1. Concepts related to Z-axis accuracy

• Vertical resolution

The smallest change in height that can be resolved when measuring differences in surface height.

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Low resolution and high resolution

• RMS Repeatability

The standard deviation of multiple groups of SiC wafer Rq is generally a measure of the average degree of deviation of 32 groups of sample values from their average value;

RMS Repeatability

• Step repeatability

The degree of consistency and stability between the measurement results obtained when measuring the same step or similar microstructure multiple times.

Step repeatability = 1σ step height standard deviation / Hˉ

Step repeatability

• Step accuracy

When measuring the same step or similar microstructure multiple times, the deviation between the average value and the true value of the measurement results.

Step accuracy = |Hˉ -H_true|/H_true

H_true is the true value of the step

Hˉ is the average value of the sample

Step accuracy

The vertical accuracy of the Z axis depends on the following points:

1. Optical path design, lens distortion rate, and lens aberration;

2. The wavelength range and stability of the light source;

3. Data acquisition devices, such as nano-displacement piezoelectric ceramics and micron-displacement motors;

4. Image processing algorithms for collecting and processing interference fringes.

2. Concepts related to XY lateral accuracy

• Concepts related to XY lateral accuracy in single field of view:

Camera Pixels

Refers to the number of pixels on a camera sensor, which determines the amount and accuracy of detail that the camera can capture in an image. Each pixel represents a point in the image, and its color and brightness information is captured and recorded by the camera sensor.

Low resolution and high resolution of camera

Lateral resolution

Refers to the minimum feature size that can be resolved when measuring surface features.

Higher optical magnification means higher resolution, which can capture more details and clearer images.

Low magnification and high magnification

Concepts related to XY lateral accuracy during image stitching

When stitching the field of view, in addition to the camera pixels and horizontal resolution mentioned above, the accuracy of platform movement and image stitching accuracy are introduced.

Positioning accuracy

Refers to the ability of a system to accurately place the object being measured or positioned at the desired location. Usually used to describe the position deviation of a system in the XY plane.

Repeat positioning accuracy

Refers to the consistency and stability of the measurement results on the XY plane during repeated measurements or positioning. A system with good repeatability can accurately repeat the same measurement or positioning at different times and under different conditions.

First to N times image stitching

Normal positioning accuracy & repeatability

Image stitching under worse repeat positioning accuracy

Platform splicing accuracy

Refers to the level of precision and accuracy that can be achieved when stitching data, images or information from multiple platforms or systems. It is generally ensured by spatial precision (accurate alignment of platform position and rotation angle) and image processing algorithms.

Good spatial accuracy

Good spatial accuracy

Worse spatial accuracy

Worse spatial accuracy

Precise algorithm

Precise algorithm

Worse algorithm

Precise algorithm

3. In addition to the accuracy of the instrument itself, the environment in which it is used is also very important

• Stable temperature and humidity control:

White light interferometers have high requirements for the stability of temperature and humidity, because temperature and humidity changes will affect the size and refractive index of optical components, thereby affecting the stability of the interference pattern and measurement accuracy. It is usually required to operate in an environment with small temperature and humidity changes.

• Low vibration environment:

Due to the stability of the optical path and the sensitivity of phase measurement of the white light interferometer, it is required to be used in a low vibration environment to avoid interference caused by airflow, building shaking, and operation of peripheral equipment.

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