KR20150124915A - Electroless deposition of continuous nickel layer using complexed titanium (iii) metal cations as reducing agents - Google Patents

Abstract

A solution for electroless deposition of nickel is provided. A reducing agent of Ti^3+ ions is provided to the solution. Ni^2+ ions are provided to the solution.

Description

ELECTROLESS DEPOSITION OF CONTINUOUS NICKEL LAYER USING COMPLEX TITANIUM (III) METAL CAUTION AS REDUCING AGENTS USING COMBINED TITANIUM 3 CURABLE METAL CUTS As a reducing agent,

The present invention relates to a method of forming semiconductor devices on a semiconductor wafer. More particularly, the present invention relates to a method of depositing a nickel layer to form semiconductor devices.

Upon formation of semiconductor devices, a thin layer of nickel may be deposited. Such a deposition may be provided by electroless plating.

In order to achieve the foregoing and in accordance with the purpose of the present invention, a solution for electroless deposition of nickel is provided. A reducing agent of Ti ^& lt ^{; 3 + &} gt ^; ions is provided in the solution. Ni ^{2 +} ions are provided in the solution.

In another embodiment of the present invention, a method of electroless plating a nickel-containing layer is provided. A Ti ^{3 +} enriched stock solution is provided. A Ni ^{2 +} enriched stock solution is provided. It is mixed with a flow from the Ti ^{+ 3} with the flow of the stock solution from the concentrate the Ni ^{+ 2} concentration stock solution and water to provide an electrolyte mixture to de-plating the Ni position (combine). The substrate is exposed to the mixed electrolyte to electrolessly deposit the Ni.

In another embodiment of the present invention, a method of electroless plating of a nickel layer is provided. A solution is provided for the electroless deposition of nickel, comprising Ti ^{3 +} ions and Ni ^{2 +} ions, wherein the ratio of Ti ^{3 +} ions to Ni ^{2 +} ions is from 100: 1 to 2: 1 to be. The substrate is exposed to a solution for electroless deposition of nickel.

These and other features of the present invention will be described in more detail below with the following detailed description of the invention in conjunction with the drawings.

The invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings in which like reference numerals refer to like elements.
1 is a flow chart of an embodiment of the present invention.
2 is a schematic diagram of a system that may be used in an embodiment of the present invention.

The present invention will now be described in detail with reference to several preferred embodiments, as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be understood by those skilled in the art that the present invention may be practiced without some or all of these specific details. In other instances, well-known process steps and / or structures have not been described in detail so as not to unnecessarily obscure the present invention.

In electroless deposition (ELD) on substrates that are difficult to plated, it is important to activate the substrate using Ni-containing solutions prior to deposition. This may be achieved by simply dipping (dipping) with a solution of NiCl ₂ in aqueous solution or other soluble salts. Ni ^{2 +} ions are adsorbed onto the substrate to produce an active surface that may or may not have uniform Ni surface coverage after reduction. This causes undesirable non-homogeneous nucleation in semiconductor applications. Thus, prior to plating, the ability to deposit a thin, continuous Ni layer on substrates is important. Ni can be displaced by ELD. The electroless deposition of nickel is accomplished using hydrazine or other hydrogen containing compounds as reducing agents. In addition to the environmental problems associated with these hydrogen containing reducing agents, the oxidation reaction of these species involves the production of H ₂ gas, which is incorporated into the deposition water. This affects the purity of the deposited film. Additionally, hydrazine-nickel electrolytes require operation at elevated temperatures and high pH. These are undesirable for back end metallization applications because dielectric materials are susceptible to damage at high pH and high temperatures.

In an electroless plating bath containing Ti ^{3 +} , the metal to be deposited, Ni ^{2 +,} is reduced from the solution while Ti ^{3 +} is oxidized to higher and more stable oxidation states. Ti ^{3 +} has considerable advantages over hydrazine and other hydrogen containing compounds in solving the above-mentioned problems.

Replacing hydrazine with Ti ^{3 +} ionic reductants eliminates the toxicity and volatility inherent in the hydrazine and makes the plating bath more environmentally friendly. Additionally, gas (i.e., H ₂ and N ₂ ) evolution or side effects are not observed at the electrodes. This results in a smooth, continuous, pure Ni film. Metal ion containing plating baths can also be operated over a wide temperature and pH range.

