JP2004140178A - Chemical mechanical polishing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To evenly polish a polished surface very accurately while preventing the occurrence of scratches, suction of a work, and decline in polishing speed. <P>SOLUTION: In a chemical mechanical polishing apparatus 10 equipped with a polishing pad having a plurality of grooves and a plurality of holes in the polishing surface, the plurality of grooves are formed into concentric annular grooves 33, with a distance P<SB>1</SB>between the adjacent annular grooves 33 set smaller than a distance P<SB>2</SB>between the adjacent holes. Regardless of centrifugal force arising from the rotation of the polishing pad, slurry can be held in the annular grooves and hence the decline in polishing speed can be prevented. Since the annular grooves can connect between the polished surface and the polishing surface outside, a phenomenon of vacuum suction of the polished surface to the polishing surface can be prevented. Moreover, foreign matters which might be a cause for scratches can be trapped in the holes, resulting in the prevention of the occurrence of scratches. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a chemical mechanical polishing technique, and more particularly, to a technique of chemically mechanical polishing a main surface on a patterned side of a patterned semiconductor wafer (hereinafter, referred to as a patterned wafer).
[0002]
[Prior art]
Recently, a chemical mechanical polishing apparatus for polishing the surface of a patterned wafer by a combination of mechanical action and chemical action has been used. A conventional chemical mechanical polishing apparatus of this type includes a polishing pad stuck on a rotated base plate, and a wafer holding head for holding a wafer as a work, and a wafer held by the wafer holding head. Is rubbed against a polishing pad on which a polishing solution called a slurry is dropped to perform chemical mechanical polishing.
[0003]
This polishing pad is formed by laminating a foamed polyurethane on a nonwoven fabric impregnated with a polyurethane, and the foamed polyurethane side is a side for polishing a wafer. Conventional polishing pads of this type include, for example, the following. First, a plurality of holes having a diameter of 1.5 mm are formed on the entire surface of the polyurethane foam at intervals of 5 mm so that the slurry is held by the plurality of holes and brought into contact with the surface of the wafer. Polishing pad. Secondly, by forming grooves having a width of 2 mm and a depth of 0.5 to 0.8 mm in a grid pattern at intervals of 15 mm on the surface of the polyurethane foam, the slurry is held by the grid-shaped grooves and the wafer is formed. This is a polishing pad configured to be brought into contact with the surface. Thirdly, holes of about 1.5 mm in diameter are opened over the entire surface at 5 mm intervals on the surface of the polyurethane foam, and a plurality of grooves having a width smaller than the diameter of the holes and a depth of about 0.3 mm are formed in the holes. A polishing pad configured to be formed in a grid shape with an interval larger than the interval, thereby preventing the wafer from being attracted to the polishing pad, suppressing the required amount of slurry, and reducing the deterioration over time of the polishing pad. . As a document describing such a polishing pad, there is JP-A-11-235656.
[0004]
[Problems to be solved by the invention]
However, in the first polishing pad in which only the holes are formed, there is a problem that the wafer is attracted to the polishing pad when the wafer holding head is lifted to remove the wafer after the polishing is completed. Further, in the second polishing pad in which only the grooves are formed, a local pressure load is applied to the nonwoven fabric impregnated with the polyurethane, which is the lower soft layer, due to the deep grooves being formed at a high density. Therefore, there is a problem that the uniformity is easily deteriorated. Further, in the third polishing pad having the holes and the lattice-shaped grooves, the slurry falls into the lattice-shaped grooves by centrifugal force due to the rotation of the polishing pad during polishing, and passes through the lattice-shaped grooves to outside the polishing pad. Therefore, there is a problem that the polishing rate is reduced due to the discharge of the polishing liquid. In this type of conventional chemical mechanical polishing apparatus, it is most important to prevent scratches (polishing scratches) from being generated on the polished surface of the patterned wafer.
[0005]
SUMMARY OF THE INVENTION An object of the present invention is to provide a chemical mechanical polishing apparatus capable of uniformly polishing a surface to be polished with high accuracy while preventing generation of scratches, adsorption of a work, and reduction of a polishing rate.
[0006]
The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.
