Graded Antireflective Coating for High-NA Lithography
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Solution Overview
Problem
Conventional single-layer antireflective coatings (BARCs) are inadequate in controlling reflectivity to less than 1% for all incident angles in lithographic applications with a numerical aperture exceeding 1.0, particularly in immersion and double patterning/immersion lithographies, where finely tuned wetability and minimal interaction with photoresist are critical for good lithographic performance.
Innovation Solution
A novel antireflective coating composition comprising a mixture of a first polymer with fluoroalcohol, aliphatic hydroxyl, and acidic moieties, and a second polymer derived from an aminoplast compound, along with a thermal acid generator, forming a graded coating with optimized refractive index and absorption for improved reflectivity control and developer compatibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional single-layer BARC is used, then the coating process is simple, but reflectivity control is inadequate (cannot achieve less than 1% for all incident angles in high NA applications)
Solution Approach 1:
The single-layer BARC is divided into two distinct polymer layers: a hydrophobic acidic top layer (first polymer) and a hydrophilic bottom layer (second polymer). This segmentation allows each layer to perform its specific function - the top layer provides reflectivity control and hydrophobicity, while the bottom layer ensures developer wetability, thereby achieving superior reflectivity control (<1%) that resolves the limitation of conventional single-layer BARCs.
Solution Approach 2:
The invention uses a composite material system consisting of two different polymers with complementary properties. The first polymer (hydrophobic acidic) and second polymer (hydrophilic) are combined in a single coating formulation, creating a graded composite structure that achieves both excellent reflectivity control and developer compatibility, resolving the trade-off between simplicity and performance.
2Manufacturing precision
If the BARC surface is made hydrophobic to match photoresist contact angle, then coating uniformity is improved, but developer wetability after exposure deteriorates (causes scumming and footing)
Solution Approach 1:
The BARC coating is designed with spatially varying properties: the top layer (first polymer) is hydrophobic to match photoresist contact angle and ensure coating uniformity, while the bottom layer (second polymer) is hydrophilic to ensure developer wetability after exposure. This local quality differentiation resolves the contradiction by providing the appropriate surface property at each location within the coating thickness.
Solution Approach 2:
The invention changes the chemical composition parameter along the coating thickness - from hydrophobic acidic groups at the top to hydrophilic groups at the bottom. This gradient in chemical parameters allows the coating to exhibit both hydrophobicity for coating uniformity and hydrophilicity for developer wetability, resolving the apparent contradiction between these two requirements.
3Strength
If the BARC interacts strongly with photoresist to improve adhesion, then bonding is improved, but lithographic performance deteriorates (causes scumming and footing)
Solution Approach 1:
The BARC acts as an intermediary layer between the substrate and photoresist. The first polymer layer provides appropriate surface energy and chemical properties that enable good photoresist adhesion without excessive interaction, while the second polymer layer ensures developer access. This intermediary structure resolves the contradiction by providing controlled, optimal interaction strength that satisfies both adhesion and lithographic performance requirements.
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 composition achieves optimal antireflective characteristics, minimizing scumming and footing, and ensuring good wetability with developers, thereby enhancing the resolution and depth of focus in photoresist imaging processes.
Implementation Method 1
The composition further comprises a thermal acid generator (TAG) whose function is to enhance crosslinking
Implementation Method 2
The two polymers crosslink during baking such that the coating is resistant to spin casting solvents of the photoresist coated over the novel coating
Implementation Method 3
Brodsky et al U.S. Pat. No. 7,588,879 B2 graded organic BARC's have been described that can be formed in one spin coating operation from a mixture of two polymers that phase separate from each other and have different optical properties
Implementation Method 4
Graded BARC's with tuned n and k values offer improved reflectivity control
Data Source
AI summary
The invention related to an antireflective coating comprising a mixture of a first polymer and a second polymer, and a thermal acid generator, where the first polymer comprises at least one fluoroalcohol moiety, at least one aliphatic hydroxyl moiety, and at least one acid moiety other than fluoroalcohol with a pKa in the range of about 8 to about 11; where the second polymer is a reaction product of an aminoplast compound with a compound comprising at least one hydroxyl and/or at least one acid group. The invention further relates to a process for using the novel composition to form an image.