JP2000340537A - Polishing apparatus and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a film left on the surface of a polished work to vary in thickness within a certain tolerance limit. SOLUTION: A polishing apparatus is equipped with a turn table 17 possessed of a polishing surface and a top ring 26 which presses a semiconductor wafer against the polishing surface, where the turn table 17 and the top ring 26 are rotated to polish a film formed on the surface of a semiconductor wafer W. In this case, ammeters 27a and 28a, which measure currents fed to the drive motors 27 and 28 of the turn table 17 and the top ring 26 in a polishing operation and physical quantity measuring sections 30, 31, 33, 34, and 38, which measure the vibrations of the top ring 26 at polishing, polishing sounds, and physical quantities such as frictional heat and the like generated by the physical contact of the polished surface of a semiconductor wafer with the polishing surface of the turn table 17 in a polishing operation, are provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polishing apparatus and a polishing method, and more particularly, to polishing a film deposited on a surface of an object to be polished such as a semiconductor wafer into a flat and mirror-like surface (residual film). The present invention relates to a polishing apparatus and a polishing method capable of minimizing the variation in the film thickness of the polishing.

[0002]

2. Description of the Related Art In recent years, as the degree of integration of semiconductor devices has increased, circuit wiring has become finer, and the distance between wirings has become smaller. In particular, in the case of optical lithography with a line width of 0.5 μm or less, the depth of focus becomes shallow, so that the image plane of the stepper needs to be flat. Therefore, it is necessary to planarize the surface of the semiconductor wafer. One of the planarization methods is polishing (polishing) using a polishing apparatus.
That is being done.

Conventionally, a polishing apparatus of this type has a turntable having a polishing cloth adhered to the upper surface, a turntable constituted by a grindstone having a polishing surface on the upper surface, and a turntable which rotates at an independent rotation speed. The top ring applies a predetermined pressure to the turntable, and the polishing target is interposed between the turntable and the top ring to polish the surface of the polishing target flat and mirror-finished.

When polishing a film on the surface of a semiconductor wafer by the above-described polishing apparatus, it is necessary to detect the end point of polishing and reduce the variation in the film thickness of the remaining film. For this reason, as one of the end point detection means of polishing, a method of detecting a change in polishing frictional force when polishing is transferred to a different material is known. Specifically, the semiconductor wafer to be polished has a laminated structure made of different materials of semiconductor, conductor, and insulator, and the friction coefficient is different between the different materials. This is a method for detecting a change in polishing frictional force caused by the polishing. According to this method, the end point of the polishing is when the polishing reaches the dissimilar material layer.

Here, a change in the polishing frictional force is detected, for example, as follows. Since the polishing frictional force acts on a position eccentric from the rotation center of the turntable, it acts as a load torque on the rotating turntable. Therefore, the polishing frictional force can be detected as a torque acting on the turntable. When the means for driving the turntable to rotate is an electric motor, the torque can be measured as a current flowing through the motor. Therefore, the end point of the polishing is detected by monitoring the motor current with an ammeter and performing signal processing. In addition to the current value, for example, the end point of polishing can be detected by vibration, sound,
It was also performed by capturing physical quantities such as frictional heat.

[0006]

By the way, as the degree of integration as a semiconductor device increases, there is a problem that the film thickness of a film remaining after polishing has a large variation.
For example, in the oxide film forming process, as shown in FIG. 4A, a trench 2 is provided on the surface of the silicon substrate 1 and a SiN is formed on the surface of the silicon substrate 1 excluding the trench 2.
After forming the film 3, an SiO ₂ film 4 is deposited on the surfaces of the trench 2 and the SiN film 3. Next, as shown in FIG. 4B, the surface of the SiO ₂ film 4 is polished flat and mirror-like. Thereafter, as shown in FIG. 4C, the SiN film 3 is removed by etching to form a shallow trench 5, and as shown in FIG. The wiring material 6 is formed. here,
The thickness t of the SiN film 3 remaining after the polishing needs to be a constant thickness. Therefore, the variation in the thickness of the film remaining after the polishing is, for example, ± 20%.
It is desired to be within a certain tolerance range such as 0 °.

However, in the conventional method, even if the variation in the film thickness of the film remaining after the polishing is to be kept within a certain tolerance range, as described above, the physical quantity such as the motor current, vibration, sound, frictional heat, etc. Therefore, the control of this film thickness is limited, and there is no effective method for detecting the end point of polishing especially in the oxide film process. there were.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has a polishing apparatus and method capable of keeping a variation in film thickness of a film remaining on the surface of a polishing object within a certain tolerance range. The purpose is to provide.

