Stability Characterization of High-Sensitivity Silicon-Based EUV Photodiodes in a Detrimental Environment

In extreme-ultraviolet (EUV)-based applications, such as next-generation EUV lithography, the detector surface has to be periodically exposed to aggressive gasses as a cleaning step to prevent the build-up of contaminating layers. In this paper, we report excellent EUV radiation hardness and robustness to harsh working conditions of a Si-based boron-doped ultrashallow junction photodiode (B-layer diode) fabricated by a pure boron chemical vapor deposition (CVD) technology. Experimental results show unchanged responsivity of the photodiode (within the measurement uncertainty) with radiation dose up to 0.22 MJ/cm². The surface cleaning tests with hydrogen radicals (H*) confirm that the electrical/optical performance of the detector is stable with only minor change of the characteristics. In addition, the detectors must be operated in vacuum without an air-cooling system, as air is not transparent for EUV photons. An on-chip sensor system, which contains B-layer diodes and bipolar- transistor-based temperature sensors, is developed for compensating the thermal drift of the photodiode output signal when the diode is heated up by the EUV radiation. Furthermore, this on-chip sensor system also demonstrates the full compatibility of this novel pure boron CVD technology with standard Si-based integrated circuit processing.