US 20050153556 A1
A method for substantially simultaneously polishing a copper conductive structure of a semiconductor device structure and an adjacent barrier layer includes use of a slurry that is formulated so as to oxidize copper at substantially the same rate as or at a faster rate than a material of the barrier layer is oxidized. Thus, copper and the barrier layer material have substantially the same oxidation energies in the slurry or the oxidation energy of the barrier layer material in the slurry may be greater than that of copper. The slurry may be configured for use with a fixed-abrasive type polishing pad and, therefore, may be substantially abrasive-free.
1. A method for chemical-mechanical polishing a copper structure and an adjacent barrier layer of a semiconductor device structure, comprising:
providing a semiconductor device structure including at least one recess formed in a surface thereof, a barrier layer lining at least the at least one recess, and a conductive layer comprising copper at least partially filling the at least one recess; and
substantially concurrently polishing the conductive layer and the barrier layer without removing the barrier layer at a substantially greater rate than the copper is removed.
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9. A method for chemical-mechanical polishing a copper conductive structure and an adjacent barrier layer of a semiconductor device structure, comprising:
providing a semiconductor device structure including at least one recess formed in a surface thereof, a barrier layer lining at least the at least one recess, and a conductive layer comprising copper within the at least one recess; and
substantially concurrently polishing the barrier layer and the conductive layer without oxidizing a material of the barrier layer at a substantially greater rate than the copper is oxidized.
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20. A method for polishing a surface of a semiconductor device structure, the surface including a conductive structure including copper and a barrier layer adjacent the conductive structure, the method comprising substantially concurrently oxidizing a material of the barrier layer at substantially the same rate as or at a slower rate than a rate at which the conductive structure is oxidized.
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This application is a continuation of application Ser. No. 10/132,827, filed Apr. 25, 2002, now U.S. Pat. No. 6,830,500, issued Dec. 14, 2004, which is a divisional of application Ser. No. 09/651,808, filed Aug. 30, 2000, now U.S. Pat. No. 6,602,117, issued on Aug. 5, 2003.
1. Field of the Invention
The present invention relates generally to slurries that are useful in chemical-mechanical polishing or chemical-mechanical planarization processes and, more specifically, to slurries that are used to polish or planarize electrically conductive structures of semiconductor devices that include copper and an adjacent tungsten barrier. The present invention also relates to methods for substantially concurrently polishing or planarizing structures formed from copper and tungsten.
2. Background of Related Art
Chemical-mechanical polishing and chemical-mechanical planarization, both of which are referred to in the art as “CMP,” are abrasive techniques that typically include the use of a combination of chemical and mechanical agents to planarize, or otherwise remove material from a surface of a semiconductor material substrate during the fabrication of devices thereon. A chemical component, typically a slurry that includes one or more oxidizers, abrasives, complexing agents, and inhibitors, oxidizes the surface of one or more material layers that are being polished or planarized (i.e., at least partially removed). A polishing pad formed from a material such as polyurethane or acrylic is used with the slurry and, in combination with abrasives present in the slurry, effects mechanical removal of the layer or layers from the surface of the semiconductor device structure. It should be noted that abrasive-only polishing and planarization, e.g., without the use of active chemical agents to effect material removal, are becoming more prevalent due to environmental concerns. Thus, the term “CMP” as used herein encompasses such abrasive-only (i.e., strictly mechanical) methods and apparatus.
Conventional CMP pads are round, planar, and have larger dimensions than the semiconductor substrates (e.g., wafers or other substrates including silicon, gallium arsenide, indium phosphide, etc.) upon which the structures or layers to be planarized or otherwise polished have been formed. In polishing one or more layers or structures formed on a substrate, the substrate and the conventional CMP pad are rotated relative to one another, with the location of the substrate being moved continuously relative to the polishing surface of the pad so that different areas of the pad are used to polish one or more of the layers or structures formed on the substrate.
