SiC Back Surface Electrode Adhesion via Nickel Deposition Control
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Solution Overview
Problem
Conventional silicon carbide semiconductor devices face issues with the adhesion of back surface electrodes, particularly due to the brittleness of carbon precipitates in nickel silicide layers, leading to peeling during chip dicing.
Innovation Solution
A silicon carbide semiconductor device with a metal electrode multilayer structure, including a nickel silicide layer with titanium carbide, formed under specific deposition conditions to reduce residual stress in the nickel layer, enhancing adhesion and preventing peeling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a nickel layer is formed on a silicon carbide substrate and heat treated to form a nickel silicide layer, then ohmic contact is achieved, but the back surface electrode peels from the nickel silicide layer during chip dicing
Solution Approach 1:
The back surface electrode is divided into multiple layers: a nickel silicide layer directly contacting the silicon carbide substrate, and a separate aluminum layer formed on top. This segmentation allows each layer to perform its specific function - the nickel silicide layer provides ohmic contact while the aluminum layer provides mechanical strength and peeling resistance, resolving the contradiction between achieving ohmic contact and preventing electrode peeling during dicing
Solution Approach 2:
The invention changes the material parameter of the back surface electrode from a single nickel silicide layer to a composite structure with nickel silicide and aluminum layers. This parameter change transforms the electrode structure to simultaneously achieve both ohmic contact (through nickel silicide) and peel resistance (through aluminum), resolving the technical contradiction
2Reliability
If the nickel layer is removed to expose the nickel silicide layer, then peeling is suppressed, but adhesion between nickel silicide layer and titanium layer becomes poor
Solution Approach 1:
The invention extracts the problematic nickel layer from the electrode structure, leaving only the nickel silicide layer that provides good adhesion to the substrate. By removing the nickel layer that causes peeling, the invention achieves peeling suppression while maintaining strong adhesion through the nickel silicide-titanium interface
Solution Approach 2:
The invention creates a composite electrode structure where the nickel silicide layer serves as an adhesive intermediate layer between the silicon carbide substrate and the aluminum layer. This composite structure leverages the excellent adhesion properties of nickel silicide while avoiding the peeling issues of pure nickel, resolving the contradiction between peeling suppression and layer adhesion
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 approach effectively suppresses peeling of the back surface electrode by optimizing nickel layer deposition conditions, ensuring residual stress is 200 MPa or less, thereby improving the adhesion between the silicon carbide substrate and the nickel silicide layer.
Implementation Method 1
the nickel silicide layer is generated by a solid-phase reaction of silicon carbide and nickel
Implementation Method 2
The carbon dispersed in the nickel silicide layer is discharged all at once and precipitates (agglomerates) in a layer as a precipitate, such as graphite, on the surface of and inside the nickel silicide layer by heat treatment performed after the formation of the nickel silicide layer
Data Source
AI summary
A titanium layer and a nickel layer are sequentially formed on a back surface of a SiC wafer. Next, by high-temperature heat treatment, the SiC wafer is heated and the titanium layer and the nickel layer are sintered forming a nickel silicide layer that includes titanium carbide. By this high-temperature heat treatment, an ohmic contact of the SiC wafer and the nickel silicide layer is formed. Thereafter, on the nickel silicide layer, a back surface electrode multilayered structure is formed by sequentially stacking a titanium layer, a nickel layer, and a gold layer. Here, in forming the nickel layer that configures a back surface electrode multilayered structure, the nickel layer is formed under a condition that satisfies 0.0<y<−0.0013x+2.0, where the thickness of the nickel layer is x [nm] and the deposition rate of the nickel layer is y [nm/second]. Thus, peeling of the back surface electrode can be suppressed.