Ximing Ding

Laser-Induced Backside Wet Etching of Sapphire

Sapphire plates were etched with the approach of laser-induced backside wet etching (LIBWE) using neat toluene or saturated pyrene/acetone solutions as the etching medium. Using this approach, flexible patterns on the scale of 4-µm can be fabricated on the surface of the plates. The etching process was observed in situ by a CCD camera, which revealed the deposition of black particles and the formation thereafter of a laser-absorbing film in the etched area. By Raman spectroscopic analysis, the film was characterized to be amorphous carbon resulting from the decomposition of toluene or pyrene upon laser irradiation, which is an essential factor contributing to the etching process.

Fabrication of 1 μm patterns on fused silica plates by laser-induced backside wet etching (LIBWE)

Laser-induced backside wet etching of fused silica plates using aqueous solutions of naphthalene-1,3,6-trisulfonic acid trisodium salt (Np) and pyranine (py) was performed upon KrF excimer laser irradiation at 248 nm. The two etching media show different etching behavior with changing laser fluence and medium concentrations. Well-defined line-and-space and grid micropatterns at 1 μm scale were fabricated using an aqueous solution of Np and the etched pattern was free of debris and microcracks.

Site-selective dye deposition on microstructures of fused silica fabricated using the LIBWE method

Using laser-induced backside wet etching (LIBWE) technique, microstructures were fabricated onto the surface of fused silica plates, which were pre-coated with self-assembled monolayers (SAMs). Dye molecules and proteins were alternately deposited onto the laser-irradiated or non-irradiated areas by either chemical bonding or physical adsorption.

Surface microfabrication of fused silica glass by UV laser irradiation

Surface micro-structuring of fused silica glass plates was performed by single-shot irradiation with a single-mode laser beam from a diode-pumped solid state UV laser at 355 nm. Well-defined micropattern without debris and microcrack formations around the etched area was fabricated by laser ablation with a focused laser-beam in the ambient air. The time-resolved optical emission spectra of plume were measured to elucidate the ablation behavior of silica glass induced by nanosecond-pulsed laser irradiation at 355 nm where absorption of silica glass is negligibly small. This method is suitable for rapid prototyping of surface microstructuing without a clean room environment.

Surface microfabrication of silica glass by excimer laser irradiation of toluene solution

Laser-induced backside wet etching of silica glass plates was performed by the excitation of a pure toluene solution with a ns-pulsed KrF excimer laser at 248 nm. Well-defined grid micropattern was fabricated without debris and microcrack around the etched area. To understand the etching mechanism, the formation and propagation of shockwave and bubble were monitored by time-resolved optical microscopy at the interface between the silica glass and the toluene solution after laser irradiation. Transient high-pressure as well as high-temperature generated by UV laser irradiation plays a key role in the etching process.

Surface microstructuring of transparent materials by laser-induced backside wet etching using excimer laser

Silica glass is an important material in optics and optoelectronics because of its outstanding properties, such as transparence in a wide wavelength range, strong damage resistance for laser irradiation, and high chemical stability. In order to develop simpler processes of micro-fabricating silica glass using a pulsed laser, we have investigated a one-step method to microfabricate a silica glass plate using laser-induced backside wet etching (LIBWE) upon irradiation with a ns-pulsed excimer laser. Our idea of LIBWE is based on the deposition of laser energy on the surface of silica glass using ablation of a dye solution. When the dye solution was ablated upon the laser irradiation, the etching of a surface layer was performed on the silica glass. We have succeeded in the micro-fabrication of such transparent materials as silica glass, quartz, calcium fluoride, sapphire and fluorocarbon resin. The advantages of our LIBWE method are as follows, (1) a lwo laser fluence and constant etch rate, (2) microfabrication without debris and cracks formation, (3) large area irradiation with an excimer laser beam through a mask projection, (4) simple pre/post-treatment on target substrates. This is a one-step process simpler method at ambient pressure, which would be used for mass production.

Surface micro-structuring of silica glass by laser-induced backside wet etching using ns-pulsed UV lasers: application into micropatterning of functional materials using self-assembled monolayers

Silica glass is an important material in optics and optoelectronic devices because of its outstanding properties, such as transparence in a wide wavelength range, strong damage resistance for laser irradiation, and high chemical stability. In order to develop simpler processes of micro-fabricating silica glass using a pulsed laser, we have investigated a one-step method to microfabricate a silica glass plate using laser-induced backside wet etching (LIBWE) upon irradiation with ns-pulsed UV lasers. Two laser irradiation systems were employed for the fabrication; (1) mask projection system with a KrF excimer laser and (2) Galvanometer-based point scanning system with a single mode laser beam from a diode-pumped solid state laser at 266 nm. We have succeeded in a fine micro-fabrication of silica glass surface. In addition, a novel approach in the fabrication of microarrays of dye and protein on fused silica plates using LIBWE technique was achieved. The surace of fused silica plates was initially pre-coated using trimethoxysilane self-assembled monolayers (SAMs), then etched using the LIBWE method to obtain the desired microstructures on the plate surface. Using this technique, the SAMs on the non-irradiated areas were able to survive the LIBWE process, and were used as templates for the subsequent deposition of dye molecules, proteins, or polystyrene microbeads via chemical bonding or physical adsorption.

Site-selective dye deposition onto micropatterns of fused silica fabricated with laser-induced backside wet etching (LIBWE)

A novel approach for the fabrication of micropatterns where dye molecules can be site-selectively desposited is described. The micropatterns were fabricated on the surface of fused silica plates using the technique of laser-induced backside wet etching (LIBWE). Prior to the LIBWE process, the surface properties of the fused silica plates were modified with self-assembling trimethoxysilanes bearing functional moieties. On the non-irradiated areas, the self-assembled monolayers (SAMs) survived the LIBWE process, and the remaining SAM acted as a template for the subsequent dye deposition either with chemical bonding or physical adsorption. Site-selective dye deposition was visualized with fluorescence microscopic observation. These results are applicable for micro-fluidic reactors and chemical sensors.