Another polishing format is the so-called “web” format, wherein the pad has an elongated, planar configuration. The web is moved laterally from a supply reel to a take-up reel so as to provide “fresh” areas thereof for polishing one or more layers or structures formed on a semiconductor substrate. A similar, newer polishing format is the so-called “belt” format, wherein the pad is configured as a belt, or continuous loop, of polishing material. In both the “web” and “belt” formats, the semiconductor substrate is rotated or revolved upon being brought into contact with the pad. The pad is moved when a “fresh” polishing surface is needed or desired.
A new type of polishing pad, known in the art as a fixed-abrasive pad, may be used to polish or planarize layers formed on a semiconductor substrate. Fixed-abrasive pads, which may be embodied in the conventional, web, or belt formats, are typically formed from an acrylic material and embedded with particles of abrasive materials. The pad and embedded abrasives effect the mechanical part of CMP processes. During use of the fixed-abrasive pad to planarize or polish one or more layers on the surface of a semiconductor device during fabrication thereof, the abrasive material is exposed at a polishing surface of the pad. Some of the abrasive material may also be leached out of the pad. As a result of the inclusion of abrasive particles in the pad, the chemical slurries that are used to effect the chemical portion of chemical-mechanical polishing or chemical-mechanical planarization need not include the abrasives that are often required when conventional, abrasive-free pads are employed.
Copper Conductive Structures
The use of copper as a conductive material in semiconductor devices is also ever-increasing. When copper is used in semiconductor devices, however, a barrier layer is typically required between the copper and adjacent structures or layers. The barrier layer prevents diffusion of the copper into the adjacent layers or structures, as well as the formation of copper suicides, both of which may cause electrical shorts in semiconductor devices that include copper. Tantalum is an example of a material that is useful as a copper barrier. When tantalum is used, the semiconductor device, including any features thereof into which copper is to be disposed (e.g., trenches), is lined with a layer of tantalum. The tantalum layer is then typically covered with a thin copper layer, often formed by physical vapor-deposition (“PVD”) processes. The thin copper layer then acts as a so-called “seed layer” for the formation of a copper structure, such as a conductive line, such as by electroplating processes.
Once the tantalum and copper layers have been formed, it is necessary to isolate separate tantalum-copper conductive structures from one another. CMP processes are typically used to remove the tantalum and copper between the structures from over the active surface of the semiconductor device being fabricated. Slurries that are used in copper CMP processes typically have a pH of about 7.0. Many of these slurries include hydrogen peroxide (H2O2) as an oxidizing agent. Since hydrogen peroxide readily generates hydroxy free radicals (OH.), hydrogen peroxide is a very strong oxidizing agent. Tantalum, however, is substantially chemically inert. Thus, the oxidizers of CMP slurries that remove copper do not effectively oxidize tantalum and, thus, do not adequately effect the removal of tantalum. Likewise, slurries that are useful for removing tantalum by CMP processes are likewise not effective for removing copper. As a result, when conventional CMP processes are used to isolate the tantalum-copper conductive structures of a semiconductor device, two separate slurries must be used.
It has been proposed that tungsten be used in place of tantalum in semiconductor devices as a barrier material for copper conductive structures. Nonetheless, when known copper CMP slurries are used to substantially simultaneously CMP tungsten and copper, the tungsten barrier layer may dissolve, or be removed, at a faster rate than the copper. This is at least partially because, as the following chemical equations illustrate, tungsten (W) is more readily oxidized than copper (Cu):
This phenomenon is illustrated in the electron micrograph of
The inventors are not aware of a slurry that is useful in CMP processes and that effectively polishes or planarizes both copper and tungsten without causing oxidation or dissolution of the tungsten.
The present invention includes a method for substantially simultaneously chemical-mechanical polishing a copper conductive structure and an adjacent barrier layer with a fixed-abrasive type polishing pad, as well as slurries that are useful with fixed-abrasive type polishing pads for substantially simultaneously polishing a copper conductive structure and a barrier layer adjacent thereto.
