Research On Depth Measurement Method And System Of High Aspect Ratio Microstructure Based On Reflectance Spectroscopy

The development of micro-nano fabrication technique has led to the continuous advancement of processing accuracy from traditional macro scale to micro scale.A large number of miniaturized,intelligent micro-nano structured sensors with excellent performance have emerged in frontier research fields and various consumer grade products.The micron-scale high aspect ratio structure is one of the typical structural forms.Its efficient three-dimensional geometric space form,while increasing the lateral integration density,ensures the energy storage effectiveness and signal transmission rate of the device,and is now widely used in the fields of microelectromechanical systems(MEMS)and three-dimensional integrated circuits(3D-IC),providing a broad prospect for the development of the semiconductor industry.Depth,as one of the key functional features of high aspect ratio microstructures,largely determines both the performance of micro-nano structured sensors and the process difficulty.In particular,the trend of higher aspect ratio processes exacerbates the scale effect,triggering defects such as filled voids and defects,resulting in poor depth uniformity,which greatly affects the actual performance of the device.Therefore,it is necessary to develop high aspect ratio microstructure depth testing methods,especially in-line testing methods for micro-nano fabrication technique process control.To focus on this problem,a measurement method based on reflectance spectroscopy technique is proposed in this paper,and the main research includes the following aspects:1.The typical forms of high aspect ratio microstructures are studied,the current development status of measurement methods is systematically analyzed,and the defects and limitations of existing methods are discussed.2.The mathematical model of reflectance spectral signal of high aspect ratio microstructure is established,the mapping relationship between spectral features and geometric parameters of microstructure is studied,and the resolution strategy of feature parameters such as film thickness and microstructure depth is formulated by combining the basic principles of reflection spectroscopy.3.Design and build a high aspect ratio microstructure measurement system that integrates the micro-region fast reflectance spectroscopy optical path structure with the reflectance microscopy imaging optical path structure.Study the spatial optical filtering technology,design the numerical aperture(NA)regulation system with aperture angle limitation function,and improve the system bathymetry capability by combining the signal band selection technology;develop the control software based on Visual Studio and Qt Creator platform,and verify and optimize the system performance.4.Experimental studies were conducted on typical micron-scale trenches and through-silicon vias(TSV)with high aspect ratios.The minimum line width of the measurable array trench is 1.91 μm with aspect ratio of 56.5:1;the minimum line width of the single trench is 1.93 μm with aspect ratio of 56.0:1;the minimum line width of the TSV structure is 3 μm with aspect ratio of 27.3:1.The experimental results fully verify the depth measurement capability of the measurement system for high aspect ratio microstructures.