Chemical mechanical polishing liquid for molybdenum barrier layer of copper wiring with low removal rate and preparation method thereof

Abstract

The present invention provides a low-removal-rate copper interconnect molybdenum barrier chemical mechanical polishing solution and a preparation method thereof. The polishing solution comprises the following components: an oxidant concentration of 2.9 to 3.1 mM, a total inhibitor concentration of 59.7 to 90.3 mM, a nano-scale silica solid concentration of 0.6 to 1.8 wt.%, an additional additive concentration of 9.9 to 20.1 mM, a pH regulator with a pH of 3.9 to 4.1, and the balance being water; the oxidant is potassium iodate (KIO3); the inhibitor is 2,2'-{[(methyl-1H-benzotriazole-1-yl)methyl]imino}diethanol (TT-LYK), L-histidine (L-Histidine), and cerium acetate (Ce(Ac)3). The present invention provides an acidic polishing solution for copper interconnect molybdenum barrier layers at low-tech nodes. The polishing solution has a low static corrosion rate and a small galvanic corrosion difference (less than 20 mV), and can achieve controllable removal rates of molybdenum, copper, and TEOS under low removal rate conditions.

Description

Technical Field

[0001] The invention belongs to the field of polishing liquids, and in particular relates to a chemical mechanical polishing liquid for a copper wiring molybdenum barrier layer. The polishing liquid can realize the regulation of the removal rate selectivity ratio of molybdenum, copper and TEOS. Background Art

[0002] Compared with other barrier layer materials, metallic molybdenum (Mo) has a body-centered cubic structure and is relatively hard (Mohs hardness is 5 to 5.5). Molybdenum has a high melting point (2688°C), does not form intermetallic compounds with copper, and has a relatively high reaction temperature with silicon, so the interface is stable. Molybdenum can effectively block the diffusion of copper into silicon and silicon dioxide at 600°C. The bulk resistivity of molybdenum is 5.34μΩ·cm, which is much lower than 14μΩ·cm of tantalum, and can greatly reduce RC delay. At the same time, the wiring material copper (Cu) can adhere well to molybdenum. Therefore, molybdenum has great development potential as a barrier layer material.

[0003] Uneven wafer surfaces make it difficult to achieve precise pattern transfer. Chemical mechanical polishing (CMP) is a processing technology that combines chemical etching with mechanical grinding. It can achieve a nanometer-level flat surface. Polishing fluid is an important factor affecting polishing performance. It provides both chemical and mechanical effects during the polishing process.

[0004] At advanced technology nodes, the barrier layer is only a few nanometers thick. During the barrier layer polishing process, a lower removal rate is required, and defects such as dishing pits and etch pits need to be corrected. This requires different removal rates between the barrier layer material, wiring material copper, and dielectric material (TEOS). Therefore, the configured polishing liquid needs to achieve an adjustable and controllable ratio of the removal rates of the three.

[0005] Usually, the barrier metal and copper have different corrosion potentials in the polishing solution, which will cause galvanic corrosion. Galvanic corrosion refers to the phenomenon that when two metals with different corrosion potentials form a circuit with the surrounding medium, the corrosion rate of the metal with low potential increases and the corrosion rate of the metal with high potential slows down. It is generally believed that controlling the galvanic corrosion difference between the two metals within 20mV can reduce the impact of galvanic corrosion. However, the standard corrosion potential difference between Mo and Cu is relatively large (E corr-Cu =340mV,E corr-Mo =-220mV), galvanic corrosion is likely to occur. At the same time, the static corrosion rate of the metal needs to be as low as possible, otherwise it will lead to excessive dissolution of the metal and affect the reliability of the structure. Usually the static corrosion rate should be controlled at the following.

