Objective Positioning Stage for Tall Target Metrology Alignment
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Solution Overview
Problem
Traditional metrology systems struggle to image multiple layers and features at increasingly higher distances from each other while maintaining alignment tolerances, lacking the necessary focal plane adjustment distances and speed to efficiently move between tall target features.
Innovation Solution
A metrology system with an objective lens and detectors, equipped with an objective positioning stage and proximity sensors, allows for adjusting focal planes via movement along the optical axis, capturing images at multiple focal planes, and using air bearings for longitudinal movement, constraining lateral translation and tilt, to accurately measure and align features across large distances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional metrology systems use fixed focal plane positioning, then alignment is simple, but the system cannot image multiple layers with increasing height differences
Solution Approach 1:
The patent implements a dynamic focal plane positioning system with motorized stages that can adjust the position of objectives or sample holders along the optical axis. This allows the system to adapt to varying layer heights in 3D NAND and D2W structures while maintaining focus and alignment through programmable movement sequences.
Solution Approach 2:
The patent replaces manual mechanical adjustment with automated motorized positioning systems and computer-controlled focal plane adjustment. This substitution enables precise, repeatable positioning across multiple layers while eliminating alignment errors introduced by manual operation.
2Productivity
If the metrology system moves quickly between targets, then productivity increases, but alignment precision deteriorates
Solution Approach 1:
The system performs preliminary alignment calculations and pre-positions the focal plane before actual measurement begins. By calculating the required adjustment distance based on known layer heights and performing the positioning in advance, the system maintains precision while enabling rapid sequential measurement of multiple layers.
Solution Approach 2:
The patent implements feedback mechanisms including interferometric sensors and alignment markers that continuously monitor the position of moving components. This real-time feedback allows the control system to compensate for positioning errors and maintain alignment tolerance even during rapid focal plane transitions.
3Adaptability or versatility
If the focal plane adjustment range is increased to cover taller structures, then measurement capability improves, but system complexity increases
Solution Approach 1:
The patent employs a nested stage configuration where a coarse adjustment stage provides large-range focal plane positioning and a fine adjustment stage provides precision positioning within a smaller range. This nested arrangement enables the system to cover both the large adjustment range needed for tall 3D NAND structures and the fine precision needed for accurate measurement, without requiring a single overly complex mechanism.
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
Enables accurate and efficient measurement of overlay errors and critical dimensions across tall features, with improved alignment and faster focal height adjustments, supporting metrology measurements up to 1000 microns within tight alignment tolerances.
Implementation Method 1
a coarse stage of an objective positioning stage, the coarse stage structurally supported radially about the optical axis by one or more air bearings configured to allow for a longitudinal movement of the coarse stage along the optical axis, and constrain a lateral translation and a tilt of the coarse stage relative to the optical axis
Data Source
AI summary
A metrology system includes an imaging system. The imaging system may include an objective lens. The metrology system may include one or more detectors. The metrology system may include an objective positioning stage structurally coupled to the objective lens and configured to adjust a focal plane of at least one of the one or more detectors via movement along an optical axis of the metrology system. The metrology system may include one or more proximity sensors configured to measure lateral positions of a stage element as the objective positioning stage moves along the optical axis. The metrology system may be configured to determine a metrology measurement associated with a target on a sample using the images and lateral positions of the stage element when implementing a metrology recipe.