The method of the present invention includes employing a fixed-abrasive type polishing pad along with a substantially abrasive-free liquid polishing formulation, which is referred to herein as a substantially abrasive-free slurry or, more simply, as a slurry. The slurry is formulated to oxidize copper and a material of the barrier layer, such as tungsten, at substantially the same rates. Thus, in a slurry incorporating teachings of the present invention, the oxidation energies of copper and the barrier material are substantially the same. Preferably, in the slurry, the oxidation energy, or oxidation potential, of a barrier material, such as tungsten, is about 0.25 V greater to about 0.20 V less than an oxidation energy, or oxidation potential, of copper. As the barrier material is oxidized by the slurry at about the same rate as copper or at a slower rate than copper, use of a slurry so formulated to substantially simultaneously polish a copper conductive structure and an adjacent barrier layer prevents dissolution of the barrier layer. When used with a fixed-abrasive polishing pad, the slurry of the present invention removes a barrier material, such as tungsten, at a rate that is about the same as or up to about ten times slower than the rate at which the slurry removes copper and, preferably, at a rate that is about two to about four times slower than the rate at which the slurry removes copper.
Slurries that are useful in the method of the present invention include at least one oxidizer, at least one complexing agent, and at least one inhibitor. The relative amounts of at least the oxidizer, the pH control agent, and the inhibitor are balanced so as to facilitate substantially concurrent polishing of a copper structure and another structure adjacent thereto, such as a barrier layer formed from tungsten. Thus, the slurry is formulated such that the relative amounts of the oxidizer, the complexing agent, and the inhibitor oxidize copper and a barrier material, such as tungsten, at substantially the same rates, or such that the oxidation energies of copper and the barrier material are substantially the same in the slurry. The pH of the slurry may also be optimized so as to provide for oxidation of copper and a barrier material, such as tungsten, at substantially the same rates.
The present invention also includes a system for substantially simultaneously polishing a copper conductive structure and an adjacent barrier layer of a semiconductor device. Such a system includes a fixed-abrasive type polishing pad and a substantially abrasive-free slurry within which copper and the material of the barrier layer are oxidized at substantially the same rates, or have substantially the same oxidation energies.
Other features and advantages of the present invention will become apparent to those of ordinary skill in the art through consideration of the ensuing description, the accompanying drawings, and the appended claims.
A method incorporating teachings of the present invention is illustrated in
In forming a conductive structure from copper layer 20, portions of copper layer 20 and of barrier layer 18 that are not located within recess 14 must be removed from semiconductor device structure 10. As discussed previously herein, CMP processes are typically used to remove unwanted portions of copper layers. With reference to
Eventually, regions of barrier layer 18 overlying active surface 16 are exposed through copper layer 20, as shown in
Barrier layer 18 is removed from active surface 16 by continued polishing with slurry 30 and fixed-abrasive polishing pad 40. Once barrier layer 18 is substantially removed from active surface 16 and the surface 26 of the portion of copper layer 20 that remains within recess 14 is located substantially in the plane of active surface 16, as depicted in
In order to effect removal of copper and the material or materials (e.g., tungsten) of an adjacent barrier layer 18 or other structure by CMP at substantially the same rates, slurry 30 is formulated so as to oxidize copper and the material or materials of the adjacent barrier layer 18 at substantially the same rates. Stated another way, copper and the material or materials (e.g., tungsten) of the adjacent barrier layer 18 have substantially the same oxidation energies in slurry 30. As a result, as an interface 19 between layers 18 and 20 is exposed to slurry 30, the material or materials of barrier layer 18 will not dissolve, or be removed from semiconductor device structure 10, at a significantly greater rate than copper of copper layer 20 is dissolved or removed from semiconductor device structure 10. By way of example only, and not to limit the scope of the present invention, the oxidation energy, or oxidation potential, of tungsten in slurry 30 is preferably about 0.25 V more to about 0.20 V less than the oxidation energy, or oxidation potential, of copper in slurry 30. Slurry 30 preferably removes a barrier material, such as tungsten, at a rate that is about the same as or up to about ten times slower than the rate at which slurry 30 removes copper when a fixed-abrasive polishing pad is employed and, more preferably, at a rate that is about two to about four times slower than the rate at which slurry 30 removes copper.