[0006] Zhang Baoguo, Wu Pengfei et al.'s patent (CN115678437B - Weakly acidic molybdenum barrier layer chemical mechanical polishing solution based on hydrogen peroxide system and its preparation method) found that using hydrogen peroxide as an oxidant and TT-LYK as an inhibitor under acidic conditions can achieve a lower static corrosion rate of molybdenum. and material removal rate However, there are still problems such as the removal rate of Mo is too high, the galvanic corrosion difference between Mo and Cu has not been studied, and the removal rate selection ratio of Mo / Cu / TEOS has not been studied. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to address the shortcomings of the current technology and provide a weakly acidic chemical mechanical polishing solution for molybdenum barrier layer based on potassium iodate system and its preparation method. The polishing solution uses TT-LYK and L-histidine to inhibit the static corrosion rate of metal and control the galvanic corrosion difference between the two metals; while adjusting the concentrations of cerium acetate and SiO2 to achieve different removal rate selectivities, potassium citrate is also added to avoid flocculation and Ce 3+ Precipitation, using Ce 3+ Combined with citrate to form cerium citrate, it protects molybdenum and reduces the removal rate of molybdenum. The present invention is an acidic polishing liquid for molybdenum barrier layer of copper interconnection at low technology nodes. The polishing liquid has a low static corrosion rate. The galvanic corrosion difference is small (less than 20mV), and the removal rates of molybdenum, copper and TEOS can be controlled under low removal rate conditions.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is:

[0009] A low-removal-rate chemical mechanical polishing solution for molybdenum barrier layers of copper wirings, the polishing solution comprising the following components: an oxidant concentration of 2.9 to 3.1 mM, a total inhibitor concentration of 59.7 to 90.3 mM, a nano-scale silicon dioxide solid concentration of 0.59 to 1.81 wt.%, an additional additive concentration of 9.9 to 20.1 mM, a pH adjuster having a pH of 3.9 to 4.1, and the balance being water;

[0010] The oxidant is potassium iodate (KIO3);

[0011] The inhibitor is 2,2'-{[(methyl-1H-benzotriazole-1-yl)methyl]imino}bisethanol (TT-LYK) at a concentration of 39.9-40.1 mM, L-histidine at a concentration of 9.9-10.1 mM, and cerium acetate (Ce(Ac)3) at a concentration of 9.9-40.1 mM. The total inhibitor concentration is 59.7-90.3 mM based on the sum of the concentrations of the three substances.

[0012] The silica solid particle size is 64 to 65 nm;

[0013] The additional additive is potassium citrate (C6H5K3O7);

[0014] The pH regulator is citric acid (C6H8O7)

[0015] The method for preparing the chemical mechanical polishing solution for the molybdenum barrier layer of copper wiring with a low removal rate comprises the following steps:

[0016] Step S1: adding KIO3, L-histidine and C6H5K3O7 according to the mass of the materials calculated based on the target volume to deionized water with a volume of 30-40% of the target volume and stirring to mix evenly;

[0017] Step S2: adding TT-LYK in an amount calculated based on the target volume to the solution of step S1 and stirring evenly;

[0018] Step S3: The pH of the solution obtained in step S2 is adjusted to "target pH + 0.3 to 0.5" with C6H8O7;

[0019] Step S4: adding Ce(Ac)3 in an amount calculated based on the target volume to deionized water (30-40% of the target volume) and stirring thoroughly until completely dissolved;

[0020] Step S5: Stir the solution obtained in step S3 and slowly add the solution obtained in step S4, stirring and mixing until uniform;

[0021] Step S6: adding silica sol in an amount calculated based on the target volume to the solution obtained in step S5, and stirring to mix uniformly; the silica sol has a solid content of 40 wt.% of silicon dioxide;

[0022] Step S7: Deionized water is added to the polishing liquid obtained in step S6 to reach the target volume, and then the pH is adjusted to the target pH with C6H8O7.

[0023] The application of the low removal rate copper wiring molybdenum barrier layer chemical mechanical polishing liquid is used for polishing the copper wiring molybdenum barrier layer in integrated circuits;

[0024] The specific parameters are: polishing liquid flow rate is 290~310ml / min, polishing head speed is 85~90r / min, polishing disc speed is 90~95r / min, and pressure is 1.3~1.7psi.

