Intel’s Angela Butler traces the discovery of a pioneering silicon gate technology back to two young Irish emigrants arriving in the US at the turn of the 20th century.
In 1911, Thomas Kerwin moved from the small town of Mountrath in Co Laois to the United States, where he made the city of Quincy, Massachusetts his home. He took advantage of the opportunities available to him, joining the US Navy during World War I and later forging a career as a police officer.
Tom Kerwin married Elizabeth O’Driscoll in 1925. Like Tom, Liz had made the move from Ireland to Massachusetts, having grown up in Rathmore, Baltimore, Co Cork. The couple had four children: Thomas, William, Elizabeth and Robert.
Tom and Liz’s youngest child Robert, or Bob as he is known, was raised in Quincy, attending the Massachusetts Fields School and North Quincy High School. In 1954, he earned a bachelor’s degree in science from Boston College and was awarded a master’s in science from MIT in 1958. In 1964, he completed a PhD in chemistry at the University of Pittsburgh, serving as a junior fellow in polymer science at the Mellon Institute. At that time, he joined AT&T’s Bell Telephone Laboratories as a member of technical staff in the electronic component processes laboratory in Murray Hill, New Jersey.
Silicon gate technology
At Bell Labs in early 1966, Bob Kerwin’s team was tasked with finding a solution to two major challenges that persisted in transistor development. First, it was difficult to maintain the surface cleanliness of the silicon wafer necessary to prevent current leakage and deterioration of the gate structure in MOS devices. Second, the precise alignment of the gate structure to the underlying source and drain diffused areas was prone to tool and operator-induced errors in the photolithographic process.
The group proposed to solve the cleanliness problem through the use of a dual dielectric, silicon nitride over thin silicon oxide, which could be deposited early in the processing sequence while the pristine wafer surface was clean. Differential etching steps would have to be developed to make this possible.
Kerwin proposed to solve the alignment problem by inverting the process steps. Instead of attempting to perfectly align the gate structure with the edges of the diffused source and drain areas, put the gate in first and let it define and thus be aligned with the edges of the source and drain through the diffusion process. This would require that the gate structure be capable of withstanding the high temperatures of the diffusion process, in excess of 900 degrees Celsius.
Amongst Kerwin’s colleagues at this initial group meeting were those with years of experience in studying solid state diffusion processes and their susceptibility to contamination by impurities. They were reluctant to allow him to experiment with gate electrodes with high melting point metals such as vanadium and titanium in their diffusion furnaces. So, he suggested the use of deposited polycrystalline silicon as the gate electrode, betting that it would be made conductive enough by the diffusion itself and it wouldn’t contaminate silicon wafers.
The team went ahead and developed the optimum evaporation times and temperatures to deposit polycrystalline silicon, and recipes for differential etching of silicon nitride and silicon dioxide. They thus produced the first MOS transistors with the self-aligned silicon gates within four months.
Kerwin and his colleagues Don Klein and Jack Sarace wrote up the process details and filed a patent application in January 1967 and presented a paper on this at a technical symposium in August of that year. The new process provided a distinct improvement in production yields.
Meeting with Moore
Kerwin’s innovation in circuit technology created an enduring legacy. According to the Computer History Museum, “Within five years silicon-gate MOS had become the industry standard process for new [integrated circuit] product development replacing bipolar technology in all but the highest speed applications.”
In 1980, Intel co-founder Gordon Moore swore an affidavit acknowledging the significant contributions that Kerwin and colleagues made to silicon gate technology stating that it was “an important part of Intel’s strategy when the company started in 1968, and it has subsequently been responsible for Intel’s growth and success.”
In accordance with a consent decree, AT&T was required to make all its patented innovations available to others for reasonable licensing fees. The objective of the decree was to share patents for the purpose of advancing the state of the art rather than for market control. Intel and many other companies took advantage of these licensing opportunities to foster their success in the semiconductor industry.
Kerwin met Moore in person in 1998 at a symposium at Murray Hill celebrating the 50th anniversary of the invention of the transistor. During a coffee break they discussed the self-aligned gate and its contribution to the success of Intel. Moore offered to pour Kerwin a coffee from the urn as thanks for his innovation.
Honouring a legacy
Bob Kerwin’s self-aligned gate process is still used by Intel across its manufacturing sites. Along with Klein and Sarace, he was the recipient of the Institute of Electrical and Electronics Engineers’ Jack A Morton Award in 1994. The trio were credited “for pioneering work and the basic patent on the self-aligned silicon-gate process, a key element in fabrication of very large scale integrated circuits”.
Bob Kerwin’s parents left Ireland over 100 years ago in search of new opportunities. The story of his research coupled with the wider story of his parent’s journey to America is one that embodies fearlessness, inclusion and collaboration.
At the first Global Irish Civic Forum held in Dublin in 2015, President Michael D Higgins spoke of a global Irish family: “As is often stated, emigration has been a defining characteristic of the Irish people. While some often focus on the large numbers who left Ireland during and following the dark days of the Famine, and it is true that it represented a mass exodus of our people from these shores, over the generations it has been our propensity to be a migratory people.”
Ireland’s reputation is built both on the people who live here and those who travel to every corner of the world to succeed in their given calling. Bob Kerwin and his family are testament to this. In recognition of Kerwin’s contribution to science, Intel has established a new award in his name to be conferred as part of the Intel Ireland Mini Scientist programme from 2021 onwards.
By Angela Butler
Angela Butler is a programme manager at Intel. Lynda Connolly, inclusion project manager at Intel Ireland, uncovered this short history of the Kerwin family while researching her family’s history and discovering that Bob Kerwin is a first cousin of her grandmother.