KR20030063763A - Slurry for tungsten cmp - Google Patents

Abstract

PURPOSE: A slurry for a tungsten CMP (chemical mechanical polishing) is provided, which shows an excellent dispersion stability of nano-sized ceramic particles in an aqueous solution and a high polishing efficiency. CONSTITUTION: The slurry comprises 5-25 wt% of a polishing agent; 1-5 wt% of an oxidizing agent; 0.4-4 wt% of an oxidation accelerator; and 1-10 wt% of an oxidation acceleration stabilizer, and is stable at pH 3-5. Preferably the polishing agent is 5-10 wt% of nano-sized alumina or 5-25 wt% of nano-sized silica, and has an average particle size of 200 nm or less; the oxidizing agent is hydrogen peroxide; the oxidation accelerator is 0.05-0.5 M Fe(NO3)3; and the oxidation acceleration stabilizer is 1-10 wt% of citric acid, 0.5-5 wt% of malonic acid or 0.6-6 wt% of oxalic acid.

Description

Slurry for Tungsten CMP {Slurry for Tungsten CMP}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a slurry using nano-sized ceramic powder used as an abrasive in a CMP process for removing a tungsten metal used as a wiring material on a semiconductor substrate by a mechanical chemical method. The slurry for CMP of the present invention is controlled in dispersion stability to stably disperse nano-sized ceramic powder, and includes chemical additives containing hydrogen peroxide as the main oxidant for electrochemical corrosion of tungsten metal.

With high performance and high integration of semiconductors, multilayer wiring structures are becoming an essential requirement for the design and manufacture of ULSI devices. In such a multilayer wiring structure, an insulating film, a metal wiring layer, and the like are gathered in each layer to form a complicated circuit. The precision of the newly formed circuit for each layer depends on the flatness of the lower layer. Therefore, the planarization work has become a very important process in the super-integrated semiconductor process, and the REB process has been mainly used until now. However, as the trend of chip design technology is becoming more and more integrated, REB is showing limitation in its application. In recent years, the CMP technology that the line width of the integrated circuit becomes very fine and the whole planarization can be achieved even when manufacturing a semiconductor having a multilayer structure The only alternative is in the spotlight.

CMP is a process that is expected to expand rapidly and its enormous ramifications. It has already been used successfully for the planarization of SiO ₂ interlayer dielectric (WLD) and W stud layers in integrated circuit semiconductor manufacturing. However, in recent years, various kinds of materials such as Si ₃ N ₄ and polymers have been attempted as ILD layers, and various metallic materials such as Al, W, and Cu have been attempted as conductive layers. The development of and the development of consumables became necessary. In particular, the development of slurry for CMP in consideration of the polishing characteristics and efficiency according to the target material is attracting attention as the most important point in the optimization of the next generation CMP process. Until now, the slurry for CMP process has been developed mainly by dividing it into oxide and CMP slurry for metal materials. Recently, as various materials having different polishing characteristics are used at the same time in the circuit design, the conventional slurry composition is used for polishing rate and selectivity. A number of difficulties have been found in effectively regulating this (see Chemical mechanical planarization of microelectronic materials / John Wiley & Sons, Inc. 1997).

At present, the most basic constituents of the slurry for metal CMP are composed of abrasive particles, which are in charge of the mechanical polishing effect, and chemical components to help stabilize the slurry and various chemical reactions generated during polishing. These components are ultimately selected to achieve the desired polishing rate and to minimize defects on the polishing surface. To date, silica or alumina is mainly used as an abrasive for slurry for metal CMP. However, the colloidal suspension in which nano-sized fine silica or alumina is dispersed in an aqueous solution has a problem that separation occurs within several hours when left alone. This instability causes the presence of large particles and aggregates in the slurry, which provides a cause of defects such as scratches during polishing.

On the other hand, in order to effectively advance the metal CMP, passivation of the metal by the chemical component in the slurry must occur so that the surface of the metal to be polished is easily polished by the abrasive. In addition, the passivation phenomenon of the metal serves to protect the metal surface of the low-level region from melting, thereby enabling wide-area leveling after polishing. To this end, an oxidizing agent is added to the slurry for metal CMP. Many oxidizing agents used so far include Fe (NO 3) ₃ , KIO ₃ , H ₂ O _2, etc. However, the following problems have been reported when these oxidizing agents are used alone as main oxidizing agents (Korean Patent Application No. 1999-85105). Reference).

