Retaining Rings for CMP

Abstract

To provide a retaining ring configured to be provided on a carrier head for chemical mechanical polishing.SOLUTION: A retaining ring includes a substantially annular body having an inner surface to constrain a substrate and a bottom surface. The bottom surface has a plurality of channels extending from an outer surface to the inner surface, and a plurality of islands separated by the channels and providing a contact area to contact a polishing pad, which contact area is approximately 15-40% of a plan area of the bottom surface.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to a retaining ring for a carrier head for chemical mechanical polishing. [Background technology]

[0002] Integrated circuits are typically formed on substrates, particularly silicon wafers, by successive deposition of conductive, semiconducting, or insulating layers. One manufacturing step involves depositing a fill layer over a non-planar surface and planarizing the fill layer. In certain applications, the fill layer is planarized until the top surface of the patterned layer is exposed. For example, a conductive fill layer can be deposited over an insulating patterned layer to fill trenches or holes in the insulating layer. After planarization, the portions of the conductive layer remaining between the raised patterns of the insulating layer form vias, plugs, and lines that provide conductive paths between thin-film circuits on the substrate. In other applications, such as oxide polishing, the fill layer is planarized until a predetermined thickness remains over the non-planar surface. Additionally, photolithography also typically requires planarization of the substrate surface. Chemical mechanical polishing (CMP) is one commonly accepted method of planarization. This method of planarization typically requires mounting a substrate on a carrier head. The exposed surface of the substrate is typically placed in contact with a rotating polishing pad. The carrier head provides a controllable load on the substrate to press the substrate against the polishing pad. Typically, a polishing fluid, such as a slurry containing abrasive particles, is supplied to the surface of the polishing pad. The substrate is typically held under the carrier head by a retaining ring, which, however, is prone to wear due to contact with the polishing pad and is sometimes replaced. Some retaining rings have an upper portion made from metal and a lower portion made from wearable plastic, while others are a single plastic portion. Summary of the Invention [Means for solving the problem]

[0003] In one aspect, the retaining ring includes a generally annular body having an inner surface that restrains the substrate and a bottom surface, the bottom surface having a plurality of channels extending from the outer surface to the inner surface and a plurality of islands separated by the channels and providing a contact area for contacting the polishing pad, the contact area being approximately 15-40% of the flat area of ​​the bottom surface. Implementations may include one or more of the following features. The contact area can be about 25 to 30% of the flat area of ​​the bottom surface. The channels can be evenly spaced around the annular body. There can be between 8 and 30 channels.

[0004] Each channel of the plurality of channels may include an inlet portion at the outer surface, a constriction extending substantially perpendicular to a width of the retaining ring, and an outlet portion extending from the constriction to the inner surface. The outlet portion may widen toward the inner surface. The inlet portion may be circumferentially longer than the outlet portion. Each channel of the plurality of channels can include a leading edge and a trailing edge, and the leading edge and the trailing edge need not be symmetrical about a centerline of the channel. The leading edge can include a linear section that extends across substantially all of the radial width of the bottom surface. The linear section can be oriented at an angle of about 30-60° relative to the radial direction. The trailing edge can include a first portion that extends substantially along the radial direction and a second portion that extends substantially perpendicular to the first portion and is closer to the outer surface than the inner portion. The channel may include a recessed region adjacent the outer surface such that the channel is deeper in the recessed region than in the remainder of the channel. The recessed region and the remainder of the channel may each have a substantially uniform depth.

