oxidation. In this experiment thermal oxidation was used to produce a thin layer of silicon dioxide on the surface of a wafer. The technique forces an oxidizing agent to diffuse into the wafer at high temperatures and react with the wafer. The Deal-Grove model predicts the rate of oxide growth.
Deal-Grove Model: X^2＋A*X＝B*(t＋τ）
This model describes the kinetics of thermal oxidation of silicon based on the chemical reaction between silicon and oxidizing species. In this equation, X is the thickness of the oxide layer, t is the reaction time, andτis the time required for native oxide thickness to grow. A and B are constants which correspond to the oxidation conditions. When t is very short and X is very thin (X^2＜＜A*X), the formula approaches A*X＝B*(t＋τ), and the thickness is X＝B*(t ＋τ）/A, which is a linear growth regimen. Here B/ A is called Linear rate Constant, which is controlled by reaction rate K. In other words, when t is very long and X is very thick (X^2＞＞A*X), the formula approaches X^2＝B*(t ＋τ), which is a diffusion-limited regimen. B is controlled by the oxidant in the diffusion rate of SiO2.
Thermal oxidation may be applied to different materials, but this experiment only considered oxidation of silicon substrates to produce silicon dioxide. Initially, in this type of experiment the growth of silicon dioxide is a surface reaction only. The change in thickness, which results in different colors, can quickly be observed whether there is an obviously uneven finding without measuring the thickness of the silicon oxide layer. However, after the SiO2 thickness begins to build up, the arriving oxygen molecules must diffuse through the growing SiO2 layer to get to the silicon surface in order to react.
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