Slurry circulation device and its control method

Abstract

The stirring speed of the slurry can be controlled appropriately according to the operating status of the processing equipment. [Solution] The wire saw comprises a slurry tank 11 for storing slurry, a stirrer 12 for stirring the slurry inside, a slurry supply unit 21 for supplying the slurry stored in the slurry tank 11 to the wire saw, a mass flow meter 24 for measuring the flow rate and density of the slurry supplied, and a control panel for controlling the rotation speed of the stirrer 12. The control panel is configured to predict the relationship between the cutting depth and the slurry density by taking into account the amount of workpiece chips inside the slurry which gradually increases as the workpiece is processed by the wire saw, and to control the rotation speed of the stirrer 12 in accordance with the flow rate and density of the slurry measured by the mass flow meter 24 and the predicted value of the slurry density at the time of measurement.

Description

Technical Field

[0001] The present invention relates to a slurry circulation device for supplying and recovering slurry to a processing device such as a wire saw, and a control method thereof.

Background Art

[0002] Conventionally, a multi-wire saw is known as a device for cutting a workpiece such as a semiconductor substrate into wafers. In a wire saw, a slurry (a mixture of abrasive grains and coolant) having viscosity is attached to a wire running at high speed, and when the wire and the workpiece are brought into contact with each other, the slurry is introduced into the gap therebetween to advance the cutting process.

[0003] The slurry always needs to be stirred so that sedimentation and deposition of the abrasive grains do not occur. For example, as disclosed in Patent Document 1, a slurry circulation device is known in which the slurry fed from a slurry tank is supplied to a processing device by a slurry supply mechanism, and the slurry recovered from the processing device to the slurry tank is circulated and fed to the slurry supply mechanism again. In this device, a stirring blade for stirring the slurry in the slurry tank, measuring means for measuring the amount of slurry in the slurry tank, and control means for controlling the rotation speed of the stirring blade according to the amount of slurry measured by the measuring means are provided.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] As abrasive grains mixed with the coolant, green silicon carbide abrasive (GC) etc. are used, but diamond abrasive grains are also used for cutting high-hardness materials such as silicon carbide (SiC).

[0006] In particular, in such cases, because abrasive grains are expensive, there is a growing demand to use small-capacity slurry tanks and operate at low concentrations.

[0007] However, the stirring speed in conventional stirrers is set arbitrarily based on empirical rules, and there is no established method for maintaining an optimal stirring speed.

[0008] Furthermore, since slurry circulation does not occur due to the slurry pump's pumping action during standby, it is necessary to set the stirring speed to a relatively high level.

[0009] However, if the stirring speed is too high during processing, the diameter of the slurry tank decreases, making it easier for stirring vortices to form inside the slurry tank, and the slurry flow rate tends to decrease due to the inclusion of air. In addition, the frequency of the stirring blades blocking the suction port of the slurry pump increases, making it difficult to discharge the required amount of slurry.

[0010] On the other hand, if the stirring speed is too slow, the abrasive particles will settle in the slurry tank, reducing the slurry density during processing and negatively affecting cutting speed and processing accuracy due to a decrease in cutting performance.

[0011] The present invention has been made in view of the above, and its objective is to enable the appropriate stirring speed of the slurry to be controlled according to the operating state of the processing apparatus. [Means for solving the problem]

[0012] To achieve the above objectives, this invention monitors not only the slurry flow rate but also its density to ensure that the appropriate flow rate and density are maintained.

[0013] Specifically, in the first invention, A slurry tank for storing slurry, A stirrer for stirring the slurry inside the slurry tank, A slurry supply unit that supplies the slurry stored in the slurry tank to the processing device, A mass flow meter for measuring the flow rate and density of the slurry supplied by the slurry supply unit, A slurry recovery unit recovers the slurry supplied to the processing apparatus by the slurry supply unit and collects it in the slurry tank, The system includes a control unit that controls the rotational speed of the agitator, The control unit, The relationship between the depth of cut and the slurry density is predicted by taking into account the increase in the amount of chips from the workpiece inside the slurry, which gradually increases as the workpiece is processed by the processing device. The system is configured to control the rotation speed of the agitator in accordance with the flow rate and density of the slurry measured by the mass flow meter and the predicted value of the slurry density at the time of measurement.

[0014] With the above configuration, since chips from the workpiece processed by the processing device are also mixed into the slurry, the slurry density increases as processing progresses. Therefore, by predicting the increase in slurry density from the depth of cut and comparing it with the measured value, the rotation speed of the agitator can be adjusted to approach the predicted value, thereby controlling the slurry flow rate and density to an appropriate level.

