Electron Projection Lithography (EPL): Technology Too Slow?
Low throughput may be the key deterrent
According to spectrum.ieee.org, throughput is the most important factor that will determine whether or not electron projection lithography (EPL) will be the technology of choice when the semiconductor industry abandons today`s optical tools. The moves to a next-generation lithography capable of resolving IC features as small as 45nm, is expected in 2009.
Throughput refers to the number of wafers that a lithographic tool can process in an hour – it determines how fast a semiconductor maker can build ICs. But EPL`s throughput is low and the likelihood is that it will be unable to achieve the dominant position once expected of it. At most, it is expected to process 30 wafers per hour. It is believed that to meet the needs of the industry, throughput should be in the range of 50-80 wafers per hour.
EPL works by passing a beam of electrons through a mask containing holes that define the circuit pattern for one layer of the IC. But since charged electrons repel each other and limit the strength of the beam and slow down the process. Another factor that limits throughput is that the diameter of the electron beam is slightly larger than a millimeter. To expose a typical chip, the wafer, which can be as large as 300mm, must be shifted many times. This again adds a good deal of time to the process.
However, the EPL`s large depth of focus is still seen as a strong advantage in printing transistor contacts.
