Forming nanoscale patterned thin film metal layers
View Patent ↗The specification describes a contact printing technique for forming patterns of thin films with nanometer resolution over large areas. The procedure, termed here “nanotransfer printing (nTP)”, relies on tailored surface chemistries for transferring thin films, typically metal films, from the raised regions of a stamp to a substrate when these two elements are brought into intimate physical contact. This technique is purely additive, it is fast (<15 s contact times), and the printing occurs in a single processing step at room temperature in open air. nTP is capable of producing patterns with a wide range of features with sizes down to ˜100 nm, and edge resolution better than 25 nm. Electrical contacts and interconnects have been fabricated for high performance organic thin film transistors (TFTs) and complementary inverter circuits, to demonstrate one of the many potential applications for nTP.
1. A method for forming a thin film pattern on a surface of a substrate comprising:
depositing a transfer layer on the surface of a patterned stamp, the transfer layer having an upper surface and a lower surface, with the lower surface contacting the surface of the patterned stamp;
treating one or both of the upper surface of the transfer layer and the surface of the substrate to activate the one or both thereof; and
placing the upper surface of the transfer layer and the surface of the substrate in contact to transfer the transfer layer from the patterned stamp to the substrate.
2. The method of claim 1 wherein the transfer layer is a metal transfer layer comprising a metal.
3. The method of claim 2 wherein the patterned stamp has features with an edge resolution of less than 100 nm.
4. The method of claim 3 wherein the features have a size of less than 100 microns.
5. The method of claim 2 wherein the metal transfer layer comprises a bi-layer of two metals.
6. The method of claim 5 wherein the bi-layer comprises gold and titanium.
7. The method of claim 5 wherein the bi-layer comprises a gold layer in contact with the pattern layer.
8. The method of claim 5 wherein the bi-layer comprises a first metal layer on the surface of the stamp, and a second metal layer on the first metal layer, and wherein the second metal layer has greater adhesion to the substrate than the first metal has to the surface of the stamp.
9. The method of claim 8 wherein the transfer of the metal transfer layer from the stamp surface to the substrate occurs with the formation of chemical bonds between the second metal layer and the substrate.
10. The method of claim 2 wherein the stamp is a resilient polymer stamp.
11. The method of claim 10 wherein the resilient polymer stamp is prepared by the steps comprising:
a. forming a master mold by:
i. forming a pattern layer on a substrate;
ii. patterning the pattern layer by forming a pattern of openings through the pattern layer;
b. applying a prepolymer of the resilient polymer to the master mold;
c. curing the prepolymer; and
d. removing the resilient polymer, leaving a pattern of raised portions on the surface of the resilient polymer.
12. The method of claim 11 wherein the pattern layer is sensitive to actinic radiation, and the pattern is formed using lithography.
13. The method of claim 11 wherein the resilient polymer is PDMS.
14. The method of claim 2 wherein the stamp is a rigid stamp.
15. The method of claim 14 wherein the rigid stamp is prepared by steps comprising:
a. forming a pattern layer on a stamp substrate; and
b. patterning the pattern layer by forming a pattern of openings through the pattern layer.
16. The method of claim 15 wherein the pattern layer comprises a material selected from the group consisting of glass, silicon, GaAs, polyester, and polyacrylate.
17. The method of claim 2 wherein a surface of the metal transfer layer is activated by exposing the surface of the metal transfer layer to an oxygen plasma.
18. The method of claim 2 wherein a surface of the substrate is activated.
19. The method of claim 18 wherein a surface of the substrate is activated by exposing the surface to an oxygen plasma.
20. The method of claim 2 wherein the substrate comprises a resilient polymer.
21. The method of claim 2 wherein the substrate is rigid.
22. The method of claim 2 wherein the upper surface of the transfer layer and the surface of the substrate are placed in contact with a pressure below 50 psi.
23. The method of claim 1 wherein the transfer layer comprises a non-metal.
24. The method of claim 23 wherein the non-metal is selected from the group consisting of Si 3 N 4 , SiO 2 , indium tin oxide, and TaN.
25. A method for forming a thin film metal pattern on a surface of a substrate comprising the steps of:
preparing the substrate by forming a raised pattern on the surface of the substrate;
preparing a stamp by steps comprising depositing a metal transfer layer on the surface of the stamp, the metal transfer layer having an upper surface and a lower surface, with the lower surface contacting the surface of the stamp;
treating one or both of the upper surface of the transfer layer and the surface of the substrate to activate the one or both thereof; and
placing the upper surface of the transfer layer and the surface of the substrate in contact to transfer the metal transfer layer from the stamp surface to the raised pattern on the substrate.
26. The method of claim 25 wherein the upper surface of the transfer layer and the surface of the substrate are placed in contact with a pressure below 50 psi.