JP7349791B2 - CMP equipment - Google Patents

Description

The present invention relates to a CMP apparatus for CMP polishing a wafer.

In the field of semiconductor manufacturing, CMP apparatuses are known that planarize semiconductor wafers (hereinafter referred to as "wafers") such as silicon wafers.

The polishing apparatus described in Patent Document 1 is a polishing apparatus to which chemical mechanical polishing, so-called CMP (Chemical Mechanical Polishing) technology is applied. In this polishing apparatus, a polishing head polishes a wafer by pressing it against a polishing cloth using air pressure in an air chamber formed in a gap between a carrier and an elastic sheet whose peripheral edge is held by a template retainer. Further, in this polishing apparatus, by providing a plurality of airbags on the lower surface of the carrier, the amount of polishing of the wafer is locally changed for each zone where the airbags are provided.

Patent No. 3683149

By the way, CMP polishing is performed on a ground wafer. In this grinding process, as shown in FIG. 8, the upper surface of the wafer W is gradually ground by pressing the cup-shaped grindstone 100 against the wafer W while the wafer W and the cup-shaped grindstone 100 are rotating.

Further, the cup-shaped grindstone 100 may press against the wafer W at an angle of inclination θ with respect to the rotating shaft 101. Thereby, the contact distance (grinding distance) between the wafer W and the cup-shaped grindstone 100 is shortened, and damage to the wafer W due to excessive heat generation accompanying the grinding process is suppressed.

However, when the wafer W is ground with the cup-shaped grindstone 100 inclined with respect to the rotation axis 101, the shape of the wafer W after grinding is such that the amount of grinding is reduced near the midpoint in the radial direction of the wafer W, as shown in FIG. The thickness was maximum, and the vicinity of the center of the wafer W tended to be thicker than the surrounding area.

When performing CMP polishing on a wafer W with a characteristic shape where the center area is thicker than the surrounding area, the entire surface of the wafer W can be polished to a high degree of flatness using only local pressure using a conventional air bag. The problem was that it was difficult.

Therefore, a technical problem arises that must be solved in order to polish a wafer with a characteristic shape that is thick near the center to a high degree of flatness, and it is an object of the present invention to solve this problem.

In order to achieve the above object, in the CMP apparatus according to the present invention, compressed air is supplied between a carrier and a membrane film provided below the carrier, and the membrane film expands to remove the wafer. A CMP apparatus that polishes the wafer by pressing it against a polishing pad, the central pressing means capable of locally pressing approximately the center of the membrane film includes a pressing member provided approximately at the center of the carrier. , a first air bag provided between the carrier and the pressing member and inflated with compressed air to move the pressing member downward; The formed lower end surface has a radius of curvature set according to the center thickness of the wafer, the diameter and thickness of the pressing member, and the diameter and thickness of the first airbag .

According to this configuration, when the airbag is inflated, the pressing member locally presses approximately the center of the membrane film, compared to the conventional case where the amount of polishing is adjusted by the amount of inflation of the airbag. Since the pressing force acting near the center of the wafer becomes sharper, it is possible to flatten a wafer with a characteristic shape that is thick near the center. Further, since the pressing force exerted on the wafer by the pressing member is suppressed from being excessively concentrated, the wafer can be flattened without damaging the wafer.

Further, in the CMP apparatus according to the present invention, the pressing member is provided on the lower surface of the carrier and between the membrane film and the pressing member, and compressed air is applied to the outer peripheral side of the first airbag. Preferably, the membrane film is pressed through a second airbag forming one or more inflatable zones.

According to this configuration, the pressing member indirectly presses the membrane film through the second airbag , so that a pressure distribution that gradually changes from near the center of the wafer to the periphery can be obtained, and the pressure distribution is applied to the wafer. Wafers can be processed flat without causing damage.

Moreover, in the CMP apparatus according to the present invention, it is preferable that the pressing member directly presses the membrane film.

According to this configuration, when the pressing member directly presses the membrane film, the pressing force acting near the center of the wafer becomes particularly sharp, so that a wafer with a characteristic shape that is thick near the center can be flattened. can do.

