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Layer Thickness and Crystalline Standards

Workinggroup 5.13



Micrometer layer thickness standards

Foil thickness standards

Foils of uniform and defined thickness may serve as layer thickness standards if they are placed on appropriate substrate surfaces. They are frequently used to calibrate the widely spread electromagnetic layer thickness measuring instruments.
Usual designs:

  • 10...500 µm of plastics
  • 10...30 µm of bronze
  • > 500 µm of pertinax, brass

The reference area range is marked on the standards.

Coated substrates

In case of some important procedures applied to measure the layer thickness (e.g. X-ray fluorescence method), the measurement values indicated include material-dependent parameters. For the calibration of these instruments, standards are used which must be made of exactly the same material as provided for the existing measurement task. For this reason and due to the variety of possible material combinations, it is expedient that interested users manufacture their own samples with their own technology and then have them calibrated at PTB.

Figure 1: Example of a set of layer thickness standards with galvanic nickel layer on diamond-turned copper substrate surface





Nanometer-Layer thickness standards

In the nm-range two different types of layer thickness standards are offered. The first type is intended for X-ray techniques, like the X-ray reflectometry (XRR) and the X-ray fluorescence (XRF) and the second type for the calibration of ellipsometers.


Type 1: Nanometer layer thickness standards for X-ray techniques
(Currently not available. Modified upgrade is under investigation.)

For the X-ray reflectometry thin metal films on fused silica substrates are offered. For the calibration of X-ray reflectometers and the model used to evaluate the measurement the thickness of the metal layer is measured under grazing incidence (GIXRR).
The layer thickness standards consist of a fused silica substrate with the dimensions: 40 × 20 × 10 mm (L×W×H). Metal layers with nominal thicknesses of 10 nm and 50 nm serve as material measure. Pt and Ni are used as metal layers, where the Ni layer has a carbon base and a carbon cover layer with each 3 nm thickness. By these protection layers the diffusion of the Ni into the substrate and the corrosion of the Ni on the surface are avoided.
A typical set of layer thickness standards for the X-ray reflectometry consists of four samples with:

Nominal layer thickness /nm Layer
10 Pt
50 Pt
10 (3//10//3) Ni (C//Ni//C)
50 (3//50//3) Ni (C//Ni//C)

The expanded measurement uncertainty of the thickness value of the metal layer in the case of a nominal layer thickness of 10 nm amounts to 0.2 nm and for the layer thickness 50 nm to around 0.5 nm for U(k=2).

Figure 1: Layer thickness standards for X-ray reflectometry

Type 2: Nanometer layer thickness standards for ellipsometry

The layer thickness standards for ellipsometry consist of a thermal SiO2-layer on a Si substrate with Si(100) surface orientation. The substrate has a size of 30 × 20 mm and its height is about 0.5 mm. On the substrate in one corner is a lithographical micro structure, on which step height measurements with a Scanning Force Microscope (SFM) or with a high resolution profilometer can be carried out. The main area of the standard is intended for the ellipsometric layer thickness determination. The micro structure for SFM investigations and their position on the chip are shown in the following sketch. SiO2-layer thicknesses with nominal thicknesses of 6, 70, 160, 400 and 1000 nm are offered. 5nm and 100 nm will bee available soon. The uncertainty of the actual SiO2-layer thickness value depends on the thickness. In the case of a nominal 6 nm thick layer, the expanded measurement uncertainty is about 0.6 nm, for a nominal 1000 nm thick layer it amounts to around 5 nm.

Figure 2: Layer thickness standard for ellipsometry with magnified representation of the micro structure for step height measurement with a scanning force microscope



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