A chemical mechanical polishing liquid and chemical mechanical polishing method for cobalt interconnect barrier layer titanium

Abstract

The present invention discloses a chemical mechanical polishing liquid and a chemical mechanical polishing method for a cobalt interconnected barrier layer titanium. The chemical mechanical polishing liquid comprises 1-10 wt.% of an abrasive, 0.5-5 wt.% of an oxidant, 10-150 mmol / L of a complexing agent, a pH regulator, and the remainder of water, wherein the complexing agent is citric acid or a citrate. The chemical mechanical polishing liquid of the present invention selects suitable oxidant, complexing agent types and concentration ratios, and under the synergistic effect of the chemical reaction of the chemical substances in the polishing liquid and the mechanical wear of the abrasive particles, improves the material removal rate of the metallic titanium, and obtains a high-quality smooth surface. The polishing liquid has broad application prospects in the CMP process of the cobalt interconnected barrier layer titanium.

Description

Technical Field

[0001] The present invention relates to the technical field of polishing of cobalt interconnect barrier layer titanium, in particular to a chemical mechanical polishing liquid and a chemical mechanical polishing method for cobalt interconnect barrier layer titanium. Background Art

[0002] In traditional integrated circuit technology nodes of 14nm and above, tungsten (W) metal is used as contact plugs and via fill materials, while titanium / titanium nitride (Ti / TiN) bilayer structures serve as liners / diffusion barriers, widely used in local interconnect structures in the middle-of-line (MOL) process. As integrated circuits evolve toward narrower feature sizes and higher aspect ratios, W contact plugs face drawbacks such as high resistivity and the difficulty of conformal deposition without voids. Furthermore, the feature sizes of copper (Cu) used as M0-M1 interconnect fill structures are approaching the physical dimensions of Cu (Cu's electron mean free path is approximately 40nm), leading to a sharp increase in contact resistance in Cu interconnect structures, exacerbating signal transmission delays and interconnect power consumption. Although cobalt (Co) has a higher bulk resistivity, its electron mean free path is only one-quarter that of Cu. Using Co instead of W and Cu as contact plugs and local interconnect fill materials offers lower resistivity and thinner diffusion barriers at low linewidths (<10nm). In addition, Co has the advantages of good substrate adhesion, high electromigration resistance, and easy conformal deposition without voids in high-aspect-ratio interconnect trenches. Therefore, Co is considered to be a new interconnect material that can replace tungsten and copper in MOL.

[0003] Chemical mechanical polishing (CMP) is a process that removes material from the wafer through the synergistic effect of chemical reaction and mechanical wear of abrasive particles. Chemical mechanical polishing runs through all aspects of chip manufacturing and is the only enabling technology for wafer surface flattening. The CMP of Co interconnect structures is specifically divided into two steps: the first step is to remove the material at a higher rate. Rapid removal of bulk Co capping and stopping at the barrier layer; second step with lower removal rate The Co / Ti / TiN / dielectric layer is removed simultaneously, and a controllable heterogeneous material removal rate selectivity and good surface quality after polishing are obtained. It needs to be larger than the interconnect metal Co to avoid the formation of dishing defects in the Co interconnect trench.

[0004] In the traditional W / Ti polishing process, the polishing liquid is generally selected to be acidic, so Ti can maintain a high MRR. However, acidic solutions will cause severe corrosion to the interconnect metal Co, greatly reducing the reliability of logic devices. Therefore, the polishing liquid for the Co interconnect barrier layer Ti still needs to remain weakly alkaline. Usually, the polishing liquid used for metal mainly uses colloidal silicon dioxide (SiO2) as abrasive, hydrogen peroxide (H2O2) as an oxidant, and amino acids or carboxylic acids as complexing agents. Among them, the complexing agent promotes the dissolution rate of the metal by chemically reacting with the outer oxide of the metal and the metal, thereby increasing the MRR of the metal. In a weakly alkaline solution containing H2O2, the surface of Ti will be oxidized to TiO2 with stronger density and higher passivation, thereby reducing the removal rate of Ti. Therefore, it is necessary to find a suitable complexing agent to improve the MRR of Ti. Summary of the Invention

[0005] The purpose of the present invention is to provide a chemical mechanical polishing solution for titanium in a cobalt interconnect barrier layer, in order to solve the problem in the prior art that the surface of Ti will be oxidized into TiO2 with higher density and passivation in a weak alkaline solution containing H2O2, thereby reducing the removal rate of Ti.

