JP7590131B2 - Polishing Equipment - Google Patents

Description

The present invention relates to a polishing device for polishing a workpiece.

In the field of semiconductor manufacturing, CMP devices are known for polishing and flattening silicon wafers and the like (hereafter referred to as "workpieces").

The polishing device described in Patent Document 1 is a polishing device that applies chemical mechanical polishing, or CMP (Chemical Mechanical Polishing) technology. This CMP device polishes a workpiece by pressing the workpiece, which is attached to a polishing head, against a polishing pad.

JP 2016-159385 A

In back-side reference polishing, in which the back side of the workpiece is held in the chuck of the polishing head and the front side of the workpiece is pressed against the polishing pad to polish it, it is known that the flatness of the chuck holding the workpiece is transferred to the pressure distribution acting on the workpiece, affecting the shape of the workpiece after polishing.

In conventional polishing heads, the flatness of the chuck is set to 1 μm or less by lapping the chuck's suction surface. However, even when a workpiece is held on such a flat suction surface and polished under the same polishing conditions, there is a problem in that the workpiece shape is not stable, meaning that high reproducibility cannot be achieved.

As a result, technical problems arise that must be solved in order to polish workpieces with good reproducibility, and the present invention aims to solve these problems.

As a result of extensive research, the inventors discovered that in conventional polishing devices, the difference in linear expansion coefficient between the alumina chuck table that houses the chuck and the metal base member that is fastened to the chuck table and transmits the rotational driving force input to the polishing head to the chuck table causes nonlinear responsive distortion in the chuck in response to temperature changes during polishing.

The inventors also discovered that by setting the difference between the linear expansion coefficient of the chuck table and the linear expansion coefficient of the base member within a predetermined range, the flatness of the chuck changes in an approximately linear manner.

In order to achieve the above object, the polishing apparatus of the present invention is a polishing apparatus that polishes a workpiece held by a polishing head by pressing it against a polishing pad on a platen, and is provided with a holding mechanism including a chuck table provided at the lower end of the polishing head, a chuck accommodated on the underside of the chuck table and capable of holding the workpiece on the holding surface, and a base member that is fastened to the chuck table and transmits the rotational driving force input to the polishing head to the chuck table, and the chuck table and the base member are made of a material that exhibits a linear expansion coefficient such that the flatness of the holding surface, which changes depending on the temperature of the chuck due to the difference between the linear expansion coefficient of the chuck table and the linear expansion coefficient of the base member, changes approximately linearly over the operating temperature range of the polishing apparatus.

With this configuration, the flatness of the holding surface responds linearly over the operating temperature range of the polishing device, making it easy to control the flatness of the holding surface by controlling the temperature of the chuck, so the workpiece can be polished flat with good reproducibility.

In addition, in the polishing apparatus according to the present invention, it is preferable that the chuck table is made of alumina and the base member is made of an Invar alloy.

With this configuration, the base member is made of Invar alloy, a low thermal expansion alloy, so that the base member and the chuck table expand and contract almost uniformly over the operating temperature range of the polishing device, making it easy to control the flatness of the holding surface by controlling the temperature of the chuck, and allowing the workpiece to be polished with good reproducibility.

In addition, in the polishing apparatus according to the present invention, it is preferable that the difference between the linear expansion coefficient of the base member and the linear expansion coefficient of the chuck table is set to 2.2 ppm/°C or less.

With this configuration, the flatness of the holding surface is easy to control, allowing the workpiece to be polished with high reproducibility.

The present invention can polish a workpiece to a flat surface with good reproducibility.

