Nitridation of Substrates With Hydrazine Cyanurate for The Growth of Gallium Nitride
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Unfortunately, high temperature or plasma processing can be damaging to the substrate and detrimental to microelectronic device performance. Hydrazine (N 2H4) has a lower activation energy and is easier to crack than other sources; however, the use of liquid hydrazine involves issues of purity, safety, and difficulties in handling a liquid source. Hydrazine cyanurate (N2 H4 *C3 H 3 N30 3) is a promising solid source of hydrazine for nitridation reactions because it can be easily handled and purified before use in the solid phase, and it evolves pure hydrazine upon heating. We have developed this solid complex of hydrazine for use in a nitridation process, and the details have been published elsewhere [7]. In this paper we report on the application of hydrazine cyanurate to the nitridation of GaAs (100) and (111) and sapphire (0001) substrates. These substrates were nitridated at 400 °C or less, which is several hundred degrees lower than typical nitridation temperatures reported in the literature [8], because hydrazine cracks easily. With hydrazine, volatile III-V semiconductors such as GaAs and InP can be easily nitridated, providing a convenient route to substrate preparation for the growth of group II nitrides or surface passivation for other III-V devices. EXPERIMENT Details of the reaction apparatus for the use of hydrazine cyanurate in a low pressure chemical vapor deposition (LPCVD) process have been published elsewhere [7]. AXT GaAs (100) wafers were double side polished and received no wet processing prior to their introduction 227 Mat. Res. Soc. Symp. Proc. Vol. 512 0 1998 Materials Research Society
into the LPCVD reactor. Crystal Specialties Inc. GaAs (111) wafers were degreased with trichloroethylene, acetone, and methanol and were then etched in 5H 2SO 4 : H20 2 : H 2 0 before being introduced into the LPCVD reactor. Both Crystal Systems and Union Carbide sapphire (0001) samples were degreased with trichloroethylene, acetone, and methanol and were then etched in 3H 2SO 4 : H 3 PO 4 prior to their introduction into the LPCVD reactor. After the vacuum system was baked and the samples were outgassed, the samples were treated with H2 at an equivalent pressure of 2.8x10-7 torr for 1 hour. Samples were then nitridated between 5 minutes and 2.5 hours at total system pressures between 10 and 100 mtorr and substrate temperatures between 200 and 400 'C. The chemical composition of the surface was then determined by Xray Photoelectron Spectroscopy (XPS) using Al Kax radiation in a Surface Science SSX-100 ESCA spectrometer. The nitridated surface morphology was analyzed with a Digital Instruments NS3A Atomic Force Microscope (AFM). RESULTS Nitridation of GaAs (100) with hydrazine cyanurate A typical Ga 3d XPS spectrum of nitridated GaAs (100) is shown in Figure 1. Gaussian curves were fitted to the experimental photoelectron peak assuming constituent peaks of GaN (19.5 eV [9]), Ga 20 3 (20.2 [10] or 21.0 eV [11]), and GaAs (18.8 eV [12]). As can be seen from the composite curvefit, the agreement with the experim
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