Gradient Porosity Sacrificial Pattern for High-Aspect-Ratio Hole Fabrication
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Solution Overview
Problem
In semiconductor device fabrication, particularly for three-dimensional memory devices, the removal of sacrificial materials from high-aspect-ratio structures is challenging due to their high porosity, which complicates the formation of through-holes and channel holes, leading to difficulties in maintaining the shape and structure of the device.
Innovation Solution
A method involving the formation of a sacrificial pattern with increasing porosity towards the substrate, where the lower part is more porous and easily removable, while the upper part is less porous and provides structural support, allowing for the easy formation of through-holes with a high aspect ratio by adjusting the concentration and temperature of sacrificial materials during the spin coating process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a sacrificial material is used to form high-aspect-ratio structures, then the structural support is provided, but the removal of the sacrificial material becomes difficult
Solution Approach 1:
The sacrificial pattern is designed with non-uniform porosity where the lower portion (near substrate) has higher porosity for easy removal, while the upper portion has lower porosity for structural support. This local variation in material properties resolves the contradiction between ease of removal and structural strength.
Solution Approach 2:
The sacrificial pattern utilizes controlled porosity gradients to achieve different functional requirements in different regions. The porous structure at the bottom facilitates easy removal through the opening, while the less porous upper region maintains structural integrity during fabrication.
2Ease of manufacture
If the porosity of sacrificial material is increased for easy removal, then the removal process is simplified, but the structural integrity is compromised
Solution Approach 1:
Different porosity levels are applied to different regions of the sacrificial pattern. The lower region has higher porosity (e.g., 50-80%) to facilitate easy removal, while the upper region has lower porosity (e.g., 20-40%) to maintain structural integrity during the fabrication process.
Solution Approach 2:
The solution transitions from a uniform one-dimensional structure to a vertically-gradient structure where porosity varies along the vertical dimension. This dimensional variation allows simultaneous optimization of removal ease (bottom) and structural strength (top).
3Device complexity
If a uniform sacrificial pattern is used, then the fabrication process is simplified, but the selective removal is difficult
Solution Approach 1:
The sacrificial pattern incorporates local quality variations with different porosity regions. The high-porosity lower region enables selective removal through the opening while the lower-porosity upper region remains intact, achieving selective removal without significantly complicating the fabrication process.
Solution Approach 2:
The porosity gradient is pre-established in the sacrificial pattern before the removal process. This preliminary structuring with varying porosity allows subsequent selective removal to proceed easily through the high-porosity region while preserving the low-porosity structural regions.
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 facilitates the efficient formation of high-aspect-ratio through-holes by ensuring the sacrificial pattern is easily removable, maintaining structural integrity and supporting the shape of the device, thus enhancing the fabrication process for semiconductor devices.
Implementation Method 1
adjusting the concentration and temperature of sacrificial materials during the spin coating process
Data Source
AI summary
A method for fabricating a semiconductor device, including forming a lower structure on a substrate. The lower structure includes a first sacrificial layer and a first insulating layer alternately and repeatedly stacked. A first hole is formed in the lower substrate. The first hole exposes an upper surface of the substrate. A sacrificial pattern is formed in the first hole. A porosity of the sacrificial pattern increases toward the substrate. An upper structure is formed on the lower structure and the sacrificial pattern. The upper structure includes a second sacrificial layer and a second insulating layer alternatively and repeatedly stacked. A second hole is formed in the upper structure. The second hole exposes the sacrificial pattern. The sacrificial pattern is removed.