Polishing method and apparatus

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a polishing method and a polishing apparatus that polishes a substrate such as a semiconductor wafer with a high level of precision while supplying a slurry thereto.

2. Description of Related Art

In recent years, there have been advances in the miniaturization and level of integration of semiconductor devices. In conjunction with this, planarization technology has become a critical problem. Because of this, chemical mechanical polishing (CMP) apparatuses are attracting attention as processing devices that make it possible to polish to a high degree of accuracy semiconductor wafers such as SOI substrates and the like, wafers that have a non-conductive film or metal film formed on a surface thereof in a semiconductor integrated circuit formation process, and various types of semiconductor substrates such as substrates for displays and the like, and to thereby planarize the surface of such substrates.

FIG. 8 is a block diagram showing a conventional CMP apparatus.

As is shown in FIG. 8, a CMP apparatus is provided with a CMP polishing section 101 which has a polishing table on which a polishing pad is mounted, and has a substrate holding device that holds a substrate on which is formed a material to be polished; and a slurry mixture supply section 102 that supplies a polishing agent (i.e., slurry) onto the polishing pad. In this CMP polishing section 101, a structure is employed in which both the substrate and the polishing table are rotated respectively. The surface of the substrate that is to be polished is then brought into contact with the polishing pad, and this surface to be polished is polished while slurry is supplied to the polishing pad from the slurry mixture supply section 102.

The slurry that is supplied from the slurry mixture supply section 102 may be, for example, a slurry in which fine particles of SiO₂(i.e., abrasive grain) ranging from a micro order size to a sub micron order size are dispersed in an alkaline dispersion medium or in an acidic aqueous solution. The slurry is supplied from a position above the pad and on the outer side of the substrate to a position between the polishing pad and the surface of the substrate to be polished, and the surface to be polished is polished and planarized using the chemical action of the slurry and the physical action of the abrasive grain present in the slurry. Because of this, it is necessary to keep the composition of the slurry constant and perform the polishing with the polishing rate per unit time kept constant. Therefore, in order to maintain uniform electrochemical characteristics of the slurry such as, for example, pH and concentration and the like, a CMP apparatus is provided with an electrochemical characteristics evaluation and analysis unit 103, and a control unit 105 that controls the flow rates of the various chemicals that make up the slurry based on data analyzed by the evaluation and analysis unit 103.

Moreover, as is shown, for example, in Patent document 1, a structure is known in which measurement instruments are provided in a polishing liquid supply system, and electromotive force is generated between dissimilar metals between two electrodes that are immersed in a polishing solution contained in a polishing solution tank, and the current flowing between the electrodes is monitored.

[Patent document 1] Japanese Unexamined Patent Application, First Publication No. 2004-6499

SUMMARY OF THE INVENTION

Parameters for the electrochemical characteristics of the material to be polished in the slurry include spontaneous potential, corrosion potential, corrosion current and the like, and it is known that there is a considerable difference in these characteristics between when the material to be polished is in a stationary state (i.e., is not being polished) inside the slurry, and when it is being polished. Accordingly, determining the optimum slurry composition simply from the electrochemical characteristics in a stationary state, as in Patent document 1, does not necessarily reflect the polishing conditions for an object being polished during an actual CMP process, and achieving a highly reliable CMP process is difficult.

Moreover, the polishing material that is formed on the substrate surface is not formed by a single material, but, as in the case of a wiring pattern, for example, is formed by stacking non-conductive films, metal films, and the like. In particular, what is known as a Damascene process is used as a process for forming the wiring of a semiconductor device. In this process, wiring metal is embedded inside recessed portions for wiring such as trenches and via holes that are provided in a non-conductive film. In the Damascene process, in order to prevent spreading of the wiring metal and secure good adhesion, the wiring metal is embedded after a barrier film has been formed inside the wiring recessed portions. Because of this, initially, the CMP process performs the polishing of a single material, however, in the final stages of the CMP process, a plurality of types of material are exposed. As a result, complex electrochemical phenomena are generated at the polishing surface, and a situation is created in which defect formation such as corrosion occurs easily. Accordingly, there is now an even greater need than hitherto for slurry characteristics to be stabilized, and a CMP apparatus is required that can maintain these characteristics to a high level of accuracy.

Accordingly, the present invention was conceived in view of the above described circumstances, and it is an object thereof to provide a polishing method and polishing apparatus that maintain the electrochemical characteristics of slurries for various materials to be polished to a high level of accuracy and make precise polishing possible.

