AVS 47th International Symposium
    Manufacturing Science and Technology Thursday Sessions
       Session MS-ThM

Paper MS-ThM9
Feedback Control of Morphology During III-V Semiconductor Growth by Molecular Beam Epitaxy@footnote 1@

Thursday, October 5, 2000, 11:00 am, Room 304

Session: Advanced Modeling and Control for IC Manufacturing
Presenter: R.L. Kosut, SC Solutions
Authors: R.L. Kosut, SC Solutions
J.L. Ebert, SC Solutions
S. Ghosal, SC Solutions
R. Caflisch, University of California, Los Angeles
M. Gyure, HRL Laboratories
J.J. Zinck, HRL Laboratories
Correspondent: Click to Email
This paper addresses the modeling and control of epitaxial growth of III-V semiconductor material by Molecular Beam Epitaxy. In layer-by-layer growth mode, oscillations and envelope decay in the specular intensity of the reflection high energy electron diffraction (RHEED) pattern have been correlated to the instantaneous density of steps on the surface. This allows for the possibility of in situ monitoring and control of surface morphology during growth. A control algorithm and strategy was first developed using a KMC simulation model of III-V growth together with dynamic thermal models of the effusion cells and cracker valves. The strategy discovered from the simulations was to control growth layer-to-layer which turns out to have two important features: (1) it is very robust to chamber variations and uncertainties, and (2) the resulting form of the system is well modeled as a discrete-time system where sample times are replaced by layer number. There is a vast body of control theory which can be applied to such systems. The control was implemented on the MBE system to control RHEED oscillations and decay rates in real-time during III-V growth in HRL Laboratories MBE chamber. The RHEED signals were used to estimate oscillation period which was compared to a reference and the error was used in a control algorithm to adjust, in real-time, the set-point temperature of the III material effusion cell. The RHEED signals were also used to estimate oscillation decay and then used to adjust the V material cracker valve opening. Simulations compared well with experimental data in both open and closed loop. Investigations are currently under way to use a photoemission (PE) sensor in place of the RHEED sensor. Hopefully results will be available at the time of the AVS conference. @FootnoteText@ @footnote 1@ Research supported by DARPA, Applied Computation & Mathematics Program.