Chiral metasurfaces, supported by photonic bound states in the continuum (BICs), provide a novel platform for studying chiral light-matter interactions. However, achieving near-unity chirality and ultrahigh Q factors simultaneously in dielectric metasurfaces remains a significant challenge. Here, we propose a planar chiral dielectric metasurface featuring tilted holes driven by the half-integer topological charge. This design decouples the circular dichroism (CD) and Q factors and achieves both near-unity CD and ultrahigh Q factors. We exploit the properties of the half-integer topological charge to stabilize one of the C points near the $\mathrm{\Gamma }$ point despite variations in the hole width. This provides an additional degree of freedom for independently tuning Q factors without compromising the near-unity CD values. Furthermore, the metasurface exhibits unparalleled robustness against variations in tilt angle, maintaining near-unity CD ($>0.95$) over the range of $11.{74}^{\circ }$, which extends to $25.1^{\circ }$ when perturbations are introduced to two adjacent sides. Moreover, the metasurface demonstrates a superchiral field enhancement greater than ${10}^3$. These findings highlight the potential of our design for applications requiring near-unity CD and ultrahigh Q factors, providing a practical solution to the longstanding challenge of decoupling Q factors and near-unity chirality in chiral metasurfaces.

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• Bound states in the continuum
• Metasurfaces
• Nanophotonics