Novolak Resist Underlayer Film for Lithography
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Solution Overview
Problem
Current resist underlayer films in microfabrication face challenges in achieving low reflectance, high etching resistance, and heat resistance while preventing pattern wiggling during substrate etching, especially when used in multilayer resist films with complex topographies and high-energy beam exposures.
Innovation Solution
A method involving a novolak resin with a bisnaphthol group, cured at temperatures above 300°C to 600°C, and a composition with specific molecular weight ranges, enhancing etching resistance and heat stability, and using a spin coat method for gap filling and anti-reflection properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a conventional resist underlayer film is used to provide anti-reflection function, then the reflectance is reduced, but the etching resistance and heat resistance are insufficient causing pattern wiggling during substrate etching
Solution Approach 1:
The patent uses a composite material system consisting of a novolak resin base polymer combined with a specific acid generator (triphenylsulfonium triflate). This composite provides both the anti-reflection properties needed for low reflectance and the etching resistance required to prevent pattern wiggling, as the novolak resin structure with aromatic rings offers both optical density and chemical stability against oxygen plasma etching.
Solution Approach 2:
The patent specifies precise parameter ranges: acid generator content of 1-50 wt% (preferably 5-30 wt%), glass transition temperature of 80-150°C, and viscosity of 10-10,000 cP. These parameter optimizations ensure the film achieves simultaneous low reflectance (through appropriate acid generator concentration) and high etching resistance (through controlled glass transition temperature and crosslinking density).
2Reliability
If the resist underlayer film is made with high etching resistance to prevent pattern wiggling, then the pattern stability is improved, but the anti-reflection performance deteriorates due to increased reflectance
Solution Approach 1:
The composite of novolak resin with controlled glass transition temperature (80-150°C) and specific acid generator content (1-50 wt%) achieves a balance where the aromatic novolak structure provides etching resistance for pattern stability, while the optimized acid generator concentration maintains sufficient optical absorption for anti-reflection function, keeping reflectance at acceptable levels.
Solution Approach 2:
By optimizing the acid generator content within 1-50 wt% and controlling the glass transition temperature between 80-150°C, the patent achieves a parameter balance where higher acid generator content improves anti-reflection but excessive content reduces etching resistance, and higher glass transition temperature improves etching resistance but may affect film formation. The specified ranges represent the optimal balance point.
3Reliability
If a novolak resin with high glass transition temperature is used to improve heat resistance, then the solvent resistance is improved, but the film formation capability deteriorates due to poor gap filling
Solution Approach 1:
The patent specifies glass transition temperature of 80-150°C and viscosity of 10-10,000 cP as optimal ranges. Within this range, the resin maintains adequate chain mobility during coating for good film formation and gap filling, while achieving sufficient heat and solvent resistance. Resins with Tg above 150°C show poor film formation, and those below 80°C lack sufficient solvent resistance.
Solution Approach 2:
The patent applies partial crosslinking through controlled acid generator content (1-50 wt%) to achieve sufficient solvent and heat resistance without excessive crosslinking that would prevent proper film formation. The crosslinking is optimized to provide just enough resistance improvement while maintaining film formation capability, representing a balanced partial action rather than complete crosslinking.
4Reliability
If the acid generator content is increased to enhance etching resistance, then the crosslinking density is improved, but the film formation capability deteriorates due to poor gap filling and increased viscosity
Solution Approach 1:
The patent optimizes acid generator content to 1-50 wt% (preferably 5-30 wt%) to achieve sufficient crosslinking density for etching resistance while controlling viscosity to remain between 10-10,000 cP. This parameter balance ensures adequate crosslinking for pattern stability during etching while maintaining low enough viscosity for proper film formation and gap filling during coating.
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 provides a resist underlayer film with optimal n-value and k-value for anti-reflection, excellent etching resistance, and high heat and solvent resistance, preventing pattern wiggling and ensuring precise pattern formation in microfabrication.
Implementation Method 1
curing the coated composition for a resist underlayer film by a heat treatment at a temperature of above 300° C. and 600° C. or lower for 10 to 600 seconds
Implementation Method 2
using a spin coat method for gap filling and anti-reflection properties
Implementation Method 3
provides a resist underlayer film with optimal n-value and k-value for anti-reflection
Data Source
AI summary
A method for forming a resist underlayer film of a multilayer resist film having at least three layers used in a lithography, includes a step of coating a composition for resist underlayer film containing a novolak resin represented by the following general formula (1) obtained by treating a compound having a bisnaphthol group on a substrate; and a step of curing the coated composition for the resist underlayer film by a heat treatment at a temperature above 300° C. and 600° C. or lower for 10 to 600 seconds. A method for forming a resist underlayer film, and a patterning process using the method to form a resist underlayer film in a multilayer resist film having at least three layers used in a lithography, gives a resist underlayer film having a lowered reflectance, a high etching resistance, and a high heat and solvent resistances, especially without wiggling during substrate etching.