Fundamental characterization of silicon-containing spin-on hardmask for 193nm photolithography

ABSTRACT In this contribution, we have performed the fundamental characterization of silicon-containing spin-on hardmasks.There has been an interest in using these materials as part of multi-layer resist (MLR) technologyto replace CVD filmsinorder to improvelithographicperformance andlower theoverall process cost. However, not muchis known about thecharacteristics of these materials in terms of their resist compatibilityand etch performance, based on their composition.We have characterized these materials using a number of analytical techniques, including: FTIR, XPS, etc .Wehavealso studied the effect of numerous etching chemistries, such as CF 4 and SO 2 /O 2 , to determine their etch characteristics.Finally, we provide some after-dry-develop etch profiles.Keywords: hardmask,spin-on, MLR, photolithography, 193nm 1. INTRODUCTION As the semiconductor industry continues to move towards smaller feature sizes, resist thickness needs to bedecreased for workable aspect ratios. Furthermore, due to the high absorption of resists at short wavelengths, resistthickness has to be relatively thin, around 100nm to 150nm. However, when thin single layer resist (SLR) process isused, imaging layer etch resistance is not sufficient for transferring the image into the substrate below. For KrF and ArFphotolithography, chemical vapor deposition(CVD) films have been widelyused as effective masks for pattern transfer.Spin-on hardmask stacks, suchas bilayer resists (2-LR) and multiplelayer resists (MLR), couldbe used as an alternativeto CVD films. The spin-on hardmask stack offers a number of advantages over the CVD stack: better resistcompatibility among spin-on hardmask layers; all materials can be plumbed on photo tool tracks; a smaller cost isassociated with MLR stack, especially when including CVD tool cost; and spin-on stacks generally improve patternedsubstrate flatness. Additionally, 2-LR and MLR stacks eliminate the need for organic bottom anti-reflective coating(BARC), which is usually required with the CVD layers for resist compatibility. This helps reduce the number ofmaterials that need to be plumbed on the photo tool and further reduces the overall process cost.A 2-LR system consists of an imaging layer, which also acts as hardmask, and an organic underlayer. Theimaging layer is a silicon-containing photosensitive polymer. Although these imaging layers are contin uouslyimprovedupon, their resolution and image contrast are inferior compared to that of conventional single-layer photoresists becauseof thedual requirements of imagingand maskfor patterntransfer. Therefore,for high-resolutionlithography(65nm andbelow) this imaging layer usually does not give good photolithographic performance. A MLR system consists of: animaging resist, which is the same photoresist used in SLR or CVD-hardmask stacks; a silicon-containing hardmask; andan organic underlayer. The hardmask material is based on silsesquioxane polymer (chemical structure shown in Figure1). This polymer contains both chromophore groups and the reactive sites for cross-linking reactions on the polymerbackbone. Hardmask light absorption is controlled by the number of chromophore groups on the polymer backbone.Since the imaging layer and the hardmask are separate for MLR stacks, hardmask optical properties can be tuned to givenegligible reflectanceinto theresist, which eliminates the needfor BARC.Although there have been a number of published reports