Mumbai University > Electronics Engineering > Sem 8 > MEMS Technology

Marks: 5M

• Substrates in LIGA process must be electrical conductive to facilitate subsequent electroplating over photoresists mold.
• Metals such as : steel copper plates, titanium and nickel, or
• Silicon with thin titanium or silver / chrome top layer, glass with thin metal layers.

Photoresists materials

Basic requirements:

• Must be sensitive to x-ray radiation.
• Must have high resolution and resistance to dry and wet etching.
• Must have thermal stability up to 1400C.
• The unexposed part must be absolutely insoluble during development.
• Good adhesion to substrate during electroplating.
• PMMA appears most popular for LIGA process, but other polymers are available:

Electroplating

• The inner surfaces of the photoresists mold produced by X-ray lithography need to be plated with thin metal layers for securing permanent microstructure geometry.
• Metals available for the plating are: Ni, Cu, Au, NiFe and N/W.
• In case of plating with Ni, the process is:
• Nickel ions (Ni2+) are produced from electrolysis of NiCl2 solution.
• They are attracted to the electrons at the cathode:
• Ni2 + 2e $\rightarrow$ Ni
• There could be H+ ions presence at the same cathode in the process.
• These H+ ions may form H2 bubbles on the cathode, and thus Ni plate.
• Proper control of the pH in the solution is important to miligate this effect.