JP2001176826A - Chelating agent for slurry selectivity control and associated method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a slurry for chemical mechanical polishings(CMP), where its polishing selectivity and removing speed with respect to a barrier metal layer are improved in comparison with a bulk metal layer. SOLUTION: Diethylene triamine penta acetate(DTPA) as a chelating agent is contained in a chemical and mechanical polishing(CMP) slurry for polishing the surface of a metal semiconductor wafer. A CMP process is used to polish the surface of the semiconductor wafer during the step for forming an interconnecting line or a via. The interconnecting line includes a bulk metal layer and a barrier metal layer which are formed over a trench of an insulating layer in the semiconductor wafer. The DTPA increases the polishing selectivity of the slurry, with respect to the barrier metal layer. Concurrently with the increased removing speed of the barrier metal layer, dishing of the bulk metal layer is prevented in the trench during the process of the CMP.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a semiconductor process,
In particular, it relates to a slurry used for polishing a semiconductor wafer surface.

[0002]

BACKGROUND OF THE INVENTION Typically, semiconductor wafers include a semiconductor substrate, such as silicon, on which transistors are formed. The transistors are interconnected via metal interconnect lines, vias or contacts to form a functional circuit. For example, interconnect lines are formed by depositing a metal layer in vias and trenches etched in an insulating layer on a semiconductor substrate. Chemical mechanical polishing (CMP) is used to polish the surface of a metal layer during a semiconductor processing step.

[0003] In general, CMP is a process in which the overlying first layer is simultaneously polished chemically and mechanically until the surface of the second layer on which the first layer is formed is exposed. Contains. The CMP process uses a polishing pad and a slurry to remove the first layer until the top surface of the first layer is flush with the top surface of the second layer.

[0004] Slurries generally include a solution containing abrasive particles. The semiconductor wafer is immersed in the slurry while the elastic pad is pressed against the first layer and rotated such that the slurry particles are pressed against the first layer under load. Or washed. Lateral movement of the pad causes slurry particles to move across the first layer, leading to attrition and removal of the surface of the first layer. Often, the surface removal rate is determined by the applied pressure,
It is determined by the rotation speed of the pad and the degree of chemical activity of the slurry.

[0005] The interconnect lines include at least one barrier metal layer and a bulk metal layer in a semiconductor wafer. The barrier metal layer is about 50-500 °, typically 100
The thickness is in the range of from about 250 ° to about 250 °, and prevents the bulk metal layer from protruding and coming into contact with the semiconductor substrate. The bulk metal layer is on the barrier metal layer and forms the conductor of the interconnect line. The thickness of the bulk metal layer is about 1000-8000Å
And typically between 3000 and 6000 °.

[0006]

Prior to the CMP process, a bulk metal layer 20 covers the surface of the barrier metal layer 22 in a semiconductor wafer 44, as shown in FIG. During the CMP process, both the barrier metal layer 22 and the bulk metal layer 20 are in contact with the slurry. The polishing rate of the slurry on the bulk metal layer 20 is
One problem arises because the polishing speed is very high as compared with the polishing speed. Therefore, the barrier metal layer 22 and the bulk metal layer 20
Is in contact with the slurry, the bulk metal layer 20 is polished faster than the barrier metal layer 22. This causes a dishing in the groove 24 due to the low selectivity of the slurry with respect to the barrier metal layer, as in FIG. Indentations are not desired because they cause non-planarities that affect the reliability of the interconnect lines formed during the CMP process.

After the barrier metal layer has been polished or planarized to the surface of the oxide layer 26, the CMP process typically continues for a few more seconds until any remaining barrier metal layer is completely oxidized. It is reliably removed from the surface of the material layer 26.
During this over-polishing in the CMP process, the oxide layer 2
6 erosion occurs. This problem is particularly acute where the pattern density of the interconnect lines or vias is larger in certain areas, as shown in FIG. Indentations in the bulk metal layer 20 in these dense regions cause erosion of the oxide layer 28 therebetween as compared to less dense regions of the oxide layer, such as regions 30 where flats remain.