[0025] The essential features of the present invention are:

[0026] Since the corrosion potential of Cu is easily affected by inhibitors and increases, the corrosion potential of Mo is not easy to change. In addition, the corrosion potential of Cu is much higher than that of Mo, which further aggravates the corrosion of Mo. The present invention introduces the oxidant KIO3 to make the corrosion potential of Mo higher than that of Cu, and then adjusts the corrosion potential difference between Mo and Cu to less than 20 by adding inhibitors L-histidine and TT-LYK, while also reducing the static corrosion rate (TT-LYK can be firmly adsorbed on the surface of Cu to form a dense protective film, which increases the corrosion potential of Cu, not only inhibits the static corrosion rate of Cu, but also reduces the removal rate of Cu. TT-LYK and L-histidine can be adsorbed on the surface of Mo to form a protective film, but the protective film is thin and loose, and can only play a role in inhibiting static corrosion. Under mechanical force during polishing, the protective film is destroyed, resulting in a relatively high removal rate of Mo). Then, the removal rate of Mo is further reduced by adding Ce(Ac)3 to meet the needs of low-tech nodes (Ce 3+ C6H5O7 provided by C6H8O7 3- The formation of C6H5O7Ce plays a protective role on Mo and reduces the removal rate of Mo), and the problem of Ce(Ac)3 being insoluble in the mixed solution of KIO3, L-histidine and TT-LYK is solved by adding C6H5K3O7 (Ce 3+ Will cause TT-LYK to flocculate, sufficient K + This phenomenon can be prevented; at the same time, Ce 3+ It will also generate white precipitate with IO3, sufficient C6H5O7 3- Can be used with Ce 3+ Bind and reduce free Ce 3+ By adjusting the concentration of the SiO2 abrasive, the TEOS removal rate is changed, thereby obtaining different removal rate selectivities (TEOS is composed of SiO2, and its removal relies primarily on the mechanical action of the abrasive and polishing pad. Increased abrasive concentration leads to more effective mechanical friction, resulting in an increased TEOS removal rate).

[0027] The beneficial effects of the present invention are:

[0028] The present invention prepares a polishing solution for molybdenum barrier layers on copper wiring. The polishing solution has a pH of 3.9 to 4.1, uses KIO3 as an oxidant, and contains multiple inhibitors, including L-histidine, TT-LYK, and Ce(Ac)3. This ensures a low static corrosion rate for Mo and Cu. and mild galvanic corrosion (galvanic corrosion difference within 20mV). At low SiO2 abrasive concentration (0.6-1.8wt.%), while achieving low removal rate, different Mo / Cu / TEOS removal rate selectivity ratios were obtained: 1.5:1:3.2 (121: 0.9:1:2.9 1.5:1:1.6 0.9:1:1.5 1:1:2.1 Compared with the invention patent of Zhang Baoguo, Wu Pengfei et al. (CN115678437B), a different oxidant KIO3 was used, and inhibitors L-histidine and Ce(Ac)3 were introduced, and the static corrosion rate remained basically unchanged. When the galvanic corrosion difference is less than 20mV, a lower Mo removal rate is achieved. Different Mo / Cu / TEOS removal rate selectivity ratios were obtained, which can basically meet the needs of barrier layer polishing in low-tech nodes. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0030] Figure 1 is the Tafel curve of Mo in Examples 1-5;

[0031] Figure 2 The Tafel curve of Cu in Examples 1-5 is

[0032] Figure 3 The static corrosion rate results of Mo and Cu in Examples 1-5 are shown;

[0033] Figure 4 Graph showing the polishing removal rate and removal rate selectivity of Mo / Cu / TEOS in Examples 6-10;

[0034] Figure 5 Graph showing the polishing removal rate and removal rate selectivity of Mo / Cu / TEOS in Examples 11-15. DETAILED DESCRIPTION

[0035] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below with reference to the accompanying drawings and the best embodiments.

[0036] Example 1 (comparative example):

[0037] Prepare 400 mL of a base component solution containing 3 mM KIO3, 10 mM L-histidine, and 40 mM TT-LYK at a pH of 4.

[0038] Step S1: Add 0.256 g KIO3, 0.62 g L-histidine and 4 g TT-LYK to 150 mL of deionized water and stir well.

