Cut Epitaxial Source/Drain Structure for Fin Spacing Control
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Solution Overview
Problem
As semiconductor devices scale down, epitaxially growing source/drain (S/D) features becomes increasingly challenging due to merging defects, where large EPIs are prone to accidental contact and cause short circuit defects, hindering device integration and yield.
Innovation Solution
The implementation of a cut EPI process after epitaxial growth but before depositing a contact etch stop layer, which involves an anisotropic etching process to separate merged S/D EPIs and increase spacing between them, thereby preventing merging defects and improving device integration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If large epitaxial source/drain features are grown to reduce contact resistance, then S/D contact resistance decreases, but spacing requirements increase and device integration is reduced
Solution Approach 1:
The patent applies segmentation by dividing the epitaxial growth process into two distinct stages: a first epitaxial growth stage that forms initial S/D features, and a second epitaxial growth stage that forms additional S/D features. This segmentation allows independent optimization of each growth stage - the first stage can grow features with sufficient spacing to avoid merging, while the second stage adds more material to reduce contact resistance. The isolated S/D features formed by this segmented approach prevent merging defects while achieving low contact resistance.
Solution Approach 2:
The patent employs preliminary action by performing the first epitaxial growth stage before the second stage, establishing a foundation of properly spaced S/D features that prevent merging. This preliminary structure with adequate spacing is created before additional epitaxial material is grown to further reduce contact resistance. The preliminary action of forming spaced features first allows subsequent growth without risking merging defects.
2Reliability
If spacing among S/D features is increased to prevent merging, then merging defects are prevented, but device integration is reduced
Solution Approach 1:
The patent resolves this contradiction through segmentation of the epitaxial growth into two stages. The first stage grows S/D features with sufficient spacing to prevent merging, while the second stage adds more epitaxial material to the same features. This segmented approach allows the structure to have both the spacing needed to prevent merging and the total volume needed for low contact resistance, achieving both reliability and integration goals.
Solution Approach 2:
The patent applies parameter changes by varying the epitaxial growth conditions between two stages. The first growth stage uses parameters that produce moderate feature sizes with adequate spacing. The second growth stage uses different parameters (such as extended growth time or adjusted temperature) to add more material volume. This parameter variation allows the S/D features to achieve both sufficient spacing for defect prevention and adequate volume for low contact resistance.
3Productivity
If device scaling is continued to increase functional density, then production efficiency increases, but epitaxial growth control becomes more difficult
Solution Approach 1:
The patent addresses scaling challenges by segmenting the epitaxial growth into two controlled stages. Rather than attempting to grow large volumes in a single stage (which becomes difficult at scaled dimensions), the process divides growth into manageable steps. The first stage establishes properly spaced features, and the second stage adds volume. This segmentation makes the overall process more controllable and reproducible at scaled device dimensions, enabling continued productivity improvement.
Solution Approach 2:
The patent uses preliminary action to simplify scaled epitaxial growth control. The first growth stage preliminarily forms S/D features with appropriate spacing and dimensions for the scaled geometry. This preliminary structure provides a controlled foundation that makes the subsequent second growth stage more predictable and easier to control. By breaking the total growth into preliminary and final stages, the complexity of controlling epitaxial growth at scaled dimensions is reduced.
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 cut EPI process enhances device yield by preventing merging defects, allows for more densely packed fins, and improves S/D contact formation and long-term reliability by creating an asymmetric S/D feature profile with near-vertical surfaces for deeper contact etching.
Implementation Method 1
involves an anisotropic etching process to separate merged S/D EPIs and increase spacing between them
Implementation Method 2
epitaxially growing source/drain (S/D) features
Data Source
AI summary
A device includes a substrate, an isolation structure over the substrate, and two fins extending from the substrate and above the isolation structure. Two source/drain structures are over the two fins respectively and being side by side along a first direction generally perpendicular to a lengthwise direction of the two fins from a top view. Each of the two source/drain structures has a near-vertical side, the two near-vertical sides facing each other along the first direction. A contact etch stop layer (CESL) is disposed on at least a lower portion of the near-vertical side of each of the two source/drain structures. And two contacts are disposed over the two source/drain structures, respectively, and over the CESL.