JP2001115145A - Polishing agent for metal film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an excellent polishing agent for a metal film, which is the one using hydrogen peroxide as an oxidizing agent, retaining a high polishing rate markedly stabilized against a change in the concentration of hydrogen peroxide, and not causing the scratching and dishing of the film. SOLUTION: This agent comprises a silica slurry comprising silica particles, an ammonium salt of an organic acid, hydrogen peroxide, and water and adjusted to a specified pH and a specified hydrogen peroxide concentration. It is desirable that the silica slurry has a hydrogen peroxide concentration of 2-8 wt.% and a pH of above 9 to 10. The ammonium salt is desirably used in a concentration of 0.2-2 wt.% and is exemplified by ammonium oxalate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a novel polishing agent for metal films. Specifically, in a polishing agent for metal films using hydrogen peroxide as an oxidizing agent, dishing does not easily occur during polishing, has a high polishing rate, and furthermore, a high polishing rate extremely stable against changes in the concentration of hydrogen peroxide. The present invention provides a metal film polishing agent having excellent characteristics of maintaining the following.

[0002]

2. Description of the Related Art Along with the high integration of semiconductor devices, wiring technology has been increasingly miniaturized and multilayered. The multi-layered wiring technology increases the level difference on the surface of the semiconductor substrate. As a result, there is a problem in that the processing accuracy and reliability of wiring formed thereon are reduced, and miniaturization is hindered.

In order to solve the above-mentioned problems caused by the multi-layering, a technique has been developed in which a layer on which wiring patterns, electrodes, etc. (hereinafter, referred to as wirings, etc.) are formed is flattened, and further wirings, etc. are formed thereon. ing.

That is, an insulating film having a concave portion for metal wiring is formed on the surface of a semiconductor substrate, and a metal film is formed thereon so as to fill the concave portion via a barrier film. In this method, the film and the barrier film are removed by polishing to form a flattened surface of the insulating film and the metal film present in the concave portion.

In the above method, the barrier film has a function of preventing aluminum or copper used as a metal film from diffusing into the insulating film and improving the adhesion of the metal film to the surface of the semiconductor substrate. In general, titanium nitride, tantalum nitride, or the like is used.

In the above method, in order to realize high polishing performance, a polishing method using both mechanical polishing and a chemical reaction for promoting the polishing is employed. This polishing method is called a chemical mechanical polishing (hereinafter abbreviated as CMP) method, and various compositions of polishing agents to be used according to a polishing target such as a metal film, an insulating film, and a barrier film have been proposed. The general composition of the above-mentioned abrasive is composed of abrasive grains and a chemical.

As a polishing agent useful for a metal film, particularly a polishing agent useful for a substrate using a copper-based metal, metal oxide abrasive grains such as alumina abrasive grains are used, and an oxidizing agent and tartaric acid or An aqueous slurry containing a salt such as oxalic acid and an anticorrosive such as benzotriazole for preventing dishing caused by preferentially eroding a metal portion due to dissolution of the metal is known.

[0008]

However, the above metal film polishing agent requires an anticorrosive agent for preventing dishing, and has a problem that the polishing rate of the metal film is reduced in proportion to the amount of the anticorrosive agent. .

In the above metal film abrasive, alumina particles are generally used as abrasive grains, but there is a concern that polishing scratches (scratch) after polishing may occur.

On the other hand, as an oxidizing agent in the metal film polishing agent, hydrogen peroxide is more advantageous than other oxidizing agents in terms of handleability, wastewater treatment after polishing, and the like, and is preferably used.

Accordingly, an object of the present invention is to provide a polishing agent for a metal film capable of achieving a high polishing rate while effectively preventing dishing during polishing and suppressing generation of scratches. It is in.