In the present invention, the airbag is inflated and the pressing member locally presses approximately the center of the membrane film, thereby improving the polishing amount of the wafer compared to the conventional case where the amount of polishing is adjusted by the amount of inflation of the airbag. Since the pressing force acting near the center becomes sharper, it is possible to flatten a wafer with a characteristic shape that is thick near the center.

1 is a perspective view schematically showing a CMP apparatus according to an embodiment of the present invention. FIG. 3 is a vertical cross-sectional view schematically showing the main parts of the polishing head. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical cross-sectional view showing essential parts of a polishing head according to a first embodiment of the present invention, and a schematic diagram showing a pressure distribution obtained with the polishing head. FIG. 3 is a schematic diagram showing a pressing member. FIG. 7 is a vertical cross-sectional view showing the main parts of a polishing head according to a second embodiment of the present invention, and a schematic diagram showing a pressure distribution obtained with the polishing head. Graph showing polishing rates when polishing using various polishing heads. 7 is a graph showing the wafer thickness and polishing amount before and after polishing in polishing using the polishing head according to the second example. FIG. 2 is a schematic diagram showing how a wafer is ground with a grindstone tilted. A diagram schematically showing the thickness of a wafer after grinding. FIG. 2 is a vertical cross-sectional view schematically showing a state in which pressure is applied near the center of a conventional polishing head, and a schematic diagram showing a pressure distribution obtained with the polishing head. 11 is a graph showing the wafer thickness and polishing amount before and after polishing in polishing using the polishing head shown in FIG. 10.

Embodiments of the present invention will be described based on the drawings. In addition, in the following, when referring to the number, numerical value, amount, range, etc. of constituent elements, it is limited to that specific number, unless it is specifically specified or it is clearly limited to a specific number in principle. It doesn't matter if it's more than or less than a certain number.

In addition, when referring to the shape or positional relationship of constituent elements, etc., unless it is specifically specified or it is clearly considered that it is not the case in principle, etc., we refer to things that are substantially similar to or similar to the shape, etc. include.

Further, in the drawings, characteristic parts may be enlarged or exaggerated in order to make the features easier to understand, and the dimensional ratios of the constituent elements are not necessarily the same as in reality. Further, in the cross-sectional views, hatching of some components may be omitted in order to make the cross-sectional structure of the components easier to understand.

FIG. 1 is a perspective view schematically showing a CMP apparatus 1 according to a first embodiment of the present invention. The CMP apparatus 1 polishes one surface of a wafer W to a flat surface. The CMP apparatus 1 includes a platen 2 and a polishing head 10.

The platen 2 is formed into a disk shape and is connected to a rotating shaft 3 arranged below the platen 2. As the rotary shaft 3 is rotated by the drive of the motor 4, the platen 2 rotates in the direction of arrow D1 in FIG. A polishing pad 5 is attached to the upper surface of the platen 2, and CMP slurry, which is a mixture of an abrasive and a chemical, is supplied onto the polishing pad 5 from a nozzle (not shown).

The polishing head 10 is formed into a disk shape with a smaller diameter than the platen 2, and is connected to a rotating shaft 10a arranged above the polishing head 10. The polishing head 10 rotates in the direction of arrow D2 in FIG. 1 by rotating the rotating shaft 10a by driving a motor (not shown). The polishing head 10 can be moved up and down in the vertical direction V by a lifting device (not shown). The polishing head 10 descends to press the wafer W against the polishing pad 5 when polishing the wafer W. The wafer W polished by the polishing head 10 is transferred by a wafer transport mechanism (not shown).

The operation of the CMP apparatus 1 is controlled by a control means (not shown). The control means controls each of the constituent elements constituting the CMP apparatus 1. The control means is, for example, a computer, and is composed of a CPU, memory, and the like. Note that the functions of the control means may be realized by controlling using software, or may be realized by operating using hardware.

Next, the polishing head 10 will be explained. FIG. 2 is a vertical cross-sectional view schematically showing the main parts of the polishing head 10. As shown in FIG. Note that in FIG. 2, the elastic pressing member 70 is omitted. FIG. 3A is a vertical cross-sectional view schematically showing the lower part of the polishing head 10. FIG.