[0007]
[Means for Solving the Problems]
The outline of a typical invention disclosed in the present application will be described as follows.
[0008]
That is, a chemical mechanical polishing apparatus provided with a polishing pad having a plurality of grooves and a plurality of holes on a polishing surface, wherein the plurality of grooves are formed in concentric annular grooves, and The distance between adjacent ones of the holes is set to be equal to or less than the distance between adjacent ones of the holes.
[0009]
According to the above-described means, since the slurry can be held by the annular groove regardless of the centrifugal force due to the rotation of the polishing pad, a decrease in the polishing rate can be prevented. In addition, since the annular groove can connect the surface to be polished and the surface to be polished to the outside, it is possible to prevent the phenomenon that the surface to be polished is vacuum-adsorbed to the surface to be polished. Further, since the foreign matter causing the scratch can be trapped by the hole, the generation of the scratch can be prevented.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[0011]
As shown in FIG. 1, a chemical mechanical polishing apparatus 10 according to the present embodiment includes a polishing head 11. The polishing head 11 has a disk-shaped base plate 12 having a radius sufficiently larger than the diameter of a patterned wafer (hereinafter, referred to as a wafer) 1 which is a work, and the base plate 12 is rotatable in a horizontal plane. Supported. A rotating shaft 13 arranged vertically is fixed to the center of the lower surface of the base plate 12, and the base plate 12 is configured to be driven to rotate by the rotating shaft 13. The polishing pad 30 shown in FIG. 2 is uniformly attached to the entire upper surface of the base plate 12. On the center line of the polishing head 11, a slurry supply nozzle 14 for dropping a slurry 15, which is a polishing solution, is installed vertically downward. There are many types of the slurry 15 depending on the application. For example, when polishing an oxide film, a material containing about 10 to 20% of silica (SiO ₂ ) particles and adjusted to about pH 10 to 11 with KOH or NH ₄ OH is used.
[0012]
Above the polishing head 11, a wafer holding head 16 is installed horizontally. The wafer holding head 16 is reciprocated by a transfer device (not shown) between a station in which the polishing head 11 is installed and a loading station (not shown) from which the wafers 1 are discharged one by one. The wafer holding head 16 is slightly lowered during the polishing operation. The polishing head 11 includes a disk-shaped head body 17 having a diameter slightly larger than the diameter of the wafer 1. A circular holding hole 18 having a constant depth is concentrically arranged on the lower surface of the head body 17. Has been laid down. The size of the holding hole 18 is formed slightly larger than the size of the wafer 1. A vent hole 19 is formed at the center of the holding hole 18, and a positive pressure and a negative pressure are supplied to the holding hole 18 by connecting the vent hole 19 to an air pump and a vacuum pump (both not shown). It is supposed to be. Incidentally, the air pump and the vacuum pump are appropriately switched by a switching valve. A disc-shaped backing pad 20 having an outer diameter substantially equal to the inner diameter of the holding hole 18 is concentrically arranged on the lower surface of the holding hole 18 and adhered by an adhesive layer (not shown). The backing pad 20 is formed of a polyurethane foam, and a highly flexible layer is uniformly formed on the surface in contact with the wafer 1 by the porous and porous group of the foam. A circular ring-shaped retainer ring 21 is in contact with an outer peripheral portion on the lower surface of the head main body 17, and the retainer ring 21 is fastened to the head main body 17 by a plurality of bolts (not shown). The retainer ring 21 is formed in a circular ring shape having an outer diameter equal to the outer diameter of the head body 17 and an inner diameter substantially equal to the inner diameter of the holding hole 18. The retainer ring 21 holds the wafer 1 with the surface to be polished exposed from the lower end downward, while preventing the wafer 1 from jumping out during the polishing operation. On the center line of the head main body 17, a rotating shaft 22 is projected upward in the vertical direction, and the rotating shaft 22 is driven to rotate by a rotation driving device (not shown).