[0039] Step S2: The solution obtained in step S1 was supplemented with deionized water to 400 mL, and the pH was adjusted to 4 with C6H8O7;

[0040] Example 2

[0041] Prepare 400 mL of a solution containing 3 mM KIO3, 10 mM L-histidine, 40 mM TT-LYK, 10 mM C6H5K3O7, and 10 mM Ce(Ac)3 at a pH of 4.

[0042] Step S1: Add 0.256 g KIO3, 0.62 g L-histidine and 1.224 g C6H5K3O7 to 150 mL of deionized water and stir well;

[0043] Step S2: Add 4 g of TT-LYK to the solution obtained in step S1 and stir evenly;

[0044] Step S3: adjusting the pH of the solution obtained in step S2 to 4.3-4.5 ("target pH + 0.3-0.5") with C6H8O7;

[0045] Step S4: Add 1.268 g of Ce(Ac)3 to 150 mL of deionized water and stir thoroughly until completely dissolved;

[0046] Step S5: slowly add the solution obtained in step 4 to the solution obtained in step 3, and stir continuously to mix evenly;

[0047] Step S6: The solution obtained in step S5 was supplemented to 400 mL with deionized water, and then the pH was adjusted to 4 with C6H8O7.

[0048] Examples 3-4

[0049] The other steps were the same as in Example 2, except that the concentrations of Ce(Ac)3 were changed to 20 mM and 30 mM respectively;

[0050] Example 5

[0051] The other steps were the same as those in Example 2, except that the concentration of C6H5K3O7 was changed to 20 mM and the concentration of Ce(Ac)3 was changed to 40 mM.

[0052] Since the static corrosion test and the galvanic corrosion test mainly consider the chemical effect of the polishing liquid and do not consider the mechanical effect of the abrasive silica, silica was not added in the above Examples 1-5.

[0053] The conditions for the galvanic corrosion test of Mo and Cu are:

[0054] 2×10×20 mm Mo and Cu electrode sheets (purity 99.99%) were polished with 2000# sandpaper until the surface was smooth to remove the oxide layer. The Tafel curves of Mo and Cu were measured using a CHI 660E electrochemical workstation in a three-electrode system. The corrosion potential was obtained based on the curves. The starting potential was "open circuit potential (keep one decimal place, unit: V) -0.3 V", and the ending potential was "open circuit potential (keep one decimal place, unit: V) +0.3 V". The scan rate was 0.005 V / s.

[0055] The Tafel curves of Mo and Cu electrodes are as follows: Figure 1 and Figure 2 As shown. The electrochemical parameters of Examples 1-5 are shown in Table 1. The corrosion potentials of Mo and Cu are 31mV / 41mV; 32mV / 38mV; 28mV / 37mV; 20mV / 37mV; and 14mV / 29mV, respectively. The potential difference between the two is always within 20mV, which meets the requirements of low galvanic corrosion. It can be concluded from Examples 2-4 that in this basic component, as the concentration of Ce(Ac)3 increases, the corrosion potential of Mo decreases slightly, and the corrosion potential of Cu remains basically unchanged. It can be concluded from Example 5 that as the concentration of C6H5K3O7 increases, the corrosion potential of Cu decreases slightly. The above-mentioned changes in corrosion potential are small, which is because L-histidine and TT-LYK in the basic component have formed protection on the surface of Mo and Cu, so that the effects of C6H5K3O7 and Ce(Ac)3 are not so severe.

[0056] Table 1 Electrochemical corrosion parameters of Mo and Cu in Examples 1-5

[0057]

[0058] The conditions for static corrosion of Mo and Cu are:

[0059] 3-inch Mo and Cu targets (99.99% purity) were polished with 2000# sandpaper until the surface was smooth to remove the oxide layer. The targets were weighed with an analytical balance and immersed in the sample for 30 minutes. The targets were then taken out, rinsed with deionized water, dried with nitrogen, and weighed again with an analytical balance. The removal thickness was calculated based on the material density and divided by the immersion time to obtain the removal rate.

[0060] The static corrosion rates of Mo and Cu targets are as follows: Figure 3 As shown, the static corrosion rates of Mo and Cu in the solutions of Examples 1-5 were measured to be The static corrosion rate of both is always less than This is because the added L-histidine and TT-LYK can be adsorbed on the surface of Mo and Cu to form a protective film, thereby inhibiting the static corrosion rate of both.

