Wafer Thickness Detection for Back-Side Mark Alignment
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Solution Overview
Problem
Current detection systems for aligning marks on the back side of Si wafers are inefficient, requiring large search areas and increasing measurement time, leading to reduced throughput and inaccurate alignment due to variations in wafer thickness, which affects the manufacturing of devices like MEMSs and CISs.
Innovation Solution
A detection device comprising a first detection unit for marking on the back side and a second detection unit for surface position, with a processing unit determining the wafer thickness by calculating the difference between focus positions, allowing for quick and accurate detection of both mark position and thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the search area is increased to detect alignment marks on the back side of Si wafers, then the detection coverage is improved, but the measurement time increases and throughput is reduced
Solution Approach 1:
The patent applies preliminary action by performing wafer thickness measurement before alignment mark detection. The thickness measurement unit measures the wafer thickness in advance, and the control unit calculates the expected depth position of back-side alignment marks based on this thickness data. This allows the detection system to directly search at the calculated position without performing a large-area search, thereby reducing measurement time while maintaining detection coverage.
2Productivity
If the measurement pitch is increased to reduce measurement time, then the throughput is improved, but the alignment accuracy deteriorates due to increased computational errors
Solution Approach 1:
The patent implements feedback by using the measured wafer thickness as input data for calculating the precise depth position of alignment marks. The control unit receives thickness measurement data and automatically adjusts the detection position calculations accordingly. This feedback mechanism ensures that even with larger measurement pitches, the system maintains high alignment accuracy by compensating for individual wafer thickness variations.
3Difficulty of detecting and measuring
If the wafer thickness varies, then the detection of alignment marks becomes more difficult, but this variation also provides information about wafer processing quality
Solution Approach 1:
The patent applies parameter changes by measuring and utilizing the wafer thickness parameter to adjust the detection process. The thickness measurement unit obtains wafer thickness data, and the control unit uses this parameter to calculate the appropriate depth position for alignment mark detection. This approach transforms the thickness variation from a detection obstacle into a useful parameter that guides the detection process, maintaining reliability despite variations.
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 solution enables rapid and precise detection of back-side marks and wafer thickness, improving alignment accuracy and manufacturing yield by optimizing the detection process and providing feedback for wafer thinning and etching.
Implementation Method 1
the Si wafer is transmissive in respect of infrared light (wavelength of 1,000 nm or greater)
Implementation Method 2
an image of the alignment mark is acquired while the wafer stage is being driven in the optical axis direction of the alignment detection system to thereby calculate the position with highest contrast
Data Source
AI summary
A detection device that detects a mark provided on the back side of an object, the detection device includes a first detection unit configured to detect the mark from a surface side of the object; a second detection unit configured to detect a surface position of the object; and a processing unit. The processing unit determines a thickness of the object based on a difference between a first focus position acquired with reference to the position of the mark detected by the first detection unit and a second focus position acquired with reference to the surface position detected by the second detection unit.