Severe technical challenges and bottlenecks to quality monitoring, especially in critical dimensional measurement for vias below 1 micrometer are currently faced in advanced packaging. To break through the bottleneck, broadband deep-ultraviolet light (DUV) is proposed to develop a novel optical system, so the optical wave can penetrate through the test structure effectively. More importantly, the proposed optical approach based on reflectometry and scatterometry is integrated with novel AI machine-learning optimization to achieve the best multi-CD measurement. As proved by industrial via tests, the method is capable of measuring CDs of submicron vias and RDL, which is regarded as the best measuring specification in the world.