Multi-Step Etching for SiN Spacer Removal on 3D Fins
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional methods for removing silicon nitride (SiN) spacers around fins in semiconductor fabrication often damage the underlying silicon structures, which is a challenge in the production of 3-D transistor gates, especially when trying to maintain a low-k film around the gate without etching the bottom SiN spacer.
Innovation Solution
A multi-step etching process involving anisotropic etching of low-k material with high selectivity to SiN, followed by isotropic etching of SiN with high selectivity to the low-k material, using a halogen-containing process gas mixture and oxygen-based plasma to form L-shaped spacers and dual layer spacers without damaging the silicon fin.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional etching methods are used to remove SiN spacers around fins, then SiN removal is achieved, but underlying silicon structures are damaged
Solution Approach 1:
The etching process is divided into multiple sequential steps with different chemistries and selectivity characteristics. First, an anisotropic etch removes low-k material selectively, then an isotropic etch removes SiN selectively, and finally a third step completes SiN removal. This segmentation allows each step to target specific materials without damaging others, resolving the contradiction between complete SiN removal and silicon fin protection.
Solution Approach 2:
The patent changes etching parameters including gas chemistry (switching between halogen-based and oxygen-based plasmas), pressure, power, and temperature between steps. These parameter changes create different selectivity windows that enable selective removal of SiN while protecting silicon fins, achieving precise control over which material is etched at each stage.
2Manufacturing precision
If high selectivity etching is used to remove low-k material, then low-k film removal precision is improved, but process complexity increases
Solution Approach 1:
The complex etching requirement is segmented into three manageable steps: (1) anisotropic etch of low-k material with halogen-based plasma, (2) isotropic etch of SiN with oxygen-based plasma, and (3) final SiN removal. Each step has a single primary function with optimized parameters, making the overall complex process controllable and repeatable.
Solution Approach 2:
The patent uses a polymer layer as an intermediary protective barrier during the etching process. The polymer deposits on silicon surfaces during the halogen-based etch and provides protection during subsequent steps, enabling selective removal of low-k material and SiN while protecting underlying silicon structures from damage.
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 method effectively removes SiN spacers around fins without damaging the underlying silicon, achieving high selectivity and preventing etching of unexposed silicon nitride, thereby preserving the low-k film around the gate and reducing silicon fin loss.
Implementation Method 1
An anisotropic etch process is executed that etches a portion of the low-k film using plasma products from a halogen-containing process gas mixture
Implementation Method 2
Executing the anisotropic etch process deposits a CFy-based polymer on exposed silicon nitride surfaces
Implementation Method 3
An isotropic etch process is executed that etches silicon nitride using plasma products from an oxygen-based process gas
Implementation Method 4
An anisotropic etch process is executed that etches a portion of the low-k film
Implementation Method 5
An isotropic etch process is executed that etches silicon nitride
Data Source
AI summary
Methods herein can be used for removing silicon nitride around fins and other structures without damaging underlying silicon structures. Methods herein also include forming dual layer spacers and L-shaped spacers, as well as other configurations. Techniques include a multi-step process of anisotropic etching of low-k material with high selectivity to silicon nitride, followed by isotropic etching of SiN with high selectivity to the low-k material. Such techniques, for example, can be used to form an L-shaped spacer on a 3-D gate structure, as well as providing a method for completely removing silicon nitride without damaging surrounding or underlying materials.