JP2008196047A - Electrolytic liquid for electrolytic polishing and electrolytic polishing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a machined surface having high flattening characteristics while ensuring a higher processing rate for an conductive material with a low voltage applied, and to remove an unnecessary conductive material and expose a barrier film without causing dishing, erosion, or etching at the interface between the barrier film and a metal (conductive material) in polishing of a conductive material such as copper formed on a surface of a substrate in a semiconductor manufacturing process in particular. <P>SOLUTION: The electrolytic liquid for use in electrolytic polishing for polishing a conductive material on a surface of a polishing object comprises an aqueous solution containing at least one organic acid or its salt, at least one strong acid having a sulfonic acid group, a corrosion inhibitor, and a water-soluble polymeric compound. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrolytic solution used for polishing an electroconductive substance on the surface of an object to be polished by electropolishing and an electropolishing method using the electrolytic solution, and more particularly to a substrate surface of an electronic device such as a semiconductor device and a display. The present invention relates to an electrolytic solution used for polishing an electroconductive material formed on a metal, a metal material that requires high-precision finishing such as a vacuum device and a high-pressure device, and an electropolishing method using the electrolytic solution. .

  Conventionally, aluminum or an aluminum alloy has been generally used as a wiring metal material for a semiconductor integrated circuit. Recently, however, copper having a low electrical resistance and a high electromigration resistance has been used. For copper wiring, copper is embedded in via holes (connection holes) and trenches (grooves) provided in the insulating layer of the substrate by plating, and then an excessive copper or barrier film for preventing copper diffusion is CMP (Chemical Mechanical Polishing: It is generally formed by a damascene method that is removed by chemical mechanical polishing and flattened. This type of CMP apparatus has a polishing table with a polishing pad (polishing cloth) and a polishing head for holding a substrate such as a semiconductor wafer as an object to be polished, and the substrate held by the polishing head is used as a polishing table. The substrate and the polishing table are simultaneously rotated while being pressed against the affixed polishing pad with a predetermined pressure, and the surface of the substrate is flattened with the polishing pad by supplying an abrasive (slurry) to both sliding surfaces. In addition, the mirror surface is polished.

  1A to 1D show an example of a conventional manufacturing method of a copper wiring board in the order of steps. As shown in FIG. 1A, after a lower layer wiring 14 made of copper surrounded by a barrier film 16 is formed inside an insulating film (interlayer insulating film) 10 and a hard mask 12, Si— While sequentially laminating the N barrier film 18, the first insulating film 20, the second insulating film 22, and the hard mask 24, a via hole 26 and a trench 28 are formed therein by, for example, a lithography etching technique. Then, a barrier film 30 is formed thereon, and a copper seed film 32 is formed thereon as a power feeding layer for electrolytic plating.

The barrier film 30 for preventing copper _{diffusion, W, Ta / Ta X N} Y, Ti X N Y, W X N Y, W X Si Y (X, Y represents any numeric an alloy), Ta _{X Si Y N Z, Ti X} Si Y N Z (X, Y, Z is any number of an alloy), metal material such as Ru or Ru / WCN are generally employed.

  Then, as shown in FIG. 1B, copper 34 as a wiring material is filled in the via hole 26 and the trench 28 of the substrate W by plating or the like, and the copper 34 is deposited on the hard mask 24. Thereafter, as shown in FIG. 1C, the copper 34 and the seed film 32 on the outermost surface of the substrate W are removed by chemical mechanical polishing (CMP) using an abrasive slurry, and further on the insulating film 22. The barrier film 30 is removed and the polishing process is completed. Thereby, as shown in FIG. 1D, the upper layer wiring 36 made of copper 34 is formed inside the insulating films 20 and 22.

In the field of the semiconductor industry, with the recent high integration of semiconductor devices, an organic or inorganic material called a low-k material having a dielectric constant lower than that of a conventional CVD-SiO ₂ film is used as an insulating film (interlayer insulating film). Tend to use. One of the methods for lowering the dielectric constant of the material is a method of lowering the film density. Due to the lowering of the film density, these low-k materials have lower mechanical strength than the conventional SiO ₂ film. For this reason, a low-k material (low dielectric constant insulating layer) is used as the insulating films (interlayer insulating films) 20 and 22, and the copper 34 and the outermost surface of the substrate W are formed by chemical mechanical polishing (CMP). If the seed film 32 and further the barrier film 30 are to be removed, the insulating film (low-k material) 22 and the hard mask 24 and the like are not easily peeled off, but the insulating film (by the pressing force applied at this time) The interlayer insulating films 20 and 22 are easily broken. In order to prevent the insulating films (interlayer insulating films) 20 and 22 from being destroyed, if the pressing force is suppressed to a low value, the polishing rate is lowered, resulting in a problem in productivity. For this reason, application of the CMP process is generally difficult.

  As a means for solving this problem, it is conceivable to polish copper, a seed film or the like on the outermost surface of the substrate by chemical polishing or electrolytic polishing. In contrast to conventional CMP, these polishing methods chemically or anodically dissolve a conductive material such as copper on the surface of the substrate without using a mechanical action, thereby smoothing and polishing the polished surface. It is to make it. Therefore, defects such as work-affected layers and dislocations due to plastic deformation do not occur, and the problem of polishing without impairing the properties of materials such as low-k materials is achieved.

  However, chemical polishing and electropolishing generally perform polishing without bringing a polishing pad or the like into contact with an object to be polished and applying pressure as in conventional CMP, which may cause the following problems. . That is, when polishing and planarizing a metal (copper) surface formed by plating or the like so as to be buried in a via hole or a trench that becomes a metal wiring in a substrate by using these methods, a polishing rate equivalent to CMP is used. If it is going to ensure, the uneven | corrugated recessed part and convex part of the metal surface which were formed at the time of film-forming will be removed at an equivalent speed. Therefore, even if polishing is continued, the metal surface is not flattened, and the central portion of the metal wiring becomes thinner. In other words, when the wiring part is observed from the cross section, dishing that is over-polished into a curved shape like a dish occurs.

  As one means for solving this problem, a method of flattening a metal surface by composite electropolishing (electrochemical mechanical polishing), which is a method combining the principle of CMP and electropolishing, which is a form of electropolishing. There is. In this method, for example, a polishing table with a polishing pad (polishing cloth) is used as a cathode, and a metal (copper) on the surface of a substrate (object to be polished) such as a semiconductor wafer held by a polishing head is used as an anode. While applying a voltage to the substrate, the substrate held by the polishing head is pressed against the polishing pad with a constant pressure while rotating the two, and supplying the electrolyte to the sliding surfaces of both, This is a method of electrochemical mechanical polishing (see, for example, Patent Documents 1 to 4).

  The processing principle of these methods is that the metal surface is flattened by promoting the oxidation and dissolution of the metal surface of the substrate (object to be polished) by electrolytic action and promoting the removal of the oxide film on the substrate by the polishing pad. Based on. However, electropolishing including electrochemical mechanical polishing is generally difficult to meet the high demands of ensuring a processing speed comparable to CMP for metal and obtaining flatness of the processed surface higher than CMP. . One of the reasons is that, generally, when the voltage applied between the metal and the polishing pad is increased, the processing speed for the metal increases, but along with this, the processing surface becomes rough and defects generated on the processing surface increase. To do.

JP 2004-141990 A JP 2005-518670 Gazette JP-A-2005-340600 US Patent Application Publication No. 2006/00000074

  As described above, in electropolishing including composite electropolishing (electrochemical mechanical polishing), when the electrolysis voltage is increased to increase the processing speed, the roughness of the processed surface increases or defects occur on the processed surface. Problems occur. The biggest problem with these polishing methods is that the metal (conductive material) such as copper to be polished during electropolishing is excessively dissolved (etched), resulting in sufficient dishing and erosion on the polished surface. The flatness cannot be obtained. In particular, in the process of etching away metal such as copper located between the wiring parts (field part and space part) to expose the barrier film, etching is performed at the interface between the barrier film and the metal (conductive substance). Is likely to occur. This is because the protective film forming agent contained in the electrolytic solution loses its protective effect on the portion that should be protected originally by applying a high voltage. Therefore, if a high processing speed for a conductive material equivalent to that of CMP can be obtained even at a low electrolysis voltage where the protective film forming agent is effective, electropolishing including composite electropolishing (electrochemical mechanical polishing) Is useful as a processing method with less damage than CMP for semiconductor devices having fragile materials such as Low-k materials.

  Generally, the resistivity of the barrier film is higher than that of the conductive material (metal) such as copper, which is the object to be polished, and the barrier film has a higher oxidation (dissolution) potential than the conductive material. Therefore, it is difficult to control the electrolysis voltage. For example, in bulk polishing, if the polishing is continued with a high voltage set to increase the polishing rate, the protective film forming agent loses the protective effect on the portion that should be protected originally, or the conductive material having a significantly different resistivity. Abnormal machining is likely to occur because the electric field concentrates on the interface with the barrier film.

  In the initial stage of polishing, where the uneven step on the surface is generally large, the polishing pad has a sufficient difference in surface pressure between the surface pressure acting on the convex portion and the surface pressure acting on the concave portion. The protective film is removed by the polishing pad, and the polishing proceeds while the recess is protected by the protective film. As a result, surface irregularities are gradually eliminated. However, as the unevenness of the surface becomes smaller as the polishing progresses, the surface pressure difference with respect to the unevenness gradually becomes smaller, so the protective film formed on the part where overpolishing is desired is resistant to polishing of the polishing pad. If the barrier film is not present, the protective property is insufficient, and if the barrier film is exposed, a strong protective property is required.

  Electropolishing as used herein refers to a polishing method in which a conductive substance and a counter electrode are electrically connected to each other by an electrolytic solution, and the conductive substance is processed by an electrochemical action. Including polishing. Chemical mechanical polishing (CMP) was developed for the purpose of planarization of VLSI devices (planarization of the interlayer film of multilayer wiring) and is a wet mechanochemical that utilizes the solid-liquid reaction between the workpiece and polishing liquid. It is a processing method. Electrochemical mechanical polishing is a polishing method in which an electrically conductive substance and a counter electrode are electrically connected with an electrolyte solution, and the conductive substance is processed by an electrochemical action and a mechanical action.

  Thus, when applying electropolishing to a semiconductor manufacturing process, if an attempt is made to expose the barrier film by electropolishing, there is a problem that conductive material such as wiring metal that should be left is overpolished (dishing). For this reason, such over-polishing for conductive materials such as wiring metal is eliminated, and when the barrier film between the wiring portions (field portion and space portion) is exposed by polishing, dishing or barrier film and metal (conductive material) A polishing method that does not cause etching at the interface is required.

  The present invention has been made in view of the above circumstances, and in particular, in polishing a conductive material such as copper formed on a substrate surface in a semiconductor manufacturing process, while ensuring a higher processing speed for the conductive material with a low applied voltage. Get a processed surface with high planarization characteristics, remove unwanted conductive material and expose the barrier film without causing dishing or erosion, etching at the interface between the barrier film and metal (conductive material) An object of the present invention is to provide an electrolytic solution for electropolishing and an electropolishing method which can be performed.

  The invention described in claim 1 is an electrolytic solution used for electropolishing that polishes a conductive material on the surface of an object to be polished, and includes one or more organic acids or salts thereof and one strong acid having a sulfonic acid group. An electrolytic solution for electropolishing which is an aqueous solution containing the above, a corrosion inhibitor, and a water-soluble polymer compound.

