Metrology Systems Laser

Residual stress states are “fingerprints” that give an insight into the formation or use of a material or component. Their analysis is essential, for example in order to identify local stress states and defects on semiconductor substrates and component structures or to optimize production processes on the basis of information on stress states and defect distributions. This is made possible by the SIRD and SIREXsystems from Metrology & Plasma Solutions that operate entirely without contact or destruction.

SIRD and SIREX are polariscopes that can make visible stresses in materials that are transparent for the examination wavelength (e.g. silicon). The effect of stress-induced birefringence is used here:
If a material is exposed to shear stresses, its refractive index becomes anisotropic and the material becomes birefringent. Incident linear polarized light (laser) is therefore depolarized by the sample in transmission or reflection. Consequently, the obtained depolarization maps of SIRD and SIREX can be interpreted as shear stress distributions.

Defects and material inhomogeneities are often accompanied by stress fields whose spatial expansion is several times greater than that of the cause itself. A microscope like SIREX is able to make visible even the tiniest defects in the submicron range.

Intelligent software solutions help MPS to convert the obtained maps into interpretable results efficiently.

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Our systems to analyse residual stress states

  • SIRD Stress Measurement

    SIRD (Scanning Infrared Depolarization System) is a transmission dark-field plane polariscope. When the machine is in use, a fixed-position, linear polarized laser beam penetrates the wafer to be examined. If its crystal structure is perfect and stress-free, the polarization of the laser beam does not change. However, if there are shear stresses or defects in the crystal, the laser beam undergoes depolarization caused by stress-induced birefringence.

    Function at a Glance:

    • The SIRD operates in a similar way to a record player: the wafer rotates on a rotary table and is intermittently or continuously (spiral mode) moved in a radius direction
    • The data is recorded in line with a preset measuring protocol; the minimum and maximum radius are each freely selectable
    • The measuring time is determined by the selected lateral resolution (≥50 µm) and the scanning speed (max. approx. 1 cm² s⁻¹)
    • The most important measuring results are present as maps of depolarization and transmission

    SIRD operates in line with the ARD (alternating retarder depolarization) principle. This allows the discrimination of depolarization components not caused by birefringence. Consequently, it is possible to see even the tiniest stress differences (>100 Pa).

    SIRD application examples:

  • SIREX Stress Measurement

    SIREX (Scanning Infrared Stress Explorer) is a reflection dark-field plane polariscope. When it is in use, a fixed-position, linear polarized laser beam penetrates the sample to be examined, and is reflected on the back or the inner boundary surfaces. If the crystal structure of the sample is perfect and stress-free, the polarization of the laser beam does not change. However, if there are shear stresses or defects in the crystal, the laser beam undergoes depolarization caused by stress-induced birefringence. The sample is scanned via conventional X-Y movement of the sample table. The measuring results are ultimately present as maps of depolarization and reflection. The area to be measured is freely selectable. The measuring time is determined by the selected lateral resolution (≥3 µm) and the scanning speed (max. approx. 1 mm² min⁻¹) Automated rotation of the sample table enables the maps to be recorded at different polarization angles.

    SIREX operates in line with the ARD (alternating retarder depolarization) principle. This allows the discrimination of depolarization components not caused by birefringence. Consequently, it is possible to see even the tiniest stress differences (>100 Pa).

    SIREX application examples:

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PVA TePla AG
Im Westpark 10 - 12
D-35435 Wettenberg

Phone: +49 (0) 641/68690-0
Fax: +49 (0) 641/68690-800