JP3834521B2 - Polishing method and polishing apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a polishing method and a polishing apparatus for flattening a workpiece such as a semiconductor wafer.
[0002]
[Prior art]
With the high integration of LSI, the depth of focus of the exposure machine used in the LSI manufacturing process is decreasing year by year. Along with this, the exposure margin has decreased. For this reason, the flatness of a film formed on a workpiece, for example, a semiconductor wafer (hereinafter simply referred to as a wafer) needs to be made more accurate.
[0003]
A CMP (Chemical Mechanical Polishing) apparatus is used as a planarization technique used for polishing.
[0004]
FIG. 12 is a schematic perspective view showing an outline of the polishing unit 46 of the CMP apparatus. In a state in which a polishing pad (polishing cloth) 51 based on foamed polyurethane is rotated on a surface plate 52 fixed on the upper surface, and a semiconductor wafer 54 is fixed to a top ring 53 provided facing the polishing pad 51, While dripping the polishing slurry 55 in which the silica abrasive grains are turbid on the surface of the polishing pad 51, the semiconductor wafer 54 is pressed against the polishing pad 51 with a predetermined load and polished to the polishing end point to perform a predetermined polishing amount. It was.
[0005]
In JP-A-2000-223448, in order to obtain a constant polishing rate during polishing, the depth of the concave portion of the polishing cloth is measured with a displacement meter, and the polishing rate is controlled to a constant rate based on the result. Technology is disclosed.
[0006]
[Problems to be solved by the invention]
However, in the conventional CMP apparatus, since the polishing end point is obtained from the top ring vibration width or the surface plate motor current value, the condition of the workpiece is not directly measured, so it is difficult to detect the end point with high accuracy. Met. Note that the technique disclosed in Japanese Patent Application Laid-Open No. 2000-223448 is not a technique for directly measuring the state of the workpiece, so it is difficult to say that the detection is highly accurate.
[0007]
Further, although the amount of polishing was obtained using a non-contact or contact displacement meter, a mechanism for simultaneously measuring the amount of polishing and detecting the end point has not been realized.
[0008]
Conventionally, there has been no function for reporting abnormal types of polishing during polishing.
[0009]
The present invention has been made on the basis of these circumstances, it is possible to easily and simultaneously perform the polishing amount measurement and the end point detection that were conventionally measured separately, and also has a function of notifying the abnormal type during polishing, An object of the present invention is to provide a polishing method and a polishing apparatus that can control the attitude of a displacement meter so that the polishing amount and end point can be detected by each wafer, top ring, and polishing cloth.
[0010]
[Means for Solving the Problems]
According to the means of the first aspect of the present invention, the workpiece is held by the top ring provided facing the surface plate to which the polishing cloth is attached, and pressed against the polishing cloth while rotating the workpiece. A polishing method for polishing ,
A back surface position of the workpiece on a plurality of concentric circles of the workpiece is measured by a non-contact displacement meter through a translucent window that can observe the back surface of the workpiece provided on the top ring. A polishing method characterized by measuring and detecting a polishing amount of the workpiece being polished based on a measurement result.
[0011]
According to the second aspect of the present invention, the workpiece is held by the top ring provided opposite to the surface plate to which the polishing cloth is attached, and pressed against the polishing cloth while rotating the workpiece. A polishing method for polishing,
The position of the back surface of the workpiece is measured by a non-contact displacement meter through a translucent window provided on the top ring through which the back surface of the workpiece can be observed. A polishing method characterized in that measurement is performed using an approximate line of waviness caused by a shape error of a workpiece, and a polishing amount of the workpiece being polished is detected based on a measurement result .
[0012]
According to the third aspect of the present invention, the workpiece is held by the top ring provided opposite to the surface plate to which the polishing cloth is attached, and pressed against the polishing cloth while rotating the workpiece. A polishing method for polishing,
A back surface position of the workpiece on a plurality of concentric circles of the workpiece is measured by a non-contact displacement meter through a translucent window that can observe the back surface of the workpiece provided on the top ring. , Measuring using a shape error of the surface plate or an approximate line of waviness caused by a shape error of the workpiece, and detecting a polishing amount of the workpiece being polished based on a measurement result This is a polishing method.
