Influence of Coil Power on the Etching Characteristics in a High Density Plasma Etcher

Abstract

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...

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