SEMI S2-93: The Semiconductor Industry's Global Approach to Safety

By James F. Wright

Global Semiconductor Safety Services (Menlo Park, CA)

Much has been written about the compliance issues that manufacturers of semiconductor manufacturing equipment are facing. In fact, the same issues are faced by virtually all manufacturers regardless of the type of product they make. Each manufacturer must develop and manufacture the best product it can. Next, it must find buyers for that product. And then, finally, often near the end of the design/manufacturing cycle, the buyer's internal or local regulatory compliance needs must be met.

This cycle tends to result in a constant stream of reevaluation, reengineering, and modification as the product is forced to meet each different set of compliance criteria during that last, crucial phase. This situation is all too familiar to manufacturers of semiconductor processing equipment, which have been dealing with this challenge within their own industry for years. Until recently, they also had to endure, as well, the financial and engineering burdens of catering to each end-user's internal safety expectations and requirements.

Fortunately for these manufacturers, some forward-thinking industry professionals decided that there was too much waste in the "business-as-usual" system and that it was time for a change. The cost of retrofit and of the delays in the shipment of equipment while it was brought into compliance was also taking its toll.

In 1985, Semiconductor Equipment and Materials International (SEMI), a group of industry representatives, put forward a plan for developing their own performance-based industry standard for the safety of semiconductor manufacturing process equipment. The group was concerned that if the industry did not take action to develop its own standard, outside agencies would impose other requirements and thus expand the wasteful cycle even more.

From 1985 to 1988, a SEMI task force worked on developing such a document. Its efforts were focused on delivering a standard that would cover all facets of process equipment, while providing equipment manufacturers with relief from the myriad of hoops through which they were then forced to jump. Many of these requirements had no inherent safety benefit, but merely led to a duplication of effort and a high financial burden on both the manufacturer and the end-user. With a consensus standard, manufacturers could instead concentrate their efforts on a single design specification and undergo a single evaluation that every end-user would accept.

In 1988, SEMI distributed a draft proposal to members of the industry for comment. The document, a collection of requirements aimed at increasing the safety, quality, and reliability of process tools, continued to be modified based on industry comments until its eventual publication in 1991 as SEMI S2-91, "Safety Guidelines for Semiconductor Manufacturing Equipment."

Whereas it had taken SEMI six years to develop and adopt SEMI S2-91, it took the task force less than a year to realize that its work was not done. Inadequacies were identified by those using and requiring SEMI S2-91, and modifications were proposed. Work was begun in 1992 on the rewriting and correction of those areas in which change was needed. SEMI S2-93 was born and published a year later.

SEMI S2-93

Currently in revision, SEMI S2-93 is a performance-based environmental, health, and safety guideline incorporating requirements aimed at improving safety, enhancing reliability, and reducing waste—everything its authors intended.

For all of its ambitious scope, SEMI S2-93 takes only 11 pages to detail the 20 sections that make up the entire document. Its brevity is due largely to its liberal use of reference documents and standards, which makes SEMI S2-93 a sort of a shell standard that draws its strength from the best industry standards. Those standards considered to be the best on their topics—NFPA, UL, and ANSI for electrical and mechanical safety; UFC for fire safety; FDA-CDRH, NIOSH, SEMI, and 29 CFR 1910 for health and occupational safety—are all used.

In leaving it up to the individual assessor to choose the best document, depending on the concern, this approach allows for changes in technology, while at the same time covering a broad range of product types. Additionally, because the various reference documents are constantly being amended and updated to ensure that they keep pace with technology, SEMI S2 can continue to be effective with a minimal need for revision.

Scope

The 20 sections of SEMI S2-93 address the following concerns:

Philosophy

If there is one basic philosophy behind the SEMI S2-93 document, it is that safety measures should be incorporated into equipment from the start, not added as an option or a retrofit after it is designed or manufactured. Optimally, all potential hazards should be identified early in the design stage, when most problems can still be easily and cost-effectively corrected or eliminated (modifications implemented later, after manufacture, often tend to hinder performance as well).

