Plasma monitoring device using a cylindrical hollow electrode

A semiconductor process apparatus, comprising:

• a process chamber configured to execute a semiconductor manufacturing process and having an exhaust line extending therefrom;
• a housing including an inflow port connected to the exhaust line of the process chamber and a partition dividing an inner space thereof into a first area and a second area, wherein the partition includes a window therein between the first and second area;
• a plasma unit positioned in first area of the housing and configured to generate plasma by ionizing an exhaust gas flowing from the process chamber into the housing through the inflow port;
• and
• an optical emission spectroscopy unit positioned in the second area of the housing and configured to analyze light emitted from the plasma, wherein the plasma unit comprises:
• an open ended hollow cylindrical first electrode extending in a length direction from proximate the inflow port to proximate the window in the partition;
• a second electrode positioned within and displaced from the first electrode with a distance therebetween and extending in the length direction from proximate the inflow port to proximate the window in the partition, wherein the first electrode has an inner diameter and the second electrode has an outer diameter selected to vary the distance between the electrodes in the length direction so that the plasma generating unit generates a plasma by ionizing the exhaust gas flowing between the electrodes at a different position in the length direction based on a pressure of the exhaust gas, wherein the inner diameter of the first electrode varies substantially uniformly in the length direction and the outer diameter of the second electrode varies substantially uniformly in the length direction and decreases as the inner diameter of the first electrode increases;
• and
• a power supply coupled to the first and second electrodes configured to power the electrodes to ionize the gas flowing therebetween.