[0013]
According to the means of the invention of claim 4, the surface plate to which the polishing cloth is attached and the workpiece can be held so as to face the polishing cloth, and the workpiece is held on the polishing cloth while rotating the workpiece. A polishing apparatus having a top ring provided so as to be capable of being pressed, the top ring being provided on a plurality of concentric circles of the workpiece, and a translucent material capable of observing the back surface of the workpiece. Windows are provided,
In the polishing apparatus, a non-contact displacement meter is provided at a position facing the rotation locus of the window.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0017]
FIG. 1 is a schematic diagram showing the configuration of a polishing unit and its control unit of a CMP apparatus according to the present invention.
[0018]
The polishing unit of the CMP apparatus is attached so that the top ring 2 that holds the workpiece 1, for example, the wafer 1 is continuously rotated in the direction of arrow A by the drive source of the top ring rotation mechanism 3 around the axis A _1. It is done. The top ring 2 is configured to press the wafer 1 against a polishing cloth 4 described later with a predetermined force. Further, at a position facing the lower surface of the top ring 2 is provided with a base plate 6 mounted for rotation to the direction of the arrow B successively by the platen rotating mechanism 5 about the axis A _2. A polishing cloth 4 made of a material such as polyurethane is attached to the surface of the surface plate 6.
[0019]
Further, at a position facing the upper surface of the top ring 2, a displacement measuring module 7 is provided by each non-contact sensor via each 6-degree-of-freedom fine movement stage 9 fixed to the fixed holding portion 8 of the top ring rotating mechanism 3. A non-contact displacement meter 11 (for example, a laser displacement meter) is provided.
[0020]
As shown in a cross-sectional view of the top ring 2 in FIG. 2, the top ring 2 forms a hollow disk body 14 in which flatness is ensured by combining a SUS plate 12 and a ceramic base 13. A guide ring 15 made of, for example, polycarbonate is provided on the lower surface side of the hollow disk body 14 to guide the wafer 1. The hollow disc body 14 is provided with a polishing pressure control hole 16 connected to polishing pressure control means (not shown) such as a vacuum pump. In addition, a buffer material 17 that adsorbs the wafer 1 is provided in a ring-shaped interior formed on the lower surface side of the gantry 13. Furthermore, a plurality of light-transmitting windows 18 formed of a light-transmitting material that penetrates the hollow disk body 14 and the buffer material 17 in the Z-axis direction are formed. As shown in FIG. 1, for example, the window 18 having a diameter of 2 mm is arranged on a concentric circle having a radius of 15 mm pitch at an angle of 45 degrees. Accordingly, the non-contact displacement meter 11 provided facing the concentric circles that are the rotation trajectories of the respective windows 18 is used to accurately observe the back surface position of the wafer 1 being processed while being held by the top ring 2 through the windows 18. Can be measured.
[0021]
As shown in a schematic perspective view in FIG. 3 (a) and a cross-sectional view in FIG. 3 (b), each 6-DOF fine movement stage 9 has three piezoelectric tube actuators 19A, 19B, and 19C arranged positively. It is provided in the fixed holding part 8 of the top ring rotating mechanism 3 so as to be positioned at the apex of the triangle. A steel ball 23 that engages with a concave steel ball receiver 22 provided on the stage 21 is provided at the tip of each piezoelectric tube actuator 19A, 19B, 19C.
[0022]
4A, the piezoelectric tube actuators 19A, 19B, and 19C (for example, Stavely Sensor Inc. EBL # 2) have four electrodes EI, EII, EIII, and EIV (+ X, − X, + Y, -Y), and an actuator driver (not shown) controls the combination of voltage application to the electrodes EI, EII, EIII, EIV and the voltage value. And it is displaced in the horizontal plane (X, Y). For example, when a voltage of V [V] is applied to the + X electrode EI and −V [V] is applied to the −X electrode EII, the piezoelectric element of the + X electrode EI portion expands, and the piezoelectric element of the −X electrode EII portion contracts, As a result, the distal end portion of the piezoelectric tube actuator 19 is displaced in the + X direction (in StlverySensors Inc. EBL # 2, the displacement is 16 × VI [nm]). FIG. 4B shows the relationship between the voltage applied to the electrodes EI, EII, EIII, and EIV and the movement direction.