[0015] In the second invention, in the first invention, The aforementioned processing device is a wire saw, The amount of chip increase is predicted from the contact length of the wire that is fed out from the wire saw and comes into contact with the workpiece.

[0016] With the above configuration, an approximate value of the cutting depth can be calculated from the contact length of the wire in contact with the workpiece, so the amount of chips inside the slurry can be predicted.

[0017] In the control method for the circulation device of the third invention, A slurry tank for storing slurry, A stirrer for stirring the slurry inside the slurry tank, A slurry supply unit that supplies the slurry stored in the slurry tank to the processing device, A mass flow meter that measures the flow rate and density of the slurry supplied by the slurry supply unit, ((ID=2))A slurry recovery unit that recovers the slurry supplied to the processing device by the slurry supply unit and recovers it into the slurry tank, Connect a slurry circulation device having a control unit that controls the rotation speed of the stirrer to the wire saw, While circulating the slurry by the slurry circulation device and measuring the flow rate and density of the slurry with the mass flow meter, supply the slurry between the wire of the wire saw and the workpiece to cut the workpiece, By the control unit, Predict the relationship between the cutting amount and the slurry density in consideration of the increase amount of the chips of the workpiece due to the processing of the wire saw, Compare the measured value by the slurry density measurement unit with the predicted value of the slurry density at the time of measurement, and control the rotation speed of the stirrer so that the two approach each other.

[0018] According to the above configuration, the increase value of the slurry density is predicted from the material of the workpiece and the cutting amount of the wire, and while comparing with the measured value, the rotation speed of the stirrer is controlled so that the appropriate slurry flow rate and density are obtained. can do.

Effect of the Invention

[0019] As described above, according to the present invention, the stirring speed of the appropriate slurry can be controlled according to the operating state of the processing device.

Brief Description of Drawings

[0020] [Figure 1A] It is a perspective view showing a wire saw including a slurry circulation device according to an embodiment of the present invention. [Figure 1B] It is a perspective view showing the slurry circulation device according to the embodiment of the present invention taken out. [Figure 1C] It is a perspective view showing a slurry tank. [Figure 1D] It is a front view showing a slurry tank. [Figure 2]This diagram shows a schematic representation of how an ingot is cut with a wire saw. [Figure 3] This graph shows the predicted slurry density in relation to the amount of cutting. [Figure 4] This flowchart outlines the control method for the slurry circulation device. [Figure 5] This graph shows the slurry flow rate and stirring speed in relation to the amount of material cut. [Modes for carrying out the invention]

[0021] Embodiments of the present invention will be described below with reference to the drawings.

[0022] Figure 1A shows the overall configuration of the wire saw 1 as a processing device, which includes a slurry circulation device 10 according to an embodiment of the invention. As outlined in Figure 2, the wire saw 1 has a large number of wires 4 wound between a pair of opposing guide rollers 2 and 3, and cuts the workpiece 5 by pressing these wires 4 against it. During this cutting process, slurry S is sprayed onto the cutting area and its surroundings. For example, the workpiece 5 is a cylindrical or prismatic silicon ingot.

[0023] The wire saw 1 has a control panel (controller) 6 as a control unit for operating and controlling the entire wire saw 1. The configuration of the control panel 6 is not particularly limited.

[0024] As shown in Figure 1B, the slurry circulation device 10 is a device that supplies and recovers slurry S at the cutting point of the wire saw 1. The slurry circulation device 10 is equipped with a slurry tank 11 for storing slurry S.

[0025] As shown in Figures 1C and 1D, the slurry tank 11 is, for example, a container with a circular cross-section, and its capacity tends to be small because the slurry S is relatively expensive. The shape of the slurry tank 11 is not particularly limited.

[0026] A stirrer 12 is provided in the center of the slurry tank 11 to agitate the slurry S inside. The stirrer 12 has a stirring blade 12a that extends vertically and a stirring motor 12b consisting of an electric motor or the like. The shape of the stirring blade 12a is not particularly limited. The control panel 6 acts as a control unit that controls the rotational speed of the stirrer 12.

[0027] Furthermore, the slurry circulation device 10 includes a slurry supply unit 21 that supplies the slurry S stored in the slurry tank 11 to the wire saw 1.

[0028] The slurry supply unit 21 has a slurry pump 13 which has a suction port 13a for drawing in slurry S from the slurry tank 11. The slurry S drawn into the slurry pump 13 is discharged from the discharge port 13b and sent to the heat exchanger 22. For example, a temperature sensor 23 is provided on the discharge side of the heat exchanger 22, and the control panel 6 is configured to adjust the heat exchanger 22 according to the measurement value of this temperature sensor 23 to maintain the slurry S at an appropriate temperature.

