Embedded metal contamination removal from BEOL wafers
A novel bevel etch sequence for embedded metal contamination removal from BEOL wafers is provided. In one aspect, a method of processing a wafer includes: performing a bevel dry etch to break up layers of contaminants with embedded metals which, post back-end-of line metallization, are deposited on a bevel of the wafer, which forms a damaged layer on surfaces of the wafer, and then performing a sequence of wet etches, following the bevel dry etch, to render the bevel of the wafer substantially free of contaminants, wherein the sequence of wet etches includes etching the damaged layer to undercut and lift-off any remaining contaminants. A wafer, processed in this manner, having a bevel that is substantially free of contaminants is also provided.
1. A method of processing a wafer, the method comprising:
breaking up contaminants that include layers of embedded metals and dielectrics formed on a bevel of the wafer using a bevel dry etch, wherein the dry bevel etch leaves behind structures comprising the remaining portions of the contaminants on the surfaces of the wafer, and wherein at least one of the structures is present on the edge of the wafer and includes portions of a first dielectric layer, a first metal layer, a second dielectric layer, a second metal layer, and a third dielectric layer, and wherein the first metal layer and the second metal layer each comprise a metal selected from the group consisting of: aluminum, copper, iron, ruthenium, tantalum, titanium, chromium, cobalt and combinations thereof, and wherein the first dielectric layer, the second dielectric layer, and the third dielectric layer each comprises a material selected from the group consisting of: silicon oxide, silicon nitride, and combinations thereof, and wherein the bevel dry etch is performed in multiple cycles alternating between a F-containing plasma for etching the first dielectric layer, the second dielectric layer, and the third dielectric layer and a Cl-containing plasma for etching the first metal layer and the second metal layer, in a layer by layer manner;
creating pathways in the wafer undercutting any remaining portions of the contaminants using a first wet etch, the first wet etch further removing a damaged layer resulting from the bevel dry etch;
lifting off the undercut remaining portions of the contaminants using a second wet etch that follows the pathways in the wafer made by the undercutting; and
removing residue and surface roughness from the wafer using a third wet etch.
2. The method of claim 1 , wherein the bevel comprises a portion of the wafer that is less than or equal to about 3 millimeters in from the edge of the wafer.
3. The method of claim 1 , wherein the contaminants comprise at least one continuous layer that wraps wrap around the bevel from a front side of the wafer to the back side of the wafer.
4. The method of claim 1 , wherein the bevel dry etch is performed using a fluorine (F)-containing plasma and a chlorine (Cl)-containing plasma.
5. The method of claim 4 , wherein the F-containing plasma is selected from the group consisting of: a tetrafluoromethane (CF 4 )-containing plasma, a sulfur hexafluoride (SF 6 )-containing plasma, a nitrogen trifluoride (NF 3 )-containing plasma, and combinations thereof.
6. The method of claim 4 , wherein the Cl-containing plasma is selected from the group consisting of: a dichlorine (Cl 2 )-containing plasma, a boron trichloride (BCL 3 )-containing plasma, and combinations thereof.
7. The method of claim 1 , wherein the bevel dry etch is performed on the bevel while a remainder of the wafer is protected using a plasma exclusion zone.
8. The method of claim 1 , wherein the structures are selected from the group consisting of: pillars, whiskers, grass structures, and micromasking.
9. The method of claim 1 , wherein the first wet etch is performed using an etchant selected from the group consisting of: hydrofluoric acid (HF), and a hydrogen peroxide (H 2 O 2 ):ammonium hydroxide (NH 4 OH) mixture.
10. The method of claim 1 , wherein the first wet etch is performed on the back side of the wafer before the first wet etch is performed on a front side of the wafer.
11. The method of claim 1 , wherein the second wet etch is performed using an etchant comprising a quaternary ammonium hydroxide solution.
12. The method of claim 11 , wherein the quaternary ammonium hydroxide solution is selected from the group consisting of: tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide (TEAH), and combinations thereof.
13. The method of claim 11 , wherein performing the second wet etch comprises varying the etchant comprising the quaternary ammonium hydroxide solution applied to a front side and the back side of the wafer.
14. The method of claim 1 , wherein the third wet etch is performed using an etchant comprising hydrofluoric acid (HF).
15. The method of claim 1 , wherein, following the bevel dry etch and the sequence of wet etches, the bevel of the wafer has a final contamination level of less than or equal to about 5×10 10 at/cm 2 .
16. The method of claim 1 , wherein the first dielectric layer directly contacts the second metal layer on the back side of the wafer, and wherein the first metal layer directly contacts the third dielectric layer on a front side of the wafer.