JP3801325B2 - Polishing apparatus and semiconductor wafer polishing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to, for example, a polishing apparatus that polishes a semiconductor substrate, and more particularly to a polishing apparatus that can stably supply a polishing liquid at a constant flow rate and perform stable polishing.
[0002]
[Prior art]
In recent years, as semiconductor devices are highly integrated, circuit wiring is becoming finer and the distance between wirings is becoming narrower. Along with this, the depth of focus becomes shallow when circuit formation is performed by optical lithography or the like, so that a higher flatness of the imaging surface of the stepper is required.
[0003]
As means for flattening the surface of a semiconductor wafer, a polishing tool (for example, a polishing table having a polishing cloth) and a gripping member that grips a material to be polished against the polishing table and presses the polishing surface are provided. A polishing apparatus that performs polishing by relatively sliding a tool and a polishing surface while supplying a polishing liquid between these contact surfaces is known. Such an apparatus not only performs mechanical polishing using a polishing liquid as a polishing liquid, but also performs polishing with chemical action using an alkaline or acidic polishing liquid as the case may be.
[0004]
In order to perform good polishing in such a polishing apparatus, it is required to stably supply an abrasive liquid having a certain concentration and flow rate. The abrasive liquid is usually mixed with a stock solution and a diluting liquid for diluting it in a mixing tank before use, and supplied from this mixing tank to a nozzle of a polishing apparatus via an abrasive liquid supply pipe. It is required to supply abrasive liquid from one mixing tank to a plurality of polishing apparatuses in order to reduce equipment and operating costs. Therefore, the abrasive liquid is constantly flowed into the main pipe, and a metering pump such as a roller pump is provided in the extraction pipe that branches off from the main pipe and extends to each polishing apparatus. There has been proposed a method for avoiding the agglomeration of the abrasive liquid due to stopping.
[0005]
[Problems to be solved by the invention]
However, in the conventional technology as described above, the roller pump is used to supply the abrasive fluid at a substantially constant flow rate regardless of the pressure change of the main pipe. The deformation of the tube and a slight change in the flow rate are unavoidable, and the flow rate pulsates, and since the roller pump uses the flexible tube, it deteriorates over time (sagging) due to deterioration over time. There were problems such as the inability to expect stable operation.
[0006]
In addition, because the flow rate changes due to pressure fluctuations in the circulation piping due to differences in the length and diameter of the extraction pipes and fluctuations in the number of operating polishing units, a constant concentration and flow rate of abrasive fluid is stably supplied to each polishing unit. In some cases, a good polishing state could not be obtained.
[0007]
In view of the above problems, an object of the present invention is to provide an abrasive liquid supply device capable of stably supplying an abrasive liquid at a constant flow rate with a low equipment cost even to a plurality of polishing apparatuses. It is another object of the present invention to provide a polishing apparatus that can flexibly cope with a layout change in a factory by having the function of supplying such an abrasive liquid at a constant flow rate to a polishing unit.
[0008]
[Means for Solving the Problems]
According to the first aspect of the present invention, there are provided a polishing section that performs polishing by pressing an object to be polished against a polishing tool, and an abrasive liquid pipe that is connected to an external abrasive liquid supply device and supplies an abrasive liquid to the polishing section. A polishing apparatus housed in one housing, comprising: a circulation pipe for circulating the abrasive liquid; and an extraction pipe for supplying the abrasive liquid from the circulation pipe to a plurality of polishing apparatuses. A circulating pump that circulates the abrasive fluid, a back pressure valve that keeps the pressure in the circulating pipe above a certain pressure, and a pressure sensor, and controls the operation of the circulating pump according to the detected value of the pressure sensor. The pressure in the circulation pipe is kept constant, the flow rate control means for adjusting the valve opening degree based on the instruction signal to obtain a desired abrasive fluid flow rate, and the means for stopping the inflow of the abrasive fluid in the extraction pipe in which characterized in that a and.
[0009]
As a result, regardless of the conditions on the external abrasive fluid supply device side, for example, even if there is some pressure fluctuation, the abrasive fluid is always supplied to the polishing unit by the flow rate control means. High polishing apparatus is provided.