[0006] Another object of the present invention is to provide a chemical mechanical polishing method based on the chemical mechanical polishing solution.

[0007] The technical solution adopted to achieve the purpose of the present invention is:

[0008] A chemical mechanical polishing liquid for cobalt interconnect barrier layer titanium consists of 1-10 wt.% abrasive, 0.5-5 wt.% oxidant, 10-150 mmol / L complexing agent, pH regulator and balance water, wherein the complexing agent is citric acid or citrate.

[0009] In the above technical solution, the abrasive is colloidal silica, and the particle size of the colloidal silica is 20-100 nm, preferably 40 nm.

[0010] In the above technical solution, the oxidant is hydrogen peroxide.

[0011] In the above technical solution, the pH regulator is potassium hydroxide, sodium hydroxide, sulfuric acid or nitric acid.

[0012] In the above technical solution, the pH range of the chemical mechanical polishing liquid is 7-10, preferably pH=8.

[0013] In the above technical solution, the complexing agent is potassium citrate.

[0014] Another aspect of the present invention provides a chemical mechanical polishing method for a titanium cobalt interconnect barrier layer, comprising the following steps:

[0015] Step 1, preparing the chemical mechanical polishing solution for the cobalt interconnect barrier layer titanium;

[0016] Step 2: Use a polishing machine to perform chemical mechanical polishing on the titanium metal for 2-5 minutes.

[0017] In the above technical solution, the flow rate of the chemical mechanical polishing liquid is 20-100 mL / min, preferably 50 mL / min.

[0018] In the above technical solution, the polishing machine is a 2-4 inch polishing machine, and the rotation speed of the polishing disk of the polishing machine is 60-90 rpm, preferably 79 rpm.

[0019] In the above technical solution, the rotation speed of the polishing head of the polishing machine is 60-90 rpm, preferably 81 rpm; the polishing pressure is 1-2 psi, preferably 1.5 psi.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The chemical mechanical polishing liquid of the present invention selects appropriate types and concentration ratios of oxidants and complexing agents. Under the synergistic effect of the chemical reaction of the chemical substances in the polishing liquid and the mechanical wear of the abrasive particles, the material removal rate of metallic titanium is improved, and a high-quality and smooth surface is obtained. It has broad application prospects in the CMP process of cobalt interconnect barrier layer titanium. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Shown are MRR graphs of colloidal silica to titanium at different weight ratios.

[0023] Figure 2 Shown are MRR graphs of hydrogen peroxide to titanium at different weight ratios.

[0024] Figure 3 Shown are the electrochemical experimental results of titanium in hydrogen peroxide solutions with different weight ratios: (a) is the electrochemical impedance spectroscopy; (b) is the Tafel polarization curve.

[0025] Figure 4 Shown are the MRR diagrams of different types of complexing agents on titanium.

[0026] Figure 5 Shown is the MRR graph of different concentrations of potassium citrate on titanium.

[0027] Figure 6 The following are the electrochemical experimental results of titanium in potassium citrate (CAK) solutions with different concentrations containing hydrogen peroxide: (a) is the electrochemical impedance spectroscopy; (b) is the Tafel polarization curve.

