what is photolithography?

Answer 1

Photolithography or optical lithography is a process used in semiconductor device fabrication to transfer a pattern from a photomask (also called reticle) to the surface of a substrate.

Answer 2

Photolithography is a term used mostly to describe a process used in semiconductor fabrication and other related processes. In today’s semi technology there are usually more than 20 photolithography steps, one for each layer of the device, required to fabricate a device. My description will deal with mainstream photolithography and CMOS devices that are slightly less than leading/bleeding-edge, but most commonly used in industry and academia.

First, the device (circuit) layer is drawn with the aid of a CAD system. This information is then transferred to a mask/reticle fabricator. It is called a mask if the results of the drawn device will be at 1X size. If the mask will go into a reduction stepper, it will be called a reticle. The output of the mask/reticle fabricator will be something analogous to a photographic negative. The difference being that the substrate is quartz glass and the image is typically etched in chrome.

Next, the device substrate, typically a silicon base, is coated with a thin coat of photoresist. This is protective coat of a material that may be though of as a thin paint or plastic. (Note: since negative resists are less often used and will complicate this description, I will deal with only positive acting resist.) The material is then dried by baking at an elevated temperature somewhere in the range of boiling water. Ultraviolet light is then used to illuminate the mask/reticle. The open areas (patterned) of chrome allow the light to get through and expose the selected areas of photoresist.

Next is the develop process. Exposed areas of positive photoresist become more soluble than unexposed areas in the photoresist developer. Think of developer as a selective etchant. The developer is then rinsed, dried and dehydrated and hardened by baking. At the end of this step there are selected open area and protected areas on the surface.

The next step maybe an etch step. This explains the next step after completion of the photolithography, but provides justification for the photolithography process. So now visualize the selected open areas are in contact with the etchant while the photoresist (resist) covered areas are protected from the chemical reactions. After the eching is complete, there are device patterns remaining on the wafer. As an example, a metal conductor (wire like) may remain on the surface and will be used to conduct current to desired locations.

The cost of photolithography in a CMOS process is about 45% of the overall cost. A single reticle may cost from >$3,000 to >$20,000. However, reticles are reused and have a long life expectancy.

Answer 3

Material to be printed was once etched into stone (litho - graphy, or writing on stone) which was then inked and paper pressed on the stone to result in a printed sheet. This could be used for printing, or for doing pictures.
Photo lithography is a technique which uses light to etch the picture on the lithograph stone.
Instead of actually cutting into the stone, as they used to do originally, the stone is now coated with a light sensitive material, and the light is projected onto it, through a negative image. It's a fascinating process.

Answer 4

photolithography - a planographic printing process using plates made from a photographic image