AVS 56th International Symposium & Exhibition
    Vacuum Technology Wednesday Sessions
       Session VT-WeM

Paper VT-WeM4
Decomposition Characteristic of Metal-organic Gases

Wednesday, November 11, 2009, 9:00 am, Room J1

Session: Partical and Theoretical Aspects of Gas Dynamics
Presenter: S. Yamashita, Tohoku University, Japan
Authors: S. Yamashita, Tohoku University, Japan
M. Nagase, Fujikin Inc., Japan
K. Ikeda, Fujikin Inc., Japan
M. Kitano, Tohoku University, Japan
Y. Shirai, Tohoku University, Japan
T. Ohmi, Tohoku University, Japan
Correspondent: Click to Email
The Film formation process by using Metal-Organic (MO) CVD method is used for various applications such as interlayer dielectric of silicon semiconductor devices, ferroelectric substance film formations and transparent electrode formation. MO gases that are used in MOCVD processes are either in the liquid state or the solid state at room temperature and the vapor pressure of these gases is very low. In order to supply MO gases to the process chamber effectively, MO gases are heated to increase the vapor pressure and are supplied by using various means including the bubbling method. But many MO gases have high reactivity. So there is a possibility that MO gases may decompose during use. Due to this problem, there is the issue that byproduct of MO gas decomposition tend to be deposited in the gas supply system. So we evaluated the thermal decomposition property and the oxidation property of three kinds of MO gases [Tetraethoxysilane (TEOS), Trimethylphosphite (TMP) and Trimethylborate (TMB)] by using the FT-IR method to examine the cause of decomposition in MO gases. When MO gases are heated at an inert gas atmosphere, MO gases can be stably supplied without decomposition occurring until 400℃. This result shows that these gases have high stability regarding heat levels. However, when MO gases are heated at an atmosphere including 50 percent oxygen, decomposition temperature of each gas was significantly reduced and carbon dioxide was produced with the decomposition of MO gases. This result shows that the oxidative decomposition of MO gases occurs during heating in an atmosphere including oxygen. Next, MO gases were heated with a resin material used for the valve seat of the gas supply system. We used polyimide (PI) and Perfluoro-Alkoxy (PFA) as a resin material that can be used for the seat of the valve until 150℃. Firstly, TEOS could be stably supplied through tubing containing resin samples. When TMP and TMB flow through the tubing containing the PI test piece, the TMP and TMB could not be stably supplied even at 50℃ and these gases decomposed. And when we raised the heat temperature, decomposition of these gases furthered the progress. When TMP and TMB flow through the tubing containing PFA test piece, the TMB could be supplied stably at 50℃. Afterwards TMP decomposed and could not stably supplied at 50℃. But when TMP continued to flow for a designated duration of time, TMP could be stably supplied. In this case, when we raised the heat temperature, the decomposition of these gases did not occur. This phenomenon was caused by moisture evaporated from resin materials.