In order to achieve the above described object, a first aspect of the present invention is a polishing method in which, at the same time as a slurry is being supplied to a surface of a polishing pad by a slurry supply apparatus, a material to be polished is polished by moving the polishing pad relatively to the material to be polished that is formed on a substrate surface while also bringing the polishing pad and the material to be polished into mutual contact, and that includes: a polishing characteristics measurement step in which electrochemical characteristics of the slurry in relation to the material to be polished are measured; and a preparation step in which the slurry is prepared based on the measured electrochemical characteristics, wherein in the polishing characteristics measurement step, a slurry is supplied from the slurry supply apparatus, and using a sample polishing pad that is formed from the same material as the polishing pad and a sample material to be polished that is formed from the same material as the material to be polished, the electrochemical characteristics are measured both when the sample material to be polished is being polished by the sample polishing pad and when the sample material to be polished is not being polished by the sample polishing pad. According to this structure, it is possible to quantitatively ascertain in all states during a polishing step the electrochemical reaction state between a slurry and a material being polished. Namely, by supplying slurry from the slurry supply apparatus separately from the actual polishing step, and using a sample polishing pad and a sample material to be polished, measuring the electrochemical characteristics both when the sample material to be polished is being polished and when the sample material to be polished is not being polished, it is possible to ascertain the behavior of the same electrochemical characteristics as those present in the actual polishing step. Because of this, it is possible to determine the optimum slurry characteristics in accordance with the polishing conditions. In addition, by preparing a slurry based on the measured electrochemical characteristics, it is possible to control the electrochemical characteristics of the slurry relative to the material to be polished to a high level of accuracy. Accordingly, it is possible to predict the occurrence of unanticipated faults such as corrosion of the material to be polished, over-polishing, defect creation, and the like, before these faults actually occur, and thus perform highly accurate polishing. Moreover, it is possible to always maintain optimum control of the composition ratio and the like of a slurry, and achieve a stabilization of the polishing process. Furthermore, it also becomes possible to choose an optimum slurry using these evaluations, so that the development of an optimum process in an even shorter time becomes possible.

In a preferred aspect of the present invention, in the polishing characteristics measurement step, the electrochemical characteristics are measured using a plurality of the sample materials to be polished that correspond to a plurality of the sample materials to be polished that are formed on the substrate surface.

According to this structure, even if a plurality of types of material to be polished are exposed on a substrate surface, it is possible to ascertain the reactivities of the electrochemical characteristics of the slurries in relation to each individual one of the materials to be polished. Accordingly, it is possible to predict the occurrence of unanticipated faults such as corrosion of the material to be polished, over-polishing, defect creation, and the like, before these faults actually occur, and thus perform highly accurate polishing.

In a preferable aspect of the present invention, in the polishing characteristics measurement step, the corrosion potentials of each of the plurality of sample materials to be polished are measured, and when the corrosion potential of a primary material is measured in the polishing characteristics measurement step as being lower than the corrosion potential of a secondary material from among the respective sample materials to be polished, the composition of the slurry is adjusted in the preparation step such that the corrosion potential of the secondary material is set within a passive state area or a stable area of a Pourbaix diagram of the primary material.

According to this structure, when the corrosion potential of the secondary material is higher than the corrosion potential of the primary material, the composition of the slurry is adjusted such that the corrosion potential of the secondary material is set within a passive state area or a stable area on a Pourbaix diagram of the primary material. As a result, the primary material does not get drawn inside the corrosion area by the potential gradient in boundary portions between the primary material and the secondary material, and the primary material is reliably polished within the passive state area or the stable area. Accordingly, it is possible to prevent corrosion of the primary material.

In a preferable aspect of the present invention, the pH of the slurry is adjusted in the preparation step.

According to this structure, by adjusting the pH of the slurry, It is possible to set the corrosion potential of the secondary material within a passive state area or a stable area on a Pourbaix diagram of the primary material. As a result, the primary material does not get drawn inside the corrosion area, and the primary material can be reliably polished within the passive state area or the stable area.

Another aspect of the present invention is a polishing apparatus that is provided with a polishing pad, and a slurry supply apparatus that supplies slurry onto the polishing pad, in which, at the same time as the slurry is being supplied by the slurry supply apparatus, a material to be polished is polished by moving the polishing pad relatively to the material to be polished that is formed on a substrate surface while also bringing the polishing pad and the material to be polished into mutual contact, wherein there are provided a polishing characteristics measurement section that measures electrochemical characteristics of the slurry in relation to the material to be polished, and a preparation section that prepares the slurry based on the measured electrochemical characteristics, and wherein a slurry is supplied from the slurry supply apparatus, and a sample material to be polished that is formed from the same material as the material to be polished and a sample polishing pad that is formed from the same material as the polishing pad are held in the polishing characteristics measurement section, and the polishing characteristics measurement section measures the electrochemical characteristics both when the sample material to be polished is being polished by the sample polishing pad and when the sample material to be polished is not being polished by the sample polishing pad.

According to this structure, it is possible to quantitatively ascertain in all states during a polishing step the electrochemical reaction state between a slurry and a material being polished. Namely, as a result of slurry being supplied from the slurry supply apparatus separately from the actual polishing step, and the electrochemical characteristics both when the sample material to be polished is being polished by a sample polishing pad and when the sample material to be polished is not being polished, it is possible to ascertain the behavior of the same electrochemical characteristics as those present in the actual polishing step. Because of this, it is possible to determine the optimum slurry characteristics in accordance with the polishing conditions. In addition, by preparing a slurry based on the measured electrochemical characteristics, it is possible to control the electrochemical characteristics of the slurry relative to the material to be polished to a high level of accuracy. Accordingly, it is possible to predict the occurrence of unanticipated faults such as corrosion of the material to be polished, over-polishing, defect creation, and the like, before these faults actually occur, and thus perform highly accurate polishing. Moreover, it is possible to always maintain optimum control of the composition ratio and the like of a slurry, and achieve a stabilization of the polishing process. Furthermore, it also becomes possible to choose an optimum slurry using these evaluations, so that the development of an optimum process in an even shorter time becomes possible.

