Plasma Doping for Ultra Shallow Junctions in Fin Structures
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional ion beam doping methods fail to achieve uniform dopant profiles and shallow junction depths required for advanced field-effect transistors, especially at technology nodes below 90 nanometers, due to the high energy of ion beams and shadowing effects, leading to variations in device performance.
Innovation Solution
The use of plasma doping with a two-step process, where a heavy carrier gas like Ar is used in the first step to make the substrate surface amorphous, reducing dependence on crystalline orientation, followed by a lighter gas like H2 in the second step to achieve uniform dopant profiles and shallow junction depths, and subsequent rapid thermal annealing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional ion beam doping is used, then doping process is simple and fast, but dopant profile uniformity is poor and junction depth is too deep
Solution Approach 1:
The doping process is divided into multiple sequential steps: first forming a shallow trench isolation structure, then performing ion implantation at a tilted angle to create LDD regions, followed by a second ion implantation step for source/drain regions. This segmentation allows each step to be optimized independently for uniformity and depth control
Solution Approach 2:
A shallow trench isolation structure is formed beforehand to define the doping regions and protect adjacent areas. This preliminary structuring enables precise dopant placement and prevents unwanted diffusion, achieving uniform profiles without increasing overall process complexity
2Productivity
If high energy ion beams are used for doping, then doping speed is fast, but shadowing effects cause non-uniform dopant distribution
Solution Approach 1:
Ion implantation is performed at a tilted angle (e.g., 7 degrees) relative to the normal of the semiconductor surface. This asymmetric approach allows the ion beam to bypass shadowing effects from overhanging structures while maintaining high doping speed and achieving uniform dopant distribution in the target regions
3Manufacturing precision
If ion implantation is used to achieve shallow junctions, then doping is localized and controlled, but junction depth cannot be reduced below 25 nm
Solution Approach 1:
The ion implantation parameters are precisely controlled: low energy ions (e.g., 5-50 keV) are used to achieve shallow penetration depths, and the implantation is performed in multiple steps with intermediate annealing. This parameter optimization enables junction depths below 25 nm while maintaining dopant activation and electrical performance consistency
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 consistent and repeatable dopant profiles with junction depths less than 25 nm, improving device performance by enhancing on-current saturation and maintaining mobility, while being independent of crystalline orientation, thus addressing the limitations of conventional ion beam doping.
Implementation Method 1
The use of plasma doping with a two-step process, where a heavy carrier gas like Ar is used in the first step to make the substrate surface amorphous
Implementation Method 2
make the substrate surface amorphous, reducing dependence on crystalline orientation
Implementation Method 3
followed by a lighter gas like H2 in the second step to achieve uniform dopant profiles and shallow junction depths
Implementation Method 4
Dopant ion implantation by ion beams has widely been used to locally modify the electrical properties of silicon
Implementation Method 5
subsequent rapid thermal annealing
Data Source
AI summary
The embodiments of methods and structures are for doping fin structures by plasma doping processes to enable formation of shallow lightly doped source and drain (LDD) regions. The methods involve a two-step plasma doping process. The first step plasma process uses a heavy carrier gas, such as a carrier gas with an atomic weight equal to or greater than about 20 amu, to make the surfaces of fin structures amorphous and to reduce the dependence of doping rate on crystalline orientation. The second step plasma process uses a lighter carrier gas, which is lighter than the carrier gas for the first step plasma process, to drive the dopants deeper into the fin structures. The two-step plasma doping process produces uniform dopant profile beneath the outer surfaces of the fin structures.