A chemical mechanical polishing solution for copper barrier layer of BEOL

Abstract

The application discloses a kind of copper barrier layer chemical mechanical polishing fluid for BEOL, belong to the field of semiconductor manufacturing technology.The polishing fluid includes abrasive particles, chelating agent, corrosion inhibitor, oxidizing agent, pH regulator and water.The abrasive particles are P (MMA-EDMA-HEMA) tri-block copolymer nanoparticles, particle size is 60~150 nm, content is 0.5~5wt%;The corrosion inhibitor is triazole small molecule compound, content is 0.005~0.5wt%.The present application replaces traditional inorganic hard abrasive particles with soft elastomeric polymer nanoparticles, provides gentle mechanical force, cooperates with triazole corrosion inhibitor to form a dense passivation film on the copper surface, while maintaining the removal rate of Ta / TaN barrier layer and dielectric material to meet the process requirements, can effectively inhibit the static corrosion of copper, significantly reduce the total amount of scratch, depression and other polishing defects, make wafer surface planarization effect more optimal.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, and in particular to a chemical mechanical polishing slurry for copper barrier layers (BEOL). Background Technology

[0002] With the continuous development of VLSI technology, copper interconnect technology has completely replaced traditional aluminum interconnect technology due to its low resistivity and high electromigration resistance. Copper interconnects are typically implemented using damascus damascene technology, which requires an embedded multilayer interconnect structure. This process involves the removal and planarization of excess copper, the underlying barrier layer Ta / TaN, and dielectric materials. Currently, the most effective method for achieving planarization in copper interconnect technology is chemical mechanical planarization (CMP).

[0003] Chemical mechanical planarization (CMP) is a wafer surface polishing technology based on wet processes. It achieves complete planarization of materials by combining chemical and mechanical forces and is one of the key technologies in integrated circuit manufacturing. For integrated circuit chip manufacturers, producing devices with nanoscale dimensions, low defect rates, and high wafer yields is a crucial foundation and important guarantee for improving corporate economic efficiency and core market competitiveness.

[0004] Chemical mechanical polishing (CMP) slurries are indispensable raw materials in CMP processes, where abrasive particles have a decisive impact on the removal rate, uniformity, defect control, and selectivity of wafer surface materials. Abrasive particles are the source of mechanical force, and traditional CMP abrasives mainly consist of inorganic polishing particles such as fumed silica, colloidal silica, alumina, zirconium oxide, and cerium oxide. However, using polishing slurries containing these inorganic particles for CMP processes easily leads to defects such as scratches, pits, and residues. Since defects directly affect the yield of each chip on the wafer, and thus the competitiveness of the integrated circuit industry, it is necessary to strictly control the uniformity and low defect rate of the wafer surface while meeting the polishing rates and selectivity of various materials during the polishing process. The various materials deposited on the wafer have different physical hardness and chemical resistance, resulting in differences in their polishing performance. Compared to inorganic hard nanoparticles, polymer nanoparticles can provide a relatively mild mechanical force mechanism, and their soft elasticity can effectively reduce the incidence of polishing defects.

[0005] In copper CMP (Chemical Metal Processing), in addition to removing a large amount of copper from the substrate, it is also necessary to consider copper surface defects such as dish-shaped depressions, excessive edge etching, and scratches. Simultaneously, the polishing rates of the barrier layer and dielectric material must be carefully controlled. The core challenge lies in balancing the removal rates of multiple materials and effectively controlling polishing defects: on the one hand, sufficiently high removal rates for the barrier layer and dielectric material are required to achieve planarization efficiency; on the other hand, the static etching rate and dynamic over-etching rate of copper must be strictly controlled to prevent defects such as dish-shaped depressions and excessive edge etching.

[0006] In summary, traditional chemical mechanical polishing slurries mostly use inorganic nanoparticles as abrasive particles. These hard particles mainly undergo rigid deformation during the polishing process, resulting in strong mechanical forces that easily produce defects such as scratches and pits on the wafer surface, seriously affecting chip yield.

