• Surface - micromachined devices are typically made up of 3 types of components.

1. a sacrificial component ]spacer layer]

2. a micro structural component

3. An insulator component

• The sacrificial components are usually made of phosphosilicate glass [PSG] or si $o_2$ deposited on substrates by LPCVD techniques

• PSG can be etched more rapidly than si $o_2$ in HF etchants. These components in the form of films can be as long as 1 to 2000 $\mu$ m and 0.1 to 5 $\mu$ m thick.

• Both microstructural and insulator components can be deposited in thin films. polysilicon is a popular material

• The etching rates for sacrificial components must be much higher than those for the two other components.

• Step 1 - A silicon substrate base with a PSG deposited on its surface.

1.

• Step 2 - A mast [ mask 1 ] is made instep 2 to cover the surface of the PSG layer for the subsequent etching to allow for the attachment of the future contileve, beam as shown in step 3.

• Step 4 - Another mask [ mask 2 ] is made for the deposition of polysilicon micro structural material in step 4.

• The PSG that remains in step 5 is subsequently etched way to produce the desired cantilever beam as shown in step 6.

After etching of sacrificial layer.

• The most suitable etchant used in the last step for the sacrificial PSG layer is 1 : 1 HF, Which is made of 1 : 1 HF : $H_2$O + 1 : 1 HCI : $H_2$ O

• After itching, the structure is rinsed in deionized water thoroughly followed by drying under infrared lamp.