Wafer polishing head of CMP apparatus

Abstract

The present invention relates to a wafer polishing head of a CMP apparatus, comprising: a head body which is connected to a driving part that rotates, and which has a hollow portion therein; a retainer ring provided in the head body; and a membrane, which is made from an elastic material, is positioned at the inner side of the retainer ring, and is in contact with the upper surface of a wafer so as to apply pressure to the wafer, wherein the retainer ring includes: an outer ring (120) positioned at the outer side; an inner ring (130) having an outer peripheral surface that is in contact with the inner peripheral surface of the outer ring, and having an inner peripheral surface that is in contact with the outer surface of the wafer; and an O-ring (140) provided between the outer ring and the inner ring so as to prevent the inflow of slurry, the polishing head including a ring-shaped elastic body (200) having an outer part (210) in contact with the upper surface of the inner ring and having an inner part (220) coupled to the membrane.

Description

Wafer polishing head of CMP device

[0001] The present invention relates to a head of a CMP device, which is equipment for flattening a wafer surface, and more specifically, to a technology for a wafer polishing head having an improved internal structure to enable uniform polishing even at the wafer edge during the wafer surface polishing process.

[0002] Integrated circuits are typically formed on a substrate, typically a silicon wafer, by successively depositing conductive, semiconductor, or insulating layers. After each layer is deposited, it is etched to develop the circuit characteristics. As these successive layers are deposited and etched, the outer or top surface of the substrate—the exposed surface—becomes increasingly non-planar. This non-planar outer surface presents a challenge to integrated circuit manufacturers. If the outer surface of the substrate is not planar, the photoresist layer that sits on top of it is also non-planar.

[0003] Photoresist layers are typically patterned by photolithographic devices that focus optical images onto the photoresist. If the substrate's outer surface is too uneven, the maximum height difference between peaks and valleys on the outer surface will exceed the depth of focus of the imaging device, preventing the optical image from being properly focused onto the substrate's outer surface. Designing new photolithographic devices with improved depth of focus is a significant expense. Furthermore, as feature sizes within integrated circuits become smaller, shorter wavelengths of light must be utilized, further reducing the available depth of focus. Therefore, periodic planarization of the substrate surface is necessary to provide a substantially flat layer surface.

[0004] Chemical Mechanical Polishing (CMP) is a method of planarization. In this process, a wafer (substrate) to be planarized is mounted on a polishing head. The substrate is mounted on the polishing head by contacting a membrane, which is a soluble thin film mounted on the lower surface of the polishing head. The substrate mounted on the head then comes into contact with a rotating polishing pad, the surface of which, opposite the surface contacting the membrane, is brought into contact with the rotating polishing pad. The head presses the substrate against the polishing pad and also rotates to provide additional movement between the substrate and the polishing pad. A polishing slurry containing an abrasive and at least one chemical reagent is distributed on the polishing pad to provide a polishing chemical solution at the interface between the pad and the substrate. This CMP process is quite complex and differs from simple wet sanding. In the CMP process, the reagent in the slurry reacts with the outer surface of the substrate to form reaction sites. Polishing is achieved through the interaction of the polishing pad, which has reaction sites, and the abrasive particles.

[0005] In particular, the polishing rate, finish, and flatness in the CMP process are determined by the combination of the pad and slurry, the relative velocity between the substrate and the pad, and the force pressing the substrate against the pad. Insufficient flatness and finish will result in defective substrates, so the combination of the polishing pad and slurry is selected based on the required finish and flatness. Under these conditions, the polishing rate determines the maximum throughput of the polishing machine. The polishing rate depends on the force with which the substrate is compressed against the pad. In particular, the greater this force, the faster the polishing rate. If the carrier head applies an uneven load, that is, if it applies a greater force to only one area of ​​the substrate, the area of ​​high pressure will be polished faster than the area of ​​low pressure, so the uneven load will result in uneven polishing of the substrate. In addition, one problem in the CMP process is that the edges of the substrate are often polished at a different rate (typically faster, sometimes slower) than the center of the substrate.

