Title: Theoretical modelling and experimental verification of gradient thickness function for thin film deposition of linear variable filter

Authors: Cheng-Hao Ko; Kuei-Ying Chang; You-Min Huang

Addresses: National Taiwan University of Science and Technology, No. 43, Sec. 4, Keelung Rd., Da'an Dist., Taipei 106, Taiwan ' National Taiwan University of Science and Technology, No. 43, Sec. 4, Keelung Rd., Da'an Dist., Taipei 106, Taiwan ' National Taiwan University of Science and Technology, No. 43, Sec. 4, Keelung Rd., Da'an Dist., Taipei 106, Taiwan

Abstract: This study proposes a theoretical model for a gradient thickness function for thin film deposition of a linear variable filter (LVF), which is used for order sorting for a diffraction grating. To achieve linear variable filtering, the thin film must be fabricated with a gradient of increasing thickness along the direction of wavelength dispersion. The thickness gradient is created using a local mask on top of the substrate during thin film deposition inside the evaporation chamber. A theoretical model and ray tracing simulation are developed to obtain the thin film thickness distribution and the parameters for the fabrication of LVFs. Within the 25%-75% thickness range, the profile distribution exhibits a high degree of linearity (coefficient of determinations are greater than 0.9939). This study shows that the proposed theoretical model and ray tracing predict a thin film profile for an LVF with high precision (root-mean-square deviations are less than 4.52%).

Keywords: surface science; surface engineering; manufacturing processes; thin film deposition; evaporation; diffraction grating; order sorting; linear variable filters; LVF; modelling; gradient thickness function; simulation; ray tracing.

DOI: 10.1504/IJSURFSE.2015.068241

International Journal of Surface Science and Engineering, 2015 Vol.9 No.2/3, pp.216 - 230

Received: 24 Jan 2014
Accepted: 12 Aug 2014
Published online: 26 Mar 2015 *

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