Update to SEMI E33: Guide for Electromagnetic Compatibility
By Vladimir Kraz, OnFILTER, Inc.
SEMI E33-1012, Guide for Semiconductor Manufacturing Equipment Electromagnetic Compatibility (EMC) replaces its predecessor, SEMI E33-94, a SEMI Standard governing electromagnetic compliance for semiconductor manufacturing equipment. This equipment has common needs for electromagnetic compliance, just like any other equipment, plus some very specific needs outlined further in the text.
Basics of EMC
EMC stands for ElectroMagnetic Compatibility. All electronic equipment generates undesirable electrical noise — electromagnetic fields, called radiated emission; voltage and current in cables, wires, and metal structures, called conducted emission. In return, this electrical noise injects undesirable signals into equipment that may cause errors in operation, lockups, and even damage to sensitive components. Undesirable electrical noise, or electromagnetic emission, is regulated by various government regulations. These regulations are in place to make sure that operation of one piece of equipment does not negatively influence other equipment — in essence, to make sure that different devices are "good neighbors." In the U.S., EMC compliance is governed by FCC Title 47 part 15; in Europe by the European EMC Directive. Other countries have similar requirements. Arguably, the most comprehensive is the European EMC Directive that is the basis of the SEMI E33 Standard. The European EMC Directive governs both noise emission and immunity to noise.
It is very seldom that electrical equipment becomes EMC-compliant by accident. The more complex the equipment, the more work goes into lowering its electromagnetic emission and into its EMC-hardening to make equipment more immune to noise. This complexity adds both to development and to product cost, as well as to delivery time; therefore a balance needs to be achieved to have reasonable EMC performance and low cost. EMC regulations provide the benchmark for minimum acceptable compliance, and the customers of EMC-compliant products know what the maximum emission levels they should expect are and what levels of emission these products can tolerate without any problems.
What's New in SEMI E33-1012?
SEMI E33-1012 introduces a number of changes from its predecessor, SEMI E33-94. First, SEMI E33-94 was a "Specification," that is, a regulatory document. SEMI E33-1012 is a "Guide." It provides recommendations on EMC compliance, not mandatory requirements. This change is due to evolving complexity of electromagnetic regulations and equipment itself. Compliance with governmental EMC regulations is not superseded nor negated; it is still in force.
The cornerstone of SEMI E33-1012 is compliance with the European EMC Directive. The Standard augments this directive with specific requirements for semiconductor manufacturing environment where applicable.
SEMI E33-1012 adds several sections that were not present in SEMI E33-94, such as Electromagnetic Interference (EMI) Audit, Near and Far Fields, Transient Signals, and Facility Infrastructure. These sections reflect the increasing importance of electromagnetic interference in the semiconductor manufacturing environment due to higher sensitivity of equipment, smaller geometry of the devices, and more complex equipment and processes.
Specifics of Semiconductor Manufacturing Equipment
In addition to general EMC requirements that are applicable to all equipment, semiconductor manufacturing has some unique properties. SEMI E33-1012 addresses some of them such as:
ELF (Extra Low Frequency) Magnetic Fields
In presence of a magnetic field of very low frequency, electron microscopes (e.g., scanning electron microscope [SEM]) produce "wavy" images heavily distorting features of miniature structures making it difficult if not impossible to analyze devices with small geometry. Such magnetic fields are generated by power lines and transformers nearby and even by moving metal objects, such as elevators and the like. SEMI E33-1012 augments and updates recommended ELF values for different levels guided by geometry. It also provides recommendations on their measurements. These recommendations are applicable only to the areas where electron microscopes are installed.
Complexities of Equipment Installation and Maintenance
Semiconductor equipment requires proper installation and maintenance. Often, an installation includes equipment from different manufacturers assembled or connected together at the end-user's location. Several parties may be involved in this process, including the equipment manufacturer or manufacturers, subcontractors, independent installers, and the user. This presents challenges of whose responsibility it is to assure electromagnetic performance of the entire installation. SEMI E33-1012 provides recommendations on assigning responsibilities for this performance as shown in the Table below:
|Semiconductor manufacturing equipment itself||Supplier (semiconductor manufacturing equipment manufacturer)|
|Semiconductor manufacturing equipment in combination with other equipment if supplied (i.e., integrated) by one supplier||Supplier (semiconductor manufacturing equipment integrator)|
|Semiconductor manufacturing equipment in combination with other equipment if integrated by the user||User|
|Facility-level electromagnetic environment||User|
|Semiconductor manufacturing equipment installation-related compliance and EMI-performance||Party responsible for installation|
|Semiconductor manufacturing equipment collocation||User|
|Semiconductor manufacturing equipment after repair or maintenance||Party responsible for repair or maintenance|
|Post-sale additions or modifications made by the supplier that affect ||Supplier (semiconductor manufacturing equipment manufacturer or integrator)|
|Post-sale additions or modifications made by the user that affect ||User|
This table clearly lays out the responsibilities and greatly simplifies the relationship between different parties involved in installing and servicing equipment, as well as provides guidance on mitigation of EMC-related problems at the factory level.
EMI (Electromagnetic Interference) Audit
There are several significant challenges specific to the semiconductor manufacturing area, among them equipment installation, equipment colocation, power line and grounding schemes, and the possibility that equipment maintenance may alter electromagnetic performance of the equipment (e.g., leaving the covers open, forgetting to reconnect ground properly). In order to help with maintaining good EMC performance and to reduce EMI in the semiconductor manufacturing area, SEMI E33-1012 includes a separate section on EMI Audit — in essence, measurement of critical electromagnetic parameters in locations in the semiconductor manufacturing area where electromagnetic performance is of importance. Several recommended parameters, measurements, and observations are listed:
- Radiated EMI levels near semiconductor manufacturing equipment—both continuous and transient (peak).
- Conducted EMI on cables—both continuous and transient (peak). Note that it may be difficult to devise an acceptable method to measure conducted EMI on hard-to-reach cables.
- EMI levels on the ground of semiconductor manufacturing equipment.
- Proper fastening of all connectors.
- Closed equipment covers with good electrical connection.
- Unnecessarily long (i.e., beyond effective service loops) or coiled ground and other wires and cables.
Addressing all of these issues helps to maintain low levels of EMI in the semiconductor manufacturing area.
The Next Step
The SEMI E33-1012 Standard guides electromagnetic compliance of the equipment. However, what is most important for the users of this equipment is the electromagnetic environment in the semiconductor manufacturing areas. Equipment by itself is only one component of a complex electromagnetic environment in the semiconductor manufacturing areas. Power and ground routing, equipment colocation, and many other factors add to overall electromagnetic "universe" on the production floor. To address these issues, the SEMI Standards Metrics Global Technical Committee approved creation of a new Standard providing guidance and criteria for electromagnetic environment in the semiconductor manufacturing area. The EMC Task Force is looking for active participants specifically among the companies that manufacture semiconductors, not just semiconductor manufacturing equipment. If you are interested in participating, please contact the author at firstname.lastname@example.org or SEMI at email@example.com.
SEMI E33-1012 is an important update of the EMC Standard governing electromagnetic compliance of semiconductor manufacturing equipment, addressing issues that affect semiconductor manufacturers as technology advances. I encourage all readers to learn more about EMI, EMC, and electromagnetic compliance. SEMI is a good platform to do so and participation in Standards development activities makes you a valuable contributor to your company as well as to the semiconductor industry.
October 1, 2013