CN119061402A

CN119061402A - A chemical mechanical polishing liquid for polishing aluminum and a use of maltol in polishing aluminum

Info

Publication number: CN119061402A
Application number: CN202310585820.0A
Authority: CN
Inventors: 李守田; 徐鹏宇
Original assignee: Anji Microelectronics Shanghai Co Ltd
Current assignee: Anji Microelectronics Shanghai Co Ltd
Priority date: 2023-05-23
Filing date: 2023-05-23
Publication date: 2024-12-03
Also published as: TW202446903A

Abstract

The invention provides a chemical mechanical polishing solution for polishing aluminum, which comprises grinding particles and maltol, wherein the pH value of the chemical mechanical polishing solution is 3.5-8.3. The technical proposal uses silicon oxide as grinding particles, can reduce cost and reduce the abrasion condition of the surface of the Al material, and has higher Al/SiO2 polishing selection ratio.

Description

Chemical mechanical polishing solution for polishing aluminum and application of maltol in polishing aluminum

Technical Field

The invention relates to the field of chemical mechanical polishing, in particular to a chemical mechanical polishing solution for polishing aluminum and application of maltol in polishing aluminum.

Background

In the prior art, alpha-Al ₂O₃ is typically used as abrasive particles in polishing Al materials. However, α -Al ₂O₃ is very hard (Mohs hardness is 9, only less than diamond) and scratches are easily made on soft metallic aluminum with Mohs hardness of 2.5. In addition, aluminum corrosion defects (pitting) are also a common problem with aluminum slurries on the market that use aluminum oxide as abrasive particles.

The hardness of the abrasive grain silica commonly used in the art is much less than that of α -Al ₂O₃. However, if silicon oxide abrasive particles are used, the polishing rate of aluminum is low, while the polishing rate of silicon oxide (TEOS) is high, resulting in a smaller polishing selection of Al/SiO ₂. Even so, for cost reasons, there is a need for an aluminum polishing liquid capable of using silicon oxide as an abrasive, having a desirable polishing selectivity of Al/SiO ₂, and capable of reducing scratches and corrosion on the Al surface.

Disclosure of Invention

In order to solve the technical problems, the invention provides a chemical mechanical polishing solution for polishing Al, which uses a polishing selection ratio of Al/SiO ₂ which is ideal and can reduce scratch and corrosion of the surface of Al.

Specifically, the invention discloses a chemical mechanical polishing solution for polishing aluminum, which comprises grinding particles and maltol, wherein the pH value of the chemical mechanical polishing solution is 3.5-8.3.

Preferably, the abrasive particles are negatively charged surface abrasive particles.

Preferably, the abrasive particles are selected from one or more of alumina or silica.

Preferably, the particle size of the silicon oxide abrasive particles is in the range of 35nm-70nm, and the mass percentage concentration of the silicon oxide abrasive particles is 0.5-5 wt%.

Preferably, the maltol accounts for 0.1-1 wt%.

Preferably, the hydrogen peroxide is contained, and the mass percentage concentration of the hydrogen peroxide is 1.0wt% to 3.0wt%.

In another aspect of the invention, the invention provides an application of maltol in a chemical mechanical polishing solution of aluminum, wherein the mass content of the maltol is in the range of 0.1-1 wt%, and the pH value of the chemical mechanical polishing solution is 3.5-8.3.

In the invention, the pH value of the chemical mechanical polishing solution is regulated to be close to the neutral pH value, so that the TEOS speed of the silicon dioxide abrasive can be reduced, and meanwhile, in a neutral environment, al is in a passivation state rather than a corrosion state, so that the corrosion condition of the Al can be effectively relieved.

Maltol (3-hydroxy-2-methyl-4H-pyran-4-one) is a naturally occurring organic compound mainly used as a odorant (e.g.EP 971599B 1). Maltol was reported by wikipedia. Org to be present in larch bark, pine needles and roasted malt (hence the name). Maltol, like related 3-hydroxy-4-pyrones (e.g., kojic acid), binds to hard metal centers (e.g., fe ³⁺、Ga³⁺ and Al ³⁺). Maltol combined with Al ³⁺ can form soluble Al complexes in a certain pH range (Chris Orvig, aluminum Water coordination chemistry, chapter 3, aluminum coordination chemistry, new York: VCH, 1993). It is very important that the aluminum-maltol complex is neutral in charge because it requires three maltol molecules to be ionically bound to one Al ³⁺. Thus, under neutral conditions, maltol is able to form soluble, charge neutral compounds of aluminum complexes such that the aluminum complex cannot bridge silica particles to form large agglomerated particles. Therefore, in the technical scheme of the invention, the maltol is used in the chemical mechanical polishing solution of aluminum, and has the following beneficial effects:

1. the silicon oxide is used as the grinding particles, so that the cost can be reduced, and the abrasion condition of the surface of the Al material can be reduced;

2. Has higher Al/SiO ₂ polishing selection ratio.

Drawings

FIG. 1 is a Bubye plot of Al in solutions of different pH values.

