The Scaling Cliff-Hanger
Moore’s Law has always been a cliff-hanger. Even Gordon Moore says he has never been able to see more than two generations ahead.
Two generations ahead from today’s 32nm/28nm generation is 16nm and immersion lithography, today’s mainstream lithography tool, may not be up to the task.
The most likely tool to perform that task is EUV, and ASML is scheduled to ship its first production EUV machine next year.
The machine is rated to achieve a throughput of 125 wafers per hour.
But the prototype EUV machine currently installed at Imec is achieving a throughput of six wafers per hour.
The target rate for the Imec machine was 60 wph. The reason why it’s performing so poorly is, says Imec, because of the dim light source.
The dimmer the light source, the longer wafers have to be exposed and, consequently, the lower the throughput.
The two providers of light sources to ASML are Cymer of San Diego and Xtreme Technologies of Aachen which is owned by the Japanese company Ushio.
Cymer’s technology is called ‘laser-produced-plasma.’
According to IEEE Spectrum, it uses a carbon dioxide laser to ‘vaporise speeding droplets of molten tin. As the resulting plasma cools, excited tin electrons relax back to lower-energy orbits, emitting EUV light that is steered through the machine and eventually used to cast patterns on a wafer’.
Cymer is looking to boost the power to ‘by shooting another laser at the tin droplet before the main laser hits it’.
This ‘pre-pulse’ will heat the tin, causing it to expand and allowing the second laser pulse to penetrate further into the droplet, creating more plasma.
Cymer says this technique will increase the power which it puts into a EUV’s optical system from 11W to 80W by the end of this year boosting throughput nearer to 60 wph.
Xtreme says it expects to be able, by the end of this year, to boost the power which it puts into EUV machines optical systems to 100W – and that this will deliver sufficient brightness to permit 60 wafer-per-hour processing.
But immersion lithography is currently delivering about 140 wph and the semiconductor manufacturers won’t want to settle for anything much slower.
Time is getting short, and he difference between 6 wph and 120 wph is huge.
If Moore’s Law scaling is to suffer a blip, then it will become all the more important to find another way to reduce die cost.
And the most likely way to do that is 450mm.Tags: cliff hanger, lithography tool, molten tin, two generations, wafers