Success using e-Diagnostics at LSI Logic
09/01/2003
Overview
e-Diagnostics has been highly touted, but slow to start in semiconductor manufacturing. Only now are we seeing concrete examples of its power. Here is a strong example of how the ability to electronically look at production processing, right into process chambers, helps to quickly solve and even prevent problems, and dramatically improve supplier-to-user communications.
LSI Logic and INFICON have worked together to develop and integrate e-Diagnostics capabilities over six-to-nine months at the LSI Logic facility in Gresham, OR. The installation includes INFICON FabGuard PCs at individual Applied Materials 200mm Endura PVD-CVD tools. These FabGuard real-time analysis systems are connected to:
- each tool through the Endura's secondary SECS port to monitor process-critical status variable IDs (SVIDs), such as process start triggers, DC power, and gas flow rates;
- scanning laser particle counters through an Ethernet connection;
- residual gas analyzers (RGAs) on individual chambers; and
- the fab-wide network.
Through the fab network, each PC connects to an SQL server database and an executive program. The latter handles data transfer, data backup, e-mail and instant messaging services, scheduled reports that are delivered electronically, and communication with the web server (Fig. 1).
The web server is a key component that allows the use of Microsoft Internet Explorer to mimic most of the functions of working at the FabGuard PC next to the tool. This includes the ability to view real-time data from each sensor, check alarms, load database reports, load multiple runs for viewing, and start or stop acquisition. This web-based functionality permits process engineers, from any desktop, to look at their tool's real-time and historical data.
All of these functions are not limited to inside the fab. Using a virtual private network (VPN), LSI Logic engineers, INFICON applications engineers, and other technical experts can log onto the manufacturing network and assist with problems that may occur, answer questions the customer may have, and create customer reports. The VPN also allows INFICON engineers to install routine feature upgrades and bug fixes as soon as they become available, thus providing a high level of customer service.
A new program from LSI Logic made this VPN connection possible. Sponsored by LSI Logic Corp.'s Global Network Services, the request for non-LSI employee access allows vendor-partners, such as INFICON, the opportunity to justify remote access and sign confidentiality agreements. Once completed, an account is set up and Cisco Systems VPN client software is distributed for installation. Upon launch of the VPN client, a secure tunnel is made through the Internet that allows users' PCs to be remotely connected to the LSI Logic network.
A new level of data and control
Armed with SVIDs, RGA readings, particle counts, and statistical process control (SPC), LSI Logic engineers can actively control fab tools by way of alarms and shutdown limits. Process critical SVIDs have been determined by process engineers for each chamber, and are checked weekly through automatically generated SPC reports.
SVIDs were chosen for redundant monitoring where possible, to reduce dependence on tool gauge accuracy or inadvertent system constant changes. For example, on a PVD chamber, monitoring both the forward power signal from the power supply and the DC bias on the target will avoid missed deposition-rate changes due to a drifting power supply. In addition, target bias monitoring can detect changes in pressure. By coupling these measurements with captured signals from a pressure gauge and MFCs, all gauges are independently kept in check and the root cause of out-of-control signals can be quickly determined.
At LSI Logic, RGAs monitor chambers in real time and are continuously looking for changes in chamber and gas integrity. They are also being used to detect photoresist, look for changes in low-k film quality on incoming wafers, and for monitoring chamber out-gassing levels after any preventative maintenance shutdown. We have also used RGA analysis to confirm the results of SVID monitored parameters.
 Figure 1. e-Diagnostics installation at LSI Logic. |
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To facilitate automated data analysis and control, mathematical algorithms and Boolean logic evaluate SVID and RGA data and check for measured parameters between high and low limits after a certain trigger point. A trigger point is a step in a recipe or change in signal, such as a throttle valve moving to process position. For related SVID signals that signify gauge drifts and for complex RGA analysis, parameter sets have been created that are the results of mathematical manipulation of individual signals. The manipulations may be ratios or weighted sums, depending on the physical interpretation of the data being evaluated. The algorithms also check for data persistence to avoid problems with false alarms due to mis-polled data or polling latency.
