Patent Application
20170144267
With a recent trend toward higher integration and higher density in semiconductor devices, circuit interconnects become finer and finer and the number of levels in multilayer interconnect is increasing. In the fabrication process of the multilayer interconnects with finer circuit, as the number of interconnect levels increases, film coverage (or step coverage) of step geometry is lowered in thin film formation because surface steps grow while following surface irregularities on a lower layer. Therefore, in order to fabricate the multilayer interconnects, it is necessary to improve the step coverage and planarize the surface. It is also necessary to planarize semiconductor device surfaces so that irregularity steps formed thereon fall within a depth of focus in optical lithography. This is because finer optical lithography entails shallower depth of focus.
Accordingly, the planarization of the semiconductor device surfaces is becoming more important in the fabrication process of the semiconductor devices. Chemical mechanical polishing (CMP) is the most important technique in the surface planarization. This chemical mechanical polishing is a process of polishing a wafer by bringing the wafer into sliding contact with a polishing surface of a polishing pad while supplying a polishing liquid containing abrasive grains, such as silica (SiO2). onto the polishing surface.
A polishing apparatus for performing CMP has a polishing table that supports the polishing pad thereon, and a substrate holding apparatus, which is called a top ring or a polishing head, for holding a wafer. When the wafer is polished using such polishing apparatus, the substrate holding apparatus holds the wafer and presses it against the polishing surface of the polishing pad at a predetermined pressure, while the polishing table and the substrate holding apparatus are moved relative to each other to bring the wafer into sliding contact with the polishing surface to thereby polish a surface of the wafer.
During polishing of the wafer, if a relative pressing force applied between the wafer and the polishing surface of the polishing pad is not uniform over the entire surface of the wafer, insufficient polishing or excessive polishing would occur depending on a force applied to each portion of the wafer. Thus, in order to make the pressing force against the wafer uniform, the substrate holding apparatus has a pressure chamber defined by an elastic membrane at a lower part thereof This pressure chamber is supplied with a fluid, such as air, to press the wafer through the elastic membrane with a fluid pressure.
However, since the above-described polishing pad has elasticity, the pressing force becomes non-uniform in an edge portion (or a peripheral portion) of the wafer during polishing of the wafer. Such non-uniform pressing force would result in so-called “rounded edge” which is excessive polishing that occurs only in the edge portion of the wafer. In order to prevent such rounded edge, a retaining ring for retaining the edge portion of the wafer is provided so as to be vertically movable relative to a top ring body (or carrier head body) and to press the polishing surface of the polishing pad around a circumferential edge of the wafer.
As the types of semiconductor devices have been increasing tremendously in recent years, there is an increasing demand for controlling a polishing profile in the wafer edge portion for each device or each CMP process (e.g., an oxide film polishing process and a Metal film polishing process). One of the reasons is that each wafer has a different initial film-thickness distribution because a film-forming process, which is performed prior to the CMP process, varies depending on the type of film. Typically, a wafer is required to have a uniform film-thickness distribution over its entire surface after the CMP process. Therefore, different initial film-thickness distributions necessitate different polishing profiles.
Other reason is that types of polishing pads and polishing liquids, both of which are consumables of the polishing apparatus, are increasing greatly from a viewpoint of costs. Use of different polishing pads or different polishing liquids results in greatly different polishing profiles particularly in the wafer edge portion. In a semiconductor device fabrication, the polishing profile in the wafer edge portion can greatly affect a product yield. Therefore, it is very important to precisely control the polishing profile of the wafer edge portion particularly in a narrow area of the wafer edge portion in a radial direction.
In order to control the polishing profile of the wafer edge portion, various elastic. membranes as disclosed in Japanese laid-open patent publication No. 2013-111679 have been proposed. However, these elastic membranes are suitable for controlling the polishing profile in a relatively wide area of the wafer edge portion.
According to an embodiment, there is provided an elastic membrane (or a membrane) capable of precisely controlling a polishing profile in a narrow area of a wafer edge portion. Further, there is provided a substrate holding apparatus and a polishing apparatus having such an elastic membrane.
