Strained Silicon Transistor Cavities via Pre-Amorphization
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Solution Overview
Problem
The variability in transistor performance due to the incorporation of strained silicon/germanium material in P-channel transistors, caused by variations in germanium concentration, lattice mismatch, and cavity size and shape, leads to inconsistent performance across die and substrate, complicating the fabrication of advanced semiconductor devices.
Innovation Solution
A manufacturing strategy that modifies the semiconductor material using ion implantation to create an amorphous template, followed by isotropic or crystallographically anisotropic etching to form cavities with reduced pattern loading effects, allowing for precise control of cavity size and shape, and subsequent selective epitaxial growth of a strain-inducing semiconductor alloy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If strain-inducing silicon/germanium material is incorporated in P-channel transistors to enhance charge carrier mobility, then transistor performance is improved, but variability in transistor performance across die and substrate increases due to variations in germanium concentration, lattice mismatch, and cavity size and shape
Solution Approach 1:
The patent applies pre-amorphization ion implantation to the semiconductor region before etching. This preliminary action modifies the material structure in advance, creating an amorphous template that ensures uniform etching behavior and reduces variability in cavity dimensions. The pre-amorphization step is performed at a first energy level to create sufficient damage without excessive depth, establishing a consistent foundation for subsequent isotropic etching processes.
Solution Approach 2:
The patent changes the physical state of the semiconductor material from crystalline to amorphous through ion implantation. This parameter change in material structure fundamentally alters the etching characteristics, enabling isotropic removal with reduced pattern loading effects. The amorphous state provides uniform etch rates regardless of crystal orientation, directly addressing the cavity uniformity issue while maintaining the strain-inducing material's performance benefits.
2Ease of manufacture
If conventional etching processes are used to form cavities for strain-inducing material, then cavity formation is achieved, but pattern loading effects cause significant variability in cavity size and shape across different transistor densities
Solution Approach 1:
The patent changes the material phase from crystalline to amorphous through pre-amorphization ion implantation. This parameter change eliminates the crystallographic anisotropy that causes pattern loading effects in conventional etching. The amorphous semiconductor material exhibits uniform etch rates in all directions and across different pattern densities, enabling consistent cavity formation regardless of transistor density variations across the substrate.
Solution Approach 2:
The patent replaces the conventional mechanical/physical etching approach with a chemically-driven isotropic etching process on amorphous material. This substitution eliminates the mechanical dependencies on crystal orientation and pattern density that cause variability. The chemical etching of amorphous material provides uniform removal rates that are independent of the underlying pattern, directly resolving the pattern loading problem.
3Manufacturing precision
If ion implantation is used to create amorphous template followed by isotropic etching, then cavity uniformity is improved, but additional process steps are required
Solution Approach 1:
The patent combines the pre-amorphization ion implantation step with the subsequent isotropic etching process into an integrated workflow. The amorphization and etching are performed in sequence as a unified process module, where the first ion implantation creates the amorphous template that is immediately utilized in the following etching step. This merging approach minimizes the need for separate, standalone process steps while achieving superior cavity uniformity.
Solution Approach 2:
The pre-amorphization ion implantation serves as a preliminary preparation step that enables the subsequent isotropic etching to proceed with reduced variability. By performing the amorphization in advance, the patent creates a uniform material foundation that simplifies the etching process and reduces the need for additional corrective or adjustment steps, thereby limiting the increase in overall process complexity.
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 achieves superior uniformity and controllability in transistor performance by minimizing the impact of pattern loading effects, resulting in consistent strain distribution and enhanced transistor performance across the substrate.
Implementation Method 1
modifies the semiconductor material using ion implantation to create an amorphous template
Implementation Method 2
subsequent selective epitaxial growth of a strain-inducing semiconductor alloy
Data Source
AI summary
When forming cavities in active regions of semiconductor devices in order to incorporate a strain\-inducing semiconductor material, superior uniformity may be achieved by using an implantation process so as to selectively modify the etch behavior of exposed portions of the active region. In this manner, the basic configuration of the cavities may be adjusted with a high degree of flexibility, while at the same time the dependence on pattern loading effect may be reduced. Consequently, a significantly reduced variability of transistor characteristics may be achieved.