[0006] This problem, called "edge effect," occurs even when the load is applied uniformly across the substrate. Edge effect typically occurs at the periphery of the substrate, typically within the outermost 5 to 10 mm, reducing the overall flatness of the substrate, making the periphery unsuitable for use in integrated circuits, and reducing yield.

[0007] Descriptions of the carrier head CMP device of the present invention can be found in U.S. Patent No. 5,738,574 and U.S. Publication No. 2008 / 0119119, etc., and the entire descriptions thereof are incorporated herein by reference, and parts overlapping with the present invention are omitted.

[0008] An elastic membrane applies pressure to the wafer from above, pressing it toward the pad below. However, this causes the depth between the wafer and the pad (pocket depth) to become uneven, which in turn causes uneven wafer polishing. For example, if the pocket depth is deep, the wafer edge is less polished, and if the pocket depth is shallow, the wafer edge is more polished.

[0009] Figures 1 and 2 conceptually illustrate a part of a wafer polishing head according to the prior art, where Figure 1 illustrates a state at the beginning of a polishing operation, and Figure 2 illustrates a state at the end of a polishing operation.

[0010] As disclosed in the above prior art patents, etc., the chemical polishing head has a hollow head body connected to a rotating driving unit, and the head is provided with a retainer ring (R) for fixing an outer surface of a wafer (W) rotating on a polishing pad (P) at the lower portion thereof, a membrane (M) made of an elastic material for applying pressure to the wafer (W) by contacting it, and a chuck plate (C) for binding the membrane onto the head within the head, etc. In addition, the head is configured with a membrane zone (MZ), which is a space for applying pressure by injecting air to pressurize the membrane (M) in a direction toward the wafer.

[0011] Looking at Figures 1 and 2, it can be seen that the pocket depth (Pd-2) at the end of the polishing process is reduced compared to the pocket depth (Pd-1) at the beginning of the polishing process. This reduction in pocket depth is because, as the polishing process progresses, the retainer ring (R), which rotates in contact with the polishing pad (P), is made entirely of a soft material, and thus wears out as it comes into contact with the polishing pad during the polishing process.

[0012] When the forget depth changes due to wear of the retainer ring, the pressure between the wafer edge and the polishing pad, which was set at the beginning of the operation, changes (pressure increases), and the removal rate (R / R) at the wafer edge changes (increases) over time (see Fig. 3). In addition, during the wafer polishing process, it is desirable for the removal rate to be uniform throughout from the center of the wafer to the wafer edge, but the actual removal rate changes at the wafer edge. This phenomenon occurs at the beginning of the polishing operation and remains the same at the end of the polishing operation, although the degree varies. This problem at the wafer edge reduces the overall flatness of the substrate, causes defects at the periphery of the substrate, and reduces the yield.

[0013] The present invention provides a retainer ring having a novel structure capable of reducing the wafer edge effect, and specifically, the purpose is to reduce the wafer edge effect by configuring a retainer ring of a conventional single structure into two physically separated outer rings and inner rings, and applying different pressures to the two separated outer rings and inner rings, respectively.

[0014] The present invention relates to a wafer polishing head of a CMP device, which includes a head body connected to a rotational drive and having a hollow portion therein, a retainer ring provided on the head body, and a membrane made of an elastic material positioned on the inside of the retainer ring and contacting the upper surface of the wafer to apply pressure to the wafer.

[0015] And, the retainer ring is composed of an outer ring (120) located on the outside, an inner ring (130) whose outer circumference is in contact with the inner circumference of the outer ring and whose inner circumference is in contact with the outer surface of the wafer, and an O-ring (140) provided between the outer ring and the inner ring to prevent slurry from flowing in. And, the present invention further includes a ring-shaped elastic body (200), wherein the outer part (210) of the elastic body is in contact with the upper surface of the inner ring, and the inner part (220) is coupled to the membrane. It has an intermediate part (230) that connects the outer part and the inner part of the elastic body and flexibly operates as the membrane moves up and down, and it is preferable that the hardness (H1) of the elastic body is formed to be less than or equal to the hardness (H2) of the membrane, so as not to interfere with the up and down movement of the membrane.