FIG. 2 is a schematic representation of the solubility of aluminum hydroxide as a function of pH.

FIG. 3 is a graph showing the polishing rates of Al and TEOS in polishing solutions containing different concentrations of hydrogen peroxide.

FIG. 4 is a graph showing Al polishing rates of polishing solutions containing maltol at different concentrations.

FIG. 5 is a graph showing TEOS polishing rates for polishing solutions containing different concentrations of maltol.

FIG. 6 is a graph showing Al polishing rates of polishing solutions containing different concentrations of citric acid.

FIG. 7 is a graph showing TEOS polishing rates for polishing solutions containing different concentrations of citric acid.

Detailed Description

Advantages of the invention are further illustrated in the following description, taken in conjunction with the accompanying drawings and detailed description.

In an aluminum polishing liquid using silicon oxide abrasive particles, the pH has a large influence on the properties of the polishing liquid. First, according to fig. 1, the risk of corrosion of aluminum in neutral pH solutions is low. Second, since the surface of Al ³⁺ ions has a positive charge and aluminum hydroxide can bridge the surface-negatively charged silica, the presence of Al ³⁺ cations or aluminum hydroxide can affect the stability of the silica colloid. During the Al polishing process, metallic aluminum is first oxidized and then removed by grinding. At near neutral pH, the removed aluminum is more likely to exist in the form of aluminum hydroxide. Therefore, in aluminum polishing using a silica-based slurry, it is necessary to reduce the content of aluminum hydroxide, otherwise the silica particles may undergo agglomeration phenomenon, resulting in high scratch defects. As can be seen from fig. 2, the solubility of aluminum hydroxide reaches the lowest point around neutral pH.

In view of the above, and in conjunction with fig. 1 and 2, the near neutral pH is a desirable choice of Al slurry using silica as the abrasive particles, considering the corrosion of the slurry to the aluminum material and the stability of the silica abrasive particles.

In a neutral pH environment, in order to maintain the stability of the silica, the aluminum hydroxide can be dissolved to form a soluble aluminum complex. See table 1 for details, which is the colloidal stability of colloidal silica particles for complexing agents common in the art with aluminum hydroxide at neutral pH and with silica at neutral pH, wherein the concentration of silica is 5%.

Table 1 properties of common complexing agents in neutral environments

Based on Table 1, it is clear that the amino acid compound cannot form soluble Al ³⁺ complex under neutral condition of pH 6.5-7.5, that maltol and few carboxylic acids can form soluble Al ³⁺ complex, and that only maltol complex has neutral charge.

Further, the influence of the types and the contents of the hydrogen peroxide and the complexing agent on the polishing effect of the polishing solution is explored. Polishing solutions were prepared according to the respective components and contents shown in table 2. The remainder was made up with water.

TABLE 2 Components and contents of the polishing solutions of comparative examples 1 to 3 and example 1

The polishing test conditions were as follows:

aluminum polishing was performed in a class I clean room environment using a polisher capable of polishing 8 inch wafers, with 200mm (8 in) wafers used for polishing. The polishing down pressure was set at 3psi (back pressure 2.5 psi), platen speed 93rpm, carrier speed 87rpm.

FIG. 3 is a graph showing the polishing rates of the polishing liquid on Al and TEOS materials measured by adjusting the concentration of hydrogen peroxide in comparative example 2. As can be seen from fig. 3, the concentration of hydrogen peroxide does not significantly affect the polishing rate of the polishing liquid on both. However, in the art, while polishing Al materials, it is often desirable to remove the barrier film (TiN and/or TaN), while hydrogen peroxide is beneficial for polishing the barrier layer. It is known that the properties of other common components of the aluminum polishing liquid are not affected when maltol is used as an additive.

