Alignment of a sample is crucial for many use cases. Mostly Fine Alignment is used to align the sample. For samples with a die/ element layout it might also useful to use Site Alignment. Before processing a die/ element, Site Alignment will be performed for this die/ element only. The die/ element alignment is a superposition of the Fine Alignment and Site Alignment.
Fine Alignment as well as Site Alignment is based on pattern recognition. The pattern recognition needs to be taught during recipe creation by grabbing a system camera image and defining a part of the image as pattern. An image processing interface will then create a pattern from the image data. During Fine or Site Alignment, another system camera image is grabbed at the same position as the teaching position. The image recognition algorithm will detect the pattern within the image data and detect the offset to the teaching position in x/y-direction and the rotation of the pattern. This information will be passed on to each following process step.
The Area Alignment task is an independent task that has been introduced as an addition to the less flexible Fine and Site Alignment. The following points mark the greatest differences:
· As an independent task it can be placed anywhere in the task composition.
· Pattern recognition can be based on system camera images, sensor camera images, or measurement data of any sensor.
· Artificial pattern can be imported as image files.
· Several result values can be activated that will be added to the task results. It can also be used to only detect the position of a feature on a sample without using the alignment information in the following process steps.
· The optional result image that will be saved alongside the other result values clearly marks the recognized pattern area in the grabbed image data or measurement data for further investigation.
· It can be executed multiple times to increase detection quality and improve offset detection.
Setting up the Area Alignment task is a two step process. First the general task settings – camera/ sensor selection, scan settings, behavior on error - must be set. Afterwards the pattern itself must be taught. After setting up the fundamental task settings one Area Scan must be created. After the Area Scan has been defined the pattern teaching dialog can be used to teach the pattern required for pattern recognition.
Area Alignment tasks are tasks comparable to Area Scan tasks. Thereby they will appear as every other task in the Process view. They will be executed for every die/ element (if a layout is used) and the alignment will only be kept for the current die/ element. During the process, Area Alignment tasks provide preview images in the same style as that of the Fine Alignment and Site Alignment. If a pattern has been detected, it will show the header label Area Alignment found and the detected quality/ score as well as the detected pattern rotation. If the detection failed the expected absolute position is shown. If a remote interface like SECS/GEM is used, result values can also be included in the wafer result list.
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