[0016] The above head body (110) includes a head outer portion (112) that comes into contact with the upper surface of the outer ring (120) and a head inner portion (114) that is located on the upper side of the inner ring (130), and the head inner portion (114) is configured to have a shape that protrudes more downward than the head outer portion (112).

[0017]

[0018] *On the lower surface of the outer portion (210) of the elastic body, a lower protrusion (215) is formed to be received in a mounting groove formed on the upper surface of the inner ring, and on the upper surface of the outer portion (210) of the elastic body, an upper protrusion (217) is formed to be coupled to a fastening groove (115) formed on the head body. In addition, a coupling ring (155) that couples the inner portion (220) of the elastic body to the membrane may be provided on the outer circumferential surface of the membrane.

[0019] As another embodiment of the present invention, the lower surface of the elastic body (200-1) may be coupled to the upper surface of the inner ring (130), and the upper surface of the elastic body (200-1) may be configured to be in contact with the head body.

[0020] In addition, it may further include an upper ring (200-2) provided between the elastic body (200-1) and the head body, and the lower surface of the elastic body (200-1) may be coupled to the upper surface of the inner ring (130), and the upper surface of the elastic body (200-1) may be configured to be in contact with the upper ring (200-2).

[0021] An outer curved portion (126) is formed from the inner circumferential surface of the outer ring (120) to a predetermined height, and an inner curved portion (136) is formed from the outer circumferential surface of the inner ring (130) to a predetermined height, thereby reducing the wear rate occurring on the pad during the polishing process and reducing pad defects.

[0022] The present invention comprises a retainer ring composed of two physically separated outer rings and inner rings, and more specifically, a dual-type ring structure composed of an inner ring that directly contacts the outer surface of a wafer and an outer ring that does not directly contact the outer surface of a wafer.

[0023] The present invention, due to this dual-type ring structure, enables the pressure applied equally to a conventional retainer ring to be distributed differently between an inner ring that directly contacts the outer surface of a wafer and an outer ring that does not directly contact the outer surface of a wafer. Specifically, the pressure applied to the inner ring located on the inside is made lower than the pressure applied to the outer ring, and as a result, the effect of reducing the wafer edge effect is exhibited.

[0024] In addition, the present invention can control the wear rate of the outer ring and the inner ring by forming an outer curved portion and an inner curved portion at the bottom of the outer ring and the inner ring to maintain a gap, and also has the effect of enhancing the ring cleaning function by utilizing the gap between the bottoms of the two retainer rings.

[0025] Figures 1 and 2 conceptually illustrate a part of a wafer polishing head according to the prior art, showing the pocket depths at the beginning and end of polishing, respectively.

[0026] Figure 3 shows how the removal rate (R / R) of the wafer edge portion changes over time when polishing a wafer with a wafer polishing head according to the prior art.

[0027] Figure 4 is a cross-sectional view of a wafer polishing head of a CMP device according to the present invention.

[0028] Figures 5 and 6 are enlarged cross-sectional views of the portion indicated as A in Figure 4.

[0029] Figure 7 is a cross-sectional view of an elastic body, which is one component of a wafer polishing head according to the present invention.

[0030] Figure 8 is an enlarged cross-sectional view of the lower part of the outer ring and the inner ring constituting the retainer ring in the wafer polishing head of the CMP device according to the present invention.

[0031] FIGS. 9 and 10 illustrate another embodiment of an elastic body in a wafer polishing head of a CMP device according to the present invention.

[0032] The purpose, specific advantages, and novel features of the present invention will become more apparent from the following detailed description and preferred embodiments, which are illustrated in the accompanying drawings. Furthermore, the terms used are defined based on the functions of the present invention and may vary depending on the user's intentions or practices. Therefore, the definitions of these terms should be based on the overall content of this specification.

