# Patent

## Title
Configurable polishing apparatus

## Abstract

A polishing apparatus for polishing semiconductor wafers comprises a main polishing structure, which includes a plurality of polishing tables, a plurality of polishing heads and a plurality of load-and-unload stations, and an add-on polishing structure, which includes an additional polishing table and an additional polishing head. The add-on polishing structure can be attached to the main polishing structure to form a larger polishing structure with the additional polishing table and the additional polishing head.

## Background
CROSS REFERENCE TO RELATED APPLICATION
This application is entitled to the benefit of U.S. Provisional Patent Application Ser. Nos. 60/813,498, filed on Jun. 14, 2006, 60/830,472, filed on Jul. 13, 2006, and 60/844,578, filed on Sep. 13, 2006, which are incorporated herein by reference.


FIELD OF THE INVENTION
The invention relates generally to semiconductor processing equipments, and more particularly to a polishing apparatus.
BACKGROUND OF THE INVENTION
Chemical mechanical polishing (CMP) process is widely used for planarization during fabrication of semiconductor devices. In general, CMP process involves polishing a surface of a semiconductor wafer on a polishing surface, e.g., a polishing pad, using a solution, e.g., a slurry solution, supplied between the wafer surface and the polishing surface. Depending on the CMP process, multiple CMP steps may be performed to produce a single planarized layer on the semiconductor wafer. As an example, multiple CMP steps may be performed during fabrication of a semiconductor device with copper damascene structures.
In order to facilitate multi-step CMP processes, CMP equipments with multiple polishing stations have been developed. A concern with conventional CMP equipments is that each CMP equipment can only perform specific multi-step CMP processes, which depends on the number of polishing stations of that CMP equipment. For example, a CMP equipment with two serially arranged polishing stations, which is designed for two-step serial CMP processes, cannot perform three-step serial CMP processes.
In view of this concern, what is needed is a polishing apparatus that can perform different multi-step CMP processes.
SUMMARY OF THE INVENTION
A polishing apparatus for polishing semiconductor wafers in accordance with an embodiment of the invention comprises a main polishing structure, which includes a plurality of polishing tables, a plurality of polishing heads and a plurality of load-and-unload stations, and an add-on polishing structure, which includes an additional polishing table and an additional polishing head. The add-on polishing structure can be attached to the main polishing structure to form a larger polishing structure with the additional polishing table and the additional polishing head.
A polishing apparatus for polishing semiconductor wafers in accordance with an embodiment of the invention comprises a main polishing structure and an add-on polishing structure. The main polishing structure includes a plurality of polishing tables, a plurality of polishing heads and a plurality of load-and-unload stations that are operatively coupled to a main frame structure. The polishing heads are operatively coupled to the main frame structure such that each of the polishing heads can be moved between one of the polishing tables and at least one of the load-and-unload stations. The add-on polishing structure includes an additional polishing table and an additional polishing head that are operatively coupled to an add-on frame structure. The add-on polishing structure is configured to be attached to the main polishing structure to form a larger polishing structure with the additional polishing table and the additional polishing head.
A polishing apparatus for polishing semiconductor wafers in accordance with another embodiment of the invention comprises a main polishing structure and an add-on polishing structure. The main polishing structure includes a plurality of polishing tables, a plurality of polishing heads and a plurality of load-and-unload stations that are operatively coupled to a main frame structure. The polishing tables and the load-and-unload stations are positioned such that each polishing table is situated between the load-and-unload stations. The polishing heads are operatively coupled to the main frame structure such that each of the polishing heads can be linearly moved between one of the polishing tables and two of the load-and-unload stations. The one of the polishing tables is situated between the two of the load-and-unload stations. The add-on polishing structure includes an additional polishing table, an additional polishing head and a plurality of additional load-and-unload stations that are operatively coupled to an add-on frame structure. The add-on polishing structure is configured to be attached to the main polishing structure to form a larger polishing structure with the additional polishing table, the additional polishing head and the additional load-and-unload stations.
A polishing apparatus for polishing semiconductor wafers in accordance with another embodiment of the invention comprises a main polishing structure and an add-on polishing structure. The main polishing structure includes a first polishing table, a first polishing head and a first load-and-unload station that are operatively coupled to a main frame structure. The first polishing head is operatively coupled to the main frame structure such that the first polishing head can transfer the semiconductor wafers in a linear manner from the first polishing table to the first load-and-unload station using a first linear rail. The add-on polishing structure includes a second polishing table and a second polishing head that are operatively coupled to an add-on frame structure. The second polishing head is operatively coupled to the add-on frame structure such that the second polishing head can transfer the semiconductor wafers in a linear manner from the first load-and-unload station to the second polishing table using at least a second linear rail such that the second polishing head can receive the semiconductor wafers from the first load-and-unload station and polish the semiconductor wafers on the second polishing table. The add-on polishing structure is configured to be attached to the main polishing structure such that the first linear rail and the second linear rail are aligned to form a straightly connected linear rail.
Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrated by way of example of the principles of the invention.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram of a polishing apparatus in accordance with an embodiment of the present invention.
FIG. 2 is a diagram of an expanded polishing apparatus using the polishing apparatus of FIG. 1 in accordance with an embodiment of the invention.
FIG. 3 is a front view of a frame structure of the polishing apparatus of FIG. 1 in accordance with an embodiment of the invention.
FIG. 4 is a side view of the frame structure of FIG. 3.
FIG. 5 is a front view of the polishing apparatus of FIG. 1 in accordance with an alternative embodiment of the present invention.
FIG. 6 is an enlarged view of a portion of the polishing apparatus of FIG. 5, illustrating a polishing head assembly, an associated linear drive mechanism and an associated end point detecting mechanism.
FIG. 7 is a cross-sectional view of the portion shown in FIG. 6.
FIG. 8 is a front view of the expanded polishing apparatus of FIG. 2 in accordance with an embodiment of the present invention.
FIG. 9 is a cross-sectional view of a portion of the polishing apparatus of FIG. 5, illustrating an enclosing structure in accordance with an embodiment of the invention.
FIG. 10 is a diagram showing an opening of the enclosing structure and a thin neck section in the opening in accordance with an embodiment of the invention.