[0009]

A polishing apparatus according to the present invention includes a turntable having a polishing surface, and a top ring for pressing an object to be polished against the polishing surface,
In a polishing apparatus for rotating a turntable and rotating a top ring to polish a film on a surface of an object to be polished, a current value measuring unit for measuring a current value supplied to a drive motor of the turntable and the top ring during polishing. And a physical quantity that measures the physical quantity generated by the physical contact between the polished surface of the object to be polished and the polished surface of the turntable during polishing, such as vibration of the top ring during polishing, sound during polishing, and frictional heat during polishing. And a measuring unit. The arithmetic unit is capable of estimating the film thickness of the remaining film from the film thickness before polishing after estimating the polishing amount of the film.

According to the present invention, the polishing amount of the film formed on the surface of the object to be polished is measured with a current value until the film thickness can be measured with a film thickness measuring instrument having a high measurement accuracy and a very narrow range for measuring the film thickness. The polishing can be performed while estimating based on signals from the section and the physical quantity measuring section. Then, after actually measuring the film thickness with a film thickness measuring device, the film is polished again to have a predetermined film thickness, thereby improving the processing accuracy and keeping the film thickness variation within a certain tolerance range. it can.

The polishing method according to the present invention comprises a turntable having a polished surface and a top ring for pressing an object to be polished against the polished surface. In a polishing method for polishing a film formed on an object surface, the polishing amount of the film is estimated while monitoring the polishing state of the film formed on the surface of the polishing object during polishing, and the polishing amount is estimated until the polishing amount reaches a predetermined value. A step of performing primary polishing, a step of measuring a film thickness of a film remaining on the surface of the polishing object after the primary polishing, and a step of performing secondary polishing based on the measured value of the remaining film thickness It is characterized by having.

According to the present invention, primary polishing is performed until the film thickness can be measured with a film thickness measuring instrument having high measurement accuracy and a very narrow range in which the film thickness can be measured. After the measurement, the film is polished again so as to have a predetermined film thickness, so that the processing accuracy can be improved and the variation in the film thickness can be kept within a certain tolerance range.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a polishing apparatus and method according to the present invention will be described below with reference to FIGS. FIG. 1 is a plan view showing an overall configuration of a polishing apparatus of the present invention, FIG. 2 is a side view showing a configuration of a polishing section, and FIG. 3 is an explanatory view showing an example of polishing a semiconductor wafer.

The polishing apparatus includes a polishing section 10, a loading / unloading section 11, a transfer robot 12, three cleaning machines 13a, 13b, 13c, and a reversing machine 14. The transfer robot 12 may be a type that runs on a rail as shown in FIG. 1 or a fixed type that has a robot hand at the tip of an articulated arm. A film thickness measuring unit 16 provided with a film thickness measuring device 15 is provided at a position along the transfer path of the semiconductor wafer W taken out by the transfer robot 12 from the wafer cassette 50 placed on the load / unload unit 11.
Is arranged. On the other hand, the polishing section 10 is provided with a turntable 17 having a polishing cloth on the upper surface, and a pusher 18 for transferring the semiconductor wafer W to the side of the turntable 17 and a film thickness measuring device 19. The thickness measuring unit 20 is disposed.

The film thickness measuring device 15 measures the film thickness of the film formed on the surface of the semiconductor wafer W before the polishing is started, for example, as shown in FIG.
This is for measuring the thickness t1 of the SiO ₂ film 4 shown in (A), and a film whose measurement range is quite wide is used. On the other hand, the film thickness measuring device 19 calculates the film thickness of the film remaining on the surface of the semiconductor wafer W after the primary polishing after polishing for a predetermined time, for example, the film thickness t2 of the SiN film 3 shown in FIG. It is used for measurement, which has a high measurement accuracy and a considerably narrow measurement range.

The cleaning machine 13a has a plurality of upright rollers 21 arranged so as to surround the semiconductor wafer W, and the semiconductor wafer W is held by a holding groove formed at the top of the roller 21.
Is a low-speed rotation type washing machine that holds the edge of the semiconductor wafer W and rotates the semiconductor wafer W by the rotation of the roller 21. Washing machine 1
Reference numerals 3b and 13c denote high-speed rotary type cleaning machines having a rotary table 24 formed at the upper end of a rotary shaft 22 and extending radially from an arm 23 for gripping the semiconductor wafer W. In any of the cleaning machines, a nozzle for supplying a cleaning liquid or the like to the surface of the semiconductor wafer W, a peripheral wall for preventing splash scattering, a duct for forming a downward airflow for preventing mist diffusion, and the like are provided.

