Sidewall Doping via Knock-In Ion Implantation
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Solution Overview
Problem
The challenge in integrating more transistors on a single substrate is exacerbated by inadequate or non-uniform doping of vertical non-volatile memory (NVM) devices, such as NAND FLASH, which affects string current and threshold voltage, particularly in high aspect ratio features like trenches and vias, leading to performance degradation.
Innovation Solution
A method involving the 'knock-in' phenomenon, where ions in the fill material are implanted into the sidewalls of three-dimensional features by striking them with ions of a second species, allowing for controlled doping of sidewalls in vertical NVM devices, using alternating layers and sequential deposition and implantation processes to achieve uniform dopant concentration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional doping methods are used in high aspect ratio features, then the doping process is simple, but the doping uniformity is poor leading to degraded device performance
Solution Approach 1:
The method deposits fill material containing dopant species into the high aspect ratio feature before the actual doping step. This preliminary placement of dopant sources within the feature enables subsequent uniform doping through the knock-in process, resolving the contradiction by preparing the structure in advance to achieve better doping uniformity.
Solution Approach 2:
The fill material acts as an intermediary medium that contains and delivers dopant species to the sidewalls. By using this intermediate material layer, the dopants can be uniformly transferred to the sidewall surfaces through ion knock-in, achieving precise doping control without direct conventional doping methods.
2Manufacturing precision
If direct ion implantation is used to dope sidewalls, then the doping concentration can be controlled, but the dopant distribution becomes non-uniform in high aspect ratio features
Solution Approach 1:
The doping process is segmented into distinct steps: first depositing fill material containing dopants, then performing ion knock-in to transfer dopants to sidewalls, and finally removing excess fill material. This segmentation allows each step to be optimized independently, achieving uniform dopant distribution while maintaining manufacturing feasibility.
Solution Approach 2:
The method replaces direct mechanical ion implantation into sidewalls with an indirect knock-in mechanism. Ions are implanted into the fill material, which then transfers dopants to the sidewalls through lateral displacement. This mechanical substitution enables better dopant distribution by utilizing the fill material as a transfer medium.
3Reliability
If the fill material completely fills the high aspect ratio feature, then the sidewalls are fully protected, but the knock-in efficiency decreases
Solution Approach 1:
The fill material is deposited to a controlled thickness that provides adequate sidewall coverage and protection while leaving sufficient space for efficient ion knock-in. This local optimization of fill material thickness ensures both sidewall protection and doping efficiency are achieved simultaneously.
Solution Approach 2:
The fill material is deposited in a controlled partial amount rather than completely filling the feature. This partial filling approach provides sufficient sidewall protection while maintaining open space that allows ions to effectively knock-in dopants to the sidewalls, balancing protection and efficiency.
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 method enables optimized performance parameters by ensuring uniform doping of sidewalls in high aspect ratio features, improving device operating characteristics and threshold voltage control in NVM devices, such as NAND FLASH, and can be applied to other types of NVM memory devices.
Implementation Method 1
The methods utilize a phenomenon known as knock-in, which causes a first species of ions, already disposed in the fill material, to become implanted in the sidewall when these ions are struck by ions of a second species being implanted into the fill material.
Data Source
AI summary
Methods to implant ions into the sidewall of a three dimensional high aspect ratio feature, such as a trench or via, are disclosed. The methods utilize a phenomenon known as knock-in, which causes a first species of ions, already disposed in the fill material, to become implanted in the sidewall when these ions are struck by ions of a second species being implanted into the fill material. In some embodiments, these first species and second species have similar masses to facilitate knock-in. In some embodiments, the entire hole is not completely filled with fill material. Rather, some fill material is deposited, an ion implant is performed to cause knock-in to the sidewall adjacent to the deposited fill material, and the process is repeated until the hole is filled.