DETAILED DESCRIPTION
With reference of FIG. 1, a polishing apparatus 1 in accordance with an embodiment of the invention is described. The polishing apparatus 1 comprises polishing tables 30a and 30b, load-and-unload stations 40a, 40a′, 40b, 40b′, 40c and 40c′, polishing heads 51a, 51a′, 51b and 51b′, and a frame structure 3, which is generally indicated as a rectangle in FIG. 1. The polishing tables 30a and 30b, the load-and-unload stations 40a, 40a′, 40b, 40b′, 40c and 40c′, and the polishing or carrier heads 51a, 51a′, 51b and 51b′ are directly or indirectly attached to the frame structure 3. The frame structure 3 is described in more detail below with reference to FIGS. 3 and 4.
As shown in FIG. 1, the polishing tables 30a and 30b and the load-and-unload stations 40a, 40a′, 40b, 40b′, 40c and 40c′ are attached to the frame structure 3 such that the first polishing table 30a is situated between the first and second load-and-unload stations 40a and 40a′ and the third and fourth load-and-unload stations 40b and 40b′ and the second polishing table 30b is situated between the third and fourth load-and-unload stations 40b and 40b′ and the fifth and sixth load-and-unload stations 40c and 40c′. The first polishing head 51a is operatively attached to the frame structure 3 so that the polishing head 51a can be linearly moved between the first load-and-unload station 40a, the first polishing table 30a and the third load-and-unload station 40b. The second polishing head 51a′ is also operatively attached to the frame structure 3 so that the polishing head 51a′ can be linearly moved between the second load-and-unload station 40a′, the first polishing table 30a and the fourth load-and-unload station 40b′. Similarly, the third polishing head 51b is operatively attached to the frame structure 3 so that the polishing head 51b can be moved between the third load-and-unload station 40b, the second polishing table 30b and the fifth load-and-unload station 40c and the fourth polishing head 51b′ can be moved between the fourth load-and-unload station 40b′, the second polishing table 30b and the sixth load-and-unload station 40c′. 
The operation of the polishing apparatus 1 in accordance with an embodiment of the invention is now described. Two semiconductor wafers to be polished are transferred to the first and second load-and-unload stations 40a and 40a′ by one or more external devices (not shown), e.g., wafer transfer robots. The polishing heads 51a and 51a′ then transfer the wafers from the first and second load-and-unload stations 40a and 40a′, respectively, to the first polishing table 30a, where the wafers are polished on the first polishing table 30a by the first and second polishing heads 51a and 51a′. After the wafers are polished on the first polishing table 30a, the wafers are transferred to the third and fourth load-and-unload stations 40b and 40b′ by the first and second polishing heads 51a and 51a′, respectively. The first and second polishing heads 51a and 51a′ then move back to the first and second load-and-unload stations 40a and 40a′ to process the next two wafers.
The third and fourth polishing heads 51b and 51b′ transfer the polished wafers from the third and fourth load-and-unload stations 40b and 40b′, respectively, to the second polishing table 30b, where the wafers are further polished on the second polishing table 30b by the third and fourth polishing heads 51b and 51b′. After the wafers are polished on the second polishing table 30b, the wafers are transferred to the fifth and sixth load-and-unload stations 40c and 40c′ by the third and fourth polishing heads 51b and 51b′, respectively. The polished wafers on the fifth and sixth load-and-unload stations 40c and 40c′ can then be transferred to the next destination by one or more external devices (not shown), e.g., wafer transfer robots. The third and fourth polishing heads 51b and 51b′ then move back to the third and fourth load-and-unload stations 40b and 40b′ to continue to process the next two wafers.
In order to polish the wafers on the polishing tables 30a and 30b, a solution is dispensed on the polishing tables. In an embodiment, slurry containing abrasive particles is dispensed on polishing pads, which are attached on the polishing tables 30a and 30b. The polishing pads on the polishing tables 30a and 30b are conditioned by pad conditioners 91a and 91b, which are operatively attached to the frame structure 3 such that each pad conditioner can be moved in a linear manner to access different parts of the polishing pad being conditioned by that pad conditioner.
Since the polishing apparatus 1 has two polishing tables, the polishing apparatus 1 can sequentially perform two sequential or serial CMP processes on semiconductor wafers. Thus, the polishing apparatus 1 can be used to execute fabrication methods that require two serial CMP processes. However, unlike conventional polishing equipment, the polishing apparatus 1 can be modified or configured to perform more than two serial CMP processes.
In an embodiment, the polishing apparatus 1 can be converted into a larger, expanded polishing apparatus 10, which is shown in FIG. 2, by attaching an add-on polishing structure 5 to the polishing apparatus 1. Thus, the polishing apparatus 1 is the main polishing structure to which the add-on polishing structure 5 is attached to form the expanded polishing apparatus 10. As shown in FIG. 2, the add-on polishing structure 5 includes a polishing table 30c, load-and-unload stations 40d and 40d′, polishing heads 51c and 51c′, a pad conditioner 91c, and an add-on frame structure 7, which is generally indicated as a rectangle in FIG. 2. The polishing table 30c, the load-and-unload stations 40d and 40d′, and the polishing heads 51d and 51d′ are directly or indirectly attached to the add-on frame structure 7. The add-on frame structure 7 is described in more detail below with reference to FIG. 8.
As shown in FIG. 2, the third polishing table 30c and the seventh and eight load-and-unload stations 40d and 40d′ are attached to the add-on frame structure 7 such that third polishing table 30c is positioned between the fifth and sixth load-and-unload stations 40c and 40c′ and the seventh and eighth load-and-unload stations 40d and 40d′ when the add-on polishing structure 5 is attached to the polishing apparatus 1. The fifth polishing head 51c is operatively attached to the add-on frame structure 7 so that the fifth polishing head 51c can be linearly moved between the fifth load-and-unload station 40c, the third polishing table 30c and the seventh load-and-unload station 40d. The sixth polishing head 51c′ is also operatively attached to the add-on frame structure 7 so that the sixth polishing head 51c′ can be linearly moved between the sixth load-and-unload station 40c′, the third polishing table 30c and the eighth load-and-unload station 40d′. 
The operation of the expanded polishing apparatus 10 in accordance with an embodiment of the invention is now described. The operation of the expanded polishing apparatus 10 with respect to the section corresponding to the original polishing apparatus 1 is similar to the operation of the polishing apparatus 1 of FIG. 1, and thus, will not be repeated. After the wafers are transferred to the fifth and sixth load-and-unload stations 40c and 40c′ by the third and fourth polishing heads 51b and 51b′, respectively, the fifth and sixth polishing heads 51c and 51c′ transfer the wafers from the fifth and sixth load-and-unload stations 40c and 40c′, respectively, to the third polishing table 30c, where the wafers are polished on the third polishing table 30c by the fifth and sixth polishing heads 51c and 51c′. After the wafers are polished on the third polishing table 30c, the wafers are transferred to the seventh and eighth load-and-unload stations 40d and 40d′ by the fifth and sixth polishing heads 51c and 51c′, respectively. The polished wafers on the seventh and eighth load-and-unload stations 40d and 40d′ can then be transferred to the next destination by one or more external devices (not shown), e.g., wafer transfer robots. The fifth and sixth polishing heads 51c and 51c′ then move back to the fifth and sixth load-and-unload stations 40c and 40c′ to continue to process the next two wafers.
