Microelectronics surface analysis

This paper is a synopsis of the introductory lecture at the American Chemical Society Symposium on "Industrial Applications of Surface Analysis." Following a review of the objectives of surface analysis, an outline is given of the design principles for measurements to achieve these objectives. Then common techniques for surface analysis are surveyed briefly. An example of the application of these techniques in microelectronics is indicated. The paper concludes with an assessment of the major advances in surface analysis during the past decade and an indication of the major current trends which could lead to comparable advances during the coming decade. 

The development of new methods for studying surfaces is progressing rapidly, precipitated by the phenomenal growth and interest in surface physics and chemistry which was stimulated, in part, by the need for clean, well-characterized surfaces for microelectronic and other high-technology applications. The biomaterials field should be able to capitalize upon this plethora of new methods which have appeared primarily in the past 15 years. In particular, many of the new techniques measure surface chemistry directly, in contrast to older methods which often required indirect or thermodynamic data. At the present stage of development in the field of surface analysis, a picture of a surface must be built up by using a variety of methods. Combinations of the classic surface analysis methods (e.g., con-... 

Dowsett, M., Clark, E. (1992) Dynamic SIMS and its application in microelectronics. In Practical Surface Analysis, edited by Briggs, D., Seah, M. Chichester, UK John Wiley Sons, pp. 229-301. 

Surface Anatysis. Surface analysis can be employed in many situations, but it is particularly well suited for the analysis of contamination or surface damage. In many industries, contamination at the nanometer scale can spell disaster for a process. For example, semiconductor materials have very predictable conductive behavior, which is essential for designing microelectronics that work properly. The addition of contaminants to the system will change the behavior of the materials and can cause failures, so it is essential that surface analysis be employed in the development of a product and sometimes during manufacturing stages to ensure that the materials are clean and reliable. 

Before describing the surface analysis of the materials listed above, the advantages and limitations of the surface-specific techniques to be used should be discussed. The basic principles, instrumentation and main applications of photoemission (1-3] and Auger [4,51. spectroscopies, as well as of SAM [6.7] and ELS [8-11] have already been described in several reviews, while Seah and Briggs [12] have surveyed in detail the principal features of many suri ace-specific techniques. Of major interest here are those characteristics of each technique that, on the one hand, may be employed strategically to solve a given analytical problem, but that on the other may affect the reliability of the results. In Table 1 the relative merits of the techniques are rated with respect to those properties likely to be important in the surface analy.sis of semiconductors and microelectronic devices. 

Parallel developments in the physical chemistry of surfaces have also proceeded rapidly during the same period. An extensive battery of new spectroscopic and microscopic techniques have brought analysis and even observation down to the molecular and atomic ideal of seeing and manipulating these ultimate units of chemistry. Much of the driving force for these advances has come from the microelectronics industry, where the ability towards mass production of microstructures approaching nanometer dimensions is proceeding with remarkable speed and success. 

The most frequently applied analytical methods used for characterizing bulk and layered systems (wafers and layers for microelectronics see the example in the schematic on the right-hand side) are summarized in Figure 9.4. Besides mass spectrometric techniques there are a multitude of alternative powerful analytical techniques for characterizing such multi-layered systems. The analytical methods used for determining trace and ultratrace elements in, for example, high purity materials for microelectronic applications include AAS (atomic absorption spectrometry), XRF (X-ray fluorescence analysis), ICP-OES (optical emission spectroscopy with inductively coupled plasma), NAA (neutron activation analysis) and others. For the characterization of layered systems or for the determination of surface contamination, XPS (X-ray photon electron spectroscopy), SEM-EDX (secondary electron microscopy combined with energy disperse X-ray analysis) and... 

The chemical spatial resolution of state-of-the-art scanning AES systems coupled with the surface sensitivity of the technique make them uniquely capable for characterization of modern microelectronic devices. This will mean greater dependence on AES for both failure analysis and process development. The demands of greater production... 

Recent advances in microelectronic fabrication techniques, in development of modified electrode surfaces and ion-selective membranes, and in availability of new materials give promise for development of new electrochemical sensors. For both gas and liquid sensors, the possibility of much higher sensitivity exists. Lower detection limits are possible for environmental, clinical, and general analysis situations. Sensors developed to date are primarily based on classical and relatively unsophisticated approaches. With newer methodologies and device designs, one may anticipate at least a ten-fold improvement in detection limits. 

Depending on the X-ray source and the spectral modification devices, the LD are in the pg range for 2—3 kW X-ray tubes and in the fg range with excitation by means of synchrotron radiation. Figure 11.15 shows a typical TXRF spectrum the absolute detection limit values of typical TXRF instruments are shown in Fig. 11.10. Thus, TXRF permits to simultaneously determine trace elements in samples of small volume. Additional advantages are insensitivity to matrix effects, easy cahbration, fast analysis times and low cost. In practice, the method is in particular apphed for multi-element determinations in water samples of various nature and for the routine analysis of Si-wafer surfaces employed in the microelectronics industry. 

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