JP2003309090A - Polishing agent for copper-system metal and polishing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high processing characteristic in which, as a polishing agent for polishing a plane having Cu and a Cu alloy applied on a semiconductor device, adhesive grains leading to a factor of surface defects such as dishing or the like are not at all included, and a practical processing speed of 200 nm/min can be attained, and an etching speed is very low. <P>SOLUTION: In the polishing agent for a copper-system metal, a slurry contains condensed phosphate such as pyrophosphoric acid, triphosphoric acid, hexametaphosphate, and a salt thereof of 0.2 weight % or more, periodate of 0.1 to 0.5 weight % and a reaction inhibitor such as benzotriazole or the like of 0.01 to 0.1 weight %, and a pH of the slurry is more than 3 and equal to or less than 6. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copper-based metal polishing liquid and a polishing method. More specifically, the present invention relates to a polishing liquid used for flattening a device by a chemical mechanical polishing technique in a copper wiring process of a semiconductor integrated circuit. It is about.

[0002]

2. Description of the Related Art In recent years, with rapid development of information technology, miniaturization of large scale integrated circuits (LSI, ULSI, VLSI), high density and high speed due to high integration are required, and high precision wiring is required. The development of multi-layer technology is being earnestly pursued. In order to achieve the multi-layered wiring, it is necessary to reduce the wiring pitch width and the inter-wiring capacitance, and the existing metal wiring material such as aluminum is changed to copper (Cu) having a low electric resistivity. The change technology development is being energetically carried out.

It is difficult to form Cu wiring by the dry etching method due to the vapor pressure of the product, and the damascene process by embedding is becoming the mainstream.

Further, by using Cu as the wiring material,
Wafer material silicon (Si) and thermal oxide film (Si
Since the diffusion rate into O ₂ ) becomes extremely high and affects the transistor function, a structure in which a barrier metal intervening Cu diffusion is interposed is applied.

One of the problems in multilayer wiring is to establish high smoothness and high flatness without step defects in the wiring pattern and wiring layer of each layer. As a highly accurate flattening technique, damascene is used. The so-called CMP (Chemical Mechanical), in which the synergistic action of mechanical polishing and chemical polishing is applied to the wiring embedded by the method,
Polishing) technology is used.

Cu is a soft and noble metal, and has the property of easily forming an oxide film and making it passivated in the presence of oxygen. In order to induce electrochemical elution of Cu, a stronger oxidizing power than hydrogen ion is required, and elution is usually attempted by adding an oxidizing agent. Further, in a system in which an oxidizing agent is not present, it is made by adding an ion-containing agent such as CN ⁻ or NH ₄ ⁺ .

The polishing mechanism of CMP mechanically removes an oxide film formed on the surface by an oxidizer with a pad and abrasive grains, and again removes a film re-formed on the removed surface.
It is considered that the polishing process proceeds by the repeating mechanism. In addition, the complex-forming agent that forms a complex with Cu ions eluted on the Cu surface promotes the reaction on the Cu surface, changes the quality of the oxide film formed on the surface, facilitates the polishing process, and also facilitates polishing. It is considered to have a function of immobilizing Cu ions released and eluted in the solution, and having a function of improving processing characteristics.

When the chemical reaction becomes remarkable due to the synergistic action of the oxidizing agent and the complex forming agent, the dissolution of the Cu surface has priority over the formation of the oxide film, and the surface irregularity becomes severe. Further, in polishing, a mechanical action is accompanied, so that the progress of partial polishing becomes remarkable, resulting in a phenomenon that the smoothness on the Cu surface is significantly reduced.

As a countermeasure against this, a reaction inhibitor for controlling the reaction with Cu is added.

A typical CMP slurry composition is as follows:
Formed on the surface, an oxidizing agent for the purpose of promoting the oxidation reaction of the metal surface, an acid for promoting the elution and complexation of Cu and acting as a hydrogen ion donor, a reaction inhibitor for controlling the overetching of the metal and the surface. It is composed of abrasive grains for the purpose of mechanically removing the oxide film and increasing the processing characteristics.

