Flash Memory Floating Gate Insulation Against Hydrogen Diffusion
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Solution Overview
Problem
The data retention characteristics of nonvolatile memory circuits in semiconductor devices are deteriorated due to the diffusion of hydrogen ions and water through the silicon nitride film, which acts as an etching stopper but has a low barrier property against hydrogen ions and is prone to cracking, allowing invasion of the floating gate electrode.
Innovation Solution
A finer and more effective insulating film made of silicon nitride, formed by the low-pressure CVD method, is deposited between the existing silicon nitride film and the cap insulating film to cover the floating gate electrode, preventing water and hydrogen ions from reaching the floating gate electrode and improving data retention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a silicon nitride film is used as an etching stopper to cover the floating gate electrode, then the etching process can be controlled effectively, but the film has low barrier property against hydrogen ions and is prone to cracking, allowing water and hydrogen ions to invade the floating gate electrode
Solution Approach 1:
The patent applies a composite insulating film structure consisting of multiple layers: a first insulating film (silicon oxide) directly covering the floating gate electrode, a second insulating film (silicon nitride) as etching stopper, and a third insulating film (silicon oxide) as cap layer. This composite structure combines the low hydrogen ion permeability of silicon oxide with the etching control capability of silicon nitride, resolving the contradiction between manufacturability and reliability.
Solution Approach 2:
The first insulating film made of silicon oxide acts as an intermediary layer between the floating gate electrode and the silicon nitride film. This intermediary layer provides high barrier property against hydrogen ions and water, preventing their invasion to the floating gate electrode while allowing the silicon nitride film to perform its etching stopper function effectively.
2Productivity
If the silicon nitride film is made thinner to reduce processing time, then the etching stopper function is maintained, but cracks are more likely to occur and barrier property against hydrogen ions deteriorates
Solution Approach 1:
The patent uses a composite insulating film structure where the first insulating film (silicon oxide) provides the primary barrier against hydrogen ions, the second insulating film (silicon nitride) provides etching control, and the third insulating film (silicon oxide) provides additional protection. This composite structure maintains reliability even when the silicon nitride film is made thinner for faster processing.
Solution Approach 2:
Different regions of the insulating film structure have different functions optimized for their specific roles: the first insulating film region directly contacts the floating gate electrode and provides hydrogen ion barrier, the second insulating film region provides etching control, and the third insulating film region provides cap protection. This local optimization allows thin silicon nitride film while maintaining overall reliability.
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 solution significantly enhances the data retention characteristics of nonvolatile memory circuits by preventing the diffusion of hydrogen ions and water, leading to stable threshold values and improved reliability of data storage.
Implementation Method 1
an insulating film containing nitrogen, and an insulating film containing oxygen formed by the plasma chemical vapor deposition method are deposited sequentially
Implementation Method 2
an insulating film containing nitrogen, and an insulating film containing oxygen formed by the plasma chemical vapor deposition method are deposited sequentially
Implementation Method 3
If the hydrogen ions diffuse to the floating gate electrode of the nonvolatile memory circuit, electrons in the floating gate electrode contributing to the storage of information are neutralized by the hydrogen ions
Data Source
AI summary
In a memory cell array on a main surface of a semiconductor substrate, a floating gate electrode for accumulating charges for information is arranged. The floating gate electrode is covered with a cap insulating film and a pattern of a first insulating film formed thereon. Further, over the entire main surface of the semiconductor substrate, a second insulating film is deposited so that it covers the pattern of the first insulating film and a gate electrode. The second insulating film is formed by a silicon nitride film formed by a plasma CVD method. The first insulating film is formed by a silicon nitride film formed by a low-pressure CVD method. By the provision of such a first insulating film, it is possible to suppress or prevent water or hydrogen ions from diffusing to the floating gate electrode, and therefore, the data retention characteristics of a flash memory can be improved.