be analyzed, solid-sampling techniques have been used for flame AA, ICP, and the furnace. These opportunities deserve greater attention. Slurries are sometimes satisfactory samples for flame AA, ICP, or the furnace if they are not allowed to settle. Ultrasonic agitation of the autosampler table is useful for automated sampling. For the ICP the Babbington nebulizer is helpful for viscous samples or slurries. The graphite furnace is particularly useful for solid sampling in situations in which a few hundred micrograms provides a homogeneous representation of the sample. The modern furnace technology permits such samples to be calibrated by solution working curves. Hydride methods. Metals such as As, Se, Sb, Bi, and others can be readily converted to their metal hydrides, which are gaseous at room temperatures. This permits relatively large samples—10 to 50 mL—to be extracted with minimal sample handling and quantitated by thermal decomposition of the hydride in flame AA instruments. Designs are now available that extend the signals over sufficient time to permit ICP analysis in rapid sequential systems. Furnaces have also been used for the hydride technique. By now, hydride methods provide parts-per-billion sensitivity for As and Se in simple matrices such as environmental waters and plant and animal fluids and tissues. All chemical forms of the element of interest must be converted to a single valence state prior to hydride generation, and some interferences persist. The relative sensitivity (ppb) of hydride methods is similar to that of the furnace, and the hydride equipment is less expensive. Modern furnace methods have fewer interferences for As and Se. Nonspectroscopic techniques There are techniques other than spectroscopy that are used for the determination of metals both at major and at trace levels. Some of these techniques have advantages in certain situations. Others are quite general and are recommended by their supporters. Using my own judgment, I will try to put them into perspective compared with spectroscopic techniques. Electroanalytical techniques. Electrochemical methods are probably the most widely used competition for spectroscopy in trace metal determinations. Of these methods, anodic stripping voltammetry is the most widely used. The technique predates AA, and flame AA took over many analytical problems previously solved by electroanalytical means. However, electroanalytical techniques have been greatly improved in recent years. The
availability of sophisticated electronics at low cost has stimulated further interest in the field. For many metals, electroanalytical methods are about equally sensitive to flame AA or ICP. They are generally less sensitive than furnace AAS. It is usually necessary to pretreat a sample prior to electroanalytical measurement to put all of the analyte metal into the same chemical form. In other words, interferences occur as a result of differences in the chemical state of the analyte metals. This can sometimes be turned to advantage. For instance, in seawater analysis, the free ionic metal is sometimes preferred over total metal, which includes the metal adsorbed to particles. Electroanalytical techniques will distinguish between these two states of the metal, whereas the spectroscopic techniques measure total metal. X-ray fluorescence. X-ray fluorescence has been used for many years to measure major metal content of many classes of samples, especially alloys. X-ray fluorescence provides high precision, often 0.1% or 0.2% RSD. Standardization requires reasonably close matching of standard and sample. In recent years improvements have been made in the sensitivity of X-ray fluorescence so that the technique is now also applied to trace metals. However, it seems to me that modern flame AA and ICP are simpler to use (except for very routine analyses), somewhat less expensive, and can achieve equal precision and accuracy—and usually better sensitivity. Mass spectroscopy. Isotope dilution mass spectroscopy (IDMS) has been highly recommended by many workers who are trying to reach the very lowest detection levels in unknown and complex matrices. IDMS is the only technique permitted by the National Bureau of Standards for establishing reference values on standard reference materials. The technique requires considerable handling of the sample and a great deal of time for each sample. Also, the equipment is very expensive. Only those with specialized skills can obtain good results. The new technique of ICP-mass spectroscopy (ICP-MS) can be used effectively in some IDMS applications. The ICP is an ideal ion source for the mass spectrometer. It is still a little early to assess the eventual success of ICP-MS, although it is likely to become a highly useful technique. Neutron activation analysis. Neutron activation analysis (NAA) has been used for a long time for trace metal determinations. Neutron activation can be accomplished by a pile or by instrumental techniques, and the choice between these two options will determine the sensitivity and the cost. I ANALYTICAL
Microelectronics Processing Inorganic Materials Characterization
L.A. Casper, Editor Honeywell, Inc. Highlights leading-edge research in the field of materials development. Provides a thorough overview of techniques used in analyzing and characterizing inorganic materials in integrated circuits. Covers all major aspects of materials science, along with applications to a wide variety of high-technology areas. Includes extensive discussion on the role of chemistry in high-technology materials. CONTENTS Analytical Approaches and Expert Systems · Electrical Characterization of Semiconductor Materials · Dopant Profiles by the Spreading Resistance Technique · Semiconductor Materials Characterized by S E M · Semiconductor Materials Defect Diagnostics · Microelectronic Materials Characterized by SIMS · Applications of AES in Microelectronics · X-ray Photoelectron Spectroscopy · NDP Applied to Microelectronic Materials Processing · Thermal-Wave Measurement of Thin-Film Thickness · Optical Reflectance and Ellipsometric Techniques · Oxygen and Carbon Content of Silicon Wafers · Raman Microprobe Applied to Analytical Problems · Characterization of GaAs · Thermal-Wave Imaging in an SEM · Microelectronics Service Laboratory · Elemental and Isotopic Analysis · Activation Analysis of Electronics Materials · Trace Element Survey Analysis · Plasma Phosphorous-Doped Oxides · Vacuum-Deposited Nickel-Chromium · SpinOn Glass Film as a Planarizing Dielectric · Silicon-Wafer Cleaning · Monitoring Gas Particles · Microelectronics Processing Problem Solving Based on a symposium sponsored by the Division of Industrial and Engineering Chemistry of the American Chemical Society ACS Symposium Series No. 295 440 pages (1985) Clothbound LC 85-30648 ISBN 0-8412-0934-0 US & Canada $79.95 Export $95.95 Order from: American Chemical Society Distribution Dept. 95 1155 Sixteenth St., N.W. Washington, DC 20036 or CALL TOLL FREE 800-424-6747 and use your credit card!
C H E M I S T R Y', V O L . 5 8 , N O . 4 , A P R I L
1986
·
595 A