  By performing electropolishing using an electrolytic solution containing both one or more organic acids or salts thereof and one or more strong acids having a sulfonic acid group, a high processing speed for a conductive material at a lower applied voltage Is obtained. Thereby, since the processing speed for the conductive material can be increased without increasing the applied voltage, it is possible to suppress an increase in the roughness of the processed surface as the processing speed increases. Furthermore, by performing electrolytic polishing using an electrolytic solution containing a corrosion inhibitor and a water-soluble polymer compound, generation of surface defects such as pits can be suppressed, and a processed surface with good flatness can be obtained.

The invention according to claim 2 is the electrolytic solution for electropolishing according to claim 1, wherein the organic acid has a carboxyl group.
An organic acid having a carboxyl group easily forms a soluble complex with a metal ion dissolved by an electrolytic reaction, and facilitates diffusion of the metal ion. Therefore, by using an organic acid having a carboxyl group, the processing speed for the conductive substance can be increased.

The invention according to claim 3 is the electrolytic solution for electropolishing according to claim 2, wherein the organic acid further has a hydroxy group.
An organic acid having both a carboxyl group and a hydroxy group easily forms a soluble complex with a metal ion dissolved by an electrolytic reaction. Therefore, by using an organic acid having both a carboxyl group and a hydroxy group, the processing speed for the conductive material can be increased.

In the invention described in claim 4, the organic acid is acetic acid, propionic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, citric acid, aconitic acid, glyoxylic acid, glycol. 2. The electrolytic solution for electropolishing according to claim 1, wherein the electrolyte is one or two or more selected from the group consisting of acid, lactic acid, gluconic acid, malic acid, and tartaric acid.
The invention according to claim 5 is the electrolytic solution for electropolishing according to claim 1, wherein the concentration of the organic acid is 0.1 to 80% by weight.

According to a sixth aspect of the present invention, the strong acid having a sulfonic acid group is methanesulfonic acid, benzenesulfonic acid, taurine, cysteic acid, alkylbenzenesulfonic acid having 1 to 6 carbon atoms in total, or trifluoromethanesulfone. The electrolytic solution for electropolishing according to claim 1, wherein the electrolytic solution is one or more of acid and fluorosulfonic acid.
The invention according to claim 7 is the electrolytic solution for electropolishing according to claim 1, wherein the concentration of the strong acid having a sulfonic acid group is 0.1 to 20% by weight.

The invention according to claim 8 is the electrolytic solution for electropolishing according to claim 1, wherein the corrosion inhibitor is at least one selected from the group of benzotriazole and derivatives thereof.
A corrosion inhibitor composed of benzotriazole and its derivatives is highly effective as a processed surface protective film during electropolishing, and good step resolution can be obtained by using a corrosion inhibitor composed of benzotriazole and its derivatives. Examples of benzotriazole and derivatives thereof include benzotriazole, tolyltriazole, 1-hydroxybenzotriazole, 4-hydroxybenzotriazole, 5-chlorobenzotriazole, benzotriazole-5-carboxylic acid, and 5-nitrobenzotriazole. .

  The invention according to claim 9 is the electrolytic solution for electropolishing according to claim 8, wherein the concentration of the corrosion inhibitor is 0.001 to 5% by weight.

The invention according to claim 10 is characterized in that the water-soluble polymer compound is polyacrylic acid or a salt thereof, polymethacrylic acid or a salt thereof, polyethylene glycol, polyisopropylacrylamide, polydimethylacrylamide, polymethacrylamide, polymethoxyethylene, The electrolytic solution for electropolishing according to claim 1, wherein the electrolytic solution is one or more selected from polyvinyl alcohol, hydroxyethyl cellulose, carboxymethyl cellulose, and polyvinyl pyrrolidone.
The invention according to claim 11 is the electrolytic solution for electropolishing according to claim 1, wherein the concentration of the water-soluble polymer compound is 0.005 to 5% by weight.

The invention according to claim 12 is the electrolytic solution for electropolishing according to any one of claims 1 to 11, further comprising abrasive grains.
In electrolytic polishing, by using an electrolytic solution containing abrasive grains, the processing speed can be increased and defects and roughness of the processed surface can be suppressed. As an abrasive grain, one or more types chosen from alumina, colloidal silica, fumed silica, zirconia oxide, cerium oxide, titanium oxide, and manganese oxide are mentioned.

The invention according to claim 13 is the electrolytic solution for electropolishing according to claim 12, wherein the concentration of the abrasive grains is 0.01 to 10% by weight.
The invention according to claim 14 is the electrolytic solution for electropolishing according to any one of claims 1 to 13, further comprising a surfactant.
In the electrolytic polishing, by using an electrolytic solution containing a surfactant, it is possible to improve the dispersibility of the abrasive grains and further suppress the roughness of the polished surface.

The invention according to claim 15 is the electrolytic solution for electropolishing according to any one of claims 1 to 14, wherein the conductivity is 5 to 200 mS / cm.
By using electrolytic solutions having different electrical conductivities during electropolishing, the processing speed obtained with the same applied voltage varies. Therefore, by adjusting the conductivity of the electrolytic solution, the electrolytic solution can be adjusted so that a desired processing speed can be obtained at a certain voltage.

The invention according to claim 16 is the electrolytic solution for electropolishing according to any one of claims 1 to 15, wherein the pH is 2 to 10.
By adjusting the pH of the electrolytic solution, it is possible to prepare an optimal electrolytic solution for each of processing speed, level difference elimination property, and surface roughness.

The invention according to claim 17 is the electrolytic solution for electropolishing according to any one of claims 1 to 16, wherein 0.001 to 10% by weight of the conductive substance is contained in a component. is there.
When the conductive material to be polished is previously dissolved in the electrolytic solution, the resistance at the interface between the electrolytic solution and the conductive material is suppressed, and polishing including the conductive material from the surface of the polishing target during polishing is performed. Diffusion of the product into the electrolyte is promoted. As a result, the polishing rate is improved and surface roughness of the polished surface can be suppressed.

  The invention according to claim 18 is an electrolytic solution used for electrolytic polishing for polishing a conductive substance on the surface of an object to be polished, wherein the composition of the electrolytic solution is (a) 2 to 80 with respect to the total composition weight. % By weight organic acid, (b) a strong acid having 2-20% by weight sulfonic acid groups, (c) 0.01-1% by weight corrosion inhibitor, (d) 0.01-1% by weight water-soluble Electrolysis for electropolishing comprising a polymer compound, (e) 0.01 to 2% by weight of abrasive grains, and (f) 0.01 to 1% by weight of a surfactant, wherein the pH is adjusted to 2 to 10 It is a liquid.

  The invention according to claim 19 is an electrolytic polishing method for polishing a conductive material on the surface of an object to be polished, wherein the conductive material is polished with a polishing pad in the presence of the electrolytic solution according to any one of claims 1 to 18. A voltage is applied between the conductive material and the counter electrode while rubbing the surface of the conductive material.

  According to a twentieth aspect of the present invention, an electrolyte is present between a conductive material formed on a barrier film on a surface of an object to be polished and a counter electrode disposed at a position facing the conductive material. When removing the conductive material other than the wiring portion in which the conductive material is embedded in the wiring recess by applying a voltage while rubbing the surface of the conductive material with a polishing pad, (a) an organic acid or its Using the electrolytic solution comprising one or more kinds of salts, (b) one or more strong acids having a sulfonic acid group, (c) a corrosion inhibitor, and (d) a water-soluble polymer compound, The conductive material located above the wiring portion is polished at a slower rate than the conductive material located outside the upper portion of the wiring portion, and the conductive material located above the wiring portion is located outside the upper portion of the wiring portion. A first step of forming a convex shape with respect to the conductive material; An electropolishing method characterized by comprising a second step of polishing a conductive material located on a portion other than the upper portion of the wiring portion until the barrier film is exposed at the same time as polishing the convex conductive material formed by the step. is there.

  For example, the conductive material located at the top of the wiring part where the conductive material is embedded in the wiring recess is slower than the conductive material located outside the upper part of the wiring part (between the wiring part including the field part and the space part) The conductive material located on the upper part of the wiring part is made convex with respect to the conductive substance located between the wiring parts until the barrier film is exposed together with the conductive substance located between the wiring parts. By polishing, the amount of dishing when the conductive material located between the wiring portions is removed and the barrier film begins to be exposed can be reduced. Dishing due to overpolishing of the conductive material (wiring metal) and the barrier film and metal ( It is possible to polish without leaving the conductive material between the wiring portions in a state where the occurrence of etching at the interface of the conductive material) is as small as possible.

The invention according to claim 21 is the electrolytic polishing method according to claim 20, wherein the pH of the electrolytic solution is adjusted to 3 to 4.5.
Thereby, in the initial uneven | corrugated shape of the surface of an electroconductive substance, electropolishing can be performed, for example, forming the protective film which has sufficient tolerance on the recessed part surface with little pad press influence. Here, when electrolytic polishing is performed using an electrolytic solution having a pH of 4.5 or more, the strength of the protective film formed on the concave surface is insufficient. It becomes difficult to make the upper shape convex during polishing. On the other hand, when electrolytic polishing is performed using an electrolytic solution having a pH lower than 3, not only the concave portion does not become convex due to excessive etching, but also the level of unevenness is poor and the roughness of the polished surface increases.

The invention according to claim 22 is the electrolytic polishing method according to claim 20 or 21, wherein the electrolytic solution further contains abrasive grains and a surfactant.
By performing electropolishing using an electrolytic solution containing abrasive grains, it is possible to prevent the polished surface from becoming rough or causing defects on the polished surface. Further, by further including a surfactant in the electrolytic solution, it is possible to improve the dispersibility of the abrasive grains and further suppress the roughness of the polished surface.

23. The electropolishing method according to claim 20, wherein the corrosion inhibitor is at least one selected from the group of benzotriazole and derivatives thereof. It is.
24. The invention according to claim 24, wherein the one or more corrosion inhibitors selected from the group of benzotriazole derivatives are 5-methyl-1H-benzotriazole. This is an electrolytic polishing method.

The invention according to claim 25 is characterized in that the corrosion inhibitor is 3-amino-5-methyl-4H-1,2,4-triazole. This is an electrolytic polishing method.
The invention according to claim 26 is the electrolytic polishing method according to any one of claims 20 to 22, wherein the corrosion inhibitor is at least one selected from the group of bismuthiol and derivatives thereof. is there.
The invention according to claim 27 is characterized in that the corrosion inhibitor is at least one selected from the group of salicylaldehyde and derivatives thereof. This is an electrolytic polishing method.

The invention according to claim 28 is the electropolishing method according to any one of claims 20 to 27, wherein the remaining film thickness of the conductive material is detected by a change in eddy current.
Changes in the film thickness of the conductive material that is the object to be polished and the exposure state of the barrier film can be monitored by sensing changes in the eddy current, and this is fed back, for example, between the conductive material and the counter electrode. By controlling the voltage applied during this period, it is possible to prevent the conductive material (wiring metal) embedded in the trench or the like from being excessively polished after the exposure of the barrier film.

According to the electrolytic solution for electrolytic processing of the present invention, for example, when electropolishing (processing) a conductive material such as copper formed on the surface of a substrate, excessive etching is prevented at a low processing pressure and at a higher processing speed. However, it is possible to process with good planarization characteristics.
According to the electrolytic polishing method of the present invention, for example, when wiring is formed by removing excess wiring metal (conductive material) such as copper on the barrier film by polishing, dishing due to overpolishing of the wiring metal and the barrier film Polishing can be performed without leaving the conductive material between the wiring portions in a state where the occurrence of etching at the interface of the metal (conductive material) is as small as possible.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following example, an example in which an unnecessary portion of the copper (and seed film) of the wiring material formed on the surface of the barrier film of the substrate as an object to be polished is removed to expose the barrier film.