1 is a perspective view showing a schematic diagram of a CMP apparatus according to a first embodiment of the present invention; FIG. 2 is a vertical cross-sectional view showing a schematic view of a main part of a polishing head. 13 is a graph showing the temperature dependence of the flatness of a holding surface in a CMP apparatus to which a base member according to a comparative example of the present invention is applied. 5 is a schematic diagram showing how a holding surface is deformed due to a temperature change. 5A and 5B are schematic diagrams showing expansion of a base member and a chuck table due to an increase in temperature. 6 is a graph showing the relationship between the temperature of a chuck and the flatness of a holding surface when a workpiece is polished by the CMP apparatus according to Example 1 and Example 2 of the present invention. 11 is a graph showing the finished shape of a workpiece for each polishing temperature when the workpiece is polished using a CMP apparatus according to a comparative example. 4 is a graph showing the finished shape of a workpiece for each polishing temperature when the workpiece is polished using the CMP apparatus according to Example 1. 13 is a graph showing the finished shape of a workpiece for each polishing temperature when the workpiece is polished using the CMP apparatus according to Example 2. 13 is a graph showing the temperature dependence of the flatness of a holding surface in a CMP apparatus according to a comparative example, in which the slope of the flatness of the holding surface is added. 13 is a schematic diagram showing the state in which the holding surface is deformed into a convex shape in order to accommodate a polishing pad with a depressed center.

One embodiment of the present invention will be described with reference to the drawings. Note that in the following, when referring to the number, numerical value, amount, range, etc. of components, unless otherwise specified or when it is clearly limited to a specific number in principle, it is not limited to that specific number and may be more or less than the specific number.

In addition, when referring to the shape or positional relationship of components, etc., this includes things that are substantially similar or similar to that shape, etc., unless otherwise specified or considered in principle to be clearly different.

In addition, drawings may exaggerate characteristic parts to make the features easier to understand, and the dimensional ratios of components may not be the same as in reality. In addition, in cross-sectional views, hatching of some components may be omitted to make the cross-sectional structure of the components easier to understand.

Figure 1 is a perspective view showing a schematic diagram of a CMP apparatus 1 according to one embodiment of the present invention. The CMP apparatus 1 polishes one surface of a workpiece W to a flat surface. The CMP apparatus 1 includes a platen 2 and a polishing head 10. The workpiece W is, for example, a silicon wafer, but is not limited to this.

The platen 2 is formed in a disk shape and is connected to a rotating shaft 3 arranged below the platen 2. When the rotating shaft 3 is rotated by the drive of a motor 4, the platen 2 rotates in the direction of the arrow D1 in FIG. 1. A polishing pad 5 is attached to the upper surface of the platen 2, and CMP slurry, which is a mixture of an abrasive and a chemical agent, is supplied onto the polishing pad 5 from a nozzle (not shown).

In addition, a circulating cooling device 6 is connected to the platen 2, and temperature-controlled chilled water supplied from the circulating cooling device 6 is passed through the platen 2, allowing the temperature of the platen 2 to be adjusted according to the temperature and flow rate of the chilled water during polishing.

The polishing head 10 is formed with a smaller diameter than the platen 2 and is connected to a rotating shaft 10a disposed above the polishing head 10. The rotating shaft 10a is rotated by the drive of a motor (not shown), causing the polishing head 10 to rotate in the direction of arrow D2 in FIG. 1. The polishing head 10 is configured to be movable vertically and horizontally by a head movement mechanism (not shown). When polishing the workpiece W, the polishing head 10 descends to press the workpiece W against the polishing pad 5.

The operation of the CMP apparatus 1 is controlled by a control device (not shown). The control device controls each of the components that make up the CMP apparatus 1. The control device is, for example, a computer, and is composed of a CPU, memory, etc. The functions of the control device may be realized by controlling it using software, or may be realized by something that operates using hardware.

Next, the structure of the polishing head 10 will be described. Figure 2 is a vertical cross-sectional view showing the main parts of the polishing head 10.

The polishing head 10 has a head body 11 connected to a rotating shaft 10a. The head body 11 is connected to a base member 13 via a rotation transmission unit 12, and the head body 11, the rotation transmission unit 12, and the base member 13 rotate together with the rotating shaft 10a.

A PPS plate holder 14 is fastened to the top of the base member 13 via bolt B1. This allows the rotational driving force input to the polishing head 10 to be transmitted to the plate holder 14 via the base member 13.

