Silicon nitride, masking material

Electrochemical experiments have been carried out on materials deposited by PVD on silicon microfabricated arrays of Au pad electrodes [Guerin et al., 2006a]. The substrate is made up of a square silicon wafer capped with silicon nitride (31.8 mm x 31.8 mm), which has an array of 100 individually addressable Au pad electrodes. These electrodes make up a square matrix on the wafer, which can be masked when placed in a PVD chamber, allowing deposition of thin films on the Au electrodes. Figure 16.3 is a schematic drawing of the configuration. Small electrical contact pads in Au for the individual addressing of electrodes (0.8 mm x 0.8 mm) are placed on the boundaries. 

The main goal of another microhotplate design was the replacement of all CMOS-metal elements within the heated area by materials featuring a better temperature stability. This was accomplished by introducing a novel polysilicon heater layout and a Pt temperature sensor (Sect. 4.3). The Pt-elements had to be passivated for protection and electrical insulation, so that a local deposition of a silicon-nitride passivation through a mask was performed. This silicon-nitride layer also can be varied in its thickness and with regard to its stress characteristics (compressive or tensile). This hotplate allowed for reaching operation temperatures up to 500 °C and it showed a thermal resistance of 7.6 °C/mW. 

The selective oxidation can be accomplished with the use of an oxidation mask. Typical of such a masking material is a film of silicon nitride. 

CVD and physical vapour deposition processes, and the resulting crystal structures, have been much studied and used to deposit silicon nitride films and grow epitaxial layers as electrical insulators and as masks for the deposition of other materials in electronic integrated circuitry. 

Dielectric inorganic materials also find widespread utilization in microfabrication as insulators. Common examples are silicon dioxide (Si02) and silicon nitride (SiN). They can also serve as masking materials during the etching steps, which we will discuss later. 

Recent developments in the area of microengineered structures for chemical processing [24] made possible to manufacture meshes of various materials (i.e., steel, silicon nitride), by techniques such as standard mask lithography, or laser interference lithography [56,57]. 

Silicon dioxide has selectivity to many silicon etchants and therefore is a good mask material for self-aligned etching process. In combination with silicon nitride, multistep etching process of three-dimensional structure is possible. Silicon dioxide is also used to seal microchannels. The insulating property of sihcon dioxide makes it a good coating layer of channels in microfluidics. 

Silicon nitride is a good insulator and acts as barrier against all kinds of diffusion to water and ions. Due to thermal insulation properties, heater structures are suspended on silicon nitride membrane or fixtures. Its ultrastrong resistance to oxidation and many etchants makes it a superior material for masks in deep etching. It is also used as high-strength electrical insulator. 

Mask structures are commonly fabricated using lithographic processes. The most frequently used masking materials for the etching of glasses are aluminium, chromium/gold, alumina, gold, silicon nitride and photoresists. 

MOSFETT s, and silicon oxide is deposited. The source/drain positions where electrical contact is to be made to the MOSFETs are defined, using the oxide-removal mask and an etch process. For shallow trench isolation, anisotropic silicon etch, thermal oxidation, oxide fill and chemical mechanical leveling are the processes employed. For shallow source/drains formation, ion implantation techniques are still be used. For raised source/drains (as shown in the above diagram) cobalt silicide is being used instead of Ti/TLN silicides. Cobalt metal is deposited and reacted by a rapid thermal treatment to form the silicide. Capacitors were made in 1997 from various oxides and nitrides. The use of tantalmn pentoxide in 1999 has proven superior. Platinum is used as the plate material. 

EDP (ethylene diamine, pyrocatechol, and water [9]) etches silicon anisotropi-cally and with a high selectivity, allowing a large variety of materials to be used as masks, such as silicon oxide and nitride, chromium, gold, and even aluminum. 

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