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In this paper, we tested a novel methodology of measuring critical dimension (CD) uniformity, or CDU, with electron beam (e-beam) hotspot inspection and measurement systems developed by Hermes Microvision, Inc. (HMI). The systems were used to take images of two-dimensional (2D) array patterns and measure CDU values in a custom designated fashion. Because this methodology combined imaging of scanning micro scope (SEM) and CD value averaging over a large array pattern of optical CD, or OCD, it can measure CDU of 2D arrays with high accuracy, high repeatability and high throughput.

This paper assesses the readiness of EUV masks for pilot line production. The printability of well characterized reticle defects, with particular emphasis on those reticle defects that cause electrical errors on wafer test chips, is investigated. The reticles are equipped with test marks that are inspected in a die-to-die mode (using DUV inspection tool) and reviewed (using a SEM tool), and which also comprise electrically testable patterns. The reticles have three modules comprising features with 32 nm ground rules in 104 nm pitch, 22 nm ground rules with 80 nm pitch, and 16 nm ground rules with 56 nm pitch (on the wafer scale). In order to determine whether specific defects originate from the substrate, the multilayer film, the absorber stack, or from the patterning process, the reticles were inspected after each fabrication step. Following fabrication, the reticles were used to print wafers on a 0.25 NA full-field ASML EUV exposure tool. The printed wafers were inspected with state of the art bright-field and Deep UV inspection tools. It is observed that the printability of EUV mask defects down to a pitch of 56 nm shows a trend of increased printability as the pitch of the printed pattern gets smaller - a well established trend at larger pitches of 80 nm and 104 nm, respectively. The sensitivity of state-of-the-art reticle inspection tools is greatly improved over that of the previous generation of tools. There appears to be no apparent decline in the sensitivity of these state-of-the-art reticle inspection tools for higher density (smaller) patterns on the mask, even down to 56nm pitch (1x). Preliminary results indicate that a blank defect density of the order of 0.25 defects/cm 2 can support very early learning on EUV pilot line production at the 16nm node.

Reticle defectivity was evaluated using two known approaches: direct reticle inspection and the inspection of the wafer prints. The primary test vehicle was a reticle with a design consisting of 45 nm and 60 nm comb and serpentine structures in different orientations. The reticle was inspected in reflected light on the KLA 587 in a die-todie and a die-to-database mode. Wafers were exposed on a 0.25 NA full-field EUV exposure tool and inspected on a KLA 2800. Both methods delivered two populations of defects which were correlated to identify coinciding detections and mismatches. In addition, reticle defects were reviewed using scanning electron microscopy (SEM) to assess the printability. Furthermore, some images of the defects found on the 45 nm reticle used in the previous study [1] were collected using actinic (EUV) microscopy. The results of the observed mask defects are presented and discussed together with a defect classification.