Adaptive Wafer Bonding for Reduced Overlay Distortion
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing wafer bonding techniques suffer from overlay distortion due to mechanical and thermal stresses, leading to misalignment of patterns and features, which results in reduced device yield and increased fabrication costs.
Innovation Solution
A method is developed to determine optimal vacuum conditions, bonding gap distance, and striker pressure based on residual distortions from previously bonded wafers, using an adaptive wafer bonding process that adjusts these parameters to minimize overlay distortions by forming a target process recipe and applying it to subsequent bonding cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If direct wafer bonding, thermocompression bonding, or adhesive bonding is used to achieve strong bonding between wafers, then bonding strength is improved, but overlay distortion increases due to mechanical and thermal stresses
Solution Approach 1:
The patent applies preliminary actions by performing surface preparation (cleaning, plasma treatment, or chemical etching) on wafer surfaces before bonding to enhance surface energy and promote strong bonding without requiring excessive mechanical or thermal stress during the bonding process itself. This preliminary surface activation allows achieving strong bonding strength while minimizing the stress-induced overlay distortion that would otherwise occur.
Solution Approach 2:
The patent employs parameter changes by precisely controlling bonding parameters such as temperature, pressure, and bonding time to optimize the bonding process. By adjusting these parameters within specific ranges, the method achieves sufficient bonding strength while minimizing thermal and mechanical stresses that cause overlay distortion, thus resolving the contradiction between bonding strength and alignment precision.
2Reliability
If high mechanical and thermal stresses are applied during bonding to ensure strong adhesion, then bonding reliability is improved, but overlay distortion increases leading to misalignment of patterns
Solution Approach 1:
The patent applies preliminary surface treatment (plasma treatment, chemical etching, or surface activation) before bonding to enhance surface energy and create strong chemical bonding potential. This preliminary action ensures bonding reliability through chemical adhesion rather than relying on high mechanical/thermal stresses, thereby preventing overlay distortion and maintaining pattern alignment precision.
Solution Approach 2:
The patent substitutes mechanical and thermal stress-based bonding with chemistry-based bonding mechanisms. By using surface activation, plasma treatment, or chemical etching to create reactive surface groups that form chemical bonds during bonding, the method achieves reliable bonding without the overlay distortion caused by high mechanical and thermal stresses, thus resolving the contradiction between bonding reliability and alignment precision.
3Ease of manufacture
If conventional wafer bonding methods are used, then bonding process simplicity is maintained, but overlay distortion requires additional corrective processes increasing fabrication complexity
Solution Approach 1:
The patent incorporates preliminary surface treatment steps (cleaning, plasma treatment, or chemical etching) into the bonding process flow. While these add initial steps, they eliminate the need for subsequent overlay correction processes by preventing distortion at the source, thus maintaining overall process simplicity despite the added preliminary treatments.
Solution Approach 2:
The patent converts the potential harm of added preliminary treatment steps into a benefit by showing that these steps prevent overlay distortion, thereby eliminating the need for complex post-bonding correction processes. The initial simple additions of surface treatment actually simplify the overall fabrication process by avoiding subsequent complex alignment correction steps.
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 overlay distortions, enhancing the yield of semiconductor devices without the need for new processing tools, thereby reducing fabrication costs.
Implementation Method 1
applying the upper vacuum condition to an upper wafer using an upper wafer holder, the upper vacuum condition applied to a backside of the upper wafer
Implementation Method 2
striking the backside of the upper wafer with a striker using the striker pressure condition to bond the front side of the upper wafer and the front side of the lower wafer together
Data Source
AI summary
An embodiment method includes determining an upper vacuum condition, a lower vacuum condition, a bonding gap distance, and a striker pressure condition based on measuring residual distortions from a previously bonded wafer. The method includes applying the upper vacuum condition to an upper wafer using an upper wafer holder, the upper vacuum condition applied to a backside of the upper wafer, and the upper wafer having a front side being opposite of the backside. The method includes applying the lower vacuum condition to a lower wafer using a lower wafer holder. The method includes positioning the front side of the upper wafer over the front side of the lower wafer to create the bonding gap distance between the upper wafer and the lower wafer and striking the backside of the upper wafer with a striker using the striker pressure condition to bond the front side of the upper wafer and the front side of the lower wafer together.