An integrated solutions approach to frequently encountered vibration problems is most useful in solving real-world problems. By ''amalgamating'' several levels of vibration control--in the form of both new designs and existing technologies--one is able to create a foundation upon which a variety of requirements can be met. The combination of time-proven damping of optical bench tops and a novel technological advance involving a new damping technology for pneumatic isolators, leads to enhanced performance of passive isolation systems.

High resolution scanning electron microscopes (SEMs) are placed in a wide variety of application sizes. The site environmental vibration levels can vary considerably due to geographical location. building construction, location within the building and any processes which may be running within or near the building. This paper briefly reviews the primary sources of mechanical disturbances which can have a detrimental effect on the resolution of the SEM showing the importance of considering the entire SEM structure. The use of finite element techniques to investigate system structural performance and its relevance to low frequency ''rigid body'' motion at nanometric levels is discussed together with an improved design of passive vibration isolation using a focalized system. In this method, the lines of action of the support forces are considered with regard to the position of the center of gravity of the supported structure.

The control of environmental vibration is a prime consideration in designing sensitive electro- optical equipment. Pneumatic isolation systems with low natural frequencies are commonly used to shield the payload from random seismic vibration. In order to further optimize the isolation characteristics, it is desirable to decrease natural frequencies in all translational axes to well below 0.5 Hz, while at the same time achieving maximum damping at resonance. The limitations of conventional systems, however, are such that the lowest natural frequency achievable is 1 Hz. Typical resonance amplification is measured at approximately 10 to 20 dB. The use of low-frequency pneumatic isolators in precision machinery with built-in XY-stages (i.e., microlithography, submicron inspection systems (highlights an additional problem. Low natural frequencies are equivalent to low spring stiffnesses. Inertial forces applied to mass- spring systems with low spring stiffnesses results in large dynamic deflections. This kind of motion has an impact on the stability and settling time of XY-stages mounted on the mass spring system. The positioning controller of the XY-stage must overcome these disturbances which are induced by the reacting mass-spring system. The softer the isolation system, the large the dynamic deflection of the mass-spring system will be. It would be ideal to have a system that would act like a perfectly soft suspension system for all floor induced motion, while simultaneously creating an infinitely stiff system for all payload-induced forces. This can only be accomplished by using servo-control mechanisms with feedback and feed forward capabilities. This technology is introduced and analyzed in the body of this paper.

A rapid back-and-forth motion of a secondary mirror is required for enhancement of weak signal-to-noise ratio by chopping the incoming beam to an infrared telescope. For a very large infrared telescope with a large secondary mirror (diameter of 500 mm, mass of 7 kg), a unique secondary mirror chopping system which is very light and suppresses mechanical vibration of a telescope during chopping motion is developed. The system has an active damper which cancels large reaction force to restrain excitement of the telescope. The damper is very compact and light, because a linear motor of the damper uses the same magnetic circuit as for a motor driving the mirror. The controller for moving the mirror and the damper consists of feedback and feedforward parts. A unique position command of the feedforward part accomplishes short transition time of the chopping motion without exciting resonances of the chopping mechanism. The system achieves a total mass of 100 kg, secondary mirror maximum chopping amplitude of 1.21 mrad, secondary mirror positioning accuracy of 4 microrad, and transition time of less than 10 msec without remaining vibration.

A new type of vibration isolation system offers significant improvement in performance compared with current state-of-the-art systems. The system uses negative-stiffness mechanisms to cancel the stiffness of a spring suspension. Reduction in stiffness magnifies the damping inherent in the system creating a practical means for achieving high hysteretic damping. The result is a simple, compact 6-DOF passive isolation system capable of system resonant frequencies below 0.2 Hz and first isolator resonances above 100 Hz. Resonant transmissibilities below 1.4 can be achieved with transmissibilities at the higher frequencies close to that of the ideal undamped system. The negative-stiffness mechanisms can cancel the stiffness of power cables, hoses or other lines connected to payloads. This paper develops the theory, describes typical configurations and summarizes test data with prototype systems.

