Laser-Processing for Patterned and Free-Standing Nitride Films
- PDF / 2,767,271 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 86 Downloads / 183 Views
ABSTRACT Films of GaN and related materials can be processed by methods that invoke thermal decomposition, induced by intense illumination with a pulsed laser. At elevated temperatures, the nitride semiconductors undergo decomposition, with the effusion of nitrogen gas. We exploit this mechanism as an alternative to etching for the patterning of nitride films and for the opening of buried interfaces. Films of GaN have been etched to a depth of 1 gtm in less than three seconds. This interface decomposition allows in particular the separation of nitride films from transparent growth substrates such as sapphire.
INTRODUCTION The many proposed and developing applications of Group III-nitride materials call for the parallel development of various processing technologies, including methods for etching and patterning. The high chemical stability of these materials causes most etch processes that are used for other semiconductors to be either slow or inapplicable. Another complication for applications comes from the inavailability of solid wafers of the same materials, for use as substrates in homoepitaxial growth of thin films. This makes it difficult to obtain sufficiently low defect densities for some uses and, in the case of sapphire substrates, prevents the use of the substrate for
electrical contact with devices in the film. In contrast to the room-temperature stability however, the materials decompose readily at elevated temperatures with the rapid evolution of nitrogen gas. This reaction can be excited by heating the material with a pulsed laser in order to make well defined and highly resolved removal of the nitride material.' As one application, this process allows a very direct patterning by direct activation with appropriate illumination, as an alternative to chemical etching. In addition, it was found that internal interfaces can be parted in this way, which allows the removal of entire layers or films from a film/substrate system. 2 This can be used to remove material to a chosen depth, similarly to using a selective etch with an etch-stop layer. In addition it provides a means of producing free-standing nitride films by decomposing the interface with the substrate. EXPERIMENTAL DETAILS Our experiments were carried out on hexagonal-lattice nitride films deposited on sapphire by metallorganic chemical vapor epitaxy (MOCVD) 3, molecular beam epitaxy 4, and hydride vapor phase epitaxy5 . These included primarily GaN films, but also some systems including layers of AlGa,_ýN which were grown by MBE. As a special adaptation for these experiments, some of the samples have been grown on sapphire which has been polished on both sides in order to allow illumination of the substrate-film interface through the sapphire. The relevant details of particular samples are included with the results. 973 Mat. Res. Soc. Symp. Proc. Vol. 482 01998 Materials Research Society
The decomposition was effected using the 355 nm, third harmonic from a Q-switched Nd:YAG laser, with a pulse width of about 5 ns. The pulse energy was regu
Data Loading...