[0011]
And since the abrasive fluid is circulating in the main piping, even when the polishing apparatus is stopped, the retention in the introduction piping is prevented, and fluctuations in concentration and clogging due to precipitation of components in the abrasive fluid are prevented. Therefore, it is possible to shorten the length of the extraction piping that tends to stay and to supply the abrasive fluid smoothly. If the main pipe is configured as a circulation pipe for circulating the abrasive liquid, the abrasive liquid can always be circulated. The circulation piping may be provided with a buffer tank or the like that suppresses the influence caused by fluctuations in the abrasive fluid flow rate. Further, it is preferable to provide a control device for controlling the circulation pump so as to suppress pressure fluctuation by arranging a pressure sensor or the like in the circulation pipe.
[0012]
The invention according to claim 2 is characterized in that the flow rate control means includes an air pressure chamber and a valve that opens and closes according to the air pressure of the air pressure chamber, and controls the flow rate of the abrasive fluid. Is. The invention according to claim 3, wherein the flow control means is for the air pressure of said air pressure chamber, wherein the to Turkey to a predetermined value by pneumatic transducer electricity based on the instruction signal. Thereby, if the secondary pressure becomes a predetermined value, the flow rate can be made constant as a result. If necessary, an orifice may be provided downstream, or the instruction signal may be output by an electropneumatic converter that electropneumatically converts the electric signal into a pilot pressure.
[0013]
According to a fourth aspect of the invention, the discharge pipe, is characterized in that the washing liquid pipe for supplying cleaning liquid to said flow control means. Thereby, the stable operation | movement of a flow control means can be maintained. As the cleaning liquid, for example, a part of the components of the abrasive liquid such as pure water or a liquid that is not harmful to polishing is used.
[0014]
The invention according to claim 5 is a polishing part, an abrasive liquid supply means for supplying an abrasive liquid to the polishing part, an abrasive liquid circulation pipe provided between the polishing part and the abrasive liquid supply means, and the abrasive Using a polishing system having an extraction pipe extending from the liquid circulation pipe to the polishing section, diluting the abrasive liquid to a desired concentration, a circulation pump for circulating the abrasive liquid in the abrasive liquid circulation pipe, and the circulation A back pressure valve that keeps the pressure in the pipe above a certain pressure and a pressure sensor are provided, and the operation of the circulation pump is controlled according to the detection value of the pressure sensor to keep the pressure in the circulation pipe constant. Circulating the diluted abrasive liquid in the abrasive liquid circulation pipe, extracting the abrasive liquid from the abrasive liquid circulation pipe toward the polishing section, and an instruction signal corresponding to a preset abrasive liquid supply amount The valve opening is adjusted based on the It is characterized in that performing the step of supplying the parts.
[0015]
The invention according to claim 6, further is characterized in that a step of said stop polishing liquid extraction of from abrasive liquid circulation piping to said polishing unit, washing the extraction pipe.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an overall configuration of a polishing system 1 of this embodiment. This polishing system includes an abrasive liquid supply device 3 for supplying an abrasive liquid having a desired concentration from a stock solution and a diluting liquid, and an object to be polished. And a circulation path 20 that guides the polishing liquid to the vicinity of each polishing apparatus 4.
[0018]
The abrasive liquid supply device 3 includes two supply sources, a stock solution tank 10 for storing the stock solution, a dilution solution tank 12 for storing a dilution solution for diluting the stock solution to a predetermined concentration, and pipes 14 and 16 from these supply sources. The mixing part 18 which joins the raw material supplied through this and makes it the abrasive liquid of a predetermined density | concentration is comprised. The supply source of the diluent may be a pure water supply line that flows in the factory.
[0019]
The polishing apparatus 4 includes, for example, a polishing unit 22 that performs polishing by pressing a surface to be polished of a semiconductor wafer against a polishing cloth affixed to a rotating polishing table 22a, a nozzle 58 that supplies abrasive liquid thereto, and a circulation path 20 The unit includes a discharge pipe 24 for introducing the abrasive liquid to the nozzle and a control system for the abrasive liquid associated therewith. The abrasive liquid supply system 2 is formed by the abrasive liquid supply device 3, the circulation path 20, and the extraction pipe 24.