We have recently completed an evaluation of a scanning-laser particle detector on sputter preclean chambers. The evaluation demonstrated a close correlation to defect scans and to end-of-line yield analyses. As a result, LSI Logic is now using a particle detector with FabGuard's real-time analysis to give approval for manufacturing specialists to run the chamber based on "M out of N" runs above total particle counts or "L out of N" runs above sized particle counts (i.e., estimated particle size). These reports and alarms are necessary to make this integration possible and are distributed to involved engineers by e-mail and connectivity that was brought about by the e-Diagnostics capability.
Particle count data are also being used to determine when enough conditioning wafers have been run after preventive maintenance on a chamber or after an idle period, and to determine process chamber kit life. For particle excursions, which are detected mid-life of the process kit, SVID and RGA data have proven useful in determining the root cause (Fig. 2).
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e-Diagnostics advantages
One of the main advantages from our experiences with this e-Diagnostics setup is that it allows alarms to equipment users and suppliers. The computers that are involved in the installation are equipped with their own instant messaging capabilities as well as their own simple mail transfer protocol (SMTP) server. This allows real-time fault monitors to send information to fab engineers, such as daily reports or errors via instant messaging (IM) and e-mail as well as sending e-mail to application engineers if there are hardware, software, or communication issues with systems.
In addition, suppliers are able to respond faster to tool and sensor issues. With VPN technology, engineers responsible for fab equipment installations are able to respond no matter where they are located. Each can utilize VPN client software built into Windows to log in and view his or her own installation. This way, the person who knows the most about a given application and setting is the one who diagnoses problems. The time saved by not having to share and transfer specific details is invaluable, not to mention the money saved on airfare and travel time.
An extension to providing a higher-quality product is its ability to perform remote software updates. By using remote VPN, equipment supplier engineers can remotely perform software updates that include both new features requested by users as well as bug fixes, without requiring an applications engineer to enter the fab or asking a user to perform the task.
The VPN also allows vendor software modifications such as remote FabGuard recipe and analysis changes. Real-time and run-to-run FabGuard analysis recipes are an evolving process during the course of an installation and the maturing of a process tool. e-Diagnostics allows for collaboration between users and suppliers' applications engineers onsite, but also for the assistance of off-site specialists who can help fine-tune an installation. Modifications to these important parameters can take place during an installation; process engineers may request assistance and advice for tighter tolerances on certain parameters that can then be fulfilled remotely using the same VPN connections.
e-Diagnostics can also help a supplier offer the service of its expertise to a user. Whether for requested assistance or for paid consulting, a remote link allows work to begin immediately when a problem needs resolving. The same remote help that can be offered to a customer by a supplier's technical experts can also be given to onsite supplier engineers. For example, recently an INFICON onsite engineer experienced a problem beyond his experience. Using the remote VPN connection, an applications engineer, elsewhere, was able to diagnose and repair the problem by taking over control of the FabGuard PC while teaching the onsite engineer at the same time.
An extension of this is how the e-Diagnostics link allows suppliers to acquire real-time data to provide technical reports that can assist users in improving overall efficiency. This also helps a supplier show a higher value in its products without increasing costs. A simple example of this is when a tool or process has a problem. The real-time analysis engine that INFICON and LSI Logic engineers have worked to fine-tune will notice an anomaly and alert equipment and process engineers as well as supplier engineers who are responsible for the project. By way of this remote link, INFICON can be aware of the problem and offer assistance. Together, they can use their process and tool expertise to diagnose and remedy the problem.
One such instance where this took place was soon after LSI Logic implemented an integrated liner barrier process. One of the tools began experiencing frequent cryo-pump crashes in the transfer chamber that resulted in significant reduction in tool availability. Upon implementing e-Diagnostics, it was soon noticed that small amounts of helium were entering the transfer chamber. The additional analysis of SVID data showed that helium was escaping from one of the CVD TiN chambers when the slit valve opened after processing was completed. Cryopumps' low tolerance for helium can cause their efficiency to decrease quickly. This information was relayed to LSI Logic's process and equipment engineers, who were able to make corrections and improve tool availability.
