Processing methods

Abstract

To provide a processing method capable of appropriately forming a modified layer inside a workpiece.SOLUTION: A processing method includes: a holding step of holding a workpiece by a chuck table 8 provided with an upper surface having a holding surface for holding the workpiece; a sheet covering step of covering the upper surface of the chuck table 8 together with the workpiece by a transparent sheet 14; an adhesion step of making the workpiece adhering to the upper surface of the chuck table 8 with an atmospheric pressure applied to the sheet 14 by depressing a region coated with the sheet 14 by generating a suction force on the holding surface of the chuck table 8; and a modified layer forming step of forming a modified layer 20 by irradiating the workpiece with a laser beam LB while positioning a condensing point of the laser beam LB inside the workpiece via the sheet 14.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a processing method in which a focal point of a laser beam having a wavelength that is transparent to the workpiece is positioned inside the workpiece, and the laser beam is irradiated onto the workpiece to form a modified layer inside the workpiece. [Background technology]

[0002] Wafers with multiple devices such as ICs and LSIs formed on their surface along planned dividing lines are then divided into individual device chips using a laser processing machine, and each of the divided device chips is used in electrical equipment such as mobile phones and personal computers.

[0003] The laser processing device includes a chuck table that holds the wafer, a laser irradiation means that irradiates a laser beam of a wavelength that is absorbed by the wafer held on the chuck table, and a processing feed means that relatively feeds the chuck table and the laser irradiation means, and can perform ablation processing along the intended division lines to divide the wafer into individual device chips (see, for example, Patent Document 1).

[0004] Also, some laser processing devices include a chuck table for holding a wafer, a laser irradiation means for irradiating the wafer held on the chuck table with a laser beam having a wavelength that is transparent to the wafer, and a processing feed means for relatively feeding the chuck table and the laser irradiation means. This laser processing device can perform internal processing by positioning the focal point of the laser beam within the planned dividing line and irradiating the wafer with the laser beam to form a modified layer within the planned dividing line. Then, by applying an external force to the wafer that has been internally processed, the wafer can be divided into individual device chips (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 10-305420 [Patent Document 2] Patent No. 3408805 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when internal processing is performed inside the dividing line, volume expansion occurs due to the formation of a modified layer, causing the wafer to bend and the holding force of the chuck table to become unstable, which makes it impossible to continue the internal processing properly and makes it impossible to divide the wafer into individual device chips.

[0007] The applicant has also proposed a technology for producing wafers from wafers or ingots by positioning the focal point of a laser beam inside a wafer or ingot at a depth corresponding to the thickness of the wafer to be produced, and irradiating the wafer or ingot with the laser beam to form a modified layer.However, there is a problem, particularly when forming a modified layer inside the wafer, in that the wafer curves and the modified layer cannot be formed properly.

[0008] In view of the above, an object of the present invention is to provide a processing method that can properly form a modified layer inside a workpiece. [Means for solving the problem]

[0009] According to the present invention, the following processing method is provided to solve the above-mentioned problems: Namely, a processing method in which a focal point of a laser beam having a wavelength that is transparent to the workpiece is positioned inside the workpiece, the laser beam is irradiated onto the workpiece, and a modified layer is formed inside the workpiece, the processing method including a holding step of holding the workpiece by a chuck table having a holding surface on its upper surface that holds the workpiece, a sheet covering step of covering the upper surface of the chuck table together with the workpiece with a transparent sheet, a contact step of generating a suction force on the holding surface of the chuck table, reducing the pressure in the area covered by the sheet, and bringing the workpiece into close contact with the upper surface of the chuck table by the atmospheric pressure applied to the sheet, and a contact step of contacting the focal point of the laser beam through the sheet. , which is in close contact with the chuck table and a modified layer forming step of positioning the workpiece inside and irradiating the workpiece with a laser beam to form a modified layer.

