GB2344302A

GB2344302A - Retainer ring for chemical mechanical polishing machine

Info

Publication number: GB2344302A
Application number: GB9920572A
Authority: GB
Inventors: Juen-Kuen Lin; Chien-Hsin Lai; Peng-Yih Peng; Kun-Lin Wu; Daniel Chiu; Chih-Chiang Yang; Juan-Yuan Wu; Hao-Kuang Chiu
Original assignee: United Microelectronics Corp
Current assignee: United Microelectronics Corp
Priority date: 1997-09-01
Filing date: 1998-09-16
Publication date: 2000-06-07
Anticipated expiration: 2018-09-16
Also published as: GB9920574D0; GB2342605B; GB9820209D0; GB2345257A; GB9920573D0; GB2344303A; GB9920572D0; GB2344302B; GB2342605A; GB2344303B; GB2345257B

Abstract

A chemical mechanical polishing machine includes a retainer ring 50 for holding a semiconductor wafer to be polished. The retainer ring comprises slurry passages 52 on the bottom of the retainer ring and extending from an inner surface of the ring to an outer surface, the passages being interconnected by at least one circular path 54. The ring allows slurry to be delivered more evenly to the wafer giving improved planarization of the wafer.

Description

CHEMICAL-MECHANICAL POLISHING MACHINE AND RETAINER RING THEREOF This application is a divisional of GB patent application No. 9820209.6, and relates to semiconductor fabrication technologies, and more particularly, to an improved structure for the retainer ring used on the polishing head of a chemical-mechanical polishing (CMP) machine to retain a semiconductor wafer in position while performing the CMP process.

In semiconductor fabrication, the chemicalmechanical polishing (CMP) technique is widely used for the global planarization of semiconductor wafers that are used for the fabrication of VLSI (very large-scale integration) and ULSI (ultra large-scale integration) integrated circuits.

Figs. 1A and 1B are schematic diagrams showing a conventional CMP machine. The CMP machine comprises a polishing table 10 on which a polishing pad 12 is layered, a polishing head 14 for holding a semiconductor wafer 16 in position, and a nozzle 18 for applying a mass of slurry to the semiconductor wafer 16 during the CMP process.

Fig. 1C shows a perspective view of the structure inside of the polishing head 14. As shown, the polishing head 14 includes an air-pressure means 20 which applies air pressure to a wafer loader 22 used to hold the wafer 16. In addition, a retainer ring 24 is mounted around the loader 22 and the wafer 16, which can retain the wafer 16 in fixed position during the CMP process. Moreover, a cushion pad (not shown) is placed between the wafer 16 and the loader 22.

Figs. 2A-2B show a conventional structure for the retainer ring 24. Through the retainer ring structure of Figs. 2A-2B, the slurry is supplied for polishing under the polishing head 14, that is, over the surface of a wafer to be polished. However, without a proper conduit or passage of the retainer head, the slurry is non-uniformly distributed over the surface of the wafer. It is found that the slurry can not circulate fluently over the wafer surface. Thus, drawbacks such as a large wafer-edge exclusion range, a low waste (refuse) removing rate, an inefficient use of the slurry, and a reduced life of the cushion pad are caused. The resultant surface flatness of the wafer after undergoing a CMP process using the retainer ring of Figs. 2A-2B is shown in Fig. 3. The graph of Fig. 3 shows the thickness of the wafer in relation to the various points of a straight line passing through the spinning center of the wafer. From the plot shown in Fig. 3, it can be seen that the flatness is not quite satisfactory. The standard deviation of the thickness data is about 5.06%.

The following documents also relate to the polishing of a semiconductor wafer.

GB 2315694A discloses a wafer polishing machine which uses a wafer mount plate to hold a semiconductor wafer. A retainer ring encloses the semiconductor wafer, and the semiconductor wafer as well as the retainer ring is in contact with the polishing pad.

