1. Field of the Invention
This invention relates generally to a semiconductor fabrication process, and, more particularly, to controlling the semiconductor fabrication process based on an estimated process result.
2. Description of the Related Art
There is a constant drive within the semiconductor industry to increase the quality, reliability and throughput of integrated circuit devices, e.g., microprocessors, memory devices, and the like. This drive is fueled by consumer demands for higher quality computers and electronic devices that operate more reliably. These demands have resulted in a continual improvement in the manufacture of semiconductor devices, e.g., transistors, as well as in the manufacture of integrated circuit devices incorporating such transistors. Additionally, reducing the defects in the manufacture of the components of a typical transistor also lowers the overall cost per transistor as well as the cost of integrated circuit devices incorporating such transistors.
Generally, a set of processing steps is performed on a group of wafers, sometimes referred to as a “lot,” using a variety of processing tools, including photolithography steppers, etch tools, deposition tools, polishing tools, rapid thermal processing tools, implantation tools, etc. The technologies underlying semiconductor processing tools have attracted increased attention over the last several years, resulting in substantial improvements.
One technique for improving the operation of a semiconductor processing line includes using a factory wide control system to automatically control the operation of the various processing tools. The manufacturing tools communicate with a manufacturing framework or a network of processing modules. Each manufacturing tool is generally connected to an equipment interface. The equipment interface is connected to a machine interface which facilitates communications between the manufacturing tool and the manufacturing framework. The machine interface can generally be part of an Advanced Process Control (APC) system. The APC system initiates a control script based upon a manufacturing model, which can be a software program that automatically retrieves the data needed to execute a manufacturing process. Often, semiconductor devices are staged through multiple manufacturing tools for multiple processes, generating data relating to the quality of the processed semiconductor devices.
During the fabrication process, various events may take place that affect the performance of the devices being fabricated. That is, variations in the fabrication process steps result in device performance variations. Factors, such as feature critical dimensions, doping levels, contact resistance, particle contamination, film optical properties, film thickness, film uniformity, etc., all may potentially affect the end performance of the device. Various tools in the processing line are controlled in accordance with performance models to reduce processing variation. Commonly controlled tools include photolithography steppers, polishing tools, etching tools, and deposition tools. Pre-processing and/or post-processing metrology data is supplied to process controllers for the tools. Operating recipe parameters, such as processing time, are calculated by the process controllers based on the performance model and the metrology information to attempt to achieve post-processing results as close to a target value as possible. Reducing variation in this manner leads to increased throughput, reduced cost, higher device performance, etc., all of which equate to increased profitability.
Metrology data collected after the processing of a wafer or lot of wafers may be used to generate feedback information for use in determining a control action for the previous process tool. The collection of metrology data, however, may be costly in terms of process delay and resource expenditure. The delay in the process may be introduced because the processed wafers are routinely removed from the production flow and transferred to a remotely located metrology tool where characteristics of the lot are measured. The collected metrology data may then be used to control the previous or subsequent process tool in the process flow. Typically, there is a significant time period required to complete the metrology cycle of collecting the data and determining a control action based on the metrology data. The delay inherent in the metrology cycle may introduce inefficiency in the process control. Moreover, the cost of collecting metrology data can be high, as metrology tools tend to be expensive. Thus, in view of the above-mentioned reasons, it may sometimes be desirable to reduce the reliance on metrology tools for process control.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.