Patent Grant
7089782
The present invention relates generally to chemical mechanical polishing of substrates, and more particularly to a test station for testing the polishing head and other equipment for a chemical mechanical polishing of semiconductor substrates.
Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semiconductive or insulative layers. After each layer is deposited, it is often etched to create circuitry features. As a series of layers are sequentially deposited and etched, the outer or uppermost surface of the substrate, i.e., the exposed surface of the substrate, can become increasingly non-planar. This non-planar surface may present problems in the photolithographic steps of the integrated circuit fabrication process. Therefore, there is often a need to periodically planarize the substrate surface.
Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically includes mounting a substrate on a carrier or polishing head. The exposed surface of the substrate is placed against a rotating polishing pad. The polishing pad may be either a “standard” or a fixed-abrasive pad. A standard polishing pad has a durable roughened surface, whereas a fixed-abrasive pad typically has abrasive particles held in a containment media. The polishing head provides a controllable load, i.e., pressure, on the substrate to push it against the polishing pad. A polishing slurry, including at least one chemically-reactive agent, and abrasive particles, if a standard pad is used, is supplied to the surface of the polishing pad.
The polishing head can undergo periodic maintenance in which the head is disassembled, worn parts replaced and then reassembled. Prior to returning the head to polishing additional wafers, the refurbished head can be tested at a test station to determine whether the head operates properly before using it on expensive wafers or other semiconductor substrates.
A test station for testing a chemical and mechanical polishing head has a continuous head positioning control system which can precisely position the polishing head at one of many controlled positions above the test station platform. In the illustrated embodiment, the head position control system includes an electronically controlled linear actuator which can position a polishing head mounted in a mount at one end of a mount arm, at a precise vertical position selected by a controller relative to a test surface or test wafer support surface of the test station. This vertical position is measured along a Z-axis which is orthogonal to the test surface which supports a test wafer for testing with the polishing head.
In one embodiment, the linear actuator includes a servo motor assembly and a vertical carriage assembly which guides the mount arm and restricts the movement of the mount arm and hence the head to linear, nonrotational movements along the Z-axis. The servo motor of the assembly is preferably of the type that has an output shaft which can be positioned to specific angular positions by sending the servo a coded signal. In general, the servo motor will maintain the angular position of the motor output shaft as long as the coded signal exists on the input line. When the coded input signal changes, the angular position of the shaft changes to a new angular position corresponding to the new coded input signal. Other types of precision motors such as stepper motors may be used as well. Other actuators may include a pressure cylinder which may be used to position the head at a controlled position in response to selective applications of different pressures to the cylinder.
The ability of the head test station to precisely position the polishing head at a precise, electronically controlled position can significantly facilitate testing of the polishing head. For example, a wafer loss sensor may be tested when the polishing head is located at a particular desired height above a test wafer.
A head test station in accordance with another aspect includes a lateral carriage assembly which can significantly facilitate loading and mounting a polishing head into the test station for testing. The lateral carriage assembly supports the polishing head above a base plate of the station and permits the polishing head to be moved in a gliding motion above the surface of the test station test wafer. The carriage assembly includes a carriage which slides between a load position at which the polishing head may be loaded onto the carriage and a mount position at which the polishing head may be mounted onto the test station mount. In this manner, heavy polishing heads may be readily moved into position by the carriage for mounting to a head mount for testing while reducing the chances for damage to the test wafer or the polishing head which could be caused by inadvertent dropping of the polishing head onto the test wafer.
In another aspect of the present invention, a sensor senses when the carriage is moved from the load position. In response, the test station controller causes a vertical actuator to lift the head mount in the vertical or Z direction. In this position, there is sufficient clearance for the polishing head being carried by the carriage to slide under the head mount and into position for mounting to the head adapter.
With the polishing head mounted to the head mount, the carriage may be withdrawn back to the load or standby position. As the carriage approaches the sensor indicating that the carriage is in or is close to the load/standby position, the vertical actuator lowers the head mount and the polishing head mounted to the adapter, down to the test position.
