The New Method Of Nano-Metrology And The Development Of Dual Imaging Unit Atomic Force Microscope

Nanotechnology is a new subject developed from the end of 20th century. Scanning Probe Microscopes (SPMs), especially Atomic Force Microscopes (AFMs), are the most important instruments used in the field of nanotechnology. Nowadays, AFM is used not only for imaging the nanometer order topography of material surfaces, but also for nano-machining. With the development of nanotechnology, more excellent performance of AFM system is required. Metrological AFMs must be developed to take the place of traditionally observational AFMs. In this dissertation, a new idea of Dual Imaging Unit Atomic Force Microscope (DIU-AFM) is put forward. Theoretic researches on the principle and method of DIU-AFM have been carried out. DIU-AFM system is developed to realize the new method of nano-metrology. The development of DIU-AFM system improves the performance and application of AFM. It not only has import theoretical significations and scientific value, but also has a great application prospect in nanotechnology.This dissertation represents SPM technology and the status of the metrological technology. And then introduces the principle of SPM, especially AFM, and its limitation in nano-metrology. Normal AFM system has to be calibrated with well-defined reference scale. In the viewpoint of metrology, however, AFMs designed and produced differently and then calibrated by different reference scales have different performance and precision. Even the performance and precision of a same AFM will be different while the environment and time change. Therefore, the measurement result of normal AFM system is not metrological. New metrological AFM system has to be developed to realize nano-metrology in strictly speaking.New principle and method of nano-metrology based on DIU-AFM has been presented. In DIU-AFM, two AFM units were combined, one as a reference unit, and the other a test one. Their probes with Z piezo elements and tips were horizontally set in parallel at the same height to reduce Abbe's errors. A reference sample and a test sample were attached to one single XY scanner on same surface, and were imaged by the AFM units at the same time. The two images have the same lateral size, and thus the length of the test sample image could be accurately measured by counting the periodic features in the reference one. The length of theperiodic feature in the reference sample can be trace to the national standard, so the measurement results of DIU-AFM are also traceable.DIU-AFM system has been developed. Unique DIU-AFM probe combined reference unit and test unit was designed, including one single XY scanner, two independent AFM cantilevers and tips that were installed at the end of Z feedback controllers, two particular optical paths of laser beam deflection method for the measurement of cantilevers' displacement and two pairs of coarse and fine adjusting mechanism for sample-tip approach. Scanning control circuits were employed to drive the XY scanner. Preamplifiers were developed to process the signals from PSDs. And two independent PID feedback circuits were built to control the movement of the Z piezos. Software system was developed to generate scanning control signals and collect data through A/D&D/A converter. The functions of software system also include image display, image processing, automatic nano-metrology calculation based on reference sample and automatic image splicing for wide-range nano-metrology.Experiments were carried out to prove the feasibility of nano-metrology based on DIU-AFM. Lengths, line widths and particle sizes of nanostructures on several sample surfaces were measured by DIU-AFM while porous alumina or periodic grating as the reference sample. The experiments show the excellent performance of DIU-AFM. By employing different reference samples, this system can carry out nano-metrology on different scale nanostructures with one nanometer measuring accuracy and the measurement results can be traced to the national standard. Besides these, DIU-AFM has high repeatability, reliable stability and convenient operation. And the low requirement of work environment benefits the wide application of the system.A new method of implementing wide-range nano-metrology was developed on the basis of serial images and image splicing. To realize wide-range (100 u m~l mm order) nanometer precision (lnm~10nm) nano-metrology, the whole XY scanner of DIU-AFM was set upon a XY stage. The XY stage can move in parallel along X direction. After the DIU-AFM scanned and gained one pair of reference image and test image, the XY stage moved a certain distance, then DIU-AFM scanned for the second time and the second pair of images was gained. The rest may be deduced by analogy. In this way, by alternatively moving the XY stage andscanning the reference sample and test sample by DIU-AFM, a series of pairs of images were obtained. And also, every pairs of images were of the same lateral size. These serial images can be spliced into a pair of wide-range reference and test images that have nanometer order precision. The two spliced images are of the same size, and the length in test image can be measured based on the reference sample.The performance of DIU-AFM has been improved. After analyzing the nonlinearity of PZT, calibration was carried out on PZT both in hardware and software to eliminate the nonlinearity. The errors of DIU-AFM were analyzed and corresponding improvement programs were brought forward to improve the performance of the system so that DIU-AFM can be applied widely.