FLX Flexus thin film stress measurement systems

From Toho Technology

Toho FLX thin film stress measurement systems allow the determination of stresses and the linear expansion coefficient of thin and thick films on silicon wafers and other substrate materials. The system’s functions are industry standard for mass production and research facilities that demand accurate stress measurements on various films and substrates. Working with KLA-Tencor’s patented “Dual Wavelength” technology, systems of the FLX series accurately determine and analyze surface stresses caused by deposited thin films.

Available temperature range from -65 °C up to 500 °C
Patented dual wavelength technology for optimal signal readout
Calculation of coefficient of thermal expansion and biaxial modulus
3D mapping of sample deflection/stress distribution
Sample sizes from 25 mm up to 300 mm possible

The Flexus-S thin film measurement systems from Toho Technology allow stress measurements in the temperature range -65 °C up to 500 °C. Film stress that occurs during coating processes leads to voids and cracking and thus constitutes one of the main causes for the failure of electronic parts. With KLA-Tencor's patented "Dual Wavelength" technology a laser beam is moved above the sample along an axis. The reflected beam strikes a position-sensitive photo diode. The curvature radius of the wafer along the axis is measured by a line scan before and after the film deposition and hence allows the determination of the change of curvature due to the deposition. The wafer’s film stress is then calculated by way of Stoney’s equation. Several scans along different axes allow the creation of a 3D image of the stress distribution or curvature of the wafer.

The new FLX-R systems are a cost-effective alternative for applications where temperature measurements are not important. Along with the standard FLX functions, they feature an automated rotation stage which rotates the sample around any customer-determined angle and performs several scans. 3D mapping software plots both the three-dimensional distribution of the film stress and the sample deflection.

The Flexus stress measurement systems come in two versions: FLX-2320 for sample sizes 25  mm – 200 mm and FLX-3300 for sample sizes up to 300 mm.

Maximum Scan Diameter/Sample Size

  • 50-200 mm for the FLX-2320 (1 inch on request)
  • 75-300 mm for the FLX-3300


  • Measurement Range: 1 to 4000 MPa1 (3500 MPa for the FLX 3300)
  • Repeatability: 1.3 MPa
  • Accuracy: Less than 2.5% or 1 MPa whichever is larger
  • Minimum Radius: 2 m
  • Maximum Radius: 33 km

Operating Temperatures (for FLX-2320-S and FLX-3300-T)

  • Operating Temperature: -65°C to 500°C
  • Purge Gas: Nitrogen or Argon
  • Gas Flow: 1,5L/min, 0.3 kg/cm²
  • Cooling Option: with Liquid nitrogen
  • Temperature ramp rate to 500°C: 25°C/minute
  • Cooling rate: 500°C to 100°C in 1 hour, 30 minutes with LN²
  • Determination of Coefficient of thermal Expansion/biaxial film modulus
Thin film stress measurement

In general, stress is induced when materials of dissimilar coefficients of thermal expansion are bonded together. Films may behave similarly at high temperatures but as films are cooled, materials may contract/expand differently, thus causing stress in the film. With a stressed film, defects such as dislocations, voids, and cracking may occur.

With the Flexus, the user can easily determine the stress induced due to the film deposition process and can optimize the coatings according to the application and its durability.

Temperature cycling

Often the stress changes with Test-Temperature. The Flexus-S Series allows for temperature cycling with temperature ramp rates up 25° C per minute up to a maximum temperature of 500° C. Using argon or nitrogen as purging gas, sample oxidation can be minimized during the tests.

3D mapping

The Flexus software allows for 3D mapping of the stress and the deflecftion of the tested sample. Using the manual or the automated rotation option (only available for the Flexus-R version), the sample is rotated multiple times under a defined angle and the various scans are automatically stitched together by the software to create a 3D image of the stress distribution, as well as the sample deflection.

Measurement of coefficient of thermal expansion (CTE) and biaxial modulus of thin films

Both the CTE and the biaxial modulus of a thin film can be determined by the Flexus-S system. Only temperature measurements of the same film, deposited of two different subtrates with known properties are needed to extract said values.


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