GaN MOSFET Gate Insulator Impurity Control
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Solution Overview
Problem
Conventional silicon dioxide gate insulating films in semiconductor devices, particularly those using TEOS and plasma CVD, often incorporate carbon and gallium impurities, leading to fluctuations in gate threshold voltage and reliability issues due to fixed charges, which are challenging to control.
Innovation Solution
A silicon dioxide film is formed using a TEOS gas and oxygen plasma CVD on a gallium nitride semiconductor layer, with controlled TEOS gas flow rates and temperature between 300°C to 400°C, to maintain carbon concentrations below 2E+18 cm−3 and gallium concentrations below 1E+17 cm−3, thereby minimizing fixed charges and stabilizing the gate threshold voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a silicon dioxide film is formed using TEOS and plasma CVD, then the gate insulating film can be formed on gallium nitride semiconductor layer, but carbon and gallium impurities are incorporated leading to fixed charges and gate threshold voltage fluctuations
Solution Approach 1:
The patent applies parameter changes by precisely controlling the TEOS gas flow rate (0.5-5 sccm) and substrate temperature (300-400°C) during plasma CVD to optimize the deposition conditions. These parameter adjustments reduce the incorporation of carbon and gallium impurities into the silicon dioxide film, thereby minimizing fixed charges and stabilizing the gate threshold voltage.
Solution Approach 2:
The patent implements preliminary anti-action by performing oxygen plasma treatment before forming the silicon dioxide film. This preliminary step removes adsorbed substances and reduces gallium out-diffusion to the surface, preventing impurity incorporation in subsequent steps and reducing fixed charges that would cause threshold voltage fluctuations.
2Ease of manufacture
If thermal oxidization is used to form silicon dioxide gate insulating film, then the process is simple, but it cannot effectively control impurity concentration and fixed charges
Solution Approach 1:
The patent transitions from thermal oxidization to plasma CVD with controlled parameters (TEOS flow rate, temperature, oxygen plasma power). This enables precise control over impurity concentration in the silicon dioxide film while maintaining manufacturing feasibility through standardized plasma processing equipment and procedures.
3Productivity
If higher TEOS gas flow rate is used to increase film formation speed, then productivity improves, but carbon concentration increases leading to more fixed charges
Solution Approach 1:
The patent optimizes the TEOS gas flow rate to a specific range (0.5-5 sccm) that balances film formation rate with impurity control. This parameter optimization ensures adequate deposition speed while maintaining carbon concentration below 2×10^18 cm^-3, preventing excessive fixed charge accumulation.
Solution Approach 2:
The patent performs oxygen plasma treatment before TEOS deposition to remove surface contaminants and reduce carbon incorporation. This preliminary action allows for higher TEOS flow rates to achieve desired film thickness while maintaining low carbon concentration through reduced surface adsorption sites.
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 concentration of fixed charges in the silicon dioxide film, stabilizing the gate threshold voltage and preventing variations across different channel regions, enhancing the reliability of gallium nitride semiconductor devices.
Implementation Method 1
supplying an oxygen gas as an oxygen raw material and forming the silicon dioxide film by plasma CVD
Implementation Method 2
forming the silicon dioxide film by plasma CVD
Implementation Method 3
supplying an oxygen gas as an oxygen raw material and forming the silicon dioxide film by plasma CVD
Implementation Method 4
supplying a TEOS gas as a silicon raw material and supplying an oxygen gas as an oxygen raw material and forming the silicon dioxide film
Data Source
AI summary
If a SiO2 film is formed on a semiconductor substrate using TEOS (tetraethylorthosilicate: Si(OC2H5)4), carbon (C) may be mixed in the SiO2 film in some cases. In a SiO2 film, carbon may function as fixed charges. For example, if carbon (C) is mixed in a SiO2 film as a gate insulating film of a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), the gate threshold voltage (Vth) may fluctuate. A semiconductor device using a gallium nitride semiconductor layer is provided. The semiconductor device includes: a silicon dioxide film that is provided at least partially in direct contact with the gallium nitride semiconductor layer and has impurity atoms, wherein the silicon dioxide film contains as the impurity atoms: carbon at concentration higher than 0 cm−3 and lower than 2E+18 cm−3; and gallium at concentration equal to or lower than 1E+17 cm−3.