Control of stray radiation in a CVD chamber
View Patent ↗An apparatus and method for controlling stray radiation within a CVD chamber. A heater array disposed beneath a wafer carrier for radiatively heating of the wafer carrier includes a peripheral or outermost heating element or elements. Scattered radiation originating from a designated segment of the peripheral heating element(s) can be reduced locally by one of several mechanisms, including reducing the emission (e.g., operating temperature) of the designated segment, or capturing or deflecting a portion of the radiation originating from the designated segment. In one embodiment, an electrical connector on a resistance heating element provides the reduced emission from the designated segment. It has been found that radiation thermometers fixed proximate an axis that extends from the center of the wafer carrier and across the designated segment is subject to less stray radiation, thus providing a more reliable temperature reading in the optical wavelengths.
1. A system for limiting stray radiation received by a radiation thermometer, comprising:
a chemical vapor deposition (CVD) chamber;
a cylinder disposed within said CVD chamber, said cylinder defining a cylinder axis and having an interior surface and an exterior surface, said interior surface defining an inner cylinder diameter, said exterior surface defining an outer cylinder diameter and, said cylinder having a top edge defining an upper plane that is substantially normal to said cylinder axis;
a peripheral heating element disposed within said cylinder and proximate said interior surface of said cylinder;
a spindle disposed within said cylinder and extending through peripheral heating element, said spindle having a distal portion that extends above said upper plane of said cylinder;
a wafer carrier having a top surface that is substantially planar and defining a target plane, said wafer carrier being configured for connection to said distal portion of said spindle for suspension above said peripheral heating element;
means for reducing scattered radiation that is emitted from a designated portion of said peripheral heating element, said means for reducing scattered radiation being located proximate said peripheral heating element; and
a radiation thermometer arranged to view a target on said target plane that is proximate an axis of reduced scattered radiation, said axis of reduced scattered radiation being coplanar with said target plane and having an origin at said cylinder axis extending in a direction of said means for reducing scattered radiation, wherein the target is within a rectangular region on said wafer carrier, said rectangular region having a width that is approximately the same as a width of a low heat flux portion of said designated portion of said peripheral heating element.
2. The system of claim 1 , wherein said target is within a rectangular region on said wafer plane that includes a portion of said axis of reduced scattered radiation, said rectangular region extending from said spindle to an outer edge of said wafer carrier.
3. The system of claim 1 , wherein said means for reducing scattered radiation comprises an electrical connector of said peripheral heating element.
4. The system of claim 1 , wherein said means for reducing scattered radiation includes one of a radiation trap and a radiation deflector located proximate said designated portion of said peripheral heating element.