JP7568808B2 - CMP Equipment - Google Patents

Description

The present invention relates to a CMP apparatus for CMP polishing of wafers.

In the field of semiconductor manufacturing, CMP apparatuses are known for planarizing semiconductor wafers (hereafter referred to as "wafers") such as silicon wafers.

The polishing device described in Patent Document 1 is a polishing device that applies chemical mechanical polishing, or so-called CMP (Chemical Mechanical Polishing) technology. In this polishing device, the polishing head polishes the wafer by pressing it against the polishing cloth using air pressure from an air chamber formed in the gap between the carrier and an elastic sheet whose periphery is held by a retainer ring.

Patent Document 2 also discloses a configuration in which an elastic substrate is attached to the top surface of the template that is pressed against the polishing cloth during polishing, and a backing film is interposed between the elastic substrate and the wafer.

Patent No. 3683149 JP 2016-159385 A

However, in the CMP apparatus described above, the template itself is polished as the wafer is polished, and the thickness of the template gradually decreases with repeated polishing. As a result, there is a risk that the polishing rate at the edge of the wafer will vary significantly compared to the polishing rate in other areas of the wafer due to the template thickness changing over time.

It is also possible to replace the template material with one that is more wear-resistant, but if the template hardness is set too high, there is a risk that the wafer will be damaged when it collides into the template.

Therefore, a technical problem arises that must be solved in order to suppress changes in the polished shape of the wafer that accompany changes in the template thickness over time, and the present invention aims to solve this problem.

In order to achieve the above object, a CMP apparatus according to the present invention is a CMP apparatus that polishes a wafer by pressing the wafer against a polishing pad, and includes a template formed in a circular ring shape and having a storage pocket in the center capable of storing the wafer, a membrane film affixed to the upper surface of the template, and a backing film formed with a smaller diameter than the wafer and affixed to the membrane film within the storage pocket, the backing film pressing the wafer against the polishing pad in a state in which the wafer can rotate relatively to the backing film , and where R1 is the radius of the backing film, R2 is the radius of the wafer, and R3 is the radius of the storage pocket, the CMP apparatus satisfies the relational expression R1<2R2-R3.

The present invention prevents the polishing rate at the edge of the wafer from fluctuating significantly compared to the polishing rate in other areas of the wafer, even if the template thickness changes over time, making it possible to process the wafer into the desired polished shape.

FIG. 1 is a perspective view showing a CMP apparatus according to an embodiment of the present invention. FIG. 2 is a vertical cross-sectional view showing a schematic view of a main part of a polishing head. FIG. 1 is an enlarged cross-sectional view showing the vicinity of the peripheral edge of a wafer in a conventional CMP apparatus. 2 is an enlarged cross-sectional view showing the vicinity of the peripheral edge of a wafer in the CMP apparatus shown in FIG. 1 . FIG. 4 is a bottom view of the polishing head showing a state in which the wafer is in contact with the inner periphery of the template. 13 is an enlarged cross-sectional view showing the vicinity of the peripheral edge of a wafer in a CMP apparatus according to a modified example of the present invention. 13 is a graph showing the polishing rate for each pocket depth of a CMP apparatus according to a comparative example using a hard pad. 11 is a graph showing the polishing rate for each pocket depth of the CMP apparatus according to the first embodiment using a hard pad. 13 is a graph showing the polishing rate for each pocket depth of the CMP apparatus according to the second embodiment using a hard pad. 13 is a graph showing the polishing rate for each pocket depth of a CMP apparatus according to a comparative example using a soft pad. 11 is a graph showing the polishing rate for each pocket depth of the CMP apparatus according to the first embodiment using a soft pad. 13 is a graph showing the polishing rate for each pocket depth of the CMP apparatus according to the second embodiment using a soft pad.

The embodiment of the present invention will be described with reference to the drawings. Note that in the following, when referring to the number, numerical value, amount, range, etc. of components, unless otherwise specified or when it is clearly limited to a specific number in principle, it is not limited to that specific number, and it may be more or less than the specific number.

In addition, when referring to the shape or positional relationship of components, etc., this includes things that are substantially similar or similar to that shape, etc., unless otherwise specified or considered in principle to be clearly different.

