Process Monitoring System for Real Time Statistical Process Control

1. Field of Invention

This invention relates to manufacturing process control and in particular, real time monitoring of process parameters and statistical process control.

2. Description of Related Art

High yield is maintained through a high level of process control which includes having the right process recipe, collecting process parameter data and comparing the data to a set of established control limits. Often this entails fine tuning of the process in an attempt to optimize the process to produce higher yield. Measurements of key process parameters needed to understand the status of a process has been manually collected and often without the continuity or history to produce the desired results. Attempts have been made to automatically collect and warehouse the parameter data. This can be difficult because of the volume of data. The development of statistical techniques has led to the ability to handle the volume of data while providing a continuous real time monitor of the status of a process.

In U.S. Pat. No. 5,483,468 (Chen et al.) is described a system and method for concurrently recording and displaying system performance data for a computing system. In this invention is described a method in which a user interacts with the data being displayed to create various analysis of that data with the intentions of improving the computer system performance.

Referring to U.S. Pat. No. 5,479,340 (Fox et al.) is described a multivariate analysis of components of an ongoing semiconductor process for real time in-situ control. In this invention the algorithm calculates the T.sup.2 value from Holding's T.sup.2 statistical analysis which in turn creates a feedback signal if the T.sup.2 value is out of range and stopping the process.

In U.S. Pat. No. 5,440,478 (Fisher et al.) a method and system for controlling a manufacturing process using statistical indicators of performance from the production process and specification data. The data is enter into a computer and displayed in tables and bar graphs to enable the production control manager to see unfavorable trends and processes out of control to allow adjustment of the manufacturing process before the process run is completed. Whereas U.S. Pat. No. 5,440,478 appears to have similarity to the invention described herein, it relies on manual collection and entry of data into a computing system for analysis and display.

A major problem with real time process control using real time data can be the volume of data that is produced by a process machine. This requires a system be established that can handle the volume of data without overwhelming the resulting process. It is important that old data to be available for long term trends analysis as well as for trouble shooting the process. Thus a system is needed that provides real time collection and analysis of the process data and allows the archiving of data no longer needed for real time analysis.

The invention describe herein is a process parameter monitoring system for real time statistical process control having the capability to monitor multiple process machines at the same time with a mix of different types of machines. The specific implementation is in connection with semiconductor wafer fabrication process machinery such as for ion implantation. It is also applicable to other processes and process equipment where it is necessary for automatic collection of process parameter data for statistical process control (SPC) and the subsequent usage of the data to show trends and the goodness of the operating machinery.

The process parameter monitoring system is controlled by a production control computer. Contained within the production control computer is a data base used to store process parameter data used in the monitor and control of the process machinery. The process parameter data is stored for several months and is used to determine process control limits as well as trends in the characteristics of the process. The process control computer is connected to a company wide network through a server. Through the company wide network the process parameter monitoring system communicates with a production manufacturing information system (PROMIS) from which data such as the process recipe can be stored and retrieved, and process data can be archived.

Data is connected between production process machinery and a production control computer by means of a single RS 485 network and various network adapters. Each adapter has its own network address, and through means of control by the production control computer, communication is synchronized between adapters. Multiple process machinery of various types can be collected to the production control computer through the RS 485 network. Each process machine providing key process parameter data to be applied to a real time SPC analysis. The data for each machine is accumulated separately and applied to its own SPC analysis.

The data once analyzed is presented on the screen of the production control computer through a graphical users interface (GUI). The presentation is in the form of graphs and charts showing the trend of the data for important parameters like vacuum, E-shower and energy for ion implantation machinery. Along with the graphics is shown specific values such as rough time and pump time for ion implantation machinery and values for Cp and Cpk from SPC analysis. There is also an alarm indicator when the process is out of control, and an accounting for the number of alarms that have occurred over the time interval of data being shown in the charts and graphs.

The process parameter monitoring system can display historical data on the production control computer. This historical data can go back several weeks or months for each process parameter for each machine and is obtained from the data base contained within the production control computer. This display of historical data can be important in the analysis of problems leading to poor yield. When there is a particular problem with a process or associated machinery, a short interval monitor of the particular process can be initiated that accumulates three data points in one second; although, not limited to 1 second in duration. Thus providing a quick sampling of a process that may be producing a problem. When debugging a particular process on a particular machine, the monitoring of that machine can be stopped or started without affecting the monitoring of the other processes on other process machinery.

