Gate Oxide Thickness Control via Nitride Mask Segmentation
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Solution Overview
Problem
The existing methods for forming gate oxide films with different thicknesses on a single silicon substrate result in a thin gate oxide film being partly thinner than desired, leading to gate leakage and reduced gate breakdown voltage due to significant thickness differences between thin and thick films.
Innovation Solution
A method involving the formation of a nitride film as a protective layer, followed by specific oxidation and etching steps to ensure the thin gate oxide film maintains its desired thickness, including the use of sacrificial oxidation to prevent nitrogen diffusion and oxidation hindrance, thereby reducing film loss and maintaining optimal transistor properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If gate oxide films with different thicknesses are formed on a single silicon substrate, then devices with different gate breakdown voltages can be manufactured, but the thin gate oxide film becomes partly thinner than desired causing gate leakage
Solution Approach 1:
The process is divided into multiple sequential oxidation steps (first oxidation forming first and second oxide films, second oxidation forming third and fourth oxide films, third oxidation forming fifth and sixth oxide films) with selective mask removal between steps. This segmentation allows different regions to receive different total oxide thicknesses while maintaining precise control over the thin gate oxide film thickness in each region.
Solution Approach 2:
A nitride film is formed as a protective layer before the oxidation process begins. This preliminary action prevents nitrogen diffusion into the oxide films during subsequent high-temperature oxidation steps, which would otherwise cause oxidation hindrance and non-uniform thickness. The nitride film is strategically removed only from areas where thick oxide is desired.
2Reliability
If a nitride film is used as a protective film to prevent oxidation, then oxidation hindrance is reduced, but nitrogen diffusion causes the thin gate oxide film to become thinner
Solution Approach 1:
The nitride film is formed as a protective barrier before oxidation begins, preventing nitrogen diffusion into the oxide films during high-temperature processing. This preliminary protective action maintains oxidation uniformity throughout the multi-step process.
Solution Approach 2:
The nitride film is selectively removed from specific regions using mask patterns, creating local differences in oxide film thickness. Areas with nitride film retained receive thicker oxide, while areas where nitride is removed receive thinner oxide, achieving local quality variation without compromising overall oxidation uniformity.
3Manufacturing precision
If multiple oxidation steps are performed with mask removal, then precise thickness control is achieved, but the process complexity increases
Solution Approach 1:
Multiple functions are merged into the nitride film: it serves as a protective barrier against nitrogen diffusion, a thickness control layer, and a sacrificial mask for pattern definition. This consolidation reduces the need for separate process steps and simplifies the overall manufacturing process despite achieving precise thickness control.
Solution Approach 2:
The oxide films serve multiple purposes: they provide electrical insulation, define gate structure thickness, and control electrical characteristics for different device types. The nitride film similarly provides protection, pattern definition, and thickness control functions, reducing the need for multiple specialized layers.
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 prevents the thin gate oxide film from becoming partly thinner, reducing gate leakage and maintaining the desired gate breakdown voltage, thus enhancing semiconductor device performance by minimizing film loss and nitrogen-induced oxidation issues.
Implementation Method 1
forming a nitride film as a protective film... prevents nitrogen diffusion and oxidation hindrance
Implementation Method 2
forming gate oxide films... forming a first oxide film and a second oxide film... forming a third oxide film and a fourth oxide film... forming a fifth oxide film and a sixth oxide film
Data Source
AI summary
An object is to provide a technique for preventing an oxide film from being partly thin. A third oxide film is formed onto a nitride film in a first area; in addition, a fourth oxide film is formed onto a main surface in a second area. The third oxide film, the nitride film, and a first oxide film are removed from the first area using a mask. After the third oxide film, the nitride film, and the first oxide film are removed, a fifth oxide film is formed onto the main surface in the first area. The fifth oxide film is removed from the first area using a mask. After the fifth oxide film is removed, a sixth oxide film is formed onto the main surface in the first area.