The metal ion reducing agent-containing bath of the present invention can operate at normal temperature and low pH. This is not possible with hydrazine and other reducing agent containing electrolytes. The extended operating window makes this bath attractive for application in semiconductor applications. Additionally, this embodiment enables the formation of a very thin and continuous Ni film that can be used as a catalyst layer for subsequent ELD of other metals such as Cu, Co, etc. on the substrates. Additionally, this embodiment provides an environmentally friendly " greener " alternative to highly toxic and unstable hydrazine based electroless Ni electrolytes.

Gas generation (mainly hydrogen and / or nitrogen), a by-product of the hydrazine oxidation reaction, is removed by the titanium oxidation reaction. Deformation of a pure, continuous Ni film is possible.

The cost and complexity associated with maintaining a high temperature during plating can also be reduced due to near room temperature operation of the metal ion reductant electrolyte.

The following table describes the preparation of the Ti ^{3 +} / Ni electroless plating bath. Deposition takes place on Cu substrates without any activation. Deposition can be extended to non-conductive or lightly conductive substrates such as glass and 1 to 2 nm Ru by following appropriate pre-cleaning protocols.

Species Concentration (M) NiSO ₄ 0.025 NaOH 0.075 Sodium gluconate 0.025 NH ₄ OH 0.32 TiCl ₃ 0.05 Ascorbic acid 0.29 Temperature 20-25 ° C pH 5-5.5

The bath containing Ti ^{3 +} metal ion reducing agent used in the embodiment of the present invention is capable of operating at room temperature and low pH. This is not possible with hydrazine and other reducing agent containing electrolytes.

The formation of Ni electrodes for memory applications using plasma etching is difficult. Embodiments of the present invention realize selective patterning of Ni electrodes during semiconductor fabrication without plasma etching. The cost and complexity associated with maintaining a high temperature during plating can also be reduced due to near room temperature operation of the Ti ^{3 +} metal ion reductant electrolyte.

1 is a high-level flow chart of an embodiment of the present invention. In this embodiment, a Ti ^{3 +} enriched stock solution is provided (step 104). A Ni ^{2 +} enriched stock solution is provided (step 108). Ti ^{3 +} a concentrated stock solution, and Ni ^{2 +} to provide an electrolyte solution mixture of a concentrated stock solution Ti flow from a ^{3 +} a concentrated stock solution is mixed with a flow from the stock solution and water of Ni ^{2 +} concentration (Step 112). The wafer is exposed to an electrolyte solution, a mixture of Ti ^{3 +} a concentrated stock solution, and Ni ²⁺ a concentrated stock solution (step 116). The mixed electrolyte solution may be collected and reactivated or disposed of for later use (step 120).

In one example, a Ti ^{3 +} enriched stock solution is provided in a Ti ^{3 +} enriched stock solution source (step 104). A Ni ^{2 +} enriched stock solution is provided in a Ni ^{2 +} enriched stock solution source (step 108). Figure 2 is a schematic diagram of a system 200 that may be used in an embodiment of the present invention. The system Ti ^{3 +} A containing a concentrated stock solution Ti ^{3 +} concentrated stock solution source (208), Ni ^{2 +} a Ni ^{2 +} concentration containing the concentrated stock solution stock solution source 212, and deionized water ( RTI ID = 0.0 > DI). ≪ / RTI > The flow 220 from the Ti ^{3 +} enriched storage solution source 208 to provide a mixed electrolyte solution of the Ti ^{3 +} enriched storage solution and the Ni ^{2 +} enriched storage solution results in a Ni ^{2 +} (Step 112) with the flow 224 from the DI number source 212 and the flow 228 from the DI number source 216. The wafer 236 is exposed to a mixed electrolyte solution 232 of Ti ^{3 +} enriched stock solution and Ni ^{2 +} enriched stock solution (step 116). The mixed electrolyte solution 232 is collected (step 120). A disposal system 240 may be used to dispose of the mixed electrolyte solution 232. An alternative embodiment provides for the collection of the mixed electrolyte solution 232 to be reactivated.

In this example, the Ti ^{3 +} enriched storage solution comprises a TiCl ₃ solution with ascorbic acid. Ni ^{2 +} enriched stock solutions include NiSO ₄ , sodium gluconate, and ammonium hydroxide.