[0028] Figure 7 Shown are AFM images of titanium after polishing in a 5 wt.% colloidal silica, 3 wt.% hydrogen peroxide, and 100 mmol / L potassium citrate solution. DETAILED DESCRIPTION

[0029] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0030] The preparation method of the polishing liquid in this specific embodiment is as follows: a certain amount of abrasive, oxidant, and chelating agent are added to deionized water, the pH of the polishing liquid is adjusted using a pH regulator, and a magnetic stirrer is used to stir for 10 minutes to ensure that the abrasive particles are evenly dispersed and the chemical reagents are fully dissolved. The polishing liquid is continuously stirred using a magnetic stirrer during the chemical mechanical polishing process.

[0031] Chemical mechanical polishing (CMP) was performed using a commercial 2- to 4-inch polisher, using titanium (99.99% purity) with a 3-inch diameter and 1.5-mm thickness, and an IC 1010 hard polishing pad. Polishing parameters were: polishing pressure 1.5 psi, polishing disk speed 79 rpm, polishing head speed 81 rpm, polishing fluid flow rate 50 mL / min, and polishing time 3 minutes.

[0032] The measurement and characterization methods used in the present invention are: using a weighing method to measure the weight change of titanium before and after chemical mechanical polishing to calculate the material removal rate of titanium; using an atomic force microscope to measure the surface roughness Ra and surface morphology of the titanium after polishing.

[0033] Example 1

[0034] 1.1 Comparison of the effect of abrasive content on titanium MRR

[0035] A 1000g polishing slurry was prepared containing varying weight percentages (1wt.%, 3wt.%, and 5wt.%) of colloidal silica (SiO2, 40wt.%), with the remainder being deionized water. The pH of the slurry was adjusted to 8. Chemical mechanical polishing of titanium was performed to investigate the effect of abrasive content on the MRR of titanium.

[0036] like Figure 1The following table shows the effect of adding different weight ratios of colloidal silica on the MRR of titanium. When 1wt.% colloidal silica is added, the MRR of titanium is 0.54nm / min. When 3wt.% colloidal silica is added, the MRR of titanium increases slightly to 1.08nm / min. When the weight ratio of colloidal silica is increased to 5wt.%, the MRR of titanium increases to 2.16nm / min. Based on the above results, it can be seen that the change in the abrasive content in the polishing liquid has no significant effect on the MRR of titanium. Therefore, 5wt.% colloidal silica was determined as the abrasive addition amount.

[0037] 1.2 Comparison of the effect of oxidant content on titanium MRR

[0038] A 1000g polishing slurry containing 5 wt.% colloidal silica (SiO2, 40 wt.%) was prepared. Hydrogen peroxide (H2O2, 30 wt.%) was selected at varying weight percentages (0.5 wt.%, 1 wt.%, 3 wt.%, and 5 wt.%) of the oxidant, with the remainder being deionized water. The pH of the polishing slurry was adjusted to 8. Chemical mechanical polishing of titanium was performed to investigate the effect of the oxidant content on the MRR of titanium.

[0039] like Figure 2 The figure shows the effect of adding hydrogen peroxide in different weight ratios on the MRR of titanium. When 0.5wt.% hydrogen peroxide was added on the basis of adding 5wt.% colloidal silica, the MRR of titanium increased to 3.26nm / min; when the amount of hydrogen peroxide added gradually increased, the MRR of titanium also gradually increased. When the amount of hydrogen peroxide added increased to 5wt.%, the MRR of titanium increased to 12.98nm / min, which still could not meet the removal rate requirement of the barrier layer titanium. At this time, due to the high content of hydrogen peroxide, the degree of corrosion on the polishing head and polishing pad was high, and obvious corrosion could be observed with the naked eye. Therefore, the amount of hydrogen peroxide added was determined to be 3wt.%. However, it is still necessary to find a suitable titanium complexing agent to improve the MRR of titanium.

