Noninvasive, real-time measurements of plasma parameters via optical emission spectroscopy

Abstract

Absorption spectroscopy measurements of argon metastable and resonant atom density in atmospheric pressure Ar-He surface-wave plasmas using a low pressure lamp Dynamics of reactive high-power impulse magnetron sputtering discharge studied by time-and space-resolved optical emission spectroscopy and fast imaging J. Appl. Phys. 107, 043305 (2010); 10.1063/1.3305319Characterization of the behavior of chemically reactive species in a nonequilibrium inductively coupled argonhydrogen thermal plasma under pulse-modulated operation Plasma process control applications require acquisition of diagnostic data at a rate faster than the characteristic timescale of perturbations to the plasma. Diagnostics based on optical emission spectroscopy of intense emission lines permit rapid noninvasive measurements with low-resolution ($1 nm), fiber-coupled spectrographs, which are included on many plasma process tools for semiconductor processing. Here the authors report on rapid analysis of Ar emissions with such a system to obtain electron temperatures, electron densities, and metastable densities in argon and argon/mixed-gas (Ar/N 2 , Ar/O 2 , Ar/H 2 ) inductively coupled plasmas. Accuracy of the results (compared to measurements made by Langmuir probe and white-light absorption spectroscopy) are typically better than 615% with a time resolution of 0.1 s, which is more than sufficient to capture the transient behavior of many processes, limited only by the time response of the spectrograph used.

Comparison of surface vacuum ultraviolet emissions with resonance level number densities. II. Rare-gas plasmas and Ar-molecular gas mixtures

“…For argon and neon plasmas, a Verity spectrograph with Dk $ 1.4 nm resolution was used to measure the 350-800 nm wavelength range in about 100 ms. 51 This update time is a combination of the exposure time, data transfer, and data processing times. For krypton and xenon, a 0.275 m spectrometer fitted with a 147 mm À1 grating and 3648 pixel CCD detector with Dk $ 0.7 nm was used to measure the 450-1150 nm wavelength range with an update time of $4 s. 53 Procedures for processing the emission spectra to correct for the system's spectral sensitivity and for background subtraction (particularly important in Ar-N 2 mixtures) can be found in Ref.…”

“…Here, we describe the method as employed to perform real-time measurements with this technique using low-resolution (i.e., Dk % 1 nm) spectrometers for the various rare-gases. 51 Briefly, the degree of radiation trapping of a particular 2p x ! 1s y transition depends upon the number density of atoms in the 1s y lower level.…”

Time-resolved spectroscopy using a chopper wheel as a fast shutter

“…A more detailed description of this system is found in Ref. 9. The plasma is generated by a RFPP model RF-10S/PWT 13.56 MHz RF power supply operating in pulsed-mode.…”

“…The time-resolved emission intensities are converted to time-resolved plasma parameters using the analysis methods described in Ref. 9.…”

“…[4][5][6][7][8] Many of these applications can be accomplished with low-cost, low-resolution, fiber-coupled spectrometers which are common features on many industrial and research plasma sources, albeit with a time-resolution of seconds or longer. 9 Nevertheless, there is a desire for time-resolved spectroscopic measurements at higher time resolution, particularly in the field of pulsed plasmas, which has emerged as a promising technique in plasma-aided material processing. 10,11 These plasmas typically operate with modulation frequencies between 10 2 and 10 5 Hz, which correspond to 10 ms-10 µs pulse periods.…”