Sublithographic Hole Patterning via ALD Sidewall Spacers
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Solution Overview
Problem
Current photolithographic techniques, limited by 193 nm wavelength, struggle to uniformly shrink geometries smaller than 60 nm, leading to increased chip area and cost due to non-uniform reduction of hole sizes, where longitudinal dimensions shrink more than lateral dimensions, causing adjacent holes to merge and requiring increased pitch.
Innovation Solution
The method involves depositing a low-temperature atomic layer deposition (ALD) film conformally on photolithographic patterns to form sidewalls, which are then anisotropically etched to uniformly reduce both longitudinal and lateral dimensions of holes and spaces to sublithographic dimensions, preserving the shape and profile of the underlying pattern.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional hole size reduction process is used, then hole dimensions are reduced below lithographic capability, but longitudinal hole size reduction is significantly larger than lateral hole size reduction causing non-uniform shrinkage
Solution Approach 1:
A mandrel structure is formed preliminary before the hole etch process. This mandrel serves as a template that defines the final hole dimensions and ensures uniform shrinkage in both longitudinal and lateral directions. The mandrel is positioned and sized such that when holes are etched around it, the resulting holes achieve the desired sub-lithographic dimensions with uniform geometry.
Solution Approach 2:
The mandrel acts as an intermediary structure between the lithographic pattern and the final hole geometry. It mediates the transformation from lithographically-defined features to sub-lithographic holes with uniform dimensions, enabling precise control over hole size and shape without direct lithographic patterning at that scale.
2Manufacturing precision
If longitudinal hole size is increased on reticle to compensate for additional shrinkage, then adjacent holes may merge when printing
Solution Approach 1:
The patent replaces the conventional approach of directly printing holes at their final dimensions with a two-step process: first forming a mandrel structure, then etching holes around it. This substitution allows precise control of hole dimensions through the mandrel geometry rather than relying solely on lithographic resolution, enabling sub-lithographic hole sizes without increasing pitch or causing hole merging.
3Ease of manufacture
If polymer is deposited on contact sidewalls during contact etch, then contacts are formed, but sidewalls have sloped shape and top dimension is significantly larger than bottom dimension
Solution Approach 1:
The patent extracts the mandrel structure after it has served its purpose as a patterning template. By removing the mandrel after hole formation, the process achieves precise hole dimension control without the sidewall slope and dimension variation problems caused by polymer deposition methods. The mandrel is taken out after transferring its pattern, leaving clean vertical sidewalls.
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 allows for uniform shrinkage of hole and space geometries, reducing the integrated circuit area and cost by maintaining the shape integrity of smaller features, preventing adjacent hole merging and enabling more efficient use of chip space.
Implementation Method 1
depositing a low-temperature atomic layer deposition (ALD) film conformally on photolithographic patterns to form sidewalls
Implementation Method 2
which are then anisotropically etched to uniformly reduce both longitudinal and lateral dimensions of holes and spaces to sublithographic dimensions
Data Source
AI summary
A method of uniformly shrinking hole and space geometries by forming sidewalls of an ALD film deposited at low temperature on a photolithographic pattern.