To guarantee the reproducibility, uniformity and high yield of the fabrication results even with the unavoidable disturbances during the process, the robustness of the batch fabrication process of SThM probes has been improved. First, the shape of the hard mask used for the anisotropic tip etching was redesigned to fit to certain crystal surfaces of silicon wafer so that the sharpness of the tip is kept for a while even after the hard mask falls apart during the bulk tip etch process. Second, the aspect ratio of the tip was maximized by utilizing high concentration KOH solution. Third, the uniformity of etch rate across the wafer was improved by using ultrasonic bath during the anisotropic wet tip etching step. Through the synergistic effects of the modifications of the key steps, the tip fabrication process has become very robust and uniform. Taking advantage of the robustness of the process, we reduced the tip radius of the SThM probe down to 50 nm and the diameter of the thermocouple junction located at the end of the tip to 100 nm. As a result, the sensitivity and the spatial resolution of the new probe were demonstrated to be improved more than two times.

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