Die-to-Wafer Bonding for Dissimilar Die Thickness and Void Control
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Solution Overview
Problem
Current die-to-wafer bonding processes are low-yield due to voids caused by dicing aberrations and the inability to re-polish the bond surface of singulated dies with dissimilar heights, which limits the manufacturing of compact multi-chip modules.
Innovation Solution
A method involving bonding singulated dies with planarized oxide layers to a handle wafer, thinning the back sides uniformly, applying a protective conformal coating, and then bonding to a second handle wafer, while removing the first handle wafer and oxide layers to reveal metallized post structures, thereby overcoming thickness and handling debris issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If singulated die with dissimilar heights are bonded directly to a wafer, then the bonding process can be performed, but voids and debris from dicing cause low yield
Solution Approach 1:
The patent applies preliminary action by performing planarization of the oxide layer over the metallized posts before bonding. This pre-processing step eliminates dicing debris and creates a flat bonding surface, preventing void formation and improving bonding yield. The planarized oxide layer serves as a clean interface for subsequent bonding operations.
Solution Approach 2:
The patent uses a sacrificial handle wafer that is discarded after serving its temporary purpose of supporting the die during processing. This disposable handle wafer allows the thin die to be handled and processed without requiring the die themselves to be thick enough for direct handling, thus enabling high-yield bonding of dissimilar thickness die.
2Length of moving object
If thin die are used to reduce package thickness, then compactness is improved, but handling and processing becomes difficult
Solution Approach 1:
The patent introduces a handle wafer as an intermediary object that supports thin die during handling and processing. The handle wafer acts as a mediator between the thin die and the processing equipment, enabling easy manipulation of die that would otherwise be too thin to handle directly. This allows thin die to be processed with the same ease as thicker die.
Solution Approach 2:
The patent solves the handling problem by transitioning from direct die handling to handle-wafer-based handling. The handle wafer provides a larger dimensional platform (wafer scale) that makes manipulation easier, while the thin die maintain their reduced thickness for compact packaging. This dimensional approach allows thin die to be handled as easily as thicker die.
3Productivity
If dissimilarly sized die from different wafers are stacked vertically, then integration density is improved, but bonding yield decreases due to dicing aberrations
Solution Approach 1:
The patent applies preliminary planarization of the oxide layer before bonding to eliminate dicing debris and create a flat surface. This pre-processing step is crucial for achieving high bonding yield when stacking dissimilarly sized die from different wafers, as it removes the harmful effects of dicing aberrations that would otherwise cause voids and reduce reliability.
Solution Approach 2:
The patent applies local quality by planarizing the oxide layer specifically over the metallized posts and bonding areas, rather than uniformly thinning the entire die. This localized planarization removes dicing debris from critical bonding regions while preserving the overall die structure and enabling high-yield bonding of dissimilarly sized die from different wafers.
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 increases the yield of Known Good Die bonding by eliminating voids and debris-related issues, enabling the integration of dissimilar thickness dies into a composite wafer structure with improved mechanical stability and reduced package thickness.
Implementation Method 1
each face side including a planarized oxide layer protecting one or more metallized post structures
Implementation Method 2
bonding each face side of the plurality of die to a front side of a first handle wafer... to form a covalent bond between wafers
Implementation Method 3
thinning each of the substrate material back sides of the bonded plurality of die to a uniform thickness
Implementation Method 4
preparing the respective backsides of the plurality of die and an exposed front side of the first handle wafer with a protective conformal coating of SiO 2
Data Source
Figure 1
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AI summary
Methods, assemblies, and equipment are described for bonding one or more die (100a-100c) that may be of dissimilar thickness to a wafer. The die may be fabricated and singulated with a planarized oxide layer (114a) protecting from wafer dicing and handling debris one or more metallized post structures (112a-112c) connecting to an integrated circuit. Face sides (16a-106c) of the die are bonded to a first handle wafer (118), such that the respective post structures are aligned in a common plane. The substrate material back sides (108a-108c) of the bonded die are then thinned to a uniform thickness and bonded to a second handle wafer. The assembly may then be flipped, and the first handle wafer and protective layer including potential dicing and handling debris removed. The post structures are revealed, resulting in a composite wafer assembly including the second handle and one or more uniformly thinned die mounted thereto.