[0012]

Means for Solving the Problems The present inventors have intensively studied to achieve the above object. As a result, the metal oxide abrasive grains, an oxidizing agent, a polishing agent comprising an aqueous slurry of a salt and an anticorrosive, using hydrogen peroxide as an oxidizing agent,
By adjusting the concentration in the abrasive to a relatively high concentration of 2% by weight or more, dishing can be effectively reduced even without adding an anticorrosive, and furthermore, an organic acid such as ammonium oxalate can be added. It was found that the polishing rate was significantly improved by adding ammonium as a salt and adjusting the pH of the polishing agent to the alkali side.

However, when the pH of the abrasive having the above composition is adjusted to the alkali side, a phenomenon occurs in which the polishing rate of the abrasive significantly changes due to the change in the concentration of hydrogen peroxide.

Incidentally, in an abrasive having a pH of about 8,
When the hydrogen peroxide concentration changes by 3% by weight, the polishing rate changes almost twice. Therefore, in the semiconductor manufacturing process, the polishing rate of the metal is not stabilized due to the batch of the polishing agent or the difference in the number of storage days, and the influence on the production becomes a problem.

The inventors of the present invention have further studied and found that the polishing rate can be suppressed from being dependent on aqueous hydrogen peroxide in an extremely limited pH range on the alkali side. By using silica particles,
Good dispersibility can be achieved even at the above pH, and in addition,
The inventors have found that the occurrence of scratches can be effectively prevented, and have come to propose the present invention.

That is, the present invention comprises silica particles, an organic acid ammonium salt, hydrogen peroxide and water, wherein the concentration of the hydrogen peroxide is 2 to 8% by weight and the pH exceeds 9 and
An abrasive for a metal film, comprising the following silica slurry.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the abrasive according to the present invention will be described in detail.

In the present invention, the use of silica particles as abrasive grains is important for preventing scratches and for stabilizing the abrasive. That is, other types of abrasive grains, such as alumina particles, are likely to cause scratches in the CMP polishing step, and when the scratches occur, the wiring of the device may be disconnected or short-circuited, and the yield of the device may be reduced. Cause a decrease. Further, the polishing slurry of the present invention has a pH of 9 as described below.
The silica particles are stable in this pH range, unlike the alumina particles, with little aggregation.

Known silica particles can be used without any particular limitation. For example, fumed silica produced by burning silicon tetrachloride or a silane-based gas in a flame, or sol-gel silica produced by hydrolysis using alkoxysilane as a raw material (hereinafter also referred to as high-purity colloidal silica) And precipitated silica produced by using sodium silicate as a raw material and neutralized with a mineral acid, and colloidal silica produced by using the sodium silicate as a raw material by the Ostwald process.

Among the above, fumed silica and high-purity colloidal silica have high purity and are therefore suitable as a polishing agent for metal films for semiconductor devices.

The specific surface area of the silica particles is not particularly limited, but is preferably 20 to 200 m.
The range of ² / g is preferred, more preferably 20-100.
m ² / g. That is, when the specific surface area is smaller than 20 m ² / g, the silica particles tend to settle easily. On the other hand, when the specific surface area is larger than 200 m ² / g, silica particles in the abrasive may be easily gelled.

In the metal film abrasive of the present invention, the concentration of the silica particles is preferably in the range of 0.5 to 20% by weight.
The range of from 10 to 10% by weight is optimal. When the concentration of the silica particles is less than 0.5% by weight, the polishing rate of the metal film tends to decrease, and when the concentration is more than 20% by weight,
Problems such as gelling of the abrasive may occur.

In the present invention, by using an organic acid ammonium represented by ammonium oxalate,
It has the effect of increasing the polishing rate of the metal film, suppressing the dissolution rate of the metal film to a low level, and suppressing dishing during polishing. The concentration of the above-mentioned organic acid ammonium in the abrasive is preferably in the range of 0.2 to 2% by weight. If the concentration of the organic acid ammonium is less than 0.2% by weight, the polishing rate of the metal film may be low. On the other hand, when the concentration of the organic acid ammonium exceeds 2% by weight, the dissolution rate of the metal film may increase, or silica particles in the abrasive may be easily aggregated.