In order to polish the wafers on the third polishing table 30c, a solution is dispensed on the third polishing table 30c. In an embodiment, slurry containing abrasive particles is dispensed on a polishing pad, which is attached on the third polishing table 30c. The polishing pad on the third polishing table 30c is conditioned by the third pad conditioner 91c, which is operatively attached to the add-on frame structure 7 so that the third pad conditioner 91c can be moved in a linear manner to access different parts of the polishing pad on the third polishing table 30c. 
Since the expanded polishing apparatus 10 has three polishing tables, the expanded polishing apparatus can sequentially perform three serial CMP processes on semiconductor wafers. Thus, the polishing apparatus 1 can be used to sequentially perform two serial CMP processes, or be converted to the polishing apparatus 10 to sequentially perform three serial CMP processes. However, in other embodiments, the polishing apparatus 1 and/or the expanded polishing apparatus 10 may be modified to include more than the described numbers of polishing tables so that the polishing apparatus 1 can sequentially perform more than two serial CMP processes and/or the expanded polishing apparatus 10 can sequentially perform more than three serial CMP processes. In other embodiments, more than one add-on polishing structure may be attached to the polishing apparatus 1 to form a larger polishing structure with more polishing tables.
Turning now to FIGS. 3 and 4, the frame structure 3 in accordance with an embodiment of the invention is shown. FIG. 3 shows a front view of the frame structure 3 of the polishing apparatus 1. FIG. 4 shows a side view of the frame structure 3 of the polishing apparatus 1.
As best shown in FIG. 3, the frame structure 3 includes lower supporting structures 21a, 21b and 21c. The first lower supporting structure 21a comprises a vertical portion 26a and a tilted portion 26a′, as illustrated in FIG. 4. One of the ends of the vertical portion 26a is connected to a first base frame 23a near a first end of the first base frame 23a, which is mounted on legs 24a. The other end of the vertical portion 26a is connected to one of the ends of the tilted portion 26a′. The other end of the tilted portion 26a′ is connected to a central portion of a bottom surface of a first middle mounting plate 25a. 
The second lower supporting structure 21b also comprises a vertical portion 26b and a tilted portion 26b′. One of the ends of the vertical portion 26b is connected to a second base frame 32b near a first end of the second base frame 23b, which is mounted on legs 24b. The other end of the vertical portion 26b is connected to one of the ends of the tilted portion 26b′. The other end of the tilted portion 26b′ is connected to a central portion of a bottom surface of a second middle mounting plate 25b. 
The third lower supporting structure 21c also comprises a vertical portion 26c and a tilted portion 26c′. One of the ends of the vertical portion 26c is connected to a third base frame 23c near a first end of the third base frame 23c, which is mounted on legs 24c. The other end of the vertical portion 26c is connected to one of the ends of the tilted portion 26c′. The other end of the tilted portion 26c′ is connected to a central portion of a bottom surface of a third middle mounting plate 25c. 
The frame structure 3 further includes a lower mounting plate 22a, which is mounted to the vertical portions 26a-26c of the first, second and third lower supporting structures 21a-21c. The frame structure 3 also includes upper supporting structures 11a, 11b and 11c. The first upper supporting structure 11a is mounted on a top surface of the first middle mounting plate 25a. The second upper supporting structure 11b is mounted on a top surface of the second middle mounting plate 25b. The third upper supporting structure 11c is mounted on a top surface of the third middle mounting plate 25c. 
The frame structure 3 further includes an upper mounting plate 12a, which is welded to the upper supporting structures 11a and 11b such that a first side end of the mounting plate 12a is connected to the first upper supporting structure 11a and a bottom surface of the mounting plate 12a is mounted on the second upper supporting structure 11b. The upper mounting plate 12a is jointed to the third upper supporting structure 11c such that a second side end of the mounting plate 12a is jointed to the third upper supporting structure 11c. The upper supporting structure 11c comprises a male portion 18, which is jointed to a female portion of the second side end of the upper mounting plate 12a. The frame structure 3 also includes an upper frame 17a, which is mounted to the first and third upper supporting structures 11a and 11c at their tops.
Mounted on the mounting plate 12a are lower linear rails 13a and 13a′, upper linear rails 14a and 14a′ and conditioner linear rails 15a and 15b. The first lower linear rail 13a and the first upper linear rail 14a are mounted on the front vertical surface of the mounting plate 12a such that the rails 13a and 14a are parallel to a longitudinal side of the front surface of the mounting plate 12a. Thus, the rails 13a and 14a are parallel to each other. The second lower linear rail 13a′ and the second upper linear rail 14a′ are mounted on the back vertical surface of the mounting plate 12a such that the rails 13a′ and 14a′ are parallel to a longitudinal side of the back surface of the mounting plate 12a. Thus, the rails 13a′ and 14a′ are parallel to each other, and also to the rails 13a and 14a. The first conditioner linear rail 15a and the second conditioner linear rail 15b are mounted to the bottom surface of the mounting plate 12a, and are also parallel to the rails 13a, 13a′, 14a and 14a′. The bottom surface of the mounting plate 12a is perpendicular to the front and back surfaces of the mounting plate 12a. The conditioner linear rails 15a and 15b are separated by the second upper supporting structure 11b, which is connected to the bottom surface of the mounting plate 12a. 
Turning now to FIG. 5, a front view of the polishing apparatus 1 is shown. In FIG. 5, the frame structure 3 of FIG. 3 is shown with the polishing tables 30a and 30b, the load-and-unload stations 40a, 40a′, 40b, 40b′, 40c and 40c′, and the polishing heads 51a, 51a′, 51b and 51b′. However, in FIG. 5, the load-and-unload stations 40a′, 40b′ and 40c′, and the polishing heads 51a′ and 51b′ are hidden from view. As illustrated in FIG. 5, the polishing apparatus 1 further include a polishing head assembly for each of the polishing heads 51a, 51a′, 51b and 51b′ and a pad conditioner assembly for each of the pad conditioners 91a and 91b. In FIG. 5, only the polishing head assemblies 50a and 50b for the polishing heads 51a and 51b, respectively, are shown. The other two polishing head assemblies 50a′ and 50b′ for the polishing heads 51a′ and 51b′, respectively, are hidden from view. However, these hidden polishing head assemblies are similar to the shown polishing head assemblies 50a and 50b. Also shown in FIG. 5 are polishing table drive mechanisms 32a and 32b, which rotate the polishing tables 30a and 30b. 