As shown in FIG. 2, the polishing section 10 includes a turntable 17 having a polishing cloth 25 adhered on the upper surface thereof, and a top for holding the semiconductor wafer W and pressing the polishing cloth 25 and rotating the semiconductor wafer W. A ring 27, a motor 27 for driving the top ring 26 to rotate on the turntable 17, and a motor 28 for driving the turntable 17 to rotate
And The top ring 26 is held on the free end side of the swing arm 29 and is swingable, so that the turntable 17, the pusher 18, and the film thickness measuring unit 20 can be accessed. The polishing liquid Q can be supplied from the polishing liquid supply nozzle 41 onto the polishing cloth 25. Although not shown, in the case of a turntable made of a grindstone, the polishing pad 25 is not necessary, and the polishing liquid Q or pure water is supplied onto the turntable 17 made of a grindstone.

Above the turntable 17, a radiation thermometer 30 for measuring the surface temperature of the polishing cloth 25 or the grindstone during polishing is arranged.
An acceleration sensor 31 for measuring vibration of the top ring 26 during polishing and / or an amplitude sensor (not shown) are attached. A temperature control water pipe 32 for supplying temperature control water is provided inside the turntable 17, and thermometers 33, 3 for measuring the temperature of the temperature control water are provided at the inlet and the outlet of the temperature control water pipe 32.
4 are attached. Further, a noise measuring device 38 for measuring noise during polishing is provided near the top ring 26. The film thickness measuring device 19 disposed adjacent to the turntable 17 is attached to the tip of the arm 35a of the robot 35.

The polishing apparatus includes an arithmetic unit 36.
And an additional polishing condition setting unit 37, and a current value measuring unit for measuring the measured values of the film thickness measuring devices 15 and 19 and the current flowing through the turntable driving motor 28 and the top ring driving motor 27 in the arithmetic unit 36. The current values from 27a and 28a, the measurement values of the radiation thermometer 30, the acceleration sensor 31, the amplitude sensor, the thermometers 33 and 34, and the noise meter 38 are input. Further, the measured value of the film thickness measuring device 19 is input to the additional polishing condition setting unit 37. The radiation thermometer 3
0, acceleration sensor 31, amplitude sensor, thermometer 33, 34
And the noise measuring device 38 constitute a physical quantity measuring unit.

The arithmetic unit 36 estimates the polishing amount of the film while monitoring the polishing state of the film on the surface of the semiconductor wafer W during polishing. That is, the work amount for the semiconductor wafer W to be polished includes the turntable driving motor 27 and the top ring driving motor 28.
Corresponds to the integral value of the current value of the current flowing through. The energy loss includes vibration that causes the top ring 26 to run wild, noise that escapes as sound energy, and heat loss caused by heat exchange between the surface of the polishing pad 25 and the turntable 17. Therefore, the integral value of the current value of the current flowing through the turntable drive motor 27 and the top ring drive motor 28 is Δf (1), and the integral value based on the measurement value of the radiation thermometer 30 is Δf (2). The integral value based on the measurement value of the acceleration sensor 31 is ∫f (3), the integral value based on the measurement value of the thermometers 33 and 34 is ∫f (4), and the integral value based on the measurement value of the noise meter 38 is ∫f (3). When f (5) is set, the polishing amount can be estimated as: polishing amount = ∫f (1)-∫f (2)-∫f (3)-∫f (4)-∫f (5) .

The arithmetic unit 36 includes a film thickness measuring device 15
Is input. The film thickness measuring device 15 measures the film thickness of the film formed on the surface of the semiconductor wafer W before polishing, and subtracts the estimated polishing amount from the measured value to obtain the film thickness of the remaining film. Is required. When the thickness of the remaining film reaches a certain value, the arithmetic unit 36 is configured to output a signal to the control device 40 of the polishing apparatus.

On the other hand, the additional polishing condition setting section 37 sets additional polishing conditions based on the measured values of the film thickness measuring device 19. That is, in the additional polishing condition setting unit 37, a film thickness of a film to be left is input in advance as a set value, and by comparing this set value with a value measured by the film thickness measuring device 19, for example, Additional polishing conditions such as an additional polishing time are set, and the output signal is input to the controller 40 of the polishing apparatus.