With continued reference to
Examples of oxidizers that are useful as the oxidizer component of slurry 30 include, without limitation, hydrogen peroxide, potassium iodate, potassium permanganate, ammonia, other amine compounds, ammonium compounds, nitrate compounds, and combinations thereof. Exemplary ammonium compounds include, without limitation, ammonium persulfate and ammonium molybdate. Exemplary nitrate compounds include, but are not limited to, ferric nitrate, nitric acid, and potassium nitrate. The oxidizer component preferably comprises about 0.1 to about 20%, by weight, of slurry 30. It is preferred that slurry 30 include about 0.1 to about 5.0%, by weight, of the oxidizer component. Even more preferred is a potassium iodate oxidizer component that makes up about 3 to about 5% of the weight of slurry 30.
The one or more complexing agents of slurry 30 may include, but are not limited to, glycine, ammonium citrate, ammonium phosphate, ammonium acetate, and combinations thereof. Slurry 30 preferably includes about 1 to about 15% of the one or more complexing agents, by weight. It is more preferred that the one or more complexing agents make up about 3 to about 5% of the weight of slurry 30. For example, slurry 30 may include about 1% of the complexing agent glycine, including a concentration of 0.1 M (molar) polyethylene glycol (PEG), by weight of slurry 30. As another example, slurry 30 may include about 3% ammonium acetate, by weight.
Inhibitor component 32 of slurry 30 prevents corrosion of copper during polishing. Inhibitor component 32 may include an azole, such as benzenetriazole (BTA), mercaptobenzothiazole, and tolytriazole, an amine, such as methylamine and diethylamine, a ring compound, such as pyridine, quinoline, and dicyclohexamine nitrate, as well as other compounds, such as potassium silicate, ammonium borate, ammonium phosphate, and potassium dichromate, or mixtures of any of these corrosion inhibitors. While inhibitor component 32 may make up about 0.05 to about 2% of the weight of slurry 30, it is preferred the inhibitor component 32 comprise about 0.05 to about 0.2% of the weight of slurry 30. For example, slurry 30 may include about 0.1% BTA, by weight.
Slurry 30 may have a pH in the range of about 2 to about 6, but the pH of slurry 30 is preferably in the range of about 3 to about 5 and, more preferably, is about 4. One or more buffers, which are also referred to herein as pH control agents, may be used, as known in the art, to adjust the pH of slurry 30 to a desired level. Exemplary buffers that may be used in slurry 30 include, without limitation, potassium hydrogen phthalate, ammonium acetate, ammonium oxalate, ammonium carbamate, ammonium phosphate, ammonium hydrogen phosphate, ammonium dihydrogen phosphate, dibasic ammonium citrate, tribasic ammonium citrate, and mixtures thereof. Acetic acid, phosphoric acid, and sulfuric acid are examples of other pH control agents that may be used in a slurry 30 incorporating teachings of the present invention. Preferably, the pH control agent will adjust the pH of slurry 30 to a desirable range or point without significantly etching the insulator (e.g., borophosphosilicate glass (BPSG), phosphosilicate glass (PSG), or borosilicate glass (BSG)) that underlies the layer or layers being polished. Without limitation, acetic acid is an example of a buffer that may be used to adjust the pH of slurry 30 and that will not etch an underlying glass insulator.
In addition, slurry 30 may include a surfactant component, which may comprise from about 1% to about 15% of the volume of slurry 30 and, more preferably, about 1% to about 2% of the weight of slurry 30. The surfactant component may include, for example, polyethylene glycol, polyoxyethylene ether, glycerol, polypropylene glycol, polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene oleyl ether, and mixtures thereof.