An air bag 15 is interposed between the plate holder 14 and the head body 11. The air bag 15 can be inflated and contracted freely by air supplied from a compressed air source (not shown) via a vacuum line 15a. The pressure of the air supplied from the compressed air source is adjusted by a regulator (not shown). The air bag 15 pressurizes the plate holder 14 according to the pressure of the supplied air, thereby adjusting the polishing pressure with which the workpiece W is pressed against the polishing pad 5.

A porous chuck 16 is provided below the base member 13. The porous chuck 16 includes an alumina chuck table 17 and a porous alumina chuck 18.

The chuck table 17 is fastened to the base member 13 via bolt B2. This allows the rotational driving force input to the polishing head 10 to be transmitted to the porous chuck 16 via the base member 13.

The chuck 18 is embedded in the underside of the chuck table 17. The chuck 18 is connected to a vacuum source and a cooling water source (not shown) via a line 18a. By activating the vacuum source, the workpiece W is adsorbed and held on the holding surface 16a of the porous chuck 16. The cooling water supplied from the cooling water source is adjusted to be approximately the same temperature as room temperature, and the chuck 18 is cooled by passing the water through it after polishing.

In this way, the polishing head 10 presses the surface of the workpiece W against the polishing pad 5 while the back surface of the workpiece W is held by suction on the chuck 18, and the load is transmitted to the workpiece W as the airbag 15 inflates, so that the workpiece W is polished so that the shape of the holding surface 16a is transferred to it (back surface reference polishing). The holding surface 16a is set to a flatness of approximately 1 μm or less by lapping, and in such back surface reference polishing, the flatness of the holding surface 16a of the chuck table 17 affects the finished shape of the workpiece W.

The base member 13 is made of a material that exhibits a linear expansion coefficient close to that of the alumina that constitutes the chuck table 17 (7.2 ppm/°C). The base member 13 is, for example, a low thermal expansion alloy (Invar alloy) that is formulated to have a linear expansion coefficient close to that of alumina.

The linear expansion coefficient of the base member 13 and the linear expansion coefficient of the chuck table 17 being close to each other means that the linear expansion coefficients of the base member 13 and the chuck table 17 are set so that the flatness of the holding surface 16a, which changes in response to the temperature change of the chuck 19 due to the difference between the linear expansion coefficients of the base member 13 and the chuck table 17, changes in an approximately linear manner (responds linearly) over the operating temperature range of the CMP apparatus 1 (for example, about 10 to 40°C) when the base member 13 and the porous chuck 16 expand and contract while fastened to each other by the bolts B2. The operating temperature range of the CMP apparatus 1 varies depending on the pressure pressing the workpiece W, the rotation speed of the polishing head 10, the rotation speed of the platen 2, the slurry flow rate, the temperature and flow rate of the chiller water, etc.

Next, evaluation data comparing the change in flatness of the holding surface 16a over the operating temperature range for a CMP device 1 (Example 1) that uses a base member 13 made of an Invar alloy with a linear expansion coefficient of 5.0 ppm/°C, a CMP device 1 (Example 2) that uses a base member 13 made of an Invar alloy with a linear expansion coefficient of 7.0 ppm/°C, and a CMP device 1 (Comparative Example) that uses a conventional base member 13 made of SUS316 will be described.

[Evaluation method]
First, FIG. 3 shows the relationship between the temperature of the chuck 18 and the flatness of the holding surface 16a when the temperature of the polishing head 10 of the CMP apparatus 1 according to the comparative example is changed by an external factor.

Figure 3 is a graph showing the temperature dependence of the flatness of the holding surface 16a in the polishing head 10 of the CMP apparatus 1 according to the comparative example. In the graph of Figure 3, the vertical axis represents the flatness of the holding surface 16a, and the horizontal axis represents the temperature of the chuck 18. Note that a positive flatness corresponds to a state in which the center of the porous chuck 16 is convex compared to the outer periphery, and a negative flatness corresponds to a state in which the center of the porous chuck 16 is concave compared to the outer periphery. The flatness of the holding surface 16a was measured using a Flat Master 200XRA-Indstrial manufactured by Corning Tropel. The temperature of the chuck 18 was measured using a digital thermometer HA-202K manufactured by Anritsu Keiki Co., Ltd.