In addition, drawings may exaggerate characteristic parts to make the features easier to understand, and the dimensional ratios of components may not be the same as in reality. In addition, in cross-sectional views, hatching of some components may be omitted to make the cross-sectional structure of the components easier to understand.

Figure 1 is a perspective view showing a schematic diagram of a CMP apparatus 1 according to one 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 in a disk shape and is connected to a rotating shaft 3 arranged below the platen 2. When the rotating shaft 3 is rotated by the drive of a motor 4, the platen 2 rotates in the direction of the arrow D1 in FIG. 1. 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 agent, is supplied onto the polishing pad 5 from a nozzle (not shown).

The polishing head 10 is formed in a disk shape with a smaller diameter than the platen 2, and is connected to a rotating shaft 10a disposed above the polishing head 10. The rotating shaft 10a is rotated by the drive of a motor (not shown), causing the polishing head 10 to rotate in the direction of arrow D2 in FIG. 1. The polishing head 10 can be raised and lowered in the vertical direction V by a lifting device (not shown). When polishing a wafer W, the polishing head 10 descends to press the wafer W against the polishing pad 5. 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 components that make up the CMP apparatus 1. The control means is, for example, a computer, and is composed of a CPU, memory, etc. The functions of the control means may be realized by control using software, or may be realized by something that operates using hardware.

Next, the polishing head 10 will be described. FIG. 2 is a vertical cross-sectional view showing the main parts of the polishing head 10. FIG. 3 is a bottom view of the polishing head 10.

The polishing head 10 comprises a head body 20, a carrier 30, a retainer ring 40, a membrane film 50, and a backing film 60.

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

Air lines 31 are provided on the carrier 30, spaced at equal intervals around the periphery of the carrier 30. The lower ends of the airlines 31 open into an air chamber A formed between the lower surface 30a of the carrier 30 and the membrane film 50. The airlines 31 are connected to an air supply source (not shown) as an air supply means, and air is introduced into the air chamber A via the airlines 31. The pressure of the air supplied to the airlines 31 is adjusted by a regulator (not shown).

A carrier pressing means 32 is provided between the head 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 the air supplied from the air supply source is adjusted 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 lower surface 30a of the carrier 30 is provided with a plurality of elastic pressing members (not shown) arranged coaxially. The pressing members are formed in annular shapes with different diameters. The elastic pressing members are fixed to the lower surface 30a of the carrier 30 and are detachably attached to the carrier 30 with a two-component epoxy resin adhesive or the like. The elastic pressing members are arranged coaxially with the rotation axis of the polishing head 10 and define an air chamber A.

The retainer ring 40 is arranged to surround the periphery of the carrier 30. The retainer ring 40 has a retainer ring holder 41 as a template with a membrane film 50 attached to its upper surface.

The retainer ring holder 41 is made of a resin such as glass epoxy, polyether ether ketone (PEEK), or polyphenylene sulfide (PPS). The retainer ring holder 41 is formed in an annular shape and has a storage pocket 41a in the center for storing the wafer W. The retainer ring 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 body 20 and the retainer pressing member 43. Reference numeral 45 denotes a cover that covers the top 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 the air supplied from the air supply source is adjusted by a regulator (not shown). The retainer pressing means 44 presses the retainer ring 40 against the polishing pad 5 via the retainer pressing means 44 according to the pressure of the air supplied.

The membrane film 50 is made of a resin such as tetrafluoroethylene perfluoroalkoxyvinylether copolymer (PFA) or polyethylene terephthalate (PET). The membrane film 50 is attached to the retainer ring holder 41 so as to cover the storage pocket 41a, and when compressed air is introduced into the air chamber A, the membrane film 50 is elastically deformed toward the inside of the storage pocket 41a by the air pressure.

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 rotation axis 10a of the polishing head 10. When compressed air is introduced into the air chamber A, the backing film 60 elastically deforms in accordance with the elastic deformation of the membrane film 50, and pressurizes the wafer W. As shown in FIG. 3, the backing film 60 is formed with a diameter smaller than the outer diameter of the wafer W. In the following, the height from the bottom end of the retainer ring holder 41 to the bottom end of the backing film 60 is referred to as the "pocket height."

