PPT - Time for a Reality Check?

摘要

As the progress toward smaller linewidths and higher complexity continues, industry chemical and material purity and contamination requirements are becoming increasingly exacting. Chemical purity specs have risen from parts per million (ppm) to parts per billion (ppb), and now suppliers must provide parts per trillion (ppt) levels - sometimes even parts per quadrillion (ppq). It is no better for materials. A 4N5 (99.995%) purity for elements such as those used in sputtering targets and other applications is considered adequate for most current applications, but it is theorized that 6N (99.9999%) may be needed for 0.18 μm (180 nm).