Embodiments, which will be described below, relate to an elastic membrane for use in a substrate holding apparatus fur holding a substrate, such as a wafer. Further, the embodiments relate to a substrate holding apparatus and a polishing apparatus having such an elastic membrane.
In rata embodiment, there is provided an elastic membrane for use in a substrate holding apparatus, comprising: a contact portion to be brought into contact with a substrate for pressing the substrate against a polishing pad; a first edge circumferential wall extending upwardly from a peripheral edge of the contact portion; and a second edge circumferential wall having a horizontal portion connected to an inner circumferential surface of the first edge circumferential wall, wherein the inner circumferential surface of the first edge circumferential wall includes an upper inner circumferential surface and a lower inner circumferential surface, both of which are perpendicular to the contact portion, the upper inner circumferential surface extends upwardly from the horizontal portion of the second edge circumferential wall, and the lower inner circumferential surface extends. downwardly from the horizontal portion of the second edge peripheral wall.
In an embodiment, the upper inner circumferential surface and the lower inner circumferential surface lie in a same plane.
In an embodiment, an annular groove extending in a circumferential direction of the first edge circumferential wall is formed in the lower inner circumferential surface.
In an embodiment, the annular groove is located at a lower end of the lower inner circumferential surface.
In an embodiment, the elastic membrane further comprises a third edge circumferential wall located radially inwardly of the second edge circumferential wall, the third edge circumferential wall having a lower end connected to the contact portion, the lower end of the third edge circumferential wall being located adjacent to the first edge circumferential wall.
In an embodiment, there is provided a substrate holding apparatus comprising: an elastic membrane that forms pressure chambers for pressing a substrate; a head body to which the elastic membrane is secured; and a retaining nag surrounding the elastic membrane, wherein the elastic membrane comprises (i) a contact portion to be brought into contact with the substrate tier pressing the substrate against a polishing pad, (ii) a first edge circumferential wall extending upwardly from a peripheral edge of the contact portion, and (iii) a second edge circumferential wall haying a horizontal portion connected to an inner circumferential surface of the first edge circumferential wall. The inner circumferential surface of the first edge circumferential wall includes an upper inner circumferential surface and a lower inner circumferential surface, both of which are perpendicular to the contact portion, the upper inner circumferential surface extends upwardly from the horizontal portion of the second edge circumferential wall, and the lower inner circumferential surface extends downwardly from the horizontal portion of the second edge peripheral wall.
In an embodiment, there is provided a polishing apparatus comprising: a polishing table for supporting a polishing pad; and a substrate holding apparatus configured to press a substrate against the polishing pad, the substrate holding apparatus including an elastic membrane that forms pressure chambers for pressing the substrate, a head body to which the elastic membrane is secured, and a retaining ring surrounding the elastic membrane, wherein the elastic membrane comprises (i) a contact portion to be brought into contact with the substrate for pressing the substrate against the polishing pad, (ii) a first edge circumferential wall extending upwardly from a peripheral edge of the contact portion, and (iii) a second edge circumferential wall having a horizontal portion connected to an inner circumferential surface of the first edge circumferential wall. The inner circumferential surface of the first edge circumferential wall includes an upper inner circumferential surface and a lower inner circumferential surface, both of which are perpendicular to the contact portion, the upper inner circumferential surface extends upwardly from the horizontal portion of the second edge circumferential wall, and the lower inner circumferential surface extends downwardly from the horizontal portion of the second edge peripheral wall.
Use of the above-described elastic membrane in the substrate holding apparatus of the polishing apparatus makes it possible to precisely control a polishing rate in a narrow area of a periphery portion of the substrate. Therefore, a uniformity of the polishing rate over the substrate surface is improved in various types of processes, and as a result, a product yield can be improved.
Embodiments will be described below with reference to the drawings.
The polishing table 18 is coupled via a table shaft 18a to a table motor 29 disposed below the polishing table 18, so that the polishing table 18 is rotatable about the table shaft 18a. The polishing pad 19 is attached to an upper surface of the polishing table 18. A surface 19a of the polishing pad 19 serves as a polishing surface for polishing, the wafer W. A polishing liquid supply nozzle 25 is provided above the polishing table: 18 so that the polishing liquid supply nozzle 2 supplies a polishing liquid Q onto the polishing pad 19 on the polishing table 18.
