WO2014066119A1

WO2014066119A1 - Retaining ring with selected stiffness and thickness

Info

Publication number: WO2014066119A1
Application number: PCT/US2013/065320
Authority: WO
Inventors: Hung Chih Chen; Samuel Chu-Chiang Hsu; Gautam Shashank Dandavate
Original assignee: Applied Materials Inc
Current assignee: Applied Materials Inc
Priority date: 2012-10-26
Filing date: 2013-10-16
Publication date: 2014-05-01
Anticipated expiration: 2015-04-26
Also published as: US20150209930A1; TWI625196B; TWI590912B; US20140120803A1; TW201728408A; US8998676B2; US9492905B2; TW201429625A

Abstract

A retaining ring for holding a substrate below a carrier head during chemical mechanical polishing includes an annular lower portion and an annular upper portion secured to the lower portion. The annular lower portion has a main body with a bottom surface for contacting a polishing pad during polishing, and is a first material. A top surface of the upper portion is configured to be secured to the carrier head. The upper portion is a second material that is more rigid than the first material. A thickness and stiffness of the lower portion is selected for a particular polishing environment to improve polishing uniformity near an edge of the substrate.

Description

RETAINING RING WITH SELECTED STIFFNESS AND

THICKNESS

TECHNICAL FIELD

The present disclosure relates to a retaining ring for a carrier head for chemical mechanical polishing.

BACKGROUND

Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semiconductive or insulative layers. One fabrication step involves depositing a filler layer over a non-planar surface and planarizing the filler layer. For certain applications, the filler layer is planarized until the top surface of a patterned layer is exposed. A conductive filler layer, for example, can be deposited on a patterned insulative layer to fill the trenches or holes in the insulative lay er. After pianarization, the portions of the conductive layer remaining between the raised pattern of the insulative layer form vias, plugs, and lines that provide conductive paths between thin film circuits on the substrate. For other applications, such as oxide polishing, the filler layer is planarized until a predetermined thickness is left over the non-planar surface. In addition, pianarization of the substrate surface is usually required for photolithography.

Chemical mechanical polishing (CMP) is one accepted method of pianarization. This pianarization method typically requires that the substrate be mounted on a carrier head. The exposed surface of the substrate is typically placed against a rotating polishing pad. The carrier head provides a controllable load on the substrate to push it against the polishing pad. A polishing liquid, such as slurry with abrasive particles, is typically supplied to the surface of the polishing pad.

The substrate is typically retained below the carrier head by a retaining ring. Some retaining rings include an upper metal portion and a lower plastic portion.

SUMMARY

The geometry of the bottom surface of a retaining ring can impact the pressure distribution on the substrate near the substrate edge, and thus affect the polishing uniformity. However, the stiffness and height of the lower plastic portion of the retaining ring can also impact the pressure distribution near the substrate edge, selecting a combination of stiffness and height of the lower plastic portion of tl retaining ring, pressure uniformity can be improved.

In one aspect, a retaining ring for holding a substrate below a carrier he during chemical mechanical polishing includes an annular lower portion and aj annular upper portion secured to the lower portion. The annular lower portion main body with a bottom surface for contacting a polishing pad during polisliii is a first material. A top surface of the upper portion is configured to be secure the carrier head. The upper portion is a second material that is more rigid than first material . A thickness and stiffness of the lower portion is selected for a particular polishing environment to improve polishing uniformity near an edge substrate.

Impleme tations may include one or more of the following features. T material may be a plastic and the second material may be a metal. The lower p may have a flexural modulus of about 0.5 to 1.5 x 10" psi. The lower portion n have a thickness of 25 to 50 mils.

In another aspect, a retaining ring for holding a substrate below a carrie during chemical mechanical polishing includes an annular lower portion and ai annular upper portion secured to the lower portion. The annular lower portion main body with a bottom surface for contacting a polishing pad during polishir annular lower portion has a thickness between 5 and 45 mils and is a first mate having a flexural modulus between 1.1 and 1.5 x 10⁶ psi. A top surface of the portion is configured to be secured to the carrier head. The upper portion is a s material that is more rigid than the first material,

Implementations may include one or more of the following features. T annular lower portion may have a thickness between 10 and 20 mils. The anni lower portion may have a thickness between 25 and 45 mils.

I another aspect, a method of selecting a retaining ring includes polish first test substrate with the first test substrate held in a carrier head having a fir; retaining ring having an upper portion and a lower portion with a first stiffness lower portion with a second stiffness and a second thickness, polishing a secon substrate with the second test substrate held in the carrier head having the seco retaining ring, and polishing a plurality of device substrates using a pluralit carrier heads having a pluralit}' of retaining rings, each retaining ring of the pk of retaining rings having an upper portion and a lower portion with a second st and the second stiffness.

