Nonvolatile Memory Gate Stack Nitrogen Concentration Control
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Solution Overview
Problem
Conventional nonvolatile semiconductor memory devices with a gate electrode structure featuring an insulating film between a charge storage layer and a control electrode are insufficient in improving threshold voltage characteristics and preventing interference between memory cells, due to challenges in effectively removing the silicon nitride film from the element isolation insulating layer during oxidizing treatments.
Innovation Solution
A method involving the formation of a stacked insulating film structure with a silicon nitride film, silicon oxide film, an intermediate insulating film with a relative dielectric constant of at least 7, and another silicon oxide film, where the silicon nitride film is formed with a nitrogen concentration of at least 21×10^15 atoms/cm², and a radical oxidation treatment is applied to selectively remove the silicon nitride film from the element isolation insulating layer, thereby improving threshold voltage characteristics and reducing interference between adjacent memory cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a silicon nitride film is formed on the element isolation insulating layer to prevent interference between memory cells, then interference prevention is improved, but the threshold voltage characteristic deteriorates due to difficulty in selectively removing the silicon nitride film
Solution Approach 1:
The patent divides the silicon nitride film into two distinct parts: a first silicon nitride film formed on the charge storage layer (floating gate) and a second silicon nitride film formed on the element isolation insulating layer. This segmentation allows selective removal of the second film through oxidizing treatment while preserving the first film, thereby resolving the contradiction between interference prevention and threshold voltage control
Solution Approach 2:
The patent extracts and removes the second silicon nitride film from the element isolation insulating layer through oxidizing treatment that converts it to silicon oxide. This selective extraction eliminates the source of threshold voltage deterioration while maintaining the first silicon nitride film's interference prevention function
2Ease of manufacture
If an oxidizing treatment is applied to sidewalls of gate electrodes after stacking the control electrode, then the process follows conventional sequence, but the silicon nitride film on element isolation insulating layer cannot be effectively removed
Solution Approach 1:
The patent performs the oxidizing treatment as a preliminary action immediately after forming the silicon oxide film and before forming the control electrode. This timing allows the second silicon nitride film to be converted to silicon oxide and removed before the control electrode is stacked, enabling effective interference prevention while maintaining manufacturing simplicity
3Manufacturing precision
If the silicon nitride film is completely removed from the element isolation insulating layer, then threshold voltage characteristic is improved, but interference prevention between adjacent memory cells becomes insufficient
Solution Approach 1:
The patent applies local quality by differentiating the fate of silicon nitride films in different locations: the first silicon nitride film on the charge storage layer is preserved to maintain interference prevention, while the second silicon nitride film on the element isolation insulating layer is removed to improve threshold voltage characteristic. This location-based differentiation resolves the contradiction
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 approach enhances the threshold voltage characteristic of memory cells and improves charge retention by ensuring the silicon nitride film is only present on the side ends of the element isolation insulating film, reducing the likelihood of charge movement between adjacent floating gate electrodes and maintaining desired threshold voltage values.
Implementation Method 1
an oxidation treatment is executed after the first silicon nitride film has been formed, or immediately after the first silicon oxide film has been formed
Implementation Method 2
forming a second insulating layer on the exposed surface of the charge storage layer and the element isolation insulating film by stacking a first silicon nitride film, a first silicon oxide film, an intermediate insulating film having a relative dielectric constant of not less than 7 and a second silicon oxide film sequentially
Data Source
AI summary
A nonvolatile semiconductor memory device includes a first insulating layer, charge storage layers, element isolation insulating films, and a second insulating layer formed on the charge storage layers and the element isolation insulating films and including a stacked structure of a first silicon nitride film, first silicon oxide film, intermediate insulating film and second silicon oxide film. The first silicon nitride film has a nitrogen concentration of not less than 21×1015 atoms/cm2. Each element isolation insulating film includes a high-temperature oxide film formed along lower side surfaces of the charge storage layers between the charge storage layers and a coating type insulating film. The first silicon nitride film is formed on an upper surface of the high-temperature oxide film in upper surfaces of the element isolation insulating films and not on the upper surface of the coating type insulating film.