JP5331463B2 - Retainer ring and chemical mechanical polishing apparatus having the same - Google Patents

Description

  The present invention relates to a retainer ring and a chemical mechanical polishing apparatus provided with the retainer ring, and more particularly, a holding head of a CMP (Chemical Mechanical Polishing) apparatus that chemically and mechanically polishes a wafer (object to be polished). The retainer ring disposed (attached) in the inside, particularly the groove for supplying and draining slurry to the contact surface between the wafer and the polishing pad, has no process fluctuation with respect to the fluctuation of the retainer ring thickness. And a chemical mechanical polishing apparatus provided with the retainer ring.

  The increase in the density of semiconductor devices has not been limited, and is continuing to progress. Some of the various obstacles associated with the increase in density are being overcome by various technologies and methods. One of the major issues is the flattening of the global device surface. As device integration increases, further stacking of electrodes and others is inevitable. Considering the reduction of the focal depth during exposure accompanying the shortening of the lithography wavelength, there is a great demand for flattening the interlayer layer at least within the exposure area. In addition, there is a high demand for embedding the metal electrode layer. In this case, it is required to remove and planarize an extra metal layer after lamination.

  Conventionally, many methods for locally planarizing an interlayer layer by improving the film forming method have been proposed and implemented. A polishing process called CMP is attracting attention as an efficient planarization technique in a larger area that will be further required in the future. CMP is a process of removing surface irregularities of a wafer by using a chemical action (polishing with an abrasive and a solution) in combination with physical polishing, and is a leading candidate for global planarization technology. Specifically, an abrasive called slurry in which abrasive grains (silica, alkali, cerium oxide, etc.) are dispersed in a soluble solvent of an abrasive such as acid or alkali, and the wafer surface with an appropriate polishing cloth is used. Polishing is performed by pressurizing and rubbing by relative motion. By uniformly applying pressure and relative motion speed over the entire surface of the wafer, it becomes possible to polish the surface uniformly (see Patent Document 1).

FIG. 5 is a schematic side view for explaining the basic structure of a conventional CMP polishing apparatus.
6A and 6B are views showing a conventional retainer ring, in which FIG. 6A is a schematic bottom view of the retainer ring, and FIG. 6B is a schematic cross-sectional view of a groove portion thereof.
In FIG. 5, KR is a CMP polishing apparatus, 100 is a surface plate (platen) that is rotationally driven by a surface plate rotation driving device 100a, 101 is a polishing pad as a "polishing member", and 102R is an object to be polished (semiconductor wafer). A retainer ring (annular holding member) that surrounds the periphery of U and prevents the polishing object U from popping out, 103 is a polishing head (holder) that is rotated and rocked by a polishing head drive device, and 104 is an abrasive (slurry) A supply unit 105 is an abrasive (slurry).

  In the polishing apparatus KR, a polishing pad 101 as a “polishing member” is provided on a surface plate 100 that is rotationally driven by a surface plate driving device 100 a, while a wafer U that is an “object to be polished” is provided on the polishing head 103. The wafer U is held and is in contact with the polishing pad 101. In this state, the surface plate 100 is rotationally driven, a load is applied to the polishing head 103 from above, and the surface plate 100 is swung in the radial direction while rotating.

  Along with these operations, the polishing agent 105 is discharged from the polishing agent supply unit 104 onto the polishing pad 101, the polishing agent 105 is supplied to the polishing surface of the wafer U, and the outermost surface of the wafer U is polished flatly. Yes. The polishing agent 105 diffuses at the polishing pad 101, enters between the polishing pad 101 and the wafer U with the relative movement of the polishing pad 101 and the wafer U, and polishes the surface of the wafer U.