[0013]
On the opposite side of the polishing head 11 from the wafer holding head 16, a dresser 23 for removing and regenerating the surface layer of the polishing pad 30 damaged by polishing is horizontally installed, and the dresser 23 is a polishing pad 30. Is configured to be able to move horizontally with respect to the polishing head 11 in a state of contact with the polishing head 11. The dresser 23 includes a disk-shaped base plate 24 having a diameter sufficiently smaller than the radius of the polishing head 11, and the base plate 24 is rotatably supported in a horizontal plane. A rotating shaft 25 arranged vertically is fixed to the center of the upper surface of the base plate 24, and the base plate 24 is configured to be driven to rotate by the rotating shaft 25. On the lower surface of the base plate 24, a diamond pad 26 for polishing the surface layer of the polishing pad 30 is uniformly adhered throughout.
[0014]
As shown in FIG. 2, the polishing pad 30 is formed by laminating a foamed polyurethane 32 on a nonwoven fabric 31 impregnated with polyurethane. The nonwoven fabric (hereinafter, referred to as a soft layer portion) 31 is softer than the foamed polyurethane 32 so that the polishing pad 30 can follow the shape of the wafer 1. The foamed polyurethane (hereinafter, referred to as a hard layer portion) 32 is configured to be hard in order to polish the surface of the wafer 1 flat, but can be deformed on the micron order by a load received from the wafer 1. I have. On the surface of the hard layer portion 32, which is the polishing surface of the polishing pad 30, a plurality of annular grooves 33 having a constant width and a constant depth are laid in concentric circles, and a plurality of cylindrical holes 34 are formed at regular intervals. lattice shape are opened are arranged, the interval of annular grooves 33, 33 adjacent (pitch) P ₁ is set to the interval of the holes 34, 34 adjacent (pitch) P ₂ or less.
[0015]
Distance _{P 1} of adjacent annular grooves 33, 33 to each other is preferably set to 1.5 to 5 mm. In the present embodiment, the interval _{P 1} of the annular groove 33 adjacent is set to approximately 1.5 mm. It is desirable that the width W of the annular groove 33 be set to 0.25 to 2 mm. In the present embodiment, the width W of the annular groove 33 is set to about 0.25 mm. It is desirable that the depth H of the annular groove 33 be set to 0.15 to 1.8 mm. In the present embodiment, the depth H of the annular groove 33 is set to about 0.4 mm. The diameter D of the hole 34 is desirably set to 1 to 4 mm. In the present embodiment, the diameter D of the hole 34 is set to about 1.5 mm, interval _{P 2} between adjacent holes 34, 34 is set to about 5.5 mm.
[0016]
Next, the operation and effect of the chemical mechanical polishing apparatus according to the above configuration will be described.
[0017]
As shown in FIG. 1, the wafer 1 is inserted into the retainer ring 21 of the wafer holding head 16 with the surface to be polished facing downward. When the wafer 1 is inserted into the retainer ring 21, a negative pressure is supplied to the vent 19. Since the negative pressure is applied to the main surface of the wafer 1 opposite to the surface to be polished (hereinafter, referred to as the back surface) through the perforations of the backing pad 20, the wafer 1 is vacuum-sucked to the wafer holding head 16. The wafer holding head 16 to which the wafer 1 has been vacuum-sucked is transferred to a position directly above the polishing head 11 by the transfer device and then lowered. When the surface to be polished of the wafer 1 comes into contact with the surface of the polishing pad 30 which is the polishing surface by the lowering of the wafer holding head 16, the switching valve is switched and the air is supplied to the vent hole 19.
[0018]
Subsequently, the polishing head 11 and the wafer holding head 16 are rotated while the slurry 15 is supplied from the slurry supply nozzle 14 to the surface of the polishing pad 30. When the wafer holding head 16 is rotated, the slurry 15 supplied to the surface of the polishing pad 30 is taken in and held by a plurality of annular grooves 33 arranged concentrically. At this time, since a large number of annular grooves 33 having a width W of about 0.25 mm and a depth H of about 0.4 mm are concentrically provided at intervals of about 1.5 mm, a large amount of slurry 15 A state of being held on the surface which is the 30 polished surface is obtained.
