Transparent Film Surface Height Determination via Opaque Reference
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Solution Overview
Problem
Accurate measurement of surface topography on samples with partially transparent surface layers is challenging for optical metrology devices, as underlying patterns and films contribute more to measurement variations than the actual surface height, leading to unreliable defect detection and characterization.
Innovation Solution
Measuring the surface topography of a reference sample before and after depositing an opaque film, and then using these measurements to determine the actual surface height of a test sample with a partially transparent surface layer, allowing for accurate characterization and defect detection by comparing relative height differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical metrology is used to measure surface topography of samples with partially transparent surface layers, then non-contact evaluation is achieved, but measurement accuracy deteriorates because underlying patterns and films contribute more to measurement variations than actual surface height
Solution Approach 1:
An opaque film is deposited as an intermediary layer over the partially transparent surface layer. This opaque film acts as a mediator that blocks light from reaching the underlying patterns and films, thereby eliminating their interfering contributions to the measurement. The surface topography of the opaque film directly reflects the underlying surface without distortion from transmitted light, enabling accurate measurement of the actual surface height.
Solution Approach 2:
The optical properties of the surface layer are changed by depositing an opaque film, transforming the measurement target from a partially transparent surface to an opaque surface. This parameter change (from transparent to opaque) modifies how light interacts with the surface, preventing light transmission through the surface layer and eliminating the interference from underlying structures, thus improving measurement accuracy.
2Measurement precision
If an opaque film is deposited to improve measurement accuracy, then actual surface height can be determined, but the process becomes destructive and more complex
Solution Approach 1:
The opaque film is deposited in advance as part of the sample preparation process before the actual surface topography measurement is performed. This preliminary action ensures that the measurement is conducted under optimal conditions (with the opaque film already in place to block light transmission), eliminating the need for complex real-time adjustments or corrections during measurement.
Solution Approach 2:
The surface topography of the opaque film is measured, which serves as a copy or proxy for the underlying surface topography. Since the opaque film conformally follows the underlying surface contours, measuring its topography provides an accurate representation of the actual surface height without requiring direct measurement of the partially transparent surface, which would be inaccurate.
3Productivity
If conventional optical metrology measures surface topography of transparent films, then measurement is performed, but the measured height reflects contributions from underlying patterns rather than actual surface height
Solution Approach 1:
The partially transparent nature of the surface layer, which causes harmful light transmission and measurement errors, is converted into a benefit by depositing an opaque film. The opaque film exploits the same optical path to block light completely, transforming the problematic transparency into a controlled opaque state that prevents light transmission and eliminates the harmful effect of underlying pattern interference, thereby preserving the actual surface height information.
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 enables precise characterization of surface topography, including defect detection, warp, bow, and 3D topology, without the need for destructive processes or modeling interactions with underlying patterns, improving the accuracy and reliability of optical metrology in semiconductor processing.
Implementation Method 1
Interferometry and many other optical metrology techniques rely on the reflection of light from the surface of the sample
Implementation Method 2
One type of optical metrology device is an interferometer which superimposes electromagnetic waves, e.g., light, reflected from a reference surface and a sample surface resulting in interference from which information about the sample may be extracted
Data Source
AI summary
A surface topography of a sample with a transparent surface layer is measured using surface topographies of a reference sample. The surface topographies of the reference sample are measured before and after the deposition of an opaque film over the surface layer. A surface topography of the sample is measured at the same relative positions as the surface topography measurements of the reference sample. A height difference at multiple corresponding positions on the sample and the pre-opaque film reference sample is determined. The actual surface height of the reference sample at each position is known from the surface topography of the post-opaque reference sample. The actual surface topography of the sample is determined by combining the actual surface heights of the reference sample with the determined height differences. The resulting surface topography of the sample may be used to characterize the sample, such as detecting defects on the sample.