Roughness of Si Wafer

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 is becoming more and more difficult to find suitable techniques for quality control. Atomic force microscopy can 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 General Purpose probe of the 14 series and the other obtained with a High Resolution probe of the same series. The two height images are compared below in Fig. 1a-b.

Fig.1. AFM images of a silicon wafer surface from a conventional silicon probe (left) and a Hi'Res-C probe (right). Scan size 1 µm. Dimension 5000 AFM. Images courtesy of Dr. S. Magonov (Agilent).

Not surprisingly, the roughness determined with the high resolution probe is 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 a qualitative comparison of the roughness of similar samples is needed, a regular tip may be sufficient. However, if accurate quantitative roughness data is needed, it may be necessary to use a Hi'Res-C 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. Please refer to the High Resolution page for details).

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Roughness measurements of flat or corrugated surfaces
Hi'Res-C probes with medium spring constant
Hi'Res-C14/Cr-Au

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