Memory Select-Gate Transistor Dopant Control via Mid-Material Diffusion
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Solution Overview
Problem
Current memory circuitry manufacturing methods face challenges in controlling the concentration and vertical spread of conductivity-enhancing dopants, which can damage gate insulators and are difficult to control, especially when using ion implanting techniques.
Innovation Solution
The method involves forming a stack with vertically-alternating insulative and conductive tiers, where channel-material strings extend through these tiers, and a mid-material with conductivity-increasing dopants is out-diffused into the channel material within a cylinder, optimizing the threshold voltage of select-gate transistors while minimizing damage to the gate insulator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If ion implanting techniques are used to introduce conductivity-enhancing dopants, then dopant concentration can be increased, but damage to gate insulators occurs and control of vertical spread becomes difficult
Solution Approach 1:
A separate dopant introduction region is introduced as an intermediary structure between the dopant source and the gate insulator. This region allows dopants to be introduced into the channel material through diffusion while physically isolating the gate insulator from direct ion implantation damage, thus enabling high dopant concentration without insulator damage
Solution Approach 2:
The structure is segmented into distinct functional regions: a dopant introduction region separate from the gate insulator region, and a channel material region where dopants are selectively introduced. This segmentation allows independent optimization of dopant concentration in the channel while protecting the gate insulator structure
2Quantity of substance
If ion implanting techniques are used to introduce conductivity-enhancing dopants, then dopant concentration can be increased, but control of vertical spread becomes difficult
Solution Approach 1:
The dopant introduction region acts as a mediator that enables controlled dopant diffusion into the channel material. By using thermal diffusion through this intermediate region rather than direct ion implantation, the vertical spread of dopants is naturally limited and controlled by the diffusion process and the physical boundaries of the regions, achieving precise dopant placement
Solution Approach 2:
The mechanical ion implantation process is replaced with a thermal diffusion process. Instead of physically shooting ions into the material (mechanical approach), dopants are introduced through thermal energy-driven diffusion, which provides better control over the depth and distribution of dopant penetration
3Ease of manufacture
If conventional dopant introduction methods are used, then process simplicity is maintained, but threshold voltage consistency across select-gate transistors deteriorates
Solution Approach 1:
Different regions of the structure are given different properties: the dopant introduction region is designed with specific characteristics that enable controlled dopant diffusion, while the channel material region is optimized for receiving dopants. This local differentiation ensures consistent threshold voltage across transistors by providing uniform, controlled dopant distribution in each channel region
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 allows for precise control of dopant concentration and placement, reducing damage to gate insulators and improving the consistency of threshold voltage settings across select-gate transistors, enhancing the performance and reliability of memory circuitry.
Implementation Method 1
The conductivity-enhancing dopant is out-diffused from the mid-material into the channel material of the cylinder and the select-gate transistors
Data Source
AI summary
A method used in forming memory circuitry comprises forming a stack comprising vertically-alternating different-composition first tiers and second tiers. Channel-material strings extend through the first and second tiers. The channel material of an upper portion of the channel-material strings is part of individual select-gate transistors in a finished-circuitry construction. A lower portion of the channel-material strings is part of memory-cell strings in the finished-circuitry construction. The upper portion of the channel-material strings individually comprise a cylinder comprising the channel material of the individual select-gate transistors. A mid-material is formed within an internal volume of the cylinder radially-inside of the channel material. The mid-material material comprises conductivity-increasing dopant therein. The conductivity-increasing dopant is out-diffused from the mid-material into the channel material of the cylinder and the individual select-gate transistors. The mid-material is insulative or semiconductive in the finished-circuitry construction. Other embodiments, including structure independent of method, are disclosed.