JP2008098314A - Polishing composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polishing composition which can provide higher speed polishing operation. <P>SOLUTION: The polishing composition is suitable for a metallic film, in particular, for a copper (Cu) film and contains ammonia, ammonium salt and water as the balance. As ammonium salt, ammonium chloride or ammonium carbonate is preferable. The polishing composition may contain abrasive grains. In particular, in applications that require a good surface smoothness after polishing, it is preferable that the polishing composition contain abrasive grains. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a polishing composition for polishing a metal film, particularly for polishing a copper film.

  In order to meet the demand for higher integration and miniaturization of semiconductor integrated circuits (LSIs), a plurality of semiconductor elements having various functions such as a memory function and a logic function are three-dimensionally mounted on one semiconductor substrate. A technique called system in package (SIP) has been developed. As a result, the number of wirings formed on the substrate increases, the diameter of each wiring decreases, wiring resistance increases, and the signal transmission speed decreases.

  For this reason, it replaces with aluminum conventionally used as wiring material, and copper, copper alloy, etc. whose electric resistance is lower than aluminum are used alternatively. However, since copper is difficult to form wiring by dry etching like aluminum due to its characteristics, a wiring forming method called a damascene method has been established.

According to the damascene method, for example, on the surface of a substrate covered with a silicon dioxide film, it corresponds to a groove corresponding to a wiring pattern to be formed and a plug to be formed (electrical connection portion with wiring inside the substrate). After forming the hole, a barrier metal film (insulating film) made of titanium, titanium nitride, tantalum, tantalum nitride, tungsten, or the like is formed on the inner surface of the groove and hole, and then a copper film is formed on the entire surface of the substrate by plating or the like. Cover and bury copper in the grooves and holes, and then remove excess copper film in areas other than the grooves and holes by chemical mechanical polishing (CMP)
By removing by mechanical polishing, wiring and plugs are formed on the substrate surface. A multi-layer LSI manufactured by the damascene method has a high degree of integration and has six layers. High integration and miniaturization are remarkably advanced.

  In the damascene method, the thickness of a metal film such as a copper film coated on the substrate surface often reaches 5 μm or more. Therefore, when the polishing performance of CMP is low, the polishing rate becomes low and the per unit time. The amount of polishing is reduced, and a very long time is required for polishing, which increases the manufacturing cost of the multilayer LSI.

  In CMP for a metal layer, it is considered that polishing is progressing in a process of polishing a compound generated on a metal surface by a chemical reaction in an acidic region with abrasive grains. It is usually acidic (see Patent Document 1).

  However, the acidic slurry tends to decrease the polishing rate as the number of polished sheets increases, and when an alkaline cleaning liquid for removing abrasive grains after polishing is used, the abrasive grains aggregate due to pH shock. Therefore, an alkaline slurry capable of high-speed polishing is desired in place of the acidic slurry.

  The alkaline slurry contains, for example, organic particles having an acetoacetoxy group, water, a complexing agent and an oxidizing agent. The complexing agent includes at least one selected from carboxylic acids, amines, amino acids and ammonia. A polishing slurry to be used has been studied (see Patent Document 2).

JP 2002-270545 A JP 2005-019481 A

When polishing copper by CMP, in an alkaline slurry typified by a polishing slurry described in Patent Document 2, ammonia is mainly used as a complexing agent, but it is difficult to increase the polishing rate beyond this.
An object of the present invention is to provide a polishing composition capable of higher speed polishing.

The present invention is a polishing composition comprising ammonia and an ammonium salt.
Moreover, this invention is characterized by including an abrasive grain.

  In the present invention, the ammonium salt may be ammonium chloride, ammonium carbonate, ammonium nitrate, ammonium sulfate, ammonium disulfate, ammonium nitrite, ammonium sulfite, ammonium hydrogen carbonate, ammonium acetate, ammonium oxalate, ammonium peroxoacid, ammonium phosphate, pyrophosphate. It is characterized by being one or more selected from ammonium and ammonium adipate.

  According to the present invention, ammonia and an ammonium salt are included. As a result, it is possible to realize higher-speed polishing than in the prior art.

