Two-Layer Silicon Oxide Gate Insulator for Trench Gate Devices
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The existing ONO film structure in trench gate type semiconductor devices experiences threshold voltage (Vth) fluctuations due to charge trap phenomena, leading to potential breakdown of power ICs as holes are trapped in the silicon nitride film, causing uneven current distribution and element failure.
Innovation Solution
A two-layered structure for the second silicon oxide film, comprising a thermal oxide film and a CVD oxide film, is formed with a total thickness of 4 nm or more, specifically 5 nm or more, to prevent hole trapping and Vth fluctuations, while managing the bird's beak length to maintain device stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single-layer silicon oxide film is used as the gate insulating film in trench gate type semiconductor devices, then the manufacturing process is simple, but threshold voltage fluctuations occur due to charge trap phenomena in the silicon nitride film
Solution Approach 1:
The gate insulating film is segmented into three distinct layers: a first silicon oxide film (50-100 nm), a silicon nitride film (5-10 nm), and a second silicon oxide film (3-7 nm). This segmentation allows each layer to perform its specific function - the first oxide film provides baseline insulation, the nitride film offers electrolytic relaxation, and the second oxide film prevents hole trapping, collectively resolving the threshold voltage stability issue while maintaining manufacturing feasibility
Solution Approach 2:
The invention uses a composite ONO (oxide-nitride-oxide) film structure combining different materials with complementary properties. The silicon oxide films provide electrical insulation and hole barrier functions, while the silicon nitride film provides electrolytic relaxation effect. This composite structure addresses both the reliability requirement for stable threshold voltage and the manufacturing consideration by using standard semiconductor fabrication processes
2Reliability
If the second silicon oxide film thickness is increased to prevent hole trapping, then threshold voltage stability improves, but the bird's beak length increases causing device instability
Solution Approach 1:
The invention optimizes the thickness parameter of the second silicon oxide film to a specific range of 3-7 nm. This parameter change is critical: it is thick enough to effectively prevent hole trapping and stabilize threshold voltage, yet thin enough to control the bird's beak length and maintain device structural stability. The first silicon oxide film thickness (50-100 nm) and silicon nitride film thickness (5-10 nm) are also optimized to achieve the desired balance
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 configuration effectively prevents Vth fluctuations and element breakdown by suppressing charge trap phenomena and controlling the bird's beak length, ensuring stable current distribution and device reliability.
Implementation Method 1
a thermal oxide film formed on the surface of the silicon nitride film (6b)
Implementation Method 2
a CVD oxide film formed over the thermal oxide film
Data Source
AI summary
On the surface of a silicon nitride film, there is formed a thermal oxide film, over which a CVD oxide film is then formed to provide a silicon oxide film of two-layered structure films. Moreover, the total thickness of the two-layered structure films is set to a value from 5 nm to 30 nm. Thus, the silicon oxide film is made into the two-layered structure films of the thermal oxide film and the CVD oxide film to thereby achieve the thickness of the silicon oxide film. As a result, it is possible to prevent a Vth from being lowered by a charge trap phenomenon and to prevent the Vth from fluctuating due to the enlargement of the bird's beak length by the silicon oxide film.