Soft Material Wafer Bonding for Distortion Control
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Solution Overview
Problem
The existing wafer bonding techniques for semiconductor devices require high forces to prevent misalignment, which can lead to wafer surface distortion and reduced image resolution in backside illumination sensors due to the use of adhesives or epoxy, and existing bonding methods like hydrophilic and hydrophobic bonding also face challenges with alignment and distortion.
Innovation Solution
Incorporating soft material layers with low Young's modulus between the wafers to absorb bonding forces, combined with a wafer bonding apparatus using vacuum ports and a push pin to exert controlled forces, allowing for higher bonding forces without distortion, and forming van der Waals bonds between oxide layers that are later annealed into covalent bonds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If large magnitude force is exerted onto the wafers during bonding to prevent misalignment, then alignment precision is improved, but wafer surface distortion increases
Solution Approach 1:
A soft material layer is introduced as an intermediary between the wafer and the bonding force application point. This soft layer absorbs and distributes the bonding force, preventing direct transmission of high magnitude force to the wafer surface while still enabling effective bonding. The soft material acts as a buffer that mediates between the need for high bonding force and the need to prevent wafer distortion.
Solution Approach 2:
The bonding process utilizes changes in material properties through plasma treatment to enable bonding at lower forces. Plasma treatment modifies the surface energy and chemical properties of the wafer surfaces, creating hydrophilic or hydrophobic bonding conditions that reduce the magnitude of force required for effective bonding, thereby preventing wafer distortion while maintaining alignment precision.
2Strength
If adhesive or epoxy is used to attach wafers, then bonding strength is improved, but image resolution deteriorates
Solution Approach 1:
The invention changes the bonding mechanism from adhesive/epoxy-based chemical bonding to plasma-based van der Waals bonding. By modifying surface properties through plasma treatment (changing surface energy, creating hydrophilic/hydrophobic surfaces), the process achieves strong bonding without requiring adhesive materials that would interfere with optical paths and degrade image resolution in backside illumination sensors.
Solution Approach 2:
The invention extracts and eliminates the adhesive or epoxy layer from the bonding process. By using plasma treatment to create direct van der Waals bonds between wafer surfaces, the harmful adhesive material is completely removed, preventing its negative impact on optical performance while maintaining bonding strength.
3Strength
If plasma treatment is applied to increase bonding sites density, then bonding strength is improved, but process complexity increases
Solution Approach 1:
Plasma treatment modifies surface parameters (surface energy, hydrophilicity/hydrophobicity, chemical composition) to create optimal bonding conditions. By controlling plasma parameters (gas type, power, duration), the process achieves enhanced bonding strength through increased bonding site density while maintaining a relatively simple and controllable process flow that is standard in semiconductor manufacturing.
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 significantly reduces wafer distortion, increasing the percentage of devices with acceptable distortion levels to above 84.7% and achieving 100% when soft material layers are used on both wafers, thereby enhancing the image resolution and alignment precision of semiconductor devices.
Implementation Method 1
Soft material layers with low Young's modulus between the wafers to absorb bonding forces
Implementation Method 2
The surfaces of the wafers are subjected to a plasma or chemical treatment to increase the density of bonding sites on the wafer surfaces
Implementation Method 3
Van der Waals bonds are formed between the two surfaces
Implementation Method 4
Van der Waals bonds are formed between the two surfaces, which can be annealed to form stronger covalent bonds
Data Source
AI summary
A semiconductor device including a first wafer assembly having a first substrate and a first oxide layer over the first substrate. The semiconductor device further includes a second wafer assembly having a second substrate and a second oxide layer over the second substrate. The first oxide layer and the second oxide layer are bonded together by van der Waals bonds or covalent bonds. A method of bonding a first wafer assembly and a second wafer assembly including forming a first oxide layer over a first substrate. The method further includes forming a second oxide layer over a second wafer assembly. The method further includes forming van der Waals bonds or covalent bonds between the first oxide layer and the second oxide layer.