Connectivity is driving toward smart front-end modules

12/01/2001

Fab managers need to worry less about wafer automation or tool-to-factory integration, and concentrate more on manufacturing, scheduling, line balance, and order fulfillment. Some solutions lie in better connectivity via an effective equipment front-end module (EFEM), which could help solve mechanical, electrical, and software interface problems that have continually led to fab slowdowns and work stoppages.

Can this needed connectivity and the integration of tools and software be designed to answer many of these industry-wide challenges? Recent industry advances suggest that a more intelligent EFEM may not be far off. The industry is also beginning to recognize the need to include integrated metrology requirements into the EFEM. This is in the form of Semi's recently introduced draft document No. 3398 titled "Provisional Specification for Integrated Metrology on 300mm Equipment Front-End Modules."

A big problem is automated front-end connectivity. Future tool-to-EFEM interfaces must include a "single wire" communications link whereby all communications about wafer movement (i.e., motion in the EFEM, front opening unified pod [FOUP] ID, wafer ID, lot ID, etc.) are passed seamlessly to the tool or directly to the factory manufacturing execution system by the EFEM. The module should also be able to communicate to overhead transport or automated guided vehicles. Envision a fully connectable interface — an EFEM that will talk to everything, knowing the exact status of all wafers, tools, and processes.

So far, suppliers have not yet provided that level of omniscience. Currently, the process designed for connectivity within the EFEM is inefficient. Traditionally, end users (i.e., fab customers) and consequently tool suppliers (OEMs) drive specifications that lead to the design and development of hardware and software subsystems and automation components. These are then shipped to OEMs for integration into a process or metrology tool's automated front-end. The OEM then installs the tool and completes integration into the fab. Factory integration and testing is then conducted by a combination of OEM, fab, and factory automation system personnel.

Today's EFEMs must provide a complete solution for automated handling and information collection for 200mm and 300mm wafers. EFEM components include, but may not be limited to, a wafer handling robot, a linear track, a pre-aligner, an enclosure with a filter, interface software, carrier and wafer ID subsystems, and a FOUP opener. Hardware within EFEMs is being built to minimize cost of ownership, and to reduce wafer swap times and manufacturing lead times. The hardware also needs to be ready for current and future 300mm application integration, while being backward-compatible with current robotic systems.

The products being developed by major manufacturers are designed to meet not only Semi specifications and fab guidelines, but also future functionality needs (i.e., connectivity and interoperability). Ideally, they are designed using a common architecture for products across hardware and software to allow for volume cost savings.

As alluded to above, added intelligence (driven by advances in connectivity and communications) is needed to take the EFEM to the next generation. The introduction of a single board controller will provide this level of intelligence and the necessary step toward a next-generation EFEM.

Without intelligence, there will be no way for an EFEM to communicate both material status and potential problems to the rest of the fab's operations. For example,

• Performing alignment on-the-fly. Alignment on-the-fly would improve throughput and reduce particle contamination in the area surrounding and under the pre-aligner. One way in which notch or flat alignment could be performed on-the-fly would be to use a rotary, moving chuck with a camera. This would eliminate the need for a separate pre-aligner — saving maintenance and replacement costs.
  
  
• Performing calibration on-the-fly. On-the-fly calibration would address additional, peripheral tasks required of the EFEM in controlling the minienvironment with closed-loop monitoring and fan filter unit control, robotics calibration and external system monitoring, and diagnostics.
  
  
• Identifying wafers. Once the door to the FOUP is open, it is necessary to locate each wafer in its slot within the FOUP and detect any cross-slotted and double-slotted wafers. Today, this can be accomplished with sensors mounted either on the loadport door or robot arm, yet a more efficient means would be through enhanced machine vision.

Intelligence could also lead to a system that re-teaches itself when a part is replaced, or enables a user to discover and fix faults even over Internet connections.

The next-generation EFEM needs improved communications throughout all tool controls — from system, software, and loadport, to minienvironment controls. EFEM-to-tool communications software needs to provide links between the EFEM, the tool, and the host computer. At this position, the FOUP and lot ID and processing information should travel between the electronic traveler (i.e., "tag") and the process tool. It may also pass information between the tool and the host computer.

Wafer data-tracking software interfaces with robotics motion-control software by reading the wafer ID information and matching it with wafer processing information to load the correct wafer into the tool for processing. The output data from these operations should then be captured and passed to the host through EFEM process tool communication software. This software package is the glue that holds the entire materials handling process together, orchestrating all communications necessary to successfully move information between the EFEM, the tool, and the host system. Tool automation suppliers are just now beginning to recognize this need and provide software packages to OEM tool suppliers that address some of these connectivity requirements.

The ideal system should also support ISO Class 1 technology and beyond with full coverage filtration. Having laminar flow throughout the minienvironment would eliminate recirculation zones to better meet SIA wafer front and backside particles-per-wafer-pass requirements.

Next-generation EFEMs will also have reduced equipment footprint compared to current linear track EFEM designs. Also, with its flow-through design configuration, mean time to repair should be reduced.

The architecture of the system electronics needs to be open to allow for integration of any OEM's single board controller,

interface hardware, and firmware. Its design needs to include a standard card cage and I/O, while being easily configured and expanded. For ultimate flexibility, these electronics must support any OEM-supplied automation controller. The electronics should provide loadport control and, finally, the E84 interface — the Semi standard that defines the communications protocol associated with material handling operations.

The EFEM is an integral part of the overall wafer handling manufacturing process. Although current processes and equipment are performing in pace with today's standards, fabs continue to look for an edge in productivity, efficiency, and cost savings for 300mm and beyond.

By enhancing the connectivity and intelligence of EFEM hardware, software, and its operations, fab managers will be able to solve potential problems before they occur, avoid downtime, and get operations back up to speed in the shortest time possible.

Peter Gise is marketing manager at Nanometrics Inc., 1550 Buckeye Drive, Milpitas, CA 95035-7418; ph 408/436-9600, e-mail [email protected].