moisture measurement
Peak ring-down times are entered into the formula of the Beer-Lambert Law, the result is the moisture concentration. This time-based measurement contrasts with other laser-based measurement techniques relying on hard-to-control factors such as differences in light intensity, rendering them “relative” techniques, requiring external calibration.
and T
While a true zero measurement is insured by capturing the ring-down time off-peak, the on-peak performance is verified via a reference cell. A small fraction of the laser light is diverted through a reference cell that contains a small amount of the analyte in question.
When the laser is exactly on peak, the amount of light reaching a detector at the far end of the reference cell is minimal. If the intensity begins to increase (indicating a drift from the correct wavelength), the laser is adjusted by changing the supplied current until the intensity is again at a minimum. This “laser locking” ensures that the proper T
Figure 2: Laser Trace3 vs LaserTrace Moisture Specifications
Peak wavelength is being used and eliminates any long-term drift that continues to plague other technologies. While the underlying science is relatively complex, the instruments are very simple to operate. All of the calculations are
performed by the system’s software and the concentration is continuously updated on the touch- screen display. Tiger analyzers are effortless to install and do not require the use of calibration gases or null gases. Once the system is taken out of the crate, measurements on a dry gas can be taken in just a matter of minutes.
Tiger’s Reach Since 2001, Tiger’s R&D team has developed a variety of analyzer versions from its CW-CRDS technology. These include the LaserTrace family, HALO family, Tiger-i (for ambient and environmental contaminants), ALOHA-H2O (for UHP ammonia), and Prismatic. Each platform addresses specific market needs. Foremost on Tiger’s agenda: anticipating the requirements of the semiconductor industry, with its ever-decreasing line geometries coupled with increasing wafer sizes. No instrument maker is more attuned to a fabrication plant’s constant need for gas purity analyzers with lower LDLs, reduced cost of ownership (COO), and increased uptime.
Accordingly, Tiger introduced its LaserTrace system in 2003. The platform provides users with a modular product line that allows for the monitoring of their bulk gases (Ar, He, H2, N2, O2) to sub-ppb levels for moisture, oxygen, methane, and other analytes. By 2008, the LaserTrace+ system was able to provide users with an LDL as low as 200 ppt (depending upon the gas matrix). The LaserTrace has become the company’s most popular product family, with nearly 500 systems in use worldwide.
The EURAMET 1002 Study The absolute nature of the CW-CRDS technology is heralded not only by industrial users, but by the scientific community as well. Throughout the world, national metrology institutes (NMIs) have established their own methods of generating precise levels of moisture to develop and compare standards and to perform vital calibration processes in their own country or region.
As each NMI’s moisture generator is large and of complex design, it has not been feasible to ship these generators around the globe for comparison studies. The NMIs needed a portable, absolute measurement technique that could be shipped from one institute to another to perform the analysis. Enter Tiger Optics.
Using two Tiger instruments, the European Association of National Metrology Institutes (EURAMET) recently completed an international study of different moisture generating techniques from four (4) NMIsii. The participants included the National Institute of Standards and Technology (NIST, USA), National Metrology Institute of Japan (NMIJ, Japan), National Physical Laboratory (NPL,
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www.siliconsemiconductor.net Issue 2 2012
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