[0010] Preferably, the workpiece is a wafer having a surface on which a plurality of devices are formed and partitioned by dividing lines, and the modified layer is formed inside the dividing lines in the modified layer forming step. The workpiece may be an ingot, and the modified layer may be formed throughout the entire interior of the ingot in the modified layer forming step, the entire interior of the ingot corresponding to the thickness of the wafer to be produced from the ingot. [Effects of the Invention]

[0011] The processing method of the present invention is a processing method in which a focal point of a laser beam having a wavelength that is transparent to the workpiece is positioned inside the workpiece, the laser beam is irradiated onto the workpiece, and a modified layer is formed inside the workpiece, and includes a holding step of holding the workpiece with a chuck table having a holding surface on its upper surface that holds the workpiece; a sheet covering step of covering the upper surface of the chuck table together with the workpiece with a transparent sheet; a contact step of generating a suction force on the holding surface of the chuck table, reducing the pressure in the area covered by the sheet, and bringing the workpiece into close contact with the upper surface of the chuck table by the atmospheric pressure applied to the sheet; and a contact step of contacting the focal point of the laser beam through the sheet. , which is in close contact with the chuck tableand a modified layer forming step in which the workpiece is positioned inside the workpiece and a laser beam is irradiated onto the workpiece to form a modified layer, thereby making it possible to suppress curvature of the workpiece and properly form a modified layer inside the workpiece. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 10 is a perspective view showing a state in which a holding step is being performed. [Figure 2] FIG. 10A is a perspective view showing a state in which a sheet covering process is being performed, and FIG. 10B is a perspective view showing a state in which the sheet covering process is being performed using a sheet supported by an annular frame. [Figure 3] FIG. 1A is a perspective view showing a state in which a bonding step is being performed, and FIG. 1B is a side view showing a state in which the bonding step is being performed. [Figure 4] FIG. 10A is a perspective view showing a state in which a modified layer forming step is being performed, and FIG. 10B is a side view showing a state in which a modified layer forming step is being performed. [Figure 5] FIG. 2A is a perspective view showing a state in which the back surface of the wafer is ground to divide the wafer into individual device chips, and FIG. 2B is a perspective view showing a state in which the wafer has been divided into individual device chips. [Figure 6] FIG. [Figure 7] Schematic diagram showing the sheet being expanded to separate the wafer into individual device chips. [Figure 8] FIG. 2A is a perspective view showing a state in which a modified layer forming step is being performed on an ingot, and FIG. 2B is a perspective view of a wafer produced from the ingot. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, preferred embodiments of the processing method of the present invention will be described with reference to the drawings.

[0014] 1 shows a disk-shaped wafer 2 as a workpiece to be processed by the processing method of the present invention. The wafer 2 may be formed from an appropriate semiconductor material such as silicon (Si) or silicon carbide (SiC). The thickness of the wafer 2 is, for example, approximately 700 μm. The surface 2 a of the wafer 2 is partitioned into a plurality of rectangular regions by grid-like dividing lines 4, and a device 6 such as an IC or LSI is formed in each of the rectangular regions.

[0015] In the illustrated embodiment, a holding step is first performed in which the workpiece is held by a chuck table having a holding surface on its upper surface for holding the workpiece. In the holding step, for example, the chuck table 8 shown in FIG. 1 can be used.

[0016] A circular porous suction chuck 10 connected to a suction means (not shown) is disposed at the upper end of the chuck table 8. The suction means generates a suction force on the upper surface of the suction chuck 10, thereby suction-holding a workpiece placed on the upper surface of the suction chuck 10. In this manner, the upper surface of the suction chuck 10 serves as a holding surface, and the chuck table 8 has a holding surface on its upper surface that holds the workpiece. The chuck table 8 is movable in the X-axis and Y-axis directions, and is also rotatable about an axis extending in the vertical direction.

[0017] The X-axis direction is the direction indicated by the arrow X in Fig. 1, and the Y-axis direction is the direction indicated by the arrow Y in Fig. 1, which is a direction perpendicular to the X-axis direction. The XY plane defined by the X-axis and Y-axis directions is substantially horizontal.

[0018] 1, in the holding step of the illustrated embodiment, first, a circular protective tape 12 for protecting the device 6 is attached to the front surface 2a of the wafer 2. Next, the wafer 2 is placed on the holding surface (the upper surface of the suction chuck 10) of the chuck table 8 with the protective tape 12 facing downward. In this manner, the wafer 2 is held by the chuck table 8.