[0029] The slurry S, after passing through the temperature sensor 23, flows into, for example, a bifurcated pipe and is sprayed onto the cut point and its surroundings from slurry nozzles 25 at the end of each pipe. At the base of the pipe, a mass flow meter 24 is provided to measure the flow rate and density of the slurry S supplied by the slurry supply unit 21. The mass flow meter 24 may be configured with separate flow rate measurement and mass (density) measurement functions.

[0030] Although not shown in detail, the bottom of the wire saw 1 is provided with a slurry recovery unit (details not shown) that recovers the slurry S supplied to the wire saw 1 by the slurry supply unit 21 and stores it in the slurry tank 11. The recovered slurry S is collected and stored in the slurry tank 11 through a recovery port 14. The slurry S in the slurry tank 11 can be discharged through a discharge port 15.

[0031] The control panel 6 is configured to control the rotational speed of the agitator 12 in accordance with the flow rate and density of the slurry S measured by the mass flow meter 24 and the predicted value of the slurry density at the time of measurement.

[0032] -Control method for slurry circulation device- Next, the control method for the slurry circulation device 10 according to this embodiment will be described.

[0033] As described above, a wire saw 1 having a slurry circulation device 10 is prepared.

[0034] The control panel 6 has already predicted the relationship between the cutting depth and the slurry density, taking into account the increase in chips from the workpiece 5 inside the slurry S, which gradually increases as the workpiece is processed by the wire saw 1.

[0035] To illustrate a specific calculation method using Figure 2, if workpiece 5 is a cylindrical ingot with radius r, and the cutting depth is c1, then if the contact length is a1, the removal volume is V1, the kerf (cutting allowance) is w, and the number of wafers is N, When the depth of cut c1 is sufficiently small, V1 can be approximated by the following equation.

[0036] V1 = a1 × w × c1 × N When the depth of cut is c2, and the contact length is a2 and the volume removed is V2, c2-c1=Δc When Δc is sufficiently small, V2 can be approximated by the following equation: V2 = a² × w × Δc × N + V1 Therefore, the volume removed Vc for any cut depth c is Vc = V1 + V2 + V3 + ... This is the result.

[0037] In this way, by determining the volume of ingot removed according to the cutting depth, calculating the removed mass from the ingot density, and adding it to the initial slurry density, the predicted slurry density according to the cutting depth can be calculated. Figure 3 shows an example of the calculation. The calculation was performed using an ingot radius r of 150 mm, a kerf w of 0.151 mm, a wafer count N of 400 wafers, an ingot density of 2.33 kg / L, an initial slurry volume of 236 L, and an initial slurry mass of 372.88 kg. It can be seen that the calculated predicted slurry density increases quadratically as the cutting depth increases.

[0038] Even if the ingot shape is different, the predicted slurry density can be calculated in the same way by calculating the wire contact length a.

[0039] As shown in Figure 2, the wire contact length a is given by, when the ingot radius is r, the distance between the cut position and the center is b, and the cut amount is c, r 2 =(a / 2) 2 +b 2 b = r - c a = 2√(2rc - c 2 ) This is the result.

[0040] Next, the control flow in the wire saw 1 will be explained based on Figures 4 and 5.

[0041] First, the cutting process of the ingot is started in step S01. In this case, the initial slurry flow rate is 90 L / min, the initial slurry density is 1.5 kg / L, the initial slurry stirring speed is 40 rpm, and the maximum cutting depth is 150 mm.

[0042] In step S02, the system verifies whether the set flow rate during processing is correct. In the example in Figure 5, the system determines the difference between the initial setting of 90 L / min and the mass flow meter 24. If there is no difference, the system proceeds to step S03. If the flow rate is less than 90 L / min, as shown in Figure 4, the system proceeds to step S04. For example, if air is trapped in the system, the flow rate will decrease.

[0043] In step S04, the stirring speed is gradually reduced, for example, from 40 rpm to 20 rpm, to achieve the set flow rate. Then, by maintaining 20 rpm, the flow rate recovers to the set flow rate.

[0044] Return to step S02 and verify again that the set flow rate during processing is correct. Once the flow rate returns to 90 L / min, gradually increase the stirring speed.