Implementations may include one or more of the following features. Measuring polishing uniformity may include determining that a perimeter port the first test substrate is overpolished relative to a center portion of the first tes substrate, and the second hardness may be greater than the first hardness and'O second thickness may be less than the first thickness. Measuring polishing uni may include determining that a perimeter portion of the first test substrate is underpolished relative to a center portion of the first test substrate, and the secc hardness may be less than the first hardness and'or the second thickness may b greater than the first thickness.

Advantages of implementations may include one or more of the follow: Pressure uniformity can be improved, and within-wafer non-uniformity (WIVv^r can be reduced.

The details of one or more implementations are set forth in the accomp; drawings and the description below. Other features, objects, and advantages w apparent from the description and. drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional view of a carrier head.

FIG. 2 is a schematic expanded cross-sectional view of a substrate beinj by a retaining ring.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

During a polishing operation, one or more substrates can be polished b^~i Referring to FIG. 1, an exemplary simplified carrier head 100 includes housing 102, a flexible membrane 104 that provides a mounting surface for the substrate, a pressurizable chamber 106 between the membrane 104 and the hoi 102, and a retaining ring 1 10 secured near the edge of the housing 102 to hold substrate below membrane 104. Although FIG. 1 illustrates the membrane UK clamped between the retaining ring 1 10 and the base 102, one or more other ρε e.g., clamp rings, could be used to hold the membrane 104. A drive shaft 120 i provided to rotate and/or translate the carrier head across a polishing pad. A pi may be fluidly connected to the chamber 106 though a passage 108 in the hous control the pressure in the chamber 106 and thus the downward pressure of the flexible membrane 104 on the substrate.

The retaining ring 1 10 may be a generally annular ring secured at the o edge of the base 102, e.g., by screws or bolts 136 that extend through passages the base 102 into aligned threaded receiving recesses 139 (see FIG. 2) in the u surface 1 12 of the retaining ring 110. in some implementations, the drive shaf can be raised and lowered to control the pressure of a bottom surface 1 14 of t retaining ring 1 10 on a polishing pad. Alternatively, the base 102 can be mova relative to the drive shaft 120, e.g., a housing can be connected the drive shaft ; carrier head 100 can include an internal chamber which can be pressurized to c a downward pressure on the base, e.g., as described in U.S. Patent No. 6,183,3: which is incorporated by reference. Alternatively, the retaining ring 1 0 can b movable relative to the base 120 and the carrier head 100 can include an intern chamber which can be pressurized to control a downward pressure on the retail ring, e.g., as described in U.S. Patent No.7, 575, 504, which is incorporated by reference.

The retaining ring 1 10 can be removable from the base 102 (and the res caixier head) as a unit. This means that an upper portion 142 of the retaining ri remains secured to a lower portion 40 of the retaining ring while the retaining 1 10 is remo ved, without requiring disassembly of the base 102 or removal of tl 102 from the carrier head 100. An inner surface 1 16 of retaining ring 110 defines, in conjunction with lower surface of the flexible membrane 104, a substrate receiving recess. The retaining ring 1 0 prevents the substrate from escaping the substrate receiving Referring to FIGS. 1-2, the retaining ring 1 10 includes two vertically st sections, including the annular lower portion 140 having the bottom surface 1 1 may contact the polishing pad, and the annular upper portion 142 connected to 104. The lower portion 140 can be secured to the upper portion 142 with an ac e.g., epoxy, or with mechanical fasteners 144, e.g., screws or bolts. The retain: 110 is structured so that there is no passage between the upper surface 1 12 and bottom surface 1 14. In some implementations, the passages 138 can extend pa but not entirely through the upper portion 142. In some implementations, the passages 138 can extend through the upper portion 142 and into, but not throui lower portion 140.

The upper portion 142 of retaining ring 110 is composed of a more rigi material than the lower portion 140. The lower portion 140 can be a plastic, w the upper portion can be a metal, e.g., stainless steel or aluminum, or a ceramic material. An advantage of having the material of the upper portion 142 be hart the material of the lower portion 140 is that the overall rigidity of the retaining 1 10 can be increased, thus reducing deformation of the lo wer portion 140 whei retaining ring 1 10 is attached to the carrier head 100, and reducing break-in tin The material of the lower portion 140 is chemically inert in a CMP proi addition, lower portion 140 should be sufficiently elastic that contact of the sul edge against the retaining ring does not cause the substrate to chip or crack. O other hand., lower portion 140 should be sufficient rigid to have sufficient lifeti under wear from the polishing pad (on the bottom surface) and substrate (on th surface).

