Silicon Carbide Substrate Resistivity Control via Particle Irradiation
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Solution Overview
Problem
There is a need for a cost-effective method to produce a silicon carbide substrate with appropriate resistivity for high-voltage applications, as thick, lightly doped silicon carbide epilayers are expensive, and semi-insulating silicon carbide substrates have high resistivity leading to low forward currents in bipolar diodes.
Innovation Solution
A method involving the irradiation of a silicon carbide substrate with particles such as electrons, hydrogen, helium, lithium, beryllium, boron, sodium, magnesium, or aluminum atoms to increase resistivity, creating a semiconducting substrate with a resistivity range of 10^2 to 10^5 Ωcm, which can be used as an alternative to both semi-insulating and thick, lightly doped epilayers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick, lightly doped silicon carbide epilayer is used, then the substrate can block high voltages (>10 kV), but the production cost increases significantly
Solution Approach 1:
The patent applies parameter changes by modifying the resistivity of the silicon carbide substrate through particle irradiation. The substrate is irradiated with particles (electrons, protons, or ions) to create defects that increase resistivity from typical conducting levels (0.1-10 Ωcm) to semi-insulating levels (10^2-10^5 Ωcm). This allows the use of thinner, cheaper substrates while achieving the high voltage blocking capability previously requiring expensive thick epilayers.
2Reliability
If a semi-insulating silicon carbide substrate is used, then the resistivity is high (10^9 Ωcm), but the forward current in bipolar diodes becomes too low (μA range)
Solution Approach 1:
The patent precisely controls the resistivity parameter through particle irradiation dose and energy selection. By adjusting these parameters, the substrate resistivity is increased to the optimal range (10^2-10^5 Ωcm) rather than excessive levels (10^9 Ωcm). This controlled parameter change maintains sufficient resistivity for high voltage blocking while preserving adequate carrier concentration for functional operation in bipolar diodes.
3Reliability
If particle irradiation is applied to increase resistivity, then the substrate becomes semiconducting with appropriate resistivity, but the substrate structure is modified
Solution Approach 1:
The patent uses controlled particle irradiation that modifies the electrical properties through defect creation rather than fundamental structural transformation. The irradiation creates point defects (vacancies, interstitials) that increase resistivity while maintaining the crystalline silicon carbide structure and lattice integrity. The substrate remains structurally stable and suitable for further semiconductor processing.
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 method results in a cost-effective, high-voltage capable silicon carbide substrate with increased resistivity, suitable for power semiconductor devices, reducing material waste and achieving homogeneous net doping concentration and carrier lifetime.
Implementation Method 1
irradiating the silicon carbide substrate with particles. The particles are out of a group comprising electrons, hydrogen atoms, helium atoms, lithium atoms, beryllium atoms, boron atoms, sodium atoms, magnesium atoms and aluminum atoms
Implementation Method 2
the irradiation by particles induces e.g. an increase of a concentration of silicon vacancies and of carbon vacancies in the silicon carbide substrate
Implementation Method 3
a silicon vacancy causes doping passivation and a carbon vacancy causes carrier compensation
Implementation Method 4
a carbon vacancy causes carrier compensation. Therefore, a concentration of free electrons in the SiC substrate is reduced by the irradiation
Data Source
AI summary
A method for producing a silicon carbide substrate (11) comprises providing the silicon carbide substrate (11) and irradiating the silicon carbide substrate (11) with particles (14) out of a group comprising electrons, hydrogen atoms, helium atoms, lithium atoms, beryllium atoms, boron atoms, sodium atoms, magnesium atoms and aluminum atoms. An energy of the particles (14) for irradiation is selected such that a resistivity (p) is increased by the irradiation at least in a part of the silicon carbide substrate (11) and the silicon carbide substrate (11) is semiconducting after irradiation.