JP2009255235A - Polishing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polishing apparatus achieving improved control accuracy of polishing pressure. <P>SOLUTION: This polishing apparatus is provided with: a pad pressurization mechanisms 224 pressing polishing pads 220 by wafers by the use of pressure of air supplied from an air pressure source A; and first electropneumatic regulators 61 arranged in conduits 50, 60 connecting the air pressure source A to the pad pressurization mechanisms 224 and controlling pressure of air supplied from the air pressure source A to the pad pressurization mechanisms 224. The first electropneumatic regulators 61 control air pressure within a range of positive pressure and vacuum, and have venturi tubes 62 forcibly exhausting air in the conduits 60 connecting the first electropneumatic regulators 61 to the pad pressurization mechanisms 224 when depressurizing air pressure. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a polishing apparatus for polishing a substrate such as a semiconductor wafer or a glass substrate.

A CMP apparatus is exemplified as a polishing apparatus for polishing the substrate surface. A CMP apparatus is widely used for polishing a substrate such as a semiconductor wafer or a glass substrate as a technique for polishing a substrate surface with high precision by chemical mechanical polishing (CMP). In such a polishing apparatus, a polishing pad mounted on a polishing head is pressed against a substrate held by a chuck at a predetermined pressure (polishing pressure) and relatively rotated, and the contact between the substrate and the polishing pad is subjected to polishing contents. By supplying a corresponding slurry (Slurry) to cause a chemical and mechanical polishing action, the substrate surface is polished flatly (see, for example, Patent Document 1).
JP 2006-319249 A

  However, in order to polish the substrate surface more flatly, it is necessary to improve the control accuracy of the polishing pressure.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a polishing apparatus with improved control accuracy of polishing pressure.

  In order to achieve such an object, a polishing apparatus according to the present invention includes a polishing tool for polishing a substrate, and an actuator for pressing the polishing tool against the substrate using the pressure of air supplied from an air pressure source. In the polishing apparatus configured to polish the substrate by moving the polishing tool relative to the substrate in a state where the polishing tool is pressed against the substrate using the actuator, the air pressure source And an electropneumatic regulator that controls the pressure of air supplied from the air pressure source to the actuator, and the electropneumatic regulator converts the pressure of the air to positive pressure and negative pressure. The air in the pipeline connecting the electropneumatic regulator and the actuator is strengthened when the pressure of the air is reduced. Configured with a Venturi tube for exhausting.

  According to the present invention, the control accuracy of the polishing pressure can be improved.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. A CMP apparatus (chemical mechanical polishing apparatus) is shown in FIG. 1 as an example of a polishing apparatus in which the polishing method according to the present invention is used. First, the overall configuration of the polishing apparatus PM will be outlined with reference to this drawing. The polishing apparatus PM is roughly classified into a cassette index unit 1 that carries in and out a semiconductor wafer (hereinafter referred to as a wafer W), a polishing unit 2 that performs polishing, and a cleaning of the wafer W that has been subjected to polishing. And a substrate cleaning unit 3 that performs the transfer and a transfer device 4 (the first transfer robot 41 and the second transfer robot 42) that transfer the wafer W in the polishing apparatus. Each unit is partitioned by an automatic opening / closing shutter. A clean chamber is constructed. The operation of the polishing apparatus PM is controlled by a control device (not shown).

The cassette index unit 1 is provided with a wafer mounting table 12 on which cassettes (also referred to as carriers) C _{1 to} C ₄ each holding a plurality of wafers W are mounted, and in front of the wafer mounting table 12. A first transfer robot 41 is provided. The first transfer robot 41 is an articulated arm type robot, and a swivel that can be swung horizontally and moved up and down is provided on an upper part of a base that can move along a linear guide provided on the floor. The articulated arm attached to the arm can be extended and contracted, and the outer peripheral edge of the wafer W can be gripped by the wafer chuck at the tip of the arm. The unprocessed unprocessed wafer W taken out from the send cassettes C ₁ and C ₂ by the first transfer robot 41 is subjected to a polishing processing section in a path for transporting the unprocessed wafer provided in the substrate cleaning section 3. The second second transfer robot 42 is handed over.

