Real-time monitoring of homoepitaxial and heteroepitaxial processes by p-polarized reflectance spectroscopy

Abstract

In this communication we describe a simple, inexpensive technique for the real-time monitoring of epitaxial processes based on the reflection of a parallel-polarized light that impinges onto the surface of the substrate close to the Brewster angle for the substrate material. In the case of heteroepitaxy, a quarter-wavelength modulation of the intensity of the reflected light is observed, which contains information concerning the evolution of the optical properties as well as a record of the growth rate for the entire duration of film deposition. Changes in the amplitude of this signal provides information about deviations in bulk dielectric properties of the growing film caused by absorption and inhomogeneities in the refractive index of the film as well as changes in the surface roughness. Furthermore, under the conditions of pulsed chemical beam epitaxy (PCBE), the reflected intensity contains a periodic oscillation that is superimposed on the polarized reflectance spectroscopy (PRS) signal with an Å scale period and is maintained over thousands of Å of film growth. The periodicity of this fine structure matches the period of the sequence of precursor pulses of the PCBE process. Also, an amplitude modulation of the superimposed oscillation is observed which may be understood on the basis of the results of PRS studies of homoepitaxial growth. Under the conditions of homoepitaxy, the quarter-wavelength oscillations in the PRS signal cease to exist since the epitaxial film and the substrate have the same dielectric function. However, the fine structure can still be observed and may be utilized for both analysis of the growth mechanism and in conjunction with the observation of heteroepitaxial growth for the same material, the real-time monitoring of the growth rate.