SiC Ohmic Contact via Laser-Induced Impurity Diffusion
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Solution Overview
Problem
Existing methods for forming ohmic junctions in silicon carbide (SiC) semiconductor devices require expensive ion implantation processes, and achieving low resistance ohmic junctions without ion implantation is challenging, especially for vertical power devices where contact resistance is high.
Innovation Solution
A manufacturing method involving the formation of a metal thin film with an impurity on a SiC substrate, followed by laser light irradiation to create a metal reaction layer that diffuses both the metal atom and impurity, forming a low resistance ohmic junction without the need for ion implantation, with the impurity and metal atom diffusion depths being the same.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ion implantation is performed to form an ohmic electrode, then contact resistance is reduced, but manufacturing cost and process complexity increase
Solution Approach 1:
The patent extracts the impurity introduction function from the expensive ion implantation process and replaces it with a simple metal thin film deposition process. The metal thin film inherently contains impurities that diffuse during laser irradiation, eliminating the need for separate ion implantation equipment and processes while achieving the same ohmic contact effect.
Solution Approach 2:
The patent changes the parameter of impurity introduction from external ion implantation to intrinsic impurity inclusion in the metal thin film. By controlling the metal thin film composition and laser irradiation parameters, the impurity diffusion is achieved through thermal energy alone, transforming a high-cost process into a low-cost process while maintaining effective ohmic contact formation.
2Ease of manufacture
If only metal silicide is formed without ion implantation, then manufacturing cost is reduced, but ohmic junction resistance is insufficient
Solution Approach 1:
The patent creates a composite structure in the metal reaction layer that combines metal silicide with impurity atoms. This composite material approach allows the formation of an ohmic junction with sufficiently low resistance using only metal thin film deposition and laser irradiation, without requiring ion implantation. The impurities embedded in the metal thin film become integral components of the composite reaction layer, enabling effective ohmic contact.
3Ease of manufacture
If laser light irradiation is used to activate impurity, then ion implantation equipment cost is reduced, but process temperature control becomes critical
Solution Approach 1:
The patent performs preliminary action by incorporating impurities into the metal thin film during deposition, before laser irradiation. This pre-positioning of impurities eliminates the need for subsequent ion implantation and simplifies the thermal processing requirements. The laser irradiation only needs to provide sufficient heat for diffusion, rather than requiring precise temperature control for ion implantation activation, thereby reducing equipment complexity while maintaining manufacturing precision.
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 method effectively reduces contact resistance and achieves a low resistance ohmic junction, as demonstrated by contact resistance measurements, outperforming methods that rely on ion implantation or metal silicide formation alone.
Implementation Method 1
the metal thin film is irradiated with a laser light
Implementation Method 2
concurrently diffusing a metal atom that forms the metal thin film and the impurity that is included in the metal thin film
Implementation Method 3
forming a metal reaction layer in which the metal atom reacts with at least one of carbon or silicon that forms the semiconductor substrate
Data Source
AI summary
In a manufacturing method of a silicon carbide semiconductor device, a semiconductor substrate made of single crystal silicon carbide is prepared. At a portion of the semiconductor substrate where a first electrode is to be formed, a metal thin film made of electrode material including an impurity is formed. After the metal thin film is formed, the first electrode including a metal reaction layer in which the impurity is introduced is formed by irradiating the metal thin film with a laser light.