3D NAND Flash Memory Array Polysilicon Channel Crystallization
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Solution Overview
Problem
The existing three-dimensional NAND flash memory devices face challenges with reduced read current due to high resistance in polysilicon channels and lowered electric field mobility as the number of stacked layers increases, limiting the long-term expansion of these devices.
Innovation Solution
A method for manufacturing a three-dimensional NAND flash memory array that involves alternately stacking gates and gate insulating layers, forming openings, depositing silicon and oxide fillers, injecting metal to form a metal film, and using microwave annealing and hydrogen annealing to perform metal-induced lateral crystallization (MILC) at a relatively low temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If polysilicon is used as channel material to reduce cost, then manufacturing cost is reduced, but read current decreases due to increased resistance
Solution Approach 1:
The patent changes the physical state of polysilicon from amorphous to crystalline through controlled crystallization processes (SPC, ELC, or MILC), which fundamentally alters the electrical properties including resistance and read current characteristics while maintaining the polysilicon material system
Solution Approach 2:
The patent replaces conventional thermal crystallization methods with alternative crystallization mechanisms such as solid-phase crystallization (SPC), excimer laser crystallization (ELC), or metal-induced lateral crystallization (MILC), each offering different approaches to achieving crystalline structure with varying process conditions
2Quantity of substance
If the number of stacked layers is increased to improve integration, then bit density is improved, but electric field mobility in the channel is lowered
Solution Approach 1:
The patent changes the crystalline structure of the polysilicon channel from amorphous to crystalline, which improves carrier mobility and electric field transport properties, thereby maintaining performance even as the number of stacked layers increases to four digits
3Reliability
If solid phase crystallization is performed at high temperature to crystallize polysilicon, then crystallization is achieved, but process difficulty increases
Solution Approach 1:
The patent introduces metal particles as an intermediary substance that facilitates lateral crystallization of polysilicon at lower temperatures, acting as a catalyst or nucleation site to enable crystallization without requiring extreme thermal conditions
Solution Approach 2:
The patent replaces conventional thermal field-based crystallization with alternative mechanisms such as laser-induced crystallization or metal-mediated lateral crystallization, fundamentally changing the physical mechanism from thermal diffusion to localized energy deposition or surface-mediated growth
4Adaptability or versatility
If excimer laser crystallization is used to crystallize local area polysilicon, then process constraints are reduced, but equipment cost and crystallization yield become problematic
Solution Approach 1:
The patent introduces metal particles as an intermediary that enables crystallization to proceed at lower temperatures through lateral growth mechanisms, replacing the need for expensive laser equipment while achieving similar or better crystallization results
Solution Approach 2:
The patent uses metal particles that can be introduced in small amounts and consumed or transformed during the crystallization process, replacing expensive reusable laser equipment with a consumable material approach that is cheaper and equally effective
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 minimizes the reduction in read current, reduces manufacturing process time, and lowers the heat load, enabling the expansion of three-dimensional NAND flash memory devices while maintaining device performance.
Implementation Method 1
the polysilicon is formed, and metal is injected thereto to achieve growth of NiSi2 crystals, and then, NiSi2 expansion is performed
Implementation Method 2
using microwave annealing and hydrogen annealing to perform metal-induced lateral crystallization (MILC) at a relatively low temperature
Implementation Method 3
using microwave annealing and hydrogen annealing to perform metal-induced lateral crystallization (MILC) at a relatively low temperature
Implementation Method 4
a crystal phase transition and growth step of irradiating a first microwave to the opening to grow crystalline silicon between the metal film and the polysilicon
Implementation Method 5
a crystal phase expansion step of irradiating a second microwave to the opening to expand the crystalline silicon toward a bottom surface of the opening
Data Source
AI summary
According to one embodiment of the present invention, a method for manufacturing a three-dimensional NAND flash memory array may include a polygate forming step of alternately stacking gates and gate insulating on a substrate to form a polygate; an opening forming step of forming an opening in the polygate; a polysilicon forming step of depositing silicon and an oxide filler into the opening to form a polysilicon; a metal film forming step of injecting metal into the polysilicon to form a metal film along a sidewall of the polysilicon; a crystal phase transition and growth step of irradiating a first microwave to the opening to grow crystalline silicon between the metal film and the polysilicon; and a crystal phase expansion step of irradiating a second microwave to the opening to expand the crystalline silicon toward a bottom surface of the opening.