Lithography is a method of printing. A lithography system is one that utilizes mechanical and thermal effects to print onto a film. In the semiconductor industry, these systems can be used to print onto microchips in a form of microlithography or nanolithography. The print is placed into a film called a resist so that it can then be later etched onto the substrate. Though each lithography system is constructed differently and uses different techniques to create the pattern, they all require some type of lens to guide the source of the lithography.
There are several different lithography systems which can be used for nanolithography. These include, but are not limited to, interference lithography, x-ray lithography, nanoimprint lithography, scanning probe lithography, photolithography and electron beam lithography. The last two of these techniques are the most widely accepted ones being used currently in the semiconductor industry. These systems are rather large, complex machines that require an exact temperature at all times so that overheating does not occur.
Photolithography systems are used to remove individual parts of a thin film or substrate. The system transfers a pattern from a photo mask to a photo resist using light, as the name would suggest. Chemicals are then used to etch the pattern in, beneath the photoresist. To prepare for this process, the wafer must be heated in order to remove the excess moisture from the wafer's surface. A photoresist is then applied through spin coating. Once it is reheated, driving away any lingering solvent, the resist is then exposed to the light pattern. This exposes the basic pattern to the resist and then allows it to be etched on using a chemical agent. The photoresist can then be removed with the use of a resist stripper. The printing systems used for this process require a mask that lets in some light while keeping out other rays, creating a specific pattern. This type of mask lithography is most commonly used in industries.
Electron-beam lithography uses a similar system as photolithography, but without a mask and utilizes a different form of energy to create the pattern. This lithography system uses a source of electrons called a field electron emissions. The lens can be either electrostatic or magnetic, and the stage for this system must be very accurate in order for pattern overlay. This process does not need a mask, so it has the advantage of being able to generate the pattern from a computer. It is at a disadvantage to photolithography, however, because it is a great deal slower.
Lithography systems are used in numerous industries, as well as for a plethora of purposes. It can even be used to make art, apart from printing onto wafers and substrates. The photoresist allows for the pattern to be placed on without disrupting the substrate. These systems take substrates and imprint a pattern onto them, some with masks, some without them. The process allows important patterns to be made effectively and inexpensively. If controlled meticulously for heat and mechanics, lithography is important for the semiconductor industry.