As nanotechnology research moves forward demand for these highly sensitive instruments increases. Representatives from two well-known instrument manufacturers offer lessons from their respective experiences with delivering and installing high-precision lab equipment.

Electron Microscopes

Hitachi High Technologies America (HTA) manufactures electron microscopes. By nature, these are susceptible to electromagnetic interference as well as vibration, humidity, and other environmental factors.

Electromagnetic interference (EMI) comes from both AC and DC sources. Common sources of AC interference are light ballasts, electrical wiring, and power distribution points. DC fields are more often from remote sources such as subways, trains, and elevators, or from nearby (and sometimes not-so-nearby) EMR labs.

Vibration also limits the function of electron microscopes, and can be either rhythmic—like that from fans, motors, and background highway traffic—or variable—like nearby foot traffic, passing trucks, or loading docks.

"Sound can be difficult to distinguish from floor vibration without advanced test equipment, because the image disturbance is often similar," says Eric Johnson of HTA. "Also, look at natural resonant frequencies of the instrument platform, as well as vibration at the site."

Humidity is one of the most often overlooked environmental conditions affecting electron microscopes, according to Johnson. Common water-based cooling systems can lead to condensation inside the instrument, which can cause serious electrical and mechanical problems.

Distance requirements between electron microscopes and other types of instruments can vary significantly, and planners don't always know what types of interference they need to plan around, especially in new facilities, because these can change as other equipment comes on line.

Laser Lithography Writers

Heidelberg Instruments manufactures a range of direct-write laser lithography tools, which have specialized requirements of their own, including temperature, atmospheric pressure, and vibration.

According to Heidelberg's Niels Wijnaendts van Resandt, the most important variable for these instruments is temperature, which should be maintained between 65°F and 75°F. Even more important than the actual temperature is its stability over time: A two-degree change over the course of a day can introduce significant errors due to expansion of the substrate material. Some Heidelberg models incorporate flow units and/or dust covers, both of which can help in controlling temperature.

Atmospheric pressure is normally carefully controlled in cleanroom conditions, and Heidelberg's customers typically—but not always—install their lithography writers in rooms rated to at least Class 1000. The flow box attachment generally increases this rating inside the unit by a factor of ten.

Wijnaendts van Resandt emphasizes that planning for cleanroom air conditioning capacity must take into account the fact that the unit generates a considerable amount of heat. Air vents must be positioned not to blow directly into the system, as this can compromise temperature stability.

To combat vibration interference, Heidelberg's laser lithography writers employ granite mounts for optics and substrate stage, isolated via constant-pressure air bellows, which requires a very stable source of 88 to140 psi compressed air. An active, real-time beam-position correction system generally makes additional measures—like isolating the entire machine or using a separate, active vibration compensation system—unnecessary.

The instrument also requires a stable, constant vacuum source to hold the substrate onto the stage, and 11 percent humidity for the compressed air autofocus (at the etching site), as the substrate material becomes insensitive in dry air.

Clean Power, A Good Ground

Clean power and a good ground are crucial to successful installation of essentially all high-precision instrumentation. Hitachi's Johnson recommends standard 208-volt Wye configuration for their electron microscopes' main power, with a single distribution box and common ground throughout the room.

Because Heidelberg's machines are manufactured in Europe, they require 230-volt, 60-hertz, 16-amp power, and normally require a transformer when used in North America.

Planning for Delivery and Installation

In addition to ensuring loading docks and all access ways, including corners and stairs, are spacious enough to allow instrument delivery, Johnson emphasizes the importance of making sure that all these areas—including elevators—can handle the weight of the instrument and its sub-components.

Wijnaendts van Resandt adds that utmost care must be taken during delivery and installation, because Heidelberg's systems are pre-qualified and fully calibrated at the company's manufacturing facilities. Johnson echoes this caution:

"These are very expensive instruments, and you don't want them sitting out in the rain or getting knocked around," he says.

By John Treat

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