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Icons of Progress

Copper Interconnects

The Evolution of Microprocessors
IBM100 Copper Interconnects: The Evolution of Microprocessors iconic mark

In 1997, IBM rocked the technology industry when it announced chips with copper interconnects that could make microprocessors faster, smaller and less expensive than chips made with aluminum interconnects—the industry standard at the time. One Japanese newspaper headline on the announcement called it “The IBM Shock!” The San Jose Mercury News reported that IBM’s announcement “puts it as far as three years ahead of its competitors.”

Developed by a dedicated, cross-discipline US research and technology team from Yorktown Heights and East Fishkill, NY, and with members from the Burlington, Vermont microelectronics group, the work was performed in a low-profile manner and furthered through an alliance with Motorola, which was pursuing development of the same technology.

Many in the industry didn’t believe in copper’s promise. Yet the limitations of aluminum in microprocessors were obvious.

Moore’s Law—a yardstick by which chip and system manufacturers gauge progress—posits “the number of transistors that can be placed inexpensively on an integrated circuit doubles approximately every two years,” driving continuing performance gains over time. Historically, the semiconductor industry kept pace by continuously shrinking feature size to increase the number of transistors on a chip, thus increasing the speed of the circuits.

Copper wires conduct electricity with about 40 percent less resistance than aluminum wires, which results in an additional 15 percent burst in microprocessor speed. Copper wires are also significantly more durable and 100 times more reliable over time, and can be shrunk to smaller sizes than aluminum.

Copper also offered an opportunity to add more layers of interconnects using a radically different manufacturing process. IBM had to develop new manufacturing techniques to build chips with copper.

However, unlike aluminum, copper atoms have the capability to float across the insulating layer of the chips. Copper also has the potential to alter the silicon, changing its electrical properties and corrupting the device operability. IBM’s pioneering effort in new materials such as refractory metals contacts—tungsten, liners and deposition techniques—helped separate the copper from the silicon and prevent these adverse effects.

When copper interconnects were announced in 1997, six levels of copper interconnects on a semiconductor were possible. Today, advancements in the technology have led to interconnects that are 10 times smaller, allowing up to 13 to 15 levels of interconnects to be laid out on chip.

IBM’s contact and copper interconnect work created a new technology platform. The rest of the industry would spend the next decade trying to catch up.

Copper interconnects have since become the industry standard, enabling future generations of smaller, faster microprocessors. The technology also enabled IBM breakthroughs in multicore-processor integration, e-DRAM (embedded dynamic random access memory), the use of copper on-chip wiring, silicon-on-insulator (SOI) technology and high-speed silicon germanium chips [read more about this Icon of Progress]. IBM’s contact and copper interconnects technique is continuing to find its way into 3-D chip integration across the globe. This new technology has more than one layer of conductivity, with connections being made both horizontally and vertically.

In 2004, IBM received the US National Medal of Technology for “four decades of innovation in semiconductor technology that has enabled explosive growth in both the information technology and consumer electronics industries through the development and fabrication of smaller, more powerful microelectronic devices.” IBM’s copper technology breakthrough was featured among the innovations.

Smaller and more efficient chip technologies continue to be developed, made possible by the last 15 years of advancements in copper interconnects. And even as new exascale technologies such as nanophotonics—using pulses of light to transmit data at the nanoscale—advance, copper will continue to be an essential component of microprocessor design and evolution.


Selected team members who contributed to this Icon of Progress:

  • Randy Issac Vice President of Systems, Technology and Science at IBM Research
  • John Heidenreich Manager of Interconnect Technology, IBM Research, oversaw IBM’s work on copper since May 1994
  • Dan Edelstein Research Staff Member who had a leading role in the copper project since October 1993
  • Barbara Luther A project manager
  • Jill Slattery Development Manager at the Microelectronics Division who oversaw the program beginning in 1994
  • Jurij Paraszczak A Manager on the project at IBM Research
  • Lubomyr Romankiw IBM Fellow who researched the use of copper since the 1960s
  • Panos Andricacos Led team of electrochemists at Watson and their colleague from East Fishkill, Cyprian Uzoh, in pioneering electrolytic plating
  • Frank Kaufman, Vlasta Brusic, Naftali Lustig IBM Watson Laboratory researchers who pioneered a chemical-mechanical process that proved critical to IBM's success with copper technology
  • Tom Theis Senior Manager of Silicon Science and Technology at Watson Lab
  • Jeff Gambino Has worked on copper interconnect processes for CMOS (complementary metal oxide semiconductor) logic and CMOS imager technology
  • Rajiv Joshi Master Inventor at Watson Lab, pioneered tungsten and other metallurgies and holds key patents in tungsten-copper interconnect structure
  • Robert Wisnieff Manager of Interconnect Technology
  • Rao Varanasi IBM Senior Technical Staff Member