Sonic Irradiation During Wafer Immersion for Bubble Removal
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Solution Overview
Problem
The challenge in integrated circuit fabrication is the formation of bubbles during wafer immersion in liquid processing baths, which leads to defects such as pits, craters, and voids in electroplated copper layers due to trapped air and multiple wetting fronts, affecting the uniformity and quality of the plating layer.
Innovation Solution
A method involving the tilting of the wafer at an angle during immersion and the application of sonic radiation to the leading outer edge region, using a sonic transducer with a planar radiating surface, to minimize bubble formation and ensure good wetting of features, while avoiding cavitation in the liquid bath.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If wafer is immersed horizontally into liquid bath, then immersion process is simple, but bubbles form on wafer surface causing plating defects
Solution Approach 1:
The wafer is tilted at an angle (e.g., 5-15 degrees) relative to the horizontal plane during immersion, creating an asymmetric immersion configuration. This asymmetric tilt causes the leading edge to contact the liquid first, establishing a single wetting front that progresses across the wafer surface, thereby preventing bubble entrapment while maintaining process simplicity
Solution Approach 2:
The immersion process transitions from a two-dimensional horizontal immersion to a three-dimensional angled immersion. By introducing the angular dimension, the liquid contacts the wafer surface in a controlled sequence from leading to trailing edge, eliminating the formation of multiple wetting fronts and associated bubbles
2Speed
If multiple wetting fronts occur during immersion, then liquid contacts wafer quickly, but bubbles are trapped between wetting fronts causing defects
Solution Approach 1:
By tilting the wafer at an angle during immersion, the liquid front contacts the wafer surface asymmetrically, creating a single progressive wetting front rather than multiple simultaneous fronts. This single front moves across the entire wafer surface without trapping bubbles, maintaining both fast liquid contact and high plating quality
Solution Approach 2:
The wafer is pre-positioned at a tilted angle before immersion begins. This preliminary angular positioning ensures that as the liquid bath rises or the wafer descends, the liquid contacts the leading edge first and progresses smoothly across the surface, preventing bubble entrapment from the outset
3Reliability
If sonic radiation is applied to entire wafer surface, then all bubbles are removed, but energy consumption increases and cavitation occurs
Solution Approach 1:
Sonic radiation is applied locally only to the leading outer edge region of the wafer where bubbles are most likely to form during immersion. The sonic transducer is positioned to target this specific zone, providing effective bubble removal at the critical location while minimizing energy consumption and avoiding cavitation in other regions
Solution Approach 2:
The wafer surface is segmented into different zones with different sonic treatment requirements. Only the leading outer edge region receives sonic radiation, while the rest of the wafer surface is left untreated. This segmented approach focuses energy where it is most needed, reducing overall energy consumption and preventing cavitation
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 effectively reduces bubble attachment and defects on the wafer surface, enhancing the uniformity and quality of the plating layer by applying sonic energy specifically to the wafer portion where bubbles tend to form, thus improving the shear force and mass transfer during the electroplating process.
Implementation Method 1
applying sonic radiation in the liquid bath... applying sonic radiation to a wafer portion of a planar wafer surface being immersed into the liquid bath
Implementation Method 2
avoiding cavitation in the liquid bath
Implementation Method 3
enhancing the uniformity and quality of the plating layer by applying sonic energy specifically to the wafer portion where bubbles tend to form, thus improving the shear force and mass transfer during the electroplating process
Data Source
AI summary
Sonic radiation is applied to a wafer portion of the planar surface of a rotating, tilted wafer as it is being immersed into a liquid treatment bath. The portion includes the leading outer edge region of the wafer. The area of the wafer portion is significantly less than the total surface area of the planar wafer surface. Power density is minimized. As a result, bubbles are removed from the wafer surface and cavitation in the liquid bath is avoided. In some embodiments, the liquid bath is de-gassed to inhibit bubble formation.