SiC Substrate Ohmic Junction via Titanium Carbide Barrier
Solution Overview
Problem
The formation of graphite layers during the fabrication of silicon carbide semiconductor apparatus leads to peeling issues with metal wiring films, as existing methods either remove necessary Ni silicide layers or introduce contaminants that degrade cohesion, making it difficult to achieve a stable connection with external apparatus.
Innovation Solution
A method involving the deposition of a first metal layer with nickel (Ni) and metals from group IV, V, or VI, such as titanium (Ti), which forms a highly cohesive layer through heat treatment above 1100°C, followed by Ar sputtering to remove impurities, creating a titanium carbide or silicide layer resistant to physical methods and reducing graphite-induced peeling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heat treatment is executed to form Ni silicide film, then low resistance connection is achieved, but graphite layer forms on the surface causing peeling
Solution Approach 1:
A titanium layer is introduced as an intermediary between the Ni silicide layer and the silicon carbide substrate. During heat treatment, titanium reacts with carbon to form titanium carbide, which acts as a barrier preventing carbon diffusion to the Ni silicide surface and subsequent graphite formation. This intermediary layer solves the contradiction by maintaining low resistance connection while preventing harmful graphite layer formation.
Solution Approach 2:
The titanium layer is deposited in advance before the heat treatment process. This preliminary action ensures that when heat treatment is executed to form Ni silicide, the titanium is already in position to react with carbon and prevent graphite formation on the Ni silicide surface.
2Reliability
If multiple process steps are executed to form ohmic electrode, then low resistance connection is achieved, but contaminants are deposited degrading cohesion
Solution Approach 1:
The titanium carbide layer formed during heat treatment serves as a protective intermediary that prevents contaminant deposition on the Ni silicide surface. This layer maintains cohesion by blocking contaminants from adhering to the electrode surface during subsequent processing steps.
3Ease of manufacture
If metal wiring film is deposited on graphite layer, then connection structure is formed, but peeling occurs due to poor cohesion
Solution Approach 1:
The titanium carbide layer acts as a protective intermediary that prevents graphite formation on the Ni silicide surface. By blocking carbon diffusion, it eliminates the graphite layer that would otherwise cause poor adhesion and peeling of the metal wiring film.
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 enhances the cohesion between the metal wiring film and external apparatus, preventing peeling and ensuring a stable connection by forming a titanium carbide or silicide layer with a high carbon atom bond rate, thereby improving the durability and adhesion of the metal wiring film.
Implementation Method 1
Heat treatment is executed for the silicon carbide substrate to form an ohmic junction between the first metal layer and the other principal surface of the silicon carbide substrate
Implementation Method 2
Heat treatment is executed for the silicon carbide substrate at a temperature of 1,100 degrees C. or more
Implementation Method 3
Ar sputtering to remove impurities
Implementation Method 4
metals of a group IV, V, or VI which reacts with carbon to produce a compound
Data Source
AI summary
Process (A) of preparing a silicon carbide substrate of a first conductivity type; process (B) of forming an epitaxial layer of the first conductivity type on one principal surface of the silicon carbide substrate; process (C) of forming on another principal surface of the silicon carbide substrate, a first metal layer; process (D) of heat treating the silicon carbide substrate after the process (C) to form an ohmic junction between the first metal layer and the other principal surface of the silicon carbide substrate, and a layer of a substance (10) highly cohesive with another metal on the first metal layer; and a process (E) of removing impurities and cleaning a surface of the first metal layer (8) on the other principal surface of the silicon carbide substrate (D), are performed. The heat treatment at process (D) is executed at a temperature of 1,100 degrees C. or more.