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in the past two days, many netizens have been discussing the news about the new domestic argon fluoride lithography machine disclosed by the ministry of industry and information technology. for a time, various remarks about major breakthroughs in domestic lithography machines were flying all over the place. some people even thought that this was an 8nm lithography machine when they saw "overlay ≤8nm", which was ridiculous.

in fact, as early as june 20, the ministry of industry and information technology issued the "guidelines for the promotion and application of the first major technical equipment (2024 edition)" for public notice. in the column of integrated circuit production equipment, a krypton fluoride lithography machine and an argon fluoride lithography machine were announced. then on september 9, the ministry of industry and information technology reissued the notice:

the krypton fluoride lithography machine is actually an old-fashioned krf lithography machine with a 248nm light source, with a resolution of ≤110nm and an overlay accuracy of ≤25nm; the argon fluoride lithography machine is an arf lithography machine with a 193nm light source (also known as a duv lithography machine), but the one disclosed is still a dry duv lithography machine, rather than the more advanced immersion duv lithography machine (also known as an arfi lithography machine).

according to the parameters officially disclosed, the resolution of this duv lithography machine is ≤65nm, and the overlay accuracy is ≤8nm. although it is improved compared with the previous ssa600 lithography machine of shangwei (resolution is 90nm), it is still not enough to produce 28nm chips, let alone 8nm or 7nm chips. many netizens directly confuse the overlay accuracy with the lithography manufacturing process node level.

the accuracy of lithography mainly depends on the resolution of the lithography machine. if the resolution is 65nm, then the process node that can be achieved by a single exposure is approximately around 65nm.

overlay accuracy refers to the alignment accuracy between each photolithography layer. as we all know, the chip manufacturing process is actually to realize and stack many layers of photolithography patterns layer by layer. after one layer of pattern lithography is completed, it is necessary to continue the lithography of the next layer of pattern on it, and the two layers need to be accurately aligned. the accuracy of this alignment is the overlay accuracy, which does not refer to the process node of the chip that can be manufactured.

so, how many nanometer processes can this 65nm lithography resolution and overlay accuracy ≤8nm achieve? and what level of lithography machine does it correspond to at present? you can compare the parameters of asml lithography machine below:

the twinscan xt:1460k shipped by asml in the second quarter of 2015 has a lithography resolution of ≤65nm, but a higher overlay accuracy (<5nm). although the resolution of this domestic duv lithography machine is also ≤65nm, and it can produce 65nm process or even more advanced chips, the overlay accuracy error of this domestic lithography machine is larger, which will also lead to a relatively lower yield level.

in other words, the performance of the domestic duv lithography machine is even lower than the xt:1460k lithography machine shipped by asml nine years ago. if we look back further, the resolution of the dry duv lithography machine xt:1450 launched by asml in 2006 has reached 57nm, and the overlay accuracy is 7nm. the performance of the domestic duv lithography machine is more than 18 years behind asml's technology.

although the 65nm lithography resolution uses multiple exposures and may be able to achieve more advanced process nodes, it will be limited by the error superposition and amplification caused by the overlay accuracy.

according to an internal expert from a major lithography company who revealed to xinzhixun, a 65nm resolution arf lithography machine, combined with a good opc (optical proximity correction) algorithm, can be advanced to a 55nm process.

"the control window of overlay (overlay accuracy) of a single exposure is 1/4 to 1/5 of the line width, so a chip with a line width of 55nm requires at least 11nm overlay to be manufactured. although the overlay accuracy of the lithography machine is ≤8nm, this is only the factory standard. various processes in the wafer processing process will also bring errors, so the overlay of the entire chip manufacturing will be lower than the factory standard. therefore, the overlay accuracy of 8nm may actually fall on about 11-12nm on the product. therefore, the maximum level of a single exposure can reach is 55-65nm."

"if multiple exposures are used, such as double exposure, the required overlay will be cut in half. so for the existing single exposure level of 55nm, if double exposure is to be done, at least 55÷5÷2=5.5nm of overlay is required. the quadruple exposure overlay will be cut in half again, which means 2.75nm of overlay is required. therefore, it is impossible to do multiple exposures with an 8nm overlay." the lithography technology expert further explained to xinzhixun.

so, in summary, if you want to do multiple exposures, the overlay accuracy needs to be high enough. in other words, the overlay error needs to be small enough.

for example, the industry's earliest mass production of 28nm process basically used the advanced asml nxt: 1970 (immersion duv), which has a higher resolution of ≤38nm and an overlay accuracy of <3.5nm.

since the domestic 28nm process was mass-produced relatively late, the more advanced asml nxt:1980 was used for 28nm mass production. although its resolution is still ≤38nm, the overlay accuracy has been further improved to <2.5nm, which also enables wafer manufacturers to perform multiple exposures through this model and realize the manufacturing of 7nm process. for example, tsmc's first-generation 7nm process was made by multiple exposures using asml nxt:1980. of course, multiple exposures will greatly increase costs.

this is also why the united states and the netherlands initially limited the export of lithography machines to china to nxt:1980 and above, and later restricted the export of nxt:1970 and nxt:1980 lithography machines that use multiple exposures to achieve advanced process capabilities to mainland wafer fabs with advanced process capabilities.

in summary, the 65nm resolution domestic duv lithography machine exposed this time should be just an improved version of the previous 90nm resolution domestic lithography machine, and can only be used for the manufacturing needs of 55-65nm mature process chips, and is far from meeting the requirements of manufacturing 28nm process chips that everyone expects. of course, compared with the most advanced 90nm resolution domestic lithography machine before, the new 65nm resolution domestic lithography machine has at least made some progress. however, we still need to be soberly aware of the gap between us and the advanced level of foreign countries, and we should not be blindly optimistic.

for domestic lithography machine manufacturers, there are still many technical problems to be solved in the process of switching from dry duv to immersion duv. it should be noted that around the 2010s, asml relied on immersion duv lithography machines (it launched the first mass-produced immersion duv lithography machine xt:1700i in 2006) to defeat the two lithography machine giants canon and nikon at the time and established its dominant position.

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