Wafer Inspection System Using Multiple Interference Fringes
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing wafer inspection systems using laser Doppler velocimetry struggle to accurately determine the size of defects, especially when visibility is less than 0.15, leading to ambiguity in defect size measurement and failure to detect defects larger than 0.9 µm, due to the limitations of visibility curves that correspond to multiple defect sizes and zero visibility for certain sizes.
Innovation Solution
The system employs multiple measurement volumes with different interfringe distances and bandpass filtering to enhance defect detection dynamics, allowing for unambiguous size determination by cross-checking visibility values across these volumes, ensuring defects are detected over a wide range of sizes from tens of nanometers to hundreds of micrometers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single measurement volume with fixed interfringe distance is used, then the inspection system can detect defects of a specific size range, but it fails to accurately determine defect sizes when visibility is less than 0.15 and cannot detect defects larger than 0.9 µm
Solution Approach 1:
The patent divides the single measurement volume into multiple measurement volumes with different interfringe distances. Each measurement volume is optimized for detecting defects of specific size ranges, allowing the system to accurately measure defects across a broad spectrum from small to large sizes without ambiguity
Solution Approach 2:
The patent introduces an additional dimension by varying the interfringe distance across multiple measurement volumes. This dimensional variation enables the system to distinguish between defects of different sizes that would otherwise produce identical visibility values in a single measurement volume
2Loss of information
If laser Doppler velocimetry with fixed interfringe distance is used, then the system can provide qualitative and quantitative information on defects, but the visibility curve ambiguity causes multiple defect sizes to correspond to the same visibility value
Solution Approach 1:
The patent segments the measurement function into multiple measurement volumes, each with a specific interfringe distance optimized for particular defect sizes. This segmentation eliminates the information loss caused by visibility curve ambiguity by ensuring each defect size produces a unique visibility signature across the multiple volumes
Solution Approach 2:
The patent creates a multi-functional measurement system where multiple measurement volumes serve different functions - each optimized for specific defect size ranges. Together, they provide universal coverage for detecting and characterizing defects of any size on the wafer surface
3Device complexity
If a single interferometric device is used, then the system structure remains simple, but it cannot provide unambiguous defect size determination across a wide range of defect sizes
Solution Approach 1:
The patent merges multiple measurement volumes with different interfringe distances into a unified inspection system. By combining the results from multiple volumes, the system achieves unambiguous defect size determination across a wide range while maintaining a relatively simple overall structure based on a single interferometric device
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 accurate and efficient detection and sizing of defects across a broad size range, overcoming the limitations of existing systems by providing clear and repeatable results, even for transparent wafers, with improved detection dynamics and reduced ambiguity.
Implementation Method 1
an interferometric device 30 coupled to the light source arranged facing the surface S of the wafer 2 to be inspected... two branches for dividing the beam issuing from the light source into two incident beams... form, at the intersection between the two beams, a measurement volume comprising a plurality of parallel fringes
Implementation Method 2
an optical fiber 40 arranged between the surface of the wafer and a detection module 50, so as to guide the light backscattered by the surface of the wafer towards the detection module
Implementation Method 3
The presence of a defect on the surface of the wafer results, when this defect crosses the interference fringes, in the diffusion of a Doppler burst measured by the detection module... corresponding to the Doppler frequency containing information on the speed of the fault
Implementation Method 4
Document WO 2009/112704 describes a semiconductor wafer inspection system implementing laser Doppler velocimetry (LDV)... the Doppler frequency f D is linked to the displacement speed v of the defect in the direction perpendicular to the fringes and to the distance Δ between the interference fringes by the relationship: v=f*Δ
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
The invention includes a method for inspecting a wafer (2) for electronics, optics or optoelectronics, wherein said method includes: rotating the wafer (2) about an axis of symmetry perpendicular to a main surface (S) of said wafer; emitting, from at least one light source (20), at least two pairs of incident coherent light beams, in order to form two measurement spaces containing interference fringes having different fringe spacings; collecting a light beam diffused by the surface of the wafer; acquiring the collected light and emitting an electric signal representing the temporal variation of the light intensity of the collected light; detecting a frequency component in said signal, said frequency being the time signature of the passage of a defect through a respective measurement space; determining a parameter, referred to as defect visibility, for each detected signature, using the visibility determined for each measurement space; obtaining respective information on the size of said defect; and cross-checking information obtained for each measurement space in order to determine the size of the defect.