[0005] Advantages may include one or more of the following: The pad rebound effect may be reduced, thus providing better control of the polishing rate at the substrate edge and improved polishing uniformity, especially at the substrate edge, e.g., the outer 5 mm of the substrate. The details of one or more implementations are set forth in the accompanying drawings and the description below. Other aspects, features, and advantages will become apparent from the description and drawings, and from the claims. [Brief description of the drawings]

[0006] [Figure 1] 2 is a schematic cross-sectional view of a carrier head. [Diagram 2] FIG. [Diagram 3] FIG. 2 is a schematic bottom view of the retaining ring. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] Like reference symbols in the various drawings refer to like elements. The retaining ring can be used to compress the surface of the polishing pad in the area around the substrate. In particular, the retaining ring must press with enough force that the substrate is effectively trapped without accidentally sliding under the ring. The retaining ring can also be used to compress the polishing pad near the edge of the substrate and thus affect the polishing rate at the substrate edge. However, when the pad is compressed in this manner, the elasticity of the polishing pad, together with the relative motion between the pad and the retaining ring, can result in a "pad rebound effect," which can increase radial non-uniformity. Two techniques can be used to reduce the pad's repulsion. First, by reducing the contact area of ​​the retaining ring against the polishing pad, a smaller portion of the pad is compressed, and therefore a smaller portion of the substrate is subjected to the pad's repulsion. Second, the particular shape of the contact area is less likely to cause the pad's repulsion. During a polishing operation, one or more substrates may be polished by a chemical mechanical polishing (CMP) apparatus that includes carrier head 100. A description of a CMP apparatus can be found in U.S. Patent No. 5,738,574.

[0008] Referring to FIG. 1, an exemplary simplified carrier head 100 includes a base 102, a flexible film 104 that provides a mounting surface for a substrate, a pressurized chamber 106 between the film 104 and the base 102, and a retaining ring 110 secured near an edge of the base 102 to hold the substrate under the film 104. Although FIG. 1 shows the film 104 clamped between the retaining ring 110 and the base 102, one or more other parts, e.g., a clamp ring, may be used to hold the film 104. A drive shaft 120 may be provided to rotate and / or translate the carrier head across the polishing pad. A pump may be fluidly connected to the chamber 106 through a passage 108 in the base to control the pressure in the chamber 106 and thus the downward pressure of the flexible film 104 against the substrate. The retaining ring 110 may be a generally annular ring and is secured, for example, at an outer edge of the base 102 by screws or bolts 136 that extend through passages 138 in the base 102 into aligned threaded receiving recesses in the top surface 112 of the retaining ring 110. In some implementations, the drive shaft 120 may be raised or lowered to control the pressure of the bottom surface 114 of the retaining ring 110 against the polishing pad. Alternatively, the retaining ring 110 may be movable relative to the base 102 and the carrier head 100 may include an internal chamber that may be pressurized to control the downward pressure on the retaining ring, as described, for example, in U.S. Pat. Nos. 6,183,354 or 7,575,504. The retaining ring 110 is removable from the base 102 (and the remainder of the carrier head) as a unit. In the case of retaining ring 110, this means that even when retaining ring 110 is removed, upper portion 142 of retaining ring 110 remains secured to lower portion 140 of the retaining ring, without requiring dismantling of base 102 or removal of base 102 from carrier head 100. An inner diameter surface 116 of the retaining ring 110, in conjunction with the lower surface of the flexible film 104, defines a substrate-receiving recess. The retaining ring 110 prevents the substrate from escaping the substrate-receiving recess.

[0009] The retaining ring 110 may include multiple vertically stacked sections and may include an annular lower portion 140 having a bottom surface 114 that may contact a polishing pad, and an annular upper portion 142 connected to the base 102. The lower portion 140 may be bonded to the upper portion 142 by an adhesive layer 144. The bottom portion 140 is a plastic, such as polyphenol sulfide (PPS). The plastic of the bottom portion 140 is chemically inert in the CMP process. Additionally, the bottom portion 140 should be elastic enough to prevent the substrate edge from contacting the retaining ring and chipping or cracking the substrate. On the other hand, the bottom portion 140 should be rigid enough to have a sufficient lifespan to withstand wear from the polishing pad (on the bottom surface) and the substrate (on the inner surface). The plastic of the bottom portion 140 may have a durometer hardness of about 80-95 Shore D. Typically, the elastic modulus of the material of the bottom portion 140 is about 0.3-1.0×10 6 psi. The lower portion can have a low wear rate, but gradual wear of the lower portion 140 is acceptable because it is believed this will prevent the substrate edge from cutting deep grooves into the inner surface 116. The plastic of the lower portion 140 may be (eg, consist of) polyphenylene sulfide (PPS), polyaryletherketone (PAEK), polyetheretherketone (PEEK), or polyetherketoneketone (PEKK).

