JP2009136926A - Conditioner and conditioning method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide conditioner for CMP (Chemical Mechanical Polishing) pad exerting a stable polishing performance in a Cu wiring process of a semiconductor device. <P>SOLUTION: The CMP pad conditioner formed by fixing a single layer of diamond abrasive grains with mean grain size of 30-1,000 μm on the surface of a base metal by a binding material consisting primarily of nickel plating or brazing material, superabrasive grain contains 40 wt.% or more of hexoctahedron whose crystal faces consist of both of (100) surfaces and (111) surfaces so as to reduce the abrasion amount of the pad, and the pad surface is smoothly finished so as to exert the stable polishing performance by the CMP process of a Cu film. When the length of the ridge line formed by the (111) surface and the (111) surface is defined as A and the length of the ridge line formed by the (100) surface and the (111) surface is defined as B, preferably the shape of the superabrasive grain forming the hexoctahedron satisfies a relationship of 0≤A≤2B. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a conditioner, and more particularly to a conditioner of a polishing pad for CMP (Chemical Mechanical Polishing), which is one of semiconductor manufacturing processes, particularly for CMP of a Cu film.

  CMP is a process in which a multilayer wiring portion is planarized by polishing with loose abrasive grains in a device process for forming a semiconductor element on a silicon wafer. Examples of the material of the layer to be planarized include silicon dioxide as an insulating film for insulation between wirings, and tungsten and copper as wiring materials. These various materials are flattened by CMP after being deposited on the device wafer. For CMP, a slurry in which fine particles such as silica or alumina are turbid in an acidic or basic aqueous solution and a polishing pad made of foamed polyurethane, polyester nonwoven fabric or the like is used. When polishing various deposited layers, clogging occurs on the surface of the polishing pad, which causes problems such as a decrease in polishing speed and generation of minute defects on the wafer. It is necessary to grind and eliminate clogging. A CMP conditioner is used here, in which a single layer of superabrasive grains such as diamond is fixed to the surface of a disk-shaped or ring-shaped metal base metal.

  In conventional conditioning of an oxide film in CMP, the conditioner is emphasized in sharpness, and a conditioner having a sharp cutting edge has been used. The reason is that a conditioner with a sharp cutting edge can efficiently remove clogging on the polishing pad in a shorter time and can finish the surface of the polishing pad more roughly, resulting in a higher polishing rate. is there. If the unevenness of the polishing pad surface is large, the area in contact with the wafer is reduced, and it is considered that the polishing rate is increased by increasing the pressure applied to the contact with the wafer.

  In the case of a CMP conditioner using superabrasive grains having a tetrahedral or octahedral shape, it is known that the sharpness of these shapes can be utilized to improve the grinding ability for the polishing pad and to obtain a high polishing rate of the oxide film. (For example, refer to Patent Document 1).

  As another CMP conditioner using hexahedron diamond abrasive grains, a CMP conditioner made for the purpose of increasing the grinding ability with respect to a polishing pad is known (for example, see Patent Document 2).

  Another CMP conditioner made for the purpose of increasing the grinding ability is a CMP conditioner having a base metal having a convex shape, thereby concentrating the processing pressure on the polishing pad and increasing the grinding ability for the polishing pad. It is known (see, for example, Patent Document 3).

  As another CMP conditioner for the purpose of increasing the grinding ability, a plurality of cylindrical protrusions are arranged on the surface of the base metal, thereby increasing the processing pressure on the polishing pad and enhancing the grinding ability for the polishing pad. A CMP conditioner is known (see, for example, Patent Document 4).

Japanese Patent Laid-Open No. 2002-127011 JP 2001-71267 A Japanese Patent No. 3295888 Japanese Patent No. 3656475

In recent years, with the increase in integration and performance of semiconductor devices, the number of layers of devices has increased, and the planarization process of metal films, particularly Cu films, as wiring materials tends to increase. However, since the conditioner for this process uses the conventional conditioner for CMP of oxide film as it is, it is currently mass-produced without fully taking out the polishing characteristics in the planarization process of the metal film. is there.
That is, the present invention provides a conditioner for a Cu film CMP polishing pad that can stably maintain a high polishing rate and has a long life.