The range indicated by the symbol a in Figure 3 corresponds to the state in which the polishing head 10 of the CMP apparatus 1 according to the comparative example is on standby at room temperature (approximately 22 to 24°C), and shows the change in flatness of the holding surface 16a when the temperature of the chuck 18 is changed at room temperature (approximately 22 to 24°C). It can be seen that within this range, the flatness of the holding surface 16a responds linearly, becoming negative (concave) as the temperature increases.

The range indicated by the symbol b in FIG. 3 corresponds to the state in which the chuck 18 is heated due to frictional heat during polishing, and shows the change in the flatness of the holding surface 16a when the chuck 18 is heated to about 37°C, which is the polishing temperature, on a hot plate set at 40°C. The range indicated by the symbol c in FIG. 3 corresponds to the state in which the polishing head 10 after polishing is cooled by passing cooling water through it, and shows the change in the flatness of the holding surface 16a when it is left at room temperature after heating on the hot plate and cooled to approximately room temperature. It can be seen that the range indicated by the symbol b and the range indicated by the symbol c do not match, and the flatness of the holding surface 16a deviates from a linear response and changes in a hysteretic manner. It can also be seen that the flatness of the holding surface 16a cooled to room temperature (23°C) after heating is positively (about 5 μm) deformed into a convex shape.

The range indicated by the symbol d in FIG. 3 corresponds to a state in which the polishing head 10 is placed in an environment below room temperature for reasons such as transportation, and shows the change in the flatness of the holding surface 16a when the polishing head 10 is cooled to near the lower limit of the operating temperature range (about 11°C) with chiller water at 10°C. The range indicated by the symbol e in FIG. 3 shows the change in the flatness of the holding surface 16a when the polishing head 10 is left at room temperature after being cooled with chiller water at 10°C and warmed to approximately room temperature. It can be seen that the range indicated by the symbol d and the range indicated by the symbol e do not match, and the flatness of the holding surface 16a deviates from a linear response and changes to hysteresis. It can also be seen that the flatness of the holding surface 16a warmed to room temperature (23°C) after cooling is negative (about -4 μm) and deformed into a concave shape.

In this way, it can be seen that there is a large discrepancy between the flatness of the holding surface 16a waiting at approximately room temperature and the flatness of the holding surface 16a that has reached approximately room temperature after being heated during polishing and cooled by the outside air during cold weather. Furthermore, the flatness of the holding surface 16a changes with hysteresis, making it very difficult to manage the flatness of the holding surface 16a.

Furthermore, considering that the flatness of the holding surface 16a after lapping is approximately 1 μm, while the flatness of the holding surface 16a that has reached approximately room temperature after heating and cooling is approximately 5 μm, it is clear that the workpiece W cannot be polished stably, and that it is necessary to reduce the fluctuation in flatness that accompanies temperature changes in the porous chuck 16.

Such temperature dependence of the porous chuck 16 is believed to be due to the following reasons. That is, due to the bimetal effect caused by the difference in linear expansion coefficient between the SUS316 base member 13 (linear expansion coefficient: 16.0 ppm/°C) and the alumina chuck table 17 (linear expansion coefficient: 7.2 ppm/°C), it is presumed that when heated, the base member 13 expands relatively more, causing the holding surface 16a to deform into a concave shape, as shown in FIG. 4, and when cooled, the base member 13 contracts relatively more, causing the holding surface 16a to deform into a convex shape.

When the base member 13 and the porous chuck 16 warm up, as shown in FIG. 5(a), the chuck table 17 is fastened to the base member 13 with bolt B2, and as shown in FIG. 5(b), in the early stages of thermal expansion, the base member 13 and the chuck table 17 are thought to expand uniformly (respond linearly) as the temperature rises due to the fastening force of bolt B2 and the surface friction force acting on the contact surface between bolt B2 and the base member 13 and the contact surface between the base member 13 and the chuck table 17 (indicated by the dashed line in FIG. 5(b)).