Polishing liquid is supplied to the inside of the retainer ring via grooves from the face of the retainer ring allowing the polishing liquid to infiltrate the centre of the wafer.

GB 2292254A discloses a method for polishing a semiconductor substrate which involves a step of vacuum chucking the substrate on to a substrate holder and simultaneously pressing the substrate onto a polishing cloth. A flowing liquid layer is formed between the substrate and the surface of the substrate holder to support the substrate using surface tension. The substrate is surrounded by a guide ring and the surface of the guide ring is formed with grooves for discharging the flowing liquid layer.

US 5695392 discloses a retainer ring for retaining a thin workpiece during machining polishing. The retaining ring fits over the workpiece during polishing and is provided on its lower portion with an enlarged angular extension in which there are a plurality of non-radial channels extending from the outer periphery to the inner periphery.

The retaining device acts to direct abrasive slurry into the centre of the workpiece during polishing.

US 5597346 discloses a semiconductor wafer carrier which holds a semiconductor wafer during a CMP process intended to achieve a more uniform layer of slurry at greater polishing speeds. The carrier directs slurry between the semiconductor wafer and a conditioning pad and includes a wafer holding surface for holding the semiconductor wafer as the semiconductor wafer contacts the conditioning pad and slurry. An outer rim portion surrounds the semiconductor holding surface. A plurality of slurry channels associated with the outer rim portion direct the slurry between the semiconductor wafer and the conditioning pad.

It is therefore a consideration of the present invention to provide a new retainer ring for use on the polishing head of a CMP machine. The new retainer ring in the CMP machine allows the slurry to be supplied more uniformly over the surface of a wafer. Thus, the above mentioned problems of the conventional CMP machine, such as a large wafer-edge exclusion range, a low refuse removing rate, an inefficient use of the slurry, and a reduced life of use of the cushion pad, are addressed.

In accordance with the foregoing and other considerations of the present invention, there is provided a retainer ring for use in a chemical mechanical polishing machine. comprising: a plurality of slurry passages extending from an inner surface to an outer surface of the retainer ring; and at least one circular path intercrossing the slurry passages between an inner perimeter and an outer perimeter of the retainer ring.

Thus, the retainer ring of the invention employs a circular path between the inner perimeter and the outer perimeter of the retainer ring. An optional equally spaced arrangement of the straight grooves causes the slurry to be drawn into the inside of the retainer ring from all radial directions, thus allowing the slurry to be spread uniformly over the wafer held on the inside of the retainer ring. Furthermore, the provision of the circular path allows the slurry to be buffered and circulate therein, thus allowing those edge portions of the wafer proximate to the inner ends of the straight grooves to receive a buffered flow of slurry.

To planarize a wafer having a deposition layer thereon, the wafer is disposed within a polishing head with the deposition layer facing down on the polishing table. The wafer is retained within the polishing head by the retainer ring of the invention having a plurality of slurry passages. A slurry is supplied from a slurry supplier to be evenly distributed over the deposition layer through the retainer ring. The polishing table is rotating and the polishing head is spinning to perform polishing.

Thus, in use of the retainer ring of the invention, first, a deposition layer is formed on a wafer. A chemical mechanical process is performed on the deposition layer using a chemical mechanical polishing machine with the retainer ring having a plurality of slurry passages at the bottom thereof.

The invention can be more fully understood by reading the following detailed description of the preferred embodiments with reference made to the accompanying drawings, wherein: Fig. 1A is a schematic top view of a CMP machine for performing a CMP process on a semiconductor wafer; Fig. 1B is a schematic sectional view of the CMP machine of Fig. 1A ; Fig. 1C is a cross-sectional view showing a detailed inside structure of the polishing head used on the CMP machine of Figs. 1A and 1B ; Fig. 2A is a schematic top view of a conventional retainer ring used on the polishing head of Fig. 1C ; Fig. 2B is a schematic bottom view of the conventional retainer ring of Fig. 2A; Fig. 3 is a graph, showing the resultant flatness of the semiconductor wafer after undergoing a CMP process using the conventional retainer ring of Figs.

