A chemical mechanical polishing liquid suitable for copper-cobalt interconnect structure and preparation method thereof

Abstract

The present invention discloses a chemical mechanical polishing liquid suitable for a copper-cobalt interconnect structure and a preparation method thereof, wherein the polishing liquid comprises 0.1-10% abrasive particles, 0.01-3% oxidant, 0.1-5% complexing agent and 0.01-1.0% inhibitor by mass fraction, and the remainder is deionized water; wherein the inhibitor is rosin acid and its salt, preferably disproportionated rosin acid and its salt, effectively inhibiting the static corrosion of copper and cobalt, and the pH of the polishing liquid is 8-11. An inhibitor of rosin acid and its salt is added to the polishing liquid of the present invention, which can inhibit the crystalline corrosion of copper while maintaining a higher polishing rate of copper, and effectively improve the surface quality after polishing. At the same time, the static corrosion and removal rate of cobalt by the polishing liquid are extremely low, which can meet the requirements of high selectivity in the first step of the polishing process of the interconnect structure.

Description

Technical Field

[0001] The invention belongs to the technical field of microelectronics technology, and in particular relates to a chemical mechanical polishing liquid suitable for a copper-cobalt interconnect structure and a preparation method thereof. Background Art

[0002] Electronicization is an important symbol of the information age, and chips are the foundation of the electronic information industry. The characteristic size of integrated circuits has rapidly developed from the submicron level at the beginning of the century to the nanometer level today, making the chip performance more superior while also consuming less power. Today, each square millimeter of chip substrate can accommodate up to hundreds of millions of transistors, and these transistors are often connected through copper interconnects. The copper interconnect structure includes a copper interconnect layer and a common tantalum / tantalum nitride barrier layer, which can prevent copper atoms from diffusing into the dielectric layer to avoid short circuits and failures of the device. However, at the nanometer-level characteristic size, the difficult-to-thin tantalum / tantalum nitride structure, on the one hand, restricts the further miniaturization of transistors and interconnects, and on the other hand, begins to dominate the resistivity of the entire interconnect structure, causing RC delays in the circuit. Therefore, in the chip manufacturing process, new materials and new processes are urgently needed to meet higher performance and functional requirements.

[0003] As a barrier layer, metal cobalt has been introduced into the structure of advanced chips as a solution by some chip manufacturers who have mastered cutting-edge manufacturing technology. Studies have shown that cobalt as a barrier layer can not only meet the requirements of thinner barrier layers, but also simplify the deposition process, directly electroplating copper without depositing copper seed crystals, and has better electroplating gap filling properties. In addition, compared with tantalum, cobalt has the advantages of lower resistivity and better adhesion to copper. However, chip manufacturing is a complex multi-process process. Although the realization of copper / cobalt interconnection structure has the above advantages, it brings difficulties to the subsequent chemical mechanical planarization (CMP) process: the current mature copper interconnection CMP technology is only applicable to copper / tantalum / tantalum nitride structure, especially commercial CMP polishing liquid, which is not suitable for cobalt, which has large differences in physical and chemical properties with copper and tantalum. And cobalt is often used in chip structures below ten nanometers, and this scale has more stringent and higher precision requirements for CMP itself.

[0004] The flatness of the surface after polishing is related to the requirements of the chip structure itself and also affects the focusing accuracy in the subsequent photolithography process. Therefore, in the context of the continuous miniaturization and multi-layering of chip structures, CMP has become a key technology in chip manufacturing, directly affecting the manufacturing yield and final performance of the chip. The advantage of CMP technology lies in the combination of the physical friction of nanoparticles in the polishing slurry (liquid) and the chemical action of other additive components. It is necessary to achieve high-efficiency removal of excess materials on the surface of the interconnect layer and maintain the roughness of the surface at the nanometer or even atomic level after polishing. Compared with copper and tantalum, cobalt has more active chemical properties. Common commercial acidic polishing liquids have a severe corrosive effect on cobalt, and excessive corrosion can easily cause the loss of the barrier layer. In addition, the polishing rate of cobalt may even exceed that of copper itself, which cannot meet the high selectivity requirements in the first step of CMP, that is, the removal rate of interconnect metal copper should be much greater than the removal rate of barrier layer cobalt. Contradictory to this, too low corrosion rate usually greatly reduces the removal rate of interconnect metal, affecting polishing efficiency.

