Vibration isolation is critical for many applications including bioimaging, optical alignment, and microelectronics manufacturing and inspection Many of these applications and their processes occur in environments where contamination must be controlled and cleanliness levels must be maintained.

Laboratories and manufacturing/inspection areas which require contamination control procedures can be exposed to a wide variety of vibration and shock inputs. Vibration isolation solutions used in those areas must therefore meet cleanliness standards.

Vibration from sources such as street traffic, HV AC units, pumps, and other equipment can be present in the floor, which supports manufacturing and inspection equipment. These vibrations can decrease the performance, reliability, and accuracy of measurements and processes.

Vibration measurements quantify the amplitude and frequency content of vibration in the laboratory or facility. The data are compared to either the equipment's allowable vibration specification or allowable vibration criteria for the laboratory. Vibration amplitudes which exceed the allowable specification must be reduced to within acceptable limits for the equipment to operate properly. Vibration measurements should be made by qualified personnel following the recommended practices of lEST -RP-CCO24.1, Measuring and Reporting Vibration in Microelectronics Facilities.1

Contamination specifications and cleanliness levels are used to define molecular residue and particle allowances These levels apply to surfaces, assemblies, components, fluids and materials to be used in the cleanroom Specifications should follow the format given in lEST -STD-CC1246D, Product Cleanliness Levels and Contamination Control Program.1

Isolation Systems

Measurement results and their comparison to the allowable limits of vibration will determine the type of isolation system and its isolation characteristics required to reduce the unwanted environmental vibration. Scanning electron microscopes (SEMs), atomic force  microscopes (AFMs), steppers, mask aligners, and optical experiments are typically installed on workstations or tables which incorporate vibration isolators (Photo). Pneumatic isolators are widely used in the tables and workstations due to their superior isolation efficiency at low frequencies.

Vibration isolation tables and workstations are required to meet the same cleanroom and contamination standards  that the components they are protecting from vibration must meet.

Hardware should be stainless steel, which is either cleaned by passivation or electropolishing to reduce particulates. All surfaces of the isolation table should be accessible for cleaning and constructed so that they can be easily wiped to maintain cleanliness. Isolator diaphragms should meet the specified outgassing, nonvolatile residue (NVR) and total mass loss (TML) specifications to keep molecular contamination to an absolute minimum. Pneumatic isolation tables operate on a supply of compressed air or GN2' When used in cleanroom environments (Class 10,000 and lower), the supply and exhaust gases used to maintain the interior pressure of the isolators and level of the isolated work surface should be vented and piped out of the controlled areas. This requirement does not allow gases which are not filtered properly to contaminate the environment.

Providing a design that maintains cleanliness and contamination levels and is clean room compatible is the responsibility of the vibration isolation table supplier.

REFERENCES

1 lEST, 5005 Newport Drive, Suite 506, Rolling Meadows, IL 60008-3841; 847-255-1561, fax 847-255-1699; iest@iest.org