The above-mentioned organic ammonium salt may be added to the abrasive in the form of a salt from the beginning, or an organic acid and ammonia may be separately added to form the organic ammonium in the abrasive. Can also be used.

In the polishing agent for a metal film of the present invention, hydrogen peroxide is used as an oxidizing agent so that its concentration in the polishing agent is 2 to 8% by weight. It is important to suppress the dishing of the metal film and to improve the polishing rate of the metal film.

It is extremely important that the pH of the polishing slurry for a metal film of the present invention is adjusted to a range of more than 9 and not more than 10 in order to suppress the above-mentioned dependence on the concentration of hydrogen peroxide. That is, when the pH is 9 or less, although the polishing rate is high to some extent, the concentration dependency of hydrogen peroxide is large, and the polishing rate is greatly changed by a slight change in the hydrogen peroxide concentration.

Further, depending on the kind of the salt, the polishing rate is remarkably reduced, which may be impractical.
On the other hand, when the pH exceeds 10, the solubility of the metal film increases, and dishing tends to occur.

In the present invention, the pH of the metal film polishing agent
If necessary, a known basic compound can be added in order to adjust the above to the above range. The basic compound is not particularly limited, but ammonia, various amines, and salts thereof can be suitably used.

The amount of the basic compound to be added cannot be unconditionally determined because it varies depending on the type of the compound. However, the amount necessary for adjusting the pH of the metal film polishing agent to the above range may be appropriately added. .

The metal film polishing agent of the present invention can reduce the dissolution rate of the metal film so that dishing during polishing can be sufficiently prevented by the above-mentioned composition, but within the range not significantly impairing the effects of the present invention. Anticorrosives can also be added. That is, when an anticorrosive such as benzotriazole is added, its concentration is 100 ppm or less, preferably 80 ppm.
pm or less is more preferable. If it is added in excess of 100 ppm, the polishing rate of the metal film is greatly reduced, and it may not be practical.

Further, if necessary, various other known additives may be added to the metal film polishing agent of the present invention. For example, surfactants, water-soluble polymers, alcohols, stabilizers, anti-settling agents and the like.

In the method for producing a polishing agent for metal films of the present invention, the order of addition of each component is not particularly limited.
It is sufficient that all components are contained at the time of polishing.

In general, if hydrogen peroxide is present in the metal film polishing agent, it often gradually decomposes upon contact with air or other components, and its oxidizing power often decreases. It is desirable to add at the time of use.

Specifically, in order to prevent the decomposition of the hydrogen peroxide, it is preferable to store the main component of the abrasive and the hydrogen peroxide separately.

That is, according to the present invention, there is provided an abrasive for a metal film which is divided and stored into an A component comprising silica particles, an organic acid ammonium and water and a B component comprising hydrogen peroxide. The pH of the component A is the pH after mixing with the component B.
May be adjusted to be within the above range. Since the direction and width of fluctuation of pH due to the addition of the component B vary depending on the amount of hydrogen peroxide contained therein, it is desirable to conduct a mixing experiment in advance to determine the optimum pH.

The concentrations of the silica particles, the organic acid ammonium and the hydrogen peroxide, which have been described so far, mainly describe the optimum concentration ranges when they are used as abrasives. There is no problem if a high product is manufactured and diluted with pure water when used.

The manufacture of a semiconductor device using an abrasive is performed by laminating an insulating film, a barrier film, and a metal film on a semiconductor substrate in a predetermined pattern and polishing the laminated film.

The above-mentioned semiconductor substrate is typically a silicon substrate used for a semiconductor device such as an IC or an LSI, but a semiconductor substrate such as a germanium or a compound semiconductor is also used.

The insulating film is used for electrical isolation between wiring layers, and is not particularly limited as long as it is insulating. Generally, a silicon oxide film (plasma-TE
OS film and SOG film) and organic SO
A G film or the like is used.

Further, the barrier film is a thin film formed between the insulating film and the metal film to prevent the diffusion of the wiring metal into the insulating film and to improve the adhesion of the metal film to the insulating film. In addition, a tantalum film, a tantalum nitride film, a titanium film, a titanium nitride film, a tungsten nitride film, and the like can be given. Among them, a titanium nitride film and a tantalum nitride film are preferable.

