Monocrystalline Silicon Layer Formation for Semiconductor Memory
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Solution Overview
Problem
Conventional semiconductor memory devices face limitations in miniaturization due to the short channel effect, leading to decreased on-off ratios and unstable transistor operation, especially when channel lengths are 50 nm or less, and challenges in forming large-area silicon layers with good crystallinity on insulating films.
Innovation Solution
A method involving the formation of monocrystalline silicon layers on insulating films using solid-phase-epitaxial growth, followed by oxidation and CMP techniques to achieve ultrathin-film SOI-structure memory cells with improved crystallinity and reduced cell-to-cell variations, thereby suppressing the short channel effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the channel length is miniaturized to 50 nm or less, then the integration density is improved, but the on-off ratio decreases due to short channel effect
Solution Approach 1:
The patent changes the physical state of the silicon layer from polycrystalline to monocrystalline through solid-phase-epitaxial growth, fundamentally altering the material parameters to eliminate grain boundaries and improve carrier mobility, thereby maintaining high on-off ratio at miniaturized dimensions
Solution Approach 2:
The patent applies selective oxidation to create a thin oxide layer only at the surface of the monocrystalline silicon layer, providing localized electrical control and enabling stable transistor operation at small channel lengths while maintaining high integration density
2Shape
If a silicon layer is formed on an insulating film, then the SOI structure is achieved, but the crystallinity deteriorates due to difficulty in forming large-area silicon layer with good crystallinity
Solution Approach 1:
The patent performs preliminary formation of an amorphous silicon layer on the insulating film before applying solid-phase-epitaxial growth, creating a uniform base layer that enables subsequent monocrystallization and ensures large-area coverage with consistent crystallinity
Solution Approach 2:
The patent utilizes the phase transition from amorphous to monocrystalline silicon through controlled solid-phase-epitaxial growth, transforming the material structure to achieve high crystallinity across large areas on the insulating film substrate
3Manufacturing precision
If solid-phase-epitaxial growth is used, then the monocrystalline structure is formed, but surface non-conformity develops on the buried insulating film
Solution Approach 1:
The patent introduces an amorphous silicon layer as an intermediary between the insulating film and the monocrystalline silicon layer, allowing the epitaxial growth to proceed uniformly and preventing direct contact that would cause surface non-conformity on the buried insulating film
Solution Approach 2:
The patent replaces direct mechanical contact between the silicon layer and insulating film with a chemically bonded amorphous silicon intermediate layer, eliminating surface non-conformity while maintaining the monocrystalline structure through solid-phase-epitaxial growth
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 enables the formation of high-crystallinity silicon layers, reducing cell-to-cell variations and short channel effects, resulting in enhanced memory device performance with improved current characteristics and reduced erroneous operations.
Implementation Method 1
forming a monocrystalline silicon layer by changing the amorphous silicon thin film into a monocrystal in the <100> direction by solid-phase-growth, with the opening as a seed
Implementation Method 2
forming an oxide film at the surface of the crystal layer by heat-treating the monocrystal layer in an oxidizing atmosphere
Data Source
AI summary
In a method of manufacturing a semiconductor memory device, an opening is made in a part of an insulating film formed on a silicon substrate. An amorphous silicon thin film is formed on the insulating film in which the opening has been made and inside the opening. Then, a monocrystal is solid-phase-grown in the amorphous silicon thin film, with the opening as a seed, thereby forming a monocrystalline silicon layer. Then, the monocrystalline silicon layer is heat-treated in an oxidizing atmosphere, thereby thinning the monocrystalline silicon layer and reducing the defect density. Then, a memory cell array is formed on the monocrystalline silicon layer which has been thinned and whose defect density has been reduced.