  FIG. 2 is a plan view showing an example of an electropolishing apparatus, and FIG. 3 is a longitudinal front view of FIG. In this electrolytic polishing apparatus, for example, as shown in FIG. 1B, copper plating is applied to the surface to fill the via hole 26 and the trench 28 as the wiring recess with the copper 34 as the wiring metal and A substrate (polishing object) W on which copper 34 is deposited on the mask 24 is prepared, and the surface of this substrate is subjected to a polishing process to form copper 34 (and a seed film 32 as a conductive material on the hard mask 24). ) And thereby used to expose the barrier film 30, as shown in FIG. 1 (c). Further, by removing the barrier film 30 on the hard mask 24, as shown in FIG. 1D, an upper wiring 36 made of copper 34 is formed inside the insulating films 20 and 22.

  As shown in FIGS. 2 and 3, the electrolytic polishing apparatus includes a rotatable polishing table (turn table) 50 and upper and lower surfaces that hold the substrate W detachably with the surface (formation surface of the copper 34) facing downward. A movable and rotatable substrate holder (polishing head) 52, and surroundings of the polishing table 50 and the substrate holder 52, an electrolytic solution or pure water supplied toward the upper surface of the polishing table 50 during and after polishing A bottomed cylindrical processing chamber 54 is provided to prevent the liquid from splashing outside. At the side of the processing chamber 54, there is provided a discharge port 54a for discharging the liquid accumulated inside to the outside. The substrate holder (polishing head) 52 is configured to be movable between a predetermined polishing position on the polishing table 50 and a substrate delivery position on the side of the polishing position.

  On the upper surface of the polishing table 50, a disk-shaped processing electrode 56 having a size covering almost the entire region of the polishing table 50 is disposed. The upper surface of the processing electrode 56 is covered with a polishing pad (polishing cloth) 58 over the entire region. The upper surface of the polishing pad 58 is a polishing surface. Inside the polishing pad 58, a large number of through holes 58a penetrating vertically are provided. Thereby, the liquid such as the electrolyte supplied to the upper surface of the polishing table 50 is held inside the polishing pad 58. During polishing, the processing electrode 56 and a conductive material such as copper 34 provided on the surface of the substrate W are electrically connected through the electrolytic solution held in the through hole 58a of the polishing pad 58. The polishing pad 58 may be a CMP polishing pad. In this example, the polishing pad 58 is composed of an IC-1000 manufactured by Nitta Haas having a large number of through holes 58a on the entire surface.

  If there are through holes over the entire surface, the entire polishing pad 58 may be formed with a lattice-like or annular groove. Further, if the polishing pad 58 itself has liquid permeability, the polishing pad 58 may not necessarily have a through hole.

  An electrolytic solution supply nozzle 60 is disposed above the polishing table 50 and supplies an electrolytic solution toward the upper surface of the polishing table 50 during polishing. The electrolytic solution supply nozzle 60 extends from an electrolytic solution storage tank 62 that temporarily stores the electrolytic solution, and an electrolytic solution supply line 64 in which an electrolytic solution supply unit (not shown) such as a tube pump, a diaphragm pump, or a bellows pump is provided. It is connected to the. Further, a pure water supply nozzle 66 is disposed above the polishing table 50 to supply rinse and cleaning pure water toward the upper surface of the polishing table 50 after polishing.

  In this example, an additive component that is likely to precipitate or decompose is stored in a separate storage container 68 from the electrolytic solution storage tank 62, and the storage container stores the electrolytic solution stored in the electrolytic solution storage tank 62. While adding the additive components stored in 68, an electrolyte prepared under predetermined conditions is supplied from the electrolyte supply nozzle 60 toward the upper surface of the polishing table 50. Without providing the storage container 68, the electrolyte prepared under predetermined conditions and stored in the electrolyte storage tank 62 may be supplied directly from the electrolyte supply nozzle 60 toward the upper surface of the polishing table 50. Good.

  A cylindrical power supply electrode 70 is disposed so as to be positioned outside the polishing table 50 in the processing chamber 54 so that the upper surface is substantially flush with the surface of the polishing pad 58. Thus, when the substrate holder 52 is lowered and the substrate W held by the substrate holder 52 is pressed against the polishing pad 58 with a predetermined pressing force, the upper surface of the power supply electrode 70 is made of copper 34 at the outer peripheral portion of the substrate W. The surface is contacted with the surface (lower surface) of the conductive material such as a power source, and thereby power is supplied to the conductive material as the object to be polished. The power supply electrode 70 is connected to the anode of a power source 72 that can control the voltage to be applied and the voltage waveform, and the processing electrode 56 is connected to the cathode of the power source 72.

  Next, electropolishing using the electropolishing apparatus shown in FIGS. 2 and 3 will be described. First, the substrate holder 52 holding the substrate W with the surface facing downward is positioned at a predetermined position above the polishing table 50. Next, while rotating the polishing table 50, the electrolyte solution is supplied from the electrolyte solution supply nozzle 60 toward the upper surface, and at the same time, the substrate holder 52 is lowered while rotating together with the substrate W, thereby pushing the substrate W to a predetermined level. Press toward the polishing pad 58 with pressure. When the feeding electrode 70 contacts the copper 34 on the surface of the substrate W, the feeding electrode 70 is connected to the anode of the power source 72 and the processing electrode 56 is connected to the cathode of the power source 72. A predetermined voltage is applied to the copper 34. Thus, the copper 34 is polished by causing an electrolytic reaction on the surface of the copper 34 serving as an anode. At this time, the space between the processing electrode 56 and the surface of the copper 34 of the substrate W is filled with the electrolytic solution through the through hole 58a provided in the polishing pad 58.

  That is, the surface of the copper 34 of the substrate W serving as the anode is anodized, and at the same time, a protective film is formed on the surface of the copper 34 by the corrosion inhibitor and the water-soluble polymer compound in the electrolytic solution. At this time, the copper 34 of the substrate W pressed toward the polishing pad 58 is moved relative to the polishing pad 58 and mechanically polished by the rotational motion of the substrate W and the rotational motion of the polishing table 50. The protective film formed in the concave portion existing on the surface of the copper 34 of W is not removed, and the electropolishing proceeds only to the protective film formed in the convex portion existing on the surface of the copper 34. As described above, by selectively removing only the protective film of the convex portion from the protective film formed on the concave and convex portions present on the surface of the copper 34 of the substrate W, the copper 34 has its surface flattened. Polished.

  Then, after the electropolishing is completed, the processing electrode 56 and the feeding electrode 70 are disconnected from the power source 72, the supply of the electrolytic solution is stopped, the substrate holder 52 is raised, and the polished substrate W is then transferred to the substrate holder 52. Transport to process.

Next, an electrolytic solution used in the electropolishing apparatus shown in FIGS. 2 and 3 will be described.
The electrolyte is (1) one or more organic acids or salts thereof, (2) one or more strong acids having a sulfonic acid group, (3) a corrosion inhibitor (nitrogen-containing heterocyclic compound), and (4) water-soluble. It contains a polymer compound, (5) a pH adjuster, (6) abrasive grains, and (7) a surfactant. Further, the electrolytic solution may contain (8) a conductive substance to be polished, such as copper, in its components.

  In this example, copper is polished, but as the conductive material to be polished, in addition to copper, for example, copper alloy, silver or its alloy, gold or its alloy, aluminum or its alloy Tungsten, alloys thereof, nitrides, carbides, nitrogen carbides, titanium, alloys thereof, nitrides, carbides, nitrogen carbides, tantalum, alloys thereof, nitrides, carbides, nitrogen carbides, ruthenium, alloys thereof, and combinations thereof. Can be mentioned.

Each component contained in the electrolytic solution will be described below.
The organic acid contained in the electrolytic solution needs to form a soluble complex with a metal (conductive substance) such as copper to be polished. That is, it is coordinated with a metal such as copper and is dissolved in an aqueous solution, and at least an organic acid needs to be dissolved in water alone. The organic acid preferably has one or more carboxyl groups (—COOH) in the molecule and one or more hydroxy groups (—OH) together with the carboxyl groups. These organic acids also have a pH buffering action that stabilizes the pH of the liquid.

  Examples of the carboxylic acid having one carboxyl group that can be preferably used in the electrolyte include formic acid, acetic acid, propionic acid, n-butyric acid, isobutyric acid, n-valeric acid, isovaleric acid, and sorbic acid. , Glyoxylic acid, pyruvic acid, levulinic acid, benzoic acid, m-toluic acid, or acetylsalicylic acid. In addition, carboxylic acids having two or more carboxyl groups, which are organic acids that can be preferably used in the electrolyte, include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, maleic acid. Examples thereof include acid, fumaric acid, citraconic acid, mesaconic acid, itaconic acid, α-ketoglutaric acid, aconitic acid, phthalic acid, and pyromellitic acid.

  In addition, examples of carboxylic acids having at least one hydroxy group together with a carboxyl group, which are organic acids that can be preferably used in an electrolytic solution, include citric acid, glycolic acid, lactic acid, gluconic acid, malic acid, tartaric acid, oxalacetic acid, Examples include salicylic acid, m-hydroxybenzoic acid, gentisic acid, protocatechuic acid, gallic acid, glucuronic acid, sialic acid, or ascorbic acid.

Examples of these carboxylic acid salts include potassium salts, ammonium salts, alkylamine salts, and hydroxylamine salts. One of these may be added to the electrolytic solution, or a mixture of two or more may be added.
Among the organic acid groups listed above, those that can be particularly preferably used are malonic acid, succinic acid, citric acid, glycolic acid, lactic acid, gluconic acid, malic acid, or tartaric acid. It has been confirmed that when a polishing experiment is performed using an electrolytic solution to which these organic acids are added, a smooth processed surface can be obtained at a relatively high processing speed.

  The concentration of the organic acid needs to be equal to or lower than the saturation solubility at the processing temperature. This is because when the saturation solubility is exceeded, the organic acid is precipitated in the electrolytic solution and stable processing cannot be performed. For example, the solubility of maleic acid is 78% by weight (25 ° C.). On the other hand, if the concentration of the organic acid is lower than 0.1%, the supply amount of the organic acid coordinated with the dissolved metal to the surface of the processed portion is insufficient, the processing does not proceed quickly, and the processing surface becomes rough. Problems arise. On the other hand, if the concentration is low, the pH buffering action is not sufficient. For the above reasons, the concentration of the organic acid is preferably 0.1 to 80% by weight, and more preferably 1 to 50% by weight.

The strong acid having a sulfonic acid group contained in the electrolytic solution is for accelerating the etching action and increasing the conductivity of the electrolytic solution so that a current for processing can easily flow. Here, the strong acid means a pKa having a logarithm of the reciprocal of the first dissociation constant indicating the strength of the acid is 3 or less.
In general, when a strong acid is used, the potential at which copper dissolution begins is low. That is, copper can be processed with a low applied voltage. However, when sulfuric acid, nitric acid or perchloric acid is used, the roughening of the processed surface is severe due to copper etching, etc., and phosphoric acid has high viscosity in the concentration range where surface gloss can be obtained, so the voltage required for processing copper There are problems such as relatively high. On the other hand, for example, when methanesulfonic acid is used, it is confirmed that the voltage required for copper processing is low, the processing surface is relatively smooth, and good processing characteristics can be obtained.

