Patent Grant
7182677
Embodiments of the present invention relate to a chemical mechanical polishing pad and related methods and apparatus.
Chemical mechanical planarization (CMP) is used to planarize the surface of a substrate, in the manufacture of the integrated circuits and displays. A typical CMP apparatus comprises a polishing head that oscillates and presses a substrate and polishing pad against one another, while a slurry of abrasive particle is supplied therebetween. CMP can be used to planarize the surfaces of dielectric layers, deep or shallow trenches filled with polysilicon or silicon oxide, metal films, and other such layers. It is believed that CMP polishing typically occurs as a result of both chemical and mechanical effects, for example, a chemically altered layer is repeatedly formed at the surface of the material being polished and then polished away. For instance, in the polishing of metal features or layers, a metal oxide layer is formed and then removed repeatedly from the surface of the metal being polished.
To control slurry distribution, the polishing pad surface typically has a pattern of perforations or grooves to control the distribution of polishing slurry across the substrate. CMP polishing results depend upon the chemical and mechanical interaction of the polishing surface of the polishing pad which is pressed against the substrate the polishing pad, the abrasive particles of the polishing slurry, and the reactive material of the substrate. A non-uniform distribution of polishing slurry across the substrate surface can result in uneven polishing of the substrate surface. Thus, it is desirable to have a polishing surface of the polishing pad capable of providing a uniform distribution of slurry across the substrate surface.
Several pad designs have been developed to provide more uniform polishing slurry distribution across the surface of the substrate. One pad design uses concentric circular grooves or spiral grooves, as for example, disclosed in commonly assigned U.S. Pat. No. 5,984,769 which is incorporated herein by reference in its entirety. The circular grooves fill with polishing slurry during the polishing process to maintain a more uniform distribution of polishing slurry across the substrate surface. While such pad designs improve overall polishing uniformity, they also tend to trap slurry in predefined regions of the polishing surface of the pad resulting in excessive polishing of corresponding substrate regions. Also, because the slurry is trapped in a closed circular groove, the polishing slurry is prevented from continuously flowing from the center of the pad to its outer edge, which is desirable to remove polishing byproduct and worn slurry particles. In another pad design, an X-Y grooving pattern is provided on the polishing surface with different channel lengths. However, when the polishing pad and substrate oscillated with a rotating motion, the X-Y pattern generates a polishing slurry flow imbalance due to the axial symmetry of the groove pattern, and can also result in slurry being rapidly ejected from the edge of the pad surface.
A further problem with conventional designs arises because the pad has to be both sufficiently rigid to planarize the substrate surface and sufficiently compliant to press the polishing pad with uniform pressure against the substrate surface. To properly planarize the substrate, the polishing pad should polish only the peaks and not the valleys of the surface topography of the substrate. However, if the polishing pad is too easily compressed under localized stresses applied at pad regions which are directly above peaks in the substrate topography, the substrate region that surrounds the peak becomes excessively polished, which is undesirable. The pad has to be sufficiently rigid so that it does not compress too much under the load applied by the topographic peaks on the substrate, and yet sufficiently flexible to conform to, and uniformly polish, a slightly warped substrate.
To address the simultaneous flexibility and rigidity requirements, polishing pads are typically fabricated with two stacked layers of different materials, the bottom layer being made of a compliant springy material and the top layer being made of a rigid material that serves as the polishing surface. However, in use, polishing slurry tends to wick into the interface between the two layers starting from the outer peripheral edge of a layer toward the center of the two layers. This wicking can cause undesirable changes in the compressibility of the compliant spring layer. Excessive wicking can also cause polishing slurry to penetrate deep enough between the layers to reach and change optical properties of a pad window in the pad. It is desirable to have a polishing pad that is compliant and springy as well as sufficiently rigid to serve as a polishing surface.
Accordingly, it is desirable to have a polishing pad with a polishing surface that provides uniform and repeatable planarization of substrates. It is further desirable to have patterned features on the polishing surface of the polishing pad that cause the slurry to be uniformly distributed across the substrate surface. It is further desirable to have a polishing pad that is compliant while still providing a substantially rigid polishing surface.
In one version, a polishing pad for a chemical mechanical polishing apparatus has a body with a polishing surface having a radius and central and peripheral regions. The polishing surface has a plurality of main radial-line channels extending radially outwardly from the central to the peripheral region, each main radial-line channel having an angled outer segment at the peripheral region that is directed at an angle relative to a radius of the polishing surface. The polishing surface also has a plurality of primary tributary radial-line channels that are each connected by an angled transition segment to a main radial-line channel, the tributary radial-line channels being spaced apart from the main radial-line channels. The polishing pad provides an improved distribution and flow of polishing slurry during a polishing process.
