JP2007158135A - Retainer ring for cmp equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a retainer ring which can minimize the time required for moderating polishing. <P>SOLUTION: In the retainer ring 8 arranged in the holding head 4 of CMP equipment 1 for polishing a wafer W chemically and mechanically and pressing the polishing surface 3a of a polishing pad 3 while surrounding the outer circumference of the wafer W in ring-shape, surface roughness of the surface 8a for pressing the polishing surface 3a is set at 0.2 μm or less in term of centerline average roughness (Ra). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a CMP (Chemical Mechanical Polishing) apparatus for chemically and mechanically polishing a wafer (object to be polished), and more particularly to an outer periphery of a wafer disposed (mounted) in a holding head of a CMP apparatus. Retainer ring surrounding

  As the integration and performance of semiconductor devices increase, the dimension in the horizontal direction (on the plane) becomes smaller, and the structure in the vertical direction becomes finer and multilayered. In order to realize such miniaturization and multilayering, the flatness (flatness) of a semiconductor substrate (silicon substrate or the like) needs to be high. For this reason, it is required to increase the flatness at the wafer stage, and a CMP apparatus is used to meet such a demand.

The CMP apparatus includes, for example, a rotatable surface plate, a polishing pad disposed on the surface plate, a holding head that holds the wafer and presses it against the polishing pad, and a slurry supply nozzle. . Further, the holding head includes a retainer ring that surrounds the outer periphery of the wafer, an elastic film that presses the upper surface of the wafer, an air chamber that is surrounded by the elastic film, the retainer ring, and the head body, and the air chamber. An air supply path for supplying pressurized air to the air. The retainer ring surrounds the outer periphery of the wafer to prevent the wafer from popping out, and presses the polishing surface (surface) of the polishing pad to flatten and refine (optimize) the polishing surface of the polishing pad for polishing the wafer. (For example, refer to Patent Document 1).
Japanese Patent Laid-Open No. 11-226865

  By the way, since such a retainer ring presses the polishing pad, the pressing surface of the retainer ring (surface that presses the polishing pad) itself is polished and consumed by the polishing pad. For this reason, the retainer ring must be periodically replaced with a new retainer ring. However, if the surface roughness of the pressing surface of the new retainer ring is large, a predetermined polishing performance cannot be obtained. That is, adhesion of polishing debris or scratches (scratches) may occur on the surface to be polished of the wafer. For this reason, when the retainer ring is replaced, it is necessary to perform the break-in polishing of the newly installed retainer ring before starting the polishing of the product wafer (wafer produced as a product). That is, a new retainer ring is mounted on the holding head of the CMP apparatus, and several tens to several hundreds of dummy wafers (break-in wafers) are polished, and after confirming that an appropriate polishing performance is obtained, It was necessary to start polishing. Such break-in polishing requires a lot of time and labor, which has been a factor of reducing the production operation rate of wafers.

  Accordingly, an object of the present invention is to provide a retainer ring that can minimize the time required for break-in polishing.

  In order to achieve the above object, the invention described in claim 1 includes a polishing pad disposed on a surface plate and a holding head that holds the wafer and presses the wafer against the polishing pad, In a CMP apparatus for polishing, a retainer ring for a CMP apparatus that is disposed in the holding head, surrounds the outer periphery of the wafer in a ring shape, and presses the polishing surface of the polishing pad, The surface roughness of the pressing surface that presses the polished surface is 0.2 μm or less in terms of centerline average roughness.

  The present inventor has repeatedly conducted tests and studies, and found that the time required for break-in polishing can be minimized by setting the surface roughness of the pressing surface of the retainer ring to 0.2 μm or less in terms of the center line average roughness. It was. According to the first aspect of the present invention, the time required for break-in polishing can be minimized. That is, when the surface roughness of the pressing surface of the retainer ring is 0.2 μm or less in terms of the center line average roughness, immediately after the retainer ring is mounted on the holding head of the CMP apparatus or after performing break-in polishing for a short time, High polishing performance can be obtained. In other words, the polishing surface of the polishing pad is flattened and miniaturized well (to a high level) by the pressing surface of the retainer ring, and adhesion of polishing debris and scratches (scratches) to the polished surface of the wafer occur. It is drastically reduced. As a result, it is possible to effectively reduce the time and labor required for break-in polishing and improve the production operation rate of the CMP apparatus. In addition, since the time required for break-in polishing is minimized, the amount of polishing debris due to break-in of the dummy wafer is reduced, and scratches and scratches on the wafer (product wafer) due to the polishing debris and the occurrence of impurities are generated. The rate will decrease further. As a result, the production quality of the wafer is improved and stabilized, and the productivity is further improved by reducing defective products.

  Hereinafter, the present invention will be described based on the illustrated embodiments.

