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A comparison of SEM measurements versus electrical measurements of contact holes is presented. Inline SEM measurements on a Hitachi S6000 and measurements of micrograps from an off-line JEOL 845 SEM are compared to electrical measurements on a Prometrix LithoMap system for metrology of contacts down to 0.25j.trn size. The electrical measurements of contacts through focus/exposure vanations on the stepper are shown to correlate very well with SEM measurements. Electrical measurement of contact holes in conductive films is shown to reflect actual process latitudes on oxide wafers, allowing electrical metrology to be used in optimizing lithography processes. INTRODUCTIONMeasurement of contact holes following the lithography and etch process steps presents one of the most difficult challenges to semiconductor metrology, particularly when contact sizes approach 0.5km. Non-destructive rn-line SEM measurements suffer from resist changing effects and lack of contrast. Wei Lee et. al. investigated contacts down to 0.8pm with the use of conductive-coated SEM metrology versus SEM metrology of thin relief images of the contacts etched into polysiicon. The conductive-coated SEM measurements provided good details of sizing and resist slope, but the technique requires off-line analysis. The technique of shallow-etching the contacts into poly correlated well with the conductive-coated results, and avoided the low-contrast and changing effects of directly measuring the resist. Another techniqie that minimizes the low-contrast and changing effects on resist images is the photocleave technique' , where a second-pass exposure of a straight edge followed by another develop step is used to remove the front half of the resist contact. Uncoated samples can then be imaged on an rn-line SEM with higher contrast and less changing. However all of the SEM-based techniques are time-consuming when vast amounts of data are required, as in the initial process development stage. B .J. Lin et at investigated the ability to employ electrical measurements to measure contacts down to 0.6im. Lm et al used measurements from SEM micrographs to calibrate the electrical measurements of dense contact arrays. The benefits of electrical measurements are improved precision over SEM-based techniques and the ability to accumulate a vast amount of data in a short time.In this paper we present the results of our comarison of in-line SEM measurements (Hitachi 56000) to electrical measurements (Prometrix LithoMap (EM1)) and to SEM micrographs (JEOL 845) for metrology of contacts down to 0.25.i.m size. We have extended the initial work of Lm et al to investigate the effects of contact separation and relative density to the electrical measurement results, and to examine the applicability of this technique to smaller contact sizes. The three different metrology tech-104 / SPIE Vol. 1464 Integrated Circuit Metrology, Inspection, and Process Control V (1991) O-8194-0563-9/91/$4.OO Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/20/2016 Terms of Use: ht...