Backside Nano-Twinned Metallization for Low-Temperature Wafer Bonding
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Solution Overview
Problem
Existing back side metallization techniques face challenges in achieving high-density nano-twinned thin film structures uniformly distributed over large areas, particularly with metals like silver, copper, gold, and nickel, due to high production costs, low efficiency, and environmental concerns associated with electroplating methods, and issues with interface separation and damage at high bonding temperatures.
Innovation Solution
The use of ion-beam bombardment-assisted evaporation to form metallic nano-twinned thin films with a transition layer and a twin layer, where the twin layer accounts for at least 70% of the film's thickness, featuring parallel-arranged twin boundaries with an average distance of 1 nm to 100 nm and over 50% (111) crystal orientation, allowing for bonding at low temperatures below 250°C without a Ni diffusion barrier layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional evaporation or sputtering methods are used to form metallic thin films, then production cost is reduced and efficiency is improved, but nano-twinned density cannot exceed 50% and uniform distribution over large areas is difficult to achieve
Solution Approach 1:
The wafer surface is pre-treated with ion beam bombardment before evaporation to activate the surface and prepare it for nano-twin formation. This preliminary action enables the subsequent evaporation process to produce high-density nano-twinned structures that would otherwise require expensive sputtering methods
Solution Approach 2:
The invention changes the physical and chemical parameters of the evaporation process by applying ion beam bombardment during deposition. This modifies the atomic arrangement and crystal structure formation, enabling nano-twinned density to reach 75% or higher while maintaining the cost and efficiency advantages of evaporation over sputtering
2Manufacturing precision
If electroplating methods are used to form metallic thin films, then nano-twinned structures can be formed, but production cost increases, environmental impact worsens, and process control difficulty increases
Solution Approach 1:
The invention replaces the electrochemical plating process with a physical vapor deposition process assisted by ion beam bombardment. This substitution eliminates the need for chemical baths, electrodes, and complex electrochemical control, thereby reducing environmental impact and simplifying process control while still achieving high-density nano-twinned structures
Solution Approach 2:
By changing from electrochemical parameters (current density, electrolyte composition) to physical parameters (ion beam energy, evaporation rate), the invention achieves similar nano-twinned structure formation without the environmental and control issues associated with electroplating
3Reliability
If Ni/Ag thin film structure is used for back side metallization, then adhesive and diffusion barrier functions are provided, but interface separation occurs at bonding temperatures above 250°C
Solution Approach 1:
The invention changes the material composition parameter by using pure silver without nickel intermediate layers. The nano-twinned structure of the pure silver provides both adhesive strength and oxidation resistance, eliminating the interface separation problem that occurs in Ni/Ag structures at high bonding temperatures
Solution Approach 2:
The nano-twinned silver structure acts as a composite material with enhanced properties. The twin boundaries within the silver crystal structure provide both mechanical strength for adhesion and chemical stability for oxidation resistance, replacing the need for separate Ni and Ag layers
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 enables high-density nano-twinned thin film structures to be formed uniformly over large areas, reducing production costs and environmental impact, while avoiding interface separation and damage issues, and achieving better thermal, electrical, and oxidation resistance.
Implementation Method 1
activating the back side of the wafer using ion beam bombardment
Implementation Method 2
forming a metallic nano-twinned thin film on the activated back side of the wafer by ion-beam bombardment-assisted evaporation
Data Source
AI summary
A back side metallization thin film structure is provided, which includes a wafer and a metallic nano-twinned thin film on the back side of the wafer. A plurality of integrated circuit devices are formed on the front side of the wafer. The metallic nano-twinned thin film includes silver, copper, gold, palladium, or nickel. The metallic nano-twinned thin film has a transition layer near the wafer and a twin layer away from the wafer. The twin layer accounts for at least 70% of the thickness of the metallic nano-twinned thin film and includes parallel-arranged twin boundaries. The parallel-arranged twin boundaries include more than 50% of (111) crystal orientation. The back side metallization thin film structure is formed by activating the wafer surface by ion beam bombardment, followed by an evaporation deposition process performed on the activated wafer surface with simultaneous ion beam bombardment.