Avalanche Photodiode Data Age Compensation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In multi-axis interferometric systems, data age differences between measurement axes lead to significant measurement errors due to varying delays and phase shifts caused by avalanche photodiode (APD) bias voltage changes, which are difficult to compensate for effectively.
Innovation Solution
A method and apparatus that condition interferometric measurement signals using an APD, with adjustable bias voltage to compensate for measurement errors such as data age, group delay, and phase shift, utilizing look-up tables and mathematical formulas to determine adjustment values for precise signal adjustment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If avalanche photodiode (APD) bias voltage is adjusted to compensate for measurement errors, then measurement precision is improved, but device complexity increases due to additional control circuits and look-up tables
Solution Approach 1:
The system performs preliminary characterization of the APD's group delay and phase shift characteristics across different bias voltages and stores these values in look-up tables during system setup or calibration. This preliminary action allows the control system to quickly retrieve and apply appropriate compensation values without performing complex real-time calculations, thereby improving measurement precision while minimizing the computational complexity during operation.
Solution Approach 2:
The patent introduces an intermediary control system that acts as a mediator between the APD bias voltage adjustment and the measurement process. This intermediary system uses pre-stored look-up tables to determine the appropriate bias voltage adjustments needed to compensate for group delay and phase shift errors, eliminating the need for complex real-time mathematical formulas and reducing overall system complexity while maintaining high measurement precision.
2Productivity
If multiple measurements are taken across different axes simultaneously, then productivity is improved, but measurement precision deteriorates due to data age differences between axes
Solution Approach 1:
The system implements a feedback mechanism where the measured group delay and phase shift values from each axis are continuously monitored and used to dynamically adjust the APD bias voltage on each axis. This feedback loop ensures that all axes maintain synchronized data timing despite variations in measurement conditions, allowing simultaneous multi-axis measurements to maintain high precision while improving overall productivity.
Solution Approach 2:
The patent applies dynamic bias voltage adjustment where the APD bias voltage on each measurement axis is dynamically modified based on real-time measurements of group delay and phase shift. This dynamic adaptation allows the system to compensate for timing differences between axes during simultaneous measurements, maintaining measurement precision across multiple axes and thereby enabling high-productivity multi-axis operation without sacrificing accuracy.
3Reliability
If APD bias voltage changes to condition measurement signals, then signal quality is improved, but measurement precision worsens due to varying group delay and phase shift
Solution Approach 1:
The system exploits parameter changes by deliberately and precisely adjusting the APD bias voltage to specific predetermined values that correspond to optimal operating points where group delay and phase shift are minimized or standardized. By changing the bias voltage parameter to specific discrete values rather than allowing continuous variation, the system maintains signal quality while ensuring that timing characteristics remain consistent and predictable, thereby preserving measurement precision.
Solution Approach 2:
The patent performs preliminary characterization of the APD device to identify specific bias voltage values that result in minimal group delay and phase shift variations. These optimal bias voltage settings and their corresponding compensation values are pre-calculated and stored in look-up tables. During operation, the system simply retrieves and applies these pre-determined settings, ensuring signal quality is maintained while avoiding the precision errors that would result from arbitrary bias voltage changes.
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 significantly reduces measurement errors by dynamically adjusting the measurement signal to ensure accurate and synchronized data across multiple axes, enhancing the precision of interferometric measurements in applications like lithography and integrated circuit manufacturing.
Implementation Method 1
an avalanche photodiode (APD) to detect and condition an interferometric measurement signal
Implementation Method 2
The interferometer optics split the laser light into a reference path and a measurement path, then recombine the light returning from the two paths and direct the recombined light to a photodiode where it produces an interference signal
Implementation Method 3
In many applications, heterodyne interferometry, in which the measurement and reference beams differ in frequency, is preferred
Implementation Method 4
If the lengths of the measurement and reference paths are changing relative to one another, e.g., by translating a stage that includes the measurement object, the measured beat frequency includes a Doppler shift equal to 2vnp/λ
Data Source
AI summary
A method is disclosed including conditioning a measurement signal from an interferometer, said conditioning characterized by one or more conditioning parameters; measuring a plurality of values for the conditioned measurement signal; providing one or more values indicative of the conditioning parameters; determining an adjustment value at each measured value of the conditioned measurement signal based on the one or more of the measured values indicative of the conditioning parameters; and adjusting a measured value of the measurement signal according to the adjustment value.