[0010] The upper portion 142 of the retaining ring 110 can be of a more rigid material than the lower portion 140, such as a metal, ceramic, or a more rigid plastic. An adhesive layer 144 can be used to secure the upper portion 140 to the lower portion 142, or the upper and lower portions 140 and 142 can be connected by threads (e.g., extending through apertures in the upper portion 140 into threaded receiving recesses or threaded sheaths in the lower portion 142), press fit together, or sonic molded together. Alternatively, rather than having a lower portion and an upper portion, the entire retaining ring 110 can be formed from the same material, such as the plastic of the lower portion described above.

[0011] The inner surface 116 of the lower portion 140 of the retaining ring may have an inner diameter D that is slightly larger than the diameter of the substrate, for example, about 1-2 mm larger than the diameter of the substrate, to accommodate the positioning tolerances of the substrate loading system. The retaining ring 110 may have a radial width of about one-half inch.

[0012] 2 and 3 show a retaining ring 110 with a bottom surface 114 including a plurality of channels 150 extending from an inner diameter surface 116 to an outer diameter surface 118. The bottom surface 114 also includes islands 152, with each pair of adjacent islands 152 separated by one of the channels 150. Each channel 150 can have the same shape as the other channels in a plan bottom view, and similarly, each island 152 can have the same shape as the other islands. The islands 152 provide a contact area of ​​the bottom surface 140 to the polishing pad. The islands 152 may provide a contact area of ​​about 15-40%, such as 25-30%, of the flat area of ​​the bottom surface. The flat area of ​​the bottom surface is determined by π(R O 2 -R I 2 ) where R O is the radius of the outer diameter of the ring 110, and R I is the inner radius.

[0013] The sidewalls of the channels 150 can be substantially perpendicular to the surface of the islands 152, so that the contact area, which is a portion of the flat area, does not change as the retaining ring wears. The channels 150 (and thus the islands 152) can be positioned at uniform intervals circumferentially around the retaining ring 110. There can be between 8 and 30 channels 150, for example 18 channels. Each channel 150 includes a leading edge 160 and a trailing edge 170. Assuming that the carrier head, and therefore the retaining ring, rotates in a counterclockwise direction (viewed from the bottom side of the ring, as indicated by arrow A), leading edge 160 is the right edge and trailing edge 170 is the left edge (again, viewed from the bottom side of the ring).

[0014] The leading edge 160 may be a wholly or primarily linear section 162. The linear portion 172 may extend across approximately 90-100% of the radial width W of the bottom surface 114 of the retaining ring 110. However, one or more of the corners 164 where the leading edge 160 intersects the inner diameter surface 116 or the outer diameter surface 118 may be rounded. At the outer edge 118, the linear section of the leading edge 160 may make an angle α with respect to a radial direction R passing through the center of the retaining ring 110. The angle α may be between 30° and 60°, for example 45°. The trailing edge 170 includes a linear portion 172 that extends substantially radially, for example, in a direction passing through the center of the retaining ring 110. The angle between the linear portion 172 and the radial direction from the center of the linear portion 172 may be less than 10°. The linear portion 172 may extend across approximately 25-75% of the radial width W of the bottom surface 114 of the retaining ring 110. A corner 174 where the trailing edge 170 intersects the inner diameter surface 116 may be rounded.

