Titanium-Containing Hard Mask Films for Lithography Alignment
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Solution Overview
Problem
Conventional hard mask materials, such as amorphous carbon, have high extinction coefficients, making them non-transparent and challenging for overlay alignment in lithography processes, and they lack sufficient conformality and etch selectivity, especially with increasing underlayer thickness.
Innovation Solution
The use of titanium-containing hard mask films, deposited using chemical vapor deposition methods with precursors like tetrakis(dimethylamido)titanium and titanium isopropoxide, which form conformal, substantially amorphous films with reduced stress and improved etch selectivity, comprising titanium, silicon, oxygen, and carbon atoms, suitable for reactive ion etching processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If amorphous carbon is used as hard mask material, then high etch selectivity to organic materials and dielectric materials is achieved, but the material is non-transparent with high extinction coefficients, making overlay alignment difficult
Solution Approach 1:
The patent uses composite hard mask materials comprising carbon and titanium (e.g., Ti-doped carbon, TiC_xO_y, or Ti-Si-O-C compositions). The titanium component provides transparency to visible light for overlay alignment, while the carbon matrix maintains high etch selectivity to organic photoresist and dielectric materials. This composite approach resolves the contradiction by combining materials with complementary properties.
Solution Approach 2:
The patent modifies the composition parameters of the hard mask by incorporating titanium at controlled concentrations (e.g., 1-50 at% Ti). By adjusting the titanium content and stoichiometry (e.g., C:Ti ratios, oxygen content), the material achieves optimal balance between transparency and etch selectivity. The deposition conditions (temperature, pressure, precursor ratios) are also tuned to control the final material properties.
2Device complexity
If conventional hard mask materials are used, then etching process is simplified, but conformality and etch selectivity are insufficient, especially with increasing underlayer thickness
Solution Approach 1:
The patent employs atomic layer deposition (ALD) or chemical vapor deposition (CVD) processes with controlled temperature, pressure, and precursor flow parameters to achieve superior conformality. The deposition temperature (e.g., 200-400°C) and precursor ratios are optimized to ensure uniform film thickness on high aspect ratio structures. The titanium-containing precursors (e.g., TDMAT, titanium isopropoxide) react to form dense, conformal films that maintain etch selectivity.
Solution Approach 2:
The composite titanium-carbon-hard mask materials inherently provide better conformality on vertical sidewalls and high aspect ratio features compared to pure carbon. The titanium component forms a more stable, adherent film that conforms better to complex topographies, while maintaining the etch resistance needed for deep feature etching.
3Reliability
If amorphous carbon hard mask thickness is increased to match increasing underlayer thickness, then etch selectivity is maintained, but overlay alignment becomes more difficult due to increased non-transparency
Solution Approach 1:
The titanium-doped carbon hard mask provides inherent transparency to visible light even at thicknesses required for etching deep features through thick underlayers. The titanium component reduces the extinction coefficient compared to pure carbon, allowing overlay alignment to proceed effectively. This enables the hard mask to be thick enough for etch selectivity while remaining transparent enough for alignment.
Solution Approach 2:
By controlling the titanium concentration and material stoichiometry, the optical properties of the hard mask are tuned to achieve sufficient transparency. The C:Ti ratio and oxygen content are optimized so that the hard mask maintains appropriate optical transmission for overlay alignment while providing adequate thickness for etch selectivity against the underlayer.
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
These titanium-containing hard mask films provide enhanced conformality and etch selectivity, maintaining a thermal budget and offering improved etch resistance, with a 300% improvement in etch selectivity compared to standard carbon hard masks during RIE processes.
Implementation Method 1
exposing a substrate surface to a titanium-containing precursor in a processing chamber to form a titanium-containing hard mask
Data Source
AI summary
Methods for forming a titanium-containing hard mask film on a substrate surface by exposing the substrate surface to a titanium-containing precursor. The titanium-containing hard mask comprises one or more of silicon, oxygen or carbon atoms and, optionally, nitrogen atoms.