Photolithography

The production of an electronic device will often require many stages of photolithography. Photolithography is the process of defining a pattern on the surface of a device material slice. By sequentially using such patterns to define metal contacts or etched areas a complete device is gradually built up.

Pattern definition is accomplished by spinning a layer of photoresist (an ultraviolet light sensitive liquid) onto a slice of device material. The resist is then selectively exposed to ultraviolet light through a mask. In the case of a positive photoresist, where the light hits the resist the structure of the resist changes and it can then be dissolved by a developer. One speck of dust invisible to the human eye can short out the source - drain contact of a transistor, this is the reason why most device processing takes place in a cleanroom.

After one layer has been defined and etched or had contacts made to it, subsequent mask layers must be very accurately aligned to the first layer to ensure that the final device functions correctly. To accomplish this we have a Karl Suss MJB3 Mask Aligner and a Quintel Expoline 4K6 Aligner .

The MJB3 aligner operates at a wavelength of 400nm ). It can also operate at a shorter wavelength and has a better resolution of roughly 0.4 microns(1 micron = 1/10,000th of a centimetre). The UV light the aligner uses to expose photoresist is generated by a high pressure mercury arc lamp and the sophisticated optics of the aligner. The output spectrum of each aligner is shown graphically below.

 

 

Available Photoresists & Related Chemicals

All resists have the recommended developers available. Resist removal is usually carried out with acetone, or Microposit remover 1165 or an oxygen plasma in the IPC barrel etcher.