[0040] The polishing liquid mentioned in Example 1.2 was configured to conduct electrochemical experiments to explore the mechanism of action of the oxidant hydrogen peroxide on Ti. The prepared solution did not contain abrasives to prevent the silica particles from agglomerating into flocs and affecting the results of the electrochemical experiment. The instrument used in the electrochemical experiment was the VersaSTAT 3F electrochemical workstation of Princeton, USA. A three-electrode system was used, including a working electrode (titanium electrode, purity 99.99%), a counter electrode (platinum electrode), and a reference electrode (saturated Ag / AgCl electrode). The electrochemical impedance spectrum and Tafel polarization curve of the working electrode in different hydrogen peroxide contents were measured, and its surface electrochemical parameters were calculated and analyzed. The measurement results are shown in the figure. Figure 3 As shown in Table 1.

[0041] Table 1 Electrochemical experimental results of titanium in different hydrogen peroxide contents

[0042]

[0043] According to the results in Table 1, it can be seen that with the increase of hydrogen peroxide addition, the polarization impedance of the titanium surface gradually decreases. When no hydrogen peroxide is added initially, the polarization impedance of the titanium surface is 191600Ω·cm 2 When 5wt.% H2O2 is added, the surface polarization resistance of titanium decreases to 2047Ω·cm 2 , reduced by 98.93%; with the increase of hydrogen peroxide addition, the corrosion current of titanium surface increases. When no hydrogen peroxide is added, the corrosion current density of titanium surface is 0.22μA·cm -2 When the amount of hydrogen peroxide added increased to 5wt.%, the corrosion current density on the titanium surface increased to 14.80μA·cm -2 , an increase of 98.51%. Therefore, the addition of hydrogen peroxide can reduce the density and passivation of the natural oxide titanium dioxide on the titanium surface, thereby reducing its surface impedance and increasing the corrosion of the titanium surface.

[0044] 1.3 Comparison of the effects of complexing agent types on titanium MRR

[0045] A 1000g polishing slurry was prepared containing 5wt.% colloidal silica (SiO2, 40wt.%) and 3wt.% hydrogen peroxide (H2O2, 30wt.%). The type of complexing agent was used as a variable, with different additives (glycine, citric acid, potassium citrate, and arginine) added at the same dosage. The remainder was deionized water, and the pH of the polishing slurry was adjusted to 8. Chemical mechanical polishing of titanium was performed to investigate the effect of complexing agent type on the MRR of titanium.

[0046] like Figure 3 The results show the effect of adding different types of complexing agents on the MRR of titanium. On the basis of adding 5wt.% colloidal silica and 3wt.% hydrogen peroxide, 100mmol / L glycine, citric acid, potassium citrate, and arginine were added respectively. Among them, the surface morphology of titanium after polishing in 5wt.% colloidal silica, 3wt.% hydrogen peroxide and 100mM potassium citrate solution is shown as follows. Figure 7 The results show that the addition of citric acid / potassium citrate significantly increases the MRR of titanium, reaching approximately 120 nm / min. However, after polishing with the addition of glycine and arginine, the MRR of titanium remains essentially unchanged or increases slightly. Therefore, this comparison demonstrates that citric acid and potassium citrate have a significant complexing effect on titanium.

[0047] Example 2

[0048] A 1000g polishing solution was prepared containing 5wt.% colloidal silica (SiO2, 40wt.%) and 3wt.% hydrogen peroxide (H2O2, 30wt.%). The amount of complexing agent added was varied, with potassium citrate at different concentrations (10mmol / L, 25mmol / L, 50mmol / L, and 100mmol / L). The remainder was deionized water, and the pH of the polishing solution was adjusted to 8. Chemical mechanical polishing of titanium was performed to investigate the effect of complexing agent content on the MRR of titanium.

[0049] like Figure 4 The results show the effect of adding different concentrations of potassium citrate on titanium MRR. Figure 4 It can be seen that in the basic polishing solution of 5wt.% colloidal silica and 3wt.% hydrogen peroxide, as the concentration of potassium citrate increases, the MRR of titanium also increases, which once again proves the effective complexation effect of potassium citrate on titanium.

