JPWO2008149937A1 - Polishing pad and polishing method for device wafer - Google Patents

Abstract

Provided is a polishing pad for a device wafer, which improves the uniformity of the conductive layer of the device wafer in the wafer surface and enables stable electrochemical mechanical polishing for a long period of time. All the electrolyte solution storage portions F from the inner diameter side to the outer diameter side are set to w (mm) in the radial direction of the opening of the electrolyte solution storage portion F, and the maximum installation radius of the electrolyte solution storage portion F is set to R (mm). ) Is disposed on the polishing pad 60 so as to satisfy the relational expression of 45 / SQRT (R) <w <73 / SQRT (R).

Description

  The present invention relates to a polishing pad for a device wafer and a polishing method for electrochemically polishing a conductor layer formed on a semiconductor wafer.

  In recent years, in semiconductor devices (semiconductor devices), introduction of a low dielectric constant material (so-called low-k material) into an interlayer insulating film has been studied for the purpose of reducing power consumption and speeding up. This low dielectric constant material has poor mechanical strength and chemical stability, and the copper wiring material is peeled from the interlayer insulating film by the frictional force depending on the rotational speed and polishing pressure in chemical mechanical polishing (CMP). Therefore, an ultra-low pressure polishing method (ultra-low pressure CMP) in which polishing is performed with an extremely low polishing pressure has been employed.

  However, because ultra-low pressure CMP has the problem of lowering the polishing rate and degradation of uniformity in the wafer surface, an electrochemical mechanical polishing method and a polishing pad using the following apparatus are proposed in place of CMP. Has been.

First, a rotating platen on which a polishing member is placed is placed in a container (begin) filled with an electrolytic solution, and a cathode and a rotating platen placed on the bottom of the container are opposed to each other, and an anode electrode and This is an apparatus for pressing a polishing member against a Cu film of a device wafer and polishing the Cu film electrochemically (for example, Patent Document 1).
However, since this polishing apparatus is dedicated to electrochemical mechanical polishing, a separate CMP apparatus for performing barrier metal CMP is required after electrochemical mechanical polishing of the Cu film. There was a problem of becoming expensive.
The second is a polishing pad that is mounted on a platen of a conventional CMP apparatus and is used for electrochemically polishing a Cu film, and is a polishing pad having an anode and a cathode at or near the polishing surface (for example, Patent Document 2).
However, since this pad supplies the electrolyte solution so as to cover the surface of the polishing pad, by increasing the number of rotations of the platen, the electrolyte solution is scattered by the action of centrifugal force, and the uniformity within the wafer surface deteriorates. There was a problem that stable polishing could not be performed.
JP-T-2004-531885 USP 6,893,328

  SUMMARY OF THE INVENTION An object of the present invention is to provide a polishing pad for a device wafer that improves the in-wafer uniformity of the conductor layer of the device wafer and can perform stable electrochemical mechanical polishing for a long period of time.

  The present invention solves the above problems by the following means. In order to facilitate understanding, description will be made with reference numerals corresponding to the embodiments of the present invention, but the present invention is not limited to this.

  The first invention has a plurality of electrolytic solution storage portions (F) for storing an electrolytic solution (E) and a cathode electrode (66) formed at the bottom of the electrolytic solution storage portion, and includes a device wafer (D). An anode electrode (63) in which a conductor layer (D1) is brought into contact with a surface of the electrolyte solution in the electrolyte solution storage portion and electrically or electrochemically connected to the cathode electrode and the conductor layer; A plurality of electrolytic cells (C) are formed by applying a voltage to a polishing pad for electrochemically polishing the conductor layer. The polishing pad is formed of a synthetic resin and is in contact with the conductor layer. A polishing surface layer (62) that is rotationally moved relative to the conductor layer is provided, and all the electrolytic solution storage portions from the inner diameter side to the outer diameter side are in the radial direction of the openings of the electrolytic solution storage portions. The length of w (mm), the maximum installation half of the electrolyte container For a device wafer, wherein w is a radial length, and w satisfies a relational expression of 45 / SQRT (R) <w <73 / SQRT (R). It is a polishing pad.

According to a second invention, in the polishing pad of the first invention, the plurality of electrolytic solution storage portions (F) have one or more polar coordinates in which the opening portion is on the polishing surface when the polishing surface is viewed from the normal direction. The polishing pad is formed along a virtual uniform helix defined by the following formula r (θ) = a · θ, and the distance between the spiral lines is 5 mm to 22.5 mm.
3rd invention is the polishing pad of the device wafer of 1st and 2nd invention, The width | variety is the surface of the said polishing surface layer (62), or the width | variety is equal to or less than the said electrolyte solution accommodating part (F), A polishing pad for a device wafer, characterized in that the depth thereof is shallower than that of the electrolyte solution storage portion, and a groove portion is provided so as to connect the plurality of electrolyte solution storage portions.
A fourth invention is a polishing pad for device wafers according to the first and second inventions, wherein the polishing surface layer is made of polyurethane or polyurethane foam.
A fifth invention is characterized in that in the device wafer polishing pad of the first and second inventions, the cathode electrode (66) is formed of gold, platinum, titanium alloy, stainless steel, or carbon. This is a polishing pad for a device wafer.

