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The transition from aluminum to copper: What revolutionary technological advances are behind this?
With the growing demand for microelectronics technology, the widespread use of copper interconnects has created a technological revolution. Copper conducts electricity better than aluminum, allowing integrated circuits (ICs) to operate in narrower dimensions and consume less energy. Since IBM and Motorola first introduced copper as an interconnect material in 1997, copper interconnect technology has ushered in significant process advancements.
The advent of copper interconnects has transformed IC performance since its introduction in 1997.
Because copper has lower resistance, ICs using copper can transmit current over a smaller range, which is critical for driving computing speeds. However, incorporating copper into microchips requires a series of challenges, including entirely new manufacturing techniques and the introduction of isolation metal layers to prevent potential damage to silicon by copper atoms.
Changes in models and process technology
In the past, traditional photo-blocking and plasma etching techniques have made the patterning process simple and smooth for aluminum, but these techniques were unavailable for copper. This required scientists to rethink the patterning process of metals, so a new technology called "additive patterning" was developed, which is also known as the "Damask" or "Double Damask" process. This new method excavates a trench in the insulation layer where the conductor is located, and then fills the trench with copper to form the desired conductor structure.
The introduction of additive mode technology makes copper processing possible, which is a key technological advancement.
The role of barrier metal
The introduction of barrier metal layers is another important breakthrough in copper interconnect technology. Copper is highly diffusible, and if not isolated, it can further damage the silicon material underneath. The barrier metal must effectively surround the copper interconnect while maintaining good conductivity. This is critical to maintaining good electrical contact. The thickness of the barrier metal is also very important. If it is too thin, it will cause the Honey glass effect. If it is too thick, it will increase the resistance of the entire conductor and reduce its performance.
The demand for barrier metals has undoubtedly promoted continued research into more efficient interconnect materials.
Electromigration resistance
Electromigration is a phenomenon in which a metallic conductor changes shape due to the flow of electric current, a process that can eventually cause the conductor to break. Copper is more resistant to electromigration than aluminum, allowing copper conductors to withstand higher currents for the same size. Due to a combination of several factors, the conversion of copper from aluminum offers huge potential for performance improvements in semiconductor devices.
Copper's superior resistance to electromigration has finally driven massive investment in the semiconductor industry.
Super structure electroplating technology
As chip frequencies reached 3 GHz in 2005, interconnect capacitance and inductance created speed limitations. In order to reduce resistance and capacitance during transmission, the transition from aluminum to copper has become a top priority. Along with advances in low-k dielectric materials, copper plating methods have dictated new processing techniques, such as top-down plating processes, and increased underfill requirements.
In copper electroplating technology, bottom-up filling method has become the most effective method to solve interconnection problems.
Future Outlook
Scientists are now working hard to develop new materials and process technologies to further reduce the diffusion rate of copper and improve conductivity. For example, the use of copper-germanium alloys could be an alternative that does not require a barrier layer, showing great potential. However, between copper applications and alternative materials, the microelectronics industry still faces many challenges.
As technology continues to develop, how will the semiconductor industry transform again in the future?
