Optical 3D Inspection When Laser Triangulation Reaches Its Limits

Related Vendors

FAULHABER Drive Systems

SIMTOS (Seoul International Machine Tool Show)

In semiconductor production, the smallest structure sizes and complex material layers require new approaches to quality assurance. Thanks to the combination of confocal line sensor technology (LCI) and vibration-free positioning technology, precise 3D inspection is possible even with highly reflective or transparent surfaces.

High-precision measurement methods are essential in electronics production to ensure the performance of components. With advancing miniaturization in semiconductor production and complex structures in PCB assembly, conventional optical inspection systems often reach their physical limits. Any irregularity on the wafer surface can jeopardize the entire production process. Measuring systems are required that are not only high-resolution, but also suitable for cycle times and robust against the often difficult optical properties of the test specimens.

LCI Compared to Laser Triangulation

One technological answer to this challenge is Line Confocal Imaging (LCI). In contrast to conventional laser triangulation, which often has to contend with disruptive reflections, scattered light and shadows on shiny or highly reflective wafer surfaces, LCI technology uses focused white light.

Sensors such as the Gocator 5512 from LMI Technologies separate the white light spectrally (chromatically) using special optics. By detecting the exact wavelength of light that is focused on the respective surface, 3D topographies, tomographies and 2D intensity data can be generated in a single step. A significant physical advantage of this optical profiling in wafer production is the ability to penetrate even transparent multi-layer materials without artifacts. The sensor achieves a profile resolution (X-axis) of 6.5 µm and a Z-repeat accuracy of up to 0.17 µm, with scan rates of several kilohertz.

Granite And Sensor Synchronization As A Basis

However, this optical resolution in the nanometer and sub-micrometer range can only be used in an industrial environment if the mechanical basis of the system has corresponding tolerances. For demanding inspection tasks, system integrators such as Jumavis therefore rely on high-precision mechanics, such as the positioning systems from PEAK Metrology.

A solid granite table forms the absolutely essential, vibration-free base to effectively dampen environmental influences and vibrations from the production environment. Sensor software and axis control work closely together to inspect entire wafers: With so-called X-Y stitching, the continuously traversed scan paths are combined into an overall image without distortion. Additional Z-stitching enables different layer heights to be captured in a continuous 3D model. Positioning in the sub-micrometer range ensures that the object always remains within the narrow focus range of the confocal line sensor.

Reduce Pseudo Defects in Photoresists

The technological added value of the hardware and software synergy is particularly evident in the inspection of wafers coated with transparent photoresist layers. With conventional inspection systems, the reflections of such coatings often lead to so-called false calls (pseudo defects), as particles or scratches located underneath the transparent layer are optically distorted.

Using the chromatic confocal method, defects in the nanometer range can be clearly assigned to the respective material depth. In combination with the submicrometer positioning system, even finely structured micro-bumps on large-area wafers can be measured automatically and precisely. This significantly reduces the pseudo error rate and increases the overall yield in the production process.

The combination of high-resolution LCI sensor technology and ultra-stable mechanical positioning is a key technology for modern electronics and semiconductor production. Automated, perfectly coordinated inspection solutions sustainably reduce rejects and ensure that future generations of components with even higher packing densities can be reliably inspected. The successful integration of such complete systems requires in-depth application-specific expertise, which is made available to users by experienced system partners. (heh)

This article is based on material from Jumavis.

How to Choose the Right Laser Cutter in 2025

5 Key Tips for Selecting Your Next Laser Cutting Machine