Semiconductor Storage Device Silicon Oxynitride Inter-Poly Dielectric
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Solution Overview
Problem
As memory cells in semiconductor storage devices like NAND flash memory are downscaled, the thinning of the Inter-Poly Dielectric (IPD) film between charge accumulation layers makes it difficult to embed a control gate, leading to increased charge de-trapping and leakage, which affects threshold voltage and data retention.
Innovation Solution
Incorporating a laminated film structure of silicon oxide and silicon nitride films with a silicon oxynitride film interposed between them, where the nitrogen content of the silicon oxynitride film is controlled to suppress charge trapping and leakage, maintaining the physical thickness while reducing charge de-trapping and leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the IPD film is made thinner to enable control gate embedding in downscaled memory cells, then the control gate can be embedded between charge accumulation layers, but charge de-trapping increases and leakage current increases
Solution Approach 1:
The patent applies composite materials by creating a laminated structure consisting of multiple layers: a first dielectric layer (SiO2), a second dielectric layer (SiON with controlled nitrogen content of 10-50 at%), and a third dielectric layer (SiO2). This composite structure combines materials with different properties to achieve both thin film requirements and charge retention performance. The specific composite of SiO2/SiON/SiO2 layers with controlled nitrogen content resolves the contradiction by providing adequate charge trapping capability while maintaining thin physical thickness for control gate embedding.
2Reliability
If charges are trapped in the IPD film to relax electric field and reduce leakage current, then electron leakage from floating gate is prevented, but charge de-trapping occurs when voltage is applied affecting threshold voltage
Solution Approach 1:
The patent applies local quality by creating regions with different charge trapping characteristics within the IPD film. The laminated structure has the SiON layer (with nitrogen content of 10-50 at%) positioned between two SiO2 layers, where each layer serves a specific function: the SiO2 layers provide charge trapping to suppress leakage, while the SiON layer with controlled nitrogen content modulates the electric field and reduces charge de-trapping. This spatial differentiation of material properties resolves the contradiction between leakage suppression and charge stability.
Solution Approach 2:
The patent applies parameter changes by precisely controlling the nitrogen content in the SiON layer (10-50 at%) and adjusting the thickness ratios of the laminated layers. By changing the nitrogen content parameter, the patent optimizes the balance between charge trapping capability and charge stability. The specific nitrogen content range modifies the dielectric properties and charge binding energy, allowing the IPD film to trap charges for leakage suppression while preventing excessive de-trapping that would affect threshold voltage.
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 configuration effectively reduces charge trapping and leakage current, maintaining data integrity and retention by controlling the nitrogen content in the silicon oxynitride film, ensuring the charge amount remains within standard values and preventing unwanted charge transfer during data writing and retention.
Implementation Method 1
the silicon oxynitride film is provided between adjacent ones of the silicon oxide films and the silicon nitride films... the nitrogen content of the silicon oxynitride film is controlled to suppress charge trapping and leakage
Data Source
AI summary
A semiconductor storage device according to the present embodiment includes a semiconductor substrate. A tunnel insulating film is provided on the semiconductor substrate. A charge accumulation layer is provided on the tunnel insulating film. An intermediate dielectric film is provided on the charge accumulation layer. A control gate electrode is formed on the intermediate dielectric film. The intermediate dielectric film includes a laminated film of silicon oxide films of multiple layers and silicon nitride films of at least one layer, and a silicon oxynitride film provided between adjacent ones of the silicon oxide films and the silicon nitride films.