Compare Deposition techniques used in MEMS with respect to their applications.

• Deposition techniques used in MEMS are chemical vapour deposition and physical vapour deposition.

• In Chemical vapour Deposition (CVD), a pressure is introduced into a reaction chamber and is controlled by balanced flow regulators and control valves. Pressure molecules pass by the substrate are drawn into the boundary layer and are deposited on the surface of the substrate.

• Physical vaper Deposition (PVD) consists of different methods, such as evaporation, sputtering and molecular beam epitaxy [MBE].

• Evaporation: Material is heated to gas phase, where it then diffuses through a vacuum to the substrate.

• Sputtering: Plasma is generated first. This plasma contains argon ions, and electrons next atoms from the target are ejected after being struck by argon ions. The atoms from the target then travel through the plasma and form a layer on the substrate.

• Molecular beam epitaxy: The substrate is cleaned and loaded into a chamber that is evacuated and heard to drive off surface contaminants and to roughen the surface of the substrate. The molecular beam emit a small amount of source material through a shutter, which then collect on the substrate.

• One reason to use a physical vapor instead of CVD is the temperature requirement. CVD run at much higher temperature than PVD, usually 300°C and 900°C.

• This heat is supplied by a furnace, RF Coil or laser but it always heats the substrate.

• Substrates that cannot tolerate this temperature must have thin films deposited by PVD instead.

• The benefit of the substrate temperature in some CVD processes is that there is less waste deposition, especially in cold-wall reactors, because only the heated surfaces are coated.

• With the use of laser heating system, CVD becomes selective to the path of the laser, this is a distinct advantage over PVD.

• Molecular beam epitaxy has a distinct advantage of atomic level control of chemical composition, film thickness and transition sharpness. This process is expensive but is worth the added cost for applications that demand higher precision.

• Sputtering does not require the use of specialized precursor materials as used in CVD. Sputtering has a wider range of materials readily available for deposition.

• Another advantage of PVD or CVD is the safety issue of the materials that are used for CVD.