Amorphous thin films and method of making
Aqueous solutions of halogenides (oxyhalides) of zirconium and hafnium (M) with values of α=X/M near one, for X=Cl, Br and I form amorphous solids or glasses, designated as M,X, in contrast to important crystalline oxyhalide end members with α=2 (designated as MOX). The present disclosure describes methods for producing amorphous thin films comprising halogenides upon evaporation, and provides some measured physical properties, with attention to compositions for α<2. The value of a below which only glasses are formed is about one for oxychlorides and oxybromides of both Zr and Hf. The chemical formulas for all the halogenide thin films prepared as noted above can be written as a function of the single parameter α, according to M(OH) 4-α X α .(4α-1)H 2 O. This is valid for e.g., crystalline zirconium oxychloride octahydrate, and for the glassy solids found for α<2 and down to the onset of hydrolysis, α≈0.5. Thin films made by the disclosed methods are highly dense (90% of theoretical crystal density), extremely smooth (rms<0.4 nm), and highly transparent in the visible spectrum, >90%. Such thin films are useful as alkali diffusion barriers.
1. An aqueous solution for depositing amorphous metal oxides as a diffusion barrier, the aqueous solution comprising a metal halogenide, or combinations of metal halogenides, wherein each halogenide has a formula M(OH) 4-α X α .(4α-1)H 2 O where M is hafnium, zirconium or combinations thereof; X is Cl, Br or I; and α is from greater than 0.6 to 1.2.
2. The solution according to claim 1 where the halogenide structure comprises:
4 linked tetramers and α is 1; or
3 linked tetramers and α is 1.2.
3. A method, comprising:
preparing an aqueous solution comprising a metal halogenide or combinations of metal halogenides, each halogenide having a formula M(OH) 4-α X α .(4α-1)H 2 O where M=hafnium, zirconium or combinations thereof; X is Cl, Br or I; and a is from greater than 0.6 to 1.2;
applying the solution to a substrate to form a film; and
heating the film
to provide a metal oxide film on the substrate.
4. The method according to claim 3 where X is Cl.
5. The method of claim 3 wherein the film is substantially amorphous.
6. The method of claim 3 wherein heating the film comprises annealing the film using an annealing time between 15 minutes and 1 hour, and an annealing temperature of from 300° C. to 500° C.
7. The method of claim 3 wherein the film has a roughness, Rq, of 1 nm or less.
8. The method according to claim 3 , further comprising assembling a device incorporating the film.
9. A device made according to the method of claim 8 .
10. A metal halogenide, or combinations of metal halogenides, wherein each halogenide has a formula M(OH) 4-α X α .(4α-1)H 2 O where M=hafnium, zirconium or combinations thereof; X is Cl, Br or I; and a is from greater than 0.6 to 1.2.
11. A method for making a solution according to claim 1 , comprising:
forming a first solution comprising a source of zirconium, a source of hafnium, or combinations thereof; and
processing the first solution to form a second solution comprising a halogenide having a formula M(OH) 4-α X α .(4α-1)H 2 O where M=hafnium, zirconium or combinations thereof, X is Cl, Br or I, and a is from greater than 0.6 to 1.2.
12. The method according to claim 11 , wherein:
the first solution comprises zirconium oxychloride, hafnium oxychloride, or combinations thereof, the first solution having a first acidic pH; and
processing comprises reducing acidity of the first solution to a second pH higher than the first pH by dialysis to form the second solution comprising the halogenide having the formula M(OH) 4-α X α .(4α-1)H 2 O where M=hafnium, zirconium or combinations thereof; X is Cl, Br or I, and α is from greater than 0.6 to 1.2.
13. The method according to claim 11 , wherein the first solution comprises zirconium oxychloride, hafnium oxychloride, or combinations thereof, and wherein processing comprises:
treating the first solution with NH 4 OH to form a precipitate;
washing the precipitate sufficiently to substantially completely remove chloride and ammonium ions; and
dissolving washed precipitate with hydrochloric acid to form the second solution comprising the halogenide having the formula M(OH) 4-α X α .(4α-1)H 2 O where M=hafnium, zirconium or combinations thereof; X is Cl, Br or I; and α is from greater than 0.6 to 1.2.
14. The method according to claim 11 , wherein:
the first solution comprises zirconium basic carbonate, hafnium basic carbonate, or a combination thereof; and
processing comprises adding sufficient hydrochloric acid to form the second solution comprising the halogenide having the formula M(OH) 4-α X α .(4α-1)H 2 O where M=hafnium, zirconium or combinations thereof; X is Cl, Br or I; and α is from greater than 0.6 to 1.2.