Finally, as a welcomed consequence, we have found that e-Diagnostics provides an added communications channel that allows both the IC manufacturer and e-Diagnostics supplier to work closer together and develop a better business relationship. This leads to higher sales for the supplier, and user assistance creates a better e-Diagnostic product through experienced suggestions.
Implementation challenges
A big challenge of an e-Diagnostics installation compared to a standard sensor or tool installation is the added complexity necessary to enable components, such as network access, data storage, host or manufacturing execution system (MES) connectivity, e-mail capability, and remote access. Another problematic requirement of an e-Diagnostics connection is the use of remote VPN access. This is undoubtedly the most difficult aspect, not in terms of complexity, but more in terms of a manufacturer's policies.
VPNs have been around for a long time and offer a highly encrypted connection between points through the Internet. The hardware requirements typically consist of an Internet connection through a router designed to accept private connections and perform the encryption necessary to make it safe. The difficulty with using a VPN is in changing corporate policy to allow outsiders to access the fab network and to set up the infrastructure to maintain accounts and the proper confidentiality agreements.
LSI Logic dissolved this barrier to entry by developing corporate policies that allow the company to better take advantage of the expertise that suppliers, such as INFICON, can offer on a daily basis.
Wide acceptance of e-Diagnostics and the integration and connectivity that is required for it is going to necessitate an improved ability to prove that mathematical models and data-monitoring algorithms are capable of detecting a greater range of anomalies, such as instability, changed ramp rates (up or down), and overshoot in brief process recipe steps or intermediate steps. Many of the difficulties do not lie within the software itself, but in how the data is acquired from equipment. Modern real-time analysis software is capable of detecting most types of problems through specialized analysis techniques, but many manufacturing tools do not have the ability to send data often enough for proper monitoring. In many cases there are also significant problems with polling-latency (i.e., data not being sent when it is requested) under high-traffic situations.
Problems such as these prevent more aggressive control and analysis, and need to be improved in future-generation tools and in minimal-cost hardware upgrades for current tools. New techniques are enabling "intelligent" sharing of data from one source to multiple recipients to maximize communication efficiencies.
Overall, e-Diagnostics requires a higher level of trust between equipment users and suppliers. This is something that can sometimes be difficult in the highly competitive realm of semiconductors where everyone is looking for his own advantages. By developing this trust, LSI Logic and INFICON have gone from being a customer and a vendor to business partners.
For the future
The future of e-Diagnostics lies with its role within e-Manufacturing, a concept dependent upon its "ability to seamlessly integrate all of the hardware and software components from various suppliers in the supply chain" [1]. What e-Diagnostics needs to offer is the connectivity of mission-critical process equipment controllers and real-time fault monitors with field experts who may be needed to maintain uptime and diagnosis of process anomalies.
This offering involves external connectivity through a leased line or VPN and also the means for storing, reporting, and displaying data. Web-based graphical user interfaces developed for e-Diagnostics can then be adapted within a fab by process engineers. Also, the experience gained by working closely with manufacturing for process control allows for knowledgeable data exchange with fab-wide SPC systems, process metrology, and yield management. Systems integration is a much-sought feature of semiconductor manufacturing with e-Diagnostics being a large piece of the map to get us there.
Zach Prather, LSI Logic Corp., Gresham, Oregon
Nathan Graff, INFICON Inc., Watertown, Massachusetts
Reference
- B. Shade, http://www.e-insite.net/semiconductor/index.asp?layout=article&articleId=CA224703l.
Zach Prather is a thin films process engineer at LSI Logic Corp., 23400 N.E. Glisan St., M/S R-220, Gresham, OR 97030-8411; ph 503/618-4222, fax 503/618-0308, e-mail [email protected].
Nathan Graff is a semiconductor applications engineer at INFICON Inc.