A post-ti n hard mask etch cleaning composition

Abstract

This invention discloses a fluorine-based TiN hard mask cleaning agent containing amino acid ionic liquid, its preparation method, and its application, belonging to the field of semiconductor wet cleaning technology. The cleaning agent comprises, by mass percentage: 0.5%–15% fluoride etchant, 1%–25% oxidant, 0.05%–8% amino acid ionic liquid, 0.1%–10% chelating agent, 0.1%–5% pH adjuster, with the balance being deionized water, and a pH value of 4.0–7.5. This invention uses a choline-amino acid type ionic liquid as a multifunctional special additive, simultaneously exerting the multiple functions of corrosion inhibitor, complexing agent, pH buffer, and surfactant. It can efficiently remove TiN hard masks and etching residues, while exhibiting excellent compatibility with back-end metal materials such as Cu, Co, and W, as well as ULK dielectric materials. It leaves no organic residue after cleaning, has a long lifespan, and is suitable for advanced back-end processes at technology nodes of 14nm and below.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor wet cleaning technology, specifically relating to a fluorine-based TiN hard mask cleaning agent containing amino acid ionic liquid, its preparation method and application, which is particularly suitable for selective removal of TiN hard masks and cleaning of etching residues in back-end interconnect (BEOL) processes at 14nm and below technology nodes. Background Technology

[0002] As integrated circuit manufacturing technology advances to 14nm, 7nm and more advanced nodes, metal hard mask technology is widely used in back-end of line (BEOL) processes. Titanium nitride (TiN) has become one of the most mainstream hard mask materials in back-end processes due to its excellent dry etching resistance, good conductivity, and compatibility with low-k materials.

[0003] In typical back-end processes, after the TiN hard mask is patterned using dry etching, it needs to be completely removed or pulled back using a wet cleaning process to remove fluoropolymer residues generated during etching. However, cleaning processes in advanced manufacturing processes face multiple challenges: First, the back-end processes expose metals such as copper (Cu), cobalt (Co), and tungsten (W), as well as ultra-low dielectric (ULK) dielectric materials, which are susceptible to corrosion damage in fluorinated cleaning solutions. In particular, copper and cobalt are prone to electrochemical corrosion in acidic fluorinated systems, leading to increased metal wire roughness, increased resistance, and even device failure.

[0004] Secondly, traditional wet TiN removal methods are mainly divided into two categories: alkaline hydrogen peroxide systems and acidic fluorine-containing systems. Alkaline systems have relatively low corrosivity to metals, but the TiN etching rate is slow, making it difficult to meet the production capacity requirements of thick-film hard masks; acidic fluorine-containing systems have a fast etching rate, but corrosion control of metals such as Cu and Co is difficult, and usually requires the addition of multiple corrosion inhibitors.

[0005] In existing technologies, benzotriazole (BTA) and triazole compounds are commonly used as copper corrosion inhibitors. However, these nitrogen-containing heterocyclic compounds tend to leave residues on metal surfaces, making subsequent cleaning difficult, and they also exhibit some environmental toxicity. Furthermore, a single corrosion inhibitor cannot effectively protect multiple metals such as Cu, Co, and W simultaneously. The core of benzotriazole (BTA) corrosion inhibition lies in the triazole ring in the BTA molecule providing a lone pair of electrons, which interact with the Cu on the Cu surface. +It forms a one-dimensional chain-like chelate polymer, densely covering the metal surface and blocking the penetration of corrosive media. Co has high metallic reactivity, and zero-valent Co atoms are difficult to stably exist on the surface. BTA and Co... 2+ The resulting complex has high solubility and a porous film, making it unable to block H. + and F - Furthermore, under acidic conditions, the Co surface continuously undergoes active dissolution, making it difficult for BTA to stably adsorb and form a film. Typically, the BTA concentration needs to be increased several times to achieve a weak effect, which poses a serious risk of residue. The W surface is normally covered by a WO3 oxide film. BTA is an adsorption-type corrosion inhibitor targeting metallic atoms and cannot form effective coordination adsorption on the metal oxide surface; simultaneously, BTA lacks fluoride ion shielding capability and cannot block F. - It erodes the WO3 passivation film, therefore it has virtually no inhibitory effect on tungsten corrosion.

[0006] Amino acid ionic liquids (AAILs) are a class of green ionic liquids prepared from natural amino acids, possessing advantages such as low toxicity, biodegradability, and designable structures. Existing research indicates that AAILs exhibit good corrosion inhibition effects on steel in acidic media, but there are no reports on their application in semiconductor TiN hard mask cleaning systems.

