Sidewall passivation assisted by a silicon coverplate during Cl2–H2 and HBr inductively coupled plasma etching of InP for photonic devices

Abstract

Energy dispersive x-ray (EDX) spectroscopy coupled to transmission electron microscopy (TEM) is used to analyze the passivation layer deposited on the sidewall of InP submicron patterns etched in Cl2–H2 and HBr inductively coupled plasmas. It is shown that a thin Si-containing layer is deposited on the sidewalls of the etched patterns, resulting from the reaction of Cl2 or HBr with the Si wafer used as the sample tray. For Cl2-containing plasma, the deposition layer becomes thicker when hydrogen is added to the gas mixture, leading to highly anisotropic InP etching at an optimized H2 percentage. A similar effect is obtained in HBr plasma by increasing the ICP power. When O2 is added to the gas mixture, the deposited layer is changed from Si rich to more stoichiometric silicon oxide (SiO2) and the passivation effect is enhanced. EDX-TEM analysis has also been carried out on InP samples etched in Cl2–N2 plasma for comparison. A similar impact of the coverplate material on the sidewall profile is evidenced, the InP sidewall being moreover strongly In deficient in this case. These results give useful guidelines to define anisotropic etching processes scalable to large-diameter InP wafers.

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

“…This layer may influence the deposition of silicon oxide, acting as a sidewall passivation layer in many cases. 2,[8][9][10][11] This phosphorus layer may also favor the formation of a PN x layer on the surface, which would explain the anisotropic etching profiles observed in Cl 2 -N 2 etching of InP. 5,6 Indeed, P 3 N 5 (solid) is more thermodynamically stable than PCl 3 (g), 36 and may therefore form a sidewall passivation layer.…”

“…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.…”

“…Using energy-dispersive x-ray spectroscopy coupled with a transmission electron microscope (EDX-TEM), we showed in a previous study that anisotropic etching of InP in plasma containing Cl 2 /H 2 or HBr is generally due to the deposition of a silicon oxide passivation layer on the etched sidewalls, which occurs when silicon and oxygen are present in small quantities in the gas phase. [10][11][12] However, the composition of the InP surface itself, which may impact the sidewall passivation process, could not be analyzed with this technique.…”