Next, a description will be given of a polishing operation by the polishing apparatus having the above configuration. FIG. 3 is a cross-sectional view of a semiconductor wafer W to be polished. As shown in FIG. 3A, a trench 2 is provided on the surface of a silicon substrate 1 and the silicon substrate excluding the trench 2 is removed. After a SiN film 3 is formed on the surface of
A semiconductor wafer W having a SiO ₂ film 4 deposited on the surface of the SiN film 3 is housed in a wafer cassette 50.

Next, the semiconductor wafer W is taken out from the wafer cassette 50 placed on the loading / unloading section 11 by the transfer robot 12 and transferred to the film thickness measuring section 16. Then, the film thickness on the surface of the semiconductor wafer W, that is, the film thickness t1 of the SiO ₂ film 4 is measured by the film thickness measuring device 15 (see FIG. 3A). Thereafter, the semiconductor wafer W is transferred to the pusher 18 by the transfer robot 12 and
Hand over to 6.

Next, while rotating the top ring 26 holding the semiconductor wafer W by driving the motor 27,
The turntable 17 is rotated by driving a motor 28. Then, the semiconductor wafer W is pressed against the polishing pad 25 by the top ring 26, and at the same time, the polishing liquid Q is supplied to the polishing pad 25 from the polishing liquid supply nozzle 41. As a result, film formation on the surface of the semiconductor wafer W, that is, Si shown in FIG.
The O ₂ film 4 and the SiO ₂ film 4 and the SiN film 3 are simultaneously polished (primary polishing).

During this polishing, the current value of the current flowing through the turntable driving motor 28 and the top ring driving motor 27, and the measured values of the radiation thermometer 30, the acceleration sensors 31, the thermometers 33 and 34, and the noise measuring device 38 Is input to the calculation unit 36, and the calculation unit 36 estimates the polishing amount of the film formation. Then, when a value obtained by subtracting this polishing amount from the initial film thickness t1 of the initial film reaches a certain value such as 4500 to 5500 °, a signal is sent to the control device 40 of the polishing apparatus.

When this signal is received, the polishing operation is temporarily interrupted, the swing arm 29 is turned, and the semiconductor wafer W is positioned on the film thickness measuring section 20 while holding the semiconductor wafer W with the top ring 26 as shown in FIG. Then, the thickness of the remaining film, that is, the film thickness t2 of the SiN film 3 shown in FIG. 3B is measured by the film thickness measuring device 19, and the measurement result is input to the additional polishing condition setting unit 37. As described above, by performing the primary polishing while estimating the polishing amount, the thickness t of the SiN film 3 can be measured by the film thickness measuring device 19 with high measurement accuracy and a very narrow range in which the film thickness can be measured.
2 can be measured.

The additional polishing condition setting unit 37 includes a film thickness measuring device 1
Upon receiving the signal from the control unit 9, the measured value is compared with a previously set value, and based on the difference, an additional polishing condition such as an additional polishing time is set. Send a signal. In this case, in order to obtain the additional polishing time, it is necessary to know the polishing rate. However, the polishing amount is calculated by the calculating unit 36 from the measured value of the film thickness measuring device 15 and the measured value of the film thickness measuring device 19. The polishing amount can be determined by dividing the polishing amount by the polishing time.

Then, as described above, the top ring 26
The semiconductor wafer W is pressed against the polishing cloth 25 of the rotating turntable 17 while rotating, and at the same time, the polishing liquid Q is supplied to the polishing cloth 25, thereby forming a film on the surface of the semiconductor wafer W, ie, SiO 2 _{The second} film 4 and the SiN film 3 are simultaneously polished (secondary polishing). Thus, as shown in FIG. 3C, the polishing is completed so that the thickness t3 of the SiO ₂ film 4 and the thickness t4 of the SiN film 3 become predetermined values. Through the above steps, the processing accuracy can be improved so that the variation in the film remaining after the polishing falls within a certain tolerance range, for example, ± 200 °.

Next, the polished semiconductor wafer W is transferred to the cleaning machine 13a, where the semiconductor wafer W is polished.
While rotating the wafer, scrub cleaning (primary cleaning) is performed by a cleaning member from above and below while supplying pure water or a cleaning liquid to the upper and lower surfaces of the semiconductor wafer W. Thereafter, it is transferred to the washing machine 13b or 13c.

