Photolithography

Photolithography emerged from the same printing technique used to mark rivet holes in aircraft wings. In 1957, Jay Lathrop and James Nall at the U.S. Army Diamond Ordnance Fuze Laboratory needed to shrink transistors for proximity fuzes—radio-triggered artillery shells that demanded miniaturization. They noticed that photoresist from Eastman Kodak, designed for aircraft manufacturing, could protect semiconductor surfaces during etching. By exposing the resist through patterned masks, they could transfer intricate circuit designs onto silicon.

The adjacent possible stretched back to 1798, when Alois Senefelder invented lithography using porous stone and greasy substances. Nicéphore Niépce's 1820s photography experiments with Bitumen of Judea—a natural asphalt that hardened when exposed to light—established the photoresist principle. By the 1940s, printed circuit board manufacturing had adapted these techniques for electronics. Lathrop and Nall extended the chain to semiconductors, coining the term "photolithography" at their April 1958 presentation.

The cascade followed light itself. Contact printing in the 1960s pressed masks directly against wafers, limiting resolution by the diffraction of visible light. Canon's 1970 projection aligner separated mask from wafer; their 1975 stepper achieved submicron features. The wavelength shrank through mercury lamps (436nm, 405nm, 365nm), then to excimer lasers (248nm, 193nm), each step enabling smaller transistors.

Today's extreme ultraviolet (EUV) lithography operates at 13.5 nanometers—near X-ray frequencies—using tin droplets blasted by CO2 lasers to generate light. ASML, the Dutch company that spent 30 years and $25 billion developing EUV, holds 100% of the market for these machines. Each costs over $400 million. Their High-NA systems can print transistors at 8 nanometers—features so small that quantum effects threaten their function. The technique invented to shrink proximity fuzes now enables chips with over 100 billion transistors, following Moore's Law with remarkable fidelity from millimeters to nanometers over seven decades.