The probe type profilometer uses a physical probe to contact the surface of the sample and measure the microstructure with high accuracy. The core principle is that when the probe (usually made of diamond material, with a curvature radius of 50nm-25 μ m optional) moves on the surface of the sample, the micro roughness of the surface causes the probe to produce vertical displacement. Displacement sensors (such as piezoelectric ceramics or laser interferometry) convert the mechanical displacement into electrical signals, which are amplified and filtered to reconstruct the three-dimensional contour. This technology can achieve a vertical resolution of 0.1nm and a lateral resolution of 0.05-0.2 μ m, with a measurement range of 55mm. It is suitable for scenarios such as wafer film thickness and metal surface roughness.
The factors affecting accuracy can be summarized into the following core dimensions:
Probe parameters
Radius: Although a radius that is too small (such as<1 μ m) can improve lateral resolution, it is prone to wear and may scratch soft materials (such as photoresist and aluminum film); If the radius is too large, the resolution will be reduced.
Measurement force: It needs to be controlled at the micro level (usually 2-5mg). Excessive force can cause deformation of the soft material surface, while insufficient force may lead to poor contact. High equipment adopts a force feedback system to dynamically adjust pressure.
Equipment calibration and motion control
Calibration error: It is necessary to periodically verify the reproducibility of step height using standard blocks (such as 1 μ m steps) (with a requirement of<4 Å).
Scanning speed: If the speed is too fast (>1mm/s), it may cause the probe to detach from the surface or generate dynamic measurement force, while if the speed is too slow, it will reduce efficiency. The typical optimization speed is 0.1-0.5mm/s.
Stage accuracy: Adopting an ultra flat scanning stage and piezoelectric ceramic drive to ensure a translation difference of<0.1 μ m in the X/Y direction.
Environmental and operational factors
Temperature and humidity: Temperature fluctuations (>± 1 ℃) or humidity changes (>± 10% RH) may cause thermal expansion or electrostatic interference, and should be operated in a constant temperature and humidity chamber (16-25 ℃/30-40% RH).
Sample processing: The surface should be clean and free of oil stains, and the measurement direction should be perpendicular to the processing pattern to avoid directional errors.