[0045] In step S03, it is determined whether the density measured by the mass flow meter 24 is approximately equal to the predicted slurry density. As shown in Figure 5, when the stirring speed decreases, the slurry density decreases below the predicted slurry density due to abrasive sedimentation at the bottom of the slurry tank 11, so the process proceeds to step S05 to increase the stirring speed and returns to step S02. After confirming that the set flow rate is met in step S02, it is checked again in step S03 whether the slurry density is equal to the predicted density. The stirring speed is increased until it equals the predicted slurry density, and in Figure 5, the two become equal when the cutting depth is 50 mm. The control ends in step S06, and the stirring speed is maintained at the optimal stirring speed while cutting is performed up to a cutting depth of 150 mm, and wafers are cut from the ingot.

[0046] In this embodiment, since the ingot chips produced by the wire saw 1 are also mixed into the slurry, the slurry density increases as the processing progresses. Therefore, by predicting the increase in slurry density from the amount of cut and comparing it with the measured value, the rotation speed of the agitator 12 can be adjusted to approach the predicted value, thereby controlling the flow rate and density of the slurry S to an appropriate level.

[0047] Furthermore, since the approximate depth of cut can be calculated from the contact length of the wire in contact with the ingot, the increase in chips inside the slurry S can be easily calculated.

[0048] Therefore, according to the slurry circulation device 10 of this embodiment, the stirring speed of the slurry S can be controlled appropriately according to the operating state of the wire saw 1.

[0049] (Other embodiments) The present invention may also have the following configuration in the above embodiment.

[0050] In other words, although the above embodiment described a wire saw 1 as the processing device, it is not limited to this, and any processing device that uses a slurry, such as a lapping machine, CMP machine, or polishing machine, may also be used.

[0051] In this embodiment, a control panel 6 was described as an example of a control unit. The control panel 6 controls the wire saw 1 and the slurry circulation device 10, and can be physically configured in any way as long as it has a CPU (processor) and memory. For example, the control panel 6 may utilize software (programs), such as a programmable logic controller (PLC). Alternatively, the control panel 6 may be realized by combining hardware (circuit components).

[0052] The embodiments described above are essentially preferred examples and are not intended to limit the scope of the present invention, its applications, or uses. [Explanation of Symbols]

[0053] 1. Wire saw (processing device) 2,3 Guide rollers 4 wires 5 Work 6. Control Panel (Control Unit) 10. Slurry circulation device 11 Slurry Tank 12 Stirrers 12a Agitator blade 12b Stirring motor 13. Slurry pump 13a Inlet 13b Discharge port 14 Collection port 15 Outlet 21 Slurry supply unit 22 Heat exchanger 23 Temperature Sensor 24 Mass flow meter 25 Slurry Nozzle

Claims

1. A slurry tank for storing slurry, A stirrer for stirring the slurry inside the slurry tank, A slurry supply unit that supplies the slurry stored in the slurry tank to the processing device, A mass flow meter for measuring the flow rate and density of the slurry supplied by the slurry supply unit, A slurry recovery unit recovers the slurry supplied to the processing apparatus by the slurry supply unit and collects it in the slurry tank, The system includes a control unit that controls the rotational speed of the agitator, The control unit, The relationship between the depth of cut and the slurry density is predicted by taking into account the increase in the amount of chips from the workpiece inside the slurry, which gradually increases as the workpiece is processed by the processing device. The system is configured to control the rotation speed of the agitator in accordance with the flow rate and density of the slurry measured by the mass flow meter and the predicted value of the slurry density at the time of measurement. A slurry circulation device characterized by the following features.

2. The aforementioned processing device is a wire saw, The amount of chip increase is configured to be predicted from the contact length of the wire that is fed out from the wire saw and contacts the workpiece. The slurry circulation device according to feature 1.

3. A slurry tank for storing slurry, A stirrer for stirring the slurry inside the slurry tank, A slurry supply unit that supplies the slurry stored in the slurry tank to the wire saw, A mass flow meter for measuring the flow rate and density of the slurry supplied by the slurry supply unit, A slurry recovery unit that recovers the slurry supplied to the wire saw by the slurry supply unit and collects it in the slurry tank, A slurry circulation device having a control unit for controlling the rotational speed of the agitator is connected to the wire saw, The slurry is circulated by the slurry circulation device, and the flow rate and density of the slurry are measured with the mass flow meter. The slurry is then supplied between the wire of the wire saw and the workpiece to cut the workpiece. The control unit, Taking into account the increase in chips from the workpiece due to the wire saw processing, the relationship between the cutting depth and slurry density is predicted. The rotation speed of the agitator is controlled by comparing the measurement value obtained by the slurry density measuring unit with the predicted value of the slurry density at the time of measurement, so that the two values ​​become as close as possible. A control method for a slurry circulation device, characterized by the following features.

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