Fabrication of large-area patterned porous silicon distributed Bragg reflectors

D Mangaiyarkarasi,Eric T Xioasong,Vincent L Fuh,Ow Y Sheng,Mark B Breese

doi:10.1364/oe.16.012757

Abstract

A process to fabricate porous silicon Bragg reflectors patterned on a micrometer lateral scale over wafer areas of several square centimeters is described. This process is based on a new type of projection system involving a megavolt accelerator and a quadrupole lens system to project a uniform distribution of MeV ions over a wafer surface, which is coated with a multilevel mask. In conjunction with electrochemical anodisation, this enables the rapid production of high-density arrays of a variety of optical and photonic components in silicon such as waveguides and optical microcavities for applications in high-definition reflective displays and optical communications.

Highlights

IntroductionOne dimensional photonic structures based on alternating high and low porosity silicon (PSi) layers have been used for many years as dielectric mirrors in the form of distributed Bragg reflectors (DBRs) and microcavities [1,2,3,4]
A process to fabricate porous silicon Bragg reflectors patterned on a micrometer lateral scale over wafer areas of several square centimeters is described
One dimensional photonic structures based on alternating high and low porosity silicon (PSi) layers have been used for many years as dielectric mirrors in the form of distributed Bragg reflectors (DBRs) and microcavities [1,2,3,4]

Summary

Introduction

One dimensional photonic structures based on alternating high and low porosity silicon (PSi) layers have been used for many years as dielectric mirrors in the form of distributed Bragg reflectors (DBRs) and microcavities [1,2,3,4] These are produced by periodically raising and lowering the electrochemical hole current density flowing through highly doped p-type silicon during anodization resulting in periodic variations of the effective refractive index [5]. The peak wavelength reflected from PSi DBRs can be blue-shifted [6,7] using highenergy ion irradiation, where the resultant lattice damage locally increases the wafer resistivity, leading to a reduced hole current passing through the irradiated regions during subsequent anodisation [8] To achieve this a 2 MeV proton beam focused to about 100 nm in a nuclear microprobe was used to selectively irradiate millimeter-size areas of 0.02 Ω.cm ptype Si with fluences up to 2×1015/cm. By irradiating the wafer in a channeled alignment [9] (beam aligned with a major crystallographic axes or plane) line widths of 300 nm were produced

Patterning PSi Bragg reflectors over large wafer areas

Large area irradiation through freestanding nickel grids

Large area patterning through multilevel photoresist mask

Findings

Conclusion