circuit-designintegrated-circuit
How are the lenses and other apparatus required for projecting a miniaturized version of the circuit using photo lithographic technique for IC manfuacture made?
Its known that even the tiniest spec of dust can ruin an entire chip so do you make sure the lens is perfectly clean and devoid of any distortions or scratches that may ruin the projection?
There are multiple steps but the basic process is that you use a photoresist.
At the beginning of a process step, a photoresist is "spun" on to the wafer. It is a very literal thing, they spin the wafer while dripping the polymer onto the surface which spreads out into a thin layer of precise thickness. This is cured and then placed into a photolitographic machine, which projects an image onto the wafer that leaves latent images in the Photoresist (AKA PR).
The PR is developed (some resists are negative and some are positive, which means the exposed areas stay or the exposed areas are eliminated). the development process removes the parts of the PR that are to be removed leaving behind the desired pattern.
The PR can define areas that are etched (removed) or windows through which ions are implanted. Implanting is the process through which the Si is doped.
Once the area is implanted, the remaining PR is removed and the wafer is thermally treated to anneal the implant damage.
In between litho steps are depositions, growths, etches, wet baths, plasma treatments etc.
The first thing to realize is that the first integrated circuit was not a very complicated circuit. It maybe had one or two transistors, a few resistors, and a capacitor or two.
My evidence is a photo of the first IC at Wikipedia:
You can see there's only 4 or so contacts to the circuit. Kilby's 1959 patent also indicates this level of complexity, although several different "realizations" are shown and its not clear which of these was actually made first.
And using the microscope slide that the chip is mounted on for scale, you can estimate that the size of the components is likely in the millimeter scale, not the submicron scale of current ICs.
The patent does give some information on how the circuit was made:
This shows that the diffusion was done uniformly over the whole wafer. The Kilby patent also refers to a Bell System Technical Journal article from 1959 that gives more details on how individual transistors were fabricated at that time. Kilby would have done his diffusion steps using a reactor designed for manufacturing individual transistors.
Different devices were isolated from each other by etching through the diffusion layer. Given the scale of the devices, the photolithography steps to define the etched shapes could probably have been done with ordinary photographic equipment.
Best Answer
Actually, for the most part dust on the lens surface won't produce intolerable results at the wafer. At the lens surface the image being projected is not in focus, so a dust particle will not produce an image of the particle at the wafer.
The everyday example of this used to be called the "screen door effect", although don't bother to Google it - the meaning of the term has changed. It used to refer to the fact that a screen door can be optically opaque from a distance, but transparent up close. Put your nose up against a screen door and you can't see the screen pattern.
What you do see is a slight blurriness. This means that cleanliness is, as the saying goes, next to godliness, particularly in clean rooms. So a resist projector will undergo scrupulous cleaning before it is installed - it's just that a single speck on the lens surface is unlikely to cause significant issues.