Spectral Reflectance Control for High Aspect Ratio Layer Etch
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Solution Overview
Problem
In 3D-NAND manufacturing, controlling the etch process through multiple layers is challenging due to difficulties in accurately detecting the end point to avoid underetch and overetch, particularly in identifying layer boundaries during the formation of voids like gate trenches and channel holes.
Innovation Solution
A method and system that calculate the spectral derivative of reflectance during the etch process to identify discontinuities indicating layer boundaries, allowing for precise control actions such as terminating the etch process at preselected layers, with an optical profile monitor illuminating and measuring reflectance and an etch layer detector determining the currently etched layer and etch rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional end point detection methods are used during high aspect ratio etch, then the etch process can be monitored, but accurate layer boundary detection is difficult leading to underetch or overetch
Solution Approach 1:
The patent transforms the reflectance signal by calculating its spectral derivative, converting a difficult-to-interpret signal into one with clear discontinuities at layer boundaries. This parameter transformation enables precise detection of layer boundaries that were previously difficult to identify in the raw reflectance data during high aspect ratio etch processes.
2Loss of information
If the etch process is monitored through multiple layers, then layer boundary identification is required, but the complexity of identifying discontinuities in spectral data increases
Solution Approach 1:
The patent extracts the critical information (layer boundary positions) by calculating the spectral derivative of the reflectance signal. This extraction process isolates the boundary detection task from the complex multi-layer spectral data, converting it into a simplified discontinuity detection problem that can be reliably solved even for multiple layers.
3Manufacturing precision
If the etch process is terminated precisely at layer boundaries, then manufacturing precision is improved, but the risk of underetch or overetch increases if boundary detection is inaccurate
Solution Approach 1:
The patent implements a feedback mechanism where the spectral derivative signal is continuously monitored during the etch process. When a discontinuity is detected in the spectral derivative, it provides immediate feedback that a layer boundary has been reached, enabling precise termination of the etch process and preventing harmful underetch or overetch conditions.
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 control of the etch process, ensuring precise termination at preselected layer boundaries, thereby preventing underetch and overetch, and improving the manufacturing efficiency of 3D-NAND structures.
Implementation Method 1
measuring the reflectance of the illuminated region of interest
Data Source
AI summary
Controlling an etch process applied to a multi-layered structure, by calculating a spectral derivative of reflectance of an illuminated region of interest of a multi-layered structure during an etch process applied to the multi-layered structure, identifying in the spectral derivative a discontinuity that indicates that an edge of a void formed by the etch process at the region of interest has crossed a layer boundary of the multi-layered structure, determining that the crossed layer boundary corresponds to a preselected layer boundary of the multi-layered structure, and applying a predefined control action to the etch process responsive to determining that the crossed layer boundary corresponds to the preselected layer boundary of the multi-layered structure.