Conducting early assessments of semiconductor manufacturing tools
Mark A. Krauss, Environmental Health and Safety Services (EHS2);
and Mark S. Frankfurth, Cymer
In a technologically advanced and socially responsible manufacturing world, employing environmentally safe methods of development and production is critical to mitigating environmental, health, and safety (EHS) concerns at the earliest stages of a product’s life. Just as medical professionals urge that people take precautionary daily actions by brushing their teeth, exercising regularly, and following a healthy diet to prevent disease, so too must semiconductor equipment manufacturers perform preliminary equipment inspections to identify and prevent safety issues during the life of their capital equipment.
Beginning safety and compliance activities as early as possible is a good rule of thumb to follow and will provide the best opportunity to effect change. Although an early start may mean that the equipment under review will not be ready for a conformance assessment to standards, a systematic approach can result in valuable equipment improvement and advance the tool toward the maturity level expected by an evaluator.
Often during the development of large prototype tools and initial integration of complex systems, the various “roadmaps and signposts” used to identify wires, hoses, and modules have not yet been established. Consequently, describing the location, component, nature, and impact of safety issues is difficult for those who are not intimate with the design. How does a safety reviewer navigate an unmarked road without a map? In some cases, it is beneficial to make one’s own.
Using a scalable topologic grid to map the location of possible problem areas creates a starting point for recognizing and recording potentially dangerous issues. This approach can be compared to National Transportation Safety Board (NTSB) accident investigation methods, in which debris is mapped after an accident to determine its causes. In the case of large industrial equipment development programs and semiconductor industry installations, the NTSB mapping method has been adapted to prevent potentially damaging or dangerous incidents instead of investigating them after they occur. Using this method to address semiconductor equipment EHS concerns requires an understanding of tool preparation, materials, methods, benefits, and weaknesses.
Avoiding EHS surprises when designing and constructing semiconductor capital equipment is a manageable goal that is supported by many initiatives, standards, and processes. Several such initiatives come from the semiconductor industry itself, while others are developed by international safety standards committees. For example, some equipment safety programs are based on international standards, such as IEC/EN 61508, which support European Union directives. In addition, many equipment manufacturers have company-specific product development processes. These methods include a set of best practices for EHS-compatible design and construction. When implemented successfully, these methods significantly reduce the number of design defects and construction errors in complex equipment and systems.
In the broadest terms, the semiconductor industry Design for Environment, Safety, and Health (DfESH) initiative is a systematic management approach for evaluating and mitigating EHS concerns at the earliest possible stages of a process design or product life cycle. The initiative includes ongoing evaluations during a product’s life cycle and also optimizes the balance between EHS priorities and competing factors such as cost, features, production schedule, product quality, and performance. This optimization requires that an organization make value judgments based on the best information available.
The SEMI S2 safety guideline expects suppliers to establish and maintain a safety management program to achieve efficient and effective safety and compliance objectives—specifically, the identification and elimination of safety hazards. Depending on its needs, a firm may establish a companywide program covering all projects and a wide range of related topics, or it may develop separate programs that are tailored to individual projects. A combination of both approaches is also possible.
The use of systems engineering methods to guide products through the entire life cycle from concept to disposal is the preferred way to manage the wide range of EHS objectives related to semiconductor-manufacturing capital equipment. The approach discussed in this article represents an early entry point for safety practitioners to engage in the product development process. The method involves spatial analysis that is used to identify and document the location and nature of observed defects in a complex piece of equipment, an integrated system, or a workspace. By following this approach, assessors can better detect problems in tools that are difficult to review because of system complexity, incomplete construction, inadequate documentation, excessive construction deficiencies, or alpha-level/prototype product construction.
Factors to Consider in the Safety Development Process
When employing a systems engineering approach to the development of semiconductor capital equipment, it is advantageous to follow a process such as that outlined in the requirements and verification flow diagram in Figure 1.
Figure 1: Schematic diagram illustrates the system engineering requirements verification process, also known as a V-model.