  Further, according to the present invention, the polishing composition further comprises abrasive grains, whereby a polishing composition having high speed and excellent surface smoothness can be realized.

  According to the present invention, the ammonium salt includes ammonium chloride, ammonium carbonate, ammonium nitrate, ammonium sulfate, ammonium disulfate, ammonium nitrite, ammonium sulfite, ammonium hydrogen carbonate, ammonium acetate, ammonium oxalate, ammonium peroxoacid, ammonium phosphate, One or more selected from ammonium pyrophosphate and ammonium adipate can be used.

  The polishing composition of the present invention is a polishing composition suitable for a metal film, particularly a copper (Cu) film, and contains ammonia and an ammonium salt, with the balance being water. By including ammonia and an ammonium salt, a high polishing rate that cannot be achieved by ammonia alone can be realized.

  Ammonium salts include ammonium chloride, ammonium carbonate, ammonium nitrate, ammonium sulfate, ammonium disulfate, ammonium nitrite, ammonium sulfite, ammonium hydrogen carbonate, ammonium acetate, ammonium oxalate, ammonium peroxoacid, ammonium phosphate, ammonium pyrophosphate and ammonium adipate Etc. Among these, ammonium chloride and ammonium carbonate are preferable.

In the alkaline region, ammonia (NH ₃ ) acts as a complexing agent and an oxidizing agent for Cu, and reacts to form a complex as represented by formula (1).
Cu + 4NH ₄ ⁺ → [Cu (NH ₃ ) ₄ ] ²⁺ (1)

  In CMP of a copper film, it is considered that this tetraammine copper complex is removed by contact with a polishing pad, and polishing proceeds.

  When an ammonium salt is present in the polishing composition, the anion liberated from the ammonium salt functions to promote polishing.

When the ammonium salt is, for example, ammonium chloride (NH ₄ Cl), chlorine ions (Cl ⁻ ) act on the tetraammine copper complex or the copper surface, and as a result, the polishing rate is greatly increased even at a low load. become. For example, the polishing rate at a load 35gf / cm ² is 7 [mu] m / min, the polishing rate at a load 140 gf / cm ² to achieve a 9.5 .mu.m / min.

  Furthermore, clogging of the polishing pad due to polishing scraps can be suppressed, and the polishing rate can be stabilized and the life of the polishing pad can be extended.

  Thus, the ammonium salt functions as a polishing accelerator and also as a pH adjuster.

  The content of ammonia in the polishing composition of the present invention is 1 to 30% by weight, preferably 5 to 10% by weight, based on the total amount of the polishing composition. If the ammonia content is less than 1% by weight or more than 30% by weight, a sufficient polishing rate cannot be obtained.

  The content of the ammonium salt in the polishing composition of the present invention is 0.1 to 25% by weight of the total amount of the polishing composition, and if it is less than 0.1% by weight, the desired pH cannot be maintained, The polishing rate decreases, and if it exceeds 25% by weight, a sufficient polishing rate cannot be obtained.

  In the polishing composition of the present invention, the pH may be neutral and alkaline, that is, in the range of 7 to 14, preferably 9 to 11.

  The polishing composition of the present invention may contain abrasive grains. In particular, in applications where surface smoothness after polishing is desired, it is preferable to include abrasive grains.

  As the abrasive grains, those commonly used in this field can be used, and examples thereof include colloidal silica, fumed silica, colloidal alumina, fumed alumina, and ceria.

  The content of abrasive grains in the polishing composition of the present invention is 0.01 to 10% by weight, preferably 0.01 to 7% by weight, based on the total amount of the polishing composition. If the content of abrasive grains is less than 0.01% by weight, the surface is not sufficiently smoothed, and if it exceeds 10% by weight, various problems such as particle aggregation, generation of scratches, increased waste treatment load, and cost increase are caused. appear.

  The polishing composition of the present invention may further contain an anticorrosive material, a surface smoothing agent, a pH adjuster and the like in addition to the above ammonia, ammonium salt and abrasive grains.

  Examples of the anticorrosive material include phosphoric acid compounds such as ammonium dihydrogen phosphate, potassium pyrophosphate, pyrophosphoric acid, potassium tripolyphosphate, benzotriazole (BTA), ethylenediaminetetraacetic acid (EDTA), and the like.

