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ASML: SNF Utility Mask & Combining Zero/First Layers

This process describes how to combine your zero and first layer exposures in ASML and when you should consider this process.

Picture and Location

 To use the "SNF utility mask," you must understand the challenges and warnings described on this page. After reading this page, you can find the "SNF utility mask" in a locked toolbox in the lithography area. Acquiring access is described below.



 Before reviewing this page, remember that:

* * * ASML policy dictates that SNF users never open the two SMIF boxes owned by ASML. This is for cleanliness and logistical reasons. * * *

For processes that require your images and important ASML features such as alignment marks and the mark clearout image to be exposed at the same time, SNF staff provides a mask with a copy of these important features (hereafter referred to as the "SNF utility mask").


This page describes:

  • What you need to do to get your process qualified to use the SNF utility mask
  • Suggestions and warnings about using this process.
  • Examples of when you might use this capability.
  • Examples of when you should not use this capability.
  • How to set up your job file for exposing your alignment marks and first layer at the same time.
  • Test result of Combi reticle vs. Utility reticle



* * * ASML policy dictates that SNF users never open the two SMIF boxes owned by ASML. This is for cleanliness and logistical reasons. * * *

Any user found opening the ASML-owned SMIF boxes will be punished. NO EXCEPTIONS. This includes if there is an issue with the SNF utility mask (e.g. lost); in this case, you must put your process on hold and you MUST NOT open the ASML-owned SMIF boxes as a workaround.



Process Capabilities

Warning! SNF staff strongly recommends that you do not combine your zero and first layers.

The reason is doing so has caused some users in the past to find that their zero layer does not survive their whole process. Understand that the safest method of ensuring your alignment marks' survival is investing the time to do separate rounds of lithography for your zero and first layers.

* * * Only pursue this if you are willing to accept the risk associated with this process. You accept responsibility for your time and resources spent on attempting to make this process work for you. * * *


Cautions about combining your zero and first layer exposure

  • Your priority is making sure your alignment marks survive through all your layers of processing. Thus, do not sacrifice alignment mark integrity.

For example, do not drastically adjust the etch depth of your alignment marks to "match" it to your first layer and "save" one round of lithography. You risk making your alignment marks unrecognizable by the ASML in future processing steps by doing this. In this case, SNF staff recommends you keep your exposures for your zero and first layer separate. Or, if you feel you must try this, you should run a test wafer through your whole process before committing your lot. 


What the process CAN be used for

  • Example 1: One research project uses a large border around each die. The requirement for this border is simply that it is optically visible. By exposing this border along with the alignment marks, the subsequent alignment mark etch also creates this border image in the wafer. The depth at which the alignment marks were etch were not changed for this additional image, and thus, this process is ok.
  • Example 2: One research project has a 2nd layer that is medium-sized squares (10s of microns) that must be patterned in a first layer that is an enormous trench (100s of microns). The trench can be etched to a depth that works for alignment marks. Therefore, this process works for combined zero/first layer exposure.


What the process CANNOT be used for

  • Do not combine your zero/first layers just to save one round of lithography. Again, if the process to create your first layer is a drastic change from the recommended processes to create alignment marks, you risk creating alignment marks that may not be recognizable by ASML after more layers of processing.


Contact List and How to Become a User


Training to Become a Tool User

  1. Acquire SNF lithography staff approval for your process that requires loading the SNF utility mask at the same time as your own mask(s). The following form to be submitted to litho staff is supplied to help with this step: Utility Mask request form.
  2. Register with the owners of the toolbox that contains the SNF utility mask. Understand the usage rules of this toolbox, which can be found here: Litho Toolbox.


Operating Procedures


Step-by-step instructions for modifying your job file to expose your zero and first layers together can be found here:

ASML: Step-by-step instructions for Combining Zero/First Layers



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