Next, in FIG. 6, the retainer ring 102 </ b> R surrounds the periphery of the polishing target (semiconductor wafer) U and prevents the polishing target U from popping out. The retainer ring 102R has a groove 102Ra in the wafer polishing side surface portion 102Rb. The groove guides the slurry to the wafer polishing surface, and discharges polishing debris together with the slurry from the wafer polishing surface.
JP 11-337712 A

  Due to recent improvements in CMP technology, the role of retainer is not only to prevent the wafer from popping out, but also to widely press the polishing surface of the polishing pad distorted by the pressure applied to the wafer during polishing along the wafer surface. It also plays a role and is essential to uniformly planarize the wafer.

As shown in FIGS. 6A and 6B, the retainer ring 102R is groove-shaped, and the groove 102Ra has the same width from the opening to the bottom. The groove 102Ra efficiently supplies so-called polishing scraps such as SiO ₂ and metal removed from the wafer polishing surface by polishing and polishing pad debris (the polishing pad itself is also worn by polishing). Well, it has the role of discharging out of the wafer polishing surface.

  However, since the retainer ring 102 </ b> R itself is pressed against the polishing cloth in the same manner as the wafer U and is rotated together with the polishing head 103, wear cannot be avoided. Therefore, the groove 102Ra of the retainer ring 102R becomes shallow and the composition and amount of the slurry 105 in contact with the wafer U vary, thereby causing a variation in polishing characteristics. For example, there arises a problem that the polishing surface is damaged (scratched) due to fluctuations in the polishing rate or residual polishing scraps.

  Accordingly, one of the main objects of the present invention is a retainer ring capable of maintaining the polishing characteristics required for polishing a wafer for a longer time even when the groove becomes shallow due to wear of the retainer ring, and a chemical mechanical polishing apparatus having the retainer ring Is to provide.

The present invention relates to a chemical mechanical device comprising a polishing pad that receives a supply of slurry on its surface, and a polishing head that holds a semiconductor wafer to be polished and polishes the semiconductor wafer while rotating relative to the polishing pad. A retainer ring mounted on the polishing head of the polishing apparatus and holding the semiconductor wafer around its periphery,
The retainer ring has a groove on the side surface of the wafer polishing for guiding the slurry to the wafer polishing surface and discharging the polishing debris together with the slurry from the wafer polishing surface. There is provided a retainer ring characterized by having a wide portion with a larger groove width between the bottom portion.

According to another aspect of the present invention, there is provided a polishing head for polishing a semiconductor wafer while holding the polishing pad that receives the supply of slurry on the surface and the semiconductor wafer to be polished and rotating relative to the polishing pad. And a retainer ring which is mounted on the polishing head and holds the semiconductor wafer so as to surround the periphery of the polishing head.

  According to the present invention, since the groove formed on the wafer polishing side surface portion of the retainer ring has a wide portion with a larger groove width between the opening and the bottom portion, the groove becomes shallow due to wear of the retainer ring. However, the influence on the induction of the slurry and the discharge of the polishing scraps can be reduced, whereby the polishing characteristics necessary for polishing the wafer can be maintained for a longer time.

The present invention relates to a chemical mechanical device comprising a polishing pad that receives a supply of slurry on its surface, and a polishing head that holds a semiconductor wafer to be polished and polishes the semiconductor wafer while rotating relative to the polishing pad. A retainer ring mounted on the polishing head of the polishing apparatus and holding the semiconductor wafer so as to surround the periphery thereof is an object.
Here, the retainer ring holds a semiconductor wafer (hereinafter sometimes simply referred to as a wafer) around its periphery and prevents the semiconductor wafer from popping out, so it is called an annular holding member or a ring-like holding member. Sometimes.

  Further, the present invention has a groove for guiding the slurry to the wafer polishing surface and discharging the polishing debris together with the slurry from the wafer polishing surface to the wafer polishing side surface portion of the retainer ring. Further, it is characterized in that a wide portion having a larger groove width is provided between the opening and the bottom.

