Chemical Mechanical Polishing of Exfoliated III-V Layers

Abstract

The chemical mechanical polishing of III-V materials including GaAs, InP, InAs, and GaSb is investigated with sodium hypochlorite and citric acid solutions. It is found that the surfaces can be polished to below 0.5 nm RMS surface roughness without the induction of crystalline damage using similar abrasive-free polishing solutions for all the materials with controlled polishing rates of 10 nm / min which is important for touch polishing of exfoliated III-V layers. The optimal composition of the slurry is adjusted for the particular material. A balance between reduced sub-surface mechanical damage and smooth surface morphology is obtained by adjusting the amount of citric acid. However, the damage-free planarization in these cases may be aided by an oxide formation as predicted by Pourbaix diagrams. Additionally, triple axis x-ray diffraction is found to be an extremely sensitive, nondestructive method for evaluating damage induced by the CMP process.

Exfoliation of β-Ga2O3Along a Non-Cleavage Plane Using Helium Ion Implantation

“…the full width at thousandth maximum (FW(0.001)M), from the pre-anneal state (310") to this annealed state (515") as shown in Figure 1b. While FWHM values are more commonly reported, previous work 21,25 demonstrated that the tails of ω peaks are more sensitive to changes in crystallinity, i.e. mosaicity or tilt in the exfoliated layer.…”

“…This is a common occurrence observed in previous work with implanting other semiconductor materials. [18][19][20][21][25][26][27][28][29][30] The furthest left fringe in the ω:2θ scan typically corresponds to the maximum strain in the implanted region, 19 which is about 1.01%. The strain oscillation intensity decreased and shifted slightly after annealing at 200°C for 12 hours as shown in the ω:2θ scan in plots (i) through (iii) of Figure 1a.…”

“…The mechanism of exfoliating with ion implantation is applicable to a wide variety of semiconductor materials and works for arbitrary surface orientations. [18][19][20][21][25][26][27][28][29][30] The general mechanism is the nucleation and growth of helium bubbles (or hydrogen as in the literature for other materials) at the projected range beneath the substrate surface to achieve surface blistering or wafer splitting. While this experiment was performed on a (010)-oriented β-Ga 2 O 3 substrate, this process would naturally extend out to other orientations of interest and is expected to lead to materials integration opportunities to take advantage of the desirable properties of β-Ga 2 O 3 (e.g., high field strength) while mitigating some of the less desirable properties (low thermal conductivity).…”

“…This anneal sequence was based on previous work on exfoliation via ion implantation with other semiconductor materials. 18,20,21,[25][26][27][28][29][30] The low temperature step is associated with He blister nucleation which could be correlated to changes in X-ray diffraction (XRD) ω curves and the higher temperature step is correlated with growth of the blisters. We attempted individual annealing steps at a series of low temperatures to assess the onset of blister nucleation.…”

“…Post-exfoliated substrates are also easily recyclable for subsequent exfoliation. 18,20,21 First introduced to exfoliate layers of silicon, ion implantation of hydrogen 17 or helium 22 and subsequent annealing was used to produce silicon-on-insulator structures. Under the appropriate annealing conditions, an implanted substrate surface will blister from the nucleation and growth of hydrogen or helium gas bubbles present near the implanted species projected range beneath the substrate surface.…”