However, as shown in FIG. 5(c), if the base member 13 expands to the extent that it cannot be supported by the fastening force of bolt B2 and the surface friction of the base member 13 and chuck table 17, the base member 13 reaches its holding limit and slides sideways relative to the chuck table 17, causing the base member 13 and chuck table 17 to not expand uniformly, and the flatness of the holding surface 16a is thought to tend to saturate with changes in temperature. It is also thought that a similar tendency occurs when the base member 13 and porous chuck 16 cool down.

The temperature range in which the linear response occurs can be expanded by increasing the fastening torque of bolt B2. However, since the chuck table 17 is fastened to bolt B2 via a helical insert tap (not shown), there is a risk that the chuck table 17 may chip or crack if it is fastened with a torque greater than a certain value.

Next, Fig. 6 shows the relationship between the temperature of the chuck 18 and the flatness of the holding surface 16a when the workpiece W was polished by the CMP apparatus 1 according to Example 1 and Example 2 under the polishing conditions shown in Table 1. In the graph of Fig. 6, the flatness of the holding surface 16a is set on the vertical axis, and the temperature of the chuck 18 is set on the horizontal axis. The flatness measurement of the holding surface 16a and the temperature measurement of the chuck 18 are performed in the same manner as in the comparative example described above.

Figure 6 shows that, compared to Figure 3, the variation in flatness of the porous chuck 16 due to temperature changes is smaller. That is, the range of change in flatness of the holding surface 16a in the operating temperature range is -4 to 4 μm around the flatness at room temperature (0 μm) in Example 1, and 2 to 2.5 μm around the flatness at room temperature (2.2 μm) in Example 2. Therefore, it can be seen that the flatness of the holding surface 16a in a standby state at room temperature does not deviate from the flatness of the holding surface 16a after heating associated with polishing and cooling by a chiller, and the workpiece W can be polished stably with high reproducibility.

In addition, when the base member 13 is made of a material that exhibits a linear expansion coefficient close to that of the alumina chuck table 17, the flatness of the holding surface 16a responds linearly, and it is therefore easy to control the flatness of the holding surface 16a by controlling the temperature of the chuck 18.

Next, Figures 7 to 9 show the finished shape of the workpiece W at each polishing temperature (adjusted by changing the chiller water temperature passing through the platen 2) when the workpiece W is polished using each CMP apparatus 1 according to Example 1, Example 2, or Comparative Example.

In the graphs of Figures 7 to 9, the vertical axis represents the finished thickness of the workpiece W, and the horizontal axis represents the radial coordinate. In Figures 7 to 9, the finished thickness at a point 70 mm away from the center in the radial direction R is used as the standard, and the finished thickness at each measurement point (R = 0 mm, approximately 17 mm, approximately 35 mm, approximately 53 mm) is plotted as a relative height to the standard, thereby representing the finished shape of the workpiece W for each polishing temperature. Note that multiple measurement points on the workpiece W are set at the same radial coordinate, and the finished thickness is indicated by the average value of multiple measurement points on concentric circles.

In addition, in the back surface reference polishing in which the holding surface 16a is transferred to the finished shape of the workpiece W, if the holding surface 16a is deformed into a convex shape with the center convex, the finished shape of the workpiece W will be a concave shape with the center concave, and if the holding surface 16a is deformed into a concave shape with the center concave, the finished shape of the workpiece W will be a convex shape with the center convex. In other words, the finished shape of the workpiece W and the shape of the holding surface 16a are reversed.

Figure 7 shows the finished shape of the workpiece W at each polishing temperature when the workpiece W is polished using the CMP device 1 according to the comparative example.

According to FIG. 7, when the polishing temperature is below room temperature (approximately 23°C), the finished shape of the workpiece W is a curved surface that is convex in the middle and the inclination gradually decreases toward the outer periphery, and when the polishing temperature is above room temperature (approximately 23°C), the finished shape of the workpiece W is a curved surface that is concave in the middle and the inclination gradually increases toward the outer periphery.

Figure 8 shows the finished thickness of the workpiece W at each polishing temperature when the workpiece W is polished using the CMP apparatus 1 of Example 1.