[0061] Example 6 (Comparative Example)

[0062] 2.5 L of a basic component polishing solution was prepared, which contained 3 mM KIO3, 10 mM L-histidine, 40 mM TT-LYK and 0.6 wt.% SiO2 solid, and had a pH of 4.

[0063] Step S1: Add 1.605 g KIO3, 3.875 g L-histidine and 25 g TT-LYK to 900 mL of deionized water and stir well;

[0064] Step S2: adding 37.5 g of silica sol (silica solid content in the silica sol is 40 wt.%) to the solution obtained in step S1 and stirring evenly;

[0065] Step S3: Add deionized water to the polishing liquid obtained in step S2 to 2.5 L, and adjust the pH to 4 with C6H8O7;

[0066] Example 7

[0067] 2.5 L of a polishing solution containing 3 mM KIO3, 10 mM L-histidine, 40 mM TT-LYK, 10 mM C6H5K3O7, 10 mM Ce(Ac)3 and 0.6 wt.% SiO2 solid was prepared with a pH of 4.

[0068] Step S1: Add 1.605 g KIO3, 3.875 g L-histidine and 7.65 g C6H5K3O7 to 900 mL deionized water and stir evenly;

[0069] Step S2: Add 25 g of TT-LYK to the solution obtained in step S1 and stir evenly;

[0070] Step S3: adjusting the pH of the solution obtained in step S2 to 4.3-4.5 ("target pH + 0.3-0.5") with C6H8O7;

[0071] Step S4: Add 7.925 g of Ce(Ac)3 to another 900 mL of deionized water and stir thoroughly until completely dissolved;

[0072] Step S5: slowly add the solution obtained in step 4 to the solution obtained in step 3, and stir continuously to mix evenly;

[0073] Step S6: Add 37.5 g of silica sol to the solution in step S5 and stir to mix evenly;

[0074] Step S7: Deionized water was added to the polishing liquid obtained in step S6 to make 2.5 L, and the pH was adjusted to 4 with C6H8O7.

[0075] Examples 8-9

[0076] The other steps were the same as in Example 7, except that the concentrations of Ce(Ac)3 were changed to 20 mM and 30 mM respectively;

[0077] Example 10

[0078] The other steps were the same as those in Example 7, except that the concentration of C6H5K3O7 was changed to 20 mM and the concentration of Ce(Ac)3 was changed to 40 mM.

[0079] The conditions for chemical mechanical polishing using the polishing solution of the embodiment are:

[0080] 4-inch Mo and Cu targets (99.99% purity) and 4-inch TEOS-coated wafers were used. The polishing machine used was a Huahai Qingke U300B polisher with a POLITEX REG polishing pad. The polishing fluid flow rate was 300 ml / min, the polishing head speed was 87 rpm, the polishing disc speed was 93 rpm, and the pressure was 1.5 psi. The target mass before and after polishing was weighed to calculate the removal rate. The TEOS-coated wafer film thickness was measured using an F50 dielectric thickness meter. The target polishing time was 3 minutes, and the coated wafer polishing time was 1 minute.

[0081] Using Examples 6-10, Mo target, Cu target and TEOS coating sheet were polished and the removal rate was calculated. The results are as follows: Figure 4 As shown, the removal rates and selectivities of Mo / Cu / TEOS when the polishing solutions of Examples 6-10 were measured were (2:1:1.4); (1.5:1:1.6); (1:1:1.6); (0.9:1:1.5); (1:1:2.1). As the Ce(Ac)3 concentration increases, the Mo removal rate decreases significantly, as the generated C6H5O7Ce protects Mo. The removal rates of Cu and TEOS remain essentially unchanged. When the C6H5K3O7 concentration reaches 20 mM, the Cu removal rate also decreases, likely due to the protective effect of C6H5K3O7 adsorbed on the Cu surface.

[0082] Examples 11-15

[0083] The other steps are the same as in Example 6-10, except that the SiO2 solid concentration is changed to 1.8wt.%.