The polishing table drive mechanisms 32a and 32b are mounted to the first lower mounting plate 22a of the frame structure 3. The polishing tables 30a and 30b are connected to the polishing table drive mechanisms 32a and 32b through rotation shafts 31a and 31b, respectively. The polishing table 30a is rotated by the polishing table drive mechanism 32a via the rotation shaft 31a. Similarly, the polishing table 30b is rotated by the polishing table drive mechanism 32b via the rotation shaft 31b. 
The first and second load-and-unload stations 40a and 40a′ are mounted to the top surface of the first middle mounting plate 25a. The third and fourth load-and-unload stations 40b and 40b′ are mounted to the top surface of the second middle mounting plate 25b. The fifth and sixth load-and-unload stations 40c and 40c′ are mounted to the top surface of the third middle mounting plate 25c. 
The first and third polishing head assemblies 50a and 50b are mounted to the first lower and upper linear rails 13a and 14a such that these polishing head assemblies 50a and 50b, which includes the polishing heads 51a and 51b, respectively, can move linearly along the rails 13a and 14a. Similarly, the second polishing head assembly 50a′ (not shown) and the fourth polishing head assembly 50b′ (not shown) are mounted to the second lower and upper linear rails 13a′ and 14a′ (not shown) such that these polishing head assemblies 50a′ and 50b′, which include the polishing heads 51a′ and 51b′, respectively, can move linearly along the rails 13a′ and 14a′. 
The first and second pad conditioner assemblies 90a and 90b are mounted to the first and second conditioner linear rails 15a and 15b such that these pad conditioner assemblies 90a and 90b, which include the pad conditioner 91a and 91b, respectively, can move linearly along the rails 15a and 15b, respectively.
In order to detect the end point of a polishing process at each of the polishing tables 30a and 30b, a current sensor 34 that is coupled to the polishing table drive mechanism 32a or 32b for that polishing table can be used. The current sensor 34 detects current that is used to spin a motor of the polishing table drive mechanism 32a or 32b. When frictional force between the polishing pad on the polishing table 30a or 30b and the two wafers being polished on that polishing pad changes, the current is changed in order to keep the spinning speed constant without being affected by the frictional force change. The current sensor 34 detects the current change, which can be used to determine the end point.
However, the current sensor 34 cannot be used to tell which of the two wafers that are polished at the same time on the same polishing table 30a or 30b is reaching or approaching the end point. To solve this problem, the current sensor 34 can be used in conjunction with load cells or other current sensors to determine the polishing end point for each of the two wafers being polished on the same polishing table 30a or 30b. 
With reference to FIGS. 6 and 7, the polishing head assembly 50a, an associated linear drive mechanism and an associated end point detecting mechanism are described. Since the polishing head assemblies 50a, 50a′, 50b and 50b′ are similar to each other, the description of the polishing head assembly 50a and the associated mechanisms will also serve as a description of the other polishing head assemblies and their linear drive mechanisms and end point detecting mechanisms. FIG. 6 is a front view of the polishing head assembly 50a, the associated linear drive mechanism and the associated end point detecting mechanism. FIG. 7 is a side view from the cross section A of FIG. 6.
The polishing head 51a is connected to a head rotating mechanism 53a through a head rotating shaft 52a. The head rotating mechanism 53a is connected to a supporting plate 54a, which is connected to a head vertical drive mechanism 56a through a shaft 55a. The head vertical drive mechanism 56a is mounted to a head assembly plate 45a. The supporting plate 54a is slidably mounted to a guide rail plate 46a such that the polishing head 51a can move vertically by the head vertical drive mechanism 56a along a guide rail of the guide rail plate 46a. The head assembly plate 45a is slidably coupled to the first lower and upper linear rails 13a and 14a through a lower rail gripper 47a and an upper rail gripper 48a. The lower and upper rail grippers 47a and 48a are slidably coupled to the lower and upper linear rails 13a and 14a, respectively.
A lead nut 61a is coupled to the head assembly plate 45a. The lead nut 61a is also coupled to a lead screw 71a. One end of the lead screw 71a is connected to a head transport motor 70a, which is suspended from the upper frame 17a by at least one elastic metallic or polymeric plate 72a. The other end of the lead screw 71a is connected to a bearing 70b, which is suspended from the upper frame 17a by at least elastic metallic or polymeric plate 72b. The lead nut 61a moves back and forth along the lead screw 71a as the lead screw 71a is rotated by the head transport motor 70a. 
First and second position sensors 73a and 73b are mounted to the first upper frame 17a so that these position sensors can detect when the polishing head assembly 50a passes the position sensors. A reference pin 62a is mounted to the head assembly plate 45a so that the reference pin triggers one of the position sensors 73a and 73b when the polishing head assembly 50a passes that position sensor. The positioning sensors 73a and 73b may be magnetic sensors or photo sensors.
The position of the first position sensor 73a is set along the upper frame 17a such that first polishing head 51a is vertically aligned with the first load-and-unload station 40a when the first position sensor 73a detects the reference pin 62a. Similarly, the position of the second position sensor 73b is set along the upper frame 17a such that second polishing head 51a is vertically aligned with the third load-and-unload station 40b when the second position sensor 73b detects the reference pin 62a. 
In an embodiment, a load cell 74a is used along with the current sensor 34 to detect the end point of a polishing process for the semiconductor wafer being polished by the first polishing head 51a on the first polishing table 30a. The load cell 74a is coupled to a first connect 75a, which is rigidly connected to the head transport motor 70a. The load cell 74a is also coupled to a second connect 76a, which is rigidly connected to the upper frame 17a. 
During a polishing process, the first polishing head 51a moves linearly back and forth along the lead screw 71a in a cyclic manner. The torque to move the first polishing head assembly 50a back and forth is detected by the load cell 74a. The torque changes as frictional force between the polishing pad on the first polishing table 30a and the wafer being polished by the first polishing head 51a changes. The frictional force changes either when a top layer deposited on the wafer is planarized or when an under-layer deposited on the wafer is exposed after the top layer is removed by the polishing process. By detecting changes in torque using the load cell 74a and changes in current to the motor of the polishing table drive mechanism 32a using the current sensor 34, the end point of the polishing process is detected. A similar load cell for the second polishing head 51a′ can be used to detect the end point of a polishing process for the wafer being polished by the second polishing head. Thus, the end point for each of the two wafers being simultaneously polished on the first polishing table 30a can be detected individually.
Specifically, by monitoring torque changes of two wafers being polished by two polishing heads on the same polishing table using the load cells associated with the two polishing heads, the wafer that is reaching or approaching the end point is identified. After identifying the wafer that is reaching or approaching the end point, the current sensor 34 coupled to the polishing table drive mechanism for the polishing table is used to detect and determine the end point of the wafer. After one of the two wafers has reached the end point, the polishing process for that wafer is stopped but the polishing process for the other wafer continues until the current sensor 34 detects and determines end point of the other wafer. This end point detecting and determining algorithm using the current sensor 34 with the help of load cells works well when signals obtained from the current sensor 34 has better quality (less noise) than signals obtained from the load cells.