In a preferable aspect of the present invention, a plurality of the sample materials to be polished that correspond to a plurality of the sample materials to be polished that are formed on the substrate surface are held in the polishing characteristics measurement section.

According to this structure, even if a plurality of types of material to be polished are exposed on a substrate polishing surface, it is possible to ascertain the reactivities of the electrochemical characteristics of the slurries in relation to each individual one of the materials to be polished. Accordingly, it is possible to predict the occurrence of unanticipated faults such as corrosion of the material to be polished, over-polishing, defect creation, and the like, before these faults actually occur, and thus perform highly accurate polishing.

According to the present invention, it is possible to quantitatively ascertain in all states during a polishing step the electrochemical reaction state between a slurry and a material being polished. Namely, by supplying slurry from a slurry supply apparatus separately from an actual polishing step, and using a sample polishing pad and a sample material to be polished, measuring the electrochemical characteristics both when the sample material to be polished is being polished and when the sample material to be polished is not being polished, it is possible to ascertain the behavior of the same electrochemical characteristics as those present in the actual polishing step. Because of this, it is possible to determine the optimum slurry characteristics in accordance with the polishing conditions. In addition, by preparing a slurry based on the measured electrochemical characteristics, it is possible to control the electrochemical characteristics of the slurry relative to the material to be polished to a high level of accuracy. Accordingly, it is possible to predict the occurrence of unanticipated faults such as corrosion of the material to be polished, over-polishing, defect creation, and the like, before these faults actually occur, and thus perform highly accurate polishing. Moreover, it is possible to always maintain optimum control of the composition ratio and the like of a slurry, and achieve a stabilization of the polishing process. Furthermore, it also becomes possible to choose an optimum slurry using these evaluations, so that the development of an optimum process in an even shorter time becomes possible.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a CMP apparatus according to an embodiment of the present invention.

FIG. 2 is a perspective view showing essential portions of a CMP apparatus according to an embodiment of the present invention.

FIG. 3 is a schematic structural view of a polishing characteristics measurement portion according to an embodiment of the present invention.

FIG. 4 is a process diagram of a CMP apparatus according to an embodiment of the present invention.

FIG. 5 is a graph showing polarization characteristics during polishing and not during polishing of three types of materials for polishing.

FIG. 6 is a graph showing OCP changes, and shows corrosion potential during polishing and not during polishing of the respective materials from the graph of polarization characteristics shown in FIG. 5.

FIG. 7 is a Pourbaix diagram when the material B is being polished.

FIG. 8 is a block diagram showing a conventional CMP.

BRIEF DESCRIPTION OF THE REFERENCE NUMERALS

- 44
  a to 44c . . . Sample materials (sample materials to be polished)
- 47 . . . Polishing pad (sample polishing pad)
- 50 . . . Slurry
- 64 . . . Barrier film (material to be polished)
- 65 . . . Polishing pad
- 66 . . . Conductive film (material to be polished)
- 200 . . . CMP apparatus (polishing apparatus)
- 201 . . . CMP polishing section
- 202 . . . Slurry supply device
- 203 . . . Polishing characteristics measurement section
- W . . . Substrate

DETAILED DESCRIPTION OF THE INVENTION

Next, embodiments of the present invention will be described with reference made to the drawings.

Firstly, a CMP apparatus according to the present embodiment will be described.

(CMP Apparatus)

FIG. 1 is a block diagram showing a CMP apparatus according to the present invention, and FIG. 2 is a perspective view showing essential portions of a CMP apparatus.

As is shown in FIG. 1, a CMP 200 is formed by a CMP polishing section 201, a slurry mixture supply section 202, a polishing characteristics measurement section 203, and a control unit 207 that controls the slurry mixture supply section 202 and polishing characteristics measurement section 203.

As is shown in FIG. 2, the CMP polishing section 201 is provided with a polishing object holding device 25 that removably holds a substrate W on which are formed materials for polishing (i.e., a barrier film 64 and a wiring film 66; see FIG. 4—these are described below) such that a surface for polishing is facing downwards, and a polishing table 26 that is positioned facing the substrate W that is being held on the polishing object holding device 25. A polishing pad 65 whose aperture diameter is larger than the aperture diameter of the substrate W is mounted on the polishing table 26. This polishing pad 65 is formed, for example, from polyurethane or the like, and bumps and indentations and multiple pores and the like are formed on a surface thereof.

Returning to FIG. 1, the slurry mixture supply section 202 mixes a slurry that has been supplied under optimum conditions (i.e., mixture ratios, flow rate, and the like) by a slurry flow rate control unit 206 (described below), and then supplies it onto the polishing pad 65. A slurry that is formed by dispersing fine particles of SiO₂(i.e., abrasive grain) ranging from a micro order size to a sub micro order size in ammonium persulfate ((NH₄)₂S₂O₈) is used as the slurry of the present embodiment. By using ammonium persulfate as a solvent in this manner, it is possible to obtain an excellent polishing speed. Note that in addition to the above described materials, it is also possible to mix in corrosion inhibitors, complexing agents, and oxidizing agents and the like such as benzotriazole (BTA).

