KR20010035668A - Slurries for Chemical Mechanical Polishing of metal layer and CMP Method using the slurry - Google Patents

Abstract

PURPOSE: A chemical and mechanical grinding slurry reduces the quantity of an oxidizer and improves the quality and the safety of a slurry with maintaining a metal removing speed higher than ordinary speed. CONSTITUTION: Many oxidizing agent and abrasive are provided on an aqueous medium. At least one of the oxidizing agent is a first oxidizing agent for reducing another oxidizing agent. The other oxidizing agent is a second oxidizing agent for oxidizing a metal to be reduced and recycled. Thus the metal removing speed with smaller oxidizing agent is possible.

Description

Slurries for Chemical Mechanical Polishing of metal layer and CMP Method using the slurry}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to slurries used in chemical-mechanical polishing (hereinafter, referred to as CMP) and to a CMP method using such slurries. By using a compound, the present invention relates to a slurry for CMP and a CMP method using the same, which can improve the polishing rate even with a small amount of oxidant.

As semiconductor devices become more integrated, faster, and more versatile, metal wiring layers for connecting chip internal elements and external circuits are also becoming multilayered. The vertical connection between the multilayered metal wiring layers is made through contacts or vias.

Such contacts or vias are filled in contact or via holes formed in the interlayer insulating film having a flat surface by forming contact holes or via holes in the interlayer insulating film, and then depositing metal and polishing and removing the deposited metal by a CMP process. It is formed by leaving only the metal.

In the CMP process, the rotating polishing pad and the wafer are in direct pressure contact with their polishing slurry. Thus, the wafer surface is polished mechanically and chemically and smoothed by a polishing pad coated with a slurry. The composition of the slurry will vary the properties such as polishing rate, defects on the polishing surface, scratches and corrosion and erosion.

The slurry for CMP contains an abrasive and an oxidant such as silica or alumina suspended in an oxidizing aqueous medium.

For example, US Pat. No. 5,340,370 discloses a tungsten polishing slurry comprising potassium ferricinide as an oxidizing agent, silica as an abrasive, and acetium calcium. The patent discloses that the removal rate of tungsten is 1,600-2,400 m 3 / min with a slurry composition containing 0.1 molar potassium ferricinide, 5% silica and adjusted to pH 3.4-3.6.

U.S. Patent 5,527,423 discloses a tungsten polishing slurry comprising an oxidizing agent ferric nitrate, an abrasive alumina or silica, deionized water and the like. This patent discloses that the removal rate of tungsten is 3,000 or 2,000 mW / min with slurry compositions containing 5% ferric nitrate, 3% alumina or silica.

U.S. Patent 5,783,489 discloses a slurry for polishing multiple metals containing an abrasive, a first oxidant, a second oxidant, an organic acid, and deionized water. This patent discloses a technique for effectively removing multiple metal layers composed of aluminum and copper alloys and titanium or alloys thereof using one polishing slurry.

FIG. 1 relates to tungsten (W) among conductive metals. FIG. 1 is a view for explaining two cases of an oxidation reaction performed on a tungsten surface by an oxidant added to a slurry. Referring to FIG. 1, an oxidant contained in tungsten undergoes an oxidation reaction with tungsten to extract electrons and reduce itself. On the other hand, the lost tungsten combines with oxygen provided from the oxidant to form an oxide film 12 in the form of WO ₂ / WO ₃ on the surface of the tungsten 10 or is dissolved in the slurry in the form of an anion 14 such as WO ₄ ^2- . . Since the oxide film formed by such an oxidant is easier to remove than the metal itself, it is easily removed by the frictional force between the abrasive and the polishing pad.

In order to achieve such a metal CMP process, the removal rate of metal, for example, tungsten, must be at least 2000 mW / min. However, in the case of producing a slurry using a single oxidant as in the conventional method described above, it is possible to add a large amount of oxidant for the tungsten removal rate characteristic of 2000 kPa or more.

However, when the slurry is prepared by adding an excessive amount of an oxidizing agent according to the conventional method to increase the metal removal rate, the metal removal rate may be increased while the impurity concentration in the slurry is increased, resulting in deterioration of the electrical characteristics of the device after the CMP process. This may adversely affect device yields, such as increased metal corrosion. In addition, there is a problem in that the competitiveness of the product is lowered due to a decrease in the quality of the slurry, an increased risk, and an increase in the manufacturing price of the slurry.

An object of the present invention is to reduce the amount of oxidant added to the slurry while maintaining the same or higher metal removal rate in order to solve the problems of the prior art can reduce the production cost of the slurry, improve the quality and safety of the slurry To provide a slurry for CMP.