The polishing head 1 includes a head body 2 for pressing the wafer W against the polishing surface 19a. and a retaining ring 3 for retaining the wafer W therein so as to prevent the wafer W from slipping out of the polishing head 1. The polishing head 1 is coupled to a head shaft 27, which is vertically movable relative to a head arm 64 by a vertically moving mechanism 81. This vertical movement of the head shaft 27 causes the entirety of the polishing head 1 to move upward and downward relative to the head arm 64 for positioning of the polishing head 1 and enables positioning of the polishing head 1. A rotary joint 82 is mounted to an upper end of the head shaft 27.
The vertically moving mechanism 81 for elevating and lowering the head shaft 27 and the polishing head 1 includes a bridge 84 that rotatably supports the head shaft 27 through a bearing 83, a ball screw 88 mounted to the bridge 84, a support pedestal 85 supported by support posts 86, and a servomotor 90 mounted to the support pedestal 85. The support pedestal 85, which supports the servomotor 90, is fixedly mounted to the head arm 64 through the support posts 86.
The ball screw 88 includes a screw shaft 88a coupled to the servomotor 90 and a nut 88b that engages with the screw shaft 88a. The head shaft 27 is vertically movable together with the bridge 84. When the servomotor 90 is set in motion, the bridge 84 moves vertically through the ball screw 88, so that the head shaft 27 and the polishing head 1 move vertically.
The head shaft 27 is coupled to a rotary sleeve 66 by a key (not shown). A timing pulley 67 is secured to a circumferential surface of the rotary sleeve 66. A head motor 68 is fixed to the head arm 64. The timing pulley 67 is coupled through a timing belt 69 to a timing pulley 70, which is mounted to the head motor 68. When the head motor 68 is set in motion, the rotary sleeve 66 and the head shaft 27 are rotated together with the timing pulley 70, the timing belt 69, and the timing pulley 67, thus rotating the polishing head 1. The head arm 64 is supported by an arm shaft 80, which is rotatably supported by a frame (not shown). The polishing apparatus includes a controller 40 for controlling devices including the head motor 68 and the servomotor 90.
The polishing head 1 is configured to be able to hold the wafer W on its lower surface. The head arm 64 is configured to be able to pivot on the arm shaft 80. Thus, the polishing head 1, when holding the wafer W on its lower surface, is moved from a position at which the polishing head 1 receives the wafer W to a position above the polishing table 18 by a pivotal movement of the head arm 64.
Polishing of the wafer W is performed as follows. The polishing head 1 and the polishing table 18 are rotated individually, while the polishing liquid Q is supplied four the polishing liquid supply nozzle 25, located above the polishing table 18, onto the polishing pad 19. In this state, the polishing head 1 is lowered to a predetermined position (i.e., a predetermined height) and then presses the wafer W against the polishing surface 19a of the polishing pad 19. The wafer W is placed in sliding contact with the polishing surface 19a of the polishing pad 19, so that a surface of the wafer W is polished.
Next, the polishing head (substrate holding apparatus) 1, which is installed in the polishing apparatus shown in
The elastic membrane 10 has a plurality of (eight in the drawing) annular circumferential walls 10a, 10b, 10c, 10d, 10e, 10f, 10g, and 10h, which are arranged concentrically. These circumferential walls 10a, 10b, 10c, 10d, 10e, 10f, 10g, and 10h form a circular central pressure chamber 12 located at a center of the elastic membrane 10, annular edge pressure chambers 14a, 14h located at the outermost part of the elastic membrane 10, and five (in this embodiment) annular intermediate pressure chambers (i.e., first to fifth intermediate pressure chambers) 16a, 16b, 16c, 16d, and 16e located between the central pressure chamber 12 and the edge pressure chambers 14a, 14b. These pressure chambers 12, 14a, 14b, 16a, 16b, 16c, 16d, and 16e are located between an upper surface of the elastic membrane 10 and the lower surface of the head body 2.