[0020]
First, the abrasive fluid supply device 3 will be described. As the stock solution of the abrasive liquid, for example, an acid, alkali, or neutral liquid containing particles of a predetermined particle size such as silica gel is used depending on the object to be polished, and the diluting liquid is usually pure water without impurities. Etc. are used. In this example, the stock solution is stored in the stock solution tank 10, and the stock solution supply line 14 is provided with two systems so as to be switched and used when one becomes empty. The stock solution line 14 and the diluent solution line 16 are respectively connected to a buffer tube 18 as a mixing unit via, for example, an on-off valve 26 and a pressure adjustment valve 28, and thereby, an abrasive having a predetermined mixing ratio in the buffer tube 18. A liquid is produced. The configuration of the pressure adjustment valve 28 will be described later.
[0021]
In this example, the buffer tube 18 that is a mixing unit is installed in the middle of a circulation path 20 that supplies abrasive liquid to a plurality of polishing apparatuses. The buffer tube 18 is vertically arranged as a cylindrical container 30 having a diameter larger than that of the circulation pipe 21 that forms the circulation path 20, a discharge port 32 is provided at the bottom, and the upper part is joined via an O-ring. Covered with a lid 36. The lid 36 is connected to the return pipe of the circulation pipe 21 and the pipes 14 and 16 of the stock solution and dilution solution lines, respectively.
[0022]
The container 30 is provided with level detectors 40a, 40b, and 40c that detect the level of the liquid level, and this detects, for example, an upper limit, a lower limit, and a lower limit, and outputs the signal to a control device (not shown). It has become. Based on this signal, the control device outputs a signal to the open / close valve 26 and the pressure regulating valve 28 of the stock solution and dilution solution lines, and supplies the stock solution and dilution solution when the liquid level becomes the lower limit. When it comes, control to stop the supply. In the unlikely event that the liquid level reaches the lowest limit, a warning or a stop signal for polishing processing is issued to the polishing unit 22.
[0023]
The lid 36 is further provided with an air circulation pipe 44 that communicates air in the container 30 with an airbag 42 made of a stretchable material. The air bag 42 keeps the space in the container 30 airtight with respect to the outside air, and suppresses internal pressure fluctuations due to fluctuations in the liquid level inside. For example, Teflon (trade name) having flexibility and durability. The material is formed into a size having a volume corresponding to the level fluctuation.
[0024]
Next, the circulation path 20 will be described. The circulation pipe 21 circulates in the vicinity of one or a plurality of polishing portions 22 to which the abrasive liquid is to be supplied from the discharge port 32 at the lower end of the buffer tube 18, returns to the buffer tube 18, and is connected to the return pipe 38. ing. The circulation pipe 21 is provided with a circulation pump 46 for circulating the abrasive liquid, a back pressure valve 48 for keeping the pressure of the circulation pipe constant, a pressure sensor 50 and the like.
[0025]
The output of the pressure sensor 50 is input to a control device (not shown) and monitored. The control device may control the operation of the circulation pump 46 in accordance with the detected value so as to keep the pressure in the circulation pipe 21 constant. Normally, the circulation pump 46 is maintained in a constant operation state, and the pressure in the piping is maintained constant by the back pressure valve 48. A distribution pipe 23 having an on-off valve 25 and a connection flange 23a is branched from the position close to each polishing apparatus 4 to the circulation pipe 21, and a flange 24a of an extraction pipe 24 of the polishing apparatus 4 is connected to the flange 23a. Connected.
[0026]
Next, the polishing apparatus 4 will be described. The extraction pipe 24 is provided with an on-off valve 52, a pressure regulating valve 54 for controlling the pressure on the secondary side (downstream side) from the upstream side, and an orifice 56 on the downstream side, and a polishing device on the downstream side. The nozzle 58 is connected. The pressure regulating valve 54 and the orifice 56 on the downstream side serve as a flow regulating valve as will be described later. An electropneumatic converter 60 is connected to the pressure adjusting valve 54 for inputting a constant electric signal from the controller 61 and supplying a constant air pressure corresponding to the signal.
[0027]
That is, the controller 61 arbitrarily sets the abrasive fluid supply amount, and based on this, the electropneumatic converter 60 can supply a predetermined pilot air pressure to the pressure regulating valve 54 from a pilot air source (not shown). It has become. A cleaning liquid pipe 64 having an on / off valve 62 is joined between the on / off valve 52 and the pressure regulating valve 54.