It is another object of the present invention to provide a CMP method which allows the control of the metal removal rate using the improved slurry.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a view for explaining two cases of an oxidation reaction occurring on a metal surface by an oxidizing agent of a slurry for metal CMP according to the prior art.

2A to 2D are process cross-sectional views sequentially illustrating a method of forming a metal wiring using a general CMP process.

3 is a view for explaining the mechanism of the chemical and mechanical polishing process of a metal using a slurry to which a plurality of oxidizing agents are added according to the present invention.

Figure 4 is a graph showing the relationship between the polishing rate of the metal layer according to the type of oxidizing agent.

<Explanation of symbols for main parts of drawing>

100 semiconductor wafer or substrate 102 interlayer insulating film

104: trench 106: barrier layer

108, 110: metal layer 112: polishing pad

114: rotation table 116: carrier

118: slurry 120: reduced iron ions

122: iron ion restored oxidizing power 124: hydrogen peroxide

126: water 128: oxide film

130: abrasive

The polishing slurry of the present invention for achieving the above object comprises a slurry for chemically and mechanically polishing a metal layer used in a semiconductor integrated circuit, a plurality of oxidizing agents (oxidizing agent); And an abrasive in an aqueous medium, wherein at least one of the plurality of oxidants is a first oxidant for oxidizing a reduced oxidant, and at least the other is oxidized by the metal layer and reduced by itself. It is characterized in that it comprises a second oxidizer which is oxidized and the oxidizing power is restored and recycled. That is, in the present invention, since the second oxidant having a rapid oxidation reaction oxidizes the metal surface and is reduced by itself, the first oxidant having a large reduction potential is oxidized again to reduce the oxidizing power of the second oxidant. Is restored. Therefore, such a recycling mechanism of the second oxidant makes it possible to maintain a high removal rate even with a small amount of oxidant.

The method of the present invention is a method of chemically and mechanically polishing a metal layer on a semiconductor wafer, the method comprising: a first oxidizing agent for oxidizing an abrasive, a reduced oxidizing agent in an aqueous medium, oxidizing a metal, thereby reducing itself and the first oxidizing agent Supplying a slurry having a second oxidant on which the oxidizing power is restored by the oxidizing agent on the semiconductor wafer, and rotating the polishing pad contacted on the semiconductor wafer using the slurry supplied on the semiconductor wafer. And removing a portion of the metal layer to polish the surface of the semiconductor wafer to be flat.

Here, the metal layer has a single layer or a multilayer structure made of tungsten, titanium, titanium nitride, copper, aluminum or alloys thereof. In particular, the slurry of the present invention is most suitable for tungsten.

The first oxidant is a peroxide compound having a high reduction potential in order to oxidize the reduced oxidant, and the second oxidant or metal oxidant is an iron compound having a rapid oxidation reaction rate with the metal. Peroxide compounds include hydrogen peroxide (H ₂ O ₂ ), benzoyl peroxide (C ₆ H ₅ CO) ₂ O ₂ , calcium peroxide (CaO ₂ ), barium peroxide BaO ₂ ), or sodium peroxide (Na ₂ O ₂ ). Among them, hydrogen peroxide is most preferred. It is most preferred that the hydrogen peroxide is present in the slurry composition in an amount in the range of about 0.01 wt% to 10 wt%, particularly in an amount in the range of about 0.5 wt% to 3 wt%. If it is less than 0.01%, the removal rate is too low, making it difficult to apply the process. If it is more than 10%, the removal rate is improved but the metal corrosion is intensified.

The iron compound is ferric nitrate, ferric phosphate, ferric sulfate or potassium ferricyanide, of which ferric nitrate is most preferred. Ferric nitrate is present in the slurry composition in an amount in the range of about 0.025 wt% to 5 wt%. It is particularly preferred to be present in an amount in the range of about 0.025 wt% to 1 wt%, most preferably in an amount in the range of about 0.05 wt% to 0.5 wt%. In the case of 0.025 wt% or less, the removal rate is too low, making it difficult to apply the process. In the case of 5 wt% or more, the self-dispersibility of the slurry decreases, and the slurry aggregates.

The slurry of the present invention preferably has a pH within the range of 2 to 3, preferably within the range of 2 to 2.5. That is, not exceeding 3 is effective in terms of dispersion stability of the slurry. Sulfuric acid (H ₂ SO ₄ ), nitric acid (HNO ₃ ), hydrochloric acid (HCl), or phosphoric acid (H ₃ PO ₄ ) is included to adjust the pH of the slurry.