During the development process, numerous factors can result in equipment construction deficiencies—particularly when an outsourced design or manufacturing model is followed. These factors should be examined closely, and solutions should be developed to prevent manufacturers from making the same mistakes in the future. The factors underlying a hazardous first attempt at assembling a product can include:
• A poorly assembled prototype or alpha of the product.
• An incomplete or nonfunctional tool.
• An equipment manufacturer that is unfamiliar with the semiconductor industry and its safety requirements.
• Inexperienced junior-level engineers.
• A lack of descriptive engineering documents.
• Subsystems that are outsourced without vendor support.
• The use of multiple subsystems and multiple suppliers, leading to a lack of “ownership.”
• Poor or hasty workmanship and assembly.
Outsourcing and the Nonideal Result. With the rising trend of outsourcing equipment construction (and even design), additional and seemingly avoidable challenges arise. If the company responsible for the project does not thoroughly understand the safety and compliance expectations of the customer or the industry, frustrations will peak as the time for safety evaluation and assessment approaches and roadblocks appear. The piece of equipment that is expected versus the piece of equipment that actually arrives may be shockingly different if the equipment manufacturer does not receive clear communications or is unfamiliar with the rigorous requirements of the semiconductor industry. Common problems include wiring routed over unprotected metal edges, sharp corners on parts, and mismatched cable and connector ratings.
The product safety workspace expanded in all directions as outsourcing appeared on the scene. New areas requiring attention (or increased attention) include requirements and specifications, dissemination of safety guidance information, procurement, and the decommissioning of products at the end of their lives. Subsequent ownership (the used-equipment market) may also become a concern for those that provide product-safety support. Complications may arise in relatively well-known product-safety areas such as sample acquisition for reviews and testing, manufacturing, and service procedures. New approaches and methods are needed to address these challenges.
Preparation and Tools
The goal of the spatial analysis method presented in this article is to move equipment toward a suitable-for-use level of safety. Suitable for use refers to a condition in which the safety and compliance aspects of the equipment are not wholly complete or perfect but are acceptable for an intended purpose and in a planned environment. Furthermore, in a suitable-for-use situation, sufficient knowledge has been gained during equipment assessment so that all visibly detectable defects and potential issues have been identified, allowing risk-assessment methods to be applied. Although possible hazards may still be present, the equipment has been brought to a known state so that decisions can be made on which risks are acceptable and which must be corrected. Ultimately, this procedure can accelerate the development process in a systematic manner.
A spatial constructional assessment represents the first “eyes on the equipment” step in the equipment’s safety inspection. This method is well suited for ensuring the safety of complex equipment and integrated systems to a basic level. It may also be applied to the occupational safety of work cells and environments.
Before performing a spatial constructional inspection of semiconductor equipment, assessors should have the following equipment-specific materials available in a format suitable for use in the inspection area (including in a cleanroom environment):
• Hard copies of standards and guidelines applicable to the equipment under test (EUT).
• Orthographic drawings of the constructed system and the system’s major modules.
• “Memory trigger” hazard checklists.
• Installation, operation, and service maintenance manuals.
• Existing safety information.
• Facilities’ requirement documents.
• Electrical wiring and interconnection diagrams.
• Process piping and instrumentation diagrams.
• Lists of critical components.
• Mechanical data.
• EMO circuit diagrams and descriptions.
• Interlock circuit diagrams and descriptions.
• Information on ionizing and nonionizing radiation sources.
• Fire detection/suppression information.
• Seismic anchorage materials.
• Transportation and handling instructions.
Although equipment assessment is impeded by the absence of this information, it is commonplace for inspections to be requested when the documentation is in the process of development, undergoing change, or unavailable. Inspectors should also have background knowledge of the system’s function and expected performance as well as an understanding of possible system hazards.
During an inspection, assessors should carry the proper tools to capture and record findings. A digital camera, a tape measure, an inspection mirror, cleanroom-compatible masking tape, a laptop computer, and a pen are helpful tools to aid accurate and detailed data collection. It is important for assessors to allow adequate time for a thorough on-site equipment inspection and for documentation creation. The photograph in Figure 2 shows inspectors in bunnysuits using cleanroom-compatible tools. Once the analysis is complete, they should provide debriefing information that details the complete findings of the inspection and precipitates a schedule for corrective actions and follow-up inspections.
