Page 31 - Microsensors, MEMS and Smart Devices - Gardner Varadhan and Awadelkarim

ELECTRONIC MATERIALS AND THEIR DEPOSITION 13

Figure 2.3 (continued)

CVD is used extensively in depositing SiO 2, Si 3N 4, and polysilicon. CVD SiO 2 does
not replace thermally grown SiO 2 that has superior electrical and mechanical properties as
compared with CVD oxide. However, CVD oxides are instead used to complement thermal
oxides and, in many cases, to form oxide layers that become much thicker in relatively
short times than do thermal oxides. SiO 2 can be CVD-deposited by several methods. It
can be deposited by reacting silane and oxygen at 300 to 500 °C in an LPCVD reactor
wherein
500 °C
SiH 4 + O 2 - > SiO 2 + 2H 2 (2.3)

It can also be LPCVD-deposited by decomposing tetraethylorthosilicate,
The compound, abbreviated as TEOS, is vaporised from a liquid source. Alternatively,