Wule Zhu

On-machine measurement of a slow slide servo diamond-machined 3D microstructure with a curved substrate

A scanning tunneling microscope-based multi-axis measuring system is specially developed for the on-machine measurement of three-dimensional (3D) microstructures, to address the quality control difficulty with the traditional off-line measurement process. A typical 3D microstructure of the curved compound eye was diamond-machined by the slow slide servo technique, and then the whole surface was on-machine scanned three-dimensionally based on the tip-tracking strategy by utilizing a spindle, two linear motion stages, and an additional rotary stage. The machined surface profile and its shape deviation were accurately measured on-machine. The distortion of imaged ommatidia on the curved substrate was distinctively evaluated based on the characterized points extracted from the measured surface. Furthermore, the machining errors were investigated in connection with the on-machine measured surface and its characteristic parameters. Through experiments, the proposed measurement system is demonstrated to feature versatile on-machine measurement of 3D microstructures with a curved substrate, which is highly meaningful for quality control in the fabrication field.

Scanning tunneling microscopy-based in situ measurement of fast tool servo-assisted diamond turning micro-structures

We propose a new in situ measurement system based on scanning tunneling microscopy (STM) to realize spiral scanning of a micro-structure without removing it after fast tool servo (FTS) cutting. To avoid distortion of the machined and measured surface, the center alignment of the FTS tool and the STM tip was first implemented by an STM in situ raster scan of two circular grooves cut by the machine tool. To originally observe the machined surface, the trace of the STM tip is put in accord with that of the FTS by setting the same start and end points of cutting and scanning and the same feed rate, and both are triggered by the subdivided rotary encoder of the spindle of the diamond turning machine. The profile data of the in situ spiral scanning of the machined micro-lens array can be fed back to compensate the depth of the cut to guarantee sub-micron form accuracy after second machining. The efficient spiral scanning, proper matching and accurate evaluation results demonstrate that the proposed STM in situ measurement approach is of great significance to the fabrication process.

Note: long range and accurate measurement of deep trench microstructures by a specialized scanning tunneling microscope.

A compact but practical scanning tunneling microscope (STM) with high aspect ratio and high depth capability has been specially developed. Long range scanning mechanism with tilt-adjustment stage is adopted for the purpose of adjusting the probe-sample relative angle to compensate the non-parallel effects. A periodical trench microstructure with a pitch of 10 μm has been successfully imaged with a long scanning range up to 2.0 mm. More innovatively, a deep trench with depth and step height of 23.0 μm has also been successfully measured, and slope angle of the sidewall can approximately achieve 67°. The probe can continuously climb the high step and exploring the trench bottom without tip crashing. The new STM could perform long range measurement for the deep trench and high step surfaces without image distortion. It enables accurate measurement and quality control of periodical trench microstructures.

Note: Symmetric modulation methodology applied in improving the performance of scanning tunneling microscopy

A symmetric modulation methodology is proposed to combine robust control of external disturbance, rapid response to steep sidewalls with the high speed of a traditional scanning tunneling microscopy. The 1400 × 200 μm(2) topography of a comb-like steep sidewalls micro-structure with the depth of 23 μm was acquired at a high scanning speed of 120 μms(-1) and the detectable slope angle is up to 85°. The total measuring time was only 17 min. In addition, a 4 × 4 mm(2) aluminum dual-sinusoidal array has been successfully measured with a scanning speed up to 500 μms(-1). It improved the performance of the normal scanning tunneling microscope and enables efficient and stable measurement of large-area complex micro-structures, and thus can be introduced to engineering applications.