The sixth invention is a polishing surface layer (62) formed of a synthetic resin and installed on a table (51) that moves relative to a conductor layer (D1) of a device wafer (D), and an electrolytic solution (E ) And a cathode electrode (66) formed at the bottom of the electrolyte container, and is electrically or electrically connected to the cathode electrode and the conductor layer. A plurality of electrolytic cells (C) are formed by applying a voltage to the chemically connected anode electrode (63), and a polishing pad (60) for electrochemically polishing the conductor layer is used. A polishing method for electrochemically polishing the conductor layer, supplying the electrolytic solution to a polishing surface of the polishing surface layer, filling the electrolytic solution in the plurality of electrolytic solution storage portions, A polishing surface layer and the anode electrode are formed on the conductor layer. An electrolytic cell is formed by supplying electric power to the cathode electrode and the anode electrode in a state of being electrically or electrochemically connected, and the polishing pad and the conductor layer are relatively moved. In all the electrolyte accommodating parts up to the outer diameter side, the radial length of the opening part of the electrolyte accommodating part is w (mm), and the maximum installation radius of the electrolyte accommodating part is R (mm). In this case, the device wafer polishing method is characterized in that the radial length w satisfies a relational expression of 45 / SQRT (R) <w <73 / SQRT (R).
According to a seventh aspect of the present invention, in the polishing method of the sixth aspect, the polishing pad (60) is moved to 100 (rotation / min) after the polishing of the conductor layer (D1) of the device wafer (D) or before the polishing. A device wafer polishing method characterized by comprising a step of rotating at the above rotation speed and discharging the electrolytic solution or rinsing water stored in the electrolytic solution storage part (F).

According to the present invention, the following effects can be obtained.
(1) In the present invention, the shape of the opening of the electrolytic solution container satisfies the relational expression of 45 / SQRT (R) <w <73 / SQRT (R) when the polished surface is viewed from the normal direction. To do. Thus, during polishing, the rotation speed of the platen (polishing pad) is set to 60 (rotation / min) to 90 (rotation / min), so that the electrolytic solution is held in the polishing liquid container and is stable. Polishing can be performed (condition of w <73 / SQRT (R)). On the other hand, after polishing or before polishing (when exchanging wafers), the platen (polishing pad) rotation speed is set to 100 (rotation / min) or more to disperse the electrolyte solution in each electrolyte container by centrifugal force. (45 / SQRT (R) <w condition). For this reason, it is possible to discharge the electrolytic solution and the rinsing liquid (cleaning water for high-pressure water flow cleaning) remaining in the electrolytic solution storage unit, and stably polish a plurality of device wafers with a single polishing pad. .

(2) In the present invention, the opening of the electrolytic solution housing part is formed along a uniform spiral, and the distance between the spiral lines of the uniform spiral is 5 mm to 22.5 mm. As a result, the electrolyte solution in the electrolyte container and the polished surface of the conductor layer of the device wafer are uniformly distributed over the entire surface to be polished without increasing the radial length of the opening of each electrolyte container. It is possible to abut, and the uniformity within the wafer surface can be improved. Moreover, by forming the electrolytic solution storage part along a plurality of uniform spirals, the total opening area of the electrolytic solution storage part can be further increased, and the polishing efficiency can be improved.

1 is a perspective view of a polishing apparatus to which an embodiment of a polishing pad to which the present invention is applied is attached. It is sectional drawing (II-II part arrow sectional drawing of FIG. 1) of the polishing apparatus 50 and the polishing pad 60 of a present Example. It is sectional drawing to which the polishing apparatus 50 and the polishing pad 60 of the present Example were expanded. FIG. 6 is an enlarged view of one of the electrolytic solution housing portions when viewed from the normal direction of the polishing surface of the polishing member layer 62. It is a figure which shows the polishing pad 260 utilized for experiment. It is the table | surface which put together the relationship between the diameter of each electrolyte solution accommodating part in which electrolyte solution was hold | maintained, and the largest installation radius, after rotating a platen with each rotation speed. It is a graph which shows the relationship between an installation radius and the diameter of the electrolyte solution accommodating part in which electrolyte solution is hold | maintained. It is a table | surface which shows the proportionality constant (A) at the time of approximating the graph of FIG. 7 to D = A / SQRT (r). It is a graph which shows the comparative experiment result of the in-plane uniformity by the presence or absence of discharge process of the electrolyte solution etc. of the polishing pad 60 of a present Example. It is a figure when the polishing pad 60 of a present Example is seen from the normal line direction of a polishing surface.

Explanation of symbols

DESCRIPTION OF SYMBOLS 50 Polishing apparatus 51 Platen 52 Polishing head 53 Power supply 56 Nozzle 60 Polishing pad 62 Polishing member layer 63 Anode electrode 66 Cathode electrode C Electrolysis cell D Device wafer D1 Conductor layer E Electrolyte solution F Electrolyte container

BEST MODE FOR CARRYING OUT THE INVENTION

  The object of the present invention is to provide a polishing pad for a device wafer that improves the uniformity of the conductive layer of the device wafer within the wafer surface and can perform stable electrochemical mechanical polishing for a long period of time. When the length in the radial direction of the opening of the electrolyte container is w (mm) and the maximum installation radius of the electrolyte container is R (mm), This was realized by arranging so as to satisfy the relational expression of SQRT (R) <w <73 / SQRT (R).

Next, embodiments of the polishing pad according to the present invention will be described with reference to the drawings.
First, an outline of the polishing apparatus 50 to which the polishing pad 60 of this embodiment is attached will be described.
FIG. 1 is a perspective view showing a polishing apparatus 50 to which a polishing pad 60 of this embodiment is attached.
The polishing apparatus 50 is a polishing apparatus that performs platen rotary type chemical mechanical polishing (CMP). The polishing apparatus 50 includes a platen 51 (a surface plate), a polishing head 52, a power source 53, an apparatus-side minus electrode 54, an apparatus-side plus electrode 55, and a nozzle 56.

The platen 51 is a disk-shaped member that mounts the polishing pad 60 and rotates around the vertical axis Z1 (in the direction of the arrow θ1).
The polishing head 52 is a disk-shaped member that has the device wafer D mounted on its lower surface and rotates around the vertical axis Z2 (in the direction of the arrow θ2). The device wafer D is mounted on the polishing head 52 so that the conductor layer D1 is on the lower side.

