Optical Wafer Characterization for Pyrometer Temperature Correction
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Solution Overview
Problem
Conventional non-contact optical pyrometry systems for measuring semiconductor wafer temperatures provide apparent temperatures rather than true temperatures due to the unknown and difficult-to-measure emittance of real bodies, which varies with chemical composition, thickness, surface roughness, and coatings, leading to inaccuracies in temperature control during semiconductor fabrication.
Innovation Solution
A method that determines the optical characteristics of semiconductor wafers by emitting light onto the wafer, separating light reflected from the first and second surfaces, and using detectors to measure these characteristics, allowing for accurate determination of reflectivity, emissivity, absorptivity, and transmissivity, which can be used to correct temperature measurements and optimize heating processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional non-contact optical pyrometry systems are used to measure wafer temperature, then measurement speed and non-contact capability are improved, but temperature accuracy deteriorates due to unknown emittance
Solution Approach 1:
The patent applies preliminary action by measuring the optical properties (emittance, reflectivity, transmissivity) of the wafer before temperature measurement. The system characterizes the wafer's optical characteristics at room temperature or known conditions, then uses these pre-determined properties to correct the pyrometer readings during rapid thermal processing, thereby achieving accurate temperature measurement without sacrificing speed.
Solution Approach 2:
The patent introduces an intermediary approach by using the wafer's optical properties as a mediator between the pyrometer measurement and the true temperature. The system measures reflectivity and transmissivity separately, calculates emittance from these measurements, and then uses the emittance value to correct the apparent temperature reading from the pyrometer, yielding the accurate true temperature.
2Measurement precision
If emittance measurements are performed to correct temperature readings, then temperature accuracy is improved, but measurement complexity and difficulty increase
Solution Approach 1:
The patent applies segmentation by dividing the emittance measurement into two separate, easier measurements: reflectivity measurement and transmissivity measurement. Instead of directly measuring emittance (which is difficult), the system measures reflectivity at the wafer surface and transmissivity through the wafer, then calculates emittance from these segmented measurements using the relationship: emittance = 1 - reflectivity - transmissivity.
Solution Approach 2:
The patent replaces the difficult direct emittance measurement with an optical substitution approach. The system uses reflectivity measurements (which are easier to obtain) and transmissivity measurements to substitute for the direct emittance measurement, calculating the emittance value through optical property relationships rather than direct thermal radiation measurement.
3Manufacturing precision
If wafer optical properties are determined and used for temperature correction, then temperature control accuracy is improved, but system complexity increases
Solution Approach 1:
The patent applies universality by designing an optical measurement system that performs multiple functions: it measures reflectivity, measures transmissivity, and calculates emittance, all within a single integrated system. The same optical pathway and detectors are used to obtain multiple optical properties that are then used for temperature correction, reducing the need for separate measurement systems.
Solution Approach 2:
The patent implements feedback by using the measured optical properties (emittance, reflectivity, transmissivity) to continuously correct the pyrometer temperature readings during the thermal processing. The system establishes a feedback loop where the optical characterization data is fed back into the temperature calculation algorithm, allowing real-time correction of temperature measurements based on the actual wafer optical properties.
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 method improves the accuracy and repeatability of temperature measurements and control during semiconductor processing by accounting for the wafer's optical properties, enabling more precise temperature control and uniform heating.
Implementation Method 1
emit light onto a first surface of a semiconductor wafer... separate light reflected from the first surface from light reflected from a second, opposite surface of the wafer
Implementation Method 2
detect the amount of light reflected from the first surface... determine at least one optical characteristic of the semiconductor wafer
Data Source
AI summary
A method and system are disclosed for determining at least one optical characteristic of a substrate, such as a semiconductor wafer. Once the optical characteristic is determined, at least one parameter in a processing chamber may be controlled for improving the process. For example, in one embodiment, the reflectivity of one surface of the substrate may first be determined at or near ambient temperature. From this information, the reflectance and/or emittance of the wafer during high temperature processing may be accurately estimated. The emittance can be used to correct temperature measurements using a pyrometer during wafer processing. In addition to making more accurate temperature measurements, the optical characteristics of the substrate can also be used to better optimize the heating cycle.