Fabrication And Research On Subwavelength Structured Antireflection Coating Based On Nanoimprint Lithography

Nanoimprint Lithography is a low cost, high resolution and high throughput technique, and is now applied in the fabrication of subwavelength antireflection coatings. Traditionally, the pattern on the template is usually fabricated with high resolution techniques, such as Electron Beam direct-write Lithography or Extreme Ultra-Violet Lithography, which is high cost and low speed. Anodized aluminum oxide(AAO) and porous silicon fabricated with anodization have relatively well-distributed nano-hole arrays, and their parameters can be modulated easily. This thesis introduced a fabrication method for subwavelength structured antireflection coatings using AAO membrane as a mask by means of UV nanoimprint lithography, which was conducted at room temperature and normal atmosphere. The antireflection film could reduce the silicon surface reflection to about 4% in the wavelength range of 425–1200 nm, and improved solar cell conversion efficiency by 19%.Moreover, the thesis also introduced the application of porous silicon to nanoimprint lithography for the first time, in which porous silicon was used as mask for the fabrication of subwavelength structured antireflection coatings with thermal nanoimprint lithography. After many experiments, the selected method was that using a current with density of 80mA/cm2 opened hole, a current with density of 40mA/cm2 etched the nano-holes, and was then followed by KOH solution enlarging the holes. With the method, a porous silicon mask of nano-holes whose diameter was about 60—80 nm can be made, which met with the specifications of Nanoimprint Lithography. Polydimethylsiloxane(PDMS), Ethylene Vinyl Acetate copolymer(EVA) and Polystyrene(PS) were then used to fabricate subwavelength antireflection films with this mask. The nano-holes in the porous silicon mask were transferred to resist using these three materials. The antireflection film fabricated with PS exhibited the best anti-reflection result, which could reduce the reflection on the silicon surface from above 40% to around 16% in 530-850 nm wavelength range, and it is valuable for further research.