All next-generation lithography (NGL) technologies will be faced with meeting the stringent error budgets for the sub-100 nm regime. One of the major contributors to overlay error in NGL masks is the thermomechanical distortions induced during exposure. The focus of this research is to identify the thermal and structural response of the PREVAIL mask system under typical exposure conditions. Three-dimensional finite element (FE) models were used to simulate the thermomechanical response of the 100 mm. PREVAIL prototype mask. Due to the relative size of the pattern features, equivalent modeling techniques were employed for computational expedience. Equivalent thermal properties such as thermal conductivity and thermal emissivity were calculated for the perforated membrane as functions of the void fraction. The resulting mask temperature distributions were used as input into the FE structural model, where equivalent stiffness properties were employed to determine the corresponding thermal displacements. The stitching errors between adjacent subfields were also investigated in this article.