  In order to solve the above problems, a conditioner of the present invention is a CMP conditioner having a superabrasive layer in which a superabrasive grain is fixed to the surface of a base metal, the crystal plane being (100) plane and ( It is characterized by containing at least 40% by weight of hexahedron superabrasive grains composed of both (111) faces.

Since the angle formed by the crystal planes of the hexahedron superabrasive grains is an obtuse angle, the force to bite into the polishing pad is weak, and as a result, the surface of the polishing pad is processed smoothly. At this time, the ratio of the hexahedron superabrasive grains is preferably 40% by weight or more.
The reason why the numerical value is limited to 40% by weight or more is that if it is less than 40% by weight, a sufficient polishing rate cannot be obtained in the CMP process of the Cu film. More preferably, it contains 60% by weight or more of hexahedron superabrasive grains. In addition, although a diamond abrasive grain, a CBN abrasive grain, etc. can be used for a superabrasive grain, a diamond abrasive grain is more preferable when abrasion resistance is considered.

  Among them, the (111) plane having the highest wear resistance among the crystal planes of diamond is fixed so as to be substantially parallel to the plane perpendicular to the rotation axis of the conditioner on the base metal. The conditioner can be used for a longer time.

FIG. 1 shows a schematic diagram of hexahedral hexagonal diamond grains. The hexahedron diamond abrasive grains are characterized by being composed of both the (100) plane 1 and the (111) plane 2 as crystal planes. When the length of the ridge line formed between the (111) plane and the (111) plane is A and the length of the ridge line formed between the (100) plane and the (111) plane is B, in the present invention, the length of A In a range satisfying the relationship of 0 ≦ A ≦ 2B is preferable. FIG. 2 is a schematic diagram in the case where (a) satisfies A = 0 and (b) satisfies A = 2B in a hexahedron diamond abrasive.
Here, the length of A is more preferably 0.5B ≦ A ≦ 1.5B, and the length of A is most preferably A≈B.

In this invention, the average grain size of the superabrasive grains is preferably 30 μm or more and 300 μm or less.
When the average particle size is less than 30 μm, the conditioning ability with respect to the polishing pad is extremely lowered, which is not practical. On the other hand, if the average particle size exceeds 300 μm, the conditioning ability is increased, but the surface of the polishing pad becomes too rough, so that the processing quality of the wafer surface is lowered, which is not practical in terms of quality.

Moreover, in this invention, it is preferable that the average protrusion amount of superabrasive grains is 3% or more and 50% or less of the average particle diameter.
If the average protrusion amount is less than 3%, the conditioner will not be sharp enough to cause a reduction in processing efficiency. If it exceeds 50%, the holding power of the diamond abrasive grains will decrease and cause dropout. is there. In order to increase the holding power of the diamond abrasive grains to prevent dropping and to obtain sufficient processing efficiency, the average protrusion amount is more preferably 10% or more and 45% or less, and more preferably 10% or more and 40% or less. Most preferred.

  In order to measure the protruding amount of superabrasive grains, a method using a dial gauge or the like has been proposed, but zygo (three-dimensional) is most accurately used to measure the level difference from the protruding end of superabrasive grains to the binder. It is appropriate to use a surface structure analysis microscope.

  For example, the average protrusion amount is determined by measuring the protrusion amount of 100 superabrasive grains arbitrarily selected, and multiplying the average value by the average grain diameter of the superabrasive grain by multiplying by 100. Defined. Since several tens of thousands to several hundreds of thousands of superabrasive grains are fixed to the superabrasive grain layer, it takes a lot of labor to measure the protruding amount of all superabrasive grains. For this purpose, it is practical to employ an average value of about 100 abrasive grains.

  The binder used for the conditioner of the present invention is not particularly limited as long as it is a binder that can firmly fix the superabrasive grains to the disc-shaped base metal. The demagnetized superabrasive grains adhere to the polishing pad and remain even when the wafer is polished with the polishing pad, causing scratches on the workpiece. Therefore, since a stronger abrasive grain holding force is required as the bonding material, a plated metal or brazing material is suitable.

