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This paper reports that the low-frequency noise in p-channel MOSFETs fabricated on  and (100) crystallographic oriented silicon is related to the microroughness of the silicon surface. Since the conventional RCA cleaning process makes the surface rough, especially in the case of  orientation, the authors developed the so-called 5-step room temperature cleaning process that does not use alkaline solution. The combination of this new cleaning process with the microwave-excited high-density plasma oxidation process for the formation of the gate oxide, instead of the standard 900°C thermal oxidation process, leads to a reduction of the microroughness and a drop in the 1/f noise level of more than one decade. Furthermore, this reduction is not only observed for the  orientation but also seen, albeit to a much lesser extent, for (100) if it is treated in the same way.