[0008] One attempt at solving the above problem is to utilize two different slurries. Bulk metal layer 2
0 for the first slurry and the second slurry for the barrier metal layer 22, the second slurry having an increased polishing rate for the barrier metal layer. However, using a single slurry for the CMP process is more desirable than using multiple slurries.

[0009] Another known attempt to increase the polishing rate of the barrier metal layer 22 is to add a chelating agent to the slurry. Chelating agents are used with the abrasive particles in the slurry to achieve high polishing rates. Examples of chelating agents added to slurries to facilitate polishing are disclosed in several US patents. For example, U.S. Pat. No. 5,700,383 to Feller et al. Discloses a slurry containing citric acid, oxalic acid or ascorbic acid as a chelating agent. U.S. Pat. No. 5,916,819 to Scroban et al. Discloses a slurry containing ethylene diphosphonic acid as a chelating agent.

[0010] In order to improve the selectivity and removal rate of the barrier metal layer compared to the bulk metal layer, known slurries disclose the use of a chelating agent.
There is a continuing need to improve this selectivity during the process.

[0011]

SUMMARY OF THE INVENTION In view of the above background,
SUMMARY OF THE INVENTION It is an object of the present invention to provide a slurry for chemical mechanical polishing a semiconductor wafer containing a barrier metal layer and a bulk metal layer, in order to avoid denting when forming interconnect lines, vias or contacts of the bulk metal layer, especially semiconductor wafers. To provide.

[0012] This and other objects, advantages and features according to the present invention are provided by a slurry for polishing a semiconductor wafer that includes at least one metal layer. Preferably, the slurry comprises a water-soluble vehicle and abrasive particles therein, and diethylenetriaminepentaacetate (DTPA) as a chelating agent in the water-soluble vehicle for metals scraped from semiconductor wafers. DTPA preferably ranges from about 0.5 to 2% by weight in the slurry.
Preferably, the abrasive particles include at least one of alumina, cerium oxide, silica, and mixtures thereof. Preferably, the pH of the slurry is less than about 7.

Another feature of the present invention is a method for chemical mechanical polishing (CMP) of a semiconductor substrate comprising an insulating layer and at least one metal layer on the insulating layer. Distributing the CMP slurry to the interface between the semiconductor wafer and the abrasive particles while providing relative movement therebetween. The slurry is composed of diethylenetriaminepentaacetate (DTP) as a chelating agent for a water-soluble medium, abrasive particles, an oxidizing agent, and a metal scraped from a semiconductor wafer.
It is preferable to include A).

[0014] Preferably, the at least one metal layer includes a barrier metal layer and a bulk metal layer over the barrier metal layer when the interconnect line is formed over the groove in the semiconductor wafer. DTPA increases the selectivity of the slurry with respect to the barrier metal layer. With the increased removal rate of the barrier metal layer, dents in the bulk metal layer are prevented in the trench during the CMP process. As a result, the selectivity of the semiconductor device is improved. Preferably, the bulk metal layer has at least one of aluminum, copper, tungsten and alloys thereof. Preferably, the barrier metal layer comprises at least one of titanium, titanium nitride, tantalum, tantalum nitride and alloys thereof.

[0015]

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be more fully described with reference to the accompanying drawings, which show preferred embodiments of the invention. However, the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth below. Rather, this disclosure is complete and is provided to tell those skilled in the art the scope of the invention. Like reference numerals indicate like components. The dimensions of the layers and regions are exaggerated in the figures for clarity.