In another version, the polishing pad has also a bottom surface opposite the polishing surface, with a pattern of pressure-load accommodating features that include a plurality of protrusions and depressions. The depressions are sized and shaped to accommodate a lateral expansion of the protrusions upon application of a pressure to the polishing surface.
The polishing pad can be used in a chemical mechanical apparatus which has a polishing station comprising a platen to hold the polishing pad and a support to hold a substrate against the polishing pad; a slurry dispenser to dispense slurry on the polishing pad; and a polishing motor to drive at least one of the platen and support to oscillate the polishing pad and substrate against one another.
In one method of fabrication, the polishing pad can be fabricated by cutting material from the polishing surface to form the main and tributary radial-line channels, at a cutting speed that is sufficiently high to heat the material in the main and tributary radial-line channels to a temperature that melts the material to substantially seal off the bottom of the channels.
In yet another version, a chemical mechanical polishing pad has a body having a polishing surface having a radius and central and peripheral regions. The polishing surface has a plurality of main radial-line channels extending radially outwardly from the central region to the peripheral region, each main radial-line channel having an angled outer segment at the peripheral region that is directed at an angle relative to a radius of the polishing surface. The length L1 of the main-line radial channel, the length L2 of the angled outer segment, and the angle α formed between the angled outer segment and main-line radial channel, are selected to provide a uniform distribution of polishing slurry across the substrate surface.
In still another version, the length L1 of the main-line radial channel, the length L2 of the angled outer segment, and the angle α formed between the angled outer segment and main-line radial channel are selected such that the centripetal force Fc acting on the polishing slurry in the angled outer segment is controlled to provide a desired flow rate of slurry through the channel, where Fc=mv2/r, m is a mass of the slurry in the channel, v is the velocity of the slurry, and r is the average radial distance of the angled outer segment across the polishing pad.
In one more version, the length L1 of the main-line radial channel, the length L2 of the angled outer segment, and the angle α formed between the angled outer segment and main-line radial channel are selected such that the centripetal force Fc acting on the polishing slurry in the angled outer segment is balanced against an opposing force Fo which acts on the slurry in the angled outer section of the channel to provide a desired flow rate of slurry through the channel,
where Fc=mv2/r, m is a mass of the slurry in the channel, v is the velocity of the slurry, and r the average radial distance of the angled outer segment across the polishing pad, and
Fo=mr(dθ/dt)2cos(α−(π/2)), where, dθ/dt is the angular velocity of the polishing pad, and α is the angle between the main-line radial channel and angled outer segment.
These features, aspects and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings, which illustrate examples of the invention. However, it is to be understood that each of the features can be used in the invention in general, not merely in the context of the particular drawings, and the invention includes any combination of these features, where:
a is a partial sectional side view of an embodiment of a polishing pad having pressure load-accommodating features;
b is a partial sectional side view of the embodiment shown in
a and 6b are partial bottom views of embodiments of polishing pads having different patterns of pressure load-accommodating features;
a is a perspective view of an embodiment of a CMP polisher;
b is a partially exploded perspective view of the CMP polisher of
c is a diagrammatic top view of the CMP polisher of
a and 8b are partial top views of embodiments of polishing pad surfaces having improved slurry flow channels.
