Stabilized Optical Measurement System for Semiconductor Processing
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Solution Overview
Problem
Optical measurement systems in the semiconductor processing industry face challenges with drift, fade, and errors due to absorption and solarization effects, particularly with UV and DUV radiation, which affect measurement accuracy and precision, especially with shorter wavelengths that cannot be consistently transmitted through optical fibers.
Innovation Solution
The system mitigates these issues by purging areas with inert gases to prevent ozone and oxygen absorption, using low-solarization optical materials, eliminating or replacing susceptible components, and creating a reference signal path to compensate for signal variations through ratioing of calibration and measurement signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If optical fibers are used to transmit UV and DUV light, then light transmission is achieved, but absorption and solarization effects cause measurement errors and signal degradation
Solution Approach 1:
The patent removes optical fibers from the optical path wherever possible to eliminate the solarization problem. Free-space optical coupling is implemented between the light source, optical assembly, and detector, extracting the harmful fiber component from the system while maintaining light transmission functionality.
Solution Approach 2:
The patent introduces an inert gas atmosphere (nitrogen or other inert gases) into the optical chamber to replace air. This prevents oxygen absorption of UV/DUV light and eliminates ozone formation, creating an inert environment that protects against absorption and solarization effects.
2Object-affected harmful factors
If optical fibers are eliminated and free-space coupling is used, then absorption and solarization effects are reduced, but design complexity and integration challenges increase
Solution Approach 1:
The patent merges the light source, optical assembly, and detector into a tightly integrated free-space optical system. By combining these components in close proximity with direct optical coupling, the system eliminates the need for complex fiber routing and alignment while reducing solarization effects.
Solution Approach 2:
The patent introduces an inert gas atmosphere as an intermediary medium between optical components. This mediator allows UV/DUV light to travel through the optical path without being absorbed by oxygen or causing solarization, while also serving as a protective environment for the optical components.
3Measurement precision
If reference signal path is added to compensate for variations, then measurement precision is improved, but system complexity increases
Solution Approach 1:
The patent segments the optical system into two separate but identical optical paths: a measurement path that interacts with the sample and a reference path that does not. This segmentation allows independent monitoring of system variations in the reference path, which can then be used to compensate for variations affecting the measurement path.
Solution Approach 2:
The patent creates a reference optical path that is an exact copy of the measurement optical path in terms of components and configuration. This duplicate reference path captures all system variations (lamp intensity changes, detector drift, optical component aging) without being affected by sample interactions, enabling accurate compensation through ratioing or differential measurement.
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 and drift, ensuring high repeatability and accuracy by accounting for short-term and long-term solarization, oxygen/ozone effects, detector variations, and lamp aging, thereby enhancing the reliability of optical measurements in semiconductor processing.
Implementation Method 1
UV and DUV radiation adversely affects light analyzing device 110, light source 120, optical assembly 130 and optical fiber assembly 140 such that analysis performed by computer 150 of reflected light signals from workpiece 160 will contain errors (e.g., drifts, variations, noise, signal fade)
Implementation Method 2
UV and DUV radiation exposure causes measurement errors as a result of solarization of optical fibers, degradation of measurement system elements, and absorption by oxygen and the creation of and absorption by ozone in the optical signal path
Data Source
AI summary
A referenced and stabilized optical measurement system includes a light source, a plurality of optical elements and optical fiber assemblies and a detector arranged to compensate for the effects of system variation which may affect measurement performance. A non-continuous light source provides a common source light on a common source path. A reference light and a measurement light are derived from the common source light and propagated across separate paths of optically matching optical components in order to produce a common signal variation on both the reference light signal and the measurement light signal. Light paths exposed to air are contained indiscrete volumes for purging gasses from the volumes. Ratios of the reference signal and measurement signal are acquired under various conditions for compensating the measurement signal for system variations.