The abrasive is preferably any one of alumina, silica or ceria. In particular, preferably, colloidal silica is present in the slurry composition in an amount in the range of about 3 wt% to 25 wt%. Most preferably, it is present in an amount of about 3-10 wt%.

The slurry of the present invention preferably further comprises an additive such as a surfactant.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2A to 2D show a process sequence for forming a metal wiring layer using a general CMP process.

In FIG. 2A, an interlayer insulating film 102, which is a low dielectric film, is deposited on a semiconductor wafer or substrate 100, and a trench 104 is formed in the deposited interlayer insulating film 102 by a photolithography process.

In FIG. 2B, a barrier layer 106 composed of a composite layer of titanium and titanium nitride is covered with a uniform thickness on the interlayer insulating film 102 on which the trench 104 is formed. Next, a thick layer of tungsten is deposited on the barrier layer 106 to sufficiently fill the trench 104 to form the metal layer 108.

In FIG. 2C, the semiconductor wafer 100 on which the metal layer 108 is formed is press-bonded to the polishing pad 112 formed on the turntable 114 by the carrier 116 of the CMP apparatus. At this time, since the slurry 118 is provided in the polishing pad 112, the slurry is supplied to the interface between the semiconductor wafer 100 and the polishing pad 112. The supplied slurry 118 is an improved slurry according to the present invention.

In FIG. 2D, the surface of the semiconductor wafer 100 is polished by the above-described CMP process so that the metal layer and the barrier layer existing on the interlayer insulating film 102 are all removed, and the barrier layer 106 filled in the trench 104 is removed. ) And only the metal layer 110 remains. The remaining barrier layer 106 and the metal layer 110 are provided as wiring layers.

Figure 3 shows the reaction mechanism of the chemical and mechanical polishing process of a metal using a slurry to which a plurality of oxidants are added according to the present invention. That is, Fe ^{+ 3} ions 122 provided from ferric nitrate, a second oxidant having a fast reaction rate, take electrons from tungsten (W) and are reduced to Fe ^{+ 2} ions 120. On the other hand, tungsten loses electrons and oxidizes to become an anion of W ⁻ .

The reduced Fe ^{+ 2} ions 120 are deprived of electrons by the hydrogen peroxide 124 having a high reduction potential and restored to Fe ^{+ 3} ions 122, and the hydrogen peroxide 124 becomes water 126. Accordingly, the second oxidant which directly oxidizes tungsten is oxidized and reused by recycling of reduced and oxidized by oxidizing the metal, so that a high removal rate can be obtained in a small amount. On the other hand, the oxidized metal anions combine with oxygen contained in the slurry to form the oxide film 120. The oxide film 120 is easily removed by friction with the solid silica 418, which is an abrasive, or the polishing pad.

That is, in the present invention, when the second oxidant oxidizing the metal is reduced by the oxidation reaction, the first oxidant oxidizes the reduced second oxidant again to restore the oxidizing power, thereby allowing the restored second oxidant to participate in the oxidation reaction again. Since the process is cyclically generated during the CMP process, it is possible to improve the metal removal rate with a smaller amount of oxidant.

As such, an embodiment of the improved slurry of the present invention comprising two kinds of oxidants is as follows.

Example 1

In this embodiment, in order to evaluate the change in the characteristics of the slurry according to the amount of the first oxidant added, the amount of the second oxidant is fixed at 0.5wt%, and the amount of the first oxidant is changed from 0.01wt% to 3wt% Sample slurry was prepared. The prepared slurry consists of colloidal silica, acid, and deionized water in addition to the oxidizing agent, and the sample deposits about 1,000 Å of a low dielectric film such as a thermal oxide film (HTO) on a polysilicon substrate, and then the TiN barrier layer and the W metal layer. Were deposited to a thickness of about 1,000 kPa and 10,000 kPa, respectively.

Polishing was carried out in a 6-inch PRESI facility, and pads and carrier films were used Rodel IC1000 stack pad and R200 carrier film. In addition, the polishing conditions were load pressure = 9 psi, table speed = 30 rpm, spindle speed = 30 rpm, and flow rate of slurry = 250 ml / min. These CMP conditions and evaluation results for each slurry are shown in Table 1 below.

sample Hydrogen peroxide (wt%) Ferric Nitrate (wt%) Metal layer removal rate (Å / min) Interlayer dielectric removal rate (Å / min) Selectivity One 0.5 0.05 2,293 25 91: 1 2 One 0.05 3,004 26 115: 1 3 2 0.05 3,568 30 119: 1 4 3 0.05 4,133 25 165: 1

As can be seen from the results of Table 1, as the amount of hydrogen peroxide, which is the first oxidant, increased, the removal rate of the interlayer insulating film was almost unchanged, while the removal rate of tungsten gradually increased. . However, as the amount of the first oxidant added increases, the removal rate of tungsten is gradually saturated.