  The content of the anticorrosive is not particularly limited and can be appropriately selected from a wide range according to various polishing conditions, but considering that the performance of the present invention can be sufficiently exerted without adversely affecting the polishing composition of the present invention, Usually, it is 0.001 to 10.0% by weight, preferably 0.001 to 5.0% by weight of the total amount of the polishing composition.

Examples of the pH adjuster include nitric acid (HNO ₃ ), sulfuric acid, hydrochloric acid, acetic acid, and lactic acid as acidic components, and potassium hydroxide (KOH), calcium hydroxide, and lithium hydroxide as alkaline components.

  The polishing composition of the present invention can contain one or more of various additives conventionally used in polishing compositions in this field as long as the preferred properties are not impaired.

  Although there is no restriction | limiting in particular as water used with the polishing composition of this invention, When use in the manufacturing process of a semiconductor device etc. is considered, a pure water, an ultrapure water, ion-exchange water, distilled water etc. are preferable, for example.

The manufacturing method of the polishing composition of this invention is demonstrated.
When the polishing composition does not contain abrasive grains and consists only of ammonia and ammonium salt, and other water-soluble additives, these compounds are used in appropriate amounts, and water is used in an amount that makes the total amount 100% by weight. These components can be produced by uniformly dissolving or dispersing them in water to a desired pH according to a general procedure.

  First, an aqueous solution whose pH is adjusted to 4.0 to 11.0 is prepared by mixing ammonium salt with water, and an aqueous ammonia solution having a concentration of 30% is mixed by a predetermined mass to obtain an alkaline solution. Furthermore, the polishing composition of this invention is obtained by mixing the silica dispersion liquid adjusted to pH 4.0-10.0 with the said alkaline solution so that it may become a predetermined density | concentration.

  The polishing composition of the present invention can be suitably used for polishing various metal films in an LSI manufacturing process. In particular, a polishing slurry for polishing a metal film in a CMP process when forming a metal wiring by a damascene method. Can be suitably used. More specifically, a metal wiring for stacking LSI chips in SIP, an upper layer copper wiring of a semiconductor device (a copper film having a film thickness of 5 μm or more must be polished to form this copper wiring), etc. It can be used very favorably as a metal film polishing slurry. That is, the composition of the present invention is particularly useful as a metal film polishing composition for CMP process by damascene method.

  Further, examples of the metal film to be polished here include metal films such as copper and copper alloy coated on the substrate surface, tantalum, tantalum nitride, titanium, titanium nitride, tungsten, and the like. Among these, a copper metal film is particularly preferable.

Hereinafter, examples and comparative examples of the present invention will be described.
(1) Abrasive-less slurry An abrasive-less slurry that does not contain abrasive grains, contains ammonia and an ammonium salt, and a pH adjuster, and the balance is water. The composition and polishing conditions are shown below.

(Example 1)
Ammonia 5% by weight
Ammonium salt: 5% by weight of ammonium chloride
pH adjuster: potassium hydroxide 2.4% by weight
Water balance pH was adjusted to 10.5.

[Polishing conditions]
Polishing substrate: φ100mm copper plating substrate Polishing device: ECOMET4 (manufactured by BUEHLER)
Polishing pad: IC1400 K-Grv. (Nitta Haas)
Polishing surface plate rotation speed: 300rpm
Carrier rotation speed: 65rpm
Polishing load surface pressure: 150 gf / cm ²
Flow rate of semiconductor polishing composition: 20 ml / min
Polishing time: 120 seconds Conditioning: ex situ (not simultaneously with polishing)

[Polishing speed]
The polishing rate is represented by the thickness (μm / min) of the wafer removed by polishing per unit time. The thickness of the wafer removed by polishing was calculated by measuring the amount of decrease in wafer weight and dividing by the area of the polished surface of the wafer.

  FIG. 1 is a graph showing the polishing rate stability when using an abrasive-free slurry (Example 1). The vertical axis represents the polishing rate [μm / min], and the horizontal axis represents the number of polished sheets [sheets].

