In Compound Semiconductor fabs housekeeping is a vital part of the Environmental Health and Safety (EH&S) compliance. Toxic particulates comprised of GaN, GaAs, InP and other III-V elements are present on fab floors, walls and tool skins and the housekeeping practices must be designed to efficiently and thoroughly clean all these surfaces.
In order to control toxic particulate levels, compound semiconductor fabs employ stringent housekeeping SOP’s. A common practice is that fab floors are mopped multiple times per day while walls are cleaned daily or weekly.
In order to measure the effectiveness of current housekeeping practices, a GaAs fab employed Foamtec’s surface cleanliness audit procedure. This involves sampling the previously mopped or wiped surface with a PolyCHECK inspection wiper to measure post clean results. PolyCHECK is a black polyester fabric with high static attraction and is designed to collect samples from surfaces for further analysis by SEM/EDX or FTIR. The ability to collect samples from a larger surface area and then use a SEM stub to transfer the sample from the wiper to the SEM produces a much more rich set of data at far lower cost.
Figure 1 is the condition of a .25 square meter of surface as analyzed via SEM/EDX after the fab floor have been mopped by the process of record(POR)
Given the amount of toxic particulates in compound wafer fabs, an important component of a robust housekeeping SOP is the ability to clean underneath and behind process equipment.
In Figure 2 about .1 square meters underneath a process tool was sampled and highlights the difficulty housekeeping staff faces cleaning tight restricted spaces.
Taking into account high spaces and large surface areas, vertical equipment surfaces and cleanroom walls present cleaning challenges to both equipment techs and housekeepers.
Cleanroom walls, depending on the type of mop employed often must be wiped. This is extremely time-consuming and prone to error given the inefficiency of hand wiping considering the amount of surface area involved.
Figure 3 is the surface cleanliness of .5 square meters of wall space at eye level after hand wiping with polycellulose non woven wipers.
More problematic yet are tool skins which are often no man’s land for cleaning. Housekeeping staff is banned from touching equipment while the techs who are charged with equipment cleaning often do not have the time or ability to efficiently reach all the surfaces.
Figure 4 is the surface cleanliness after hand wiping with polycellulose of 25 square CM of a section of tool skin easily accessible to the tech.
The data collected in figures 1-4 suggests that POR cleaning materials currently employed in housekeeping and equipment cleaning SOP are not sufficient to achieve EHS compliance goals.
To help Compound wafer fabs achieve safe working conditions, Foamtec has introduced PharmaSAT.
PharmaSAT employs two strips of Sahara foam laminated to a microfiber fabric and is presaturated with 100% ultrapure water of 10% IPA. The Sahara strips are designed to afford scratch free scrubbing of glass, plastic, ceramic and metal surfaces and to dislodge particulates that are stubbornly adhered and then entrapped and removed by the MiraWIPE microfiber fabric. The mop head fits on a super flexible mop frame and handle that offers great ergonomics and control enabling operators a tool to quickly and efficiently clean fab floors, walls, ceilings and even tool skins.
PharmaSAT’s unique MiraWIPE microfiber fabric enables all surfaces to dry within seconds of mopping to eliminate risks associated with drips and wet floors.
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The lightweight swivel design of the handle and the scrubbing and pickup properties of the mop enable operators to achieve much more thorough cleaning of tight spaces underneath and behind equipment.
Unlike other mops, the PharmaSAT mop heads are more similar to presaturated wipers which allow techs to efficiently clean equipment skins before and after PM’s improving both safety and contamination control practices.
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