Here, specifically, the wide portion is formed, for example, by increasing the groove width linearly, substantially stepwise, or curvedly.
The position of the wide portion is (1) from the opening to the bottom of the groove, (2) from the opening to the bottom of the groove, and (3) from the middle of the groove to the bottom. Or (4) from the middle of the groove to the bottom.

The groove having these wide portions further includes a wide portion from the opening, and the same width portion that is the same as the groove width, continuing from the wide portion, to the bottom, or halfway toward the bottom. You may have each. Then, the wide portion and the same width portion of the groove may be repeated, and the groove width may be increased in a substantially step shape from the opening to the bottom of the groove.
The processing angle of the groove in the groove opening, that is, the inclination angle or gradient of the side wall in the groove opening with respect to the surface in the groove opening (the surface on the wafer polishing surface side of the retainer ring) (for example, α in FIG. Is preferably 95 to 120 degrees, more preferably 100 to 110 degrees.

In contrast to the configuration of these grooves, the groove has an equal width portion having the same width from the opening toward the bottom, and the wide portion follows the same width portion and is directed toward the bottom. May be. Then, the same width portion and the wide portion of the groove may be repeated, and the groove width may be increased in a substantially step shape from the opening to the bottom of the groove.
When the wide portion is formed in a curved line, for example, the outline of the cross section of the groove can include a line such as a circle, a semicircle, or an arc.
In addition, each said groove | channel may contain the narrow part which made the groove | channel width small from the middle of (2) or before the bottom part of (3) to the bottom part, respectively.

  In the present invention, it is preferable to retain at least 50% of the initial cross-sectional area of the groove when the groove becomes shallower by 1.8 mm by using a retainer ring. In addition, by allowing the retainer ring to be replaced with a new one with a setting value of 2.8 mm or less, even if the groove becomes shallow due to wear of the retainer ring, the influence on the induction of slurry and the discharge of polishing debris is reduced. This makes it possible to maintain the polishing characteristics necessary for polishing the wafer for a longer time.

  The grooves formed in the retainer ring are annular (a plurality of concentric circular grooves), linear radial (a plurality of grooves at equal angular intervals), a lattice shape, a curved radial shape along the wafer polishing side surface portion of the retainer ring ( The grooves are equiangularly spaced) or spiral, and has a function of guiding the slurry to the wafer polishing surface as the retainer ring rotates, and discharging the polishing debris together with the slurry from the wafer polishing surface.

Here, the retainer ring is literally formed in a ring shape, and the inner diameter of the ring is preferably 200.5 to 201.0 mm, the ring width is 46.5 to 48.0 mm, and the ring thickness is preferably 15 to 20 mm.
The groove formed in the retainer ring has a minimum width of the wide portion (minimum width of the opening) of 2.0 to 7.5 mm, preferably 2.5 to 5.0 mm, and a maximum width of the wide portion. The depth of the wide portion is set to 2.0 to 6.0 mm, preferably 3.0 to 4.5 mm, respectively, from 2.8 to 13.5 mm, preferably 4.5 to 6.5 mm. Further, when the groove has the same width portion having the same width from the opening toward the bottom, the width of the same width portion is 2.5 to 4.5 mm, from the opening of the same width portion. The depth is preferably set to 2.5 to 4.5 mm.

  The present invention further includes a polishing pad that receives supply of slurry on the surface, a polishing head that holds a semiconductor wafer as an object to be polished, and polishes the semiconductor wafer while rotating relative to the polishing pad. It is possible to provide a chemical mechanical polishing apparatus comprising the retainer ring mounted on the polishing head in order to prevent popping out.

  Here, the retainer ring can be attached to and detached from the polishing head with a set screw, etc., so that when the groove becomes shallow due to wear of the retainer ring and proper polishing characteristics cannot be maintained, it can be replaced with a new retainer ring. This is preferable because it is possible.