[0084] Using Examples 11-15, Mo target, Cu target and TEOS coating sheet were polished and the removal rate was calculated. The results are as follows: Figure 5 As shown, the removal rates and selectivities of Mo / Cu / TEOS when the polishing solutions of Examples 11-15 were measured were (1.9:1:3); (1.5:1:3.2); (1.1:1:3.1); (0.9:1:3.2); Comparing Examples 6-10, it can be found that the removal rates of Mo and Cu remain essentially unchanged, while the removal rate of TEOS increases significantly. This is because the removal of Mo and Cu primarily relies on chemical reactions. Since the inhibitor concentration remains unchanged, the surfaces of Mo and Cu remain well protected. However, the removal of TEOS primarily relies on mechanical friction. The increase in abrasive concentration makes the mechanical friction more effective, thereby increasing the TEOS removal rate.

[0085] In summary, the present invention ensures that Mo and Cu have a lower static corrosion rate. Under the conditions of relatively mild galvanic corrosion (galvanic corrosion difference within 20mV), while achieving low removal rate, different Mo / Cu / TEOS removal rate selectivity ratios were obtained: 1.5:1:3.2 0.9:1:2.9 1.5:1:1.6 0.9:1:1.5 1:1:2.1 It can basically meet the needs of barrier layer polishing at low-tech nodes.

[0086] The above description 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 considered within the scope of protection of the present invention.

[0087] Matters not covered by the present invention are known technologies.

Claims

1. A low-removal-rate chemical mechanical polishing solution for molybdenum barrier layers of copper wiring, comprising the following components: an oxidant at a concentration of 2.9 to 3.1 mM, a total inhibitor concentration of 59.7 to 90.3 mM, a nano-silica solid concentration of 0.59 to 1.81 wt.%, an additional additive concentration of 9.9 to 20.1 mM, a pH adjuster at a pH of 3.9 to 4.1, and the balance being water; The oxidant is potassium iodate; The inhibitor is 2,2'-{[(methyl-1H-benzotriazol-1-yl)methyl]imino}diethanol at a concentration of 39.9-40.1 mM, L-histidine at a concentration of 9.9-10.1 mM, and cerium acetate at a concentration of 9.9-40.1 mM. The total inhibitor concentration is 59.7-90.3 mM based on the sum of the concentrations of the three substances. The silica solid particle size is 64-65 nm; The additional additive is potassium citrate; The pH adjuster is citric acid.

2. The method for preparing a chemical mechanical polishing solution for a molybdenum barrier layer of copper wiring with a low removal rate according to claim 1, wherein the method comprises the following steps: Step S1: adding potassium iodate, L-histidine, and potassium citrate according to the mass of the materials calculated based on the target volume to deionized water with a volume of 30-40% of the target volume, and stirring and mixing; Step S2: adding 2,2'-{[(methyl-1H-benzotriazole-1-yl)methyl]imino}diethanol in an amount calculated based on the target volume to the solution of step S1 and stirring evenly; Step S3: The pH of the solution obtained in step S2 is adjusted to "target pH + 0.3-0.5" with citric acid; Step S4: adding cerium acetate in an amount calculated based on the target volume to deionized water (30-40% of the target volume), and stirring thoroughly until completely dissolved; Step S5: Stir the solution obtained in step S3 and slowly add the solution obtained in step S4, stirring and mixing until uniform; Step S6: adding silica sol in an amount calculated based on the target volume to the solution obtained in step S5, and stirring and mixing; the silica sol has a silica solid content of 40 wt.%; Step S7: Deionized water is added to the polishing liquid obtained in step S6 to reach the target volume, and then the pH is adjusted to the target pH with citric acid.

3. The use of the low removal rate copper wiring molybdenum barrier layer chemical mechanical polishing liquid as claimed in claim 1, characterized in that it is used for polishing the copper wiring molybdenum barrier layer in an integrated circuit.

4. The use of the chemical mechanical polishing solution for the molybdenum barrier layer of copper wiring with a low removal rate as claimed in claim 3, characterized in that: The liquid flow rate is 290~310 ml / min, the throwing head speed is 85~90 r / min, the throwing disc speed is 90~95 r / min, and the pressure is 1.4~1.6 psi.

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