Scanning probe microscopy based on novel micro electromechanical system probes are called active cantilevers. Cantilevers with integrated actuation and sensing provide several advantages over passive cantilevers, which rely on piezoelectric excitation and optical beam deflection measurement. The most recent development in this field is the realization of arrays of active cantilevers for high throughput parallel SPM imaging.
The arrays of active cantilevers use integrated piezo resistive sensors to offer sensitivity comparable to optical readout methods without diffraction limits, to allow smaller, softer, and more compact AFM probes. The results of this technique paved the way for the operation and building of high throughput atomic force microscopes using high speed multichannel electronics. The advances in this technique can facilitate the faster and more reliable operation of massively parallel active cantilever systems in the future.
Begin by operating the AFM software and loading the sample substrate on a wafer into the AFM system. Ensure that the bottom surface in contact with the sample is parallel to the top surface. To locate the area of interest, ensure to fine tune the sample stage before adjusting the in plain XY position.
using the micrometer on the AFM stage. Then mount and secure the AFM cantilever probe array on the probe holder. Perform a frequency sweep to automatically identify the resonance frequency of each cantilever for imaging.
Select the relative position of the cantilever array onto the first area of interest to be imaged. Next, establish a global coordinate by clicking the XYZ zero button before closing and sealing the acoustic shield. Begin the topography imaging and parameter tuning by selecting the imaging parameter setup tab.
Enter the top left corner coordinates before scanning the size for a single panoramic image. Then enter the desired in plain pixel resolution and use the software's default recommended line scan speed for imaging. For tapping mode operation, use the default tapping drive amplitude, frequency, and set point in the software obtained from the cantilever characteristics.
Next, let the system automatically bring the sample and the probe into contact. Adjust the proportional integral derivative controller parameters for each cantilever, based on the scanned trace per image before saving the data and removing the probe. To verify the spatial resolution of the active cantilever array, high resolution images of highly oriented pyrolytic graphite were captured with a small in plain image range of 5 by 5 micrometers and 10 28 by 10 28 pixels.
The effectiveness of AFM using parallel active cantilevers was demonstrated by capturing the stitched images of a calibration grading, with four cantilevers operated in parallel. The AFM scanning revealed that the silicon wafer calibration structure had 45 micrometer long features with a 14 nanometer height. Each cantilever covered a 125 by 125 micrometer area, which gave a stitched panoramic image of 500 by 125 micrometers.
Imaging an extreme UV lithography mask for creating semiconductor features showed an overall stitched panoramic image with a five nanometer spatial resolution covering a 505 by 130 micrometer area. Various areas of the circuit were clearly seen in the image. At 10 lines per second, 101, 000 by 26, 000 pixels were captured in roughly 40 minutes, which is significantly faster than conventional AFM systems.