The object of this paper is to outline the fundamental requirements and principles for establishing basic standards of acceptable levels of vibration. These standards apply to ultra sensitive scientific environments, such as on large telescopes and different areas in and around an observatory complex.

The microelectronics industry must address a number of important issues when attempting to avoid vibration problems in the design and selection of vibration-sensitive equipment. An effective design methodology is described. Vibration requirements from selected vendors are compared and found to vary greatly in both form and content. Two different proposed vibration ''standards'' are compared.

When designing facilities for research, microelectronics manufacturing and similar activities, it is generally necessary to have vibration criteria which are generic (i.e., applicable to classes of equipment and activity) rather than specific to particular items of equipment. This paper describes the derivation and use of one such set of criteria that is based on one-third octave band vibration velocity spectra. The paper also discusses the need to develop methods and standards for measuring the vibration sensitivity of equipment. Some examples are given which illustrate the considerable confusion in equipment sensitivity standards that exists at the present time. A plea is made to equipment manufacturers and users to develop and call for, respectively, specifications that are real and precise. This is especially important as the high- technology community enters the ''age of the nanometer.''

The paper reviews the vibration issues which should be considered in siting high-technology facilities and proposes some guidelines for ordinances which address these issues.

In most state-of-the-art microelectronics facilities, process equipment (tools), including vibration-sensitive equipment, is set on a structure to bring the equipment to the level of the raised access floor. Depending upon their design these bases can amplify, through resonance, the vibration amplitudes that travel from the structural floor to the equipment base. Similarly, benches that are commonly used to support microscopes and other equipment will often amplify the floor vibrations. Data are presented from recent measurements that illustrate the nature and magnitude of these effects. The concept of ''rigid body rotation'' as a source of horizontal vibration on bases and tables is discussed briefly.

In object scanning confocal microscopes the mechanical noises caused by the step motors have some effects on quality of image. This paper analyzes the mechanical noises and puts forward a new kind of system which isolates the vibration source from the scanning plate so as to minimize mechanical noises. The paper also gives some experiment results.

Change of wavelength in a CSOM (confocal scanning optical microscope) can be used as a depth scanner without any mechanical movement so as to improve the quality of sectional images in a CSOM. This paper puts forward such a new CSOM system.

The Advanced Photon Source (APS), a new synchrotron radiation facility being built at Argonne National Laboratory, will provide the world''s most brilliant x-ray beams for research in a wide range of technical fields. Successful operation of the APS requires an extremely stable positron closed orbit. Vibration of the storage ring quadrupole magnets, even in the submicron range, can lead to distortion of the positron closed orbit and to potentially unacceptable beam emittance growth, which results in degraded performance. This paper presents an overview of the technical approach used to minimize vibration response, beginning at the conceptual stage, through design and construction, and on to successful operation. Acceptance criteria relating to maximum allowable quadrupole magnet vibration are discussed. Soil properties are used to determine resonant frequencies of foundations and to predict attenuation characteristics. Two sources are considered to have the potential to excite the foundation: far-field sources, which are produced external to the facility, and near-field sources, which are produced within the facility. Measurements of ambient ground motion, monitored to determine far-field excitation, are presented. Ambient vibration was measured at several operating facilities within Argonne to gain insight on typical near-field excitation sources. Discussion covers the dynamic response characteristics of a prototype magnet support structure to various excitations, including ambient floor motion, coolant flow, and magnet power.

Building foundation design is important for controlling structural environmental vibration caused by external transportation and stationary sources, and by internal sources such as mechanical systems. The dynamic response of grade slabs, footings, and pilings are reviewed. A lumped parameter model presented in the literature is described and used to estimate the response of a massive foundation on an elastic half-space with some representative examples. The effect of vibration radiation losses, and foundation bearing area are discussed. Finally, some informal test results are discussed for deep friction piles. These results indicate that pile foundations can be effective in reducing environmental vibration.

