High resolution powder blast micromachining

Powder blasting, or Abrasive Jet Machining (AJM), is a technique in which a particle jet is directed towards a target for mechanical material removal. It is a fast, cheap and accurate directional etch technique for brittle materials like glass, silicon and ceramics. By introducing electroplated copper as a new mask material, the feature size of this process was decreased. It was found that blasting with 9 µm particles (compared with 30 µm particles) result in a higher slope of the channel sidewall. The aspect ratio of powder blasted channels was increased by using the high resistance of the copper mask in combination with the use of 9 µm particles. Furthermore, our measurements show how the blast lag (small channels etch slower compared to wider channels) is decreased by using smaller particles

Inactive lifestyle in adults with bilateral spastic cerebral palsy

Objective: To quantify the level of everyday physical activity in adults with bilateral spastic cerebral palsy, and to study associations with personal and cerebral palsy-related characteristics. Participants and methods: Fifty-six adults with bilateral spastic cerebral palsy (mean age 36.4 (standard deviation (SD) 5.8) years, 62% male) participated in the study. Approximately 75% had high gross motor functioning. Level of everyday physical activity was measured with an accelerometry-based Activity Monitor and was characterized by: (i) duration of dynamic activities (composite measure, percentage of 24 h); (ii) intensity of activity (motility, in gravitational acceleration (g)); and (iii) number of periods of continuous dynamic activity. Outcomes in adults with cerebral palsy were compared with those for able-bodied age-mates. Results: Duration of dynamic activities was 8.1 (SD 3.7) % (116 min per day), and intensity of activity was 0.020 (SD 0.007) g; both outcomes were significantly lower compared with able-bodied age-mates. Of adults with cerebral palsy, 39% had at least one period of continuous dynamic activities lasting longer than 10 min per day. Gross motor functioning was significantly associated with level of everyday physical activity (Rs -0.34 to -0.48; p≤0.01). Conclusion: Adults with bilateral spastic cerebral palsy, especially those with low-level gross motor functioning, are at risk for an inactive lifestyle

Reduction of sidewall inclination and blast lag of powder blasted channels

Powder blasting (abrasive jet machining) is a fast directional machining technique for brittle materials like silicon and glass. The cross-section of a powder blasted channel has a rounded V-shape. These inclined sidewalls are caused by the typical impact angle dependent removal rate for brittle materials. It has a negative influence on the channel depth and aspect ratio, and results in the blast lag: wide channels become deeper compared to smaller channels. Two approaches are studied in this paper that can influence this effect: using smaller powder particles and decreasing the particle jet impact angle (oblique blasting). Calculations and measurements show that the blast lag can be reduced for these two cases. However, oblique blasting requires additional equipment and results in low mask/target selectivity while the reduction in blast lag is relatively small. Powder blasting with smaller particles is much easier to perform and leads to straighter sidewalls and a large blast lag reduction

A closer look at the ductile brittle transition in solid particle erosion

Two types of solid particle erosion are often distinguished: brittle erosion and ductile erosion. In the first case, material is removed by crack formation (maximum erosion at 90° impact angle), in the latter case by cutting and ploughing (maximum erosion around 30° impact angle). When very low particle kinetic energies are used to erode brittle targets, the impacts are not powerful enough to initiate cracks and the erosion is ductile instead of brittle. This paper looks at the transition from brittle to ductile erosion for three brittle materials: sodalime glass, Pyrex glass and single crystalline left angle bracket1 0 0right-pointing angle bracket silicon. Besides the erosion rate, we also measure the "erosion classification value" (ECV), which is the ratio of the erosion rate at 45° and 90° impact angle (ECV¿0.45 for brittle erosion and >1 for ductile erosion). The change of ECV in relation to the change in erosion rate is studied for particle kinetic energies between 6×10¿10 and 6×10¿7 J (using alumina particles of 3¿29.2 ¿m and speeds between 75 and 200 m/s). The transition is not suddenly, but extends over at least one decade of kinetic energy. During this transition, the ECV slowly rises to a value >1. SEM pictures of the eroded surfaces accompany the measurement

Mask materials in powderblasting

Powderblasting has the opportunity to become a standard technology in micromachining. To machine small details with powderbalsting, it is necessary to use a suiabled mask. In this paper four mask types ares examined. BF400 resist foil is most suitable for standard use in powderblasting for reason of simplicity. A simples metal plate can be used with less accurate dimensions (> 1mm) but having the advantage of being reusable. Electroplated copper has the opportunity to be a suitable mask for machining lateral dimentions of 50 um and less. These mask materials show that there are manu ways of using powderblasting as a microtechnology