Nickel plating is most preferred as the binder.
The method of fixing the superabrasive grains to the base metal by nickel plating is as follows: (1) Superabrasive retention is superior to other binders; (2) Superabrasive protrusion is large, Smooth discharge, excellent sharpness, (3) High abrasive grain density, low tool wear and excellent machining accuracy, (4) Even if super abrasive grains are worn and used, damage to the base metal If there is no distortion, the base metal can be reused.

As another binder, a brazing material can be used.
The brazing material used in the present invention has a low brazing temperature and high fluidity. Not only a Ti alloy used as a base metal but also an Ag—Cu—Ti activated brazing material that is particularly excellent in wettability with diamond and that provides a high adhesive strength is optimal. In addition, a Ni—Cr brazing material or a Co—Ni—Cr brazing material is also applicable.

In order to fix the superabrasive grains with the brazing material, it is appropriate to use a pasty brazing material.
Here, the paste-like brazing material is generally a brazing material powder kneaded with a binder, and has an appropriate viscosity, so that the operation is easy. In actual work, first, a paste-like brazing material is applied to the fixed surface of the superabrasive grains of the base metal, and a mixture of superabrasive grains and brazing powder is sprinkled on the brazing material to arrange them randomly and densely. When the brazing material is dried and no longer flows, it is placed in a furnace and heated to melt the brazing material. Thereafter, the superabrasive grains are fixed by cooling in a furnace.

  The conditioner of the present invention is preferably used for conditioning a CMP polishing pad for a metal film.

  Furthermore, the pad conditioner of the present invention is more preferably used for conditioning a CMP polishing pad made of a Cu film, an aluminum film and an aluminum alloy film. An aluminum alloy includes an aluminum-copper alloy film.

  In the conditioning method described above, after the conditioning by the conditioner, the unevenness on the pad surface, which has been uneven by polishing the dummy wafer, is aligned within a certain range, so that more stable polishing performance can be obtained.

  According to the present invention, it is possible to obtain a CMP polishing pad conditioner that suppresses the consumption of the polishing pad and exhibits stable polishing performance in the Cu wiring process of the semiconductor device.

  The best mode for carrying out the invention will be described in detail in the section of the following embodiments.

  First, as shown in FIG. 3, a disk-shaped base metal having an outer diameter D of 100 mm and a height T of 10 mm was prepared. The material of the disk-shaped base metal is stainless steel SUS304. In addition, the area | region which adheres a superabrasive grain layer is only an area | region of 8 mm of the outer peripheral part W. FIG. The portions where the superabrasive grains were not fixed were masked with an insulating tape and an insulating paint.

Next, the disk-shaped base metal 3 was immersed in a degreasing solution having a liquid temperature of 45 ° C. with 50 g / liter of sodium hydroxide, and cathodic electrolytic degreasing and anodic electrolytic degreasing were performed at a current density of 5 A / dm ² . Then, after washing with pure water, immersed in hydrochloric acid for 3 minutes, washed again with pure water, and then subjected to nickel strike plating in a nickel plating bath of nickel chloride 150 g / liter and hydrochloric acid 100 g / liter, with a current density of 5 A / dm ^2. For 5 minutes. Next, the substrate was plated for 15 minutes at a current density of 1 A / dm ² in a nickel plating bath of 250 g / liter of nickel sulfate, 45 g / liter of nickel chloride and 30 g / liter of boric acid.

Thereafter, diamond abrasive grains having an average grain diameter of 150 μm and containing 70% by weight or more of hexahedron diamond abrasive grains were placed on the base metal and plated at a current density of 0.3 A / dm ² for 3 hours. Next, the disk-shaped base metal was pulled up from the plating bath to remove excess diamond abrasive grains. Subsequently, plating was performed until the average protrusion amount of diamond abrasive grains was 30%, and the pad conditioner of Example 1 of the present invention was completed.

  The conditioner of Example 2 was completed by the same manufacturing method as in Example 1 above, using diamond abrasive grains containing 50% by weight of hexahedron diamond abrasive grains. In addition, as a comparative example, a conditioner using diamond abrasive grains having a sharp cutting edge that is usually used for CMP of an oxide film was prepared (Comparative Example 1). The diamond abrasive grains do not include hexahedron diamond grains.