[0007] Therefore, developing a TiN hard mask cleaner with controllable etching rate, excellent multi-metal compatibility, environmental friendliness, and no residue is an urgent need in the field of advanced semiconductor manufacturing processes.

[0008] Amino acid-based ionic liquids are not traditional single-adsorption corrosion inhibitors, but multifunctional interface modifiers designed specifically for the corrosion characteristics of three metals. Their special functions are reflected in the following four aspects: 1. Multifunctional group adaptation enables differentiated coordination protection of three metals. The side chain functional groups of amino acid anions can precisely match the surface properties of the three metals, an advantage that neither BTA nor ordinary amino acids possess. For Cu: strong coordination with thiol / amino groups results in enhanced antioxidant capacity. The sulfhydryl group (-SH) of cysteine ​​has a much stronger affinity for Cu than the nitrogen heterocycle of BTA, and can simultaneously bind to Cu. + / Cu² + It forms stable coordination bonds; even under high oxidant conditions, the coordination stability of the thiol group is better than that of BTA, and it is not easily oxidized and deactivated.

[0009] Targeting strong chelation of Co: imidazole ring / polyamino groups, adapted to oxidized surfaces The imidazole ring of histidine and the α-amino group plus the side-chain amino group of lysine can react with Co²⁻. + It forms a five-membered chelate ring, and the film stability is much higher than that of the BTA-Co complex. At the same time, the carboxyl group can form hydrogen bonds / coordination with the oxidation sites on the Co surface, so that it can be adsorbed on both metallic Co and oxidized Co surface, thus solving the problem that BTA cannot be adapted to active metals.

[0010] Targeting the effects of W: guanidinyl / polyamino acid bases to seal passivation film defects. The guanidinyl group of arginine and the polyamino group of lysine are strong basic groups. They can be adsorbed onto the acidic WO3 passivation film on the W surface through acid-base interactions, forming a dense organic adsorption layer that directly blocks F. - Penetration into defects in the passivation film. This is a pathway that BTA completely lacks, and it is also the core reason for achieving W corrosion inhibition.

[0011] By combining amino acid ionic liquids with different side chains, synergistic corrosion inhibition of Cu, Co, and W metals can be achieved, and the etching rates of all three metals in a single system can be controlled below 2 Å / min. Summary of the Invention

[0012] The purpose of this invention is to overcome the technical defects of existing fluorine-based TiN hard mask cleaning agents, such as severe corrosion of downstream metal materials like Cu, Co, and W, easy residue of corrosion inhibitors, and poor environmental friendliness. This invention provides a fluorine-based TiN hard mask cleaning agent with amino acid ionic liquid as a multifunctional special additive.

[0013] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: A fluorine-based TiN hard mask cleaning agent containing amino acid ionic liquid, comprising the following components by mass percentage: Fluoride etchant 0.5%–15%; Oxidizing agent 1%–25%; Amino acid ionic liquids: 0.05%–8%; Chelating agent 0.1%–10%; pH adjuster 0.1%–5%; The remainder is deionized water; The pH value of the cleaning agent is 4.0 to 7.5.

[0014] Further, the fluoride etchant is selected from one or more combinations of ammonium bifluoride, ammonium fluoride, hydrofluoric acid, tetramethylammonium fluoride, and tetraethylammonium fluoride. Preferably, the fluoride etchant is a buffered fluorine system composed of ammonium bifluoride and ammonium fluoride in a mass ratio of 1:0.5 to 1:3.

[0015] Under acidic conditions, ammonium bifluoride dissociates to produce HF2. - It is the main active species in TiN etching, capable of effectively breaking Ti-N bonds and reacting with Ti. 4+ A soluble fluorine-titanium complex is formed. Ammonium fluoride, as a buffer component, can regulate the concentration of free fluoride ions, thereby achieving precise control of the etching rate.

[0016] Furthermore, the oxidant is selected from one or more combinations of hydrogen peroxide, ammonium persulfate, peracetic acid, and m-chloroperoxybenzoic acid; preferably hydrogen peroxide.

[0017] The role of the oxidant is to oxidize the Ti in TiN. 3+ Oxidation to Ti 4+ This promotes the dissolution reaction of TiN. The overall dissolution reaction of TiN can be expressed as: 2TiN + 3H2O2+ 12HF → 2H2TiF6+ N2↑+ 6H2O Furthermore, the amino acid ionic liquid is a choline-amino acid type ionic liquid, wherein the cation is a choline ion and the anion is a deprotonated amino acid ion. The amino acid is selected from one or more of glycine, alanine, serine, cysteine, histidine, lysine, arginine, aspartic acid, and glutamic acid.

