Photoresist Top-Layer Crosslinking for EUV Pattern Stability
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Solution Overview
Problem
The challenge in semiconductor photolithography is creating images with minimum feature sizes below the resolution limit, where the glass transition temperature (Tg) of photoresist layers decreases from the bottom to the top, leading to roughness, increased acid diffusion, and pattern deformation during the patterning process, especially with EUV lithography.
Innovation Solution
A novel photoresist with an additive that cross-links to form a film on the top of the resist, increasing the Tg and preventing pattern deformation, using a cross-linking agent that separates during spin coating and forms a rectangular-shaped profile.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional photoresist is used for EUV lithography, then the patterning process can be performed, but the glass transition temperature decreases from bottom to top causing roughness, acid diffusion, and pattern deformation
Solution Approach 1:
The patent applies local quality by creating a photoresist composition with vertically differentiated properties through the additive. The additive concentrates at the top surface during spin coating and forms a cross-linked film only in the top portion, creating a gradient structure where the top has different properties (higher Tg, cross-linked) than the bottom (lower Tg, uncross-linked). This resolves the contradiction by providing local stability enhancement exactly where needed (at the top surface) without affecting the overall composition uniformity.
Solution Approach 2:
The patent changes the glass transition temperature parameter locally by introducing an additive that cross-links upon exposure to form a film. This cross-linking reaction increases the Tg of the top portion of the photoresist layer, counteracting the natural Tg gradient and preventing pattern deformation. The parameter change is spatially selective, affecting only the top portion where the additive concentrates.
2Length of moving object
If the photoresist layer is made thinner to achieve smaller features, then the resolution limit is approached, but the pattern deformation and roughness increase due to Tg gradient effects
Solution Approach 1:
By concentrating the additive at the top surface and forming a cross-linked film only in the top portion, the invention provides localized structural support and stability enhancement. This local quality improvement prevents pattern deformation and roughness even in thin photoresist layers, enabling smaller feature sizes without sacrificing manufacturing precision.
3Stability of the object's composition
If an additive is added to increase Tg and prevent deformation, then the photoresist composition becomes more complex, but the additive must separate and float during spin coating
Solution Approach 1:
The additive acts as an intermediary substance that mediates between the photoresist polymer matrix and the cross-linking reaction. It has specific properties (surface tension different from polymer, cross-linkable groups) that enable it to separate and float during spin coating, then cross-link upon exposure to form the stabilizing film. This intermediary approach achieves Tg enhancement without requiring fundamental changes to the photoresist system.
Solution Approach 2:
The patent creates a composite photoresist composition by combining the polymer matrix with a specific additive that has different properties. This composite structure enables the additive to separate and float during spin coating while providing the desired Tg enhancement and pattern stability benefits. The composite material approach resolves the complexity issue by using a well-defined additive-polymer system with predictable separation behavior.
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 solution ensures accurate pattern formation by preventing unwanted deformation and improving etch resistance, maintaining a rectangular-shaped profile and enhancing critical dimension control.
Implementation Method 1
The additive includes a cross-linkable group and undergoes a cross-linking reaction to form a film on a top portion of the photoresist layer
Implementation Method 2
The photoresist layer is exposed by using an extreme ultraviolet (EUV) radiation
Implementation Method 3
The photoresist layer is developed
Data Source
AI summary
A photoresist includes a solvent, a polymer and an additive. The polymer is dissolved in the solvent, and the additive is dispersed in the solvent. The additive includes a double bond or includes an epoxy group. The additive has a surface tension different from a surface tension of the polymer.