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MAV Design Aspects Using MEMS

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1.

Lithography: It is a process of defining pattern by applying a thin uniform

layer containing viscous liquid (in general, it is termed as photo-resist, PR) on

a water surface. PR is hardened by baking and is removed at selective sections

by projecting it to the light with a reticule consisting of mask information.

2.

Etching: It is a process of removing unwanted materials from the wafer surface

in a selective manner. Then this pattern of PR is transferred to the wafer by

using etching agents.

3.

Deposition: Films of different materials in desired forms are applied on wafers.

Two methods generally used for this purpose are physical vapour deposition

(PVD) and chemical vapour deposition (CVD).

4.

Chemical Mechanical Polishing: It is a Planarization technique, which uses

chemical slurry with etchant agents on the wafer surface.

5.

Oxidation: Two types of oxidation methods are used, and they are (1) Dry

Oxidation (only oxygen is used) and (2) Wet Oxidation (H2O is used). In this

process oxygen or H2O molecules will convert Si layers on top of wafers to

Silicon dioxide.

6.

Ion Implantation: This method is popularly used to introduce the dopant impu-

rities in a semiconductor. Ionized particles will be accelerated in an electric field

and will target the semiconductor wafer.

7.

Diffusion: This is used to anneal bombardment-induced lattice defects.

Surface Micromachining (SMM) Process

It is a well known core technological process for underlying MEMS from deposited

thin films [4]. There are four steps in surface micromachining as shown in Fig. 11.3.

An isolation layer is coated to the substrate in Fig. 11.3a to protect it during etching

steps. An opening of sacrificial layer is terminated on isolation layer as shown in

Fig. 11.3b. A mictrostructural thin layer will be deposited and etched as shown in

Fig. 11.3c.

In the final stage only selective etching of sacrifical layers will create a free-

standing micromechanical structure like a cantilever beam as shown in Fig. 11.3d.

The above steps are extendable for preparing multi layered micro-structures. This

Fig. 11.3 Steps of surface micromachining process