Application Notes
Lasers for Semiconductor Inspection, Metrology, Optical Manipulation
Author:Unilasers Time:Nov 10, 2020 View:

1. Lasers for Semiconductor Inspection and Metrology

As the complexity on the wafer surfaces grows, it is essential that these fabricated devices are monitored for optimisation and quality control, both during and after processing.

Critical parameters - such as thin film thickness or non-uniformity in deposition, defects, holes and scratches, overall flatness, deviations in the crystal structure or consistency of doping - can be detected and optimised using several interferometric techniques.

Laser interferometry, and the monitoring of an interference pattern from the wafer surface, is essential for controlling a number of these parameters, as well as laser ellipsometry, which allows sub-wavelength resolution of these features, below the diffraction limit of light. Controlling the accuracy and uniformity of layer thickness optimises the material use, improves performance and reduces the number of in-process failures - thereby making the manufacturing process more efficient and lowering the cost per unit.

These same techniques can also be applied to other high precision industries - such as optics and precision tooling.

Laser sources used in these applications must be single frequency to ensure a precise interference pattern, where narrow linewidths increase the signal to noise ratio. These lasers also require exceptional spectral and power stability, as well as long coherence lengths, in order to eliminate errors in prolonged measurement and ensure stable operation. Beam quality, such as pointing stability or ellipticity, are also vital for high quality interferometry measurements.

UniKLasers design and manufacture high power, single frequency laser sources with unrivalled wavelength stability, narrow linewidths and long coherence lengths over a range of wavelengths within a small footprint. We currently offer single frequency lasers in the red and green areas of the visible spectrum with our Solo 640 Series and Duetto 532 Series respectively; to complement our development of a range of UV sources, to facilitate metrology at decreasing feature sizes.

2. Lasers for Optical Manipulation

As laser light is focussed onto a particle, it experiences a change of refractive index and slightly changes its direction of travel, moving along the gradient in electrical field strength. This exerts an opposite force on the particle and, if the particle is smaller than the light beam itself, causes it to be ‘trapped’ in the centre of the beam waist, where the electric field strength is at a maximum.

This has proved to be a highly useful tool in many fields. Everything from individual atoms, custom micro-machines, and biological cells are being manipulated using this technique. Most biological samples are undamaged by NIR radiation, such as 1064 nm. As such, scientists can now easily isolate individual bacteria and viruses for study without mechanically interfering with them.

Key to this technique, to gain a ‘firm grip’ on the particles, is exceptional power and pointing stability, along with excellent beam circularity and low noise.

UniKLasers design and manufacture high power, single frequency laser sources with exceptional beam quality over a range of wavelengths within a small footprint. We currently offer single frequency lasers in the red and green areas of the visible spectrum with our Solo 640 Series and Duetto 532 Series respectively; to complement our Solo 1064, to facilitate biological measurements over a range of applications.

For more information on the lasers, please click here.

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