[0019] In the holding step, the back surface 2b of the wafer 2 may be placed downward and held on the holding surface of the chuck table 8. In this case, it is not necessary to apply the protective tape 12 to the front surface 2a of the wafer 2.

[0020] After the holding step is performed, a sheet covering step is performed in which the upper surface of the chuck table 8 together with the workpiece is covered with a permeable sheet.

[0021] In the sheet covering step, for example, a transparent sheet 14 made of synthetic resin as shown in FIG. 2(a) can be used. The sheet 14 is circular, and the diameter of the sheet 14 is larger than the diameter of the wafer 2. The material of the sheet 14 may be any material that is transparent to the laser beam irradiated when forming a modified layer inside the wafer 2. Specific examples of the material of the sheet 14 include polyolefin (polyethylene, polypropylene, polystyrene, etc.). Furthermore, in the following adhesion step, a relatively hard material (for example, polyethylene terephthalate, polyvinyl chloride, etc.) may be used as long as it is thin enough to be deformable along the upper surface of the wafer 2 and the upper surface of the chuck table 8.

[0022] In the sheet covering step, as shown in FIG. 2( a ), the sheet 14 is placed over the chuck table 8 holding the wafer 2 , and the upper surface of the chuck table 8 together with the wafer 2 is covered with the sheet 14 .

[0023] In the sheet covering step, as shown in Fig. 2(b), a sheet 14 whose peripheral edge is supported by an annular frame 15 may be used. The annular frame 15 is fixed by a plurality of clamps (not shown) arranged around the chuck table 8. From the viewpoint of ease of handling the wafer 2 in the subsequent steps, it is preferable that the sheet 14 be fixed to the annular frame 15.

[0024] After the sheet covering process is performed, a suction force is generated on the holding surface of the chuck table 8, the area covered with the sheet 14 is depressurized, and the atmospheric pressure applied to the sheet 14 causes the workpiece to adhere to the upper surface of the chuck table 8, thereby performing a contact process.

[0025] In the adhesion step, suction means connected to the chuck table 8 is operated to generate suction force on the upper surface of the suction chuck 10, which is the holding surface of the chuck table 8, and the wafer 2 is suction-held on the upper surface of the suction chuck 10. At this time, a small gap is formed between the lower surface of the wafer 2 and the upper surface of the suction chuck 10, and the suction force of the chuck table 8 acts on the sheet 14 covering the wafer 2 through the small gap between the lower surface of the wafer 2 and the upper surface of the suction chuck 10.

[0026] Therefore, when a suction force is generated on the upper surface of the suction chuck 10, the area covered by the sheet 14 is depressurized, and the atmospheric pressure acting on the upper surface of the sheet 14 causes the wafer 2 to adhere to the upper surface of the chuck table 8, and the sheet 14 to adhere to the upper surface of the wafer 2 and the upper surface of the chuck table 8, as shown in Figures 3(a) and 3(b).

[0027] Furthermore, even if the wafer 2 has warpage or undulation before the adhesion process is performed, the adhesion process can correct the warpage or undulation of the wafer 2 and allow the wafer 2 to be adhered along the upper surface of the chuck table 8.

[0028] Although the diameter of the suction chuck 10 is generally slightly smaller than the diameter of the wafer 2, by using a suction chuck having a diameter slightly larger than the diameter of the wafer 2 (for example, about 2 to 3 mm larger), the suction force of the chuck table 8 may be applied to the sheet 14 from the outer periphery of the wafer 2.

[0029] After the adhesion step, a modified layer forming step is carried out in which the focal point of the laser beam is positioned inside the workpiece through the sheet 14 and the laser beam is irradiated onto the workpiece to form a modified layer. The modified layer forming step can be carried out using, for example, a laser processing device 16, a portion of which is shown in Figure 4.

[0030] The laser processing device 16 includes a pulsed laser beam oscillator (not shown), a condenser 18 that focuses the pulsed laser beam LB emitted by the pulsed laser beam oscillator and irradiates the pulsed laser beam LB onto a workpiece held on the chuck table 8, and an imaging means (not shown) that images the workpiece held on the chuck table 8 and detects the area to be processed.

