Development Of Dual-probe Atomic Force Microscope Measurement System

The semiconductor industry is closely bound up with micro-nano dimensionmeasuring technology. The precise measurement of geometrical dimension is a keyprerequisite for the rapid development of the integrated circuit manufacturing, in turn,the requirements of semiconductor process bring the nano-dimensional measurementon. The geometrical deviations of size and shape will influence the electricalperformance of the chip significantly. As the critical dimension (line-width) is one ofthe main technology parameters, its measurement and control will become greatchallenges in the future. For the inability to characterize the real3D morphology ofline-width, the conventional methods are replaced by dual-probe atomic forcemicroscope (AFM) in this paper. This dual-probe system is based on the research ofsingle probe and uses the tuning fork probe as the force sensor. After a test which isone probe’s tip approaching to touch another, the feasibility of the measurement isverified with this tip-to-tip mode. The main contents on the project are shown asfollows:1. The A-Probe finite element model is constructed based on ANSYS. Throughthe piezoelectric and static analysis, the work principle is explained. And themodal and working frequency is studied by the modal and harmonic responseanalysis. Also it analyzes the relationship between natural frequency andgeometric size of A-Probe. At last, the spring element is used to emulate thetip and sample interaction.2. The experiment set-up and prober head device are designed. The wholesystem mainly includes probe head, nanometer positioning platform,electrical signal processing board and optical auxiliary approaching system.The head includes probe holder and external electrical circuit design.3. The dynamic mode measurement is realized and implemented depending onLocked-in amplifier (LIA) and Phase-locked Loop (PLL). The headperformance experiment is conducted working on amplitude, frequency andphase modulation. Through the experiment verification, the resolution of thethree modes can lessen than1nm.4. The amplitude signal from probe is extracted to verify the dual-probe tip-to-tip measurement. With the static probe scanned by the scanning probe,the tips can be aligned within100nm. The dual-probe measurement plan isverified feasible based on near-field force interaction.