Method for the rapid processing of polymer layers in support of imidization processes and fan out wafer level packaging including effiecient drying of precursor layers
A process for the drying, and subsequent imidization, of polyimide precursors which minimizes or eliminates voids and which minimizes or eliminates discoloration. The process uses a sequential set of descending pressure operations that allow for time efficient processing of wafers. The set of descending pressure operations are interspersed with evacuation processes using heated gasses, which combine heating and byproduct evacuation. The process results in layers with reduced or eliminated voiding, discoloration, and solvent retention.
1. A process for drying of substrates in support of temperature imidization of polymer layers, said process comprising the steps of:
inserting one or more substrates into a process chamber, said one or more substrates coated with a layer of polyimide precursor, said polyimide precursor comprising N-Methyl-2-pyrrolidone;
reducing the pressure in said process chamber to a first drying pressure;
first flushing said process chamber with inert gas to a first flushing pressure;
reducing the pressure in said process chamber to a second drying pressure after said first flushing, wherein said second drying pressure is lower than said first drying pressure;
second flushing said process chamber with inert gas to a second flushing pressure after the step of reducing the pressure in said process chamber to a second drying pressure;
reducing the pressure in said process chamber to a third drying pressure after the step of second flushing said process chamber, wherein said third drying pressure is lower than said second drying pressure; and
third flushing said process chamber with inert gas to a third flushing pressure after the step of reducing the pressure in said process chamber to a third drying pressure.
2. The process of claim 1 wherein said process chamber is heated to a first chamber temperature.
3. The process of claim 2 wherein said first flushing said process chamber with inert gas comprises flushing with inert gas heated to a first gas temperature.
4. The process of claim 3 wherein said second flushing said process chamber with inert gas comprises flushing with inert gas heated to a second gas temperature.
5. The process of claim 4 wherein said third flushing said process chamber with inert gas comprises flushing with inert gas heated to a third gas temperature.
6. The process of claim 5 wherein said first chamber temperature is in the range of 135 C to 180 C.
7. The process of claim 6 wherein said first drying pressure is in the range of 30-60 Torr.
8. The process of claim 6 wherein said first drying pressure is in the range of 30-50 Torr.
9. The process of claim 8 wherein said second drying pressure is in the range of 15-30 Torr.
10. The process of claim 9 wherein said third drying pressure is in the range of 1-15 Torr.
11. The process of claim 1 wherein said first gas temperature is in the range of 135 C-180 C.
12. The process of claim 11 wherein said first gas temperature is in the range of 135 C-180 C.
13. The process of claim 11 wherein said second gas temperature is in the range of 135 C-180 C.
14. The process of claim 12 wherein said second gas temperature is in the range of 135 C-180 C.
15. The process of claim 13 wherein said second gas temperature is in the range of 135 C-180 C.
16. The process of claim 14 wherein said second gas temperature is in the range of 135 C-180 C.
17. The process of claim 16 further comprising the step of temperature imidizing a polymer layer on said one or more substrates after the step of third flushing said process chamber while having maintained the low oxygen level of the drying steps.