In fabrication of micro-electronic circuits, the decrease of yield caused by contamination of wafers is an important issue. The dust particles contaminating wafers are categorized into two different types. One is the flake type which is originated from chamber wall, and the other is the sphere type of the typical size of 0.1 μm which is generated inside of plasmas.
The nanometer-sized particles from chamber wall or wafers grow in plasma through the chemical interaction with plasma ions. Since dust particles are negatively charged, they exprience electrostatic force in the sheath area. When a wafer is located in the plasma, the sheath potential around the wafer is changed into the non-uniform shape. The dust particles are trapped by this non-uniform potential and fall down to the wafer when the plasma is turned off.
In this thesis work, the 0.05μm alumina powder is utilized as particle seed and the evaporated acetone is used as working gas. SEM pictures show dust particles grown up to about 1μm size in the acetone plasma. These particles are observed at the edge of glass substrate. Negative voltage is biased to the grid which is placed above the glass substrate. The glass substrate is more contaminated when the bias voltage is -200V compared with the unbiased case. However, when the bias voltage is -100V, the contamination is decreased.