Self-Aligned Spatial Frequency Doubling in Lithography
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Solution Overview
Problem
Current optical lithography techniques are limited in producing feature pitches smaller than 74 nm, and existing methods for spatial frequency doubling are either expensive or require multiple lithographic steps and precise alignment, which are not economically viable for all applications.
Innovation Solution
A method for self-aligned spatial frequency doubling in one and two dimensions, involving the formation of a film stack with a photoresist layer, where a one-dimensional periodic pattern is created with a pitch smaller than twice the bandpass limit, followed by nonlinear processing steps to achieve a second pattern with half the pitch, and optionally repeating this process at an angle to achieve further frequency doubling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional optical lithography is used, then manufacturing simplicity is maintained, but manufacturing precision deteriorates with minimum pitch of 74 nm
Solution Approach 1:
The patent segments the pattern formation process into distinct stages: first forming a pattern at pitch p, then using nonlinear processing to generate harmonics, and finally isolating the doubled frequency component. This segmentation allows achieving pitch p/2 without requiring the entire process to be performed in a single complex lithographic step.
Solution Approach 2:
The patent performs preliminary pattern formation at the relaxed pitch p before applying nonlinear processing. By pre-forming the pattern and then using chemical or physical nonlinear effects to generate the doubled frequency, the method avoids the need for precise alignment in subsequent steps, simplifying the overall manufacturing process.
2Manufacturing precision
If spatial frequency multiplication is used to extend beyond optical limits, then manufacturing precision improves, but device complexity increases due to multiple lithographic steps
Solution Approach 1:
The patent employs self-aligned nonlinear processing where the pattern itself serves as the template for generating the doubled frequency. The first pattern automatically generates the second pattern through nonlinear effects without requiring external alignment references, making the process self-service and reducing complexity.
Solution Approach 2:
The patent changes the spatial frequency parameter through nonlinear processing of the photoresist pattern. By applying nonlinear chemical or physical treatments to the formed pattern, the spatial frequency is multiplied without changing the fundamental optical exposure parameters, thus extending beyond optical limits while maintaining process simplicity.
3Manufacturing precision
If phase shift masks are used to double frequency, then manufacturing precision improves, but ease of operation deteriorates due to alignment requirements
Solution Approach 1:
The patent uses self-aligned nonlinear processing where the first pattern automatically serves as the reference for generating the second pattern. The nonlinear effects occur in situ at the pattern locations, eliminating the need for separate alignment operations and making the process easier to operate.
Solution Approach 2:
The patent merges the pattern formation and frequency doubling operations into a single integrated process. Instead of performing frequency doubling in a separate aligned step, the nonlinear processing is applied directly to the formed pattern, combining both functions and eliminating alignment requirements.
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 method enables the production of patterns with higher spatial frequency than conventional optical lithography, achieving pitches beyond the standard limits with fewer lithographic steps and without the need for precise alignment, making it economically viable for a wider range of applications.
Implementation Method 1
A simple example is the use of a high-contrast photoresist layer that converts a sinusoidal aerial image pattern into a square wave developed photoresist pattern
Implementation Method 2
Interferometric lithography (IL) is a maskless technique, involving the interference of a small number of coherent laser beams
Data Source
AI summary
In accordance with the invention, there are methods for self-aligned spatial frequency doubling in one dimension and also in two dimension. The method for self-aligned spatial frequency doubling in one dimension can include forming a film stack over a substrate, wherein the film stack comprises a photoresist layer and forming a one-dimensional periodic first pattern having a first pitch p on the photoresist layer using an optical exposure, wherein the first pitch p is at least smaller than twice the bandpass limit for optical exposures. The method can also include forming a second pattern using the first pattern by nonlinear processing steps, wherein the second pattern has a second pitch p2=p/2.