Metal-Compound Hard Mask for Lithographic Alignment
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Solution Overview
Problem
Titanium nitride (TiN) layers in lithographic stacks have high extinction coefficients, leading to weak optical signals for alignment, causing unreliable alignment in semiconductor manufacturing when too thick, and image distortion when too thin, affecting overlay alignment and pattern fidelity.
Innovation Solution
A lithographic material stack incorporating a metal-compound hard mask layer, such as titanium oxynitride, formed by oxidation of titanium nitride, which reduces the extinction coefficient, allowing for improved optical transparency and alignment without compromising etch selectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a TiN layer is made thick to provide sufficient etch selectivity, then etch selectivity is improved, but optical signal strength for alignment deteriorates
Solution Approach 1:
The patent employs a composite hard mask structure consisting of multiple layers including TiN, TiO2, and SiO2. This composite approach allows the system to leverage the high etch selectivity of TiN while using the optically transparent TiO2 and SiO2 layers to restore optical signal transmission for alignment, thereby resolving the contradiction between etch selectivity and optical signal strength.
Solution Approach 2:
The patent changes the optical parameters of the hard mask system by introducing materials with different extinction coefficients. The TiO2 and SiO2 layers have low extinction coefficients that compensate for the signal attenuation caused by thick TiN layers, effectively changing the overall optical transmission parameter of the hard mask stack to enable reliable alignment.
2Reliability
If a TiN layer is made thin to improve optical signal strength for alignment, then alignment reliability is improved, but image fidelity and pattern shape accuracy deteriorate
Solution Approach 1:
The multi-layer composite hard mask structure enables the system to achieve both goals simultaneously: the TiN layer provides the necessary etch selectivity protection for pattern fidelity, while the additional TiO2 and SiO2 layers ensure sufficient optical signal transmission for reliable alignment, thus resolving the contradiction between alignment reliability and pattern shape fidelity.
3Reliability
If TiN extinction coefficient is high to provide etch selectivity, then etch selectivity is improved, but alignment precision deteriorates
Solution Approach 1:
The TiO2 and SiO2 layers act as intermediary layers between the high-extinction TiN layer and the alignment marks below. These intermediary layers with low extinction coefficients allow optical signals to pass through to the alignment marks and reflect back, enabling precise alignment measurements while the TiN layer maintains its etch selectivity function.
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 metal-compound hard mask layer enhances transparency and overlay performance, enabling reliable alignment and pattern fidelity by reducing the extinction coefficient, thus improving lithographic processes over conventional TiN-based stacks.
Implementation Method 1
The metal-compound hard mask layer does not attenuate optical signals from lithographic alignment marks in underlying material layers
Implementation Method 2
A lithographic material stack incorporating a metal-compound hard mask layer, such as titanium oxynitride, formed by oxidation of titanium nitride
Data Source
AI summary
A lithographic material stack including a metal-compound hard mask layer is provided. The lithographic material stack includes a lower organic planarizing layer (OPL), a dielectric hard mask layer, and the metal-compound hard mask layer, an upper OPL, an optional anti-reflective coating (ARC) layer, and a photoresist layer. The metal-compound hard mask layer does not attenuate optical signals from lithographic alignment marks in underlying material layers, and can facilitate alignment between different levels in semiconductor manufacturing.