ICP-RIE etching of polar, semi-polar and non-polar AlN: comparison of Cl₂/Ar and Cl₂/BCl₃/Ar plasma chemistry and surface pretreatment

Abstract

We report a comprehensive investigation of inductively-coupled plasma reactive ion etching (ICP-RIE) of polar (0001) c-plane, semi-polar (11-22) and non-polar (11-20) a-plane AlN epilayers and show that under optimized conditions a combination of BCl 3 -based surface oxide removal pretreatment and Cl 2 /Ar ICP etching allows fast etch rates (750 nm min −1 ) with a smooth surface morphology. We compare samples of different orientation etched in Cl 2 /Ar and Cl 2 /BCl 3 /Ar plasmas, with and without BCl 3 /Ar ICP pretreatment, and show that the effective removal of surface oxide is a crucial step for reliable ICP-RIE etching of AlN layers. For such pretreated samples, optimization of etch parameters such as RF power, ICP power, and chamber pressure then permit very high etch rates to be obtained with a smooth surface morphology. We also study the effect of varying the BCl 3 fraction in BCl 3 /Cl 2 /Ar plasmas on the etch rate and surface morphology and find that increasing the BCl 3 fraction reduces the etch rate for AlN. However, above 20% BCl 3 content, samples with and without pre-treatment show similar etch rates.

Improved crystallinity and surface morphology of a-plane AlN grown on high temperature annealed AlN/sapphire template by pulsed-flow mode metal-organic vapor phase epitaxy

“…Various methods have been developed to suppress BPSFs, such as introducing an SiN x interlayers [9][10][11], epitaxial lateral overgrowth [12][13][14], replacing the AlN buffer with ZnO buffer layers, optimizing the thickness of AlN buffer layers and ammonia thermal treatment [15][16][17]. To effectively eliminate the surface undulated morphology, approaches including surface pretreatment [18][19][20], two-step growth process with modulation of V/III ratio [21,22] and pulsed flow growth [23,24] methods have been proposed. These attempts are encouraging, though some of them are complex and have a noticeable effect only on reducing BPSFs or on improving the surface morphology.…”

Study of dry etched N-polar (Al)GaN surfaces obtained by inductively coupled plasma etching

“…Wet etching in hot alkaline solutions such as potassium hydroxide [19] and dry etching in inductively coupled plasma (ICP) system by chlorine-based gases [20][21][22] are the two main processes used for N-polar materials removal. N-polar surfaces after wet-etching are usually of poor morphology with a high density of pyramidal hillocks [19,23], whereas dry-etching can lead to much smoother surface morphologies [24].…”

“…A very low etch rates ~1 Å/s was used by Chung et al for a smooth N-polar GaN surface [13]. The ICP byproducts GaCl x /AlCl x (could not be fully desorbed) [20,22,26] were claimed to be responsible for the poor etched surface. Alternatively, Yu et al chose to remove N-polar buffer layers by selectively chemical mechanical polishing (CMP), with a selection ratio as high as 35: 1 (Al x Ga 1-x N: GaN = 1400 nm/min: 40 nm/min).…”

Aluminum nitride integration on silicon nitride photonic circuits: a new hybrid approach towards on-chip nonlinear optics

“…Nevertheless, the fabrication of AlN circuitry, in particular its etching, can be challenging. The presence of surface oxides gives rise to a dead time at the start of the etching process [23], which results in slow and not easily reproducible etching rates [24]. A high inductively coupled plasma (ICP) power exceeding 500 W is needed to achieve sidewalls with modestly steep angles such as 84°in Ref.…”