The power supply 53 is a device that supplies electric power for forming an electrolytic cell. As will be described later, the power source 53 forms an anode on the conductor layer D1 of the device wafer D and forms a cathode on a cathode electrode 66 (described later) of the polishing pad 60. The power to be supplied is generally DC power, but the power waveform may be pulsed. Further, the supplied power may be AC power that varies between plus and minus if there is a DC component.
The device-side negative electrode 54 is electrically connected to the negative terminal of the power source 53 via a wiring, and is in sliding contact with the platen 51 to thereby provide a cathode electrode 66 (described later) of the polishing pad 60 via the platen. Is electrically conducted.

The apparatus-side positive electrode 55 is electrically connected to the positive terminal of the power supply 53 via a wiring, and is electrically connected to the anode electrode 63 by contacting the anode electrode 63 of the polishing pad 60. Is done. The device-side positive electrode 55 is preferably made of the same material as that of the anode electrode 63 in contact with the anode electrode 63, and stably and electrically with respect to the rotating anode electrode 63. It is desirable to have wear resistance for contact.
The nozzle 56 is a member that is disposed above the polishing pad 60 and supplies the electrolytic solution E. The electrolytic solution E can contain a protective film forming agent, abrasive grains, an oxidizing agent, and the like.

  With the configuration as described above, the polishing apparatus 50 contacts the device wafer D and the polishing pad 60 while supplying the electrolytic solution E, and moves them relative to each other to move the surface layer of the conductor layer D1 of the device wafer D. At the same time as forming an electrochemical protective film, the protective film is mechanically removed, and the conductor layer D1 is dissolved and removed electrochemically. That is, the polishing apparatus 50 can perform electrochemical mechanical polishing (ECMP) of the conductor layer D1 by attaching the polishing pad 60, although it is a polishing apparatus for CMP.

Next, the configuration and the like of the polishing pad 60 will be described.
FIG. 2 is a cross-sectional view of the polishing apparatus 50 and the polishing pad 60 of this embodiment (a cross-sectional view taken along the line II-II in FIG. 1).
FIG. 3 is an enlarged cross-sectional view of the polishing apparatus 50 and the polishing pad 60 of this embodiment.
In each drawing, the thickness is emphasized for easy understanding of the configuration of each layer of the polishing pad 60.
As shown in FIGS. 2 and 3, the polishing pad 60 is a disk-shaped pad provided with a plurality of electrolyte solution storage portions F for storing the electrolyte solution E. The polishing pad 60 includes a polishing member layer 62 (polishing surface layer), an anode electrode 63 (power transmission unit), and a cathode electrode 66.

  The polishing member layer 62 is a member for mechanically polishing and removing the protective film formed on the surface of the conductor layer D1 by relatively moving while being pressed against the conductor layer D1 of the device wafer D. is there. The polishing member layer 62 can move relative to the device wafer D when the platen 51 and the polishing head 52 (see FIG. 1) of the polishing apparatus 50 rotate. The polishing member layer 62 is a disk-shaped member, and is provided with a through-hole for forming the electrolyte solution storage portion F.

  The polishing member layer 62 is made of a non-metallic and insulating urethane-based material (a polyurethane material with a grooved foam structure, a polyurethane material with a foam structure having a cushion layer, or the like) or silica (silicon oxide) abrasive grains. The fixed abrasive polishing member is formed. As the material of the polishing member layer 62, a material obtained by impregnating the above-described non-metallic material with a thermosetting resin or an elastomer material may be used. In this case, it is preferable to use a thermosetting resin or an elastomer material in which abrasive grains are dispersed because the surface roughness of the conductor layer D1 can be reduced and polished to a mirror surface. The polishing member layer 62 does not have to be a single layer structure made of a single material, but is a laminated structure of a synthetic resin support or a cushion material made of foamed resin or the like for elastically supporting the anode electrode 63. There may be.

Further, the polishing member layer 62 may be formed by alternately arranging the above-described nonmetallic material and a sheet containing polishing abrasive grains perpendicular to the polishing surface. As the abrasive grains, silicon oxide, aluminum oxide, iron oxide, zinc oxide, silicon carbide, boron carbide, and synthetic diamond powder can be used alone or in combination.
Further, on the surface of the polishing member layer 62, as shown in FIG. 2, the width is equal to or smaller than the width of the electrolyte solution storage portion F, and the depth thereof is shallower than that of the electrolyte solution storage portion F. Xy of about 1 mm to 2 mm may be provided. Thereby, since the contact pressure with the conductor layer D1 increases in the polishing member layer 62, the frictional force with the conductor layer D1 increases, so that the efficiency of mechanical polishing can be improved. By connecting the accommodating portions F with xy grooves, the electrolyte solution E can be supplied and discharged smoothly. In addition, this groove | channel is not restricted to an xy groove | channel, For example, a concentric groove | channel may be sufficient.
Since the polishing member layer 62 is formed of an insulating material having an insulating property, it also functions as an insulating layer that electrically insulates between the anode electrode 63 and the cathode electrode 66.

  The anode electrode 63 is a disk-shaped member for electrically connecting the apparatus-side plus electrode 55 (see FIG. 1) of the polishing apparatus 50 and the conductor layer D1 of the device wafer D. The anode electrode 63 transmits electric power to the conductor layer D1, and forms an anode in the conductor layer D1. The anode electrode 63 is disposed on the surface of the central portion of the polishing member layer 62. As shown in FIG. 3, the anode electrode 63 is provided so that the surface 63a thereof is equal to the surface of the polishing member layer 62 or protrudes from the surface of the polishing member layer 62, and the outer peripheral portion of the bottom surface of the conductor layer D1 and By contacting the device-side plus electrode 55, the device-side plus electrode 55 and the conductor layer D1 are brought into conduction, and the power of the power source 53 can be supplied to the conductor layer D1. Since the anode electrode 63 is in contact with only the outer peripheral portion of the bottom surface of the conductor layer D1, it is within the range inside the bottom surface of the conductor layer D1 (that is, the range of the bottom surface of the conductor layer D1 that is not in contact with the anode electrode 63). Damage (damage) can be reduced, and surface contact with the bottom surface of the conductor layer D1 makes it possible to make the current density on the contact surface more appropriate than point contact.

