Ultra-thin structure to protect copper and method of preparation
Methods of depositing thin, low dielectric constant layers that are effective diffusion barriers on metal interconnects of semiconductor circuits are described. A self-assembled monolayer (SAM) of molecules each having a head moiety and a tail moiety are deposited on the metal. The SAM molecules self-align, wherein the head moiety is formulated to selectively bond to the metal layer leaving the tail moiety disposed at a distal end of the molecule. A dielectric layer is subsequently deposited on the SAM, chemically bonding to the tail moiety of the SAM molecules.
1. A method of forming a diffusion barrier on a metal layer disposed on a semiconductor substrate, the method comprising:
depositing a first monolayer of molecules in a self-limiting reaction on the metal layer, each molecule of the first monolayer of molecules having a first head moiety having an affinity for the metal layer and a first tail moiety having an affinity for one or more dielectric materials;
depositing a second monolayer of molecules on top of the first monolayer, each molecule of the second monolayer having a second head moiety and a second tail moiety, wherein first tail moieties of at least some molecules of the first monolayer bond with second head moieties of at least some molecules of the second monolayer, and wherein the second tail moiety has an affinity for one or more dielectric materials; and
depositing a dielectric layer on top of the second monolayer to form a bond between second tail moieties of at least some molecules of the second monolayer and the dielectric layer.
2. The method of claim 1 , wherein a layer of Si 3 N 4 is deposited on the second monolayer of molecules before depositing the dielectric layer.
3. The method of claim 1 , wherein the dielectric layer comprises SiCN.
4. The method of claim 1 , wherein a chelating agent is applied to the metal layer forming a metal complex before depositing the first monolayer of molecules.
5. The method of claim 1 , wherein the first head moiety includes a thiol group.
6. The method of claim 1 , wherein the first head moiety includes an amine group.
7. The method of claim 1 , wherein the first head moiety includes an alkoxy group.
8. The method of claim 1 wherein the thickness of the first monolayer of molecules is less than 5 nanometers.
9. A method of forming a metal diffusion barrier, the method comprising:
depositing a metal layer on a substrate;
depositing a first monolayer of molecules on the metal layer wherein each molecule of the first monolayer of molecules includes a head moiety and a tail moiety, the head moiety forming a bond with the metal layer and the tail moiety configured to form a bond with one or more dielectric materials;
depositing a first chelating agent on top of the first monolayer of molecules such that the chelating agent is unbound to metal atoms; and
depositing a dielectric layer on the first monolayer of molecules and the chelating agent.
10. The method of claim 9 wherein the dielectric layer comprises SiCN.
11. The method of claim 9 wherein the metal layer comprises copper.
12. The method of claim 9 wherein a second monolayer of molecules is deposited on the first monolayer of molecules before depositing the dielectric layer.
13. The method of claim 12 , wherein each molecule of the second monolayer of molecules includes a second head moiety and a second tail moiety, at least some of the second head moieties forming a bond with the first monolayer of molecules and the second tail moiety configured to form a bond with the dielectric layer.
14. The method of claim 9 wherein a layer of Si 3 N 4 is deposited on the first monolayer of molecules before depositing the dielectric layer.
15. The method of claim 9 , wherein a second chelating agent is applied to the metal layer forming a metal complex before depositing the first monolayer of molecules.
16. The method of claim 9 , wherein the chelating agent is configured to bond with atoms diffusing from the metal layer.
17. The method of claim 9 , wherein a second chelating agent is applied to the metal layer before depositing the first monolayer of molecules and Si 3 N 4 is deposited on the first monolayer of molecules before depositing the dielectric layer.
18. A metal interconnect structure on a substrate, comprising:
a first dielectric layer disposed on the substrate;
a metal interconnect disposed within the first dielectric layer;
a first monolayer of molecules disposed on the metal interconnect, wherein each molecule of the first monolayer of molecules includes a first head moiety and a first tail moiety, the first head moiety forming a chemical bond with the metal interconnect;
a second monolayer of molecules disposed on the first monolayer, wherein each molecule of the second monolayer includes a second head moiety and a second tail moiety, the second head moiety forming a chemical bond with the first tail moiety; and
a second dielectric layer disposed on the second monolayer, the second dielectric layer forming a chemical bond with the second tail moiety.
19. The metal interconnect structure of claim 18 , wherein the first dielectric layer includes a low-k dielectric material.
20. The metal interconnect structure of claim 18 , further comprising one or more additional monolayers of molecules between the metal interconnect and the second dielectric layer, wherein a total number of monolayers between the metal interconnect and the second dielectric layer and a thickness of each monolayer are determined based on a desired total thickness of the monolayers.