This traceable high precision areal standard, is designed to calibrate the metrological characteristics of areal surface topography measuring instruments. The NPL areal standard enables users to:
NPL areal standard
The NPL areal standard is a 50 mm square toughened glass plate bearing a silicon wafer of 10 mm square in the middle of the plate. The silicon wafer contains geometrical patterns, designed for the calibration of areal surface topography measuring instruments, including vertical and lateral scale calibration, flatness deviation and testing the lateral resolution. The patterns on the NPL areal standard that are calibrated are listed in the table below.
| Name | Description | Feature | Size | |
| Type PGR | Groove, Rectangular (profile) | Step height | 2 µm | |
| 1 µm | ||||
| 500 nm | ||||
| 200 nm | ||||
| 100 nm | ||||
| 50 nm | ||||
| Type ACG | Cross grating (areal) | Pitch | 100 µm | |
| 50 µm | ||||
| 20 µm | ||||
| Type AFL | Flat | Flatness | Sz <=30nm | |
| Type ASG | Star shape grooves (areal) | Resolution | Range | Depth |
| 0.7 µm to 50 µm | 200 nm | |||
| 0.7 µm to 25 µm | 200 nm | |||
| 0.7 µm to 25 µm | 50 nm | |||
| 0.2 µm to 6 µm | 50 nm | |||
| Type AIR | Irregular (areal) | Sa, Sq, Sz, Ssk, Sku | 40 µm autocorrelation length | |
| 70 µm autocorrelation length | ||||
Influence parameters and metrological characteristics
The metrological characteristics of an areal surface texture instruments are shown in the table below. The NPL areal standard has been designed to directly address each of the metrological characteristics.
| Metrological Characteristics | Symbol* | Main Potential Error along | Calibrated patterns that addresses characteristic | |
| Amplification coefficient | ax , ay , az | x, y, z | Type PGR Type ACG |
|
| Linearity | lx , ly , lz | x, y, z | ||
| Perpendicularity | ΔPERxy | x, y | ||
| Flatness deviation | ZFLT | z | Type AFL | |
| Measurement noise | NM | z | ||
| Lateral period limit | DLIM | z | Type ASG | |
*As per ISO DIS 25178-600:2016, Date: 20-02-2016
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