  The strong acid having a sulfonic acid group that can be preferably used includes methanesulfonic acid, benzenesulfonic acid, taurine, cysteic acid, alkylbenzenesulfonic acid having 1 to 6 carbon atoms in total, trifluoromethanesulfonic acid, or Examples thereof include fluorosulfonic acid, and one or more of these can be used. The concentration of the strong acid having a sulfonic acid group is preferably 0.1 to 20% by weight, and more preferably 5 to 20% by weight. If the concentration of the strong acid having a sulfonic acid group is too low, the electrical conductivity of the electrolytic solution is lowered, and it becomes difficult for current to flow. For this reason, it is preferable that the density | concentration of the strong acid which has a sulfonic acid group is 5 weight% or more. On the other hand, when the concentration of the strong acid having a sulfonic acid group exceeds 20% by weight, the saturated solubility of the organic acid and other components in the electrolytic solution may be reduced, thereby causing precipitation.

  The corrosion inhibitor contained in the electrolytic solution is preferably a nitrogen-containing heterocyclic compound, and forms a compound with a metal such as copper to be processed, and forms a protective film on the metal surface, thereby corroding the metal. It may be a compound known as a compound that suppresses the above. Such a corrosion inhibitor has an effect of promoting flattening in order to suppress excessive processing and prevent dishing and the like.

  Examples of corrosion inhibitors that can be preferably used include benzotriazole and its derivatives, which are conventionally known corrosion inhibitors for copper. In addition to the above-described effects of promoting flattening, indole, 2-ethylimidazole, benzimidazole, 2-mercaptobenzimidazole, 3-amino-1,2,4-triazole, 3-amino- 5-methyl-4H-1,2,4-triazole, 5-amino-1H-tetrazole, 2-mercaptobenzothiazole, 2-mercaptobenzothiazole sodium, 2-methylbenzothiazole, (2-benzothiazolylthio) acetic acid, 3- (2-benzothiazolylthio) propionic acid, 2-mercapto-2-thiazoline, 2-mercaptobenzoxazole, 2,5-dimercapto-1,3,4-thiadiazole, 5-methyl-1,3,4 -Thiadiazole-2-thiol, 5-amino-1,3,4-thiadiazole-2 Thiol, pyridine, phenazine, acridine, 1-hydroxypyridine-2-thione, 2-aminopyridine, 2-aminopyrimidine, trithiocyanuric acid, 2-dibutylamino-4,6-dimercapto-s-triazine, 2-anilino-4 , 6-dimercapto-s-triazine, 6-aminopurine, 6-thioguanine, and combinations thereof.

  When the concentration of the corrosion inhibitor is low, the formation of a protective film becomes insufficient, so that excessive etching occurs in a metal such as copper and a flat processed surface cannot be obtained. On the other hand, even if it is below the saturation solubility, if the concentration of the corrosion inhibitor is too high, the protective surface is excessively formed on the metal surface such as copper, the processing speed is reduced, and the processing surface cannot be uniformly processed. It also causes rough and pits. From the above, the concentration of the corrosion inhibitor is preferably 0.001 to 5% by weight, and more preferably 0.02 to 2% by weight.

  The water-soluble polymer compound contained in the electrolytic solution is effective in forming a protective film together with the corrosion inhibitor, suppressing excessive etching, and flattening the surface of a metal such as copper. In addition, in an electrolytic solution containing a water-soluble polymer compound, the viscosity of the electrolytic solution near the surface of a metal surface (processed surface) such as copper is increased, so that a viscous film is formed on minute concave and convex portions present on the metal surface. Is formed, and fine irregularities are also polished to obtain a glossy surface.

  Among the water-soluble polymer compounds that can be preferably used, polyacrylic acid or a salt thereof, polymethacrylic acid or a salt thereof, polyethylene glycol, polyisopropylacrylamide, polydimethylacrylamide, One or more types selected from methacrylamide, polymethoxyethylene, polyvinyl alcohol, hydroxyethyl cellulose, carboxymethyl cellulose, polyvinyl pyrrolidone, and the like can be given.

  As these water-soluble polymer compounds, those having a mass average molecular weight of 1,000 to 500,000 can be used. If the weight average molecular weight exceeds 500,000, it will not dissolve in the electrolyte solution and cause aggregation with corrosion inhibitors and abrasive grains. If the weight average molecular weight is less than 1,000, sufficient protection is provided for metal surfaces such as copper. A film cannot be formed and the planarization performance deteriorates. The mass average molecular weight of the water-soluble polymer compound is preferably 1,000 to 100,000, and more preferably 2,000 to 25,000.

  The concentration of the water-soluble polymer compound is preferably 0.005 to 5% by weight and 0.01 to 2% by weight in order not to reduce the processing rate of electropolishing and to suppress excessive processing action. More preferably it is.

  In order to adjust the pH of the electrolytic solution, a pH adjusting agent may be added to the electrolytic solution. As a preferable pH adjuster, alkali is mainly used, and one or more kinds selected from ammonia, alkylamine, hydroxyamine, polyamine, alkali metal compound (for example, potassium hydroxide), and alkaline earth metal compound can be selected. The alkali concentration is generally 0.1 to 20% by weight, and may be appropriately determined depending on the use of the workpiece, the material, the concentration of the organic acid or organic acid salt and strong acid contained, and the pH to be adjusted.

  The pH of a preferable electrolytic solution is 2-10. When the pH of the electrolytic solution is low, corrosion resistance must be taken into consideration when selecting the material for the electropolishing apparatus, and the processing speed increases, while the roughness of the processed surface increases, resulting in excessive etching of metals such as copper. As a result, it becomes difficult to obtain a flat processed surface. When the pH of the electrolytic solution is high, formation of a protective film between the corrosion inhibitor and / or the water-soluble polymer compound and copper may be insufficient, and the planarization action may be insufficient. Therefore, the pH of the electrolytic solution is particularly preferably 3 to 6 when flattening is required on a glossy surface having a high processing speed and no surface roughness as in a copper wiring process of a semiconductor substrate.

  The electrolyte solution preferably contains abrasive grains. The abrasive grains have an action of mechanically removing metals such as copper, but in the present invention, an action of mechanically removing the metal protective film formed of the corrosion inhibitor and the water-soluble polymer compound appropriately. There is also. By the action of the abrasive grains, an extra protective film is removed, and the processing speed in electropolishing is sufficiently increased.

  As an abrasive grain that can be preferably used as an electrolytic solution, one or more kinds selected from alumina, colloidal silica, fumed silica, zirconium oxide, cerium oxide, titanium oxide, and manganese oxide can be exemplified. Among these, alumina, colloidal silica, or fumed silica is preferably used.

  The concentration of abrasive grains in the electrolytic solution in the case of effectively functioning as electrolytic polishing is preferably 10% by weight or less. In order to exert the effect of abrasive grains, the concentration of abrasive grains is 0.01% by weight. That is necessary. On the other hand, the effect of removing the protective film is effective by using fixed abrasive grains such as a polishing pad even if there are no abrasive grains used dispersed in the electrolyte, and contacting the polishing pad with a metal surface such as copper. Therefore, in such a case, there is no need to have abrasive grains in the electrolytic solution, and of course, combined use with fixed abrasive grains is also possible. When using abrasive grains, if the concentration of the abrasive grains exceeds 10% by weight, the aggregation of the abrasive grains increases, and the viscosity of the electrolytic solution may become extremely high. Electropolishing by depositing abrasive grains on the work surface may occur. It may cause inhibition and scratching. For this reason, the optimal abrasive grain concentration is 0.05 to 2% by weight.

  The electrolytic solution may contain a surfactant. The surfactant is not particularly limited as long as it improves the dispersibility of the abrasive grains, and any of cationic, anionic, amphoteric and nonionic can be used. For example, as the anionic surfactant, alkyl ether carboxylate, alkyl sulfate, alkyl sulfonate, amide sulfonate, alkyl allyl sulfonate, naphthalene sulfonate, or a formalin condensate thereof is used. As the cationic surfactant, for example, an aliphatic amine salt or an aliphatic ammonium salt is used. These are appropriately selected and used depending on the concentration of the abrasive grains and the pH of the electrolytic solution. The surfactant is preferably an anionic surfactant, particularly preferably an alkyl sulfonate or a naphthalene sulfonic acid formalin condensate.

  The conductivity of the electrolytic solution is preferably 5 to 200 mS / cm. If the electrolyte conductivity is low, the applied voltage or current must be increased in order to increase the processing speed. In this case, however, the current efficiency decreases due to the generation of oxygen, the generation of pits on the processed surface, and protection. There is an adverse effect on the flattening action due to the destruction of the film. Therefore, it is desired to perform electropolishing at a lower voltage, and for this purpose, the conductivity of the electrolytic solution is preferably 5 to 200 mS / cm.

  In order to suppress an increase in the polishing rate in electrolytic polishing and to suppress surface roughness of the polished surface, the electrolytic solution preferably contains a conductive substance to be polished, such as copper, in its components. The concentration of the conductive substance such as copper in the electrolytic solution is 0.001% by weight or more, more preferably 0.005% by weight or more, and still more preferably 0.01% by weight or more. This promotes diffusion of a conductive substance from the surface of the object to be polished, such as copper, or a polishing product containing the same into the electrolytic solution during polishing. The concentration of the conductive substance, for example, copper, in the electrolytic solution is 10% or less, preferably 1% or less. This is because when the concentration of the conductive material is 1% or more, the conductive material component in the electrolytic solution is likely to consume other electrolytic solution components in the electrolytic solution. In the case where the conductive material is a compound, a plurality of conductive material components may be included in the electrolytic solution in accordance with the component ratio.

  Examples of the composition of the electrolyte include (1) 2 to 80% by weight organic acid, (2) 2 to 20% by weight sulfonic acid group strong acid, and (3) 0.01 to 1% by weight corrosion inhibition. An agent, (4) 0.01 to 1% by weight of a water-soluble polymer compound, (5) 0.01 to 2% by weight of abrasive grains, and (6) about 0.01 to 1% by weight of a surfactant. An aqueous solution is provided. The electrolyte solvent is deionized water, preferably ultrapure water.

  The electropolishing using the electrolytic solution of the present invention is a method in which the uneven surface of a conductive material such as copper formed on the surface of an object to be polished such as a substrate is protected by a corrosion inhibitor while the uneven surface of the conductive material is protected. The portion is preferentially processed and flattened, and is particularly effective for electrochemical mechanical polishing in which the surface of the conductive material is rubbed with a polishing pad while being electropolished. That is, first, after forming a protective film with a corrosion inhibitor to suppress excessive etching on the surface of the conductive material, the surface of the conductive material is rubbed with a polishing pad having hardness and flatness. The protective film formed on the convex surface of the conductive substance is selectively removed while leaving the protective film formed on the concave surface of the substance. Then, by conducting electropolishing, the convex portions of the conductive material can be processed preferentially, and the irregularities on the surface of the conductive material can be eliminated. As the polishing pad, for example, a polishing pad for CMP can be used.

Hereinafter, the results when a copper processing (polishing) experiment is performed using various electrolytic solutions and a self-made chip tester capable of processing a 40 mm diameter portion will be described. The chip testing machine can control the copper electrode potential, and while applying a voltage between the copper and the counter electrode, polishing is performed by polishing the exposed copper with a polishing pad affixed to the processing table. proceed. The polishing table rotation speed is 250 rpm (linear speed at 30 mm from the center is 0.78 m / s), surface pressure is 0.5 psi (35 g / cm ² ), and the current density or copper electrode potential is constant. Was polished (processed). However, in the case of confirming the effect of the corrosion inhibitor, it is also possible to measure the current density and the electrode potential in a state where the polishing pad is not in contact with the copper surface (surface pressure 0 psi).

The substrate used for processing has an oxide film (SiO ₂ ) with a thickness of about 250 nm, a barrier metal made of a TaN film with a thickness of 30 nm, a copper seed layer with a thickness of 100 nm, and a copper plating film with a thickness of 1500 nm on the surface. It is a silicon substrate made of a formed copper film-coated substrate (copper blanket wafer).

