Dry Etching of InP-based Materials using Cl2/H2/Ar Chemistry (UCSB)
Ning Cao, PhD. UCSB Nanofab Development Engineer
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 Figure 1) 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.
Figure1 (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=125/800 W. 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 2 (a) and (b). Etch profile of InGaAs/InP nano-wires using the recipe mentioned in Figure 1 (etch time=60s). (reference: work by Dr. Ning Cao, UCSB process staff)
This process was developed by and is available at the NNIN UCSB Site.