The control unit 207 is provided with an electrochemical characteristics evaluation and analysis unit 204, a central processing unit CPU 205, and the slurry flow rate control unit 206.

The electrochemical characteristics evaluation and analysis unit 204 is formed by a computer-controlled potentiostat/galvanostat or the like, and converts electrochemical characteristics obtained by the polishing characteristics measurement section 203 into quantified data which it then outputs to the central processing unit CPU 205.

The central processing unit CPU 205 receives the electrochemical characteristics data that has been converted by the electrochemical characteristics evaluation and analysis unit 204. It then refers to electrochemical characteristics and the like in an individual and typical composition in a basic slurry that has been prepared in advance, and calculates the compositions of each component of a slurry structure that will provide the optimum electrochemical characteristic conditions.

The slurry flow rate control unit 206 supplies the respective slurry structural components under the optimum conditions (i.e., mixing ratios, flow rates, and the like) based on the compositions of the slurry structural components calculated by the central processing unit CPU 205.

In this manner, a structure is employed in which the slurry composition is controlled by the electrochemical characteristics evaluation and analysis unit 204, the central processing unit CPU 205, and the slurry flow rate control unit 206, and is supplied to the slurry mixture supply section 202.

Here, the aforementioned polishing characteristics measurement section is described in detail below. FIG. 3 is a schematic structural view of a polishing characteristics measurement section.

As is shown in FIG. 3, the polishing characteristics measurement section 203 is provided with a storage tank 31 that has a plurality of (for example, three) aperture portions 32a to 32c formed in a bottom surface thereof. A plurality of sample materials to be polished (referred to below as sample materials) 44a to 44c are held below this storage tank 31. These sample materials 44a to 44c are the same material as the material to be polished that is formed on the aforementioned substrate W and, for example, copper (Cu), tantalum (Ta), and ruthenium (Ru) and the like are used for the sample materials. The respective sample materials 44a to 44c are plate-shaped components, and are pressed towards the bottom surface of the storage tank 31 with O-rings 49 sandwiched between the respective sample materials and the storage tank 31, so that the aperture portions 32a to 32c are blocked off. Namely, the sample materials 44a to 44c are formed such that the surfaces thereof are exposed to the interior of the storage tank 31 via the aperture portions 32a to 32c.

A sample slurry is stored in the storage tank 31. This sample slurry has the same composition as the slurry that is supplied to the aforementioned CMP polishing section 201, and is supplied from the slurry mixture supply section 202 in the same way as the slurry supplied to the CMP polishing section 201.

A polishing section 43 is immersed inside the storage tank 31. The polishing section 43 is provided with a rotation shaft 48. The rotation shaft 48 is a circular column-shaped component, and is constructed such that it is able to be rotated around an axis of the rotation shaft 48 by a drive apparatus (not shown). Moreover, the rotation shaft 48 is constructed such that it is moved by a drive apparatus inside the storage tank 31 as far as a position facing the respective sample materials 44a to 44c (shown by the arrow in FIG. 3), and such that it is able to move in a direction towards or away from the surfaces of the respective sample materials 44a to 44c.

A polishing pad 47 (i.e., a sample polishing pad) is mounted on a distal end of the rotation shaft 48. This polishing pad 47 is a disk-shaped component that has the same structure as that of the polishing pad of the above described CMP polishing section 201. By lowering the rotation shaft 48 as it is being rotated, the polishing pad 47 is pressed against the surface of the respective sample materials 44a to 44c, and the surfaces of the sample materials 44a to 44c and the polishing pad 47 move relatively to each other so that the sample materials 44a to 44c become polished. Namely, a structure is employed in which, in the polishing characteristics measurement section 203, polishing is carried out on the sample materials 44a to 44c, which are the same as the materials to be polished that are to be actually polished by the CMP polishing section 201, using a sample slurry that has the same composition as the slurry used by the CMP polishing section 201.

Moreover, a reference electrode 45 that is formed, for example, from silver/silver chloride (Ag/AgCl), and an auxiliary electrode 46 that is formed, for example, from platinum (Pt) are immersed inside the storage tank 31.

In addition, using the respective sample materials 44a to 44c as working electrodes, a potentiostat that is formed by a three-electrode system is constructed by sequentially applying voltage between the reference electrode 45 and auxiliary electrode 46 and any one of the respective sample materials 44a to 44c using a power supply (not shown). As a result, current flows between the three electrodes, and it is possible to measure the electrochemical characteristics of the sample slurry with regard to each of the sample materials 44a to 44c inside the storage tank 31. In this manner, in the polishing characteristics measurement section 203, the electrochemical characteristics of a sample slurry are measured under the same polishing conditions as those present in the CMP polishing section 201 both when the respective sample materials 44a to 44c are being polished and when they are not being polished.

(Polishing Method)

Next, the polishing method of the present embodiment will be described.