A polishing slurry containing diethylenetriaminepentaacetate (DTPA) as a chelating agent increases the selectivity of the slurry during chemical mechanical polishing (CMP) of a metal on a semiconductor wafer containing at least one metal layer. At least one metal layer of the illustrated embodiment includes a barrier metal layer 20 and a bulk metal layer 22 in a semiconductor wafer 44 as shown in FIG. The increased selectivity of the slurry for the barrier metal layer 20 increases its removal rate when in contact with the slurry. This advantageously provides for the grooves 24 as described above with reference to FIG.
Of the bulk metal layer 20 in the inside. Further, erosion of the oxide layer 28 in dense areas of the semiconductor wafer 44 is minimized due to the increased selectivity of the slurry to the barrier metal layer 22, as shown in FIG.

Referring again to FIG. 1, the bulk metal layer 20 is
It is preferred that copper or aluminum be included when the interconnect lines are formed. If the bulk metal layer 20 is copper, the barrier metal layer 22 is preferably a titanium layer or titanium nitride over the titanium layer. If the bulk metal layer 20 is aluminum, the barrier metal layer 22 is preferably a layer of tantalum or tantalum nitride on tantalum. Alternatively, for aluminum as the bulk metal layer 20, the barrier metal layer 22 can also be a titanium layer or a layer of titanium nitride over the titanium layer. These barrier metals are also referred to as heavy metals, as will be readily appreciated by those skilled in the art. Other metals and their alloys are also contemplated by the present invention.

The titanium and tantalum nitride layers adhere to the bulk metal layer 20, while the bulk metal layer prevents the titanium and tantalum layers from contacting or spiking the semiconductor substrate 32. If the bulk metal layer is copper, a seed layer may be used to provide adhesion instead of a layer of titanium nitride. In addition to forming interconnect lines, the slurry may also be used to polish vias and contacts in semiconductor wafers, as will be readily appreciated by those skilled in the art.

An illustrative embodiment of a CMP apparatus assembly for polishing a surface of a semiconductor wafer 44 is described with reference to FIG. 4 in accordance with the present invention. As those skilled in the art will readily appreciate, various other embodiments of the CMP apparatus assembly 40 are also applicable. For example, some CMP apparatus assemblies do not utilize rotating plates and rotating wafer holders.

The CMP assembly 40 includes a rotary way holding a semiconductor wafer 44 and a holder. A slurry or liquid composition 46 according to the present invention is introduced onto a polishing pad 48. The polishing pad 48 is disposed on a rotary table platen 50. Polishing pad 48 is applied to the surface of semiconductor wafer 44 in the presence of slurry 46 at some pressure to perform planarization. Pressure is applied as indicated by the arrow labeled P.
This pressure P indicates the backside pressure and downforce pressure applied by the CMP apparatus assembly 40. As will be readily appreciated by those skilled in the art, the rotating element 42
And 50 are moved and rotated by the motor.

Semiconductor wafer holder 42 rotates semiconductor wafer 44 at a selected speed about axis 48 and moves the wafer under controlled pressure P across pad 48. The semiconductor wafer 44 contacts the pad 48 when moved. As the wafer is moved in a predetermined pattern, the area of pad 48 that contacts the surface of semiconductor wafer 44 changes.

Chemical supply system 52 introduces slurry 46 onto pad 48 at a specific flow rate. Slurry 46 can be applied to pad 48 without detracting from the advantages of the present invention.
Is introduced at various locations. For example, slurry 4
6 may be introduced over pad 48 by something like dripping or spraying. Alternatively, the slurry 46 may be introduced by spraying from the side of the turntable.

The slurry 46 contains a water-soluble carrier, an abrasive in the water-soluble carrier, an oxidizing agent in the water-soluble carrier, and diethylenetriaminepentane as a chelating agent in the water-soluble carrier for the metal polished from the semiconductor wafer 44. Contains acetate (DTPA). The abrasive preferably comprises a metal oxide abrasive such as alumina, ceria, silica and mixtures thereof. The oxidizing agent includes hydrogen peroxide, and the water-soluble medium includes deionized water or distilled water.

The rotary table 50 is rotated at a selected speed and rotated in the same direction as the wafer holder 42. The surface of the semiconductor wafer 44 is held in parallel with respect to the pad 48, and the pad can polish the surface of the wafer. The slurry 46 and pad pressure will initially determine the polishing rate or surface material removal rate.