Figure 2: Cleanroom-compatible tools and clothing may be needed during tool inspections.
Documentation and Assessment
Before the detailed examination of the semiconductor equipment, the overall condition of the EUT must be documented. These notes record the state of construction (e.g., missing panels and components or metrology tools attached), the status of documents and hazard warnings (e.g., missing user manuals, marked-up schematics, and missing hazard warnings), and facilitization (e.g., connections for electrical power, exhaust ventilation, cooling water, and gases.) In short, the documentation must describe the state of the equipment at the time of assessment. Whether that means noting a missing manufacturer’s nameplate, nonexistent hazard-warning labels, incomplete piping diagrams, or missing user manuals, each detail must be considered and recorded. Drawings and photographs are invaluable for maintaining an accurate record of system condition.
The ever-increasing cost of cleanroom space has forced manufacturers to package modules and components more densely while increasing the size and complexity of equipment. Lack of access to internal areas as a result of crowding has reduced equipment serviceability while increasing the likelihood that the edges of parts and modules will damage hoses, wiring, and tubing. Electrical safety concerns have increased as electronic controls, electric drives, and the power consumption levels of electromechanical machinery have grown. Tools have become bigger, more complex, and more power hungry.
When preparing to perform a spatial construction assessment, evaluators must understand the benefits and deficiencies of their approach. Spatial inspection requires hands-on visual observation “inside the box,” detailed preparation and proper tools, and knowledge of product safety. It allows for significant EHS progress on grossly deficient equipment, promotes EHS progress on poorly documented equipment, and enables inspectors to identify specific issues. Spatial inspection and recording do not directly produce compliance reports, detect all design or construction deficiencies, collect conforming characteristics, correlate hazards to the construction tasks that were performed, provide risk potential, define corrective actions, allocate responsibility, or correct the development process flaws that created the problem in the first place.
Assessing IC Equipment
The size and construction of semiconductor equipment drives decisions about how to partition a tool into segments to make it more manageable during inspection. Small, simple modules need not be divided into smaller segments unless it facilitates the understanding of observed constructional defects. Small modules usually do not require partitioning unless they have a very large number of defects.
Once it has been decided to map the equipment for inspection, tape markers are applied to the perimeter of the equipment frame to demonstrate the map divisions or segments. These markings are then transferred to orthographic drawings of the equipment, as shown in Figure 3, and assigned identifiers. As illustrated in Figure 4, a grid may be used to segment large systems.
Figure 3: Diagram of equipment physical layout. It is helpful to sketch the equipment’s physical layout to organize the inspection process.
Figure 4: Equipment diagram with reference grid overlay. An equipment drawing such as that shown in Figure 3 may be referenced with a grid overlay to divide up the equipment to facilitate the inspection process.
Once the tools have been partitioned, each tool area is examined in detail against checklists to ensure completeness. Every construction defect is carefully noted on a laptop or notepad. Defects and hard-to-describe areas may also be recorded using a digital camera. For example, a photograph may be taken of a cable connection that has a subtle missing or incorrectly terminated strain-relief feature. After the inspectors are certain that a segment has been thoroughly examined against the checklist, they can move on to the next segment and repeat the process. This procedure continues until the entire unit has been examined and all findings have been recorded. The photograph in Figure 5 shows a group of assessors performing a detailed inspection of a laser.
Figure 5: Reviewers performing a visual inspection on a laser.
After the equipment examination has been completed, all identified design and construction defects must be communicated to the manufacturer. This may be done at a wrap-up or debriefing meeting at which the findings are written up and distributed to the engineers who are responsible for the equipment. At this point, the findings can be discussed. A face-to-face meeting at the equipment is a very effective means of assuring that the findings and the defective tool areas are well understood by the recipients of the report.
A few simple steps should be followed to prepare materials for the debriefing:
• The preliminary nature of the findings should be stressed.
• Specific findings for each tool segment should be included.