Thickeners may also be included in slurry 30 to impart slurry 30 with a desired viscosity (e.g., about 10 to about 20 cps. at ambient temperature). Exemplary thickeners that may be included in slurry 30 include, but are not limited to, POLYOX®, available from Union Carbide of Danbury, Conn., and CARBOPOL®, available from B.F. Goodrich of Cleveland, Ohio.
Water may be used as the balance of slurry 30.
The specific amounts of the components of slurry 30 may be determined by identifying slurry 30 formulations in which copper gives up electrons at substantially the same rate as a barrier material, such as tungsten, of a barrier layer 18 to be polished substantially simultaneously with copper layer 20. Stated another way, slurry 30 may be formulated so that copper and a barrier material therefor, such as tungsten, have the substantially same oxidation energies therein, or are oxidized at substantially the same rates therein. Preferably, the oxidation energy of tungsten or another barrier material in slurry 30 is within the range of about 0.25 V more than to about 0.20 V less than the oxidation energy of copper in slurry 30, the range including the end point values thereof. These formulations of slurry 30 will facilitate the removal of copper and a barrier material, such as tungsten, from a semiconductor device structure 10 at substantially the same rates.
Slurry 30 formulations having these characteristics may be determined as known in the art, such as by measuring the open circuit potentials of copper and a barrier material, such as tungsten, in slurry 30.
Referring now to
Any known CMP apparatus, including conventional, rotary CMP apparatus, web format CMP apparatus, and belt format CMP apparatus, may comprise polishing apparatus 42, substrate support 44, and slurry applicator 47 of polishing system 50. Fixed-abrasive polishing pad 40 may similarly include any known fixed-abrasive polishing pad, such as the acrylic fixed-abrasive polishing pads available from 3M Company, in any known pad format (e.g., conventional, web, or belt).
In use of polishing system 50, one or more semiconductor device structures 10 having one or more layers thereon that are to be chemical-mechanical polished are secured to substrate support 44. If necessary, fixed-abrasive polishing pad 40 is also secured to polishing apparatus 42. Slurry 30 is introduced by slurry applicator 47 onto one or both of semiconductor device structure 10 and fixed-abrasive polishing pad 40. Once slurry 30 has been applied to fixed-abrasive polishing pad 40, one or both of semiconductor device structure 10 and fixed-abrasive polishing pad 40 are substantially continuously laterally moved (e.g., rotated or vibrated or otherwise moved side-to-side) and brought into frictional contact with one another so as to effect the CMP process. For example, when a web format or belt format polishing apparatus is employed, the apparatus may precess semiconductor device structure 10 (i.e., rotate semiconductor device structure 10 around the axis of a support therefor), while the polishing pad remains substantially stationary.
Once the desired portions of one or more layers 18, 20 (
While polishing in accordance with the present invention may be conducted at any suitable polishing temperature, polishing with slurry 30 and a fixed-abrasive polishing pad 40 may be conducted at lower temperatures than those of conventional polishing processes. For example, polishing methods that incorporate teachings of the present invention may be conducted at temperatures of about room temperature (e.g., about 23-27° C.) or cooler. It has been found that polishing causes fewer defects when conducted at cooler temperatures. The abrasive components of conventional slurries do not, however, remain soluble in or, thus, evenly dispersed throughout such slurries at cooler temperatures.
Although the foregoing description contains many specifics, these should not be construed as limiting the scope of the present invention, but merely as providing illustrations of some of the presently preferred embodiments. Similarly, other embodiments of the invention may be devised which do not depart from the spirit or scope of the present invention. Features from different embodiments may be employed in combination. The scope of the invention is, therefore, indicated and limited only by the appended claims and their legal equivalents, rather than by the foregoing description. All additions, deletions and modifications to the invention as disclosed herein which fall within the meaning and scope of the claims are to be embraced thereby.