AFM Lithography - Scratching

Ploughing is a well-known technique used since the earliest days of agricultural cultivation. By scaling this tool down in size to a few nanometers and combining it with conventional scanning probe techniques, one can facilitate nanolithography with nanometer resolution.

In the more common AFM scratching techniques, the tip is scanned under strong loading forces to remove the substrate or resist. This technique utilizes the principle of ploughing in the same way as the traditional tool: material is removed from the substrate in a well-defined way, leaving behind deep trenches with the characteristic shape of the plough used.

The advantages of applying a nanoscratching for lithography are obviously the precision of alignment, the nondamaging definition process compared to electron- or ion-beam structuring techniques, and the absence of additional processing steps, such as etching the substrate. Nanoploughing (nanoscratching) was applied, for example to defining supereconducting nanoconstrictions(Josephson junctions) [1], surface quantum wells patterning [2].

When the AFM is operated in contact mode, not only deep scratching but also several regimes from frictionless sliding to permanent wear are observed, depending on the applied load. In this way, AFM has been successfully used to characterize microwear processes on materials of technological interest, as silicon for magnetic head sliders, polymers for electronic packaging and liquid crystals displays etc as is reviewed in [3].

In NTMDT devices two different nanolithography modes are possible: vector and raster. In the case of vector lithography the influence is applied in single points or along the determined lines. In the case of raster lithography it is made from the already determined template. The advantage of vector lithography is a high speed while disadvantage is that the force is equal in each point. Raster lithography is slower, but it enables to change the force applied according with the template. Besides there are two ways to change the applied force when making vector lithography: 1. Changing of the beam bending by setting of the scanner displacement on defined distance along Z axis. 2. Changing of the beam bending, by setting of the SetPoint value. When doing raster lithography you can use only the first way.

References

1. Appl. Phys. Lett., Vol. 73, 2051 (1998).
2. Appl. Phys. Lett., Vol. 73, 2684 (1998).
3. Chem. Rev. 97, 1163 (1997).