Pyrometer Filter for Laser Annealing Temperature Control
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Solution Overview
Problem
In thermal processing of silicon and semiconductor wafers, existing methods face challenges in reducing the thermal budget for advanced integrated circuits, particularly in achieving precise and uniform heating to minimize thermal damage and optimize processing time.
Innovation Solution
A thermal processing system utilizing a source of laser radiation with a beam splitting reflective member, projection optics, and a pyrometer system, where an amorphous carbon optical absorber layer on the substrate ensures uniform heating and a razor-edge filter blocks fluorescence interference, allowing for precise temperature control and reduced thermal impact on underlying integrated circuit features.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional thermal processing methods are used, then the substrate can be heated to required temperatures, but the thermal budget cannot be reduced and thermal damage to integrated circuit features increases
Solution Approach 1:
The patent employs pulsed laser radiation instead of continuous heating, delivering thermal energy in short, intense pulses that rapidly heat the substrate to required temperatures and then quickly cool it, thereby reducing the total time the substrate spends at high temperature and minimizing thermal budget
Solution Approach 2:
The patent uses selective laser heating that targets specific regions of the substrate containing integrated circuit features, allowing localized thermal processing at required temperatures while keeping other areas at lower temperatures, thus reducing overall thermal budget and preventing thermal damage to sensitive features
2Speed
If laser radiation is used for thermal processing, then heating speed increases, but fluorescence emission from optical components interferes with pyrometer temperature measurement
Solution Approach 1:
The patent extracts or removes the harmful fluorescence emission from the optical path by using optical filters that selectively block fluorescence wavelengths while transmitting the pyrometer measurement wavelengths, thereby eliminating interference and restoring temperature measurement accuracy
Solution Approach 2:
The patent introduces optical filters as intermediary components in the optical path that mediate between the laser radiation source and the pyrometer, allowing the pyrometer to accurately measure temperature by blocking harmful fluorescence while permitting measurement wavelengths to pass through
3Stability of the object's composition
If an amorphous carbon optical absorber layer is applied, then uniform heating is achieved, but the layer's absorption characteristics must be precisely matched to the laser wavelength
Solution Approach 1:
The patent optimizes the parameters of the amorphous carbon layer, specifically its thickness and optical absorption characteristics, to precisely match the laser wavelength being used, thereby achieving uniform heating across the substrate while maintaining a relatively simple optical system configuration
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 system achieves efficient and uniform thermal processing by minimizing the thermal budget, ensuring high precision in heating and reducing the impact on integrated circuit features, thereby enhancing the quality and speed of semiconductor wafer processing.
Implementation Method 1
An amorphous carbon optical absorber layer covers the surface of the substrate being processed
Implementation Method 2
A pyrometer on an opposite side of the reflective member and responsive to a pyrometer wavelength range or response band
Implementation Method 3
A pyrometer passband filter in the pyrometer optical path having a narrow passband lying in a wavelength window between the laser emission band and an emission band of fluorescence of the optical components
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
In a laser annealing system for workpieces such as semiconductor wafers, a pyrometer wavelength response band is established within a narrow window lying between the laser emission band and a fluorescence emission band from the optical components of the laser system, the pyrometer response band lying in a wavelength region at which the optical absorber layer on the workpiece has an optical absorption coefficient as great as or greater than the underlying workpiece. A multi-layer razor-edge interference filter (72) having a 5-8 nm wavelength cut-off edge transition provides the cut-off of the laser emission at the bottom end of the pyrometer response band.