Search

Ultraviolet (UV) absorption spectroscopy is used to monitor the CF radical density in CF4 inductively coupled plasma (ICP) plasmas as a function of the substrate temperature. The CF density decreases dramatically when the wafer temperature is reduced from 20 to −130 °C by applying identical plasma conditions, demonstrating that the CF surface sticking coefficient increases as the surface temperature is reduced. This suggests that CF4 plasma could be used to form sidewall passivation layers and perform anisotropic etching at cryogenic temperature, which is impossible at room temperature. Subsequently, a cyclical Bosch type etching process of silicon was evaluated at −100 °C using CF4 plasma to passivate the trench sidewalls. Anisotropic etch profiles were obtained with an etch rate of 4.4 μm/min. Compared to a typical Bosch process using highly polymerizing c-C4F8 plasma, chamber wall contamination could be significantly reduced, alleviating a major issue of this cyclic process. Furthermore, CF4 has a 28% lower global warming potential than c-C4F8. [ABSTRACT FROM AUTHOR]

Absorption at 355 nm, with a pulsed frequency tripled yttrium-aluminum-garnet laser as light source, is used to monitor the time evolution of the Cl2 density in high-density inductively coupled plasmas. The detection limit over a 0.1 s acquisition time is about 0.2 mTorr of Cl2. This technique is well suited for monitoring chlorine density when studying elementary processes in Cl2 containing plasmas. Furthermore, it can be applied to control the process drift in industrial etch reactors resulting from the modification of the chamber walls conditions: by measuring the Cl2 density in a reference Cl2 plasma before etching a wafer, it can be determined if the chamber wall conditions are kept identical from one wafer to another. [ABSTRACT FROM AUTHOR]