Whenever possible, efforts should be made in the design stage to utilize technology and materials that are inherently less hazardous. If equipment hazards cannot be designed out, steps must be taken to design safeguards into the equipment to ensure that no single failure mode or operator error can effect a hazardous exposure of the operator, facility personnel, or the environment.

Performance

One of the driving goals in the development of SEMI S2 was to create a standard that was performance based to allow for innovations in design. The authors did not want to produce a document that would dictate what parts manufacturers must use or which circuit designs they must implement; rather, it would be the performance of the machine that would be scrutinized. SEMI S2-93 is thus a performance-based document, containing very few prescriptive clauses.

Seventeen of the 20 sections of SEMI S2-93 are dedicated to the actual performance criteria that a process tool is required to meet. The 10 concerns noted above work their way, either directly or indirectly, into each of the performance sections of the standard, the titles of which give a good indication of the topic and the focus of each. The complete list of sections, including the introductory general statements of purpose, scope, and philosophy, is as follows:

The precise impact that each section will have on a piece of equipment will depend to a great extent upon the equipment itself. For devices that are mostly electrical in nature, sections 5, 11, 12, 16, and 18 will have the greatest impact, with additional concerns addressed in sections 9, 14, 17, and possibly 19. In almost all cases, sections 1, 2, 3, 4, 5, 9, 11, 12, 14, 16, 17, 18, and 19 will apply to semiconductor process equipment.

SEMI S2-93's Global Impact

SEMI S2-93's original charter intended the standard to be international in scope and implementation. It has fallen short in that respect, with its actual implementation having resulted in its being considered mainly a domestic guideline, neither endorsed nor enforced for the most part in Japan, Southeast Asia, and Europe. Few manufacturers limit their marketing strictly to domestic end-users, and Europe is becoming an important market for U.S. equipment manufacturers. Unfortunately, those trying to market their equipment in Europe are now discovering a new hurdle in their way in the form of CE marking requirements. The need for CE marking, a complication not anticipated during the original development of SEMI S2-93, has forced U.S. manufacturers back into the cycle of redesign and reengineering, this time for equipment destined for Europe.

Compliance with the European Directive on Machine Safety, 89/392/EEC (known as the Machinery Directive) became mandatory on January 1, 1995, as did the marking of compliant equipment with the CE mark. Compliance with the related Low Voltage Directive (73/23/EEC), the European safety directive for equipment powered by voltages below 1000 V ac became mandatory on January 1, 1996. Compliance with a third directive, the EMC directive, also became mandatory on January 1, 1996. This directive governs the emissions of and the immunity to electromagnetic radiation and electric field phenomena. Even though the European Commission had provided for phase-in periods for all of these directives, their coming into force took many manufacturers by surprise.

The general consensus of the industry is that semiconductor manufacturing equipment by and large falls within the scope of these three directives. For this reason, SEMI, with the help of members representing the manufacturing community, has been trying hard to find ways to minimize the rework involved when a piece of equipment designed for the domestic market and compliant with SEMI S2-93 is sent to Europe. Numerous letters and questions have been directed to the European Commission in an attempt to clarify each side's position and interpretation, and to better define the issues involved.

Thanks to this effort, the European Commission has agreed that for those sections of SEMI S2-93 that overlap with the "essential health and safety requirements" of Annex I of the Machinery Directive or with the Essential Health and Safety requirements of the Low Voltage Directive, equipment that complies with those similar sections of SEMI S2 will be deemed also to comply with the Machinery and/or Low Voltage Directives. This is tantamount to blasphemy for EU safety purists as the Commission is essentially stating that the U.S. requirements have been accepted, and that in this case the use of European Harmonized or EN documents will not be mandatory! It is important to note that while this position still allows for at least an equivalent level of protection for the end-user, at the same time it will definitely save U.S. manufacturers the time and expense involved in performing reviews to two separate but nearly equivalent guidelines. With regard to those sections of Annex I of the Machinery Directive and SEMI S2-93 that do not overlap, SEMI has tabulated the differences and has listed them in an appendix to the '96 rewrite of the SEMI S2-93 standard, titled SEMI S2-93A.

