IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Electronics Thursday Sessions
       Session EL-ThA

Paper EL-ThA4
Integrated Multiwavelength Parallel-processing Rotating-compensator Ellipsometer/Reflectance-difference Spectrometer for Real-time Measurement and Control of OMCVD Growth

Thursday, November 1, 2001, 3:00 pm, Room 124

Session: In-Situ Semiconductor Characterization
Presenter: K. Flock, North Carolina State University
Authors: K. Flock, North Carolina State University
M. Ebert, North Carolina State University
K.A. Bell, North Carolina State University
D.E. Aspnes, North Carolina State University
Correspondent: Click to Email
Previous research has underlined the importance of real-time diagnostics for epitaxial growth of semiconductor materials and structures. We describe an optical system integrated with a modified rotating-sample commercial organometallic chemical vapor deposition (OMCVD) reactor that combines the functions of spectroscopic ellipsometry (SE) and reflectance-difference spectroscopy (RDS) in a single optical path to return information about growth rates, compositions, and film thicknesses (SE) and surface chemistry (RDS). The system is essentially a rotating-compensator ellipsometer for increased diagnostic power relative to rotating-polarizer or rotating-analyzer designs, with the rotation rate of the compensator synchronized to that of the sample. Synchronization reduces noise in the SE data by eliminating random optical-anisotropy contributions and also allows us to measure the non-normal-incidence RD spectrum directly. The original sample spindle was replaced with a design that allows sample runout to be adjusted dynamically to provide additional improvements in signal-to-noise ratios. A 1024-element photodiode array detector with a 0.2 m spectrograph provides a spectral range of 240 to 840 nm. Software designed to optimize both real-time response and repetition rate permits complete spectra to be obtained at a 6 Hz rate with a 400 MHz computer. Using a prototype rotating-polarizer system we demonstrated sample-driven closed-loop feedback control of a graded-composition InGaP structure grown on GaAs, where the composition was varied parabolically with thickness. During the growth of this structure it was necessary to reduce the flow through the trimethylindium by about half, which the RD data indicate is due to a change of incorporation efficiency due to an observed change of surface reconstruction.