As the microelectronics industry moves into ever increasing miniaturization, the requirements for the amount and purity levels of chemicals being provided to support these technology changes are dramatic. Historically, the necessity for chemical purity was secondary at best; most concerns about contamination control were either airborne or gas delivery issues.

As these elements have matured to parts per trillion (ppt) purity requirements, however, the defects being considered today have evolved to a point at which molecular contamination and other elements of process are coming under ever-increasing scrutiny. It is for this reason we are being challenged to redefine the configuration and materials of construction of delivery systems and the resulting point-of-use purity levels over a wide band of bulk and specialty chemicals. This article will discuss some of the more prevalent aspects of this evolving requirement.

Engineering Considerations

With the increasing numbers and volumes of chemicals required to support processes that are defined in line widths as small as 0.065 microns, the semiconductor fab engineer must rethink the effects that chemical solutions and chip processes might have on the yield.

Compounding this challenge is the recognition of molecular contamination as a measurable concern. Trace metals historically recognized in chemicals, but often disregarded, are potential risks to acceptable yields. What is still not clearly defined is to what degree molecular contamination impacts yield; we are, therefore, now seeing owner chemical purity specifications at levels at or below 100 ppt for assurance.

With this in mind, two technologies may need to be employed to reach future purity requirements:

Membrane filtration. Ultrafiltration may be required for removing submicron particles too small to be removed via cartridge-type depth filters (which currently filter down to as low as 0.1 micron).

Ion Exchange. Ion exchange may be required to remove trace heavy metals or other ionic contaminants.