I get it that lasers with a lower wave length are stronger, but how do strong lasers help one cut smaller circuit?
In: Physics
Well, they don’t actually “cut circuits”. The lasers are shined through a mask to expose photoresist, a chemical that is sensitive to light. But that’s not the point here.
And it’s not a matter of the “strength” of the light. If you wanted more “strength”, you could use a brighter laser.
The issue is that light is a wave (and a particle, but let’s not get into that). A wave with a shorter wavelength can be used to make smaller features. As an analogy, imagine you were trying to create an image by throwing balls very accurately at something. Which would allow you to make finer features, basketballs or BBs? The smaller the thing you are using is, the finer you can make the features you want.
With ICs the situation is made even more complex by a couple of factors. One is that the wavelength of the laser light typically used is much much larger than the size of the features that we’re trying to etch. (Which should be impossible to do.) The other is that because light is a wave, it will cause interference patterns to be created.
This is dealt with a few ways, the primary one being “phase constrast masks”. The patterns made on the mask that you shine the light through to expose the photoresist on the wafer is not the same as the pattern you want to create on the wafer. It’s actually a fairly different, fuzzy looking pattern that has been calculated to interact with the light’s interference pattern in such a way that you get what you want at the end. It’s very difficult, but it allows us to do something that would otherwise be physically impossible…image things smaller than the wavelength of the light used.
Can someone explain these answers AND the question like I’m five too?
Imagine drawing a picture with a very fine point pencil vs a big fat marker. The pencil can draw much thinner lines than the marker.
For more details (not ELI5 but still simplified) consider the equation for the smallest detail (“critical dimension”) that can be drawn. This is some factor (a constant) times (wavelength / aperture). So to draw something smaller, you either decrease the wavelength (numerator) or increase the aperture (denominator). Increased aperture means you “tighten the beam” so you draw a finer point.
The lower wave length is physically smaller. This gives it more precision on what it can cut. Its like the difference between digging with a shovel and an excavator.
This is due to diffraction.
A diffraction pattern will form always when light hits an edge.
Smaller wavelength light experiences less diffraction.
For example if you put laser through a small hole (90 micrometer) you get pattern like this https://en.wikipedia.org/wiki/File:Laser_Interference.JPG
Smaller wavelength means the hole (or wahtever feature) can be smaller before this pattern becomes problem.
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