Surface Topography Metrology and Properties · 2016 · 119 citations · 22 references
EngineeringManufacturing EngineeringMetrologySemiconductor DevicesSensorsIndustrial MetrologyLevel MeasurementOptical MetrologyOptical SensingOptical SensorsSurface MetrologyCritical Dimension MetrologyOptical LithographyOverlay ControlOverlay MetrologyPrecisionSemiconductor Device CharacterizationSemiconductor MetrologySemiconductor Technology
Sub‑nanometer precision at high throughput across diverse processed wafers and unknown variations is the key challenge for optical wafer metrology sensors. This paper explains the sub‑nanometer precision challenge and reviews process‑robust solutions developed for optical wafer metrology. The authors describe three sensors—a level sensor, an alignment sensor, and an optical scatterometer—that measure wafer height maps, wafer positions, and post‑exposure critical dimension and overlay variations.
This paper presents three optical wafer metrology sensors that are used in lithography for robustly measuring the shape and position of wafers and device patterns on these wafers. The first two sensors are a level sensor and an alignment sensor that measure, respectively, a wafer height map and a wafer position before a new pattern is printed on the wafer. The third sensor is an optical scatterometer that measures critical dimension-variations and overlay after the resist has been exposed and developed. These sensors have different optical concepts but they share the same challenge that sub-nm precision is required at high throughput on a large variety of processed wafers and in the presence of unknown wafer processing variations. It is the purpose of this paper to explain these challenges in more detail and give an overview of the various solutions that have been introduced over the years to come to process-robust optical wafer metrology.
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