Spacer Wafer Edge Structure for Bubble-Free Wafer Bonding
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Solution Overview
Problem
Current wafer-scale manufacturing processes for integrated optical devices face challenges in achieving cost-effective and high-quality wafer stacks due to complexities in spacer wafer design and bonding, leading to issues with air bubble formation and mechanical stability during the dicing process.
Innovation Solution
A spacer wafer design with elevated edges and flow control cavities is introduced, utilizing a shape replication process to create a spacer wafer that utilizes capillary forces to draw bonding agents into the gap between wafers, ensuring a sealed edge and reducing air bubble formation, while also incorporating dicing channels to facilitate efficient cutting and minimize material wear.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional spacer wafer design is used, then manufacturing process is simpler, but air bubble formation occurs and bonding quality deteriorates
Solution Approach 1:
The spacer wafer is segmented into multiple functional regions: bonding areas with elevated edges for capillary action, flow control cavities for air bubble removal, and dicing channels for separation. This segmentation allows each region to perform its specific function optimally, improving bonding quality while maintaining manufacturability through standardized patterns.
Solution Approach 2:
The spacer wafer is designed with pre-formed elevated edges and flow control cavities before the bonding process. These features are created during spacer fabrication, so when bonding agent is applied, capillary forces automatically draw the agent into the gap between wafers, and air bubbles are预先 positioned in flow control cavities for easy removal, eliminating the need for complex real-time bonding control.
2Productivity
If conventional bonding process is used, then process steps are fewer, but air bubble formation increases and yields decrease
Solution Approach 1:
The bonding process leverages the self-service principle by utilizing capillary forces generated by the elevated edges to automatically draw bonding agent into the wafer gap. The flow control cavities self-manage air bubble collection and removal. This eliminates the need for complex external bonding equipment or multi-step degassing processes, improving yield while keeping the process relatively simple.
3Manufacturing precision
If standard dicing process is used, then cutting speed is faster, but material wear on tools increases and precision decreases
Solution Approach 1:
The spacer wafer is pre-equipped with dicing channels that define the exact cutting paths before the dicing process begins. These channels are formed during spacer fabrication, so when dicing occurs, the cutting tool follows pre-defined pathways, reducing tool wear and improving precision without requiring slower, more careful cutting operations. This maintains high productivity while achieving better precision.
4Reliability
If spacer wafer without flow control features is used, then manufacturing is simpler, but air bubble formation increases and bonding reliability decreases
Solution Approach 1:
The spacer wafer manufacturing process is segmented into standard fabrication steps that include forming elevated edges and flow control cavities using conventional photolithography and etching techniques. These features are integrated into the standard spacer fabrication flow, so while the design is more complex, the manufacturing process remains relatively simple and does not require specialized equipment or processes.
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 spacer wafer design enhances the quality and yield of wafer stacks by ensuring a sealed edge, reducing air bubbles, and improving the dicing process efficiency, leading to more stable and precise optical devices with reduced material deformation and wear on cutting tools.
Implementation Method 1
a spacer wafer that utilizes capillary forces to draw bonding agents into the gap between wafers
Data Source
Figure 1~8
Figure 9~12
Figure 13~14
AI summary
A spacer wafer (1) for a wafer stack (8) comprises a spacer body (10) with a first surface (1 1) and a second surface (12), and is intended to be sandwiched between a first wafer (6) and a second wafer (7). That is, the spacer (1) is to keep a first wafer (6) placed against the first surface (11) and a second wafer (7) placed against the second surface (12) at a constant distance from each other. The spacer (1) provides openings (13) arranged such that functional elements (9) of the first wafer (6) and of the second wafer (7) can be aligned with the openings. The spacer (1) is formed from a forming tool (2) by means of a shape replication process and is preferably made of a material hardened by curing. In a preferred embodiment of the invention, at least one of the first and second surface (11, 12) comprises edges (15) separating said surface (11, 12) from the openings (13), and the thickness of the spacer wafer (1) at the edges (15) exceeds the thickness of the spacer wafer (1) at surface locations around the edges (15).