A. Table 1 shows the relationship between various organic acids and electrode potentials. A constant current density (40 mA / cm ² ) flows in the electrolytic solution while using the above-described chip tester and using an electrolytic solution with different types of organic acids. The electrode potential when copper is polished is shown. A low electrode potential means that a large amount of current flows when the same electrode potential is maintained, and the processing speed increases. Therefore, it is preferable that the electrode potential is low.

  In Table 1, organic acids other than ascorbic acid have a carboxyl group. From Table 1, it can be seen that the organic acid having a carboxyl group has a low electrode potential and is a preferable organic acid as compared with ascorbic acid having no carboxyl group (7.55 V vs. Ag / AgCl).

B. Table 2 shows the relationship between various strong acids and electrode potentials. Table 2 shows the electrodes when copper is polished by the above-mentioned chip tester so that a constant current density (40 mA / cm ² ) flows in the electrolyte while changing the type of strong acid. Indicates potential. Similar to Table 1, a low electrode potential means that a large amount of current flows when the same electrode potential is maintained, and the processing speed increases. Therefore, it is preferable that the electrode potential is low.

  From Table 2, the electrode potential in electropolishing using an electrolytic solution (No. 2) added with phosphoric acid is an electrolytic solution (No. 1) added with methanesulfonic acid or an electrolytic solution (No. 3) mixed with nitric acid. It can be seen that it is higher than the electropolishing performed. Moreover, in the electrolytic polishing using the electrolytic solution added with nitric acid (No. 3) or the electrolytic solution added with sulfuric acid (No. 4), the processed surface is rough, and the electrolytic solution added with methanesulfonic acid (No. 1) is used. The electrolytic polishing used was in a better processing state. Therefore, it can be seen that methanesulfonic acid is the most preferred electrolyte among these strong acids.

C. Decrease in electrode potential due to mixing of various organic acids and strong acid Table 3 shows electrode potentials when copper is processed using an electrolytic solution in which a strong acid is added to various organic acids and an electrolytic solution in which no strong acid is added. From Table 3, for example, in the case of malonic acid, the electrode potential is 4.51 [Vvs. Ag / AgCl] to 2.04 [Vvs. It can be seen that [Ag / AgCl] is lowered. These results show that the current density increases and the processing speed increases when compared with the same electrode potential by mixing organic acid and strong acid.

D. Effect of addition of corrosion inhibitor and water-soluble polymer compound Table 4 shows that 1M malonic acid + 1.4M methanesulfonic acid is used as the base electrolyte, and various corrosion inhibitors and water-soluble polymer compounds are added or added. In the above-described chip tester, 2 [Vvs. The result of having measured the current density in the state maintained at the electrode potential of [Ag / AgCl] is shown. Polishing is not performed (surface pressure 0 psi).

  From Table 4, the current density obtained from the liquid to which the corrosion inhibitor or both the corrosion inhibitor and the water-soluble polymer compound (numbers 2 to 24) are added is lower than the liquid to which these are not added (number 1). It can be seen that corrosion (electrolytic reaction) is suppressed. On the other hand, the addition of the water-soluble polymer compound alone (Nos. 25 to 30) does not show a decrease in current density, indicating that corrosion (electrolytic reaction) is not suppressed.

E. Effect of Abrasive Grains Using the electropolishing apparatus shown in FIGS. 2 and 3, the influence of the presence or absence of abrasive grains in the electrolytic solution on the surface roughness and processing speed of the processed surface was investigated. A substrate (substance to be polished) subjected to processing is a copper blanket wafer. As the polishing pad, a foamed polyurethane polishing pad (IC1000: manufactured by Nitta Haas Co., Ltd.) was used. Electropolishing was performed under the conditions of a polishing pressure of 0.5 psi (about 35 g / cm ² ), a relative speed of 1.6 m / s between the polishing pad and the center of the workpiece (substrate W), and an electrolytic solution amount of 100 ml / min. The planarization characteristics were evaluated by measuring the unevenness of the pattern formed on the substrate with a stylus type profiler (Dektak 3ST: ULVAC).

  That is, 1M malonic acid + 1.4M methanesulfonic acid + 0.3% benzotriazole + 0.49% polyacrylic acid (molecular weight: 5000) +0.7 methanol + 0.05% surfactant (β-naphthalenesulfonic acid formaldehyde condensate) MX2045L (manufactured by Kao Corporation), surface roughness and processing when copper is electropolished using an electrolytic solution in which abrasive grains are added to a solution of pH 4.3 and an electrolytic solution in which abrasive grains are not added The speed was compared. When electrolytic polishing of copper was performed using an electrolytic solution without adding abrasive grains, the surface roughness Rmax = 328 nm and the processing speed was 736 nm / min, whereas 0.5% silica abrasive grains were added. When electrolytic polishing of copper was performed using the electrolytic solution, the surface roughness Rmax = 49 nm and the processing speed was 777 nm / min. Thereby, it turned out that surface roughness is improved and processing speed improves by using the electrolyte solution which added the abrasive grain.

F. Effect of water-soluble polymer compound Using the electropolishing apparatus shown in FIGS. 2 and 3, the effect of the presence or absence of the water-soluble polymer compound in the electrolyte solution on the processing speed, level difference elimination of the processed surface, and surface roughness I investigated. The substrate (substance to be polished) subjected to processing is a copper plating pattern wafer (Sematech 854AZ). The polishing pressure is 1.5 psi, and the other conditions are the same as those in the case where the influence of the presence or absence of abrasive grains in the electrolytic solution on the surface roughness and processing speed of the processing surface is examined.

  In other words, 1M malonic acid + 1.4M methanesulfonic acid + 0.3% benzotriazole + 0.6% ammonium polyacrylate (molecular weight: 10,000) + 0.7% methanol + 0.05% surfactant MX2045L (formaldehyde β-naphthalene sulfonate) Condensation) When electrolytic polishing was carried out using an electrolyte solution having a pH of 3, a good processing speed, level difference elimination property and surface roughness were obtained.

  On the other hand, 1M malonic acid + 1.4M methanesulfonic acid + 0.1% benzotriazole + 0.7% methanol + 0.05% surfactant MX2045L (β-naphthalene) obtained by removing ammonium polyacrylate from the electrolytic solution described above. When electrolytic polishing was carried out using a sulfonic acid formaldehyde condensate) and an electrolyte solution having a pH of 3, good processing speed, level difference elimination property and surface roughness were not obtained. In particular, etch pits having a diameter of several μm and a depth of several hundred nm were generated on the processed surface. This is considered to be because ammonium polyacrylate, which is a water-soluble polymer compound, enhances the effect of the corrosion inhibitor and facilitates mechanical polishing.

G. Effect of Concentration of Conductive Substance Component in Electrolyte Solution Using the electropolishing apparatus shown in FIGS. 2 and 3, the presence or concentration of the electroconductive substance in the electrolyte solution, in this example, copper, is determined by the polishing rate. And the influence on surface roughness after polishing was investigated. A substrate (substance to be polished) subjected to processing is a copper blanket wafer. Polishing pressure 0.5 psi (1M malonic acid + 1.4M methanesulfonic acid + 0.3% benzotriazole + 0.6% ammonium polyacrylate (molecular weight: 10,000) +0.7 as an electrolyte under the condition of about 35 g / cm ² Copper (conducting substance) based on a solution of 0.5% methanol + 0.05% anionic surfactant (β-naphthalene sulfonic acid formaldehyde condensate), pH 3 and abrasive grains at a concentration of 0.5% The other conditions were the same as in the case of examining the influence of the presence or absence of abrasive grains in the electrolyte on the surface roughness and processing speed of the processed surface.

  4 and 5 show the copper concentration dependence of the surface roughness (Rmax) and the polishing rate after polishing. As shown in FIG. 4, when the copper concentration in the electrolytic solution increases and the surface roughness decreases, and when polishing is performed using an electrolytic solution having a copper concentration of 0.005% or more, an electrolytic solution containing no copper is used. It can be seen that a surface roughness of 1/2 or less can be obtained as compared with the case of polishing. Also, from FIG. 5, the polishing rate is about 10% higher when the copper concentration is polished using an electrolytic solution than copper, and compared with the case where the copper-free electrolytic solution is used for polishing. It can be seen that a polishing rate of 2.5 times or more can be obtained.

Next, an example of a process for removing an unnecessary portion of the wiring material formed on the surface of the barrier film of the substrate as an object to be polished and exposing the barrier film will be described.
In the electrolytic solution used for the process of exposing the barrier film (hereinafter referred to as the second electrolytic solution), the conductive material located above the wiring portion is polished at a slower rate than the conductive material located outside the upper portion of the wiring portion. Then, the first step of making the conductive material located above the wiring portion convex with respect to the conductive material located outside the upper portion of the wiring portion, and the convex shaped conductivity formed by the first step At the same time as polishing the material, the second step of polishing the conductive material located outside the upper portion of the wiring portion until the barrier film is exposed is performed without changing the electrolytic solution.
FIG. 6 is a longitudinal front view showing an example of an electropolishing apparatus used in this process. In the electropolishing apparatus shown in FIG. 6, the same or corresponding members as those in the electropolishing apparatus shown in FIGS.

  An electrolytic solution supply nozzle 60 is provided above the polishing table 50 and supplies an electrolytic solution (second electrolytic solution) for a barrier film exposure process (hereinafter, this process) toward the upper surface of the polishing table 50 during polishing. Has been placed. The electrolyte supply nozzle 60 extends from an electrolyte storage tank 62 that temporarily stores the second electrolyte, and includes an electrolyte supply line (not shown) such as a tube pump, a diaphragm pump, or a bellows pump. 64. Further, a pure water supply nozzle 66 is disposed above the polishing table 50 to supply rinse and cleaning pure water toward the upper surface of the polishing table 50 after polishing.

  In this example, an additive component that is likely to precipitate or decompose is stored in a separate storage container 68 from the electrolytic solution storage tank 62, and the second electrolytic solution stored in the electrolytic solution storage tank 62 is stored in the second electrolytic solution. While adding the additive components stored in the storage container 68, the second electrolyte prepared under predetermined conditions is supplied from the electrolyte supply nozzle 60 toward the upper surface of the polishing table 50. Without providing the storage container 68, the second electrolytic solution prepared under predetermined conditions and stored in the electrolytic solution storage tank 62 is supplied directly from the electrolytic solution supply nozzle 60 toward the upper surface of the polishing table 50. May be.

  The polishing table 50 is provided with a film thickness detection sensor 74 composed of, for example, an eddy current sensor for detecting the film thickness (remaining film thickness) of a conductive material such as copper 34 on the surface of the substrate W. It is buried exposed. An output signal from the film thickness detection sensor 74 is input to the control unit 76 via a slip ring (not shown). With the output signal from the control unit 76, a power source 72, a table driving unit 78 that rotates the polishing table 50, and A holder driving unit 80 for rotating and moving the substrate holder 52 up and down is controlled.

  The film thickness detection sensor 74 senses the film thickness, detects the polishing end point, and outputs a signal for finishing the polishing. The timing for stopping the applied voltage at the end of the polishing is preferably the order in which the application of the voltage is stopped and then the supply of the second electrolytic solution is ended so as not to impair the polishing performance.

Next, the second electrolytic solution used in the barrier film exposure process using the electropolishing apparatus shown in FIG. 6 will be described.
The second electrolyte includes (1) one or more organic acids or salts thereof, (2) one or more strong acids having a sulfonic acid group, (3) a corrosion inhibitor, (4) a water-soluble polymer compound, ( 5) A pH adjuster, (6) abrasive grains, and (7) a surfactant. The second electrolytic solution may contain (8) a conductive material to be polished, for example, copper, in its components.