  FIG. 1 is a front view showing a schematic configuration of a CMP apparatus 1 according to an embodiment of the present invention. The CMP apparatus 1 has the same configuration as that of a widely used CMP apparatus except for a retainer ring 8 to be described later, and a detailed description of the CMP apparatus 1 is omitted here. 2 is provided with a polishing pad 3 (such as a cloth) disposed on 2, a holding head 4, a slurry supply nozzle 5 and a dresser 6 (shaping means), and polishes the wafer W chemically and mechanically.

  The holding head 4 holds the wafer W and presses the surface to be polished W1 against the polishing pad 3. The holding head 4 can move on the polishing pad 3 while rotating (spinning). As shown in FIG. 2, the holding head 4 includes a head main body 7, a retainer ring 8 disposed at a lower portion of the head main body 7, and is positioned in the retainer ring 8 to press the upper surface W <b> 2 of the wafer W. And an elastic film 9. Then, pressure air is supplied to the air chamber 10 surrounded by the head body 7, the retainer ring 8, and the elastic film 9, and the wafer W is pressed against the polishing pad 3 through the elastic film 9.

  The retainer ring 8 surrounds the outer periphery of the wafer W, prevents the wafer W from jumping out of the holding head 4, and presses the polishing surface 3 a (surface) of the polishing pad 3 to polish the wafer W. 3a (a portion in contact with the surface to be polished W1 of the wafer W) is flattened and miniaturized (optimized). That is, the polishing surface 3a of the polishing pad 3 has a low flatness due to the slurry (abrasive) 5a and a rough surface, and the flatness of the polishing surface 3a is increased by the retainer ring 8, and The surface roughness is reduced.

  This retainer ring 8 is made of PPS (polyphenylene sulfide, engineering plastic) material in consideration of chemical resistance, mechanical properties, etc., and has a ring shape as shown in FIG. A plurality of groove-like slits 8b for releasing (discharging) polishing debris are formed on the pressing surface 8a that presses the three polishing surfaces 3a. In addition, a plurality of screw inserts 8d formed with female screws 8e are inserted into the back surface 8c of the retainer ring 8 located on the back surface of the pressing surface 8a. That is, the screw insert 8d has a substantially cylindrical shape, a male screw is formed on the outer periphery, and a female screw 8e is formed on the inner periphery.

  The surface roughness of the pressing surface 8a of the retainer ring 8 is set (processed) to 0.2 μm or less in terms of centerline average roughness (arithmetic average roughness, Ra). This means that the time required for break-in polishing can be minimized by the inventor's repeated testing and research, and setting the surface roughness of the pressing surface 8a to 0.2 μm or less in terms of the center line average roughness. This is due to the finding. The data that proves this is shown in FIG.

  This data shows the number of defects after break-in polishing in each surface roughness (centerline average roughness Ra). That is, “defect number after ten dummy wafers (DN1)” in the figure indicates the number of defects confirmed on the tenth dummy wafer after polishing ten dummy wafers (break-in wafers). Here, the defect includes all defective elements such as foreign matters such as polishing scraps and scratches. “Dummy wafer polishing number (PN)” in the figure indicates the number of polished dummy wafers. In the figure, “number of defects after PN sheets (DN2)” indicates the number of defects that are confirmed on the PN-th dummy wafer after polishing the dummy wafer and the size (length) is larger than 0.16 μm. ing. In the drawing, “number of scratches (SN) in DN2” indicates the number of scratches having a size (length) larger than 1.0 μm in the number of defects DN2.

  The break-in polishing conditions with the dummy wafer are as follows.

Slurry: SS-25 (Cabot)
Polishing pad: IC1000 / SUBA400 (Rohm & Haas)
Polishing time per dummy wafer: 60 seconds Polishing pressure (pressing force) on the dummy wafer: 210 hPa
As is apparent from this data, when the surface roughness Ra of the pressing surface 8a of the retainer ring 8 is larger than 0.2 μm (when the surface roughness Ra is 0.4 μm or 0.3 μm), FIG. As shown in the figure, the number of defects DN1 after polishing 10 dummy wafers reaches several hundreds, whereas when the surface roughness Ra is 0.2 μm or less, it is drastically reduced to 20 or less. When the surface roughness Ra of the pressing surface 8a is larger than 0.2 μm, the number of defects DN2 reaches about 30 after polishing several hundred (PN) dummy wafers, whereas the surface roughness When Ra is 0.2 μm or less, the number of defects DN2 is 20 or less simply by polishing 10 dummy wafers. Furthermore, when the surface roughness Ra of the pressing surface 8a is larger than 0.2 μm, the number of scratches SN in the defect number DN2 is about 5 to 10, whereas when the surface roughness Ra is 0.2 μm or less. There is almost no scratch.

