Wafer Curvature Measurement Using Multiwavelength Light
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Solution Overview
Problem
Existing systems for in-situ curvature measurement of wafers in multi-wafer epitaxial reactors are complex, prone to destructive interferences, and unreliable, especially when wafers are loaded onto a rotating susceptor, making it challenging to accurately determine wafer curvatures in real-time.
Innovation Solution
A system utilizing a multiwavelength light source module emitting incident light with multiple wavelengths, combined into a single beam, which hits the wafer surface at a single measuring spot, allowing for curvature determination from reflected light, even in the presence of destructive interferences, using a deflection detector to collect and analyze the reflected light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single-wavelength light source is used for curvature measurement, then the system is simpler, but destructive interferences occur during epitaxial growth making measurement unreliable
Solution Approach 1:
The light source is segmented into multiple discrete wavelengths (e.g., 633nm, 650nm, 680nm, 700nm, 750nm) rather than using a single wavelength. This segmentation allows the system to select wavelengths that do not suffer from destructive interferences during epitaxial growth, thereby improving measurement reliability without requiring a completely complex new system architecture
Solution Approach 2:
The system changes the parameter of wavelength selection dynamically. By having multiple discrete wavelengths available and selecting appropriate ones based on the epitaxial growth conditions, the system avoids destructive interferences. The controller can adjust which wavelengths are used based on real-time measurement conditions, transforming a static single-wavelength system into a dynamic multi-wavelength system
2Measurement precision
If multiple measurements are performed at subsequent sampling times during susceptor rotation, then curvature measurement accuracy is improved, but the system becomes more complex and time-consuming
Solution Approach 1:
The system performs preliminary calibration measurements on a flat reference surface before actual wafer measurements. This preliminary action establishes baseline information about the optical path and detector characteristics, allowing subsequent wafer curvature measurements to be made more accurately without requiring complex real-time calibration during susceptor rotation
Solution Approach 2:
The system creates an optical copy or image of the wafer surface curvature through the reflected light pattern. By measuring the position and intensity distribution of the reflected light spot on the detector, the system creates a measurable copy of the curvature information, allowing accurate curvature determination without complex direct measurement mechanisms
3Productivity
If a single beam hits the wafer surface at a single measuring spot, then the measurement is simpler and faster, but the system becomes more sensitive to destructive interferences
Solution Approach 1:
Instead of using a single wavelength beam, the system segments the light source into multiple discrete wavelengths. Each wavelength can be independently evaluated for its susceptibility to destructive interferences. By having multiple segmented wavelengths, the system maintains the simplicity of single-spot measurement while adding the reliability of wavelength diversity to overcome interference problems
Solution Approach 2:
The system changes the wavelength parameter of the incident light to optimize measurement reliability. By selecting from multiple discrete wavelengths and adjusting which wavelengths are used based on the epitaxial growth stage and detected interference patterns, the system maintains fast single-spot measurement speed while adapting the wavelength parameter to avoid destructive interferences
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
The system provides a robust and accurate method for in-situ curvature measurement, reducing the impact of destructive interferences and enabling reliable determination of wafer curvatures, thus improving the monitoring of strain in growing layers and enhancing epitaxial process control.
Implementation Method 1
a multiwavelength light source module, adapted to emit incident light comprising a plurality of wavelengths
Implementation Method 2
an optical setup configured to combine the incident light into a single beam
Implementation Method 3
the single beam hits the surface at a single measuring spot on the surface
Implementation Method 4
a deflection detector, adapted to collect reflected light corresponding to the single beam being reflected on the surface at the single measuring spot
Data Source
AI summary
A system for in-situ measurement of a curvature of a surface of a wafer comprises: a multiwavelength light source module, adapted to emit incident light comprising a plurality of wavelengths; an optical setup configured to combine the incident light into a single beam and to guide the single beam towards a surface of a wafer such that the single beam hits the surface at a single measuring spot on the surface; and a curvature determining unit, configured to determine a curvature of the surface of the wafer from reflected light corresponding to the single beam being reflected on the surface at the single measuring spot.