The polishing unit 2 is divided into four areas around a circular index table 20 that is rotated and fed every 90 degrees, and a transfer stage S ₀ that carries in unprocessed wafers and carries out processed wafers. The first polishing stage S ₁ for polishing the wafer surface, the second polishing stage S ₂ , and the third polishing stage S ₃ . The index table 20 is divided into four corresponding to these four stages.

The transfer stage S _0, the second transfer robot 42 is provided. Wafer W carried into the polishing unit 2, the adsorption is held by being placed on a wafer chuck 200 which is positioned in the conveying stage S ₀ by the second transfer robot 42.

In the first polishing stage S ₁ , the second polishing stage S ₂ , and the third polishing stage S ₃ , a surface polishing mechanism 22 that polishes the surface of the wafer W attracted and held by the wafer chuck 200 and a polishing surface of the polishing pad, respectively. And a dressing mechanism 23 for dressing.

  As shown in FIG. 2, the surface polishing mechanism 22 has a polishing pad 220, a polishing head 222 that holds and rotates the polishing surface 220s of the polishing pad in a downward horizontal posture, and a horizontal swing and lift operation of the polishing head. The wafer arm 200 is polished and the wafer surface is polished under processing conditions corresponding to the contents of the process performed on each stage. The diameter of the polishing pad 220 is set smaller than the diameter of the wafer W to be polished.

  The wafer surface is polished by the surface polishing mechanism 22 while the polishing arm 223 is horizontally swung and the polishing head 222 is positioned above the wafer chuck. The polishing arm 223 is pressed while pressing the polishing surface 220s of the polishing pad 220 with a predetermined pressure (polishing pressure) against the surface (surface Ws to be polished) of the wafer W that is sucked and held and rotated, and supplying slurry from the center of the polishing head. The entire surface of the wafer W is polished flatly.

  In addition, as shown in FIG. 4, a so-called airbag-type pad pressurizing mechanism 224 that pressurizes the polishing pad 220 downward using air pressure is provided inside the polishing head 222. The pressure of the polishing pad 220, that is, the polishing pressure, is controlled by controlling the pressure of the air supplied into the polishing head 222 while the polishing surface 220s of the wafer W is in contact with the surface to be polished Ws of the wafer W. It is possible. The pad pressurizing mechanism 224 is connected to the air pressure source A via a spindle 225 connected to the upper end of the polishing head 222 and each pipe line described later. In order to reduce hysteresis when controlling the polishing pressure, it is preferable to reduce the spring constant of a drive ring (not shown) that connects the polishing pad 220 and the polishing head 222, and piping in the polishing head 222. It is preferable to use a soft tube. The polishing head 222 is provided with a slurry supply structure that passes through the center and supplies the slurry to the center of the annular polishing pad 220. During the polishing process, slurry corresponding to the processing purpose is supplied from the slurry supply device. It comes to be supplied.

  The polishing pad 220 used in each polishing mechanism 22 is a processing process such as interlayer insulating film CMP or metal CMP, circuit pattern fineness, primary polishing (rough polishing) to third polishing (finish polishing), or the like. An appropriate pad is selected and mounted according to the processing stage. In addition, an end point detector for optically detecting the polishing state of the wafer W being polished is attached to the tip of the polishing arm 223, and a decrease in film thickness during the polishing process is detected in real time so that the polishing process can be performed. The end point can be feedback controlled.

