Reasearch On Alignment System Of Dual-probe AFM Used For Linewidth Measurement

The measurement of nanoscale linewidth has always been important and difficult in the field of nanometer measurements, while the rapid development of integrated circuit greatly raises the demand again. As one kind of scanning probe microscope (SPM), atomic force microscope (AFM) can realize quasi three-dimensional measurement, which is widely used in nanometer scale linewidth measurement. However, compared to line height and line spacing measurement, because of the limitation caused by probe size and measurement principle, traditional AFM can not attain accurate linewidth measurement.In this dissertation, the dual-probe of AFM which can eliminate the prevalent effect of probe width on measurement results in the AFM is presented. The key lies in the two probes alignment in three dimensional directions. To solving the problem, the dissertation researched a dual-probe alignment method, and designed a dual-probe alignment experimental instrument which realizes the dual-probe alignment in the nanoscale. The detail is discussed as follows:1. The differences between single probe of specialized shape and dual-probe in linewidth measurement have been researched, and how to eliminate the effect of probe size on measuring results has been analyzed. The linewidth measurement method as well as dual-probe alignment method utilizing quartz fork Akiyama probe has been proposed. The dissertation alse utilizes finite element technologies to analyze the moving trajectories of probe tip to propose theoretical basis for near field force alignment method.2. Measuring head based on Akiyama probe and the signal processing system have been developed. There are two measurement models in tip alignment and linewidth measurement procedure, namely top model and critical dimensional (CD) model respectively. Measuring heads with different structures which can achieve nanometer scale measurement resolution based on the two models have been developed. Especially, the performance tests of measuring head under CD model provide experimental basis for nanoscale dual-probe alignment.3. The dual-probe alignment method has been studied. The visual alignment method based on sub-pixel edge detection for Akiyama probe has been proposed. The nanoscale alignment method based on near field force is studied. The scanning range and step is gradually narrowing in constant height mode.4. The dual-probe alignment experimental instrument has been designed and the performance tests have been finished. The alignment instrument intetrated by machine vision and near force scanning method have been built. Through the high resolution vertical and horizontal real time images, the visual alignment method can make two probes approach within1μm level. When vision alignment is finished, the instrument utilizes one probe to scan the other probe to get image can calculating the peak coordinates values of amplitude and frequency signals, which is later considered as tip coordinate. Later, gradually narrows the scanning range and step to get more accurate images of tip. Finally nanoscale dual-probe alignment is realized, and the accuracy is3nm.