SPM Principles

AFM Lithography - Dynamic Plowing

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AFM enables the direct machining the sample surface by means of AFM cantilever tips. This can be achieved in two ways, called Static Plowing (Scratching) and Dynamic Plowing. In the static plowing the AFM is employed in contact mode to pattern a sample surface or some layer on them, e.g. single resist layer and subsequently use it as an etch mask. This technique, while being a low-cost and low-effort technique, presents some drawbacks.

It has been proved that, while cutting a furrow into the resist by static plowing, torsion of the cantilever may lead to edge irregularities. Additionally, depending on the local stiffness of the sample, while imaging the surface before or after the modification, further modifi- cations may occur due to dragging of the surface.

By Dynamic Plowing Lithography (DPL) the surface is modified by indenting it with a vibrating tip in the AFM semicontact mode. This method provides a lithography technique that is nearly free from problems due to cantilever torsion and permits to image the modified surface without any further modification.

Dynamic Plowing Lithography can be performed in a vector scan mode or in an image pattern scan mode. In the vector scan mode, the software provides a set of commands that permit us to write lines of arbitrary length and direction with defined scan speed and oscillation amplitude. The image pattern scan mode (see Example), is a synchronization of the raster scan mode with the desired pattern. The pattern can be constructed with a simple pixel-oriented paint program.

The non-contact mode has the advantage that the tip never makes contact with the sample and therefore cannot disturb or destroy the sample. This is particularly important in biological applications. 

References 

1. J. Appl. Phys. 85, 3897 (1999).
2. Rev. Sci. Instrum. 72, 136 (2001).