Dear Misen:
Perhaps we are talking about two different things. These things happen when discussions become illustrative. Some terms I use are non standard looking as an outsider.
The mask set I refer to is to make one scan pass of the wafer. So a SESP process uses one scan to make a step in the process. One metal layer must use at least 4 scans to fabricate, one for the vias, one for the insulating layer, one for the interconnect metal and one for the insulation between the metal lines. AMD's 65nm process uses 11 metal layers thus there are 44 scans at a minimum assuming SESP just for that.
According to this there are up to 50 layers in a semiconductor device. At 2 mask scans a layer, thats 100 masks using SESP throughout. Now DEDP is different, DP uses two masks to create one photoresist layer, one for each part of the photoresist to be removed and that resulting mask is used to etch the wafer. Now that takes two to three sets of steps to do what one set with a better tool would need. Thus twice the number of scans are required for those layers. It is not that bad overall because these layers are only those that are critical, the rest can use the standard SESP. The DE portion exposes each mask for twice as long to get the better edges needed to create the photoresist layer. It doesn't take twice as long to do that scan step because some of the time is used to reposition for the next exposure and that time isn't doubled.
sharif.edu
So if all of the layers had to use DEDP, we would have 200 scans required. The thing is that some layers are used to remove previous layers to be replaced by other materials. The gate first MG process that Intel uses does such a thing. As does adding strain. FOr IBM/AMD/etal's process with dual strain, the same layer has to have more than two scans to accomplish. So its quite possible for a very complex cutting edge process to have 200+ scans needed with DEDP.
I don't know the most complicated process currently in production. There is a process in the lab that uses 4 scans to make a single photoresist layer. It is called multipatterning or MP for short. It covers from three to as many as needed to do the job. Unfortunately that naming convention will make it more difficult to know just how many scans are required per layer in a MEMP process. And as the tools required to go to a smaller process become more late, that is the way everyone in the industry are all going.
So a 200+ layer (scan) production process may not be as far away as you think.
BTW, I used 200+ scans to just prove a point. It works just as well between a 50 scan process and a 75 scan one. Like I said, IIRC, DD normalizes to a 25 scan (SESP) process with a 100mm die.
BTW, what do you call a single scan relative to a given process?
Pete |