  As shown in FIG. 2, the dressing mechanism 23 includes a dressing tool 230, a support mechanism that supports the dressing tool 230 so that it can be raised and lowered in an upward horizontal posture, and a rotation mechanism that rotates the dressing tool 230 in an upward horizontal posture. A polishing pad configured to swing the polishing arm 223, move the polishing head 222 onto the dressing tool 230, and raise the dressing tool 230 while rotating it by the support mechanism and the rotating mechanism to relatively rotate the dressing surface 230s. 220 is brought into contact with the polishing surface 220s, and pure water (cleaning water) is supplied from a nozzle (not shown in detail) to the dressing processing portion to wash away grinding scraps and the like, thereby dressing the polishing surface 220s.

As shown in FIG. 1, the index table 20 is rotated 90 degrees when the polishing process in the _first to third polishing stages S ₁ , S ₂ , S ₃ is completed, and is held by the wafer chuck 200 by suction. Are sequentially transferred from the transfer stage S ₀ to the first polishing stage S ₁ → the second polishing stage S ₂ → the third polishing stage S ₃ and subjected to CMP processing at each polishing stage, and polishing processing at the third polishing stage S _3. but finished wafer W is fed to the transfer stage S _0. The processed wafer W that has been sent to the transfer stage S ₀ and released from the suction and holding is transferred from the polishing unit 2 to the substrate cleaning unit 3 by the second transfer robot 42.

  The substrate cleaning unit 3 is composed of four chambers, a first cleaning chamber 31, a second cleaning chamber 32, a third cleaning chamber 33, and a drying chamber 34. The polishing process on both the front and back surfaces is completed, and the substrate is transferred by the second transfer robot 42. The processed wafer W is sequentially sent to the first cleaning chamber 31-> second cleaning chamber 32-> third cleaning chamber 33-> drying chamber 34 to remove and wash the slurry and abrasive wear powder adhering to the polishing processing section 2. Is done. There are various examples of cleaning methods in each cleaning chamber. For example, in the first cleaning chamber 31, double-sided cleaning with a rotating brush, in the second cleaning chamber 32, surface pencil cleaning under ultrasonic vibration, the third cleaning chamber In 33, spinner cleaning with pure water is performed, and in the drying chamber 34, a drying process is performed in a nitrogen atmosphere. A passage for transferring the unprocessed wafer W is provided below the first cleaning chamber 31.

The processed wafer W cleaned by the substrate cleaning unit 3 is taken out from the substrate cleaning unit by the first transfer robot 41 and is placed in predetermined slots of the receive cassettes C ₃ and C ₄ mounted on the wafer mounting table 12, or It is accommodated in the empty slots of the send cassettes C ₁ and C ₂ .

Next, a method for polishing the semiconductor wafer W using the polishing apparatus PM configured as described above will be described with reference to FIG. Here, FIG. 3 shows that the unprocessed wafers accommodated in the send cassette C ₁ of the cassette index unit 1 are sequentially polished by the polishing unit 2, cleaned by the substrate cleaning unit 3, and received by the cassette index unit 1. the flow of wafers to be stored in the cassette C ₄ illustrates denoted by the dotted arrow. The operation of the polishing apparatus PM is controlled by a control device (not shown), and the control device controls the operation of each unit based on a preset control program.

When the polishing processing program is started by the polishing apparatus PM, the first transfer robot 41 moves to the position of the send cassette C ₁ , horizontally swings and lifts the swivel, and expands the articulated arm to operate the wafer chuck. The unprocessed wafer W in the slot is taken out, and the swivel base is swiveled 180 degrees toward the passage installed below the first cleaning chamber 31, and the second transfer robot 42 on the polishing processing unit 2 side in this passage. The unprocessed wafer W is delivered to

The second transfer robot 42 that has received the unprocessed wafer W from the first transfer robot 41 carries the unprocessed wafer W into the polishing unit 2. The raw wafer W is transferred by the second transfer robot 42 to the surface polishing mechanism 22, it is placed on the wafer chuck 200 of the conveying stage S ₀ positioned stopped index table 20. When the wafer W is placed, the wafer chuck 200 holds the back surface of the wafer W by vacuum suction, and the second transfer robot 42 retreats.

