Using Light to Make Processors with Features Smaller than It's Wavelength?

[peter.ell]

I've been reading up on photolithography trying to understand how processors with sub-wavelength features can be made through photolithography, but I just don't get it.

Can someone please help me by explaining in a conceptual way how light with a wavelength of, say, 200nm can be used to make a processor with 65nm features? Even with a large lens used to focus the light, you still can't make a point smaller than the wavelength of the light being focused, right?

Thank you so much!

Also, what is meant by numerical aperture in regards to a lens? Wikipedia didn't help me understand this.

 

[Andy Resnick]

The photolithography guys use a lot of tricks- using a phase mask (as opposed to intensity masks) is one technology, near-field contact mode is another. There are more exotic technologies under development. The mechanisms by which these technologies work are quite complex.

Loosely speaking, numerical aperture is a relationship between the focal length and diameter of a lens. Recall that diffraction occurs as a result of limiting the spatial extent of a wavefront. Collecting more of the wavefront (by increasing the diameter of the lens) means that diffraction effects are reduced, leading to a smaller spot size.

 

[JeffKoch]

Basically, use a big lens, plus some other tricks, for projection lithography. There is nothing limiting a focal spot size to the dimension of a wavelength, though in practice it becomes increasingly challenging to do this.

 

[chrisbaird]

When you go to sizes smaller then a light beam's wavelength, the electromagnetic fields of the light do not just disappear and become unusable. Rather, at sub-wavelength sizes, our neat intuitive picture of light being a bundle of rays traveling in straight lines and bouncing off things like billiard balls breaks down. For example, the air molecules in the sky are sub-wavelength to most of sunlight's spectrum, yet we have no problem seeing the blue sky. All that is required at sub-wavelength sizes is to return to full-wave electromagnetic solutions to Maxwell's equations and avoid assumptions or mental constructs from the world of optics (easy to do in principle, hard to do practice). When you go sub-wavelength, you have to really know what the electromagnetic fields are doing (typically using numerical em codes), and not just ray-trace.

 

[sardar]

I can understand your confusion about how light with a larger wavelength can be used to create smaller features on a processor. Let me try to explain it in a simple way.

Firstly, it is important to understand that the wavelength of light used in photolithography is not the limiting factor for creating smaller features on a processor. Instead, it is the resolution of the lithography system that determines the size of the features.

In photolithography, a pattern is created on a mask, which is then transferred onto a photosensitive material on the surface of the processor. This pattern is created using a process called photoresist, where light is used to expose specific areas of the photosensitive material. The exposed areas then undergo a chemical reaction, making them either soluble or insoluble, depending on the type of photoresist used.

Now, coming to your question about how light with a wavelength of 200nm can be used to create features with 65nm size, it is important to note that the resolution of a lithography system is not limited by the wavelength of light, but by the numerical aperture of the lens used to focus the light.

Numerical aperture is a measure of how much light can be collected and focused by a lens. It is determined by the refractive index of the material through which the light is passing and the angle at which the light enters the lens. A higher numerical aperture means a greater ability to focus light and thus, a higher resolution.

In photolithography, the numerical aperture of the lens is increased by using specialized lenses and techniques such as immersion lithography, where the lens is placed in a liquid with a higher refractive index than air. This allows for a higher resolution and smaller features to be created.

In summary, the key to creating smaller features on a processor is not the wavelength of light, but the resolution of the lithography system, which can be improved by increasing the numerical aperture of the lens. I hope this explanation helps to clarify your doubts.