[0031] The imaging means of the laser processing device 16, although not shown, includes a normal imaging element (CCD) that images the workpiece using visible light, an infrared irradiation means that irradiates the workpiece with infrared rays, an optical system that captures the infrared rays irradiated by the infrared irradiation means, and an imaging element (infrared CCD) that outputs an electrical signal corresponding to the infrared rays captured by the optical system.

[0032] Continuing the explanation with reference to Figure 4, in the modified layer forming step, first, the chuck table 8 to which the wafer 2 is in close contact is positioned below the condenser 18. Next, the wafer 2 is imaged by imaging means, and based on the image of the wafer 2 imaged by the imaging means, the dividing lines 4 are aligned in the X-axis direction, and the condenser 18 is positioned above the dividing lines 4 aligned in the X-axis direction. Next, the focal point of the laser beam LB is positioned inside the wafer 2 below the dividing lines 4.

[0033] When the wafer 2 is imaged by the imaging means, the back surface 2b of the wafer 2 faces upward and the front surface 2a on which the planned dividing lines 4 are formed faces downward, but as described above, the imaging means includes an infrared irradiation means, an optical system for capturing infrared rays, and an imaging element (infrared CCD) for outputting an electrical signal corresponding to the infrared rays, so that the planned dividing lines 4 on the front surface 2a can be imaged through the back surface 2b of the wafer 2. This makes it possible to position the focal point of the laser beam LB inside the wafer 2 below the planned dividing lines 4.

[0034] Next, the chuck table 8 is moved in the X-axis direction at a predetermined feed rate, thereby moving the focal point of the laser beam LB relative to the wafer 2, and the laser beam LB having a wavelength that is transparent to the wafer 2 is irradiated from the condenser 18 onto the wafer 2. This allows a modified layer 20 to be formed inside the wafer 2 along the planned dividing line 4.

[0035] Next, the chuck table 8 is indexed in the Y-axis direction by the distance in the Y-axis direction between the planned dividing lines 4. Then, by alternately repeating the irradiation of the laser beam LB and the indexing, modified layers 20 are formed inside the wafer 2 along all of the planned dividing lines 4 aligned in the X-axis direction. Furthermore, after rotating the chuck table 8 by 90 degrees, by alternately repeating the irradiation of the laser beam LB and the indexing, modified layers 20 are formed inside the wafer 2 along all of the planned dividing lines 4 that are perpendicular to the planned dividing lines 4 on which the modified layers 20 were previously formed.

[0036] Such a modified layer forming step can be carried out, for example, under the following conditions. Pulse laser beam wavelength: 1064nm Average power: 1.0W Repetition frequency: 100kHz Chuck table feed speed: 100mm / s

[0037] When the modified layer 20 is formed inside the wafer 2, volume expansion occurs in the modified layer 20, but in the illustrated embodiment, the atmospheric pressure applied to the upper surface of the sheet 14 causes the wafer 2 to be in close contact with the upper surface of the chuck table 8, so the wafer 2 does not bend. Therefore, when the modified layer 20 is being formed, the holding force of the wafer 2 by the chuck table 8 does not become unstable, and the modified layer 20 can be properly formed inside the wafer 2.

[0038] In the illustrated embodiment, after the modified layer forming step is performed, a dividing step is performed in which the wafer 2 is divided into device chips for each individual device 6. The dividing step can be performed using, for example, a grinding device 22 shown in FIG.

[0039] The grinding device 22 is equipped with grinding means 24 that grinds the wafer 2 held on the chuck table 8. The grinding means 24 includes a spindle 26 that extends in the vertical direction and a disk-shaped wheel mount 28 fixed to the lower end of the spindle 26. An annular grinding wheel 32 is fixed to the lower surface of the wheel mount 28 by bolts 30. A plurality of grinding stones 34 are fixed to the outer periphery of the lower surface of the grinding wheel 32, and are arranged in an annular shape at intervals in the circumferential direction.

