Dopant SIMS detection limits

The most common application of dynamic SIMS is depth profiling elemental dopants and contaminants in materials at trace levels in areas as small as 10 pm in diameter. SIMS provides little or no chemical or molecular information because of the violent sputtering process. SIMS provides a measurement of the elemental impurity as a function of depth with detection limits in the ppm—ppt range. Quantification requires the use of standards and is complicated by changes in the chemistry of the sample in surface and interface regions (matrix efiects). Therefore, SIMS is almost never used to quantitadvely analyze materials for which standards have not been carefiilly prepared. The depth resoludon of SIMS is typically between 20 A and 300 A, and depends upon the analytical conditions and the sample type. SIMS is also used to measure bulk impurities (no depth resoludon) in a variety of materials with detection limits in the ppb-ppt range. 

In this review the various modes of SIMS and examples of their applications are discussed. SIMS depth profiles are widely used to study dopant profiles and Intermetallic diffusion. The extreme surface sensitivity and low concentration detection limits of SIMS make It useful for Investigation of substrate and metallization cleaning processes. SIMS elemental Imaging Is also used In contamination studies. The ability of SIMS to provide Isotopic Information has allowed elegant mechanistic studies. The Identification and determination of the relative abundance of various molecular or elemental species by SIMS Is applicable to the development characterization and understanding of microelectronic processing. The capability of SIMS In the area of quantitative analyses Is also discussed. 

SIMS Is more sensitive than the other common surface or Interface analysis techniques of Auger X-ray Photoelectron Spectroscopy Rutherford BackscatterIng Spectroscopy or Energy Dispersive X-ray Analysis. Detection limits and background signal levels for a large number of semiconductor materials have been reported under typical operating conditions (Ji). Table I lists the detection limits for a number of dopants used In semiconductors obtained under optimized conditions. 

Dynamic SIMS using chemically active atomic or small molecular primary ion beams (Cs" ", 0 , O2 ) provides the utmost in detection limits in localized elemental analysis. As a result, this is the technique of choice for following dopant distributions as a function of depth in the semiconductor industry (a sector of Materials Sciences) and for mapping isotopic dishibutions in the Earth Sciences (for further details, see Section 1.2.3). Little in the way of molecular information is accessible under these conditions. 

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