Fe (NO ₃ ) ₃ exhibits a high polishing rate, but strong acid oxidation is so strong that it causes corrosion problems of peripheral devices and the like, and not only causes contamination by Fe components, but also decreases the stability of the slurry, especially the alumina slurry. Let's do it. The KIO ₃ is limited in solubility in aqueous solution, so that it is difficult to obtain a desired oxidation degree and there is a problem of contamination by K component. The H ₂ O ₂ has a high oxidizing power but does not have activity alone, and when excessively acted as an oxidizing agent, defects due to excessive etching occur.

These problems are, firstly, the result of failing to secure the dispersion stability of the nano-sized ceramic powder in the aqueous solution, and secondly, the selection of an appropriate oxidant and other auxiliary chemicals.

Accordingly, the present invention is to solve the problems of the conventional slurry described above, to ensure a stable dispersion stability of the nano-sized ceramic particles in the aqueous solution, and to minimize the metal component acting as a contaminant during the CMP process as much as possible It is intended to provide.

1 is a graph showing the particle size characteristics according to the high-energy milling of the nano-size ceramic abrasive used in the present invention.

Figure 2 is a graph showing the results of the potentiodynamic test (tensiodynamic test) in the oxidant composition used in the present invention and the oxidant composition in the conventional use.

Figure 3 is a graph comparing the tungsten wafer polishing rate in the slurry used in the present invention and commercially available slurry.

The present inventors used a dispersion technique of nano-sized ceramic particles using high energy milling and a compound containing no metal component as a main oxidant in preparing a slurry for tungsten CMP. It was found that the stability and the high polishing rate of can be secured to arrive at the present invention.

Accordingly, an object of the present invention is to provide a slurry for tungsten CMP having excellent slurry stability and high polishing rate.

Another object of the present invention is to provide a slurry for tungsten CMP, which ensures dispersion stability of nano-sized ceramic particles that are stable in aqueous solution.

Another object of the present invention is to provide a slurry using H ₂ O ₂ as a main oxidizing agent in order to minimize contamination of metal components.

Still another object of the present invention is to prepare a slurry having excellent stability, including a main oxidizing agent, an oxidation promoter, and a stabilizer of the oxidation promoter.

The slurry for tungsten CMP according to the present invention uses nano-sized ceramic particles as an abrasive and hydrogen peroxide (H ₂ O ₂ ) as an oxidant for electrochemical corrosion of metals, Fe (NO ₃ ) ₃ as an accelerator of the oxidant, Stabilizers of oxidation promoters are slurries that contain citric acid, malonic acid or oxalic acid and are stable at pH 3-5.

The nano-sized ceramic particles contained in the slurry are in a state in which agglomerates are controlled by high-energy milling, which is excellent in dispersion stability in an aqueous solution. The average particle size of the aggregate controlled ceramic abrasive is 200 nm or less, as shown in FIG. The slurry uses nano-sized alumina or silica as an abrasive and ceria (CeO ₂ ) is also applicable.

Examples of the abrasive used in the slurry are 5-10% by weight of alumina or 5-25% by weight of silica, 1-5% by weight of hydrogen peroxide (H ₂ O ₂ ) as the main oxidizing agent, and promote oxidation As a zero, Fe (NO ₃ ) ₃ is used at a concentration of 0.05-0.5 molar. The slurry uses 1-10% by weight citric acid, 0.5-5% by weight malonic acid or 0.6-6% by weight oxalic acid as stabilizer to stabilize the oxidation promoter.

Hereinafter, with reference to the specific embodiment including the following drawings of the present invention will be described in detail.

Nano-size alumina or silica used as an abrasive in the present invention contains a large amount of aggregates in the powder synthesis method. Without control of such aggregates, nano-sized ceramic particles are difficult to obtain dispersion stability in aqueous solution. In the present invention, a mechanical milling method is introduced to grind these aggregates.

In general, mechanical milling is performed by putting high strength metal oxide balls such as zirconia or alumina together with the powder to be pulverized and stirring them. At this time, the smaller the size of the ball used and the higher the stirring speed, the smaller the particle size of the average aggregate is. In the present invention, high energy milling using a ball having a much smaller particle size than a ball used for general ball milling, for example, a zirconia ball having a particle diameter of 0.1 mm, and also at a much higher speed than a general stirring speed, for example, about 2,500 rpm Through controlling the aggregates through to secure the dispersion stability of these nano-sized ceramic particles.

1 shows the result that the average particle size of alumina or silica decreases with milling time in high energy milling. As can be seen in FIG. 1, ceramic particles having an average particle diameter of 200 nm or less after high energy milling of about 3 minutes can be obtained. Through high energy milling, the aggregated ceramic particles were found to have much improved dispersion stability in aqueous solution than before the aggregates were controlled.

