Understanding microfabricated nanocalorimeter performance and responses to the energy fluxes from low-temperature plasma discharges

Abstract

Plasma diagnostics have a shortage of fast and sensitive calorimetric sensors that can track substrate temperature during plasma-assisted microfabrication. In this work, energy fluxes from argon and oxygen radiofrequency (RF) glow discharges have been probed using a novel nanocalorimeter sensor. The probe consists of an ultrathin SiNx membrane (100 nm) with a lithographically defined Pt micro-strip (100 nm) that serves as a calibrated resistance thermometer. The sensor temperature can increase from room temperature to several hundred degrees within a second upon exposure to RF plasma, depending on the experiment's geometry and plasma parameters. Such sensitivity and response time are due to the pre-designed reduced heat capacity of the sensor and significantly reduced thermal conductance of the cooling channels. These features enable the sensitive detection of low-energy plasma fluxes on surfaces and their rapid discrimination, as in the case of ion and electron fluxes, by biasing the sensor at negative or positive potentials. These biased nanocalorimeter energy readings have been compared with ion and electron kinetic energy dissipations assessed using a Langmuir probe and retarding field energy analyzer (RFEA). Finally, the robustness of the plasma nanocalorimeter is discussed in terms of its baseline drifts, degradation, and longevity.