Lithography Cleanroom Design: Controlling Vibration and EMI

A lithography cleanroom is far more involved than simply a “cleaner room.” Ground micro-vibration, equipment vibration, airflow turbulence, static discharge and electromagnetic interference all need consideration during build-out as they can negatively impact overlay accuracy and repeatability of a process.

Inadequate addressing of these factors is often done by placing isolation pads or metal mesh over slabs after equipment arrives. By this time, the best and least expensive control window has already passed. A structural solution needs to be provided in the building shell, room enclosure, ceiling grid, FFU layout, HVAC, pipe isolators, grounding and equipment foundations from the first day of construction.

Figure: Integrated design for structural slab, equipment foundation, floating floor, EMI-shielded envelope, FFU ceiling and utility supports.

Why Integrated Control for Vibration and EMI is Essential for Lithography Cleanrooms

Standard solutions for electronic cleanrooms generally fail because they regard vibration, EMI and particle controls as unrelated topics. For lithography, these factors act on each other continuously.

For a cleanroom to achieve process stability, it’s inadequate to target ISO standards for particle counts. A semiconductor cleanroom design must consider the interaction of particle and structural dynamics, temperature, humidity, airflow, shielding, and construction quality as a single cohesive system.

Three risks affecting lithography stability

• Disturbance to the structure and ground: Movement and operation of personnel, equipment, CHT, pumps, HVAC fans, etc. impart energy to the floor.
• Disturbance to the air: The operation of FFUs, flow patterns to and from the cleanroom, air dampers, and pressure fluctuation will disrupt the airflow in the vicinity of the stepper.
• Disruptions in EMI grounding can occur due to the operation of devices, motors, and power distribution RF sources. Disruptions can also occur on interrupted metallic shield interfaces and can create circuits that leak and cause interference with metrology and exposure equipment.

Key Elements for Cleanroom Design for Lithography Areas in Semiconductors

The design should start with process zoning, not peripheral wall panels. Identify the functional process zones of exposure, coat/develop, metrology, maintenance access, and transfer of materials.

Identify vibration sensitive areas, EMI sensitive areas, high heat areas, and high traffic areas. Depending on the zone, determine the classification of cleanliness, pressure differentials, temperature and humidity, vibration, noise, and EMI.

Design interfaces that require close coordination

• Foundations for equipment and structural slabs
• Wall panels, ceilings and door/window systems of the cleanroom
• FFU/HEPA supply and plenum
• MAU/AHU and pathways of return air
• Process exhaust and chemical fume management
• Grounded cable trays and shield layers
• Supports for equipment, pipe and duct
• Doors for logistics, for access to equipment, and for maintenance

Mitigation of Vibrations in Lithography Rooms

Mitigation should remove or isolate sources of vibration, not simply add isolators to the feet of equipment. The starting point for lithography room vibration control is mapping the sources of vibration and the means of transmission.

Examples of sources can include: traffic, building and mechanical systems, AHU/FFU, ducts, pipes, ceiling grids and even the walkways used by personnel.

Isolate products selectively after identifying sources of vibration

• Roads and rail systems
• Structures
• Rotating machinery
• Fan assemblies
• Air ducts
• Ceiling suspension systems
• Tool foundations and access routes

Vibration criterion (VC) curves – choose the grade according to your system

Lithography tools have particular limitations on vibration velocity. The following table summarises the VC grades that are commonly found in the design of semiconductor fabrication. Always check the specifications with your tool vendor.

Source: Generic VC curves adapted from IEST‑RP‑CC024.1 and tool vendor recommendations.

Vibration control design has four levels.

1. The strategy for structural and equipment foundations

Determine the stiffness and natural frequency of the slab, and if isolated, the sensitive equipment is separated from the rest of the operation. Avoid placing heavy MEP equipment directly above, below, or next to the lithography zones.

2. Isolate all mechanical services from the cleanroom envelope

To break the rigid vibration path from the fans, AHUs, and ductwork, use flexible duct connectors. In practice, flexible connector lengths are typically ≤300 mm and 150–250 mm are the most common. Anti‑sway supports should be installed as close as 1 m from the flexible connector to mitigate secondary vibrations.

AHU fan outlet → flexible connector → independently supported duct → cleanroom ceiling penetration.

3. Develop systems to minimize vibration

Direct-drive EC fans eliminate the belt-drive vibration and droplet formation while decreasing maintenance. FFU modules typically provide consistent airflow at around 0.45 m/s ±20%. Final air velocities need to be confirmed via CFD and the heat load of the tool. Deiiang™ FFU’s measured airflow uniformity with a CV (coefficient of variation) of ≤ 4.8% — an important factor for airflow stability.

