Masking process

The most commonly used powder blasting processes are the mask process using just an unconfined powder jet, and microblasters that utilise a well-defined and confined powder jet. 

Wensink et al. [556] compared a variety of masking materials. The best results for powder blasting of structures with dimensions larger than 50 pm have been achieved using BF 400, which is an elastic negative photoresist foil. 

If the dimensional tolerances had to be less accurate, thicker metal plates attached to the surfaces by a wax seal were favoured. 

A 60-pm-wide channel was realized with an aspect ratio of 2.5 with a particle size of 9 pm and a powder velocity of 180 m s using a 50 pm wide copper mask. 

Belloy et al. [36,38] investigated the oblique powder blasting, in which the jet of abrasive particles is directed to the masked workpiece at an angle different from normal incidence, which opens the way to new underetching effects and perspectives in the 3D microfabrication. A symmetrical shape is created if the abrasive particles impact the surface at normal incidence. An oblique particle impact, however, i.e. at an angle away from 90°, leads to the formation of an asymmetrical erosion profile. More material is removed in the 

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In resolving complex metal-ion mixtures, more than one masking or demasking process may be utilized with various aliquots of the sample solution, or applied simultaneously or stepwise with a single aliquot. In favorable cases, even four or five metals can be determined in a mixture by the application of direct and indirect masking processes. Of course, not all components of the mixture need be determined by chelometric titrations. For example, redox titrimetry may be applied to the determination of one or more of the metals present. 

Jensen stresses the great flexibility in reactor design that can be achieved by means of microfabricahon, in particular when parallel, MEMS-based mask processes are followed, having a mulhtude of miniature designs on one mask [75], This should invigorate the innovahve nature of reactor design and allow one to overcome... 

A Pt catalyst was applied by dry and wet techniques. By means of sputtering using a mask process protecting parts of the microstructure, the micro channel bottom was coated selectively. In addition, an y-alumina layer was applied by the sol-gel technique. Initially, the whole micro structure was covered by such a layer. Then, photoresist was applied and patterned so that only the channel part remained covered. After removal of the exposed photoresist and unprotected y-alumina, only the channel bottom was coated with y-alumina. 

Figure 19.6. Growth of deposit in vias and trenches during Cu electrodeposition in (a) damascene and (b) deposition through- mask process.

In 2009, Ayela and coworkers proposed the large scale fabrication of MIP microbiochips using an optimized photo-masking process [75]. A resolution of... 

Device Fabrication. A four-mask process was used for the fabrication of tin oxide microsensors on silicon substrates. The major processing steps are shown in Figure 1 ... 

TYPICAL STEPS IN PROCESSING A BIPOLAR DEVICE MASK PROCESS STEP... 

A micromachined CE device featuring a truly monolithically integrated detector has been recently reported by Webster et al. [79]. A semiconductor radiation detector was fabricated together with a separation channel on a silicon substrate in a 10-mask process. The preliminary results achieved with the detection of beta decay events of 32P-labeled DNA at 27 V/cm demonstrate the feasibility of the concept. 

After etching, access holes can be created on the Si substrate by wet etch-through [1,89,90,281,306] or by drilling [442,495]. A two-mask process was also used to create channel access holes on the Si wafers [90],... 

Normally, a one-mask process was employed for glass etching, but for specific applications, a two-mask process was used to create the shallow channel (1-6 pm deep) and the deep channel (20-22 pm deep) [115,117]. In order to fabricate shallow (18 pm) and deep (240 pm) glass channels, they were etched separately on the bottom and top plates using two masks. Alignment was achieved during bonding... 

A two-mask process has been used to create a glass master containing two levels of positive photoresist relief structures. The master was used to cast a PDMS chip consisting of the channel/chamber (25-30 pm deep) and weir (7-12 pm clearance) [960]. Another two-mask process was used to create a Si molding master consisting of 3-pm-high Si relief stmctures and 25-pm-high photoresist relief structures [364]. 

As a first demonstration of the fabrication of TFT devices by digital lithography, tri-layer insulated-gate thin-film transistors were fabricated on four-inch glass substrates using a three-layer wax-mask process. Mask layers were used to define the... 

A field shielded pixel structure is used. The cross-section of the active-matrix stack is shown in Fig. 14.6. The first four layers, defining the TFT, are identical with the stack presented in Section 14.2. The rows of the display are processed on the first metal level whereas the columns are processed on the second metal level. In the field-shielded pixel design, the pixel electrode is defined in a third metal level of gold, resulting in a six-mask process. The pixel pad overlaps the storage capacitor, TFT, and column lines with a 6 pm thick polyvinylphenol layer acting as inter-layer dielectric. The optical aperture thereby increases to over 95%. The TFT channel length (L) and width (W) are 5 pm and 140 pm, respectively. 

Fig. 23. Production of a vertical slope by shadow mask processing...

There is a basic difference between the damascene and the plating-through-mask processes in the way in which the trenches and vias are filled with electrochemically deposited Cu, either through electro- or electroless technique. In multilevel metal structures, vias provide... 

Preferred growth from the bottom may be achieved by the addition of suitable additives. In the plating through mask process only the bottom is active wliile the sidewalls are inactive, resulting in the grow of Cu deposit from the bottom, as depicted in Fig. 

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