As he puts it, “The world’s largest chip maker is turning to EUV lithography to maintain the lead in the semiconductor industry, as it faces an uphill battle in developing chips with finer pitch than those the company can etch with today’s mainstream ArF-based immersion lithography technology.
EUV lithography technology is expected to become a next-generation of photo lithography, as the extreme ultraviolet light source features wavelength shorter than today’s immersion technology.
The width of the circuitry pitch is in proportion to the wavelength of the light source. The shorter the wavelength is, the finer the circuitry pitch gets. EUV boasts of a wavelength of 13.5nm. As with the case, it has been thought of as the most feasible one for drawing patterns of below 10nm node.
Yet, it has a trade-off. As the EUV light is less dense in the amount of photons than ArF, its drawn line edge tends to get blurred, compromising the line sharpness of the circuitry pitch. The blurred lines stand higher chances to cause errors, risking sacrificing productivity, or yield –the ratio of sellable chips versus total production.
The less amounts of photons also translate into the requirement for lengthier exposure time to the EUV light for chip circuitry patterning , as it tends to disperse photons. To compensate for it, there is a dire need for PR, or photoresist materials of stronger surface tension. Samsung assumes that PR of at least 60mJ㎠ in the surface tension can compensate for the light dispersion phenomenon. An alternative solution, metal components-ingrained PR materials are now in development, it also has cons, as it stands a chance to pollute an optical lens.
Generally speaking, the formula for attaining finer circuitry pitches is to enhance the resolution of the patterned lines. The resolution goes up in disproportion to the wavelength of a light source. The higher the resolution goes, the shorter the wavelength gets. It also disproportionally depends on the numerical aperture of the optical lens, as the higher it goes up, the shorter the NA gets.
To forgo EUV in its effort to attain 20nm and below circuitry pattern, the chip making industry has been using ArF immersion photolithography technology that shortened the wavelength of ArF by having it filter through layers of liquid. Either, it narrows the NA of the optical lens. Double and quadruple pattering technology was also put to the use as it allows chip makers to draw another pattern in between patterns two times or four times to finally attain the fine pitch than otherwise.
Yet, all these technologies have pros and cons. The drawback is that as they require two times and four times more of photo mask processes, it takes a longer while to complete the lithography processes from the start to the finish, compromising Samsung’s chip-making productivity.
Samsung Electronics is working overnight on both of the technologies –EUV and quadruple pattering – to attain 10nm and below circuitry. “We have no alternative to straddle the fence on both technologies, “ said director Kim Hyun-woo.