Polishing is started in the first polishing stage S ₁ to the third polishing stage S ₃ of the surface polishing mechanism 22. Since the wafer surface polishing performed in such a three-stage polishing stage is already known (for example, Japanese Patent Application Laid-Open No. 2002-93759 by the present applicant), detailed description thereof is omitted in this specification. The following is a brief description.

When the second transfer robot 42 is retracted, the index table 20 is positioned suction-held wafer W is in a first polishing stage S ₁ the wafer chuck 200 is rotated 90 degrees clockwise, the polishing arm 223 simultaneously swing Then, the polishing head 222 moves on the wafer W. Then, the polishing head 222 and the wafer chuck 200 start to rotate in opposite directions, and the polishing head 222 descends to press the polishing pad 220 (polishing surface 220s) against the wafer surface (surface to be polished Ws) to perform the first polishing process. I do. During the polishing process, the polishing arm 223 is swung so that the polishing pad 220 reciprocates between the rotation center and the outer peripheral end of the wafer W while supplying the slurry from the axis of the polishing head 222, and the wafer surface. Is uniformly flat polished.

When the first polishing process is completed, the control device further rotates the index table 20 90 degrees clockwise, and the wafer W after the first polishing process is moved to the second polishing stage S ₂ and the transfer stage S ₀ . positioning the standby wafer W in the first polishing stage S _1. Then, the polishing head 222 is lowered on the first and second polishing stages, respectively, and the first polishing process and the second polishing process are simultaneously performed in parallel.

When the second polishing process is finished, the control device checks whether or not the first polishing process is finished, and when the first polishing process is finished, the control unit further turns the index table 20 90 degrees clockwise. The wafer W that has been rotated and rotated is transferred to the third polishing stage S ₃ , and the wafer W that has been subjected to the first polishing process is moved to the second polishing stage S ₂ on the transfer stage. W is positioned in the first polishing stage S _1, lowers the polishing head 222, respectively, first, second, to take such a third-order polished simultaneously.

When the third polishing process is completed, the control device checks whether or not the first polishing process and the second polishing process have been completed. further by 90 degrees rotation around the conveying stage S ₀ the wafer W third polishing is completed, also positioned by moving by the one stage in the same manner as described above the wafer W positioned at other stages.

When the positioning of the index table 20 is stopped and the wafer W that has undergone surface polishing through the first to third polishing stages is positioned on the transfer stage S ₀ , the second transfer robot 42 releases the vacuum suction on the wafer chuck 200. The outer peripheral edge of the processed wafer W is gripped and lifted and swiveled, moved horizontally along the linear guide, and transferred to the substrate cleaning unit 3. Further, after the processed wafer W is transferred, the unprocessed wafer W is received from the first transfer robot 41 and carried into the polishing processing unit 2.

When the processed wafer W is transferred to the substrate cleaning unit 3, the substrate cleaning unit 3 performs double-sided cleaning with a rotating brush in the first cleaning chamber 31, surface pencil cleaning under ultrasonic vibration in the second cleaning chamber 32, Spinner cleaning with pure water is performed in the third cleaning chamber 33, and drying processing is performed in the nitrogen chamber in the drying chamber 34. The thus cleaned finished wafer W in the is removed from the substrate cleaning unit 3 by the first transfer robot 41 of the cassette index portion 1 is accommodated in the specified slot from the receive cassette C _4.

The above operations are sequentially repeated, and after the polishing of the first wafer W is completed, the wafer W whose surface is polished flat is stored in the cassette C ₄ at every rotation interval of the index table 20. . The rotation interval of the index table 20 is defined by the polishing time divided into three stages. For example, the finished wafer W is continuously produced at every time interval of the first polishing process. Further, dressing by the dressing mechanism 23 is performed each time before each polishing process is performed in each polishing stage (that is, at a timing before each polishing process is performed), and the polishing pad surface (polishing surface 220s) is clogged. It is corrected to ensure flatness.