[0018] Preferably, the amino acid ionic liquid is selected from one or more combinations of choline glycine salt [Ch][Gly], choline cysteine ​​salt [Ch][Cys], choline histidine salt [Ch][His], choline lysine salt [Ch][Lys], and choline arginine salt [Ch][Arg].

[0019] In this invention, amino acid ionic liquids perform multiple functions: Corrosion inhibition function: The carboxyl, amino, and thiol groups in amino acid anions can form coordination bonds with empty orbitals on the surface of metals such as Cu, Co, and W through lone pair electrons, forming a dense adsorption protective film on the metal surface and blocking F. - and H + Erosion; Complexing function: Amino acid anions can react with dissolved Ti 4+ Cu 2+ Co 2+ The metal ions form a stable complex to prevent redeposition of metal ions and maintain the service life of the etching solution. pH buffering function: Amino acid ionic liquid itself has acid-base buffering capacity, which can maintain the stability of pH value during the cleaning process; Surface-active function: Choline cations have certain surface activity, which can reduce the surface tension of the solution and improve the wetting and penetration ability of high aspect ratio structures.

[0020] In particular, cysteine ​​ionic liquids containing thiol groups exhibit excellent corrosion inhibition effects on copper, histidine ionic liquids containing imidazole rings show outstanding corrosion inhibition effects on cobalt, and arginine ionic liquids containing guanidine groups provide good protection for tungsten. By compounding different types of amino acid ionic liquids, synergistic corrosion inhibition of multiple metals can be achieved.

[0021] Furthermore, the chelating agent is selected from one or more combinations of ethylenediaminetetraacetic acid and its salts, diethylenetriaminepentaacetic acid and its salts, citric acid, tartaric acid, oxalic acid, aminotriacetic acid, and hydroxyethylethylenediaminetriacetic acid.

[0022] Chelating agents are used to complex metal ions in the solution, preventing the precipitation of metal hydroxides, while also enhancing the dissolution driving force of TiN.

[0023] Furthermore, the pH adjuster is selected from one or more of sulfuric acid, phosphoric acid, acetic acid, ammonia, and tetramethylammonium hydroxide.

[0024] Furthermore, the cleaning agent also includes 0.01% to 3% of a nonionic surfactant, wherein the nonionic surfactant is selected from one or more of fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, polyethylene glycol, polypropylene glycol, and ethylene oxide-propylene oxide copolymer.

[0025] Furthermore, the cleaning agent also includes 1% to 20% of an organic solvent selected from one or more of ethylene glycol, propylene glycol, glycerol, dimethyl sulfoxide, sulfolane, and N-methylpyrrolidone. The organic solvent can improve the solubility of fluoropolymer residues.

[0026] The present invention also provides a method for preparing the above-mentioned cleaning agent, comprising the following steps: (1) Add the chelating agent to the deionized water and stir until completely dissolved; (2) Add amino acid ionic liquid and stir until homogeneous; (3) Add fluoride etchant and stir until completely dissolved; (4) Add pH adjuster to adjust the pH of the system to 4.0-7.5; (5) Finally, add the oxidant and stir until the product is obtained.

[0027] This invention also provides the application of the above-mentioned cleaning agent in semiconductor back-end processes for selectively removing TiN hard mask layers and etching residues. The application process temperature is 25°C to 60°C, and the cleaning time is 30 seconds to 30 minutes.

[0028] Furthermore, the semiconductor back-end process includes copper interconnect, cobalt interconnect or tungsten interconnect structures, and includes low dielectric constant dielectric materials or ultra-low dielectric constant dielectric materials.

[0029] Compared with the prior art, the present invention has the following beneficial effects: Amino acid ionic liquids form coordination adsorption protective films with metal surfaces such as Cu, Co, and W through various functional groups in their molecular structure, which can simultaneously inhibit the corrosion of multiple downstream metals. The etching rates of Cu, Co, and W can all be controlled below 2 Å / min.

[0030] Amino acid ionic liquids are made from natural amino acids, are low in toxicity and have good water solubility, thus avoiding the residue problem of traditional BTA-type corrosion inhibitors.

[0031] It maintains stable etching performance and material compatibility over a wide range of pH 4.0–7.5 and temperatures 25℃–60℃, making it suitable for different production line process conditions. Detailed Implementation

[0032] The technical solution of the present invention will be further illustrated below through specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0033] Reference example for the preparation of amino acid ionic liquids Preparation of choline glycine salt [Ch][Gly]: An equimolar amount of aqueous solution of choline hydroxide was mixed with glycine and stirred at room temperature for 24 hours. After most of the water was removed by rotary evaporation, the mixture was dried under vacuum at 80°C to constant weight to obtain a choline glycinate ionic liquid.

