Nanotechnology-Enabled Sensors

4.5 Chemical Vapor Deposition (CVD) 165
films such as; silicon oxide; silicon nitride; polycrystalline, amorphous,
and epitaxial forms of silicon; gallium arsenide; synthetic diamond and
even carbon nanotubes.
In a typical CVD process (Fig. 4.23) the substrate is exposed to one or
more volatile precursors. A precursor is a substance from which another,
usually more stable substance, is formed. 45 The precursors are first vaporized
and then transported to the substrate by carrier gases. The precursor
then reacts or decomposes on the substrate’s surface to produce the desired
film upon receiving energies. The desired atoms are released from the precursor
onto the surface. There they may interact with other atoms to establish
strong binding sites, resulting in nucleation and growth of the thin
film. At this point, unwanted chemical groups are released from the surface
and carried out of the chamber by the flow of gas. Volatile byproducts
are frequently produced as a result of the detachment of unwanted chemicals
reacting. CVD can produce uniform coatings that grow conformally
on the substrate.
Fig. 4.23 The CVD process.