Substrate Temperature Measurement Using Interference Reference Mirror
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Solution Overview
Problem
In substrate processing apparatuses, accurate measurement of substrate temperature is hindered by changes in optical fiber length due to ambient temperature fluctuations, affecting the measurement of optical path lengths and thus the determination of physical quantities like thickness and temperature.
Innovation Solution
A method involving a light receiving device and a movable reflection device to calculate interference position-related values in two directions, with an average value calculated to cancel out temperature influences, allowing for precise measurement of physical quantities like substrate thickness and temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical fiber is used to guide measurement light in substrate processing apparatus, then contactless temperature measurement of substrate becomes possible, but measurement precision deteriorates due to optical fiber length changes caused by ambient temperature fluctuations
Solution Approach 1:
The patent introduces a reference mirror as an intermediary element with known, stable optical path length. By comparing the measurement light's optical path length (through interference patterns) against this stable reference, the system eliminates the harmful effect of optical fiber length changes, allowing accurate substrate thickness and temperature measurement despite environmental temperature fluctuations.
Solution Approach 2:
The patent utilizes interference patterns formed by combining measurement light with reference light. By analyzing changes in the interference pattern (phase shifts) as the reference mirror is positioned at different known locations, the system determines the optical path length of the measurement light. This parameter transformation allows compensation for optical fiber length variations, enabling precise physical quantity measurement of the substrate.
2Reliability
If optical fiber length changes due to temperature increase, then device complexity increases to compensate for measurement errors, but measurement precision remains compromised
Solution Approach 1:
The reference mirror serves as a stable intermediary that provides a known optical path length reference. By measuring the interference pattern between measurement light and reference light at multiple known positions of the reference mirror, the system can reliably determine the optical path length of the measurement light despite temperature-induced fiber length changes, improving measurement reliability without excessive complexity.
Solution Approach 2:
The system employs interference pattern analysis as a feedback mechanism. By observing the interference fringes and calculating phase shifts based on known reference mirror positions, the system continuously compensates for optical path length variations caused by temperature changes, maintaining reliable measurements through real-time feedback correction.
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 substrate temperature and thickness by compensating for ambient temperature changes, ensuring reliable and precise physical quantity determination.
Implementation Method 1
interference of irradiation light and reflected light
Implementation Method 2
reflected light from the rear-side surface of the substrate and reflected light from the front-side surface
Implementation Method 3
the reference light is irradiated onto a reference mirror that is movable parallel to the direction in which the reference light is irradiated
Implementation Method 4
the measurement light and the reference light are respectively guided to the substrate and the reference mirror using optical fibers
Implementation Method 5
a photoelectric conversion device that converts the received light into an electrical signal
Data Source
AI summary
A method capable of accurately measuring a physical quantity of a measurement object in a substrate processing apparatus. In a temperature measurement apparatus for implementing the method, two interference positions are measured at different timings when a reference mirror is caused to move in the direction away from a collimator fiber, and a difference between the two interference positions is calculated. When the reference mirror remote from the collimator fiber is caused to move toward the collimator fiber, two interference positions are measured at different timings, and a difference between the two interference positions is calculated. An average value of the interference position differences is calculated, an optical path length difference is determined from the average value, and a wafer temperature is calculated from the optical path length difference.