Validating and Improving a Measurement System for a Deformable Mirror

Validating and Improving a Measurement System for a Deformable Mirror

Ursum, L.J.

Saathof, R. (mentor)

Mechanical, Maritime and Materials Engineering

Precision and Microsystems Engineering

2013-03-07

The semiconductor industry is on an ongoing quest to realize smaller feature size, requiring the constant implementation of new technology. A possible new technology is the use of a spatially controlled heat source to actively deform a mirror substrate to compensate for wavefront aberrations. In order to validate the ability to generate deformations, and to hold them, a measurement system is required. Although many off the shelf surface measurement system exist, none fulfill all requirements (measurement speed, working environment, mirror size, ect) to be implemented right away. Therefore a dedicated measurement setup is build consisting of an interferometer based fringe projection method. However an initial evaluation of the measurement system showed the performance to be insufficient. To improve the performance of the measurement system, the system is divided into four subsystems: Illumination system, interferometer, imaging system and data processing which all have been improved. The illumination system is improved by the addition of an optical isolator and polarizer to clean the laser beam, an extra beam expander to improve beam quality and pinhole overlay to reduce reflections. The interferometer is improved with the addition of beam stops to generate calibration images. The imaging system is improved by introducing: An aperture to focus on, a lens is added to improve the focus, the protection window on the CCD is removed and an aperture is introduced to reduce reflections. The data processing is improved by the tuning the filter shapes and introducing another filter to decrease edge effects. With the improvement the stability error of the measurement system improved form 2.5 nm to 0.29 nm. The reproducibility error decreased from 4.85 nm to 0.80 nm. The spatial resolution of the improved measurement system is 0.4 mm To validate the scaling of the measured deformations, an absolute shape measurement is done. This absolute shape measurement requires the system shape (measured shape due to all components in the measurement setup) to be known. While measuring the system shape, the topology of the measurement mirror is assumed to be flat, the topology amplitude of this mirror is validated by an auto-calibration measurement and proved correct. However, the drift in the measurement setup prevents the system from measuring an absolute shape with an high accuracy. Although the accuracy is not sufficient for absolute shape measurements, the scaling of the measured differences is proved correct (order of magnitude). The improved measurement system is able to validate the viability of deformable mirrors for the use in the semiconductor industry.

validate
measurement system
deformable mirror

http://resolver.tudelft.nl/uuid:b9e6ed9f-3d96-4382-bb2b-300392af1d06

2013-04-24

Student theses

master thesis

(c) 2013 Ursum, L.J.