Lathrop has spent years working through a microscope to make something small look bigger. While debating how to shrink transistors, he and Nall wondered if the optics of an upside-down microscope could allow for the miniaturization of something huge—a template for a transistor. To find out, they coated a piece of germanium material with a chemical called a contrast agent, which they purchased from Eastman Kodak, the camera company. The light reacts with the contrast medium, making it harder or weaker. Lathrop took advantage of this feature and created a “mask” in the shape of a mesa, placing it on a microscope with an inverted optical system. Light that passes through the holes in the mask is reduced by the microscope’s lens and projected onto the contrast chemicals. Where the light hits it, the chemical hardens. When the light is blocked by the mask, they can be washed away, leaving behind a precise, miniature germanium mesa. A way to produce miniature transistors has been found.
Lathrop named the process photolithography—printing with light—and he and Nall filed for a patent. They presented a paper on the subject at the International Electronic Equipment Annual Conference in 1957 and the Army awarded him a $25,000 prize for the invention. Lathrop bought his family a new station wagon with this money.
In the middle of the Cold War, the mortar market was growing, but Lathrop’s lithography was successful because companies that made transistors for consumer electronics realized the potential to transform its. The lithography technique not only creates transistors with unprecedented precision, but also opens the door to further miniaturization. The two leading companies in the commercial transistor race—Fairchild Semiconductor and Texas Instruments—early understood what it meant. The lithography technology was the tool they needed to produce millions of transistors, turning them into mass-market goods.
Painting with light
Robert Noyce, one of the co-founders of Fairchild, studied with Lathrop when they were both PhD students in physics at MIT. The two of them spent their college weekends hiking in New Hampshire, and they stayed in touch after graduation. At Fairchild, Noyce quickly hired Nall, Lathrop’s lab partner, and spearheaded his company’s lithography efforts by equipping his equipment with a set of 20mm camera lenses. which he bought from a photography store in the Bay Area.
Meanwhile, Lathrop took a job at Fairchild’s competitor, Texas Instruments, driving his new station wagon down to Dallas. He arrived just as his new colleague and longtime friend, Jack Kilby, was preparing to create a piece of semiconductor material with many electronic components fabricated—or integrated—into it. It is clear that these integrated circuits can only be efficiently manufactured using Lathrop’s lithography method. As chip companies try to shrink transistors to cram more transistors into chips, lithography provides the precision that miniaturization requires.
Fairchild and Texas Instruments built their first lithographic machines, but the increasing complexity of these machines soon attracted new entrants. As the scale of the transistor decreases from centimeters to millimeters then microns, the importance of precise optics increases. Perkin-Elmer is a Connecticut-based company that manufactures specialized optical equipment for the United States military, ranging from bomb sightings to spy satellites. In the late 1960s, it realized that this expertise could also be used for lithography. It has developed a scanner that can project mask patterns onto a silicon wafer while aligning them with near-perfect accuracy. The scanner then moves a light through the wafer like a copy machine, painting it with lines of light. The tool has been shown to be capable of making transistors as small as microns—a millionth of a meter.
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But this approach is impractical because chip features are getting smaller and smaller. In the late 1970s, scanners began to be replaced by steppers, which move light in separate steps on a wafer. The challenge with step lights is moving the light with micron-level precision, so that each flash is perfectly aligned with the chip. GCA, a Boston-based company that has its roots in spy balloons, invented the first step tool, allegedly on the advice of Texas Instruments chief executive Morris Chang—later named founder of TSMC, today the largest chip manufacturer in the world.
New England’s professional lithography companies soon faced fierce competition. In the 1980s, when Japanese chipmakers began to gain a large market share in memory chip production, they started buying from Nikon and Canon, two domestic manufacturers of lithography tools. Around the same time, Dutch chipmaker Philips established its own lithography tool manufacturing unit, calling the new company ASML.