[0023]
Further, the display of FIG. 5 shows that the tips of the piezoelectric tube actuators 19A, 19B, and 19C are displaced by applying voltages to the electrodes EI, EII, EIII, and EIV of the piezoelectric tube actuators 19A, 19B, and 19C. Applied voltages to the electrodes EI, EII, EIII, EIV when the stage 21 fixed to the piezoelectric tube actuators 19A, 19B, 19C through the steel ball receiver 22 performs position control (attitude control) with six degrees of freedom The movement direction of the stage 21 is shown.
[0024]
FIG. 6 shows an example in which the stage 21 is rotated about the X axis. By applying each voltage in the thick frame portion in FIG. 6 to each electrode EI, EII, EIII, EIV, FIG. The piezoelectric tube actuators 19A and 19B are extended, and the piezoelectric tube actuator 19C is contracted. As a result, the stage 21 rotates around the X axis.
[0025]
As shown in FIG. 1, the control unit is configured to control each unit of the CMP apparatus by the controller 25. Therefore, the following are connected to the controller 25 respectively. A pressure sensor 26 for detecting the pressure of the top ring 2, a fine movement stage amplifier 27 for controlling the fine movement stage 9 with 6 degrees of freedom, a displacement gauge amplifier 28 for controlling the non-contact displacement meter 11, and a surface plate rotating mechanism 5 are controlled. And a flow rate sensor 32 for detecting the flow rate of the polishing liquid / chemical solution.
[0026]
Next, the operation of the present invention will be described.
[0027]
In the CMP apparatus, in order to perform high-precision polishing, first, it is necessary to accurately grasp the mounting state of the wafer 1, and the non-contact displacement meter 11 must be adapted thereto. For that purpose, the piezoelectric tube actuators 19A and 19B are measured so that the wafer positions are measured using the non-contact displacement gauges 11 through the windows 18 of the top ring 2 before the polishing process so that they become set values. , 19C is operated to adjust the 6-degree-of-freedom fine movement stage 9 holding the non-contact displacement meter 11, and the position and posture of the non-contact displacement meter 11 are adjusted.
[0028]
The basic operation of the CMP apparatus is to press the wafer 1 held on the top ring 2 while rotating it while discharging the polishing liquid or chemical liquid onto the polishing cloth 4 affixed to the surface of the rotating surface plate 6. The thin film formed on the surface of 1 is polished mechanically. The polishing cloth 4 is then repeatedly dressed, initialized, and then polished again.
[0029]
FIG. 7 is an explanatory diagram of polishing amount / end point detection measurement during polishing. The polishing amount is the polishing amount of the thin film formed on the wafer 1, and since the thickness of the thin film formed on the wafer 1 before polishing is known, it is processed that the polishing amount is known. This means that the thickness of the thin film on the wafer 1 is also detected at the same time. In the following description, the undulation caused by the shape error of the surface plate 6 and the shape error of the top ring 2 is ignored to simplify the description. Further, the waviness caused by the shape error of the surface plate 6 and the shape error of the wafer 1 is ignored.
[0030]
The film of the wafer 1 being polished is measured with respect to the wafer 1 being polished by measuring the position of the back surface of the wafer 1 from the back surface of the rotating top ring 2 through a plurality of windows 18 using a non-contact displacement meter 11. The thickness change is measured. Further, the vibration state in the vertical direction of the top ring 2 is measured from measured values (= position information on the back surface of the top ring 2) other than the window 18 on the back surface of the top ring 2, and the polishing end point detection is determined from this amplitude value. . For example, in the case of interlayer film polishing, the end point is not detected if there is vibration, and the end point is detected if the vibration falls below a specified value.
