Wafer Temporary Bonding via Silicon Direct Bonding
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Solution Overview
Problem
Existing methods for thinning silicon wafers to reduce die package height face challenges in maintaining structural strength, as larger wafers become easily damaged during processing, and conventional temporary bonding processes are defective due to adhesive irregularities and complex adhesive layer formation and removal processes.
Innovation Solution
A wafer temporary bonding method using silicon direct bonding (SDB) is employed, where the roughness of carrier and device wafers is adjusted through processes like plasma processing, wet etching, or thin film deposition, allowing for strong bonding during back-grinding and easy separation, eliminating the need for adhesives and simplifying the bonding and separation processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional adhesive bonding is used to attach device wafer to carrier wafer, then mechanical strength is improved, but process complexity increases due to adhesive layer formation and removal
Solution Approach 1:
The patent removes the adhesive layer from the bonding process entirely, using direct silicon-to-silicon bonding instead. This extraction of the adhesive component eliminates the complexity of adhesive layer formation and removal while maintaining bonding strength through direct wafer bonding mechanisms.
Solution Approach 2:
The patent introduces a roughness control mechanism as an intermediary to enable direct bonding. By controlling surface roughness to be 0.1 µm or less, the patent creates optimal bonding conditions that allow direct adhesion without adhesives, replacing the need for adhesive-mediated bonding.
2Stability of the object's composition
If adhesive layer is used for temporary bonding, then structural stability is improved, but manufacturing defects increase due to adhesive irregularities
Solution Approach 1:
By removing the adhesive layer entirely and using direct silicon bonding, the patent eliminates all defects associated with adhesive irregularities, contamination, and non-uniform adhesive distribution, achieving superior bonding uniformity.
Solution Approach 2:
The patent changes the bonding interface parameters by controlling surface roughness to 0.1 µm or less and optimizing bonding conditions (pressure, temperature, atmosphere), enabling direct bonding that provides both structural stability and manufacturing precision.
3Length of moving object
If device wafer is thinned to reduce package height, then product size is improved, but structural strength deteriorates making wafer easily destroyed
Solution Approach 1:
The patent merges the device wafer with the carrier wafer through direct bonding, creating a combined structure where the carrier wafer provides mechanical support to the thinned device wafer, enabling thinning without compromising structural strength.
Solution Approach 2:
The patent performs bonding before thinning operations, establishing a strong mechanical support structure in advance. This preliminary bonding allows subsequent thinning to proceed safely while the carrier wafer maintains structural integrity.
4Strength
If roughness of wafer surface is increased to enhance bonding, then bonding strength is improved, but separation difficulty increases
Solution Approach 1:
The patent optimizes surface roughness to a specific range (0.1 µm or less) that provides sufficient bonding strength through direct silicon bonding while maintaining ease of separation. This precise parameter control achieves the optimal balance between bonding and separation requirements.
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 enhances the structural integrity of thin wafers during back-grinding while facilitating easy separation of the carrier wafer, reducing defects and operational costs by avoiding adhesive-related issues and enabling the reuse of carrier wafers.
Implementation Method 1
combining the carrier wafer and the device wafer using SDB
Implementation Method 2
adjusting a roughness of a surface of the carrier wafer, wherein the adjusting of roughness of a surface of the carrier wafer is performed by at least one of plasma processing
Implementation Method 3
cleaning the device wafer by dipping the device wafer in deionized water
Implementation Method 4
combining the carrier wafer to the device wafer, and annealing the combined carrier wafer and device wafer
Implementation Method 5
back-grinding the device wafer
Implementation Method 6
The separating of the carrier wafer from the device wafer may be performed using a blade or separation solvent
Data Source
AI summary
A wafer temporary bonding method using silicon direct bonding (SDB) may include preparing a carrier wafer and a device wafer, adjusting roughness of a surface of the carrier wafer, and combining the carrier wafer and the device wafer using the SDB. Because the method uses SDB, instead of an adhesive layer, for a temporary bonding process, a module or process to generate and remove an adhesive is unnecessary. Also, a defect in a subsequent process, for example, a back-grinding process, due to irregularity of the adhesive may be prevented.