Nanometer Metrology of Periodic Structures with Ultrafast Optoacoustics
- PDF / 434,721 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 82 Downloads / 223 Views
1249-F10-05
Nanometer Metrology of Periodic Structures with Ultrafast Optoacoustics T.J. Grimsley1, G.A. Antonelli2, F. Yang1, H. J. Maris1, A. V. Nurmikko1,3 1. Department of Physics, Brown University, Providence RI, 02912 USA. 2. External Research & Development, Novellus Systems, Albany, NY 12203 USA. 3. Division of Engineering, Brown University, Providence RI, 02912 USA. ABSTRACT We present an optoacoustic method to non-destructively measure the average dimensions of a periodic array of simple structures with aspect ratios greater than 10:1, which are inaccessible to AFM techniques. The technique that we describe could be used as the basis of an inline metrology tool for wafer inspection. The samples examined were test structures with high precision lithographically defined lines of silicon dioxide deposited on a silicon substrate. The thickness of the silicon dioxide was around 400 nm, and the gaps between the lines ranged from 100 nm down to smaller than 40 nm. A drop of water was placed on the sample, and an optoacoustic transducer was placed on top; measurements were taken with a water thickness less than 1 micron between the optoacoustic transducer and the sample. The water filled the spaces between the lines due to the hydrophilic nature of the sample surface. Using the picosecond ultrasonics technique, acoustic pulses are generated in a special optoacoustic transducer, transmitted through a coupling fluid (water), scattered off of the sample being examined and then return to the transducer. The returning acoustic signal shows nanometer sensitivity to the height of the lines and the specific details of their profile. INTRODUCTION In the transition to the 22nm node processes and beyond, the semiconductor industry fabricates structures that are difficult to characterize non-destructively with existing techniques. In this paper, we examine samples that consist of silicon dioxide lines on a silicon substrate, with a cap layer of silicon nitride approximately 5 nm thick. The lines were part of a test structure fabricated by Novellus Systems using precision lithography techniques. The spacing between the lines was as narrow as 35 nm, and the lines were 405 nm thick. White light scatterometry [1] can be used to non-destructively characterize these structures at the wafer level; however, destructive cross-sectional scanning electron microscopy (SEM) remains the industry standard for extracting geometric information from patterned structures. As dimensions continue to shrink, these structures will become more difficult to measure with optical techniques; furthermore, optical techniques require both the dimensional and the optical parameters of the system to model the measured scattered white light. We present a method for measuring the dimensions of the nanostructures that is non-destructive, insensitive to its optical properties, and possible to perform at the wafer level. The technique of picosecond ultrasonics [2] uses pulses from a mode-locked laser to generate and detect sound pulses with durations on the orde
Data Loading...
