A Nonperturbing Real-Time In Situ Plasma Diagnosis Technique Using an Optical Emission Spectrometer (OES)

An optical emission spectrometer (OES) is utilized to measure the sheath thickness (i.e., dark space) of a pulsed glow discharge in a nonperturbing real-time in situ manner. The ion density can be obtained based on the sheath thickness measurements because the ion density is a function of the sheath thickness and applied voltage. Because this method is simple and straightforward, most of the issues involved with a conventional Langmuir probe measurement are eliminated. The ion density measured by this technique was compared with that measured by a time-delayed time-resolved Langmuir probe technique and with measurements simulated by PDP1 plasma simulation code. A good agreement between the measurements taken by the different tools has been demonstrated. Therefore, this method is suitable for a better plasma-based process, which monitors process controllability and repeatability