Firstly, the film structure of a substrate which is to be polished of the present embodiment will be described. FIG. 4 is a process diagram of a CMP apparatus according to an embodiment of the present invention.

As is shown in FIG. 4A, an interlayer non-conductive film 62 that is formed from a non-conductive material such as SiO₂, SiOF, SiOC, or a Low-k material (i.e., a low dielectric constant non-conductive film) or the like is formed on a surface of a substrate W that is formed from silicon or the like. A recessed portion 63 for wiring formation is formed in a surface of the interlayer non-conductive film 62. A barrier film (i.e., a material to be polished) 64 is formed at a thickness of approximately 10 nm on the surface of the interlayer non-conductive film 62 including the recessed portion 63. The barrier film 64 is provided in order to prevent the metal material of the wiring film 66 (described below) spreading over the substrate W, and in order to improve the adhesion between the wiring film 66 and the interlayer non-conductive film 62. The barrier film 64 is conventionally formed solely from tantalum (Ta) or from a Ta compound, however, recently, it is being formed by sandwiching a ruthenium (Ru) layer which has excellent conductivity between a pair of tantalum (Ta) layers which have excellent adhesiveness.

A conductive film (i.e., a material to be polished) 66 that is formed from (Cu) is formed at a thickness of approximately 500 to 1000 nm on the surface of the barrier film 64. When this wiring film 66 is formed by means of an electroplating method, then a seed film (not shown) is formed first on the surface of the barrier film 64 so as to provide an electrode for the electroplating. Note that a recessed portion 67 having a height of approximately 300 nm and a width of approximately 100 μm is formed on the surface of the wiring film 66 so as to match the recessed portion 63 in the interlayer non-conductive film 62. Note also that the dimensions of the wiring formation recessed portions shown here are shown as examples thereof. Moreover, in the present embodiment, a description is given of when copper is used as the wiring film 66, however, in addition to copper, examples of a conductive substance to be polished include conductive metal materials such as aluminum (Al), silver (Ag), gold (Au), nickel (Ni), tungsten (Zn), ruthenium (Ru), and alloys of these.

Because only the wiring film 66 with which the inner side of the recessed portion 63 of the interlayer non-conductive film 62 is filled is used as metal wiring, the wiring film 66 and the barrier film 64 that are formed on the outside of the recessed portion 63 are not required. Moreover, because a plurality of wires are stacked via the interlayer non-conductive film 62, when the wiring film 66 and the barrier film 64 have been removed, it is necessary for the surface of the wiring film 66 in the recessed portion 63 and the surface of the interlayer non-conductive film 62 to be located on the same plane, and for the surface of the substrate W to be planarized. Therefore, surplus metal wiring (i.e., the wiring film 66 and the barrier film 64) are removed and planarized by CMP polishing.

As is shown in FIG. 4B, in CMP polishing, a slurry 50 is interposed between the metal film on the surface of the substrate W and the polishing pad 65, and the substrate W and polishing pad 65 are moved (i.e., rotated) relatively while the surface of the substrate W is pressed against the polishing pad 65, thereby polishing the surface of the metal film. At this time, abrasive grain and oxidizing agent and the like are contained in the slurry 50 and an oxide film is formed on the surface of the polishing material by this oxidizing agent. Because the oxide film that is formed on an upper portion H of the polishing material (i.e., the outer side of the recessed portion 63) is removed by the contact with the polishing pad, the polishing material on the upper portion H is polished. In contrast to this, an oxide film 70 that is formed on a lower portion L of the polishing material (i.e., the inner side of the recessed portion 63) does not come into contact with the polishing pad, it is not removed in the polishing material of the lower portion L is not polished. As a result, as is shown in FIG. 4C to 4E, the height differences in the polished surfaces (i.e., the recessed portion 67) are gradually eliminated.

The polishing method of the present embodiment is principally made up of a polishing characteristics measurement step, steps to prepare both bulk and clear slurries, bulk and clear polishing steps, a step to prepare a barrier slurry, and a barrier polishing step. Namely, polishing of the wiring film 66 is performed in two polishing stages, namely bulk polishing (see FIG. 4B) and clear polishing (see FIG. 4C) corresponding to the thickness of the film which changes as the polishing progresses. Next, as is shown in FIG. 4D, a barrier polishing step is performed in which the wiring film 66 and the barrier film 64 are exposed on the same polishing surface plane, and these two are both polished simultaneously.

(Polishing Characteristics Measurement Step)

Parameters for the electrochemical characteristics of the material to be coated in the slurry include spontaneous potential, corrosion potential, corrosion current and the like, and it is known that there is a considerable difference in these characteristics between when the material to be coated is in a stationary state (i.e., is not being polished) inside the slurry, and when it is being polished. Accordingly, determining the optimum slurry composition simply from the electrochemical characteristics in a stationary state, as is the case conventionally, does not necessarily reflect the polishing conditions for an object being polished during an actual CMP process, and achieving a highly reliable CMP process is difficult.

