Henri Camon

Roughning and smoothing dynamics during KOH silicon etching

Abstract We studied the influence of surface preparation prior to KOH etching and of surfactants added to the etchant over the etching rates and roughness of the Si (111) and Si (100) surfaces. The investigated etchants were 25% KOH at 70°C, and 25% KOH with small amounts of anionic, cationic and non-ionic surfactants. The surface preparation refers to the use of the following solutions for the native oxide removal: HF:H2O 1:10 (followed by DI water rinsing and drying), HF:C2H5OH 1:10 (dried without any further rinsing), and 10% HCl in HF:H2O 1:1 (also dried without rinsing). The evaluations were made by mechanical profilometry and AFM. No difference between the samples dipped in HF–water and HF–alcohol could be observed. The etching rate of the samples dipped in HCl-containing solutions were greater, while their roughness was diminished. We analyzed the influence of surfactants on the roughness and the anisotropy. The etch rates increased when using cationic and anionic surfactants and decreased with non-ionic ones. The anisotropy is modified by surfactants. Tentative explanations for the roughning mechanisms are proposed.

New trends in atomic scale simulation of wet chemical etching of silicon with KOH

Abstract A new atomic scale model has been developed to simulate anisotropic etching of silicon in KOH solutions. This model is based on the influence of the number of hydroxide groups attached to atoms. Etch rates and macroscopic activation energies have been calculated and compared with experimental data. Microscopic surface roughness has been investigated for 〈100〉 and 〈111〉 surface.

Analysis and testing of a fluidic vortex microdiode

A new design of fluidic microdiode is proposed. An initial numerical simulation of this so-called vortex microdiode allows us to understand the working principle of the diode. It is shown that the complex relationship between the inertial and viscous effects may lead to paradoxical results: as an example, an increase in the viscosity can involve an increase in the flow rate. The simulated performances, confirmed by experimental measurements with a microdiode etched by deep reactive ion etching on a silicon wafer, are compared to the performances of other microdiodes described in the literature. The efficiency of the vortex microdiode is found to be comparable to that of the Tesla microdiode, which was the most efficient microdiode. This is very encouraging, all the more so since the optimization perspectives are varied, due to a sophisticated design.

Atomic scale simulation of silicon etched in aqueous KOH solution

In this paper we present the theoretical bases of an atomic scale model and the Monte Carlo implementation. We present results for oriented surfaces like etching rates, and more detailed results for low-index surfaces such as and . For these two directions we present results concerning the surface morphology and the time evolution of the roughness.

VHDL?AMS modelling and simulation of a planar electrostatic micromotor

System level simulation results of a planar electrostatic micromotor, based on analytical models of the static and dynamic torque behaviours, are presented. A planar variable capacitance (VC) electrostatic micromotor designed, fabricated and tested at LAAS (Toulouse) in 1995 is simulated using the high level language VHDL–AMS (VHSIC (very high speed integrated circuits) hardware description language–analog mixed signal). The analytical torque model is obtained by first calculating the overlaps and capacitances between different electrodes based on a conformal mapping transformation. Capacitance values in the order of 10−16 F and torque values in the order of 10−11 N m have been calculated in agreement with previous measurements and simulations from this type of motor. A dynamic model has been developed for the motor by calculating the inertia coefficient and estimating the friction-coefficient-based values calculated previously for other similar devices. Starting voltage results obtained from experimental measurement are in good agreement with our proposed simulation model. Simulation results of starting voltage values, step response, switching response and continuous operation of the micromotor, based on the dynamic model of the torque, are also presented. Four VHDL–AMS blocks were created, validated and simulated for power supply, excitation control, micromotor torque creation and micromotor dynamics. These blocks can be considered as the initial phase towards the creation of intellectual property (IP) blocks for microsystems in general and electrostatic micromotors in particular.

Modelling of anisotropic etching in silicon-based sensor application

Abstract Preliminary results of an atomic-scale simulation of the wet-etching process are reported. This model assumes an atomic-etching probability depending on the local surface configuration. The cases of flat Si(100), rough Si(100), and flat Si(111)-oriented surfaces are examined.

Monte Carlo simulation of anisotropic etching of silicon: investigation of surface properties

The etching rate of the surface family is of prime importance for micro-fabrication. However, the experimental values of the corresponding etch rate are often scattered and the etching mechanism of remains unclear. In this paper the Monte Carlo simulation results obtained from etching of small size substrate are presented. Simulations were carried out to simulate the behaviour of the surface in contact with strong base aqueous solutions (R - OH). Simulation shows that when etching a small substrate , the etch depth against time curve shows a constant part and a linear part. The former is related to the magnitude of Monte Carlo time steps while the latter corresponds to the evacuation of one sublayer. However, the substrate size fails to impact the etching mechanism which remains unchanged even for an infinite size. The same remark applies to roughness which exhibits a series of alternative peaks.

High-order modes in cavity-resonator-integrated guided-mode resonance filters (CRIGFs).

Cavity-resonator-integrated guided-mode resonance filters (CRIGFs) are optical filters based on weak coupling by a grating between a free-space propagating optical mode and a guided mode, like guided-mode resonance filters (GMRFs). As compared to GMRFs they offer narrowband reflection with small aperture and high angular acceptance. We report experimental characterization and theoretical modeling of unexpected high-order reflected modes in such devices. Using coupled-mode modeling and moiré analysis we provide physical insight on key mechanisms ruling CRIGF properties. This model could serve as a simple and efficient framework to design new reflectors with tailored spatial and spectral modal reflectivities.

First steps towards design, simulation, modelling and fabrication of electrostatic micromotors

Following the principles proposed by workers at Berkeley University, we have developed a version of the electrostatic micromotor based on the sacrificial layer method combined with oxidation of the rotor. In order to study the behaviour of this electrostatic micromotor, we have elaborated two softwares. The first, called EFCREL, is to simulate the static operation of the electrostatic micromotors and the second, called EFDYN, is to simulate their dynamic operation. Both are based on a finite-element code, called EFCAD, for electromagnetic field computation. They help us with the design of the fabricated micromotor and the simulation of its dynamic working, respectively. The elaboration of these two softwares represents our first steps towards a fully integrated CAD (computer aided design) system for micromotors.

VHDL-AMS modelling, simulation and testing of electrostatic micromotors

A good agreement has been found between the proposed micromotor model simulation results and the collected experimental dat. A better understanding of friction modelling issues has also been achieved through iterative simulation. Developed VHDL-AMS blocks can be considered as an initial phase towards the creation of Intellectual property (IP) blocks for microsystems in general and electrostatic micromotors in particular, enabling MEMS disign reuse and exchange between different designer teams. These blocks can subsequently be used for high level simulation of different types of systems along with other electronic or mechanical blocks, all within the same standard framework provided by VHDL-AMS. Experimental data from the MUMPS fabricated wobble micromotors will be presented in a future along with their VDHL-AMS models.