Reflective Photomask Shading Structure for Out-of-Band Light Suppression
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Solution Overview
Problem
Conventional reflective photomasks for EUV lithography fail to adequately suppress the reflection of out-of-band light, leading to increased exposure and reduced accuracy in circuit pattern formation, particularly in the boundary regions between adjacent chips on a wafer.
Innovation Solution
A reflective photomask design featuring a multilayer reflection film, an absorption film with a circuit pattern, and a shading region with projections having a pitch of 3000 nm or less, forming a hole pattern with inverted pyramidal recesses to minimize the reflection of out-of-band light on the front surface of the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the light absorption film is made thinner to reduce shadow effects, then the projection effect is minimized, but the light attenuation becomes insufficient causing increased EUV light reflection and degraded pattern accuracy
Solution Approach 1:
The mask structure is segmented into multiple functional layers: a light absorption film for EUV attenuation, a multilayer reflection film for controlled reflection, and a shading region with groove structure for shadow minimization. This segmentation allows each layer to optimize its specific function without compromising overall performance.
Solution Approach 2:
The mask employs composite material structures including alternating Mo/Si layers in the reflection film and Ta-based materials in the absorption film. These composite structures provide synergistic effects where the Mo/Si multilayer enhances EUV reflection while the Ta absorption film provides selective wavelength attenuation, solving the contradiction between light attenuation and reflection control.
2Object-generated harmful factors
If projections are added to suppress out-of-band light reflection, then multiple exposures are minimized, but the device complexity increases
Solution Approach 1:
The projection structure is merged with the groove structure in the shading region, combining two functional elements into a unified geometric feature. The projections extend from the groove walls or base, integrating the out-of-band light suppression function with the existing EUV shading region without requiring separate components.
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 effectively reduces the reflection of out-of-band light, minimizing multiple exposures and enhancing the accuracy and throughput of circuit pattern transfer onto the wafer, while maintaining the necessary EUV light reflection properties.
Implementation Method 1
a multilayer reflection film that includes a molybdenum (Mo) layer and a silicon (Si) layer, which are alternately laminated on a glass substrate, and forming a light absorption film having tantalum (Ta) as a main component on the multilayer reflection film
Implementation Method 2
forming a light absorption film having tantalum (Ta) as a main component on the multilayer reflection film
Implementation Method 3
a plurality of projections formed at a pitch of 3000 nm or less on part of a surface of the substrate exposed in the shading region, for suppressing reflection of out-of-band light with a wavelength of 140 nm to 800 nm
Data Source
Figure 1(a)~1(b)
Figure 2(a)~2(b)
Figure 3(a)~3(b)
AI summary
A reflective photomask (10) includes: a substrate (11); a multilayer reflection film (12) formed on the substrate and reflecting exposure light including light with a wavelength of 5 nm to 15 nm for lithography; an absorption film (14) formed on the multilayer reflection film (12) and absorbing the exposure light, and formed therein with a circuit pattern (15) or a circuit pattern forming region where the circuit pattern is formed; a shading region (B) formed by removing part of the multilayer reflection film (12) and the absorption film (14) on the substrate (11), on an outer peripheral side of the circuit pattern (15) or the circuit pattern forming region to shade part of the exposure light reflected by the multilayer reflection film (12); and a plurality of projections (1) formed at a pitch of 3000 nm or less on part of a surface (1b) of the substrate exposed in the shading region (B), and suppressing reflection of out-of-band light with a wavelength of 140 nm to 800 nm included in the exposure light and incident on the shading region (B).