Variable-Hardness ACL Mask for High-Aspect-Ratio Profile Control
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Solution Overview
Problem
Existing etch masks used in microelectronic device formation suffer from profile distortion, particularly at high aspect ratios, due to the uniform hardness of the masks, which leads to issues like twisting and inconsistent feature transfer.
Innovation Solution
The development of a variable hardness amorphous carbon (ACL) mask, comprising a soft ACL portion with a lower hardness and a hard ACL portion with a higher hardness, allows for improved profile control and throughput while maintaining high etch selectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a uniform hardness ACL mask is used, then the mask structure is simple and easy to manufacture, but profile distortion and twisting occur during etching, especially at high aspect ratios
Solution Approach 1:
The ACL mask is divided into multiple layers with different hardness characteristics. A soft ACL layer (lower hardness) is deposited first, followed by a hard ACL layer (higher hardness). This segmentation allows each layer to perform its specific function: the soft layer provides good profile control during etching, while the hard layer offers sufficient etch resistance, thereby resolving the contradiction between profile control and structural simplicity.
Solution Approach 2:
Different regions of the ACL mask are given different hardness properties to optimize performance. The lower ACL layer has softer characteristics that facilitate profile control, while the upper ACL layer has harder characteristics that provide etch resistance. This local differentiation of material properties enables the mask to simultaneously achieve good profile control and maintain structural integrity during high aspect ratio etching.
2Reliability
If the ACL mask thickness is increased to reduce twisting, then etch resistance improves, but the etching time increases and throughput decreases
Solution Approach 1:
The ACL mask is segmented into layers with different thicknesses and hardness values. The soft ACL layer can be thinner because it provides good profile control, while the hard ACL layer provides the necessary etch resistance. This segmentation allows the total mask thickness to be optimized, providing sufficient etch resistance without requiring excessive thickness that would slow down the etching process and reduce throughput.
Solution Approach 2:
The hardness parameter of the ACL mask is changed by creating a layered structure with different hardness values. The hard ACL layer (higher hardness) provides enhanced etch resistance, allowing the mask to be thinner overall while maintaining sufficient protection during etching. This parameter change enables faster etching speeds and improved throughput without sacrificing etch resistance.
3Reliability
If a hard ACL mask is used to improve etch resistance, then etch selectivity improves, but profile distortion and twisting increase
Solution Approach 1:
The ACL mask is segmented into a soft lower layer and a hard upper layer. The soft ACL layer (lower hardness) is positioned to provide profile control during etching, while the hard ACL layer (higher hardness) provides etch resistance and selectivity. This segmentation allows the mask to simultaneously achieve good profile control and high etch selectivity by assigning different functions to different layers.
Solution Approach 2:
Different regions of the ACL mask have different hardness qualities optimized for specific functions. The lower ACL layer has softer characteristics that prevent profile distortion and twisting, while the upper ACL layer has harder characteristics that provide high etch selectivity. This local quality differentiation resolves the contradiction between etch selectivity and profile control.
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
The use of a multilayer ACL mask with varying hardness profiles effectively reduces profile distortion and enhances etching performance, allowing for more accurate feature transfer at high aspect ratios without the need for increased mask thickness.
Implementation Method 1
depositing a soft ACL layer of a multilayer ACL stack on an underlying layer and depositing a hard ACL layer of the multilayer ACL stack over the soft ACL layer
Implementation Method 2
forming an ACL mask by etching through both the soft ACL portion and the hard ACL portion of the ACL to expose the underlying layer using the patterned layer as an etch mask
Data Source
AI summary
A method of fabricating an amorphous carbon layer (ACL) mask includes forming an ACL on an underlying layer. The ACL includes a soft ACL portion that has a first hardness and a hard ACL portion that has a second hardness. The soft ACL portion underlies the hard ACL portion. The second hardness is greater than the first hardness. The method further includes forming a patterned layer over the ACL and forming an ACL mask by etching through both the soft ACL portion and the hard ACL portion of the ACL to expose the underlying layer using the patterned layer as an etch mask. Forming the ACL may include depositing one or both of the soft ACL portion and the hard ACL portion. Processing conditions may also be varied while forming the ACL to create a hardness gradient that transitions from softer to harder.