Choose Your Design or Fracture Grid
This is a very important factor in the design of your photomask. Most layout systems will have a feature/concept of “grid”. This is the coordinate system on which all of your vertices, edges and polygon paths must fit. It is important to note the difference between design grid and fracture grid.
Your design grid should be small enough to achieve the position, line widths, and spaces that you need for the design, however, not any smaller than necessary because the smaller the grid, the longer the write time. The longer the write time, the greater the cost. Typical address units for mask lithography tools are 5nm, 10nm, 20nm, 25nm, 50nm, 100nm, 125nm, 250nm, and 500nm.
Unless you submit “write ready data”, we’ll need to translate your design to the data format required by the mask exposure tools through a process referred to as “fracturing”. If your design grid is different than the fracture grid (or address unit), there will be grid snapping during the translation process. Ideally, you want your design grid to match the fracture grid but, rarely does this happen. Therefore, choosing an address unit that minimizes grid snapping can be important to retaining the viability of your design.
Smaller grids should be used for features that require finer resolution on the mask. Waveguide and some photonic features where the “smoothness” of a curved feature is an important parameter in the functionality of these types of devices. Features such as circles, curves, and rings all require more trapezoids to replicate in the mask data, which again, is a function of write time and cost. If your device can use octagons rather than perfect circles, you should consider the option.
If you have any questions we will be happy to advise and help during your mask design layout phase, just get in touch.