A polishing pad 20 for a chemical mechanical polishing apparatus (
The polishing surface 24 of the polishing pad 20 comprises one or more grooves 26 formed therein to enhance the flow of the polishing slurry over the polishing surface 24, as shown for example in
The improved grooves 26 comprise a plurality of main radial-line channels 30 extending radially outwardly from a central region 32 of the polishing pad 20, to the peripheral region 28 of the polishing pad, as shown for example in
The main radial-line channels 30 further comprise an angled outer segment 34 at the peripheral region 28 that is directed at an angle relative to the radial-line r of each main radial-line channel 30, as shown for example in
The angled outer segments 34 are desirably curved or bent in a direction that coincides with the direction of rotation of the polishing surface 24 during substrate polishing to provide “impeller blade” type forces that slow the slurry flow to the desired rate. For example, In
The main radial-line channels 30 comprising the angled outer segments 34 provide improved control of the polishing slurry flow across the polishing surface 24. The angled outer segments 34 act to slow the flow of the slurry radially outwardly along the channels 30. During rotation of the polishing surface 24, the polishing slurry is propelled by a centripetal force towards the periphery 38 of the polishing surface 24. However, upon flowing into the angled outer segments 34, the centripetal force is counteracted by “impeller-like” forces pushing the polishing slurry in the opposite direction. The effect of the angled outer segments 34 on the flow of polishing slurry is diagrammatically shown in
However, as the slurry enters the angled outer segment 34, the angle of the segment slows the flow of the slurry. The force opposing the flow of slurry though the angled outer segment 34 can be written as Fo=mr(dθ/dt)2cos(α−(π/2)), where r is the radius of the slurry mass on the polishing pad, dθ/dt is the angular velocity of the polishing pad, and α is the drive angle between the angled outer segment 34 and main-line radial channel. Thus, by selecting smaller drive angles α, the polishing slurry is induced to slow in the angled outer segment 34, whereas larger drive angles result in less slowing of the drive angle. Similarly, the lengths L1 and L2 can be selected to change the radius at which the angled segment begins, and thus change the flow rate of the polishing fluid through the slurry. In one version, the lengths L1 and L2 and the angle α may be selected to provide an opposing force that is substantially equal to the centripetal force, to counterbalance the force. Other opposing forces may also slow the flow of the polishing slurry through the angled sections, such as for example an opposing frictional force, or the opposing force of air entering the spinning segments 34 with a certain pressure.
The slowing action of the angular segments 34 can also be understood with respect to
In one version, the lengths L1 and L2 of the main-line radial channel 30 and angled outer segment 34, and the drive angle α therebetween, can be selected such that the flow rate of the polishing slurry is slowed to a net flow out of the angled segments 34 that does not waste slurry. While the slurry flow rate is desirably slow, the flow rate may also be desirably greater than zero, such that used slurry and slurry by-products can be spun off of the polishing surface 24 to provide a fresh surface. Thus, the main radial-line channels 30 comprising the angled outer segments 34 provide an improved flow of polishing slurry through the channels 30 that maintains a desired level of polishing slurry in the channels 30, substantially without trapping the slurry on the polishing surface 24, such that used slurry and slurry by-products can be spun off of the polishing surface 24.
The distribution and flow of the polishing slurry on the polishing surface 24 can be further enhanced by providing a plurality of primary tributary radial-line channels 42 that are each connected by an angled transition segment 44 to a main radial-line channel 30. The transition segment 44 may comprise, for example, a curved segment 45, as shown for example in
The primary tributary radial-line channels 42 are spaced apart from the main channels 30 at a distance that is selected to improve the slurry flow distribution over the polishing surface 24. For example, the primary tributary radial-line channels 42 may bisect regions where the distance between adjacent main channels becomes too great to provide a desired polishing slurry distribution. The number and density of the primary tributary radial-line channels 42 is furthermore selected to provide a desired distribution of polishing slurry across the polishing surface 24. For example, the polishing surface 24 can comprise from 1 to 10 primary tributary radial-line channels 42 across each 10 degree arc of the polishing surface 24. The main channels 30 may also comprise from 1 to 10 primary tributary radial-line channels 42, such as 2 primary tributary radial-line channels 42 as shown for example in
In one version, the polishing surface 24 further comprises a plurality of secondary tributary radial-line channels 46 each connected to a primary tributary radial-line channel 46 by a second transition section 48, such as a curved or otherwise angled transition section. The secondary tributary radial-line channels 46 may further distribute the flow of polishing slurry over the polishing surface 24, and may be sized and shaped to provide further control of the overall flow rate of the polishing slurry from the central region 32 to the peripheral region 28. In one version, the polishing surface 24 comprises from 1 to 10 secondary tributary channels across each 10 degree arc of the polishing surface 24.
Each main radial-line channel 30 may further comprise a plurality of primary tributary radial line channels 42 that branch off of the main channel 30 at different lengths along the radius of the polishing surface 24. For example, as shown in
The widths between the main and tributary channels 30, 42, 46 can furthermore be selected to provide an improved distribution of polishing slurry. For example, a ratio of a width w1 between main radial-line channels 30 to a width w2 between a main radial-line channel 30 and a primary tributary radial-line channel 42 at the same radius on the surface 24 may be from about 1 to about 30. Furthermore, the widths of the channels themselves may be selected to provide the desired polishing slurry flow characteristics. In one version, the main radial-line channels 30 may comprise a width that is greater than the tributary channels to accommodate a greater flow of polishing slurry therein. For example, a ratio of a width of the main radial-line channel 30 to a width of a primary tributary radial line channel 42 may be at least about 2:1, such as from about 3:1 to about 6:1. In one version, the lengths and widths of the grooves 26, including the main and tributary radial line channels 40,42,46 are selected to provide a volume of polishing slurry in the channels of typically from about 1 ml to about 300 ml, however, other volumes are also desirable depending on the application.