2A-2B; Fig. 4A is a schematic top view of a first embodiment of the retainer ring according to the invention; Fig. 4B is a schematic bottom view of the retainer ring of Fig. 4A; Fig. 5A is a schematic top view of a second embodiment of the retainer ring according to the invention; Fig. 5B is a schematic bottom view of the retainer ring of Fig. 5A ; Fig. 6 is a graph, showing the resultant flatness of the semiconductor wafer after undergoing a CMP process using the retainer ring of Figs. 4A-4B; Fig. 7 is a graph, showing the resultant flatness of the semiconductor wafer after undergoing a CMP process using the retainer ring of Figs. 4A-4B; Fig. 8A and Fig. 8B are a top view and a side view of a retainer ring in a third according to the invention ; Fig. 8C is a schematic cross section view of the slurry passage; Fig. 9A to Fig. 9D shows the mechanism of the slurry flow; Fig. 10 is a schematic top view of a fourth embodiment of the retainer ring according to the invention; Fig. 11A to Fig. 11B show cross sectional views of the process for planarizing a deposition layer on a wafer; Fig. 12A to Fig. 12B are cross sectional views showing an etch back process; and Fig. 13A to Fig 13D are cross sectional views showing a method of fabricating a shallow trench isolation by using the chemical mechanical machine provided in the invention.

In accordance with the invention, an improved structure of a retainer ring is provided. The improved structure of the retainer ring enables slurry to be supplied for polishing the wafer evenly distributed over the wafer. A first embodiment of the invention is described in the following with reference to Figs.

4A-4B.

First Embodiment Fig. 4A is a schematic top view of the retainer ring 40 in the first embodiment according to the invention, and Fig. 4B is a schematic bottom view of the retainer ring 40 shown in Fig. 4A. The inner diameter of the retainer ring 40 ranges from 4 in.

(inch) (10.16cm) to 12 in. (30.48cm), or even larger 12in. (30.48cm). However, since the retainer ring 40 functions to retain a semiconductor wafer during the CMP process, therefore, the actual inner diameter of the retainer 40 depends on the size of the wafer to be polished. As shown in Fig. 4B, the retainer ring 40 is formed with a plurality of slurry paths, passages or conduits 42. The slurry passages 42 can be formed as grooves under the retainer ring, channels or tubes through the retainer rings, or recesses of other shape.

In this embodiment, straight grooves spaced at substantially equal angular intervals around the retainer ring 40 are employed. Each of these slurry passages 42 is oriented at an angle with respect to the radius in such a manner that its outer end leads its inner end in angular position in reference to the spinning direction of the retainer ring 40. While performing a polishing process, the retainer ring 40 is spinning with a speed as required, these slurry passages 42 are oriented with an acute angle of attack against the slurry supplied from outside of the retainer ring 40. Thus, the slurry is distributed evenly over the surface of the wafer inside the retainer ring 40 by being supplied to the retainer ring 40 with the aid of the slurry passages 42. In the case of Fig. 4B, for example, the orientation of the straight grooves 42 shows that the retainer ring 40 is to be spinning in the counterclockwise direction. It is appreciated that persons skilled in the art could rearrange the slurry passages 42 in another way such that the retainer ring 40 would be spinning in the clockwise direction during polishing. In the invention, each of the slurry passages 42 has a width of 0.050.3mm (millimeter) and a depth of 2-4mm. The actual width and depth of these slurry passages should be chosen according to the specific requirements for the polishing process. The manner of equally spacing the slurry passages 42 enables the slurry to be drawn inside the retainer ring 40 with a substantially equal amount from all radial directions, thus allowing the slurry to be spread uniformly over the surface of the wafer.