[0033] FIG. 4 is a longitudinal cross-sectional view of a wafer polishing head (100) of a CMP device according to the present invention, FIGS. 5 and 6 are enlarged cross-sectional views of a portion indicated by A in FIG. 4, FIG. 7 is a cross-sectional view of an elastic body which is a component of a wafer polishing head according to the present invention, and FIG. 8 is an enlarged cross-sectional view of the lower portion of an outer ring and an inner ring which constitute a retainer ring in a wafer polishing head of a CMP device according to the present invention. In addition, FIGS. 9 and 10 illustrate other embodiments of an elastic body in a wafer polishing head of a CMP device according to the present invention.

[0034] The structure of the CMP head (100) according to the present invention is a hollow head connected to a rotating driving unit (not shown), and the head accommodates a wafer inside and presses the wafer against the lower pad to polish the wafer surface.

[0035] The CMP head of the present invention comprises a head body (110) forming an overall shape, a retainer ring (120, 130) positioned at the lower portion of the head body (110) to secure the outer surface of a wafer rotating on a polishing pad, a membrane (140) made of an elastic material that applies downward pressure to the wafer while contacting the upper surface of the wafer, and a chuck plate that binds the membrane to the inside of the head body. However, since the present invention relates to a retainer ring and a membrane provided in a head of a CMP device and an elastic body positioned therebetween, a description of the general structure of the CMP device rather than these characteristic components will be omitted.

[0036] While conventional retainer rings consist of a single ring structure, the retainer ring of the present invention consists of two physically separate structures, namely, an outer ring (120) located on the outside and an inner ring (130) located on the inside. The outer circumference of the inner ring (130) is in contact with the inner circumference of the outer ring (120), and an O-ring (140) is placed between them to prevent slurry from entering the space during the polishing process. The outer ring (120) and the inner ring (130) receive downward pressure from the head body (110), but since the present invention has two separate retainer ring structures, the pressures received by the outer ring (120) and the inner ring (130) are different. In addition, the outer ring (120) and the inner ring (130) move up and down relative to each other (differently). During the relative movement, the O-ring prevents slurry from entering.

[0037] In order to ensure that the outer ring (120) and the inner ring (130) have different vertical movement amounts, the head body (110) of the present invention has a structure including a head outer portion (112) that contacts the upper surface of the outer ring (120) and a head inner portion (114) located on the upper side of the inner ring (130). The head inner portion (114) has a shape that protrudes downwards more than the head outer portion (112). The upper part of the inner surface of the outer ring comes into contact with the outer surface of the protruding portion of the downwardly protruding head inner portion (114).

[0038] In addition, the inner side of the head (114) is located on the upper side of the inner ring (130), but is not in direct contact with the upper surface of the inner ring, and an elastic body (200) to be described below exists between them. A groove for mounting an O-ring (140) between the inner ring and the outer ring can be formed in the outer ring or the inner ring. In addition, during the polishing process, the inner peripheral surface of the inner ring (130) comes into contact with the outer surface of the wafer.

[0039] In addition, the present invention is characterized by further including a ring-shaped elastic body (200). The elastic body is arranged between the inner ring (130), the membrane (150), and the head body (110), and has an overall ring-shaped structure and is arranged along the outer circumferential surface of the membrane. The cross-sectional structure of the elastic body (200) is illustrated in detail in FIG. 7, and its installation structure is illustrated in FIGS. 5 and 6.

[0040] For convenience, the structure of the elastic body (200) is such that the member located on the outside is called the outer part (210), the member located on the inside is called the inner part (220), and the member connecting them in the middle is called the middle part (230). As illustrated in the drawing, the outer part (210) of the elastic body (200) is in contact with the upper surface of the inner ring. However, the head inner part (114) is located on the upper side of the inner ring (130), but does not directly contact the upper surface of the inner ring, and the elastic body (200) is provided between them.