In another aspect, the carriage includes a carriage plate, the top surface of which defines a generally disk segment shaped recess which is sized and shaped to receive the bottom of a polishing head of a first size, such as a polishing head adapted to hold 300 mm semiconductor wafers for polishing, for example. The polishing head is loaded into the carriage recess when the carriage is in the load position. As the carriage is moved to the head mount position, the carriage plate recess inhibits sliding of the polishing head relative to the plate and facilitates aligning the polishing head with the head mount in the mount position.
In accordance with yet another aspect of the present invention, a test station may readily accommodate testing a variety of polishing heads having different exterior dimensions and includes an adapter plate which may be placed onto the carriage plate of the carriage instead of a polishing head. The adapter plate has a recess which is sized to receive a different sized polishing head.
In accordance with still another aspect, a test station may include a wafer chuck which can chuck test wafers of different sizes, such as 200 mm wafers and 300 mm wafers, for example. In the illustrated embodiment, the wafer chuck includes a plate which defines a first set of annular-shaped grooves in a first area which is a central disk-shaped area. A second set of annular-shaped grooves are positioned in a second area which is annular shaped and surrounds the central area. The test station has two independent vacuum lines coupled to the first and second sets of grooves respectively, which draw vacuum pressure through the grooves to draw a test wafer down and chuck the test wafer in place on the wafer chuck.
To chuck a smaller test wafer such as a 200 mm wafer, for example, the test station controller opens a control valve for the central area line and closes a control valve for the outer area line so that vacuum pressure is applied to the test wafer through the grooves of the central area covered by the test wafer but not the grooves of the outer area which would be left exposed by a smaller test wafer. Conversely, to chuck a larger test wafer such as 300 mm test wafer, for example, the test station controller opens both the control valve of the central area and the control valve of the outer area so that vacuum pressure is applied to the test wafer both through the grooves of the central area and the grooves of the outer area which are both covered by a larger test wafer. It is appreciated that the number, size and shapes of the grooves and areas may vary, depending upon the particular application.
In accordance with another aspect, the test station may have pneumatic pressure, vacuum and exhaust circuits for devices other than polishing heads used in the polishing of semiconductor wafers. For example, the test station may have pneumatic circuits for testing F.I. pad conditioners as well as the chambers of various other polishing materials.
There are additional aspects to the present inventions. It should therefore be understood that the preceding is merely a brief summary of some embodiments and aspects of the present inventions. Additional embodiments and aspects of the present inventions are referenced below. It should further be understood that numerous changes to the disclosed embodiments can be made without departing from the spirit or scope of the inventions. The preceding summary therefore is not meant to limit the scope of the inventions. Rather, the scope of the inventions is to be determined by appended claims and their equivalents.
a and 5b are schematic diagrams illustrating operation of a wafer loss sensor of the polishing head of FIG. 2.
a is a top schematic view of a test station in accordance with an alternative embodiment, showing a carriage in a load position.
b is a top schematic view of the test station of
c is a top schematic view of the test station of
a is a front schematic view of the test station of
b is a front schematic view of the test station of
a is a perspective view illustrating the carriage assembly in the mount position.
b is a perspective view illustrating the carriage assembly in the standby position.
a and 15b are side and top views, respectively, of the adapter plate of FIG. 14.
A test station in accordance with one embodiment of the present invention is indicated generally at 10 in FIG. 1. The test station 10 includes a platform 12 which supports a head positioning control system 14 which positions a chemical and mechanical polishing head 16 above the platform 12. As will be explained in greater detail below, the head position control system 14 can precisely position the head 16 at one of many electronically controlled positions above the platform 12 as shown in FIG. 2. As a consequence, testing procedures of the head 16 are facilitated as described below. By comparison, it is believed that in prior head testing stations, the polishing head was mounted at a fixed height or was movable between two mechanically fixed heights.
A polishing head such as the head 16 of
The polishing head 16 also has three pressure sealed chambers, that is, a retaining ring chamber 20, an inner tube chamber 22 and a membrane chamber 24. The test station 10 can apply various tests to the chambers to ensure proper sealing and operation. It is appreciated that the number and types of chambers may vary from head type to head type. For example, the head may have from three to eight chambers.
