EUV Reflective Mask Light Shielding Layer
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Solution Overview
Problem
EUV lithography masks face challenges in minimizing exposure of resists to reflected light from outside the mask pattern region, particularly due to the sensitivity of resists to DUV-Vis light and the inability of absorber layers to effectively suppress reflection across the EUV and DUV-Vis wavelength ranges.
Innovation Solution
A reflective mask design is implemented with a light shielding layer containing chromium and oxygen, or chromium, oxygen, and nitrogen, which is strategically placed outside the mask pattern region to suppress reflections within the EUV and DUV-Vis wavelength ranges, ensuring low reflectivity (<30% for DUV-Vis and <0.5% for EUV) and enhancing the accuracy of pattern transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a thin absorber layer is used to reduce shadow effects in EUV lithography, then the form accuracy and dimension accuracy of mask patterns improve, but the absorber layer cannot completely absorb incident EUV light, resulting in reflected light that exposes the resist
Solution Approach 1:
The mask structure is segmented into multiple functional layers: a reflective layer (Mo/Si multilayer) for EUV reflection, a thin absorber layer (Ta, 20-40nm) for phase shift and partial absorption, and an additional absorber layer (Cr, 5-20nm) specifically added to suppress reflected light from reaching the resist. This segmentation allows each layer to perform its specialized function, resolving the contradiction between thin absorber layer benefits and reflected light suppression needs.
Solution Approach 2:
The mask employs composite material structures: Mo/Si multilayer for high EUV reflectivity, Ta for phase shift absorption, and Cr for additional light absorption. The combination of these materials with different optical properties creates a composite system that achieves both thin absorber layer advantages and effective reflected light suppression, preventing resist exposure while maintaining pattern accuracy.
2Manufacturing precision
If the absorber layer thickness is reduced to enable pattern miniaturization, then the resolution and detail of mask patterns improve, but the contrast between patterned and non-patterned regions deteriorates due to insufficient light absorption
Solution Approach 1:
The mask design applies local quality by creating spatial variation in absorber layer distribution: in patterned regions, the absorber layer is present with optimized thickness (20-40nm Ta) to provide phase shift and absorption; in non-patterned regions, an additional Cr absorber layer (5-20nm) is present to suppress reflected light. This local differentiation maintains high pattern contrast while enabling miniaturization through the thin absorber layer design.
Solution Approach 2:
The invention changes the optical parameters of the mask structure by introducing a Cr absorber layer with specific thickness (5-20nm) and composition. This parameter change adjusts the overall absorption characteristics of the mask, enabling the use of thinner Ta absorber layers (20-40nm) for phase shift while compensating for reduced absorption contrast through the Cr layer, thus maintaining pattern contrast at reduced dimensions.
3Reliability
If a conventional photolithography method with visible or ultraviolet light is used, then the process is well-established and reliable, but the resolution limit is about 1/2 of the exposure wavelength, preventing further miniaturization below 45 nm
Solution Approach 1:
The invention changes the fundamental parameter of exposure wavelength from visible/UV (193nm for ArF) to EUV (13.5nm), a 14-fold reduction. This parameter change enables resolution well below the conventional 45nm limit. The accompanying structural changes (catoptric system with Mo/Si reflective layer, thin absorber layer for phase shift) are optimized for this new wavelength regime, maintaining process reliability while achieving superior resolution.
Solution Approach 2:
The invention substitutes the conventional dioptric photolithography system with a catoptric system using EUV light and a Mo/Si reflective layer. This substitution replaces the traditional lens-based UV system with a reflective optics approach optimized for EUV wavelengths, enabling the shorter wavelength to be effectively utilized for high-resolution patterning while maintaining system stability and reliability.
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 design effectively reduces unnecessary exposure of resists to reflected light, allowing for thinner absorber layers and improved pattern miniaturization with enhanced form and dimension accuracy in EUV lithography.
Implementation Method 1
a light shielding layer for suppressing reflection of EUV light and DUV-Vis light having a wavelength of from 190 to 500 nm
Implementation Method 2
a reflective layer for reflecting EUV light
Implementation Method 3
an absorber layer for absorbing EUV light
Data Source
AI summary
A reflective mask for an extreme ultra violet (EUV) lithography obtained by forming a mask pattern in an absorber layer of an reflective mask blank is useful in semiconductor production. The EUV reflective mask has two regions of a mask pattern region and a region outside the mask pattern region. The mask pattern region has the absorber layer and a non-absorber layer on the reflective layer of an substrate, wherein the region outside the mask pattern region has an EUV reflective layer, an EUV absorber layer, and a light shielding layer for suppressing reflection of EUV light and DUV-Vis light having a wavelength of from 190 to 500 nm. The EUV reflective mask reduces unnecessary exposure of resist formed on a substrate to reflected light from the region outside the mask pattern region and reduces a pattern size to produce an accurate transfer pattern.