[0028]
In the polishing system having such a configuration, the abrasive liquid in the abrasive liquid pipe for guiding the abrasive liquid to each polishing apparatus 4 is constantly circulated. Clogging due to deposition can be prevented. In addition, as a result, the abrasive liquid piping can be lengthened, so that the abrasive liquid can be stably supplied from the single abrasive liquid supply source (mixing unit) 18 to the plurality of polishing apparatuses 4, and the apparatus cost as a whole can be reduced. Can be reduced.
[0029]
The configuration of the pressure regulating valve 54 (and the pressure regulating valve 28) will be described below. As shown in FIG. 2, the valve device 72 is accommodated in a casing including an upper casing 66, a lower casing 68, and a lower presser plate 70. That is, the upper casing 66 is formed with an air pressure chamber 76 having a pressure introduction path 74 that is connected to the electropneumatic converter 60, and the lower casing 68 is provided with a fluid introduction path 78, a primary valve chamber 80, and a secondary valve chamber 82. A fluid flow path comprising a fluid outlet path 84 is formed, and a diaphragm 86 is sandwiched between the upper casing 66 and the lower casing 68 to partition the air pressure chamber 76 and the secondary valve chamber 82.
[0030]
A valve seat 88 is formed between the primary valve chamber 80 and the secondary valve chamber 82, and a valve body 90 is inserted into the valve seat 88 from below, and the valve body 90 is attached to the diaphragm 86 by a presser plate 92 and bolts 94. It is attached to a fixed valve stem 96 and can be raised and lowered. O-rings 98 for sealing are respectively arranged at predetermined locations on the joint surfaces of the members constituting the pressure regulating valve 54.
[0031]
The operation of the abrasive fluid supply apparatus configured as described above will be described. The control device controls the circulation pump 46 to operate so that the pressure on the downstream side thereof is equal to or higher than a predetermined value, thereby constantly forming a circulation flow in the circulation path 20 of the abrasive liquid.
[0032]
When each polishing apparatus 4 is operated, each controller 61 outputs an open signal to each on-off valve 52 and outputs a flow rate instruction signal corresponding to a preset abrasive liquid supply amount to each electropneumatic converter 60. The electropneumatic converter 60 sends the corresponding air pressure as pilot air pressure to the air pressure chamber 76 of the pressure regulating valve 54 based on the flow rate instruction signal, thereby opening the space between the valve body 90 and the valve seat 88. . In the pressure regulating valve 54, the abrasive fluid that has flowed from the fluid inlet 78 flows into the fluid pressure chamber 82 through an opening formed by the valve device 72, the valve body 90, and the valve seat 88. The pressure in the fluid pressure chamber 82 is uniquely determined by the flow rate of the abrasive fluid flowing through the orifice 29. Therefore, the flow rate of the abrasive liquid can be controlled to a desired amount by controlling the pressure of the fluid pressure chamber 82 to a desired pressure.
[0033]
At this time, the flow rate of the abrasive liquid output from the fluid outlet 84 is kept constant as follows by controlling the pressure in the fluid pressure chamber 82. The pilot pressure in the air pressure chamber 76 and the abrasive pressure in the fluid pressure chamber 82 are balanced through the diaphragm 86 and flow out from the fluid outlet 84. At this time, when the pressure in the fluid pressure chamber 82 is increased, the valve rod 96 and the valve body 90 are pushed up, and the space formed by the valve seat 88 and the valve body 90 serving as a fluid flow path is narrowed. Since the resistance increases, the abrasive pressure in the fluid pressure chamber 82 instantaneously returns to a predetermined pressure (a pressure that balances with the pilot air pressure of the air pressure 76). When the pressure in the fluid pressure chamber 82 becomes low, the action is reversed and the pressure returns to a predetermined pressure. As a result, the fluctuation range and cycle of the pilot air pressure are shortened, and a predetermined flow rate of the abrasive fluid determined by the pilot air pressure and the downstream pipe resistance is stably discharged from the nozzles 58 of the polishing units 22.
[0034]
In order to change the flow rate range level of the abrasive liquid, the resistance by the orifice 56 provided downstream of the pressure regulating valve 54 may be changed. In order to change the resistance of the orifice 56, orifices having different hole sizes may be attached.
