Wafer Optical Testing Using Multiple Taps to Isolate Loss
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Solution Overview
Problem
Existing optical wafer testing methods face challenges in accurately distinguishing between on-chip optical loss and loss due to alignment issues with input/output device coupling, leading to significant measurement errors and preventing repeatable measurements over time.
Innovation Solution
The method involves propagating light through a waveguide with multiple optical taps and using a photodetector to measure optical power differences between these taps, allowing for the determination of optical power loss and wafer parameters, thereby isolating on-chip and alignment-related losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional optical testing methods are used to measure on-chip optical loss, then optical measurements can be obtained, but measurement precision deteriorates due to inability to distinguish between on-chip loss and alignment-related loss
Solution Approach 1:
The patent divides the optical testing process into two separate measurements: one for on-chip optical loss and another for alignment-related loss. By using multiple optical taps at different locations, the total measured loss is segmented into distinct components that can be independently analyzed and subtracted to obtain accurate on-chip loss values.
Solution Approach 2:
The patent introduces an intermediary measurement approach by using optical taps as intermediate detection points between the input and output waveguides. These taps serve as mediators to capture and measure the alignment-related loss component separately, enabling its subtraction from the total loss measurement.
2Measurement precision
If multiple optical taps are used to separate loss components, then measurement precision improves, but device complexity increases
Solution Approach 1:
The patent designs the optical taps to serve multiple functions: they act as both measurement points for alignment loss characterization and as part of the overall optical testing infrastructure. This multi-functionality reduces the need for separate dedicated alignment loss measurement devices, thereby limiting the increase in device complexity.
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 measurement of optical power loss and wafer parameters, reducing measurement errors and improving the reliability of repeatable tests by separating on-chip and alignment-related losses.
Implementation Method 1
obtain a first measurement of an optical power at a first optical tap and a second measurement of an optical power at a second optical tap using a photodetector placed at a selected location with respect to the wafer
Implementation Method 2
a waveguide disposed in a silicon layer of the wafer. Light is input at an input end of the waveguide and exits at an output end of the waveguide
Data Source
AI summary
A method of determining a parameter of a wafer is disclosed. Light is propagated through a waveguide disposed in the wafer. A first measurement of optical power is obtained at a first optical tap coupled to the waveguide and a second measurement of optical power is obtained at a second optical tap coupled to the waveguide using a photodetector placed at a selected location with respect to the wafer. A difference in optical power is determined between the first optical tap and the second optical tap from the first measurement and the second measurement. The parameter of the wafer is determined from the determined difference in optical power.