Optimization of a Cl2–H2 inductively coupled plasma etching process adapted to nonthermalized InP wafers for the realization of deep ridge heterostructures

Abstract

Inductively coupled plasma etching using Cl2–H2 chemistry with no additive gas (CH4, Ar, or N2) is studied to realize deep (>5μm) ridges with smooth and vertical sidewalls. The process is optimized for nonthermalized InP wafers to avoid the use of thermal grease. Cleaning of the rear side of the wafer after etching is avoided, which is suitable for an industrial process or for critical subsequent steps such as epitaxial regrowth. The influence of the Cl2∕H2 ratio on the etching mechanism is investigated for both InP bulk layers and InGaAs∕InP or InGaAlAs∕InP heterostructures. The authors show that this ratio is the main parameter controlling the ridge profile, in a similar way for both bulk InP and InGa(Al)As∕InP samples. Smooth and vertical sidewalls with neither undercuts nor notches can be obtained in the 0.5–1mT pressure range for a hydrogen percentage of 35%–45% in the gas mixture. Etching rates from 900to1300nm∕min together with a selectivity over SiNx dielectric mask as high as 24:1–29:1 are measured for the InP bulk layers under these conditions. Etching does not affect the optical quality of the heterostructures as evidenced from micro-photoluminescence measurements performed on 1.6-to0.85-μm-wide deep etched ridge waveguides. The process is well adapted to the realization of low loss deep ridge waveguides or buried heterostructures.

X-ray photoelectron spectroscopy analysis of the effect of temperature upon surface composition of InP etched in Cl2-based inductively coupled plasma

“…12 that Cl 2 has the dominant impact upon the stoichiometry of the InP etched surface. In this study, the two main conditions that were chosen were that of a pure Cl 2 plasma at 0.5 mTorr pressure with a Cl 2 flow-rate of 20 sccm (the conditions used in the SI500 reactor 2,10,11 ), and that of a Cl 2 /Ar gas mixture at 4 mTorr pressure with Cl 2 /Ar flow rates of 17.5/70 sccm (as used in the Centura etch platform 12 ). The DC bias was varied between À20 and À140 V. Finally, the electrode temperature was varied between 130-240 C. Affixing the InP samples or leaving the samples unaffixed to the c-Si wafer strongly influenced the actual sample temperature, as will be discussed below.…”

“…For purposes of comparison, the parameters were chosen to be equivalent to those used for InP etching in the Centura 300 etch platform 12 and to those previously optimized in the SI500 etch system for anisotropic etching of InP-based waveguides using a Cl 2 -H 2 chemistry. 2,10,11 The ICP power was fixed at 800 W, the Cl 2 partial pressure was kept in the 0.5-1 mTorr range, and the feed gas was either pure Cl 2 or a Cl 2 /Ar mixture. It was shown in the in-situ XPS study of Ref.…”

“…2,8,10,11 The temperature of the radio frequency (RF)-biased electrode was regulated in the range from $30-240 C during etching. A crystalline silicon (c-Si) wafer 100 mm in diameter was used as a sample carrier on which the InP pieces were etched.…”

“…A dry-etching process that can produce highly anisotropic profiles, smooth sidewalls, and a smooth etched surface is generally required to fabricate optical waveguides or cavities with minimal optical loss. Inductively coupled plasma (ICP) etching has been widely used in the past for fabricating such InP-based optical devices, and various chlorine- [1][2][3][4][5][6] and HBr-containing [7][8][9] chemistries have been proposed for anisotropic ICP etching of InP. However, the influence of the etched surface composition upon the passivation mechanism is often unknown.…”

Widely Tunable Monolithic Mid-Infrared Quantum Cascade Lasers Using Super-Structure Grating Reflectors

“…N2 gas was added to serve as the sidewall passivation [24,25]. Several other gas combinations can also be used to selectively etch the InGaAs over Si3N4 [26][27][28]. The gas flow, etching power, chamber pressure, and sample temperature have to be optimized to achieve high etching selectivity over Si3N4, smooth etched surface, high etch rate, and minimum sidewall undercutting etching to achieve ~50% grating duty cycle.…”