1. Field of the Invention
The invention relates to chemical vapor deposition (CVD) systems and, more particularly, to temperature control apparatus, and a concomitant method, for controlling the temperature of the walls of a CVD reaction chamber.
2. Description of the Prior Art
In a conventional chemical vapor deposition (CVD) system, a reaction chamber envelopes a volume wherein the deposition process occurs. The chamber typically is fabricated of transparent quartz. As such, the reaction chamber is said to have quartz windows (accessible surfaces of the chamber) through which the temperature of the apparatus within the chamber can be optically monitored using optical pyrometers. In general, since the windows are integral with the walls of the chamber, the temperature of these windows is indicative of the chamber wall temperature. The temperature of the windows and the walls of the chamber vary depending upon the temperature of the workpiece within the chamber, the process presently being accomplished, the gases involved in the current process, and the run time of the process.
More specifically, it is desirable that during a deposition process, the quartz wall temperature be controlled within a narrow temperature range to minimize deposits on the chamber wall. Furthermore, it is desirable that, during cleaning steps, the quartz wall temperature be maintained at a different temperature to maximize the etch rate of any film that may have been deposited on the chamber walls. Such temperature maintenance minimizes particulate contamination problems.
Typically, the temperature of the walls of the chamber is maintained at a nominal value by a flow of air proximate the outer surface of the chamber. This air flow is fixed for each process performed within the chamber. Thus, the temperature of the chamber walls varies with conditions within the chamber, e.g., the wall temperature differs depending on whether the process in the chamber is depositing material or etching material from a workpiece.
Through empirical study, it has been shown that the processes performed within the chamber can be optimized when the chamber wall temperature is maintained at an optimum temperature for a particular process. However, prior art CVD systems contemplate maintaining the air flow past the chamber at a fixed flow rate. As such, these systems exhibit significant chamber wall temperature variations which preclude a high degree of temperature optimization.
Therefore, a need exists in the art for closed loop apparatus, and a concomitant method, for controlling the air flow proximate a reaction chamber such that the temperature of the chamber walls can be readily optimized for each of the processes accomplished within the chamber.