In an alternative embodiment, rather than a load cell, a current sensor 36a that is coupled to the head rotating mechanism 53a is used along with the current sensor 34 to detect the end point of a polishing process for the semiconductor wafer being polished by the first polishing head 51a on the first polishing table 30a. The current sensor 36a detects changes in electrical current that is used to rotate the polishing head 51a by the head rotating mechanism 53a. When frictional force between the polishing pad on the polishing table 30a and the wafer being polished by the first polishing head 51a changes, the current to a motor of the head rotating mechanism 53a is changed in order to keep the spinning speed constant. The current sensor 36 detects this change in current. By detecting changes in current to the motor of the head rotating mechanism 53a using the current sensor 36a and changes in current to the motor of the polishing table drive mechanism 32a using the current sensor 34, the end point of the polishing process is detected. A similar current sensor for the second polishing head 51a′ can be used to detect the end point of a polishing process for the wafer being polished by the second polishing head. Thus, the end point for each of the two wafers being simultaneously polished on the first polishing table 30a can be detected individually.
Specifically, by monitoring changes in current to rotate the two wafers using the current sensors associated with the two polishing heads, the wafer that is reaching or approaching the end point is identified. After identifying the wafer that is reaching or approaching the end point, the current sensor 34 coupled to the polishing table drive mechanism for the polishing table is used to detect and determine the end point of the wafer. After one of the two wafers has reached the end point, the polishing process for that wafer is stopped but the polishing process for the other wafer continues until the current sensor 34 detects and determines end point of the other wafer. This end point detecting and determining algorithm using the multiple current sensors works well when signals obtained from the current sensor 34 for the polishing table has better quality (less noise) than signals obtained from the current sensors for the polishing heads.
The pad conditioner assembly 90a is now described with reference to FIGS. 6 and 7. The pad conditioner head 91a is connected to a conditioner rotating-and-vertical drive mechanism 92a, which is connected to a lead nut 93a. The lead nut 93a is slidably coupled to the conditioner linear rail 15a and a lead screw 94a. One end of the lead screw 94a is connected to a conditioner transport motor (not shown). The conditioner linear transport motor is mounted to the first upper mounting plate 12a. The lead nut 93a moves along the lead screw 94a as the lead screw 94a is rotated by the conditioner linear transport motor.
Turning now to FIG. 8, a front view of the expanded polishing apparatus 10 of FIG. 2 is shown. In order to convert the polishing apparatus 1 to the expanded polishing apparatus 10, the third upper supporting structure 11c of the polishing apparatus 1 is replaced with an upper frame assembly of the add-on frame structure 7, which is part of the add-on polishing structure 5. The add-on frame structure 7 also includes a second upper frame 17b, a fourth lower supporting structure 21d, a second lower mounting plate 22b, a fourth base frame 23d, legs 24d and a fourth middle mounting plate 25d. The upper frame assembly comprises a fourth upper supporting structure 33, a fifth upper supporting structure 33′ and a second upper mounting plate 12b, which are welded together. The fourth upper supporting structure 33 comprises a male portion 18′, which is firmly jointed to the female portion of the first upper mounting plate 12a. The fourth upper supporting structure 33 is mounted on the top surface of the third middle mounting plate 25c. The fifth upper supporting structure 33′ is mounted on a top surface of the fourth middle mounting plate 25d. The second upper frame 17b is mounted to the fourth and fifth supporting structures 33 and 33′ at their tops.
The fourth middle mounting plate 25d is mounted to the fourth lower supporting structure 21d, which comprises a vertical portion 26d and a tilted portion 26d′. One of the ends of the vertical portion 26d is connected to the fourth base frame 23d near a first end of the fourth base frame 23d, which is mounted on the legs 24d. The other end of the vertical portion 26d is connected to one of the ends of the tilted portion 26d40 . The other end of the tilted portion 26d′ is connected to a central portion of a bottom surface of the fourth middle mounting plate 25d. 
The seventh and eighth load-and-unload stations 40d and 40d′ are mounted to the fourth middle mounting plate 25d. The second lower mounting plate 22b is mounted to the vertical portions 26c and 26d of the third and fourth lower supporting structures 21c and 21d. 
The add-on polishing structure 5 further includes a third polishing table drive mechanism 32c, which is mounted to the second lower mounting plate 22b. The third polishing table 30c is connected to the third polishing table drive mechanism 32c through a rotation shaft 31c. The third polishing table 30c is rotated by the polishing table drive mechanism 32c via the rotation shaft 31c. 
The add-on polishing structure 5 further includes lower linear rail 13b and 13b′, upper linear rails 14b and 14b′ and a conditioner linear rail 15c, which are mounted on the second upper mounting plate 12b. The lower linear rail 13b′ and the upper linear rail 14b′ are not shown in FIG. 8. The third lower linear rail 13b and the third upper linear rail 14b are mounted on the front vertical surface of the second mounting plate 12b such that the rails 13b and 14b are parallel to a longitudinal side of the front surface of the second mounting plate 12b. Thus, the rails 13b and 14b are parallel to each other. One end of the third lower linear rail 13b is aligned with one end of the first lower linear rail 13a such that the third lower linear rail 13b and the first lower linear rail 13a form a straightly connected lower linear rail. Similarly, one end of the third upper linear rail 14b is aligned with one end of the first upper linear rail 14a such that the third upper linear rail 14b and the first upper linear rail 14a form a straightly connected upper linear rail. Similar to the third lower linear rail 13b and the third upper linear rail 14b, the fourth lower linear rail 13b′ and the fourth upper linear rail 14b′ are mounted on the back vertical surface of the second mounting plate 12b′ such that the rails 13b′ and 14b′ are parallel to a longitudinal side of the back surface of the second mounting plate 12b. Thus, the rails 13b′ and 14b′ are parallel to each other, and also to the rails 13b and 14b. One end of the fourth lower linear rail 13b′ is aligned with one end of the second lower linear rail 13a′ such that the fourth lower linear rail 13b′ and the second lower linear rail 13a′ form another straightly connected lower linear rail. Similarly, one end of the fourth upper linear rail 14b′ is aligned with one end of the second upper linear rail 14a′ such that the fourth upper linear rail 14b′ and the second upper linear rail 14a′ form another straightly connected upper linear rail.
