Mask-free etching process

The IR filter is realized by a PS layer with a modulation of porosity, which constitutes an interference filter as described in detail in the next section. The 30 pm thick porous layer is then released from the substrate by electropolishing, which is easily done in situ by increasing the etching current density above JPS. This process is commonly applied to form free-standing PS membranes and PS tubes [Tj 1], The internal strain between the Si3N4 layer used for masking and the porous layer lifts the filter up to its rest position, as shown in Fig. 10.10. The filter is suspended at two microactuator arms, which work as thermal bimorph actua-... 

Both macroporous and mesoporous silicon are similarly exploited to achieve various types of separation and/or seed layers by high-temperature anneal and formation of active layer by epitaxial growth or epitaxial free processing (Depauw et al. 2008, 2009 Brendel et al. 2010). Similar studies of void shape evolution and SON (silicon-on-nothing) structure formation from masked anisotropic reactive ion etching resulting in square arrays of holes during H2 anneal were shown in Sudoh... 

In SMOBC processing, the metal-plated resist is removed to present a flat, clean copper surface for solder mask definition. Tin/lead alloys can be stripped in oxidizing fluoride solutions such as fluoboric acid and hydrogen peroxide or ammonium bifluoride with hydrogen peroxide or nitric acid. (Caution machine construction must be made compatible with fluorides by elimination of titanium and glass components.) Commercial formulations are available to be used inline after the etch machine rinses. Accumulations of spent solution or filtered lead-fluoride deposits must be treated as hazardous waste and have been accepted by solution vendors for treatment and disposal costs. Modern applications usually use lead-free tin plating resists, which can be fluoride containing as previously discussed, or compounds of ferric chloride... 

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