The present invention will be described below based on the embodiments shown in the drawings.
[Embodiment 1]
FIG. 1 is a schematic configuration explanatory side view for explaining a basic configuration of a chemical mechanical polishing apparatus according to the present invention, and FIG. 2 is a configuration explanatory side view including a partial cross section around a retainer ring.
3A and 3B are explanatory views of the retainer ring holding the semiconductor wafer. FIG. 3A is a schematic bottom view of the retainer ring, and FIG. 3B is a schematic cross-sectional view of the groove portion. Further, (c) and (d) are schematic cross-sectional views of a groove portion of another retainer ring example according to the present invention.
FIG. 4 is a graph showing the uniformity of the polishing rate. In addition, the same code | symbol was attached | subjected to the part of the structure substantially the same as FIG.

  First, in the chemical mechanical polishing apparatus K of FIG. 1, 100 is a surface plate (platen) that is rotationally driven by a surface plate rotation driving device 100a, 101 is a polishing pad as a “polishing member”, and 102 is a “polishing object” ( A retainer ring (annular holding member) 103 that surrounds the periphery of a semiconductor wafer (hereinafter referred to as a wafer) U and prevents the polishing object U from popping out is rotated and oscillated by a polishing head driving device (not shown). A polishing head (holder). In addition, 104 is an abrasive | polishing agent (slurry) supply part, 105 is an abrasive | polishing agent (slurry).

  In this polishing apparatus K, a polishing pad 101 as a “polishing member” is provided on a surface plate 100 that is rotationally driven by a surface plate rotation driving device 100 a, while a wafer that is a “polishing object” is provided in the polishing head 103. U is held, and this wafer is in contact with the polishing pad 101. In this state, the surface plate 100 is rotationally driven, a load is applied to the polishing head 103 from above, and the surface plate 100 is swung in the radial direction while rotating.

  At the same time, the polishing agent supply unit 104 discharges the polishing agent 105 onto the polishing pad 101, supplies the polishing agent 105 to the polishing surface of the wafer U, and polishes the outermost surface of the wafer U flatly. ing. The polishing agent 105 is diffused by the polishing pad 101 and enters between the polishing pad 101 and the wafer U as the polishing pad 101 and the wafer U move relative to each other to polish the surface of the wafer U.

  The mechanical polishing by the relative movement between the polishing pad 101 and the wafer U performed through the polishing agent 105 and the chemical action of the polishing agent 105 using an acid or alkali as a solvent act synergistically to perform good polishing. In addition, by making the pressure and the relative motion speed uniform over the entire surface of the wafer U, it is possible to polish the surface in a uniform manner. The polishing head 103 has various methods such as a backing film chuck method and a vacuum chuck method. Generally, the polishing head 103 includes a wafer attaching / detaching mechanism, a pressurizing mechanism, and a retainer ring 102 for preventing the wafer from popping out. Yes.

  2 and 3A and 3B, the retainer ring 102 is assumed to be placed on the wafer U (the polishing head 101) from the outermost position of the end surface thereof on the surface 102b in contact with the polishing pad 101. 12 grooves 102a are formed at an angular interval of 30 degrees in a straight line (in the direction of drawing a substantially tangent line).

  The groove 102a shown in FIG. 3B has a wide portion that linearly increases in width from the opening to the bottom. The wide portion has an opening of about 3.0 mm, a bottom of about 4.7 mm, and a depth of about 5.0 mm, and an angle of 100 degrees (inclination angle, opening angle, Alternatively, it can be called a processing angle).

  The radial grooves 102a of the retainer ring 102 facilitate the supply of the polishing pad 101 and the abrasive and the discharge of the polishing debris. That is, while the polishing pad is rotated and swung, the abrasive is mainly supplied from the radial grooves 102a so as to be wound on the wafer polishing surface, whereas the polishing debris is discharged along the grooves 102a. Further, by processing the groove 102a in an inverted trapezoidal shape, it is possible to suppress a reduction in the above-described effect due to wear of the retainer ring 102. That is, since the groove 102a formed on the wafer polishing side surface portion of the retainer ring has a wide portion in which the groove width is increased from the opening portion to the bottom portion, the groove 102a becomes shallow due to wear of the retainer ring 102. However, the influence on the induction of the slurry and the discharge of the polishing scraps can be reduced, whereby the polishing characteristics necessary for polishing the wafer U can be maintained for a longer time.