The polishing head 10 includes a head main body 20, a carrier 30, a template retainer 40, a membrane film 50, and a backing film 60.

The head main body 20 is connected to the rotating shaft 10a and rotates together with the rotating shaft 10a. The head main body 20 is connected to a carrier 30 disposed below the head main body 20 via a rotating part 21, and the head main body 20 and the carrier 30 rotate in conjunction with each other.

The carrier 30 is provided with airlines 31 arranged at equal intervals around the periphery of the carrier 30. The lower end of the airline 31 opens into an air chamber A formed between the lower surface 30a of the carrier 30 and the membrane film 50. The airline 31 is connected to an air supply source (not shown) as an air supply means, and air is introduced into the air chamber A via the airline 31. The pressure of air supplied to the airline 31 is regulated by a regulator (not shown). The air supplied into the air chamber A forms an air layer above the membrane film 50 by the rim formed on the outer peripheral edge of the carrier 30, and presses the entire surface of the membrane film 50 downward.

A carrier pressing means 32 is provided between the head main body 20 and the carrier 30. The carrier pressing means 32 is an air bag or the like that is inflated by air supplied from an air supply source (not shown). The pressure of air supplied from the air supply source is regulated by a regulator (not shown). The carrier pressing means 32 presses the wafer W against the polishing pad 5 via the carrier 30 according to the pressure of the supplied air.

The template retainer 40 is arranged to surround the carrier 30. The template retainer 40 includes a retainer holder 41 to which a membrane film 50 is attached on the upper surface.

The retainer holder 41 is made of resin such as glass epoxy, polyetheretherketone (PEEK), or polyphenylene sulfide (PPS). The retainer holder 41 is formed in an annular shape and includes a storage pocket 41a for storing the wafer W in the center. The retainer holder 41 is attached to a retainer pressing member 43 via a snap ring 42. A retainer pressing means 44 is provided between the head main body 20 and the retainer pressing member 43. In addition, the code|symbol 45 is a cover which covers the upper part of the snap ring 42.

The retainer pressing means 44 is an air bag or the like that is inflated by air supplied from an air supply source (not shown). The pressure of air supplied from the air supply source is regulated by a regulator (not shown). The retainer pressing means 44 presses the template retainer 40 against the polishing pad 5 via the retainer pressing means 44 according to the pressure of the supplied air.

The membrane film 50 is attached to the retainer holder 41 so as to cover the accommodation pocket 41a, and when compressed air is introduced into the air chamber A, the membrane film 50 is elastically deformed into the accommodation pocket 41a by air pressure.

The membrane film 50 is preferably made of a material that has both appropriate strength and flexibility, and is preferably made of a resin such as polyether ether ketone (PEEK), polyphenylene sulfide (PPS), or polyethylene terephthalate (PET). PEEK is particularly preferable for the membrane film 50 from the viewpoint of physical properties and availability, but PPS and PET are also preferable because their Young's modulus E is close to that of PEEK and they are relatively easily available.

The backing film 60 is, for example, a suede film. The backing film 60 is attached to the membrane film 50 with its center positioned on the rotating shaft 10a of the polishing head 10. When compressed air is introduced into the air chamber A, the backing film 60 is elastically deformed and pressurizes the wafer W as the membrane film 50 is elastically deformed.

As shown in FIG. 3(a), an elastic pressing member (zone rubber) 70 is provided on the lower surface 30a of the carrier 30 and is arranged coaxially with the rotating shaft 10a of the polishing head 10. As shown in FIG. The elastic pressing member 70 is made of, for example, polyethylene terephthalate resin (PET), fluororesin (PFA), or polyphenylene sulfide (PPS). PFA has a low water absorption rate, is moderately flexible, and is resistant to stretching and deformation. PPS has a low water absorption rate, is resistant to elongation and deformation, and is cheaper than PFA.

The elastic pressing member 70 is detachably attached to a layout base 80 interposed between the carrier 30 and the elastic pressing member 70. The layout base 80 is fastened to the carrier 30 with bolts (not shown).