[0019]
Thereafter, the wafer holding head 16 is lowered very slightly. As the wafer holding head 16 is lowered, the wafer 1 is urged vertically via the backing pad 20. At the same time, since the air supplied to the vent hole 19 is supplied to the back side surface, the wafer 1 is also urged in the vertical direction by the action force of the air pressure. Therefore, the surface to be polished of the wafer 1 is rubbed against the polishing surface of the polishing pad 30 while being simultaneously urged by the mechanical force and the acting force of the air pressure on the polishing surface of the polishing pad 30. At this time, since the slurry 15 is held by the group of annular grooves 33, mechanochemical polishing that enhances the polishing effect is performed in addition to mechanical polishing (polishing).
[0020]
In a state where the wafer 1 is simultaneously urged against the polishing pad 30 by the mechanical force and the acting force of the air pressure, the surface to be polished is a large amount of the slurry 15 held in the multiple annular grooves 33 of the polishing pad 30. Therefore, the polishing amount of the polished surface by the polishing pad 30 becomes uniform throughout. During chemical mechanical polishing, the irregular and complicated strain force acting from the wafer 1 side pressed by the mechanical pressing force of the wafer holding head 16 causes the deformation of the soft layer portion 31 and the hard layer portion 32 of the polishing head 11. Is corrected in a self-aligned manner by the micron-order deformation, so that the polished amount of the polished surface becomes uniform over the entire surface.
[0021]
After the chemical mechanical polishing of the set polishing amount is completed, the surface to be polished of the wafer 1 is flattened with extremely high precision, and the insulating film is left with a predetermined layer thickness. The wafer 1 in this state is sucked and held by the wafer holding head 16 and transferred from above the polishing head 11. At this time, as shown in FIG. 1B, the annular groove 33 group in contact with the wafer 1 is open at both ends outside the lower surface of the wafer 1, so that the wafer 1 is Since the wafer 1 does not stick to the surface of the polishing pad 30, the wafer 1 can be reliably pulled up from the surface of the polishing pad 30 by the wafer holding head 16.
[0022]
By the way, in the above chemical mechanical polishing, foreign substances such as agglomerates of abrasive grains contained in the slurry 15, debris and chips generated by crushing the wafer 1 during polishing, and chips generated by polishing the dresser 23 are removed. Many foreign substances are present on the surface of the polishing pad 30, and these foreign substances cannot be completely removed by pouring the slurry 15, so that they may remain on the surface of the polishing pad 30. Then, the surface to be polished of the wafer 1 is damaged by foreign matter remaining on the surface of the polishing pad 30, so that a scratch is formed on the surface to be polished of the wafer 1.
[0023]
However, in the present embodiment, the hard layer portion 32 of the polishing pad 30 has a cylindrical hole 34 having a diameter of about 1.5 mm, which is entirely formed at intervals of about 5.5 mm. Since the foreign matter generated on the surface of the pad 30 can be immediately trapped by the group of holes 34, the polished surface of the wafer 1 is damaged by the foreign matter remaining on the surface of the polishing pad 30. The occurrence of scratches formed on the surface of the substrate can be prevented beforehand.
[0024]
FIG. 3 is a graph showing the effect of reducing scratches. In FIG. 3, the horizontal axis represents the usage time (hr) of the polishing pad, and the vertical axis represents the number of scratches. A solid broken line A indicates the case of the present embodiment, and a broken broken line B indicates the case of the comparative example. The comparative example is a case where a polishing pad is used in which grooves having a width of 0.25 mm and a depth of about 0.3 mm are formed concentrically on the surface of the polyurethane foam at intervals of 1.5 mm. According to FIG. 3, in the case of the comparative example, the number of scratches starts to increase exponentially after 1.5 hours of use, whereas in the case of the present embodiment, the number of scratches increases. It is understood that not seen.
[0025]
FIG. 4 is a graph showing the transition of the polishing rate (vertical axis) with the use time (horizontal axis) of the polishing pad. In FIG. 4, a solid line C indicates the case of the present embodiment, and a broken line D indicates the case of the comparative example. The comparative example is a case where the same polishing pad as that of FIG. 3 is used. According to FIG. 4, it is understood that the polishing rate of the present embodiment is about 10% higher than that of the comparative example.