Synchrotron light sources have undergone three generations of development in the last two decades. The National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory has two "second generation" storage rings that currently provide the world's most intense sources of photons in the VUV and X-ray spectral ranges. There are almost 90 beam lines serving a community of 2600 scientists from 370 institutions. They are engaged in basic and applied research in physics, chemistry, biology, medicine, materials science and various technologies. When design of the NSLS began in 1977, emphasis was given to the stability of the concrete slab on which the storage rings and experimental beam lines were placed. Stability is the result of controlling: . vibration from sources internal and external to the building, . thermal effects of air and water temperature variations, . foundation settlement and contact between the slab and underlying subsoil. With the advent of new research where highly focused beams of x-rays must be placed on increasingly smaller targets located 35 meters or more from the source, and the development of x-ray lithography with resolutions approaching 0. 1 micron at chip exposure stations, even greater attention to stability is required in building designs.

SGS-Thomson Microelectronics is currently building a new facility dedicated to submicron technologies. During the early stage of the project programming, various site surveys were conducted to ensure that the ambient vibration level of the selected site was compatible with the design of a low-vibration building. Once a site was selected, in-situ measurements and test foundations were used to analyze in real situations the propagation characteristics of the soil and the dynamic response of different types of foundations. These experiments provided the site background noise level, the soil damping coefficient and the transfer function between different contiguous foundation systems. Impact of future on-site road traffic was simulated and measured directly on the test foundation. Measurements were also carried out within existing facilities to practically collect vibration input levels at the support pad of mechanical systems like pumps, chillers and axial fans. All these measurements were used to adjust a numerical model predicting the dynamic behavior of the process floor under operational conditions. This paper presents the result of the various measurements carried out and describes the methodology used to finalize the structural design of the building and optimize the facility lay-out concept. Some results concerning the predicted value of the vibration velocity at the process-floor level are presented.

This presentation reviews the evolution of the microelectronics industry in terms of sophistication of facility requirements as related to process equipment and the ever decreasing size of circuit features into the present sub-micron level.

The design of vibration-sensitive laboratories normally requires the protection of these areas from incoming vibration generated by plant, road traffic and footfall impacts. The compact nature of the new HKUST campus requires a more exact design than one would find for a spacious campus with laboratory buildings nicely separated. The HKUST user required a centralized laboratory service with easy access to the major testing facilities. This resulted in the location of vibration sensitive areas (micro-fabrication center and metrology laboratory) close to a Structural Laboratory housing large shakers. These were to be used for seismic and modal testing of structural elements and prototypes. The design of the support structure for the shakers, known as the reaction floor, was critical to the success of the building. Particular attention was paid to the design and construction of the foundations for the reaction floor. For controlling the vibration generated by 10-ton-force rated shakers, a massive structure with caisson supports was designed for the reaction floor and reaction wall. Finite element models were employed to calculate the response of the laboratory floors located above the reaction floor in other parts of the building. The metrology laboratory structure and the foundation design of the reaction floor and a wafer fab built in the U.K. will be presented.

Many aspects must be considered in the design of low-vibration buildings. One major aspect is the floor supporting the vibration-sensitive equipment. This paper addresses the design of several types of floors for low-vibration environments, drawing from some of the authors'' design projects.

The typical concrete and steel building structure has very little inherent damping, resulting in a very large Q, a measure of the sharpness of the amplitude response at resonance. Some damping effects are provided through the inertia and friction provided by a building''s full height partitions, hung ceilings, furniture, and suspended ducts and piping. These items have an effect on the very low amplitude vibration that affects sensitive laboratory equipment and the processes used in the microelectronic industry. This paper presents studies of transient vibration of floors in two existing buildings. The floors have been treated by adding a two inch thick concrete topping to the structural floor. This additional layer of concrete was treated by using a viscoelastic damping admixture in place of some of the water used to form the concrete. The admixture can dramatically reduce the Q of concrete from the normal 200 to between 20 and 50, depending on the amount of admixture used per yard of concrete. The measured velocity and frequency of the transient vibration excited by footfalls is compared to the predicted velocity and frequency of the same floor structure without the damping admixture. A formula to predict the peak transient vibration velocity due to footfalls for a concrete floor with a viscoelastic admixture is proposed.