  As can be seen from the graph of FIG. 1, in the copper film polishing using Example 1, even when the number of polishing increases, the polishing rate does not decrease, and a high polishing rate of 9 μm / min or more is obtained while polishing 5 sheets. Maintained.

FIG. 2 is a graph showing the influence of the load on the polishing rate when Example 1 is used. The vertical axis represents the polishing rate [μm / min], and the horizontal axis represents the load [psi]. 1 psi is about 70.3 gf / cm ² .

As shown in FIG. 2, even if the load is as small as 0.25 psi (17.6 gf / cm ² ), the polishing rate is 3 μm / min or more, and the load is 0.5 psi ( 35gf / cm ²⁾ polishing rate is 7 [mu] m / min, load polishing rate at 2psi (140gf / cm ²⁾ was achieved 9.5 .mu.m / min.

  Thus, even with an abrasive-free slurry, a very high polishing rate was achieved, and even if the number of polished sheets was increased, no reduction in speed was observed.

Below, the examination result about polishing composition containing an abrasive grain is shown.
(2) Effect of Addition of Ammonium Salt The polishing composition obtained by adding abrasive grains to the above abrasive-less slurry was examined.

  As examples, a composition containing ammonia and ammonium chloride (Example 2) and a composition containing ammonia and ammonium carbonate (Example 3) were used.

  As comparative examples, a composition containing no ammonium salt and containing ammonia (Comparative Example 1), a composition containing no ammonium and containing ammonium chloride (Comparative Example 2), and a composition containing no ammonium and containing ammonium carbonate (Comparative Example 3) ) Was used. These compositions and polishing conditions are shown below.

(Example 2)
Ammonia 2% by weight
Ammonium salt: 5% by weight of ammonium chloride
Abrasive grain: 5% by weight of colloidal silica
pH adjuster: potassium hydroxide 4.0% by weight
Water balance pH was adjusted to 10.5.

(Example 3)
Ammonia 2% by weight
Ammonium salt: 5% by weight of ammonium carbonate
Abrasive grain: 5% by weight of colloidal silica
pH adjuster: potassium hydroxide 4.0% by weight
Water balance pH was adjusted to 10.5.

(Comparative Example 1)
Ammonia 2% by weight
Abrasive grain: 5% by weight of colloidal silica
pH adjuster: potassium hydroxide 0.2% by weight
Water balance pH was adjusted to 10.5.

(Comparative Example 2)
Ammonium salt: 5% by weight of ammonium chloride
Abrasive grain: 5% by weight of colloidal silica
pH adjuster: potassium hydroxide 2.4% by weight
Water balance pH was adjusted to 10.5.

(Comparative Example 3)
Ammonium salt: 5% by weight of ammonium carbonate
Abrasive grain: 5% by weight of colloidal silica
pH adjuster: potassium hydroxide 4.0% by weight
Water balance pH was adjusted to 10.5.

[Polishing conditions]
Polishing substrate: 300mm copper plating substrate Polishing device: ECOMET4 (manufactured by BUEHLER)
Polishing pad: IC1400 (Nitta Haas)
Polishing surface plate rotation speed: 300rpm
Carrier rotation speed: 65rpm
Polishing load surface pressure: 150 gf / cm ²
Flow rate of semiconductor polishing composition: 30 ml / min
Polishing time: 60 seconds Conditioning: ex situ (not simultaneous with polishing)

  FIG. 3 is a graph showing the polishing rate when Examples 2 and 3 and Comparative Examples 1 to 3 are used. The vertical axis represents the polishing rate [μm / min].

  As can be seen from FIG. 3, in Comparative Example 1 that does not contain an ammonium salt, the polishing rate was as low as 1 μm / min or less, and in Comparative Examples 2 and 3 that did not contain ammonia, it was 0.7 μm / min or less. . On the other hand, in Example 2 containing ammonia and ammonium chloride and Example 3 containing ammonia and ammonium carbonate, they were 1.7 μm / min and 1.2 μm / min, which were higher than those of Comparative Examples 1 to 3, respectively.

  Thus, it can be seen that by including ammonia and an ammonium salt, a higher polishing rate can be realized as compared with the case where each of them is included alone.