  As the material of the retainer ring 102 according to the first embodiment, acrylic resin (soft type can be used), ABS resin, epoxy resin, polyurethane, Teflon (registered trademark, polytetrafluoroethylene), ceramic, etc. are used. It is done. The groove structure of the groove pitch, groove width, and groove depth is not limited to the example of the first embodiment, and can be variously changed depending on the polishing conditions.

[Example 1]
The retainer ring 102 of the first embodiment is applied to the polishing head 103 as shown in FIG. 2, and the silicon wafer U on which the thermal oxide film having a thickness of 10,000 mm is formed is used with the polishing apparatus shown in FIG. Then, polishing was performed under the following processing conditions.
The polishing head 103 has a retainer ring 102 attached to the polishing head main body. Further, the pressure in the air chamber 14 is applied to the wafer U through the elastic film 13 in order to perform the polishing process.

Processing conditions / polishing pad rotation speed: 120rpm
-Polishing head rotation speed: 110 rpm
・ Slurry flow rate: 200 ml / min
・ Load applied to polishing head: 4.0PSi
・ Abrasive: CeO ₂ acidic aqueous solution

When polishing was performed with a polishing time of 1 minute, when SiO _{2 of} about 200 nm was removed, when the groove depth was initially 5.0 mm, the polishing rate (polishing rate, thickness removed per unit time by polishing: nm / Min) was good at about ± 3%. Further, the uniformity of the polishing rate was able to be kept substantially equal until the groove depth was about 2.7 mm.

[Comparative example]
When the polishing head 103 to which the conventional retainer ring 102R shown in FIGS. 5 and 6 was applied instead of the retainer ring 102 of Example 1 was used to remove SiO ₂ of about 200 nm in 1 minute, the polishing rate was The uniformity was about ± 4% when the groove depth was 5.0 mm at the beginning, which was almost the same as the embodiment. However, the uniformity of the polishing rate suddenly deteriorated when the groove depth was about 3.0 mm or less, and the uniformity of the polishing rate was about ± 15% at about 2.7 mm.

  FIG. 4 shows the relationship between the groove depth of the retainer ring and the uniformity of the polishing rate in Example 1 and the comparative example. By using the retainer ring 102 of the first embodiment, the polishing rate can be uniformly polished even when the groove depth of the retainer ring 102 is 3.0 mm or less.

  Further, the pattern (groove direction) of the groove 102a formed in the retainer ring 102 is not limited to the linear radial groove 102a shown in the first embodiment, but is an annular groove, a lattice-shaped groove, a curved (distorted) radial pattern. A groove, a spiral groove, or the like can be used.

  The shape (cross section) of the groove formed in the retainer ring 102 is not limited to the inverted trapezoidal groove shown in the embodiment, and a step-like structure [see FIG. 3C] or a curved structure [figure 3 (d)] or the like can be used.

  As described above, in the retainer ring according to the present invention, the groove shape formed on the surface in contact with the polishing pad is formed so that a constant amount can be secured for a long time even when the cross-sectional area of the retainer ring is worn. The supply of the abrasive and the discharge of the polishing debris, which are the roles of the ring, can be stably performed. As a result, the polishing rate can be kept constant, and stable polishing can be performed.

  Since the groove shape formed on the contact surface of the retainer ring with the polishing pad is formed so that the cross-sectional area is kept constant even by wear of the retainer ring, fluctuations in the polishing characteristics can be reduced. In this material, the range of selection is widened, an inexpensive material such as an acrylic resin can be selected, and the running cost can be reduced as compared with the case where an expensive material such as ceramics is selected. Furthermore, since the flow of the abrasive (supply and discharge to the polishing surface) can be stabilized, the wafer can be efficiently polished with a small amount of abrasive.