The fifth polishing head assembly 50c is mounted to the third lower and upper linear rails 13b and 14b. The fifth polishing head assembly 50c moves linearly between the fifth load-and-unload station 40c, the third polishing table 30c and the seventh load-and-unload station 40d along the straightly connected lower linear rail formed by the first and third lower linear rails 13a and 13b and the straightly connected upper linear rail formed by the first and third upper linear rails 14a and 14b. The fifth polishing head assembly 50c is linearly moved using a lead screw 71c connected to a head transport motor 70a′′ in a similar manner as the first polishing head assembly 50a using the lead screw 71a and the head transport motor 70a, which was previously described with reference FIGS. 6 and 7.
Although not shown, the sixth polishing head assembly 50c′ is mounted to the fourth lower and upper linear rails 13b′ and 14b′. The sixth polishing head assembly 50c′ moves linearly between the sixth load-and-unload station 40c′, the third polishing table 30c and the eighth load-and-unload station 40d′ along the straightly connected lower linear rail formed by the second and fourth lower linear rails 13a′ and 13b′ and the straightly connected upper linear rail formed by the second and fourth upper linear rails 14a′ and 14b′. The sixth polishing head assembly 50c′ is linearly moved using a lead screw connected to a head transport motor in a similar manner as the first polishing head assembly 50a using the lead screw 71a and the head transport motor 70a, which was previously described with reference FIGS. 6 and 7.
In an embodiment, a load cell (not shown) is used to detect changes in torque with respect to each of the fifth and sixth polishing head assemblies 50c and 50c′. The load cell for each of the fifth and sixth polishing head assemblies 50c and 50c′ is used with a current sensor 34 that is coupled to a motor of the polishing table drive mechanism 32c to detect the end point of a polishing process for each wafer being polished by the polishing heads 51c and 51c′. In an alternative embodiment, additional current sensors 36c or 36c′ (the current sensor 36c′ not shown) in the fifth and sixth polishing head assemblies 50c and 50c′ are used to detect changes in current being used to rotate the polishing heads 51c and 51c′. The additional current sensors 36c or 36c′ for the fifth and sixth polishing head assemblies 50c and 50c′ are used with the current sensor 34 that is coupled to a motor of the polishing table drive mechanism 32c to detect the end point of a polishing process for each wafer being polished by the polishing heads 51c and 51c′. 
The third conditioner linear rail 15c is mounted to the bottom surface of the second mounting plate 12b, and are also parallel to the rails 13b, 13b′, 14b and 14b′. The bottom surface of the second mounting plate 12b is perpendicular to the front and back surfaces of the second mounting plate 12b. The third pad conditioner assembly 90c is slidably coupled to the third conditioner linear rail 15c. 
With reference to FIG. 9, a pad conditioner assembly for the polishing apparatus 1 according to an embodiment of the invention is described. In the polishing apparatus 1 of FIG. 9, the conditioner rotating-and-vertical drive mechanism 92a is connected to a mounting plate 77. The mounting plate 77 has a shape of “”, which includes an upper horizontal portion 77a, a lower horizontal portion 77b and a vertical portion 77c. The upper horizontal potion 77a of the mounting plate 77 comprises a thin neck portion 81, which is similar to thin neck portions 81 of the lower and upper rail grippers 47a, 48a, 47a′ and 48a′ that are described below. The upper horizontal portion 77a of the mounting plate 77 is coupled to the lead nut 93a. The lower horizontal portion 77b of the mounting plate 77 is connected to the conditioner rotating-and-vertical drive mechanism 92a. The upper horizontal potion 77a and the lower horizontal portion 77b are connected to each other through the vertical portion 77c. 
The lead nut 93a is slidably coupled to the conditioner linear rail 15a and the lead screw 94a. One end of the lead screw 94a is connected to the conditioner transport motor (not shown). The conditioner linear transport motor is mounted to the first upper mounting plate 12a. The lead nut 93a moves along the lead screw 94a as the lead screw 94a is rotated by the conditioner linear transport motor.
With reference to FIG. 9, an enclosing structure 78 for the polishing apparatus 1 in accordance with an embodiment of the invention is described. FIG. 9 shows a cross section of the enclosing structure 78 and the polishing apparatus 1. In the polishing apparatus 1 of FIG. 9, the lower and upper rail grippers 47a, 48a, 47a′ and 48a′ are connected to the respective head assembly plates 45a and 45a′ through their respective thin neck portions 81.
As shown in FIG. 9, the enclosing structure 78 encloses the first upper mounting plate 12a, the lower linear rails 13a and 13a′, the upper linear rails 14a and 14a′, the conditioner linear rails 15a, most of the lower rail grippers 47a and 47a′, most of the upper rail grippers 48a and 48a′, the lead nut 93a, the lead screw 94a, and all other similar components of the polishing apparatus 1. The enclosing structure 78 also encloses a part of the horizontal portion 77a of the mounting plate 77. The enclosing structure 78 does not enclose the horizontal portion 77b of the mounting plate 77. Thus, the polishing heads 51a, 51a′, 51b, 51b′, 51c and 51c′ and the pad conditioner 91a and 91b are external to the enclosing structure 78. Although the enclosing structure 78 is described with reference to the polishing apparatus 1, the enclosing structure 78 may be modified to be used with the expanded polishing apparatus 10 to enclose similar components of the expanded polishing apparatus 10.
The enclosing structure 78 comprises linearly elongated openings for the thin neck portions 81 of the lower and upper rail grippers 47a, 48a, 47a′ and 48a′ and the thin neck portion 81 of the mounting plate 77. The neck portions 81 move along the openings of the enclosing structure 78. The openings are sealed with soft polymeric material 79, such as Teflon, polyurethane and silicon rubber, such that friction between the neck portions 81 and the sealing do not generate hard particles that may fall into the polishing pads and damage the wafers. The neck portions 81 of the lower and upper rail grippers 47a, 48a, 47a′ and 48a′ move through the sealing when the associated head assembly moves along the linear rails 13a and 14a or the linear rails 13a′ and 14a′. Similarly, the thin neck portion 81 of the mounting plate 77 moves through the sealing when the pad conditioner 91a and other components connected to the pad conditioner 91a move along the linear rail 15a. The neck portions 81 may be coated with same soft polymeric material 79 that is used for the sealing.
As illustrated in FIG. 10, both ends 83 of each neck portion 81 may be shaped to be sharp. That is, each end 83 of the neck portion 81 may taper to a sharp point. This configuration ensures that the opening of the enclosing structure 78 is tightly sealed at the ends 83 of the neck portion 81 by the sealing, as shown in FIG. 10.
Although the foregoing description sets forth exemplary embodiments and methods of operation of the invention, the scope of the invention is not limited to these specific embodiments or described methods of operation. Many details have been disclosed that are not necessary to practice the invention, but have been included to sufficiently disclose the best mode of operation, and manner and process of making and using the invention. Modification may be made to the specific form and design of the invention without departing from its spirit and scope as expressed in the following claims.

