Specific Process Knowledge/Lithography/EBeamLithography/eLINE: Difference between revisions
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To minimize stitching errors it is important to perform WF alignment. | To minimize stitching errors it is important to perform WF alignment before writing. WF alignment should be done on either a particle or an existing feature close to the writing area. WF alignment can be done in three different ways: | ||
:1. Manual alignment by image scan to a particle or feature | :1. Manual alignment by image scan to a particle or feature | ||
:2. Automatic alignment by image scan of particle or feature | :2. Automatic alignment by image scan of a particle or feature | ||
:3. Automatic alignment by line scan of feature (preferably a cross) | :3. Automatic alignment by line scan of feature (preferably a cross) | ||
The concept is illustrated in the two drawings and relies on the high precision of the laser interferometer driven stage (about 1 nm precision). When using image scan for WF alignment the user must center the chosen feature or particle in the image field. When executing the WF alignment the stage will displace a bit less than half a WF in one direction. The beam will then deflect back by the same amount and make an image scan. If the WF is perfectly aligned the deflected image will be show the feature in the center of the image. In manual alignment mode the user will indicate any offset, in automatic mode the system will do image analysis and determine the offset. For WF alignment 3-8 different stage positions will be scanned in this way and at the end a correction is calculated and applied. | |||
WF alignment can also be done by line scanning, preferably over a cross from a previous lithography step. The procedure is the same as above except that at each position instead of making an image scan the system makes two line scans and detects each leg of the cross to calculate the center of the cross and in turn the offset of the cross. Again this is done for 3-8 different positions. | |||