Air Gap Formation in NAND Flash Memory via Dual Sacrifice Films
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Solution Overview
Problem
The existing methods for forming air gaps in shallow trench isolation (STI) structures in NAND flash memory devices face challenges such as insufficient insulating characteristics due to adhesion issues and high etching resistance of sacrifice films, leading to increased leak current and malfunction in memory read/write operations, particularly at 30-nm element sizes.
Innovation Solution
A method involving the formation of a tunnel insulating film, a first conductive film, and a trench structure with a first sacrifice film and a second sacrifice film of higher density, where the second sacrifice film is exposed and both sacrifice films are removed to create an air gap with improved insulating characteristics between floating gate electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a film with bad burying characteristic is deposited by CVD to form an air gap, then the trench is not filled, but adhesion of the film to the sidewall adversely affects charge retaining characteristic and insulating characteristic is insufficient
Solution Approach 1:
The patent divides the air gap formation process into multiple stages: first forming a liner film on the sidewall, then depositing the main insulating film, and finally creating the air gap. This segmentation allows the liner film to provide adhesion while the main film provides insulation, resolving the contradiction between air gap formation and charge retention.
Solution Approach 2:
The patent applies different materials with different properties to different locations: a liner film with good adhesion properties is applied to the sidewall surface, while the main insulating film is deposited in the trench. This local differentiation ensures both adhesion to sidewalls and sufficient insulating characteristics.
2Reliability
If PSZ film is used as sacrifice film, then interelectrode insulating film can be formed on it, but large cavity serving as air gap is hardly formed due to high etching resistance
Solution Approach 1:
The patent extracts the sacrifice film removal step by using a selective etching process that targets the PSZ film specifically. By controlling the etching conditions, the PSZ film is removed to form the air gap while leaving the interelectrode insulating film intact, thus achieving both reliable film formation and ease of air gap creation.
Solution Approach 2:
The patent changes the etching parameters (such as etchant composition, temperature, and time) to achieve selective removal of the PSZ film. By optimizing these parameters, the high etching resistance of PSZ is overcome, allowing large cavities to be formed while maintaining the integrity of other films.
3Object-affected harmful factors
If air gap is formed to reduce Yupin/Enda effect, then leak current decreases, but various problems are generated in forming the air gap
Solution Approach 1:
The patent performs preliminary actions by forming the liner film and main insulating film before creating the air gap. This preliminary preparation ensures that the structure is ready for air gap formation, reducing the complexity of the overall process while achieving the desired leak current reduction.
Solution Approach 2:
The patent uses the liner film as an intermediary between the sidewall and the main insulating film. This intermediary layer facilitates the formation process by providing a foundation for the main film while allowing subsequent air gap creation, thus simplifying the overall device complexity.
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 approach effectively reduces the Yupin/Enda effect by forming a large air gap with enhanced insulating properties, improving the reliability and device characteristics of the semiconductor device by allowing better charge retention and reduced leak current.
Implementation Method 1
The second sacrifice film is exposed by processing the second conductive film. The first sacrifice film and the second sacrifice film are removed.
Data Source
AI summary
According to one embodiment, a method of manufacturing a semiconductor device is provided. In the method, a tunnel insulating film and a first conductive film are formed on a semiconductor layer. A trench is formed. A first sacrifice film is buried in the trench. A second sacrifice film having density higher than that of the first sacrifice film is formed on the first sacrifice film in the trench. An insulating film is formed on the first conductive film and the second sacrifice film. A second conductive film is formed on the insulating film. The second sacrifice film is exposed. The first sacrifice film and the second sacrifice film are removed.