Moreover, the polishing material that is formed on the substrate surface is not formed by a single material, but, as in the case of a wiring pattern, for example, is formed by superposing non-conductive films, metal films, and the like. In particular, in the aforementioned Damascene process, initially, the CMP process performs the polishing of a single material, however, in the final stages of the CMP process, a plurality of types of material are exposed. As a result, complex electrochemical phenomena are generated at the polishing surface, and a situation is created in which defect formation such as corrosion occurs easily. Accordingly, there is now an even greater need than hitherto for slurry characteristics to be stabilized, and a CMP apparatus is required that can maintain these characteristics to a high level of accuracy.

The applicants of the present invention made measurements using the method described below of the electrochemical characteristics of slurries in relation to materials to be polished. Firstly, the specific electrochemical characteristics to be measured are broadly divided into two types. One type is polarization characteristics, and the other type is open circuit potential (OCP).

FIG. 5 shows polarization characteristics when three types of polishing materials are being polished and are not being polished. While the potential is being scanned from a low potential side to a high potential side the current is measured, and the polarization characteristics are plotted between a logarithmic scale of the current density and the potential. In addition, as the polishing materials used in this experiment, ruthenium (Ru) is used for sample A, copper (Cu) is used for sample B, and tantalum (Ta) is used for sample C, while ammonium persulfate ((NH₄)₂S₂O₈) is used as an oxidizer in the slurry solvent.

As is shown in FIG. 5, it was found that as the potential was increased from a low potential, the current density was on a decreasing trend in each of the samples A through C. In addition, it was found that at a particular predetermined potential, the current density maintained a minimum value, and as the potential was further increased from that point, the current density changed to an increasing trend. On the low potential side of the potential where the current density is at the minimum a reductive reaction occurs, while on the high potential side thereof an oxidation reaction occurs. Specifically, in the reductive reaction on the low potential side a phenomenon occurs in which, for example, hydrogen ions contained in the slurry bond with electrons to generate hydrogen gas, and the material to be polished is placed in a stable state. In contrast, in the oxidation reaction on the high potential side, the surface of the polishing material is oxidized and ionized, and melts in the slurry.

Here, the potential where the current density is at the minimum value is called the corrosion potential (Ecorr), while the current density at this time is called the corrosion current density (icorr).

Furthermore, the current density for sample A is the largest both during polishing and when there is no polishing, and next comes sample B and then sample C. From this data, it was found that sample A had the greatest reactivity with the slurry, while that of sample C was the smallest. Moreover, when the current densities during polishing and when there was no polishing were compared, it was found that the current density was greater during polishing in each of the three samples A to C. This shows that the surface layer was erased by the polishing to expose a new surface, and that this new surface provided a vigorous surface reaction.

Next, in the same way as the current density, the potential for sample A is the largest both during polishing and when there is no polishing, and next comes sample B and then sample C. Moreover, in regard to the potentials for each polishing material, in the cases, for example, of materials A and C, there was a shift towards the lower potential side and the higher current density side during polishing in comparison to when polishing was not being performed. However, in material B, it was found that there was a shift to the high potential side during polishing. In this manner, by comparing the material B, and the materials A and C, it was found that there were differences in the behavior of the reactions during polishing and when polishing was not being performed.

FIG. 6 is a graph showing OCP changes in which the horizontal axis indicates time and the vertical axis indicates OCP. The OCP corresponds to the corrosion potentials when polishing was and was not being performed on the respective materials A through C for the polarization characteristics shown in FIG. 5.

As is shown in FIG. 6, for the OCP when polishing is not being performed, the material A was in a noble state (namely, the potential was highest), while the material C was in a base state (namely, the potential was lowest).

As is shown in FIG. 6, the value of the OCP decreased in material A and material C following the progression from a non-polishing state to a polishing state, however, this value increased in material B. In contrast, the value of the OCP increased in material A and material C following the progression from a polishing state to a non-polishing state, however, this value decreased in material B. As a result, in a non-polishing state, a sizable potential difference was generated between material A and material B. From these changes, it was found that, for example, if material A and material B were present in the same slurry, then material B was in a base potential state and was easily corrodible.

FIG. 7 shows a Pourbaix diagram (i.e., showing potential—pH) of material B, that is the primary material for forming the metal wiring. In this case, the potential of the primary material B is lower than the potential b of the material A and, moreover, is in a stable region. As is shown in FIG. 7, in a slurry in which the pH is α, when a secondary material (for example, the material A) which is nobler than the material B which is the primary material is exposed to the polishing surface and is present in the same slurry, namely, when this secondary material is in the same state as the wiring being processed, then the potential a of the material B is pulled to the potential b of the material A and the potential of the material B increases. The potential of the primary material B approaches particularly close to the potential of the material A in a portion close to the contact portion between the material B and the material A. This is due to the potential gradient between the material A and the material B. Moreover, the greater the potential difference between the material A and the material B, the greater the possibility that the potential b of the material A will be present in a corrosion area.

Namely, when there is a sizeable potential difference between the materials A and B, and the potential b of the material A is present in a corrosion area, there is a possibility that the potential of the material B will also be pulled towards the corrosion area. As a result of this, there is also a possibility that the material B which is the primary material will become corroded. Namely, even if a slurry is prepared having a composition in which the material B was set inside the stable area prior to polishing, then depending on the polishing conditions there is a possibility that the potential of the material B will increase as far as a corrosion area.

