JP7125839B2 - CMP equipment - Google Patents

Description

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

2. Description of the Related Art In the semiconductor manufacturing field, a CMP apparatus for flattening a semiconductor wafer such as a silicon wafer (hereinafter referred to as "wafer") is known.

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, the polishing head polishes the wafer by pressing it against the polishing cloth with the air pressure of the air chamber formed in the gap between the carrier and the elastic sheet whose peripheral edge is held by the retainer ring.

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

Japanese Patent No. 3683149 JP 2016-159385 A

However, in the CMP apparatus as described above, since the template itself is also polished as the wafer is polished, the thickness of the template gradually decreases as the polishing is repeated. The polishing rate at the periphery of the wafer could vary significantly compared to the polishing rate in other areas of the wafer.

It is also conceivable to replace the material of the template with one having high wear resistance, but if the hardness of the template is set too high, the wafer may be damaged when it collides with the template. rice field.

Therefore, there arises a technical problem to be solved in order to suppress the change in the polishing shape of the wafer due to the temporal change in the template thickness, and an object of the present invention is to solve this problem.

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, the CMP apparatus being formed in an annular shape and capable of accommodating the wafer in the center. A template having a pocket, a membrane film attached to the upper surface of the template, and a backing film having a diameter smaller than that of the wafer and attached to the membrane film within the accommodation pocket.

According to this configuration, even if the template is worn and the thickness of the template is gradually reduced, the pressing force with which the backing film presses the peripheral edge of the wafer is prevented from becoming excessively high. Even if the polishing rate changes over time, it is possible to prevent the polishing rate at the peripheral edge of the wafer from significantly fluctuating compared to the polishing rate at other regions of the wafer.

Further, in the CMP apparatus according to the present invention, the backing film is preferably formed so that the backing film does not protrude from the edge of the wafer while the wafer is in contact with the inner periphery of the template.

According to this configuration, even when the wafer moves relative to the backing film, the backing film always presses the inside of the wafer, so that the backing film presses the peripheral edge of the wafer with an excessive pressing force. Therefore, even if the template thickness changes over time, it is possible to further suppress significant fluctuations in the polishing rate at the peripheral edge of the wafer compared to the polishing rate in other regions of the wafer.

The present invention suppresses significant variations in the polishing rate at the periphery of the wafer compared to the polishing rate at other regions of the wafer, even when the template thickness changes over time. It can be processed into an abrasive shape.

1 is a perspective view schematically showing a CMP apparatus according to one embodiment of the present invention; FIG. FIG. 2 is a vertical cross-sectional view schematically showing main parts of the polishing head; Bottom view of the polishing head. FIG. 2 is an enlarged cross-sectional view showing the vicinity of the peripheral edge of a wafer in a conventional CMP apparatus; FIG. 2 is an enlarged cross-sectional view showing the vicinity of the periphery of the 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; FIG. 5 is an enlarged cross-sectional view showing the vicinity of the periphery of a wafer in a CMP apparatus according to a modification of the present invention; 5 is a graph showing the polishing rate for each pocket depth of a CMP apparatus according to a comparative example using a hard pad; 5 is a graph showing the polishing rate for each pocket depth of the CMP apparatus according to the first embodiment using a hard pad; 5 is a graph showing the polishing rate for each pocket depth of the CMP apparatus according to the second embodiment using a hard pad; 5 is a graph showing the polishing rate for each pocket depth of a CMP apparatus according to a comparative example using a soft pad; 5 is a graph showing the polishing rate for each pocket depth of the CMP apparatus according to the first embodiment using a soft pad; 5 is a graph showing the polishing rate for each pocket depth of the CMP apparatus according to the second embodiment using a soft pad;

An embodiment of the present invention will be described based on the drawings. In addition, hereinafter, when referring to the number, numerical value, amount, range, etc. of the constituent elements, unless otherwise specified or clearly limited to a specific number in principle, it is limited to the specific number It does not matter if the number is greater than or less than a certain number.

In addition, when referring to the shape or positional relationship of components, etc., unless otherwise specified or in principle clearly considered otherwise, etc. include.

