HBr Chemistry Research Articles

High synergy atomic layer etching of AlGaN/GaN with HBr and Ar

Here, we show a process of AlGaN/GaN atomic layer etching with a high synergy of >91%. Achieved by means of a cyclical HBr and Ar process, highly controllable layer removal was observed within the atomic layer etching window and is attributed to careful parameter calibration plus lower reactivity of the HBr chemistry. Such etching is a valuable component in the production of high-performance enhancement-mode GaN field effect transistor devices.

Atomic-layer etching of GaN by using an HBr neutral beam

In the gate-recess formation process, normally-off operation is achieved by removing the barrier layer by dry etching to reduce the two-dimensional-electron-gas concentration under the gate electrode. An atomic-layer defect-free etching of GaN is thus indispensable to achieve high-frequency, high-power, and normally-off operation. More-precise atomic-layer defect-free GaN etching was investigated by using an HBr neutral beam. This investigation found that the HBr neutral beam could achieve more-precise atomic-layer etching than the Cl2 neutral beam because the HBr chemistry can control the reactivity of atomic-layer etching by forming a thinner and less-volatile reaction layer.

HBr-based inductively coupled plasma etching of high aspect ratio nanoscale trenches in GaInAsP∕InP

The authors report inductively coupled plasma (ICP) dry etching of nanoscale trenches with feature sizes of approximately 140nm wide by 20μm long by 3μm deep in InP with and without quantum wells, based on HBr chemistry. Both focused ion beam and electron beam lithography nanopatterned features are presented with high aspect ratios in excess of 30:1. Importantly, with HBr, hybrid GaInAsP∕InP heterostructures can be anisotropically and vertically etched through with reasonable smoothness at 165°C, which is comparatively lower than what chlorine-based chemistry requires and is therefore beneficial for achieving reliable InP devices. The phenomenon of aspect ratio dependent etching, or reactive ion etch lag, begins to manifest itself when the etch aspect ratio of InP approaches 30:1 using this ICP technique. The application of interest is a novel coupler for integrated photonics.

Anisotropic and Smooth Inductively Coupled Plasma Etching of III-V Laser Waveguides Using HBr- O2 Chemistry

HBr inductively coupled plasma (ICP) etching is investigated to realize ridge laser waveguides on InP and GaAs substrates. It has been reported that pure HBr chemistry leads to undercut ridge profiles when a hard dielectric mask is used. In this paper we show that a passivation layer can build up on the sidewalls and prevent lateral etching at high ICP powers if a Si wafer is used as the sample tray. Ex situ energy-dispersive X-ray analysis coupled to transmission electron microscopy shows that the passivation layer is a Si-rich silicon oxide. Vertical sidewalls, a smooth etched surface, and a moderate etch rate compatible with the processing of shallow ridge lasers can be obtained for InP-based heterostructures. The optimized HBr etching process is used to etch InAs quantum dot shallow ridge lasers grown on InP(100) substrate and compared to a classical HCl selective chemical etch. The waveguide losses of the HBr-etched waveguide do not differ from those of the chemically etched waveguide by more than . Finally, we show that a similar passivation mechanism can be obtained during HBr ICP etching of ridge waveguides, demonstrating that the same HBr chemistry is suitable for both GaAs and InP systems.

Low sidewall damage plasma etching using ICP-RIE with HBr chemistry of Si/SiGe resonant interband tunnel diodes

The effect and influence of dry plasma etching processes of Si/SiGe using HBr for the formation of diode mesa structures has been investigated to minimise sidewall leakage current. To characterise sidewall damage electrically, Si-based resonant interband tunnel diodes (RITD) were processed and the completed RITDs compared by their peak-to-valley current ratio (PVCR) and valley current density (VCD), which are sensitive to defect related currents. Dry processed RITDs were compared to reference RITDs fabricated by wet chemical etching (HNO3:HF:H2O=100:1:100). The combination of HBr process gas and very low substrate bias power (10 W) for inductively coupled plasma reactive ion etching (ICP-RIE) yielded the better results. The resulting RITDs processed by ICP-RIE using HBr chemistry show high PVCR of 4.02 with VCD of 32 A/cm2 while wet etched RITDs show a PVCR of only 2.81 with VCD of 40 A/cm2. Hydrogen passivation during the HBr plasma process may play a role that overcomes the slightly higher surface roughness compared to wet etching.

