Wafer Surface Quality Assessment Using Rotated Optical Sensor
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Solution Overview
Problem
Current methods for assessing the surface quality of disc-shaped workpieces, particularly wafers, are limited in their ability to perform large-area, high-speed, non-contact measurements with high accuracy, especially in detecting subtle surface features like waviness and roughness across the entire surface, due to the anisotropic nature of grinding marks which require precise alignment of optical sensors.
Innovation Solution
The method involves rotating an optical sensor about its measurement axis to determine the initial angle of rotation where the intensity characteristic is maximum, allowing for the calculation of surface features like waviness and roughness by aligning the sensor with the direction of transverse or longitudinal roughness, and using the variance of scattering angle distribution as a parameter for microstructure assessment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional contactless measurement methods are used, then measurement speed is improved, but measurement precision deteriorates due to inability to detect subtle surface features across large areas
Solution Approach 1:
The measurement process is segmented into multiple discrete angular positions (e.g., 0°, 45°, 90°, 135°) around the measurement axis. At each position, the optical sensor captures scattered light intensity in specific angular ranges, and these segmented measurements are combined to calculate comprehensive surface characteristics including roughness, waviness, and form features across the entire wafer surface.
Solution Approach 2:
The measurement system transitions from conventional two-dimensional surface scanning to three-dimensional angular space measurement by rotating the optical sensor around the measurement axis and detecting scattered light at multiple angles simultaneously. This adds the angular dimension (azimuthal rotation + polar detection angles) to the measurement space, enabling comprehensive surface assessment without increasing linear scanning distance.
2Measurement precision
If optical sensors are aligned with grinding mark directions, then detection accuracy of anisotropic surface features is improved, but device complexity increases due to precise alignment requirements
Solution Approach 1:
The optical sensor is mounted on a rotation mechanism that enables dynamic adjustment of the measurement angle around the measurement axis. This dynamic positioning allows the sensor to be oriented at specific angles (0°, 45°, 90°, 135°) relative to the grinding marks, adapting to the anisotropic surface structure without requiring complex fixed alignment mechanisms. The system automatically captures scattered light patterns at each angular position to characterize surface features in different directions.
3Length of moving object
If the wafer is thinned to reduce IC thickness, then product miniaturization is improved, but manufacturing precision deteriorates due to increased sensitivity to surface defects
Solution Approach 1:
The measurement system performs comprehensive surface assessment at multiple angular positions before the wafer undergoes final thinning or subsequent processing steps. By detecting and mapping surface defects, roughness variations, and form features in advance, the system provides feedback that allows adjustment of grinding and polishing parameters to ensure surface quality meets the stringent requirements of ultra-thin wafer applications.
Solution Approach 2:
The system calculates surface characteristics (roughness, waviness, form features) from scattered light intensity patterns detected at multiple angular positions and provides this information as feedback for process control. This feedback mechanism enables real-time monitoring and adjustment of surface quality during manufacturing, ensuring that thinned wafers maintain the required surface integrity for functional reliability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables precise, high-speed, non-contact assessment of surface quality across the entire wafer surface, improving the detection of waviness and roughness down to sub-nanometer levels, reducing measurement errors and ensuring the integrity of ICs by maintaining uniform surface conditions.
Implementation Method 1
an optical sensor emits a beam of light with a defined intensity distribution onto the surface of the workpiece to be assessed and illuminates a measurement spot. The reflected intensity of the radiation is detected by a line sensor with a discrete number of photodetectors within a defined angular range
Data Source
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Figure 2a
Figure 2b
AI summary
A method and a device for contactless assessment of the surface quality of a workpiece (W) according to the angle-resolved scattered light measuring technique comprises an optical sensor (10) which illuminates a measuring spot (14). The intensity of the radiation which is reflected back is detected by means of a line sensor (16), and an intensity characteristic value (Ig) is determined therefrom. A horizontal initial rotation angle (θ) at which the intensity characteristic value is at a maximum is determined. In a measuring operating mode, surface characteristic values are calculated taking into account this initial rotational angle (θ). The measuring method is defined by extremely high lateral and vertical spatial resolution, extending into the subnanometer range, and by a high measuring speed.