Dry Etching of InP-based Materials using Cl2/H2/Ar Chemistry at the UCSB Nanofabrication Facility
Ning Cao, PhD. UCSB Nanofab Development Engineer
Brian Thibeault, Ph D. UCSB Nanofab Project Scientist
Steve Nichols, Ph D.
For InP-based photonic circuits and other applications, it is often desired that the etch profiles are vertical and smooth so that light scattering losses are minimized. Cl2/N2 or Cl2/Ar ICP etching of InP at 200C sample temperature is often used to create smooth, high aspect ratio structures. However, these etches often produce micro-trenching at the base of the structure and bowing of the sidewalls due to ion deflections caused by the electron build-up within and on the surfaces of the etched structures. One way to eliminate (or reduce) the effects of these charges is to add a hydrogen gas into the plasma to create H+ ions to neutralize the excess electrons on the side-wall. Here,with the use of Unaxis ICP etcher at a chuck temperature of 200 C in the UCSB Nano-fabrication facility, a Cl2/H2/Ar etch-chemistry recipe was developed by Prof. Larry Coldren’s group (see Figures 1 and 2) to obtain an etch profile with no micro-trenching or bowing and extremely smooth sidewalls and no lateral notching of InGaAs. These types of structures are used regularly in photonic circuits produced in the facility (Figure 2 is an example). Figure 3 shows the effect of using H2 rather than N2 to eliminate trenching. Figure 4 shows nanowire structures that were etched using this method.Dry Etching of InP-based Materials using Cl2/H2/Ar Chemistry at the UCSB Nanofabrication Facility.
Figure 1 Effect of varying Cl2:H2:Ar ratio (etch condition: total gas flow=21sccm, pressure=1.5mT, bias/ICP power=125/800W) (reference: internal report of Dr. Steve Nichols of Prof. Larry Coldren’s group).
Figure2 (a) and (b).InP (InGaAs) etch profile with the etch condition of Cl2/H2/Ar flow-rate=7.4/11.6/2 sccm, pressure = 1.5 mTorr, Bias/ICP power=125/800W. Silicon carrier wafers were used with InP samples mounted using DOW high vacuum grease. The etch rate is 15-20 nm/s for InP and 7-10 nm/s for InGaAs (reference: internal report of Dr. Steve Nichols of Prof. Larry Coldren’s group).
Figure 3 Effect of varying etch chemistry: (a) InP Etch with Cl2/H2/Ar: flat trench bottom (no micro-trench). Etch condition: 1.5mT, 125/800W, Cl2/H2/Ar flow-rate=7.4/11.6/2 SCCM, and time=90 s. Etch rate=1.57m/min (open area) and etch selectivity(InP/SiO2)=15.5; (b) InP Etch with Cl2/N2/Ar: micro-trench at trench bottom. Etch condition: 1.4mT, 125/800W, Cl2/N2/Ar flow-rate=7.4/11.6/2 SCCM, and time=120 s. Etch Rate=0.69m/min and etch selectivity(InP/SiO2)=9.3 (reference: work by Dr. Ning Cao, UCSB process staff).
Figure 4 (a) and (b). Etch profile of InGaAs/InPnano-wires using the recipe mentioned in Figure 2 (etch time=60s) (reference: work by Dr. Ning Cao, UCSB process staff).