  As described above, when the surface roughness Ra is 0.2 μm as a boundary (critical value) (see FIG. 5), the polishing performance is remarkably improved, and the surface roughness of the pressing surface 8a of the retainer ring 8 is the centerline average roughness. When the thickness is 0.2 μm or less, the time required for break-in polishing can be minimized. That is, when the surface roughness Ra of the pressing surface 8a is 0.2 μm or less, high polishing performance can be obtained immediately after mounting the retainer ring 8 on the holding head 4 of the CMP apparatus 1 or after performing break-in polishing for a short time. It is obtained. That is, the pressing surface 8a of the retainer ring 8 makes the polishing surface 3a of the polishing pad 3 flattened and miniaturized well (to a high level). And compared with the case where surface roughness Ra is larger than 0.2 micrometer, generation | occurrence | production of the adhesion | attachment of a grinding | polishing waste, scratch, etc. to the to-be-polished surface W1 of the wafer W reduces sharply. For example, if the required accuracy (required specification) of the wafer W and the number of defects (DN2) larger than 0.16 μm on the polished surface W1 of the wafer W must be 20 or less, the retainer ring 8 is pressed. When the surface roughness Ra of the surface 8a is 0.4 μm, 250 or more dummy wafers must be polished. Similarly, when the surface roughness Ra is 0.3 μm, 100 or more dummy wafers must be polished. On the other hand, when the surface roughness Ra is 0.2 μm or less, it is only necessary to polish 10 or less dummy wafers.

  As a result, it is possible to effectively reduce the time and labor required for break-in polishing and improve the production operation rate of the wafer W. In addition, since the time required for break-in polishing is minimized, the polishing debris due to break-in of the dummy wafer is reduced, and the rate of occurrence of scratches (scratches) and impurity adhesion to the wafer W due to the polishing debris is further increased. Decrease. As a result, the production quality of the wafer W is improved and stabilized, and the productivity is further improved by reducing defective products.

  By the way, by setting the surface roughness of the pressing surface 8a of the retainer ring 8 to 0.2 μm or less in terms of the center line average roughness, the time required for break-in polishing can be minimized as described above. By setting the roughness to 0.01 μm or less in terms of the center line average roughness, the time required for break-in polishing can be further minimized. That is, as shown in FIG. 4, when the surface roughness Ra of the pressing surface 8a is 0.2 μm, for example, the number of defects DN1 after polishing 10 dummy wafers is 20, whereas the surface roughness When Ra is 0.01 μm or less, the number of defects DN1 is 10 or less. Then, the required accuracy of the wafer W is increased, and the surface roughness Ra is 0.01 μm even if the number of defects (DN2) larger than 0.16 μm on the polished surface W1 of the wafer W must be 10 or less. In the retainer ring 8 below, required accuracy can be obtained by polishing 10 or less dummy wafers.

  In the present embodiment, the retainer ring 8 is made of PPS. However, PEEK (polyether ether ketone), PET (polyethylene terephthalate), POM (polyacetals), PI (polyimide) Of course, even if it is made of other engineering plastics, the time required for break-in polishing can be minimized by setting the surface roughness of the pressing surface 8a to 0.2 μm or less in terms of the center line average roughness. It is. In the present embodiment, the retainer ring 8 is made of PPS and has an integral structure (one-layer structure), but may be a two-layer retainer ring. That is, for example, in a two-layer retainer ring in which a first ring made of stainless steel and a second ring made of engineering plastic are overlapped, the surface roughness of the pressing surface of the second ring located in the lower layer is the center line average By setting the roughness to 0.2 μm or less, the time required for break-in polishing can be minimized. Further, it goes without saying that the first ring and the second ring of the retainer ring having a two-layer structure may be fastened by bolting or joined by an adhesive.

It is a front view which shows schematic structure of the CMP apparatus concerning embodiment of this invention. It is a schematic sectional drawing of the holding head of the CMP apparatus concerning embodiment of this invention. It is the front view (a) and bottom view (b) of the retainer ring for CMP apparatuses concerning embodiment of this invention. It is a figure which shows the number of defects etc. after break-in polishing in each surface roughness of the pressing surface of a retainer ring. It is a log-log graph showing the relationship between the surface roughness of the pressing surface of the retainer ring and the number of defects after polishing 10 dummy wafers.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 CMP apparatus 2 Surface plate 3 Polishing pad 3a Polishing surface 4 Holding head 5 Slurry supply nozzle 5a Slurry 6 Dresser 7 Head body 8 Retainer ring 8a Pressing surface 8b Slit 8c Back surface 8d Screw insert 8e Female screw 9 Elastic body film 10 Air chamber W Wafer W1 Surface to be polished

Claims (1)

In a CMP apparatus that comprises a polishing pad disposed on a surface plate and a holding head that holds and presses the wafer against the polishing pad, the CMP apparatus that chemically and mechanically polishes the wafer is disposed in the holding head. A retainer ring for a CMP apparatus that surrounds the outer periphery of the wafer in a ring shape and presses the polishing surface of the polishing pad,
The surface roughness of the pressing surface that presses the polishing surface of the polishing pad is 0.2 μm or less in terms of centerline average roughness.
A retainer ring for a CMP apparatus.

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