[0026]
FIG. 5 is a graph showing a change in the polishing rate (vertical axis) with respect to the use time (horizontal axis) of the polishing pad in another comparative example. A solid line E indicates the case of the present embodiment, and a broken line. Represents the case of the comparative example. In this comparative example, a hole having a diameter of about 1.5 mm is formed over the entire surface at an interval of 5 mm on the surface of the polyurethane foam, and a plurality of grooves having a width smaller than the hole diameter and a depth of about 0.3 mm are formed. This is a case where a polishing pad formed in a lattice shape with an interval larger than the interval between the holes is used. According to FIG. 5, it is understood that the polishing rate of the present embodiment is about 50% higher than that of the comparative example. The reason why the polishing rate of the present embodiment is higher than that of the comparative example is considered as follows. In the polishing pad of the comparative example, since the slurry falls into the lattice-shaped grooves due to centrifugal force due to the rotation of the polishing pad during polishing and is discharged out of the polishing pad through the lattice-shaped grooves, the polishing speed is reduced. Will drop. On the other hand, in the polishing pad 30 according to the present embodiment, since the groove for holding the slurry 15 is formed in the annular groove 33, the slurry is formed by the centrifugal force due to the rotation of the polishing pad during polishing. Since it is held without being discharged from the 33rd group, the polishing rate does not decrease.
[0027]
FIG. 6 is a graph showing the transition of the uniformity of the polishing amount (vertical axis) according to the use time (horizontal axis) of the polishing pad. The uniformity of the polishing amount is a characteristic represented by the following equation.
Uniformity of polishing amount = (maximum polishing amount-minimum polishing amount) / (maximum polishing amount + minimum polishing amount)
In FIG. 6, a solid line G indicates the case of the present embodiment, and a broken line curve H indicates the case of the comparative example. The comparative example is a case where the same polishing pad as that of FIG. 3 is used. As is clear from FIG. 6, in the case of the comparative example, the polishing uniformity increases in a curve with the elapse of use time, whereas in the case of the present embodiment, the polishing uniformity is reduced. It gradually increases linearly as the use time elapses. Therefore, in the case of the present embodiment, the life of polishing pad 30 can be set longer.
[0028]
By the way, when the configuration of the annular groove 33 and the hole 34 formed on the surface of the hard layer portion 32 of the polishing pad 30 was investigated, the following results were obtained.
[0029]
It is desirable that the interval between the adjacent annular grooves 33 is set to 1.5 to 5 mm. If the interval between the adjacent annular grooves 33, 33 is less than 1.5 mm, the annular groove 33 becomes excessive, and the contact area between the surface of the hard layer portion 32 of the polishing pad 30 and the wafer 1 becomes insufficient. Slurry 15 is required. When the interval between the adjacent annular grooves 33 exceeds 5 mm, the slurry 15 is insufficient due to the lack of the annular groove 33, and the polishing rate is reduced.
[0030]
It is desirable that the width of the annular groove 33 be set to 0.25 to 2 mm. If the width of the annular groove 33 is less than 0.25 mm, processing of the annular groove 33 becomes difficult. If the width of the annular groove 33 exceeds 2 mm, the contact area between the surface of the hard layer 32 of the polishing pad 30 and the wafer 1 becomes insufficient, and the polishing rate decreases.
[0031]
It is desirable that the depth of the annular groove 33 be set to 0.15 to 1.8 mm. When the depth of the annular groove is less than 0.15 mm, the polishing speed becomes lower than that without the annular groove 33, and the polishing rate is reduced. If the depth of the annular groove exceeds 1.8 mm, it becomes difficult to process the annular groove due to restrictions due to the thickness of the hard layer portion 32 of the polishing pad 30.
[0032]
The diameter of the hole 34 is desirably set to 1 to 4 mm. If the diameter of the hole is less than 1 mm, foreign substances causing scratches cannot be trapped, so that the number of scratches increases. If the diameter of the hole exceeds 4 mm, the contact area between the surface of the hard layer portion 32 of the polishing pad 30 and the wafer 1 becomes insufficient, and the polishing rate decreases.
[0033]
Preferably, the diameter of the hole 34 is larger than the width of the annular groove 33. Further, the interval between the adjacent holes 34 is preferably about 5 mm.