Design of the Electrical Engineering/Computer Science Building at the University of Minnesota included development of a very low vibration environment for research in submicron processes in microelectronics. The new facility which opened in 1988 has 325,000 gross square feet of space on six floors and cost approximately $DLR35 million. The vibration control process consisted of: (1) establishing permissible vibration levels for extremely sensitive equipment, (2) monitoring site vibration, (3) isolating the microelectronics lab, (4) analyzing expected floor motion in the structure using finite element methods, and (5) isolating the HVAC mechanical equipment. The permissible floor vibration for the facility was 100 (mu) in/sec for the microelectronics floor and 1,000 (mu) in/sec for the remainder of the facility. Since there were several large engineering buildings and a main vehicular thoroughfare directly adjacent, vibration measurements taken at the site during the design phase showed the maximum ground surface and floor motion to be 1,350 (mu) in/sec and motion in the bedrock level at only 40 (mu) in/sec. A two-foot thick, solid, reinforced concrete floor was designed for the microelectronics lab, supported on three-foot diameter caissons down to bedrock, spaced on nine-foot centers and isolated from the soil. A computerized structural vibration analysis was completed with a finite element model of a typical bay of the entire building to predict response of the building to ambient and equipment excitation. The results of these predictions along with the building performance test data show the floor motion to be less than permissible levels.

Environmental factors must be controlled including floor vibration, acoustic level and magnetic field when choosing a site for an electron microscope. A systematic procedure for selecting a site from possible candidates is presented in this paper.

Many vibration sensitive buildings have floors supported by columns without perimeter walls. Consequently, these structures are relatively weak horizontally and behave like a simple table, or entablature, demonstrating an undesirable horizontal resonance. Methods of controlling horizontal microscale vibration in floor entablatures are discussed. Empirical data collected by Frank Hubach Associates, Inc. (FHA) from tests of various building structure configurations are examined to demonstrate techniques of controlling this resonance. Vibration control methods are useful in the design of facilities housing scanning electron-beam microscopes, and other metrology instruments. Initial design treatments can be employed in a straightforward manner, but retro-treatments are nearly impossible because they are fundamental to the basic structure. An FHA design incorporating several vibration control techniques was successful in controlling the horizontal resonance.

The utility and limitations of two-dimensional Finite Element Analysis (FEA) of building foundation vibration characteristics using real eigenvalues is investigated. While concentrated dampers are often used to model radiation away from the ground model boundary, they introduce a non-proportional damping matrix and thus complex modes. This type of analysis is beyond the capability of many desktop FEA packages. The results of real mode (uniformly distributed damping) plane strain calculations of vibration transmission across typical building foundations are discussed, along with the various factors effecting their validity. These factors include: the extent of ground which must be modeled; the damping loss factor which must be applied in order to limit the effects of reflection from the boundaries (and how this relates to the ground extent); the element grid size; and the number of modes used in the modal superposition. The limited results obtained to date results show that real mode analysis, properly interpreted, can be useful in predicting the differences between alternate foundation designs as regards their vibration characteristics.

Excessive vibration of structures supporting optical equipment degrades equipment performance. Manufacturers'' maximum allowable vibration criteria are frequently insufficient for determining the acceptability of a vibration environment. Criteria development and effective dissemination are critical issues which must be adequately addressed. Criteria development must include consideration of dynamic characteristics encountered in building structures, mechanisms resulting in degraded performance, and analysis methodology most suitable for quantifying the threshold of degraded performance. Published criteria must explicitly state the required vibration analysis methodology and measurement units of RMS, O-pk, or pk-pk. This is crucial because quantitative results of vibration analysis can vary significantly with different analysis methodologies, thus influencing acceptability of the vibration environment relative to a given criterion. An Institute of Environmental Sciences working group composed of microelectronics manufacturers and researchers, FHA and other vibration consultants, has drafted a recommended practice for measuring and reporting vibration and developing criteria (''RP-24''). This paper provides a brief introduction to the IES draft Recommended Practice RP-24, ''Measuring and Reporting Vibration in Microelectronics Facilities.'' Examples are provided which illustrate quantitative effects of variations in vibration analysis methodologies.

