HOW ESSENTIAL WILL X-RAY METHODS BE FOR THE FUTURE SEMICONDUCTOR TECHNOLOGY?

Herbert E. Göbel

Siemens AG, Corp. Technology, Materials Analytics Dept., D-81730 München

The non-destructive analysis and metrology of thin films and surfaces in semiconductor manufacturing lines has, according to the National Technology Roadmap for Semiconductors (edited 1997 by the SIA), reached limitations for some of the existing (often optical) techniques, so that new methods need to be developed for the future. Also the increasing costs for the large diameter wafers (presently 300mm) will force more in-line testing on small test spots (maximum size = chip size) instead of sacrificing full dummy wafers for the analysis. The short wavelength, non-destructiveness and in-situ clean-room capability make x-ray techniques look very promising as testing equipment in production lines. Among the existing x-ray methods some have already reached the status of process control, for example the Boron analysis in BPSG by XRFA, metal contamination by TR-XRFA using the VPD (vapor phase decomposition) accumulation of contaminants. For the future metrology of ultrathin layers (1nm gate oxide) or characterization of surfaces and interfaces x-ray reflectivity and scattering could be used instead of ellipsometry and AFM. Although some recent developments were observed, suitable instruments are not on the market compared to the above mentioned other techniques. It will be necessary to develop in-situ x-ray reflectometers with immediate response thickness measurements detected on a 2*2mm² measuring spot, allowing thickness mapping, as well as density and roughness information. Also diffuse scattering should be included to characterize the surface roughness after cleaning or ion bombardment.

A great potential is also expected from microbeam x-ray diffraction analysis, especially for the future Cu-metallization schemes and the diffusion barriers. Phase identification, texture and stress measurements will have to be performed with high local resolution. Herefore systems with focussing optics and highly efficient area detectors will have to be adapted to the in-line wafer handling.