Selective Etching of Natural Silicon Oxide for Aluminum Metal Gate Transistors
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Solution Overview
Problem
Current methods for producing transistors with high dielectric material and aluminum metal gates face challenges in selectively removing natural silicon oxide films without etching aluminum, interlayer insulating films, or side walls, leading to increased leakage current and power consumption, particularly in micronized transistors used in mobile devices.
Innovation Solution
A process involving specific etching solutions is employed to selectively remove natural silicon oxide films and silicon, using a combination of fluorine compounds, water-soluble organic solvents, and alkali compounds to prevent etching of aluminum, interlayer insulating films, and side walls, allowing for precise replacement of silicon gates with aluminum metal gates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional etching methods (alkaline solution or hydrofluoric acid) are used to remove natural silicon oxide film, then the silicon oxide film can be removed, but aluminum, interlayer insulating film, and side wall are also etched unintentionally
Solution Approach 1:
The etching process is divided into two separate steps: first removing the natural silicon oxide film with diluted hydrofluoric acid, then removing the polysilicon with alkaline solution. This segmentation allows each etching step to target specific materials with appropriate selectivity, preventing unwanted etching of aluminum and insulating films.
Solution Approach 2:
The natural silicon oxide film is removed as a preliminary step before polysilicon etching. By removing this barrier layer first with hydrofluoric acid, the subsequent alkaline etching can selectively attack the polysilicon without being blocked by the oxide film, while still protecting aluminum and insulating films from damage.
2Length of moving object
If gate thickness is reduced for transistor micronization, then transistor size is reduced, but leakage current increases due to tunnel current
Solution Approach 1:
The gate structure uses a composite of high dielectric material (such as silicon nitride or silicon oxynitride) and metal (aluminum). This composite gate provides both the thin physical dimensions needed for micronization and the high effective dielectric constant needed to suppress tunnel current and leakage, resolving the contradiction between size reduction and leakage prevention.
3Object-generated harmful factors
If high dielectric material and metal gate combination is used to reduce leakage current, then power consumption is reduced, but complex etching processes are required to remove natural oxide film without damaging other components
Solution Approach 1:
The etching process is segmented into distinct steps with different chemistries: hydrofluoric acid for oxide removal, then alkaline solution for polysilicon removal. Each step is optimized for selective etching of its target material, simplifying the overall process control compared to attempting single-step selective etching of multiple materials.
Solution Approach 2:
The natural silicon oxide film acts as an intermediary layer that is selectively removed first. This intermediary step facilitates the subsequent polysilicon etching by removing the protective oxide barrier, allowing the alkaline etchant to reach and etch the polysilicon selectively without affecting aluminum or insulating films.
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 process enables the production of high-precision, high-quality transistors with reduced leakage current and power consumption by selectively removing natural silicon oxide films and silicon without damaging adjacent materials, thereby improving transistor performance and yield.
Implementation Method 1
etching the natural silicon oxide film with an etching solution containing 0.01 to 8% by weight of a fluorine compound, 20 to 90% by weight of a water-soluble organic solvent and water
Implementation Method 2
etched with diluted hydrofluoric acid
Implementation Method 3
etching solution containing 0.01 to 8% by weight of a fluorine compound, 20 to 90% by weight of a water-soluble organic solvent and water
Data Source
Figure 1
AI summary
According to the present invention, there is provided a process for producing a transistor having a high precision and a high quality with a high yield by selectively etching a natural silicon oxide film, and further by selectively etching a dummy gate made of silicon. The present invention relates to a process for producing a transistor using a structural body which includes a substrate, and a dummy gate laminate formed by laminating at least a high dielectric material film and a dummy gate made of silicon having a natural silicon oxide film on a surface thereof, a side wall disposed to cover a side surface of the laminate and an interlayer insulating film disposed to cover the side wall which are provided on the substrate, said process including an etching step using a specific etching solution and thereby replacing the dummy gate with an aluminum metal gate.