Modelling, Design, and Fabrication of High-Temperature Compatible Vacuum Gauges in Silicon Carbide

Abstract

The demand for monitoring vacuum level at a high temperature is growing rapidly. For instance, in the semiconductor industry, the deposition process of many thin films is conducted in a high-temperature environment where the vacuum needs to be precisely monitored and controlled. Although a number of micro-fabricated vacuum gauges which show great performances have been implemented by silicon technology, they are not dedicated for high-temperature applications. The traditional Si-based sensor will lose its functionality when it is exposed to high temperature because of the degradation of the silicon. This research work focuses on the implementation of a high-temperature compatible vacuum gauge, and the aim is to achieve an operation temperature (i.e. 500 ◦C) compatible with current high-temperature compatible electronics reported in the literature. The combination of poly-SiC and micro-bridge based vacuum gauge is proposed as a feasible solution. The fabrication of the vacuum gauge is conducted at the EKL cleanroom, and Pirani gauges with various geometries are fabricated by employing thin-film technologies for deposition and lithography for defining patterns. The gauge with a length up 1000 μm and a gap size down to 500 nm is achieved without any buckling. The fabrication process is a four-mask step, and it provides the potential for mass production and integration with readout electronics. The micro-fabricated Pirani gauge showed good measurement results. Empirical Pirani gauge design rules were confirmed by experiments. It is confirmed that a longer beam and a smaller gap size will bring a larger dynamic range. At room temperature, the nominal gauge (length = 250 μm, width = 8 μm, thickness = 2 μm and gap distance = 500 nm) shows a maximum resistance change of 17.8 % from around 10 Pa to 100000 Pa, with a maximum sensitivity of 0.44 Ω/Pa. The vacuum gauge also showed a successful operation up to 750 ◦C, with a maximum sensitivity of 0.787 mV/Pa (1.097 Ω/Pa). Although the high-temperature compatible gauge is successfully fabricated, some issues, such as the rectifying behaviour of Ti/SiC junctions and the non-uniformity of poly-SiC deposition, are still unsolved. The integration with high-temperature readout electronics could be the direction of future work.