Nitrogen and argon gases are probably the gases with the highest volumetric use in a semiconductor fab. They are normally supplied to the fab at "5 9s" purity or 99.999% pure. This purity level is necessary since high volumes of these gases are used for purging process equipment and even very low levels of contamination can produce damaging levels of cumulative contamination during long purge cycles. Other atmospherics (i.e., oxygen, hydrogen, helium) are used at somewhat lower volumes and slightly lower purity levels, which are acceptable (but all such gases must be greater than 99% pure at delivery and on-site storage facilities).
Hazardous high pressure gases include those with pyrophoric, flammable, corrosive, and toxic characteristics (e.g., silane, most hydrocarbons, fluorides and chlorides, phosphine, arsine, etc). Such gases are typically stored in high pressure cylinders that must be maintained in well-vented gas cabinets that are specially designed to mitigate the hazard associated with a specific gas. Most semiconductor fabrication plants have large numbers of such cabinets on site and there are strict regulations governing the placement and number of hazardous gases in a given facility. (See, for instance, the standards published by the National Fire Prevention Association, specifically NFPA 45, the Standard on Fire Protection for Laboratories using Chemicals). Figure 2 shows a schematic of a typical hazardous gas cabinet designed to contain pyrophoric gases such as silane. These cabinets are equipped with appropriate fittings for connection to the high-pressure cylinders and valve configurations that are designed for cross-purging piping connections to remove residual pockets of gas prior to disconnecting an empty cylinder. Modern gas cabinets are normally equipped with analytical sensors that can detect any leakage from the cylinders or piping.
MKS has a number of products that can be used to ensure the quality of bulk gas supplies within a semiconductor fab environment.
G-Series MFCs and MFMs are broadly applicable instruments that provide cost-effective, high performance measurement and control of gas flows between 5 cc/min (sccm) and 250 L/min (slm) with an accuracy of 1% of setpoint. They have multi-range, multi-gas capability and are available in either elastomer or metal sealed configurations.
ALTA all-digital, metal-sealed MFCs are especially suitable for mass flow control of high flows of hydrogen in pyrogenic oxidation and annealing applications. Hydrogen normally presents a notoriously difficult flow control problem.
I-Series MFCs are also suitable for hydrogen service in pyrogenic oxidation and annealing applications. The I-Series MFCs are IP66-rated for use in harsh industrial environments.
Semiconductor Fab Utilities