Further, the metal film is a wiring material for forming a wiring pattern and an electrode, and examples thereof include an aluminum film, a copper film, and a tungsten film. The metal film polishing agent of the present invention exhibits a particularly remarkable effect on a copper film.

A typical polishing method using the metal film polishing agent of the present invention will be described in detail with reference to FIG.

The recess A provided in the insulating film formed on the surface of the semiconductor substrate is a groove or a connection hole formed on the insulating film for forming a wiring or the like.

First, (a) the insulating film 2 having the concave portion A
The polishing is stopped at the position where the barrier film 3 exists by selectively polishing the barrier film 3 and the metal film 4 sequentially laminated on the upper surface using the metal film polishing agent of the present invention (b). Hereinafter, this polishing is called first-stage polishing, and the abrasive used for this is called first abrasive.)

In the first-stage polishing, the use of the metal film polishing agent of the present invention allows the metal film to be efficiently polished while suppressing the occurrence of scratching and dishing.
A flat surface composed of the barrier film and the metal film can be formed.

Next, (c) simultaneously polishing the barrier film and the metal film using a polishing agent having a different selection ratio from the first polishing agent (hereinafter, referred to as a second polishing agent) (hereinafter referred to as a second step). Polishing), and if necessary, simultaneously polishing the metal film, the barrier film, and the insulating film (hereinafter, referred to as third-stage polishing).

The polishing agent for a metal film of the present invention is a polishing agent having a high selection ratio (polishing rate ratio of metal film / barrier film), and generally achieves the selection ratio of 5 or more, and in some cases, 10 or more. And is suitable for the first abrasive.

After the removal of the metal film with the polishing agent in the first-stage polishing, the barrier film and the metal film buried in the concave portions are present in an exposed state on the surface to be polished.

Since the second polishing agent needs to remove the barrier film from the surface to be polished, the second polishing agent polishes the barrier film against the metal film at a polishing rate equal to or higher than that of the first step polishing. What can do is desirable. Therefore, the selectivity between the metal film and the barrier film (the polishing rate ratio of the metal film / barrier film) is preferably 1 or less, and more preferably 0.7 or less is suitably used. That is, when the selectivity exceeds 1, the metal film may be polished too much more than the barrier film, and the dishing characteristics may be reduced.

Further, after the barrier film is polished and removed with the second abrasive, the insulating film below the barrier film is exposed. However, if the polishing rate of the second abrasive with respect to the insulating film is too high, the insulating film may be damaged. There is a possibility of dishing. Therefore, it is preferable that the second polishing agent can polish the metal film and the insulating film at substantially the same polishing rate.

As the second polishing agent, a known polishing agent comprising silica particles and water is preferable.
The use of silica particles in the range of 100 to 100 m ² / g is preferable because the polishing rate of the barrier film is high. More preferably, it is preferable to use silica particles synthesized in a liquid phase such as a sol-gel method and produced without passing through a drying step.

That is, the silica particles synthesized in the liquid phase are excellent in dispersibility, and are spherical and soft in shape, so that scratches to be polished during polishing are particularly small.

Since the thickness of the barrier film formed on the semiconductor substrate is generally in the range of 100 to 500 angstroms, the polishing rate of the second abrasive to the barrier film is 50 to 1000 angstroms /. mi
In the range of n, preferably in the range of 200 to 500 angstroms / min, it is easier to control, and the time required for removing the barrier film is preferably within 2 minutes, more preferably within 1 minute.

The polishing rate is 50 angstroms / m.
If it is less than in, productivity may decrease, and if it is more than 1000 Å / min, not only barrier film but also
In some cases, the lower part of the insulating film or the metal film of the wiring may be polished, and it may be difficult to stop polishing at a desired position, and controllability may be reduced.