In addition, the drawings may exaggerate characteristic parts by enlarging them in order to make the characteristics easier to understand. In addition, in cross-sectional views, hatching of some components may be omitted in order to facilitate understanding of the cross-sectional structure of the components.

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

The platen 2 is disc-shaped and connected to a rotating shaft 3 arranged below the platen 2 . As the rotating shaft 3 is driven by the motor 4 to rotate, 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 abrasives and chemicals, is supplied from a nozzle (not shown) onto the polishing pad 5 .

The polishing head 10 is shaped like a disk having a diameter smaller than that of the platen 2 and is connected to a rotating shaft 10 a arranged above the polishing head 10 . The polishing head 10 rotates in the direction of arrow D2 in FIG. 1 by rotating the rotary shaft 10a driven by a motor (not shown). The polishing head 10 can be raised and lowered 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 the wafer W is polished. The wafer W to be polished by the polishing head 10 is transferred by a wafer transfer mechanism (not shown).

The operation of the CMP apparatus 1 is controlled by control means (not shown). The control means controls each component constituting the CMP apparatus 1 . The control means is, for example, a computer, and is composed of a CPU, a memory, and the like. Note that the function 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 essential parts of the polishing head 10. As shown in FIG. 3 is a bottom view of the polishing head 10. FIG.

The polishing head 10 includes 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 a carrier 30 arranged below the head body 20 via a rotating portion 21, and the head body 20 and the carrier 30 rotate together.

The carrier 30 is provided with airlines 31 spaced at regular intervals along the periphery of the carrier 30 . A lower end of the airline 31 opens into an air chamber A formed between the lower surface 30 a of the carrier 30 and the membrane film 50 . The air line 31 is connected to an air supply source as air supply means (not shown), and air is introduced into the air chamber A via the air line 31 . The pressure of air supplied to the air line 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 airbag 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 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.

A plurality of elastic pressing members (not shown) arranged coaxially are provided on the lower surface 30a of the carrier 30 . Further, the plurality of pressing members are formed in an annular shape with different diameters. The elastic pressing member is fixed to the lower surface 30a of the carrier 30 and detachably attached to the carrier 30 with a two-liquid epoxy resin adhesive or the like. The elastic pressing member is arranged coaxially with the rotating shaft of the polishing head 10 and defines an air chamber A. As shown in FIG.

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

The retainer ring holder 41 is made of resin such as glass epoxy, polyetheretherketone (PEEK), or polyphenylene sulfide (PPS), for example. The retainer ring holder 41 is formed in an annular shape and has a housing pocket 41a for housing the wafer W in the center. The retainer ring holder 41 is attached to the retainer pressing member 43 via the 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 snap ring 42 from above.

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 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 supplied air.

The membrane film 50 is made of resin such as tetrafluoroethylene perfluoroalkoxyvinyl ether copolymer (PFA) or polyethylene terephthalate (PET). The membrane film 50 is adhered 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 into the storage pocket 41a by the air pressure.

The backing film 60 is, for example, a suede film. The backing film 60 is adhered to the membrane film 50 with its center positioned on the rotating shaft 10 a of the polishing head 10 . When compressed air is introduced into the air chamber A, the backing film 60 elastically deforms with the elastic deformation of the membrane film 50 to press the wafer W. As shown in FIG. As shown in FIG. 3, the backing film 60 is formed to have a diameter smaller than the outer diameter of the wafer W. As shown in FIG. The height from the lower end of the retainer ring holder 41 to the lower end of the backing film 60 is hereinafter referred to as "pocket height".

Next, the action of the CMP apparatus 1 will be described. In the conventional CMP apparatus 70, the backing film BF is formed to have a larger diameter than the outer diameter of the wafer W, as shown in FIG. 4(a). When the retainer ring holder 71 is thick and the pocket depth H' is sufficiently secured, as shown in FIG. When the backing film BF is elastically deformed downward, a smaller pressing force acts on the peripheral edge (broken line portion) of the wafer than on other regions of the wafer W. FIG.

