Silicon Germanium Hard Mask for Cryogenic Deep Silicon Etching
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Solution Overview
Problem
Conventional etch masks for high aspect ratio structures in semiconductor devices face challenges such as cracking, low selectivity, and contamination, particularly in cryogenic deep reactive ion etching processes, which affect the surface finish and uniformity of silicon structures.
Innovation Solution
A silicon germanium etch mask is deposited and patterned on a semiconductor material, allowing for high aspect ratio feature transfer using reactive ion etching with an SF6/O2 plasma, offering improved selectivity and resistance to cracking, and can be easily removed without damaging the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thick masks are used to achieve high aspect ratio structures, then etch selectivity is improved, but mask uniformity and resolution deteriorate
Solution Approach 1:
The patent changes the material composition parameter of the mask from conventional materials (silicon oxide, silicon nitride, photoresist) to silicon germanium alloy, achieving over 100:1 etch selectivity while maintaining thin film uniformity and high resolution patterning capability
Solution Approach 2:
The patent uses silicon germanium composite material that combines the advantages of high etch selectivity with mechanical stability and pattern fidelity, resolving the contradiction between thick mask requirements for selectivity and thin mask requirements for uniformity
2Ease of manufacture
If photoresist masks are used for high aspect ratio etching, then ease of patterning is improved, but etch selectivity and resistance to cracking deteriorate
Solution Approach 1:
The patent replaces organic photoresist with inorganic silicon germanium material that maintains patterning capability while providing superior etch selectivity and crack resistance for high aspect ratio structures
Solution Approach 2:
The silicon germanium mask can be easily removed after etching using standard HF-based processes, replacing the need for complex mask stripping procedures while maintaining process reliability
3Reliability
If alumina masks are used for high aspect ratio etching, then etch selectivity is improved, but deposition complexity and mask removal difficulty worsen
Solution Approach 1:
The patent changes the mask material from alumina to silicon germanium, which can be deposited using standard CVD processes at lower temperatures and removed using conventional HF-based etchants, reducing overall process complexity
Solution Approach 2:
Silicon germanium serves as an intermediary material that provides high etch selectivity while being compatible with standard semiconductor processing equipment and chemicals, eliminating the need for specialized deposition and removal procedures
4Reliability
If metal masks are used for high aspect ratio etching, then etch selectivity is improved, but chamber contamination and electrical field effects worsen
Solution Approach 1:
The patent uses silicon germanium as a disposable-like mask material that can be easily removed after etching, preventing metal re-deposition and contamination issues while maintaining high selectivity during the etch process
Solution Approach 2:
Silicon germanium acts as a non-conductive intermediary between the photoresist pattern and the silicon substrate, eliminating electrical field effects and metal contamination while providing the necessary etch protection
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 silicon germanium mask system provides high etch selectivity, reduces chamber contamination, and maintains high mask resolution, enabling the formation of high aspect ratio structures with improved uniformity and resistance to cracking, while being compatible with CMOS backend processes.
Implementation Method 1
depositing a silicon germanium etch mask on a semiconductor material
Implementation Method 2
transferring the plurality of features in the silicon germanium hard mask to the semiconductor material using reactive ion etching with an SF6/O2 plasma
Data Source
AI summary
Polycrystalline silicon germanium (SiGe) can offer excellent etch selectivity to silicon during cryogenic deep reactive ion etching in an SF6/O2 plasma. Etch selectivity of over 800:1 (Si:SiGe) may be achieved at etch temperatures from −80 degrees Celsius to −140 degrees Celsius. High aspect ratio structures with high resolution may be patterned into Si substrates using SiGe as a hard mask layer for construction of microelectromechanical systems (MEMS) devices and semiconductor devices.