De-Crosslinkable Photoresist Patterning to Prevent Pattern Collapse
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Solution Overview
Problem
The scaling down of semiconductor integrated circuits (ICs) leads to increased complexity and defects due to pattern collapse during the photolithography process, caused by high aspect ratios of resist features and enhanced capillary forces, which affect the quality of the resist pattern and yield of ICs.
Innovation Solution
The use of photoresists capable of crosslinking and de-crosslinking to enhance mechanical strength and solvent resistance, reducing defects by increasing the resist pattern's quality through a method involving a polymer with reactive groups, a photoacid generator, and a crosslinker that can react under thermal or radiation conditions to form a crosslinked polymer, which can then be de-crosslinked under acidic conditions for easy removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If photoresist features are scaled down to achieve smaller geometry sizes, then production efficiency increases and costs decrease, but pattern collapse occurs due to high aspect ratios and enhanced capillary forces
Solution Approach 1:
The patent uses a composite photoresist system comprising a polymer matrix with embedded crosslinkable functional groups and a crosslinking agent. This composite structure provides both the mechanical strength needed to prevent pattern collapse and the chemical reactivity required for subsequent de-crosslinking and removal, resolving the contradiction between maintaining pattern integrity during processing and enabling eventual removal.
Solution Approach 2:
The patent changes the chemical state of the photoresist through controlled crosslinking and de-crosslinking reactions. By adjusting parameters such as crosslinking density, functional group selection, and reaction conditions, the photoresist transitions from a removable state to a structurally robust state during patterning, then back to a removable state for cleanup, thereby maintaining pattern quality while enabling removal.
2Strength
If crosslinking is performed to enhance mechanical strength and solvent resistance, then resist pattern quality improves, but the photoresist becomes difficult to remove
Solution Approach 1:
The patent introduces dynamic reversibility to the crosslinked structure by incorporating functional groups that can undergo de-crosslinking reactions under specific conditions (acidic environment, heat, or chemical treatment). This transforms the static crosslinked network into a dynamic system that can switch between crosslinked (strong) and de-crosslinked (removable) states, resolving the contradiction between strength and removability.
Solution Approach 2:
The patent utilizes changes in chemical parameters (pH, temperature, chemical environment) to control the crosslinking state. The photoresist is crosslinked under neutral or basic conditions to gain strength, then de-crosslinked under acidic conditions or with specific chemicals for removal, allowing the same material to exhibit both strong and removable properties at different stages of the process.
3Stability of the object's composition
If crosslinking density is increased to improve solvent resistance, then pattern stability during processing improves, but defect formation increases due to stress and cracking
Solution Approach 1:
The patent applies crosslinking locally rather than uniformly throughout the entire photoresist structure. By controlling the distribution and density of crosslinkable functional groups, the photoresist achieves sufficient solvent resistance in critical areas while maintaining flexibility and stress relief in other regions, preventing defect formation while maintaining pattern stability.
Solution Approach 2:
The patent introduces flexible spacer groups and flexible linkers as intermediaries between the crosslinked regions. These intermediary elements act as stress buffers that prevent crack propagation and reduce internal stresses, allowing high crosslinking density for solvent resistance without the harmful effects of excessive stress and cracking.
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 improves the quality of the resist pattern, reduces defects, and enhances the yield and reliability of semiconductor devices by maintaining mechanical strength and solvent resistance during the patterning process.
Implementation Method 1
exposing the photoresist layer to a radiation, during which an acid produced from exposure of the photoacid generator de-crosslinks the crosslinked polymer
Implementation Method 2
a crosslinker that can react under thermal or radiation conditions to form a crosslinked polymer
Data Source
AI summary
A method for forming a semiconductor structure is provided. The method includes forming a photoresist layer over a substrate. The photoresist layer includes a polymer, a photoacid initiator and a crosslinker containing at least two crosslinking sites. The photoresist layer is then cured to crosslink the polymer, thereby forming a crosslinked polymer. Next, the photoresist layer is exposed to a radiation. An acid produced from exposure of the photoacid generator de-crosslinks the crosslinked polymer in exposed portions of the photoresist layer. The exposed portions of the photoresist layer are subsequently removed to form a patterned photoresist layer.