I suppose photo-resists are widely used because of the advanced silicon technology that has used photolithography for many years. The technology of using photoresists is also advanced. Alternatively some people use masks made from very thin metal sheets. I am not sure how the results compare - definitely each on has its pros and cons i guess.

Today the importance of photoresists cannot be overestimated, because, as mentioned by Till and Albert, they are the means to create the patterns in Semiconductor-industry.

Photoresists are the medium where patterns are created; resist exposure is the first step where a layout becomes reality, to put it dramtically. So the resolution of the resist and the exposure method sets the limit of the pattern resolution. You can not enhance (though you could deteriorate) the resolution after various ways of transferring the pattern (e.g. metal etch, liftt-off, ion implant, ...) to the substrate, in general...Yet there are refined methods like line-doubling, but that's another story :-)  

br,

Herbert

Hi, 

Photoresist is a material changing its characteristics upon exposure with light. (softening or hardening depending on the type of photoresist) That is what is stated by calling them photoresist. There are different materials like PMMA, SU8, AZ etc, all photoresists. Surely there are other ways of making a mask as mentioned in other answers above, but as long as in Lithography we need a material which is affected by light exposure and accordingly shaped; photoresists will be indispensable. 

I hope that answers at least a part of your question. 

Kind regards,

Maria

Photo resist materials are polymer materials whose properties change when exposed to light. In the case of a positive photoresist, when exposed to light, their polymer chains break and it is softened and during development they are removed. In a negative photoresist, the exposed regions are hardened. These materials are widely used in seminconductor and photonic industries. What makes them special is their resolution and sensitivity. One can reach a resolution of tens of nanometers and a high sensitivity. Hence it is used for fabrication of binary and analog diffractive optical elements, waveguide structures, grating couplers, lenses, micro refractive optical elements etc. at research level as well as in industry.

Chromium masks are used generally for photolithography. In the case of electron beam lithography and focused ion beam lithography, no mask is required. The beam is focused to nanometer size and scanned across the polymer in a specific pattern by blanking and unblanking the beam.

The importance of photoresist materials is that they provide a simple, relatively inexpensive means of creating a two-dimensional pattern in a substrate material.  The "photo" root word refers to the fact that the material is sensitive to light; as described above, one can exploit this characteristic to create patterns by selectively exposing the material to light, and then removing the material exposed (or not exposed, in the case of negative resists) by dissolution in developing chemicals.  The "resist" root word is just as important.  The nature of photoresists are that they are very non-reactive materials when developed (and in some cases "hardened" by UV and heat exposure), so that the chemistry used to transfer the photoresist pattern into the underlying material (called the "etchant", or "etch process" can do that while not significantly eroding the photoresist process.  For special cases where the photoresist will not stand up to the chemistry, or in some special cases such as ion implantation masking, a "hard mask" is used (like silicon oxide), but thisSiO2 pattern needs to be created first through a photoresist process.

A lot of talk about microelectronics use, but another application is glass etching - same process, photo-image a pattern and etch with acids.

Hope this helps. 

Photoresist is important for building layered structures requiring a post-pattern etch.  Semiconductor lithography employs this "pattern and etch" approach, which has been the backbone of technology for over 50 years.  Today, with the advent of permanent photopatterning films, and additive manufacturing, there is a desire to move away from pattern and etch processing, as it is becoming prohibitively expensive, when compared to processes which supported Moore's Law. 

Instead of using Mask, having a sacrificial metal and then using focused ion beam milling is more precise.

http://iopscience.iop.org/article/10.1088/0957-4484/27/36/36LT01

Using FIB, it was awfully slow because the current used needs to be less. If current is high, then the device damage is high. But a very high currents/dose can be used with MAFIB and this will make the fabrication very very fast with good precision. Using resists, not all the structures are possible to fabricate. Can you fabricate grooves of any angle? you cannot, as the resist based etching is dependent on crystallinity. Also, using resist based etching, can you go to structural dimensions with high aspect ratio?Not possible. If the time is the  only issue, then MAFIB is way too faster then EBL or conventional FIB.

--

Akash

The historical significance of photoresists are that they made possible the microminiaturization of electrical components which, at the time, comprised very large computing devices such as ENIAC, in the 1940's and 1950's. Once it was realized that discrete electronic components, such as vacuum tube sized gates, could be reduced in size to something only an electron microscope could detect, then the whole idea of discrete electronic device architecture could be imagined. All of this could not have been done without micropatterning available through use of photopatterning etch resists.

George, it is definitely good for micropatterning as you mentioned. However, for nano structures use of resist based/ EUV lithography is too expensive ($ 100M) in comparison with new techniques ($ 1.5-2 M).

Akash, yes, but without photoresist, you wouldn't be contemplating EUVL, or any other lithography for nano-miniaturization.  As the question is "What is the importance of photoresist materials?", I believe this is the answer.

How much time does it take to perform the following Photolithography processes.

Applying the Photoresist:

Exposing Resisit:

Developing Photoresist:

How do these processes depend on the size of the semiconductor wafer and the power of the UV radiations?

Per wafer, the three step process could take, at most, ten minutes, but usually much less. Wafer size-wise, resist application time shouldn't be significantly different, as resist spread cycle-time will increase as f(wafer diameter). Assuming step and repeat exposure, more steps, but each step mihgt range from a few tenth's of a second, to 1-2 seconds, depending on what you're printing. Resist development time, including the flood and spread cycle 1-2 minutes. All presented here is a very rough outline.

George,

Thank you for the valuable data.

No problem :-)

Also do you know how much time on average do the ion implantation and etching processes take for a 300 nm diameter wafer?

You'll need an etch guy to answer that one! Sorry!

No problem. Again thank you for your help.

:-)

I'm trying to understand why photoresist is used at all. Isn't there a mask that determines what regions are exposed and which ones aren't? Or is photoresist the same thing as the mask? (But that can't be, since photoresist is applied everywhere and then selectively removed. So why is it on there in the first place?)

Thanks

Photoresist is, in effect, the film that is exposed or unexposed during photomask-mediated photoexposure; the resist, then, acts as the etch "mask" which protects the underlying surface from being etched away, during final surface patterning.