AIRBORNE MOLECULAR CONTAMINATION (AMC) continues to grow as a major contamination control issue for microelectronics manufacturers. Because of this, chemical filter manufacturers are offering a large number of AMC control options from which the facilities, process, and contamination control engineer must determine which is the best solution for their specific AMC control application(s). This series of articles will present information on the various types of chemical filters available, strengths and weaknesses, and the results of independent performance evaluations for a number of different chemical filter types. Over the next three issues of Controlled Environments Magazine, several AMC control strategies employingchemical filtration will be discussed. Topics to be covered will include:

Part 1:
-AMC Classifications
-AMC Monitoring
-AMC Control Considerations
-AMC Control Technologies

Part 2:
-AMC Filter Types
-Chemical Filter Application

Part 3:
-Specifying an AMC Control System
-Final Considerations for AMC Control

AMC control has become fully integrated into the cleanroom environmental management requirements of high-tech manufacturing facilities. The optimum control ofAMC involves three steps:

1. ASSESSMENT of the air quality both outside and inside the facility to identify target contaminants, as well as those that could affect the performance of the AMC control system.

2. Selection and qualification of an AMC CONTROL system.

3. Ongoing MONITORING of both the controlled environment and the performance of the AMC control system.1

Cleaning the outside air that is used for ventilation and pressurization, removing tramp and fugitive emissions from recirculation airstreams, and cleaning process emission and exhaust streams are some of the many applications that require AMC control. Just as there are a wide variety of AMC control applications in the cleanroom, there seems to be an equal number of control options available to contamination control personnel.

With what may seem to be an overwhelming number of items to be considered, how is the contamination control engineer supposed to make the proper choice for a particular application? Here are the key issues to understand and steps one needs to take to establish a successful AMC control program.

AMC Classifications
The first consideration in the selection of an AMC control system should be an assessment of the type and quantities of AMC to be controlled. This can be done by direct gas monitoring or with passive or real-time reactivity monitoring.2There can be dozens of contaminants present in a makeup or recirculation airstream, but there may only be relatively few that require close control.Contaminant classifications can both help to group similar contaminant typesand make the selection of the proper control system more straightforward.

SEMI Standard F-21-11023classifies AMC in cleanrooms by their chemical properties, providing a way to characterize the environment by groups of materials that could have similar effects on an exposed wafer. The purpose of this standard is to classify cleanrooms with respect to their molecular (non-particulate) contaminant levels. The classifications are defined as:

• -Acid: a corrosive material whose chemical reaction is that of an electron acceptor.
• -Base: a corrosive material whose chemical reaction is that of an electron donor.
• -Condensable: a chemical substance capable of condensation on a cleansurface (excluding water).
• -Dopant: a chemical element that modifies the electrical properties of a semiconductive material.

Given the recent publicity that personnel exposure to potentially toxic and hazardous materials in semiconductor manufacturing has received, AMC control systems must also be designed to protect people as well as products. Thus, another way to characterize AMC would be based on the potential health effects to exposed personnel. In this light, we could generally classify AMC as being toxic, corrosive, irritating, or odorous in order of decreasing severity.