Methods for wet atomic layer etching of tungsten using halogenation
Various embodiments of methods are provided for etching tungsten in a wet ALE process. The methods disclosed herein use a wide variety of wet etch chemistries to: (a) halogenate a tungsten surface and form a self-limiting, tungsten halide passivation layer in a surface modification step of the wet ALE process, and (b) selectively remove the tungsten halide passivation layer in a dissolution step of the wet ALE process. In the embodiments disclosed herein, a surface modification solution containing a halogenation agent dissolved in non-aqueous solvent is used to form a self-limiting, tungsten halide passivation layer, which is selectively removed in an aqueous dissolution solution via reactive dissolution/hydrolysis.
1 . A method of etching, the method comprising:
receiving a substrate having a tungsten (W) layer formed thereon, wherein a tungsten surface is exposed on a surface of the substrate;
exposing the surface of the substrate to a surface modification solution comprising a halogenation agent dissolved in a non-aqueous solvent, wherein the halogenation agent reacts with the tungsten surface to form a tungsten halide passivation layer, which is self-limiting and insoluble in the surface modification solution;
removing the surface modification solution from the surface of the substrate subsequent to forming the tungsten halide passivation layer;
exposing the surface of the substrate to a dissolution solution to selectively remove the tungsten halide passivation layer, wherein the dissolution solution reacts with the tungsten halide passivation layer to form soluble species, which are dissolved by the dissolution solution to expose an unmodified tungsten surface underlying the tungsten halide passivation layer; and
removing the dissolution solution and the soluble species from the surface of the substrate to etch the tungsten layer.
2 . The method of claim 1 , further comprising repeating said exposing the surface of the substrate to the surface modification solution, removing the surface modification solution, exposing the surface of the substrate to the dissolution solution, and removing the dissolution solution and the soluble species a number of times until a predetermined amount of the tungsten layer is removed from the substrate.
3 . The method of claim 1 , wherein the halogenation agent is a chlorinating agent, a fluorinating agent or a brominating agent.
4 . The method of claim 3 , wherein the chlorinating agent is trichloroisocyanuric acid (TCCA), oxalyl chloride, N-chlorosuccinimide, 1-chlorobenzotriazole, Chloramine-T or tert-butyl-N-chlorocyanamide.
5 . The method of claim 3 , wherein the non-aqueous solvent is an ether, a ketone, a halocarbon, a heterocyclic, an alcohol or another polar organic solvent.
6 . The method of claim 1 , wherein the surface modification solution is a non-aqueous solution comprising an electrophilic chlorinating agent dissolved in the non-aqueous solvent, wherein the electrophilic chlorinating agent reacts with the tungsten surface to form a tungsten chloride or tungsten oxychloride passivation layer, which is self-limiting and insoluble in the surface modification solution.
7 . The method of claim 6 , wherein prior to exposing the surface of the substrate to the surface modification solution, the method further comprises selecting a concentration of the electrophilic chlorinating agent in the surface modification solution to avoid substantially increasing a post-etch surface roughness of the tungsten layer compared to an initial surface roughness of the tungsten layer before etching.
8 . The method of claim 6 , wherein the surface modification solution comprises trichloroisocyanuric acid (TCCA) dissolved in a polar organic solvent, and wherein a concentration of the trichloroisocyanuric acid (TCCA) in the surface modification solution ranges between 0.05% and 0.5%.
9 . The method of claim 6 , wherein the surface modification solution comprises 0.1% trichloroisocyanuric acid (TCCA) dissolved in ethyl acetate or acetone.
10 . The method of claim 6 , wherein the dissolution solution is an aqueous solution comprising water, wherein the tungsten chloride or tungsten oxychloride passivation layer is hydrolyzed by the water to form the soluble species, which are dissolved by the dissolution solution to expose the unmodified tungsten surface underlying the tungsten chloride or tungsten oxychloride passivation layer.
11 . The method of claim 10 , wherein said exposing the surface of the substrate to the dissolution solution comprises:
exposing the surface of the substrate to the dissolution solution at an elevated temperature ranging between 25° C. and 75° C., wherein the elevated temperature increases an etch rate of the tungsten layer by increasing a dissolution rate of the tungsten chloride or tungsten oxychloride passivation layer.
