Resolutions

All our various imagers have different resolutions that they can be switched into and depending on the work type and which imager is chosen, this can give different results in the final pattern. The choosing of the correct resolution is very important to the outcome of the pattern and should not only be considered on the “smallest feature possible” but should include other factors. There is no ‘rule’ for choosing resolutions on a mask because each customer and sometimes each project has a different set of criteria and requirements.

The resolution chosen generally affects 3 main factors:

  • Accuracy of the feature sizes
  • Accuracy dimensionally across the whole pattern
  • Sharpness of corners, apex points

For every increase in resolution, edges of lines become sharper, and corners become less rounded.

guidelines

Features

This refers to specific feature sizes and can affect the accuracy of the CD (Critical Dimension). As a rule, the higher the resolution, then the more accurate the individual feature size will be. For example, some customers' patterns may have 500um feature circles and these can be imaged using any resolution, but if the size accuracy of the circle is vital, then a higher resolution should be chosen. Equally, a pattern may have 12um lines but if the size tolerance is large, then a lower resolution could be chosen.


Dimensional and Registration

Dimensional tolerances refer to the tolerances over a distance greater than 5mm – in layman’s terms, people ask us ‘how accurate will the mask be’ and these guidelines should go somewhere towards providing the tolerances in overall dimensions, depending upon the resolution chosen. Again, it goes without saying that the higher the resolution, then the more accurate the final pattern.

These dimensional tolerances across the length of the pattern will of course influence the registration of layer to layer if your device has multiple layers. Each resolution also has its own grid addressability. Due to these factors, we do not recommend mixing different resolutions if they are part of the same pattern set that must align perfectly together So, for example, if the dimensional tolerance is +/- 2um then there could be possible misregistration of up to 4um from layer to layer (this scenario is not very likely, but possible).


Rounding and Sharpness

The correct resolution is the effect that it has on corner rounding and the straightness of the edges of the lines. It is impossible to produce a corner or edge with perfect precision down to sub-micron level, there will always be a rounding effect on both inner and outer corners. For example, a triangle pattern will always lose some of the apex points – how much it loses depends on the resolution. The amount of this rounding depends on the angle involved, and the resolution chosen. Each increase in resolutions will affect how clean the edges and corners are.