This invention will be described with reference to the accompanying drawings, wherein:

FIG. 1 is an overview of the process parameter monitoring system for real time SPC, and

FIGS. 2A and 2B are a diagram of the of the connections between the process equipment and the production control computer for data monitoring, and

FIG. 3 is the process flow for collecting parameter data and determining control limits, and

FIG. 4 is the procedure when a parameter is detected beyond a process control limit, and

FIG. 5 is the procedure for applying a short interval monitor for diagnostics.

In FIG. 1 is shown an overview of a process parameter monitoring system for use in real time SPC. A production control computer 10 is connected to wafer fabrication machinery 11 for the purpose of controlling the wafer fabrication machine 11 and collecting process parameter data for analysis and display on the monitor 16 of the production control computer 10. The production control computer 10 contains a data base 15 which is used to store wafer fabrication process parameter data. The wafer fabrication process data is used to compute parameters such as Cp and Cpk for SPC analysis as well as computing various process parameter trends. The monitor 16 of the production control computer 10 is used to display various data, including charts and graphs of the process parameter data, like vacuum, E-shower and energy for ion implantation, as well single data values including some from the SPC analysis, like Cp and Cpk.

Continuing to refer to FIG. 1, the production control computer 10 is connected to a data server 12. The data server provides access to the company wide network 13 from which the production control computer 10 has access to the production manufacturing information system (PROMIS) 14. The production control computer 10 can access various data from PROMIS 14 such as the recipe for a particular wafer fabrication process and characteristics of the different process equipment.

Referring to FIG. 2A and FIG. 2B, the production control computer 10 is connected to a RS485 network 21 through a network adapter 20. The RS 485 network 21 is further connected to network converters 22 and 23 that provide a flow of data to and from one or more wafer fabrication process machines 11. The RS 485 to digital converter 22 being used to connect control data to the wafer fabrication process machines 11. The analog to RS 485 converters 23 are used to connect process parameter data from the wafer fabrication machinery 11 to the process control computer 10 by means of the RS 485 network 21 and the RS 485 network adapter 20. Each RS 485 converter 22 and 23 and the 485 adapter 20 have an address, and under the control of the production control computer 10 are synchronized such that data flows to and from the appropriate adapters at the appropriate time. Process parameter data is delivered to the production control computer 10 by means of network adapter 20, network converter 23 and the RS 485 network 21 where each parameter for each process machine 11 is sampled in a time slice when the RS 485 network 21 is free of other communication. Control data is delivered to the wafer fabrication process machinery 11 from the production control computer 10 through adapter 20, RS 485 to digital converter, and the RS 485 network 21. During a trouble shooting phase the various converters 22 and 23 can be held off by the production control computer 10, and a "short interval monitor" can be applied to a problem process on one of the wafer fabrication machines 11. The "short interval monitor" consists of several data points being collected by the production control computer 10 during a short interval of time, such as one second.

In FIG. 3 is shown the process for collecting and storing process parameter data and computing the process control limits from the process parameter data. The production control computer 10 in FIG. 1 collects process parameter data for each batch 30 of wafers being processes by each wafer fabrication machine 11. The parameter data is stored into the data base 31. An average value 32 is computed for each parameter on a batch basis. The average value is stored in a historical data file 33 contained in the database 15 within the production control computer 10. The process control limits for the various processes on the various wafer fabrication machines 11 are then computed using the data in the historical data file 34. Wafer fabrication process parameters are then compared against the control limits 35 calculated from the historical database 34. Control limits can also be established for trends in the parameter data and compared to the trend over time in the parameter data from the historical data file 34.

Referring to FIG. 4, the process parameter data being collected by the production control computer is compared against a set of control limits 50 computed from the data in the historical data file 34 in FIG. 3. When the production control computer detects a parameter beyond a control limit 51, a signal 52 is sent to hold the particular wafer fabrication process machine. Then an alarm 53 is sent to the process operator and the process engineer. This alarm is in the form of an audible tone to alert each of the process failure. Upon being alerted, the operator and the engineer review 54 the wafer fabrication machine, the product and analyze the data to determine what steps are to be taken to handle the process failure.

In FIG. 5 a procedure for a short interval monitor of a failing process is shown. The parameter monitor of the failing process is closed 60. A short interval monitor is applied to the failing process 61 where several samples of the parameters of the failing process are taken over a short interval of time 62. A short interval of time being in the neighborhood of one second, but not limited to that length of time. After the short interval monitor has been completed, the regular monitoring of the failing process is resumed.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the invention.