| 摘要 |
A method and apparatus for detecting the presence of gaseous impurities, notably oxygen, in a gas mixture that flows over an IC wafer in an etcher during the etching process. The method is based upon the discovery that the ratio of the etch rate of spin-on-glass material to the etch rate of other materials, such as plasma-enhanced chemical vapor deposition (PECVD oxide) materials, varies in a predictable manner with the amount of oxygen contaminating the gas mixture. The standard ratio, in the absence of oxygen, is determined for a given set of processing conditions by first etching an SOG wafer, then etching a PECVD oxide material wafer, measuring the amount of material etched in each case, and from that calculating the respective etch rates, and finally taking the ratio of the two calculated etch rates. This standard ratio is used as the benchmark for future tests. When a production run is to be conducted on a new material, the above procedure is repeated when the equipment is otherwise ready for the run, and the new calculated etch rate ratio is compared with the standard ratio. If they are substantially equal, this indicates a lack of oxygen contamination. If the ratio has changed, and other processing conditions have been taken into account (such as RF power and temperature), this indicates the presence of impurities in the gas mixture, and hence probably a leak in the system, or contamination of the gas source itself. In IC manufacturing, the production run is then typically stopped to correct the problem. Calibration data can be generated in advance to determine by how much to adjust the etching time, given a particular measured ratio that is not the same as the standard ratio. The system may be automatically controlled by a computer that calculates the corrected etching time based upon the measured ratio of the respective etch rates of SOG and the PECVD oxide material.
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