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.”

Copper in chips

Replacing aluminum wiring in chips had been thought by most to be impossible, for a number of technical reasons. However, an IBM team overcame those technical problems, bringing copper wires into production quickly, giving an immediate boost to chip performance.

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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.

“In 1997, IBM introduced a breakthrough in semiconductor technology with the development of smaller, faster, more powerful and less costly integrated circuits using copper ‘wiring’ in place of aluminum—a groundbreaking technological advance that had eluded chip manufacturers for decades.”

“IBM Leads in U.S. Patents for Fifth Consecutive Year Capping 1997’s Technology Breakthroughs,” IBM press release

January 12, 1998

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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.