Trench Formation Method Using Sulfur-Based Etching
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Solution Overview
Problem
Current methods for forming shallow trench isolation (STI) in microelectronic components face challenges such as the formation of cavities in the filler oxide, which can lead to short-circuits and reduced transistor efficiency, and the generation of phosphorus residues that degrade electrical performance, especially in silicon-germanium and SOI substrates.
Innovation Solution
A method involving successive anisotropic etchings to form and deepen trenches, with a fifth etching step that has equal selectivity between the hard mask layer and the substrate, avoiding the use of phosphorus-based chemistries, thereby enlarging the hard mask opening and deepening the trench without generating phosphorus residues, facilitating improved filling and reducing defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If phosphorus-based chemistries are used to enlarge the hard mask opening, then the opening is enlarged effectively, but phosphorus residues are generated that degrade electrical performance
Solution Approach 1:
The patent changes the chemical composition parameter of the etching chemistry from phosphorus-based to sulfur-based (using H2S or SF6 gases). This parameter change allows effective enlargement of the hard mask opening while eliminating the generation of harmful phosphorus residues, thereby degrading electrical performance. The sulfur-based chemistry achieves the same structural modification without the harmful byproduct.
2Productivity
If conventional etching methods are used to form trenches, then trenches are formed efficiently, but cavities are created in the filler oxide leading to short-circuits
Solution Approach 1:
The patent applies preliminary action by performing a specific etching step (the fifth etching) that creates an enlarged opening in the hard mask layer before trench filling. This preliminary enlargement prevents cavity formation during subsequent filler oxide deposition by ensuring proper material flow and consolidation, thereby eliminating short-circuits while maintaining efficient trench formation.
3Reliability
If LOCOS structures are used for isolation, then lateral electrical isolation is achieved, but bird's beak outgrowth consumes active area
Solution Approach 1:
The patent extracts and eliminates the problematic oxidation step that causes bird's beak outgrowth in LOCOS structures. By using direct physical vapor deposition or chemical vapor deposition to form the isolating material without thermal oxidation, the method achieves lateral electrical isolation while preserving the full active area, thereby increasing transistor surface density.
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 enhances the quality of STI formation by preventing cavity formation and eliminating phosphorus residues, improving the electrical performance and reproducibility of STIs, particularly in advanced technological nodes and SiGe-based architectures.
Implementation Method 1
Making at least a first opening and a second opening extending respectively through the first layer and the second layer. The first opening is made by a first, anisotropic, etching of the first layer, so as to expose at least part of the second layer. The second opening is made by a second anisotropic etching of the second layer
Implementation Method 2
Performing a fourth, isotropic, etching of the first layer so as to enlarge the first opening and obtain a first enlarged opening
Data Source
AI summary
A method is provided for forming at least one trench to be filled with an isolating material to form an isolating trench, in a substrate based on a semiconductor material, the method including at least the following successive steps: providing a stack including at least the substrate, a first hard mask layer, and a second hard mask layer; making at least a first opening and a second opening, by carrying out isotropic etchings; performing a third, anisotropic, etching of the substrate in line with the second opening, so as to obtain the at least one trench; performing a fourth, isotropic, etching of the first layer so as to enlarge the first opening and obtain a first enlarged opening; and performing a fifth, anisotropic, etching so as to simultaneously enlarge the second opening and increase a depth of the at least one trench.