In the case of nano alumina used as an abrasive of the slurry, the polishing rate is lower than 5% by weight or less, and when it is 10% or more by weight, the dispersion stability is 5-10% by weight. In the case of the nano-silica used as the abrasive of the slurry, the polishing rate is less than 5% by weight, and when it is more than 25% by weight, the dispersion stability is poor, so 5-25% by weight is suitable.

In the case of hydrogen peroxide water used as the main oxidizing agent of the slurry, it was confirmed through electrochemical analysis that the intended passivation of the metal was not effective when added to the slurry alone. The oxidizing agent was confirmed through an electrochemical analysis to maximize the passivation effect on tungsten when Fe (NO ₃ ) ₃ is added as an oxidation promoter.

An electrochemical potentiodynamic test was performed to compare the oxidation of tungsten in the slurry including the oxidizing agent and the oxidizing agent of the present invention with the oxidizing agents used in the existing slurry, which is shown in FIG. 2.

The first criterion for evaluating the action of an oxidant in a potentiodynamic test is that a limited current region should appear where the current density does not change significantly even when the potential changes in the oxidation part (+ direction part) of the potentiodynamic curve. This means that the metal exhibits a passivation phenomenon effective for polishing the metal CMP by the oxidant. The second criterion is that the limiting current should appear at the highest current density possible in the passivation region in order to have a high removal rate in tungsten CMP.

Referring to the results of FIG. 2 based on these two criteria, when H ₂ O ₂ (HO) acts alone, the oxidation power for tungsten is much lower than that of other oxidants, and it is used together with the Fe (NO ₃ ) ₃ promoter as in the slurry of the present invention. The oxidation power is greatly improved. In addition, the oxidizing agent of the present invention in Figure 2 in terms of oxidizing power than conventional oxidants (KIO: KIO ₃ , KFCN: K ₃ Fe (CN) ₆ , FNO: Fe (NO ₃ ) ₃ , HO: H ₂ O ₂ ) It can be confirmed that excellent.

Fe (NO ₃ ) ₃ , added as an oxidation promoter, appears to be stable at pH 1-2 and is unstable in the pH 3-5 region in which the slurry of the present invention operates, thereby degrading the stability of the slurry. In particular, in the pH 3-5 region, the dispersibility of nano-sized ceramic particles used as an abrasive is also reduced, and an additive for stabilizing an oxidation promoter is required.

Citric acid, oxalic acid, malonic acid, etc. are effective as stabilizers of the oxidation promoter. The proper amount of stabilizer for the oxidation promoter was found to be 1-10% by weight for citric acid, 0.5-5% by weight for malonic acid and 0.6-6% by weight for oxalic acid.

<Example>

<Examples 1 and 2>

Zirconia balls with a particle diameter of 0.1 mm were put together with alumina (Example 1) or silica (Example 2) powder and stirred at about 2,500 rpm for 3 minutes to prepare ceramic particles having an average particle diameter of 200 nm having dispersion stability as abrasives. Used.

Thus, 5% by weight of alumina or 5% by weight of silica as abrasive, 3% by weight of H ₂ O ₂ as oxidant, 4% by weight of Fe (NO ₃ ) ₃ as oxidation promoter, stabilizer Oxalic acid of 3.8% by weight was added, and the additive was dissolved by mechanical stirring at 300 to 400 rpm using a rotary stirrer to prepare a slurry for tungsten CMP.

CMP was performed on a 4 inch size wafer on which a tungsten thin film was deposited on a silicon wafer using the slurry prepared by the above method, and the polishing rate was measured.

<Example 3>

As in Example 1, but after the slurry was prepared in a composition in which the alumina fraction of the abrasive was increased to 10% by weight, CMP was performed in the same manner as in Example 1, and the polishing rate was measured.

<Example 4>

5% by weight of alumina was used as the abrasive as in Example 1, except that the chemical composition was reduced, as shown in Table 1, and then CMP was performed in the same manner as in Example 1, and the polishing was performed. The rate was measured.

<Examples 5 to 6>

In the same manner as in Example 1, 5% by weight of alumina, 3% by weight of H ₂ O ₂ as an oxidant, and 4% by weight of Fe (NO ₃ ) ₃ as an oxidation accelerator were used. After the slurry was prepared using 6 wt% citric acid (Example 5) or 3.1 wt% malonic acid (Example 6), CMP was performed in the same manner as in Example 1, and the polishing rate was measured.

<Comparative Examples 1 and 2>

For comparison, CMP was performed in the same manner as in Example 1 using a slurry for commercial tungsten CMP using alumina and silica, and the polishing rate was measured. The slurry of Comparative Example 1 is a commercial slurry using alumina as an abrasive, and no special oxidant is added. The slurry of Comparative Example 2 is a commercial slurry using silica as an abrasive, and an oxidant is added.