[0005] CN102304327 uses a polishing liquid containing a thiazole inhibitor for planarizing a copper / cobalt heterostructure. However, the static corrosion rate of the acidic polishing liquid on cobalt is as low as 20nm / min. Considering that the thickness of the cobalt barrier layer is generally less than 5 nanometers, it is very easy to cause excessive dissolution and loss of the sidewall barrier layer, and even desorption of the entire barrier layer. Summary of the invention

[0006] Based on the problems of the prior art, the present invention provides a chemical mechanical polishing liquid suitable for copper-cobalt interconnect structures and a preparation method thereof, so as to meet the requirements of high selectivity, low defects and high-quality surface of copper-cobalt interconnect structures in the chemical mechanical polishing process of chips. An inhibitor of rosin acid and its salts is added to the polishing liquid, which can inhibit the crystalline corrosion of copper while maintaining a high polishing rate of copper, and effectively improve the surface quality after polishing. At the same time, the static corrosion and removal rate of cobalt in the polishing liquid are extremely low, which can meet the requirements of high selectivity in the first step of polishing of the interconnect structure.

[0007] To achieve the above object, the technical solution of the present invention is:

[0008] A chemical mechanical polishing liquid suitable for a copper-cobalt interconnect structure, the polishing liquid comprising, by mass fraction, 0.1-10% abrasive particles, 0.01-3% oxidant, 0.1-5% complexing agent and 0.01-1.0% inhibitor, with the remainder being deionized water;

[0009] The inhibitor is rosin acid and its salts, preferably disproportionated rosin acid and its salts, and more preferably disproportionated rosin potassium solution, which effectively inhibits static corrosion of copper and cobalt. The pH of the polishing liquid is 8-11.

[0010] Preferably, the polishing liquid further comprises a pH regulator for adjusting the pH of the polishing liquid to 8-11. The pH regulator can be any one of nitric acid solution, potassium hydroxide solution, organic base hydroxylamine or a mixture thereof.

[0011] The abrasive particles are used to remove metal or metal reactants in contact with the abrasive particles by mechanical friction, thereby achieving the purpose of mechanical removal. The abrasive particles can be selected from silicon dioxide, cerium dioxide or aluminum oxide particles, wherein silicon dioxide sol is preferably used as the abrasive particles. The particle size of the abrasive particles is preferably 20-200 nm.

[0012] The function of the oxidant is to oxidize the metallic copper and cobalt barrier metals into corresponding metal oxides, hydroxides or ions. Preferably, the oxidant is hydrogen peroxide.

[0013] The role of the complexing agent is to form a chelate with the polishing surface and the metal ions in the polishing solution, which helps to reduce the metal particles in the polishing solution and the metal ion pollution of the polished metal surface. Preferably, the complexing agent is an amino acid. The amino acid can be selected from glycine, arginine, lysine, alanine, leucine, valine, histidine, cysteine, serine and proline.

[0014] Based on the same inventive concept, the present invention also provides a method for preparing a chemical mechanical polishing solution suitable for a copper-cobalt interconnect structure as described above, comprising the following steps:

[0015] According to the mass ratio, the complexing agent is added to deionized water to mix into a solution, and then the pH of the solution is adjusted to 8-11, and then abrasive particles and inhibitors are added and mixed. Before use, an oxidant is added to the solution to obtain a chemical mechanical polishing solution suitable for copper-cobalt interconnect structures.

[0016] Due to the adoption of the above technical solution, the present invention has the following advantages and positive effects compared with the prior art:

[0017] In integrated circuits, Co is used as a barrier layer for the copper interconnect layer. The Co barrier layer and the copper interconnect layer together form a copper interconnect structure. Abietic acid is used as an inhibitor for CMP of the copper interconnect structure. Among the components of the CMP polishing liquid, the inhibitor plays a decisive role in the surface quality after polishing and is the most important component in the polishing liquid. The copper interconnect structure prepared by the Damascus process has an uneven surface due to the grooves formed by photolithography and the patterned structure required by the process. The role of the inhibitor is to adsorb on the metal surface, reduce its static corrosion, effectively avoid over-polishing of the material inside the groove, improve the flattening efficiency, and determine the surface quality after polishing. Compared with the common triazole and thiazole inhibitors in the field, abietic acid is a biological substance and a green inhibitor. Since abietic acid contains conjugated unsaturated double bonds, the common product of its disproportionation, disproportionated abietic acid, is a cheap industrial raw material. Therefore, using disproportionated abietic acid as an inhibitor is relatively environmentally friendly compared to existing inhibitors.

