Split Gate Nonvolatile Memory Metal Gate Electrode Design
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Solution Overview
Problem
Conventional split gate type nonvolatile memories face challenges in achieving better electric performance and reliability, particularly in the design of gate insulating films and gate electrodes, which affect data retention and operational voltages.
Innovation Solution
The semiconductor device incorporates a metal gate electrode with a stacked structure of a metal film and a silicon film, where a metal oxide portion is formed at the upper end of the metal film, and a high-permittivity gate insulating film is used between the control and memory gate electrodes, enhancing the electric performance and reliability by preventing short circuits and improving data retention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional polysilicon gate electrode is used in a split gate type nonvolatile memory, then the device structure is simple and manufacturing is easier, but the electric performance and reliability are insufficient
Solution Approach 1:
The gate electrode is constructed as a composite structure with a metal film layer and a polysilicon film layer. The metal film provides low resistance and high conductivity for improved electric performance, while the polysilicon film maintains compatibility with conventional manufacturing processes. This composite structure resolves the contradiction by achieving high reliability through superior electrical properties without significantly increasing manufacturing complexity.
Solution Approach 2:
The metal oxide portion is selectively formed only in the upper end part of the metal film that contacts the gate insulating film, while the lower portion remains as pure metal. This localized oxidation approach improves reliability at the critical interface region where charge trapping occurs, while maintaining the overall simplicity of the gate electrode structure and conventional fabrication processes.
2Use of energy by moving object
If the gate insulating film is made thinner to enable low voltage operation, then voltage requirements are reduced, but the risk of short circuits between gate electrodes increases
Solution Approach 1:
The metal oxide portion acts as an intermediary layer between the metal film and the gate insulating film. This intermediate oxide layer provides electrical isolation and prevents direct contact that could cause short circuits, while still allowing the thin gate insulating film structure to enable low-voltage operation. The oxide layer mediates between the conflicting requirements of thin film design and short circuit prevention.
Solution Approach 2:
The gate insulating film thickness is optimized to a specific thin range (5-20 nm) that enables low-voltage write and erase operations while maintaining sufficient breakdown voltage. Concurrently, the metal oxide portion thickness is controlled at 1-5 nm to provide adequate isolation. These parameter optimizations resolve the contradiction by achieving low operating voltages while preventing short circuits through precise thickness control of multiple layers.
3Reliability
If a metal film is added to the gate electrode structure to improve conductivity, then electric performance improves, but the manufacturing process becomes more complex
Solution Approach 1:
The metal film and polysilicon film are deposited in sequence and patterned together as a single integrated gate electrode structure. This merging of materials and processes improves electric performance through the metal's high conductivity while maintaining ease of manufacture by using conventional multi-layer deposition and single-step patterning techniques that are already standard in semiconductor fabrication.
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 improves the electric performance and reliability of the semiconductor device by preventing short circuits between the memory and control gate electrodes, allowing for low-voltage write/erase operations and better data retention, while maintaining efficient data storage and retrieval.
Implementation Method 1
a metal oxide portion formed in an upper end part of the metal film... preventing short circuits between the memory and control gate electrodes
Implementation Method 2
a high-permittivity gate insulating film is used between the control and memory gate electrodes, enhancing the electric performance and reliability by preventing short circuits and improving data retention
Data Source
AI summary
To improve the electric performance and reliability of a semiconductor device. A memory gate electrode of a split gate type nonvolatile memory is a metal gate electrode formed from a stacked film of a metal film 6a and a silicon film 6b over the metal film 6a. In an upper end part of the metal film 6a, a metal oxide portion 17 is formed by oxidation of a part of the metal film 6a. A control gate electrode of the split gate type nonvolatile memory is a metal gate electrode formed from a stacked film of a metal film 4a and the silicon film 4b over the metal film 4a.