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Technology Stocks : General Lithography -- Ignore unavailable to you. Want to Upgrade?

To: Artslaw who wrote (1265)	8/9/2001 9:07:36 PM
From: Andrew Vance	Read Replies (2) \| Respond to of 1305

While this may be part of the patent, the portion we are referring to is in the abstract. A mask or reticle for a single large microcircuit device is imaged in portions by an axially centered photolithographic reduction lens having a movable mask stage in addition to a movable wafer stage so that the portions of the complete device are imaged in juxtaposed registry on the wafer. This allows a single microcircuit device larger than the image field of the reduction lens to be imaged in a scanning mode or in a succession of steps forming images at the desired resolution range of 0.1-0.50 um. The above two sentences are exactly what a "step and scan" system is designed to do. Otherwise you just have a stepper. The image to be transferred from the reticle is bigger than the lens field, so when the exposure takes place, the wafer is stepped under the reticle field and then both the reticle and the wafer stage move, much like the precursor to the steppers did (projection aligners), thereby exposing a bigger reticle field. Just to recap the history of lithography: 1. Contact Print - Mask and wafer come into contact with each other and a blanket exposure takes place. The process of coming in and out of contact (mask and wafer during the registration and exposure process) created many defects on both the wafer and the mask. the entire wafer is exposed all at once. 2. Proximity Print - same as above but the mask is slightly offset from the wafer, reducing the damage done by the full contat process. 3. Projection Alignment - the mask and the wafer are separated by a complex lens systems and are on a movable carriage with the system. The mask and wafer move across the carriage, whereby they pass over a crescent light "slit" that essentailly creates a scan of the wafer and the mask across a light source. Everyone of the situations above used a mask that had multiple die on the mask. the number of die on the mask were transferred across to the wafer. Repeatability, precise, overlay, etc. are all impacted based on the precision manufacturing of the mask, which went through a process, much like wafers, to be created. There was a great deal of variability across the mask as device geometries shrank. 4. Steppers - these were step and repeat systems, with most of the equipment based on a single die on a reticle that was nearly perfect and was resuced through the optics of the stepper and exposed one die at a time across the wafer. One perfect die "stepped" hundreds of times across the wafer, requiring individual stepping and registration aligning each time the wafer stage moved under the fixed reticle. Of course, there were a few companies, with UTEK being to only remianing one, that had multiple die and multiple layers on one reticle. 5. Step and Scan (this is the patent we were talking about) - basically this combines the functions of a stepper, with that of the scanning projection aligner. Both the reticle and the wafer move, like in the projection aligner. As we stated, the wafer is stepped under the reticle for registration and alignment (through alignment marks). Once that is accomplished and the part of the die field is lined up (which makes all of the die field properly registered), the wafer and the reticle are scanned across the light source.