[0007] Therefore, there is an urgent need to develop a new type of chemical mechanical polishing slurry that can meet the requirements for the removal rate of the barrier layer and dielectric material, and significantly reduce the static corrosion and total polishing defects of copper to achieve high-quality planarization. Summary of the Invention

[0008] In view of this, this application provides a chemical mechanical polishing slurry for copper barrier layers (BEOL), comprising: abrasive particles, chelating agent, corrosion inhibitor, oxidant, pH adjuster and water; The grinding particles are P(MMA-EDMA-HEMA) triblock copolymer nanoparticles with a particle size of 60-150 nm and a content of 0.5-5 wt%. The corrosion inhibitor is a triazole small molecule compound with a content of 0.005-0.5 wt%.

[0009] Furthermore, the P(MMA-EDMA-HEMA) triblock copolymer nanoparticles are prepared by soap-free emulsion polymerization of monomers methyl methacrylate, ethylene glycol dimethacrylate, and hydroxyethyl methacrylate in a molar ratio of (60~85):(2~10):(10~30). Preferably, the particle size range of the abrasive particles is 80-100 nm.

[0010] Furthermore, the triazole small molecule compound is selected from at least one of 1,2,4-triazole, 3-amino-1,2,4-triazole, benzotriazole, methylbenzotriazole and carboxybenzotriazole.

[0011] Furthermore, the chelating agent is an organic acid selected from one or more of acetic acid, citric acid, oxalic acid, malonic acid, succinic acid, malic acid and tartaric acid, with a content of 0.05-2 wt%.

[0012] Furthermore, the oxidant is selected from one or more of potassium persulfate, ammonium persulfate and hydrogen peroxide, and its content is 0.1-3 wt%.

[0013] Furthermore, the pH value of the polishing solution is 9-12.

[0014] Furthermore, the water is ultrapure water with a resistivity of not less than 18 megohms.

[0015] This application also provides the application of the above-mentioned chemical mechanical polishing slurry in the chemical mechanical polishing of the barrier layer in the back-end process of copper interconnect.

[0016] The beneficial effects of this invention are: (1) P(MMA-EDMA-HEMA) triblock copolymer nanoparticles with soft elasticity are used to replace traditional inorganic hard abrasives, providing a gentle mechanical force. While ensuring an effective removal rate, the total amount of polishing defects such as scratches and pits on the wafer surface can be greatly reduced, thus improving the surface quality.

[0017] (2) Selecting specific triazole small molecule compounds as corrosion inhibitors, through the strong coordination adsorption of nitrogen atoms in their molecules with the copper surface, self-assembling into a dense passivation film, can physically block the corrosive medium and inhibit electrochemical corrosion, thereby significantly reducing the static corrosion rate of copper and effectively preventing over-corrosion of the copper surface.

[0018] (3) Triazole corrosion inhibitors form a stable passivation film on the copper surface to prevent its rapid removal, while their adsorption on the Ta / TaN barrier layer and dielectric material surface is weak, thus having minimal impact on the removal rate of these materials. This allows the polishing slurry to effectively inhibit the static corrosion of copper while maintaining a removal rate for the Ta / TaN barrier layer and dielectric material that meets the process requirements, thereby achieving a high barrier layer / copper removal rate selectivity ratio.

[0019] (4) Organic soft abrasive particles and triazole corrosion inhibitors work synergistically to protect copper from static corrosion and maintain a removal rate that meets process requirements for Ta / TaN barrier layer and dielectric material, while significantly reducing the total polishing defects such as scratches, resulting in better wafer planarization effect. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1This is a comparison chart of the total defect amount on the surface of four wafers after CMP with different Cu polishing solutions in Experiment Example 1.

