We present an analytic form for the response function measured in a SIMS depth profile of an impurity layer less than 1 nm wide (a delta layer). Although the process used to evolve the function can be justified on physical grounds, we make no claim that the justification is rigorous or that the function is universal. At present we examine its use in making a consistent and utilitarian definition of frequently employed resolution parameters. The function is found to give an accurate fit (lying everywhere within the statistical noise on the profile over several orders of magnitude in signal intensity) to responses from boron, antimony, germanium and isotopically pure silicon deltas in a silicon matrix, and to silicon, aluminium and beryllium deltas in gallium arsenide. The fit is also good over the full primary ion energy range examined (1-11 keV). There are four fitting parameters for a normalized data set, one related to the depth of the delta below the surface and three independently related to depth resolution. The function has an analytic Fourier transform, and may be used as a smooth, noise-free substitute for the measured data in profile synthesis (convolution) and in deconvolution whenever convolution is a valid model for the SIMS measurement process.

The subject of this review is the secondary ion mass spectrometry (SIMS) analysis of ultrathin or delta layers of impurity in a semiconductor matrix and their use in establishing the limitations of SIMS depth profiling, exploring the fundamental processes occurring during analysis, and enhancing the quantification of SIMS data. Methods for extracting accurate information for the grower (concerning the material) and the analyst (concerning the SIMS instrument) are described. It is demonstrated that sets of SIMS profiles obtained over a range of analytical conditions are desirable if accurate information is required. In this context, the observation of dopant interaction occurring in codoped samples during SIMS analysis is reported for the first time. It is shown that quite large discrepancies exist between different measurements of decay length and associated parameters for the same impurity/matrix combination. These need to be explained before attempting to relate delta profile shape to primary ion beam induced mass transport mechanisms. The concept of the delta profile as a response function and the use of deconvolution as a complete quantification method are discussed. The use of delta profiles in setting up models of the ion–solid interaction such as IMPETUS is illustrated.

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