The resultant flatness of a wafer after undergoing a CMP process using the retainer ring of Figs. 4A-4B is shown in Fig. 6 and Fig. 7. The flatness is measured in terms of the thickness values along a straight line passing through the center of the wafer. From the graphs of Fig. 6 and Fig. 7, it is seen that the flatness of the wafer samples is significantly better than the flatness of the wafer shown in Fig. 3 by using the prior art retainer ring of Figs. 2A-2B. The standard deviation of thickness is 0.92% in the case of Fig. 6 and 1.84% in the case of Fig. 7, which-are both significantly better than the standard deviation of 5.06% in the case of Fig. 3. However, as shown in Fig.

7, since the edge portions of the wafer proximate to the inner ends of the slurry passages 42 would receive a greater amount of slurry than other portions of the wafer, the polishing effect is more significant than other portions. Consequently, the thickness of the edge portions proximate to the slurry passages is significantly less than that of other portions of the wafer.

Second Embodiment Fig. SA is a schematic top view of the second embodiment of the retainer ring 50 according to the invention, and Fig. 5B is a schematic bottom view of the retainer ring 50 shown in Fig. 5A.

As shown in Fig. 5B the design of the slurry passages 52 of the retainer ring 50 in this embodiment is identical to the previous embodiment. That is, these slurry passages 52 are in a form of substantially equally spaced straight grooves. Each of these slurry passages 52 is oriented in a similar manner as the previous embodiment and formed similarly with a width of 0. lmm and a depth of 2-4mm. Again, the width and depth of the slurry passages 52 depends on the specific requirements for the polishing process. In this embodiment, at least one circular recessed ring 54, for example, a circular groove, is formed at the bottom surface of the retainer ring 50 between the outer perimeter and inner perimeter of the retainer ring 50, intercrossing all of the straight grooves 52. The circular recessed ring 54 is functioned as a buffer ring. The slurry being drawn in through the slurry passages 52 is partly buffered and circulating in the circular recessed ring 54, thus allowing those edge portions of the wafer proximate to the inner ends of the slurry passages 52 to receive only a part of the slurry. Thus, the polished effect obtained from the previous embodiment, that is, an evenly and uniformly planarized surface of the wafer, is obtained without forming thinner edge portions. The circular recessed ring 54 has a similar dimension of the slurry passages 52, that is, a width of about 0. 05-0.3mm and a depth of about 2-4mm.

With the formation of the slurry passages, or even with the buffer circular groove intersecting the slurry passages, a much better planarized effect is achieved. However, in the above embodiments, the parameters such as the detailed shape of the slurry passages, the angle of attack, that is, the angle between the central line of the slurry passage and the tangent line, and the diffusion angle are never discussed. In the following embodiments a quantitative point of view is taken. The parameters determining the slurry flow are considered.

Third Embodiment A schematic top view of a retainer ring is shown as Fig. 8A. In this embodiment, twelve slurry passages 82 are formed at the bottom of the retainer ring 80. It is appreciated that persons skilled in the art may select a different number of the slurry passages according to specific requirements during certain polishing processes. Consider a retainer ring 80 with an outer diameter of 25.40cm and an inner diameter of 22.86cm, the width of the retainer ring 80 is thus 25.40cm-22.86cm=2.54cm. The formation of the slurry passages 82 enables the slurry flow into the retainer ring and distributed over the surface of the wafer to be polished. As mentioned above, the slurry passages 82 can be in a form of tubes, grooves, channels, or guiding holes penetrating through the whole width of the retainer ring 80. The central angle between two consecutive (two neighboring) slurry passages-82 is denoted as 0,, and the angle of attack of each slurry passage 82 is denoted as),. Assume the diameter of the inner end of the slurry passage 82 is d2, whereas the outer one is dl. Fig. 8B shows a schematic side view of the retainer ring 80 with the slurry passages 82 in a form of guiding holes.

Drawing a central line through the center points of one slurry passage 82, a diffusion angle 02 is defined as the angle between the central line and one perimeter of the slurry passage 82.