Example 2

In Example 2 of the present invention, in order to evaluate the change in the properties of the slurry according to the addition amount of the ferric nitrate as the second oxidant of the present invention, the amount of hydrogen peroxide as the first oxidant is fixed at 1wt%, and the amount of the second oxidant added Four sample slurries were prepared, varying in the range of 0.01 to 1 wt%.

Each condition was given similarly to Example 1 mentioned above. In addition, the polishing conditions were also given in the same manner as in Example 1. These CMP conditions and evaluation results for each slurry are shown in Table 1 below.

sample Hydrogen peroxide (wt%) Ferric Nitrate (wt%) Metal layer removal rateÅ / min Interlayer dielectric removal rate 제거 / min Selectivity One One 0.01 1,046 21 50: 1 2 One 0.1 2,821 22 130: 1 3 One 0.5 2,997 22 136: 1 4 One One 3,110 20 156: 1

As can be seen from the results in Table 2, the removal rate of the oxide film was hardly changed as the amount of the ferric nitrate as the second oxidant was increased, while the removal rate of tungsten was greatly increased.

4 is a graph showing a relationship between polishing rates of metal layers according to types of oxidizing agents. In FIG. 4, A represents a case where a slurry in which about 1 wt% of hydrogen peroxide (H ₂ O ₂ ) is added alone is used as an oxidizing agent, and B represents a slurry in which about 0.5 wt% of ferric nitrate is added alone as an oxidizing agent. The case used is shown. C shows a case where a slurry in which 1 wt% hydrogen peroxide (H ₂ O ₂ ) and 0.05 wt% ferric nitrate was added simultaneously was used. Thus, as shown in the graph, in the case of A and B, both showed a low tungsten removal rate of less than about 500 kW / min, while in the case of C using the slurry according to the present invention, the tungsten removal rate was about 2200 kW / min. It can be seen that the removal rate is about 6 to 7 times higher than that of using a single oxidant at about min.

It is expected that a large amount of oxidant should be added in order to have a removal rate characteristic of 2000 kPa or more using only a single oxidant. In fact, when only ferric nitrate was used, an addition amount of about 7 to 8 wt% was required to have a tungsten removal rate of about 2000 kPa. When only hydrogen peroxide was used, it was about 400 kcal / min even when 10 wt% or more was added. Low removal rate results were obtained.

Therefore, in the case of using the slurry according to the present invention, the second oxidant is recycled by the first oxidant due to different oxidation reaction rates and reduction potentials between the two kinds of oxidizers, so that even with a small amount of addition. It has the advantage that the same effect as when adding a large amount can be obtained.

This invention can be implemented in other various forms, without deviating from the mind or main characteristic. Therefore, the above-described embodiments are merely examples in all respects and should not be interpreted limitedly. In addition, all the deformation | transformation and a change which belong to the equal range of a claim are within the scope of this invention.

As described above, according to the present invention, the slurry containing two kinds of oxidizing agents exhibits the following effects.

First, while using two oxidizers can greatly reduce the total amount of oxidant added, the cost of the slurry can be greatly reduced.

Secondly, a small amount of oxidant is added to ensure the quality and safety of the slurry.

Third, the removal rate of the metal can be greatly improved, and the removal rate of the metal can be easily controlled.

Claims (32)