  It is preferable that the 2nd electrolyte solution of this process is adjusted to pH 3-6, and it is more preferable that it is adjusted to pH 3-4.5. In other words, depending on the pH of the electrolytic solution, the oxidation state of the object to be polished (conductive material) such as copper and the interaction with the corrosion inhibitor, the water-soluble polymer compound and the organic acid are different. A difference appears in the quality of the protective film formed on the surface. For example, when a polymer compound is present in the formation of a complex of a corrosion inhibitor such as copper and BTA (benzotriazole), the protective action of BTA is weak and the electrolytic etching resistance is weak when the pH of the electrolyte is near neutral. On the other hand, it is considered that a dense and strong protective film is formed by setting the pH of the second electrolytic solution to 3 to 4.5.

  The organic acid contained in the second electrolytic solution of this process needs to form a soluble complex with a metal (conductive substance) such as copper to be polished, like the above-described electrolytic solution. That is, it is coordinated with a metal such as copper and is dissolved in an aqueous solution, and at least an organic acid needs to be dissolved in water alone. The organic acid is preferably one having at least one carboxyl group (—COOH) in the molecule, and one having at least one hydroxy group (—OH) together with the carboxyl group, as in the above-described electrolytic solution. Preferable specific examples of the organic acid include those similar to the above-described electrolytic solution.

  Among the organic acids, malonic acid, succinic acid, citric acid, glycolic acid, lactic acid, or gluconic acid can be particularly preferably used.

  The corrosion inhibitor contained in the second electrolytic solution is preferably a nitrogen-containing heterocyclic compound, and forms a compound with a metal such as copper to be polished, and forms a protective film on the metal surface. It may be a compound known as a compound that inhibits corrosion. Such a corrosion inhibitor has an effect of suppressing excessive polishing and preventing dishing and the like.

  Examples of corrosion inhibitors that can be preferably used include benzotriazole and its derivatives, which are conventionally known corrosion inhibitors for copper. Examples of benzotriazole and derivatives thereof include benzotriazole (BTA), 5-methyl-1H-benzotriazole (tolyltriazole), 1-hydroxybenzotriazole, 4-hydroxybenzotriazole, 5-chlorobenzotriazole, benzotriazole-5 Examples thereof include carboxylic acid and 5-nitrobenzotriazole. Benzotriazole and 5-methyl-1H-benzotriazole are preferred for making the surface state after processing a glossy surface with little roughness, together with the effect of inhibiting corrosion.

  The above-described excessive polishing is suppressed, and a protective film is formed on the concave surface of an object to be polished such as copper to have an effect of preventing dishing after clearing a conductive substance such as copper between wiring portions. In addition, indole, 2-ethylimidazole, benzimidazole, 2-mercaptobenzimidazole, 3-amino-1,2,4-triazole, 3-amino-5methyl-4H-1,2,4-triazole Derivatives of diazole such as 5-amino-1H-tetrazole, triazole, tetrazole, 2-mercaptobenzothiazole, 2-mercaptobenzothiazole sodium, 2-methylbenzothiazole, (2-benzothiazolylthio) acetic acid, 3 -(2-benzothiazolylthio) propionic acid, 2-mercapto-2-thiazoline, 2-merca Tobenzoxazole, 2,5-dimercapto-1,3,4-thiadiazole (bismuthiol), 5-methyl-1,3,4-thiadiazole-2-thiol, 5-amino-1,3,4-thiadiazole-2 Thiazole derivatives such as thiols, pyridine, phenazine, acridine, 1-hydroxypyridine-2-thione, 2-aminopyridine, 2-aminopyrimidine, trithiocyanuric acid, 2-dibutylamino-4,6-dimercapto-s-triazine , 2-anilino-4,6-dimercapto-s-triazine, 6-aminopurine, 6-thioguanine, thiourea, salicylic acid, salicylaldehyde, salicylic aldehyde derivatives such as salicylaldehyde oxime, and 8-chilinol, 2- Methyl-8-quinolinol (2-methyl-8-hydride One or more kinds selected from the group consisting of hydroxyquinolines such as (roxyquinoline) and combinations thereof.

  These are, for example, adsorbed on the surface of copper or a copper oxide, or formed a chelate complex or a polymer complex with copper or a copper oxide, thereby forming a concave surface of a polishing object such as copper. A strong protective film can be formed.

  The water-soluble polymer compound contained in the second electrolytic solution of this process is involved in the formation of a protective film together with a corrosion inhibitor, forms a uniform protective film, and suppresses excessive etching, thereby reducing the surface of a metal such as copper. It is effective in flattening. In addition, in an electrolytic solution containing a water-soluble polymer compound, the viscosity of the electrolytic solution in the vicinity of the surface of a metal surface (polished surface) such as copper is increased, so that a viscous film is formed on a minute uneven surface on the metal surface. Is formed, and fine irregularities are also polished to obtain a glossy surface.

  Among the water-soluble polymer compounds that can be preferably used, those having the above-described effects include polyacrylic acid or a salt thereof similar to the above-described electrolytic solution. The preferable molecular weight and concentration of the water-soluble polymer compound are also the same as those of the above-described electrolytic solution.

  If an electrolytic solution containing only a corrosion inhibitor is used without adding a water-soluble polymer compound, a strong but non-uniform protective film is formed. If electropolishing is performed in this state, the polished surface is polished. Variations in speed, surface roughness, and pits are likely to occur. On the other hand, by adding a water-soluble polymer compound, surface roughness and pits can be suppressed and more uniform polishing can be achieved. Therefore, the polymer compound can be uniformly protected by adjusting the strength of the protective film with a corrosion inhibitor. It works as a film. Therefore, in the initial stage of polishing, in order to form a strong protective film on the concave surface of an object to be polished such as copper, an electrolytic solution having a low water-soluble polymer compound concentration is supplied, and when the barrier film is exposed and approaches the polishing end point, An electrolytic solution having a high concentration of the polymer compound may be supplied to adjust the strength of the protective film and be polished so as to obtain a more uniform surface state.

  In order to adjust the pH of the second electrolytic solution used in this process, a pH adjusting agent may be added in the same manner as the above-described electrolytic solution.

  The pH of the second electrolyte is generally 2-10. However, when the polishing rate is high and flattening is required on the glossy surface without surface roughness, as in the copper wiring process of the semiconductor substrate, the pH of the second electrolytic solution is preferably 3 to 6, In the case where the concave portion in the initial stage of polishing is formed into a convex shape in the middle of polishing and further copper is polished until at least a part of the barrier film is exposed, that is, in the barrier film exposure process, the pH of the second electrolytic solution is 3 to 4.5 is more preferable.

  Furthermore, the second electrolytic solution may contain abrasive grains. Abrasive grains have the effect of mechanically polishing and removing metals such as copper (objects to be polished), but when a polishing pad is used in combination, a protective film formed of a corrosion inhibitor and a water-soluble polymer compound is appropriately machined. There is also an action to polish and remove.

  The 2nd electrolyte solution of this process may contain surfactant similar to the above-mentioned electrolyte solution. The conductivity is the same as that of the above-described electrolyte.

  Examples of the composition of the second electrolyte include (1) 2 to 80% by weight organic acid, (2) 2 to 20% by weight sulfonic acid group strong acid, and (3) 0.01 to 1% by weight. A corrosion inhibitor, (4) 0.01 to 1% by weight of a water-soluble polymer compound, (5) 0.01 to 2% by weight of abrasive grains, and (6) about 0.01 to 1% by weight of a surface activity. Examples of the aqueous solution provided with the agent include those adjusted to pH 3 to 6, preferably pH 3 to 4.5. The electrolyte solvent is deionized water, preferably ultrapure water.

Next, electropolishing using the electropolishing apparatus shown in FIG. 6 will be described. First, the substrate holder (polishing head) 52 holding the substrate W with the surface facing downward is positioned at a predetermined position above the polishing table 50. Next, while rotating the polishing table 50, the second electrolyte is supplied from the electrolyte supply nozzle 60 toward the upper surface, and at the same time, the substrate holder (polishing head) 52 is lowered while rotating together with the substrate W, For example, the substrate W is pressed toward the surface of the polishing pad 58 with a pressing force of 1 psi (about 70 g / cm ² ) or less. When the power supply electrode 70 comes into contact with a conductive material such as copper 34 on the surface of the substrate W, the power supply electrode 70 is connected to the anode of the power source 72, and the processing electrode 56 is connected to the cathode of the power source 72. A predetermined voltage is applied between the surface of the substrate W and a conductive material such as copper 34 on the surface of the substrate W. As a result, an electrolytic reaction is caused on the surface of the conductive material such as copper 34 to be the anode, and the conductive material is polished. At this time, the processing electrode 56 and the surface of the conductive material such as the copper 34 of the substrate W are filled with the second electrolytic solution and electrically connected through the through hole 58a provided in the polishing pad 58. .

  A process of exposing the barrier film by carrying out electrolytic polishing by rubbing the polishing pad 58 on the surface of the conductive material such as copper 34 will be described. First, the convex part of the initial concavo-convex shape on the surface of the conductive material is polished at a polishing rate faster than that of the concave part, and is polished so that the concave shape of the surface of the conductive substance becomes a convex shape during the polishing. 1 (b)) is polished immediately before exposure or until at least a part of the barrier film 30 is exposed.

  That is, for example, the surface of the copper 34 of the substrate W serving as the anode is anodized, and at the same time, a protective film is formed on the surface of the copper 34 by the corrosion inhibitor and the water-soluble polymer compound in the second electrolytic solution. Is done. At this time, the copper 34 of the substrate W pressed toward the polishing pad 58 is moved relative to the polishing pad 58 and mechanically polished by the rotational motion of the substrate W and the rotational motion of the polishing table 50. The protective film formed on the concave surface present on the surface of the copper 34 of W is not removed, and the protective film formed on the convex portion present on the surface of the copper 34 is rubbed with a polishing pad, The protective property becomes weak, and the electrolytic processing of the convex portion proceeds. As described above, by selectively removing only the protective film of the convex portion among the protective films formed on the concave and convex portions present on the surface of the copper 34 of the substrate W, the copper 34 of the convex portion is selectively removed. The

  On the concave surface of the copper 34 that is less affected by mechanical polishing by the polishing pad 58, the convex portion of the copper 34 that is constantly rubbed with the polishing pad 58 is stronger due to the corrosion inhibitor, the water-soluble polymer compound, and the copper oxide film. A protective film is formed. Thereby, the grinding | polishing speed in the recessed part surface of the copper 34 becomes slow, and the initial concave shape which exists in the surface of the copper 34 becomes a convex shape. A portion formed with a protective film and having a convex shape is less likely to be dished when the polishing is further advanced, compared to polishing with a concave shape. As a result, even if polishing is performed until the barrier film is exposed, the conductive material (wiring metal) is overpolished and dishing due to overpolishing and etching at the interface between the barrier film and the metal (conductive material) are minimized. It is possible to polish without leaving a substance.

  As shown in FIG. 7, this principle is based on the fact that the surface of the barrier film 80 has an initial concave portion 84a on the surface corresponding to the wiring portion 82a and an initial convex portion 84b on the surface corresponding to the portion 82b between the wiring portions. The shape will be described in more detail with reference to the case of polishing the copper 84 as the conductive material, taking the shape as an example.

