Vertical NAND Polysilicon Channel Doping via Angled Ion Implantation
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Solution Overview
Problem
Inadequate or non-uniform doping of the polycrystalline channel in vertical NAND FLASH devices degrades device operating parameters and performance due to limitations in miniaturization and doping techniques for high aspect ratio features.
Innovation Solution
A method using high energy ion implants at various depths and angles to dope the polycrystalline channel in a vertical NAND device, with ions passing through the ONO stack to achieve uniform doping concentrations and optimize performance parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional miniaturization techniques are used to increase transistor density, then transistor density improves, but physical limits are reached when gate widths shrink to less than ten atomic layers
Solution Approach 1:
The patent transitions from planar (2D) transistor architecture to vertical (3D) transistor architecture by building gates in the vertical direction. This dimensional change allows continued scaling of transistor density without further reducing horizontal gate widths to physically impossible dimensions, effectively resolving the miniaturization limit by adding a vertical dimension to device architecture.
2Productivity
If vertical NAND FLASH device architecture is adopted to continue integrating more transistors, then transistor integration improves, but non-uniform doping of the polycrystalline channel degrades device performance
Solution Approach 1:
The doping process is segmented into multiple discrete ion implantation steps, each targeting specific depth ranges within the polycrystalline channel. By dividing the single doping operation into multiple staged implants with different energies and angles, the process achieves uniform doping distribution throughout the high aspect ratio channel structure, resolving the non-uniform doping problem in vertical devices.
Solution Approach 2:
Different regions of the polycrystalline channel receive tailored doping treatments through multiple ion implants with varying energies and angles. Each implant step is optimized to deliver appropriate dopant concentration to specific depth zones, ensuring locally optimized doping quality throughout the channel while maintaining overall uniformity.
3Manufacturing precision
If high energy ion implants are performed at an angle offset from normal direction to dope the channel, then doping uniformity improves, but process complexity increases due to multiple implant steps
Solution Approach 1:
The doping process utilizes systematic variation of ion implantation parameters including energy (from 200 keV to 1 MeV), angle (offset from normal direction), and dose across multiple steps. By changing these parameters in a controlled sequence, the process achieves uniform doping penetration through the high aspect ratio channel while managing complexity through parameter optimization rather than excessive process steps.
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 method ensures uniform doping concentrations throughout the channel, enhancing the performance and reliability of vertical NAND devices by improving doping uniformity and threshold voltages, thus addressing the challenges of miniaturization and doping in high aspect ratio features.
Implementation Method 1
implanting dopant ions into the polycrystalline silicon material using a plurality of high energy ion implants
Data Source
AI summary
A method of doping the polycrystalline channel in a vertical FLASH device is disclosed. This method uses a plurality of high energy ion implants to dope the channel at various depths of the channel. In some embodiments, these ion implants are performed at an angle offset from the normal direction, such that the implanted ions pass through at least a portion of the surrounding ONO stack. By passing through the ONO stack, the distribution of ranges reached by each ion may differ from that created by a vertical implant.