Metal etching, etchants

Inlqet ink compositions for etching resist have been reported which can provide cured articles having excellent adhesion to metal plates, etchant resistance and alkali developabiUty, and which can be stably ejected by inkjet printing. 

Acidic, Cifvi) solutions may be used as cleaners or etchants for metals (e.g. Cu) and plastics, e.g. ABS acrylonitrile/butadiene/styrene. In the case of metals, the Cffvi) may be used in order simply to clean the metal, etch the surface or completely remove a metal coating. The etching of plastic substrates is a key step prior to metallizing epoxy based laminates during the production of printed circuit boards. 

Modern ammoniacal etchants are mildly alkaline solutions containing ammonium carbonate, cupric and chlorite ions together with proprietary additives. Metallic etch resists including tin-lead are not usually attacked but the pH and solution composition must be maintained in order to preserve the etch rate and prevent sludge formation. A possible set of reactions is ... 

The TFTs are made on transparent glass substrates, onto which gate electrodes are patterned. Typically, the gate electrode is made of chromium. This substrate is introduced in a PECVD reactor, in which silane and ammonia are used for plasma deposition of SiN as the gate material. After subsequent deposition of the a-Si H active layer and the heavily doped n-type a-Si H for the contacts, the devices are taken out of the reactor. Cr contacts are evaporated on top of the structure. The transistor channel is then defined by etching away the top metal and n-type a-Si H. Special care must be taken in that the etchant used for the n-type a-Si H also etches the intrinsic a-Si H. Finally the top passivation SiN, is deposited in a separate run. This passivation layer is needed to protect the TFT during additional processing steps. 

Masking is required for many micromechanical applications. While Si3N4 is only suitable for a small etching depth because of its significant etch rate in HF, noble metals like gold are sufficient mask materials. In contrast to alkaline etchants, organic materials like certain resists or even some adhesive tapes are well suited to protect the silicon surface in isotropic etchants. 

Microporous silicon is suitable for sacrificial layer applications because of its high etch rate ratio to bulk silicon, because it can be formed selectively, and because of the low temperatures required for oxidation. PS can be formed selectively if the substrate shows differently doped areas, as discussed in Section 4.5, or if a masking layer is used. Noble metal films can be used for masking as well as Si02, Si3N4 and SiC. Oxidation conditions are given in Section 7.6, while the etch rates of an etchant selective to PS are given in Fig. 2.5 b. 

Curing is first performed at 200 C in air and then at 350 C in a nitrogen atmosphere. Through-holes are etched using a negative photoresist as the etching mask and an etchant containing hydrazine hydrate and ethylenediamine. Next, the second level metallization is formed. PIQ film is then formed on the second level metallization. This acts as a passivation film. 

Other non-conventional masking methods include etching as defined by (1) marker ink masking and (2) laminar flow of etchants in channel. These methods were used to fabricate metal electrodes for EC detection [268]. 

A body of HgCdTe is first mounted on a sapphire substrate 2. A first etchant mask is formed and individual detector elements 5 are formed by etching. Thereafter a second etchant mask 7 is formed, a metal layer is deposited and metal regions are formed by a lift-off process. 

Figures 1IC-E show SEM images of test patterns of silver that were fabricated using pCP with hexadecanethiol, followed by selective chemical etching [102], The SAMs protect the underlying substrates from dissolving by blocking the dilSisional access of etchants. The ability to generate arrays of microstructures of coinage metals with controlled shapes and dimensions is directly useful in fabricating sensors and arrays of microelectrodes.

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