In one _{embodiment, 0.05M TiCl 3, 0.32M NH 4} OH, 0.004M NiSO 4, 0.075M NaOH, 0.29M ascorbic acid, and 0.025M glue to form an electrolyte solution mixture of acid sodium, Ti ^{+ 3} and concentrated The flow 220 of the stored storage solution is mixed with the flow 224 of the Ni ^{2 +} enriched storage solution and the flow 228 of the DI number. The mixed electrolyte solution has a pH of 5 to 5.5 and a temperature of about 20 to 25 占 폚.

The Ti ^{3 +} enriched stock solution provides a stable Ti ^{3 +} solution with a shelf life of several months without deterioration. High concentrations are presented stock solution of Ti ^{3 +} concentration is stored at a lower volume. In addition, the Ni ^{2 +} enriched storage solution provides a stable Ni ^{2 +} solution with a shelf life of several months without deterioration. High concentration causes Ni ^{2 +} concentrated storage solution to be stored in less volume. Because the mixed electrolyte solution does not have as long a shelf life as the concentrated storage solutions, these solutions are mixed and diluted just before exposing the wafer to the mixed electrolyte solution.

An embodiment of the present invention provides a nickel-containing layer having a thickness between 1 nm and 30 nm. Preferably, the nickel-containing layer is pure nickel. Since the nickel-containing layer is relatively thin, a diluting bath is sufficient. In one embodiment, the wafer is exposed to a continuous flow of the mixed electrolyte solution. In another embodiment, the wafer is placed in a still bath of electrolyte solution mixed for a period of time. Because the concentration of nickel and titanium in the mixed electrolyte solution is very low, in one embodiment, the mixed electrolyte solution may be disposed of after being exposed to the wafer (step 120), since the lower concentration of nickel and titanium Is discarded. In another embodiment, the mixed electrolyte solution is exposed to the wafer and then recycled. Recycling may be achieved through reactivation of the mixed electrolyte solution.

In general, the solution mixtures used for plating have Ti ^{3 +} and Ni ^{2 +} ions with a Ti ^{3 +} to Ni ²⁺ ion ratio of 100: 1 to 2: 1. More preferably, the solution mixture used for plating has Ti ^{3 +} and Ni ^{2 +} ions at a Ti ^{3 +} to Ni ^{2 +} ion ratio of 50: 1 to 3: 1. Preferably, the solution mixture has a ratio of amine ligands to Ti ^{3 +} of 12: 1 to 3: 1. Additionally, the solution mixture has a gluconic acid salt from sodium gluconate or gluconic acid. Additionally, Ni ^{2 +} ions are derived from NiCl ₂ or NiSO ₄ . NH ₄ ⁺ ions, which provide an amine ligand, are derived from NH ₄ OH. Without being limited by theory, it is believed that amine ligands help provide lower temperature and lower pH nickel deposition.

Generally, a wafer or other plating surface is exposed to the solution mixture at a temperature of from 20 to 25 占 폚. The plating surface is a surface on which a nickel-containing layer is selectively deposited. This optional deposition may use a mask to protect the surfaces for which the deposition is not intended. Preferably, the solution mixture has a pH of from 5 to 5.5. Preferably, the solution mixture should provide a Ti ^{3 +} has a concentration of from 0.001 to 0.500 M. More preferably, the solution mixture should provide a Ti ^{3 +} has a concentration of 0.010 to 0.100 M. Most preferably, the solution mixture should provide a Ti ^{3 +} has a concentration of 0.020 M to 0.060. Lower temperatures and lower pHs provide deposition with less damage to the layers provided by the semiconductor manufacturing process. Additionally, this process does not require any activation step that may attack and damage the copper substrate. Additionally, this process does not produce gas byproducts.

Preferably, the solution mixture is free of boron. Preferably, the solution mixture is free of phosphorus. Preferably, the solution mixture is free of formaldehyde. It has been found that providing a solution mixture free of boron, phosphorus, hydrazine, and formaldehyde allows for more pure plating without impurities provided using boron-containing reducing agents, phosphorus containing reducing agents, hydrazine, or formaldehyde. In addition, avoiding the use of hydrazine provides a safer, more environmentally friendly process.

In other embodiments, the source of the Ti ^{3 +} Ti ₂ (SO _{4) 3,} or other soluble salts are the Ti ^{+ 3.} The ascorbic acid may be replaced by a sodium salt of tartrate, sodium citrate or isomer of citric acid. Sodium gluconate or gluconic acid may be replaced by methoxyacetic acid or other carboxylic acid ligands.