• A specific identifier should be assigned to each issue. Examples of identifiers are: “Division A1—A1-1, supply conductors, SO cord in rigid conduit; A1-2, no conduit bushing at cord entrance; A1-3, no fitting at cord entrance; A1-4, missing cover on pull elbow; A1-5, missing screws on enclosure top cover panel; A1-6, exhaust duct hose clamp missing.”
• Assessors should be prepared to discuss each issue with the equipment engineer.
• Assessors and engineers should be aware that the same issue may appear in multiple segments.
• Assessors should know who is responsible for driving all issues to conclusion.
As a part of the wrap-up meeting, inspectors must be sure to schedule necessary follow-up activities. The acting engineer who is responsible for managing the inspection should begin to initiate corrective action for each issue and schedule follow-up activities.
Benefits and Weakness of the Spatial Analysis Method
As with any vast population that must be broken down to target individual pieces accurately, the spatial inspection method provides a systematic framework for the examination of a complete semiconductor system. By identifying EHS deficiencies on tools that are not yet ready for formal conformance assessment, manufacturers can take a hands-on approach to dealing with potential equipment dangers. This method also enables assessors to list actionable items for needed EHS changes.
The spatial analysis method can also support user acceptance of alpha/prototype equipment. This feature can be valuable when a functional, albeit preliminary, sample of the equipment enables the customer to advance the development of device manufacturing processes and procedures in advance of mature equipment availability. When the spatial analysis method is used to provide customers with a snapshot of equipment in an early stage of development, it provides a means of disclosing identified hazards. When the hazards are known, strategies and methods for risk management at the user location can be developed.
The spatial analysis method also has weaknesses. Since equipment under inspection is not yet ready for standards conformance assessments, only observable construction can be taken into consideration during assessment. The method does not document conforming design elements or provide all information needed for conformance reports. It can also generate multiple reports of the same issue across multiple segments of the equipment, trying the patience of the engineer who is responsible for the tool.
The spatial analysis method described in this article was used in the early development phases of the XLA family of laser products from Cymer (San Diego). The method was instrumental in bringing the first generation of dual-chamber master oscillator power amplifier (MOPA) laser technology to the market. It provided the basis for a mature volume-production laser that is used in semiconductor lithography applications. The method has also been used successfully on preproduction test and measurement tools, providing inexpensive and quick guidance on design changes to accelerate market introduction. It can also be used to identify hazardous conditions in manufacturing, laboratory, or other work environments.
To achieve EHS objectives, it is important to start early—often before the equipment is ready. For the spatial analysis method to become valuable to industry professionals, manufacturers must understand its snapshot nature. Analysis findings reflect the equipment in a particular state. Changes implemented during the course of the inspection on sectors already documented will not be reflected in the findings.
Manufacturers must also understand the limits of spatial assessment: it covers observable construction only. While it may be an accurate constructional observation to say that a conductor does not have ratings, approvals, or markings, the statement says nothing about the protection of the conductor, the components, or the circuit. A review of electrical coordination requires accurate electrical diagrams and component information. If that information is unavailable during the assessment, the inspectors’ ability to identify additional design defects may be impeded.
Ultimately, resolving identified equipment issues requires ownership and action by the responsible engineer or manufacturer. Producing a findings list does not ensure that the deficiencies will be acted on. Nevertheless, steps must be taken to ensure action before equipment can become suitable for use.
Mark A. Krauss is a principal consultant at Environmental, Health and Safety Services (EHS2). He assists companies in managing EHS issues to develop industrial systems for the semiconductor industry. A certified laser safety officer, Krauss has performed more than 750 product safety assessments on semiconductor-manufacturing capital equipment. (Krauss can be reached at 650/588-2027 or firstname.lastname@example.org.)
Mark S. Frankfurth is an engineering manager at Cymer (San Diego), where he oversees product safety and regulatory compliance engineering. He assists in the development of high-power industrial laser systems for the semiconductor industry. A certified laser safety officer and a National Association of Radio & Telecommunications Engineers–certified electromagnetic compatibility engineer, Frankfurth received a BS in electrical engineering from Virginia Polytechnic Institute and State University in Blacksburg. (Frankfurth can be reached at 858/385-6558 or email@example.com.)