Chemical mechanical polishing solution of copper-cobalt interconnection structure and dynamic galvanic corrosion regulation and control method in copper-cobalt chemical mechanical polishing process

Abstract

The invention provides a chemical-mechanical polishing solution of a copper-cobalt interconnection structure and a dynamic galvanic corrosion regulation and control method in a copper-cobalt chemical-mechanical polishing process, and aims to regulate and control dynamic galvanic corrosion of copper and cobalt in the polishing process based on a dynamic electrochemical device, so as to develop the chemical-mechanical polishing solution suitable for the copper-cobalt interconnection structure. The polishing solution comprises, by mass concentration, 0.5%-10% of a grinding agent, 0.1%-10% of an oxidizing agent, 0.5%-5% of a complexing agent and 0.1%-5.0% of an inhibitor, the complexing agent is methylglycine diacetic acid or sodium salt thereof, the inhibitor is abietic acid or derivatives thereof, dynamic galvanic corrosion in the copper-cobalt polishing process is inhibited, and the polishing effect is good. And meanwhile, synchronous polishing of the copper material and the cobalt material is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of copper-cobalt chemical mechanical polishing, and in particular relates to a chemical mechanical polishing liquid for a copper-cobalt interconnect structure and a method for controlling dynamic galvanic corrosion in a copper-cobalt chemical mechanical polishing process. Background Art

[0002] The chip substrate contains hundreds of millions of transistors, which are connected by metal interconnect structures to form a complete circuit system. The interconnect structure consists of a metal conductive layer and an insulating dielectric layer. In the early integrated circuit process, aluminum was used as a conductive material. With the introduction of the Damascus process, it was replaced by copper wiring. Compared with metal aluminum, copper has a lower resistivity, which improves the device operation speed. At the same time, it has stronger resistance to electromigration and no wedge phenomenon, which improves chip reliability. However, the diffusion coefficient of copper in the dielectric layer is large, which is easy to cause metal contamination and has poor adhesion. Therefore, when forming metal wiring in the dielectric layer, it is necessary to first introduce a layer of tantalum as a barrier layer to inhibit the diffusion of copper and improve the adhesion between copper and the substrate. With the further reduction of chip feature size, the tantalum barrier layer is difficult to further thin, and its high resistivity disadvantages become more and more significant. In the interconnect structure of some cutting-edge chips, it is replaced by cobalt. Compared with tantalum, the cobalt barrier layer can be thinner during preparation, has a lower resistivity, and has better adhesion to copper.

[0003] After the barrier layer is formed, copper wiring is usually achieved by electroplating, and the excess copper on the surface after electroplating needs to be further removed by chemical mechanical planarization (CMP) process. At present, chemical mechanical polishing has become a key process in chip manufacturing. It can not only remove excess materials, but also achieve nano-level or even atomic-level roughness of the copper surface after polishing. However, due to the great differences in the physicochemical properties of cobalt, copper and tantalum, the current polishing liquid for copper / tantalum structure is not applicable to the new copper / cobalt interconnection structure. In particular, cobalt has active chemical properties. It will not only suffer severe chemical corrosion in the polishing liquid, but also form a corrosion couple with copper, causing electrochemical corrosion of cobalt, which in turn causes the loss of the barrier layer and the formation of defects.

[0004] It should be pointed out that although there are existing achievements in developing new chemical mechanical polishing solutions for copper / interconnect structures, they often focus on polishing rate, selectivity, chemical corrosion control and roughness of the surface after polishing. Few achievements focus on the loss of barrier layer that may be caused by galvanic corrosion of copper and cobalt, and are compatible with the above requirements. It is generally believed that if the corrosion potential difference of the metal in the solution is controlled within 20 millivolts (mV), it can be considered that galvanic corrosion inhibition has been achieved. Summary of the invention

[0005] In response to the above technical problems, the present invention provides a chemical mechanical polishing liquid for a copper-cobalt interconnect structure and a method for controlling dynamic galvanic corrosion during the copper-cobalt chemical mechanical polishing process, which can not only meet the copper-cobalt selectivity ratio during the polishing process, but also inhibit the galvanic corrosion during the copper-cobalt polishing process, thereby avoiding the generation of defects.