Here, the abrasive grains are mainly intended to mechanically remove the oxide film and the complex film formed by the chemical reaction between the surface to be polished and the slurry constituent agent to increase the processing speed. On the other hand, however, it causes excessive polishing of the metal wiring layer, which causes a dish-shaped defect called dishing and a surface scratch called scratch. Therefore, it is desirable to use a slurry that does not contain the concentration of abrasive grains and can obtain a practical processing speed. Further, in order to improve the smoothness, it is important that the corrosiveness of the polishing liquid with respect to Cu, that is, the so-called etching action is extremely low.

[0012] With no abrasive grains or at a low abrasive grain concentration,
As one aspect of the CMP slurry technique for polishing Cu or a metal film containing Cu as a main component, for example, JP-A-7-23
3485 and JP-A-11-135466 are disclosed.

Japanese Unexamined Patent Publication No. 7-233485 is a method for polishing a copper-based metal with a polishing liquid containing at least one organic acid selected from aminoacetic acid and amidosulfuric acid, an oxidizing agent and water. No. 11-135466,
Mechanically rub the metal surface with a polishing liquid containing less than 1% by weight of abrasive grains, an oxidizing substance, and a substance that solubilizes the oxide, and having a pH and a redox potential in the corrosion region of the metal film. Is the way to do it.

However, the polishing rate described in these publications is a processing rate of 100 nm / min or less and has no practical characteristics. In fact, in the study by the present inventors, it was confirmed that the processing characteristics could hardly be expressed with the slurry containing no abrasive grains.

[0015]

SUMMARY OF THE INVENTION The present invention has a characteristic of exhibiting a high surface property that does not contain any abrasive grains, which causes a surface defect such as dishing, and has a practical working speed of 200 nm / min. The present invention provides a novel polishing liquid for copper-based metals and a polishing method capable of achieving the above, and exhibiting high processing characteristics with an extremely low etching rate.

[0016]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies in order to achieve the above-mentioned objects, and as a result, by using the constituents of the present invention, high processing speed and A novel polishing liquid for copper-based metals and a polishing method capable of achieving both high surface characteristics have been completed, and the above problems have been achieved.

That is, the present invention provides a copper-based metal polishing liquid comprising a slurry having a pH of more than 3 and 6 or less, which is composed of a condensed phosphate, a periodate and a reaction inhibitor. .

The composition ratio of this copper-based metal polishing liquid is such that the concentration of condensed phosphate is 0.2% by weight or more, the concentration of periodate is 0.1% by weight to 0.5% by weight, and the concentration of reaction inhibitor is Is 0.0
It is preferably from 1% by weight to 0.1% by weight.

The present invention will be described in more detail.

The condensed phosphoric acid salt in the present invention is condensed phosphoric acid and / or a salt thereof, specifically, a chain-linked dimeric pyrroline synthesized by dehydration condensation of orthophosphoric acid. An acid, a trimer triphosphoric acid, a hexametaphosphoric acid, and / or at least one of their potassium salts, sodium salts, calcium salts, and the like.

The concentration of the condensed phosphate does not deteriorate the processing speed and the surface characteristics, and impairs the effect of suppressing and fixing the dissolution of the removed substance and preventing the redeposition on the object to be polished. 0.2% by weight or more as a non-concentration, 10
It is preferably not more than 0.5% by weight, more than 0.5% by weight,
It is more preferable that the amount is 5% by weight or less.

On the low concentration side outside this range, the surface characteristics are relatively satisfactory, but it may be difficult to stably obtain a practical level of processing speed, and on the high concentration side. In some cases, a processing speed commensurate with the increase in concentration cannot be obtained, which is economically unfavorable.

The periodate in the present invention is periodate and / or its salt, specifically potassium salt,
Although sodium salts can be mentioned, when salts are used, potassium salts, which have a large ionic radius and are relatively easy to remove by washing, are taken into consideration when the influence of residual impurities on the object to be polished in the washing step after polishing is taken into consideration. It is desirable to use.

