Broadband extreme ultraviolet (EUV) radiation has shown significant advantages in advanced-node semiconductor metrology. To meet the high-volume manufacturing demands of advanced nodes, the conversion efficiency of a laser-plasma broadband EUV source was studied. First, the wavelength and spectral intensity of the EUV spectrometer were calibrated and used to characterize the total conversion efficiency (CE) from laser to EUV radiation at 10?20 nm. Subsequently, an in-situ second pulse was applied to a solid Sn target using a 1 μm laser, thereby achieving a broadband EUV conversion efficiency of 52.5% in the 10?20 nm range, which is the highest CE reported so far. The main reason for this is that the curved surface formed by the ablation of the first laser pulse caused spatial constraints on the tin plasma. These spatial constraints were induced by the subsequent laser pulse and resulted in a significant increase in EUV emission. This study provides a new approach for generating a broadband EUV light source with high CE, presenting a novel method of semiconductor microchip metrology for advanced technology nodes of the future.