Measuring strain of epitaxial films using micro x-ray diffraction for in-line metrology

Abstract

In a method for use of x-ray diffraction to measure the strain on the top silicon germanium layer of an SOI substrate, the location of the peak diffraction area of an upper silicon layer of the SOI substrate is determined by first determining the peak diffraction area of the upper silicon layer on a reference pad (where the SOI thickness is about 700-900 Angstroms) within a die formed on a semiconductor wafer. The x-ray beam then moves to that location on the pad of interest to be measured and begins the XRD scan on the pad of interest to ultimately determine the strain of the top silicon germanium layer of the pad of interest

Description

BACKGROUND[0001]The present invention relates to semiconductor manufacturing technology, and, more specifically, to measuring strain of epitaxial films in relatively small pads using micro-spot x-ray diffraction for in-line metrology during the semiconductor manufacturing process.[0002]X-ray diffraction (XRD) is commonly used as a viable measuring technique in the research and development of epitaxial deposition processes in semiconductor manufacturing. Until recently, relatively large area sample sizes (e.g., up to several centimeters squared) were required to successfully carry out an XRD measurement due to x-ray signal strength and spot size. However, the development of new systems and, in particular, intense micro-spot XRD sources have enabled the capability of probing modern standard size measurement pads as typically employed in the industry. Typical modern pad sizes range from 50×50 um2 to 500×500 um2 and state-of-the-art x-ray spot dimensions are approximately 70 um (oval sh...

AI Technical Summary

Benefits of technology

The invention relates to a method for measuring strain on the top silicon germanium layer of an SOI substrate using x-ray diffraction. The method involves determining the location of the peak diffraction area of the upper silicon layer on a reference pad within a die formed on a semiconductor wafer, and then moving the x-ray beam to the location of interest on the pad of interest to be measured. The strain of the top silicon germanium layer of the pad of interest can then be determined by analyzing the XRD scan results. The invention provides a reliable and accurate method for measuring strain on the top silicon germanium layer of an SOI substrate.

Problems solved by technology

However, problems with the modern micro-spot XRD sources include the fact that source intensity is reduced and relatively much longer counting times are usually needed.

Alignment for measurement of peak diffraction on SOI wafers, which is important for modern high-performance technologies, is more complicated, depending upon the process used for manufacturing the wafers.

On the other hand, bonded SOI wafers inherently can have miscut or relatively slight angular tilt between the handle and the upper silicon wafer before bonding.

X-ray diffraction is extremely sensitive to crystal orientation, and a mere alignment of the XRD source to the base silicon substrate peak diffraction area is insufficient.

However, for SOI devices with upper silicon layers having a thickness starting as low as 150 Angstroms, it becomes extremely difficult to achieve alignment of the x-ray beam for strain measurements since the diffracted intensity is several orders of magnitude lower than that of the bulk silicon.

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