Next, the operation of the CMP apparatus 1 will be described. In a conventional CMP apparatus 70, as shown in FIG. 4(a), the backing film BF is formed with a diameter larger than the outer diameter of the wafer W. Then, when the retainer ring holder 71 is thick and the pocket depth H' is sufficiently secured, as shown in FIG. 4(b), when compressed air is introduced into the air chamber A and the membrane film MF elastically deforms downward, the backing film BF exerts a smaller pressing force on the peripheral edge of the wafer (broken line portion) than on other areas of the wafer W.

When polishing is then repeated, the underside of the retainer ring holder 71, which is pressed against the polishing pad 5, is gradually polished, so that the thickness of the retainer ring holder 71 becomes thinner in proportion to the processing time, and the pocket depth H' becomes smaller. When the membrane film MF elastically deforms downward with the retainer ring holder 71 being in this thin state, the backing film BF elastically deforms so as to wrap around from the periphery of the wafer W to the outer periphery, as shown by the dashed line in Figure 4(c), and a larger pressing force acts on the periphery of the wafer W than on other areas of the wafer W. In this way, the thickness of the retainer ring holder 71 changes over time, causing the polishing rate of the periphery of the wafer W to vary significantly compared to other areas of the wafer W.

On the other hand, as shown in FIG. 5(a), in the CMP apparatus 1, the backing film 60 is formed to have a smaller diameter than the outer diameter of the wafer W. When the retainer ring holder 41 is thick and the pocket depth H is sufficiently secured, as shown in FIG. 5(b), compressed air is introduced into the air chamber A, and the membrane film 50 is elastically deformed downward, so that the backing film 60 presses the wafer W against the polishing pad 5. At this time, the backing film 60 contacts the entire surface of the wafer W except for the periphery, and no excessive pressing force acts on the periphery of the wafer W. In addition, the portion 50a of the membrane film 50 that is provided to straddle the backing film 60 and the retainer ring holder 41 and receives the pressure of the compressed air is enlarged compared to the conventional CMP apparatus 70, so that the reaction force acting on the outer periphery of the backing film 60 increases with the increase in the pressure of the compressed air. Therefore, the pressing force required to polish the periphery of the wafer W can be secured.

In addition, if the thickness of the retainer ring holder 41 changes over time and the pocket depth H becomes smaller, as shown in FIG. 5(c), the backing film 60 does not elastically deform to wrap around the periphery of the wafer W, and excessive pressure is prevented from acting on the periphery of the wafer W compared to other areas of the wafer W.

In this embodiment, when the wafer W is pressed against the backing film 60, it does not matter whether the wafer W can rotate relative to the backing film 60 or not.

The wafer W is pressed against the backing film 60 in a state where it cannot rotate, for example, when an appropriate amount of deionized water or the like is applied to the underside of the backing film 60, and the backing film 60 and the wafer are brought into close contact, so that the wafer W is attracted to the backing film 60 and rotates together with the backing film 60. Since the wafer W and the backing film 60 are arranged approximately concentrically, if the backing film 60 is formed with a smaller diameter than the outer diameter of the wafer W, the backing film 60 will be prevented from wrapping around the periphery of the wafer W and pressing the wafer W excessively.

On the other hand, when the wafer W is rotatably pressed against the backing film 60, it can be considered that the wafer W can slide horizontally within the storage pocket 41a without being attracted to the backing film 60. In such a case, as shown in FIG. 6, the backing film 60 is set so that the wafer W does not protrude from the periphery of the wafer W when the wafer W is in contact with the inner circumference of the retainer ring holder 41. In other words, the radius R1 of the backing film 60, the radius R2 of the wafer W, and the radius R3 of the storage pocket 41a are set so as to satisfy the relational expression R1<2R2-R3.

Next, a modified example of this embodiment will be described. Figures 7(a) to (c) are enlarged views of the main parts of the CMP apparatus 1 according to this modified example. This modified example differs from the above-described embodiment in that the storage pocket 41a has an enlarged diameter, and the distance between the retainer ring holder 41 and the backing film 60 is increased. The configuration other than that described below is the same as that of the above-described embodiment.

As shown in FIG. 7(a), in the CMP apparatus 1 according to this modified example, the storage pocket 41a is formed with an expanded diameter. This allows the distance between the backing film 60 and the retainer ring holder 41 to be set farther.

