6.3.1 AFM Nanodot Generation

As described in Chapter 4, LON with an AFM is becoming an increasingly applicable tool for manufacturing nanosized devices. At the core of the nanolithographic potential of AFM is the generation of a SiO$_2$ nanodot on a silicon surface. AFM allows for a nanodot to be applied on a silicon surface with nanosized precision of the location and size. As discussed in Chapter 5, the ambient factors which influence the nanodot size are the pulse time, ambient humidity, and the potential difference between the AFM needle tip and the silicon substrate. The AFM nanodots shown in Figure 6.8, Figure 6.9, and Figure 6.10 are generated using the described model from  [28] with added humidity effects and the two-dimensional SCD distribution described in Chapter 5. In the figures, the top topography represents the surface between the silicon dioxide and the air/water ambient, while the bottom topography represents the interface between silicon dioxide and silicon. The heights of all nanodots have been scaled by 20 with respect to the widths for improved visualization. The results confirm the experimental results gathered from [28] and [53], on which the models are based.

Figure 6.8 shows the distribution of nanodot sizes caused by a variation of pulse times. The voltage and humidity were kept constant at 20V and 55%, respectively, while the time was set to 0.2ms, 0.3ms, 0.5ms, and 1ms. With increasing pulse times, the nanodot height and width also increase, as expected. The height varied from 1.24nm to 2.05nm, while the FWHM varied from 15nm to approximately 50nm with pulse times set to 0.2ms and 1ms, respectively.

Figure 6.8: Effects of pulse time on the AFM nanodot height and width. The vertical axis is scaled by 20 for better visualization.

Figure 6.9 shows the distribution of nanodot sizes caused by a variation of the ambient humidity. The pulse time and applied voltage were kept constant at 0.2ms and 20V respectively, while the humidity was set to 30%, 50%, 70%, and 90%. With an increasing ambient humidity, the nanodot height and width also increase, as expected. The height varied from 0.65nm to 2.07nm, while FWHM varied from 10.6nm to approximately 34nm with the ambient humidity set to 30% and 90%, respectively. In addition, a cross-section of the nanodots is shown, where the nanodot heights are more evident.

Figure 6.9: Effects of ambient humidity on the AFM nanodot height and width. The vertical axis is scaled by 20 for better visualization.

Figure 6.10 shows the distribution of nanodot sizes caused by a variation of the applied voltage. The pulse time and humidity were kept constant at 0.2ms and 55%, respectively, while the voltage was varied at 16V, 18V, 20V, and 22V. With an increasing applied voltage, the nanodot height and width also increase, as expected. The height varied from 0.51nm to 1.58nm, while FWHM varied from 10nm to approximately 18nm with the applied voltage set to 16V and 22V, respectively.

Figure 6.10: Effects of bias voltage on the AFM nanodot height and width. The vertical axis is scaled by 20 for better visualization.