It seems I can’t go a month without seeing at least one article decrying the end of Moore’s Law and another which shows that it’s still on track. Ultimately this dichotomy comes from the fact that we’re on the bleeding edge of material sciences with new research being published often. At the same time however I’m always sceptical of those saying that Moore’s Law is coming to an end as we’ve heard it several times before and, every single time, those limitations have been overcome. Indeed it seems that one technology even I had written off, Extreme Ultraviolet Lithography, may soon be viable.
Our current process for creating computing chips relies on the photolithography process, essentially a light that etches the transistor pattern onto the silicon. In order to create smaller and smaller transistors we’ve had to use increasingly shorter wavelengths of light. Right now we use deep ultraviolet light at the 193nm wavelength which has been sufficient for etching features all the way down to 10nm level. As I wrote last year with current technology this is about the limit as even workarounds like double-patterning only get us so far, due to their expensive nature. EUV on the other hand works with light at 13.5nm, allowing for much finer details to be etched although there’s been some significant drawbacks which have prevented its use in at-scale manufacturing.
For starters producing the required wattage of light at that wavelength is incredibly difficult. The required power to etch features onto silicon with EUV is around 250W, a low power figure to be sure, however due to nearly everything (including air) absorbing EUV the initial power level is far beyond that. Indeed even in the most advanced machines only around 2% of the total power generated actually ends up on the chip. This is what has led ASML to develop the exotic machine you see above in which both the silicon substrate and the EUV light source work in total vacuum. This set up is capable of delivering 200W which is getting really close to the required threshold, but still requires some additional engineering before it can be utilized for manufacturing.
However progress like this significantly changes the view many had on EUV and its potential for extending silicon’s life. Even last year when I was doing my research into it there weren’t many who were confident EUV would be able to deliver, given its limitations. However with ASML projecting that they’ll be able to deliver manufacturing capability in 2018 it’s suddenly looking a lot more feasible. Of course this doesn’t negate the other pressing issues like the interconnect widths bumping up against physical limitations but that’s not a specific problem to EUV.
The race is on to determine what the next generation of computing chips will look like and there are many viable contenders. In all honesty it surprised me to learn that EUV was becoming such a viable candidate as, given its numerous issues, I felt that no one would bother investing in the idea. It seems I was dead wrong as ASML has shown that it’s not only viable but could be used in anger in a very short time. The next few node steps are going to be very interesting as they’ll set the tempo for technological progress for decades to come.
For as long as we’ve been using semiconductors there’s been one material that’s held the crown: silicon. Being one of the most abundant elements on Earth its semiconductor properties made it perfectly suited to mass manufacture and nearly all of the world’s electronics contain a silicon brain within them. Silicon isn’t the only material capable of performing this function, indeed there’s a whole smorgasbord of other semiconductors that are used for specific applications, however the amount of research poured into silicon means few of them are as mature as it is. However with our manufacturing processes shrinking we’re fast approaching the limit of what silicon, in its current form, is capable of and that may pave the way for a new contender for the semiconductor crown.
The road to the current 14nm manufacturing process has been a bumpy one, as the heavily delayed release of Intel’s Broadwell can attest to. Mostly this was due to the low yields that Intel was getting with the process, which is typical for die shrinks, however solving the issue proved to be more difficult than they had originally thought. This is likely due to the challenges Intel faced with making their FinFET technology work at the smaller scale as they had only just introduced it in the previous 22nm generation of CPUs. This process will likely still work down at the 10nm level (as Samsung has just proven today) but beyond that there’s going to need to be a fundamental shift in order for the die shrinks to continue.
For this Intel has alluded to new materials which, keen observers have pointed out, won’t be silicon.
The type of material that’s a likely candidate to replace silicon is something called Indium Gallium Arsenide (InGaAs). They’ve long been used in photodetectors and high frequency applications like microwave and millimeter wave applications. Transistors made from this substrate are called High-Electron Mobility Transistors which, in simpler terms, means that they can be made smaller, switch faster and more packed into a certain size. Whilst the foundries might not yet be able to create these kinds of transistors at scale the fact that they’ve been manufactured at some scale for decades now makes them a viable alternative rather than some of the other, more exotic materials.
There is potential for silicon to hang around for another die shrink or two if Extreme Ultraviolet (EUV) lithography takes off however that method has been plagued with developmental issues for some time now. The change between UV lithography and EUV isn’t a trivial one as EUV can’t be made into a laser and needs mirrors to be directed since most materials will simply absorb the EUV light. Couple that with the rather large difficulty in generating EUV light in the first place (it’s rather inefficient) and it makes looking at new substrates much more appealing. Still if TSMC, Intel or Samsung can figure it out then there’d be a bit more headroom for silicon, although maybe not enough to offset the investment cost.
Whatever direction the semiconductor industry takes one thing is very clear: they all have plans that extend far beyond the current short term to ensure that we can keep up the rapid pace of technological development that we’ve enjoyed for the past half century. I can’t tell you how many times I’ve heard others scream that the next die shrink would be our last, only to see some incredibly innovative solutions to come out soon after. The transition to InGaAs or EUV shows that we’re prepared for at least the next decade and I’m sure before we hit the limit of that tech we’ll be seeing the next novel innovation that will continue to power us forward.