The periodate concentration is 0.1% by weight so that both processing speed and surface characteristics can be stably obtained.
It is preferable to be 0.5% by weight.

On the low-concentration side outside this range, sufficient action for oxidizing the surface of the object to be polished cannot be obtained, and the processing speed may decrease. On the high concentration side,
It may not be preferable in terms of solubility.

The reaction inhibitor used in the present invention includes:
Although benzotriazole, benzothiazole, mercaptobenzothiazole, tolyltriazole, and derivatives thereof can be used, it is preferable to use benzotriazole and its derivatives such as azimidol and 1-N-benzoyl in view of reactivity with Cu.

The concentration of the reaction inhibitor is preferably 0.01% by weight to 0.1% by weight, as the concentration at which excellent processing speed and surface characteristics are exhibited.

Outside the range, on the low concentration side,
The anticorrosion property may be insufficient, and on the high concentration side, the anticorrosion property may be excessive and the processing speed may decrease.

The pH of the polishing liquid used in the present invention must be more than 3 and 6 or less, preferably 3.4.
~ 5.

The slurry of the present invention exhibits a pH of 2.5 or less when not adjusted by the condensed phosphate as a constituent. Therefore, it is necessary to adjust the pH of the slurry by adding a modifier exhibiting alkalinity such as ammonium hydroxide, potassium hydroxide, or potassium carbonate.

The pH adjuster is not particularly limited, but it is desirable to apply ammonium hydroxide (ammonia water) in the sense of suppressing the mixing of impurities.

When the pH of the polishing liquid is 3 or less, the elution as Cu ²⁺ becomes remarkable, and although the processing speed shows a high value, the surface characteristics deteriorate significantly. On the other hand, when the pH exceeds 6, the elution characteristic of Cu is reduced, and the formation of the oxide film becomes dominant, so that the processing speed is reduced and it becomes difficult to achieve both the processing speed and the surface characteristics.

To the polishing liquid of the present invention, general viscosity adjusting agents, pH stabilizers, defoaming agents and the like can be added.

The polishing liquid of the present invention is a CMP which is usually applied.
It is applied to the method of polishing the surface containing copper and copper-containing wiring formed on the wafer by the damascene method, which is an accessory equipment of polishing equipment for dropping on the pad mounted on the platen or on the wafer. It is something.

[0035]

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. (Example 1) The concentration of potassium periodate (KIO ₄ ) was 0.
2 wt% and the concentration of benzotriazole (BTA) is 0.
The pH of each polishing liquid was adjusted by adding pyrophosphoric acid of any concentration to the liquid adjusted to 01 wt% and 0.05 wt%.
Was adjusted to 3.5 with aqueous ammonia.

Next, a wafer plated with electrolytic Cu is
The sample diced into 5 mm square was mounted on the work plate 1 shown in FIG. 1 and inserted into the correction ring 2.

Polishing was carried out with the rotation speed of the surface plate 3 of FIG. 1 being 30 rpm while the polishing liquid prepared above was supplied from the slurry supply nozzle 4 of FIG. 1 at a dropping rate of 30 ml / min. The load amount is 250 g / cm ² , the pad is made by Rodel Nitta, trade name "IC1000 / SUBA400"
Was used.

The processing speed was calculated by measuring the sheet resistance before and after processing using a sheet resistor according to the four-terminal method. The surface characteristics were observed and evaluated by a differential interference microscope.

The results are shown in Table 1. Here, in the evaluation symbols of the surface characteristics in the table, ◯ indicates a mirror surface having high gloss, and Δ indicates gloss (including semi-gloss) and x matte.

By setting the pyrophosphoric acid concentration to 0.2 wt% or more, good results were obtained in both processing speed and surface characteristics. (Example 2) The pyrophosphoric acid concentration was 0.5 wt%, the BTA concentration was 0.01 wt%, and the pH of the solution to which KIO _{4 of} any concentration was added was adjusted to 3.5 with ammonia water, and The same evaluation was performed.

The results are shown in Table 1.