In the head 16 of the illustrated embodiment, the retaining ring chamber 20 is located between a housing 26 and a base 28 of the head 16. The retaining ring chamber 20 is pressurized to apply a load, i.e., a downward pressure, to the base 28 during a wafer polishing operation. A rolling diaphragm 29 flexibly couples the housing to the base 28 and permits the expansion and contraction of the retaining ring chamber 20. In this manner, the vertical position of the base 28 relative to a polishing pad is controlled by the pressure in the retaining ring chamber 20.
A flexible membrane 30 extends below a support structure 32 to provide a mounting surface 34 for the wafer or other semiconductor substrate 36 to be polished. Pressurization of the membrane chamber 24 positioned between the base 28 and support structure 32 forces flexible membrane 30 downwardly to press the substrate against the polishing pad. A flexure 38 flexibly couples the support structure 32 to the base 28 and permits the expansion and contraction of the membrane chamber 24.
Another elastic and flexible membrane 40 may be attached to a lower surface of base 28 by a clamp ring or other suitable fastener to define the inner tube chamber 22. Pressurized fluid such as air may be directed into or out of the inner tube chamber 22 and thereby control a downward pressure on support structure 32 and flexible membrane 30.
The housing 26 has a spindle 44 which can be connected to a drive shaft of the polishing system to rotate the head 16 therewith during polishing about an axis of rotation 46 which is substantially perpendicular to the surface of the polishing pad during polishing. Three pressure lines 50, 52 and 54 direct fluid such as air or nitrogen to each of the chambers 20, 22 and 24 either at a pressure above ambient (pressurized) or below ambient (vacuum pressure).
The linear actuator 60 includes a servo motor assembly 70 which is controlled by the controller 62 through suitable driver circuits 76. The output of the servo motor assembly 70 is coupled to a vertical carriage assembly 78 which guides the mount arm 66 and restricts the movement of the mount arm and hence the head 16 to linear, nonrotational movements along the Z-axis. The carriage assembly 78 includes a carriage 80 to which the mount arm 66 is mounted by a pair of braces 81. The carriage 80 has a pair of guide bars 82, each of which defines a generally trapezoidal shaped guide channel 84 (FIG. 4). Each guide channel 84 receives a complementary trapezoidal shaped guide rail 86 and is adapted to slide along that guide rail 86. The guide rails 86 of the carriage assembly are mounted on a vertical support plate 90 to guide the carriage 80 and hence the head 16 in a vertical, non-pivoting, linear movement up and down along the Z-axis. The support plate 90 is mounted by braces 92 to a horizontal support plate 94 of the platform 12. It is appreciated that other mechanical arrangements may be selected to guide the polishing head along one or more selected axes of movement.
The servo motor assembly 70, together with the driver circuits 76 are commercially available devices. For example, in the illustrated embodiment, the servo motor assembly 70 is sold by Panasonic under the model name MUMS081 750 W/100V and the driver circuits 76 are sold by LOGOSOL under the model name LS173P Driver. The servo motor of the assembly 70 is preferably of the type that has an output shaft which can be positioned to specific angular positions by sending the servo a coded signal. In general, the servo motor will maintain the angular position of the motor output shaft as long as the coded signal exists on the input line. When the coded input signal changes, the angular position of the shaft changes to a new angular position corresponding to the new coded input signal. The servo motor assembly typically includes feedback circuits including an angular position sensor to monitor the current angle of the output shaft of the servo motor. If the shaft is at the correct angle, then the motor shuts off. If the feedback circuit finds that the angle is not correct, it will turn the motor in the appropriate direction until the angle is correct.
The servo motor assembly 70 is preferably capable of being controlled to move in small, precise incremental movements or steps of 0.0360 degrees or less from one angular position associated with a particular coded input signal to the next adjacent angular position associated with a different coded input signal corresponding to a resolution of 10,000 or more per revolution. The resolution of the controlled angular movements over the full range of motion of the servo motor output shaft may vary from application to application but a general range of greater than 250 controlled positions or steps is presently preferred. The output shaft of the servo motor may be mechanically constrained to travel a maximum number of degrees such as 180 degrees, for example. The linear actuator 60 includes a suitable mechanical motion converter between the servo motor assembly 70 and the carriage assembly 78. The motion converter includes gears which convert the precise, controlled angular movements of the servo motor output shaft to precise, controlled translational movements of the carriage assembly 78 in a linear direction along the Z-axis. The actuator 60 of the illustrated embodiment has a total linear movement in excess of 60 mm over the 180 degree range of the servo motor.
