We investigate the ordering of poly(styrene-bmethyl methacrylate) (PS-PMMA) lamellar copolymers (periodicity L 0 5 46 nm) confined between a free surface and brushed poly(styrene-r-methyl methacrylate) silicon substrate. The processing temperature was selected to eliminate wetting layers at the top and bottom interfaces, producing approximately neutral boundaries that stabilize perpendicular domain orientations. The PS-PMMA film thickness (t 5 0.5L 0 2 2.5L 0 ) and brush grafting density (R 5 0.2-0.6 nm
22) were systematically varied to examine their impacts on in-plane and out-of-plane ordering. Samples were characterized with a combination of highresolution microscopy, X-ray reflectivity, and grazing-incidence small-angle X-ray scattering. In-plane order at the top of the film (quantified through calculation of orientational correlation lengths) improved with t n , where the exponent n increased from 0.75 to 1 as R decreased from 0.6 to 0.2 nm 22 . Out-ofplane defects such as tilted domains were detected in all films, and the distribution of domain tilt angles was nearly independent of t and R. These studies demonstrate that defectivity in perpendicular lamellar phases is three-dimensional, comprised of in-plane topological defects and out-of-plane domain tilt, with little or no correlation between these two types of disorder. Strong interactions between the block copolymer and underlying substrate may trap both kinds of thermally generated defects. KEYWORDS: block copolymers; defectivity; directed self-assembly; grazing-incidence small-angle X-ray scattering; thin films INTRODUCTION Thin films of symmetric diblock copolymers can spontaneously self-assemble into nanoscale lamellar domains (i.e., nanolines). 1,2 These materials could improve the resolution of projection lithography by "shrinking" the sizes of patterned features, 3-6 so the leading semiconductor manufacturers are considering their use in next-generation integrated circuit manufacturing. Lithographic processes require precise control over the placement and orientation of domains with respect to the underlying substrate. Although many methods have been developed to direct the placement of domains, the in-plane and out-of-plane defectivity remains too high for production. The objective of our current work is to examine in-plane and out-of-plane defect structures in thin films of perpendicular poly(styrene-bmethyl methacrylate) (PS-PMMA) lamellae. In-plane defects are well documented in these systems, and they include dislocations and disclinations that disrupt lateral order. Out-ofplane defects are not well studied, but could include tilted, bent, or discontinuous domains.