Amorphous Silicon Hardmask Surface Termination for EUV Lithography
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Solution Overview
Problem
In extreme ultraviolet (EUV) lithography, the challenge lies in achieving high-resolution patterning with ultrathin inorganic hardmasks, as existing materials suffer from poor resist adhesion, pattern collapse, and limited etch selectivity, particularly for sub-40 nm feature sizes, due to the strong absorption of EUV light by most materials.
Innovation Solution
The use of amorphous silicon (α-Si) or low temperature oxide (LTO) as an ultrathin inorganic hardmask, treated with dilute hydrofluoric acid to terminate the semiconductor surface with silicon-hydrogen (Si—H) bonds, enabling improved resist thickness budget, higher etch selectivity, lower line width roughness, and enhanced defect elimination through negative tone development (NTD) methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional photoresist materials are used on amorphous silicon surfaces for EUV lithography, then the patterning process can be performed, but the resist adhesion is poor leading to pattern collapse
Solution Approach 1:
The amorphous silicon surface is treated with dilute hydrofluoric acid before resist coating to terminate surface silicon atoms with hydrogen, creating a non-polar surface that prevents resist dissolution and improves adhesion. This preliminary surface modification ensures reliable patterning without pattern collapse.
2Adaptability or versatility
If polar surface functionalities are present on the semiconductor surface, then the surface can be reactive, but the resist adhesion deteriorates leading to pattern collapse
Solution Approach 1:
The polar surface functionality, which initially causes resist dissolution and poor adhesion, is converted into a beneficial non-polar silicon-hydrogen terminated surface. This transformation eliminates the harmful dissolving effect while maintaining surface stability, thereby improving resist adhesion and preventing pattern collapse.
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 approach significantly improves patterning performance by converting polar surface functionalities to non-polar Si—H bonds, enhancing adhesion and etch selectivity, thereby achieving better pattern fidelity and wet strippability for EUV lithography.
Implementation Method 1
treating a semiconductor surface, e.g., amorphous silicon (α-Si), to terminate the semiconductor surface with silicon-hydrogen (Si—H) bonds
Implementation Method 2
a diluted hydrofluoric acid (dHF) may be applied to the semiconductor surface prior to forming the photoresist layer
Implementation Method 3
EUV light is strongly absorbed by almost all materials
Implementation Method 4
photolithography (in contrast to e-beam lithography, for example) uses light to form an image of the mask on a photoresist material, where the incident light can cause a photo reaction
Implementation Method 5
the extreme ultraviolet light (which also may be referred to as soft x-ray) has wavelengths from 124 nm down to 10 nm, and in particular for intended semiconductor processing, about 13.5 nm, as generated by a laser-pulsed tin (Sn) plasma source
Implementation Method 6
a laser-pulsed tin (Sn) plasma source
Implementation Method 7
negative resists in which the exposed area is made insoluble to the developer
Data Source
AI summary
A patterning method that includes providing an amorphous semiconductor surface to be patterned, and terminating the amorphous semiconductor surface by forming silicon-hydrogen (Si—H) on the surface to be patterned. A photoresist is formed on the surface to be patterned. The photoresist is then lithographically patterned using an extreme ultra violet (EUV) method. A photoresist is then developed on the surface to be patterned using negative tone development (NTD).