After that, when polishing is repeated, the lower surface of the retainer ring holder 71 pressed against the polishing pad 5 is gradually polished, so that the thickness of the retainer ring holder 71 decreases in proportion to the processing time, and the pocket depth H'. becomes smaller. When the membrane film MF is elastically deformed downward while the thickness of the retainer ring holder 71 is thin, the backing film BF wraps around the wafer W from the peripheral edge to the outer periphery as shown by the dashed line in FIG. 4(c). , and a larger pressing force acts on the peripheral edge of the wafer W than on other regions of the wafer W. As shown in FIG. As the thickness of the retainer ring holder 71 changes over time in this way, the polishing rate of the peripheral edge of the wafer W fluctuates significantly compared to other regions of the wafer W. FIG.

On the other hand, in the CMP apparatus 1, the backing film 60 is formed to have a smaller diameter than the outer diameter of the wafer W, as shown in FIG. 5(a). When the retainer ring holder 41 is thick and the pocket depth H is sufficiently secured, as shown in FIG. When elastically deformed, the backing film 60 presses the wafer W against the polishing pad 5 . At this time, the backing film 60 is in contact with the entire surface of the wafer W except for the peripheral edge, so that the peripheral edge of the wafer W is not subjected to excessive pressing force. In addition, the portion 50a of the membrane film 50 provided to straddle between the backing film 60 and the retainer ring holder 41 to receive the pressure of the compressed air is enlarged as compared with the conventional CMP device 70, thereby reducing the backing. The reaction force acting on the outer peripheral edge of the film 60 increases as the pressure of the compressed air increases. Therefore, the pressing force necessary for polishing the peripheral edge of the wafer W can be ensured.

Further, when the thickness of the retainer ring holder 41 changes with time and the pocket depth H becomes small, the backing film 60 elastically wraps around the periphery of the wafer W as shown in FIG. 5(c). It is possible to suppress the application of an excessive pressing force to the peripheral edge of the wafer W as compared to the other regions of the wafer W without being deformed.

In this embodiment, it does not matter whether the wafer W is rotatable with respect to the backing film 60 when the wafer W is pressed against the backing film 60 .

The wafer W is pressed against the backing film 60 in a non-rotatable state, for example, by applying an appropriate amount of deionized water or the like to the lower surface of the backing film 60 and bringing the backing film 60 and the wafer into close contact. , the case where the wafer W is attracted to the backing film 60 and rotates integrally with the backing film 60 can be considered. Since the wafer W and the backing film 60 are arranged substantially concentrically, if the backing film 60 is formed to have a smaller diameter than the outer diameter of the wafer W, the backing film 60 will move around the periphery of the wafer W to the outer peripheral side. It is suppressed that the wafer W is pressed excessively due to the intrusion.

On the other hand, when the wafer W is rotatably pressed against the backing film 60, the wafer W can be slid horizontally in the storage pocket 41a without being adsorbed by the backing film 60, for example. In such a case, as shown in FIG. 6, the backing film 60 is set so that the wafer W is in contact with the inner periphery of the retainer ring holder 41 and does not protrude from the periphery of the wafer W. As shown in FIG. That is, 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. FIGS. 7A to 7C are enlarged views of essential parts of the CMP apparatus 1 according to this modification. It should be noted that this modification differs from the above-described embodiment in that the accommodating pocket 41a is enlarged in diameter and the retainer ring holder 41 and the backing film 60 are spaced apart. Configurations other than those described below are the same as those of the embodiment described above.

As shown in FIG. 7(a), in the CMP apparatus 1 according to this modified example, the accommodation pocket 41a is formed with an enlarged diameter. Thereby, the distance between the backing film 60 and the retainer ring holder 41 is set long.

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

Further, as shown in FIG. 7(c), when the pocket depth H is reduced, the pressure of the compressed air applied to the membrane film 50 is increased, so that the retainer ring holder 41 and the backing film supporting the membrane film 50 are compressed. The reaction forces F1, F2 of 60 also increase. Therefore, the pressing force acting on the wafer W can be locally increased only at the peripheral edge.