In this manner, because the potential difference between material B and material A is small during polishing and large when polishing is not being performed, it can be determined that there is a need to pay attention to the occurrence of corrosion in the material B at those points in time when polishing is halted and there is a switch to a non-polishing state, and when abrupt changes occur in the OCP such as at boundary portions and the like between material A and material B.

In order to prevent corrosion of the material B, in the above described Pourbaix diagram (see FIG. 7), it is sufficient if the composition of the slurry is adjusted such that the potential of material A (for example, Ru) is kept within a passive state area or the stable area. Namely, the pH of the slurry is lowered so that it is kept within the range of β in FIG. 7. The pH may be lowered by mixing an acidic material such as sulfuric acid or hydrochloric acid in the slurry, or by diluting the concentration of alkaline material in the slurry. As a result, even if the material A is nobler than the material B, and the potential of the material B is pulled towards the material A side by the potential gradient between the material A and the material B, the material B does not get drawn inside the corrosion area. Namely, by preparing a slurry that has a composition whereby the material A, which is a noble material in comparison to the material B, is set within a passive state area or a stable area, it is possible to prevent the material B, which is the primary material, from being corroded.

Here, in consideration of the above described phenomenon, the applicants of the present invention discovered that it is possible to ascertain in advance the electrochemical characteristics of an actual polishing step by performing polishing in the polishing characteristics measurement section 203 separately from the actual polishing step under the same conditions as those for the CMP polishing section 201. By ascertaining the electrochemical characteristics of a slurry towards a material to be polished, it is possible to detect that it has not been possible to prepare a predetermined slurry because of a fault in the slurry mixture supply section 202 or the like.

Firstly, as is shown in FIGS. 1 to 4E, prior to the polishing by the CMP polishing section 201, changes in the electrochemical characteristics of a sample slurry towards a material to be polished are measured in advance in the polishing characteristics measurement section 203 (i.e., a polishing characteristics measurement step). Note that the measurement of the polishing characteristics may be performed prior to the start of polishing operations each day, or prior to the start of polishing operations of each lot, or prior to the start of the polishing operation on each substrate. Measurements may also be made during a polishing operation.

Specifically, changes in the electrochemical characteristics of a sample slurry both when the respective sample materials 44a to 44c were being polished and when these were not being polished by the sample polishing pad 47 are sequentially measured. The various types of electrochemical characteristics that were obtained by the polishing characteristics measurement section 203 are converted into quantified data in the electrochemical characteristics evaluation and analysis unit 204, and this is then output to the central processing unit CPU 205. The central processing unit CPU 205 calculates optimum slurry composition data based on the data received from the electrochemical characteristics evaluation and analysis unit 204.

Next, a slurry is prepared based on the electrochemical characteristics data during the polishing of the sample material 44a (i.e., copper) that was measured by the polishing characteristics measurement section 203 prior to the bulk polishing and clear polishing of the metal wiring layer, namely, prior to performing polishing in a state in which only the wiring film 66 that is to form the metal wiring layer (i.e., the primary material) is exposed (i.e., bulk and clear slurry preparation step). Specifically, in the slurry flow rate control unit 206, slurry structural components are supplied at the optimum conditions based on the optimum slurry composition data calculated by the central processing unit CPU 205. In addition, the slurry that is supplied at the optimum conditions is mixed in the slurry mixture supply section 202 and is then supplied onto the polishing pad 65.

Next, in the CMP polishing section 201, polishing of a material to be polished is performed using the above-described polishing method (i.e., a bulk and clear polishing step; see FIG. 4B and FIG. 4C). At this time, it is preferable for the polishing to be performed while changes in the electrochemical characteristics of the slurry in relation to the wiring film 66 in the CMP polishing section 201 are measured. In addition, when the bulk polishing and clear polishing have ended, the wiring film 66 and the barrier film 64 are exposed on the same plane of the polishing surface.

Next, prior to the barrier polishing to simultaneously polish the wiring film 66 and the barrier film 64 that are exposed on the same plane of the polishing surface, a slurry is prepared for the barrier polishing (i.e., barrier slurry preparation step).

Firstly, in the above-described polishing characteristics measurement step, it is confirmed whether or not a noble material whose potential is higher than the potential of the wiring film 66 (i.e., the primary material), which is the portion of the structural materials of the barrier film 64 (i.e., the secondary material) that forms the wiring, is present on the polishing surface.

If a structural material that will make the wiring film 66 a base is not present on the polishing surface, then, if, for example, of the structural materials making up the barrier film 64, only the tantalum (material C in FIG. 6) which has a lower potential than that of the copper (Cu) which forms the wiring film 66 is exposed, a slurry that has been prepared having the same composition as that during normal barrier polishing is supplied. A barrier polishing step is then performed to simultaneously polish the copper (Cu) of the wiring film 66 and the tantalum (Ta) of the barrier film 64. Polishing is then continued in this state. At this time, the Ta is the base material relative to the Cu, however, because a solid oxide film is formed on the surface of the Ta, corrosion of the Ta does not become a problem.