It should be noted that the traditional "standards route" using European standards is still a viable and unquestioned option for manufacturers wishing to market devices in Europe. Using established European EN documents remains the norm for many who feel uncomfortable with choosing the "essential health and safety" route. The "standards" route is more rigorous and more demanding of "European conformity" in both design and component selection, but once the manufacturer has met these requirements, there is little room for argument as to the equipment's conformity, provided that the manufacturer has chosen the correct EN standards against which to assess.

The "essential health and safety" route is less rigid and restrictive in the sense that it attests to the basic level of safety outlined in Annex I. In principle, it allows for review according to U.S. standards or even a manufacturer's own internal safety standards, so long as the manufacturer is confident that the equipment meets the basic level of safety expected. This approach also permits the use of U.S.-approved components in construction, thereby eliminating the need for multiple versions of the same equipment. It is not without risks: should an end-user require compliance with certain EN or national standards, for example, a manufacturer could be sent back to the drawing board. Moreover, it is not a silver bullet. Manufacturers must be diligent in comprehensively assessing equipment to the requirements of Annex I. Issue may always be taken with a piece of equipment or a manufacturer's Declaration of Conformity, but if the data are there, the accuser must prove that a safety risk indeed exists.

SEMI S2-XX: The Next Generation

As stated previously, SEMI S2-93 is currently in the rewrite stage. The document has reached its five-year mandatory review, and the industry is ready to apply the lessons learned through the experience of working with the document. SEMI uses a task force approach, breaking out each section by engineering or a technical discipline and assigning a volunteer champion or task force leader to each working group. Each working group is charged with bringing its section(s) up to date with current standards and best practices, and each group has been asked to consider harmonizing where possible to "internationalize" the new document. Members of SEMI Japan and SEMI Europe have also been heavily engaged in the rewrite process to bring forth a true international Environmental Health and Safety Guideline.

As a result of three years of experience with the guideline, SEMI initiated this rewrite process in February of 1996 with the goal of publishing a new version no later than April of 1998 (five-year cycle) that was designed to meet EHS expectations into the next decade. Progress on the rewrite has been slow; however, the magnitude of the undertaking has made speedy change impossible.

Changes to SEMI S2 have been sweeping. Each and every section has been reviewed and reworked to reflect industry focus and understanding. The scope has expanded now to 27 sections, 6 appendices, and 13 related (nonballoted) informational sections. Major rewrite and clarification has been coordinated by working groups comprised of individuals from the industry worldwide.

Currently, the most significant changes and modifications have been made in the seismic, fire protection, and general sections. Also, the use of risk assessment methodologies throughout many of the various sections of SEMI S2 has been added.

Internationalization of the requirements has also been a mandate of SEMI, based on a simple requirements filter. The filter was used to qualify requirements to be included in the document. The filter elements are:

Note: The related information sections will not be balloted and have been prepared from practical application by task force members as additional clarification.

Rewrite Status

The current status of the rewrite of SEMI S2 (SEMI Document 2614) is that preballot comments were reviewed at SEMICON Southwest (October 1997) and that a technical (yellow) ballot was sent out in January 1998 to allow time for a Japanese translation. The January yellow-ballot responses were required by mid-February and were evaluated in the March 1998 Standards Meetings in San Diego. As a result of the significant number of outstanding concerns with the document, SEMI decided to pull back the document and reissue it for another technical (yellow) ballot. The yellow reballot followed the same process with the 1999 version of the 2614(B) document reaching consensus to the point-of-line-item reballot, scheduled to correspond with the SEMICON West Standards meetings. At best, if the ballot items pass and if the SEMI standards members can vote on all of the changes at that time, a new SEMI S2 document (SEMI S2-99) would be released by SEMI in October 1999.

The semiconductor industry has taken the next step toward global acceptance of their equipment and of their industry safety guideline, SEMI S2. As the industry looks at expanding global markets and manufacturers fight to keep in step, consensus on a global approach to safety is critical in reducing both time-to-market and the cost of ownership. The semiconductor industry has shown continual improvement in the environmental, health, and safety aspects of its equipment and workplaces since the adoption of SEMI S2. These improvements should continue into the next millennium, bringing further value to the industry with the adoption of the next revision to the SEMI S2 Guideline.