the resolution limit. For advanced nodes, blur, rather than wavelength, becomes the key resolution-limiting factor. Minimum pitch is given by blur sigma/0.14. Blur is affected by dose as well as quantum yield, leading to a tradeoff with stochastic defects, in the case of EUV. Stochastic effects As light consists of photons, at low doses the image quality ultimately depends on the photon number. This affects the use of extreme ultraviolet lithography or EUVL, which is limited to the use of low doses on the order of 20 photons/nm2. This is due to fewer photons for the same energy dose for a shorter wavelength (higher energy per photon). With fewer photons making up the image, there is noise in the edge placement. The stochastic effects would become more complicated with larger pitch patterns with more diffraction orders and using more illumination source points. Light sources Historically, photolithography has used ultraviolet light from gas-discharge lamps using mercury, sometimes in combination with noble gases such as xenon. These lamps produce light across a broad spectrum with several strong peaks in the ultraviolet range. This spectrum is filtered to select a single spectral line. From the early 1960s through the mid-1980s, Hg lamps had been used in lithography for their spectral lines at 436 nm ("g-line"), 405 nm ("h-line") and 365 nm ("i-line"). However, with the semiconductor industry's need for both higher resolution (to produce denser and faster chips) and higher throughput (for lower costs), lamp-based lithography tools were no longer able to meet the industry's high-end requirements. This challenge was overcome in 1982 when excimer laser lithography was proposed and demonstrated at IBM by Kanti Jain. Excimer laser lithography machines (steppers and scanners) became the primary tools in microelectronics production, and has enabled minimum features sizes in chip manufacturing to shrink from 800 nanometers in 1990 to 7 nanometers in 2018. From an even broader scientific and technological perspective, in the 50-year history of the laser since its first demonstration in 1960, the invention and development of excimer laser lithography has been recognized as a major milestone. The commonly used deep ultraviolet excimer lasers in lithography systems are the krypton fluoride (KrF) laser at 248 nm wavelength and the argon fluoride laser (ArF) at 193 nm wavelength. The primary manufacturers of excimer laser light sources in the 1980s were Lambda Physik (now part of Coherent, Inc.) and Lumonics. Since the mid-1990s Cymer Inc.