It is a schematic structure explanatory side view explaining the basic composition of the chemical mechanical polishing apparatus concerning the present invention. It is a structure explanatory side view including a partial cross section around the retainer ring. It is explanatory drawing of the retainer ring holding the semiconductor wafer, (a) is a schematic bottom view of a retainer ring, (b) is a schematic sectional drawing of the groove part. Further, (c) and (d) are schematic cross-sectional views of a groove portion of another retainer ring example according to the present invention. FIG. 3 is a graph showing the uniformity of the polishing rate. These are the schematic structure explanatory side views explaining the basic composition of the conventional chemical mechanical polishing apparatus. It is explanatory drawing of the retainer ring holding the conventional semiconductor wafer, (a) is a schematic bottom view of a retainer ring, (b) is a schematic sectional drawing of the groove part.

Explanation of symbols

13... Elastic film 14... Air chamber 100 .. Surface plate 100a .. Surface plate rotation drive device 101... Polishing member (polishing pad)
102... Retainer ring 102 a .. groove 102 b.. Contact portion 103 with polishing pad... Polishing head 104... Abrasive supply portion 105.
K: Polishing device U: Object to be polished (wafer)

Claims (13)

A chemical mechanical polishing apparatus comprising: a polishing pad that receives supply of slurry on a surface; and a polishing head that holds a semiconductor wafer to be polished and polishes the semiconductor wafer while rotating relative to the polishing pad. A retainer ring mounted on the polishing head and holding the semiconductor wafer around its periphery,
The retainer ring has a groove on the side surface of the wafer polishing for guiding the slurry to the wafer polishing surface and discharging the polishing debris together with the slurry from the wafer polishing surface. A retainer ring characterized by having a wide portion with a groove width larger than that of the opening toward the bottom portion while reaching the bottom portion .   The retainer ring according to claim 1, wherein the wide portion is formed from the opening of the groove toward the bottom.   The retainer ring according to claim 2, wherein the groove has the wide portion from the opening of the groove, and the same width portion following the wide portion and having the same width toward the bottom.   The retainer ring according to claim 3, wherein the wide portion and the same width portion of the groove are repeated, and the groove width is increased in a substantially step shape from the opening portion to the bottom portion of the groove.   The retainer ring according to any one of claims 1 to 4, wherein the wide portion of the groove has a groove width that is increased in a curved manner from the opening to the bottom of the groove.   The retainer ring according to any one of claims 1 to 5, wherein the groove has a processing angle of 95 to 120 degrees in the opening.   The retainer ring according to claim 1, wherein the groove has an equal width portion having the same width from the opening toward the bottom, and the wide width portion follows the equal width portion and moves toward the bottom.   The retainer ring according to claim 7, wherein the same width portion and the wide portion of the groove are repeated, and the groove width is increased in a substantially step shape from the opening portion to the bottom portion of the groove.   The retainer ring according to claim 7 or 8, wherein the wide portion of the groove has a groove width that increases in a curved manner toward the bottom.   The retainer ring according to any one of claims 1 to 9, wherein at least 50% of the initial cross-sectional area of the groove remains when the groove becomes shallower by 1.8 mm.   The retainer ring according to any one of claims 1 to 10, wherein the direction of the groove is an annular shape, a linear radial shape, a lattice shape, a curved radial shape, or a spiral shape. A polishing pad that receives a supply of slurry on the surface;
A polishing head for holding a semiconductor wafer to be polished and polishing the semiconductor wafer while rotating relative to the polishing pad;
A chemical mechanical polishing apparatus comprising: a retainer ring according to any one of claims 1 to 10, which is mounted on a polishing head and holds a semiconductor wafer so as to surround a periphery thereof.   The chemical mechanical polishing apparatus according to claim 12, wherein the retainer ring is detachable from the polishing head.

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