[0031]
Also, by using a plurality of non-contact displacement meters 11 and synthesizing the polishing amount information on the concentric circles of the wafer 1 obtained from one non-contact displacement meter 11, the polishing amount distribution over the entire surface of the wafer 1 can be measured. is there. In consideration of the displacement of the top ring 2 due to the viscoelasticity of the polishing cloth 4 immediately after the top ring 2 has landed on the polishing cloth 4, data immediately after the landing of the top ring 2 is omitted from the polishing amount measurement data calculation.
[0032]
In addition, as shown in FIG. 8, when waviness due to the shape error of the surface plate 6 or the shape error of the top ring 2 or the waviness due to the shape error of the surface plate 6 or the shape error of the wafer 1 is observed. The waviness is approximated (for example, the least mean square linear approximate line), and the approximate value of the polishing amount can be obtained from the approximate line. Thereby, the polishing amount can be measured during polishing, and the overpolish amount after the polishing end point can be accurately determined. Next, detection of an abnormal state will be described as illustrated in FIG. Note that FIG. 1 is referred to for the configuration of each unit.
[0033]
Based on the relationship between the polishing speed during polishing and the motor current of the surface plate 6, abnormal types such as pressure abnormality, polishing liquid flow rate abnormality, motor abnormality and abnormal polishing (unknown cause abnormality) are notified.
[0034]
For the pressure abnormality, the output value of the pressure sensor 26 is monitored to distinguish between abnormal polishing and pressure abnormality in region II. That is, if the value of the pressure sensor 26 is high and the region II is abnormal, the pressure is abnormal. If the value of the pressure sensor 26 is normal and the region II is abnormal, abnormal polishing is performed.
[0035]
Similarly, for the abnormal flow rate of the polishing liquid or chemical, the output value of the flow sensor 32 is monitored to distinguish abnormal polishing and abnormal flow in the region III. That is, if the value of the flow sensor 32 is high and the region III is abnormal, the flow rate is abnormal. If the value of the flow sensor 32 is normal and the value of the pressure sensor 26 is low, the pressure is abnormal. If the value of the flow sensor 32 is normal and the value of the pressure sensor 26 is normal III, the region is abnormally polished.
[0036]
Incidentally, since each pressure sensor 26 and flow rate sensor 32 monitors the pressure and flow rate away from the processing point, it is not reliable to employ each sensor alone as an abnormality alarm. Therefore, as shown in FIG. 9, the abnormality type is determined in consideration of the relationship between the motor current and polishing speed of the surface plate 6 and the sensor monitor value. Note that the Vt value in FIG. 9 is about 10 amperes in interlayer film polishing, for example.
[0037]
Next, a modified example of the present invention will be described.
[0038]
In the above-described embodiment, the translucent window 18 is provided on the top ring 2. However, as shown in the schematic diagram of FIG. 10, film thickness measurement and end point detection when there is no hole on the back surface of the top ring 2. It is an overview of the mechanism. The same functional parts as those in FIG. 1 are denoted by the same reference numerals and their description is omitted. In this case, the position of the back surface of the top ring 2 is detected by the non-contact displacement meter 11.
[0039]
In this case, as shown in the explanatory diagram of FIG. 11, the polishing amount / end point detection when the window 18 is not provided on the back surface of the top ring 2 is performed simultaneously from the positional information on the back surface of the top ring 2. be able to. However, in this case, since the entire movement of the top ring 2 is detected, the polishing amount distribution in the surface of the wafer 1 cannot be measured.
[0040]
As described above, according to each of the embodiments described above, the piezoelectric tube actuator is provided so that the top ring and the back surface of the wafer can always be measured even if the shape of the polishing cloth of the polishing apparatus or the shape of the wafer changes. A 6-degree-of-freedom stage using a plurality can be realized.
[0041]
In addition, using a 6-DOF fine-motion stage, it is possible to accurately align a non-contact displacement meter regardless of the shape of the wafer, top ring or polishing cloth, and to accurately measure the polishing amount of the wafer and detect the end point in real time. It can be carried out.
[0042]
In addition, it is possible to simultaneously perform polishing amount (distribution) measurement and end point detection using a non-contact displacement meter. Thereby, it is possible to accurately determine the amount of overpolish after the end point is detected.
