KR19980018576A - Method and apparatus for cutting ingots - Google Patents

Abstract

The present invention relates to a method for cutting an ingot with a wire, comprising moving the wire in the longitudinal direction and contacting the moving wire with the ingot. The method further includes feeding a polishing slurry containing cutting oil and an abrasive having an average diameter of about 13 μm to about 15 μm when the wire is in contact with the ingot. Accordingly, the ingot is cut into the wire and the abrasive.

Description

Method and apparatus for cutting ingots

The present invention generally relates to methods and apparatus for cutting single crystal ingots in a plurality of wafers using wires.

As illustrated in FIG. 5, a conventional apparatus for cutting ingot I made of ceramic, glass, silicon, etc. in a plurality of wafers is generally indicated by reference numeral 10. The apparatus 10 comprises three grooved rollers 12a-12c, each roller having a plurality of circumferential guide grooves (not shown). The rollers 12a-12c are mounted on a frame (not shown) that is adjustable at predetermined intervals so as to be parallel to each other. The wire 14 is wound several times on the grouped rollers 12a-12c as shown in FIG. 5. The wires 14 are arranged in the guide grooves of the rollers so that each length of the wires extending between the rollers 12a-12c are parallel to the lengths of the adjacent wires and the lengths are evenly spaced along the rollers. . The frame is adjustable to vary the tension of the wire 14 by varying the spacing between the rollers 12a-12c. The apparatus 10 also includes spools 16a, 16b for unwinding and winding the wire 14 as the wire moves back and forth the rollers 12a-12c. Thus, the spools 16a, 16b form part of the drive mechanism, generally designated 18, which drives the wire 14 back and forth in the longitudinal direction.

The apparatus 10 also includes a fixture, generally designated 20, which holds the ingot I and advances the ingot towards the wire 14. The fixing device 20 includes a mounting table 22 coupled to support the ingot when the ingot I is sliced. The mount 22 is made of a relatively soft material such as carbon so that it does not interfere with the wire 14 when the wire slices the ingot I. The mount 22 is attached to the support head 24 supporting the mount and the ingot I when the mount and the ingot are cut. The support head 24 may be made of a high strength material such as steel. The rack 26 extends up from the support head 24, and the motorized pinion 28 is engaged with the rack advancing towards the wire 14 and retracting from the wire. The holding device 20 also includes a linear guide 32 for guiding the holding device and the ingot I, the holding device and the ingot I being perpendicular to the wire 14 as they are advanced and retracted. Stay.

As illustrated in FIG. 4, a conventional cutting device 10 includes a fluid distribution system, generally designated 40, which supplies abrasive slurry containing abrasive and cutting oil to the ingot I when the ingot is cut. . Spray nozzles 42a and 42b located above the wire 14 feed the slurry to the ingot I and the wire. The slurry attaches to the wire 14 so that the wire is dragged over the ingot I to reinforce the cutting of the ingot.

The abrasive used in the slurry should have good cutting capacity and high dispersibility in the oil. Conventional abrasives satisfy the above mentioned conditions but generate large kerf loss and deep wire marks on the cut surface of the wafer. In addition, conventional abrasives damage the surface of the ingot (I). These problems reduce the precision of the wafer cutting process and thus reduce the quality and yield of the wafer.

The present invention solves the problems described above. It is an object of the present invention to provide a method for cutting ingots which improves cutting precision, quality and yield of a wafer obtained by avoiding cuffs, wire marks and surface damage.

In brief, the method of the present invention is to cut an ingot with a wire.

The method consists of moving the wire in the longitudinal direction and contacting the moving wire with an ingot. The method also includes feeding a polishing slurry containing cutting oil and abrasive having an average diameter of about 13 μm to about 15 μm when the wire is in contact with the ingot. Accordingly, the ingot is cut into the wire and the abrasive.

In another aspect, the present invention refers to an apparatus for cutting ingots. The device consists of a wire and a drive mechanism connected to the wire for moving the wire in the longitudinal direction. The apparatus also consists of means for contacting the wire and the ingot while the drive mechanism moves the wire, and a tank containing a polishing slurry containing abrasive material in cutting oil. In addition, the apparatus consists of a fluid distribution system connected to the tank for dispensing the slurry from the tank to the ingot when a wire contacts the ingot. The apparatus further comprises a premixing device for mixing the slurry to uniformly disperse the abrasive in the cutting oil prior to introduction into the fluid distribution system tank.

Other objects and features of the invention will be set forth in part in the following.

Like reference numerals refer to like elements in some drawings.