4. Confirm with onsite measurements

Conduct baseline testing for empty room conditions, compare with HVAC systems both on and off, collect data on adjacent equipment start/stop test, and measure during the entire production cycle. After you implement corrections, re-measure and keep a log of all data.

EMI Shielding Cleanroom Design: From Material Selection to Grounding Continuity

EMI shielding cleanroom design requires a fully integrated shielding solution to create a continuous conductive enclosure. This leads to common failures of gaps between panels, doors, windows, and utility penetrations leading to uncoordinated grounding.

A grounding uncoordinated gap may result in shielding failures of ~20–40 dB with little loss of shielding in these critical frequency bands.

EMI shielding comprises a complete enclosure rather than a metal surface.

• Wall and ceiling panels: Overlaps and proper bonding techniques/disciplines ensure conductive continuity.
• Doors and windows: Conductive gaskets, coupled with shielded glazing and frame continuity, help shield windows.
• Utility penetrations: Shielded conduit, waveguides, and conductive gaskets provide continuity for ducts, cables, and conductive gaskets.
• Ceiling grid and equipment supports: Support structures shall be designed to eliminate unintentional EMI coupling.
• Grounding network: Clearly marked test points define a single-point or mesh ground.

Material strategy for cleanroom construction shields in semiconductor fabrication facilities

The panels of the cleanroom need to be flat, structurally stable, and easy to clean. Deiiang's hollow magnesium oxide sandwich panels, with 5 mm top and bottom sheets, 11 offset ribs, and 13 noncollinear splicing points, lend their support to manufacturing continuity and structural shield integrity when bonded, along with ≥1.2 kN/m² bending resistance and ≤0.5 mm/m flatness deviation.

For areas with strict fire control regulations, Class A non-combustible Fire-rat cores are available. Use sealed joints and coved corners to streamline cleaning and maintain integrity of the enclosure.

Shielding performance must be tested after installation.

• Continuity and grounding resistance tests must be performed.
• Scan for leakage around doors, windows, penetrations and air grilles.
• Test shielding effectiveness in critical frequency bands.
• Re-testing must be performed after any modifications or retrofitting.
• Test results, point maps and corrective actions must be documented.

Standard Test Protocols for Field Validation

To ensure credibility and repeatability, Deiiang integrates globally accepted test standards during the commissioning phase. These protocols provide clients with evidence and verifiable data, eliminating the need for guesswork.

• Vibration Testing per ISO 10816 / IEST‑RP‑CC024.1 — velocity and acceleration spectra, 1–100 Hz
• Shielding Effectiveness (SE) per IEEE 299 / EN 50147‑2 — 10 kHz to 18 GHz, measured using transmitting and receiving antennas
• Airflow and Cleanliness per ISO 14644‑3 (2019) — particle counting, airflow velocity and airflow uniformity
• Grounding Continuity per IEC 60364‑4‑41 — earth resistance ≤1 Ω, bonding impedance verified

Safe and Reliable HVAC, FFU and Filtration Design for Stable Lithography Environments

There is a direct correlation between air cleanliness, airflow velocity, and uniformity in a semiconductor cleanroom design. Proper FFU design, static pressure, air volume, return path, heat load and airflow, and the organization are the primary design drivers, not the grade of the filter.

Typically, the FFU outlet velocity is in the range of 0.45 m/s ±20%, however the final design velocity and the outlet placement should be determined based on tool specific requirements and validated airflow modeling.

Terminal filtration and ceiling integration.

High-efficiency supply outlets should offer filter replacement, sealing, suspension and maintenance access. A bottom-access design fosters replacement of filters from inside the cleanroom which eliminates the need for personnel to enter the ceiling plenum.

Common setups have a range of components including plenum boxes, insulation, sealing gaskets, pressure clamps, HEPA/ULPA filters, and diffuser plates. Installation must be designed to manage bypass leakage at the ceiling interface.

Bottom-access HEPA supply outlet — filter change occurs inside the cleanroom.

Control of Semiconductor MAUs and AMC

For semiconductor manufacturing facilities, make-up air units (MAUs) are designed to handle multiple concerns like particles, temperature and humidity, airflow, air management and controls (AMC), and even changes throughout the seasons. A makeup air unit (MAU) generally has the following order of components between the outside air and cleanroom air: inlet, pre-filter, pre-heat, pre-cool, scrubber, re-cool, re-heat, fan, equalization, chemical filters, a medium filter, and lastly a HEPA filter before air is supplied to the cleanroom.