In contrast, if a structural material that will make the wiring film 66 a base is present on the polishing surface, then, if, for example, of the structural materials making up the barrier film 64, ruthenium (Ru) which has a higher potential than that of the copper (Cu) which forms the wiring film 66 is exposed, it is determined that there is a possibility that the wiring film 66 will be corroded. In addition, a slurry is prepared that has a composition that does not cause the wiring film 66 to be corroded (i.e., barrier slurry preparation step).

Specifically, in the above described Pourbaix diagram (see FIG. 7), the composition of the slurry is adjusted such that the potential of the ruthenium (Ru) which is the material A is kept within a passive state area or the stable area. Namely, the pH of the slurry is lowered so that the potential of the material A is kept within the range of β in FIG. 7. As a result, even if the Ru is nobler than the Cu, and the potential of the Cu is pulled towards the Ru side by the potential gradient between the Ru and the material Cu, the Cu does not get drawn inside the corrosion area. Namely, by preparing a slurry that has a composition whereby the Ru, which is a noble material in comparison to the Cu, is set within a passive state area or a stable area, it is possible to prevent the wiring film 66, which is the primary material, from being corroded.

Note that in addition to the above described method of setting the potential of the Ru within a passive state area or a stable area, it is also possible to make the adjustment using a corrosion inhibitor such as BTA. For example, by increasing the proportion of BTA in the prepared slurry composition, it is possible to enlarge the passive state area in the Pourbaix diagram. As a result, because there is an increase in the boundary potential between the corrosion area and the passive state area, the Ru is easily kept in the passive state area or stable area. In addition, because it is possible to enlarge the range of range of β in FIG. 7, the above-described pH based adjustments can be easily made.

Finally, a barrier polishing step is then performed (see FIG. 4D) to simultaneously polish the copper (Cu) of the wiring film 66 and the ruthenium (Ru) of the barrier film 64.

In this manner, according to the above-described present embodiment, a structure is employed in which there are provided a polishing characteristics measurement step to measure electrochemical characteristics of a slurry in relation to a material to be polished (i.e., the wiring film 66 and the barrier film 64), and a preparation step to prepare a slurry based on the measured electrochemical characteristics, and in the polishing characteristics measurement step, a sample slurry having the same composition as that of the slurry is supplied from the slurry supply apparatus 202 separately from the actual polishing step, and using the polishing pad 47 and the sample materials 44a to 44c, the electrochemical characteristics are measured both during polishing and non-polishing of the sample materials 44a to 44c that are formed from the same materials as the materials to be polished.

According to this structure, it is possible to quantitatively ascertain in all states during a polishing step the electrochemical reaction state between a slurry and a material being polished. Namely, by performing polishing in the polishing characteristics measurement section 203 under the same polishing conditions as those present in the CMP polishing section 201 separately from the actual polishing step performed by the CMP polishing section 201, it is possible to ascertain the behavior of the same electrochemical characteristics as those present in the actual polishing step. Because of this, it is possible to determine the optimum slurry characteristics in accordance with the polishing conditions. In addition, by preparing a slurry based on the measured electrochemical characteristics, it is possible to control the electrochemical characteristics of the slurry relative to the material to be polished to a high level of accuracy.

When the corrosion potential of the Ru (i.e., the secondary material) is higher than the corrosion potential of the Cu (i.e., the primary material), namely, when the Cu is nobler than the Ru, the pH of the slurry is adjusted such that the corrosion potential of the Ru is set within a passive state area or a stable area on a Pourbaix diagram of copper. As a result, even if the potential of the Cu is pulled towards the Ru side, the Cu does not get drawn inside the corrosion area and the Cu is reliably polished within the passive state area or the stable area. Accordingly, it is possible to prevent corrosion of the Cu. Namely, even if a plurality of types of polishing material are exposed on a surface to be polished, it is possible to ascertain the reactivities of the electrochemical characteristics in relation to each individual one of the materials to be polished. Accordingly, it is possible to predict the occurrence of unanticipated faults in the CMP 200 such as corrosion of the material to be polished, over-polishing, defect creation, and the like, before these faults actually occur, and thus perform highly accurate polishing. Moreover, it is possible to always maintain optimum control of the composition of a slurry, and achieve a stabilization of the polishing process. Furthermore, it also becomes possible to choose an optimum slurry using these evaluations, so that the development of an optimum process in an even shorter time becomes possible.

While preferred embodiments of the invention have been described and illustrated above, it should be understood that these are exemplary of the invention and are not to be considered as limiting. Additions, omissions, substitutions, and other modifications can be made without departing from the spirit or scope of the present invention. Accordingly, the invention is not to be considered as limited by the foregoing description and is only limited by the scope of the appended claims.

For example; in the present embodiment, a description is given of when copper (Cu) is used as the primary material and ruthenium (Ru) is used as the secondary material in a wire forming method using a Damascene process, however, the present invention is not limited to this combination and a variety of combinations are possible.

Moreover, it is not necessary for the sample material to be a thin film in the same way as the material to be polished, and provided that it is the same material, it is also possible for a thick film to be formed on the substrate surface.

Polishing method and apparatus

Information

Publication Number

Date Filed

Date Published

Inventors

CPC

US Classifications

International Classifications

Abstract

Description

Claims