Diagnostic system for plasma/surface energy transfer characterization

Abstract

The knowledge of the effective energy deposited onto a surface by the reactive particles (ions, electrons, metastables, photons, etc.) in plasma processes such as thin-film deposition, sputtering, etching, etc., is of high interest to understand the basic mechanisms of energy transfer. In this article, a diagnostic is developed to directly measure the global energy transferred to surfaces (reactor walls, substrates, material to be modified, etc.) immerged in low-pressure plasmas. The diagnostic is based on a commercial HFM7-Vattel® microsensor, confined in a temperature-controlled substrate holder. The manufacturer calibration specifications are only given for atmospheric pressure. They cannot be used in low-pressure plasma conditions (typically 0.1–20Pa). Thus, for this particular application, a calibration of the microsensor is required. It is performed at various pressures, between vacuum and the ambient, according to the NIST protocol and using a homemade blackbody (BB). It is shown that only curves obtained in vacuum or pressures below 0.1Pa are valuable for a true calibration of the sensor. The others are perturbed by the heating of the gas in the BB surroundings. Measurements carried out in a typical transformer coupled plasma reactor in argon gas are presented. Typically the values are of the order of tens or hundreds of mW∕cm2 in our experimental conditions. They are consistent with an estimation of the energy transferred by charged particles (ions and electrons) performed from Langmuir probe characterization of the plasma.