Germanium Pillar 3D NAND Memory for Read Speed
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Solution Overview
Problem
The read-out speed of three-dimensionally stacked semiconductor memory devices decreases as the number of stacks increases, and the series resistance of NAND columns also increases, due to low carrier mobility in silicon-based semiconductor pillars, which leads to fluctuations in device characteristics.
Innovation Solution
The use of germanium semiconductor pillars formed through substitution heat treatment with aluminum, along with a tunneling insulating film comprising a gap and a blocking insulating film, to enhance carrier mobility and reduce defects, thereby stabilizing device characteristics and maintaining a low dielectric constant.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the number of stacks is increased to achieve higher bit densities, then storage capacity is improved, but read-out speed decreases and series resistance increases
Solution Approach 1:
The patent changes the material parameter of the semiconductor pillar from conventional silicon to germanium, which has inherently higher carrier mobility. This material substitution directly addresses the read-out speed degradation that occurs when increasing the number of stacks for higher storage capacity, allowing faster electron transport through the longer NAND column without sacrificing storage density.
Solution Approach 2:
The patent employs a composite structure where germanium semiconductor pillars are integrated with silicon-based surrounding structures (substrate, insulating layers, electrode films). This composite approach allows the germanium pillars to provide high-speed electron transport while maintaining compatibility with existing silicon manufacturing processes and device architectures.
2Ease of manufacture
If conventional silicon semiconductor pillars are used, then manufacturing process is simple, but carrier mobility is low causing read-out speed decrease
Solution Approach 1:
The patent changes the material composition parameter by substituting silicon with germanium in the semiconductor pillar. Germanium offers superior carrier mobility compared to silicon, directly improving read-out speed. The substitution heat treatment process enables this material change while maintaining compatibility with existing manufacturing workflows.
Solution Approach 2:
The patent introduces aluminum as an intermediary material that facilitates the formation of germanium semiconductor pillars through substitution heat treatment. The aluminum layer serves as a source for germanium diffusion, enabling the transformation of silicon pillars into germanium pillars through thermal processing without requiring entirely new fabrication equipment.
3Speed
If aluminum is used for substitution heat treatment to form germanium pillars, then carrier mobility increases, but manufacturing process complexity increases
Solution Approach 1:
The patent applies preliminary action by forming an aluminum film on the semiconductor pillar before the substitution heat treatment. This pre-positioned aluminum layer serves as the germanium source during subsequent thermal processing, enabling controlled in-situ formation of germanium pillars. This approach integrates the material substitution into the existing fabrication sequence without requiring separate germanium deposition steps.
Solution Approach 2:
The substitution heat treatment process is self-service in that the aluminum film on the pillar itself serves as the germanium source. During heat treatment, germanium diffuses from the aluminum into the silicon pillar, transforming it into a germanium pillar in place. This eliminates the need for separate germanium material deposition and reduces process complexity compared to alternative approaches.
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 increases carrier mobility, achieves the desired threshold voltage with fewer defects, and stabilizes device characteristics by maintaining the gap dimension within a prescribed range, thus improving read-out speed and reducing series resistance.
Implementation Method 1
germanium semiconductor pillars formed through substitution heat treatment with aluminum
Data Source
AI summary
According to one embodiment, a semiconductor memory device includes a stacked body, a semiconductor pillar, an insulating film, and a charge storage film. The stacked body includes a plurality of electrode films stacked with an inter-layer insulating film provided between the electrode films. The semiconductor pillar pierces the stacked body. The insulating film is provided between the semiconductor pillar and the electrode films on an outer side of the semiconductor pillar with a gap interposed. The charge storage film is provided between the insulating film and the electrode films. The semiconductor pillar includes germanium. An upper end portion of the semiconductor pillar is supported by an interconnect provided above the stacked body.