Cryogenic Etching of Silicon: An Alternative Method for Fabrication of Vertical Microcantilever Master Molds (original) (raw)
Related papers
2002
This paper presents guidelines for the deep reactive ion etching (DRIE) of silicon MEMS structures, employing SF 6 O 2-based high-density plasmas at cryogenic temperatures. Procedures of how to tune the equipment for optimal results with respect to etch rate and profile control are described. Profile control is a delicate balance between the respective etching and deposition rates of a SiO F passivation layer on the sidewalls and bottom of an etched structure in relation to the silicon removal rate from unpassivated areas. Any parameter that affects the relative rates of these processes has an effect on profile control. The deposition of the SiO F layer is mainly determined by the oxygen content in the SF 6 gas flow and the electrode temperature. Removal of the SiO F layer is mainly determined by the kinetic energy (self-bias) of ions in the SF 6 O 2 plasma. Diagrams for profile control are given as a function of parameter settings, employing the previously published "black silicon method". Parameter settings for high rate silicon bulk etching, and the etching of micro needles and micro moulds are discussed, which demonstrate the usefulness of the diagrams for optimal design of etched features. Furthermore it is demonstrated that in order to use the oxygen flow as a control parameter for cryogenic DRIE, it is necessary to avoid or at least restrict the presence of fused silica as a dome material, because this material may release oxygen due to corrosion during operation of the plasma source. When inert dome materials like alumina are used, etching recipes can be defined for a broad variety of microstructures in the cryogenic temperature regime. Recipes with relatively low oxygen content (1-10% of the total gas volume) and ions with low kinetic energy can now be applied to observe a low lateral etch rate beneath the mask, and a high selectivity (more than 500) of silicon etching with respect to polymers and oxide mask materials is obtained. Crystallographic preference etching of silicon is observed at low wafer temperature (120 C). This effect is enhanced by increasing the process pressure above 10 mtorr or for low ion energies (below 20 eV). [720] Index Terms-Cryogenic etching, profile control, reactive ion etching (RIE).
A survey on the reactive ion etching of silicon in microtechnology
Journal of Micromechanics and Microengineering, 1996
This article is a brief review of dry etching as applied to pattern transfer, primarily in silicon technology. It focuses on concepts and topics for etching materials of interest in micromechanics. The basis of plasma-assisted etching, the main dry etching technique, is explained and plasma system configurations are described such as reactive ion etching (RIE). An important feature of RIE is its ability to achieve etch directionality. The mechanism behind this directionality and various plasma chemistries to fulfil this task will be explained. Multi-step plasma chemistries are found to be useful to etch, release and passivate micromechanical structures in one run successfully. Plasma etching is extremely sensitive to many variables, making etch results inconsistent and irreproducible. Therefore, important plasma parameters, mask materials and their influences will be treated. Moreover, RIE has its own specific problems, and solutions will be formulated. The result of an RIE process depends in a non-linear way on a great number of parameters. Therefore, a careful data acquisition is necessary. Also, plasma monitoring is needed for the determination of the etch end point for a given process. This review is ended with some promising current trends in plasma etching.
Silicon Reactive Ion Etching for Micromachining Applications
Monocrystalline silicon was etched in a Reactive Ion Etching system with mixtures of SF 6 , Ar and H 2 to obtain deep trenches. A graphite electrode was used to increase the anisotropy of the etching processes. The effects of varying flow, pressure and power levels on etch rate and anisotropy were studied. Isotropic etching was obtained with pure SF 6 plasmas. Addition of Ar to SF 6 results in an increase of ion bombardment of the graphite electrode. This will increase the carbon content in the plasma. Using Ar additions, wall slopes of approximately 60° are obtained. Addition of H 2 to the SF 6 -Ar mixtures will decrease the free fluorine content in the plasma and increase polymer deposition. This will decrease the etch rate and increase the anisotropy of the process. Anisotropic etching has been achieved and 27 µm deep vertical trenches have been etched to form micromechanical structures.
Journal of Micromechanics and Microengineering, 2010
In this paper, we demonstrate silicon microdevice fabrication by a combination of focused ion beam (FIB) and cryogenic deep reactive ion etching (DRIE). Applying FIB treatment only to a thin surface layer enables very high writing speed compared with FIB milling. The use of DRIE then defines the micro-and nanodevices utilizing the FIB-modified silicon as a mask. We demonstrate the ability to create patterns on highly 3D structures, which is extremely challenging by other nanofabrication methods. The alignment of optically made and FIB-defined patterns is also demonstrated. We also show that complete microelectromechanical systems (MEMS) can be fabricated by this method by presenting a double-ended tuning fork resonator as an example. Extremely short process time is achieved as the full fabrication cycle from mask design to electrical measurements can be completed during one working day.
Process characterisation of deep reactive ion etching for microfluidic application
International Journal of Nanotechnology, 2018
The goal of this paper is to investigate the influence of parameters of the Bosch deep reactive ion etching (DRIE) process on etched surface profile, sidewall profile and etch rate of micrometre silicon features. By investigating these parameters, we found the conditions to obtain smooth sidewall, high etch rate and balance of chemical and physical etching in the DRIE process. In this paper, the silicon surface was covered by a thin silver patterning, created by lift-off, as a hard mask for the DRIE process. The etched samples were characterised by optical microscopy and mechanical profilometry. The results show smooth sidewall of 136 µm-deep silicon trenches obtained at a high etch rate of 4 µm/min using 5 sccm C 4 F 8 , 8 sccm O 2 and 24 W of bias power.
Fabrication of Reactive Ion Etching Systems for Deep Silicon Machining
IEEJ Transactions on Sensors and Micromachines
Reactive ion etching (RIE) systems using capacitively coupled plasma (CCP) and inductively coupled plasma (ICP) sources with SF6 gas have been developed for deep silicon machining with high aspect ratio. The developed RIE systems demonstrated high etch rate (2.3 and high selectivity (1700) for a sputtered nickel mask in silicon etching. A large capacity turbo molecular pump (TMP) with a small etching chamber was used to realize a low pressure with a high flow rate of etching gas. A circulatory cooling apparatus was used for cooling a silicon wafer. Etch rate showed uniformity within 10% for the area of 50cm2. Using the RIE system, we succeeded to etch a thick silicon wafer vertically through the thickness with an aspect ratio greater than 10. The RIE can be applied to fabricate three-dimensional silicon microstructures.
This work presents the results of a study of reactive ion etching of polycristalline silicon by using fluorine– and chlorine– containing plasmas for a CMOS transistor gate fabrication. Submicron-wide lines (as narrow as 0.25 µm) were patterned by electron beam lithography. Processes with high etch rate (up to 70 nm/min), high selectivity over gate oxide (up to 7) and high anisotropy factors (up to 1) have been developed. Two different etching regimes producing features with anisotropic profiles have been studied, characterized by: 1) strong sidewall passivation preventing lateral etching, 2) controlled lateral etching. Anisotropic structures as narrow as 90 nm wide have been produced using the latter regime, and 250 nm wide structures by the passivation– based regime. The etching mechanisms of the processes are discussed.