Wafer Geometry

© Fraunhofer ENAS
MicroProf® 300 TTV

The precise determination of wafer geometry is essential for many processes and applications. Whether in chemical-mechanical polishing or wet chemical structuring, accurate and meaningful measurements increase process stability and also serve quality assurance purposes. Depending on the application and processing step, wafer geometry is defined using various parameters:

  • Wafer/substrate thickness, thickness variation (TTV), bow, warp
  • Roughness according to DIN ISO standards
  • Flatness, coplanarity
  • Membrane thicknesses
  • Layer and layer stack thicknesses

There are two main methods for assessing these parameters: optical and tactile. The choice of method depends on the sample type and the parameters to be measured, and is made in consultation with the client.

CWL Sensor (Chromatic White Light)

FRT CWL operating instructions.
© Fraunhofer ENAS
MicroProf® 300 TTV with schematic diagram of the measuring unit (bottom left) (Source: FRT CWL Operating Manual, page 2-2)
Evaluated wafer map of an automatic measurement. The wafer is divided into predefined areas, allowing the local values to be output.
© Fraunhofer ENAS
Evaluated wafer map of an automatic measurement. The wafer is divided into predefined areas, allowing the output of local values.
The 3D display of the wafer thickness provides an immediate overview of the wafer's condition.
© Fraunhofer ENAS
The 3D display of the wafer thickness provides an immediate overview of the wafer's condition.

Measurement principle:

Chromatic distance measurement

Typical measurement tasks:

  • 2D profile
  • 3D topography
  • Step height
  • Roughness/flatness
  • Structure/contour

Technical data:

  • Measuring range z: 600 µm
  • Maximum resolution z: 6 nm
  • Maximum resolution x/y: 2 µm
  • Measurement rate: ≤ 4 kHz

Typical samples:

  • Automatic measurement of full wafers (4", 6" and 8")
  • Manual measurement of chips/fragments

FTR Sensor (Film Thickness Reflectometer)

Thin-film sensor FRT.
© Fraunhofer ENAS
MicroProf® 300 TTV with schematic representation of the measuring principle (bottom left) (Source: Data Sheet "Thin Film Sensor FRT FTR")
3D representation of the measured layer thickness over a complete 8" wafer. The mapping was carried out using a spiral point measurement, which allowed the wafer to be measured almost completely along its radius.
© Fraunhofer ENAS
3D representation of the measured layer thickness over a complete 8" wafer. The mapping was carried out using a spiral point measurement, which allowed the wafer to be measured almost completely along its radius.

Measurement principle:

Evaluation of the spectral interference pattern from the superposition of partial waves reflected at the interfaces

Typical measurement tasks:

  • Thin film thickness measurement
  • Thickness measurement of multilayer systems
  • 3D layer thickness measurement

Technical data:

  • Wavelength range: 350 – 1075 nm
  • Measuring range z: 20 nm – 130 µm
  • Resolution z: better than 1%, at least 1 nm
  • Resolution x/y: 100 – 400 µm

Samples:

  • Automatic measurement of full wafers (4", 6" and 8")
  • Manual measurement of chips/fragments

IR Sensor (Infrared)

Layer thickness sensor.
© Fraunhofer ENAS
MicroProf® 300 TTV with schematic representation of the measuring principle (bottom left) (Source: Data Sheet "Layer Thickness Sensor FRT IRT")
The data obtained using an infrared sensor can be visualized in a 3D representation. For this example, a circular point measurement with different distances from the center was chosen. This provides a good overview of the entire wafer.
© Fraunhofer ENAS
The data obtained using an infrared sensor can be visualized in a 3D representation. For this example, a circular point measurement with different distances from the center was chosen. This provides a good overview of the entire wafer.

Measurement principle:

Spectral evaluation of the superposition of partial waves from an IR light source

Typical measurement tasks:

  • Point thickness
  • 2D thickness profile
  • 3D layer thickness mapping
  • Thickness of individual layers/layer systems

Technical data:

  • Measuring range z: 18 – 3000 µm (at n=1)
  • Resolution z: 135 nm
  • Resolution x/y: ≤ 6.5 µm
  • Measurement rate: ≤ 4 kHz

Samples:

  • Automatic measurement of full wafers (4", 6" and 8")
  • Manual measurement of chips/fragments

Probing Tool

Fraunhofer ENAS
© Fraunhofer ENAS
Probing tool
  • Tactile measurement
  • Wafer is held by vacuum on a ceramic chuck
  • Measurement accuracy: ± 0.5 µm
  • Measurement force: 1 N ± 0.2

Samples:

  • Manual measurement of full wafers (4", 6" and 8")
  • Manual measurement of chips/fragments