In one embodiment, the deposited nickel-containing layer is at least 99.9% pure nickel. More preferably, the deposited nickel-containing layer is pure nickel.

While the invention has been described in terms of several preferred embodiments, there are alternatives, permutations, and various alternatives falling within the scope of the invention. It should also be noted that there are many alternative ways of implementing the methods and apparatus of the present invention. It is therefore intended that the appended claims be construed to include all such alternatives, permutations, and various alternative equivalents that fall within the true spirit and scope of the invention.

Claims (20)

A solution for electroless deposition of nickel,
Reducing agents of Ti ^{3 +} ions; And
A solution for electroless deposition of nickel, comprising Ni ^{2 +} ions. The method according to claim 1,
A solution for electroless deposition of nickel further comprising amine ligands. 3. The method of claim 2,
≪ / RTI > wherein the solution further comprises at least one of tungstate, gluconate or tinate ions. The method of claim 3,
Wherein the solution has a pH of from 5 to 5.5. 5. The method of claim 4,
Cl ^- < / RTI > ions for the electroless deposition of nickel. 6. The method of claim 5,
Ni ^{2 + 3 +} Ti ratio of the ions for the ion of 100: 1 to 2: 1, an electroless solution for the deposition of nickel. The method according to claim 6,
The solution is a solution for electroless deposition of nickel, free of boron, phosphorus, hydrazine, and formaldehyde. A method of providing electroless plating of a nickel-containing layer,
Providing a Ti ^{3 +} enriched storage solution;
Providing a Ni ^{2 +} enriched storage solution;
(Combine) step of mixing a flow with the Ni ^{2 +} a concentrated stock solution and the flow of the water from the Ti ^{3 +} a concentrated stock solution to de-plating of Ni to provide an electrolyte mixture to position; And
And exposing the substrate to the mixed electrolyte to electrolessly deposit the Ni. ≪ Desc / Clms Page number 17 > 9. The method of claim 8,
Exposing the substrate to the mixed electrolyte for electroless deposition of Ni,
Providing a solution temperature of from 20 캜 to 25 캜; And
Providing a pH in the range of 5 to 5.5. ≪ RTI ID = 0.0 > 5. < / RTI > 10. The method of claim 9,
Further comprising disposing the mixed electrolyte solution. ≪ Desc / Clms Page number 20 > 11. The method of claim 10,
Wherein the nickel-containing layer is 99.9% pure nickel. 10. The method of claim 9,
Further comprising reactivating the mixed electrolyte solution. ≪ RTI ID = 0.0 > 21. < / RTI > 9. The method of claim 8,
Wherein the Ti ^{3 +} enriched storage solution comprises a solution comprising TiCl ₃ . 14. The method of claim 13,
Wherein the Ni ^{2 +} enriched storage solution comprises a solution of NiSO ₄ and ammonium hydroxide and sodium gluconate or gluconic acid. 15. The method of claim 14,
The Ni ^{2 +} a concentrated stock solution which is a method of electroless plating, nickel-containing layer with a shelf life greater than 1 month provides a plating. 16. The method of claim 15,
The Ti ^{3 +} a concentrated stock solution which has a shelf life of more than a month, a method of providing the electroless plating of the nickel-containing layer. 15. The method of claim 14,
Wherein the mixed electrolyte solution is free of boron, phosphorus, hydrazine, and formaldehyde. 9. The method of claim 8,
Wherein the mixed electrolyte solution is free of boron, phosphorus, hydrazine, and formaldehyde. A method of providing electroless plating of a nickel-containing layer,
Providing a solution for electroless deposition of nickel comprising a reducing agent of Ti ^{3 +} ions and Ni ^{2 +} ions, wherein the ratio of Ti ^{3 +} ions to Ni ^{2 +} ions is from 100: 1 to 2: 1, providing a solution for electroless deposition of the nickel; And
And exposing the substrate to a solution for electroless deposition of nickel. ≪ Desc / Clms Page number 24 > 20. The method of claim 19,
Wherein providing a solution for electroless deposition of nickel comprises:
Providing the solution at a pH of between 5 and 5.5 and at a temperature of between 20 and 25 < 0 > C.

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