The elastic pressing member 70 is divided into two zones, each zone is connected to an air supply source, and can be independently expanded by air supplied from the air supply source. Hereinafter, each area into which the elastic pressing member 70 is divided is referred to as a ``zone Z1'' and a 20 mm diameter area on the center side of the polishing head 10 as a ``zone Z2'', respectively. Note that the number of zones is not limited to two, and may be three or more. Further, the first airbag 71 forming the zone Z1 and the second airbag 72 forming the zone Z2 may be integrated or separate.

A pressing member 90 is joined to the lower end of the first airbag 71. Specifically, as shown in FIG. 4, the first airbag 71 is adhered to the pressing member 90 with double-sided tape via a PET film 91.

Since the pressing member 90 directly contacts the membrane film 50 as described later, it is preferably made of, for example, synthetic rubber having appropriate hardness.

Further, the lower end surface (pressing surface) of the pressing member 90 is formed in a dome shape, and the radius of curvature R of the pressing surface is set according to the center thickness of the wafer W, which is the object of polishing and is thick near the center. Specifically, the center thickness of the wafer W that is thick near the center to be polished is set to 0.36 mm, the diameter d1 of the first airbag 71 is set to 20 mm, the thickness t1 is set to 1 mm, and the thickness t2 of the pressing member 90 is set to 1 mm. When the diameter d2 of the pressing member 90 is set to 2.5 mm, the radius of curvature R of the pressing member 90 is set to 2.35 mm. Further, when the center thickness of the wafer W to be polished, which is thick near the center, is 0.36 mm and the diameter d2 of the pressing member 90 is 5 mm, the radius of curvature R of the pressing member 90 is set to 8.86 mm. do.

Next, the operation of the CMP apparatus 1 will be explained. As shown in FIG. 3(a), in the CMP apparatus 1, the compressed air supplied into the air chamber A transmits the pressing force applied to the carrier 30 to the wafer W via the membrane film 50, thereby creating a uniform pressure. The wafer W can be polished by pressing the wafer W against the polishing pad 5 in a distributed manner.

Furthermore, by independently expanding zones Z1 and Z2 of the elastic pressing member 70 according to the pressure of compressed air, zones Z1 and Z2 can be selectively pressurized to locally polish the wafer W. can. Note that FIG. 3A illustrates a case where only the first airbag 71 in zone Z1 is inflated.

The polishing pressure acting on the wafer W includes the pressure at which the pressing member 90 directly presses the membrane film 50 according to the air pressure in the zone Z1, and the pressure at which the membrane film 50 presses the wafer W in accordance with the air pressure in the air chamber A. It is the sum of the pressure that

As shown in FIG. 3(b), the pressure distribution near the center of the zone Z1 is sharper than the surrounding area, in other words, the pressure distribution locally presses only a narrow area near the center of the wafer W. On the other hand, on the outer peripheral side of zone Z1, a pressure drop occurs locally due to the reaction force of the pressing force of zone Z1.

Next, a CMP apparatus 1 according to a second embodiment will be described based on FIG. 5. Note that the CMP apparatus 1 according to this embodiment differs from the CMP apparatus 1 according to the above-described embodiments in the configurations of the elastic pressing member 70 and the pressing member 90, but the other configurations are the same. Reference numerals are given and duplicate explanations are omitted.

In the CMP apparatus 1 according to this embodiment, the second airbag 72 is provided to cover the lower surface of the layout base 80, and the first airbag 71 and the pressing member 90 are arranged to cover the carrier 30 and the second airbag 72. It is interposed between the bag 72 and the bag 72.

That is, when the first airbag 71 is inflated according to the pressure of compressed air, the pressing member 90 is configured to press the membrane film 50 indirectly via the second airbag 72. . Note that FIG. 5A illustrates a case where only the first airbag 71 is inflated.

Compared to the CMP apparatus 1 according to the first embodiment described above, since the pressing member 90 contacts the membrane film 50 via the elastic pressing member 70, the pressing member 90 is made of metal, etc. in addition to synthetic rubber, for example. It does not matter if it is a hard material.