12 . The method of claim 6 , wherein the dissolution solution is an aqueous solution comprising a base dissolved in water, wherein the tungsten chloride or tungsten oxychloride passivation layer is hydrolyzed by the water to form the soluble species, which are dissolved by the dissolution solution to expose the unmodified tungsten surface underlying the tungsten chloride or tungsten oxychloride passivation layer, and wherein the base increases an etch rate of the tungsten layer by increasing a dissolution rate of the tungsten chloride or tungsten oxychloride passivation layer.
13 . The method of claim 12 , wherein the base is ammonium hydroxide (NH 4 OH), tetramethylammonium hydroxide (TMAH), potassium hydroxide (KOH) or calcium hydroxide (Ca(OH) 2 ).
14 . The method of claim 12 , wherein the dissolution solution further comprises a ligand, which prevents or at least inhibits oxidation of the unmodified tungsten surface after the tungsten chloride or tungsten oxychloride passivation layer is hydrolyzed by the water and removed.
15 . The method of claim 14 , wherein the ligand is ascorbic acid, sodium ascorbate, calcium ascorbate, potassium ascorbate, oxalic acid, formic acid, acetic acid, ethylenediamine, ethylenediaminetetraacetic acid (EDTA) or iminodiacetic acid.
16 . The method of claim 12 , wherein the dissolution solution comprises 0.05 mM to 1 M of ammonium hydroxide (NH 4 OH) and 0 mM to 10 mM ascorbic acid dissolved in water.
17 . A method of etching a substrate using a wet atomic layer etching (ALE) process, the method comprising:
receiving the substrate, the substrate having a tungsten (W) layer formed thereon, wherein a tungsten surface is exposed on a surface of the substrate; and
selectively etching the tungsten layer by performing multiple cycles of the wet ALE process, wherein each cycle comprises:
exposing the tungsten surface to a first etch solution comprising an electrophilic chlorinating agent dissolved in a non-aqueous solvent to form a chemically modified W surface layer that is self-limiting and insoluble in the non-aqueous solvent;
rinsing the substrate with a first purge solution to remove the first etch solution from the surface of the substrate;
exposing the chemically modified W surface layer to a second etch solution to selectively dissolve the chemically modified W surface layer and expose an unmodified tungsten surface underlying the chemically modified W surface layer; and
rinsing the substrate with a second purge solution to remove the second etch solution from the surface of the substrate and etch the tungsten layer.
18 . The method of claim 17 , wherein the electrophilic chlorinating agent reacts with the tungsten surface to form a tungsten chloride or tungsten oxychloride passivation layer, which is self-limiting and insoluble in the non-aqueous solvent, and wherein a concentration of the electrophilic chlorination agent in the first etch solution is selected to avoid substantially increasing a post-etch surface roughness of the tungsten layer compared to an initial surface roughness of the tungsten layer before etching.
19 . The method of claim 18 , wherein the first etch solution comprises trichloroisocyanuric acid (TCCA) dissolved in a polar organic solvent, and wherein a concentration of the trichloroisocyanuric acid (TCCA) in the first etch solution ranges between 0.05% and 0.5%.
20 . The method of claim 18 , wherein the first etch solution comprises 0.1% trichloroisocyanuric acid (TCCA) dissolved in ethyl acetate or acetone.
21 . The method of claim 18 , wherein the second etch solution is an aqueous solution comprising a base dissolved in water, wherein the tungsten chloride or tungsten oxychloride passivation layer is selectively dissolved by the water to expose the unmodified tungsten surface underlying the tungsten chloride or tungsten oxychloride passivation layer, and wherein the base increases an etch rate of the tungsten layer by increasing a dissolution rate of the tungsten chloride or tungsten oxychloride passivation layer.
22 . The method of claim 21 , wherein the second etch solution further comprises a ligand, which prevents or at least inhibits oxidation of the unmodified tungsten surface after the tungsten chloride or tungsten oxychloride passivation layer is selectively dissolved.
23 . The method of claim 21 , wherein the second etch solution comprises 0.05 mM to 1 M of ammonium hydroxide (NH 4 OH) and 0 mM to 10 mM ascorbic acid dissolved in water.