Epitaxial Germanium Vertical Channel for 3D Memory
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Solution Overview
Problem
The mobility of minority charge carriers in the vertical channel of three-dimensional memory devices is limited by scattering at grain boundaries of polycrystalline semiconductor materials, impacting the operational speed of these devices.
Innovation Solution
A three-dimensional memory device is developed with a germanium-containing epitaxial channel layer aligned with a single crystalline semiconductor substrate, enhancing charge carrier mobility by forming an alternating stack of insulating and conductive layers over a semiconductor substrate and converting a germanium-containing semiconductor layer into an epitaxial channel layer through liquid phase epitaxy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polycrystalline semiconductor material is used in the vertical channel, then the device structure can be formed, but charge carrier mobility is reduced due to grain boundary scattering
Solution Approach 1:
The patent changes the crystalline structure parameter of the semiconductor channel material from polycrystalline to single-crystalline (epitaxial) form. This parameter change eliminates grain boundaries while maintaining the vertical channel structure, thereby resolving the contradiction between formability and charge carrier mobility.
Solution Approach 2:
The patent employs a composite structure combining silicon-germanium alloy with epitaxial growth on a silicon substrate. The germanium-containing layer (SiGe) is grown epitaxially on the silicon substrate, creating a single-crystalline composite material that maintains structural integrity while eliminating grain boundary scattering effects.
2Reliability
If germanium-containing epitaxial channel layer is used, then charge carrier mobility is improved, but manufacturing complexity increases due to liquid phase epitaxy process
Solution Approach 1:
The patent utilizes liquid phase epitaxy, which involves phase transition from liquid precursor to solid crystalline structure. The germanium-containing layer is deposited from a liquid phase at elevated temperatures, transforming into a single-crystalline solid that grows epitaxially on the substrate. This phase transition mechanism enables high-quality epitaxial growth while providing process control.
3Object-affected harmful factors
If single crystalline epitaxial structure is formed, then grain boundary scattering is eliminated, but manufacturing precision requirements increase
Solution Approach 1:
The patent performs preliminary preparation of the silicon substrate surface before epitaxial growth, ensuring proper crystal orientation and surface quality. The substrate is pre-treated and positioned to provide a suitable template for epitaxial growth, which facilitates the formation of high-quality single-crystalline structures with reduced defect density.
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 use of a germanium-containing epitaxial channel layer improves charge carrier mobility, thereby increasing the operational speed and efficiency of three-dimensional memory devices.
Implementation Method 1
The germanium-containing semiconductor layer is converted into a germanium-containing epitaxial channel layer that is in epitaxial alignment with a single crystalline structure of the semiconductor substrate
Data Source
AI summary
An alternating stack of insulating layers and spacer material layers is formed over a semiconductor substrate. Memory openings are formed through the alternating stack. An optional silicon-containing epitaxial pedestal and a memory film are formed in each memory opening. After forming an opening through a bottom portion of the memory film within each memory opening, a germanium-containing semiconductor layer and a dielectric layer is formed in each memory opening. Employing the memory film and the dielectric layer as a crucible, a liquid phase epitaxy anneal is performed to convert the germanium-containing semiconductor layer into a germanium-containing epitaxial channel layer. A dielectric core and a drain region can be formed over the dielectric layer. The germanium-containing epitaxial channel layer is single crystalline, and can provide a higher charge carrier mobility than a polysilicon channel.