STI Structure with Nitride Capping for Rectangular Fin Profile
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Solution Overview
Problem
Existing fin reveal processes for semiconductor devices, particularly for finFET structures, result in either excessive STI oxide loss or a rounded fin profile, leading to performance issues such as increased contact resistance, leakage current, and difficulty in matching fin heights between single and double diffusion break devices.
Innovation Solution
A novel shallow trench isolation (STI) structure is developed using a chemical oxide removal (COR) only process, with a silicon nitride layer wrapping around and capping a substantial portion of the STI oxide, forming a 'mushroom' shape that maintains a rectangular fin profile and minimizes STI oxide loss, thereby increasing fin height and improving device performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If a chemical oxide removal (COR) only fin reveal process is used, then a rectangular fin profile is achieved, but excessive STI oxide loss occurs leading to increased device failure
Solution Approach 1:
A mandrel structure is formed prior to the fin reveal process to protect the STI oxide region. The mandrel is positioned over the STI oxide before COR is applied, preventing excessive oxide loss while allowing the COR process to create the desired rectangular fin profile. This preliminary protective structure resolves the contradiction by enabling the rectangular profile formation without the harmful side effect of excessive STI oxide removal.
Solution Approach 2:
The mandrel acts as an intermediary structure between the COR process and the STI oxide. It mediates the interaction by being selectively removed after serving its protective function, allowing the fin reveal to proceed with minimal STI oxide loss. The mandrel's temporary presence enables the rectangular fin profile formation while protecting the underlying STI oxide from excessive removal.
2Reliability
If a two-step fin reveal process (etching + COR) is used, then STI oxide loss is reduced, but the fin profile becomes rounded at the top
Solution Approach 1:
The etching step is extracted from the fin reveal process, leaving only the COR step. The mandrel structure replaces the need for etching by providing mechanical protection and defining the fin boundaries through its geometry. This extraction eliminates the rounded fin top problem caused by etching while maintaining STI oxide protection through the mandrel's protective function.
Solution Approach 2:
The process changes from a two-step etching+COR approach to a single COR step with a protective mandrel. This parameter change in the process sequence allows the COR chemistry to act uniformly without the mechanical removal of etching, producing a rectangular fin top while the mandrel continues to protect the STI oxide region from loss.
3Length of moving object
If an anisotropic etching process is used for fin reveal, then fin height is reduced due to silicon loss, but this creates wider silicon recess and raised STI region
Solution Approach 1:
The mechanical anisotropic etching process is replaced with a chemical COR process using the mandrel protection approach. COR acts isotropically but the mandrel's physical presence prevents lateral silicon removal, eliminating the wide recess problem. This substitution of mechanical etching with chemical removal plus physical protection maintains fin height while preventing excessive recess formation.
Solution Approach 2:
The mandrel is preliminarily positioned to define the fin boundaries before any material removal occurs. This preliminary structural definition prevents the wide silicon recess that would otherwise form during anisotropic etching, as the mandrel physically constrains the removal process to vertical profiles only, preserving both fin height and preventing excessive recess width.
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 new STI structure achieves a more rectangular fin profile with reduced silicon recess and raised STI height, enhancing device performance by minimizing contact resistance and leakage current while facilitating better fin height matching between different types of devices.
Implementation Method 1
a chemical oxide removal (COR) only step
Data Source
AI summary
A shallow trench isolation (STI) structure is formed from a conventional STI trench structure of a first dielectric material extending into the substrate. The conventional STI structure undergoes further processing: 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 spacer layer is formed above the 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 to a lever above the substrate. A nitride capping layer and another dielectric layer are disposed above the second material, thereby substantially encasing the STI structure in nitride. This provides a taller STI structure that results in a better fin profile during a subsequent fin reveal process.