[0018] The CMP polishing liquid of the present invention can achieve extremely low static corrosion effects on copper and cobalt during chemical mechanical polishing of a copper-cobalt interconnect structure, reduce defects after polishing, and help improve flattening uniformity and surface quality after polishing; at the same time, a relatively high copper removal rate and an extremely low cobalt polishing rate can be achieved, achieving high selectivity of copper / cobalt removal speeds, and enabling the selectivity ratio of the removal rates of copper / cobalt materials to be within a range of 21.1-50.3. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a scanning electron microscope image of the surface morphology of a copper wafer that has not been treated with a polishing liquid in an embodiment of the present invention;

[0020] Figure 2 An atomic force microscope image of the surface morphology of a copper wafer not treated with a polishing liquid in an embodiment of the present invention;

[0021] Figure 3 Scanning electron microscope image of the surface morphology of the copper wafer after static etching by the DR-0 polishing liquid in the embodiment of the present invention;

[0022] Figure 4 This is an atomic force microscope image of the surface morphology of the copper wafer after static corrosion by the DR-0 polishing liquid in the embodiment of the invention;

[0023] Figure 5 Scanning electron microscope image of the surface morphology of the copper wafer after static etching by the DR-2 polishing liquid in the embodiment of the present invention;

[0024] Figure 6 This is an atomic force microscope image of the surface morphology of the copper wafer after static corrosion by the DR-2 polishing liquid in the embodiment of the invention. DETAILED DESCRIPTION

[0025] The following is a further detailed description of a chemical mechanical polishing solution suitable for copper-cobalt interconnect structures and a preparation method thereof proposed by the present invention 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.

[0026] 1. Calculate the mass of each component according to the proportion of each component in Table 1. Add glycine to deionized water and stir to dissolve it completely. A small amount of deionized water can be left for subsequent pH adjustment. Use 5% or 45% potassium hydroxide aqueous solution to adjust the pH to the specified value. Then, add silica sol with a particle size of 80 nanometers and potassium disproportionate rosin acid aqueous solution, and finally add hydrogen peroxide when using or the day before.

[0027] Table 1: Slurry composition

[0028] Slurry Hydrogen peroxide / wt% Glycine / wt% pH Silica sol / wt% Potassium disproportionate rosin acid / wt% DR-0 0.4 1.0 9.5 0.0 0.0 DR-1 0.4 1.0 9.5 0.0 0.2 DR-2 0.4 1.0 9.5 0.0 0.3 DR-3 0.4 1.0 9.5 0.0 0.4 DR-4 0.4 1.0 9.5 0.0 0.5 RR-0 0.4 1.0 9.5 3.0 0.0 RR-1 0.4 1.0 9.5 3.0 0.2 RR-2 0.4 1.0 9.5 3.0 0.3 RR-3 0.4 1.0 9.5 3.0 0.4 RR-4 0.4 1.0 9.5 3.0 0.5 RR-5 0.5 1.0 9.5 3.0 0.0 RR-6 0.5 1.0 9.5 3.0 0.3 RR-7 1.0 1.0 9.5 3.0 0.0 RR-8 1.0 1.0 9.5 3.0 0.3 RR-9 0.4 1.0 10.0 0.5 0.3 RR-10 0.4 1.0 10.0 0.5 0.4

[0029] In the above examples, the DR series was used for static corrosion test. To avoid measurement errors, silica sol was not added. The RR series was used for polishing test. Among them, the examples DR-0 and RR-0 do not contain potassium disproportionate rosin acid and are comparative examples.

[0030] 2. Static corrosion

[0031] Static etching simulates the state of depressions formed by patterned wafer design or process during dynamic polishing. Two-inch copper wafers and cobalt wafers were placed in 200 ml of the following slurry, left to stand for 5 minutes, taken out and rinsed with deionized water, and then dried with nitrogen to calculate the static etching rate. The static etching rate is calculated by the weight loss method, that is, the mass difference before and after etching is divided by the product of the workpiece area, density and time.

[0032] Table 2: Static corrosion rate of copper and cobalt (unit: nanometers / minute)

[0033] Slurry DR-0 DR-1 DR-2 DR-3 DR-4 Copper static corrosion rate 82.2 24.1 0.7 0.0 0.0 Cobalt static corrosion rate 0.8 0.0 0.0 0.0 0.0

[0034] DR-0 is a comparative example without potassium disproportionate rosin acid. It can be seen from Table 2 that after the introduction of potassium disproportionate rosin acid, the static corrosion rates of copper and cobalt are greatly reduced, indicating that it has a significant inhibitory effect on the static corrosion of copper and cobalt. Since the concave parts of the wafer are not in contact with the polishing pad, no friction will occur, and only chemical corrosion will occur. Therefore, the static corrosion experiment simulates the state of the concave parts formed by the patterned wafer design or process during the dynamic polishing process. The low static corrosion rate means that CMP can only remove the material at the protrusions, which will be beneficial to the improvement of the flattening efficiency. On the other hand, it can also prevent the polishing liquid from further corroding the interconnect lines that have been flattened internally after polishing, resulting in the loss of the interconnect layer and the barrier layer.

