Oxide layers are grown from oxygen or HO molecules from the gas
phase above the wafer. On the ubiquitous silicon wafers oxidation
results in a layer of SiO
. The growth rate of the SiO
layer
is influenced by temperature, the doping concentration, and the
partial pressure of the oxidizing gas. Their purpose is to act as an
insulator between the substrate and conductors on top of them. The
oxidation process naturally consumes a certain amount of silicon from
the substrate.
Hence for processes where a SiO layer has to cover anything but
silicon a different process must be used. An alternative to oxidation
is the growth of SiO
layers by CVD. Its advantage is that it can
be performed at lower temperatures, which reduces undesirable
diffusion of previously introduced doping. On the other hand SiO
layers generated by CVD are generally less uniform than those
generated by oxidation.
Clemens Heitzinger 2003-05-08