(3) Influence of ammonia concentration The influence of the ammonia concentration was examined on a polishing composition containing abrasive grains, ammonia, an ammonium salt, and a pH adjuster, and the balance being water.

  As an example, an ammonia concentration of 5 to 10% by weight based on Example 2 (Examples 4 to 6) was used.

  As a comparative example, an ammonia concentration of 5 to 10% by weight (Comparative Examples 4 to 6) based on Comparative Example 1 was used. These compositions and polishing conditions are shown below.

Example 4
Ammonia 5% by weight
Ammonium salt: 5% by weight of ammonium chloride
Abrasive grain: 5% by weight of colloidal silica
pH adjuster: potassium hydroxide 2.4% by weight
Water balance pH was adjusted to 10.5.

(Example 5)
Ammonia 7% by weight
Ammonium salt: 5% by weight of ammonium chloride
Abrasive grain: 5% by weight of colloidal silica
Water balance pH was adjusted to 10.5.

(Example 6)
Ammonia 10% by weight
Ammonium salt: 5% by weight of ammonium chloride
Abrasive grain: 5% by weight of colloidal silica
pH adjuster: potassium hydroxide 2.4% by weight
Water balance pH was adjusted to 10.5.

(Comparative Example 4)
Ammonia 5% by weight
Abrasive grain: 5% by weight of colloidal silica
pH adjuster: potassium hydroxide 2.4% by weight
Water balance pH was adjusted to 10.5.

(Comparative Example 5)
Ammonia 7% by weight
Abrasive grain: 5% by weight of colloidal silica
Water balance pH was adjusted to 10.5.

(Comparative Example 6)
Ammonia 10% by weight
Abrasive grain: 5% by weight of colloidal silica
pH adjuster: potassium hydroxide 2.4% by weight
Water balance pH was adjusted to 10.5.

[Polishing conditions]
Polishing substrate: φ100mm copper plating substrate Polishing device: ECOMET4 (manufactured by BUEHLER)
Polishing pad: IC1400 (Nitta Haas)
Polishing surface plate rotation speed: 300rpm
Carrier rotation speed: 65rpm
Polishing load surface pressure: 150 gf / cm ²
Flow rate of semiconductor polishing composition: 20 ml / min
Polishing time: 60 seconds Conditioning: ex situ (not simultaneous with polishing)

  FIG. 4 is a graph showing the polishing rate when Examples 4 to 6 and Comparative Examples 4 to 6 are used. The vertical axis represents the polishing rate [μm / min].

  As can be seen from FIG. 4, the polishing rate increases as the ammonia concentration increases in any of Examples 4 to 6 and Comparative Examples 4 to 6, but if the ammonia concentration is the same, the example is always faster than the comparative example. there were.

  Furthermore, using the ammonia concentration of 1 to 10% by weight based on Example 2, the influence of the ammonia concentration was examined in detail. About each composition, since only ammonia concentration differs from Example 2, it abbreviate | omits.

[Polishing conditions]
Polishing substrate: φ100mm copper plating substrate Polishing device: ECOMET4 (manufactured by BUEHLER)
Polishing pad: IC1400 (Nitta Haas)
Polishing surface plate rotation speed: 300rpm
Carrier rotation speed: 65rpm
Polishing load surface pressure: 150 gf / cm ²
Flow rate of semiconductor polishing composition: 30 ml / min
Polishing time: 60 seconds Conditioning: in situ (simultaneous with polishing)

  FIG. 5 is a graph showing the influence of the ammonia concentration on the polishing rate. The vertical axis represents the polishing rate [μm / min], and the horizontal axis represents the ammonia concentration [wt%].

  As can be seen from FIG. 5, as the ammonia concentration increased, the polishing rate increased, and in particular, there was a tendency to increase rapidly from 3% by weight. The reason why the polishing rate higher than that when using Examples 4 to 6 is achieved is that the conditioning of the polishing pad is performed in situ simultaneously with the polishing.

