New ISO working group targets AMC
Tammy Wright
London — The effort to develop an international standard classifying molecular contamination levels in cleanrooms is officially underway. Working Group 8, established by ISO/TC 209 late last year, held its first meeting in February at the British Standards Institute here. And while members who attended are keeping mum on the details, they have reported that some of the groundwork has been laid for combating the problem, which is becoming as big of a manufacturing concern as particulation.
“We`re in the preliminary stages of development,” emphasizes Allyson Hartzell, senior staff scientist at Analog Devices (Cambridge,MA) and a U.S. delegate to the group. “Our goal
is to come up with a spec like the one in place for identifying particles
in controlled environments.”
Other delegates participating in the assembly represented Belgium, Germany, Japan, Sweden, Switzerland, and the United Kingdom, convenor of the group.
In short, the group is charged with defining, measuring and classifying molecular contamination within the envelope of current technology. That means members will have to create a generic form standard that is applicable to susceptible industries, including microelectronics, pharmaceuticals, medical, aerospace, food and nuclear processes. ISO/TC 209 has also confined the initial standard to atmospheric contamination, excluding process-generated contaminants deposited on materials or equipment.
According to Hartzell, the chemical nature of molecular contamination is a primary issue that will have to be addressed. “You have to understand the chemistry,” she says. “It will hit your yield much more subtlely [than particles] and it can be expensive to try to remedy.”
Industry concern over molecular contamination has become more prevalent in the past few years, particularly in the semiconductor sector. Hartzell says the importance placed on the subject was evidenced by attendance at a seminar she presented in mid-January for the Northern New England Chapter of the Institute of Environmental Sciences and Technology. Approximately 45 people braved a snow storm to learn more about this emerging threat. She says her audience was primarily concerned about its impact on filtration, deep ultraviolet (DUV) photolithography and outgassing of construction materials.
Devon Kinkead, co-founder and president/CEO of Extraction Systems Inc. (Franklin, MA) — a company providing airborne molecular contamination (AMC) control systems, says the semiconductor industry is currently feeling the pinch most of all because the chemically amplified photoresists that have enabled DUV photolithography are sensitive to low levels of molecular bases.
“Other effects have been noted but they do not presently constitute [such] a widespread problem,” Kinkead adds.
The truly critical element in the standard development process, according to Kinkead, is language — which the group plans to address by creating definitions of relevant terms and measurement units.
“One of the first problems that Extraction Systems experienced in the early days of the AMC discovery process was the lack of language to describe it. We would routinely arrive at customer meetings and conduct speculative discussions about some subset of the Merck index,” he explains. “Regrettably, we still have such meetings but we now try to steer our customers toward the SEMI F21-95 language system.”
While the SEMI F21-95 standard allows his company to make sense out of an otherwise unmanageable situation, Kinkead says it is very difficult to communicate a concept, much less a specification, without an application-appropriate and descriptive classification system.
The group`s next meeting is scheduled to be held in June in Belgium. Documentation for consideration by the group may be submitted via IEST headquarters. For details, call (847) 255-1561.