[0035] In the actual CMP process, polishing usually lasts about one minute. Taking copper as an example, a two-inch copper wafer is placed in slurry DR-0 and DR-2 for one minute, then taken out and rinsed with deionized water, and then dried with nitrogen. The sample is placed under an electron microscope to observe the surface morphology, and the surface roughness is measured using an atomic force microscope. Figure 1-6 The results shown in Table 3 correspond to the untreated sample and the samples after being corroded in DR-0 and DR-2. It can be seen that in the DR-0 slurry without potassium disproportionate rosin acid, the copper surface corroded more severely. In DR-2 containing 0.3% potassium disproportionate rosin acid, there is almost no difference between the copper surface and the untreated surface, which further proves the excellent corrosion inhibition effect of potassium disproportionate rosin acid.

[0036] Table 3 Roughness of copper wafer surface

[0037] sample Blank control DR-0 DR-2 Average roughness / nm 1.712 10.162 1.817 Root mean square roughness / nm 2.132 12.781 1.450

[0038] 3. Chemical mechanical polishing

[0039] CMP experiments were performed using a two-inch workpiece, and the polishing rate and selectivity were calculated. The equipment used was a Co-Jing UNIPOL-1203 chemical mechanical polisher with a rotating table and a peristaltic pump. The polishing pad used was IC1010 / SUBA IV with concentric circular grooves. The experiments were performed at room temperature, typically 15-30 degrees Celsius.

[0040] During polishing, the workpiece is adsorbed on the surface of the polishing head and pressed on a rotating table with a polishing pad. The polishing liquid is transported between the workpiece and the polishing pad through a peristaltic pump. The polishing head and the rotating table rotate simultaneously to remove excess material on the workpiece surface and flatten it.

[0041] The process conditions are as follows: polishing table speed 150 rpm, polishing liquid feed flow rate 100 ml / min, polishing head pressure 1.6 pounds per square inch. Polishing time is two minutes, after which it is rinsed with deionized water and dried with nitrogen. The polishing rate and static corrosion rate are calculated in the same way, and the selection ratio is the ratio of copper and cobalt removal rates. The results are shown in Table 4 below.

[0042]

[0043] As can be seen from Table 4, the addition of potassium disproportionate rosin acid also has a certain inhibitory effect on the dynamic CMP process of copper, which can significantly reduce the removal rate of the material. Overall, the slurry component can maintain a high dynamic copper removal rate under the condition of maintaining low static corrosion of copper. At the same time, under the joint action of the slurry composition, the removal rate of cobalt is maintained at a very low level compared to copper, thereby achieving a high selectivity removal of copper / cobalt heterostructures.

[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 suitable for copper-cobalt interconnect structures, It is characterized in that The polishing liquid comprises, by mass fraction, 0.1-10% of abrasive particles, 0.01-3% of an oxidant, 0.1-5% of a complexing agent and 0.2-0.5% of an inhibitor, and the balance is deionized water; The inhibitor is disproportionated rosin acid and its salt, and the pH of the polishing liquid is 8-11; The chemical mechanical polishing solution has a selectivity ratio of 21.1-50.3 for the removal rate of copper / cobalt in the copper-cobalt interconnect structure; The abrasive particles are silicon dioxide, cerium dioxide or aluminum oxide, the particle size of the abrasive particles is 20-200nm, and the complexing agent is amino acid.

2. The chemical mechanical polishing solution suitable for copper-cobalt interconnect structures according to claim 1, It is characterized in that The polishing liquid also includes a pH regulator for adjusting the pH of the polishing liquid to 8-11.

3. The chemical mechanical polishing solution suitable for copper-cobalt interconnect structures according to claim 2, It is characterized in that The pH regulator is any one of nitric acid solution, potassium hydroxide solution, organic base hydroxylamine or a mixture thereof.

4. The chemical mechanical polishing solution suitable for copper-cobalt interconnect structures according to claim 1, It is characterized in that The oxidant is hydrogen peroxide.

5. The chemical mechanical polishing solution suitable for copper-cobalt interconnect structures according to claim 1, It is characterized in that The amino acids are selected from the group consisting of glycine, arginine, lysine, alanine, leucine, valine, histidine, cysteine, serine and proline.

6. A method for preparing a chemical mechanical polishing solution suitable for a copper-cobalt interconnect structure as claimed in any one of claims 1 to 5, It is characterized in that The following steps are involved: According to the mass ratio, the complexing agent is added to deionized water to mix into a solution, and then the pH of the solution is adjusted to 8-11, and then abrasive particles and inhibitors are added and mixed. Before use, an oxidant is added to the solution to obtain a chemical mechanical polishing solution suitable for copper-cobalt interconnect structures.

Images