FIGS. 4 and 5 are graphs showing polishing rates of the polishing solutions on Al and TEOS materials, respectively, measured by adjusting the concentration of maltol in example 1. From the graph, the polishing rate of Al increases with the increase of the maltol concentration, but the influence of the maltol concentration on the polishing rate of TEOS is small. At a maltol concentration of 1wt%, the Al rate was comparable to that of comparative example 1, while the TEOS rate was slightly lower than that of comparative example 1. However, in comparison, the silica slurry may have a higher Al/TEOS selectivity at 1% maltol (Al/teos=89) than comparative example 1 (Al/teos=76).

Fig. 6 and 7 are schematic diagrams showing polishing rates of the polishing liquids on Al and TEOS materials, respectively, measured by adjusting the citric acid concentration in comparative example 3. The use of citric acid increases the TEOS polishing rate and decreases the Al polishing rate compared to comparative example 1. Thus, the use of citric acid reduces the Al/TEOS rate selectivity.

The compositions and contents of the inventive polishing solutions of examples 2-20 and comparative examples 4-31, as well as the Al rate and TEOS rate of 1 wt.% silica at neutral ph=7.0 for each polishing solution, are listed in table 3. The silica-1 is subjected to sulfosilane treatment, so that the Zeta potential of the surface of the silica-1 is negative, the absolute Zeta potential value is larger than 20mv, the original particle size of the silica-1 is 35nm, the silica-2 is not subjected to sulfosilane treatment, the Zeta potential of the surface of the silica-2 is close to 0, the original particle size of the silica-2 is 35nm, the silica-3 is not subjected to sulfosilane treatment, the original particle size of the silica-3 is 70nm, the silica-4 is subjected to sulfosilane treatment, the Zeta potential of the surface of the silica-4 is negative, the absolute Zeta potential value is larger than 20mv, the original particle size of the silica-5 is 70nm, the Zeta potential of the surface of the silica-5 is positive, the absolute Zeta potential value is larger than 20mv, and the original particle size of the silica-3 is 70nm.

TABLE 3 Components, contents and polishing rates of the polishing solutions of examples 2 to 20 and comparative examples 4 to 31

Based on Table 3, it is clear that maltol can achieve a high Al polishing rate, a low TEOS polishing rate, a high Al/TEOS selectivity, and the technical effect is applicable to different types of silica, as compared with other types of complexing agents such as malic acid, citric acid, oxalic acid, and lactic acid. The particle size and surface charge of silica also affect the polishing effect.

Table 4 shows the Al polishing rates with 1 wt.% and 5 wt.% silica-5, respectively, in a neutral environment (pH=7) and 3 wt.% H ₂O₂.

TABLE 4 Components, contents and polishing rates of the polishing solutions of examples 32 to 33

As can be seen from table 4, the concentration of silica has less influence on the polishing rate of the polishing liquid.

It can be seen from the data in tables 3 and 4 that maltol can increase the polishing rate of the polishing liquid to Al to achieve high Al/TEOS selectivity compared to other complexing agents commonly used in the art, such as malic acid, citric acid, oxalic acid, lactic acid, and the like. At the same time, the abrasive particles selected in the polishing liquid also have an influence on the polishing effect. Specifically, the particle size and the surface charge of the silicon dioxide have influence on the polishing effect, the surface of the silicon dioxide is provided with the grinding particles with negative charges and smaller particle size, which is beneficial to improving the polishing effect of the polishing solution, and the content of the grinding particles has less remarkable influence on the polishing rate of Al of the polishing solution.

In the polishing solution using the silicon oxide particles, the maltol is used as an aluminum accelerator, so that the polishing solution has higher polishing rate than the commercial polishing solution using alpha-phase aluminum oxide as the grinding particles, and the polishing rate of metal aluminum can be further improved by combining with hydrogen peroxide. The data are shown in table 5.

The polishing machine was Mirra (8 inch wafer), the rotation speed of the polishing disk was 130rpm, the rotation speed of the polishing head was 95rpm, the flow rate of the polishing liquid was 180ml/min, the polishing liquid contained 1% silica-1, the pH was 7.0, and the specific composition was shown in Table 5. The polishing rate (RR) units are

TABLE 5 Components, contents and polishing rates of comparative example 34, examples 21-22 polishing solutions

In table 5, the data in brackets are the percent increase in polishing rate for the example over comparative example 34 (commercial alumina polishing solution). Based on the polishing rate data in Table 5, it was found that the polishing rate of aluminum was increased by 68% at 2psi and by 85% and 78% at 2.5psi and 3psi, respectively, by adding 0.5wt% maltol to a chemical mechanical polishing slurry having a pH of 7.0 and containing 1wt% silica particles. On the basis, the polishing rate of the polishing solution can be further improved by 120% (2 psi), 142% (2.5 psi) and 130% (3 psi) by adding 1wt% of hydrogen peroxide.