In order to achieve such polishing characteristics, the concentration of the silica particles in the second abrasive is preferably 1 to 20% by weight, more preferably 2 to 10% by weight. Since the polishing of the barrier film is often performed by the mechanical action of silica particles, the desired polishing rate can be controlled by changing the concentration of the silica particles.

When the pH of the second abrasive is in the range of 5 to 11, preferably in the range of 6 to 10, the metal film and the insulating film can be polished at almost the same polishing rate. A known abrasive adjusted to pH is used.

If the pH of the polishing agent is less than 5, the polishing rate of the metal film may be significantly higher than the polishing rate of the barrier film if the polishing rate of the metal film is more than 11. In such a case, dishing easily occurs in the metal film or the insulating film, and the flatness of the semiconductor substrate surface may be reduced. When the pH is less than 5 or more than 11, the metal film tends to be easily corroded.

As described above, by polishing with a second polishing agent composed of silica particles and water, the barrier film can be efficiently removed and the surface of the semiconductor substrate can be highly flattened. It is possible.

Further, polishing of the barrier film and the metal film, that is,
Subsequent to the second-stage polishing, a third-stage polishing is performed as necessary. It is preferable that the third polishing agent used for such polishing can polish the metal film, the barrier film, and the insulating film at substantially the same polishing rate. Particularly preferably, the selectivity between the metal film and the barrier film with respect to the insulating film (metal film / insulating film polishing rate ratio and barrier film / insulating film polishing rate ratio) is preferably
0.3-3, more preferably 0.5-2, especially 0.
8 to 1.2.

If it exceeds the above range, either one of the films is selectively polished, and dishing easily occurs.

As the third abrasive, one having the above selectivity may be selected and used from known abrasives, or one having the above selectivity may be selected from the second abrasive. May be used. In the latter case, the second-stage polishing and the third-stage polishing can be performed continuously, which is preferable.

[0062]

As will be understood from the above description, the polishing agent for metal films of the present invention is the same as the polishing agent for metal films using hydrogen peroxide as an oxidizing agent, because it hardly causes dishing during polishing and has high polishing ability. It has excellent characteristics that it can maintain a very high polishing rate that is extremely stable against changes in the concentration of hydrogen peroxide.When polishing a semiconductor substrate, the metal film existing on the barrier film is removed. It is extremely useful when polishing.

[0063]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to these Examples.

(Polishing Test) Copper (Cu) film, tantalum nitride (TaN) film, or silicon oxide (SiO ₂ )
A polishing test was performed using a 4-inch silicon wafer having a film formed on the surface. Rodel IC for polishing pad
Using 1000 / SUBA400, processing pressure 300g /
cm ² , platen rotation speed 40 rpm, abrasive dripping speed 80
A polishing test was performed under the condition of ml / min, and a polishing rate was obtained.

(Solubility Test) A solubility test was performed using a silicon wafer having a Cu film formed on the surface. The test pieces were immersed in an abrasive, and the container containing them was placed in a thermostatic shaker maintained at 50 ° C. After taking out the thermostatic shaker 10 minutes later, the test piece was immediately taken out of the abrasive, and the abrasive remaining on the surface was washed away. C before and after immersion
From the change in the thickness of the u film, the dissolution rate of the Cu film in the abrasive was determined.

Examples 1-2, Comparative Examples 1-4 High-purity colloidal silica having a specific surface area of 75 m ² / g was added at 7% by weight as silica particles, and ammonium oxalate was added as an organic acid ammonium at the ratios shown in Table 1. Then, hydrogen peroxide was added so as to be 3 and 6% by weight to prepare abrasives having a predetermined pH, respectively, and evaluated.
In addition, ammonia was used as a pH adjuster.

For comparison, the pH was less than 9 and 10
Abrasives were prepared and evaluated in the same manner as described above, except that the pH was adjusted to exceed. In addition, an abrasive containing no ammonium oxalate at all, and an abrasive using alumina particles having a specific surface area of 100 m ² / g instead of silica were prepared and evaluated in the same manner.

The results of the test are shown in Table 1.

