Etch Processing of III-V Nitrides
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TRODUCTION
The family of nitride semiconductors has undergone amazing growth and development in the last decade and is now poised to play a pivotal role in a wide range of advanced semiconductor devices. This family, comprised of the binary semiconductors InN, GaN, and AlN and their ternaries, is now being applied in light emitting diodes that emit from UV to the amber regions of the visible electromagnetic spectrum and to blue lasers. Aside from these landmark optoelectronic device realizations, nitride semiconductors are also undergoing extensive research and development efforts for application in high frequency, high temperature, and high power microelectronic devices. In practically all of these applications, the ability to pattern the nitride semiconductor is required. As a result of many of the properties that make nitride semiconductors attractive in the aforementioned electronic and optoelectronic device applications, they have proven notoriously difficult to etch. This situation has placed energetic pattern transfer processes in the lead for
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nitride device development. It has also placed some restriction on acceptable masking materials for lithography – with more robust silicon dioxide and nitride often being chosen over photoresist. These requirements for etch processing of the nitrides clearly differentiates them from silicon, gallium arsenide and indium phosphide, the only semiconductors with reasonably well understood etch processes. As a result, considerable research and development will be required to realize production-quality etch processes for the nitrides. In this work, the progress in developing etch processes for the nitrides is reviewed and the remaining etch process issues are identified. The review starts with a brief overview of wet etching techniques and then moves on to cover the more prominent ion-assisted etching techniques. The first ion assisted technique addressed is the conventional reactive ion etching processes. The review then moves on to discuss the bulk of nitride etching efforts where high density plasmas have been employed. Also in this section, detailed results of experiments investigating the damage resulting from and the fundamentals of high density plasma etching will be discussed. The highlights of these efforts are then summarized and the most important remaining issues identified.
WET ETCHING METHODS
As a result of their high bond energies, group III nitrides typically are not etched by wet etching methods. The efforts to date are well reviewed in a recent chapter by Pearton and Shul[1]. Wet etchants are generally only successful on poor quality nitride films deposited by sputtering or reactive evaporation. For these poor quality films both acid and base solutions are moderately successful at elevated temperatures. If such film
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