Thus, for each rotational movement of 0.0360 degrees of the servo motor output shaft, the polishing head may be moved up or down a linear displacement of a certain number of microns in each step. The displacement of each step may be 10 or 13 microns, for example. Other displacements may also be used. The particular values will vary, depending upon the particular application.
To move the polishing head to a particular height above the test surface, the controller 62 can issue to the servo motor through the driver circuits 76 a digitally coded input signal such as 10010010 for example, which corresponds to a particular polishing head height such as 1.5 mm, for example, above the test surface. Thus, in this example, in response to the digitally coded input signal 10010010, the servo motor moves the head to 1.5 mm above the test surface and holds it in that position until another digitally coded input signal is received. In response to a different digitally coded input signal, such as 11110110, for example, the servo motor moves the head to a different height such as 43.93 mm, for example, above the test surface and holds it in that position. In the illustrated embodiment, the number of positions to which the servo motor can move the polishing head and hold it at that position corresponds to the resolution of the servo motor. Hence, if the servo motor has a resolution of 10,000, the servo motor can move the polishing head to any one of 10,000 height positions as selected by the controller 62 and hold it at the position selected by the controller 62.
Alternative to a servo motor, the linear actuator 60 may utilize a stepping motor. Like the servo motor, a stepper motor preferably has an output shaft capable of being controlled to move in small, precise incremental movements or steps of 0.0360 degrees or less from one angular position associated with a particular coded input signal to the next adjacent angular position associated with a different coded input signal. To move the output shaft of a stepping motor a particular number of steps such as 5 steps, for example, the controller typically sends to the stepping motor a corresponding number of coded input signals such as 5 coded input signals in this example, one coded input signal for each step taken. Thus, to move the polishing head to a particular height above the test surface, the controller 62 can issue to the stepping motor through the appropriate driver circuits, a series of digitally coded input signals such as 500 digitally coded input signals for example, to move the polishing head 500 steps to a particular polishing head height such as 1.5 mm, for example, above the test surface. Thus, in this example, in response to the series of 500 digitally coded input signals, the stepping motor steps the head to 1.5 mm above the test surface and holds it in that position until another digitally coded input signal is received. In response to another series of digitally coded input signals, the stepping motor moves the head to a different height such as 43.93 mm, for example, above the test surface and holds it in that position. In the illustrated embodiment, the number of positions to which the stepping motor can move the polishing head and hold it at that position corresponds to the resolution of the stepping motor.
The servo or stepping motors may be controlled to move smoothly in one continuous motion from one head position to another-head position such as from the 1.5 mm position to the 43.93 mm position, for example. Alternatively, the motors may be controlled to move one small step at a time, momentarily stopping at each incremental step. Also, motors having a linear output rather than a rotational output may be utilized as well. Such linear motors preferably have an output shaft capable of being controlled to move in small, precise incremental movements of 500 microns or less from one linear position associated with a particular coded input signal to the next adjacent linear position associated with a different coded input signal.
As previously mentioned, the test station 10 may be used to test a variety of sensors, chambers and other structures of a polishing head.
However, should the wafer drop from the head 16, ambient pressure acting on the membrane 30 drives the membrane 30 and the support structure upwardly into the membrane chamber as shown in
The valves 134, 144 and 154 are controlled by the controller 62. To conserve pressure in a particular chamber, the vent valve 154, pressure valve 134 and vacuum valve 154 are closed. By closing these valves, the chamber is isolated from being further pressurized, vacuumed or vented. The pressure within the chamber may be monitored by the controller 62 through a pressure sensor 160 such as a transducer fluidically coupled to the associated chamber. If the chamber pressure drops after closing the control valves 134, 144 and 154, the presence of a leak is indicated. As previously mentioned, if the pressure in the inner tube chamber 22 follows a curve such as that shown in
The test station 10 can test the chambers of the polishing head for pressure and vacuum leaks including leaks across the various chambers (cross talk). Testing includes height and time of rise as well as valve and sensor tests.