To alleviate dish depressions during the aforementioned polishing step, the slurry 46 contains diethylenetriaminepentaacetate (DTPA) as a chelating agent. DT
The PA facilitates the reaction rate or desorption of metal ions from the surface of the semiconductor wafer 44, particularly with respect to the barrier metal layer 22. DTPA is a water-soluble, _three- donor (N ₃ ) molecule that can locate one or more positions in the coordination sphere of metal ions that form a ring structure called a chelate complex or chelate. It is a molecular polydentate ligand.

[0026] Conventional chelators typically have two donor atoms in the molecule. DTPA is advantageous because it provides higher slurry selectivity to the barrier metal layer 22 because of its third donor atom. Barrier metal layer 2
The removal rate of 2 is increased, minimizing depressions on the dish as were present in the low selectivity slurry. Further DTP
A can apply different metals such as tungsten, copper, aluminum, tantalum, tantalum nitride, titanium and titanium nitride. DTPA forms weak bonds with the barrier metal layer 22, such as titanium or tantalum and their compounds, while rapidly hydrolyzing them. That is, the binding of surface metal ions is broken down in the water-soluble portion of the slurry, and these split ions combine with the atoms of diethylenetriamine.

Diethylenetriamine, represented by C ₄ H ₁₃ N ₃ , is the central group or ligand of the chelating agent.
Triamine N ₃ conveniently provides three N atoms among the ligands, so that the metal being polished can attach to three nitrogen atoms and form a complex reaction. As a result, a strong bond is formed between the polished metal and the chelating agent of the slurry 46 and a barrier metal layer 22 is formed.
The removal rate increases. Furthermore, the removal rate of the bulk metal layer also increases.

DTPA preferably forms chelates or chelate complexes with large conditional formation or stability constants K _f for various metals of great interest during polishing. DTPA has a different K _f for each metal. The formation constant is the equilibrium constant for the formation of a chelate complex from a solvated metal ion and ligand in its fully dissociated form. Many parameters affect stability, including size, number of chelating rings formed between the ligand and the metal ion, substituents on the chelating ring, and the nature of the metal ion and the donor atom of the chelating agent. DTP
A advantageously has a very high formation constant for the barrier metal ions. Generating constants with respect to different metal ions, since different for DTPA as chelating agent, the preferred range for K _f is the most serious concern, i.e. given in terms barrier and the bulk metal of the metal ions. Thus, chelators have a K _f greater than 5 for these metals.

An advantage of using DTPA as a chelating agent is that it is not affected by the material or type of polishing pad utilized. Because the choice of pad is application dependent, for example, the slurry 46 may use any known and suitable polishing pad 48 known to those skilled in the art. Polishing pad 48 includes one or more pads and may be of a particular shape, i.e., circular, spherical and rectangular, or of a non-uniform shape. The choice of pad may also have a particular hardness depending on the particular application. Further, as mentioned above, the pad may have elements that are polished on its surface for planarization.

Slurry 46 generally includes polishing elements and elements that chemically interact with the surface being planarized. For example, a typical oxide polishing slurry 46 has a pH
Is less than or equal to 7 in an acidic solution with an average size of 12
Contains a colloidal suspension of 0 nm oxide particles. However, DTPA may be used with alkaline solutions having a pH greater than 7. Ceria (CeO ₂ ) suspensions may also be used at the right time, in certain places where large amounts of metals need to be removed. Ceria acts in slurry 46 as a chemical and mechanical reagent. Other polishing elements of slurry 46 may be included, but are limited to alumina (Al ₃ O ₂ ) and silica or any other abrasive used in conventional polishing slurries as known to those skilled in the art. It is not something that can be done.

