Alternating Layer Overlay Metrology for 3D Die Alignment
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Solution Overview
Problem
Misalignment between stacked 2D ICs in 3D ICs can cause short circuits and connection failures, complicating the integration of complex and compact electronic devices.
Innovation Solution
An optical inspection system is used to generate images of die features, determine relative displacements, and provide updated alignment instructions to a robot end effector system for precise stacking and bonding of 2D ICs, ensuring accurate alignment using non-functional features on the die surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple 2D ICs are stacked vertically to form 3D ICs, then device complexity and functionality are improved, but alignment precision deteriorates making it difficult to avoid misalignment
Solution Approach 1:
Alignment marks are pre-formed on the surfaces of the 2D ICs before stacking. These marks serve as reference features that guide the alignment process during bonding, enabling precise positioning of multiple dies relative to each other in the vertical stack
Solution Approach 2:
An optical inspection system acts as an intermediary between the stacking process and alignment verification. The system captures images of the alignment marks, determines their relative positions, and provides feedback to adjust the stacking process, thereby achieving precise alignment without direct mechanical measurement
2Manufacturing precision
If alignment marks are formed on die surfaces, then alignment accuracy is improved, but device complexity increases due to additional features
Solution Approach 1:
The alignment marks are extracted as separate, dedicated features formed on non-functional areas of the die surfaces. By isolating the alignment function from the functional circuitry, the marks can be added without increasing the complexity of the operational device structure
Solution Approach 2:
Multiple copies of identical alignment marks are formed on different dies. These standardized mark patterns can be replicated across all dies in the stack, simplifying the alignment process through consistent reference features rather than requiring unique alignment mechanisms for each die
3Measurement precision
If optical inspection is used to determine relative displacement, then measurement precision is improved, but inspection time increases
Solution Approach 1:
Alignment marks are formed in advance on all dies before the stacking process begins. This preliminary preparation eliminates the need for complex real-time alignment measurements during bonding, as the marks are already in place to guide positioning
Solution Approach 2:
The optical inspection system replaces time-consuming mechanical measurement methods. By using optical imaging and image processing to determine relative displacements of alignment marks, the system achieves high measurement precision faster than traditional mechanical alignment techniques
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
The method ensures reliable alignment of 2D ICs, reducing the risk of electrical shorts and improving the operational efficiency of 3D ICs by minimizing misalignment issues.
Implementation Method 1
an optical inspection system is used to generate images of die features
Implementation Method 2
an optical inspection system is used to generate images of die features
Data Source
AI summary
Embodiments of the disclosure include a method for forming a device comprising generating an image of a second die that is bonded on a first die that is bonded on a base substrate, the first die having a first feature formed on a first surface of the first die and the second die having a second feature formed on a second surface of the second die, determining a relative displacement between portions of the first feature and the second feature based on the generated image, and determining updated alignment instructions based on the determined relative displacement.