As described above, the unprocessed wafers W accommodated in the send cassette C ₁ of the cassette index unit 1 are sequentially polished by the polishing unit 2, cleaned by the substrate cleaning unit 3, and finished wafers (processed wafers). ) is accommodated in the receive cassette C ₄ as W. By the way, in polishing a wiring layer using a so-called Low-K material (low dielectric constant material), it is necessary to reduce the polishing pressure in addition to hardening the polishing pad as a countermeasure against dishing or erosion generated in the wiring layer. is there. The same applies to suppression of scratches on the processed surface in smoothing polishing (pressure surface transfer polishing) of a glass substrate or the like. Therefore, if the polishing pressure can be appropriately controlled in the low pressure region, the occurrence of defects as described above can be suppressed, and the substrate surface such as a wafer can be polished more flatly.

  Therefore, a pressurized air supply system in the polishing apparatus PM of the present embodiment will be described below with reference to FIG. This supply system is connected to the air pressure source A and connected to the air pressure source A to the air cylinder 231 of the dressing mechanism 23 and the pad pressurizing mechanism 224 in the polishing head 222, and to the air pressure source A. The lock pressure line 70 for supplying air to the pad pressurizing mechanism 224 in 222, the venturi line 75 for supplying air to the venturi pipe 62 (to be described later) connected to the air pressure source A, and the air pressure source A for dressing. An air purge conduit 80 for supplying air purge air to the mechanism 23 is configured. The air cylinder 231 constitutes a support mechanism for the dressing mechanism 23.

The electropneumatic pipe line 50 whose upstream side is connected to the air pressure source A is provided with a first regulator 51 for reducing the air pressure in the electropneumatic pipe line 50, and the downstream side of the electropneumatic pipe line 50 is first polished. In order to supply air to each of the stage S ₁ to the third polishing stage S ₃ , it branches in three directions, and in each of the polishing stages S _{1 to} S ₃ , the pad pressurizing mechanism 224 in the polishing head 222 is passed through the spindle 225. The polishing head pipe 60 and the dressing pipe 55 connected to the air cylinder 231 of the dressing mechanism 23 are branched.

  A first electropneumatic regulator 61, a switching valve 67, and an opening / closing valve 68 are disposed in the polishing head pipe line 60 in order from the upstream side. In addition, a pipe line between the first electropneumatic regulator 61 and the opening / closing valve 68 includes a first pressure sensor 65 that detects air pressure in the pipe line and outputs the air pressure to the first electropneumatic regulator 61, and the pipe line. A second pressure sensor 66 for preliminarily detecting the air pressure inside is disposed.

  The first electropneumatic regulator 61 receives an air pressure control signal from a control device (not shown) and controls the air pressure in the polishing head duct 60 to a predetermined air pressure. As a result, the pressure of the air supplied from the polishing head duct 60 to the inside of the polishing head 222 can be controlled, and the pressing force of the polishing pad 220, that is, the polishing pressure can be controlled. At this time, the control device performs PID control by digital signal processing. The first electropneumatic regulator 61 is compatible with a compound pressure capable of controlling the air pressure in a range of positive pressure and negative pressure, and has a venturi pipe 62.

  The Venturi tube 62 is a tube narrowed at the center, and the exhaust port of the first electropneumatic regulator 61 is connected to the constricted portion. A venturi pipe 75 is connected to the upstream side of the venturi pipe 62, and the downstream side is opened via a silencer 69. When the air pressure in the polishing head pipe 60 (polishing head 222) is reduced by the first electropneumatic regulator 61, the air supplied from the venturi pipe 75 passes through the constricted portion of the venturi pipe 62. Using the generated negative pressure, the air in the pipe connecting the first electropneumatic regulator 61 and the inside of the polishing head 222 (pad pressurizing mechanism 224) is forcibly exhausted from the exhaust port of the first electropneumatic regulator 61.