The general characteristics of suitable slurry elements utilized in conjunction with the chelating agent are that the hardness of the abrasive particles or elements is approximately equal to the hardness of the metal being polished to avoid metal damage. It should have. Further, the particles should be a solution that is uniform and free of metallic contaminants. For example, and further, when used in a metal polishing process, the slurry has a pH of less than about 7.

The present invention also provides a pad 4 including a polishing element.
8 in conjunction with a CMP apparatus 40 using liquid, wherein the liquid composition includes a chelating agent and a liquid component that chemically interacts with the surface of the semiconductor wafer 44. Therefore, the slurry 46 does not require the polishing element provided by the pad 48. Liquid components that interact chemically, however, are still needed. Liquid chemical interaction elements may include, for example, aluminum hydroxide or any acidic solution whose pH is less than or equal to 7. The amount of DTPA used in slurry 46 is an effective amount to increase the selectivity of the slurry with respect to barrier metal layer 22. Preferably, based on the total weight of the liquid composition, DTPA as a chelating agent is about 0.
It is present in an amount of 5 to 2% by weight.

Another feature of the present invention is that the semiconductor wafer 4 includes an insulating layer 26 and at least one metal layer on the insulating layer.
4 is a method for chemical mechanical polishing (CMP). The method provides for the interface between the semiconductor wafer 44 and the abrasive particles to provide relative movement therebetween, while maintaining the CMP
A step of dispensing the slurry 46 is included. Slurry 4
Numeral 6 includes a water-soluble medium, an abrasive, an oxidizing agent, and diethylenetriaminepentaacetate (DTPA) as a chelating agent for metal polished from the semiconductor wafer 44.

At least one metal layer is a barrier metal layer 22
And the bulk metal layer 20 on the barrier metal layer when the interconnect lines are formed over the grooves in the semiconductor wafer 44. D
TPA increases the selectivity of slurry 46 with respect to barrier metal layer 22. Due to the increased barrier metal layer 22 removal rate, dish-shaped depressions in the bulk metal layer 20 are prevented in the trench during the CMP process. As a result, the reliability of the semiconductor wafer 44 is improved. The bulk metal layer 20 includes at least one of aluminum, copper, tungsten, and an alloy thereof. The barrier metal layer 22 includes at least one of titanium, titanium nitride, tantalum, tantalum nitride, and an alloy thereof.

Many modifications and other embodiments of the present invention, with the advantages of the teachings shown in the figures in connection with the preceding description, will be apparent to those skilled in the art. Therefore, it will be understood that the invention is not limited to the particular embodiments disclosed, and that modifications and embodiments are included within the scope of the appended claims.

[0036]

According to the present invention, it is possible to provide a slurry for CMP in which the selectivity and the removal rate of the barrier metal layer are improved as compared with the bulk metal layer.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a semiconductor wafer having a trench covered by a barrier metal layer and a bulk metal layer prior to a CMP process according to the prior art.

FIG. 2 is a cross-sectional view of the semiconductor wafer shown in FIG. 1, showing a dish-shaped depression of a bulk metal layer in a groove after a CMP step.

3 is a cross-sectional view of a semiconductor wafer showing erosion of an oxide layer caused by the dish-shaped depression illustrated in FIG.

FIG. 4 is a cross-sectional view of a semiconductor wafer placed in a chemical mechanical polishing apparatus in contact with a slurry according to the present invention.

[Explanation of symbols]

 Reference Signs List 20 bulk metal layer 22 barrier metal layer 24 groove 26, 28 oxide layer 32 semiconductor substrate 42 rotating element 44 semiconductor wafer 46 slurry 48 pad 50 rotating table platen 52 chemical supply system

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C09K 13/00 C09K 13/00 (72) Inventor Cyresh Mansingh Merchant United States 32835 Florida, Orlando, Vineland Oaks Boulevard 8214 (72) Inventor Pradip Kumar Roy United States 32819 Hidden Ivey Court 7706 Florida, Orlando

Claims (29)