The bottom surface 1 14 of the retaining ring 110 can be substantially fi some implementations it may have a plurality of channels 144 that extend iron inner surface 116 to the outer surface 118 of the retaining ring to facilitate the transport of slurry from outside the retaining ring to the substrate. The channel the channel. The channels on the lower surface 1 14 extend partially into, not e through, the lower portion 140, The retaining ring 1 10 can be replaced when 3' portion 140 has been sufficiently worn. As ring wears, the total ring thickness decreases and the membrane becomes more compressed, which can affect load substrate edge. The retaining ring 1 10 can be replaced after a certain reductior. thickness, e.g., 0.09 inches of wear. In addition, the impact of the substrate cai damage or wear to the inner surface 116 of the retaining ring. Moreover, the rs ring 1 10 can be refurbished by remo ving the worn lower portion 140 and attaci new lower portion to the upper portion 142.

The flexural modulus of the material of the lower portion can be in the of 0.5 to 1.5 x 10⁽⁾ psi. In some implementations, the flexural modulus of the n of the lower portion can be in the range of 1.1 to 1.5 x 10⁶ psi, e.g., about 1.2 x psi. Although the lower portion can have a low wear rate, it is acceptable for t; lower portion 140 to be gradually worn away, as this appears to prevent the sul edge from cutting a deep grove into the inner surface 144.

The plastic of the lower portion 140 may be (e.g., consist of) a "self-rei plastic", which is a polymer matrix reinforced by commonly oriented, polymer which can be derived from the same polymer as the matrix. The plastic can b< reinforced polyphenylene or polypropylene, e.g., PrimoSpire PR! 20 from Sob Plastics. Other possible materials for the lower portion 140 include polypheny sulfide (PPS), polyet eretherketone (PEEK), polyetherketoneketone (PEKK), polyetherketone (PEK), or a similar material.

Adjacent the bottom surface 1 14, the inner surface 116 of the lower poi 140 of the retaining ring can have an inner diameter just larger than the substra diameter, e.g., about 1-2 mm larger than the substrate diameter, so as to accom positioning tolerances of the substrate loading sy stem. The retaining ring 1 10 have a radial width of about half an inch to an inch. The inner surface 1 16 of t lower portion 140 can be substantially vertical. Similarly, the inner surface 1 1 upper portion 140 can be substantially vertical.

The thickness of the lower portion 140 should be larger than the permis to the flexible nature of the lower portion 140. The initial thickness T of the io portion 140 may be about 25 to 100 mils, e.g., 50 mils. In some implementatic initial thickness T of the lower portion 140 may be 25 to 45 mils.

In implementations with channels, the channels 144 can have a depth o 90%, e.g., 80%, of the thickness of the lower portion 140, e.g., 25 to 45 mils. 1 example, for a 50 mil thick lower portion 140, the channels can be about 40 mi deep. Alternatively, the channels can extend entirely though the retaining ring, even extend into the upper portion 142.

In operation, the frictional force of the polishing pad 20 against the sub 10 forces the substrate 10 toward, the "trailing edge" of the carrier head 100, i.t the same direction as the rotation of the polishing pad 20. This drives an edge the substrate 10 against the inner surface 1 16 of the bottom portion 140. In ad< there is a frictional force from the polishing pad 20 on the lower surface 1 14 ol retaining ring 1 10. The combination of these forces tends generate a local torq the lower portion 140, causing the inner surface 116 lower surface 1 14 to defoi shown in FIG. 2, the deformation and result in the inner surface 1 16 being slop outwardly (relative to the center of the retaining ring) along a downward direct

The deformation of the lower portion 140 of the retaining ring under th influence of the lateral forces during polishing creates a compression in the poi pad 20, which affects the pressure on the a perimeter portion 14 of the lower si of the substrate 10, and thus the polishing rate near the substrate edge 12. In gi the greater the deformation, the greater the polishing rate in the perimeter port!

In general, the more rigid the material of the lower portion 140, the less lower portion 140 will deform. In addition, the thinner the lower portion 140, the moment, and the less the lower portion 140 will deform.

By proper selection of the combination of the stiffness and thickness of lower portion 140 of the retaining ring, the compression distribution within the polishing pad 20, and thus the pressure on the perimeter portion 14 of the subsi 10, can be tuned. In particular, by reducing the thickness of the lower portion moment of the lower portion 140 about the interface between the upper portior For a polishing process using a low-abrasive slurry, wear of the retainii will tend to decrease. However, low-abrasive slurries have a greater tendency suffer from the edge effect. Thus, a polishing process using a low-abrasive slu particularly benefit from this technique, as the lower portion 140 can be thinne without significant loss of retaining ring lifetime, while improving polishing uniformit at the substrate edge.