  The first electropneumatic regulator 61 preferably has a resolution of 0.05% or less at full span, and further has a resolution capable of controlling 1 kPa or less with only the input signal. Moreover, it is preferable to use a completely floating force motor (linear motor) free from friction and impact for the current-pressure converter of the first electropneumatic regulator 61.

  In addition, the first pressure sensor 65 that inputs the air pressure detection signal used in the PID control to the first electropneumatic regulator 61 has a pressure detection range equivalent to the pressure control range by the first electropneumatic regulator 61, and corrects the air pressure. It supports compound pressure that can be detected in the range of pressure and negative pressure. Further, it is preferable that the first pressure sensor 65 ensures linearity accuracy even in the negative pressure region, and the detection error in the full span is 0.1% or less. The response speed of the first pressure sensor 65 is preferably 1 msec or less.

  When a switching signal for switching to the polishing head pipe line 60 side is input from the control device to the switching valve 67, the switching valve 67 connects the polishing head pipe line 60 to the polishing head 222, and a predetermined value obtained by the first electropneumatic regulator 61. The air having the air pressure is supplied into the polishing head 222. On the other hand, when a switching signal for switching to the lock pipeline 70 side is input from the control device, the lock pipeline 70 is connected to the polishing head 222 and the air from the lock pipeline 70 is supplied to the inside of the polishing head 222. To do. When the pad pressurizing mechanism 224 is operated, the polishing head conduit 60 is connected to the polishing head 222, and when the pad pressurizing mechanism 224 is stopped and locked, the lock conduit 70 is connected. Connect to polishing head 222.

  The open / close valve 68 receives the pressure of the air that is branched from the upstream side of the first electropneumatic regulator 61 and always opens the polishing head duct 60. On the other hand, when a predetermined drive signal is input from the control device, the open / close valve 68 closes the polishing head pipe line 60 and opens the inside of the polishing head 222 to atmospheric pressure, and pressurizes the polishing head 222. Air is discharged to the outside. Thereby, since the initial load (pressing force) of the polishing pad 220 (and the pad pressurizing mechanism 224 and the like) can be measured with good reproducibility in the atmospheric pressure state, the control accuracy of the polishing pressure can be further improved. A silencer 69 is attached to the exhaust port of the opening / closing valve 68 to suppress air exhaust noise.

  A second electropneumatic regulator 56 and a speed controller 59 are disposed in the dressing pipeline 55 in order from the upstream side. In addition, a pipe line between the second electropneumatic regulator 56 and the speed controller 59 includes a third pressure sensor 57 that detects the air pressure in the pipe line and outputs it to the second electropneumatic regulator 56, and the pipe line. A fourth pressure sensor 58 for preliminarily detecting the air pressure inside is disposed.

  The second electropneumatic regulator 56 receives an air pressure control signal from a control device (not shown) and controls the air pressure in the dressing conduit 55 to a predetermined air pressure. Thereby, the pressure of the air supplied to the air cylinder 231 from the dressing pipeline 55 can be controlled, and the lifting / lowering operation of the dressing tool 230 by the air cylinder 231 can be controlled. The second electropneumatic regulator 56 is compatible with a combined pressure capable of controlling the air pressure within a range of positive pressure and negative pressure, and the elevating operation of the dressing tool 230 by the air cylinder 231 is controlled only by the second electropneumatic regulator 56. Can be switched. Further, the speed controller 59 adjusts the flow rate of the air flowing through the dressing conduit 55 to a predetermined flow rate.

  In the lock pipeline 70 connected upstream to the air pressure source A, a second regulator 71 for reducing the air pressure in the lock pipeline 70 and the air pressure in the lock pipeline 70 decompressed by the second regulator 71 are detected. And a downstream side of the lock pipe line 70 is connected to the switching valve 67 of the polishing head pipe line 60. Note that the air pressure in the lock conduit 70 obtained by the second regulator 71 is set to a sufficient (relatively high pressure) air pressure to stop and lock the operation of the pad pressurizing mechanism 224.

