Semiconductor processing typically involves the formation of various layers over a semiconductor wafer or substrate. One particular process involves a formation of an oxide layer over the substrate, wherein the oxide layer is generally deposited via chemical vapor deposition (CVD). A typical chemical vapor deposition system comprises a heated chamber, wherein various components require precise positioning within the chamber. One such component is what is referred to as a “showerhead”, wherein the showerhead disperses one or more gases across a wafer positioned on a heated platen. The showerhead disperses gases in a predetermined manner over the wafer at a predetermined pressure and temperature.
A typical showerhead is seen in the Sequel CVD system manufactured by Novellus Systems, Inc. of San Jose, Calif. In the Sequel CVD system, a plurality of showerheads is positioned within a process chamber, wherein the process chamber is generally evacuated during processing of wafers. The process chamber comprises a heated platen on which a plurality of wafers are placed, and wherein the plurality of showerheads are positioned above the plurality of wafers to introduce process gases which generally form the desired layer (e.g., an oxide) over the wafers. Accuracy in the positioning of the plurality of showerheads is important in maintaining process uniformity. Variations in the positions of the showerheads can be seen over time, especially when maintenance to the system is performed.
Accordingly, the showerheads are typically positioned within the chamber and the position is controlled by what is called a “crush ball test”, wherein a plurality of balls of foil (e.g., balls of aluminum foil) are placed within the chamber between the platen and the showerheads, and the system is evacuated and placed in conditions similar to actual processing conditions, wherein the balls of foil are subsequently “crushed” between the showerheads and the platen. Once the process conditions are achieved, the crushed balls of foil are removed from the chamber, and a vertical position of the showerheads (e.g., a spacing between the bottom surface of the showerhead and a top surface of the platen) is thus determined by a measurement of the crushed balls of foil using calipers or the like by an operator of the system. The vertical position and alignment of the showerheads are accordingly adjusted based on the measurement of the crushed balls of foil.
The crushed ball measurement has several problems associated therewith. For instance, the measurement of the balls of foil can vary from operator to operator, wherein each operator may apply a differing amount of pressure in measuring the thickness with the calipers. Further, due to the generally delicate nature of the foil used in the measurement, errors in measurements are quite common, due to the removal of the foil, the measurement thereof, and the location of the measurement on the crushed ball of foil.
Thus, an improved method and apparatus for improving showerhead alignment in a CVD system is desirable.