The Effect of Thin Film Thickness on Amorphous Silicon Thin Films in Laser Induced Periodic Structures

Since Bell Labs scientists invented the world's first transistor in December 1947, a revolution in microelectronics technology has profoundly affected the way of life around the world. As electronic products become smaller and smaller, finding a simple, fast, and low-cost method to manufacture micro and nano components is a challenge. Traditional direct writing manufacturing methods, such as mechanical scribing, focused ion beam etching, electron beam lithography, multiphoton polymerization, and thermal scanning probe etching, are inefficient.

Although methods such as nanoimprinting, photolithography, plasma etching, and scanning laser interference etching can effectively improve processing speed, they typically require multiple process steps such as mask fabrication or require very harsh working environments and rely on special materials.

The use of femtosecond laser induced surface self-organizing periodic structures to manufacture nano grating structures has attracted people's attention. Laser induced periodic surface structure (LIPSS) utilizes interference between incident light and surface electromagnetic waves to etch materials, resulting in high machining accuracy. Moreover, compared to traditional laser interferometric processing methods, self-organizing processing methods have a simple experimental setup, and large spot scanning makes their processing speed very fast.

The researchers led by Professor Qiu Min of Westlake University in China have rich research experience in LIPSS. They recently found that when periodic gratings are induced on the surface of thin a-Si films, the period of the grating is affected by the interference of incident light from different sources of electromagnetic waves. Their paper "The Influence of Thin Film Thickness on Amorphous Silicon Thin Films in Laser Induced Periodic Structures" has been published in "Frontiers of Optoelectronics".

When the thickness of the amorphous silicon film is small (50 nm) and the substrate is made of non silicon material, small period LIPSS will be triggered under the dominance of the planar waveguide mode. In this case, when the substrate material changes (refractive index changes), the period of LIPSS also changes. When the thickness of the amorphous silicon film is large (200 nm), the incident light interferes with the quasi cylindrical wave, inducing the growth of LIPSS under the combined action of the near and far fields. In this mode, the period of LIPSS is slightly smaller than the laser wavelength and is independent of the substrate material. The numerical simulation based on the finite difference time domain method supports the experimental findings.

Source: Laser Network