Intra-field patterning control using high-speed and small-target optical metrology of CD and focus

ABSTRACT The continuing trend of shrinking dimension and the related specifications requires tightening of control loops. To support the tighter control loops, the metrology sampling plans will require increasing sampling density and frequency. This study shows that tighter control of scanner focus and AEI CD and profile parameters requires sampling schemes with intra-field measurement points, and a frequent update of the corrections. This drives the need for high-speed small-target metrology. Experiments show that this can be achieved by the YieldStar angle resolved scatterometer, demonstrating measurements on areas of 16×16µm 2 for focus metrology and 12×12µm for CD metrology, at a MAM time below 0.5s. Keywords: Scatterometry, focus control, CD control, profile control, CD metrology, focus metrology, optical metrology 1. INTRODUCTION Today’s CD-uniformity (CDU) requirements ask for a tight control of all undesired patterning variations. This drives on the one hand improvements in production tools, offering improved stability and increased tuning capability. On the other hand, it requires improvements in measuring tools to support monitoring and control. One of the larger contributors to variations in final CD is post-litho processing, e.g. etch and layer deposition in SADP. To reduce these variations, state-of-the-art etchers have higher-order across wafer tuning potential through multi-zone temperature control, among other added control possibilities. In addition, scanners offer higher-order inter-field and intra-field tuning capability of focus and dose, that can be used in control schemes to stay at the optimal working point and to compensate residual CD variations from the etch process or the reticle. Application of these higher-order correction capabilities requires adequate metrology after litho (ADI) and after etch (AEI). For this purpose we have investigated the YieldStar high-NA full-azimuth angle-resolved scatterometer. This tool is available in an integrated configuration, as well as in stand-alone configuration, supporting both ADI and AEI control loops, as depicted in Figure 1. Figure 1: CD and Focus control loops using, supported by integrated and stand-alone metrology, ADI and AEI.