Glass, etching

A small by-product stream is also realized in Europe from glass-etching by HF. Laboratory-scale production is readily accomphshed by exchange between metal fluorides and chlorosilanes (172). 

Hydrogen fluoride Glass Etching, becoming opaque... 

Microfabrication was made by wet-chemical glass etching [20]. Sealing was achieved by thermal bonding. 

Hydrogen fluoride Glass etching, removal of High... 

Uses Explosives, matches electric batteries in leather industry manufacturing colored glass etching copper textile mordant reagent. 

Ammonium Fluoride or Malt Salt, NH4F, mw 37.04, wh poisonous crysts sp gr 1.31, mp — decomp by heat w/o melting sol in cold w. Prepd by interaction of Amm hydroxide with HF, followed by crystn. Used in glass etching, textile mordant, wood preservation and in analytical chemistry (Refs 1 2)... 

Ammonium Fluosilicate (Cryptohalite), (NH4)2SiF6 mw 178.17 wh crystn pdr sp 2.01, mp — sublimes sol in ale w. Can be prepd by interaction of Amm hydroxide with fluosilicic acid, followed by crystn. Used for glass etching, casting of light metals and electroplating... 

Put a mixture of 5 g of calcium fluoride and 1 g of calcium sulphate into lead vessel 1 (Fig. 57). Put a paraffin-coated glass plate with an inscription onto lead support 2 with the inscription downward. Pour 5 ml of concentrated sulphuric acid onto the calcium fluoride and cover the vessel with its lead lid. In an hour, extract the plate with tongs, thoroughly wash it with water, and remove the paraffin. How does the surface of glass etched with gaseous hydrogen fluoride... 

The residue from the treatment with dilute ciel may jdW-be tested for hydrofluoric acid by the ordinary glass-etching method. 

FIGURE 2.3 Sequence for fabrication of the glass microfluidic chip, (a) Cr and Au masked glass plate coated with photoresist (b) sample exposed to UV light through a photomask (c) photoresist developed (d) exposed metal mask etched (e) exposed glass etched (f) resist and metal stripped (g) glass cover plate bonded to form sealed capillary [102]. Reprinted with permission from American Chemical Society. 

Scratch effects in glass etch can be reduced by pre-etching the glass in HF before deposition of the metal etch mask [108]. 

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... 

Two-level glass etch was also performed first over photoresist for shallow etch (10 pm), and then over black lithographical masking tape for deep etch [117]. 

In the selection of etch mask for deep glass etching, thick SU-8 is a choice, but SU-8 cannot be used in a HF bath (48%) because SU-8 does not adhere well to Si02 [123]. However, with a polycrystalline amorphous Si seed layer SU-8 adheres very well. For instance, with a 1.5-pm-thick polished poly silicon, a 50-pm-thick SU-8 can be deposited as the etch mask, leading to a maximum etch depth of 320 pm. Usually photoresist (2 pm thick) is only useful for shallow etch, less than 50 pm [123]. 

FIGURE 2.8 SEM picture of the 115- im-wide and 2-mm-long suspended glass cantilever beams fabricated by deep glass etching [130]. Reprinted with permission from the Institute of Physics Publishing. 

Various wet and dry etch methods have been employed to micromachine fused quartz chips in a similar manner as in glass etching. However, the RIE method can be more effectively employed to etch quartz than can glass. Both wet and dry etch methods for fused quartz are summarized in Table 2.6. 

One of the reasons for high-aspect-ratio (deep-glass) etching is to increase the optical detection sensitivity. Why (2 marks)... 

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