(4) Effect of pH The pH of the polishing composition was adjusted to 7 to 14 based on Example 4 and adjusted to 3% by weight of ammonia based on Example 4 to pH 7 to 14. The effect of was examined. About each composition, since only ammonia concentration and pH differ from Example 4, it abbreviate | omits.

[Polishing conditions]
Polishing substrate: φ100mm copper plating substrate Polishing device: ECOMET4 (manufactured by BUEHLER)
Polishing pad: IC1400 (Nitta Haas)
Polishing surface plate rotation speed: 120 rpm
Carrier rotation speed: 65rpm
Polishing load surface pressure: 150 gf / cm ²
Flow rate of semiconductor polishing composition: 20 ml / min
Polishing time: 60 seconds Conditioning: ex situ (not simultaneous with polishing)

  FIG. 6 is a graph showing the influence of pH on the polishing rate. The vertical axis represents the polishing rate [μm / min], and the horizontal axis represents pH [−].

As can be seen from FIG. 6, the change in pH showed the same behavior regardless of the ammonia concentration. That is, it has an optimum pH of 10.5 that maximizes the polishing rate.
Therefore, the pH of the polishing composition is preferably in the range of 9-11.

(5) Surface roughness The effect of the presence or absence of ammonium chloride on the surface roughness was examined.

  FIG. 7 is a view showing the substrate surface after polishing using Example 7 containing ammonium chloride and Comparative Example 7 not containing ammonium chloride. The right side is the time when Example 7 is used and the left side is the time when Comparative Example 7 is used.

  In Example 7, the colloidal silica of Example 4 is changed to fumed silica, and in Comparative Example 7, the colloidal silica of Comparative Example 6 is changed to fumed silica, and thus the details are omitted.

  As can be seen from the figure, the surface after polishing was mirror-finished by containing ammonium chloride, and the surface roughness was very small.

Furthermore, the effect of the presence or absence of abrasive grains on the surface roughness was also examined.
FIG. 8 is a graph showing the surface roughness (Ra) after polishing using Example 1 not containing abrasive grains and Examples 4 and 7 containing abrasive grains. The vertical axis represents the surface roughness Ra [μm].

[Surface roughness]
The surface roughness Ra was measured using a profiler (P-12) manufactured by KLA-Tencor Co., Ltd. under the conditions of a measurement distance of 100 μm, a probe load of 4 mg, and a measurement speed of 5 μm / sec. In addition, the surface roughness before polishing is also shown as reference data.

  When polished using Example 1, Ra was smaller than before polishing. Further, when Example 4 (containing colloidal silica) was used, Ra was smaller than that of Example 1, and when Example 7 (containing fumed silica) was used, Ra was further reduced.

  As described above, it has been found that it is preferable to include abrasive grains in applications where surface smoothness after polishing is desired.

It is a graph which shows the polishing rate stability at the time of use of an abrasive-less slurry (Example 1). It is a graph which shows the influence of the load with respect to the polishing speed at the time of Example 1 use. It is a graph which shows the grinding | polishing rate at the time of Example 2, 3 and Comparative Examples 1-3 use. It is a graph which shows the grinding | polishing rate at the time of Example 4-6 and Comparative Examples 4-6 use. It is a graph which shows the influence of the ammonia concentration with respect to a grinding | polishing rate. It is a graph which shows the influence of pH with respect to a grinding | polishing rate. It is a figure which shows the board | substrate surface after grinding | polishing using Example 7 containing ammonium chloride and Comparative Example 7 which does not contain ammonium chloride. It is a graph which shows (Ra) the surface roughness after grinding | polishing using Example 1 which does not contain an abrasive grain, and Example 4 and 7 containing an abrasive grain.

Claims (3)

  A polishing composition comprising ammonia and an ammonium salt.   The polishing composition according to claim 1, comprising abrasive grains.   The ammonium salt is ammonium chloride, ammonium carbonate, ammonium nitrate, ammonium sulfate, ammonium disulfate, ammonium nitrite, ammonium sulfite, ammonium hydrogen carbonate, ammonium acetate, ammonium oxalate, ammonium peroxoacid, ammonium phosphate, ammonium pyrophosphate and ammonium adipate The polishing composition according to claim 1, wherein the polishing composition is one or more selected from the group consisting of:

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