RuX Metal Cap for BEOL Interconnect Electromigration
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Solution Overview
Problem
Electromigration in back-end-of-line interconnects of integrated circuits leads to reliability issues and malfunction due to increased current density and temperature, causing voids and degradation in metal wires and vias, which existing methods fail to adequately address, especially at the via/wire interface.
Innovation Solution
A metal cap layer made of RuX, where X is Boron or Phosphorous, is selectively deposited on the metal interconnects to act as an oxygen diffusion barrier, preventing oxidation and thus reducing electromigration damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional interconnect structures are used, then manufacturing is simpler, but electromigration damage occurs at elevated temperatures leading to circuit failure
Solution Approach 1:
A RuX metal cap layer is introduced as an intermediary between the metal interconnect and the environment. This cap layer selectively blocks oxygen diffusion to the interconnect while permitting copper diffusion outward, thereby protecting the interconnect from oxidation-induced electromigration damage without requiring complete structural redesign
Solution Approach 2:
The interconnect structure is enhanced by combining the metal interconnect (e.g., copper) with a RuX metal cap layer containing boron and/or phosphorous. This composite structure leverages the electrical conductivity of the metal interconnect while the RuX cap provides selective diffusion barrier properties, creating a multi-functional protective system
2Productivity
If current density is increased to maintain performance at smaller dimensions, then circuit functionality is maintained, but electromigration damage increases
Solution Approach 1:
The RuX metal cap layer converts the potentially harmful high current density environment into a beneficial protective mechanism. Under high current stress, the cap layer maintains its integrity and continues to block oxygen diffusion, while allowing copper atoms to diffuse outward, effectively using the operational conditions to maintain protective function rather than degrade it
3Speed
If temperature is elevated to improve device performance, then circuit speed increases, but oxidation and electromigration damage increase
Solution Approach 1:
The RuX metal cap layer undergoes parameter changes in its diffusion blocking properties at elevated temperatures. Specifically, it maintains selective blocking of oxygen diffusion while permitting copper diffusion, with the ratio of these diffusion rates changing favorably at higher temperatures. This temperature-dependent parameter change enhances protection against oxidation and electromigration damage precisely when the circuit operates at higher speeds
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 RuX metal cap effectively blocks electromigration-induced damage, enhancing the reliability of interconnects by preventing oxidation and maintaining the current-carrying capability even at elevated temperatures, thereby improving the durability of BEOL interconnects.
Implementation Method 1
The metal cap comprising RuX, where X is at least one of Boron and Phosphorous... act as an oxygen diffusion barrier, preventing oxidation
Implementation Method 2
Electromigration is the transport of material caused by the gradual movement of ions in a conductor due to the momentum transfer between conducting electrons and diffusing metal atoms
Data Source
AI summary
A method of manufacturing the IC is provided, and more particularly, a method of fabricating a cap for back end of line (BEOL) interconnects that substantially eliminates electro-migration (EM) damage. The method includes forming an interconnect in an insulation material, and selectively depositing a metal cap material on the interconnect. The metal cap material includes RuX, where X is at least one of Boron and Phosphorous.