[0041] On the lower surface of the outer portion (210) of the elastic body, a lower protrusion (215) is formed to be received in a mounting groove formed on the upper surface of the inner ring, and on the upper surface of the outer portion (210) of the elastic body, an upper protrusion (217) is formed, so that the upper protrusion (217) is coupled to a fastening groove (115) formed on the inner portion (114) of the head body (110).

[0042] And, the inner part (220) of the elastic body (200) is connected to the membrane (150). An intermediate part (230) is provided that connects the outer part and the inner part of the elastic body and operates flexibly as the membrane moves up and down. That is, when the membrane (150) moves up and down, the inner part (220) of the elastic body moves up and down according to the amount of movement of the membrane, but the outer part (210) does not move along the membrane, so a connecting part (230) made of a flexible material is provided to flexibly cope with the relative amount of movement.

[0043] In addition, it is preferable that the hardness (H1) of the elastic body is formed to be less than or equal to the hardness (H2) of the membrane, so as not to interfere with the up-and-down movement of the membrane. In addition, a coupling ring (155) may be provided on the outer circumferential surface of the membrane to couple the inner portion (220) of the elastic body to the membrane.

[0044] As illustrated in Fig. 8, an outer curved portion (126) is formed from the innermost end of the outer ring (120) to a predetermined height, and an inner curved portion (136) is formed from the outermost end of the inner ring (130) to a predetermined height. This is because the retainer rings (120, 130) wear out as the polishing process progresses, but even when wear occurs, the corners of the portions that come into contact with the pad have a curved shape. In addition, since the inner curved portion and the outer curved portion are formed to a predetermined height, even if the retainer ring wears out to some extent during the polishing process, these curved portions are continuously maintained.

[0045] The head of a conventional CMP device has a problem in that the lower inner surface corner of the retainer ring is formed at a right angle, and thus, during the wafer polishing process, the right angle corner of the corner causes micro scratches on the pad and increases the wear rate. However, the present invention minimizes pad wear and prevents the occurrence of micro scratches by configuring the retainer ring with an outer ring (120) and an inner ring (130) and having an outer curved portion (126) and an inner curved portion (136) at the lower edge.

[0046] In addition, the present invention makes it possible to control the wear rate of the outer ring (120) and the inner ring (130) by forming the outer curved portion (126) and the inner curved portion (136) and maintaining a floor gap therebetween as shown. That is, by changing the curved shape of the outer curved portion (126) and the inner curved portion (136), the area of ​​each of the outer ring and the inner ring can be individually controlled, thereby controlling the degree of wear of the outer ring and the inner ring. In addition, the floor gap between the outer curved portion (126) and the inner curved portion (136) also has the effect of enhancing the ring cleaning function.

[0047] The present invention is characterized by separating the existing single retainer ring member into two external rings (120) and an internal ring (130) that are physically separated from each other. The external ring (120) is in direct contact with the head body (110), so that the external ring (120) directly receives the force applied from the head body. However, the internal ring (130) indirectly receives the force applied from the head body (110) because the elastic body (200) having flexibility is positioned between the internal ring (130) and the head body (110). Through this, the pressure transmitted to the internal ring (130) of the present invention is reduced compared to the pressure transmitted to the external ring (120).

[0048] This pressure-reducing structure of the present invention can prevent wafer slippage during wafer rotation polishing and simultaneously prevent excessive edge polishing of the wafer, compared to a conventional retainer ring under the same pressure. In other words, a portion of the pad rebounds due to the outer ring pressurized with a higher pressure, but the rebound region is formed in the inner ring area, not the edge area of ​​the wafer. As a result, the problem of excessive polishing due to pad rebound at the wafer edge area can be effectively prevented. In addition, the wafer fixing effect of the inner ring is further improved by the rebounded pad.

[0049] Figures 9 and 10 illustrate another embodiment of an elastic body in a wafer polishing head of a CMP device according to the present invention. In this embodiment, the shape of the elastic body (200-1) among the configurations of the head is different from that of the elastic body (200) described above, and other configurations are similar to those described above, so a repeated description thereof will be omitted.