As a result, as shown in FIG. 5(b), the pressure distribution near the center of the zone Z1 is sharpened compared to the surrounding area, in other words, only a narrow area near the center of the wafer W is locally pressed. A suitable pressure distribution can be obtained, and pressure is also applied to the periphery where the pressing member 90 is in contact, so that the pressure gradually decreases from the zone Z1 toward the outer circumferential side.

On the other hand, in the case of a conventional CMP apparatus 103 that locally presses the wafer W with an air bag 102 provided in the center as shown in FIG. 10(a), as shown in FIG. It is possible to obtain a pressure distribution in which the zone Z1 formed by the expansion of the bag 102 gradually increases, in other words, a pressure distribution in which a wide area including the vicinity of the center of the wafer W is pressed. In addition, in FIG. 10(a), among the components of the CMP apparatus 103, the members corresponding to the components of the CMP apparatus according to each of the above-mentioned embodiments are designated with corresponding numerals in the 100s, so that duplicates thereof are indicated. The explanation will be omitted.

In order to correct such pressure distribution to a sharp shape only in the vicinity of the center of the wafer W, it is conceivable to make the airbag 102 small in diameter and set the zone Z1 to a small diameter, for example. However, if the zone Z1 is formed to have an excessively small diameter, the reaction force acting on the airbag 102 when pressing the wafer becomes relatively large, making it impossible for the airbag 102 to maintain its shape and obtaining the desired pressure distribution. Alternatively, it is necessary to inflate the airbag 102 at high pressure, which inevitably increases the cost of the device.

Next, evaluation data comparing the amount of polishing when CMP polishing is performed using the CMP apparatus 1 according to the first and second embodiments described above will be explained based on FIG. 6.

A solid line a in FIG. 6 indicates the amount of polishing when polishing is performed using the CMP apparatus 1 according to the first embodiment, and a broken line b indicates the amount of polishing when polishing is performed using the CMP apparatus 1 according to the first embodiment. It shows. In FIG. 6, the vertical axis represents the amount of polishing, and the horizontal axis represents the radial coordinates with the rotation center of the polishing head 10 as the origin. The main polishing conditions set in this evaluation are shown in Table 1. Note that in the following, the regions of each zone are set in the radial direction from the center of rotation of the polishing head 10, 0 to 10 mm as zone Z1, 10 to 30 mm as zone Z2, and 30 to 50 mm as zone Z3.

In the CMP apparatus 1 according to the first embodiment, the zone pressures of zones Z1 to Z3 were set to 3 psi, 0 psi, and 3 psi in this order. Further, the pressing member 90 is bonded to the lower end of the first airbag 71 having a thickness of 1 mm and corresponding to the zone Z1, and is formed to have a diameter of 5 mm.

As shown by the solid line a in FIG. 6, in the CMP apparatus 1 according to the first embodiment, polishing progresses significantly in the region (Φ5 mm) where the pressing member 90 directly presses the membrane film 50. It can be seen that the amount of polishing around it (particularly Φ5 to 10 mm) is relatively low, and the amount of polishing gradually increases toward the outer periphery.

Note that when the zone pressure of zone Z1 was increased to 5 psi from the wafer pressure of 2.3 psi in order to increase the amount of polishing indicated by the solid line a in FIG. 6, the wafer W was damaged due to overpressure.

Next, in the CMP apparatus 1 according to the second embodiment, the zone pressures of zones Z1 to Z3 were set to 3 psi, 2.7 psi, and 3 psi in this order. Further, the pressing member 90 is bonded to the lower end of the first airbag 71 having a thickness of 1 mm and corresponding to the zone Z1, and is formed to have a diameter of 2.5 mm.

As shown by the broken line b in FIG. 6, the CMP apparatus 1 according to the second embodiment can perform polishing in a wide range including the area (Φ2.5 mm) where the pressing member 90 indirectly presses the membrane film 50. It can be seen that although the amount of polishing progresses and the amount of polishing around the area is relatively low, the amount of decrease in the amount of polishing is small compared to the CMP apparatus 1 according to the first embodiment described above.