The head body 2 has a fluid passage 20 communicating with the central pressure chamber 12, a fluid passage 22 communicating with the edge pressure chamber 14a, fluid passage 24f communicating with the edge pressure chamber 14b. and fluid passages 24a, 24b, 24c, 24d, and 24e communicating with the intermediate pressure chambers 16a, 16b, 16e, 16d, and 16e, respectively. These fluid passages 20, 22, 24a, 24b, 24e, 24d, 24e, and 24f are coupled to fluid lines 26, 28, 30a, 30b, 30c, 30d, 30e, and 30f, respectively, all of which are coupled to a fluid supply source 32. The fluid lines 26, 28, 30a, 30b, 30c, 30d, 30e, and 30f are provided with on-off valves V1, V2, V3, V4, V5, V6, V7, and V8 and pressure regulators R1, R2, R3, R4, R5, R6, R7, and R8, respectively.
A retainer chamber 34 is formed immediately above the retaining ring 3. This retainer chamber 34 is coupled via a fluid passage 36 and a fluid line 38 to the fluid supply source 32. The fluid passage 36 is formed in the head body 2. The fluid line 38 is provided with an on-off valve V9 and a pressure regulator R9. The pressure regulators R1, R2, R3, R4, R5, R6, R7, R8, and R9 have pressure regulating function to regulate pressure of the pressurized fluid supplied from the fluid supply source 32 to the respective pressure chambers 12, 14a, 14b, 16a, 16b, 16e, 16d, and 16e, and the retainer chamber 34. The pressure regulators R1 to R9 and the on-off valves V1 to V9 are coupled to the controller 40, so that operations of the pressure regulators R1 to R9 and the on-off valves V1 to V9 are controlled by the controller 40. According to the polishing head 1 configured as shown in
The head body 2 is made of resin, such as engineering plastic (e.g., PEEK), and the elastic membrane 10 is made of a highly strong and durable rubber material, such as ethylene propylene rubber (EPDM), polyurethane rubber, silicone rubber, or the like.
The contact portion 11 has a plurality of through-holes 17 communicating with the intermediate pressure chamber 16c. Only one through-hole 17 is shown in
The through-holes 17 may be formed at another pressure chamber, instead of the intermediate pressure chamber 16c. In such case, the vacuum suction and the release the wafer W are performed by controlling pressure in the pressure chamber at which the through-holes 17 are formed.
The circumferential wall 10h is an outermost circumferential wall, and the circumferential wall 10g is located radially inwardly of the circumferential wall 10h. Further, the circumferential wall 10f is located radially inwardly of the circumferential wall 10g. Hereinafter, the circumferential wall 10h will be referred to as first edge circumferential wall, the circumferential wall 10g will be refereed to as second edge circumferential wall, and the circumferential wall 10f will be referred to as third edge, circumferential wall.
The second edge circumferential wall 10g has an outer horizontal portion 111 which is connected to an inner circumferential surface 101 of the first edge circumferential wall 10h. The inner circumferential surface 101 of the first edge circumferential wall 10h includes an upper inner circumferential surface 101a and a lower inner circumferential surface 101b, both of which are perpendicular to the contact portion 11. The upper inner circumferential surface 101a extends upwardly from the horizontal portion 111 of the second edge circumferential wall 10g, and the lower inner circumferential surface 101b extends downwardly from the horizontal portion 111 of the second edge circumferential wall 10g. In other words, the outer horizontal portion 111 of the second edge circumferential wall 10g is connected to a position at which the inner circumferential surface 101, extending in a direction perpendicular to the contact portion 11, is divided. The lower inner circumferential surface 101b is connected to the peripheral edge of the contact portion 11. An outer circumferential surface 102, located outside the lower inner circumferential surface 101b, are also perpendicular to the contact portion 11. The upper inner circumferential surface 101a and the lower inner circumferential surface 101b lie in the same plane. This “same plane” is an imaginary plane that is perpendicular to the contact portion 11. Thus, a radial position of the upper inner circumferential surface 101a is the same as a radial position of the lower inner circumferential surface 101b.