In the cleaning machine 13b or 13c, for example, while the semiconductor wafer W is being rotated at a low speed of about 100 to 500 rpm, pure water vibrated by ultrasonic waves is applied to the semiconductor wafer W.
Is supplied so as to pass through the central portion of the semiconductor wafer W, and finish cleaning (secondary cleaning) of the surface of the semiconductor wafer W is performed. Then, the supply of the pure water is stopped, and the rotation speed of the semiconductor wafer W is set to 1500 to 5
The process is shifted to a high-speed rotation of about 000 rpm, and a drying process of the semiconductor wafer W is performed while supplying a clean inert gas as necessary. The semiconductor wafer W after the cleaning / drying process is returned to the wafer cassette 50 placed on the loading / unloading section 11 by a clean hand of the transfer robot 12.

[0032]

As described above, according to the present invention,
The polishing can be performed while estimating the polishing amount of the film formed on the surface of the object to be polished until the film thickness can be measured with a film thickness measuring instrument having a very narrow measurement range with high measurement accuracy. Then, after actually measuring the film thickness with a film thickness measuring device, the film is polished again so as to have a predetermined film thickness, so that the processing accuracy can be increased and the film thickness variation can be kept within a certain tolerance range. it can.

[Brief description of the drawings]

FIG. 1 is a plan view showing the overall configuration of a polishing apparatus according to an embodiment of the present invention.

FIG. 2 is a side view illustrating a configuration of a polishing unit in the polishing apparatus according to the embodiment of the present invention.

FIG. 3 is an enlarged sectional view showing a surface of a semiconductor wafer polished by the polishing apparatus of the present invention, and FIG.
3 shows before polishing, FIG. 3B shows after primary polishing, and FIG. 3C shows after secondary polishing.

4 is an enlarged sectional view showing a surface of a semiconductor wafer to be polished by a conventional polishing apparatus, FIG. 4 (A) before polishing, FIG. 4 (B) after polishing, and FIG. 4 (C) after etching; FIG. 4D shows the state after the wiring.

[Explanation of symbols]

1 silicon substrate 2 trench 3 SiN film 4 SiO ₂ film 5 shallow trench 6 wiring material 10 polishing unit 11 loading and unloading unit 12 the transfer robot 13a, 13b, 13c washer 14 reversing machine 15, 19 film thickness measuring device 16, Reference Signs List 20 film thickness measuring unit 17 turntable 18 pusher 21 roller 22 rotating shaft 23, 29, 35a arm 24 rotating table 25 polishing pad 26 top ring 27 top ring driving motor 27a, 28a current value measuring unit 28 turn table driving motor 30 Radiation thermometer 31 Acceleration sensor 32 Temperature control water pipe 33,34 Thermometer 35 Robot 36 Operation unit 37 Additional polishing condition setting unit 38 Noise measuring device 40 Control unit 41 Abrasive liquid supply nozzle 50 Wafer cassette W Semiconductor wafer

Claims (5)

[Claims] 1. A turntable having a polished surface and a top ring for pressing an object to be polished against the polished surface, wherein the turntable is rotated and the top ring is rotated to form a film on the surface of the object to be polished. A current measuring unit that measures the current value supplied to the drive motor of the turntable and top ring during polishing, and a vibration of the top ring during polishing, sound during polishing, and friction during polishing. A polishing apparatus, comprising: a physical quantity measuring unit for measuring a physical quantity generated by a physical contact between a polished surface of an object to be polished and a polished surface of a turntable due to polishing by heat or the like. 2. The polishing apparatus according to claim 1, further comprising: an operation section for estimating a polishing amount of a film formed on the surface of the object to be polished based on signals from the current value measurement section and the physical quantity measurement section. apparatus. 3. A film thickness measuring device for measuring a film thickness of a film formed on the surface of the polishing object before starting polishing, and a film thickness measuring device for measuring a film thickness of a film formed on the surface of the polishing object after polishing. The polishing apparatus according to claim 1, further comprising: 4. An additional polishing condition setting unit for measuring a film thickness of a film remaining on a surface of a polishing target after polishing and setting an additional polishing condition based on the measurement result. The polishing apparatus according to claim 1. 5. A turntable having a polished surface and a top ring for pressing an object to be polished against the polished surface, wherein the turntable is rotated and the top ring is rotated to form a film on the surface of the object to be polished. In the polishing method, the polishing amount of the film is estimated while monitoring the polishing state of the film on the surface of the object to be polished during polishing, and the primary polishing is performed until the polishing amount reaches a predetermined value. A step of measuring a film thickness of a film remaining on the surface of the polishing target after the completion of the primary polishing; and a step of performing secondary polishing based on the measured value of the remaining film thickness. A polishing method characterized by the above-mentioned.