[0022] Figure 2 This is a comparison chart of the total defects on the surfaces of four wafers after CMP with different Cu polishing solutions in Experiment Example 2.

[0023] Figure 3 A schematic diagram of colloidal silica as abrasive particles.

[0024] Figure 4 A schematic diagram of polymer nanoparticles used as grinding particles. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention. The following embodiments are used to illustrate this invention, but cannot be used to limit the scope of this invention.

[0026] Methods for preparing grinding particles: The P(MMA-EDMA-HEMA) triblock copolymer nanoparticles used in this invention are prepared by soap-free emulsion polymerization. Specifically, pretreated methyl methacrylate (MMA), hydroxyethyl methacrylate (HEMA), and ethylene glycol dimethacrylate (EDMA) are used as monomers, and potassium persulfate is used as an initiator. The polymerization is carried out in a one-pot reaction in a 250 mL three-necked round-bottom flask under high-purity nitrogen protection. The molar percentages of methyl methacrylate, ethylene glycol dimethacrylate, and hydroxyethyl methacrylate are: methyl methacrylate 60%–85%, ethylene glycol dimethacrylate 2%–10%, and hydroxyethyl methacrylate 10%–30%, respectively, and the sum of all components is 100%. Preferably, the monomer molar ratio is 75:5:20. The total monomer concentration is 8–12 wt%, and the initiator dosage is 0.8–1.2% of the total monomer molar amount. The reaction was stirred at 65-75℃ and 300-400 rpm for 5-7 hours. After the reaction, the nanoparticles were centrifuged, dialyzed, concentrated and purified to obtain monodisperse P(MMA-EDMA-HEMA) triblock copolymer nanoparticles with a particle size of 60-150 nm, containing hydroxyl groups on the surface and moderately cross-linked internally.

[0027] Experiment Example 1: Investigating the Effects of Grinding Particle Type and Dosage This experiment investigates the effects of the type and amount of abrasive particles on polishing performance. The comparative example used conventional inorganic colloidal silica as the abrasive particles, while the exemplary example used P(MMA-EDMA-HEMA) triblock copolymer nanoparticles synthesized in this invention.

[0028] The preparation method for each polishing solution is as follows: First, mix the abrasive particles with the chelating agent (citric acid) evenly, adjust the pH of the system to 10.5 with the pH adjuster (potassium hydroxide), and add the oxidant (hydrogen peroxide) before use and mix evenly. See Table 1 for specific formulas.

[0029] Table 1: Polishing slurry formulations for Comparative Examples 1A-1C and Examples 1A-1C

[0030] Polishing tests were conducted on blank wafers of copper (Cu), tantalum nitride (TaN), silicon dioxide (TEOS), and low dielectric (BD) materials using polishing slurries from Comparative Examples 1A-1C and Examples 1A-1C, respectively, to compare the effects of different polishing slurries on the polishing rate of the four materials.

[0031] Polishing process parameters: Universal-300T polishing machine, IC1010 polishing pad, downforce 2.0 psi, polishing disc / polishing head speed 87 / 83 rpm, polishing fluid flow rate 200 mL / min, polishing time 1 min.

[0032] Test methods: The removal rate was calculated by measuring the thickness changes of copper and tantalum nitride using a CDE four-probe tester; the removal rate was calculated by measuring the thickness changes of silicon dioxide and low dielectric materials using a non-metallic thin film thickness gauge; and the total number of defects on the surface of each wafer was detected using an SP defect detector.

[0033] Table 2: Removal rates of the six polishing slurries prepared in Experiment 1 on wafers of different materials

[0034] As shown in Table 2, the polishing removal rates of P(MMA-EDMA-HEMA) triblock copolymer nanoparticles on Cu, TaN, TEOS, and BD substrates are all lower than those of inorganic nanoparticles. However, polymer nanoparticles are relatively softer and can provide a gentler mechanical force mechanism, effectively reducing the total number of defects such as dents and scratches while still meeting the requirements of integrated circuit processes. Furthermore, the removal rates of Cu, TaN, TEOS, and BD wafers gradually increase with the increase of polymer nanoparticle dosage.

