One promising way of scanning probe microscope (SPM) based nanolithography techniques is mechanical scratching of surfaces with the SPM tip [1]. The sufficiently high force between the SPM tip and the surface can lead to remove materials and fabricate the groove on the surface. The direct patterning attracted a great deal of interest because no further processing step is required. This technique has been demonstrated for various specimens. Recently, the groove with 7 nm width was mechanically patterned on GaAs [2]. It is possible for nanometer scratching on soft materials using Si or Si3N4 tip, with a normal radius of around 20 nm. In contrast, on a hard material such as Si, we usually use a diamond tip with extremely high wear resistance. The radius of the diamond tip becomes larger because of polycrystalline diamond coating on the tip-side of the Si cantilever. The resolution in SPM-based nanolithography is limited essentially by the tip radius and it is believed to be difficult to reduce the resolution to less than 10 nm.
In this work, we investigate the effect of scan parameters on the groove size. The scratch experiments were performed using a contact-mode atomic force microscopy under ambient conditions. The relative humidity was controlled within the range of 33~46 %. The diamond coated tip with spring constant of 46 N/m was used. The dimensional characteristics of the groove size were studied as function of the normal applied load, scan cycle, scanning speed and scanning direction. The size of the fabricated grooves was successfully controlled, with minimum resolution of 11 nm in width and 0.58 nm in depth. More complex nanostructures such as line-and-space patterns and quantum dot arrays were also demonstrated on Si surface. The results suggest that the SPM scratching is possible to fabricate nanoscale devices with precisely controlled nanostructures such as single-electron transistors, quantum computing elements and nanophotonic devices.
References:
[1] X. Jin and W. N. Unertl: Appl. Phys. Lett. 61 (1992) 657.
[2] C. K. Hyon, S. C. Choi, S. W. Hwang, D. Ahn, Y. Kim, and E. K. Kim: Jpn. J. Appl. Phys. 38 (1999) 7257.
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