Alignment Verification

Process control and quality verification represent important steps in modern chip production. The quality of lithographic processes can be determined and evaluated in terms of the exact positioning of structuring relative to existing layers.

Three techniques can be used depending on the particular alignment process:

Overlay Metrology

In the context of semiconductor technology, overlay refers to the degree to which two aligned layers exactly correspond to each other at all points of the processed substrate. Overlay metrology evaluates the position of two layers located on one and the same side of the substrate.  This might involve different layers on the same substrate or, in the case of bonded wafer stacks, layers on different substrates.

Front to Back Side Metrology

In processes such as wafer-level packaging and 3D integration as well as in the manufacturing of vertical through silicon vias (TSVs) and interposers, the wafer has to be treated from both sides.

By measuring the overlay in such double-sided processing, the relative position of the marks on the front and back side is verified. Since measurement is performed using two separate microscopes, any deviation arising from the instruments has to be taken into account.

Features and Benefits

  • Superior measurement reliability

IR Metrology

When several substrate layers are integrated, the alignment marks that are typically implemented in the course of the process are embedded within the substrate stack, making them inaccessible for inspection using optical microscopes.

Such embedded structures can be detected using infrared microscopes. Common materials that are transparent for IR wavelength light include silicon, III-V semiconductors (GaAs) and adhesives for temporary bonding and debonding techniques.

Precision handling of curved substrates is required when measuring structures in optically dense materials, since the measurement result can be distorted by parallax errors resulting from the deviation of the surface normals from the orientation of the optical axis.

Features and Benefits

  • Many years of experience with handling curved substrates

Fully automated Systems

 

Manual Systems

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