Deep Vertical Etching of Silicon Wafers Using a Hydrogenation-Assisted Reactive Ion Etching (original) (raw)
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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.
Suitability of reactive ion etching on 0.13 micro_m silicon technology
This paper reports on the possibility of using reactive ion etching in selective clean etching in 0.13m silicon technology. Trifluromethane and tetrafluromethane plasmas were used to etch a layer consists of aluminum interconnections buried in a silicon dioxide dielectric layer. As the aim is to find the appropriate parameters for silicon dioxide etching, the process is carried out under different conditions by varying, gas flow, RF power an additional agents. Results show that RIE is very effective at the targeted scale in terms of both dimensionality and etch selectivity.
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.
High aspect ratio micro- and nano-machining of silicon using time-multiplexed reactive ion etching
Journal of Micromechanics and Microengineering, 2011
A low-density plasma reactive ion etching is reported to realize high aspect ratio silicon nanorods on silicon substrates. Aspect ratios with values more than 100 are obtained for features below 200 nm. The process uses a mixture of three gases of hexaflourosulfide, hydrogen and oxygen in a reactive ion etching system with a programmed passivation and etching sub-cycles. Using these three gases in both etching and passivation sub-cycles allows deep silicon etching with high rates, with no need of an inductive coupling plasma source and a special cooling system. The mask undercut can be around 30 nm, despite a high etch rate of 0.8-1.1 μm min −1. X-ray photoelectron spectroscopy and scanning electron microscopy have been used to investigate the prepared samples. Also, the Knudsen transport model has been applied to the etching process which results in a value of 0.23 for the 'S' value as the probability for the reaction at the bottom of the craters.
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 Microelectromechanical Systems, 2002
The ability to predict and control the influence of process parameters during silicon etching is vital for the success of most MEMS devices. In the case of deep reactive ion etching (DRIE) of silicon substrates, experimental results indicate that etch performance as well as surface morphology and post-etch mechanical behavior have a strong dependence on processing parameters. In order to understand the influence of these parameters, a set of experiments was designed and performed to fully characterize the sensitivity of surface morphology and mechanical behavior of silicon samples produced with different DRIE operating conditions. The designed experiment involved a matrix of 55 silicon wafers with radiused hub flexure (RHF) specimens which were etched 10 min under varying DRIE processing conditions. Data collected by interferometry, atomic force microscopy (AFM), profilometry, and scanning electron microscopy (SEM), was used to determine the response of etching performance to operating conditions. The data collected for fracture strength was analyzed and modeled by finite element computation. The data was then fitted to response surfaces to model the dependence of response variables on dry processing conditions. The results showed that the achievable anisotropy, etching uniformity, fillet radii, and surface roughness had a strong dependence on chamber pressure, applied coil and electrode power, and reactant gases flow rate. The observed post-etching mechanical behavior for specimens with high surface roughness always indicated low fracture strength. For specimens with better surface quality, there was a wider distribution in sample strength. This suggests that there are more controlling factors influencing the mechanical behavior of specimens. Nevertheless, it showed that in order to achieve high strength, fine surface quality is a necessary requisite. The mapping of the dependence of response variables on dry processing conditions produced by this systematic approach provides additional insight into the plasma phenomena involved and supplies a practical set of tools to locate and optimize robust operating conditions.
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 Hydrogen Plasma Treatment for Soft and Selective Silicon Nitride Etching
physica status solidi (a), 2018
In this paper, the development of a soft and selective method to increase the etching rate and control accurately the etched thickness of Si 3 N 4 material is reported. This technique combines the low damage characteristics of wet etching with the anisotropy of plasma etching which is compatible with the requirements of many surface sensitive electronic devices such as MOS transistors. This consists on a local modification of the Si 3 N 4 layer using hydrogen-based plasma followed by wet chemical etching in buffered oxide etch solution. The plasma conditions are optimized and a relatively high etch rate is demonstrated. FTIR analyses show clear evidence that the formation of N-H and Si-H species in the hydrogenated Si 3 N 4 layer contributes effectively to the increase of the etching rate. Finally, a chemical etching model is proposed to explain the higher etch rate of hydrogenated Si 3 N 4 .