Silicon In Chlorine Atmosphere Research Articles

Research on Laser Trimming of Silicon MEMS Vibratory Gyroscopes

A method for frequency tuning of silicon MEMS vibratory gyroscopes by laser induced etching of silicon in chlorine atmosphere has been presented. The feasibility of this method is analyzed in theory and practice. An experimental apparatus is implemented to test and verify the scheme. A silicon chip of gyroscope has been etched in this apparatus for 30 seconds. The resonant frequency of the gyroscope is changed from 3200 Hz to 3209 Hz. This result shows laser induced etching is an effective way to realize frequency tuning.

Etching of crystalline Si in Cl2 atmosphere by means of an optical fiber tip

We report experiments on laser-induced chemical etching of silicon in chlorine atmosphere using a near-field optical configuration. Crystalline (100) Si surfaces were locally illuminated in 300 mbar Cl2 through a tapered fiber tip. In most of the experiments, we used UV argon ion laser lines around 350 nm for illumination. The etched samples were analyzed by means of atomic force microscopy. Patterns with a width of 140 nm at full width half maximum and a vertical etch rate of the order of 15 nm/s have been achieved. Comparison of etching with a visible wavelength at intensities that cannot cause surface melting shows that the etching is primarily a photophysical process.

Projection-patterned etching of silicon in chlorine atmosphere with a KrF excimer laser

The formation of relief features in silicon by a one-step process that avoids resist patterning has been achieved by laser-projection-patterned etching in a chlorine atmosphere. Etching is performed with a pulsed KrF excimer laser (λ=248 nm, τ=15 ns) and deep UV projection optics having an optical resolution of 2 μm. Etching takes place in two steps. Between laser pulses, the silicon surface is covered with a monolayer of chemisorbed chlorine atoms (one Cl per Si). During the laser pulse, surface transient heating at temperatures in excess of 1250 K results in the desorption of the reaction products (mainly SiCl2). At laser energy densities that induce surface melting, this desorption results in a saturated etch. rate of 0.06 nm per pulse, corresponding to the removal of about 0.5 Si monolayer per pulse. At densities below the melting threshold, reduced thermal and possibly a small amount of photochemical etching result in lower etch rates. Projection of a resolution test photomask onto the silicon surface shows that the size of etched features differs from the size of the projected features and strongly depends on the laser energy density. As a result of the heat spread in silicon and of the highly nonlinear character of the etching reaction, etched features smaller than the irradiated area are obtained at all fluences in the range 350–700 mJ/cm2. Etched lines having a width down to about 1.3 μm were produced. Proximity effects due to heat spread were also evidenced for small projected features (<4 μm). The characteristics of the etched patterns are compared with those obtained for GaAs etching in chlorinated gases with the same experimental set-up. Significant differences in pattern resolution for Si and GaAs etching are observed. This variation in resolution is believed to result from the fact that Si has a greater thermal diffusivity than GaAs.

Projection-patterned etching of silicon in chlorine atmosphere with a KrF excimer laser

Projection-patterned etching of silicon in chlorine atmosphere with a KrF excimer laser

Excimer-laser-induced etching of silicon in chlorine atmosphere at a wavelength of 248 nm

The etching behaviour of silicon in chlorine atmosphere assisted by laser radiation at 248 nm has been studied as a function of laser fluence and gas pressure. Different process regions have been determined. The crystalline quality and the surface morphology and roughness have been investigated by transmission electron microscopy and secondary ion mass spectroscopy.

Excimer laser-assisted etching of silicon in chlorine: adsorption and desorption

The present paper is devoted to experimental identification of the excimer laser-induced etching mechanism of silicon under “high” chlorine pressures (30–160 Torr). Experimental results on pulsed KrF excimer laser etching of silicon in chlorine atmosphere by a sequence of single and double pulses are presented. The etch rate dependencies on time delay between pulses in the “double” are discussed. Two mechanisms of etching are considered. The first is laser-stimulated thermal desorption of chemisorbed layer, formed between laser pulses. The second one is direct chemical reaction of chlorine molecules with a silicon surface thermally activated by laser heating. On the basis of the analysis of experimental results it is concluded that direct pyrolytic chemical reaction of chlorine with a hot silicon surface heated by excimer laser pulse radiation (pulse duration 17.5 ns) gives a negligible contribution to the total etch rate.

Model of laser-induced chemical etching of silicon in chlorine atmosphere

A mathematical model for the chemical etching of silicon in a chlorine atmosphere induced by laser irradiation is described. The model takes into account: dissociation of molecules having absorbed radiant energy into chlorine atoms and their diffusion onto the substrate surface, generation of photocarriers in the silicon substrate, kinetics of chlorine atom chemisorption on the silicon surface, chemical reaction of chemisorbed chlorine atoms with silicon atoms, and desorption of reaction products. The obtained results are compared with experimental data.

Laser-induced chemical etching of silicon in chlorine atmosphere

Laser-induced chemical etching of silicon in chlorine atmosphere

Laser-induced chemical etching of silicon in chlorine atmosphere

Laser-induced chemical etching of silicon in chlorine atmosphere

Laser-induced chemical etching of silicon in chlorine atmosphere

Chemical etching of single-crystalline (100)Si induced by pulsed laser irradiation at 308, 423, and 583 nm has been investigated as a function of the laser fluence and C12 pressure. Without laser-induced surface melting, etching requires Cl radicals which are produced only at laser wavelengths below 500 nm. With low laser fluences (Φ(308 nm) 440 mJ/cm2) etching is thermally activated. In the intermediate region both thermal and non-thermal mechanisms contribute to the etch rate.