Fluorine Oxidation Between Etches for Source/Drain Recess Control
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Solution Overview
Problem
The existing methods for forming recesses in the middle end of line (MEOL) region of electronic devices, such as processor or memory devices, often result in excessive etching of source/drain contacts, leading to reduced electrical resistance and damage to silicide layers due to the formation of hydrofluoric acid during the etching process, which affects the performance and reliability of the channel.
Innovation Solution
The method involves oxidizing fluorine after dry etching and before cleaning to reduce the formation of hydrofluoric acid, and using multiple wet etch processes with intervening oxidation steps to control the depth-to-width ratio of the recess, ensuring it remains between 1.0 and 1.4, thereby minimizing damage to silicide layers and maintaining optimal electrical resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dry etching and wet etching are performed to form recesses in the MEOL region, then the source/drain contacts are etched to reduce electrical resistance, but excessive etching occurs leading to damage of silicide layers
Solution Approach 1:
An oxidation step is performed before the wet etching process to convert residual fluorine into oxygen fluorides. This preliminary action prevents the formation of hydrofluoric acid during subsequent wet etching, thereby protecting silicide layers from damage while maintaining precise control over recess dimensions
Solution Approach 2:
Oxidation is introduced as an intermediary process between dry etching and wet etching. This intermediary step converts harmful fluorine residues into volatile oxygen fluorides that can be removed, preventing unwanted chemical reactions during wet etching and enabling better control of etching depth and width
2Manufacturing precision
If multiple wet etch processes are used to control recess dimensions, then manufacturing precision is improved, but process complexity increases
Solution Approach 1:
The harmful fluorine residues are extracted from the system through an oxidation step that converts them into volatile oxygen fluorides. This extraction eliminates the need for multiple complex wet etching processes, as the fluorine removal is achieved in a single oxidation step followed by a simplified wet etching process
Solution Approach 2:
The chemical state of fluorine is changed from a harmful residue to a volatile oxygen fluoride through oxidation. This parameter change (chemical transformation) enables effective fluorine removal and simplifies the subsequent wet etching process, reducing the number of steps needed while maintaining precision
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 effectively reduces unexpected wet etching, maintains the integrity of silicide layers, and improves the performance of the channel by ensuring the gate turns on as expected and operates within safe voltage limits, while also allowing for precise control over the recess dimensions.
Implementation Method 1
performing an oxidation process to remove the fluorine residue from the recess after the dry etching process
Data Source
AI summary
In some implementations, fluorine is oxidized after dry etching an oxide layer above a source/drain contact and before cleaning. Accordingly, less hydrofluoric acid is formed during cleaning, which reduces unexpected wet etching of the source/drain contact. This allows for forming a recess in the source/drain contact with a depth to width ratio in a range from approximately 1.0 to approximately 1.4 and prevents damage to a layer of silicide below the source/drain that can be caused by excessive hydrofluoric acid. Additionally, or alternatively, the recess is formed using multiple wet etch processes, and any residual fluorine is oxidized between the wet etch processes. Accordingly, each wet etching process may be shorter and less corrosive, which allows for greater control over dimensions of the recess. Additionally, less hydrofluoric acid may be formed during cleaning processes between the wet etch processes, which reduces the etching of the source/drain contact between processes.