The ability of an AFM probe to profile sub-micron structures is important for a number of technological applications in the semiconductor and data storage industries. With the shrinking dimensions of semiconductor and storage devices, it becomes more difficult to find suitable techniques for quality control. Atomic force microscopy could potentially be used for such a function, but its limitations have to be considered for accurate application.

This issue is easily observed in studies of the surface roughness of Si wafers and the porosity of low-K materials. As the sharpness of the AFM tip increases, finer surface features can be revealed which leads to a larger effective roughness estimated from height images. This effect is illustrated by two images of a Si wafer, one obtained with a regular (NSC 14) and the other obtained with a DP14/Hi'RES probe. The two height images are compared below in Figures 1a-b.

larger than the roughness determined with the regular probe. Knowing that there are large quantitative differences from using different tips, it is important to clarify what type of data is necessary for your application. If you need to qualitatively compare the roughness of similar samples, a regular tip may be sufficient. However, if you need accurate quantitative roughness data, it may be important for you to use a Hi'Res tip for the best possible results.

It is worth noting that measurements taken with a sharp tip require special precautions (a gentle engagement procedure and low-force imaging) to avoid the unnecessary damage of the tip (see high-resolution imaging for details).