Research On Dual-probe Atomic Force Microscope System Used For Linewidth Measurement

With the development of the semiconductor industry in recent years,the critical dimensions of integrated circuits are toward below the 22 nm technology nodes.The size of the device becomes smaller,which makes critical dimension become an important factor to affect the electrical properties of the device.How to measure and control the critical dimensions becomes a major problem in the field of nanometer measurement.The traditional measurement tools such as optical microscopy(OM),scanning electron microscopy(SEM)and atomic force microscopy(AFM)can't achieve true three-dimensional measurement effectively for critical dimension.In this paper,a dual-probe AFM measurement system is built,and it can eliminate the probe size effect on the measurement results through two probes alignment.In order to demonstrate the feasibility of dual-probe measurement,the AFM measuring head based on a quartz tuning fork probe(A-Probe)is developed.The main contents are as follows:1.The structure characteristics and working principle of A-Probe are introduced.The mechanics and electrical equivalent model of quartz tuning fork probe are described.The principles and features of dynamic AFM in amplitude modulation(AM),frequency modulation(FM)and phase modulation(PM)are analyzed.Finally a description is given on how dual-probe system can eliminate the influence of probe size and dual-probe alignment method is put forward.2.In order to achieve the traceability of measurement results in dual-probe AFM system,the laser interferometer system is adopted.An interface circuit for subdivision card based on FPGA is designed,which can achieve readout and reset operation of position data through PC software.It verifies the trigger function of equal displacement interval.3.A single measuring head experimental system is set up based on A-Probe,which consists of the measuring head,nanometer positioning stage,visual observation module,lock-in amplifier and a digital feedback control system based on DSP.The probe holder mechanism,weak signal detection circuit and digital feedback circuit based on DSP are developed for the system.The sensitivity and resolution of the measuring head in working mode of amplitude modulation,frequency modulation and phase modulation are tested based on the experimental system.And a sample of two-dimension grid is measured.Experimental results show that the measuring head can achieve nanoscale resolution and has the ability of imaging for micro-nanometer structures.4.The dual-probe alignment experiment is implemented in AM and FM working modes.The scanning probe is used to scan the static probe through near-field force.The experimental results demonstrate the feasibility of the dual-probe alignment measurement.