SEMILAB’s Metrology Breakthrough: Optimizing Metal Needle-Glass Interactions with COMSOL Multiphysics

SEMILAB provides metrology solutions for semiconductor wafer and device manufacturers. When working on metrology system, measuring the contact surface of a metal needle’s interaction with glass presented a real challenge. Using COMSOL Multiphysics simulations and the Solid Mechanics Module, the SEMILAB Optical experts’ team determined the optimal glass material parameters, minimizing design uncertainties. Results revealed a successful correlation between simulation and measurement, streamlining the design process and cutting costs.

Challenge

The development of new measurements requires extensive planning. During the design process, questions arise that cannot be answered analytically. The objective of the SEMILAB Optical experts’ team was to examine the surface of a metal needle and determine the size of a contact surface on glass. The latter is used as a metric to measure the quality of manufactured needles.

To optically inspect the contact area, it is essential to have interference rings present. These interference rings become observable during the measurement when the height of the ‘air column’ between the needle and the deformed glass surface has the same order of magnitude as the half wavelength of the monochrome light source.

Solution

Initially, the contact surface was examined optically by measuring interference rings. Moving forward, COMSOL Multiphysics simulations helped the team find the appropriate glass material parameters for a given needle geometry, and for the needle pressure under which the contact surface may be determined.

For modeling, the Solid Mechanics Module was used, assuming cylindrical symmetry. Due to the problem’s particular characteristics, the geometry and contact mechanics had to be defined in the “Form an assembly” setting. The radial cross-section of the simulation is shown in Figure 1. A gap of ≈ 1384nm was created between the radially outermost point of the needle and the glass surface, and the maximum indentation of the glass was ≈ 155 nm.

Results

Figure 2 shows a comparison of the measurement and simulation results. The measurement coincides with the results of the simulation. COMSOL Multiphysics provided a contact area diameter of 56.6 μm, while the measurement showed a contact area diameter of 58.5 ± 4.5 μm. The deviation in the measurement result depends on how precisely the needle can be perpendicularly positioned to the surface, by the cylindrical asymmetry of the needle, and by how accurately the interference rings can be resolved.

Conclusion

COMSOL Multiphysics helped the SEMILAB Optical experts’ team to plan the measurement and predict the measurement results. The simulation showed them the expected deformation field in radial and depth directions and allowed them to select a suitable glass material. As the simulation and measurement results correlated well, the design time was reduced, thus saving on labor and material costs.

Summary

Challenge

Setting up and developing new metrology devices requires a significant amount of planning. It is critical to minimize errors to the greatest extent during the process to avoid delays and cost escalations.

Solution

With the help of COMSOL Multiphysics simulation, possible measurement combinations can be evaluated quickly and efficiently.

Results

By using structural mechanical simulations, the total time and effort spent on the design and measurements set-up were significantly reduced compared to such preparations without the use of simulation.

Products Used

All products mentioned are developed by COMSOL.

• COMSOL Multiphysics
• Structural Mechanics Module

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