[0040] In the dividing step, first, the suction means connected to the chuck table 8 is stopped, and the suction force of the vacuum chuck 10 is released. Next, the sheet 14 is removed from the chuck table 8. Next, the suction means is activated again, and the wafer 2 is held by suction on the chuck table 8. When the wafer 2 is held by suction, the back surface 2b of the wafer 2 faces upward, as can be understood by referring to FIG. 5(a).

[0041] Next, the spindle 26 is rotated at a predetermined rotational speed (e.g., 6000 rpm) in the direction indicated by arrow R1 in FIG. 5(a). Also, the chuck table 8 is rotated at a predetermined rotational speed (e.g., 300 rpm) in the direction indicated by arrow R2 in FIG. 5(a). Next, the spindle 26 is lowered to bring the grinding wheel 34 into contact with the back surface 2b of the wafer 2. Also, grinding water is supplied to the portion of the back surface 2b of the wafer 2 where the grinding wheel 34 is in contact. Thereafter, the spindle 26 is lowered at a predetermined grinding feed rate (e.g., 1.0 μm / s), thereby grinding the back surface 2b of the wafer 2.

[0042] When the wafer 2 is being ground, a pressing force due to the grinding feed acts on the wafer 2, causing cracks 36 (see FIG. 5(b)) to extend in the thickness direction of the wafer 2 from the modified layer 20 toward the planned division lines 4. Therefore, the cracks 36 extending from the modified layer 20 divide the wafer 2 into device chips 38 for each individual device 6.

[0043] The dividing step can also be carried out using a dividing device 40 shown in Fig. 6. The dividing device 40 includes a disk-shaped substrate 42, a cylindrical expansion drum 44 extending upward from the upper surface of the substrate 42, and a plurality of air cylinders 46 extending upward at intervals in the circumferential direction from the peripheral edge of the upper surface of the substrate 42. An annular holding member 48 is connected to the upper end of each of the plurality of air cylinders 46. A plurality of clamps 49 are arranged at intervals in the circumferential direction on the outer periphery of the holding member 48.

[0044] Explaining with reference to Fig. 7, each air cylinder 46 raises and lowers the holding member 48 between a reference position where the upper surface of the holding member 48 is at approximately the same height as the upper end of the expansion drum 44, and an extended position where the upper surface of the holding member 48 is located below the upper end of the expansion drum 44. Note that in Fig. 7, the expansion drum 44 when the holding member 48 is located at the reference position is shown by a solid line, and the expansion drum 44 when the holding member 48 is located at the extended position is shown by a two-dot chain line.

[0045] When the dividing step is performed using the dividing device 40, as shown in Fig. 6, adhesive tape T is applied to the back surface 2b of the wafer 2, the outer periphery of the adhesive tape T is supported by an annular frame F, and the protective tape 12 is peeled off from the front surface 2a of the wafer 2. Note that, as shown in Fig. 2(b), if the peripheral edge of the sheet 14 is supported by an annular frame 15, one side of the sheet 14 has an adhesive surface, and the wafer 2 is attached to the adhesive surface of the sheet 14, the sheet 14 and the annular frame 15 used in the sheet covering step can also be used in the dividing step.

[0046] 6 and 7, in the dividing process using the dividing device 40, first, an annular frame F is placed on the upper surface of a holding member 48 positioned at a reference position, and the annular frame F is fixed with a plurality of clamps 49. Next, the air cylinder 46 is operated to lower the holding member 48 to the extended position. This causes a radial tension to act on the wafer 2 attached to the adhesive tape T, so that the wafer 2 can be divided into individual device chips 38 along the dividing lines 4 on which the modified layers 20 are formed, as shown by the two-dot chain lines in FIG.

[0047] As described above, in the processing method of the illustrated embodiment, in the adhesion step, the wafer 2 is brought into close contact with the upper surface of the chuck table 8 by atmospheric pressure applied to the upper surface of the sheet 14, so the wafer 2 does not bend even if volume expansion occurs in the modified layer 20. Therefore, when the modified layer 20 is being formed, the holding force of the wafer 2 by the chuck table 8 does not become unstable, and the modified layer 20 can be properly formed inside the wafer 2.