[0006] To achieve the above object, the technical solution of the present invention is:

[0007] A chemical mechanical polishing liquid for a copper-cobalt interconnect structure comprises, by mass concentration, 0.5-10% of abrasive, 0.1-10% of oxidant, 0.5-5% of complexing agent and 0.1-5.0% of inhibitor.

[0008] The complexing agent is methylglycine diacetic acid or its sodium salt, and the inhibitor is rosin acid or its derivatives.

[0009] During chemical mechanical polishing, material removal is achieved through the continuous generation and removal of metal oxides. Polishing fluids often contain four basic components: abrasives, oxidants, chelating agents, and inhibitors. Oxidants can promote the formation of oxide films on the surface of copper or cobalt, which are then partially dissolved by chelating agents. The corroded oxide films are porous and loose, making them easier to be removed by abrasive particles. Inhibitors can balance this process, prevent excessive corrosion of the metal, and reduce the probability of defects. In addition, chelating agents and inhibitors have an impact on the corrosion potential of the metal.

[0010] Preferably, the abrasive comprises 5%, oxidant 0.5%, complexing agent 0.4-0.5% and inhibitor 0.5-0.9% by mass concentration. More preferably, the abrasive comprises 5%, oxidant 0.5%, complexing agent 0.4% and inhibitor 0.5% by mass concentration.

[0011] The inhibitor is rosin acid or its derivatives, such as disproportionated rosin acid and its salts. Since the salts of rosin acid or its derivatives have an amphiphilic structure, they can also act as surfactants, which can significantly reduce impurities after polishing, such as residual abrasive particles.

[0012] Preferably, the polishing liquid further comprises a pH regulator for adjusting the pH of the polishing liquid to 8-11;

[0013] The pH regulator is any one of nitric acid solution, potassium hydroxide solution, organic base hydroxylamine or a mixture thereof.

[0014] Preferably, the abrasive is selected from silicon dioxide, cerium dioxide or aluminum oxide, and the particle size of the abrasive is 20-200 nm.

[0015] Preferably, the oxidizing agent is selected from hydrogen peroxide.

[0016] The present invention also provides a method for controlling dynamic galvanic corrosion in the copper-cobalt chemical mechanical polishing process, which uses a dynamic electrochemical device for control.

[0017] The dynamic electrochemical device comprises an electrochemical workstation, a rotating disk electrode, a counter electrode and a reference electrode, a polishing head and a controllable rotating table. The rotating disk electrode, the counter electrode and the reference electrode are electrically connected to the electrochemical workstation respectively. The rotating speeds of the rotating disk electrode and the controllable rotating table are adjustable. The lower surface of the polishing head has a groove for embedding the sample.

[0018] During the electrochemical test, the electrode of the rotating disk electrode is threadedly connected to the polishing head, and the copper sample or the cobalt sample is embedded in the groove of the polishing head to form a working electrode. The rotating disk electrode presses the polishing head onto the polishing table of the controllable rotating table. The polishing head and the rotating table rotate simultaneously. The working electrode, the counter electrode and the reference electrode form a three-electrode system to perform a Tafel polarization curve test. The dynamic corrosion potential of the sample is obtained from the Tafel curve, thereby regulating the polishing liquid components.

[0019] The chemical mechanical polishing solution is used, and the polishing solution is transported between the sample and the polishing table by a peristaltic pump.

[0020] Preferably, the working electrode and the rotating stage rotate at a speed of 50-200 rpm, the peristaltic pump flow rate is 50-200 ml / min, and the pressure on the sample is 0.5-3 pounds per square inch.

[0021] Preferably, during the electrochemical test, a saturated calomel electrode is used as a reference electrode and a platinum electrode is used as a counter electrode.

[0022] Preferably, a polishing pad is laid on the polishing table, and the polishing pad is a damping cloth; a transparent shielding plate is arranged on the peripheral side of the polishing table.