Furthermore, in order to increase the amount of polishing indicated by the broken line b in FIG. 6, the wafer W was not damaged even when the zone pressure of zone Z1 was increased to 5 psi from the wafer pressure of 2.3 psi.

Next, the amount of polishing when the pressing member 90 of the CMP apparatus 1 according to the second embodiment is changed to a diameter of 5 mm is shown by the broken line c in FIG.

According to the broken line c in FIG. 6, the tendency of the amount of polishing is the same as that of the broken line b, but the peak of the amount of polishing is eased by the larger diameter of the pressing member 90, and the in-plane variation in the amount of polishing is reduced. It can be seen that it has been reduced.

Next, a comparison will be made between the case where polishing is performed using the CMP apparatus 1 corresponding to the broken line b in FIG. 6 and the case where polishing is performed using the conventional CMP apparatus 103 as shown in FIG. 10(a).

Line A in FIG. 7 shows the shape of the wafer W before polishing, line B shows the shape of the wafer W after polishing with the CMP device 1, and line C shows the polishing amount of the CMP device 1 (from line A to line B). (subtracted).

Further, line D in FIG. 10 shows the shape of the wafer W before polishing, line E shows the shape of the wafer W after polishing in the CMP apparatus 103, and line F shows the polishing amount of the CMP apparatus 103 (from line D to line (subtracted E). In addition, in FIGS. 7 and 10, the vertical axis represents the thickness, and the horizontal axis represents the radial coordinates with the rotation center of the polishing head as the origin.

According to line F in FIG. 10, the wafer shape after polishing is still locally thick at the center, whereas according to line B in FIG. 7, the entire surface of the wafer shape after polishing is flattened. Compared to line F, the flatness is improved by 108 nm.

In this manner, according to the CMP apparatus according to the embodiment of the present invention, the airbag is inflated and the pressing member locally presses approximately the center of the membrane film, thereby reducing the amount of inflation of the airbag as in the conventional case. Compared to the case where the amount of polishing is adjusted by adjusting the amount of polishing, the pressing force applied near the center of the wafer becomes sharper, so a wafer with a characteristic shape that is thick near the center can be processed flat.

Further, the present invention can be modified in various ways other than those described above without departing from the spirit of the invention, and it goes without saying that the present invention extends to such modifications.

1... CMP apparatus 2... Platen 3... Rotating shaft 4... Motor 5... Polishing pad 10... Polishing head 10a... Rotating shaft 20... Head main body 21... Rotating part 30 ... Carrier 31 ... Air line 32 ... Carrier pressing means 40 ... Template retainer 41 ... Retainer holder 41a ... Accommodation pocket 42 ... Snap ring 43 ... Retainer pressing Members 44... Retainer pressing means 50... Membrane film 60... Backing film 70... Elastic pressing member (zone rubber)
71...First airbag 72...Second airbag 80...Layout base 90...Press member 91...PET film A...Air chamber E...Young's modulus V・Vertical direction W ・Wafer

Claims (3)

A CMP apparatus in which the membrane film expands with compressed air supplied between a carrier and a membrane film spaced apart below the carrier, presses the wafer, and presses the wafer against a polishing pad for polishing. There it is,
A central pressing means capable of locally pressing approximately the center of the membrane film,
a pressing member provided approximately at the center of the carrier;
a first air bag provided between the carrier and the pressing member and inflated with compressed air to move the pressing member downward;
Equipped with
The lower end surface of the pressing member is curved in a downwardly convex manner and has a radius of curvature that corresponds to the center thickness of the wafer, the diameter and thickness of the pressing member, and the diameter and thickness of the first airbag. A CMP device characterized in that: The pressing member is provided on the lower surface of the carrier and between the membrane film and the pressing member, and has one or more zones inflatable with compressed air on the outer peripheral side of the first airbag. 2. The CMP apparatus according to claim 1, wherein the membrane film is pressed through a second airbag to be formed. The CMP apparatus according to claim 1, wherein the pressing member directly presses the membrane film.