Viewport Influence on Optical Pyrometry and Deposition Process in MOCVD Vertical Rotating Disc Reactors
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the in-situ temperature measurement with infrared pyrometer. Pyrometer applications require an optical viewport in order to separate the measurement device from the environment of the process reactor interior. When pyrometer is used together with the viewport, there are some potential problems that must be considered. First, viewports can affect the readings by reflecting and absorbing a portion of thermal radiation emitted by or reflected from the measurement target. Initial optical properties of the viewport can also change with time due to the deposition on its surface. Second, due to the glass non-flatness or defects, viewports can disturb the optical path of the pyrometer. In first part of this paper we investigate effect of viewport on accuracy and repeatability of the temperature measurements. Conventional optical viewports made of different materials are widely available now from different manufacturers [1]. Viewports made of glass 7056 and quartz are typically used with pyrometers, even though all manufacturers specify that they are suitable just for visual observations. There are several reasons behind it: low cost, wide availability, easy installation and maintenance. On the opposite, optically flat, strain-relieved viewports have to be made almost by custom request [2] and are about 10 times more expensive. Also, they should be handled with extreme care. We have analyzed potential errors related to conventional and special viewports applications. In many cases, reactants have to be introduced into the reactor uniformly (mostly through some type of showerhead injector plate) and viewports present unavoidable protrusion in this uniform inlet flow (see schematics on Figure 1). Additionally, viewports have to be purged by 315 Mat. Res. Soc. Symp. Proc. Vol. 588 ©2000 Materials Research Society
the carrier gas to prevent unwanted deposition on their surface and the temperature measurement drift associated with it. One wants to be confident that initial flow non-uniformity and viewport purge flow do not affect flow dynamics near the wafer surface. This is why in the second part of this work we describe flow modeling around viewports and experimental results that support it. In this paper we present results obtained for pyrometers and reactor geometry typical for vertical high-speed MOCVD systems manufactured by EMCORE Corporation [3]. We've demonstrated how pyrometer can be used with conventional viewports and how to minimize its effect on flow dynamic inside a reactor, but these conclusions are specific for EMCORE systems and may be transferred to another environment only after careful analysis. PURGE FLOW PYROMETER INLET FLANGE
ROTATING DISC
SENSOR HEAD
VIEWPORT TUBE WITH FLANGE WAFER EXHAUST
:ERROFLUIDIC S•EAL
ROTATION
SPINDLE
Figure 1. Schematic drawing of the vertical rotatingdisc reactorwith a viewport on the inlet flange. EXPERIMENT To investigate the viewport influence on temperature measurements, a series of measurements were performed with a Sekidenko 2000 fiber optic pyrometer [4]. The pyr
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