Hands-on vacuum training at the technical college level
11/01/1997
Hands-on vacuum training at the technical college level
Stephen P. Hansen, MKS Instruments Inc., Andover, Massachusetts
When I started in the semiconductor industry, there were only two pieces of vacuum apparatus in or near the fab - an aluminum evaporator for the deposition of really thick single metal conductors, and a gold evaporator for putting enough gold on the wafer backside so that the chips could be stuck into a ceramic package. The vacuum process was simple: load the wafers into the fixture, wrap some wire around a filament, close the bell jar, pump the system to somewhere below 10-5 torr, and evaporate.
What a difference a few years make. Today`s fabs are littered with vacuum equipment, PVD, CVD, implant, etch, strip, and so on. Operation is no longer a simple problem of getting "about the right level of vacuum." Instead, we have to admit precise quantities of gases, maintain pressures within exacting limits, and monitor the constituents within the chamber. We`ve gone from "get it to the 6s and crack the needle valve" to "maintain 20 sccm flow with a pressure setpoint of 10 mtorr ?1."
In this environment, an equipment technician or operator has to understand vacuum, its relation to processes and process systems, and how to measure and control it at a much deeper level than was required just a few years ago.
Individual companies and organizations like Sematech are working with colleges, especially two-year schools, to develop semiconductor manufacturing technology (SMT) curricula, and these curricula must include some level of vacuum training. A major driving force has been Sematech and Semi/Sematech`s Partnering for Workforce Development project [1]. One of the program`s goals is to attract and train 40,000 new semiconductor manufacturing technicians and skilled operators across the US over the next five years.
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Figure 1. A circa 1796 "traditional" vacuum training system consists of a pumping system, chamber, and pressure gauge: a) bell jar-glass, b) base plate, c) pump lever, d) pump cylinders, e) mercury nanometer, and f) mercury reservoir.
Vacuum training hardware
Historically, as John O`Hanlon has noted [2], vacuum has been treated as a secondary or background technology. In school curricula, it is frequently referred to but seldom taught. Vacuum is usually encountered as part of a physics course where the focus is on the properties of vacuum as opposed to the vacuum systems themselves. Classroom demonstrations and hands-on work might include studying Boyle`s law using balloons or marshmallows, diminished conduction of sound using an electric bell, differential pressure using "Magdeburg hemispheres," and so forth. The focus of vacuum instruction has usually been in the form of a more traditional approach: kinetic theory of gases, pumps and components, and issues related to the evacuation of simple systems.
Hands-on classroom training on process systems is a very desirable aspect of any educational program designed to prepare an expanding workforce for the semiconductor industry. A typical vacuum training apparatus from the 18th century (Fig. 1) has the basic characteristics of classroom vacuum trainers used to this day: a pump, a bell jar, and a gauge. The idea remains the same, even though hand-operated piston pumps have given way to mechanical pump/turbo pump combinations, and mercury manometers have been replaced by thermal conductivity and ion gauges.
This approach is adequate for demonstrating the function and operation of vacuum systems and for demonstrating a number of properties of low pressure environments, but is not adequate for teaching the array of concepts needed by the equipment and process technicians who maintain and characterize the increasingly complex vacuum process tools in our industry.
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Figure 2. An actual process tool embodies a wide variety of concepts that are intertwined with vacuum theory and practice. Vacuum training in SMT programs must be broad enough to encompass these issues.
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Figure 3. A practical vacuum training system designed for SMT programs.
What technicians and operators need to understand can be seen by examining the features of a "typical" process tool (Fig. 2). All of the traditional vacuum issues are present: conductance, flow regimes, real and virtual leaks, etc. But, vacuum processes no longer involve just the removal of air from a chamber. Artificial environments have to be established and controlled with great precision by high accuracy direct gauging (usually in the form of capacitance manometers), precise mass flow control of the process gases, rapid attainment and maintenance of the process conditions using closed-loop control and command over the pumpdown sequence to minimize contamination due to particle formation and redistribution, and so forth. Today`s equipment technicians and operators need to understand the overall functions of the tools, the instruments on those tools, how everything interacts to produce a working process, and what kind of operational activities can cause problems. They should also learn to establish tuning parameters, understand calibration principles, troubleshoot instruments, and input recipes.
To deal with hands-on training needs and the time, space, and funding realities of local colleges and institutes, the industry has developed benchtop vacuum trainers that resemble real tools and reflect, in a simplified way, the realities of a process tool. The students with laboratory experience with these systems and their future employers benefit from direct experience with a representative selection of key components and instruments found on vacuum systems and their operation and features. These teaching aids must be designed to invite hands-on work, be flexible and robust, and be acquired at a modest cost. They must also be well documented with student exercises that reflect the real world.