[0035]
When the abrasive liquid in the buffer tube 18 becomes lower than the lower limit, the control device opens the on-off valve 26 by the signal of the level sensor 40c, whereby the stock solution and the pure water whose flow rates are controlled by the pressure regulating valve 28 are constant. , Flows into the buffer tube 18 until the level reaches the upper limit, where it mixes. Note that the pressure regulating valve 28 has the same structure as the pressure regulating valve 54, and the flow rate is also controlled as a result because the pressure is controlled to be constant.
[0036]
When a certain polishing apparatus 4 stops polishing, the on-off valve 52 of the extraction pipe 24 is closed. As a result, the pressure in the circulation pipe 21 temporarily rises, but in the extraction pipe 24 of the other polishing apparatus 4, the pressure adjustment valve 54 keeps the pressure on the secondary side constant regardless of the pressure fluctuation on the primary side. The abrasive fluid pressure is maintained, and therefore the flow rate is kept constant.
[0037]
When the polishing is resumed, the on-off valve 62 of the cleaning liquid pipe 64 is opened and the inside of the extraction pipe 24 is cleaned before supplying the polishing liquid. Thereby, the clogging and abrasive fluid concentration change resulting from the retention of the abrasive fluid can be suppressed.
[0038]
FIG. 3 is a modification of the embodiment of FIG. 1 and more specifically shows the arrangement of the circulation path 20 and each polishing apparatus 4 in the factory. Here, the circulation path 20 is composed of a trunk path 100 connected to the abrasive liquid supply device 3, and a distribution pipe 104 having an on-off valve 106 and a connection flange 104a is provided, and each polishing apparatus 4 is provided via this flange 104a. Is connected to the flange 24a of the extraction pipe 24. The on-off valve 106 is necessary to connect the polishing apparatus 4 without stopping the present polishing liquid supply system when connecting a new polishing apparatus 4 to the present system. When constructing the trunk path 100 in the factory, by installing a large number of on-off valves 106, a new polishing apparatus 4 can be installed flexibly.
[0039]
By configuring in this way the circulation path 20, since the stem path 100 may piping to Rukoto up closer to the respective polishing unit 4, to further shorten the extraction pipe 24 to the polishing liquid residence of the expected The effect of the present invention of stabilizing the supply of the abrasive liquid can be further enhanced. In this figure, two of the four distribution pipes 104 are in a standby state in which the polishing apparatus 4 is not connected.
[0040]
FIG. 4 shows still another embodiment of the present invention. In this embodiment, an introduction pipe 120 constituting a part of the circulation path 20 is accommodated in a unit of the polishing apparatus 4A. . That is, the introduction pipe 120 extends into the polishing apparatus 4A as a reciprocating pipe, and an extraction pipe 24 is provided at the tip thereof. The introduction pipe 120 constitutes a part of the circulation path 20 by connecting flanges 120 a provided at both ends thereof to the flange 21 a of the circulation pipe 21. Similar to the previous embodiment, the extraction pipe 24 is provided with a pressure adjusting valve 54 that is a flow rate control means and an on-off valve 52 that stops the inflow of abrasive fluid.
[0041]
In this embodiment, since the abrasive fluid circulation path 20 extends into the unit of the polishing apparatus 4A, the extraction pipe 24 is shortened by that amount compared to the previous embodiment. Accordingly, the abrasive fluid stagnates due to the operation stop of the polishing apparatus 4A and the like, and the pipeline that is liable to cause precipitation or clogging of the abrasive fluid components is shortened, and the operation is further stabilized.
[0042]
In the above-described embodiment, the polishing apparatuses 4 and 4A are configured as a unit including the extraction pipe 24 and the abrasive liquid control system. However, it goes without saying that the respective elements may be combined individually. Yes. In addition, in order to perform a plurality of polishing processes by supplying different types of processing liquids such as abrasive liquids to one polishing apparatus 4, 4 </ b> A, an abrasive liquid supply apparatus for one or a plurality of polishing apparatuses 4, 4 </ b> A. A plurality of 3 may be provided.
