Study Of AFM Tip Characterization Techniques Based On Natural Constants

Natural constants are accurate quantities in the universe.The process of natural constants being materialized,reproduced and transferred can effectively improve the accuracy of measurement and control.In 2019,all 7 base units of the International System of Units are changed to being defined by constants,and this is a full recognition and development of the constants of nature,which becomes the source of quantity dissemination.Natural constants have always played an important role in the traceability of geometric quantity at nanoscale,which is reflected in two aspects.On the one hand,the silicon lattice constant can be used as a complementary method linking the definition of the "meter" at nanoscale;on the other hand,laser wavelengths based on various atomic energy level transition frequencies can be used as wavelength reference,it already became a common way to reproduce the definition of meter.Nanometer measurement technology is a high-precision measurement technology at nanoscale,which is the foundation to ensure manufacturing at nanoscale.Specially,as the critical dimension of semiconductor chips has become smaller and smaller,the quantity value of line width directly affects device performance,therefore,accurate measurement of the line width is extremely important.Atomic force microscopy is a typical instrument for fusion measurements of line widths,however,the "expansion effect of the tip" and "scanning tube nonlinear effect" of AFM are the main factors that affect its accurate linewidth measurement.The Tip characterizer has high accuracy of tip inversion results and it is easily produced.Therefore the tip characterizer is suitable for the characterization of scanning tips,which enables true 3D imaging of nanostructures.However,the tip characterization technique of AFM based on tip characterizer has problems such as difficulty in direct traceability of measurement,large error accumulation and cumbersome dissemination of measurement values due to the structure of the tip characterizer.It also faces bottlenecks such as the difficulty of manufacturing very small-scale tip characterizer,which makes it difficult to meet the measurement needs of the gradual shrinking micro and nano device structures.Therefore,this paper conducts a study about the tip characterization technique of atomic force microscope based on natural constants,meeting the needs for precision measurement of AFM.We developed a measurement technique of tip characterizer structure with direct traceability,which is based on the silicon lattice constant and chromium atomic transition frequency,and verified the validity of the quantity dissemination based on the two natural constants,which is realized by international comparison.The quantity traceability of the measurement technique based on the silicon lattice constant is realized by transmission electron microscopy;the quantity traceability of the measurement technique based on the chromium transition frequency is realized by scanning electron microscopy,which is calibrated by self tracable grating.TEM,SEM and AFM measurement technique reported in this paper form a fusion measurement technique.The main research conducted in this paper and the main results obtained are as follows:1.Based on the principles of mathematical morphology,this article illustrates the process of interaction between sets of graphs in terms of expansion and erosion.Based on the linear relationship between the gradual changed linewidth and AFM measurement data,a mathematical method,which described the process of "scan-tip parameter acquisition-optimized sample data",is developed.This provides a theoretical basis for the development of a multi-quantity tip characterizer for tip inversion.2.A multidimensional research and analysis of the tip characterizer is reported,based on the fabrication and measurement techniques of multilayer film tip characterizer,employing the silicon lattice constants.In detail,based on a selftraceable linewidth measurement method employing the silicon lattice constant,the local uniformity of linewidth in multilayer films is characterized,the surface linewidth and the inside linewidth are compared,and the influence of oxide thickness on the design of the film layer is discussed.We designed and fabricated a series of tip characterizers with nominal values of 50 nm,100 nm and 200 nm,the processing deviation and uniformity are characterized.The comparison with the German PTB’s linewidth measurement accuracy is conducted,which verified that the uniformity of multilayer film linewidth is better than 1.5 nm and indicated that the non-rectangular structure of multilayer film linewidth is an important source of error for its uncertainty and tip inversion.A long-term stability monitoring of the tip characterizers is conducted and the linewidth variation rate of the tip characterizer is measured,using the micro and nano sample calibration device of the National institute of Metrology,the multi-structured tip characterizer is approved as a secondary national standard substance.The sub-5 nm linewidth tip characterizer is fabricated and characterized,we verified that the inverse structure of different linewidth is highly consistent.We conducted an analysis of the tip’s depth-towidth ratio,and developed a method for the application of sub-5 nm tip characterizer.3.Based on the self-traceable property of the chromium atomic transition frequency,the linewidth characterization and probe function testing of the tip characterizer fabricated by EBL are investigated.In detail,based on the selftraceable grating obtained by the materialization of the chromium transition frequency,an SEM magnification calibration method was developed,and an SEM measurement method traceable to natural constants was developed by combining a particle swarm algorithm.Based on the method above,the quantitative deviation of the sample fabricated by EBL was characterized,the quantitative accuracy of the tip characterizer was optimized,of which accuracy and uniformity were evaluated.The calibration method based on self-traceable grating provides support for the accuracy of EBL fabrication;and a series of grating standard sample have been fabricated and used for international comparison in the Asia-Pacific region.Using the tip characterizer fabricated by EBL,a reconstruction calculation of unknown linewidth was performed,and the calculation results were consistent with the results of the inversion of the multilayer film tip characterizer.Finally,we also carried out a multi-scale tip inversion study based on the silicon self-traceable grating.Based on the high accuracy,uniformity and consistency of the silicon self-traceable grating,we quantified the expansion profile parameters in the probe expansion process,compared the probe tip inversion consistency in contact mode and tapping mode,and developed a method to eliminate the error of probe expansion effect introduced by scanning tube nonlinearity.