Selectively removing or depositing materials on a semiconductor wafer to form integrated circuit structures from wafers is well known in the art of semiconductor processing. Removal of material from a semiconductor wafer is typically accomplished by employing some type of etching process, such as, reactive ion etching or atomic layer etching. Depositing material on a wafer may involve processes such as chemical and physical vapor deposition (CVD/PVD), molecular beam epitaxy (MBE) or atomic layer deposition (ALD). In semiconductor processing, other plasma-based or emitting processes such as implantation are also known and optically monitored. All such processes are tightly controlled and are performed in environmentally controlled process chambers. Because exact amounts of material are to be deposited onto or removed from the surface of a wafer, the deposition or removal progress must be continually and accurately monitored to detect the precise state of a particular process and when the process should be further controlled or modified. A common control result is to stop a process. This result and its associated time is called the endpoint. Various sensors, such as optical sensors, are used to monitor semiconductor processes.
Optically monitoring processes within a chamber is commonly used for determining the processing status, processing state conditions, or endpoint, for an ongoing process. Monitored processes include semiconductor etching, deposition, implantation and other processes where film thickness and plasma/wafer emission monitoring is applicable. Additionally, chamber conditions independent of or combined with the wafer conditions, may be monitored. Depending on the process, various algorithms may be employed for deriving parameters from the optical signal intensities, typically related to chemical species signatures that are useful in assessing the state of the semiconductor process and the processed wafer, detecting faults associated with the process, chamber or other equipment and even the condition of interior surfaces of the plasma chamber.