In Situ Monitoring of MOCVD of Aluminum Nitride by Optical Spectroscopies
- PDF / 260,164 Bytes
- 6 Pages / 418.68 x 637.2 pts Page_size
- 25 Downloads / 169 Views
NITRIDE BY OPTICAL SPECTROSCOPIES S.C. AMen, H.H. Richardson Department of Chemistry and Biochemistry, Ohio University, Athens, OH 45701,
[email protected] ABSTRACT Trimethylaluminum and ammonia were used as precursors in the high temperature (900°C) deposition of AIN on silicon at vacuum pressure. The emitted radiation was collected in situ by a FTIR spectrometer. Film thickness was monitored in situ by interference oscillations in a red diode laser beam reflected off the sample. The thickness measurements were correlated with IR emission spectra from the emerging AIN film, and a principal component analysis (PCA) and principal component regression (PCR) were performed on the data. INTRODUCTION Group III nitrides have been under intense study because of their numerous possible applications in new optical and electronic devices [1]. Specifically, AIN is of interest because it possesses the largest band gap of the group III nitrides (6.2 eV) [2]. In-situ techniques such as monitoring interference effects and use of IR emission spectropscopy are potentially valuable methods in the study of nitride semiconductor growth as they are nondestructive and all data are collected during growth. Interference effects can be used to gain insight into surface roughness and thickness variation of the sample [3,4]. The optical modes of AIN can be distinguished in the IR region; and it has been shown that the sharpness of the LO mode (-890 cm-) is related to the crystalline quality of the film [5]. EXPERIMENTAL
The stainless steel MOCVD apparatus consisted of a six-way cross pumped to a base pressure of 10' torr by an Alcatel turbo-molecular pump. The Si (100) substrates were secured to a boron nitride ceramic heater by a molybdenum sample holder. An IR-transparent zinc selenide window allowed the IR emission to be collected with a Midac FTIR spectrometer. A 5 mW red diode laser (wavelength 630-680 nm) was centered on the sample and the reflected beam was directed into a Jarrell Ash monochromator set at 657 nm. The samples were flashed to 1000*C on an infrared thermometer for 60 seconds using a variable transformer. The voltage was then reduced to maintain a substrate temperature of 900 +/-10°C. Background spectra of the bare substrate were collected before gaseous NH3 and TMA were introduced in a 10:1 partial pressure ratio parallel to the substrate surface. Emission spectra were collected every 2 seconds in the 700-1300 cm" range with a resolution of 4 cm". Total pressure during growth was held constant between 10.' and 10-3 torr. After reflected laser intensity had sufficiently decreased such that oscillations were no longer observed, film deposition was halted by closing the gas inlet valves. Growth times ranged between 15 and 30 minutes. The emission spectra were averaged in groups of nine to reduce the total size of the data set, resulting in a time-averaged spectrum every 18 seconds. A thickness measurement derived 301 Mat. Res. Soc. Symp. Proc. Vol. 591 02000 Materials Research Society
from the laser interfer
Data Loading...