1 is a schematic diagram of an apparatus for cutting an ingot with a wire used to practice the method of the present invention;

2 is a schematic diagram showing a premix device of the present invention;

3 is a plan view of a wafer showing the location of a measurement point used to evaluate a wafer cut using the method of the present invention;

4 is a schematic diagram showing a conventional apparatus for cutting an ingot with a wire; And

5 is a schematic diagram showing a conventional apparatus for cutting an ingot with a wire.

※ Explanation of code about main part of drawing ※

10: cutting device 12a-12c: grooved roller

14 wire 20 fixing device

22: mounting table 40: fluid distribution system

42a, 42b: spray nozzle 50: tank

52: stirrer 54: pump

56 heating circuit 58 heat exchanger

70: premixer 80: control valve

As illustrated in FIG. 1, an apparatus for cutting an ingot I made of ceramic, glass, silicon or the like in a plurality of wafers is generally indicated by reference numeral 10. The apparatus 10 comprises three grooved rollers 12a-12c, each roller having a plurality of circumferential guide grooves (not shown). The rollers 12a-12c are mounted on a frame (not shown) that is adjustable at predetermined intervals so as to be parallel to each other. The wire 14 is wound several times on rollers 12a-12c, which are generally grouped in a triangular pattern as shown in FIG. The wires 14 are arranged in the guide grooves of the rollers so that each length of the wires extending between the rollers 12a-12c are parallel to the lengths of the adjacent wires and the lengths are evenly spaced along the rollers. . The frame is adjustable to vary the tension of the wire 14 by varying the spacing between the rollers 12a-12c. Drive mechanism 18 (FIG. 5) moves the wire 14 back and forth longitudinally around the roller 12a-12c at an average speed of 400-600 m / min and a circulation speed of 1-3 times per minute. However, other circulation speeds and average speeds are also possible within the scope of the present invention.

In addition, the apparatus 10 includes a mounting table 22 to which the ingot I is coupled to support the ingot when the ingot I is sliced. The mount 22 is made of a relatively soft material such as carbon so that it does not interfere with the wire 14 when the wire slices the ingot I. The mounting table 22 is described above with respect to a conventional device which is operated by the fixing device 20 as shown in FIG. 5 and cuts the ingot with a wire. The fixing device 20 is constituted by means for contacting the wire 14 and the ingot I while the drive mechanism 18 moves the wire.

As further illustrated in FIG. 1, the cutting device 10 comprises a fluid distribution system, generally designated 40, which supplies the polishing slurry to the ingot I when the ingot is cut. Spray nozzles 42a and 42b located above the wire 14 feed the slurry to the ingot I and the wire. The slurry adheres to the wire 14 so that the abrasive contained in the slurry is engaged with the ingot I by the wire to reinforce the cutting of the ingot.

The distribution system 40 includes a tank 50 containing the slurry. The stirrer 52 immersed in the slurry contained in the tank 50 stirs the slurry so that the abrasive is mixed uniformly in the cutting oil. Pump 54 draws the slurry from the tank 50 and distributes it to the ingot I through a nozzle 42a, 42b at a predetermined flow rate (e.g., 50-100 liters / minute). A heating circuit, generally designated 56, is used to circulate the slurry through the heat exchanger to maintain the slurry at a heat exchanger 58 and a predetermined temperature (eg, 20-30 ° C., more preferably 25 ° C.). It consists of a pump 60. The collecting fan 62 located below the roller 12a-12c and the wire 14 collects the used fluid and the drain line 64 transports the collected fluid to the tank 50. About 15-20% of the slurry used in the tank 50 is exchanged each time a new ingot is cut.

A premixer or premixer, generally designated 70, feeds the premixed slurry to the tank 50. As illustrated in FIG. 2, the premixer 70 consists of a container 72 having an inlet 74 through which abrasive and cutting oil are introduced into the tank. Stirrer 76 agitates the abrasive and cutting oil in the tank 72 so that they are uniformly dispersed. Outlet line 78 with control valve 80 transfers the slurry from the premixer 70 to the tank 50 under gravity. The vessel 72 is preferably cylindrical so that the slurry does not stagnate when the slurry is stirred.

The stirrer 76 consists of an electric motor 82 and a blade 84. Preferably, the motor 82 is a 100V single phase motor having a speed of 200 to 500 rpm. The axis of rotation A of the blade 84 is inclined at an angle of about 5-15 ° with respect to the vertical direction to circulate the fluid in the tank in the horizontal and vertical directions to disperse the abrasive. In another embodiment, an ultrasonic generator (not shown) may be used to improve the dispersion of the abrasive. Any stirrer capable of dispersing the abrasive may be used without departing from the scope of the present invention.