At least one of the width and depth of the main and tributary channels 30, 42, 46 may furthermore be varied over the length of the channels to provide the desired polishing slurry flow characteristics. For example, at least one of the width and depth of the channels may be increased in a certain region of the channel to provide a reservoir 52 of polishing fluid at that region. In one version, a width of a channel is increased by at least about 2 times to provide a slurry reservoir 52 in a region of the channel. The slurry reservoir 52 can provide desired slurry flow characteristics, and can inhibit the depletion of slurry in critical regions of the polishing surface 24. In the version shown in
The grooves 26 comprising the main and tributary radial line channels can be formed by suitable methods, such as for example by using a cutting tool to cut away pad material from the polishing surface 24 to form the grooves 26. In one version, the method of forming the grooves improves the flow of polishing slurry through the grooves 26. For example, the cutting tool may be operated with parameters that heat the polishing pad material in the grooves 26 to a temperature that is sufficient to effect a beneficial structural change in the pad material. The increased temperature desirably substantially seals surfaces 58 in the grooves 26, for example by substantially sealing exposed pores in the pad material of the grooves 26, to inhibit the infiltration of polishing slurry into the pores. Thus, the heat treated grooves 26 absorb less of the polishing slurry into the pad material, thereby improving the flow of the slurry through the grooves 26. In one version, the cutting tool may be operated to heat the pad material in the grooves 26 by employing a cutting speed of the cutting tool that is sufficient to heat the pad material to the desired temperature while simultaneously cutting the desired groove shapes. A temperature sufficient to substantially seal the surfaces 58 of the grooves may be at least about 100° C.
In yet another version, an improved polishing pad 20 is tailored to provide good pressure loading capacity, as shown for example in
The improved pressure-load accommodating pattern of features 69 allows for pressure loading of the pad 20 utilizing a single body 22 of pad material as opposed to a stacked body comprising different materials. This is because the pattern of features 69 is capable of providing the desired compliance and spring while still maintaining a sufficiently rigid polishing surface 24. Thus the polishing pad 20 does not require an extra layer of relatively more compliant and springy material below the relatively rigid material used for the polishing surface 24 to provide the desired pressure load accommodation, and is not subject to problems such as the wicking of slurry fluid between such stacked polishing pad layers. In one version, the recesses 62 are open to atmospheric pressure, and dampening of the polishing pressure is achieved primarily through the compression of the protrusions 66. In another version, the recesses 62 can be hermetically sealed to provide pockets of entrapped air in the recesses 62 that act as a dampening mechanism when compressed.
a and 6b provide examples of polishing pads 20 comprising back sides 60 having a pattern 68 of pressure-load accommodating features 69 formed in the back surfaces 64 of the pad back sides 60. In
The polishing pad 20 described herein can be used in any type of CMP polisher; thus, the CMP polisher described herein to illustrate use of the polishing pad 20 should not be used to limit the scope of the present invention. One embodiment of a chemical mechanical polishing (CMP) apparatus 100 capable of using the polishing pad 20 is illustrated in
The carousel 116 has a support plate 160 with slots 162 through which the shafts 172 of the substrate holders 120 extend, as shown in
Each polishing station 108a–c includes a rotatable platen 182a–c, which supports a polishing pad 20a–c, and a pad conditioning assembly 188a–c, as shown in
Each pad conditioning assembly 188 of the CMP apparatus 100 includes a conditioner head 196, an arm 200, and a base 204, as shown in
The present invention has been described with reference to certain preferred versions thereof; however, other versions are possible. For example, the pad conditioner can be used in other types of applications, as would be apparent to one of ordinary skill, for example, as a sanding surface. Other configurations of the CMP polisher can also be used. Furthermore, alternative channel configurations equivalent to those described can also be used in accordance with the parameters of the described implementation, as would be apparent to one of ordinary skill. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained herein.
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| Number | Date | Country | |
|---|---|---|---|
| 20060160478 A1 | Jul 2006 | US |