  That is, the conditioner P to which pressure was applied was placed on the polishing pad 3 and conditioned while rotating each in the direction of the arrow. The cut rate (speed at which the polishing pad is processed), which is a performance index of the conditioner P, was measured and listed in Table 3. The numbers in the table are relative values when Comparative Example 1 is 100.

  Next, the slurry 7 was supplied onto the polishing pad from the slurry supply nozzle 6 on the conditioned pad 5, and the wafer 8 under pressure was placed on the pad 5 and polished while rotating each in the direction of the arrow.

  FIG. 6 shows the transition of the polishing rate when the CMP process of the oxide film is performed without performing the conditioning after the initial conditioning. The polishing rate on the vertical axis is a relative value when the polishing rate value of the first sheet is 100. Here, silicon dioxide was used for the oxide film. The polishing rate for the second wafer is about 30% lower than that for the first wafer. This is thought to be because the polishing rate on the second and subsequent sheets decreased because the pressure applied to the contact between the wafer and the polishing pad decreased because the surface of the polishing pad was partially planarized by the first polishing. From the above results, it can be said that the roughness of the polishing pad surface is a very important factor for the CMP processing of the oxide film. This is also one of the reasons why a sharp conditioner is used in order to efficiently remove these minute flat portions that cause a decrease in polishing pressure. FIG. 7A is a schematic diagram of the polishing pad surface state immediately after conditioning, and FIG. 7B is a schematic diagram of the polishing pad surface state after polishing. The polishing pad 9a immediately after conditioning has fluff 10 but the flattened portion 11 appears on the polished polishing pad 9b.

  Next, in order to examine the relationship between the polishing characteristics of the Cu film CMP process and the conditioning, the above-described experiment was also performed in the Cu film CMP process. FIG. 8 shows the transition of the polishing rate when the Cu film is subjected to the CMP process without performing the conditioning after the initial conditioning. As in FIG. 6, the polishing rate on the vertical axis is a relative value when the polishing rate value of the first sheet is 100. In the case of CMP processing of the Cu film, it showed a tendency to rise to the initial three, contrary to the oxide film. From the above facts, the Cu film is processed by a mechanism different from that of the oxide film, and it is considered that there is a factor that increases the polishing rate in the polishing pad with the polishing pad flattened.

  From the processing mechanism of the Cu film CMP processing and the above experimental results, the following considerations were made on the polishing pad surface state suitable for the Cu film CMP processing. In CMP processing of a Cu film, the Cu film forms a compound layer such as an oxide or a complex on the surface by a chemical action such as an oxidizing agent or an organic acid in a slurry solution. Since these compound layers are fragile, they can be easily removed with abrasive grains in the slurry. CMP processing is generally said to be a combination of chemical action and mechanical action, but in the case of Cu film CMP processing, the chemical action is not large, and the polishing rate of the Cu film is This greatly depends on the chemical reaction rate on the surface of the Cu film. The reason why the polishing rate of the Cu film was improved despite the appearance of a minute flat portion on the surface of the polishing pad is thought to be because the chemical reaction on the surface of the Cu film was further promoted. When a flat portion appears on the surface of the polishing pad, it can be assumed that the temperature of the contact point between the polishing pad and the wafer increases due to friction due to polishing, and the chemical reaction on the surface of the Cu film progresses to increase the polishing rate. In other words, a smoother polishing pad surface state is more suitable for the CMP processing of the Cu film in order to increase the friction with the wafer.

  From the above experimental results, a stable Cu film polishing rate can be obtained by performing initial conditioning for Cu film CMP and polishing the dummy wafer to bring the pad surface into the state shown in FIG. 7B. It is done.

  Next, the effects of the present invention were obtained by conditioning the polishing pad by the method shown in FIG. 4 under the conditioning conditions shown in Table 1, and then by the method shown in FIG. 5 under the polishing conditions shown in Table 2. This was confirmed by measuring the polishing rate of each of the oxide film and the Cu film. The values of Examples 1, 2 and Comparative Example 1 regarding the polishing rates of the various films obtained at that time are also shown in Table 4. The numbers in the table are relative values when Comparative Example 1 is 100.