[0023] Due to the adoption of the above technical solution, the present invention has the following advantages and positive effects compared with the prior art:

[0024] The present invention regulates the dynamic galvanic corrosion of copper and cobalt during the polishing process based on a dynamic electrochemical device, and further develops a chemical mechanical polishing liquid suitable for a copper-cobalt interconnect structure, thereby suppressing the dynamic galvanic corrosion of copper and cobalt during the polishing process, and realizing synchronous polishing of the two materials of copper and cobalt. The polishing rate is about 1:1, and the surface roughness of the copper after polishing is at the nanometer level. At the same time, the inhibitor used also has the function of a surfactant, which greatly reduces the residue of abrasive particles. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A simplified schematic diagram of a dynamic electrochemical device is provided for the present invention;

[0026] Figure 2The present invention adopts the polishing liquid of Example 3 and Comparative Example 3, and uses the Tafel polarization curve of dynamic electrochemical test;

[0027] Figure 3 The polishing liquids of Example 3 and Comparative Example 3 of the present invention are used to test the surfaces of copper and cobalt after polishing using dynamic electrochemical testing.

[0028] Explanation of the accompanying drawings: 1-electrochemical workstation; 2-counter electrode; 3-reference electrode; 4-working electrode; 5-rotating disk electrode; 6-polishing head; 7-controllable rotating table; 8-polishing table. DETAILED DESCRIPTION

[0029] The following is a further detailed description of a chemical mechanical polishing solution for a copper-cobalt interconnect structure and a method for controlling dynamic galvanic corrosion during chemical mechanical polishing of copper-cobalt in conjunction with the accompanying drawings and specific embodiments. The advantages and features of the present invention will become more apparent from the following description.

[0030] See also Figure 1 The method for controlling dynamic galvanic corrosion during copper-cobalt chemical mechanical polishing provided by the present invention adopts a dynamic electrochemical device to control dynamic galvanic corrosion, thereby controlling the components of the polishing liquid;

[0031] The dynamic electrochemical device comprises an electrochemical workstation 1, a rotating disk electrode 5, a counter electrode 2 and a reference electrode 3, a polishing head 6 and a controllable rotating table 7. The rotating disk electrode 5, the counter electrode 2 and the reference electrode 3 are electrically connected to the electrochemical workstation 1 respectively. The rotation speeds of the rotating disk electrode 5 and the controllable rotating table 7 are adjustable. The lower surface of the polishing head 6 has a groove for embedding a sample. A transparent shielding plate is provided on the peripheral side of the polishing table 8 of the controllable rotating table 7.

[0032] During the electrochemical polishing test, the electrode of the rotating disk electrode 5 is threadedly connected to the polishing head 6, and the copper sample or the cobalt sample is embedded in the groove of the polishing head 6 to form a working electrode 4. The rotating disk electrode 5 presses the polishing head 6 onto the polishing table 8 of the controllable rotating table 7, and a polishing pad is laid on the polishing table 8. The rotating disk electrode 5 drives the polishing head 6 to rotate, and the controllable rotating table 7 drives the rotating table 7 to rotate. The polishing liquid is transported between the sample and the polishing pad through a peristaltic pump;

[0033] The Tafel polarization curve was tested in a three-electrode system consisting of a saturated calomel electrode as the reference electrode and a platinum electrode as the counter electrode. The dynamic corrosion potential of the sample was obtained from the Tafel curve, thereby adjusting the polishing liquid components.

[0034] When preparing the polishing liquid, according to the components and contents of each embodiment and comparative example in Table 1 below, first, add the complexing agent methylglycine diacetic acid to deionized water and stir evenly, leaving a small amount of deionized water for subsequent pH adjustment; use potassium hydroxide aqueous solution to adjust the pH to a specified value; then, add silica sol and disproportionate potassium rosin acid aqueous solution, and finally add the oxidant hydrogen peroxide. Wherein Table 1

[0035] Table 1: Slurry components (all mass concentrations)

[0036] Hydrogen Peroxide Methylglycine diacetic acid pH Silica Sol Potassium disproportionate rosin acid Comparative Example 1 0.5 0 9.7 5.0 0 Comparative Example 2 0.5 0.2 9.7 5.0 0 Comparative Example 3 0.5 0.4 9.7 5.0 0 Comparative Example 4 0.5 0.6 9.7 5.0 0 Comparative Example 5 0.5 0.8 9.7 5.0 0 Comparative Example 6 0.5 1.0 9.7 5.0 0 Comparative Example 7 0.5 0.4 glycine 9.7 5.0 0.5 Embodiment 1 0.5 0.4 9.7 5.0 0.1 Embodiment 2 0.5 0.4 9.7 5.0 0.3 Embodiment 3 0.5 0.4 9.7 5.0 0.5 Embodiment 4 0.5 0.4 9.7 5.0 0.7 Embodiment 5 0.5 0.4 9.7 5.0 0.9

[0037] Note: The mass concentration of silica sol in the table is the mass concentration of solid silicon dioxide.

