KOH溶液中氮化铝的湿化学蚀刻

Introduction 

Much progress has recently been made in the areas of growth, dry etching, implant isolation, and doping of the 111-V nitrides and their ternary alloys. This has resulted in nitride-based blue/UV light emitting and electronic There has been less success in developing wet etch solutions for these materials, due to their excellent chemical stability. High etch rates have been achieved in dry etch but damage may be introduced by ion bombardment, and controlled undercutting is difficult to attain. In addition, since dry etching has a physical component to the etch, selectivities between different materials is generally reduced.

Experimental 

The MN was reactively sputter deposited on a Si substrate to a thickness of —1200 A using a N2 discharge and a pure Al target. This type of A1N film has been shown to be an effective annealing cap for GaN at a temperature of 1100°C. ' The mAiN samples were grown using metallor- ganic molecular beam epitaxy (MOMBE) on semi-insulating, (100) GaAs substrates or p-type (1 11 cm) Si substrates in an Intevac Gen II system as described previously.32'33 The group III sources were triethylgallium, trimethylamine alane, and trimethylindium, respectively, and the atomic nitrogen was derived from an ECR Wavemat source operating at 200 W forward power. The layers were single crystal with a high density (1011 to 1012 cm2) of stacking faults and microtwins. mAiN samples were found to contain both hexagonal and cubic forms. The In1A11_N were either conducting n-type as grown (1018 cm3) for x 0.03 due to residual autodoping by native defects or fully depleted for x c 003. The compositions examined were 100, 75, 36, 29, 19, 3.1, 2.6, and 0% In.

Results and Discussion 

A1N.—Figure 1 shows the etch rate of the sputtered A1N as a function of etch temperature for samples as grown or annealed at 500, 700, 900, 1000, and 1100°C. The etch rates of both the as-deposited and 500°C annealed sample increase sharply as the etch temperature increases from 20 to 5 0°C, and then level off; the rate drops by approximately 10% with a 500°C anneal. The samples annealed at 700, 900, and 1000°C also show similar trends, with a monotomic decrease in rate for higher anneal temperatures. The crystal quality appears to increase significantly with anneal temperature as the etch rate drops accordingly. The etch rate continues to drop by —10% with each successive anneal, to 1000°C. After 1100°C the etch rate drops and is less temperature dependent. Overall there is an —90% reduction in etch rate from the as-deposited A1N to that annealed at 1100°C for etching at 80°C.

Fig1

Etch rates for InAl1_N grown on GaAs for 0 ≤x≥1 are shown in Fig. 4, for etch temperatures between 20 and 80°C. Up to 40°C the etch rates are very low and show little dependence on In composition. The A1N etches much faster at these temperatures than any composition of the ternary alloy mAIN. As the etch temperature increases to 60°C, the etch rates increase, showing a peak for 36% In. This is presumably due to a tradeoff between the reduction in average bond strength for InAlN relative to the pure binary MN, and the fact that the chemical sensitivity falls off at higher In concentrations. Thus the etch rates initially increase for increasing In, but then decrease at higher concentrations because there is no chemical driving force for etching to occur. InN did not etch in this solution at any temperature but was occasionally lifted off during long etches because of the defective interfacial region between InN and GaAs being attacked by the KOH.

Conclusions and Summary 

Annealing of sputtered A1N improved the crystal quality of the film, decreasing the chemical etch rate in KOH- based solutions. InA1N etch rates also increased with decreasing crystalline quality. Both MN and InA1N sam- ples had activation energies for etching in KOR 6 kcal moP1, etch which is typical of a diffusion-controlled etch mechanism. The etch rate for the InA1N initially increased as the In composition increased from 0 to 36%, and then decreased to zero for pure InN. The n-type InA1N etched approximately two times faster than the undoped material above 60°C, indicating that electrons play a role in the etch mechanism.

Acknowledgments 

The authors would like to thank the staff of the Microfabritech Facility for their help with this work. The work at the University of Florida is supported by NSF (DMR-942 1109), an AASERT grant through ARO (Dr. J. M. Zavada), a DARPA grant (A. Husain) administered by AFOSR (G. L. Witt), and a University Research Initiative Grant No. N00014-92-J-1895 administered by ONE. The work at Sandia is supported by DOE Contract DE-ACO4- 94AL85000.