Dry Etching of III-V Nitrides
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S. J. Pearton('l' R. J. Shult2 ), G. F. McLane
and C. Constantine
(1)University of Florida, Gainesville, FL 32611 USA (2)Sandia National Laboratories, Albuquerque NM 87185 USA (3)Army Research Laboratory, Ft. Monmouth NJ 07703 USA (4)Plasma Therm IP, St. Petersburg FL 33716 USA ABSTRACT The chemical inertness and high bond strengths of the III-V nitrides lead to slower plasma etching rates than for more conventional III-V semiconductors under the same conditions. High ion density conditions (>3x10 11cm3 ) such as those obtained in ECR or magnetron reactors produce etch rates up to an order of magnitude higher than for RIE, where the ion densities are in the 109cm"3 range. We have developed smooth anisotropic dry etches for GaN, InN, AIN and their alloys based on C12/CH4/H2/Ar, BCI 3/Ar, Cl2/H2 , C12/SF6, HBr/H 2 and HI/H 2 plasma chemistries achieving etch rates up to -4,OOOA/min at moderate de bias voltages (_llim/min for InP, GaAs and other more common Ill-V materials for these same conditions, emphasizing the difficulty in achieving very high rates for the nitrides. 100
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rf-power (W) Figure 3. GaN surface roughness and etch rate as a function of rf power in ECR C12/CH 4 /H2/Ar discharges. Figure 4 (top) shows SEM micrographs of features produced in nitride structures with 1OHBr/10H 2 , 1000W (microwave) discharges. The structure is an AIN/GaN/A1N multilayer, which clearly demonstrates the differential undercut between the two materials in HBr/H2 discharges. By contrast, use of a HI/H 2 plasma chemistry under the same conditions produces relatively uniform mesas (Figure 4, bottom). Note that the etched surface morphology even after removing -3.5[tm is still good, and there is little differential etching between the foot of the mesa and areas out on the field. This is a benefit of the low process pressures employed under ECR conditions, which minimize such effects. The sidewall roughness is also considerably worse under high dc bias conditions (Figure 5, left) due to mask erosion, whereas it is much smoother at dc biases _
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