For many areas of acoustics, standards organizations or regulatory bodies have mandated vibration or noise criteria and defined the appropriate processing methods. No such standards exist for vibration-sensitive facilities at this time except as defined by equipment manufacturers, facility owners, and/or vibration consultants. The existing criteria from these groups differ widely in form. This paper reviews the various candidate methods offered by current technology for processing measured vibration data.

Characterization of very low amplitude, very low frequency vibration requires specialized sensors and systems not found within the standard industrial sources. Standard seismological instrumentation can be directly adapted to these difficult industrial vibration measurement needs. This paper studies the suitability for industrial vibration measurement of various classes of active and passive seismometers and seismological instrumentation systems. Current work by a USGS-sponsored working group on Standards for Seismometer Testing provides a formal framework with which to specify the ''Operating Range'' (combined frequency and amplitude range) of various sensors. Typical operating ranges of available sensors and systems are compared with low level industrial vibration ranges. Several case studies are presented as examples of the application of seismological instrumentation to low level industrial vibration characterization.

Great strides were made during the 1980s in precision measurement and manufacturing technology. While the facilities that host these advanced processes are often different in design and function, a common concern arises in the operation of both. Excessive facility vibrations can have an adverse effect on both precision manufacturing and precision measurement operations. Frequently, vibration suppression or isolation systems are used to reduce the effects of facility vibrations on precision measurement or manufacturing equipment. The proper application of digital data acquisition and signal processing techniques can provide great insight into the influence of facility vibrations on these, and other precision operations. This paper reviews a set of techniques well suited for the measurement of facility vibrations and evaluating the need for and effectiveness of vibration isolation systems. An example of the application of these techniques to a particular facility is provided to demonstrate their use and show typical results.

Possible use of double mode gas lasers for remote recording of small vibrations of distant objects has been studies. Vibrations of the amplitude approximately 10-3(lambda) ((lambda) is the emission wavelength) have been recorded at the distance up to 30 m in the frequency range up to several megahertz. The maximum sensitivity of one of the suggested methods of vibration recording has been estimated.

A dynamical holographic interferometry technique based on reflecting grating has been developed and used to measure behavior of the vibrating surface of objects. Displacements of a steel membrane at the frequencies into the 5 kHz range can be measured over the entire surface simultaneously.

Condition monitoring programs form the basis of predictive maintenance technology which is used by many major companies worldwide to reduce costs, enhance reliability and improve safety. This paper discusses how these techniques could be beneficially applied to scientific environments and plants, such as observatories.

A PC based vibration monitoring system can be an effective tool for the prevention and diagnosis of vibration related problems in microelectronics facilities. The computing and storage power of present day PC''s, coupled with the availability of high speed data acquisition plug-in boards, allows for the creation of a powerful but low cost system. The low frequency content motion typical of buildings that support sensitive tools can be exploited by multiplexing multiple signals into a single A/D converter. By doing that, many channels of data can be monitored by a single PC without a proportional rise in system cost. Programmable A/D boards and multiplexers can be controlled by a user through the PC to provide flexibility in obtaining data samples. Once available to the PC, there is great flexibility to examine, modify, display and save data. The functions to control the system and handle the data can be integrated into a single program accessible to facility engineers. By separating the various monitoring functions into library of high level commands, a customized monitoring regimen can be assembled for each application. Commercially available software for managing and displaying data can greatly decrease development costs in the creation of such a system.