[0043]
【The invention's effect】
As described above, according to the present invention, regardless of the conditions on the side of the external abrasive liquid supply device, a constant flow rate of abrasive liquid is always supplied to the polishing unit by the flow rate control means, which is highly practical as a unit type. A polishing apparatus is provided. In addition, by combining the main pipe through which the abrasive fluid circulates and the extraction pipe branching from this, and providing the flow rate control means in the extraction pipe, the abrasive liquid tends to stay even when the abrasive liquid is supplied to a plurality of polishing units. The extraction piping can be shortened to smoothly supply the abrasive liquid. Furthermore, since the flow rate control means absorbs pressure fluctuations in the main pipe, a constant flow rate of the abrasive liquid can be stably supplied, and a good polishing operation of the semiconductor substrate or the like can be promoted.
[Brief description of the drawings]
FIG. 1 is a flowchart showing an overall configuration of a polishing system according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view showing a configuration of the pressure regulating valve of FIG.
FIG. 3 is a flowchart showing an overall configuration of a polishing system according to a second embodiment of the present invention.
FIG. 4 is a flowchart showing an overall configuration of a polishing system according to a third embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Polishing system 2 Abrasive liquid supply system 3 Abrasive liquid supply apparatus 4, 4A Polishing apparatus 10 Raw liquid tank 12 Diluent tank 14 Raw liquid supply path 18 Mixing part 20 Circulating path 21 Circulating pipe 22 Polishing part 24 Extraction pipe 28 40b, 40c Level sensor 42 Air bag 54 Pressure adjustment valve 56 Orifice 58 Nozzle 60 Electropneumatic converter

Claims (6)

A polishing apparatus in which a polishing unit that presses an object to be polished against a polishing tool and an abrasive liquid pipe that is connected to an external abrasive liquid supply device and supplies the polishing liquid to the polishing unit are accommodated in one housing. Because
A circulation pipe for circulating the abrasive liquid;
An extraction pipe for supplying the polishing liquid from the circulation pipe to a plurality of polishing apparatuses;
The circulation pipe is provided with a circulation pump that circulates the abrasive liquid, a back pressure valve that keeps the pressure in the circulation pipe at a predetermined pressure or more, and a pressure sensor, and the circulation pump according to a detection value of the pressure sensor Control the operation of the above, keeping the pressure in the circulation pipe constant,
A polishing apparatus, wherein the extraction pipe is provided with a flow rate control means for adjusting a valve opening degree based on an instruction signal to obtain a desired abrasive liquid flow rate and a means for stopping the inflow of the abrasive liquid.   The polishing apparatus according to claim 1, wherein the flow rate control unit includes an air pressure chamber and a valve that opens and closes according to the air pressure in the air pressure chamber, and controls the flow rate of the abrasive liquid.   The polishing apparatus according to claim 1 or 2, wherein the flow rate control means sets the air pressure in the air pressure chamber to a predetermined value by an electropneumatic converter based on the instruction signal.   4. The polishing apparatus according to claim 1, wherein the extraction pipe is provided with a cleaning liquid pipe for supplying a cleaning liquid to the flow rate control means. A polishing part, a polishing liquid supply means for supplying a polishing liquid to the polishing part, a polishing liquid circulation pipe provided between the polishing part and the polishing liquid supply means, and extends from the polishing liquid circulation pipe to the polishing part. Using a polishing system having an extraction tube,
Diluting the abrasive liquid to a desired concentration;
The abrasive fluid circulation pipe is provided with a circulation pump that circulates the abrasive fluid, a back pressure valve that keeps the pressure in the circulation pipe above a certain level, and a pressure sensor, and the circulation according to the detected value of the pressure sensor. Controlling the operation of the pump to circulate the diluted abrasive liquid in the abrasive liquid circulation pipe while keeping the pressure in the circulation pipe constant;
Extracting the abrasive liquid from the abrasive liquid circulation pipe toward the polishing section;
A method for polishing a semiconductor wafer, comprising: adjusting a valve opening degree based on an instruction signal corresponding to a preset abrasive liquid supply amount and supplying a desired abrasive liquid flow rate to the polishing unit. 6. The method for polishing a semiconductor wafer according to claim 5 , further comprising the step of stopping the extraction of the abrasive liquid from the abrasive liquid circulation pipe to the polishing section and cleaning the extraction pipe.

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