Wayne Thomas Mcdermott

Counting Efficiency of an Improved 30-Å Condensation Nucleus Counter

The ultrafine aerosol condensation nucleus counter (UFACNC) developed by Stolzenburg and McMurry (1990) has been improved. This new instrument can detect particles as small as 30 A in nitrogen at a sample flow rate of 2.5 cm3·s−1. This flow rate is five times that of the earlier design with the same particle counting efficiency. An increased sample flow rate causes an increase in the arrival rate of detected particles. This improves accuracy in estimating the true particle concentration in ultraclean gas systems. In order to demonstrate its high accuracy the new UFACNC was used to measure the concentration of contaminant particles in ultrafiltered nitrogen. This represents the first accurate determination of ultrafine contamination levels in large ultraclean gas systems. The nitrogen was found to contain as few as 1.28 × 10−4 particles/cm3 (3.62/ft3). The higher volumetric flow rate of the new counter reduced the sample standard deviation of the measured count rate. Therefore, in the case of a low particu...

Developments in 30 angstrom particle detection for ultraclean gas systems

The ultrafine aerosol condensation nucleus counter (UFACNC) developed by Stolzenburg and McMurry, 1990 has been improved. The improved instrument can detect particles as small as 30 Angstroms in nitrogen at a sample flow rate of 2.5 cm3.sec.−1. This flow rate is five times that of the earlier design. The increased sample flow rate provides an increase in the arrival rate of detected particles. The result is an improved accuracy in estimating the true particle concentration in ultraclean gas systems. The improved UFACNC was used to measure the concentration of ultrafine contaminant particles in two ultraclean nitrogen systems. The nitrogen was found to contain as few as 1.28 × 10−4 particles per cm3 (3.62 per cubic foot). The higher flow rate of the improved counter resulted in a relatively small standard deviation of the measured particle concentration. Therefore, the small difference between the process and instrument noise background count rates was accurately resolved. The improved UFACNC was also used to demonstrate a new technique for size classifying ultrafine particles using only a UFACNC, i.e., without a separate size classifier. The results demonstrate that particle size distributions can be obtained directly from a stand-alone UFACNC.

Particle Contamination Control and Measurement in Ultra-Pure VLSI Grade Inert Gases

particle microcontamination in the inert gases, such as nitrogen, used in the manufacture of integrated circuits greatly affects the yield loss of semiconductors. With the continuously increasing complexity of integrated circuits, there are no particles so small that their presence in the inert gas supply systems can be safely ignored. It is, therefore, necessary to accurately measure and control the level of particle contamination in gas delivery systems in order to supply virtually particle free gas. The key factors in production and supply of particle-free gas are ultra-high efficiency membrane filters, total integrity of the filter installations, and absolute cleanliness of all surfaces in contact with supplied gas.

Capture and Analysis of Particulate Contamination in Gaseous and Liquid Processing Materials

A number of methods are available for determining the particle content in chemically reactive fluids such as liquid, gaseous or supercritical processing materials. Each method has advantages and disadvantages. This paper describes the method of particle capture on filters followed by microscopic analysis. Although this method has been widely applied to measuring particle levels in various liquids and gases, and for airborne particle sampling, it has not been extensively used for highly reactive semiconductor processing materials. A sampling system suitable for implementing this method in difficult to measure fluids, and the steps necessary to perform the capture process are described. A method for quantifying the particle concentration in the fluid based upon an analysis of the particles observed on the filter is also described. Typical results of contaminant particles detected in liquid and gaseous materials used for semiconductor wafer processing are also presented. These data provide information on the particle content of fluid source containers and transfer lines, and the efficiency of filters in removing such particles in flowing systems. Particle SEM images and compositional data obtained through energy dispersive X-ray spectroscopy (EDS) are presented. Such information aids in the tracing of particle sources, and the eventual elimination of such sources.

Chapter 17 – Cleaning Using Argon/Nitrogen Cryogenic Aerosols

Aerosol jet cleaning of surfaces has become a promising technique for the anhydrous removal of particles, or other undesired materials such as films or layers. This chapter describes the methods used to produce argon/nitrogencryogenic aerosol jets, approximate operating costs, and some examples of the effectiveness of these aerosols in removing silicon wafer surface contamination. However, the technique is applicable in removing contaminants in other areas. Although operating conditions for a cleaning tool are presented, these conditions are merely illustrative, and should serve only as an approximate guide in generating cryogenic aerosols for cleaning. In production process, a pressurized mixture of high-purity gaseous argon and nitrogen is first filtered and then pre-cooled in a cryogenic heat-exchanger. The argon/nitrogen mixture may be pre-cooled to a temperature slightly above the argon dew point in the cryogenic cooler. The pre-cooled mixture is then expanded in a free jet to a lower pressure. The associated Joule-Thomson cooling condenses and solidifies microscopic argon particles in the free jet. Argon liquefaction first occurs in the cryogenic cooler, then argon droplets are formed through subsequent atomization in the nozzle.

Large-Scale Filter Testing for High-Purity Gas Supply Systems Used in Semiconductor Processing

The development of controlled aerosol generation technology at pressure has made possible fundamental performance measurements on commercial and developmental filters over a wide range of operating conditions. Aerosols were generated by dispersing sodium chloride solution into dry, clean nitrogen at pressure using a modified TSI, Inc. constant output atomizer. The size distributions of the aerosols were measured using a TSI, Inc. differential mobility particle sizer. The geometric mean particle diameter x g and geometric standard deviation of the aerosols were found to vary with atomizer operating condition. The diameter x g was found to depend upon the nitrogen pressure and solution concentration in the atomizer. The salt concentration was varied from 0.001 to 0.1 g/cm3. The aerosol size distribution deviated from log-normal behavior at each operating condition. The size distributions were stable and reproducible. The pressurized aerosols were then used as particle challenges in large-scale performance t...