How to measure polishing rate

After performing CMP using the prepared slurry, the polishing rate of a 4 inch tungsten wafer was measured by measuring the resistance before and after the CMP using DC 4-terminal method and converting it into thickness using a specific resistance value. . The measurement points were selected from 13 horizontally and 13 vertically from the center of the 4-inch wafer, and the polishing rate was determined by averaging the measured values at each measuring point.

After the polishing rate of the slurry for tungsten CMP of Example (1-6) and Comparative Example (1-2) of the present invention was measured by the above method, the results are shown in Table 1 below.

Change of Polishing Rate According to Slurry Composition abrasive H ₂ O ₂ Fe (NO ₃ ) ₃ Stabilizer Polishing rate Comparative Example 1 Al ₂ O ₃ 47 Comparative Example 2 SiO ₂ 1951 Example 1 Al ₂ O ₃ 5 wt% 3 wt% 4 wt% Oxalic acid3.8 wt% 2171 Example 2 SiO ₂ 5 wt% 3 wt% 4 wt% Oxalic acid3.8 wt% 2837 Example 3 Al ₂ O ₃ 10 wt% 3 wt% 4 wt% Oxalic acid3.8 wt% 2350 Example 4 Al ₂ O ₃ 5 wt% 2 wt% 3 wt% Oxalic acid 2.5 wt% 1980 Example 5 Al ₂ O ₃ 5 wt% 3 wt% 4 wt% Citric Acid 6% by weight 2050 Example 6 Al ₂ O ₃ 5 wt% 3 wt% 4 wt% Malonic acid3.1 wt% 2300

Comparing the results of Table 1, in the same slurry chemistry, the polishing rate of the composition using silica as the abrasive was higher than that of the alumina, and the same polishing condition was observed in the composition having high oxidation power of the slurry. In addition, when the malonic acid is used as a stabilizer under the same oxidizing conditions, the polishing rate is high.

Figure 3 is a graph comparing the polishing rate for each slurry after performing a CMP on a 4-inch wafer on which a tungsten thin film is deposited using the slurry of the comparative example and the slurry corresponding to the embodiment of the present invention.

As can be seen in FIG. 3, Comparative Example A without addition of an oxidizing agent was found to have a very low polishing rate, and Examples 1 and 2 of the present invention showed higher polishing rates than the commercial slurry of Comparative Example B. .

<Example 7>

In the same manner as in Examples 1 to 6, except in each slurry, H ₂ O ₂ as an oxidizing agent and Fe (NO ₃ ) ₃ as an oxidizing agent were added, and a slurry was added without adding oxalic acid, citric acid or malonic acid as a stabilizer. Tests in the 3-5 area resulted in brown precipitates.

On the contrary, the slurry of Examples 1 to 6 including the stabilizer did not generate precipitation in the pH 3-5 region, and showed stable characteristics.

As such, the slurry for tungsten CMP of the present invention is excellent in dispersion stability of nano-sized ceramic particles in an aqueous solution and shows high polishing rate.

In addition, if the technology to stably disperse the nano-sized ceramic particles in the aqueous solution through the present invention, it is possible to minimize the defects after polishing by using the ceramic particles such as alumina, silica or ceria as an abrasive to suit the CMP target It is possible to develop a slurry having excellent polishing effect on the metal layer by increasing the stability between the abrasive and the chemical composition. In addition, by understanding the role of chemical components in charge of the electrochemical action on the metal layer during the CMP process, it is possible to secure the basic technology for the development of slurry for copper CMP, which is the target of the next generation CMP process as well as tungsten.

Claims (7)

A slurry for tungsten CMP, which is stable at pH 3-5, comprising 5-25 wt% abrasive, 1-5 wt% oxidant, 0.4-4 wt% oxidizer, and 1-10 wt% oxidizer stabilizer. The slurry of claim 1, wherein the abrasive is a nano-sized ceramic particle having dispersion stability in an aqueous solution by a high energy milling process using a metal oxide ball having a small particle size under a high stirring speed. 3. The slurry of claim 1 or 2, wherein the abrasive is nanosized 5-10 wt% alumina or nanosized 5-25 wt% silica. The slurry of claim 3, wherein the average particle size of the abrasive is 200 nm or less. The slurry of claim 1 or 2, wherein the oxidant is hydrogen peroxide water (H ₂ O ₂ ). The slurry of claim 1 or 2, wherein the oxidation promoter is Fe (NO ₃ ) ₃ at a concentration of 0.05 to 0.5 molar. The slurry according to claim 1 or 2, wherein the stabilizer of the oxidation promoter is 1 to 10 wt% citric acid, 0.5 to 5 wt% malonic acid or 0.6 to 6 wt% oxalic acid.