The slurry is made of abrasive and cutting oil. In the present invention, the abrasive is preferably stirred in the slurry so as to uniformly disperse the abrasive before the slurry is distributed to the wire 14 and the ingot I. The abrasive used in the slurry generally has an average diameter of 13-15 μm as opposed to a conventional abrasive having an average diameter of about 20 μm. Smaller abrasives tend to agglomerate. Accordingly, the cohesive force between the abrasives may be greater than the tendency to uniformly disperse in the oil under the influence of the surfactant and the dispersant contained in the cutting oil. The abrasive is preferably uniformly dispersed in the cutting oil to avoid damage to the surface of the cuff, the wire mark and the ingot. The premixer 70 described above helps to evenly distribute the abrasive throughout the slurry, and can overcome the tendency for smaller abrasives to aggregate.

The abrasive used in the slurry of the present invention is generally made of silicon carbide having a composition in which silicon carbide (SiC) soluble in hydrochloric acid is 96.0% or more, elemental carbon is 0.5% or less, and iron is 0.3% or less. Preferably, at least 40% of the abrasive has a diameter of 13-15 μm, the maximum diameter of the abrasive is 38.0 μm or less, and the average diameter of the abrasive is 13-15 μm.

The cutting oil used in the slurry of the preferred embodiment is of the type used for hand saws and wire saws used for cutting semiconductor components made of silicon, glass, ceramics and the like. The cutting oil of this preferred embodiment has a composition of 82.0% refined mineral oil, 3.0% thickener, 4.0% of two nonionic surfactants, 2.0% inhibitor, and 5.0% dispersant. The cutting oil of the present invention has a specific gravity of 0.894 at 15 ° C. and a viscosity of 90 centipoise at 25 ° C.

The abrasive in the slurry of the preferred embodiment is mixed with the cutting oil at a rate of 1.0-1.5 kg per liter of cutting oil. The resulting slurry has a specific gravity of about 1.40-1.60 at 25 ° C. and a viscosity of about 150 to about 300 centipoise at 25 ° C.

The invention is explained in more detail below on the basis of examples. However, the present invention is not limited to the above embodiment.

Example

The ingot I was cut using the apparatus 10 shown in FIG. 1 and a slurry made of cutting oil and an abrasive having an average particle diameter of 14 탆 (for example, a grit size of GC # 800). The abrasive and cutting oil were introduced into the premixer 70 at a rate of 1.25 kg of abrasive per liter of cutting oil. They were stirred and mixed at a rotational frequency of about 300 rpm for about 30 minutes to uniformly distribute the abrasive on the wafer surface where the gloss scratches were visible after etching. The number of wire marks for the removal amount of the changed material is recorded in Table 4. The removal amount refers to the amount of material removed from the wafer during the lapping step to achieve the desired wafer thickness. This generally corresponds to the difference in thickness of the central portion of the wafer before and after lapping. Defective rates are also shown in Table 4. If the wafer was rejected regardless of the number of defects, it was counted as one defective for the failure rate.

Comparative example

In addition, the silicon ingot was cut into the wafer using conventional methods and apparatus as shown in FIG. The abrasive having a grit size of GC # 600 and the cutting oil were mixed in the premix device 34 at a ratio of 1.25 kg of abrasive per liter of cutting oil. These were stirred at 300 rpm for 30 minutes to obtain a slurry. The slurry was poured into tank 50 and the silicon ingot was cut into wire 14 having a diameter of 0.18 mm.

Similar measurements were taken with the measurements described above. The measured surface roughness is shown in Table 1. The measured wafer thickness (measured at the center of the wafer), the total thickness deviation, the warp (before etching), the warp (after etching) and the cuff are shown in Table 2. The measured thicknesses of the damaged layer are shown in Table 3. The number of wire marks and the defective rate are shown in Table 4.

Measuring point One 2 3 4 5 The present invention Surface Roughness (㎛) 7.126 17.260 6.944 16.032 5.832 Prior art Surface Roughness (㎛) 8.900 28.800 9.100 28.200 6.200

The present invention Prior art Thickness at Wafer Center (μm) 879.10 885.66 Overall thickness deviation (㎛) 15.25 22.52 Warping (μm) 16.44 10.69 Distortion after etching (㎛) 12.18 14.19 Cyprus (㎛) 230.90 244.34 Wire pitch (㎛) 1110 1130

Depth of damaged layer (μm) The present invention 8.2 Prior art About 20.0

Removal amount (㎛) Number of wire marks Number of fragments Defective rate The present invention 81.564.757.1 000 646040 000 Prior art 100.0 - - 3

Evaluation of test results:

Wafers cut using an abrasive having a grit size of GC ＃ 800 have several advantages over wafers cut with an abrasive having a grit size of GC ＃ 600 (eg, abrasives used in the prior art). .

