Understanding Stress-Induced Voiding in Metal Conductors
Stress-induced voiding (SIV), or stress migration, happens when metal conductor ions move due to high tensile stresses in the interconnect after certain processing steps, like passivation deposition. This migration leads to the formation of voids within the metal conductor. The root cause of these stresses is the difference in thermal expansion between the metal layer and the underlying Si-substrate, as well as between the metal and the passivation layer or intermetal dielectric.
Impact on ULSI Chips
The effects of SIV can be detrimental to the performance and reliability of Ultra-Large Scale Integration (ULSI) chips. Some of the consequences include:
- Changes in resistance
- Formation of voids that can lead to open circuits
- Growth of hillocks (protrusions)
- Development of whiskers (thin filaments) that may cause shorts between lines or layers
Importance of Managing SIV
These issues significantly impact the electrical properties of ULSI chips, especially with the use of advanced copper metallization. Managing stress-induced voiding is crucial for ensuring the reliability and functionality of integrated circuits, making it an important consideration during the design and manufacturing processes.