October 24, 2020

Understanding Diffractive Optics Applications

Operating the majority of passive optical elements is based on impacts that take place at an interface between two homogenous media. Traditional refractive optics has an interface that doesn’t vary on the scale of the optical wavelength. Diffractive optical elements (DOEs) embrace the use of light propagation on microstructured interfaces. The introduction of microlithographic fabrication technology has made it possible to fabricate optical devices that have complicated structural features within the optical waves’ length-scale. DOEs have a lot of technological benefits and can be designed to do functions used to be impossible with conventional optical devices. These elements are found to minimize the size, cost, and weight of different optical systems.

Diffraction Gratings

Diffraction gratings are the only classic optical devices that employ diffraction instead of reflection and refraction. These important spectroscopic instruments have corrugated interfaces. Contemporary semiconductor technologies are used to realize diffraction gratings that have applications in a lot of domains in physics and astronomy including solid-state physics, acoustics, spectroscopy, X-ray instruments, and others. It is important to note that the properties of diffraction gratings are necessary to understand all diffractive elements’ properties because an elemental area of these elements can e considered as a small grating. The application of diffractive optics technology has caused the need for mathematical models and numerical codes to offer rigorous solutions of the Maxwell equations for difficult grating structures. Furthermore, these numerical algorithms can be applied when re-building grating structures from their diffraction properties.

Scatterometric Measurement

To produce computer chips with more small details, manufacturers need to employ more accurate measurement techniques. Particularly, the development and assessment of photolithographic manufacturing techniques require a high precision measurement special test geometries generated on the surface of lithographic masks and wafers. Additionally, fast and non-destructive scatterometric methods are also useful. These methods don’t produce a true image of the target. In scatterometry, the geometry data is concealed in the measurement data and must be extracted by a mathematical optimization algorithm.

The periodic line-space structures to be tested are illuminated by light rays, measuring the distribution of the scattered wave. With the scattered light’s energy distribution and phase shifts, it will be possible to reconstruct the geometry by mathematical optimization algorithms.

In terms of real line-space structures, it is important to change the desired rectangular cross-section of the multi-layered lines to a trapezoid shape to modify the layer thicknesses’ design values. Therefore, the quality of the manufacturing process is characterized by the measured side-wall angles and the deviations of thicknesses.