Fine tuning the roughness of powder blasted surfaces

Powder blasting (abrasive jet machining) has recently been introduced as a bulk-micromachining technique for brittle materials. The surface roughness that is created with this technique is much higher (with a value of Ra between 1¿2.5 ¿m) compared to general micromachining techniques. In this paper we study the roughness of powder blasted glass surfaces, and show how it depends on the process parameters. The roughness can also be changed after blasting by HF etching or by using a high-temperature anneal step. Roughness measurements and scanning electron microscopy images show the quantitative and qualitative changes in roughness. These post-processes will allow us to investigate the influence of surface roughness on the microsystem performance in future research

The black silicon method. VIII. A study of the performance of etching silicon using SF6/O2-based chemistry with cryogenical wafer cooling and a high density ICP source

This paper presents a study of the performance of current trends in high speed, highly controllable anisotropic plasma etching of silicon for its use in micro- and nano-engineering. Optimisation rules for tuning the equipment are formulated to enable maximum results with respect to etch rate, etch selectivity, and profile control (e.g. anisotropy). The optimisation process uses the black silicon method to allow for an easy to use design-of-experiment method. After optimisation, etch rates of silicon up to 15 μm/min were obtained at a relatively high pressure (4 Pa=30 m Torr and ICP power (2 kW), while keeping the anisotropy high. At the same time, the erosion rates of thermal silicon dioxide and ordinary photoresist (Shipley S1805) were around 7 nm/min (i.e. selectivities up to 2000). Increasing the pressure to 20 Pa, the selectivity increased to 10,000, although bottling became more pronounced. The high etch rate and high selectivity are especially important in the case of micro-engineering, where wafer through etching with the help of plasmas become a standard in the near future. In the case of nano-engineering, however, profile control is the main concern. To prevent undercut in such cases, in particular, bottling due to a broad ion angular distribution, the pressure should be sufficiently low. The best results were found at pressures below 0.2 Pa=1.5 mTorr and at a low ICP power of 350 W to prevent a too strong mask erosion caused by the low pressure. The silicon etch rate decreased to 1 μm/min and the erosion rate of the oxide and resist were both approximately 20 nm/min, giving a selectivity of 50. Reproducibility (wafer-to-wafer) and uniformity were also output factors of prime concern. Surprisingly enough, for two different equipment manufacturers the results were almost identical when using the same parameter setting. This indicates that the SF6/O2-based chemistry was optimised rather than the equipment itself.\u

The black silicon method VIII: a study of the performance of etching silicon using SF6/O2-based chemistry with cryogenical wafer cooling and a high density ICP source

This paper presents a study of the performance of current trends in high speed, highly controllable anisotropic plasma etching of silicon for its use in micro- and nano-engineering. Optimisation rules for tuning the equipment are formulated to enable maximum results with respect to etch rate, etch selectivity, and profile control (e.g. anisotropy). The optimisation process uses the black silicon method to allow for an easy to use design-of-experiment method. After optimisation, etch rates of silicon up to 15 μm/min were obtained at a relatively high pressure (4 Pa=30 m Torr and ICP power (2 kW), while keeping the anisotropy high. At the same time, the erosion rates of thermal silicon dioxide and ordinary photoresist (Shipley S1805) were around 7 nm/min (i.e. selectivities up to 2000). Increasing the pressure to 20 Pa, the selectivity increased to 10,000, although bottling became more pronounced. The high etch rate and high selectivity are especially important in the case of micro-engineering, where wafer through etching with the help of plasmas become a standard in the near future. In the case of nano-engineering, however, profile control is the main concern. To prevent undercut in such cases, in particular, bottling due to a broad ion angular distribution, the pressure should be sufficiently low. The best results were found at pressures below 0.2 Pa=1.5 mTorr and at a low ICP power of 350 W to prevent a too strong mask erosion caused by the low pressure. The silicon etch rate decreased to 1 μm/min and the erosion rate of the oxide and resist were both approximately 20 nm/min, giving a selectivity of 50. Reproducibility (wafer-to-wafer) and uniformity were also output factors of prime concern. Surprisingly enough, for two different equipment manufacturers the results were almost identical when using the same parameter setting. This indicates that the SF6/O2-based chemistry was optimised rather than the equipment itself.\ud \u

Powder-blasting technology as an alternative tool for micro-fabrication of CE-chip with integrated conductivity sensors

The fabrication and characterization of a microfluidic device for capillary electrophoresis applications is presented. The device consists of a glass chip which contains a single separation channel as well as an integrated conductivity detection cell. In contrast to most microfluidic glass devices the channels are not wet etched in HF but machined by the newly developed micro powder-blasting technique which allows the creation of microstructures below 100 µm, and additionally makes parallel hole machining at very low costs outside the cleanroom environment possible [1, 2]. The integration of the conductivity detector was achieved by leading two thin-film metal electrodes inside the separation channel. For rapid sample injection the chip is mounted inside an autosampler-based capillary electrophoresis platform. The detection electrodes for conductivity detection are read out by lock-in amplifier electronics. First measurements show the successful separation of various ions in the sub-millimeter range