## Claims

1. A polishing apparatus for polishing semiconductor wafers comprising:
a main polishing structure including a plurality of polishing tables, a plurality of polishing heads and a plurality of load-and-unload stations that are operatively coupled to a main frame structure, said polishing heads being operatively coupled to said main frame structure such that each of said polishing heads can be moved between one of said polishing tables and at least one of said load-and-unload stations, wherein said polishing heads are operatively attached to said main frame structure such that each of said polishing heads can be linearly moved between said one of said polishing tables and said at least one of said load-and-unload stations; and
an add-on polishing structure including an additional polishing table and an additional polishing head that are operatively coupled to an add-on frame structure, said add-on polishing structure being configured to be attached to said main polishing structure to form a larger polishing structure with said additional polishing table and said additional polishing head.

2. The polishing apparatus of claim 1 wherein said add-on polishing structure is attached to said main polishing structure, wherein said add-on polishing structure further includes at least one additional load-and-unload station, and wherein said additional polishing head is operatively attached to said add-on frame structure such that said additional polishing head can be linearly moved between said additional polishing table, said at least one additional load-and-unload station and one of said load-and-unload stations of said main polishing structure.

3. The polishing apparatus of claim 1 wherein said polishing heads are operatively attached to said main frame structure such that each of said polishing heads can be linearly moved between two of said load-and-unload stations and one of said polishing tables that is situated between said two of said load-and-unload stations.

4. The polishing apparatus of claim 3 wherein pairs of said polishing heads are operatively attached to said main frame structure such that each pair of said polishing heads can be linearly moved to one of said polishing tables to simultaneously polish wafers on that polishing table.

5. The polishing apparatus of claim 1 wherein said main frame structure includes an upper mounting plate with at least one linear rail mounted on a vertical surface of said upper mounting plate, said at least one linear rail being used to linearly guide at least one of said polishing heads.

6. The polishing apparatus of claim 5 wherein at least one additional linear rail is mounted on another vertical surface of said upper mounting plate, said another vertical surface being the opposite surface of said vertical surface, said at least one additional linear rail being used to linearly guide at least another one of said polishing heads.

7. The polishing apparatus of claim 5 wherein said main polishing structure includes a lead screw connected to a head transport motor for each of said polishing heads, said lead screw and said head transport motor being used to linearly move that polishing head.

8. The polishing apparatus of claim 5 wherein said main polishing structure includes a load cell connected to said head transport motor for at least one of said polishing heads to detect changes in torque for polishing end point detection, and wherein said main polishing structure includes a current sensor connected to a polishing table drive mechanism for at least one of said polishing tables to detect changes in electrical current being used by said polishing table drive mechanism, said load cell being used in conjunction with said current sensor for said polishing end point detection.

9. The polishing apparatus of claim 5 wherein said main polishing structure includes a current sensor connected to a head rotating mechanism for at least one of said polishing heads to detect changes in electrical current being used by said head rotating mechanism, and wherein said main polishing structure includes another current sensor connected to a polishing table drive mechanism for at least one of said polishing tables to detect changes in electrical current being used by said polishing table drive mechanism, said current sensor being used in conjunction with said another current sensor for said polishing end point detection.

10. The polishing apparatus of claim 5 wherein said add-on frame structure includes an additional upper mounting plate with at least one additional linear rail mounted on a vertical surface of said additional upper mounting plate, said at least one additional linear rail being aligned with said at least one linear rail of said main frame structure when said add-on polishing structure is attached to said main polishing structure, said at least one additional linear rail being used to linearly guide said additional polishing head.

11. The polishing apparatus of claim 5 wherein said main polishing structure includes a pad conditioner for each of said polishing tables, and wherein a conditioner linear rail is mounted on a bottom surface of said upper mounting plate, said conditioner linear rail being used to linearly guide said pad conditioner.