[0043]
Further, since the abnormal type of the polishing state during polishing can be notified in real time, even when an abnormality of the polishing state occurs, an appropriate countermeasure can be taken for each.
[0044]
【The invention's effect】
According to the present invention, a small and highly accurate 6-DOF fine movement stage is possible.
[0045]
Further, it is possible to measure the polishing amount and detect the end point with high accuracy in real time while polishing the workpiece.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing the configuration of a polishing unit and its control unit of a CMP apparatus according to the present invention.
FIG. 2 is a cross-sectional view of the top ring of the present invention.
3A is a schematic perspective view of a six-degree-of-freedom fine movement stage of the present invention, and FIG.
4A is a structural explanatory diagram of a piezoelectric tube actuator, and FIG. 4B is a table showing a relationship between an applied voltage to an electrode and a moving direction.
FIG. 5 is a table showing the relationship between the voltage applied to each electrode of the piezoelectric tube actuator and the direction of movement of the stage.
FIG. 6 is a table showing applied voltages to the electrodes of the piezoelectric tube actuator when the stage is rotated around the X axis.
FIG. 7 is an explanatory diagram of polishing amount / end point detection measurement during polishing.
FIG. 8 is an explanatory diagram for obtaining an approximate value of the polishing amount from an approximate line when waviness occurs.
FIG. 9 is an explanatory diagram regarding detection of an abnormal state.
FIG. 10 is an explanatory diagram of another embodiment of the present invention.
FIG. 11 is an explanatory diagram of polishing amount / end point detection according to another embodiment of the present invention.
FIG. 12 is a schematic plan view showing an example of a polishing unit of a conventional CMP apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Wafer, 2 ... Top ring, 3 ... Top ring rotation mechanism, 4 ... Polishing cloth, 6 ... Surface plate, 7 ... Displacement measurement module, 9 ... 6 degree-of-freedom fine movement stage, 11 ... Non-contact displacement meter, 18 ... Window , 19A, 19B, 19C ... Piezoelectric tube actuator, 23 ... Steel ball, 25 ... Controller, EI, EII, EIII, EI5 ... Electrode,

Claims (4)

A polishing method in which a workpiece is held by a top ring provided opposite to a surface plate to which a polishing cloth is attached, and pressed against the polishing cloth while rotating the workpiece, and polished .
A back surface position of the workpiece on a plurality of concentric circles of the workpiece is measured by a non-contact displacement meter through a translucent window that can observe the back surface of the workpiece provided on the top ring. A polishing method comprising: measuring and detecting a polishing amount of the workpiece being polished based on a measurement result. A polishing method in which a workpiece is held by a top ring provided opposite to a surface plate to which a polishing cloth is attached, and pressed against the polishing cloth while rotating the workpiece, and polished.
  The position of the back surface of the workpiece is measured by a non-contact displacement meter through a translucent window provided on the top ring through which the back surface of the workpiece can be observed. A polishing method, comprising: measuring using an approximate line of waviness caused by a shape error of a workpiece, and detecting a polishing amount of the workpiece being polished based on a measurement result. A polishing method in which a workpiece is held by a top ring provided opposite to a surface plate to which a polishing cloth is attached, and pressed against the polishing cloth while rotating the workpiece, and polished.
A back surface position of the workpiece on a plurality of concentric circles of the workpiece is measured by a non-contact displacement meter through a translucent window that can observe the back surface of the workpiece provided on the top ring. , Measuring using a shape error of the surface plate or an approximate line of waviness caused by a shape error of the workpiece, and detecting a polishing amount of the workpiece being polished based on a measurement result Polishing method. Polishing having a surface plate to which a polishing cloth is attached, and a top ring that can hold the workpiece so as to face the polishing cloth and can be pressed against the polishing cloth while rotating the workpiece. In the apparatus, the top ring is provided on a plurality of concentric circles of the workpiece, and is provided with a translucent window capable of observing the back surface of the workpiece.
A polishing apparatus, wherein a non-contact displacement meter is provided at a position facing the rotation locus of the window.

Images