KIO ₄ concentration of 0.1 wt% or more, 0.5
Good processing characteristics were obtained in the region of wt% or less. (Example 3) The pyrophosphoric acid concentration was set to 1 wt%, the KIO ₄ concentration was set to 0.2 wt%, and the pH of the solution added with an arbitrary concentration of BTA was adjusted to 3.5 with ammonia water, and the same as in Example 1. An evaluation was performed. In addition, Cu in each adjusted polishing liquid
The plated sample was immersed at room temperature for 30 minutes, and the etching characteristics were examined. The corrosiveness of etching was calculated from the sheet resistance value before and after the immersion of the Cu-plated sample.

The results of the processing speed and the surface characteristics are shown in Table 1. It was confirmed that stable processing characteristics can be exhibited when the BTA concentration is 0.01 wt% to 0.1 wt%. The etching rate with each polishing liquid is 0.01 wt%.
When the BTA concentration was 5 nm / min, the concentration higher than that was 0 to 2 nm / min, which was extremely low corrosiveness. (Example 4) Pyrophosphate concentration of 0.5 wt%, KIO ₄
The concentration is 0.2 wt% and the BTA concentration is 0.01 wt%, and the pH of the liquid is arbitrarily changed with ammonia water,
The same evaluation as in Example 1 was performed.

The results are shown in Table 1.

When the pH of the polishing liquid was in the range of 4 to 6, the performance satisfying both target characteristics was exhibited. (Comparative Example 1) Evaluation was made under the same conditions as in Example 2, except that the polishing liquid containing no KIO ₄ was used.

The results are shown in Table 1, but the processing characteristics were not exhibited. (Comparative Example 2) In Example 3, the evaluation was performed under the same conditions except that BTA was not added.

The results are shown in Table 1. The processing speed showed sufficient characteristics, but the surface exhibited an etched matte surface. (Comparative Example 3) Evaluation was performed under the same conditions except that the pH of Example 4 was adjusted to 3 and 7.

The results are shown in Table 1. When the pH was 3, the processing speed was high, but the surface roughness was remarkable. Further, under the condition that the pH exceeds 6, the processing speed and the surface characteristics were inadequate.

[0049]

[Table 1]

As described above in detail, the present invention comprises a constitution of a condensed phosphate, a periodate and a reaction inhibitor.
The present invention proposes a polishing liquid containing no abrasive grains, and by using the constituents and composition ratios of the present invention, a surface having Cu and a Cu alloy on a semiconductor device can be processed with practically necessary processing characteristics. It becomes possible to process.

[Brief description of drawings]

FIG. 1 is a schematic view of a polishing apparatus used for evaluating a polishing liquid of the present invention.

[Explanation of symbols]

1 work plate 2 correction ring 3 surface plates 4 Slurry supply nozzle

─────────────────────────────────────────────────── ─── Continued Front Page (51) Int.Cl. ⁷ Identification Code FI Theme Coat (Reference) H01L 21/3205 H01L 21/88 M K

Claims (6)

[Claims] 1. A slurry comprising condensed phosphate, periodate and a reaction inhibitor, wherein the pH of the slurry is 3
A polishing liquid for a copper-based metal having a size of 6 or more. 2. The condensed phosphate concentration is 0.2% by weight or more,
The copper-based metal polishing liquid according to claim 1, wherein the periodate concentration is 0.1% by weight to 0.5% by weight and the reaction inhibitor concentration is 0.01% by weight to 0.1% by weight. 3. The acid for copper-based metal polishing liquid according to claim 1, wherein the condensed phosphate is at least one selected from the group consisting of pyrophosphoric acid, triphosphoric acid, hexametaphosphoric acid and / or salts thereof. 4. The copper-based metal polishing slurry according to claim 1, wherein the periodate is periodate and / or a salt thereof. 5. The polishing liquid for copper-based metals according to claim 1, wherein the reaction inhibitor is benzotriazole or a derivative thereof. 6. A method for polishing a surface containing copper or a copper alloy using the polishing liquid for copper-based metals according to claim 1.