Oxygen-based digital etching of AlGaN/GaN structures with AlN as etch-stop layers

Abstract

O2-plasma-based digital etching of Al0.25Ga0.75N with a 0.8 nm AlN spacer on GaN was investigated. At 40 W RF bias power and 40 sccm oxygen flow, the etch depth of Al0.25Ga0.75N was 5.7 nm per cycle. The 0.8 nm AlN spacer layer acted as an etch-stop layer in 3 cycles. The surface roughness improved to 0.33 nm after 7 digital etch cycles.Compared to the dry etch only approach, this technique causes less damages. Compared to the selective thermal oxidation with a wet etch approach, this method is less demanding on the epitaxial growth and saves the oxidation process. It was shown to be effective in precisely controlling the AlGaN etch depth required for recessed-AlGaN HEMTs.

Control of V th of the enhancement high-frequency AlGaN/GaN HEMT fabricated by oxygen-based digital etching

“…The second step is oxide etching by hydrochloric acid (HCl) solution or dry BCl 3 plasma etching. [22][23][24][25][26][27][28][29] It was reported that the digital etching depth per cycle is self-limiting and depends primarily on the oxidation depth with different plasma power and time settings. 23) Therefore, the gate recess etching depth can be controlled strictly by the etching cycles.…”

Enhancement-Mode Multi-Channel AlGaN/GaN Transistors With LiNiO Junction Tri-Gate

“…The mesa and fin structures were etched by Ar/Cl 2 inductively coupled plasma etching (ICP) with a depth of 250 nm. Four cycles of digital etching were used to remove sidewall damages during dry etching [1], [16]. To better isolate the device, a second mesa was patterned by a thicker HSQ layer (300 nm) and etched with a depth of 200 nm.…”

Au-free recessed Ohmic contacts to AlGaN/GaN high electron mobility transistor: Study of etch chemistry and metal scheme

“…This effect is similar to the variation in the threshold voltage of normally off recessed gate HEMTs across the wafer (due to etch depth nonuniformity) when BCl 3 /Cl 2 recipes are used, in contrast to BCl 3 /O 2 recipes. 34 An observation during optimization of the recess etch process was the lower degree of polymerization in BCl 3 / O 2 recipes, which can be attributed to factors like the use of an O 2 plasma cycle before each BCl 3 plasma cycle and a wider window for variation of RF power, BCl 3 flow rate, and pressure to arrive at optimum values. Higher degree of uncontrolled polymerization in the BCl 3 /Cl 2 chemistry may be one of the reasons for nonuniformity in the etch depth across the sample.…”