A residual gas analyzer (RGA) is a mass spectrometer, typically designed for process control and contamination monitoring in the semiconductor industry. RGAs may be found in high vacuum applications such as research chambers, surface science setups, accelerators, scanning microscopes, thermal degassing chambers, etc., used in most cases to monitor the quality of the vacuum and to detect minute traces of impurities (contaminants) in a low pressure gas environment. In some applications, the RGAs are capable of measuring impurities down to 10−14 Torr levels.
In one illustrative example, the RGA may be used to monitor the thermal degas process of the PVD process in a degassing chamber. In such an application, the RGA can be used to detect many types of contaminants and process variabilities within the thermal degas process. This is mainly due to the fact that most RGA applications are designed to generate generic alarms to cover many different types of contaminants (or undesirable process variabilities or equipment malfunction). However, since the RGA alarm is generic, such RGA application is not capable of determining the exact contaminant (or undesirable process variabilities or equipment malfunction); it is only capable of triggering generic alarm when any abnormal condition arises. Some of the different types of abnormal conditions which may be detected by the RGA include, amongst other types of contaminants and process variabilities:                photoresist chemicals which were not properly or completely stripped in previous processes;        photoresist developer;        ARC film residue;        chemicals used in wet cleaning process;        residual contaminations within the degas chamber, itself;        process variabilities in upstream processes, e.g., arcing in the etch process; and/or        Gas leakage in the degas chamber.        
The RGA is also capable of detecting outgassing of moisture (e.g., water) from the chamber due to water absorption by the wafer during wafer processing. Although the outgassing of water is typically considered normal, there may be situations where an excessive amount of moisture may be indicative of contamination issues.
In the case that any contamination or process variability is detected, the RGA will trig an alarm alerting a technician to a potential contamination issue. In such case, the tool (degassing chamber) is stopped to ensure that such contamination (or undesirable process variabilities or equipment malfunction) will not damage other processing chambers in the process flow. Of course, the shut-down of the tool will negatively impact the throughput of the entire wafer processing.
Once the tool is shutdown, the processing engineer (sensor/control engineer) must review the raw sensor data and compare such data to the historical data to interpret the spectrum. To find the root cause, the manufacturing team is required to check the process history of the alarmed product (e.g., the problem with the wafer). This is due to the fact that the RGA generates generic alarms, and is incapable of determining the exact contaminant or root cause of the contamination (or undesirable process variabilities or equipment malfunction). The analysis of the raw RGA data and wafer history will allow the team to properly diagnose the problem, fix any processing issues relating to such problem, and restart the wafer processing. The diagnosis of the root cause involves the collective experience of the engineering team and, of course, diagnosis will vary depending on the experience level of each team member.
It is also of importance to note that diagnosis of the root cause is very time consuming, averaging more than two hours of engineering time and two hours of the process time per RGA alarm. In some cases, depending on the complexity of the problem, the diagnosis can take even longer.
Also, due to the experience level of the engineering team, mistakes are apt to occur which can be costly to manufacturing in yield loss and process tool availability. Therefore, without knowing the root cause of RGA alarms, people usually take a very conservative approach to handle RGA alarms. In other words, technicians scrap wafers and clean tools after RGA alarms regardless of the root causes of the RGA alarms. Obviously this can cause unnecessary wafer loss and tool down time. The understanding of the root cause of the RGA alarm is required for proper and prompt handling of RGA alarms.
Also due to the complexity associated with analysis of RGA alarms, RGAs often have to be limited to specific applications; that is, the RGA may be limited to detecting a single specific type of contaminant, e.g., only to detect photoresist or O2 contaminants. The problem with this approach is such RGA applications are not designed to detect all types of contamination, which may lead to undetected contamination issues in downstream processes. These RGA applications do not address the entirety of the potential root cause. For this and other reasons, such specific application RGAs are known to cause unnecessary tool down time and yield loss for the downstream processes, when a contaminant is missed.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.