  First, in the initial stage of polishing, a protective film is formed on the surface of the initial convex portion 84b of the copper (conductive substance) 84, and this protective film is removed by mechanical polishing with the polishing pad 58. At this time, as shown in FIG. 7A, a stronger protective film 86 that is more resistant to polishing of the polishing pad 58 than the protective film formed on the initial convex portion 84b is formed on the surface of the initial concave portion 84a. . By using the second electrolytic solution containing the corrosion inhibitor, the protective film 86 stronger than the initial convex portion 84b can be formed on the surface of the initial concave portion 84a. As a result, the polishing rate of the copper 84 in the initial concave portion 84a corresponding to the wiring portion 82a is lower than the polishing rate of the copper 84 in the initial convex portion 84b corresponding to the inter-wiring portion 82b, thereby FIG. 7 (b). As shown in FIG. 4, a convex portion 84c is formed in a portion corresponding to the wiring portion 82a on the surface of the copper 84, and a concave portion 84d is formed in a portion corresponding to the inter-wiring portion 82b.

  Subsequently, when the concave portions 84d and the convex portions 84c are polished, the copper 84 located in the concave portions 84d corresponding to the inter-wiring portions 82b is removed, and at least a part of the barrier film 80 starts to be exposed. Since the polishing rate of the barrier film 80 is extremely slow, the portion of the reverse protrusion 84c on which the protective film 86 is formed is polished, and the reverse protrusion 84c is gradually flattened as shown in FIG. become.

  As described above, when polishing the conductive material 84 until the copper clear (barrier film 80 between the wiring portions 82b is exposed), the protective film 86 is formed in the initial concave portion 84a corresponding to the wiring portion 82a, and the concave and convex portions are reversed. By forming the convex portion, the surface of the conductive material 84 such as copper corresponding to the wiring portion 82a is prevented from being etched or etched at the interface between the barrier film 80 and the conductive material 84. The substance (copper) 84 can be suitably polished.

  Then, after the electropolishing is completed, the processing electrode 56 and the feeding electrode 70 are disconnected from the power source 72, the supply of the second electrolytic solution is stopped, the substrate holder (polishing head) 52 is raised, and then the polished substrate W is polished. Is transferred to the next process by the substrate holder 52.

  For the substrate where the barrier film is exposed, the barrier film is further polished. As a method for polishing the barrier film, for example, CMP can be used.

  Next, a voltage (applied voltage) applied between the processing electrode 56 and a conductive material such as copper 34 on the surface of the substrate W during electropolishing will be described. In consideration of the polishing rate and the cost of the power source 72, the applied voltage is preferably a DC voltage. The applied voltage may be a constant voltage from the start of polishing to the end of polishing, but a preferable step of changing the applied voltage will be described.

  As the voltage application changing step, first, in the initial stage of the first step, for example, the applied voltage is set to 2.5 V or less, 0. A method in which the voltage is set to a low voltage of 1 V or higher and then the applied voltage is increased is exemplified. This is because when a protective film is formed on the concave surface of a conductive material such as copper 34, the concave portion is formed when the applied voltage is high even if the polishing pad does not contact or the contact surface pressure of the polishing pad is low. This is because the protective film formed on the surface is broken and the conductive material such as copper 34 located in the recess is etched. In other words, in the initial stage of polishing, polishing is performed with a low applied voltage, so that a strong protective film is promoted in a portion where the polishing pad is not in contact or the contact surface pressure is low even if the polishing pad is in contact, and the recess surface is strongly protected. A protective film can be efficiently formed on the surface of the concave portion by forming the film and then polishing the convex portion by increasing the voltage.

  Further, in the case of bulk polishing (polishing before the barrier film is exposed), polishing is performed at a high applied voltage of, for example, 3.5 V or higher in order to increase the polishing rate. Generally, in electropolishing, the higher the voltage, the higher the polishing rate. However, the generation of bubbles or the like causes the generation of pits and surface roughness, so the voltage is 10 V or less, more preferably 5 V or less. After the film thickness detection sensor 74 detects that the barrier film starts to be exposed, the applied voltage is set to 3/4 or less and 1/10 or more of the applied voltage during bulk polishing. Accordingly, it is possible to prevent overpolishing of the conductive material in the wiring portion and to reduce damage to the conductive material in the wiring portion. Furthermore, the applied voltage after the exposure of the barrier film is preferably ½ or less of the applied voltage during bulk polishing.

  In addition, by using a pulse as the applied voltage, planarization can be performed efficiently. For example, in the case of an ON-OFF pulse, etching proceeds when ON, and formation of a protective film is promoted when OFF. However, when a pulse voltage is used in the electrolytic polishing of copper, the polishing rate is significantly reduced depending on the duty ratio. For example, when the ON-OFF time is 1: 1, that is, when the duty ratio is 50%, the polishing rate becomes about half.

Here, the duty ratio (D) is the time during which the potential of the conductive material with respect to the machining electrode is maintained at a positive potential per cycle of the pulse voltage, or the average when the potential changes periodically at the positive potential. The time when a positive value is expressed as a percentage with respect to the potential is expressed by the following equation, where T _p is the pulse width and T _tot is the period.
D = (T _p / T _tot ) × 100

  In bulk polishing that requires a high polishing rate (polishing before the barrier film is exposed), it is preferable to use a continuous wave DC voltage. On the other hand, in polishing after the barrier film starts to be exposed, a conductive material such as copper is used. In order to prevent rapid dissolution of the active substance, it is preferable to use a pulse waveform in which the voltage is once decreased and the voltage is repeatedly increased. As the pulse waveform, one of a rectangular wave shown in FIG. 8A, a sine wave shown in FIG. 8B, a ramp wave (sawtooth wave) shown in FIG. 8C, or a triangular wave (not shown) is used. Can be used. In order to prevent rapid dissolution of a conductive material such as copper, a sine wave, a ramp wave, or a triangular wave with a slow potential rise time is preferable. The rise time from the lowest potential to the highest potential is preferably 1 μs to 1 s.

  Here, the lowest potential due to a rectangular wave, a triangular wave, a ramp wave, a sine wave, or the like may be a negative potential, zero, or a positive potential of the conductive material with respect to the processing electrode. For the purpose of suppressing the generation of oxygen bubbles, a negative potential is good. However, when the conductive material to be polished is copper, polishing proceeds when the potential of the conductive material is positive with respect to the processing electrode. When a negative potential is reached, precipitates may be generated on the surface of the conductive material that is the object to be polished, and the polishing rate is also slowed. Therefore, the minimum potential is preferably zero or positive. These may be appropriately determined according to the amount of remaining film, process time, and the like.

  Further, it is preferable that the frequency of the pulse waveform is not synchronized with the period of the through-hole of the polishing pad that passes through a specific portion of the conductive material, thereby generating a polished portion and a non-polished portion on the surface of the conductive material. Thus, it is possible to prevent the in-plane uniformity of the polished surface from being deteriorated.

H. Effect of adding a corrosion inhibitor to the electrolyte To confirm the protective effect of the corrosion inhibitor added to the electrolyte, a copper processing (polishing) experiment was conducted using a chip tester capable of polishing a 40 mm diameter portion. It was. The results at this time will be described below.

The chip testing machine can control the electrode potential of copper, and polishes the exposed copper with a polishing pad affixed to the polishing table while applying a voltage between the copper and the processing electrode (counter electrode). Polishing progresses. The polishing table rotation speed is 250 rpm (linear speed at 30 mm from the center is 0.78 m / s), surface pressure is 0.5 psi (35 g / cm ² ), and the current density or copper electrode potential is constant. Was polished. In confirming the effect of the corrosion inhibitor, it is also possible to measure the current density and the electrode potential in a state where the polishing pad is not in contact with the copper surface (surface pressure 0 psi).

The substrate used for processing has an oxide film (SiO ₂ ) with a thickness of about 250 nm, a barrier film made of a TaN film with a thickness of 30 nm, a copper seed film with a thickness of 100 nm, and a copper plating film with a thickness of 1500 nm on the surface. It is a silicon substrate which consists of a board | substrate with a copper film (copper blanket wafer) formed sequentially.

  Table 5 uses 1 mol / L malonic acid + 1.4 mol / L methanesulfonic acid as a base electrolyte, and uses an electrolyte obtained by adding various corrosion inhibitors and water-soluble polymer compounds to the base electrolyte. The electrode potential of copper was 2 [Vvs. The results of measuring the current density when polishing is not performed (surface pressure of 0 psi) and when polishing is performed (surface pressure of 0.5 psi) while being maintained at [Ag / AgCl] are shown.

  Comparing the cases where the polishing in Table 5 is not performed (surface pressure 0 psi), the solutions (numbers 2 to 12) in which the corrosion inhibitor or both the corrosion inhibitor and the water-soluble polymer compound are added to the base electrolyte are as follows. It can be seen that the current density obtained is lower than that of the liquid not added with (No. 1), which suppresses corrosion (electrolytic reaction), that is, forms a protective film. Further, when the current density in the case of polishing (surface pressure 0.5 psi) when polishing is performed under the electrolytic solution conditions (numbers 2 to 9) suppressing corrosion, the conditions of numbers 3 to 9 are compared with the conditions of number 2 Then, it turns out that a current density is suppressed and a stronger protective film is formed against pad polishing.

Furthermore, 1 mol / L malonic acid + 1.4 mol / L methanesulfonic acid + 0.49% polyacrylic acid (average molecular weight: 5000) + 0.7% methanol + 0.05% (surfactant MX2045L manufactured by Kao) +0. A combination of 05% silica abrasive with 5-methyl-1H-benzotriazole as a corrosion inhibitor and 3-amino-5-methyl-4H-1,2,4-triazole added to pH 4 respectively. The substrate was polished by the above-described chip tester. As a substrate, a 4-inch diameter copper-plated pattern wafer (Sematech 854AZ) in which a barrier film and copper were formed using silicon as a base material was polished at a current density of 40 mA / cm ² and a surface pressure of 0.5 psi. However, a good glossy surface was obtained.

  Further, using the electrolytic polishing apparatus shown in FIG. 6, a processing (polishing) experiment of a copper plating pattern wafer having a diameter of 4 inches in which a barrier film and copper were formed using silicon as a base material was performed. The results at that time will be described below.

I. Effect of electrolyte pH (with residual film between wiring parts)
Using the electropolishing apparatus shown in FIG. 6, the influence of the pH of the electrolytic solution on the protective film and dishing formed on the unevenness of the patterned wafer was examined. The substrate (substance to be polished) subjected to processing is a copper plating pattern wafer (Sematech 854AZ). As the polishing pad, a foamed polyurethane polishing pad (IC1000: manufactured by Nitta Haas Co., Ltd.) was used. Electropolishing was performed under conditions of a polishing pressure of 0.5 psi (about 35 g / cm ² ), a relative speed of 1.6 m / s between the polishing pad and the center of the object to be polished (substrate W), and an amount of electrolyte of 100 ml / min. Evaluation of the level | step difference which shows the unevenness | corrugation of a pattern was performed by the stylus type profiler (Dektak3ST: ULVAC).

  That is, 1 mol / L malonic acid + 1.4 mol / L methanesulfonic acid + 0.3% benzotriazole + 0.6% ammonium polyacrylate (average molecular weight: 10,000) + 0.7% methanol + 0.05% (surfactant MX2045L Kao Comparison of the concavo-convex shape of the polished surface when electrolytic polishing of copper was performed using an electrolyte set to pH 4, pH 4.5, and pH 4.75. did. The amount of polishing was compared with copper remaining between the wiring portions. The result is shown in FIG. In FIG. 9, (A) shows the cross-sectional profile surface before polishing, and (B) shows the cross-sectional profile surface after polishing. The same applies to the following.