[0050] In order to explore the mechanism of action of potassium citrate on Ti in hydrogen peroxide solution, the effect of different concentrations of potassium citrate on the electrochemical structure of Ti was investigated using 1wt.% hydrogen peroxide as the base solution. The experimental process was as described in Example 1. The electrochemical results are shown in Figure 1. Figure 6 As shown in Table 2.

[0051] Table 2 Electrochemical experimental results of titanium in different concentrations of potassium citrate (CAK) solutions containing hydrogen peroxide

[0052]

[0053] According to the results shown in Table 2, it can be seen that in the potassium citrate solution containing hydrogen peroxide, as the concentration of potassium citrate increases, the density of the titanium surface oxide can be further reduced, the polarization resistance of the titanium surface can be reduced, and the corrosion current can be increased.

[0054] The above results show that the chemical mechanical polishing solution of the present invention can greatly improve the material removal rate of titanium during the chemical mechanical polishing process, and its surface morphology is as follows: Figure 7 As shown, the polished surface is smooth with a roughness of 0.119 nm. The mechanism of action is that hydrogen peroxide and potassium citrate reduce the compactness of titanium surface oxides, accelerating their corrosion. Consequently, the mechanical action of the abrasive rapidly removes titanium, increasing its removal rate. Therefore, the proposed effective complexing agent selection and chemical mechanical polishing method for the titanium barrier layer of cobalt interconnects can meet the required titanium barrier layer removal rate and has broad application prospects in the polishing process of cobalt interconnect titanium barrier layers in integrated circuits.

[0055] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A chemical mechanical polishing solution for cobalt interconnect barrier layer titanium, characterized in that: The chemical mechanical polishing solution consists of 5 wt.% abrasive, 3 wt.% hydrogen peroxide, 100 mmol / L complexing agent, a pH regulator, and the balance water. The complexing agent is potassium citrate, the abrasive is colloidal silica, the particle size of the colloidal silica is 20-100 nm, and the pH of the chemical mechanical polishing solution is 8.

2. The chemical mechanical polishing solution for the cobalt interconnect barrier layer titanium according to claim 1, characterized in that The particle size of the colloidal silica is 40 nm.

3. The chemical mechanical polishing solution for the cobalt interconnect barrier layer titanium according to claim 1, characterized in that The pH regulator is potassium hydroxide, sodium hydroxide, sulfuric acid or nitric acid.

4. A chemical mechanical polishing method for titanium cobalt interconnect barrier layer, characterized in that: The following steps are involved: Step 1, preparing a chemical mechanical polishing solution for a cobalt interconnect barrier layer titanium according to any one of claims 1 to 3; Step 2: Use a polishing machine to perform chemical mechanical polishing on the titanium metal for 2-5 minutes.

5. The chemical mechanical polishing method according to claim 4, wherein: The flow rate of the chemical mechanical polishing liquid is 20-100 mL / min.

6. The chemical mechanical polishing method according to claim 5, wherein: The flow rate of the chemical mechanical polishing liquid is 50 mL / min.

7. The chemical mechanical polishing method according to claim 4, wherein: The polishing machine is a 2-4 inch polishing machine, and the rotation speed of the polishing disk of the polishing machine is 60-90 rpm.

8. The chemical mechanical polishing method according to claim 7, wherein: The polishing machine is a 2-4 inch polishing machine, and the rotation speed of the polishing disk of the polishing machine is 79 rpm.

9. The chemical mechanical polishing method according to claim 4, wherein: The rotation speed of the polishing head of the polishing machine is 60-90 rpm; the polishing pressure is 1-2 psi.

10. The chemical mechanical polishing method according to claim 9, wherein: The rotation speed of the polishing head of the polishing machine is 81 rpm; the polishing pressure is 1.5 psi.

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