[0035] like Figure 1As shown, there are significant differences in the total number of defects on the surfaces of Cu, TaN, TEOS, and BD wafers after CMP in Comparative Examples 1A-1C and Examples 1A-1C in Experiment 1. This indicates that when P(MMA-EDMA-HEMA) triblock copolymer nanoparticles are used as polishing abrasives, the total number of defects on the wafer surfaces of all four materials is significantly reduced. Furthermore, the total number of defects is positively correlated with the solid content of the nanoparticles; that is, the higher the solid content, the greater the amount of defects generated.

[0036] During the CMP process, such as Figure 3 As shown, traditional inorganic silica particles mainly undergo rigid deformation, making them difficult to buffer under pressure and easily causing mechanical damage to the wafer surface; while... Figure 4 As shown, polymer nanoparticles, due to their flexibility, undergo elastic deformation under pressure, thereby reducing the amount of defects such as dents and scratches on the wafer surface.

[0037] Experiment Example 2: Investigating the Influence of Corrosion Inhibitor Type This experimental example uses triazole small molecule compounds to inhibit the static corrosion of copper. In Comparative Example 2A and Examples 2A-2E, the copper barrier polishing solution was prepared by first uniformly mixing the abrasive particles, chelating agent, and corrosion inhibitor according to the specified ratio, then adjusting the pH of the system to the required value, adding the oxidant before use, and ensuring the system is thoroughly mixed. The corrosion inhibitor addition details for Comparative Example 2A and Examples 2A-2E are shown in Table 3.

[0038] Table 3: Polishing slurry formulations for Comparative Example 2A and Examples 2A-2E

[0039] Test Method: First, static corrosion tests were conducted on the polishing solutions of Comparative Example 2A and Examples 2A-2E. 50mm copper wafers were immersed in the polishing solution at 45°C for 5 minutes, then removed, rinsed, and dried. The metal layer thickness of the wafers was measured using a CDE four-probe analyzer before and after immersion and cleaning / drying. The static corrosion rate (SER) of copper was calculated based on the wafer film thickness before and after the experiment. Detailed experimental data are shown in Table 4.

[0040] Table 4: Static corrosion results of Cu by polishing solutions of Comparative Example 2A and Examples 2A-2E

[0041] As shown in Table 4, compared with Comparative Example 2A, the addition of different triazole small molecule compounds in Examples 2A-2E all reduced the static corrosion rate of Cu to varying degrees. Furthermore, under the condition that other components such as grinding particles, chelating agents, and oxidants were consistent, the inhibition effect of using carboxybenzotriazole as a corrosion inhibitor was relatively better. Compared with other triazole small molecules, carboxybenzotriazole, in addition to containing a coordinating N atom, also has an oxygen atom in its carboxyl group that can provide an active site, resulting in a superior bidentate chelation inhibition effect.

[0042] Polishing tests were conducted on blank wafers of copper (Cu), tantalum nitride (TaN), silicon dioxide (TEOS), and low dielectric (BD) materials using polishing slurries prepared in Comparative Example 2A and Examples 2A-2E, respectively, to compare the effects of different polishing slurries on the polishing rate of the four materials.

[0043] Polishing rate and defect test: The same polishing parameters and test methods as in Experiment 1 were used to test each group of polishing fluids.