12. The polishing apparatus of claim 11 wherein said pad conditioner is attached to a mounting plate that has a shape of “”, said mounting plate including an upper horizontal portion, a lower horizontal portion and a vertical portion that connects said upper and lower horizontal portions, said mounting plate being used to connect said pad conditioner to said conditioner linear rail.

13. The polishing apparatus of claim 12 further comprising an enclosing structure to enclose said upper mounting plate such that said polishing heads and said pad conditioner are external to said enclosing structure, said enclosing structure including openings to accommodate neck portions of rail grippers for said polishing heads and said upper horizontal portion of said mounting plate, said rail grippers being used to connect said polishing heads to said at least one linear rail.

14. The polishing apparatus of claim 13 wherein at least some of said openings of said enclosing structure are sealed with sealing material, and wherein said neck portions are configured such that each neck portion tapers to a point at both ends so that said openings of said enclosing structure are sealed by said sealing material at said both ends of said neck portions.

15. A polishing apparatus for polishing semiconductor wafers comprising:
a main polishing structure including a plurality of polishing tables, a plurality of polishing heads and a plurality of load-and-unload stations that are operatively coupled to a main frame structure, said polishing tables and said load-and-unload stations being positioned such that each polishing table is situated between said load-and-unload stations, said polishing heads being operatively coupled to said main frame structure such that each of said polishing heads can be linearly moved between one of said polishing tables and two of said load-and-unload stations, said one of said polishing tables being situated between said two of said load-and-unload stations; and
an add-on polishing structure including an additional polishing table, an additional polishing head and a plurality of additional load-and-unload stations that are operatively coupled to an add-on frame structure, said add-on polishing structure being configured to be attached to said main polishing structure to form a larger polishing structure with said additional polishing table, said additional polishing head and said additional load-and-unload stations.

16. The polishing apparatus of claim 15 wherein said add-on polishing structure is attached to said main polishing structure, and wherein said additional polishing head is operatively attached to said add-on frame structure such that said additional polishing heads can be linearly moved between said additional polishing table, one of said additional load-and-unload station and one of said load-and-unload stations of said main polishing structure.

17. The polishing apparatus of claim 15 wherein pairs of said polishing heads are operatively attached to said main frame structure such that each pair of said polishing heads can be linearly moved to one of said polishing tables to simultaneously polish wafers on that polishing table.

18. The polishing apparatus of claim 15 wherein said main frame structure includes an upper mounting plate with at least one linear rail mounted on a vertical surface of said upper mounting plate, said at least one linear rail being used to linearly guide at least one of said polishing heads.

19. The polishing apparatus of claim 18 wherein at least one additional linear rail is mounted on another vertical surface of said upper mounting plate, said another vertical surface being the opposite surface of said vertical surface, said at least one additional linear rail being used to linearly guide at least another one of said polishing heads.

20. The polishing apparatus of claim 18 wherein said main polishing structure includes a lead screw connected to a head transport motor for each of said polishing heads, said lead screw and said head transport motor being used to linearly move that polishing head.

21. The polishing apparatus of claim 18 wherein said main polishing structure includes a load cell connected to said head transport motor for at least one of said polishing heads to detect changes in torque for polishing end point detection, and wherein said main polishing structure includes a current sensor connected to a polishing table drive mechanism for at least one of said polishing tables to detect changes in electrical current being used by said polishing table drive mechanism, said load cell being used in conjunction with said current sensor for said polishing end point detection.

22. The polishing apparatus of claim 18 wherein said main polishing structure includes a current sensor connected to a head rotating mechanism for at least one of said polishing heads to detect changes in electrical current being used by said head rotating mechanism, and wherein said main polishing structure includes another current sensor connected to a polishing table drive mechanism for at least one of said polishing tables to detect changes in electrical current being used by said polishing table drive mechanism, said current sensor being used in conjunction with said another current sensor for polishing end point detection.

23. The polishing apparatus of claim 18 wherein said add-on frame structure includes an additional upper mounting plate with at least one additional linear rail mounted on a vertical surface of said additional upper mounting plate, said at least one additional linear rail being aligned with said at least one linear rail of said main frame structure when said add-on polishing structure is attached to said main polishing structure, said at least one additional linear rail being used to linearly guide said additional polishing head.

24. The polishing apparatus of claim 18 wherein said main polishing structure includes a pad conditioner for each of said polishing tables, and wherein a conditioner linear rail is mounted on a bottom surface of said upper mounting plate, said conditioner linear rail being used to linearly guide said pad conditioner.

25. The polishing apparatus of claim 24 wherein said pad conditioner is attached to a mounting plate that has a shape of “”, said mounting plate including an upper horizontal portion, a lower horizontal portion and a vertical portion that connects said upper and lower horizontal portions, said mounting plate being used to connect said pad conditioner to said conditioner linear rail.

26. The polishing apparatus of claim 25 further comprising an enclosing structure to enclose said upper mounting plate such that said polishing heads and said pad conditioner are external to said enclosing structure, said enclosing structure including openings to accommodate neck portions of rail grippers for said polishing heads and said upper horizontal portion of said mounting plate, said rail grippers being used to connect said polishing heads to said linear rails.

27. The polishing apparatus of claim 26 wherein at least some of said openings of said enclosing structure are sealed with sealing material, and wherein said neck portions are configured such that each neck portion tapers to a point at both ends so that said openings of said enclosing structure are sealed by said sealing material at said both ends of said neck portions.

28. A polishing apparatus for polishing semiconductor wafers comprising:
a main polishing structure including a first polishing table, a first polishing head and a first load-and-unload station that are operatively coupled to a main frame structure, said first polishing head being operatively coupled to said main frame structure such that said first polishing head can transfer said semiconductor wafers in a linear manner from said first polishing table to said first load-and-unload station using a first linear rail; and
an add-on polishing structure including a second polishing table and a second polishing head that are operatively coupled to an add-on frame structure, said second polishing head being operatively coupled to said add-on frame structure such that said second polishing head can transfer said semiconductor wafers in a linear manner from said first load-and-unload station to said second polishing table using at least a second linear rail such that said second polishing head can receive said semiconductor wafers from said first load-and-unload station and polish said semiconductor wafers on said second polishing table,
wherein said add-on polishing structure is configured to be attached to said main polishing structure such that said first linear rail and said second linear rail are aligned to form a straightly connected linear rail.