  The venturi conduit 75 connected upstream to the air pressure source A is provided with a third regulator 76 for reducing the air pressure in the venturi conduit 75, and the downstream side of the venturi conduit 75 is the polishing head conduit 60. To the Venturi tube 62. In addition, the air purge conduit 80 connected upstream to the air pressure source A is provided with a fourth regulator 81 for reducing the air pressure in the air purge conduit 80, and the downstream side of the air purge conduit 80 is connected to the dressing mechanism 23. This is connected to an air purge nozzle (not shown) provided.

  In such a pressurized air supply system in the polishing apparatus PM, when performing polishing, the switching valve 67 connects the polishing head pipe line 60 to the polishing head 222 in order to operate the pad pressurizing mechanism 224. At this time, the first electropneumatic regulator 61 receives an air pressure control signal from a control device (not shown) and controls the air pressure in the polishing head duct 60 to a predetermined air pressure. The obtained air having a predetermined air pressure is supplied to the inside of the polishing head 222 (pad pressurizing mechanism 224). When the operation of the pad pressurizing mechanism 224 is stopped and locked, the switching valve 67 connects the lock conduit 70 to the polishing head 222, and the air from the lock conduit 70 is inside the polishing head 222. To be supplied.

  By the way, the responsiveness of the control system is evaluated in the form of a response speed to an input to an element (system property) having a certain transfer function. The response of the control system is different between when the input is raised and when it is lowered. For example, in the pressurized air supply system according to this embodiment, the primary pressure (gauge pressure) obtained by the first regulator 51 is 300 kPa, and the secondary pressure (gauge pressure) obtained by the first electropneumatic regulator 61 is 20 kPa. When the air pressure (polishing pressure) is increased, the pressure difference between the primary side pressure and the secondary side pressure is (300-20 =) 280 kPa, and the pressure before and after the first electropneumatic regulator 61 is 280 kPa. Since the gradient is secured and a lot of air flows, the response speed is fast. On the other hand, when the air pressure (polishing pressure) is reduced from 20 kPa to atmospheric pressure (0 kPa), since the reference pressure is atmospheric pressure, there is only a pressure gradient of 20 kPa, the exhaust speed becomes slow, and the response speed becomes slow.

  Therefore, a venturi for forcibly exhausting air in the pipe line connecting the first electropneumatic regulator 61 and the pad pressurizing mechanism 224 in the polishing head 222 to the exhaust port of the first electropneumatic regulator 61 corresponding to the compound pressure. If the pipe 62 is connected and the pressure gradient is increased using the negative pressure generated when the air supplied from the venturi pipe 75 passes through the constricted portion of the venturi pipe 62, the exhaust flow rate is secured. The response speed when the air pressure (polishing pressure) is reduced can be improved. As described above, according to the present embodiment, since the response speed when the air pressure (polishing pressure) is reduced can be improved, the responsiveness of the control system is improved, and the control accuracy of the polishing pressure can be improved. It becomes possible. At this time, the venturi pipe 62 uses the air supplied from the air pressure source A to forcibly exhaust the air in the pipe line connecting the first electropneumatic regulator 61 and the polishing head 222 (pad pressurizing mechanism 224). In this case, it is not necessary to provide a separate air pressure source, and the size of the apparatus can be minimized.

  If the gain on the control side is increased while ignoring the response of the system, the control error during feedback control (PID control) becomes excessive, overshooting occurs when the input rises, and undershooting occurs when it falls. To do. Further, when the delay order constant of the system is larger than the control side maximum integration time, it is difficult to improve the response of the system only by adjusting the gain such as the integration time. Further, if the control gain is increased while ignoring the response of the system, vibration (howling) occurs in the force motor (not shown) of the first electropneumatic regulator 61 to return overshoot and the like, and the first pressure Chattering occurs in the output signal of the sensor 65 or the like.