[0034] Similar methods can be used to prepare choline cysteine ​​salt [Ch][Cys], choline histidine salt [Ch][His], choline lysine salt [Ch][Lys], choline arginine salt [Ch][Arg], etc.

[0035] Examples 1-8 and Comparative Examples 1-3 The cleaning agent was prepared according to the components and mass percentages shown in Table 1. The preparation method was as follows: First, the chelating agent was dissolved in deionized water and stirred until dissolved. Then, amino acid ionic liquid was added, followed by fluoride etchant. The pH was adjusted to the target value using a pH adjuster. Finally, the oxidant was added and stirred until homogeneous.

[0036] Table 1. Composition (mass percentage) of the formulations for the examples and comparative examples

[0037] Performance testing methods TiN Etching Rate Test: PVD-deposited TiN thin film wafers were immersed and cleaned at 40°C for 5 minutes. The film thickness change before and after cleaning was measured using a four-probe resistance meter or ellipsometry, and the etching rate was calculated.

[0038] Metal etching rate test: Electroplated Cu thin film, PVD Co thin film and CVD W thin film wafers were used respectively. The film thickness change before and after cleaning was tested under the same conditions, and the etching rate of each metal was calculated.

[0039] ULK Material Compatibility Test: Using a ULK dielectric film with a k-value of 2.5, the changes in dielectric constant and film thickness before and after cleaning were tested.

[0040] Surface residue test: After cleaning, the wafer surface was rinsed with deionized water and dried with nitrogen. X-ray photoelectron spectroscopy (XPS) was used to detect the organic residue on the wafer surface.

[0041] Bath life test: TiN powder was continuously added to the solution, and the total amount of dissolved TiN was monitored when the TiN etching rate dropped to 80% of the initial value.

[0042] Test Results The performance test results are shown in Table 2.

[0043] Table 2 Performance test results of the examples and comparative examples

[0044] The test results show that: (1) The TiN etching rate of the present invention is adjustable in the range of 90 to 410 Å / min, which can meet different process requirements.

[0045] (2) Compared with Comparative Example 3 (without corrosion inhibitor), the etching rates of Cu, Co and W were significantly reduced in the example with added amino acid ionic liquid, all of which were controlled below 2 Å / min, showing excellent corrosion inhibition effect.

[0046] (3) Compared with Comparative Example 1 (traditional BTA corrosion inhibitor), the amino acid ionic liquid of the present invention has a similar or even better corrosion inhibition effect, and there is no organic residue after cleaning, while BTA has obvious surface residue problems.

[0047] (4) Compared with Comparative Example 2 (ordinary amino acids), the corrosion inhibition effect of ordinary amino acids was far worse than that of amino acid ionic liquids, proving that the structure of ionic liquids plays a key role in exerting corrosion inhibition function. The synergistic effect of choline cations and amino acid anions significantly improved the corrosion inhibition performance.

[0048] (5) Examples 5-8 By compounding multiple amino acid ionic liquids, balanced protection of Cu, Co and W metals was achieved, with the best overall performance.

[0049] (6) Regarding bath life, the formula of this invention is 28% to 50% longer than the traditional formula, thanks to the strong complexing ability of amino acid ionic liquid.

[0050] Application Examples The cleaning agent formulation of Example 6 was used to perform TiN hard mask removal on a wafer with a 14nm node back-end interconnect structure. Process conditions: temperature 40°C, single-wafer spray cleaning, time 120 seconds.

[0051] The results show that the TiN hard mask was completely removed, and the fluoropolymer residues on the sidewalls of the vias and trenches were thoroughly cleaned; the surfaces of the Cu and Co metal lines were smooth with no obvious corrosion marks; the dielectric constant of the ULK dielectric layer showed no deterioration; and the residual metal ions on the wafer surface after cleaning were all below 1×10⁻⁶. 10 atoms / cm 2 It meets the cleanliness requirements of advanced manufacturing processes.

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A fluorine-based TiN hard mask cleaning agent for advanced back-end semiconductor processes, comprising a fluoride etchant, an oxidant, a chelating agent, a pH adjuster, and deionized water, characterized in that, The content of each component, by mass percentage, is as follows: Fluoride etchant 0.5%–15%; Oxidizing agent 1%–25%; Amino acid ionic liquids: 0.05%–8%; Chelating agent 0.1%–10%; pH adjuster 0.1%–5%; The remainder is deionized water; The pH value of the cleaning agent is 4.0–7.5; The amino acid ionic liquid is a choline-amino acid type ionic liquid, with choline cations and deprotonated amino acid anions.

