Multilayer Light Shielding Film for DRAM Mask EMF Bias
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Solution Overview
Problem
The miniaturization of semiconductor devices poses challenges in lithographic techniques due to the electromagnetic field (EMF) effect, which affects the line width and optical density of transfer patterns, leading to issues with light leakage and increased film thickness requirements, particularly in the DRAM half pitch 32 nm generation and beyond.
Innovation Solution
A mask blank with a light shielding film having a multilayer structure, including a light shielding layer and a surface anti-reflection layer, and an auxiliary light shielding film, where the light shielding film is 40 nm or less in thickness and has an optical density of 2.0 to 2.7, and the auxiliary film provides additional optical density for the peripheral regions, ensuring sufficient light shielding without increasing film thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the light shielding film thickness is increased to achieve sufficient optical density (OD=3), then light shielding performance is improved, but the film thickness cannot be significantly thinned (minimum 60 nm required)
Solution Approach 1:
The patent employs a composite light shielding film structure consisting of multiple layers with different materials (e.g., MoSiN/MoSiON or CrN/TiN) to achieve high optical density with reduced total thickness. The multilayer composite structure allows each layer to contribute differently to the overall light shielding performance, enabling OD≥3 with thickness significantly less than 60 nm.
Solution Approach 2:
The patent optimizes the thickness and material composition parameters of each layer in the light shielding film to achieve the desired optical density with minimal total thickness. By carefully selecting the thickness of each layer (e.g., 10-30 nm per layer) and the material composition ratios, the patent achieves OD≥3 while maintaining film thickness well below the conventional 60 nm minimum.
2Manufacturing precision
If the light shielding film thickness is reduced to overcome EMF effect, then manufacturing precision is improved, but optical density decreases below required level (OD<3)
Solution Approach 1:
The patent uses composite material structures where each layer is optimized for specific properties. The first layer (e.g., MoSiN) provides high light shielding capability while the second layer (e.g., MoSiON or CrN/TiN) provides adhesion and additional optical density. This composite approach enables achieving OD≥3 with total thickness of 20-50 nm, which is sufficient to minimize EMF effect while maintaining required optical density.
Solution Approach 2:
The patent systematically adjusts the thickness parameters of each layer to achieve the optimal balance between optical density and thickness. By varying the thickness of each layer within specific ranges (e.g., first layer: 10-30 nm, second layer: 10-20 nm) and optimizing material composition, the patent achieves both low thickness (to minimize EMF) and high optical density (OD≥3).
3Object-affected harmful factors
If conventional light shielding films are used in peripheral regions, then light leakage is suppressed, but device complexity increases due to additional light shielding band formation
Solution Approach 1:
The patent designs the light shielding film to serve multiple functions simultaneously. The same light shielding film structure used in the transfer pattern area also serves as the light shielding band in the peripheral region. The film's optical density (OD≥3) and thickness are optimized to provide both transfer pattern definition and peripheral light shielding, eliminating the need for separate light shielding band formation and reducing overall mask structure complexity.
Solution Approach 2:
The patent merges the light shielding function into the existing light shielding film structure rather than adding a separate light shielding band. The peripheral light shielding is achieved by extending or thickening the light shielding film in the peripheral regions, combining the transfer pattern definition function and peripheral light shielding function into a single integrated structure, thereby reducing device complexity.
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 configuration effectively reduces the EMF bias, simplifies transfer mask manufacturing, and maintains sufficient optical density to prevent light leakage, enabling precise and efficient transfer pattern formation in semiconductor devices.
Implementation Method 1
a light shielding film having a multilayer structure... with an optical density of 2.0 to 2.7 for exposure light
Implementation Method 2
a surface anti-reflection layer formed on a transparent substrate
Data Source
AI summary
A mask blank and transfer mask that overcomes problems caused by an electromagnetic field (EMF) effect when a DRAM half pitch (hp) is 32 nm or less specified in semiconductor device design specifications. The mask blank is used in manufacturing a transfer mask to which ArF exposure light is applied, and includes a light shielding film 10 having a multilayer structure. The multilayer structure includes a light shielding layer 11 and a surface anti-reflection layer 12 formed on a transparent substrate 1. An auxiliary light shielding film 20 is formed on the light shielding film 10. The light shielding film 10 has a thickness of 40 nm or less and an optical density of 2.0 or more to 2.7 or less for exposure light. The optical density is 2.8 or more for exposure light in the multilayer structure of the light shielding film 10 and the auxiliary light shielding film 20.