Comparative study of Cl2, Cl2∕O2, and Cl2∕N2 inductively coupled plasma processes for etching of high-aspect-ratio photonic-crystal holes in InP

Abstract

An extensive investigation has been performed on inductively coupled plasma etching of InP. An important motivation for this work is the fabrication of high-aspect-ratio holes for photonic crystals. The essential chemistry is based on Cl 2 with the addition of N 2 or O 2 for sidewall passivation. The influence of different process parameters such as gas flows, temperature, pressure, ion energy, and inductively coupled plasma power on the hole geometry is presented. It is concluded that photonic crystals can be etched with Cl 2 only; however, temperature and pressure control is critical. Adding passivation gases largely broadens the window in the parameter space for hole etching. Most importantly, etching of narrow holes can be carried out at higher temperatures where the etching is mass limited and spontaneous etching of InP by Cl 2 occurs.

Modeling of InP Etching Under ICP Cl2/Ar/N2 Plasma Mixture: Effect of N2 on the Etch Anisotropy Evolution

“…In our InP etching model, atomic nitrogen N is introduced as a neutral species yielding to the passivation reactions along the etched surface. Indeed, previous experimental works have shown the passivating role of N 2 used in InP etching under chlorine‐based plasma 3, 4, 17, 19, 35. Lee et al4 showed that for %N 2 lesser than 30%, the isotropic etching was observed in PhC hole while for 60%N 2 , the anisotropy of PhC patterns was improved but with rough sidewalls on the bottom of holes.…”

“…This was attributed to the formation of passivating layer which protected the vertical sidewalls of the features from the reactive chlorine species. Carlstrom et al17 have reported the experimental results concerning the etched InP PhC for 200 nm hole under chlorine ICP plasma. For pure Cl 2 , bowing defect characterized by the local lateral etching was observed for p = 1.4 mTorr, substrate surface temperature T s = 200 °C and $Q({\rm Cl}_{2} ) = 14\;{\rm sccm}$ .…”

“…However, it is difficult to obtain anisotropic profiles without morphological defects such as the undercut and bowing. The alternative approaches using Cl 2 ‐based plasma chemistry and including passivating gas such as N 2 ,3, 17–19 O 2 ,17 or H 2 6 have been proposed. As example, Cl 2 /N 2 and Ar/Cl 2 /N 2 gas mixture have been used in the ICP etching to attempt improving the etch profile anisotropy and reduce the sidewall surface roughness.…”

Inductively coupled plasma etching of high aspect ratio two-dimensional photonic crystals in Al-rich AlGaAs and AlGaAsSb

“…15,17,23 All these works pointed out that pure Cl 2 plasma caused severe undercuts and that an additive gas such as N 2 or O 2 should be introduced to achieve anisotropic etching of high aspect ratio features. 15,17,23 All these works pointed out that pure Cl 2 plasma caused severe undercuts and that an additive gas such as N 2 or O 2 should be introduced to achieve anisotropic etching of high aspect ratio features.…”

Strong modes discrimination and low threshold in cw regime of 1300 nm AlInGaAs/InP VCSEL induced by photonic crystal

“…Hence, a combination of a technologically wellestablished tunnel-junction [3] with a photonic-crystal (PhC) structure [4][5][6] might be the best solution for phosphide based VCSELs. Although the PhC technology is still developing, the aspect ratios (hole depth to hole diameter ratio) of about 15-20 [7][8][9] achievable nowadays are encouraging for such PhC VCSEL design. This motivates the study of the impact of the hole depth on the modal behaviour of PhC VCSELs to define the smallest aspect ratio assuring good performance.…”