  As shown in FIG. 9 (a), when polishing is performed using an electrolyte solution having a pH of 4, a concave portion at the initial stage of the polishing has a convex shape, and a strong protective film is formed on the concave portion at the initial stage of polishing. You can see that Moreover, as shown in FIG.9 (b), when grinding | polishing using the electrolyte solution of pH4.5, it turns out that the place which was a recessed part becomes convex shape. Compared to pH 4, the flatness is good, but the degree of reversal of the uneven shape is small. On the other hand, as shown in FIG. 9C, it can be seen that when the electrolytic solution having a pH of 4.75 is used for polishing, the phenomenon that the concave portion becomes a convex shape does not occur. This is considered to be because the protective film formed on the concave surface becomes weaker as the pH increases.

J. et al. Effect of Barrier Film Exposure Between Wiring Portions Further, the influence on dishing when the barrier film between wiring portions started to be exposed was examined. The electrolytic polishing apparatus shown in FIG. 6 is used, and the polishing conditions are the same as in the case of “effect of pH of electrolytic solution (with residual film between wiring portions)” except for the electrolytic solution.

  That is, 1 mol / L malonic acid + 1.4 mol / L methanesulfonic acid + 0.3% benzotriazole + 0.49% polyacrylic acid (average molecular weight: 5000) + 0.7% methanol + 0.05% surfactant (MX2045L) The uneven shape of the polished surface was evaluated when electrolytic polishing of copper was performed using an electrolytic solution prepared by adding 0.05% silica abrasive grains and adjusting the pH to 4.3. The result is shown in FIG.

  As shown in FIG. 10, it can be seen that even if the space between the wiring portions is exposed, the wiring portions are convex due to the protective film, and dishing is suppressed.

K. Effect of applied voltage (with residual film between wiring parts)
Using the electropolishing apparatus shown in FIG. 6, the case where the voltage (applied voltage) applied between the machining electrode and copper (conductive substance) was 4 V and 3 V was compared. Polishing conditions and electrolyte components are the same as in the case of “Effect of pH of electrolyte (with residual film between wiring parts)”, and the pH of electrolyte is 4.5 and the relative speed is 0.8 m / s. went. The result is shown in FIG.

  As shown in FIG. 11 (a), dishing occurs when the voltage is 4V. However, as shown in FIG. 11 (b), the voltage applied between the machining electrode and copper (conductive substance) (application) It can be seen that by lowering the voltage from 4V to 3V, dishing does not occur and a convex shape is obtained. This is presumably because the destruction of the protective film is suppressed by lowering the applied voltage, and as a result, dishing (overpolishing) is suppressed.

L. Influence of applied voltage (barrier film exposure between wiring parts)
When the electropolishing apparatus shown in FIG. 6 was used to polish with a constant voltage (applied voltage) applied between the processing electrode and copper (conductive material), the barrier film started to be exposed. The case where the applied voltage was lowered later was compared. The pH of the electrolytic solution is 4.3 according to the polishing conditions and the electrolytic solution component according to the case of “the influence of the relative speed between the polishing pad and the center of the object to be polished and the applied voltage (with a residual film between wiring portions)”. That is, a comparison was made between the case where bulk polishing was started at an applied voltage of 4 V and the polishing was performed at 4 V as it was, and the case where the applied voltage was reduced to 2 V after the barrier film began to be exposed and the copper was cleared. The result is shown in FIG.

  As shown in FIG. 12A, when polishing is continued while the applied voltage is as high as 4 V, over-polishing occurs with the exposure of the barrier film, but the barrier film starts to be exposed as shown in FIG. 12B. When the applied voltage is lowered from 4V to 2V later, it can be seen that overpolishing is suppressed. This is presumably because the electric field concentration at the interface between the barrier film and the copper (conductive material) in the wiring portion and the destruction of the protective film are suppressed.

It is a figure which shows an example of the conventional manufacturing method of a copper wiring board in order of a process. It is a top view which shows an example of an electropolishing apparatus. FIG. 3 is a longitudinal front view of FIG. 2. It is a graph which shows the relationship between copper concentration and surface roughness at the time of grinding | polishing by changing the copper concentration in electrolyte solution. It is a graph which shows the relationship between a copper concentration and a grinding | polishing speed | rate at the time of grind | polishing by changing the copper concentration in electrolyte solution. It is a longitudinal cross-sectional view which shows the other example of an electropolishing apparatus. It is a figure which shows typically the principle of grinding | polishing in this invention using the electrolytic polishing apparatus shown in FIG. It is a figure which shows the voltage waveform in this invention. It is the cross-sectional profile of the pattern wafer of the grinding | polishing result in "the influence of pH of electrolyte solution (there is a residual film between wiring parts)". It is a cross-sectional profile of a pattern wafer as a result of polishing at the time of “barrier film exposure between wiring parts”. It is the cross-sectional profile of the pattern wafer of the grinding | polishing result in "the influence of an applied voltage (with the residual film between wiring parts)". It is a cross-sectional profile of the pattern wafer of the grinding | polishing result in "the influence of an applied voltage (barrier film exposure between wiring parts)".

Explanation of symbols

14 Lower layer wiring 26 Via hole 28 Trench 30 Barrier film 32 Seed film 34 Wiring part (copper)
36 Upper layer wiring 50 Polishing table 52 Substrate holder (polishing head)
54 Processing chamber 56 Processing electrode 58 Polishing pad 58a Through hole 60 Electrolyte supply nozzle 62 Electrolyte storage tank 64 Electrolyte supply line 66 Pure water supply nozzle 68 Storage container 70 Power supply electrode 72 Power supply 74 Film thickness detection sensor 76 Control unit 80 Barrier Film 82a Wiring part 82b Between wiring parts 84 Copper (conductive substance)
84a Initial concave part 84b Initial convex part 84c Reverse rotation convex part 84d Reverse rotation concave part 86 Protective film

Claims (28)

An electrolytic solution used for electrolytic polishing for polishing a conductive material on the surface of an object to be polished,
One or more organic acids or salts thereof;
One or more strong acids having sulfonic acid groups;
A corrosion inhibitor;
An electrolytic solution for electropolishing which is an aqueous solution containing a water-soluble polymer compound.   The electrolytic solution for electropolishing according to claim 1, wherein the organic acid has a carboxyl group.   The electrolytic solution for electropolishing according to claim 2, wherein the organic acid further has a hydroxy group.   The organic acids are acetic acid, propionic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, citric acid, aconitic acid, glyoxylic acid, glycolic acid, lactic acid, gluconic acid, malic acid The electrolytic solution for electrolytic polishing according to claim 1, wherein the electrolytic solution is any one selected from the group consisting of and tartaric acid.   The electrolytic solution for electropolishing according to claim 1, wherein the concentration of the organic acid is 0.1 to 80% by weight.   The strong acid having a sulfonic acid group is one or more of methanesulfonic acid, benzenesulfonic acid, taurine, cysteic acid, alkylbenzenesulfonic acid having 1 to 6 carbon atoms in total, trifluoromethanesulfonic acid, and fluorosulfonic acid. The electrolytic solution for electropolishing according to claim 1, wherein:   The electrolytic solution for electropolishing according to claim 1, wherein the concentration of the strong acid having a sulfonic acid group is 0.1 to 20% by weight.   The electrolytic solution for electropolishing according to claim 1, wherein the corrosion inhibitor is at least one selected from the group of benzotriazole and derivatives thereof.   The electrolytic solution for electropolishing according to claim 8, wherein the concentration of the corrosion inhibitor is 0.001 to 5% by weight.   The water-soluble polymer compound includes polyacrylic acid or a salt thereof, polymethacrylic acid or a salt thereof, polyethylene glycol, polyisopropylacrylamide, polydimethylacrylamide, polymethacrylamide, polymethoxyethylene, polyvinyl alcohol, hydroxyethyl cellulose, carboxymethyl cellulose, The electrolytic solution for electrolytic polishing according to claim 1, wherein the electrolytic solution is one or more selected from polyvinylpyrrolidone and polyvinylpyrrolidone.   The electrolytic solution for electropolishing according to claim 1, wherein the concentration of the water-soluble polymer compound is 0.005 to 5% by weight.   The electrolytic solution for electropolishing according to any one of claims 1 to 11, further comprising abrasive grains.   The electrolytic solution for electropolishing according to claim 12, wherein the concentration of the abrasive grains is 0.01 to 10% by weight.   The electrolytic solution for electropolishing according to any one of claims 1 to 13, further comprising a surfactant.   The electrolytic solution for electropolishing according to any one of claims 1 to 14, wherein the electrical conductivity is 5 to 200 mS / cm.   The electrolytic solution for electropolishing according to any one of claims 1 to 15, wherein the pH is 2 to 10.   The electrolytic solution for electropolishing according to any one of claims 1 to 16, wherein 0.001 to 10% by weight of the conductive substance is contained in a component.   An electrolytic solution used for electrolytic polishing for polishing a conductive material on the surface of an object to be polished, the composition of the electrolytic solution being (a) 2 to 80% by weight of an organic acid based on the total composition weight, (b) A strong acid having 2 to 20% by weight of a sulfonic acid group, (c) 0.01 to 1% by weight of a corrosion inhibitor, (d) 0.01 to 1% by weight of a water-soluble polymer compound, (e) 0. An electrolytic solution for electropolishing comprising 01 to 2% by weight of abrasive grains and (f) 0.01 to 1% by weight of a surfactant, the pH of which is adjusted to 2 to 10. An electropolishing method for polishing a conductive material on a surface of an object to be polished,
In the presence of the electrolyte solution according to any one of claims 1 to 18,
An electrolytic polishing method, wherein a voltage is applied between the conductive material and the counter electrode while rubbing the surface of the conductive material with a polishing pad. An electrolytic solution is present between the conductive material formed on the barrier film on the surface of the object to be polished and the counter electrode disposed at a position facing the conductive material, and the conductive material is removed by the polishing pad. When applying a voltage while rubbing the surface to remove the conductive material other than the wiring portion in which the conductive material is embedded in the wiring recess,
(A) one or more organic acids or salts thereof, (b) one or more strong acids having a sulfonic acid group, (c) an aqueous solution containing a corrosion inhibitor, and (d) a water-soluble polymer compound Use
The conductive material located above the wiring portion is polished at a slower rate than the conductive material located outside the upper portion of the wiring portion, and the conductive material located above the wiring portion is removed from the upper portion of the wiring portion. A first step having a convex shape with respect to the conductive substance located in
An electrolytic process characterized by comprising a second step of polishing the convex conductive material formed by the first step, and simultaneously polishing the conductive material located at a portion other than the upper portion of the wiring portion until the barrier film is exposed. Polishing method.   21. The electrolytic polishing method according to claim 20, wherein the electrolytic solution has a pH adjusted to 3 to 4.5.   The electrolytic polishing method according to claim 20 or 21, wherein the electrolytic solution further contains abrasive grains and a surfactant.   The electropolishing method according to any one of claims 20 to 22, wherein the corrosion inhibitor is at least one selected from the group of benzotriazole and derivatives thereof.   24. The electropolishing method according to claim 23, wherein the one or more types of corrosion inhibitors selected from the group of benzotriazole derivatives is 5-methyl-1H-benzotriazole.   23. The electropolishing method according to claim 20, wherein the corrosion inhibitor is 3-amino-5-methyl-4H-1,2,4-triazole.   The electropolishing method according to any one of claims 20 to 22, wherein the corrosion inhibitor is at least one selected from the group of bismuthiol and derivatives thereof.   23. The electropolishing method according to claim 20, wherein the corrosion inhibitor is at least one selected from the group of salicylaldehyde and derivatives thereof.   28. The electrolytic polishing method according to claim 20, wherein the remaining film thickness of the conductive material is detected by a change in eddy current.

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