Apparent roadblock in the development of quantum lithography

May 20, 2011 by Bob Yirka report
When sending two photons through a double slit they will produce an interference pattern on a detection line after the slits. Denoting the arrival position of the photons with s and t one can plot the detection probability where lighter colour indicates higher probability. If the photons are constrained to arrive at the same place the left figure applies; if they propagate independently the right figure applies. Image credit: New J. Phys. 13 043028 doi:10.1088/1367-2630/13/4/043028

( -- Just when it began to appear that scientists had found a viable way around the problem of the blurring that occurs when using masks to create smaller and smaller silicon wafers for computer chips, a previous study on beam splitting optics showed that the new approach would not work, at least as it has thus far been proposed. A group of researchers explain why in a paper in New Journal of Physics.

Currently, the that make up are made by the process of , whereby optics are used to create an image on a piece of wafer. To create the channels that make up the , are used to prevent some of the directed towards a wafer from arriving. When the wafer is then immersed in special chemicals, the parts that were struck react differently than those that weren’t, creating the channels. The problem is in the clarity of the image produced on the other side due to the use of optic lenses to focus the photons, as some degree of blurring will always occur due to the nature of lenses. As researchers try to make smaller transistors, the blurring eventually becomes a roadblock, which is why some are looking for alternatives.

One such approach is to take advantage of the unique properties of entangled photons; those wily quantum particles that for some inexplicable reason, tend to mimic the behavior of one another, without any apparent means of communication, and at a rate faster than the speed of light. Because they are correlated, the thinking went, they’d always arrive at the same place at the same time (in this case a sensor) creating a near perfect image; so if say a mask were made, in this case a simple one with just two slits in it; it would make sense that the pair of entangled photons would interfere with one another as they tend to do, as they pass through the slit, then arrive together on the other side at exactly the same place and time, which is just what you’d need if you wanted to impact the material on the other side to create your wafer the way you intended.

Unfortunately, things haven’t worked out quite that way, because as it turns out, while you can expect a pair of entangled photons to do their thing simultaneously, you can’t rely on them to arrive at the same target, or again in this case, the same sensor, while they are doing so; which of course is a big problem if you’re trying to make a where the photons have to hit their target not only at exactly the same time, but in exactly the right place or you’ve got nothing to show for your efforts.

Even so, researchers hoped that enough photons would arrive in the same place at the same time by chance to allow for the process to work; but this meant adding in an exposure time (waiting for enough of the photons to arrive at the same place) which as it turned out rose too rapidly as the feature size requirements went up, making the process unfeasible.

While it appears the original idea for using for the development of quantum lithography won’t work, researchers aren’t giving up hope just yet; the stakes are too high. The hope now is that some other new imaginative way can be thought of to get around the problems encountered, allowing for the creation of almost unimaginably small chips.

Explore further: Researchers develop the first-ever quantum device that detects and corrects its own errors

More information: On the efficiency of quantum lithography, Christian Kothe et al 2011 New J. Phys. 13 043028 doi:10.1088/1367-2630/13/4/043028

Quantum lithography promises, in principle, unlimited feature resolution, independent of wavelength. However, in the literature, at least two different theoretical descriptions of quantum lithography exist. They differ in the extent to which they predict that the photons retain spatial correlation from generation to absorption, and although both predict the same feature size, they vastly differ in predicting how efficiently a quantum lithographic pattern can be exposed. Until recently, essentially all quantum lithography experiments have been performed in such a way that it is difficult to distinguish between the two theoretical explanations. However, last year an experiment was performed that gives different outcomes for the two theories. We comment on the experiment and show that the model that fits the data unfortunately indicates that the trade-off between resolution and efficiency in quantum lithography is very unfavourable.

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not rated yet May 20, 2011
Seems like meta-material super-lenses are more promising for delivering near term advances in lithography techniques. Intel is already test fabing 22nm chips, and have in place proof of concept for 14nm chips. As their chip fabs get better, so do the processes for creating meta-materials used in chip fabs.
not rated yet May 20, 2011
this is considerably beyond current and near future techniques such as 14nm and 22nm processes.

But i think you have a point with meta-lenses or meta-wave guides. Not all avenues are closed yet.

Speaking of which, there is an opportunity in every failure. Instead of trying to overcome the interference pattern and muscle through it, why don't they use the interference pattern to their advantage? They can easily make straight lines, using entangled electrons or photons. Why not layer those perpendicular, and design a chip around the grid? The only drawback I see is that for certain features you would need to use some traditional lithography as well for certain components, but a hybrid process like that doesn't seem so bad if no viable alternatives show up.
not rated yet May 20, 2011
Unimaginably is the wrong word here, because it's easy to envision atom scale circuits, and that's as small as you can go if it ever works.
not rated yet May 20, 2011
Unimaginably is the wrong word here, because it's easy to envision atom scale circuits, and that's as small as you can go if it ever works.

Your body does it, so why not.

Well, ok the body uses physical and chemical computation to move building materials, wastes, defenses, and energy around, usually powered by electron transport mechanisms, which work by moving hydrogen atoms or other ions around to distribute energy, as we all know, but the point is, atom scale and molecule scale machines and circuitry is clearly possible.

Think about antibodies and chemical receptors. This is a form of sensor and processor.

We just have to figure out how to do electronics or other computer technologies at these scales.

Our existing computers work by electrical current.

Cellular life works by the electrical charges of ionic compounds.
not rated yet May 20, 2011
If you could some how "reload" ions into the approapriate charged state using electric current, then you could have a non-volatile circuitry which only uses power when going from "0" to "1", or when actually communicating between different systems.

This idea is not quite the same thing as spintronic memory, and certainly not the DNA computer either, but sort of like using individual molecules as a "battery" transistor to store the charge in, representing a "1".

This would save energy because you only use like 1 electron per bit operation, and don't need a continuous current to maintain the state of the memory.

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