Fig. 9A to Fig. 9D illustrates the mechanism of the polishing process using the retainer ring 80 shown in Fig. 8A to Fig. 8C. It is assumed that the polishing table 90 is rotating with an angular velocity 0), and the distance between the center of the polishing table 90 and the center of the polishing head 94 is''.

Whereas, the polishing head 94 is spinning with an angular velocity 0) 2, with a radius of r2. As shown in Fig. 9A, if the angle between rt and the j-axis is p3 and the angle between r2 and the j-axis is 4, any point at the perimeter ~ the polishing table 90 is thus rotating with a velocity Vh. The velocity can thus be calculated as: Vh = #1#(r1 + r2) + #2 # r2 =(r1#1cos#3 + r2#1 cos#4 + r2#2 cos#4)i - (r1#1 sin#3 + r2#1 sin#4 + r2#2 sin 64) j =, 4i+Bj (1) Fig. 9B shows the movement of the retainer ring 80. It is to be noted that the movement of the retainer ring 80 is synchronous to the polishing head 94 shown in Fig. 9A.

Considering forming the slurry passages with their central line along the direction of the velocity of the retainer ring 80, from the above equation, the direction of the velocity Vh that is, the angle of attack of the slurry passage, is: &num; tan~l A B For a retainer ring 80 having a minimum distance of 1.25cm between the tangent line of the inlet point and the tangent line of the outlet point, and a length of the slurry passage of i, 1. 25 sin#1 = l (3) The slurry passage can thus be designed according to the parameters derived from the above relations.

In Fig. 9C, a slurry passage with a narrow inlet and a wider outlet is shown. That is, the slurry passage has a larger cross section area of the inner end than the outer end. With this design, the path of the slurry flow is gradually expanded, and the positive pressure gradient and the diversion of the slurry flow are moderated. The slurry supplied through the slurry passage is thus increased. As shown in the figure, P" A, and V, represent the pressure and cross section area of the inlet, and the flow rate of slurry flow at the inlet, respectively. Whereas, P2, A2, and : represents the pressure and cross section area of the inlet, and the flow rate of slurry flow at the outlet, respectively. Considering the friction between the slurry and the slurry passage and the gravitation of the slurry to be negligible and the slurry as incompressible, if the diffusion angle is 02 and z is the passage length, the Bernoulli equation can be employed by ignoring the vortex of the slurry flow at the inlet, the barrier at the outlet, and any external vibration: P + 1/2 #V2 = P0 = const. (4) wherein P is the pressure, p is the density, and V is the velocity of the flow, and Po is the stagnation pressure. By introducing equation (4), the resilience coefficient of pressure C is: P0 - P2 P2-P1 P0-P2 V2 Cp=P0-P1=1-P0-P1=1-V1 (5) From the continuity equation: ..=22 (6) The resilience coefficient of pressure can be obtained as: C=1- ()'(7) Therefore, the higher Cp is, the larger X,/A2 is.

Moreover, the larger the value of A1/A2 is, the wider the diffusion angle &num;2 is, and the slurry flow is expected to be more fluent. However, as the diffusion angle &num;2 is increased over 10 , an effect of flow diversion 91 or a flow with a stall speed 93 is induced. Moreover, an inverse flow 95 can be caused, so that the cross area is reduced.

By the above discussions, to design the slurry passage, one should consider the factors: (1) tant2, (2) tan#2 < 10 , and (3) A2/A1. For a retainer-ring 80 with an outer diameter of 25.40cm and an inner diameter of 22.86cm, referring to Fig. 8A, the diameter di of the outer cross sectional area of slurry passage 82 is about lcm. Whereas, the diameter d2 of the inner cross sectional area of the slurry passage 82 is about 1. 8cm.

The central angle 0, between two neighbouring slurry passages 82 is about 30 , and the diffusion angle 82 of each slurry passage is about 30 .