  Conventional electro-pneumatic regulator control devices perform PID control (closed loop control) by analog signal processing, so adjustment of integral constant (time) and proportionality constant by various gain volumes, and electrical and mechanical zero adjustment , Span adjustment, etc. Therefore, since there are many manual adjustment items, responsiveness is likely to vary (see, for example, FIG. 5), and linearity accuracy is likely to be poor. Also, because the common circuit was used for increasing (pressurizing) and decreasing (depressurizing) the air pressure to be controlled, the response speed was slowed when increasing the air pressure, and the response speed was increased when decreasing the air pressure. Such gain adjustment was difficult.

  On the other hand, as in this embodiment, the control device of the electropneumatic regulator performs PID control by digital signal processing, thereby parameterizing various gain adjustment portions and increasing (pressurizing) the air pressure to be controlled (lowering) ( The gain parameter can be adjusted individually in the case where the pressure is reduced), and the mechanical adjustment can be reduced. Therefore, linearity accuracy (for example, see FIG. 6) and responsiveness (for example, see FIG. 7 and FIG. 8) in the pressure control range including the negative pressure region are improved, and individual differences of electropneumatic regulators are reduced. It was possible to improve polishing reproducibility.

  In the above-described embodiment, the polishing apparatus PM for polishing the semiconductor wafer W has been described as an example. However, the present invention is not limited to this, and the present invention can be applied to a polishing apparatus for polishing a substrate such as a glass substrate. It is.

It is a top view which shows the example of whole structure of a grinding | polishing apparatus. It is a schematic block diagram which shows a surface polishing mechanism and a dressing mechanism typically. It is explanatory drawing which shows the flow of the wafer in a grinding | polishing apparatus. It is a piping diagram which shows the supply system of the pressure air in a grinding | polishing apparatus. It is a graph which shows the response of the air pressure (voltage conversion value) in the conventional grinding | polishing apparatus, changing load conditions, respectively. (A) is a graph which shows the linearity precision in the range whose command voltage is -1-10V, (b) is a graph which shows the linearity precision in the range whose command voltage is -1-1V. (A) is a graph which shows the responsiveness of the air pressure (voltage conversion value) in the conventional polishing apparatus, (b) is a graph which shows the responsiveness of the air pressure (voltage conversion value) in the polishing apparatus of this embodiment. (A) is a graph which expands partially the responsiveness of the air pressure (voltage conversion value) in the conventional grinding | polishing apparatus, (b) shows the responsiveness of the air pressure (voltage conversion value) in the polishing apparatus of this embodiment. It is a graph which expands and shows a part.

Explanation of symbols

A Air pressure source W Semiconductor wafer (substrate)
PM polishing equipment
50 Electropneumatic Pipe Line 60 Polishing Head Line 61 First Electropneumatic Regulator 62 Venturi Pipe 75 Venturi Line 220 Polishing Pad (Polishing Tool)
222 Polishing head 224 Pad pressure mechanism (actuator)

Claims (2)

A polishing tool for polishing the substrate; and an actuator for pressing the polishing tool against the substrate by using a pressure of air supplied from a pneumatic pressure source. The actuator is used to press the polishing tool against the substrate. In a state, in a polishing apparatus configured to polish the substrate by moving the polishing tool relative to the substrate,
An electropneumatic regulator that is provided in a pipeline connecting the air pressure source and the actuator, and controls the pressure of air supplied from the air pressure source to the actuator;
The electropneumatic regulator can control the pressure of the air in a positive pressure range and a negative pressure range, and forcibly forces the air in a pipeline connecting the electropneumatic regulator and the actuator when the pressure of the air is reduced. A polishing apparatus comprising a venturi pipe for exhausting.   The polishing apparatus according to claim 1, wherein the venturi pipe forcibly exhausts air in a pipe line connecting the electropneumatic regulator and the actuator using air supplied from the air pressure source. .

Images