Deposit etchants

A family of chemicaJ etchants known as deposit etchants works slightly different than chemical etchants. Like electrolytic etchants, deposit etchants promote dissolution of metal on the polished surface. However, the dissolved mettil ions react with agents in the etchant solution, promoting... 

Copper etchants do not directly influence the electroless plating process, but are used merely to remove unwanted copper, and should not affect the deposit properties. The costs of waste treatment and disposal have led to disuse of throw-away systems such as chromic—sulfuric acid, ferric chloride, and ammonium persulfate. Newer types of regenerable etchants include cupric chloride, stabilized peroxide, and proprietary ammoniacal etchant baths. 

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. 

Thin films (qv) of vitreous silica have been used extensively in semiconductor technology. These serve as insulating layers between conductor stripes and a semiconductor surface in integrated circuits, and as a surface passivation material in planar diodes, transistors, and injection lasers. They are also used for diffusion masking, as etchant surfaces, and for encapsulation and protection of completed electronic devices. Thin films serve an important function in multilayer conductor insulation technology where a variety of conducting paths are deposited in overlay patterns and insulating layers are required for separation. 

Fig. 2, Process steps used to produce the structure shown in Fig. 1 (a) A film of SiO > lias been formed by oxidizing the silicon and a layer of photoresist has been deposited on the SiCd (b) Shading shows a region of the photoresist that has been exposed to light and thereby made more soluble, (c) The exposed photoresist has been removed. (cl) An etchant that reacts with the SKF. but not with the photoresist, lias been removed, (e) Anodier solvent has been used to remove the unexposed photoresist, (f) Donor atoms have diffused into the silicon through the opening in the SiCr to produce an a-type region, fg) Additional masking steps, not shown, have permitted aluminum to be evaporated onto the diode in a pattern that forms a contact to the n region of the diode. (See Fig. 1 for legend)...

Most isotropic etchants exhibit a loading effect, wherein a measurable depletion of the active etchant results from consumption in the etch process. In these cases, the overall etch rate depends upon the area of film to be etched. Under extreme circumstances, with carbon-based etch gases, etchant depletion can be so severe that polymer deposition occurs instead of etching. An analysis (85) of the loading effect, which has been extended (86) to include multiple etchant loading and other etchant loss processes, indicates that the etch rate (R) for N wafers each of area A is given by... 

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. 

Although the thermal transfer printing technique does not offer resolution as high as pCP, it does have enormous flexibility in the materials that can be patterned. It also benefits from its all dry and purely additive operation it does not require etchants or solution routes for depositing or patterning the key materials. It is necessary, however, to balance the adhesion between the layers that are sequentially transfer such that interfaces have intimate physical and electrical contact. In addition, current commercial systems have pixel sizes of 5 pm x 2.2 pm, which limit the resolution. With the current DNSSA-PANI/SWNT formulation and a printer of this type, it is possible to print 10-pm channels and 25-pm lines. 

Boron-doped diamond electrodes — Electrode material made from synthetic diamond (- diamond electrode) for example via vapor deposition techniques. In an atmosphere of methane (as a carbon source) and hydrogen (as etchant) at ca. 600 °C diamond seeds tend to grow whereas graphitic carbon deposits are etched... 

In the case of a photoresist, the ultimate definable feature size together with the ability of the material to withstand either chemical etchants or plasma environments determines the domain of utility. The feature size is in turn determined by the wavelength required for exposure, the sensitivity and contrast of the resist, and the dimensional stability of the material during exposure, development, and subsequent processing. Adhesion of the resist to the substrate is critical both for patterning and use, and adhesion can be affected by surface preparations, and by residual stresses developed during deposition and cure. While photo-imagable polyimides have been introduced, their principal intended application is as a component of the finished part, either as passivant or interlevel dielectric (see below). 

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