Structures fabricated using surface processing technology are limited to spanning no more than a few hundred microns due to stresses normal to the wafer surface. In contrast, high aspect ratio structures (HARS) are rigid in the out-of-plane direction, 1 but compliant in the plane of the wafer, and are able to span larger distances. HARS can also achieve high lateral capacitances due to large surface area, making it possible to generate large electrostatic forces. The advantages of HARS are exploited in a wide variety of applications including power microelectromechanical systems (MEMS). 2,3 Until the advent of high density plasma etchers, the options for fabricating HARS in silicon, such as reactive ion etching (RIE) and electron cyclotron resonance (ECR), had limited success in fulfilling the necessary requirements. HARS 4 require high silicon etching rate, good selectivity to masking material, anisotropy control, and compatibility with other processes. LIGA 5 (German acronym for lithography-electroplating-injection-molding), another alternative for HARS, can produce micromachined devices with the largest aspect ratio, but this technology requires a synchrotron radiation source. Thus, the low etching rates of RIE and ECR, and the requirement of an X-ray source for LIGA, have contributed to the need for a process that can yield results comparable to LIGA, but with a technology similar to the well-known RIE.One option that satisfies the needs described above is time multiplexed deep etching (TMDE), patented by Robert Bosch Gmbh, 6 which utilizes an etching cycle flowing only SF 6 , and then switches to a sidewall passivating cycle using only C 4 F 8 . The measured performance of one of these tools was reported recently. 7,8 However the role played by coil power during silicon etching was not explored, thus, it is necessary to complement the aforementioned report. In order to elucidate the influence of coil power during deep reactive ion etching, the exercise reported herein was divided in two parts. In the first part the equipment was operated suppressing all passivating variables and flowing only SF 6 to obtain isotropic profiles. In the second part, the influence of applied coil power was explored with the equipment running in the conventional time-multiplexing mode 7,8 to obtain highly anisotropic profiles.The first part of the experiment allows us to decouple four etching variables from passivating variables, and provides additional insight in the processes occurring during the etching cycle. The second part of the experiment explores the influence of coil power while operating in time multiplexing mode, incorporating the understanding and results obtained in the first part.The experimental approach and the measured performance for the isotropic part of the experiment are presented in the next section. Then we cover the anisotropic part of the exercise with the equipment operating in TMDE mode. ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of...

An investigation is made into the modeling, design and testing of micron scale Laval nozzles. Such nozzles can provide orbital maneuvering for small spacecraft or attitude control and stationkeeping for their larger counterparts. The flow in the nozzle is modeled by means of a two dimensional finite volume NavierStokes simulation which predicts viscous losses with a decrease in nozzle scale. Calculations show mass flow is reduced to 93% of the ideal in viscid flow for a throat Reynolds number of 500. The nozzles modeled are fabricated through deep reactive ion etching in an inductively coupled plasma. Nozzle throat dimensions of 30 microns reduce to 20 microns over the depth of the nozzle. Nozzle testing reveals choked conditions exist, and the flow rates are similar for different geometries of the same throat dimensions.

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We discuss deep reactive ion etching (DRIE) as a promising technology that can be readily applied in the micromanufacturing of low-thrust propulsion systems to be used on future generations of micro-and nanosatellites. This dry processing technique permits the fabrication of high-aspect-ratio silicon structures and intricate morphologies, both with tight tolerances, in a repetitive and controllable fashion that lightweight space vehicles will exploit with the introduction of smaller thrust components for precise maneuvering and attitude control. The etching approach described herein is counted among the present state of the art techniques utilized in the current trend toward miniaturization of sensors and actuators. This trend is being propelled by the increased technological capability as the enabling factor for size reduction. Scaling laws, especially the cube-square law, can be successfully applied for obtaining macropower from microdevices manufactured with the silicon technology that has developed for microelectronics applications, including DRIE. The application of this plasma etching technique in the fabrication and testing of silicon supersonic micronozzles is also described.

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