Etching methods

The etching method is one where the work is masked with a resist such as wax and successively etehed as the masking is extending from the regions that are to remain the highest to the lowest. The contour steps initially might... 

Pores with a very regular, linear shape can be produced by the track-etch method (Quinn et al. 1972). Here a thin layer of a material is bombarded with highly energetic particles from a radioactive source. The track left behind in the material is much more sensitive to an etchant in the direction of the track axis than perpendicular to it. So etching the material results in straight pores of uniform shape and size with pore diameters ranging between 6 nm and 1200 nm. To avoid overlap of pores only 2-5% of the surface can be occupied by the pores. This process has been applied on polymers (e.g. Nuclepore membranes) and on some inorganic systems like mica. Membranes so obtained are attractive as model systems for fundamental studies. 

An example of the track-etch membrane was given in Section 2.2 (Quinn et al. 1972). Booman and Delmastro (1974) have also described the layer deposition method to produce a microporous membrane by a track-etch method. 

Dry etching techniques permit etch processes to be carried out in various modes. These can be described as purely chemical, purely physical, and a mixture of chemical and physical. With plasma etching and RIE, we have concentrated on chemical and ion assisted processes. In this section, etching methods that depend either solely or primarily on physical processes (momentum transfer) will be discussed briefly. 

Optical methods such as x-ray specular reflectivity and specular ellip-sometry give very similar thicknesses to the etching method [24]. This validates to a certain extent the just described procedure, which is much easier to use. 

Our investigation of sNPS showed that the samples prepared by the chemical etching method described above have consistent photoluminescence, conductivity and photoconductivity properties, which have remained unchanged over 5 years. sNPS structure was investigated by scanning electronic microscopy (Fig. 9.1). 

After quick freezing in liquid nitrogen and fracture, another etching method was used at — 90 °C for less than 1 min in a 1.33 x 10-4 Pa chamber. The etched sample was cooled to — 130°C and coated with platinum and carbon in the same vacuum chamber and transferred to the scanning electron microscope at — 130 °C. The observed structure was closer to reality than that obtained by the method previously described. This is called the cryo-SEM technique [32]. CryoSEM images are shown in Fig. 4 which presents the structural change by stretching [16]. 

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

The limitations encountered with solution etching can be overcome by plasma-enhanced etching. Adhesion is not a major problem with dry-etch methods. Undercutting can be controlled by varying the plasma chemistry, gas pressure, and electrode potentials (2-6) and thereby generate directional or anisotropic profiles. 

Ion beam etching (IBE) is a physical etching method in which inert ions are accelerated with an ion gun, towards the substrate. The substrate itself is placed in a separate etching... 

Sputter or ion etching (IE) is also a physical etching method with inert ions (such as Ar+) from a plasma which are accelerated towards the substrate. In this case the substrate is in contact with the plasma. The etching profile is anisotropic, the selectivity is poor. 

Ion beams provide useful information either as a diagnostic tool or as a precision etching method in. adhesive bonding research. The combination of SIMS with complementary methods such as ISS or AF.S provides a powerful tool for elemental end limited structural characterization of metals, alloys and adhesives. The results shown here indicate that surface chemistry (and interface chemistry) can be decidedly different from bulk chemistry. Often it is this chemistry which governs the quality and durability of an adhesive bond. These same surface techniques also allow an analysis of the locus of failure of bonded materials which fail in service or test. 

Ion beams provide useful information either as a diagnostic tool or as a precision etching method in adhesion research. The combination ISS/SIMS method used along with other techniques such as SEM provides a powerful tool for elemental analysis of surface composition. These results, as well as earlier work in this laboratory, indicate that the surface composition can be significantly different from the bulk due to contamination, selective chemical etching and segregation. These same techniques also provide an analysis of the mode of failure in adhesive joints. Many failures classified as "adhesive" on the basis of visual inspection are frequently mixed mode failures or failures at a new interface containing elements of both adhesives and adherend. 

Precise microstructures with nearly any cross-sectional shape can be generated by means of anisotropic plasma-etching methods, where again silicon is the most important and proven material (18,20). Usually, a mask pattern is transferred into a thin layer consisting of a material resistant to plasma etching on a silicon... 

The micro mixer was made by standard photolithographic and etching methods on an ultra-flat quartz substrate [160], The microstructure created in this way was shielded by a cover plate by thermal bonding. This cover plate contained access holes for fluid supply and withdrawal. Internal surfaces of the chip were activated to have a high density of silanol groups needed for the EOF transport... 

The microfluidic structure was manufactured in glass by classical photolithography and wet-chemical HF etching methods [164], Holes for fluid connection were drilled. A polymer membrane was prepared in-house and served as a top plate to give a glass-polymer sandwich chip. Pressure sealing was applied. 

Different etch methods used to produce microfluidic chips on Si are tabulated in Table 2.1. 

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. 

Normally, one-level etching was performed, but in some applications (e.g., pre-channel filter), a two-level etching method was also performed [148]. BOE etch was chosen over HF etch for quartz because BOE produced a smoother etch (0.23 urn RSI )) than did HF (0.55 pm RSI )) [149]. The cross section of an etched channel in a quartz chip is shown in Figure 2.11 [1006]. 

To create liquid access, holes were punched through the replica. Then it was placed on another thin slab of PDMS for sealing. Because an anisotropic KOH-based etching method was employed to etch the Si master without corner compensation, the channel intersections in the replica were limited in shape by the <111> plane of the Si master [159]. 

Detector elements 11 are formed on a ceramic substrate 1. Each detector element includes a photosensitive zone 9, an output terminal 4 and a common terminal S. The detector elements are arranged in an array protruding from a common metal line 3, which is connected to a terminal pad 6. The terminal electrodes and the common metal line are formed on a comb-like patterned photo-conductive layer 2. An aperture plate 7 of silicon or ZnS having apertures 8 formed therein by an anisotropic etching method is prepared. The purpose of the aperture plate is to restrict the field of view of the photosensitive zones. An auxiliary electrode 30 is formed on the aperture plate. When the aperture plate is assembled with the substrate using an adhesive, the auxiliary electrode is pressed against the common metal line and the common terminal, which together reduce the electrical resistance. 

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