Directional etching

Once the resist has been patterned, the selected regions of material not protected by photoresist are removed by specially designed etchants, creating the resonator pattern in the wafer. Several isotropic (etching occurs in all directions at the same etch rate) and anisotropic (directional) etching processes are available. Wet chemical etching is an isotropic process that... 

Powder blasting, or abrasive jet machining, is a technique in which a particle jet (typically A1203 particles of 3-30 lm) is directed towards a target for mechanical material removal. It is a fast (typically, 500 pm depth in 20 minutes), inexpensive, and accurate directional etch technique for brittle materials like glass, silicon, and ceramics. For complex and small structures a mask can be used. 

The etchant is a gas plasma (Fig. 5.1.8), which can attack the silicon substrate in two ways chemically (nondirectional etching), that is, by chemical reactions between silicon and the generated reactive radicals or physically (directional etching), by material sputtering from the substrate as a result of collisions with the accelerated plasma ions. 

The irradiations at 308 and 222 nm were carried out in air. Effective direct etching of polymers by excimer lamps can only be observed at reduced pressures (between 0.1 to 100 mbar) [239], which was not examined in this study where only atmospheric pressure was applied. The decomposition of the polymer was analyzed at the two maxima, i.e., 196 and 330 nm. The former corresponds mainly to the absorption of the aromatic groups, the latter to the triazene groups [68]. 

In the beam-lines used for the SR direct etching, there is no mirror or other optical system, but pinholes or slits may be used to select the beam size or to improve the beam uniformity. The SR beam is quasi-continuous, having a pulse duration of 170 ps and a repetition rate of 191 MHz. The pho-... 

Table 1 Synchrotron radiation direct etching of polymers...

Fig. 15 High aspect ratio structures made of PTFE by SR direct etching in vacuum. Typically, the structural height (depth) is 500 fim and the structural width is 20 //m thus, the aspect ratio is 25...

Fig. 19 A comparison between deep lithography and direct etching with increasing irradiation time. The main difference is that the level of the resist surface is falling during the etching, but almost not at all during lithography exposure...

Fig. 20 SEM picture of the typical microstructures made of PMMA by SR direct etching in vacuum. Here, the structural depth is 200 //m, much larger than the 0.6 mm previously observed in the self-development. But the quality is not as good as that of microstructures made by deep x-ray lithography (cf., Fig. 13)...

Although the SR beam has been used to directly etch PTFE, PFA, and FEP in vacuum, like laser ablation to create microstructures and to deposit thin films, some considerable differences are found. For example, it is not applicable to polymers like PI which has good radiation resistance, and the orientation of the polymer chains in the deposited films is different from that obtained by using the laser. In this section we compare two photoprocesses, namely SR direct etching and laser ablation and discuss the fundamentals for the SR etching of polymers. 

No matter whether the photoprocess is direct etching or ablation, it involves three basic processes, namely absorption, dissociation, and desorption. 

Direct etching of polymers in vacuum with SR which was mainly x-rays between 0.2 and 3 nm has been studied. This is a process involving only photons, like laser ablation, but it is different from laser ablation both in desorption dynamics and dissociation mechanisms. 

Dry-etching techniques, in general, are methods by which a solid state surface is etched physically by ion bombardment or chemically by a chemical reaction with a reactive species at the surface or combined physical and chemical mechanisms. Under chemical methods, one distinguishes between wet etching (solvent, vapor, electrochemical) and dry etching in the gas phase. Depending on the mechanism, isotropic or anisotropic (directional) etch profiles are obtained. 

Mark III Microvia, directional etching 0-10,000 to 0-40 KW/ 40 kHz 8-32 panel loading (18 x 24-in) or custom 1 %-in shelf spacing... 

Andrew JE, Dyer PE, Forster D, Key PH (1983) Direct etching of polymeric materials using a XeCl laser. Appl Phys Lett 43(8) 717-719... 

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