Low Coherence Interferometer for Substrate Thickness and Temperature Measurement
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Solution Overview
Problem
Existing temperature measuring methods for substrates, such as semiconductor wafers, face challenges in accurately measuring temperature and thickness, especially for substrates with small thicknesses, due to limited changes in optical path length, leading to reduced measurement accuracy.
Innovation Solution
A temperature/thickness measuring apparatus and method utilizing a low coherence interferometer with a light source, beam splitter, and reference mirror to measure interference waveforms, where the reference mirror alters the optical path length, allowing for accurate measurement of the optical path length between the substrate's end surfaces by selecting interference waveforms corresponding to measurement beams reciprocally reflected multiple times, thereby amplifying the peak interval changes and improving measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a low coherence interferometer is used to measure substrate temperature and thickness, then measurement capability is provided, but measurement accuracy deteriorates for substrates with small thicknesses due to limited optical path length changes
Solution Approach 1:
The reference mirror is driven to dynamically alter the optical path length of the reference light, enabling the system to adapt to different substrate thicknesses. This dynamic adjustment allows the optical path length to be optimized for each measurement scenario, resolving the contradiction between providing universal measurement capability and maintaining high precision for specific cases like thin substrates
Solution Approach 2:
The system changes the optical path length parameter by driving the reference mirror to different positions. By adjusting this parameter, the system can compensate for the limited optical path length changes in thin substrates, thereby maintaining measurement accuracy across different substrate thicknesses while preserving overall measurement capability
2Reliability
If the optical path length of reference light is altered by driving the reference mirror, then interference waveforms can be measured, but the peak interval remains small for thin substrates leading to reduced measurement accuracy
Solution Approach 1:
The system measures multiple interference waveforms corresponding to different numbers of reciprocal reflections (different dimensions of the interference pattern). By selecting waveforms with larger peak intervals from this expanded dimensional space, the system overcomes the limitation of small peak intervals in thin substrates while maintaining reliable measurement functionality
3Measurement precision
If interference waveforms from multiple reciprocal reflections are utilized, then peak interval can be lengthened to improve accuracy, but the system complexity increases
Solution Approach 1:
The measurement target substrate itself serves as the multi-reflection cavity, naturally producing interference waveforms with different peak intervals corresponding to different numbers of reciprocal reflections. The system simply needs to detect and select the appropriate waveform, avoiding the need for complex additional components while achieving improved measurement accuracy
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 enhances the accuracy of temperature and thickness measurements for substrates of varying thicknesses by lengthening the peak interval between interference waveforms, particularly for substrates with small thicknesses, reducing measurement errors and improving the precision of temperature control in substrate processing.
Implementation Method 1
a light source that emits light to be transmitted through and reflected at two end surfaces of a measurement target
Implementation Method 2
measuring a plurality of measurement light interference waveforms obtained as interference of measurement beams each transmitted through or reflected at the measurement target and the reference light reflected from the reference light reflecting means occurs
Data Source
AI summary
In the apparatus according to the present invention, light from a light source is split into measurement light and reference light, the optical path length of the reference light is altered and a plurality of measurement light interference waveforms resulting from the interference of measurement beams reflected at a measurement target and the reference light are measured. One of these interference waveforms is designated as a reference interference waveform, another interference waveform corresponding to a measurement beam reciprocally reflected at the two end surfaces of the measurement target twice more than the measurement beam corresponding to the reference interference waveform is designated as a selected interference waveform, the optical path length of the measurement light indicated by the distance between the two end surfaces of the measurement target is measured based upon these interference waveforms. The temperature of the measurement targets is determined in correspondence to the optical path length.