[0038] Polishing tests were conducted using the above-mentioned dynamic electrochemical apparatus using a two-inch copper workpiece and a cobalt workpiece, and the polishing rates were calculated.

[0039] The process conditions are as follows: the polishing table speed of the controllable rotating table is 75 rpm, the polishing liquid feed flow rate is 50 ml / min, and the polishing head pressure is 1.6 pounds per square inch. The polishing time is two minutes, and after the end, it is washed with deionized water and dried with nitrogen. The test results are shown in Table 2.

[0040] Copper polishing rate Cobalt polishing rate Select ratio Copper Corrosion Potential Cobalt Corrosion Potential Corrosion potential difference Comparative Example 1 7.8 0 0.00 175.6 62.6 113 Comparative Example 2 21.0 8.9 0.42 164.3 32.7 131.6 Comparative Example 3 29.5 17.2 0.58 152.3 24.1 128.2 Comparative Example 4 46.5 19.3 0.42 148.7 13.9 134.8 Comparative Example 5 57.6 21.5 0.37 143.2 5.3 137.9 Comparative Example 6 75.6 23.4 0.31 139.6 -7.6 147.2 Comparative Example 7 352.1 17.6 0.039 76.4 -24.9 101.3 Embodiment 1 25.4 16.3 0.64 148.3 63.6 84.7 Embodiment 2 18.9 15.9 0.84 144.9 112.8 32.1 Embodiment 3 12.9 13.3 1.03 143.3 142.0 1.3 Embodiment 4 10.0 12.3 1.23 140.1 145.2 -5.1 Embodiment 5 9.6 11.6 1.21 139.7 152.9 -13.2

[0041] From the six comparative examples in Table 2, it can be seen that with the introduction of the complexing agent methylglycine diacetic acid, the polishing rates of copper and cobalt increase with the increase of its concentration, while the corrosion potential decreases with the increase of its concentration. From comparative example 1, it can be seen that the introduction of the complexing agent is necessary for the polishing of the copper / cobalt interconnect structure, because when methylglycine diacetic acid is not present, the polishing rate of cobalt is about 0. However, at this time, the polishing rate of copper is always greater than that of cobalt, and the value of the corrosion potential difference also increases with the introduction of the complexing agent, which is much greater than 20mV.

[0042] In Comparative Example 3 among Comparative Examples 1 to 6, the polishing rates of copper and cobalt are moderate, and the galvanic corrosion difference is relatively small. Based on this, the inhibitor potassium disproportionate rosin acid is introduced to further regulate the polishing rate and corrosion potential difference. At this time, the polishing liquid contains 5.0% silicon dioxide, 0.5% hydrogen peroxide, 0.4% methylglycine diacetic acid and the pH value is 9.7. In the embodiment, with the introduction and increase of the concentration of potassium disproportionate rosin acid, the polishing rates of copper and are reduced, and the selectivity between the two (cobalt polishing rate / copper polishing rate) gradually approaches 1. In the polishing of the barrier layer, the removal rates of copper and cobalt are close, or the polishing rate of the latter is slightly larger, which is beneficial to the overall flattening of the chip. It can be seen from Table 2 that when the concentration of potassium disproportionate rosin acid is greater than 0.5%, the requirements for the selectivity during polishing can be met. But in comparison, as shown in Table 2 and the attached Figure 2As shown in the Tafel curve, when the concentration of potassium disproportionate rosin acid is 0.5, the dynamic corrosion potential difference is the smallest, so it can be considered to be the optimal concentration ratio.