[0015] The trailing edge 170 also includes an azimuthally extending portion 176 that extends in an aft direction, i.e., away from the leading edge 160 of the channel 150. The azimuthally extending portion 176 may be a linear section or may be curved, for example, concentric with the inner diameter surface 116 and the outer diameter surface 118. The azimuthally extending portion 176 may extend approximately 50-80% of the circumferential length of the island 152 at the outer diameter surface 118. The trailing edge 170 also includes a section 178 that connects the azimuthally extending portion 176 to the outer diameter surface 118. The section 178 may be U-shaped and may curve from the azimuthally extending portion 176 to the outer diameter surface 118.

[0016] Viewed from the outside inward, the resulting channel 150 has an inlet portion 154 at the outer diameter surface 118, an abrupt narrowing 156 intersected by an azimuthally extending portion 176, and an outlet portion 158 that widens toward the inner diameter surface 116. The circumferential length L1 of the inlet at the outer diameter surface 118 can be greater than the circumferential length L2 of the outlet at the inner diameter surface 116. The wider inlet portion 154, along with a U-shaped section 178 of the inlet 154, can help to "scoop" up the slurry from the polishing pad and direct the slurry inward toward the substrate. Optionally, a recess 180 can be formed in the inlet portion 154 of the channel 150. That is, the channel 150 is deeper in the inlet portion 154 than in the outlet portion 158. The recess 180 can have a uniform depth, and the outlet portion 158 can also have a uniform depth. Several embodiments have been described. However, many variations are possible. For example, rather than the complex channel and island shapes described above, the islands can be simple linear stripes, with widths selected to provide the desired percentage of contact area. For example, the trailing and leading edges of each island can be provided by two parallel linear sections. The trailing and leading edges can be rounded on the inner and outer diameter surfaces. The scope of the invention is therefore defined by the appended claims.

Claims

1. a polishing pad having a polishing surface that contacts a polishing pad with a polishing pad and a polishing pad that is spaced apart from the polishing pad; a polishing pad that contacts a polishing pad with a polishing pad and that is spaced apart from the polishing pad with a ... and that contacts a polishing pad with a polishing pad; a polishing pad that contacts a polishing pad and that contacts a polishing pad; a polishing pad that contacts a polishing pad and that contacts a polishing pad; a polishing pad that contacts a polishing pad and that contacts a polishing pad; Retaining ring.

2. The retaining ring of claim 1 , wherein the leading edge of each island includes a radially extending portion adjacent the inner surface.

3. The retaining ring of claim 2 , wherein the azimuthally extending portion of the leading edge of each island connects the radially extending portion to the U-shaped section.

4. The retaining ring of claim 1 , wherein the azimuthally extending portion of the leading edge of each island extends from the U-shaped section.

5. The retaining ring of claim 4 , wherein the azimuthally extending portion defines a constriction between an entrance portion and an exit portion of the channel.

6. The retaining ring of claim 4 , wherein said azimuthally extending portion is linear.

7. The retaining ring of claim 4 , wherein said azimuthally extending portion is curved.

8. The retaining ring of claim 5 , wherein said inlet portion is circumferentially longer than said outlet portion.

9. The retaining ring of claim 1 , wherein the trailing edge is linear.

10. The retaining ring of claim 9, wherein the trailing edge is oriented at an angle of about 30 to 60 degrees relative to a radial direction passing through a center of the retaining ring.

11. a polishing pad having a first radially extending portion and a second radially extending portion connecting the outer surface to the azimuthally extending portion and the second radially extending portion connecting the azimuthally extending portion to the inner surface, the first radially extending portion being U-shaped; Retaining ring.

12. The retaining ring of claim 11 , wherein the second radially extending portion is linear.

13. The retaining ring of claim 12 , wherein said azimuthally extending portion is linear.

14. The retaining ring of claim 12 , wherein the azimuthally extending portion is curved.

15. The retaining ring of claim 11, wherein the azimuthally extending portion extends over 50-80% of the circumferential length of the islands at the outer surface.

16. The retaining ring of claim 11 , wherein the leading edge of each channel is linear.

17. The retaining ring of claim 11 , wherein one or more of at least one corner where the leading or trailing edge of the channel intersects the inner or outer surface is rounded.

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