The 90nm SRAM Photolithograph Technology Transfer And Improvement

Photolithography, also termed optical lithography or UV lithography, is a process used in micro fabrication to pattern parts of a thin film or the bulk of a substrate. It uses light to transfer a geometric pattern from a photo mask to a light-sensitive chemical "photo resist", or simply "resist," on the substrate. A series of chemical treatments then either engraves the exposure pattern into, or enables deposition of a new material in the desired pattern upon, the material underneath the photo resist.Photolithography shares some fundamental principles with photography in that the pattern in the etching resist is created by exposing it to light, either directly (without using a mask) or with a projected image using an optical mask. This procedure is comparable to a high precision version of the method used to make printed circuit boards. Subsequent stages in the process have more in common with etching than with lithographic printing. It is used because it can create extremely small patterns (down to a few tens of nanometers in size), it affords exact control over the shape and size of the objects it creates, and because it can create patterns over an entire surface cost-effectively. Its main disadvantages are that it requires a flat substrate to start with, it is not very effective at creating shapes that are not flat, and it can require extremely clean operating conditions.And to foundry, because of cost and power consumption, the CD is always need to be reduced, thus after the mass production of 0.13um,0.11um, the development of 90nm has been of paramount importance.The major contribution of this dissertation is to summarize the problems and challenges during the 90nm development and how to solve it, it would be benefit to smaller CD process development. Meanwhile, most of the layers do not need 90nm CD in 90nm process, consider of cost and capacity, most of the layers could production at DUV(248nm) and MUV(365nm), but some of the layer could not mass production at MUV or DUV, thus, the ArF(193nm) is needed for these high CD requirement layers production, and as most difficult is from ArF related layers and OVL issue, thus this dissertation will focus on ArF related layer and OVL issue discussion.