[0044] Table 5: Removal rates of wafers of different materials by the six polishing slurries prepared in Experiment Example 2

[0045] Analysis of the removal rates of Cu, TaN, TEOS, and BD substrates by different polishing solutions in Table 5 shows that using P(MMA-EDMA-HEMA) triblock copolymer nanoparticles as abrasive particles, keeping other components the same, and using different triazole small molecule compounds as corrosion inhibitors, the removal rates of all four substrates decreased to varying degrees. The weak adsorption of triazole small molecules on TEOS and TaN resulted in a minimal decrease in their removal rates; the formation of a protective film on the Cu surface by triazole small molecules significantly reduced the Cu removal rate; and the adsorption of triazole small molecules on the BD material surface reduced its removal rate. Therefore, adding triazole small molecules can adjust the selectivity ratios of TaN / Cu and TaN / BD, thus adapting to different application scenarios.

[0046] like Figure 2 As shown, compared with Comparative Example 2A, with all other components being identical, the addition of different triazole small molecules as corrosion inhibitors had virtually no effect on the total number of defects after TEOS polishing. The total number of defects on the TaN wafer surface decreased slightly due to weak adsorption, while the total number of defects on the Cu and BD wafer surfaces decreased significantly. In Examples 2C-2E, because benzotriazole, methylbenzotriazole, and carboxybenzotriazole had stronger inhibitory effects on Cu than on BD, the total number of defects such as pits and scratches on the Cu surface was slightly lower than that on the BD surface.

[0047] In summary, the copper barrier layer polishing slurry obtained by using P(MMA-EDMA-HEMA) triblock copolymer nanoparticles as abrasive particles, triazole small molecule compounds as corrosion inhibitors, and chelating agents and oxidants under appropriate pH conditions can not only inhibit the static corrosion of copper, but also significantly reduce the total polishing defects such as pits and scratches while ensuring that the removal rate of barrier layer / dielectric materials such as Ta / TaN and SiO2 meets the process requirements, resulting in better wafer planarization.

[0048] 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 chemical mechanical polishing slurry for copper barrier layers (BEOL), characterized in that, Includes: grinding particles, The mixture contains a chelating agent, a corrosion inhibitor, an oxidizing agent, a pH adjuster, and water; the grinding particles are P(MMA-EDMA-HEMA) triblock copolymer nanoparticles with a particle size of 60-150 nm and a content of 0.5-5 wt%; the corrosion inhibitor is a triazole small molecule compound with a content of 0.005-0.5 wt%.

2. The chemical mechanical polishing slurry according to claim 1, characterized in that, The P(MMA-EDMA-HEMA) triblock copolymer nanoparticles are prepared by soap-free emulsion polymerization of monomers methyl methacrylate, ethylene glycol dimethacrylate and hydroxyethyl methacrylate in a molar ratio of (60~85):(2~10):(10~30).

3. The chemical mechanical polishing slurry according to claim 1, characterized in that, The particle size range of the abrasive particles is 80-100 nm.

4. The chemical mechanical polishing slurry according to claim 1, characterized in that, The triazole small molecule compounds are selected from at least one of 1,2,4-triazole, 3-amino-1,2,4-triazole, benzotriazole, methylbenzotriazole and carboxybenzotriazole.

5. The chemical mechanical polishing slurry according to claim 1, characterized in that, The chelating agent is an organic acid, selected from one or more of acetic acid, citric acid, oxalic acid, malonic acid, succinic acid, malic acid and tartaric acid, with a content of 0.05-2 wt%.

6. The chemical mechanical polishing slurry according to claim 1, characterized in that, The oxidant is selected from one or more of potassium persulfate, ammonium persulfate and hydrogen peroxide, and its content is 0.1-3 wt%.

7. The chemical mechanical polishing slurry according to claim 1, characterized in that, The polishing solution has a pH value of 9-12.

8. The chemical mechanical polishing slurry according to claim 1, characterized in that, The water is ultrapure water with a resistivity of not less than 18 megohms.

9. A chemical mechanical polishing method, characterized in that, The polishing slurry described in any one of claims 1 to 8 is used to polish the barrier layer in the back-end process of copper interconnect.

10. The application of the chemical mechanical polishing slurry according to any one of claims 1 to 8 in the BEOL copper barrier layer planarization process.

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