Etch Characteristics of Ferroelectric (Bi 4−x La x )Ti 3 O 12 Thin Films in an Inductively Coupled Plasma

Reactive ion etching of ferroelectric (Bi 4 m x La x )Ti 3 O 12 (BLT) thin films has been studied using C 2 F 6 and HBr etch gases in an inductively coupled plasma (ICP). BLT thin films with bismuth layered-perovskite structure were prepared by chemical solution deposition method. Etch rate and etch selectivity of BLT films were investigated for each gas. The etch rate of 700∼900 Å were obtained for C 2 F 6 gas while the etch rate by HBr gas were in the range of 700∼1100 Å under the etch conditions used in this study. The etch profiles and surface morphologies of BLT films etched by each gas were observed using field emission scanning electron microscopy (FESEM). HBr chemistry turned out to be more effective in obtaining high etch rate and clean etch profile than C 2 F 6 chemistry.

RIE lag in diffractive optical element etching

In this study, the pattern of a 4 mm diameter diffractive optical element with linewidth ranging from 12 to 0.5 μm was adopted. With the SiO 2 layer as the etch hard mask, silicon was etched based on HBr chemistry with additions of O 2 and SF 6. The effects of O 2 content on the sidewall anisotropy, etch rate, and etch selectivity over the SiO 2 mask were also examined. The RIE lag, where etching of a small trench (hole) lags behind a large trench (hole), was investigated to produce an optimum aspect ratio for each zone of the diffractive optical element. The regression relation of the etch depth versus zone width was determined as a guideline for the feasibility of this method.

ECR plasma etching of GaN, AlN and InN using iodineor bromine chemistries

The dry etching characteristics of GaN, AlN and InN in HI-H/sub 2/-Ar and HBr-H/sub 2/-Ar were examined using electron cyclotron resonance discharges operating at high microwave power (1000 W) and low pressure (1 mtorr). For an RF-induced DC bias of -150 V, the HI chemistry provides approximately 20% faster etch rates for GaN and AlN than more conventional chlorine-based plasmas. For InN the rates were up to a factor of 5 faster. The HBr chemistry produced slower etch rates for all three nitrides compared to chlorine chemistries. Highly anisotropic etched features were obtained in the three materials with both iodine and bromine chemistries.

Magnetically enhanced etching of sub-0.5 μm polysilicon gates

We have compared Cl2 and HBr for etching polysilicon lines in a band magnetron cathode reactor. The experiments were designed utilizing response surface methodology. Our study shows a significantly wider operating window with the HBr chemistry. Typical results obtained are a polysilicon etch rate of 1500–2000 Å/min, selectivities 100:1 poly:SiO2 and 10:1 poly:photoresist. Direct-current bias values were under 100 V, and operating pressures were less than 6 mTorr. The results for 0.25 μm lines indicate that etching was free of undercut, oxide trenching, and polysilicon notching over steps. No evidence of polymer formation was observed using scanning electron microscopy and optical emission spectroscopy.

Trench process with HBr chemistry in ripe

The RIPE (Resonant Inductive Plasma Etcher) uses inductively coupled radio frequency power to generate a high density plasma at low pressure. Its capabilities in fluorine plasmas have already been demonstrated [1]. To satisfy all basic requirement for pattern transfer, Hbr chemistry for trench and polysilicon etching has been tested in a pressure range1 to10 μbar. This work is related to the study of a trench process etch in HBr chemistry. Good profiles with high etch rate (0.7 μm/min) and high selectivity with respect to the SiO2 (12:1 to 100:1) are presented.