Working Together: E-Diagnostics, SECS/GEM, EFEMs

Jack Ghiselli GW Associates/Asyst Technologies Sunnyvale, Calif. -- Semiconductor International, 7/1/2001

At a Glance
E-diagnostics seeks to add a new communications link to each unit of equipment in the 300 mm semiconductor factory. But equipment already has communication links. What is the proper relationship between e-diagnostics and existing communication?

Ideally, e-diagnostics would give us convenient, Internet-friendly access to information we need to diagnose equipment problems. It's useful to separately consider the two aspects of e-diagnostics: 1) collecting the interesting diagnostic data, and 2) accessing the data conveniently. Both are important. A huge store of diagnostic data is not very interesting if you can't access it when you need it. Convenient access without pertinent data is also not very interesting.

For some 20 years, factory equipment has been providing SECS (SEMI equipment communication standards) communication links. A wide range of factory-side software systems has been developed and deployed to use these equipment SECS links to collect and analyze data and control equipment. In the past 10 years, these links have been enhanced to meet the SEMI GEM standard (E30), and in the last three years equipment suppliers have been working to enhance the links further to meet the additional 300 mm standards E39, E40, E87, E90 and E94, required by all 300 mm fabs. All these standards have been developed at the request of IC manufacturers to meet real factory automation requirements.

All production 300 mm fabs are being designed with automated material handling systems (AMHS), which deliver wafer carriers directly to the production equipment. Most 300 mm production, process and metrology equipment is designed with an equipment front-end module (EFEM), which provides standard mechanical load ports to load and unload wafer carriers directly to AMHS transport systems. The EFEM also provides SEMI E84 parallel I/O communication links to the AMHS, used to synchronize the loading and unloading of wafer carriers. Eventually, the 300 mm fab can operate "lights out" with no human operators. The factory monitors and controls each unit of equipment via its SECS/GEM and E84 interfaces, which must be fully functional, highly reliable and time deterministic.

For the SECS link, equipment already provides all the important processing information, real-time status and fault information. The various state models required by GEM and the 300 mm standards also provide detailed visibility into important sequences, like showing that the equipment is warming up preparatory to processing wafers. Some SECS links provide equipment reliability and utilization information using SEMI E58 (ARAMS) and E79 (Equipment Productivity Tracking).

The EFEM on the equipment already provides useful logistics information that shows which carrier is loaded, which wafers are being processed, status of physical loads and unloads, and behavior of the equipment/AMHS links.

Accessing information

Communications challenges in the 300 mm fab are magnified by the need of e-diagnostics to detect problems throughout the system. There are a number of possible reasons why automated processing fails to begin. It might be the result of an equipment alarm, or simply that equipment warm-up is taking unusually long. This type of information is available from the SECS/GEM link. The cause might, however, be that the factory host computer has failed to send the required "Proceed With Carrier" SECS message, information available from the SECS Link State Model sequence. The cause might also be that the equipment is waiting for an E84 handshaking signal from the AMHS, or the wrong wafers are loaded, or a wafer is cross-slotted — information available from the EFEM. It's clear that a successful e-diagnostic system will need access to this existing information.

1. 150 and 200 mm factories used a "multi-wire" approach, but 300 mm fabs will use "single-wire."

The first sealed-pod SMIF systems were introduced as "add-on" systems. As shown in Figure 1a, these used a "multi-wire" approach. The main equipment provided the SECS link to the factory cell controller, but the EFEM load port and carrier ID reader also had independent communication links to the cell controller. The cell controller needed to make sense of data from these multiple links or "wires." 300 mm fabs insisted on the "single-wire" approach (Fig. 1b). The equipment is responsible for integrating information from the load ports and carrier ID readers into other equipment data and sends integrated data via the "single-wire" SECS link. Because the equipment synchronizes all data on the single SECS/GEM link, the job of the cell controller is much simpler.

International SEMATECH's e-diagnostics guidebook describes two alternative approaches to e-diagnostics. The one-wire approach, as shown in Figure 2a, uses the SECS/GEM link to connect the equipment to the factory cell controller or MES system, and e-diagnostics connects to that factory computer. The two-wire approach (Fig. 2b) provides an e-diagnostics communications link directly on the equipment. The one-wire approach requires no changes to the various equipment controllers, so perhaps it could be implemented more quickly. However, the two-wire approach gives e-diagnostics the desirable direct connection to the equipment operator interface and equipment data. Whichever method is used, the data that equipment suppliers have worked hard to make available via the SECS/GEM link must also be accessible via e-diagnostics.

E-diagnostic challenges

2. The one-wire approach uses the SECS/GEM link to connect the equipment to the factory cell controller or MES system, and e-diagnostics connects to that factory computer (left). The two-wire approach provides an e-diagnostics communications link directly on the equipment (right).

Some people have argued that "e-diagnostics" requires an entirely new protocol. While a new Internet-friendly protocol may indeed be useful, IC fabs point out that they've been asking for diagnostic information via SECS/GEM for years and received limited response from the equipment suppliers. They are skeptical that simply adding a new communication protocol will somehow magically make this needed information available, and some fabs even worry that equipment suppliers may hide behind e-diagnostics technology as a new excuse to delay delivery.

300 mm fabs have been very clear in requiring that equipment must continue to provide SECS/GEM, even if it also provides e-diagnostics. Equipment suppliers have made a large investment in providing SECS/GEM and 300 mm standards, and this work continues to meet IC fab requirements. The wise equipment supplier will make a robust SECS/GEM interface, fully compliant to all standards, rich in data, and able to provide flexible access and control. As e-diagnostics capabilities become more clearly defined, the equipment supplier will make the data, plus the operator interface, also available via the e-diagnostics link. Different automation methods and protocols are clearly interrelated and must work together smoothly.

Jack Ghiselli is president of GW Associates Inc., a supplier of SECS and GEM software products and services, and has 30 years' experience in software design and development. He has been active in SEMI standards since 1979, and serves as vice chairman for the SEMI North America Information and Control Committee, which is responsible for SECS and related standards.

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