Light detection and ranging (LiDAR) is of central importance for modern artificial intelligence (AI) assisted automated intelligent optical devices. Silicon-based optical phased arrays (OPAs) have attracted widespread attention due to their rapid and efficient scanning capabilities. However, the complex waveguide routing structure has limited the spacing between elements of traditional two-dimensional (2D) OPAs, limiting the achievable angle range of 2D scanning. The traditional planar architecture struggles to meet high-density integration demands. Transitioning to the third dimension to leverage spatial degrees of freedom represents the only viable path toward future ultra-high integration. Consequently, we present a dual-layer optical phased array design employing a hierarchical architecture with cascaded phase shifters. This configuration strategically positions space-intensive waveguide routing in the lower layer while putting the 2D antenna array in the upper layer, achieving unprecedented spatial efficiency. The optimized layout enables an ultra-compact 5 μm antenna pitch, supporting far-field beam steering over ± 18.1 scanning angles. The primary technical challenge lies in interlayer coupling and the manufacturing of bilayer fine structures. However, recent advances in micro/nanofabrication technology have demonstrated the capability to meet our design specifications at current process nodes. Our design thus posts a new research direction for highly efficient, compact, and wide-range 2D beam control platforms.