Fourth Embodiment Fig. 10 is a schematic top view of the fourth embodiment of the retainer ring 100 according to the invention. The design of the slurry passages 102 of the retainer ring 100 in this embodiment is identical to the third embodiment. These slurry passages 102 are in a form of substantially equally spaced grooves with a larger cross section in the inner end and a smaller cross section in the outer end, that is, a larger outlet and a smaller inlet. Each of these slurry passages 102 is oriented formed in a similar manner as the previous embodiment. Again, the width and depth of the slurry passages 102 depends on the specific requirements for the polishing process. That is, the dimensions of the slurry passages 102 are determined by the factors : (1) tan) 2, (2) tan) 2 < 10 and (3) A 2/A l which have been introduced in the third embodiment. In this embodiment, at least one circular path 104. for example, a circular groove, tube, channels, or guiding hole, is formed at the bottom surface of the retainer ring 100 between the outer perimeter and inner perimeter of the retainer ring 100, intercrossing all of the straight grooves 102. The circular path 104 functions as a buffer ring. The slurry being drawn in through the slurry passages 102 is partly buffered and circulating in the circular path 104, thus allowing those edge portions of the-wafer proximate to the inner ends of the slurry passages 102 to receive only a part of the slurry. Thus, the polished effect obtained from the previous embodiment, that is, an evenly and uniformly planarized surface of the wafer, is obtained without forming thinner edge portions. The circular path 104 has a similar dimension of the slurry passages 102.

Fifth Embodiment In semiconductor technique, chemical mechanical polishing is the only technique which can achieve a global planarization so far in the fabrication process of a very-or ultra-scaled integrated circuit. The CMP process can be applied in many fabrication processes, for example, to planarize an uneven surface on a semiconductor substrate to facilitate the subsequent process, for example, to obtain a precise alignment in the following photolithography etching process.

Examples of fabricating a semiconductor device by using CMP is drawn and described in the following paragraph.

In Fig. 11A, a semiconductor substrate 100 having an uneven surface 110 is provided. On the semiconductor substrate 100, a deposition layer 120 is formed. The deposition layer 120 is consequently formed with an uneven surface due to the uneven surface 110 under it.

In this invention, a CMP machine comprising the retainer ring with slurry passages is used. The CMP machine comprises a polishing table, a polishing head facing the polishing table, and a slurry supply which supplies slurry on the polishing table for polishing.

The retainer ring is disposed at the bottom edge of the polishing head. with the surface of the deposition layer 120 facing the polishing table, the semiconductor substrate 100 is disposed within the polishing head and retained by the retainer ring. The deposition layer 120 is thus planarized. It has to be noted that with the conventional CMP machine, due to the unevenly distributed slurry, the deposition layer 120 can not be planarized with an even surface as expected. By conducting the slurry through the slurry passages of the retainer ring or even through the circular path, the slurry is evenly distributed over the wafer surface, that is, the surface of the deposition layer 120, a uniformly planarized surface can be obtained as shown in Fig. 11B.

The CMP process can also be applied for etch back, for example, to form a plug. In Fig. 12A, a substrate 200 having an opening 210 is provided. A deposition layer 220 is formed on the substrate 200 and to fill the opening 210. To form a plug within the opening, the deposition layer 220 is then etched back. Very often, a CMP process is performed for the etch back process. By using a CMP machine with the retainer ring introduced in the invention, a plug 220A with a very uniform space is formed as shown in Fig. 12B.

Another specific and widely used application for CMP process is the fabrication of a shallow trench isolation. A method of forming a shallow trench isolation is shown as Fig. 13A to Fig. 13D. In Fig.

13A, a pad oxide layer 302 with a thickness of about 100A to 150A is formed on a substrate 300, preferably, a silicon wafer. A mask layer 304, for example, a silicon nitride layer with a thickness of about 1000A to 3000A is formed to cover the pad oxide layer 302.

Etching through the mask layer 304, the pad oxide layer 302, and the substrate 300, a trench 306 is formed with a depth of about 0. 5pm.

