REAL-TIME MONITORING OF CHEMICAL VAPOR DEPOSITION PROCESSES: EFFECTS OF PRESSURE AND FLOW. Klaus J. Bachmann, Nikolaus Dietz, Amy Miller, Christian Höpfner, Departments of Chemical Engineering^(a), Materials Science and Engineering^(b) and Physics^(C), Jeffrey S. Scroggs, Hien T. Tran, Grace Kepler, Kazufumi Ito, H. Thomas Banks, Center For Research in Scientific Computation, North Carolina State University, Raleigh, NC 27695-7919

Real-time non-intrusive optical monitoring of the reproducibility of initial surface conditioning and the kinetics of nucleation and growth in chemical vapor deposition (CVD) processes, is important for both the development of closed-loop feedback control and progress in the fundamental understanding of CVD. Recently we have shown that the combination of p-polarized reflectance (PR), laser light scattering (LLS) and reflectance difference spectroscopy (RDS) is ideally suited for this task under low pressure conditions, where the ambient is represented by a dielectric constant close to one. The accommodation of these techniques to elevated pressure/high flow CVD, which is desirable in the context of controlling point defect chemistry related optical and electrical properties of compound heterostructures presents a challenge because temporal and spatial variations in the dielectric function of the ambient phase degrades their accuracy. In this paper we briefly review the methods of optical monitoring of CVD processes that have been applied thus far in conventional regimes of pressure and flow and assess their potential under conditions of high pressure growth. This includes a critical evaluation of design criteria for the implementation of optical process monitoring under the conditions of high pressure vapor transport (HPVT) and of migration enhanced CVD processes at elevated pressure. Also, we compare optical real-time process monitoring to complementary methods, such as, mass spectrometric sampling. The results of finite difference computations for specific designs of HPVT and CVD reactors are presented and related to the monitoring and control of the growth kinetics. The paper concludes with an outlook at applications of real-time optical process monitoring in condensed phases.