Opaque Hardmask Photoalignment for 3D NAND Pillar Overlay
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Solution Overview
Problem
In semiconductor fabrication, particularly for 3D NAND memory, pillar tilt caused by plasma gradients in the etch chamber leads to alignment challenges due to systematic and random variations, making it difficult to accurately align pillars across multiple layers, especially when the substrate is transparent and light wavelengths penetrate deeply, complicating the determination of pillar locations.
Innovation Solution
A tunable hardmask layer with selective opacity is used to filter out specific wavelengths of illumination light, blocking information about pillar tilt while allowing other wavelengths to penetrate, enabling more accurate alignment by forming topographical marks in the hardmask layer that can be propagated through subsequent layers, ensuring precise alignment of pillars across stacked substrate layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If light is used to illuminate through the substrate stack to locate pillar alignment features, then alignment information can be obtained, but pillar tilt signatures are also detected making accurate alignment difficult
Solution Approach 1:
The hardmask layer is divided into multiple layers with different opacities. The first hardmask layer has selective opacity that filters out specific wavelengths carrying tilt signature information while allowing other wavelengths to pass through and reveal alignment feature locations, effectively segmenting the information carried by different wavelengths
Solution Approach 2:
Different regions of the electromagnetic spectrum (different wavelengths) are treated differently by the hardmask layer. The layer has spatially selective optical properties that allow certain wavelengths to penetrate while blocking others, creating local quality variations in light transmission based on wavelength
2Manufacturing precision
If alignment marks are formed to improve alignment accuracy, then overlay precision improves, but the marks must be visible through transparent layers which also show tilt signatures
Solution Approach 1:
The first hardmask layer is deposited and patterned with alignment features before subsequent processing steps. This preliminary structuring creates reference marks that will guide later alignment operations, and the hardmask's optical properties are specifically designed to make these marks visible while filtering tilt 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 solution effectively reduces the impact of pillar tilt signatures, allowing for more accurate alignment and reducing errors in pillar placement, thereby improving the yield and density of 3D NAND memory devices by using a hardmask layer to filter out unwanted light information and enhance visibility of alignment marks.
Implementation Method 1
A tunable hardmask layer with selective opacity is used to filter out specific wavelengths of illumination light
Data Source
AI summary
Aligning pillars of a three-dimensional NAND memory assembly can include forming a first pillar and a corresponding first pillar alignment feature in at least a portion of a first substrate stack. The alignment method can include depositing a second substrate stack on the first substrate stack, covering the first pillar alignment feature and the first pillar, and depositing a first masking layer on at least a portion of the second substrate stack. Illumination light can be used to illuminate a portion of the first masking layer. A reflected portion of the illumination light can indicate a location of the first pillar alignment feature corresponding to the first pillar. Particular wavelengths of the illumination light can be blocked or filtered by the first masking layer.