In Fig. 13B, along side walls of the etched trench 306, a liner oxide layer 308 is formed with a thickness ranging from about 150A to 200A. An insulation layer 310 is formed to cover the mask layer 304 and to fill the trench 306. Preferably, the insulation layer 310 is formed with a thickness of about 9000A to 11000A.

Typically, a densification usually follows to obtain an improved structural quality.

In Fig. 13C using the mask layer 304 as a stop layer, the insulation layer 310 shown in Fig. 13B is polished to form an insulation plug 310a by a CMP process. By using a conventional CMP machine, since the slurry can not be supplied evenly distributed over the surface of the insulation layer 310, the particles contained within the slurry cause micro-scratches or other defects. With the formation of these microscratches and defects, in the subsequent process, a bridging or short circuit effect is likely to occur.

The yield of products is degraded.

In the invention a CMP machine having a retainer ring with slurry passages is provided. The substrate 300 is retained within the retainer ring with slurry passages. While polishing, the insulation layer 310 (Fig. 13B) is facing down on a polishing pad on a polishing table of the CMP machine to form an insulation plug 310a as shown in Fig. 13C. Since the polishing slurry is supplied evenly and uniformly distributed over the insulation layer 310, the insulation plug 310a is formed with a uniform structure without micro-scratches or defects. Using a conventional method, the mask layer 304 is removed, so that the shallow trench isolation is formed.

Claims

1. A retainer ring for use in a chemical mechanical polishing machine, comprising: a plurality of slurry passages extending from an inner surface to an outer surface of the retainer ring; and at least one circular path intercrossing the slurry passages between an inner perimeter and an outer perimeter of the retainer ring.

2. The retainer ring of claim 1, wherein the slurry passages are substantially equally spaced.

3. The retainer ring of claim 1, wherein the slurry passages are radially inclined in such a way to form an acute angle of attack against the slurry flow outside of the retainer ring.

4. The retainer ring of claim 1, wherein the retainer ring has an inner diameter larger than 4 inches (10.16cm).

5. The retainer ring of claim 1, wherein the retainer ring comprises 10 slurry passages.

6. The retainer ring of claim 1, wherein the slurry passages are each formed with a width of 0.05-0.3 mm and a depth of 2-4 mm.

7. The retainer ring of claim 1, wherein the slurry has a direct path through the slurry passages.

8. The retainer ring of claim 1, wherein said circular path is formed with a width of 0.05-0.3 mm and a depth of 2-4 mm.

9. A chemical mechanical polishing machine, comprising: a polishing table; a polishing pad on the polishing table; a slurry supplier, to supply slurry onto the polishing table for polishing a wafer; a polishing head, to dispose the wafer therein; and a retainer ring, at the bottom edge of the polishing head to retain the wafer; wherein: the wafer is retained by the retainer ring with its surface to be polished facing the polishing pad; and the retainer ring further comprises: a plurality of slurry passages extending from an inner surface of the retainer ring to an outer surface thereof to direct the slurry supplied by the slurry supplier through the retainer ring over the surface of the wafer; and a circular path intercrossing the slurry passages between an inner perimeter and an outer perimeter of the retainer ring.

10. The chemical mechanical polishing machine of claim 9, wherein the slurry passages are substantially equally spaced.

11. The chemical mechanical polishing machine of claim 9, wherein the slurry passages are radially inclined in a way to form an acute angle of attack against the slurry flow outside the retainer ring.

12. The chemical mechanical polishing machine of claim 9, wherein the retainer ring has an inner diameter larger than 4 inches (10.16cm).

13. The chemical mechanical polishing machine of claim 9, wherein the slurry passages are each formed with a width of 0.05-0.3 mm and a depth of 2-4 mm.

14. The chemical mechanical polishing machine of claim 9, wherein said circular path is formed with a width of 0.05-0.3 mm and a depth of 2-4 mm.