[Claims] 1. A chemical mechanical polishing (CMP) slurry for polishing a semiconductor wafer including at least one metal layer, comprising: a water-soluble medium; an abrasive in the water-soluble medium; A polishing slurry comprising: an oxidizing agent therein; and diethylenetriaminepentaacetate (DTPA) as a chelating agent in the water-soluble medium for a metal polished from the semiconductor wafer. 2. The CMP slurry of claim 1, wherein said slurry has a pH of less than about 7. 3. The CMP slurry according to claim 1, wherein said DTPA is present in said slurry in an amount of about 0.5 to 2%.
Slurry in the range of weight percent. 4. The slurry of claim 1, wherein said DTPA has a stability constant greater than about 5. 5. The CMP slurry of claim 1, wherein said water-soluble medium comprises deionized water. 6. The CMP slurry according to claim 1, wherein the water-soluble medium comprises distilled water. 7. The CMP slurry according to claim 1, wherein said abrasive comprises a metal oxide abrasive. 8. The slurry of claim 1, wherein the abrasive comprises at least one of alumina, ceria, silica and a mixture thereof. 9. The CMP slurry according to claim 1, wherein the oxidizing agent contains hydrogen peroxide. 10. A chemical mechanical polishing (CMP) slurry for polishing a semiconductor wafer including at least one metal layer, comprising: a water-soluble medium; an abrasive in the water-soluble medium; An oxidizing agent in the diethylene triamine pentaacetate (DTPA), which acts as a chelating agent in the aqueous medium for the metal polished from the semiconductor wafer and in the slurry ranges from about 0.5 to 2% by weight. And a polishing slurry containing. 11. The CMP slurry of claim 10, wherein the slurry has a pH of less than about 7. 12. The CMP slurry according to claim 10, wherein the slurry has a stability constant of greater than about 5. 13. The CMP slurry of claim 10, wherein said water soluble medium comprises deionized water. 14. The CMP slurry of claim 10, wherein said water-soluble medium comprises distilled water. 15. The slurry of claim 10, wherein the abrasive comprises a metal oxide abrasive. 16. The CMP slurry according to claim 10, wherein the abrasive comprises at least one of alumina, ceria, silica, and a mixture thereof. 17. The slurry of claim 10, wherein said oxidizing agent comprises hydrogen peroxide. 18. A semiconductor wafer comprising an insulating layer and at least one metal layer on said insulating layer is chemically mechanically polished (C).
MP) dispensing a CMP slurry at an interface between the semiconductor wafer and the abrasive article while providing a relative movement therebetween, wherein the CMP slurry is water-soluble. A method comprising: a diluent, an abrasive, an oxidizer, and diethylene triamine pentaacetate (DTPA), which acts as a chelator for metals polished from the semiconductor wafer. 19. The method of claim 18, wherein said slurry has a pH of less than about 7. 20. The method of claim 18, wherein said DTPA is present in said slurry at about 0.5 to 2% by weight.
The methods that are in the range. 21. The method of claim 18, wherein said DTPA has a stability constant greater than about 5. 22. The method of claim 18, wherein said water-soluble media comprises deionized water. 23. The method of claim 18, wherein said water-soluble vehicle comprises distilled water. 24. The method of claim 18, wherein said abrasive comprises a metal oxide abrasive. 25. The method according to claim 18, wherein the abrasive comprises at least one of alumina, ceria, silica and mixtures thereof. 26. The method of claim 18, wherein said oxidizing agent comprises hydrogen peroxide. 27. The method of claim 18, wherein said at least one metal layer comprises at least one of aluminum, copper, tungsten, titanium, titanium nitride, tantalum, tantalum nitride and alloys thereof. 28. The method of claim 18, wherein the at least one metal layer comprises a barrier metal layer and a bulk metal layer in the barrier metal synergy. 29. The method of claim 28, wherein said barrier metal layer comprises at least one of titanium, titanium nitride, tantalum, tantalum nitride and alloys thereof.
The method wherein the bulk metal layer comprises at least one of aluminum, copper, tungsten and alloys thereof.