Each lithographic process has always been a challenge to any available presence in the world. Each node introduces a series of errors and problems to solve that as it becomes more and more difficult, for that reason, it is very important to fix it in order to properly evaluate it.
Ion beam positioning and masks: the holy grail of problems
Current technology until the arrival of EUV was based on the process of masking of the well-known masks multiple patters to speak more often.
But this is over as it is, EUV has transformed the market, which has been waiting for this technology for almost a decade, so the approach to problems must change, as well as the methods adopted.
The first step is to change the so-called blank mask, because they provide gaps in the silicon that have to be adjusted in each membgraphic.
To get an idea, the process with EUV consists of 40 or 50 layers of silicon that come in contact with different materials between molybdenum (in some cases).
This produces in parts known as particle defects and is important, because they alter the performance of the empty layers and will affect the entire reticle structure. Less particle defects, better masking and fewer problems in recording wafer.
Diagnostic test tools to detect errors
To detect these errors and to be able to further the process of making a better mask with the complete recording, some companies work based on what's known as actinic for blank check or ABI. These complex systems use the same wavelength as the lens recording the wafers, of which EUV is a known 13.5 nm.
ABI detects serious errors in gaps, discarding chip or aggregates when the error rate is too high.
If time is found, other defects can be corrected.
The good thing about ABI technology is that it allows for error detection and as a result some of these can be remedied by different techniques, some instead of those that are not treated.
ABI is not the only system available to detect these errors, since there are less obvious methods such as diagnostic tests based on a series of light signals. The problem with these masks is that they often use 193 nm for traditional immersion systems, and therefore operate on standard errors, but are not as accurate as the ABI systems.
To improve the process, mask manufacturers develop two methods of testing: die to death and die in database.
In death to die it is necessary to put the same matrices on the same mask and then have one person die and die (hence the name, obviously). This is done by the automated system, which detects the difference between the die and the mask and notifies and tags them.
The disadvantage of this system is that this program only works on large chips, such as specific processors or GPUs and this is where the second data path comes in. The difference with mortality is that in this case the test toolkit compares die with the original format data in a database, which takes longer because the points to be compared are higher than the database. Another process
Given the lack of ABI systems, manufacturers use these two test methods until it becomes apparent that sufficient availability is being made in bulk. The only problem they present is that Optical tools cannot test EUV masks for films polysilicon, such as the one created with ASML 50 nm thick, placed on top of each mask.
The reduction of nanometers with different wavelengths, the fault finding problem
Polysilicon with a wavelength of 193 nm looks opaque, and as a result does not allow to detect chip faults. The solution has been provided by ASML recently, as it has now developed a compact, automatically mounted film for the scanners to be tested.
This is also a problem, as these types of films and masks are very scarce, which has forced Samsung and TSMC not to use them and has to clean and inspect the mask continuously on the walls, so it costs a lot of time and money.
When technology allows for greater production of sandwiches with this type of film, the cost of performing each operation will decrease, but as the industry does not stop for a moment, the problem will be raised again when it drops to 5 nm or less.
Intel, TSMC and Samsung will have to record EUV through the movie twice, but ABI can test one movie, so the second one shows the program. So also trying to anticipate this, some manufacturers are developing new test equipment called APMI in association with opics.
As we can see, sometimes technology is not ahead of market demand, which is a problem from a cost point of view. But companies are slow, they want to come first and they are willing to take some measure of error, time and money to ensure sales and above all.
The first one comes with rewards when it's done good work and for the right price, otherwise they tell AMD or Apple.
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