AVS 52nd International Symposium
    Applied Surface Science Monday Sessions
       Session AS-MoP

Paper AS-MoP12
An Investigation of Photoperturbation Effects on Conductive Atomic Force Microscopy

Monday, October 31, 2005, 5:00 pm, Room Exhibit Hall C&D

Session: Aspects of Applied Surface Science Poster Session
Presenter: M.-N. Chang, National Nano Device Laboratories, Taiwan
Authors: M.-N. Chang, National Nano Device Laboratories, Taiwan
C.-Y. Chen, National Nano Device Laboratories, Taiwan
Correspondent: Click to Email
Conductive atomic force microscopy (C-AFM) with a high current sensitivity and a high spatial resolution has attracted much interest in mapping two-dimensional current distribution, investigating the local current-voltage characteristics and examining the breakdown properties of the dielectric layer in electronic devices. With atomic force microscopic setup, C-AFM can synchronously provide the current images and the corresponding topographic images. However, it has been revealed that the stray light of AFM laser beam can induce photoperturbations and hence lead to many difficulties in employing scanning capacitance microscopy to investigate carrier distribution and electrical junctions. In this work, we have qualitatively revealed that the AFM laser beam can significantly perturb the local current-voltage spectra and current distribution profiles taken by C-AFM. Studied samples were n- and p-type silicon covered with a thermally grown ultrathin SiO@sub 2@ film. The wavelength of the AFM laser ranges from 620 nm to 690 nm and the output power is 1.0 mW. The C-AFM measurement was performed in an environment with well-controlled temperature and humidity. For p-type sample, it is clearly observed that the onset voltage decreases with the photoperturbation level. The photovoltaic effect and the additional minority carrier density at the edge of the space-charge region can enhance the electric field across the SiO@sub 2@ film. For n-type sample, photoperturbations can lead to a higher injection barrier height for electrons. Experimental results indicate that the photoperturbations induced by the AFM laser beam not only significantly affects the current image of C-AFM, but also reduces the accuracy of the examination of the current-voltage characteristics, in particular for the ultrathin dielectric film on lower band-gap semiconductors, e.g., Si and Si@sub x@Ge@sub 1-x@.