Ellipsometric Porosimetry: from Thin Films to Patterned Structures Characterization

For the sub-32 nm nodes, porous SiCOH dielectrics (p-SiCOH) are integrated using dual damascene patterning by etching trenches and vias directly into the porous material. Since p-SiCOH dielectrics exhibit a poor resistance to plasma treatments one challenge is to control the process conditions to minimize the plasma-induced damage. Until now Ellipsometric Porosimetry (EP) on blanket test wafers has been used to investigate the impact of plasma treatments on porous materials and demonstrated possible surface densification and hydrophobicity loss after the process steps [1]. Unfortunately the properties of vertically patterned structures, i.e. real circuits, may differ from the bottom of the trench region. Few studies have been performed on patterned structures to determine the sidewall modification while this information is critical for device performance. In this study quantitative measurements of vertically patterned porous materials will be demonstrated using the recently developed Scatterometric Porosimetry (SP) technique [2]. It consists in coupling EP measurements of periodic structures with a scatterometric analysis (Fig. 1). A comparison between EP and SP will be detailed on different plasma-treated samples showing that material modifications strongly depend on the sample geometry. FIGURE 1. Left: Test structure for Scatterometric Porosimetry with critical dimension CD=180 nm and pitch=340 nm. Right: methanol isotherms and pore size distribution measured on an etched p-SiCOH grating.