According to Figure 8, compared to Figure 7, when the polishing temperature is below room temperature (approximately 23°C), the finished shape of the workpiece W is the same in that it is convex in the middle, but the height at the center is lower and the entire surface of the workpiece W is formed to be approximately flat, and when the polishing temperature is above room temperature (approximately 23°C), the finished shape of the workpiece W is the same in that it is concave in the middle, but the height at the center is higher and the entire surface of the workpiece W is formed to be approximately flat.

Figure 9 shows the finished thickness of the workpiece W at each polishing temperature when the workpiece W is polished using the CMP apparatus 1 of Example 2.

Figure 9 shows that, compared to Figures 7 and 8, the entire surface of the workpiece W is formed most flat, regardless of the polishing temperature.

In this way, by constructing the base member 13 from a material with a small difference in linear expansion coefficient from the chuck table 17, the finished shape of the workpiece W can be easily formed to be flat without strict control of the polishing temperature.

In this way, in order to easily manage the flatness of the holding surface 16a, when the linear expansion coefficient of the alumina that constitutes the chuck table 17 is 7.2 ppm/°C, it is preferable that the material of the base member 13 has a linear expansion coefficient of 5.0 to 9.4 ppm/°C. The reason for this is explained below.

First, the difference between the linear expansion coefficient of the SUS316 base member 13 and the linear expansion coefficient of the alumina porous chuck 16 is approximately 8.8 ppm/°C. As shown in Figure 10 (Figure 3 with the inclination of the flatness of the holding surface 16a added), the inclination of the flatness of the holding surface 16a when the change is large (part shown by the dashed line in the figure) is -1.8 μm/°C, and the inclination of the flatness of the holding surface 16a when the change is small (part shown by the dashed line in the figure) is -0.45 μm/°C, so the inclination of the flatness when the flatness of the holding surface 16a has changed the most is four times the value of the inclination of the flatness when the change is small. Therefore, by constructing the base member 13 from a material whose difference in linear expansion coefficient with the porous chuck 16 is 2.2 ppm/°C or less (approximately 8.8 ppm/°C divided by 4), the flatness of the holding surface 16a is thought to respond linearly to temperature changes over the operating temperature range (e.g., approximately 10 to 40°C).

In addition, when the workpiece W is pressed into the polishing pad 5 during polishing, as shown in FIG. 11, the polishing pad 5 may sink slightly, causing the finished shape of the workpiece W to have a concave center. In that case, by constructing the base member 13 from a material with a lower linear expansion coefficient than the alumina chuck table 17, the holding surface 16a will deform into a convex shape as the temperature rises, making it possible to polish the workpiece W in a way that cancels out the sinking of the polishing pad 5.

Furthermore, the present invention can be modified in various ways other than those described above without departing from the spirit of the present invention, and it goes without saying that the present invention extends to such modifications.

1: CMP device 2: Platen 3: Rotating shaft (of platen) 4: Motor 5: Polishing pad 6: Circulating cooling device 10: Polishing head 10a: Rotating shaft (of polishing head) 11: Head body 12: Rotation transmission part 13: Base member 14: Plate holder 15: Air bag 16: Porous chuck (holding mechanism)
16a: Holding surface 17: Chuck table 18: Chuck W: Workpiece

Claims (1)

A polishing apparatus that polishes a workpiece held by a polishing head by pressing the workpiece against a polishing pad on a platen,
a holding mechanism including a chuck table provided at a lower end of the polishing head and a chuck accommodated on a lower surface of the chuck table and capable of holding the workpiece on a holding surface;
a base member that is fastened to the chuck table by pressure and transmits a rotational driving force input to the polishing head to the chuck table;
Equipped with
the chuck table and the base member are made of materials exhibiting a linear expansion coefficient such that the flatness of the holding surface, which changes in response to the temperature of the chuck due to a difference between the linear expansion coefficient of the chuck table and the linear expansion coefficient of the base member , changes in a substantially linear manner over the operating temperature range of the polishing apparatus;
the chuck table is made of alumina;
the base member is made of an Invar alloy;
4. A polishing apparatus according to claim 1, wherein the difference between the linear expansion coefficient of said base member and the linear expansion coefficient of said chuck table is set to 2.2 ppm/° C. or less .

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