[0050] Referring to Fig. 9, in the present embodiment, the elastic body (200-1) may be formed only by a member positioned on the upper side of the inner ring (130). That is, the lower surface of the elastic body (200-1) may be coupled to the upper surface of the inner ring (130), and the upper surface of the elastic body (200-1) may be configured to be in contact with the head body. The structure in which the lower surface of the elastic body (200-1) is coupled to the upper surface of the inner ring (130) may utilize the structure of the protrusions and grooves described above.

[0051] And, in Fig. 10, it can be configured to further include an upper ring (200-2) provided between the elastic body (200-1) and the head body. That is, the lower surface of the elastic body (200-1) is coupled to the upper surface of the inner ring (130) with a protrusion and groove structure, the upper surface of the elastic body (200-1) is made to contact the upper ring (200-2), and the upper surface of the upper ring is made to contact the head body.

Claims

1. A wafer polishing head of a CMP device having a retainer ring provided in a head body and an elastic membrane located on the inside of the retainer ring and contacting the upper surface of the wafer to apply pressure to the wafer. The above retainer ring is composed of an outer ring (120) located on the outside and an inner ring (130) located on the inside of the outer ring but physically separated from each other. The outer surface of the inner ring is positioned to be in contact with the inner surface of the outer ring, and the inner surface of the inner ring is positioned to be in contact with the outer surface of the wafer. It includes a ring-shaped elastic body (200) located between the upper surface of the inner ring and the head body; The upper surface of the above outer ring (120) is placed in direct contact with the head body, The upper surface of the inner ring (130) does not directly contact the head body due to the elastic body (200), The elastic body (200) is composed of an outer part (210), an inner part (220), and a middle part (230) that connects the outer part and the inner part and operates flexibly as the membrane moves up and down. The outer portion (210) is in contact with the upper surface of the inner ring, and the inner portion (220) is coupled to the membrane. A wafer polishing head of a CMP device, characterized in that the retainer ring further includes an O-ring (140) provided between the outer ring and the inner ring to prevent slurry from flowing in.

2. In paragraph 1, The above head body (110) includes a head outer portion (112) that contacts the upper surface of the outer ring (120) and a head inner portion (114) located on the upper side of the inner ring (130), and the outer portion and the inner portion are formed integrally. A wafer polishing head of a CMP device, characterized in that the inner side of the head (114) protrudes further downward than the outer side of the head (112) and comes into contact with the upper surface of the elastic body.

3. In paragraph 2, On the lower surface of the outer portion (210) of the elastic body, a lower protrusion (215) is formed to be received in a mounting groove formed on the upper surface of the inner ring. A wafer polishing head of a CMP device, characterized in that an upper protrusion (217) is formed on the upper surface of the outer portion (210) of the elastic body to be coupled to a fastening groove (115) formed in the head body.

4. In paragraph 3, A wafer polishing head of a CMP device, characterized in that it further includes a coupling ring (155) provided on the outer surface of the membrane and coupling the inner side (220) of the elastic body to the membrane.

5. In paragraph 1, A wafer polishing head of a CMP device, characterized in that the lower surface of the elastic body is bonded to the upper surface of the inner ring (130), and the upper surface of the elastic body is in contact with the head body.

6. In paragraph 1, Further comprising an upper ring provided between the elastic body and the head body; A wafer polishing head of a CMP device, characterized in that the lower surface of the elastic body is bonded to the upper surface of the inner ring, and the upper surface of the elastic body is in contact with the upper ring.

7. In paragraph 1, An outer curved portion (126) is formed from the inner circumference of the outer ring (120) to a predetermined height. A wafer polishing head of a CMP device, characterized in that an inner curved portion (136) is formed from the outermost end of the inner ring (130) to a predetermined height.

8. In paragraph 1, A wafer polishing head of a CMP device, characterized in that the hardness (H1) of the elastic body is formed to be less than or equal to the hardness (H2) of the membrane, so that the up-and-down movement of the membrane is not hindered.

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