Ozone has been widely used in semiconductor processing. For example, ozone can be used in combination with TEOS to deposit silicon dioxide. Ozone can be used in atomic layer deposition (ALD) process to form oxide films, such as aluminum oxide or hafnium oxide. Ozone can also be used for cleaning semiconductor wafers and semiconductor equipment, especially for removing hydrocarbon residues.
In general, an ozone generator is located a distance from the processing chamber, with the ozone concentration is measured at the output of the ozone generator. However, process windows have become narrower in advanced applications of both front end of line (FEOL) and back end of line (BEOL), especially in ALD, chemical vapor deposition (CVD) and interface treatment, and the ozone settling time between the ozone generator and the process chamber can cause the ozone concentration at the process chamber to be different from the desired level, leading to a compromised semiconductor product.
Thus, monitoring, measuring or controlling the ozone concentration at the point of use becomes critical. This has imposed additional requirements on ozone-related equipment, such as ozone generator and ozone concentration sensors. For example, in most applications the ozone is fed into a chamber where the pressure is under or around a few Torr range. However, there is no ozone sensor available to measure ozone concentration at such low pressure. For example, the available ozone sensors in the market which use UV absorption method, can only measure the ozone concentration above 8 PSI (405 Torr).
Therefore, ozone concentration sensors and controllers capable of operating at low pressure are needed.