A slurry for chemically and mechanically polishing a metal layer used in a semiconductor integrated circuit, A plurality of oxidizing agents; And Abrasive is provided in the aqueous medium, At least one of the plurality of oxidants is a first oxidant for reducing another oxidant, and at least another is a second oxidant which is reduced by oxidizing the metal layer itself, oxidized by the first oxidant, and restored to oxidative power again. Slurry comprising a. The method of claim 1, The metal layer is a slurry, characterized in that any one of tungsten, titanium, titanium nitride, copper, aluminum or a combination thereof. The method of claim 2, Wherein the first oxidant is a peroxide compound and the second oxidant is an iron compound. The method of claim 3, The peroxide compound may be hydrogen peroxide (H ₂ O ₂ ), benzoyl peroxide (C ₆ H ₅ CO) ₂ O ₂ ), calcium peroxide (Calcium peroxide; CaO ₂ ), barium peroxide (Barium) peroxide; BaO ₂ ), and sodium peroxide (Sodium peroxide; Na ₂ O ₂ ) Slurry characterized in that one of. The method of claim 4, wherein And the hydrogen peroxide is present in the slurry composition in an amount in the range of about 0.01 wt% to 10 wt%. The method of claim 4, wherein And the hydrogen peroxide is present in the slurry composition in an amount in the range of about 0.5 wt% to 3 wt%. The method of claim 3, The iron compound is a slurry, characterized in that one of the iron compounds, such as ferric nitrate, ferric phosphate, ferric sulfate, potassium ferricyanide, etc., The method of claim 7, wherein And wherein the ferric nitrate is present in the slurry composition in an amount in the range of about 0.025 wt% to 5 wt%. The method of claim 7, wherein And wherein the ferric nitrate is present in the slurry composition in an amount in the range of about 0.025 wt% to 1 wt%. The method of claim 7, wherein And wherein the ferric nitrate is present in the slurry composition in an amount in the range of about 0.05 wt% to 0.5 wt%. The method of claim 1, Slurry characterized in that the pH of the slurry is in the range of 2-3. The method of claim 11, In order to adjust the pH of the slurry, sulfuric acid (H ₂ SO ₄ ), nitric acid (HNO ₃ ), hydrochloric acid (HCl), and phosphoric acid (H ₃ PO ₄ ) characterized in that it further comprises any one acid (acid). Slurry. The method of claim 1, wherein the abrasive A slurry characterized by using any one of alumina, silica and ceria. The method of claim 13, And wherein the abrasive is present in the slurry composition in an amount in the range of about 3 wt% to 25 wt%. The method of claim 13, And the abrasive is present in the slurry composition in an amount of about 5-10 wt%. The method of claim 1, The slurry is characterized in that it further comprises a surfactant. A method of chemically and mechanically polishing a metal layer on a semiconductor wafer, a) a slurry having an aqueous medium having an abrasive, a first oxidant for oxidizing a reduced oxidant, a second oxidant which is reduced by oxidizing the metal layer and oxidized by the first oxidant to restore oxidizing power ) Is supplied onto the semiconductor wafer; And and b) removing a portion of the metal layer and polishing the surface of the semiconductor wafer to be flat while rotating the polishing pad in contact with the semiconductor wafer using the slurry supplied on the semiconductor wafer. Chemical and mechanical polishing methods. The method of claim 17, The metal layer is tungsten, titanium, titanium nitride, copper, aluminum, or any combination thereof. The method of claim 18, Wherein the first oxidant is a peroxide compound and the second oxidant is an iron compound. The method of claim 19, The peroxide compound may be hydrogen peroxide (H ₂ O ₂ ), benzoyl peroxide (C ₆ H ₅ CO) ₂ O ₂ ), calcium peroxide (Calcium peroxide; CaO ₂ ), barium peroxide (Barium) peroxide; BaO ₂ ), and sodium peroxide (Sodium peroxide; Na ₂ O ₂ ), characterized in that the chemical and mechanical polishing method. The method of claim 20, Wherein the hydrogen peroxide is present in the slurry composition in an amount in the range of about 0.01 wt% to 10 wt%. The method of claim 20, Wherein the hydrogen peroxide is present in the slurry composition in an amount in the range of about 0.5 wt% to 3 wt%. The method of claim 19, The iron compound is a chemical and mechanical polishing method, characterized in that one of the iron compounds, such as ferric nitrate, ferric phosphate, ferric sulfate, or potassium ferricyanide. The method of claim 23, wherein Wherein the ferric nitrate is present in the slurry composition in an amount in the range of about 0.025 wt% to 5 wt%. The method of claim 23, wherein Wherein the ferric nitrate is present in the slurry composition in an amount in the range of about 0.025 wt% to 1 wt%. The method of claim 23, wherein Wherein the ferric nitrate is present in the slurry composition in an amount in the range of about 0.05 wt% to 0.5 wt%. The method of claim 17, Chemical and mechanical polishing method characterized in that the pH of the slurry is within the range of 2 to 3. The method of claim 27, In order to adjust the pH of the slurry, sulfuric acid (H ₂ SO ₄ ), nitric acid (HNO ₃ ), hydrochloric acid (HCl), and phosphoric acid (H ₃ PO ₄ ) characterized in that it further comprises any one acid (acid). Chemical and mechanical polishing methods. 18. The method of claim 17, wherein the abrasive A chemical and mechanical polishing method using any one of alumina, silica and ceria. The method of claim 29, Wherein the abrasive is present in the slurry composition in an amount in the range of about 3 wt% to 25 wt%. The method of claim 29, Wherein the abrasive is present in the slurry composition in an amount of about 5 wt%. The method of claim 17, The slurry is chemical and mechanical polishing method characterized in that it further comprises a surfactant.