In order to select the stiffness and thickness of the lower portion 140, a test substrates can be polished, with a first retaining ring with a first stiffness a: first thickness installed on the carrier head 100. Polishing of the first test subs! can otherwise be conducted using the same polishing recipe is expected to be u product substrates. The amount of material removed from the first test substra be measured at different radial positions, e.g., using a stand-alone metrology S] Whether the first test substrate perimeter is overpoiished or underpolished rela; the center of the first test substrate can be determined.

A second retaining ring with a second stiffness and a second thickness : selected based on the measured degree of overpolishing or underpolishing of tl test substrate. For example, if the test substrate perimeter is overpoiished, a se retaining ring with a stiffer and/or thinner lower portion 140 (relative to the fir; retaining ring) is selected. Similarly , if the test substrate perimeter is underpol second retaining ring with a softer and/or thicker lower portion 140 (relative to first retaining ring) is selected..

In some implementations, a second, test substrate is be polished with tht second retaining ring. Whether the second test substrate perimeter is overpolis underpolished relative to the center of the second test substrate can be determii the second, test substrate has an acceptable polishing uniformity, polishing of d substrates can be conducted using retaining rings with the second hardness and thickness. On the other hand, so long as a test substrate has unacceptable non- uniformity, the process of selecting another retaining ring and. polishing anothe substrate can be iterated until an acceptable or maximum degree of polishing uniformity is achieved. into the annular recess. When the retaining ring 110 is secured to the carrier hs 100, the O-ring is compressed between the rigid body to which the retaining rii attached, e.g., the base 102, and the retaining ring 110, This can help prevent s from reaching the interior of the carrier head, thereby potentially reducing corr and associated defects.

In some implementations, the retaining ring 1 10 has one or more throu< holes that extend horizontally or at a small angle from horizontal through the b the retaining ring trom the inner surface 1 16 to the outer surface 1 18 for ailowi fluid, e.g., air or water, to pass from the interior to the exterior, or from the ext the interior, of the retaining ring during polishing. The through-holes can exter through the lower portion 140. The through holes can be evenly spaced, arounc retaining ring.

Rather attach the lower portion 140 to the upper portion 142 with rnech fasteners or adhesive, the lower portion 140 could be plastic coating sprayed oi upper portion 142. The coating can cover the lower surface and the side surfac the upper portion 142. The thickness of the lower portion 140 can be about 0.( inches. Such an implementation may be suitable for some polishing recipes th. low abrasive slurries, e.g., with a low-abrasive slurry the ring may undergo ver wear of about 0.01 inches before wear or damage to the ring inner diameter be< too severe and the retaining ring needs to be replaced.

The present invention has been described in terms of a number of embodiments. The invention, however, is not limited to the embodiments depis and described. Rather, the scope of the invention is defined by the appended c

Claims

WHAT IS CLAIMED IS:

1 . A retaining ring for holding a substrate below a carrier head dui chemical mechanical polishing, comprising:

an annular lower portion having a main body with a bottom surface for contacting a polishing pad during polishing, the annular lower portion having i thickiiess between 5 and 45 mils and being a first material having a ilexural mi between 1.1 and 1.5 x 10⁶ psi; and

an annular upper portion secured to the lower portion, a top surface of t upper portion configured to be secured to the carrier head, the upper portion be second material that is more rigid than the first material.

2. The retaining ring of claim 1 , wherein the annular lower portion thickness between 10 and 20 mils.

3. The retaining ring of claim 1, wherein the annular lower portion thickness between 25 and 45 mils.

4. A method of selecting a retaining ring, comprising:

polishing a first test substrate with the first test substrate held in a cards having a first retaining ring having an upper portion and a lower portion with a stiffness and a first thickness;

measuring polishing uniformity of the first test substrate;

selecting based on the polishing uniformity a second retaining ring witl upper portion and a lower portion with a second, stiffness and. a second, thickne polishing a second test substrate with the second test substrate held in t; carrier head having the second retaining ring; and

polishing a plurality of device substrates using a plurality of carrier hea

5. The method of claim 4, wherein measuring polishing uniformity includes determining that a perimeter portion of the first test substrate is overpi relative to a center portion of the first test substrate,

6. The method of claim 5, wherein the second hardness is greater t first hardness and/or the second, thickness is less than the first thiclaiess.

7. The method of claim 6, wherein the second hardness is greater t first hardness.

8. The method of claim 6, wherein the second thickness is less tha first thickness.

9. The method of claim 4, wherein measuring polishing uniformity includes determining that a perimeter portion of the first test substrate is underpolished relative to a center portion of the first test substrate.

10. The method of claim 9, wherein the second hardness is less thai first hardness and'or the second thickness is greater than the first thickness.

1 1. The method, of claim 10, wherein the second hardness is less th∑ first hardness.

12. The method of claim 10, wherein the second, thickness is greate: the first thickness.