Major construction work is currently underway at Intel''s Aloha, Oregon, campus. Because of concerns about the effects that construction-generated vibration might have on adjacent ongoing microelectronics manufacturing activities, two important steps were taken. The first of these was to establish guidelines that would be followed by the construction contractor to limit vibration disturbance. The second was to install a computer-based monitoring system that would continuously measure the vibration on the floor of the microelectronics manufacturing facility. In this way, the vibration effects of the construction activities would be monitored and adjusted, by modifying procedures, if necessary. The monitoring program is discussed in this paper. The major characteristics of the monitoring system, the placement of the transducers, and the ways in which the data were managed are described. Some typical data are shown and discussed.

Various construction activities were planned in an area next to Intel''s sub-micron microelectronics facility in Santa Clara. We needed to develop a system to ensure the continued operation of the process equipment during construction without any yield problems due to transmission of construction-related vibrations. A computer-based vibration monitoring system was devised and built which provides continuous measurements and is suitable for ''interactive'' as well as for ''archive'' use. In ''interactive'' use, alarm levels are set at two threshold values which were chosen from operating fabrication plant characteristics. Continuous data generation and its analysis with respect to the construction related activities gives a clear indication of harmful construction activities and equipment. The transmission ability of vibration through the existing type of soil and isolated grade slab construction is also studied. The dampening or amplifications of vibration levels with respect to location and distance from the source has been characterized and evaluated.

This paper describes a floor monitoring system utilizing a PC that continuously monitors very low levels of vibration and warns the user of possible " vibration contamination" that might result. The floor monitoring system designed by DataSignal Systems Inc. in Friendswood Texas is a complete package including special purpose microvelocity sensors signal conditioning and band specific velocity detection electronics analog-todigital sampling vibration spectrum analysis parameter trending alarming and archiving measurements. An IBM or compatible computer runs the systems software and displays the measured results. The computer can be installed in a convenient location for ease of use and maintenance. In order to maximize its effectiveness for alarms and ease of data display interpretation a VGA color monitor is a must. Since the system monitors facility vibration continuously the computer must be dedicated and not time shared. 2 . MEASURE MICRO-VIBRATION In many of todays high technology manufacturing facilities vibration can have a costly impact on the process and quality of an operation. This system can be set to alarm at vibration levels determined to be critical allowing an operator to take appropriate steps including date and time coding the process or even stopping the process. The system can also be used to establish limits for manufacturing operations in an adjoining facility that causes structure borne vibration to be transmitted to the vibration sensitive manufacturing area. Up to eight micro velocity sensor can be monitored simultaneously with results being displayed in a bar chart format on the computer screen. For detailed analysis purposes to help identify the source of vibration a narrowband FFT processor is used to display a vibration spectrum from a selected sensors output signal. The vibration spectrum analysis capability can be manually activated or be automatically acquired upon an alarm condition. 0819407577/92J$4. OO SPIE Vol. 1619 Vibration Control in Microelectronics Optics and Metrology (1991)1337

Alignment sensors based on silicon position sensitive detectors intended for use in space-based vibration and pointing control systems are presented. These sensors meet angular accuracy requirements on the order of a microradian. The detectors are sensitive to a wide range of wavelengths and input beam temporal characteristics. The examples presented are responsive to radiation from a 20 kHz modulated 834 nm laser diode and a 25 ns pulsed 532 nmdoubled Nd:YAG laser. Sensors using this unique silicon position sensitive detector have achieved 1 linearity over much of the detector field and require little post-processing. The electronics required to process the detector signals are relatively straightforward although the high accuracy demands that the detector channels have well-matched gains. The overall design of these sensor packages is reviewed and performance data is presented. 1. BACKGROUND A beam control system was required to eliminate vibration and jitter effects in a large optical system designed for flight on the space shuttle. The goal of optical control systems is to maintain beam stability in angle and position. Beam correction over the optical path is performed with several steering mirrors and beam motion is detected in associated sensor systems. The control system requires accurate position and angle information in order to stabilize the beams. This implicitly requires good sensor measurement repeatability over a field of view large enough to accommodate the expected range of variation. To minimize

By using a special control device on a specially designed wheel a coherent bundle of optic fiber with large crosssection can be made.