  The anode electrode 63 is a low-resistance material such as metal (gold, copper, platinum, titanium alloy, stainless steel, carbon, etc.) or a carbon material (amorphous carbon mainly composed of carbon, carbon fiber, graphite fiber, graphite, synthetic material) A composite carbon material with a resin, a composite carbon material with a synthetic resin, composite graphite with a synthetic resin, or a combination thereof).

  As shown in FIG. 2, the cathode electrode 66 is formed in a disk shape, is laminated below the polishing member layer 62, and is placed on the platen 51. The cathode electrode 66 forms the bottom of the electrolytic solution housing part F. The cathode electrode 66 is affixed to the platen 51 with an electric adhesive tape 67 and is electrically connected to the DC power source 53 (see FIG. 1) via the platen 51. Thereby, even if the polishing pad 60 is a polishing apparatus for CMP, the electrolytic cell C can be formed and the electromechanical polishing of the conductor layer D1 can be performed. In addition, since the polishing pad 60 forms the cathode facing the anode, the electrolytic cell C can be formed stably.

  The cathode electrode 66 can be used regardless of metal or non-metal as long as it is conductive and insoluble in the electrolyte solution E. As such a material, gold, platinum, titanium alloy and the like can be used, but carbon, graphite, stainless steel, copper and the like are preferable from an economic viewpoint.

Next, the principle of polishing the conductive layer D1 of the device wafer D by the polishing pad 60 forming the electrolytic cell C will be described.
As shown in FIG. 3, at the time of polishing, the electrolyte container F is filled with the electrolyte E, and the opening is covered with the conductor layer D <b> 1 of the device wafer D. Therefore, the liquid level of the electrolytic solution E and the conductor layer D1 are in contact with each other. Since the conductor layer D1 is electrically connected to the plus terminal of the power supply 53 (see FIG. 1), it becomes an anode when a voltage is applied. On the other hand, since the cathode electrode 66 is electrically connected to the negative terminal of the power supply 53, it becomes a cathode when a voltage is applied. Thereby, the electrolytic cell C is formed by the anode and the cathode, and the electrolytic solution E filled in the electrolytic solution storage part F.
By forming the conductor layer D1 as an anode, the copper forming the conductor layer D1 is dissolved and removed by an electrochemical reaction by “Cu → Cu ²⁺ + 2e ⁻ ”. When dissolution and removal of the conductor layer D1 proceed, a protective film, that is, a passive film is formed on the conductor layer D1, and this passive film is instantaneously mechanically removed by the polishing member layer 62. .
The conductor layer D1 is electrochemically and mechanically polished by instantaneously repeating the dissolution and removal of the surface layer, the formation of the passive film, and the mechanical removal of the passive film as described above. .

Next, the relationship between the shape of the electrolyte container and the hydraulic pressure due to centrifugal force will be described in detail.
FIG. 4 is an enlarged view of one of the electrolyte solution storage portions when viewed from the normal direction of the polishing surface of the polishing member layer 62.
In order for the electrolytic solution in the electrolytic solution storage unit to be held in the electrolytic solution storage unit, a holding force that balances the hydraulic pressure by centrifugal force is required, and this holding force includes the flow resistance and surface tension of the electrolytic solution, etc. . The inventor of the present invention arranges the electrolytic solution storage part so as to satisfy the following relational expressions (1) and (2) based on various experimental results, so that the electrolytic solution is contained in the electrolytic solution storage part during polishing. It was confirmed that the electrolyte solution in the electrolyte container and the conductor layer of the device wafer can stably contact each other.
45 / SQRT (R) <w <73 / SQRT (R) (1)
w (mm) = r1-r2 (2)
here,
w (mm): length in the radial direction of the opening of the electrolyte container r1 (mm): distance farthest from the center of the platen (or pad) of the opening of the electrolyte container r2 (mm): electrolyte The closest distance from the center of the platen (or pad) of the opening of the part R (mm): Installation radius of the electrolyte container installed on the outermost side
However, installation radius r = (r1 + r2) / 2

As can be seen from FIG. 4 and the above formula, the length (w) in the radial direction of the electrolyte container is not the general width (w0) of the opening, but the platen ( Or the difference (r1−r2) between the distance (r1) farthest from the center of the pad) and the nearest distance (r2).
Further, as shown in FIG. 4, the long side in the longitudinal direction of the electrolytic solution container F is a spiral line shape, but is not limited to this, for example, as shown by a broken line in the figure, a straight line and a long hole-shaped electrolysis It is good also as a liquid storage part.
Hereinafter, the relational expressions (1) and (2) will be described based on experimental results and the like.

First, the fact that the liquid in the electrolyte container is held when the holding pressure due to surface tension becomes larger than the liquid pressure due to centrifugal force will be described based on experimental results and the like.
(Explanation of experimental pad)
FIG. 5 is a diagram showing a polishing pad 260 used in the experiment.
The polishing pad 260 is made of foamed polyurethane and is a two-layer structure, 2.7 mm thick pad. The center line is divided into eight equal parts, and circular through holes with the same diameter are installed on the eight equal lines. It installed in the range from radius 20mm to 240mm at intervals of 10mm. The diameter of the through hole was set to 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, and 6 mm for each equal line.
Thereafter, a stainless steel sheet having a thickness of 100 μm was pasted on the back surface of the polishing pad so as to prevent the electrolyte from leaking from the pasting surface, thereby closing the through hole to form an electrolyte containing part.
Note that FIG. 5 is an enlarged view of each electrolytic solution storage portion in order to make it easy to understand.