Table 6 shows the composition, content and polishing rate of Al for the chemical mechanical polishing solutions of different formulations when alumina was selected as the abrasive grain. Wherein comparative example 35 is a commercial aluminum polishing slurry containing 0.5% solids, surface coated α -alumina, pH 3.5, comparative example 36 is a chemical mechanical polishing slurry containing 0.5% α -alumina in the reference slurry, pH 3.5 and no other additives such as accelerators or suppressors, example 23 contains 0.5% α -alumina, 0.5% maltol, pH 3.5 (i.e., 0.5% maltol was added to comparative example 35). Each of the above polishing solutions was added with 3% H ₂O₂ during polishing.

The polisher used Mirra,8 inch Al wafer blank, chassis speed 130rpm, head speed 95rpm, flow 180ml/min. The test results are shown in Table 6.

TABLE 6 Components, content and polishing Rate of example 23 and comparative examples 35-36

From the data in Table 6, it is understood that the use of maltol can be similarly used for polishing solutions using alumina as abrasive grains, and that the aluminum polishing rate can be improved by more than 4 times.

In addition, maltol can also promote the polishing rate of aluminum in a negatively charged surface-treated alumina abrasive (zeta potential-30mV, code-grade alumina) polishing solution. Furthermore, even if the inhibitor TSF-20 of aluminum exists in the polishing solution, the polishing rate of aluminum can be improved.

In the chemical mechanical polishing liquid used in practice, an aluminum inhibitor (controlling dishing) and an aluminum accelerator (increasing polishing rate) are generally used at the same time.

The data are shown in Table 7. The data acquisition process is as follows, the polishing machine is Mirra (8 inch wafer), the polishing disk rotation speed is 130rpm, the polishing head rotation speed is 95rpm, the polishing liquid flow is 180ml/min, and the specific composition is shown in Table 7. Polishing Rate (RR) in units of

TABLE 7 Components, contents and polishing rates of examples 24-25 and comparative examples 37-38

The data in Table 7 shows that when alumina is used as the abrasive grains in the polishing liquid, the polishing rate of aluminum is not high even if hydrogen peroxide is added, and the polishing rate of the polishing liquid is lowered after the inhibitor TSF-20 is added to the polishing liquid, but the polishing rate of aluminum is significantly improved after the corresponding addition of maltol to the polishing liquid, regardless of whether or not the inhibitor is contained in the polishing liquid.

It should be noted that the embodiments of the present invention are preferred and not limited in any way, and any person skilled in the art may make use of the above-disclosed technical content to change or modify the same into equivalent effective embodiments without departing from the technical scope of the present invention, and any modification or equivalent change and modification of the above-described embodiments according to the technical substance of the present invention still falls within the scope of the technical scope of the present invention.

Claims

1. A chemical mechanical polishing liquid for polishing aluminum, characterized in that it comprises

Abrasive particles and maltol, the pH value of the chemical mechanical polishing liquid is 3.5-8.3.

2. The chemical mechanical polishing solution according to claim 1, characterized in that:

The abrasive particles are abrasive particles with negative charges on the surface.

3. The chemical mechanical polishing solution according to claim 2, characterized in that:

The abrasive particles are selected from one or more of aluminum oxide and silicon dioxide.

4. The chemical mechanical polishing solution according to claim 3, characterized in that:

The particle size of the silicon oxide abrasive particles ranges from 35nm to 70nm;

The mass percentage concentration of the silicon oxide abrasive particles is 0.5wt%-5wt%.

5. The chemical mechanical polishing solution according to claim 1, characterized in that:

The mass percentage content of the maltol is 0.1wt%-1wt%.

6. The chemical mechanical polishing solution according to claim 1, characterized in that:

Contains hydrogen peroxide, and the mass percentage concentration of the hydrogen peroxide is 1.0wt%-3.0wt%.

7. A use of maltol in a chemical mechanical polishing liquid for aluminum, characterized in that:

The mass content of the maltol ranges from 0.1wt% to 1wt%, and the pH value of the chemical mechanical polishing liquid ranges from 3.5 to 8.3.