In Situ Characterization of Ain Films Grown on Silicon by MOCVD
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ABSTRACT Films of AIN were grown on Si under vacuum pressure at 9000 C and examined ex situ with infrared reflectance spectroscopy and microscopy, scanning electron microscopy, x-ray diffraction and rutherford backscattering spectroscopy. Collection of IR emission spectra for in situ characterization was successful and used to identify growth parameters during film growth. INTRODUCTION Group III-Nitride thin films have sparked interest due to their desirable electrical, optical, dielectrical, and acoustical properties [1,2,3]. AIN and GaN are two semiconductors currently being studied as promising materials for blue/UV light emitting diodes because of their wide band gap, high melting point and high luminescence intensity [4-6]. The chemical and thermal stability of AIN, coupled with its high resistivity, makes it a potential candidate for use as passivation layers in semiconductor devices [2,3]. Our lab, along with many others, has explored growing AIN films on silicon by metal organic chemical vapor deposition (MOCVD) [7-16]. Temperature of deposition and overall pressure during the reaction were varied until optimum growth conditions were achieved. The AIN films were then characterized ex situ with respect to thickness, crystallinity, orientation, surface roughness and band-gap. Although ex situ analysis provides ample characterization of film quality, it lacks insight into identifying growth parameters during film growth. In situ
analysis allows direct monitoring of film thickness and film quality while the film is being grown. In this report we use IR emission spectroscopy to observe growth parameters during AIN growth at the reaction temperature of 900 'C. EXPERIMENTAL A stainless steel high vacuum MOCVD reaction chamber consisting of a growth chamber, pumping station, and gas delivery system housed the AIN film growth. Pumping into the 10' Torr range was accomplished with a corrosive resistant turbo-molecular pump. Gaseous ammonia and trimethylalluminum were used as source materials for nitrogen and aluminum and maintained at a 2.5:1 ratio, respectively. The ¼ in. by ½ in. substrates were mounted on a molybdenum sample holder and heated using a boron nitride ceramic heater. An optical pyrometer was used to determine the temperature of the substrates during deposition and an Alcatel turbo pump was used to maintain pressure between 10'3 and 10" Torr. The AIN films were characterized ax situ with IR reflectance spectroscopy, IR reflectance microscopy, UV-VIS transmission spectroscopy, X-ray crystallography, scanning electron microscopy (SEM) and Rutherford backscattering spectroscopy (RBS) [11]. In situ characterization of the AIN growth was performed using a Midac Emission FTIR spectrometer. The reference emission spectrum of the Si substrate at 900 'C was collected before exposure to 445
Mat. Res. Soc. Symp. Proc. Vol. 512 01998 Materials Research Society
TMA and NH3. During film growth, 4 cm' resolution emission spectra were collected at a rate of 1.8 spectrum per second. A band pass filter was placed in
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