MKS has developed such a trainer in a basic version that mimics a medium vacuum process tool in terms of gauging, flow control, and upstream and downstream control capabilities. The system is designed to be manually controllable or it may be programmed with recipes through a computer. To assist the student in observing system characteristics, like pressure vs. time profiles and set point acquisition, the software also has graphical display capabilities. The system is designed to be easily expandable. Features such as high vacuum capabilities, chamber options including a parallel plate electrode structure for rf training, and interchangeability of the analog instruments with digital equivalents are also available. Figure 3 depicts the complete training system. Note how the system elements compare to those of the tool shown in Fig. 2.
How does this work in the classroom?
Schools all over the country are annoucing new SMTprograms. Several dozen community colleges and technical institutes include or plan to include vacuum in their curricula, and a number of these have used our training apparatus. The following offers a few examples from colleges that have used this type of hands-on vacuum training system.
One is the program at Austin Community College (ACC) in Austin, TX. Louis Frenzel, program coordinator for ACC`s SMT program points out that, "Since most fabs tools have vacuum chambers and systems, vacuum is a key part of the SMT curriculum. Our course teaches vacuum principles including a review of the gas laws, units of measurement, measurement instruments, and techniques including pressure sensors, vacuum pumps, and other vacuum hardware. The course includes additional instruction on mass flow controllers. The MKS Vacuum Trainer is especially valuable in this curriculum as it provides a low cost and convenient way for students to get their hands on real equipment." The course also covers plasma physics, plasma generation, radio frequency (rf) generators, and associated measurements. Rf generators in the lab are used in conjunction with the Vacuum Trainers to show the coupling of rf to the vacuum chamber. ACC`s program was founded in 1995 in response to a request by AMD, Applied Materials, IBM, Motorola, Sematech, and Texas Instruments. ACC is training approximately 350 students in a 16,200-ft2 dedicated facility with three full-time and 21 part-time faculty members. ACC offers both one- and two-year programs.
A targeted education in vacuum technology is offered at some institutions. Normandale Community College in Bloomington, MN, has established within its mechanical technology sequence a two-year Associate in Applied Science degree specializing in vacuum technology. State agency Minnesota Jobs Skills Partnership provided a $200,000 grant to help develop the program, and four local companies - Seagate`s Recording Head Operations, Honeywell, Cypress Semiconductor, and VTC - made additional contributions to help develop the training program. According to Kent Maffitt, a Seagate employee and the vacuum program instructor, the practical and hands-on training is being offered in a million-dollar laboratory at Seagate Technology`s Bloomington plant. Maffitt notes, "A unique aspect of this program is that three of the four specialized vacuum courses provide laboratory experience in vacuum analysis and troubleshooting, thin-film deposition, and integrated circuit fabrication. In the lab, we have both "retired" process tools and several MKS Vacuum Training Systems. We start the students on the trainers because they are easy to work with and cover the spectrum of vacuum concepts. Because process tools are designed to perform a single function, it is not possible to get this breadth of knowledge easily without the trainers. Once the fundamental concepts of ideal gas behavior, pumping speed, conductance, effect of gas flow rates on pressure, rate of rise, mass flow, and pressure control have been explored through a number of exercises, it becomes easier for the student to transfer that knowledge to the actual tools."
ECPI Technical College has recently started a Microelectronics Technician Program at its Richmond, VA, campus. The program is in direct response to the needs of the new semiconductor fabs now being built in Virginia. Graduates of the program will be granted an associate`s degree in electrical technology with emphasis on semiconductor processing. The program consists of basic electrical and computer courses plus specialized courses that relate to the electrical, mechanical, process, and vacuum systems associated with semiconductor manufacturing. According to John Earle, lead instructor, "We decided that the approach to the vacuum course should be from a technical/maintenance standpoint as opposed to a theoretical one. We felt this would make the graduates more valuable to prospective employers. Development of the vacuum course was particularly challenging as it would have been difficult to fit a full-size production tool inside a classroom. Using the vacuum trainer approach, we were able to demonstrate the basic vacuum principles, vacuum and gas flow control, and proper handling, and maintenance of vacuum system components. The similarity of the components to those on a process tool makes it easy for the instructor to relate how vacuum systems work in process tools."
Summary
Meeting the workforce needs of the semiconductor industry represents both a challenge and an opportunity for two-year colleges in this country. While many of the necessary curriculum elements are identical or similar to those now found in existing technology programs, others, such as vacuum, process control systems, residual gas analysis, and rf power, represent new areas. Given the cost, complexity, and lack of availability of full scale process tools for educational purposes, a simple benchtop vacuum trainer has proven to be of great benefit in introducing the relevant principles of vacuum and process systems to the industry newcomer. n
References
1. "Training the Semiconductor Workforce of Tomorrow," Sematech, June 1997.
2. John F. O`Hanlon, A User`s Guide to Vacuum Technology, John Wiley and Sons, New York, 1989.
Stephen Hansen is technical training and education manager. MKSInstruments, 6 Shattuck Rd., Andover, MA 01810-2449; ph 978/975-2350; fax 978/975-0093; e-mail [email protected].