Characterization and minimization of moisture concentration in atmospheric pressure RTP tools, using an in situ absorption spectroscopy sensor

Small amounts of moisture and oxygen in the several ppm regime are key contaminants in RTP, but moisture is much more difficult to remove than oxygen and therefore it is more of a practical problem. Conventional sensors are inadequate for measuring moisture in RTP, mainly because of their slow response and inadequate sensitivity, but also because they can be damaged by vapors in the process atmosphere. A moisture sensor based on tunable diode laser absorption spectroscopy has been used to measure water vapor during RTP processes, and has been shown to overcome these drawbacks. The data presented in this paper illustrate three applications: first, monitoring the moisture concentration in a Mattson RTP tool and optimizing the tool for processes with very high sensitivity to moisture contamination, second, the effect of a NH₃-purge on moisture absorbed to the process chamber walls and the wafer, and finally, the optimization of a COP (Crystal Originated Particle) anneal process. The data prove that the moisture sensor can be used for onsite qualification of a newly-installed tool, and for real-time process monitoring. Small moisture incursions during processing can be detected, and the loss of valuable product avoided. During start-up, contamination-free performance can be verified quickly, avoiding or minimizing the consumption of test wafers.