(experimental method)
An experimental polishing pad 260 is placed on the platen of the platen / rotary type polishing apparatus, an electrolytic solution is supplied, and it is confirmed that all the electrolytic solution storage parts are filled with the electrolytic solution. The plate was rotated at 120 and 130 (rotations / min) for 20 to 30 seconds, and the state in which the electrolyte solution was filled after the platen stopped was visually observed.

(Experimental result)
FIG. 6 is a table summarizing the relationship between the maximum installation radius and the maximum installation radius among the diameters of the electrolyte solution storage portions in which the electrolyte solution is held after the platen is rotated at each rotation speed.
FIG. 7 is a graph showing the relationship between the installation radius and the diameter of the electrolyte container that holds the electrolyte.
FIG. 8 is a table showing the proportionality constant (A) when the graph of FIG. 7 is approximated to D = A / SQRT (r).
From FIG. 8, as a relational expression between the installation radius (r) and the diameter (D) of the through hole in which the electrolyte is held, the following expression (A) can be obtained by approximating the power to −0.5. .
D = A / SQRT (r) (A)
Here, D: Diameter (mm) of the electrolytic solution container capable of holding the electrolytic solution
A: Proportional constant
r: Installation radius of electrolyte container (mm)
It is. Further, the following equation (B) is obtained as an approximate relational expression between the rotation speed and the proportionality constant.
A = 4405 / N (B)
Here, N: platen rotation speed (rotation / min)

(Examination of empirical formulas (A) and (B))
On the other hand, as shown in FIG. 4, the electrolyte container F of this embodiment is disposed along a spiral line when the polishing pad 60 is viewed from the normal direction of the polishing surface, and the long side of the opening is The width of the opening is parallel to the radial direction of the opening is w0, and the maximum length is the length L in the longitudinal direction.
In general, the gradient of the hydraulic pressure generated in the electrolytic solution in the electrolytic solution storage unit installed at the installation radius (r) is equal to the centrifugal force caused by the rotation of the platen (or pad), and therefore the following formula (C) is obtained. It is done.
dP / dr = ρ · ω ² · r (C)
Where dP / dr: radial hydraulic pressure gradient
ρ: Mass per unit volume of electrolyte
ω: Rotational angular velocity of the platen (or pad) By integrating the equation (C) from r1 to r2, the pressure (P) acting so that the electrolyte in the electrolyte container overflows from the container is expressed by the following equation: It can be represented by (D).
P = (1/2) ρ · ω ² (r1 ² −r2 ² )
= Ρ · ω ² · (r1−r2) · (r1 + r2) / 2
= Ρ ・ ω ²・ w ・ r (D)
Where w = r1-r2
r = (r1 + r2) / 2
w is the difference between the distance (r1) farthest from the center of the platen (or pad) of the opening and the closest distance (r2), and is the length (w) in the radial direction of the opening of the electrolyte container. equal. Further, (r1 + r2) / 2 is an installation radius (r).
From the formula (A) and the formula (D), the holding pressure due to the surface tension of the electrolytic solution can be inferred as a pressure balanced with the pressure P of the formula (D).
In general, the holding pressure due to the surface tension of the liquid in the pores can be expressed by the following formula (E) when the pore shape is circular.
PN = K / d (E)
Where PN: holding pressure due to surface tension of the liquid
K: Constant determined by surface tension of liquid and wettability of liquid on wall surface
d: Diameter of pores From formulas (D) and (formula) E, formula (F) can be derived.
ρ · ω ² · w · r = K / d (F)
In the case of a spiral-shaped electrolytic solution container, the diameter d of the pores in the formula (F) may be replaced with the width w0. Further, in the case of the electrolytic solution container shown in FIG. 4, the difference between the width (w0) and the length (w) in the radial direction is small, so the width (w0) is approximated to the length (w) in the radial direction. Can do. Therefore, the following formula (G) can be derived.
ρ · ω ² · w · r = K / w
w ² = K / (ρ · ω ² · r)
w = K1 / SQRT (r) (G)
Here, K1 = SQRT (K / ρ) / ω (H)
Comparing the relational expression (A) for holding the electrolytic solution in the circular electrolyte containing part and the relational expression (G) for holding the electrolytic solution in the electrolytic containing part such as a spiral shape, Can be handled similarly.
That is, the conditions of the circular electrolyte container that are determined by the equations (A) and (B) obtained from the experiments shown in FIGS. 6 to 8 are used as the installation conditions of the spiral electrolyte container. Is also considered good. Therefore, the approximate expressions (A) and (B) obtained by the experiment show that the centrifugal pressure acting on the electrolytic solution in each electrolytic solution housing portion by the rotation of the platen and the surface tension acting on the pores of the electrolytic solution housing portion are as follows. It can be explained on the assumption that they are equal.

(Reason for 45 / SQRT (R) <w <73 / SQRT (R))
Next, the reason why the radial length (w) is w <73 / SQRT (R) will be described.
In order to maintain the wafer in-plane uniformity and electrochemically polish the conductive layer of the device wafer, the electrolytic cell is stabilized by the conductive layer of the device wafer as the anode, the electrolyte, and the cathode electrode. Need to be formed. In order to stably form the electrolytic cell, in the electrochemical mechanical polishing method using the platen rotary type polishing apparatus and the polishing pad of this embodiment, each electrolytic solution storage portion of the polishing pad is filled. It is important to stably bring the electrolytic solution in contact with the conductor layer of the device wafer.