[0034]
Although the invention made by the present inventor has been specifically described based on the embodiment, the present invention is not limited to the above embodiment, and various changes can be made without departing from the gist of the invention. Needless to say.
[0035]
For example, the holes 34 are not limited to being arranged in a grid pattern in a grid, but may be arranged in a staggered grid pattern as shown in FIG.
[0036]
The wafer holding head is not limited to the configuration as in the above embodiment, but may adopt another configuration. Further, the wafer holding head is not limited to being arranged on the upper side and the polishing head is arranged on the lower side. The wafer holding head may be arranged on the lower side and the polishing head may be arranged on the upper side. Further, the present invention is not limited to the configuration in which the wafer holding head side is lowered, but may be configured to raise the polishing head side.
[0037]
In the above description, the case where the invention made by the present inventor is applied to a chemical mechanical polishing technique for flattening irregularities on a patterning-side main surface of a patterned wafer, which is a field of application as a background, has been described. The present invention is not limited to this, and can be applied to all chemical mechanical polishing techniques such as a chemical mechanical polishing technique used for forming copper (Cu) wiring by a damascene technique.
[0038]
【The invention's effect】
The effect obtained by the representative one of the inventions disclosed in the present application will be briefly described as follows.
[0039]
A plurality of annular grooves are formed concentrically on the polishing surface of the polishing pad, and the distance between adjacent ones of these annular grooves is set to be equal to or less than the distance between adjacent ones of a plurality of holes formed on the polishing surface. By doing so, regardless of the centrifugal force due to the rotation of the polishing pad, the slurry can be held by the annular groove, and the foreign matter that causes the scratch can be trapped by the hole. The surface to be polished can be uniformly polished with high precision while preventing the suction of the work and the reduction of the polishing rate.
[Brief description of the drawings]
FIG. 1 shows a chemical mechanical polishing apparatus according to an embodiment of the present invention, wherein (a) is a partially cut front view and (b) is a plan view.
FIGS. 2A and 2B show a polishing pad, wherein FIG. 2A is a plan view and FIG. 2B is a cross-sectional view taken along line bb of FIG.
FIG. 3 is a graph showing the effect of reducing scratches.
FIG. 4 is a graph showing a change in a polishing rate with a use time of a polishing pad.
FIG. 5 is a graph showing a change in a polishing rate according to a use time of a polishing pad.
FIG. 6 is a graph showing the transition of the uniformity of the polishing amount with the use time of the polishing pad.
7A and 7B show a polishing pad according to a second embodiment of the present invention, wherein FIG. 7A is a plan view, and FIG. 7B is a cross-sectional view taken along line bb of FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Wafer (semiconductor wafer), 10 ... Chemical mechanical polishing apparatus, 11 ... Polishing head, 12 ... Base plate, 13 ... Rotating shaft, 14 ... Slurry supply nozzle, 15 ... Slurry, 16 ... Wafer holding head, 17 ... Head main body , 18 ... holding hole, 19 ... vent hole, 20 ... backing pad, 21 ... retainer ring, 22 ... rotating shaft, 23 ... dresser, 24 ... base plate, 25 ... rotating shaft, 26 ... diamond pad, 30 ... polishing pad, 31 ... soft layer portion (nonwoven fabric), 32 ... hard layer portion (foamed polyurethane), 33 ... annular groove, 34 ... hole.

Claims (5)

A chemical mechanical polishing apparatus provided with a polishing pad having a plurality of grooves and a plurality of holes on a polishing surface, wherein the plurality of grooves are formed in concentric annular grooves, and adjacent to the annular grooves. A chemical mechanical polishing apparatus characterized in that an interval between the mating members is set to be equal to or less than an interval between adjacent ones of the holes. The chemical mechanical polishing apparatus according to claim 1, wherein an interval between adjacent ones of the annular grooves is set to 1.5 to 5 mm. 3. The chemical mechanical polishing apparatus according to claim 1, wherein the width of the annular groove is set to 0.25 to 2 mm. The chemical mechanical polishing apparatus according to claim 1, wherein a depth of the annular groove is set to 0.15 to 1.8 mm. 5. The chemical mechanical polishing apparatus according to claim 1, wherein the diameter of the hole is set to 1 to 4 mm.

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