Optimization of sub-wavelength texturing structures in solar cells by utilizing modified illumination and defocus techniques in optical lithography

H. L. Chen, Wonder Fan, K. T. Huang, C. H. Lin, K. C. Hsieh

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

Semiconductor materials with high refractive index in visible and near infrared ray (NIR) regimes cause the high Fresnel reflection between the air / semiconductor interface. Therefore, the key issue for increasing the external quantum efficiency (EQE) of semiconductor based solar cells is how to reduce the interface reflection in the solar cell working-wavelength regime. Researches show that EQE can be improved by using texturing pyramid structures than can couple sunray substantially into the active semiconductor regions with minimum reflection. However, fabricating hexagonal close packed (HCP) structures with large-area and high-reproducibility are difficult by complicated dry and wet etching processes. In this paper, we demonstrate a simple method, combining conventional optical lithography and reactive ion etching (RIE) processes to fabricate an optimized pyramid structure by tuning the defocusing distance and expose dosage of an optical stepper as shown in Figure 1. Figure 2 (a) and (b) show that the optimum texturing resist and silicon profiles are obtained after development and common RIE processes, respectively. Figure 3 shows the low-reflectance with broad spectra regimes of zero-order light are obtained by optimal optical lithography processes. Figure 4 and Figure 5 show that the reflection, transmission and absorption properties are analyzed by the rigorous coupled-wave analysis in two-dimensional microstructure. Figure 5 shows the reflection spectra of pyramid structures with the 800 nm period that consider with and without diffraction orders. Results indicate that the reflectance is dramatically increased as the consideration of all diffraction orders. Therefore, patterning the sub-wavelength texturing structures for eliminating the diffraction order light is desired. Patterning sub-wavelength structures should use the short wavelength, incoherent light source, or a modified illumination exposure system. Figure 6 shows the optimized pyramid structures are simulated in dosage-focus matrix by the optical lithography simulation software with different types of light source. Results show the quadrupole modified illumination system with large process latitude is suitable for patterning sub-wavelength pyramid structures. By contrast with previous works, reflectance of texturing structures are affected by optical lithography processes rather than etching processes in our works. Therefore, high performance of texturing structures in solar cells with large area and high reproducibility can be obtained by conventional optical lithography.

Original languageEnglish
Title of host publicationDigest of Papers - Microprocesses and Nanotechnology 2005
Subtitle of host publication2005 International Microprocesses and Nanotechnology Conference
PublisherIEEE Computer Society
Pages230-231
Number of pages2
ISBN (Print)4990247221, 9784990247225
DOIs
Publication statusPublished - 2005 Jan 1
Event2005 International Microprocesses and Nanotechnology Conference - Tokyo, Japan
Duration: 2005 Oct 252005 Oct 28

Publication series

NameDigest of Papers - Microprocesses and Nanotechnology 2005: 2005 International Microprocesses and Nanotechnology Conference
Volume2005

Other

Other2005 International Microprocesses and Nanotechnology Conference
CountryJapan
CityTokyo
Period05-10-2505-10-28

All Science Journal Classification (ASJC) codes

  • Engineering(all)

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