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Seismic / Earthquake Protection

Seismic activity is a concern in many locations where semiconductor manufacturing equipment is installed. Although the likelihood of seismic activity is relatively low, the risk of injury to personnel and equipment or facility damage is relatively high in a seismic event. To this end, semiconductor manufacturing equipment must be designed to survive an earthquake and to control the risk of injury and equipment damage to the greatest extent possible.

The seismic requirements of SEMI S2 are included to drive equipment manufacturers to design the structure of semiconductor tools and their components to withstand seismic forces and to provide necessary information to end-users to appropriately secure the equipment in their facility upon installation.

One crucial aspect is identifying the components in which failure or the release of hazardous energies or chemicals is more likely and taking the appropriate engineering steps to reduce the risk of injury to personnel and equipment or facility damage. The design should control the failure of these components and they should be accessible for evaluation of damage after the seismic event.

Another crucial aspect is adequate anchoring of equipment to ensure its stability during a seismic event. The locations of these anchoring devices (floor tie-downs, bolt attachments, etc.) should be clearly identified on the equipment. For equipment containing hazardous production materials, the anchorage points should be capable of withstanding a horizontal loading of 94% of the weight of the equipment acting at the center of mass. Equipment that does not contain hazardous production materials should have anchors that are capable of withstanding a horizontal loading of 63% of the weight of the equipment acting at the center of mass. These loads should be calculated on the axis that produces the largest load on the anchorage points.

In addition to the above horizontal design loads, the equipment anchoring should be capable of preventing overturning during a seismic event. A maximum value of 85% of the weight of the equipment should be used to resist the overturning moment when calculating the acceptability of the anchoring equipment to resist overturning. These calculations demonstrating the equipment¹s securing against horizontal loading and overturning should be provided for review.

In order to provide the necessary information to end-users for appropriate securing of equipment, the equipment manufacturers should provide the following data and procedures:
A drawing of the equipment, its support equipment, all connections (ventilation, water, vacuum, gases, etc.) and seismic anchorage locations.
The type of feet used and their location on a base frame plan drawing.
The weight distribution on each foot.
Physical dimensions, including width, length, and height of each structurally independent module.
Center of gravity location for each independent module.
Acceptable locations on the equipment frame for anchorage.
This information should be included in the installation instructions and requirements that accompany the equipment.

The above requirements are based on the assumption that the structure of the semiconductor manufacturing equipment in question is rigid. The assumption of rigidity is not appropriate for all semiconductor manufacturing tools, because they may be designed to allow movement, or because they may be of a light and tall design. In these cases it is more appropriate to apply the SEMI S2-93A requirements that assume a seismic wave with frequency of 30 Hertz. An acceleration of 4 m/sec2 is applied on the X and Y axes simultaneously and a 2.5 m/sec2 acceleration is applied on the Z axis. The frequency of acceleration applied should be in the 0-30 Hz range. The modeling and calculation of the appropriate strength of supports and attachment points is more complex for this scenario, and the data needs to be provided for review.