As a result, as shown in FIG. 7(b), the portion 50a of the membrane film 50, which is disposed between the backing film 60 and the retainer ring holder 41 and receives the pressure of the compressed air, expands, and the reaction force F1 acting on the inner peripheral edge of the retainer ring holder 41 and the reaction force F2 acting on the outer peripheral edge of the backing film 60 each increase with the increase in the pressure of the compressed air. Therefore, even if the retainer ring holder 41 is worn and the pocket depth H is sufficiently secured, the pressing force pressing the wafer W can be increased locally only at the peripheral edge.

Also, as shown in FIG. 7(c), when the pocket depth H is reduced, the pressure of the compressed air that the membrane film 50 receives increases, and the reaction forces F1 and F2 of the retainer ring holder 41 and backing film 60 that support it also increase. Therefore, the pressing force acting on the wafer W can be increased locally only at the periphery.

Next, evaluation data comparing the CMP apparatus 1 according to the above-mentioned embodiment and its modified example with a conventional CMP apparatus 70 will be described. In the following, the conventional CMP apparatus 70 corresponding to FIG. 4 will be referred to as a comparative example, the CMP apparatus 1 corresponding to FIG. 5 will be referred to as Example 1, and the CMP apparatus 1 corresponding to FIG. 7 will be referred to as Example 2.

Figures 8 to 10 show the polishing rate when a thermal oxide film is polished using a hard pad that is mainly used for polishing semiconductor devices. In Figures 8 to 10, the vertical axis shows the polishing rate, and the horizontal axis shows the radial coordinate with the center of rotation of the polishing head as the origin. The main polishing conditions set in this evaluation are as shown in Table 1.

Figure 8 shows evaluation data of the polishing rate in the comparative example. Specifically, the inner diameter of the retainer ring holder 71 is set to 102 mm, and the outer diameter of the backing film is set to 101 mm. It can be seen that at a pocket depth of 700 μm, which corresponds to immediately after the retainer ring holder 71 is first used, the polishing rate of the peripheral edge of the wafer W is lower than other areas. However, as the retainer ring holder 71 wears, it can be seen that at a pocket depth of 500 μm, the polishing rate of the peripheral edge of the wafer W becomes higher than other areas, and at a pocket depth of 300 μm, the polishing rate of the peripheral edge of the wafer W becomes even higher than other areas. In other words, it can be seen that as the thickness of the retainer ring holder 71 changes over time, the polishing rate at the peripheral edge of the wafer W varies greatly compared to other areas of the wafer W.

Figure 9 shows evaluation data of the polishing rate in Example 1. Specifically, the inner diameter of the retainer ring holder 41 is set to 102 mm, and the outer diameter of the backing film is set to 96 mm. Figure 9 shows that as the retainer ring holder 41 wears, i.e., as the pocket depth H decreases, the polishing rate at the periphery of the wafer W increases in the same way as the polishing rate in other areas of the wafer W. In other words, even if the thickness of the retainer ring holder 41 changes over time, the polishing rate at the periphery of the wafer W fluctuates in the same way as the other areas of the wafer W.

Figure 10 shows evaluation data for the polishing rate in Example 2. Specifically, the inner diameter of the retainer ring holder 41 is set to 104 mm, and the outer diameter of the backing film is set to 96 mm. Figure 10 shows that even if the thickness of the retainer ring holder 41 changes over time, the polishing rate at the periphery of the wafer W fluctuates in the same way as the polishing rate in other areas of the wafer W.

Figures 11 to 13 show evaluation data when a thermal oxide film is polished using a soft pad that is mainly used for polishing substrates. In Figures 11 to 13, the vertical axis represents the polishing rate, and the horizontal axis represents the radial coordinate with the center of rotation of the polishing head as the origin. The polishing conditions for this evaluation were set to be the same as those for the hard pad shown in Table 1, except that a suede pad was used as the polishing pad and a nylon brush was used for dressing.