The first edge circumferential wall 10h includes a fold portion 103 that allows the contact portion 11 to move upward and downward. This fold portion 103 is connected to the upper inner circumferential surface 101a. The fold portion 103 has a bellows structure that can expand and contract in the direction perpendicular to the contact portion 11 (i.e., in vertical direction). Therefore, even if a distance between the head body 2 and the polishing pad 19 changes, the contact between the peripheral edge of the contact portion 11 and the wafer W can be maintained. Causes of the change in the distance between the head body 2 and the polishing pad 19 include an inclination of the head body 2. and the polishing pad 19 relative to each other, an oscillation of the polishing pad surface 19a with the rotation of the polishing table 18, and an axial oscillation (an oscillation in the vertical direction) with the rotation of the head shaft 27. The first edge circumferential wall 1011 has a rim portion 104 extending radially inwardly from an upper end of the fold portion 103. The rim portion 104 is secured to the lower surface of the head body 2 by the holding ring 8 shown in
The second edge circumferential wall 10g has the outer horizontal portion 111 extending horizontally from the inner circumferential surface 101 of the first edge circumferential wall 10h. Further, the second circumferential wall 10a has a slope portion 112 connected to the outer horizontal portion 111, an inner horizontal portion 113 connected to the slope portion 112, a vertical portion 114 connected to the inner horizontal portion 113, and a rim portion 115 connected to the vertical portion 114. The slope portion 112 extends radially inwardly from the outer horizontal portion 111 while sloping upwardly. The rim portion 115 extends radially outwardly from the vertical portion 114, and is secured to the lower surface of the head body 2 by the holding ring 8 shown in
The third edge circumferential wall 10f is located radially inwardly of the second edge circumferential wall 10g. The third edge circumferential wall 10f has a slope portion 121 connected to an upper surface of the contact portion 11, a horizontal portion 122 connected to the slope portion 121, a vertical portion 123 connected to the horizontal portion 122, and a rim portion 124 connected to the vertical portion 123. The slope portion 121 extends radially inwardly from the upper surface of the contact portion 11 while sloping upwardly. The rim portion 124 extends radially inwardly from the vertical portion 123, and is secured to the lower surface of the head body 2 by the holding ring 7 shown in
The circumferential wall 10e is located radially inwardly of the third edge circumferential wall 10f. The circumferential wall 10e has a slope portion 131 connected to the upper surface of the contact portion 11, a horizontal portion 132 connected to the slope portion 131, a vertical portion 133 connected to the horizontal portion 132, and a rim portion 134 connected to the vertical portion 133. The slope portion 131 extends radially inwardly from the upper surface of the contact portion 11 while sloping upwardly. The rim portion 134 extends radially outwardly from the vertical portion 133, and is secured to the lower surface of the head body 2 by the holding ring 7 shown in
The circumferential walls 10b, 10d shown in
As shown in
The upper inner circumferential surface 101a extends upwardly in the direction perpendicular to the contact portion 11, and the lower inner circumferential surface 101b extends downwardly in the direction perpendicular to the contact portion 11. Because of such configurations of the upper inner circumferential surface 101a and the lower inner circumferential surface 101b, an oblique force is not applied to a connecting portion between the first edge circumferential wall 10h and the second edge circumferential wall 10g, and as a result, the polishing rate can be controlled in a narrow area of the wafer edge portion. This feature will be described below with reference to
As shown in
In contrast, as shown in
The previous description of embodiments is provided to enable a person skilled in the art to make and use the present invention. Moreover, various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles and specific examples defined herein may be applied to other embodiments. Therefore, the present invention is not intended to be limited to the embodiments described herein but is to be accorded the widest scope as defined by limitation of the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-066999 | Mar 2014 | JP | national |
This document is a Divisional of U.S. application Ser. No. 14/668,844 filed on Mar. 25, 2015, which claims priority to Japanese Patent Application Number 2014-066999 filed March 27, 2014, the entire contents of which are hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 14668844 | Mar 2015 | US |
| Child | 15402703 | US |