The hydraulic pressure due to the centrifugal force is the largest in the electrolytic solution container disposed on the outermost peripheral side. In order to retain the electrolyte solution in the electrolyte container that is arranged on the outermost peripheral side, it is a condition that the following formula (H) is satisfied from the above formula (G), and from the inner diameter side to the outer diameter side: If the length (w) in the radial direction of all the electrolytic solution storage parts satisfies the formula (H), the electrolytic solution in all the electrolytic solution storage parts installed in the pad is held.
w <K1 / SQRT (R) (I)
Here, R (mm): the installation radius of the electrolyte storage part installed on the outermost periphery side, that is, the maximum installation radius of the electrolyte storage part.

When using the polishing pad 60 of this embodiment, it is preferable to use the platen at a rotation speed of 60 to 90 (rotation / min). When the platen rotation speed is 60 (rotation / min), the following expression is obtained by substituting N = 60 into the expressions (A) and (B).
w = A / SQRT (R) = 73 / SQRT (R)
Furthermore, when the platen is used at a rotational speed of 60 (rotations / min) or more, A <73 is required.

Next, the reason why the length (w) in the radial direction is 45 / SQRT (R) <w will be described.
In the device wafer polishing step, a plurality of device wafers are polished with one polishing pad by exchanging the device wafers. In order to improve the uniformity between wafers by polishing each conductor layer of each device wafer without variation, it is important that the polishing conditions for each device wafer are the same, especially the properties of the electrolyte. is there. For this purpose, after the polishing of one device wafer is completed, when the next device wafer is placed (hereinafter referred to as “wafer replacement”), the electrolyte remaining in the electrolyte container is discharged and polished. It is necessary to remove polishing debris remaining on the surface by pad conditioning or high-pressure water washing.
For this reason, at the time of polishing, the platen rotation speed is set to 60 to 90 (rotation / min) to stably hold the electrolytic solution filled in the plurality of electrolytic solution storage portions installed on the polishing pad, while at the time of wafer exchange The platen rotation speed is preferably set to a high speed rotation of 100 (rotation / min) or more, and the electrolytic solution remaining in the electrolytic solution storage part and the cleaning water (rinsing water) for high-pressure water flow cleaning are preferably discharged.

FIG. 9 is a graph showing the results of a comparative experiment of in-plane uniformity with and without the discharging process of the electrolytic solution or the like of the polishing pad 60.
In the experiment shown in FIG. 9, using one polishing pad 60, 25 device wafers were polished under the same conditions. When discharging the electrolytic solution or the like, the platen is rotated at a high speed of 100 (rotation / min), and when the electrolytic solution or the like is not discharged, the rotation of the platen at the time of wafer replacement is 80 (rotation / min) as in the polishing. It was.
From this experimental result, it is possible to confirm that in-plane uniformity of each device wafer is equal even when a plurality of device wafers are polished when a discharge step of the electrolytic solution or the like is included.
On the other hand, when there is no step of discharging the electrolytic solution or the like, it can be confirmed that the in-plane uniformity of each device wafer is deteriorated as the number of polishing is increased due to the influence of the residual electrolytic solution in the electrolytic solution container. In this case, the polishing rate is similarly reduced.

Even if the platen rotation number when discharging the electrolytic solution or the like is set to 100 (rotation / min), it was confirmed that the in-plane uniformity of the device wafer was not deteriorated. Therefore, N = in the equations (A) and (B) Substituting 100 gives the following equation:
w = A / SQRT (R) = 44 / SQRT (R)
Therefore, in order to increase the platen rotation number when discharging the electrolytic solution or the like to 100 (rotation / min) or more, it is necessary to satisfy the condition of w = 45 / SQRT (R) (that is, 45 <A).
When the length (w) in the radial direction is 45 / SQRT (R) or less, the electrolytic solution in each electrolytic solution storage unit is retained during polishing, whereas, when the wafer is replaced, Polishing between wafers is uniform because electrolyte and cleaning water remain in the inner periphery, that is, in the electrolyte container with a small installation radius. Sex worsens.

From the above, in order to satisfy both the holding of the electrolytic solution in the electrolytic solution storage unit at the time of polishing and the discharge of the electrolytic solution and cleaning water in the electrolytic solution storage unit at the time of wafer replacement, the following formula (J) (that is, It is considered that the above-described formula (1)) should be satisfied.
45 / SQRT (R) <w <73 / SQRT (R) (J)

(Improvement of wafer surface uniformity of polishing speed by spiral arrangement of electrolyte container)
Next, the reason why the uniformity of the polishing rate within the wafer surface can be improved by arranging the electrolytic solution containing portion along the spiral line will be described.
FIG. 10 is a view of the polishing pad 60 of this embodiment when viewed from the normal direction of the polishing surface.
In the electrochemical mechanical polishing of this embodiment, the conductivity of the electrolyte solution and the device wafer contained in a plurality of electrolyte solution storage portions is determined by the rotation of the platen (see arrow θ1) and the rotation of the device wafer itself (see arrow θ2). The body layer D1 repeats contact and non-contact. Therefore, the conductor layer D1 of the device wafer is in contact with the electrolytic solution accommodated in the electrolytic solution accommodating portion having substantially the same installation radius in the central portion, and is further inward and outward of the polishing pad from the central portion to the outer peripheral portion. It contacts the electrolyte solution accommodated in the electrolyte solution storage portion.
In order to improve the uniformity within the wafer surface, the area of the opening of the electrolytic solution containing portion through which the polished surface of the conductive layer passes during polishing is made uniform on the inner and outer circumferences, whereby the conductive layer and the electrolytic solution It is necessary to make the contact time of the housing portion with the electrolytic solution uniform on the inner and outer circumferences.
In the polishing pad 60 of this embodiment, by arranging the electrolytic solution storage part along the spiral, the contact between the conductor layer on the inner and outer periphery and the electrolytic solution in the electrolytic solution storage part is made uniform, and the in-plane uniformity is improved. is doing.
Hereinafter, the superiority of the in-plane uniformity of the polishing pad 60 will be shown by comparing with the in-plane uniformity of the concentric pad B of the comparative example.