Figure 11 shows evaluation data of the polishing rate in the comparative example. Specifically, the inner diameter of the retainer ring holder 71 is set to 102 mm, and the outer diameter of the backing film is set to 101 mm. It can be seen that the polishing rate is the same over the entire surface of the wafer W immediately after the retainer ring holder 71 begins to be used. However, as the retainer ring holder 71 wears, it can be seen that at a pocket depth of 500 μm, the polishing rate at the edge of the wafer W becomes higher than other areas, and at a pocket depth of 300 μm, the polishing rate at the edge of the wafer W becomes even higher than other areas. In other words, it can be seen that the polishing rate at the edge of the wafer W varies greatly compared to other areas of the wafer W as the thickness of the retainer ring holder 71 changes over time.

Figure 12 shows evaluation data of the polishing rate in Example 1. Specifically, the inner diameter of the retainer ring holder 41 is set to 102 mm, and the outer diameter of the backing film is set to 96 mm. According to Figure 12, although the polishing rate of the entire surface of the wafer W decreases as the retainer ring holder 41 wears, the polishing rate at the periphery of the wafer W decreases in the same way as the polishing rate in other areas of the wafer W. In other words, even if the thickness of the retainer ring holder 41 changes over time, it can be seen that the polishing rate at the periphery of the wafer W fluctuates in the same way as the polishing rate in other areas of the wafer W.

Figure 13 shows evaluation data of the polishing rate in Example 2. Specifically, the inner diameter of the retainer ring holder 41 is set to 104 mm, and the outer diameter of the backing film is set to 96 mm. Figure 13 shows that even if the thickness of the retainer ring holder 41 changes over time, the polishing rate at the periphery of the wafer W fluctuates in the same way as the polishing rate in other areas of the wafer W.

In this way, the CMP apparatus 1 according to this embodiment and the modified example can process the wafer W into the desired polished shape, because the polishing rate at the periphery of the wafer W varies in the same way as the polishing rate in other areas of the wafer W, even if the thickness of the retainer ring holder 41 changes over time.

Some examples of CMP apparatus are given below.
[1] A CMP apparatus that polishes a wafer by pressing the wafer against a polishing pad, comprising: a template formed in a circular ring shape and having a storage pocket in the center capable of storing the wafer; a membrane film affixed to the upper surface of the template; and a backing film formed with a smaller diameter than the wafer and affixed to the membrane film within the storage pocket.
According to this configuration, even if the template wears and the template thickness gradually becomes thinner, the pressing force with which the backing film presses against the edge of the wafer is prevented from becoming excessively high. Therefore, even if the template thickness changes over time, the polishing rate at the edge of the wafer is prevented from fluctuating significantly compared to the polishing rate in other areas of the wafer.

[2] The CMP apparatus described in [1], wherein the backing film is formed so that the backing film does not extend beyond the edge of the wafer when the wafer is in contact with the inner circumference of the template.
With this configuration, even when the wafer moves relative to the backing film, the backing film always presses against the inside of the wafer, thereby preventing the pressure with which the backing film presses against the edge of the wafer from becoming excessively high. This further prevents the polishing rate at the edge of the wafer from fluctuating significantly compared to the polishing rate in other areas of the wafer, even if the template thickness changes over time.

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

REFERENCE SIGNS LIST 1 CMP apparatus 2 Platen 3 Rotating shaft 4 Motor 5 Polishing pad 10 Polishing head 10a Rotating shaft 20 Head body 21 Rotating section 30 Carrier 31 Air line 32 Carrier pressing means 40 Retaining ring 41 Retaining ring holder (template)
41a...accommodating pocket 42...snap ring 43...retainer pressing member 44...retainer pressing means 50...membrane film 60...backing film A...air chamber W...wafer

Claims (1)

A CMP apparatus that polishes a wafer by pressing the wafer against a polishing pad, comprising:
a template formed in a circular shape and having a pocket in the center capable of accommodating the wafer;
a membrane film attached to an upper surface of the template;
a backing film formed to have a diameter smaller than that of the wafer and attached to the membrane film in the storage pocket, the backing film pressing the wafer against the polishing pad in a state in which the wafer can rotate relatively to the backing film ;
Equipped with
A CMP apparatus, characterized in that, when a radius of the backing film is R1, a radius of the wafer is R2, and a radius of the storage pocket is R3, the relational expression R1<2R2-R3 is satisfied.