Polymer Residues Enhance Etching Selectivity in Hard Mask Layers
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Solution Overview
Problem
Conventional integrated circuit fabrication methods using copper interconnects often result in voids due to undercutting of dielectric layers during etching, leading to reduced device yield and reliability of electrical interconnects.
Innovation Solution
A method involving a hard mask layer with a higher dielectric constant than the first dielectric layer, combined with a fluorine-based dry etching technique using specific gas ratios and an antireflective coating, to selectively etch and form electrical interconnect structures, preventing undercutting and enhancing etching selectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an ashing process is used to remove the photoresist layer, then the photoresist is effectively removed, but the sidewalls of the low-k ILD layer are converted to silicon dioxide and undercut by DHF, causing void formation
Solution Approach 1:
A polymer residue layer is intentionally retained on the ILD layer sidewalls to act as a protective intermediary barrier during the ashing and DHF cleaning processes. This polymer residue prevents the DHF from attacking and undercutting the ILD sidewalls, while still allowing the photoresist to be removed via ashing. The polymer residue serves as a sacrificial protective layer that maintains sidewall integrity throughout the fabrication process.
2Manufacturing precision
If a multi-layered mask structure with OPL layer is used, then selective etching can be performed, but the OPL layer requires ashing removal that causes ILD sidewall conversion and undercutting
Solution Approach 1:
The polymer residue layer serves as an intermediary protective barrier between the ILD layer and the DHF cleaning solution. After the OPL layer is ashed away, the remaining polymer residue on the ILD sidewalls prevents DHF from causing undercutting, thus maintaining via structure integrity while still enabling the selective etching process to proceed.
3Ease of manufacture
If DHF cleaning is performed after ashing, then organic residues are removed, but the DHF etches the converted silicon dioxide sidewalls, causing recession and voids
Solution Approach 1:
The polymer residue layer acts as a protective intermediary that shields the ILD sidewalls from DHF attack during the cleaning process. The DHF can effectively remove organic residues from surfaces it contacts, but the polymer residue barrier prevents it from reaching and etching the ILD sidewalls, thereby maintaining precise sidewall dimensions without recession or void formation.
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 reduces the formation of voids and improves the reliability of electrical interconnects by maintaining the integrity of the dielectric layers and achieving precise etching, thereby enhancing the yield and performance of integrated circuit devices.
Implementation Method 1
a fluorine-based dry etching technique using specific gas ratios
Implementation Method 2
polymer residues are accumulated directly on the upper surface of the hard mask layer
Implementation Method 3
a step to strip the patterned photoresist layer from the hard mask layer using an ashing process
Implementation Method 4
a cleaning process using a diluted hydrofluoric acid (DHF) solution may cause an undercutting (i.e., recession) of the sidewalls of the ILD layer 12 relative to the hard mask layer 14 because DHF operates as an etchant to silicon dioxide
Data Source
AI summary
Methods of forming electrical interconnect structures include forming a dielectric layer on a semiconductor substrate and forming a hard mask layer on the dielectric layer. A photoresist layer is patterned on an upper surface of the hard mask layer. This patterned photoresist layer is used as an etching mask during a step to selectively etch the hard mask layer and define an opening therein. This opening exposes the first dielectric layer. The patterned photoresist layer is then stripped from the hard mask layer using an ashing process that exposes the upper surface of the hard mask layer. Following this ashing process, a portion of the first dielectric layer extending opposite the opening is selectively etched using the hard mask layer as an etching mask. During this selective etching step, polymer residues are accumulated directly on the upper surface of the hard mask layer. These polymer residues may operate to increase a degree of selectively and inhibit recession of the hard mask layer during the step of selectively etching the first dielectric layer.