(Explanation of experimental pad)
(1) Polishing pad 60
As shown in FIG. 10, the polishing pad 60 has an electrolyte solution containing portion arranged along four uniform spiral lines (uniform spiral lines). The arrangement of the electrolytic solution container is as follows.
Pad diameter: 740mm
Maximum installation radius (R) = 350mm
Electrolyte container shape:
Width w0 = 3.0mm
Length L = 25mm
Spiral used r = (48 / 2π) · (θ-2π · m / n)
Here, the number of spirals (n): n = 4, m = 0, 1, 2, 3
Installation interval d = 3mm
(2) Concentric pad B
The concentric pad B has an electrolyte solution containing portion disposed along a plurality of concentric circles centered on the pad center. The arrangement of the electrolytic solution container is as follows.
Pad diameter: 740mm, maximum installation radius: 350mm
Electrolyte storage part shape Width w0 = 3.0mm
Length L = 25mm
Concentric circular shape Concentric radial pitch 12mm
Installation interval d = 3mm

(experimental method)
Polishing conditions Wafer: outer diameter; φ300 mm, Cu film thickness: 1 μm (in-plane uniformity: 2.1%)
Platen rotation speed: 80 (rotation / min)
Head rotation speed: 81 (rotation / min)
Head pressure: 0.2 psi (14 gf / cm ² = 140 Pa)
Head oscillation: None Electrolyte flow rate: 450 mL / min
Current: 20 A
Polishing time: 1 min

(Polishing result)
In-plane uniformity with the polishing pad 60: 2.9-3.3%
In-plane uniformity with concentric pad B: 8.6-9.5%
However, as a condition for measuring the in-plane uniformity of the wafer, the edge exclusion (length from the outer shape of the conductor layer outside the measurement range) is 7 mm, the number of measurement points is 121 points in the radial direction, and the polishing rate surface. The internal uniformity was calculated.
From the above experiment, the polishing pad 60 in which the electrolyte solution storage portions are arranged along the spiral line showed good uniformity within the wafer surface. This is considered to be because the contact between the conductor layer and the electrolytic solution in the electrolytic solution storage unit was made uniform between the inner and outer periphery by arranging the electrolytic solution storage unit along the spiral line.

(Description of spiral type)
As shown in FIG. 6, the electrolyte container F of the present embodiment is arranged along a uniform spiral line.
In general, the types of spiral include a uniform spiral and a logarithmic spiral, which can be expressed by the following polar coordinate formulas.
Uniform spiral r (θ) = a · θ (K)
Logarithmic spiral r (θ) = a · exp (b · θ) (L)
Here, a and b are constants that determine the shape of the spiral.
In the case where the electrolytic solution container is arranged along the logarithmic spiral represented by the formula (L), the larger the value of θ, the larger r4 becomes in accordance with the exponential function, and the larger the installation radius, the larger the inclination with respect to the radial direction. Becomes larger. For this reason, in order to keep the radial length (w) of the electrolytic solution storage part constant, it is necessary to set the opening of the electrolytic solution storage part small. In this case, it becomes difficult to supply the electrolytic solution to the opening of the electrolytic solution storage unit, and it is unsuitable for holding in the electrolytic solution storage unit during polishing.
On the other hand, in the case where the electrolytic solution storage unit is installed along the uniform spiral line represented by the equation (K), the radial length of the electrolytic solution storage unit is shown because it exhibits a constant radial inclination regardless of the installation radius. (W) can be kept constant.

In order to improve the polishing efficiency of the conductor layer, it is important to increase the total opening area of the electrolyte solution storage part (total value of the area of the electrolyte solution storage part). This is because it is necessary to make more contact between the conductor layer and the electrolytic solution in the electrolytic solution storage portion during polishing. The ratio of the total opening area of the electrolytic solution housing part to the pad area is 10% to 50%, preferably 20% to 30%.
As shown in FIG. 4, the polishing pad 60 has an installation radius so that the electrolytic solution storage portion is along the spiral line, that is, the center in the width (w0) direction of the electrolytic solution storage portion is aligned with the uniform spiral line. (R = (r1 + r2) / 2).
The helical constant (a) of the formula (K) is given by the following formula.
a = p / 2π
Where p: radial pitch in the same uniform spiral

Also, assuming that the electrolyte solution storage portion is continuously installed in a groove shape along the spiral line with the width (w0) of the electrolyte solution storage portion, the area (s) of the opening portion of one electrolyte solution storage portion and The total area (S) of the polishing surface of the polishing pad is given by the following equation.
s = L1 · w0
S = π · R ²
Here, L1: the total length of the spiral line from the starting point on the radially inner side to the final end on the radially outer side (the end of the spiral reaching the radius R), and L1 = πR ² / p.
The ratio (k) between the total area of the openings of the electrolyte container and the area of the pad is:
k = s / S = n · w0 / p (M)
Here, n: number of spiral lines p / n = w0 / k (N)
Here, p / n: when there are a plurality of spiral lines (n ≧ 2), the distance (pitch) between adjacent spiral lines in the radial direction
Given in.
Note that the actual polishing pad 60 has a length of the electrolyte opening portion shown in FIG. 4 (a condition that satisfies the formula (J)) according to a condition (ie, a condition that satisfies the formula (J)) of the electrolyte accommodating portion in the radial direction (w). L) and are installed independently. Therefore, the area ratio (k) according to the formula (M) is larger than the area ratio of the actual polishing pad 60 (that is, the area ratio of the actual polishing pad 60 is equal to the area ratio ( k).