  In the CMP processing of the oxide film, the cut rate and the polishing rate with respect to the polishing pad showed the same tendency. That is, when a conditioner having a high cut rate was used, a high polishing rate was exhibited. On the other hand, in the CMP processing of the Cu film, a higher polishing rate tended to be obtained by using a conditioner having a lower cut rate as opposed to the oxide film.

It is a schematic diagram of the hexahedron superabrasive grains used in the present invention. (A) is a hexahedron superabrasive grain in which the length of the ridge line formed by the (111) plane and the (111) plane is 0, and (b) is the (111) plane and the (111) plane. It is a schematic diagram of a shape when the length of the ridgeline formed by the operator is twice the length of the ridgeline formed by the (100) plane and the (111) plane. It is a cross-sectional schematic diagram of the pad conditioner of the present invention. It is a conceptual diagram which grinds a polishing pad with a pad conditioner. It is a conceptual diagram which grind | polishes a wafer with the conditioned polishing pad. It is a figure regarding transition of the polishing rate obtained when 20 oxide film wafers were ground without performing conditioning after performing initial conditioning. The vertical axis represents the polishing rate and the horizontal axis represents the number of processed wafers. (A) is the schematic showing the cross section of the pad surface state immediately after conditioning. (B) is the schematic showing the cross section of the pad surface state after grinding | polishing. It is a figure regarding transition of the polishing rate obtained when 20 Cu film | membrane wafers were grind | polished without performing a conditioning after giving an initial conditioning. The vertical axis represents the polishing rate and the horizontal axis represents the number of processed wafers.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 (100) surface 2 (111) surface 3 Polishing pad at the time of conditioning 4a Main axis at the time of conditioning 4b Main axis at the time of polishing 5 Polishing pad at the time of polishing 6 Slurry supply nozzle 7 Slurry 8 Wafer 9a Polishing pad 9b after conditioning 9b After polishing Polishing pad 10 Fluff present on the pad surface after conditioning 11 Flat portion appearing on the pad surface after polishing D Outer diameter of the conditioner T Height of the conditioner W Width of the portion where superabrasive grains are fixed on the conditioner

Claims (12)

A conditioner for a CMP polishing pad of a metal film, in which superabrasive grains are fixed to a surface of a base metal by a single layer using a binder,
The conditioner characterized in that the superabrasive grains contain 40% by weight or more of superabrasive grains that form a hexahedron composed of both (100) planes and (111) planes.   The conditioner according to claim 1, wherein the metal film is any one of an aluminum film, a Cu film, and an aluminum alloy film.   The conditioner according to claim 1 or 2, wherein the (111) plane of the superabrasive grains is substantially parallel to a plane perpendicular to the rotation axis of the conditioner.   The shape of the superabrasive grains forming the hexahedron is such that the length of the ridge line formed by the (111) plane and the (111) plane is A, and the length of the ridge line formed by the (100) plane and the (111) plane is B. 4. The conditioner according to claim 1, wherein the condition satisfies 0 ≦ A ≦ 2B. 5.   5. The conditioner according to claim 1, wherein an average particle size of the superabrasive grains is 30 μm or more and 300 μm or less.   The conditioner according to any one of claims 1 to 5, wherein an average protrusion amount of the superabrasive grains from the binder is 3% or more and 50% or less of the average grain diameter.   The conditioner according to any one of claims 1 to 6, wherein the binding material is metal plating or brazing material.   A conditioning method comprising conditioning a polishing pad for CMP of a metal film using the conditioner according to any one of claims 1 to 7. A conditioning method comprising conditioning a polishing pad for CMP of a Cu film using the conditioner according to claim 1. A conditioning method comprising: conditioning a polishing pad for CMP of an aluminum film using the conditioner according to any one of claims 1 to 7.   A conditioning method comprising: conditioning a polishing pad for CMP of an aluminum alloy film using the conditioner according to any one of claims 1 to 7.   12. The conditioning method according to claim 8, wherein finishing conditioning by dummy polishing is performed after conditioning by a conditioner.

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