As described above, the polishing agent for a metal film of the above-mentioned system which is within the pH range specified by the present invention has a small dependency on the hydrogen peroxide concentration with respect to the polishing rate. It can be seen that the abrasive that has come off has such a high dependence. In addition, it was found that the polishing agent having a higher pH had a higher dissolution rate of the Cu film.

On the other hand, when alumina was used as abrasive grains other than silica, it was found that alumina immediately aggregated immediately after the preparation of the abrasive. When a polishing experiment was performed while the abrasive was vigorously stirred, scratches were visually observed on the polished Cu film.

[0071]

[Table 1] Examples 3 to 5 Abrasives were prepared in the same manner as in Example 1 except that ammonium citrate, ammonium tartrate and ammonium malonate were used instead of ammonium oxalate as ammonium organic acid, and various tests were performed.

Table 2 shows the results of the polishing test.

[0073]

[Table 2] Examples 6 to 12 Abrasives were prepared in the same manner as in Example 1 except that various silica particles having different specific surface areas shown in Table 3 were used as the silica particles, and the content of the silica particles was also changed as shown in Table 3. It was prepared and subjected to various tests.

Table 3 shows the results of the polishing test.

[0075]

[Table 3] Example 13 The metal film abrasive of Example 1 was used as a first abrasive. Further, a high-purity colloidal silica particle having a specific surface area of 30 m ² / g, a predetermined amount of water and aqueous ammonia were mixed to prepare an alkaline (pH 9.5) second abrasive having a silica particle concentration of 7% by weight. . A 100 μm wide wiring groove having a width of 100 μm is formed on the SiO ₂ film formed on the silicon wafer surface.
The TEG wafer is formed by sequentially stacking a TaN film having a thickness of about 200 Å and a Cu film having a thickness of about 1.2 μm on the TEG wafer. Polished for 200 seconds. as a result,
The Cu film on the portion other than the wiring groove made of the SiO ₂ film was removed, and the TaN film and the Cu film in the wiring groove were exposed.

Subsequently, polishing was performed for 90 seconds with the second polishing agent. As a result, the TaN film was removed, and the SiO ₂ film in portions other than the wiring grooves and the Cu film in the wiring grooves were exposed.

When the surface of the polished silicon wafer was observed with an electron microscope, no scratch or dishing was observed, and the surface of the SiO ₂ film and the Cu film in the wiring groove except for the wiring groove had almost no steps, and were flat. It was confirmed that a perfect surface was formed.

From the above results, it was found that an extremely flat semiconductor substrate surface could be formed by using the metal film polishing agent of the present invention.

For reference, Table 4 shows the respective polishing rates of the first polishing agent and the second polishing agent for the Cu film, the TaN film, and the SiO ₂ film. As can be seen, the first abrasive used here can selectively polish the metal film with respect to the barrier film. On the other hand, it can be seen that the second abrasive can polish the barrier film at a polishing rate equal to or higher than the metal film or the oxide film, and can polish the metal film and the oxide film at substantially the same polishing rate.

[0080]

[Table 4]

[Brief description of the drawings]

FIG. 1 is a schematic view showing a typical embodiment of a polishing method using the polishing agent of the present invention.

[Explanation of symbols]

 A recess 1 semiconductor substrate 2 insulating film 3 barrier film 4 metal film

Claims (4)

[Claims] 1. A silica slurry comprising silica particles, an organic acid ammonium salt, hydrogen peroxide and water, wherein the concentration of the hydrogen peroxide is 2 to 8% by weight and the pH is more than 9 and 10 or less. An abrasive for a metal film, comprising: 2. The method according to claim 1, wherein the organic acid ammonium is contained in the polishing agent in an amount of 0.2.
The metal film abrasive according to claim 1, which is contained in an amount of from 2 to 2% by weight. 3. The metal film abrasive according to claim 1, wherein the ammonium organic acid is ammonium oxalate. 4. The concentration of silica particles is 0.5 to 20% by weight.
The abrasive for a metal film according to claim 1, wherein