Electrical and Computer Engineering ETDs

Publication Date

Fall 11-21-2019


As critical dimensions continue to shrink and structures become more complex, metrology processes are challenging to implement during in-line nanomanufacturing. Non-destructive, non-contact, and high-speed conditions are required to achieve proper metrology processes during in-line manufacturing. Optical scatterometry is a nanoscale metrology tool widely used in integrated circuit manufacturing for characterization and quality control. However, most applications of optical scatterometry operate off-line. A high-speed, in-line, non-contact, non-destructive scatterometry angular system has been demonstrated in this work to scan pattern surfaces during real-time nano-fabrication.

Our system has demonstrated scanning capabilities using flat, 1D and 2D complex structures. The flat surface samples consist (commercially and grown) of thin film native oxide, grown oxide, and alumina. The 1D samples were made by using interferometric lithography with a thin deposited layer (~85 nm) of aluminum. The 2D complex samples are hollow silicon tubes fabricated using nano-imprint lithography, atomic layer deposition (ALD) and reactive ion etching (RIE). The inside diameter, outside diameter, and the period of the hollow pillars are respectively ~100 nm, ~135 nm and ~200 nm. All samples were fabricated on silicon substrates. These are test structures to establish the metrology capabilities. The applicability of the tool is not restricted to these samples.

Our current in-line scatterometer uses 45° off-axis parabolic mirrors which allows us to have an angular scan of the angle of incidence of ~50°. The system uses a high-speed scanner at 8 kHz to vary the angle of incident of the beam at the focal spot on the moving web. The system uses a 405 nm collimated diode laser with a beam profile of 1.8×3.5 mm2. The beam is focused at the resonant scanner to vary the incident angle at the focal spot on the moving web. The number of resolvable points during the scan is ~313 set by the optical components that reduce the spot size to desire dimensions. The focal spot varies as a function of incident angle. At 45° incident angle, the focal spot is ~125×120 µm2. At 19° incident angle, the focal spot is 85×70 µm2. At 67° incident angle, the focal spot is 200×190 µm2 Our scan period is 125 µs which will allow us to accumulate 20-30 reflectance measurements before the web moves a distance comparable to the focal spot. A biased silicon detector is used to collect the high-speed reflection signal. The rise time of the detector is 14 ns. The data collected is averaged with a digital scope and further processed on the computer for analysis.

Our current system can be integrated with nano-imprint and other R2R real-time fabrication techniques. The goal is to improve quality control and monitor real-time high-speed nano fabrication processes. The angular range can be improved (up to 79°) by varying the focal length and the curvature of the parabolic mirrors. The scanning time can be reduced by increasing the frequency of the resonant scanner. Evidently, in-line angular scatterometry offers solutions to the future of R2R semiconductor nanomanufacturing.


OPTICAL, In-line, Roll-to-roll, Scatterometry, Metrology



Document Type




Degree Name

Electrical Engineering

Level of Degree


Department Name

Electrical and Computer Engineering

First Committee Member (Chair)

Steven RJ Brueck

Second Committee Member

Payman Zarkesh-Ha

Third Committee Member

P. Randall Schunk

Fourth Committee Member

Mansoor Sheik-Bahae