Semiconductor Back End Processes: Adopting GEM Judiciously

Equipment Communication Leadership in Wafer Fabrication For many years the semiconductor industry’s wafer fabrication facilities, where semiconductor devices are manufactured on [principally] silicon substrates, have universally embraced and mandated the GEM standard on nearly 100% of the production equipment. This includes the complete spectrum of front-end-of-line (FEOL – device formation) and back-end-of-line (BEOL – device interconnect) processes and supporting equipment. Most equipment also implements an additional set of SEMI standards, often called the “GEM 300” communication standards because their creation and adoption coincided with the first 300mm wafer manufacturing. Interestingly, there are no features in these standards specific to a particular wafer size.

Specifically, the GEM 300 standards are used to manage the following crucial steps in the overall fabrication process:
• automated carrier delivery and removal at the equipment
• ​load port tracking and configuration
• carrier ID and carrier content (slot map) verification
• job execution where a recipe is assigned to specific material
• ​remote control to start jobs and respond to crisis situations (e.g., pause, stop or abort processing)
• material destination assignment after processing
• precise material location tracking and status monitoring within the equipment
• processing steps status reporting
• overall equipment effectiveness (OEE) monitoring

Additionally, the GEM standard enables
• the collection of unique equipment data to feed numerous data analysis applications such as statistical process control
• equipment-specific remote control
• ​alarm reporting for fault detection
• interaction with an equipment operator/technician via on-screen text
• preservation of valuable data during a communication failure

Semiconductor Back End Process Industry Follows the Lead

After wafer processing is completed, the wafers are shipped to a semiconductor back end manufacturing facility for packaging, assembly, and test. Historically this industry segment has used GEM and GEM 300 sporadically but not universally. This is now changing.

In North America, SEMI created a new task force called “Advanced Back end Factory Integration” (ABFI) to organize and facilitate this industry segment’s implementation of more robust automation capabilities. To this end, the task force is charged with defining GEM and GEM 300 support in back end equipment, including processes such as bumping, wafer test, singulation, die-attach, wire bonding, packaging, marking, final test and final assembly. As its first priority, the task force has focused on updating the SEMI E142 standard (Substrate Mapping) to enhance wafer maps to report additional data necessary for single device traceability. Soon the task force will shift its focus to define GEM and GEM 300 back end use cases and adoption more clearly.

Why GEM?

It was selected for several reasons.
• A lot of the equipment in the industry already have the interfaces.
• ​It provides two primary forms of data collection that are suitable for all data collection applications. This includes the polling of equipment and process status information using trace reports where the factory can collect selected variables at any frequency. Additionally, collection event reports allow a factory system to subscribe to notifications of just the collection events it is interested in, and to specify what data to report with each of those collection events.
• Most of the equipment suppliers have GEM experience either from implementing it on the back end equipment or from implementing it on their frontend equipment.
• Factories can transfer experienced engineers from semiconductor frontend facilities into the back end with the specific goal of increasing back end automation.
• GEM has proven its flexibility to support any type of manufacturing equipment. GEM can be implemented on any and all equipment types to support remote monitoring and control.
• GEM is a highly efficient protocol, publishing only the data that is subscribed to in a binary format that minimizes computing and network resources.
• GEM is self-describing. It takes very little time to connect to an equipment’s GEM interface and collect useful data.
• GEM can be used to control the equipment, even when there are special features that must be supported. For example, it is straightforward to provide custom GEM remote commands to allow the factory to determine when periodic calibrations and cleaning should be performed to keep equipment running optimally.

Improved Overall Equipment Effectiveness Tracking

The ABFI task force has already proposed some changes to the SEMI E116 standard (Specification for Equipment Performance Tracking, or EPT). EPT is one of several standards that can be implemented on a GEM interface to provide additional standardized performance monitoring behavior beyond the GEM message set. This standard already enables reporting when equipment and modules within the equipment are IDLE, BUSY, and BLOCKED. A module might be a load port, robot, conveyor, or process chamber. When BUSY, this standard requires reporting what the equipment or module is doing. When BLOCKED, this standard requires reporting why the equipment or module is BLOCKED.

After analyzing the requirements of the back end industry segment, the task force decided to adopt and enhance the EPT standard. For example, the current EPT standard does not make any distinction between scheduled and unscheduled downtime. However, a few minor changes to E116 would allow the factory to notify the equipment when downtime is scheduled by the factory, greatly enhancing the factory’s ability to track overall equipment effectiveness and respond accordingly.

Additional Future Work

Many of the GEM 300 standards can be applied to some of the back end equipment when applicable and beneficial. The task force is defining specific functional requirements and evaluation criteria to make these determinations and publish the resulting recommendations in a new standard. Representatives from several advanced back end factories are already closely involved in this work, but more participation is always welcome.