Helium Pre-Implantation Amorphization for Shallow Junction Control
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Solution Overview
Problem
Existing ion implantation methods for forming ultra shallow junctions in semiconductor wafers face challenges such as channeling of ions, residual damage, and limited lateral diffusion, which can lead to leakage and overlap capacitance issues in CMOS transistors, particularly when using heavier species like germanium and silicon for pre-amorphization.
Innovation Solution
The use of helium for pre-implantation amorphization (PAI) addresses these issues by preventing ion channeling and allowing precise control over junction depth and lateral diffusion, with helium ions stopping at the amorphous-crystalline interface during annealing, thereby avoiding residual damage and enabling millisecond thermal budget anneals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heavier species like germanium and silicon are used for pre-amorphization, then ion channeling is prevented, but residual damage occurs and lateral diffusion is limited
Solution Approach 1:
The patent changes the material parameter from heavier species (germanium, silicon) to helium for pre-amorphization. This parameter change maintains the amorphization effect that prevents ion channeling while eliminating the residual damage problem associated with heavier species. The helium ions achieve the desired amorphous layer formation without creating the harmful residual damage that plagues traditional methods.
2Manufacturing precision
If helium PAI is used, then precise control over junction depth is achieved, but substrate resistance increases
Solution Approach 1:
The patent applies preliminary action by performing the helium PAI at optimized parameters before the actual dopant implantation. This preliminary amorphization step creates a controlled amorphous layer that will later serve as a diffusion barrier, enabling precise junction depth control. The subsequent thermal annealing activates the dopants within this controlled structure, achieving both precision and low resistance through the synergistic combination of helium PAI followed by optimized annealing.
3Ease of manufacture
If traditional ion implantation is used, then doping is achieved, but overlap capacitance issues occur in CMOS transistors
Solution Approach 1:
The patent introduces helium as an intermediary material that mediates between the ion implantation process and the final junction formation. The helium ions create a controlled amorphous structure that acts as an intermediary layer, preventing direct damage to the crystal lattice and eliminating the source of overlap capacitance. This intermediary approach allows standard doping processes to proceed while avoiding the harmful capacitive effects.
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
Helium PAI enables precise control over junction depth and lateral diffusion, reducing substrate resistance and preventing leakage, while ensuring that dopants do not diffuse beyond the intended interface, thus improving the formation of ultra shallow junctions without causing residual damage or overlap capacitance.
Implementation Method 1
A pre-amorphization implant (PAI) with helium prevents channeling
Implementation Method 2
upon anneal dopants will penetrate the substrate only to the original amorphous-crystalline interface
Data Source
AI summary
A method of using helium to create ultra shallow junctions is disclosed. A pre-implantation amorphization using helium has significant advantages. For example, it has been shown that dopants will penetrate the substrate only to the amorphous-crystalline interface, and no further. Therefore, by properly determining the implant energy of helium, it is possible to exactly determine the junction depth. Increased doses of dopant simply reduce the substrate resistance with no effect on junction depth. Furthermore, the lateral straggle of helium is related to the implant energy and the dose rate of the helium PAI, therefore lateral diffusion can also be determined based on the implant energy and dose rate of the helium PAI. Thus, dopant may be precisely implanted beneath a sidewall spacer, or other obstruction.