The test wafer is then dropped (step 170) in preparation for the actual wafer loss sensor test. Because the height of the polishing head may be controlled very precisely, the distance that the test wafer drops onto the test surface 68 can be carefully controlled as well. In the illustrated embodiment, it is preferred that the polishing head be displaced above the top surface of the test wafer after the test wafer is dropped by the polishing head by a distance of 1.5 mm. As a consequence, when the test wafer is dropped, it has been found that the horizontal position (that is, the position along the X-axis and Y-axis (
The controller 62 then causes the head 16 to begin the process of loading the test wafer onto the polishing head. As set forth above, in the illustrated embodiment, it is preferred that the polishing head be displaced above the top surface of the test wafer prior to loading the test wafer by a precisely controlled distance such as 1.5 mm, for example. At this distance, the membrane chamber 24 may be pressurized (step 172) to cause the head membrane 30 to become inflated prior to actually loading the wafer. As the head membrane 30 inflates, it engages the top surface of the test wafer and expresses away air pockets which may otherwise become trapped between the membrane 30 and the wafer top surface.
In the illustrated embodiment, it is preferred that the test wafer be wet for preloading and loading onto the polishing head. Accordingly, surrounding the test surface 68 of the test station platform 12 is an upstanding wall 176 which contains the wetting fluid for the test wafer. A wetted top surface of the test wafer facilitates removal of the air pockets between the membrane 30 and the test wafer top surface prior to preloading the test wafer.
To load the test wafer, the inner tube chamber 24 is also pressurized (step 172) to apply pressure to push the perimeter of the membrane 30 against the perimeter of the test wafer. The pressure in the inner tube chamber is then conserved at that pressure to test for leaks in the inner tube chamber as set forth above. If the pressure in the inner tube chamber remains steady at the preset pressurized level, a proper sealing of the inner tube chamber is indicated. In the illustrated embodiment, it is preferred that the inner tube chamber be pressurized to a level of 1 psi above ambient for the wafer loss sensor test. Other pressures in a range of 0-3 psi may also be used. The particular values will vary, depending upon the particular application.
Once maintenance of the pressure in the inner tube chamber 22 has been confirmed at the preset value, and air pockets between the membrane 30 and the wafer top surface expressed away, a vacuum pressure is applied (step 182) to the membrane chamber 24 to finish loading the test wafer. In the illustrated embodiment, it is preferred that the membrane chamber be vacuum pressurized to a level of −5 psi below ambient for the wafer loss sensor test. Other pressures in a range of −2 to −7 psi below ambient may also be used. The particular values will vary, depending upon the particular application.
If the wafer is properly loaded in a manner similar to that shown in FIG.
Sag and the wafer loss sensor has been properly installed and operates properly, the wafer loss sensor will not be actuated and the pressure in the inner tube chamber 22 should remain substantially constant as monitored (step 184) by the controller 62.
On the other hand, if the wafer is not properly picked up or is dropped, the membrane 30 will be drawn into the membrane chamber 24 causing the support structure 32 to engage the inner tube chamber and the wafer loss sensor 18 as shown in
As previously mentioned, the ability of the head test station 10 to precisely position the polishing head at a precise, electronically controlled position can significantly facilitate testing of the polishing head. For example, in the wafer loss sensor test with a test wafer as described above, if the polishing head is positioned too close to the test wafer prior to loading the wafer, it is believed that the membrane 30 and support structure 32 can be driven up into the membrane chamber 24, causing the wafer loss sensor 18 to be improperly actuated. Conversely, if the polishing head is positioned too far from the test wafer prior to loading the wafer, the test wafer may not be properly picked up. Hence, vacuum pressure applied to the membrane chamber 24 to pick up the wafer can instead cause the membrane 30 and support structure 32 to be withdrawn into the membrane chamber 24, again resulting in improper actuation of the wafer loss sensor 18. A vertical position of the polishing head spaced within a range of 1-2 mm above the test surface is believed appropriate for many such applications. Other distances may also be used. The particular values will vary, depending upon the particular application.
