Graphene as plasma-compatible blocking layer material for area-selective atomic layer deposition: a feasibility study for III-nitrides

Abstract

Plasma-assisted atomic layer deposition (PA-ALD) is a promising method for low-temperature growth of III-nitride materials. However, selective film deposition using PA-ALD is challenging mainly due to the plasma-incompatibility of conventional deactivation/blocking layers including self-assembled monolayers and polymers. The main motivation behind this work is to explore alternative plasma-resistant blocking layer materials. Toward this goal, single/multilayered graphene (SLG/MLG) sheets were investigated as potential growth-blocking layers for III-nitride grown via PA-ALD. Prior to PA-ALD growth experiments, partially graphene-covered Si(100) samples were exposed to N2/H2 and N2-only plasma cycles to evaluate the plasma resistance of SLG and MLG. While SLG degraded fairly quickly showing signs of completely etched areas and rough surface morphology, MLG surface displayed certain degree of plasma-resistance. Based on this result, III-nitride PA-ALD experiments were carried out on MLG-patterned Si(100) samples. Crystalline III-nitride film deposition was observed on both Si(100) and graphene surfaces, confirming the rather ineffective nucleation blocking property of graphene surface against PA-ALD process. However, as graphene layers feature relatively weak van der Waals bonds at the substrate/graphene interface as well as between the multilayer graphene interfaces, conventional lift-off process was sufficient to remove the deposited excessive nitride films. InN and AlN-coated samples were ultrasonicated, and blocked/unblocked surfaces were characterized using scanning electron microscopy, x-ray photoelectron spectroscopy, and spectroscopic ellipsometer. While ∼50 nm thick films were measured in the open Si(100) areas, graphene-coated sample portions exhibited limited material growth in the range of 5-15 nm. Although not completely, the MLG surface has considerably blocked the PA-ALD growth process resulting in a usable thickness difference, enabling growth selectivity with postgrowth etch process. An Ar-based physical dry etching recipe was utilized to completely etch the unwanted nitride films from graphene coated area, while about 30 and 40 nm thick InN and AlN films remained on the nonblocked parts of the samples, respectively. As a result, selective deposition of PA-ALD grown AlN and InN has been achieved via graphene-assisted lift-off technique along with subsequent dry-etch process, achieving a maximum growth selectivity of ∼40 nm. With further process recipe optimization and integrating with a suitable patterning technique, the demonstrated graphene-assisted lift-off technique might offer an alternative feasible pathway toward area-selective deposition of III-nitrides and other plasma-necessitating materials.