GaN HEMT Gate Insulation Structure for Etch Damage Relief
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Solution Overview
Problem
Conventional GaN HEMT semiconductor devices face issues with surface damage during dry etching, leading to characteristic fluctuations, increased sheet resistance, and reduced breakdown voltage due to the formation of traps and de-traps, which affect the electric field distribution and capacitance, ultimately deteriorating the device's performance.
Innovation Solution
A semiconductor device with a field effect transistor configuration that includes a first insulation film, a second insulation film with higher etching selectivity, and an embedded film with relative permittivity equal to or higher than the second insulation film, arranged to reduce surface damage and enhance electric field relief by optimizing the gate electrode structure and insulation layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If dry etching is used to form gate opening, then manufacturing precision is improved, but surface damage occurs leading to trap formation and characteristic fluctuation
Solution Approach 1:
A cap film is introduced as an intermediary protective layer between the dry etching process and the semiconductor base surface. The cap film absorbs the harmful effects of dry etching (ion bombardment, plasma exposure) while allowing the gate opening to be formed with high precision through the insulation films. This mediator prevents direct damage to the semiconductor surface, thereby reducing trap formation and characteristic fluctuation while maintaining manufacturing precision.
Solution Approach 2:
The cap film is formed preliminarily before the dry etching process to protect the semiconductor base surface in advance. By preparing this protective layer beforehand, the semiconductor surface is pre-shielded against etching damage, preventing trap formation before it occurs during the gate opening formation process.
2Reliability
If field plate structure is used to relieve electric field concentration, then reliability is improved, but device complexity increases
Solution Approach 1:
The cap film performs multiple functions: it protects the semiconductor surface from dry etching damage, serves as part of the insulation layer structure, and contributes to electric field relief at the gate ends. By combining these functions in a single component, the need for separate field plate structures is reduced, thereby improving reliability while minimizing device complexity.
Solution Approach 2:
The protective function and insulation function are merged into the cap film structure. Instead of having separate protective layers and insulation layers, the cap film combines both roles, simplifying the overall device structure while maintaining the electric field relief effect needed for improved reliability.
3Reliability
If insulation film thickness is increased to prevent surface damage, then reliability is improved, but capacitance decreases
Solution Approach 1:
The insulation structure has different local properties: the cap film provides thick protection at the gate ends where electric field concentration and surface damage risk are highest, while the main gate insulation film maintains optimal thickness for capacitance in the central region. This local differentiation allows simultaneous achievement of surface damage prevention and adequate capacitance.
Solution Approach 2:
The insulation system is segmented into multiple functional layers: the cap film segment provides protective thickness at critical locations, while the main insulation film segment maintains capacitance-optimized thickness elsewhere. This segmentation allows each layer to be optimized for its specific function without compromising the other.
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 effectively reduces characteristic fluctuations, improves capacitance, and enhances the field plate effect, leading to better reliability and performance of the GaN HEMT devices by minimizing surface damage and optimizing electric field distribution.
Implementation Method 1
an embedded film provided between the first insulation film and the body part of the gate electrode in a gate length direction of the gate electrode, and having a relative permittivity equal to or higher than a relative permittivity of the second insulation film
Implementation Method 2
It is effective to relieve concentration of an electric field to reduce fluctuation of characteristics. In general, an electric field is most concentrated on a gate end when bias is applied to a gate.
Data Source
AI summary
Fluctuation and deterioration of characteristics of a semiconductor device are reduced. The semiconductor device includes a field effect transistor mounted on a semiconductor base. In addition, the field effect transistor includes an insulation layer that includes a first insulation film provided on a main surface of the semiconductor base, and a second insulation film provided on the first insulation film and having etching selectivity higher than etching selectivity of the first insulation film, a gate electrode that has a head part located on the insulation layer and a body part extending from the head part toward the main surface of the semiconductor base and is configured such that the head part has a width larger than a width of the body part, and an embedded film provided between the first insulation film and the body part of the gate electrode in a gate length direction of the gate electrode, and having a relative permittivity equal to or higher than a relative permittivity of the second insulation film.