LIGO Vacuum System Study

A laser interferometer gravitational wave observatory (LIGO) is being developed with sensitivities that will have a high probability of detecting gravitational waves from astrophysical sources. Detectors are also planned by others in Europe and eventually in space. A major component of the proposed LIGO is a total of 16 km (10 miles) of 1.2 m (48 in.) dia tube at a pressure of less than 10-8torn It will be of 304 L stainless steel procured directly from the steel mills with the initial hydrogen content specially reduced. (Target is 1 ppm by weight.) Projections of the outgassing rates of hydrogen and of water vapor as a function of time will be given and the uncertainties discussed. Based on these, a preliminary analysis of the vacuum system will be presented.

Experimental Results of the IES Modal Plate

Studies show that a rectangular plate is a useful modal structure that can be used for several purposes, such as comparing various modal systems and modal extraction algorithms, comparing test techniques, and training new personnel in these tasks. Plates roughly 53 cm x 32 cm x 2 cm (21 in. x 13 in. x 0.8 in.) were constructed by several participants from polymethyl methacrylate. The plates were then tested by the participants and the results compared with a NASTRAN analysis. The results show about 25 useful modes in the plate between 160 and 2500 Hz. The plate has a variable modal distribution with widely separated modes easily identified to very closely coupled modes quite difficult to separate. With careful experiments, the modal frequencies of the plate can be reproduced within 2 percent of the predicted values, and the mode shapes can be reproduced with errors of 20 percent or less. Less careful experiments can lead to large errors in frequencies, mode shapes, missed modes, and mixed modes.

Principal Component Analysis for Particulate Source Resolution in Cleanrooms

Principal component analysis (PCA) is applied to particulate size distributions measured at receptor sites in two cleanrooms. The principal components are determined by evaluating the rotated component patterns. Each component is then assigned to a source by comparing the principal components to the particle size distributions emitted by the sources. Hence, sources of particulate contamination in the cleanrooms are determined. Particle volume concentration balances are used to quantitatively apportion the contaminant levels at the receptor sites to each source. PCA can thus be used to identify contaminant particle sources and to develop strategies for improvement of the cleanroom cleanliness class.

Measuring Face Mask Performance: A Real Test

A cleanroom face mask or facial covering must be capable of efficiently filtering particles that range from 0.1 microns to over 20 microns in order to significantly control particles produced by the human respiratory system of a cleanroom worker. In addition to particle filtration efficiency, there are several other important face mask performance criteria that impact the overall effectiveness of a cleanroom mask. This article reviews the evolution of the cleanroom face mask and the test methods for measuring filtration efficiency. Performance criteria and test methods for measuring cleanroom face mask performance are recommended.

Comparing Particle Counters: Cost vs. Reproducibility

Particle counters are used in evaluating particle concentrations in liquids and gases and on surfaces. Even for the same purpose, several types are commercially available. Many factors will go into a decision about which to buy. These include upper and lower particle size detection limits; particle size subdivisions; data display, communication, and analysis capabilities; ease of use; reliability; accuracy; reproducibility (precision); and cost. A method is presented to allow comparisons based on reproducibility of measurements and cost.

Status and Needs of In-Situ Real-time Process Particle Detection

Particle defects play a major role in yield losses in semiconductor device fabrication. It is generally acknowledged that about 50 percent of all yield losses are due to particles. Processing of devices with 0.35 to 0.5 μm minimum feature sizes will exacerbate the effects of particles due to the large relative abundance of submicron particles. The cleanroom is no longer the major particle contributor because current state-of-the-art cleanrooms have less than 10 particles (<0.5 μm) per cubic foot. Particles in processing equipment now play the dominant role in wafer contamination. An analysis of the status and needs of particle detection techniques for semiconductor processing equipment and processes clearly shows that they are inadequate to meet the requirements of the next generation of devices. Detection limits must be improved both in terms of particle diameter and in the number of particles on a wafer. An experimental laser particle counter was fabricated and used to show that such a detector would be extremely useful for in-vacuum realtime particle detection. Experimental studies on wafer surface measurements show that current wafer surface scanning techniques cannot provide the level of detection needed for future devices. Ideas for a new generation of particle detection equipment are presented.

Class 100 Large Spacecraft Facility

To enhance its competitive edge in producing highly contamination-sensitive space systems, TRW has recently designed and constructed a large spacecraft assembly and test facility that is fully cleanroom compatible. Features of this facility include a large assembly and test area and a smaller support room that have HEPA-filtered vertical flow, dedicated staging areas for garment application, storage, and equipment preparation, and an automated cleanroom monitoring system (CRMS). A description of the design, construction, and certification process is given. Operational data from the CRMS and lessons learned are also presented.

Wastewater Effluent vs. Safety In Its Reuse: State-of-the-Art

A state-of-the-art review of the human health risks associated with the reuse of wastewater effluent is presented. The subject is of much concern as the need for wastewater becomes more critical in the wake of worldwide shortages of good quality water. The subject of wastewater reuse has been a controversial subject during the last few decades due to the fear of harmful effects on human health and the environment. But recent technology relating to wastewater treatment methods has changed the outlook significantly. The article offers a broad review of the available data on wastewater treatment performance particularly relating to the removal of pathogenic agents. The areas specifically covered are: wastewater quality from various wastewater systems with respect to pathogens; available conventional and nonconventional wastewater treatment technologies; available laboratory methodologies for enumerating the pathogenic state of wastewater and their reliabilities; various methodologies of preuse disinfection of wastewater and their feasibility for practical use; and the pathogen survival rates in liquid water and various other media. The human health risks associated with wastewater reuse in agriculture are assessed at the present level of understanding and are discussed in detail. Areas that need further investigations are delineated.

A Clarification of the Shock/Vibration Equivalence in MIL-STD-810D/E

This paper presents a methodology for expanding the shock/vibration equivalence analysis defined in MIL-STD-810D/E, Method 516.3/516.4, Procedure I (Functional Shock), Paragraph I-3.3. Procedure I defines equivalence only for situations where the vibration response spectrum (VRS) exceeds the shock response spectrum (SRS) everywhere in the specified range of frequencies. This paper supplements the MIL-STD-810D/E methodology with an analytical procedure for evaluating possible equivalence when the SRS is greater than the VRS. Using Miner's Hypothesis, the fatigue damage potential of the vibration cycles above the 3-δ limit is compared with the fatigue damage potential of the shock pulses in each axis. An example is included.

Virtual Impactor Aerosol Concentrator for Cleanroom Monitoring

Particles equal to or larger than 1 μm in size can significantly reduce the yield in the microelectronics industry. This is particularly evident in the packaging stage of manufacturing when chips are inter-connected, because of the relatively large areas that must be kept contamination-free during this process. Monitoring is usually done with optical particle counters. The low particle concentrations in clean-rooms, however, result in low counts and high variability. This article presents a monitoring system that uses a virtual impactor to concentrate particles between 0.65 to 2.5 μm dia and counts them with a 0.3 L/min (lpm) particle counter. Theoretical concentration enhancement ratios versus particle size are given. The use of the virtual impactor in a clean environment is demonstrated. Tests show that the transition between the concentrated sizes is sharp. The dependence of the ratios versus particle size is in qualitative agreement with theory. An aerosol concentrator could be used to give more accurate micron-size particle concentrations through a data inversion process, if experimental calibration curves are provided.