Leak Detection in Semiconductor Fab Gas Processes

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Figure 1. FCT and concentration readings used to determine a leak by responding to elevated moisture levels.

Figure 2. FCT and concentration readings used to locate a leak by responding to spraying CO2.

Problem Statement

Often times in semiconductor fabs moisture levels are monitored to ensure that products aren’t damaged by excess moisture in the process. If there are above normal levels of moisture, pinpointing the source of that moisture can be difficult. The moisture could be evolving from impurities in gas tanks or leaks in the sampling lines. One way to avoid downtime while trying to identify the source of moisture is to monitor the ratio of H2O and CO2. If there are consistently high levels of H2O and CO2, chances are that there is a leak in the process. This leak, if under negative pressure, is pulling the environment air into the line increasing the levels of water and carbon dioxide.

IRGAS Applicability

The IRGAS Moisture + Plus is the most recent product added to CICP’s IRGAS line of FTIR gas analyzers. This analytical instrument is designed to give fast response (within seconds) and high sensitivity (ppb/ppm) results for the semiconductor industry and for electronic specialty gas producers. When this instrument’s powerful design and sophisticated software are combined, it offers a low cost-of-ownership that can be used for critical problem solving for semiconductor fabs.

IRGAS System Description

The IRGAS Moisture + Plus consists of a rugged Bomem WorkIR FTIR spectrometer, a 316L stainless steel 4Runner 6.0 meter gas cell, optical couplers, and a purge N2 purifier. The 4Runner contains proprietary goldcoated stainless steel mirrors, which can handle strong acidic and basic gases, and utilizes fast laminar flow from gas streams. In addition to the system hardware there are two user-friendly software programs that enhance the system. The first program is SPGAS^TM (Specialty Gas Analysis Software). SPGAS uses a weighted, multiband, multilevel, multivariate CLS method in conjunction with managing the system hardware, such as valves, regulators, sensors, and pumps. The second program, SpectraStream^TM, is anadditional feature of the SPGAS program; it provides a fast response indicator of changes in gas concentrations. The Moisture + Plus combined with the SPGAS and SpectraStream software creates an analytical solution that eliminates costly downtime and losses for semiconductor fabs.

Sample Data/Solution Achieved

As long as the system is running at negative pressure, CICP’s FTIR gas analyzer package can be used as a leak detector and detect levels of H2O and CO2 as low as the ppbs. It will also show these changes within seconds of their occurrence; thus preventing the need to stop production in order to establish the source of excess moisture. Below are graphs showing the IRGAS Moisture + Plus ability to determine leaks within process gas lines. The first graph displays the system’s fast concentration tracker (FCT) and the concentration reading of elevated moisture caused by a leak in a process line and then the reduction of H2O present once the leak was fixed, Figure 1. Figure 2 depicts the system’s concentration and FCT response to CO2 being used to determine where in the line the leak was located. The CO2 used to determine the leak was from a tank containing 15% CO2 with a N2 balance. The CO2 was sprayed along the process line until the leak was detected and corrected.