Improvement of Cyprus:

Cyprus was reduced using the method and apparatus of the present invention. In the comparative example using an abrasive having a grit size of GC # 600 (for example, a conventional technique), the cuff was 250 µm. However, since the cuff in the example using the abrasive having a grit size of GC # 800 was 230 mu m, 20 mu m was improved.

Reduced wire mark depth:

The depth of the wire mark (not shown in the above table) generated by using the prior art method and apparatus was 28 μm, but when the abrasive having a grit size of GC ＃ 800 was used, the wire mark depth was only 20 μm, which is 8 μm. Was improved.

In addition, the amount of removal and the number of wire marks per wafer were reduced when using an abrasive having a grit size of GC # 800 compared to the prior art (eg, using an abrasive having a grit size of GC # 600).

Improvement of damaged layers on the surface:

The depth of the damaged layer was about 20 μm in the comparative example using an abrasive having a grit size of GC × 600, while the depth of the damaged layer was about 8 μm in the example using an abrasive having a grit size of GC × 800.

In addition, it was found that abrasives having a grit size of GC # 800 have lower dispersibility in oil than abrasives having a grit size of GC # 600 because GC # 800 abrasives have a smaller average particle diameter. However, GC ＃ 800 abrasives can be dispersed in oil up to the independent abrasive level by using the apparatus of the present invention.

From the above-mentioned results, it has been found that the method and apparatus for cutting the ingot of the present invention contributes to reducing cuffs, the number and size of wire marks, and damage to the surface of the wafer.

Thus, the method and apparatus for cutting ingots with the wire of the present invention reduces the cuffs, the number and depth of wire marks, and damage to the surface of the wafer, thereby contributing to the improvement of cutting precision, quality and yield of wafer molded products. .

It will be appreciated from the foregoing that the various objects of the present invention are achieved and lead to other beneficial results.

Since various modifications may be made in the above configuration without departing from the scope of the present invention, it will be understood that all contents included in the above description or shown in the accompanying drawings are interpreted as illustrative and not restrictive.

Accordingly, the present invention contributes to the improvement of cutting accuracy, quality and yield of wafer-formed products by reducing cuffs, the number and depth of wire marks, and damage to the surface of the wafer.

Claims (13)

Moving the wire in the longitudinal direction; Contacting the moving wire with an ingot; And Supplying a polishing slurry containing cutting oil and an abrasive having an average diameter of about 13 μm to about 15 μm when the ingot is in contact with a wire to cut the ingot with the wire and the abrasive. A method of cutting an ingot with a wire, characterized in that. The method of claim 1, further comprising agitating the slurry to uniformly disperse the abrasive in the cutting oil prior to feeding the slurry to the ingot. The method of claim 1, wherein the abrasive and the cutting oil are mixed at a ratio of about 1.0 kg to 1.5 kg of abrasive relative to about 1 liter of cutting oil. 4. The method of claim 3, wherein the abrasive and cutting oil are mixed at a ratio of about 1.25 kg of abrasive to about 1 liter of cutting oil. The method of claim 1, wherein the slurry has a specific gravity of about 1.40 to about 1.60 at 25 ° C. The method of claim 1, wherein the slurry has a viscosity of about 150 centipoise to about 300 centipoise at 25 ° C. The method of claim 1, wherein the slurry is fed to the ingot at a flow rate of about 50 liters per minute to about 100 liters per minute. The method of claim 1, wherein the slurry is fed to the ingot at a temperature of about 20 ° C to about 30 ° C. 9. The method of claim 8, wherein the slurry is fed to the ingot at a temperature of about 25 ° C. wire; A drive mechanism coupled to the wire for moving the wire in the longitudinal direction; Means for contacting the wire with the ingot when the drive mechanism moves the wire; A tank containing a polishing slurry containing abrasives in cutting oil; A fluid distribution system connected to said tank for dispensing said slurry from said tank to said ingot when a wire contacts said ingot; And a premix device for mixing the slurry to uniformly disperse the abrasive in the cutting oil prior to introduction into the fluid distribution system tank. The method of claim 10, wherein the premix device A container containing a predetermined amount of cutting oil and abrasive; And And an stirrer for stirring the slurry to uniformly disperse the abrasive in the cutting oil. 12. The apparatus of claim 11, wherein the stirrer comprises a blade that is positionable in a slurry contained in the vessel and a motor that drives the blade about an axis. 13. The apparatus of claim 12, wherein the blade axis is inclined at an angle of about 5 degrees to 15 degrees with respect to the vertical direction.