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

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

FIG. 8 is polishing rate evaluation data in a 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 of the peripheral edge of the wafer W is lower than that of the other regions at the pocket depth of 700 μm, which corresponds to immediately after the start of use of the retainer ring holder 71 . However, as the retainer ring holder 71 wears, the polishing rate of the peripheral edge of the wafer W becomes higher than that of other areas at the pocket depth of 500 μm, and the polishing rate of the peripheral edge of the wafer W becomes higher than the other areas at the pocket depth of 300 μm. It can be seen that it is even higher than the area. That is, as the thickness of the retainer ring holder 71 changes with time, the polishing rate at the peripheral edge of the wafer W fluctuates more than other areas of the wafer W. FIG.

9 shows evaluation data of the polishing rate in Example 1. FIG. 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 FIG. 9, as the retainer ring holder 41 wears, that is, as the pocket depth H decreases, the polishing rate at the peripheral edge of the wafer W increases similarly to the polishing rate in other regions of the wafer W. I understand. That is, even if the thickness of the retainer ring holder 41 changes over time, the polishing rate at the peripheral edge of the wafer W fluctuates similarly to the other regions of the wafer W. FIG.

10 shows evaluation data of the polishing rate in Example 2. FIG. 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. As can be seen from FIG. 10, even if the thickness of the retainer ring holder 41 changes over time, the polishing rate at the peripheral edge of the wafer W fluctuates in the same manner as the polishing rate in other regions of the wafer W. .

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

FIG. 11 shows polishing rate evaluation data in a 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 is started to be used. However, as the retainer ring holder 71 wears, the polishing rate of the peripheral edge of the wafer W becomes higher than that of other areas at the pocket depth of 500 μm, and the polishing rate of the peripheral edge of the wafer W becomes higher than the other areas at the pocket depth of 300 μm. It can be seen that it is even higher than the area. That is, it can be seen that the polishing rate at the peripheral edge of the wafer W fluctuates more than other regions of the wafer W as the thickness of the retainer ring holder 71 changes over time.

FIG. 12 is polishing rate evaluation data in Example 1. FIG. 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 FIG. 12, the polishing rate of the entire surface of the wafer W decreases as the retainer ring holder 41 wears, but the polishing rate of the peripheral edge of the wafer W decreases similarly to the polishing rate of other regions of the wafer W. It is understood that In other words, even when the thickness of the retainer ring holder 41 changes over time, the polishing rate at the peripheral edge of the wafer W fluctuates in the same manner as other areas of the wafer W. FIG.

13 is polishing rate evaluation data in Example 2. FIG. 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. As can be seen from FIG. 13, even if the thickness of the retainer ring holder 41 changes over time, the polishing rate at the peripheral edge of the wafer W fluctuates in the same manner as the polishing rate in other regions of the wafer W. .

In this manner, in the CMP apparatus 1 according to the present embodiment and the modified example, even when the thickness of the retainer ring holder 41 changes over time, the polishing rate at the peripheral edge of the wafer W remains the same as that of the wafer W. Since the polishing rate varies in the same manner as in other regions, the wafer W can be processed into a desired polishing shape.

In addition, the present invention can be modified in various ways without departing from the spirit of the present invention, and it is natural 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 Rotary part 30 Carrier 31 Air line 32 Carrier pressing means 40 Retainer ring 41 Retainer 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 for polishing the wafer by pressing the wafer against a polishing pad,
a template formed in an annular shape and provided with a housing pocket in the center capable of housing the wafer;
a membrane film attached to the top surface of the template;
a backing film formed to have a diameter smaller than that of the wafer, adhered to the membrane film in the housing pocket, and presses the wafer in a relatively rotatable state;
with
satisfying a relational expression of R1<2R2-R3 , 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 backing film of the membrane film and the template are straddled so that the backing film presses the peripheral edge of the wafer when air pressure is applied to the membrane film to press the wafer. A CMP apparatus characterized in that a portion is elastically deformed toward the backing film .

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