Semiconductor Back Surface Metallization for Brazing Wettability
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Solution Overview
Problem
Semiconductor chips with exposed semiconductor material exhibit poor wettability with brazing materials, leading to compromised bond strength when mounted on assembling substrates.
Innovation Solution
A process involving the deposition of a nickel (Ni) and chromium (Cr) alloy metal layer on the back surface of a semiconductor substrate, followed by electroplating with gold (Au) and the selective removal of a third metal layer to expose NiCr/Au in scribe lines, enhancing wettability with brazing materials like eutectic alloys or conductive resins.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the back surface of the semiconductor chip exposes semiconductor material, then the semiconductor chip can be mounted on the assembling substrate, but the wettability with brazing material deteriorates leading to poor bond strength
Solution Approach 1:
The patent applies composite materials by creating a multi-layer metal structure consisting of a first metal layer (NiCr) directly on the semiconductor substrate and a second metal layer (Au or other brazing-material-wettable metal) on top of it. This composite structure combines the advantages of both materials: NiCr provides strong adhesion to the semiconductor substrate while the outer layer provides excellent wettability with brazing materials, thereby resolving the contradiction between bond strength and wettability.
Solution Approach 2:
The patent changes the surface parameters of the metal layer by controlling the thickness, composition, and structure of the metal layers. Specifically, it optimizes the thickness ratio between the NiCr layer and the outer metal layer, and controls the surface roughness and cleanliness of the outer layer to maximize wettability. These parameter changes enable the surface to exhibit both strong substrate adhesion and excellent brazing material wettability.
2Strength
If a metal layer is deposited on the back surface to improve wettability, then bond strength improves, but the process complexity increases
Solution Approach 1:
The patent applies preliminary action by forming the NiCr adhesion layer and the outer metal layer on the back surface of the semiconductor substrate before dicing the substrate into chips. This preliminary metallization process ensures that each chip will have a pre-prepared metal surface with good wettability and adhesion, eliminating the need for additional metal deposition steps after chip fabrication and reducing overall process complexity.
Solution Approach 2:
The patent merges the adhesion function and wettability function into a single integrated metal layer structure. The NiCr layer provides adhesion to the substrate while the outer metal layer provides wettability, combining both functions in one structural unit that is formed during the substrate processing stage, thereby simplifying the overall manufacturing process.
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 process significantly improves the bond strength between semiconductor chips and assembling substrates by ensuring better wetting and adherence of brazing materials, preventing voids and cracks during assembly.
Implementation Method 1
depositing a first metal layer on a whole of the back surface of the substrate
Implementation Method 2
plating the first metal layer with a second metal layer
Implementation Method 3
depositing a third metal layer on the second metal layer and the first metal layer in the scribe line that is exposed from the second metal layer
Data Source
AI summary
A process of forming a semiconductor apparatus is disclosed. The process includes steps of: depositing a first metal layer containing Ni in a back surface of a substrate, plating the back surface of the substrate so as to expose the first metal layer in a portion of the scribe line, depositing a third metal layer on the whole back surface of the substrate, and selectively removing the third metal layer in the portion of the scribe line so as to leave the first metal layer in the scribe line.