Lithography Systems Overview

Wafer handling is the process of transporting a wafer and keeping it safe throughout construction of the semiconductor. The wafer is placed into a wafer carrier, an environment that is kept immaculately clean so to avoid defects. This is where the wafer stays for a majority of the time, whether during processing or packaging. It is very important to keep the wafer protected, as it is the keystone for the entire semiconductor device.

There are several types of containers that can be used for wafer handling. Carriers, made for the purpose of keeping wafers pure and sterile, must be made to a precise specifications. An absolute must is walls with openings that allow solutions to move through in an even way while allowing in minimal detrimental particles. For this reason, they must also be resistant to chemicals. There is also the need to hold a variety of different quantities and sizes of wafer. Carriers must be specifically designed to meet the specifications and requirements of different wafers.

Canisters are also an essential part of wafer handling and protection. They are designed in order to transport wafers safely from one location to another and keeps out harmful and deleterious defects. That being said, it must also be easy to be able to remove the wafer from the container as well, so lids that can be tightly attached but easily removable are essential. There are other requirements for an ideal wafer canister, but, much like wafer carriers, must be designed to fit the specifications of a variety of different wafers, typically ranging from 150mm diameter to 300mm diameter. With the responsibility of keeping the wafer safe, wafer canisters are very important for wafer handling and making sure damage does not occur in the process of semiconductor manufacturing.

For the process of transferring the wafer once outside of its container, wafer handling can lose its complexity. Because they are so small, wafers must be transferred with tiny instruments. Though robots have been created for the purpose of this, the more common ways of wafer transferring are much more low tech. For the first method, a handler uses a pair of tweezers to transport the wafer from one container to another. The wafer must be grasped at its edge to prevent damage or defects to the whole body of the wafer. Another method is to simply take two containers and flip the wafer into the empty one by connecting the openings. These techniques must be carried out in a clean and sterile environment as all wafer handling techniques must be. Though the equipment involved is not often as high tech as most equipment in the semiconductor industry, handling the wafer during transport can be easily done and allow the wafer to make it from place to place unharmed.

Wafer handling has several different aspects to it. No matter what method or for what purpose of handling the wafer, they all must have a few things in common: they should be carried out in a sterile environment, whether in a clean room or the container holding the wafer itself, and they should be done precisely. Even if exact specifications are not made, it is still important to handle the wafer with the utmost of care. Wafer handling, though it does not build upon the semiconductor directly, protects the wafer throughout manufacturing, which makes sure it can function once apart of the device.

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.