[0043] In Comparative Example 7, glycine (0.4%) commonly used in polishing liquid is used to replace methylglycine diacetic acid in Example 3 as a complexing agent. At this time, the copper polishing rate is much greater than the cobalt polishing rate, and the requirement of a selectivity ratio of 1:1 cannot be met, indicating that methylglycine diacetic acid needs to be matched with rosin acid and its salts to achieve the requirement of a selectivity ratio of 1:1 between copper polishing and cobalt polishing.

[0044] The embodiments of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments. Even if various changes are made to the present invention, if these changes fall within the scope of the claims of the present invention and their equivalents, they still fall within the protection scope of the present invention.

Claims

1. A chemical mechanical polishing solution for a copper-cobalt interconnect structure, characterized in that: According to the mass concentration, it includes 0.5-10% abrasive, 0.1-10% oxidant, 0.5-5% complexing agent and 0.1-5.0% inhibitor. The complexing agent is methylglycine diacetic acid or its sodium salt, and the inhibitor is rosin acid or its derivatives.

2. The chemical mechanical polishing solution for copper-cobalt interconnect structure according to claim 1, characterized in that: Calculated by mass concentration, the composition includes 5% of the grinding agent, 0.5% of the oxidant, 0.4-0.5% of the complexing agent and 0.5-0.9% of the inhibitor.

3. The chemical mechanical polishing solution for copper-cobalt interconnect structure according to claim 1, characterized in that: Calculated by mass concentration, the composition includes 5% of the grinding agent, 0.5% of the oxidant, 0.4% of the complexing agent and 0.5% of the inhibitor.

4. The chemical mechanical polishing solution for copper-cobalt interconnect structure according to claim 1 or 2, characterized in that: The inhibitor is disproportionated rosin acid and its salt.

5. The chemical mechanical polishing solution for copper-cobalt interconnect structure according to claim 1 or 2, characterized in that: The polishing liquid further comprises a pH adjusting agent for adjusting the pH of the polishing liquid to 8-11; The pH regulator is any one of nitric acid solution, potassium hydroxide solution, organic base hydroxylamine or a mixture thereof.

6. The chemical mechanical polishing solution for copper-cobalt interconnect structure according to claim 1, characterized in that: The abrasive is selected from silicon dioxide, cerium dioxide or aluminum oxide, and the particle size of the abrasive is 20-200 nm.

7. The chemical mechanical polishing solution for copper-cobalt interconnect structure according to claim 1, characterized in that: The oxidizing agent is selected from hydrogen peroxide.

8. A method for controlling dynamic galvanic corrosion during copper-cobalt chemical mechanical polishing, characterized in that: Using dynamic electrochemical device for regulation, The dynamic electrochemical device comprises an electrochemical workstation, a rotating disk electrode, a counter electrode and a reference electrode, a polishing head and a controllable rotating table. The rotating disk electrode, the counter electrode and the reference electrode are electrically connected to the electrochemical workstation respectively. The rotating speeds of the rotating disk electrode and the controllable rotating table are adjustable. The lower surface of the polishing head has a groove for embedding the sample. During the electrochemical test, the electrode of the rotating disk electrode is threadedly connected to the polishing head, and the copper sample or the cobalt sample is embedded in the groove of the polishing head to form a working electrode. The rotating disk electrode presses the polishing head onto the polishing table of the controllable rotating table. The polishing head and the rotating table rotate simultaneously. The working electrode, the counter electrode and the reference electrode form a three-electrode system to perform a Tafel polarization curve test. The dynamic corrosion potential of the sample is obtained from the Tafel curve, thereby regulating the polishing liquid components. The chemical mechanical polishing liquid according to any one of claims 1 to 7 is used, and the polishing liquid is transported between the sample and the polishing table through a peristaltic pump.

9. The method for controlling dynamic galvanic corrosion during copper-cobalt chemical mechanical polishing according to claim 8, characterized in that: In the electrochemical test, a saturated calomel electrode was used as the reference electrode and a platinum electrode was used as the counter electrode.

10. The method for controlling dynamic galvanic corrosion during copper-cobalt chemical mechanical polishing according to claim 8, characterized in that: A polishing pad is laid on the polishing table, and the polishing pad is a damping cloth; A transparent shielding plate is arranged on the peripheral side of the polishing table.

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