When polishing the conductor layer of a device wafer having a diameter of 300 mm, when the installation radius (R) of the electrolyte solution storage portion disposed on the outermost periphery is R = 350 mm, the radial length (w) is 2. The range is 5 mm <w <3.8 mm.
In addition, when polishing the conductor layer of a device wafer having a diameter of 200 mm, when the installation radius (R) of the electrolyte solution storage portion arranged on the outermost periphery is R = 250 mm, the radial length (w) is: The range is 3 mm <w <4.5 mm.

(Reason why the distance (p / n) in the radial direction of the spiral wire is 5 mm to 22.5 mm)
From the above conditions, the range of the distance between the spiral lines of the uniform spiral line when the radial length (w) is 2.5 mm <w <4.5 mm is examined.
Since the width (w0) of the electrolytic solution storage part is smaller than the length (w) in the radial direction, when the width (w0) is 4.5 mm, the total value of the area of the electrolytic solution storage part is obtained from the formula (N). In order to make the ratio (k) of the area of the polishing pad to 0.2 (20%) or more, the distance (p / n) between the spiral lines needs to be 22.5 mm or less.
On the other hand, when the width (w0) is 2.5 mm, in order to make the ratio (k) of the total opening area of the electrolytic solution container and the area of the polishing pad to 0.5 (50%) or less, the spiral The distance between lines (p / n) needs to be 5 mm or more.
From the above, the polishing pad needs to have a distance (p / n) in the radial direction of the spiral wire of 5 mm to 22.5 mm.

In addition, the distance between the lines in the radial direction of the spiral varies depending on the spiral constant (a) and the number of spirals (n).
For example,
In the case of a = 5 / 2π and one spiral wire: the distance between the radial lines is 5 mm
In the case of a = 48 / 2π and four spiral wires: the distance between the radial lines 12 (= 48/4) mm
In the case of a = 120 / 2π and 10 spiral wires: the distance between the radial lines 12 (= 120/10) mm
It becomes.
When the helical constant (a) is increased, the total opening area of the electrolyte accommodating portion with respect to the entire pad surface is reduced, and thus the polishing efficiency is reduced. In such a case, a decrease in polishing efficiency can be prevented by increasing the number of spirals (n) and increasing the total opening area.

Claims (7)

A plurality of electrolytic solution storage portions for storing an electrolytic solution and a cathode electrode formed on a bottom portion of the electrolytic solution storage portion, and a conductor layer of a device wafer is in contact with a surface of the electrolytic solution in the electrolytic solution storage portion A plurality of electrolytic cells are formed by applying a voltage to the cathode electrode and an anode electrode electrically or electrochemically connected to the conductor layer, and the conductor layer is formed into an electrochemical machine. In the polishing pad that polishes automatically,
A polishing surface layer formed of a synthetic resin and rotated relative to the conductor layer in contact with the conductor layer;
All the electrolytic solution storage portions from the inner diameter side to the outer diameter side have a radial length of the opening portion of the electrolytic solution storage portion w (mm), and a maximum installation radius of the electrolytic solution storage portion R (mm) ), The radial length w satisfies the relational expression of 45 / SQRT (R) <w <73 / SQRT (R),
A polishing pad for device wafers. The polishing pad according to claim 1, wherein
When the polishing surface is viewed from the normal direction, the plurality of electrolyte solution storage portions have a uniform spiral defined by one or more polar coordinate expressions r (θ) = a · θ on the polishing surface. The distance between the radial lines of the spiral wire is 5 mm to 22.5 mm,
A polishing pad characterized by. In the polishing pad of the device wafer according to claim 1 and 2,
Provided on the surface of the polishing surface layer so that the width thereof is equal to or less than that of the electrolyte container, the depth is shallower than the electrolyte container, and the plurality of electrolyte containers are connected. Providing a grooved portion,
A polishing pad for device wafers. In the polishing pad of the device wafer according to claim 1 and 2,
The polishing surface layer is formed of polyurethane or foamed polyurethane;
A polishing pad for device wafers. In the polishing pad of the device wafer according to claim 1 and 2,
The cathode electrode is made of gold, platinum, titanium alloy, stainless steel, or carbon;
A polishing pad for device wafers. Installed on a table that moves relative to the conductor layer of the device wafer, formed on the polishing surface layer formed of synthetic resin, a plurality of electrolyte solution storage portions for storing the electrolyte solution, and the bottom portion of the electrolyte solution storage portion A plurality of electrolysis cells formed by applying a voltage to the cathode electrode and an anode electrode electrically or electrochemically connected to the conductor layer, and the conductor layer A polishing method for electrochemically polishing the conductor layer using a polishing pad for electrochemically polishing
Supplying the electrolytic solution to the polishing surface of the polishing surface layer, filling the electrolytic solution in the plurality of electrolytic solution containing portions,
In the state where the polishing surface layer and the anode electrode are electrically or electrochemically connected to the conductor layer, an electrolytic cell is formed by supplying power to the cathode electrode and the anode electrode,
Relatively moving the polishing pad and the conductor layer;
All the electrolytic solution storage portions from the inner diameter side to the outer diameter side have a radial length of the opening portion of the electrolytic solution storage portion w (mm), and a maximum installation radius of the electrolytic solution storage portion R (mm) ), The radial length w satisfies the relational expression of 45 / SQRT (R) <w <73 / SQRT (R),
A method for polishing a device wafer. The polishing method according to claim 6, wherein
After polishing or before polishing of the conductor layer of the device wafer, the polishing pad is rotated at a rotation speed of 100 (rotation / min) or more, and the electrolytic solution or rinsing water stored in the electrolytic solution storage unit is removed. Having a discharging step,
A method for polishing a device wafer.

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