MAUs for semiconductor manufacturing can be designed to handle air volumes between 40,000 to 180,000 m³/hr at a design static pressure of approximately 800 Pa for each of the manufacturing facilities. The final capacity of the MAUs is determined by the resistance of filter banks, ducting design, and the processes of the facility.

Acoustics and Airflow Control Without Risk of Particulate Contamination

Conventional duct silencers are made from fibrous materials that can shed particles and accumulate dust. Therefore, for lithography clean zones and clean zones of a higher grade, solutions to control noise must be compatible with the cleanliness of that clean zone.

The Compatibility of Cleanroom Requirements with Conventional Duct Silencers

In time, fibrous linings can break down and shed fibers or particles. In critical zones, use metal-based or non-shedding alternatives, and always ensure materials are compatible with cleanroom standards.

Cleanroom Compatibility Stipulations on Duct and Airflow Design

• To make airflow less noisy, you can lower airflow velocity and control route airflow and ducts.
• In clean supply air paths, use materials that do not shed particles.
• Choose dampers, valves, and grilles that will not vibrate or make abnormal noise at the flow rate for which they are designed.
• In general, damper face velocity should not exceed 20 m/s when fully open. Vibration and noise should not be present when dampers are near the closed position.
• Include flexible connections, damper range, and diffuser selection in the system noise budget along with duct velocity and noise level.

Rapid Assessment: Lithography cleanroom grade Estimator

Select your process node and tool type below to receive an estimated cleanliness class along with a VC grade and EMI attenuation target. This tool is based on average industry data, so it is recommended to check with your tool vendor.

Standard vs. Lithography‑grade cleanroom: Key Differences

Deiiang Project Case Study: Lithography Cleanroom Upgrade for a Semiconductor Facility

Deiiang™ was responsible for a lithography cleanroom integration within a semiconductor fab expansion project. The project included cleanroom partitioning, an FFU ceiling, EMI shielding, ductwork, and foundations for equipment that are vibration-isolated.

Project overview

• Location: [Country / City]
• Client type: Semiconductor foundry
• Project nature: Lithography area upgrade
• Area: [XX m²]
• Cleanliness class: ISO Class X
• Scope: Panels, ceiling, doors, FFU, duct shielding, installation and testing

The project challenge

Micro-vibration concerns were caused by the mechanical equipment and structural slab modes, adjacent to one another. An access plan was needed to maintain the ceiling, which was dense with FFU, cable trays, ducts, and process tools. Tight constraints on EMI, cleanliness, sealing, and the project schedule required a coordinated effort.

Deiiang's Integrated Solution

• modular cleanroom panels
• Sealed radius corners
• Flexible vibration isolating connections at fan and AHU interfaces
• Independent supports for ducts, cable trays, and heavy utilities
• FFU and HEPA terminal filtration matched to airflow and heat load
• Continuous EMI shielding and grounding along panels, ceiling, doors and penetrations
• Post-construction testing and verification of airtightness, airflow, pressure, vibrations, and EMI
• As-built documentation with tests and guides

Scenario-Based Design - How a Typical Lithography Facility Manager Communicates a Problem

Persona - Daniel, Facilities Manager, Semiconductor Expansion Project

Daniel is the facilities manager for the expansion of a lithography area in a working semiconductor fabrication facility. His team is tasked with constructing new cleanroom partitions, FFUs, and utility routes, along with the necessary shielding, in adjacent areas of the production facility. Typical construction is a concern for Daniel, as he knows that vibration paths are created with ceilings, ducts, and supports for equipment. Daniel wants a vendor that will provide him with the drawings, the materials, the construction details, testing, and documentation for the site.

Deiiang™ serves this purpose for Daniel through early zoning, interface mapping, structural and MEP (Mechanical, Electrical, and Plumbing) coordination and validation on site. The use of standardized details, traceability of materials, and testing fulfill the requirements of a low-risk handover.

Design and Commissioning Checklist for Lithography Cleanrooms

Check off items that are complete by clicking on them. Use the Print button to export your Project Checklist as a PDF.

Frequently Asked Questions

References

• ISO 14644-1:2015 — Cleanrooms and associated controlled environments
• iso 14644-4:2022 — Design, construction and start-up
• iso 14644-3:2019 — Test methods
• IEST-RP-CC012.3 — HEPA/ULPA filter testing
• IEST-RP-CC024.1 — Measuring and reporting vibration in cleanrooms
• IEEE 299 — Standard method for measuring shielding effectiveness
• EN 50147-2 — Anechoic chambers / shielding effectiveness
• GB 50243-2016 — Code for acceptance of ventilation and air conditioning construction
• Deiiang™ Technical Library — Cleanroom System Design Guide