Because of the many positions to which the head may be programmed to move, the head test station in effect provides continuous control over the movement of the head. The test position and load position of the head may be defined for many different types of heads. Any differences in the size of the heads including differences in thickness may be readily accommodated by programming the actuator control to move the head to the optimum positions for that particular head type.
Referring again to
a-11b illustrate a head test station 200 in accordance with an alternative embodiment of the present invention. The test station 200 includes a lateral carriage assembly 202 which significantly facilitates loading and mounting a polishing head 203 into the test station for testing. The lateral carriage assembly 202 supports the polishing head 203 above the base plate 204 of the test station 200 and permits the polishing head to be moved in a gliding motion above the surface of the test station base plate. The carriage assembly 202 includes a carriage 206 (
As best seen in
When the carriage 206 and polishing head 203 are moved to the head mount position, the polishing head 203 is positioned below a head adapter 208 to which it is mounted as shown in
With the polishing head mounted to the head adapter 250, the carriage 206 may be withdrawn back to the load or standby position as shown in
The guide bars 220 and guide rails 230 are sized to provide sufficient spacing between the carriage 206 and the test wafer 272 and wafer chuck 270 supported by the platform base plate 204, to permit the carriage plate 210 to pass over the test wafer 272 as the polishing head is moved into the mount position below the head adapter. In this manner, heavy polishing heads may be readily moved into position by the carriage 206 for mounting to a head adapter for testing while reducing the chances for damage to the polishing head or the test wafer which could be caused by inadvertent dropping of the polishing head onto the test wafer.
In accordance with another aspect of the present invention, the test station 200 may readily accommodate a variety of testing heads having different exterior dimensions. For example, a polishing head 310 shown in
The circular-shaped outer dimensions of the adapter plate 312 are received in the recess 212 of the carriage plate 210. In addition, the adapter plate 312 has pins 330 which are received in corresponding apertures 332 of the carriage plate 210 to interlock the adapter plate 312 to the carriage plate 210. Once the adapter plate 212 has been loaded onto the carriage plate 210 and a polishing head 310 has been loaded onto the adapter plate 312, the carriage 206 may be moved to the mount position (
The test station 200 also includes a wafer chuck 350 which as best seen in
The vacuum line 370a includes a pressure regulator 372 and a control valve 374a which couples the vacuum line 370a to a common vacuum pressure source 376. The vacuum lines 370b similarly includes a pressure regulator 372 and a control valve 374b which couples the vacuum line 370b to the common vacuum pressure source 376. To chuck a smaller test wafer such as a 200 mm wafer, for example, the test station controller 260 opens the control valve 374a and closes the control valve 374b so that vacuum pressure is applied to the test wafer through the grooves 354 of the central area 356 covered by the test wafer but not the grooves 358 of the outer area 360 which would be left exposed by a smaller test wafer. Conversely, to chuck a larger test wafer such as 300 mm test wafer, for example, the test station controller 260 opens both the control valve 374a and the control valve 374b so that vacuum pressure is applied to the test wafer both through the grooves 354 of the central area 356 and the grooves 358 of the outer area 360 which are both covered by a larger test wafer. It is appreciated that the number, size and shapes of the grooves and areas may vary, depending upon the particular application. For example, a smaller central area with an associated vacuum line may be provided for 150 mm wafers within the central area 356. Also, apertures other than grooves may be utilized.
In the illustrated embodiment, the test station has pressure, vacuum and exhaust pneumatic circuits such as those shown in
It will, of course, be understood that modifications of the illustrated embodiments, in their various aspects, will be apparent to those skilled in the art, some being apparent only after study, others being matters of routine mechanical and electronic design. Other embodiments are also possible, their specific designs depending upon the particular application. As such, the scope of the invention should not be limited by the particular embodiments described herein but should be defined by the appended claims and equivalents thereof.
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