Inductively Coupled Plasma Etching of InP with HBr∕O[sub 2] Chemistry

Abstract

Inductively coupled plasma etching of InP using HBr/O 2 -based chemistry is reported. With the introduction of oxygen in the HBr plasma, high etching rate, smooth surface morphology, and vertical sidewall profile were achieved due to sidewall passivation and enhancement of ion-assisted chemical etching. The etching behavior was systematically studied by varying different process parameters, i.e., O 2 flow rate, pressure, reactive ion etching power, and inductively coupled plasma power, in a ridge array structure with a ridge width of 1 m and a ridge spacing of 1 m. InP nanopillars with an aspect ratio of ϳ6.7 were demonstrated using this chemistry. The X-ray photoelectron spectroscopy results suggested that the etched sample surface was P-rich.Plasma etching has the advantages over chemical etching for the possibility of obtaining an anisotropic etching profile and better uniformity over the entire wafer. InP has been used extensively for the fabrication of various photonic devices, such as semiconductor lasers with an emission wavelength around ϳ1.55 m for optical communication purpose. High aspect ratio etching is often required for photonic crystals, distributed Bragg reflectors, ridge structures, etc. The critical part in realizing high aspect ratio etching is to get a straight vertical profile. Most of the plasma etchings for InP-based material systems employ either CH 4 /H 2 -or Cl 2 -based chemistries. 1-3 Etching of InP using CH 4 /H 2 is complicated because of the slow etching rate, indium enrichment, and polymer formation. 4 A substrate temperature over 200°C is required to produce highly anisotropic sidewalls using Cl 2 -based chemistry. 5 Thus, there is a strong motivation to find an alternative chemistry to achieve a better control of the etching properties. There were reports on inductively coupled plasma ͑ICP͒ etching of InP using HBr-based chemistry. 4,6-8 Bromine-based chemistry has the advantage that the reaction product, InBr 3 , has a higher vapor pressure than that of InCl 3 when using chlorine-based chemistry. 5 Furthermore, GaBr 3 and InBr 3 have a more closely matched function of vapor pressures vs temperature as compared to their chloride counterparts. This property is beneficial for the fabrication of photonic devices that often require the etching of InGaAsP quaternary materials. Several methods had been tried to improve the InP ICP etching properties using HBr chemistry. For example, Ar was mixed with HBr to improve the anisotropy of InP etching at room temperature. 6 CH 4 and N 2 were added into the plasma to passivate the sidewall and reduce the undercuts that were observed when using HBr only at elevated temperature. 4,7,8 Recently, a Cl 2 /O 2 mixture in ICP etching of InP was reported to be able to produce a highly anisotropic profile. 9 In this paper, we report the use of HBr/O 2 chemistry for the etching of InP to achieve high aspect ratio and no undercut in an ICP etching system. The etching behavior was systematically studied by varying different process parameters, i.e., O 2 ...

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.…”

“…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.…”

HBr based inductively coupled plasma etching of high aspect ratio nanoscale trenches in InP: Considerations for photonic applications

“…12 Cl 2 / Ar chemistry has been used to make photonic crystals on InP with aspect ratios greater than 35:1. Lim et al 15 compared Cl-based chemistries with HBr-based chemistries for ϳ1-2 m ridge array formations, and InP nanopillars with an aspect ratio of ϳ6.7 and slight undercut were demonstrated using HBr/ O 2 chemistry. 6 In order to produce highly anisotropic sidewalls, however, Clbased chemistries require sample temperatures above 200°C to increase the volatility of InCl x -related reaction byproducts.…”

Effect of Cl2- and HBr-based inductively coupled plasma etching on InP surface composition analyzed using in situ x-ray photoelectron spectroscopy

“…12,32 Liu and co-workers were the firsts to carry out a more detailed analysis of the ICP-etched InP surface properties using ex situ XPS analysis. 31 They computed the In(3d)/ P(2p) and In(4d)/P(2p) ratios as a measure of the surface stoichiometry for various plasma mixtures including Cl 2 , Cl 2 /H 2 /CH 4 , and Cl 2 /Ar.…”

“…10 This conclusion is supported by other studies devoted to ICP etching of InP with HBr (-O 2 ) or Cl 2 -H 2 -Ar chemistries. 1,3,11,12 In this work we investigate the transfer of a similar InP etching process to an industrial 300-mm diameter CMOS reactor devoted to Si-gate etching for large-scale microelectronics applications. The scaling of III-V etching processes to ICP tools of larger size will indeed be required for the future large-surface processing of III-Vs, when the size of the III-V wafer will reach 3 in or more.…”