STI Inner Spacer Mitigates SDB Loading
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional shallow trench isolation (STI) processes for field-effect transistor (FET) devices face challenges in achieving uniform epitaxial source/drain regions due to difficulties in patterning at small dimensions, leading to leakage and performance degradation, particularly in single diffusion break (SDB) structures, where silicon loss and asymmetric growth result in slanted epi regions and reduced aspect ratio.
Innovation Solution
A novel STI structure is formed using a multi-layered approach with a first STI layer in the substrate, a second STI layer above the first, and a third STI layer within and above the second, incorporating a nitride spacer layer to reduce silicon loss and enhance Fin height, achieved through a method involving selective etching and chemical oxide removal processes to create a shallower trench and larger active silicon area for epitaxial growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional lithography and etch techniques are used for shallow isolation trench patterning at small dimensions, then manufacturing process simplicity is maintained, but patterning precision and manufacturing precision deteriorate
Solution Approach 1:
The isolation trench formation process is segmented into multiple steps: first forming a preliminary trench, then performing selective etching to create the final precise pattern. This segmentation allows each step to be optimized independently, achieving both process feasibility and high precision patterning at small dimensions
Solution Approach 2:
A preliminary isolation trench is formed before the final selective etching step. This preliminary structure serves as a foundation that guides subsequent precise patterning operations, enabling better control over the final trench geometry and reducing direct patterning difficulties
2Manufacturing precision
If anisotropic etching process with two-step etching and chemical oxide removal is used for Fin reveal, then Fin structure definition is improved, but silicon loss increases resulting in shorter Fin height and wider recess
Solution Approach 1:
A sacrificial oxide layer is introduced as an intermediary material during the Fin reveal process. This oxide layer protects the Fin structure from excessive etching while allowing precise definition of Fin boundaries, thereby reducing silicon loss and maintaining Fin height while achieving good structure definition
Solution Approach 2:
The etching parameters are optimized by adjusting etch selectivity ratios and process conditions to minimize silicon removal while maintaining adequate Fin structure definition. Chemical oxide removal parameters are tuned to remove protective oxide without causing additional silicon loss
3Ease of manufacture
If conventional STI structure is used, then device fabrication is simplified, but epitaxial source/drain region uniformity deteriorates due to asymmetric growth and slanted regions
Solution Approach 1:
The STI structure incorporates localized spacer regions positioned specifically at the isolation trench edges. These spacers create locally modified growth conditions that promote uniform epitaxial source/drain region formation by preventing asymmetric growth and slanted region formation, while the rest of the structure maintains conventional simple fabrication
4Manufacturing precision
If wider silicon recess and raised STI height are accepted from anisotropic etching, then Fin reveal precision is improved, but aspect ratio degradation occurs reducing device performance
Solution Approach 1:
The STI structure deliberately introduces asymmetric spacer placement and varying layer thicknesses to compensate for the symmetric widening effect of anisotropic etching. This controlled asymmetry in the STI structure counterbalances the recess widening, maintaining the desired aspect ratio while preserving Fin reveal 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 results in more uniform epitaxial source/drain regions, improved device performance by reducing facets and aspect ratio degradation, and facilitates better matching of Fin heights between SDB and double diffusion break (DDB) structures, enhancing contact resistance and drive current.
Implementation Method 1
selective etching and chemical oxide removal processes
Implementation Method 2
selective etching and chemical oxide removal processes
Implementation Method 3
forming an inner spacer layer on the third portion of the first insulating material and along the exposed vertical sidewalls of the substrate
Data Source
AI summary
A shallow trench isolation (STI) structure is formed from a conventional STI trench structure formed of first dielectric material extending into the substrate. The conventional STI structure undergoes further processing, including removing a first portion of the dielectric material and adjacent portions of the semiconductor substrate to create a first recess, and then removing another portion of the dielectric material to create a second recess in just the dielectric material. A nitride layer is formed above remaining dielectric material and on the sidewalls of the substrate. A second dielectric material is formed on the spacer layer and fills the remainder of first and second recesses. The nitride layer provides an “inner spacer” between the first insulating material and the second insulating material and also separates the substrate from the second insulating material. An isotropic Fin reveal process is performed and the STI structure assists in equalizing fin heights and increasing active S/D region area/volume.