Sidewall Mask Formation for High-Density Semiconductor Patterns
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Solution Overview
Problem
Conventional photolithography methods struggle to accurately form high-density patterns with equal line width and space sizes in NAND-type flash memory fabrication, limiting the integration density and increasing costs due to performance limitations.
Innovation Solution
A method involving the formation of sidewall films through etchback processes to create mask patterns with precise line widths and spaces, allowing for the fabrication of semiconductor devices with line widths and spaces of equal sizes at the minimum process size determined by photolithographic performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional photolithography methods are used to form line patterns, then the manufacturing process is simple, but the manufacturing precision is limited by the minimum process size F, making it impossible to accurately form lines with width narrower than F
Solution Approach 1:
The fabrication process is divided into multiple stages: first forming a stripe pattern with line width F and space F using conventional photolithography, then forming sidewall films on the lines, selectively removing portions of the sidewall films, and finally forming a second stripe pattern using the remaining sidewall films as masks. This segmentation allows achieving precision beyond the photolithography limit by combining multiple simpler steps.
Solution Approach 2:
Sidewall films are formed preliminarily on the first stripe pattern lines before the final pattern formation. These sidewall films serve as preliminary structures that will be selectively removed to create the precise mask pattern for the second etching step, enabling line widths narrower than the photolithography minimum.
2Manufacturing precision
If conventional sidewall film methods are used to form narrower lines, then line width can be reduced below F, but the line space becomes non-uniform with two types of spaces (F and xs)
Solution Approach 1:
Different portions of the sidewall films are treated differently: portions on the first lines are selectively removed, while portions on the second lines are retained to form the mask pattern. This local differentiation allows precise control over which areas are etched and which serve as masks, achieving both narrow line width and uniform line space.
Solution Approach 2:
Instead of using the original photolithography pattern as the final mask, the invention inverts the approach by using selectively processed sidewall films as the mask. The sidewall films are formed on all lines, then selectively removed from alternating lines, and the remaining sidewall films become the mask for etching the second pattern, reversing the conventional masking approach.
3Quantity of substance
If photolithography with minimum process size F is used, then the fabrication process is straightforward, but the integration density is limited with minimum memory cell size of 4F2
Solution Approach 1:
The invention transitions from two-dimensional photolithography patterning to a three-dimensional approach by forming vertical sidewall films on the pattern lines. This adds a vertical dimension to the patterning process, allowing the creation of narrower features by utilizing the sidewall film thickness rather than being constrained solely by photolithography resolution.
Solution Approach 2:
Sidewall films serve as intermediary structures between the photolithography-formed first pattern and the final second pattern. These intermediary sidewall films enable the transfer and refinement of the pattern with higher precision, acting as a bridge that allows achieving sub-photolithography minimum dimensions.
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 the fabrication of highly integrated semiconductor devices with improved integration density and reduced costs by forming stripe patterns with equal line widths and spaces, achieving a cell size half that of conventional methods.
Implementation Method 1
forming first sidewall films on sidewalls of the first mask pattern by etchback of a deposited second film
Data Source
AI summary
There is provided a method of fabricating a semiconductor device including forming a first film on a base layer, forming a first mask pattern on the first film, the first mask pattern having mask portions arranged at a given pitch, forming first sidewall films on sidewalls of the first mask pattern by etchback of a deposited second film, removing the first mask pattern, and forming a second mask pattern composed of the first sidewall films and second sidewall films defined by etchback of a deposited third film. It is possible to form a stripe pattern with the line width and the line space thereof having the same sizes and at a pitch the same as the minimum process size determined by the photolithographic performance, thereby enabling fabrication of a semiconductor device with a high degree of integration.