Moisture inside a process chamber is a big silent killer during wafer production. When production yield goes down, it is hard to pinpoint the source of the problem. Most of the time wafers need to be sent to labs for analysis, while production is stopped. If the problem is related to a high level of moisture inside the reactor, there are several factors that can cause this problem: an air leak, a process gas out of specs, or a faulty moisture purifier.
The IRGAS Turnkey Gas Analysis Solution is based upon FTIR Spectroscopy, Short and/or Long Path Gas Cells, and Quantitative Software, SPGAS. FTIR spectroscopy is capable of detecting and measuring all infrared active gas and vapor species; not included are the monatomic and homopolar diatomics. A Short or Long Path Gas Cell can be selected with the appropriate pathlength to match the detection limit required. The SPGAS Quantitative Gas Analysis Software provides ppb sensitivity and fast time response, along with internal gas calibrations.
IRGAS System Description
IRGAS-100 connected at the gas outlet of the reactor chamber; the system consisting of: ABB Bomem WorkIR FTIR with DTGS Detector; Ultra-High Purity N2 Instrument Purge, Heated 4Runner 6.5-meter Gas Cell with AR-coated ZnSe windows; CICP f/5 Optical Couplers; SPGAS and SpectraStream Software.
The IRGAS System proved to be capable of detecting moisture in the low PPB concentration range. The IRGAS System allowed the operator to follow the moisture content inside the reactor at all times. The table and chart (back side of this page) show a continuous monitoring of a process chamber spanning across two days, helping to identify the source of high moisture content. The table shows the type gas or gas mixture (events) flowing through the chamber at any given time and the chart plots the moisture content of the chamber (blue line) together with an event line (red line) showing when a different type of gas is flowing through the chamber.
As can be seen, it is clear that the source of high moisture was coming from the HCl and N2 gas supply (events in bold letters). As a result of the data obtained on the first day, the moisture content on the HCl gas tank was considered out of specs, and a new HCl gas tank was used for the second day of testing. The IRGAS System provided an incredible amount of savings in time and money by reducing the total downtime of the reactor, the number of wafer samples sent to the lab, and the requirements of specialized, highly trained human resources.
Continuous monitoring of moisture present inside a process chamber