2. The fluorine-based TiN hard mask cleaning agent according to claim 1, characterized in that, The fluoride etchant is selected from one or more combinations of ammonium hydrogen fluoride, ammonium fluoride, hydrofluoric acid, tetramethylammonium fluoride, and tetraethylammonium fluoride. The fluoride etchant is a buffer fluorine system composed of ammonium hydrogen fluoride and ammonium fluoride in a mass ratio of 1:0.5 to 1:

3.

3. The fluorine-based TiN hard mask cleaning agent according to claim 1, characterized in that, The oxidant is selected from one or more combinations of hydrogen peroxide, ammonium persulfate, peracetic acid, and m-chloroperoxybenzoic acid; the amino acid corresponding to the anion of the amino acid ionic liquid is selected from one or more of glycine, alanine, serine, cysteine, histidine, lysine, arginine, aspartic acid, and glutamic acid.

4. The fluorine-based TiN hard mask cleaning agent according to claim 3, characterized in that, The amino acid ionic liquid is selected from one or more combinations of choline glycine salt [Ch][Gly], choline cysteine ​​salt [Ch][Cys], choline histidine salt [Ch][His], choline lysine salt [Ch][Lys], and choline arginine salt [Ch][Arg]. The amino acid ionic liquid is a compound mixture of choline cysteine ​​salt, choline histidine salt, and choline arginine salt, with a mass ratio of 1:0.5 to 2:0.5 to 2.

5. The fluorine-based TiN hard mask cleaning agent according to claim 1, characterized in that, The chelating agent is selected from one or more combinations of ethylenediaminetetraacetic acid and its salts, diethylenetriaminepentaacetic acid and its salts, citric acid, tartaric acid, oxalic acid, aminotriacetic acid, and hydroxyethylethylenediaminetriacetic acid. The pH adjuster is selected from one or more acidic adjusters among sulfuric acid, phosphoric acid, and acetic acid, or from one or more alkaline adjusters among ammonia and tetramethylammonium hydroxide.

6. The fluorine-based TiN hard mask cleaning agent according to claim 1, characterized in that, The cleaning agent also contains 0.01% to 3% of a nonionic surfactant, wherein the nonionic surfactant is selected from one or more of fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, polyethylene glycol, polypropylene glycol, and ethylene oxide-propylene oxide copolymer; The cleaning agent also contains 1% to 20% of an organic solvent, wherein the organic solvent is selected from one or more of ethylene glycol, propylene glycol, glycerol, dimethyl sulfoxide, sulfolane, and N-methylpyrrolidone; The pH value of the cleaning agent is 5.0 to 7.

5.

7. The fluorine-based TiN hard mask cleaning agent according to any one of claims 1-6, characterized in that, Under test conditions of 40°C, the etching rate of the cleaning agent on TiN is 50–500 Å / min, and the etching rate on copper, cobalt, and tungsten is no higher than 2 Å / min.

8. A method for preparing the fluorine-based TiN hard mask cleaning agent according to any one of claims 1 to 7, characterized in that, Specifically, the following steps are included: (1) Add chelating agent to the prescribed amount of deionized water and stir at 20-30°C until completely dissolved; (2) Add amino acid ionic liquid to the solution obtained in step (1) and stir continuously until the system is homogeneous and transparent; (3) Add fluoride etchant to the solution obtained in step (2) and stir until completely dissolved; (4) Add a pH adjuster to the solution obtained in step (3) to adjust the pH value of the system to the target range; (5) Cool the solution obtained in step (4) to 15-25°C, add the oxidant, stir evenly, filter and discharge to obtain the finished cleaning agent.

9. The application of the fluorine-based TiN hard mask cleaner according to any one of claims 1 to 7 in semiconductor back-end interconnect processes, characterized in that, The cleaning agent is used to selectively remove the TiN hard mask layer on the wafer surface and fluoropolymer residues remaining after dry etching.

10. The application according to claim 9, characterized in that, The cleaning process temperature is 25℃~60℃; when using single-wafer spray cleaning, the processing time is 30 seconds to 5 minutes; when using tank immersion cleaning, the processing time is 5 to 30 minutes. The semiconductor back-end interconnect process is a back-end interconnect process of 14nm and below technology nodes, and the wafer surface is simultaneously exposed with at least one metal interconnect material selected from copper, cobalt and tungsten, as well as a low dielectric constant or ultra-low dielectric constant dielectric material.

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