In the future, microenvironments will be required to maintain low oxygen and relative humidity levels to facilitate newer technology nodes.

Polycarbonate is an amorphous engineering thermoplastic. With excellent clarity, toughness, and a high softening temperature, it is used in a wide variety of semiconductor, medical, aerospace, and consumer applications. Within the semiconductor arena, Polycarbonate is used for containers or microenvironments that protect and transport critical materials, such as silicon and ceramics, as they are converted from raw wafers or disks into integrated circuits or rotating memory. In the past, moderate humidity and oxygen found in ambient air were usually benign. Today, some semiconductor manufacturing technologies have advanced to the point where even the water and oxygen in air can be detrimental, causing time-dependent haze or corrosion.^1,2

Purging with an inert gas is one method for lowering water or oxygen levels inside microenvironments. However, once the purge gas stops flowing, oxygen and water levels quickly rise. For example, after purge the relative humidity inside a traditional Polycarbonate wafer microenvironment can reach 30% in several hours. The post-purge rise in oxygen and water may have multiple causes: permeation from the exterior, leakage, or de-sorption from the materials of construction. Understanding these different factors and ultimately engineering a solution requires knowledge of the mass transport coefficients of the microenvironment materials of construction.

In this article, we describe measurements of the mass transport coefficients of oxygen and water through Polycarbonate. Subsequently, these coefficients were used to estimate drying times to remove absorbed oxygen or water, break-through times for oxygen or water, initial permeation rates as well as post-purge humidity rise of a 300 mm front opening unified pod (FOUP) constructed from Polycarbonate.