[0048] The workpiece that can be processed by the processing method of the present invention is not limited to the wafer 2 described above, and may be, for example, an ingot 50 as shown in FIG. 8(a). The ingot 50 may be formed from an appropriate semiconductor material such as silicon (Si) or silicon carbide (SiC). The thickness of the ingot 50 is, for example, about 700 to 2000 μm. However, unlike the wafer 2, the ingot 50 does not have any dividing lines or devices.

[0049] When the ingot 50 is used as the workpiece, the holding step, sheet covering step, and adhesion step are performed in the same manner as when the wafer 2 is used as the workpiece. Then, in the modified layer forming step for the ingot 50, a modified layer is formed over the entire interior area corresponding to the thickness of the wafer to be produced from the ingot 50.

[0050] More specifically, first, the ingot 50 is imaged by the imaging means of the laser processing device 16, and the positional relationship between the ingot 50 and the condenser 18 is adjusted based on the image of the ingot 50 captured by the imaging means. Next, the focal point of a laser beam LB having a wavelength that is transparent to the ingot 50 is positioned at a depth from the top surface of the ingot 50 that corresponds to the thickness of the wafer to be produced.

[0051] Next, the chuck table 8 is moved in the X-axis direction at a predetermined feed rate, thereby moving the focal point of the laser beam LB relative to the ingot 50, and the laser beam LB having a wavelength that is transparent to the ingot 50 is irradiated from the condenser 18 onto the ingot 50. This allows a modified layer 52 to be formed inside the ingot 50 along the X-axis direction.

[0052] Next, the chuck table 8 is indexed in the Y-axis direction by a predetermined indexing feed amount. The indexing feed amount is set to a distance such that adjacent cracks in the Y-axis direction overlap, since cracks (not shown) extend from the modified layer 52 as the modified layer 52 is formed. Then, by alternately repeating the irradiation of the laser beam LB and the indexing feed in the Y-axis direction, the modified layer 52 is formed throughout the entire interior area corresponding to the thickness of the wafer to be produced from the ingot 50.

[0053] The modified layer forming step on the ingot 50 can be carried out under the following conditions, for example. Pulse laser beam wavelength: 1342nm Average power: 2.5W Repetition frequency: 60kHz Chuck table feed speed: 300mm / s Indexing feed amount: 320 μm

[0054] The ingot 50 also undergoes volume expansion due to the modified layer 52, but the atmospheric pressure applied to the upper surface of the sheet 14 causes the ingot 50 to adhere to the upper surface of the chuck table 8, thereby suppressing curvature of the ingot 50 and allowing the modified layer 52 to be properly formed inside the ingot 50.

[0055] After forming a modified layer 52 throughout the entire interior area of ​​the ingot 50, which corresponds to the thickness of the wafers to be produced from the ingot 50, an external force (e.g., ultrasonic vibration) is applied to the ingot 50, and as shown in FIG. 8(b), the ingot 50 is divided using the modified layer 52 as a starting point to produce wafers 54 (two wafers 54 in the illustrated embodiment). Depending on the thickness of the ingot 50, the modified layer formation step may be repeated to produce three or more wafers 54. It is also preferable to grind or polish the dividing surfaces 54a of the produced wafers 54 to make them flat. [Explanation of symbols]

[0056] 2: Wafer (workpiece) 2a: Surface of wafer 2b: Backside of wafer 4: Planned division line 6: Device 8: Chuck table 14: Sheet 20: Modified layer of wafer 50: Ingot (workpiece) 52: Modified layer of ingot

Claims

1. A processing method for forming a modified layer inside a workpiece by irradiating the workpiece with a laser beam having a wavelength that is transparent to the workpiece and positioning the focused point of the laser beam inside the workpiece, the method comprising: a holding step of holding the workpiece by a chuck table having a holding surface on an upper surface thereof for holding the workpiece; a sheet covering step of covering the upper surface of the chuck table together with the workpiece with a permeable sheet; a contacting step of applying a suction force to the holding surface of the chuck table, reducing the pressure in the area covered by the sheet, and contacting the workpiece with the upper surface of the chuck table by atmospheric pressure applied to the sheet; a modified layer forming step of irradiating the workpiece with the laser beam through the sheet by positioning the focal point of the laser beam inside the workpiece that is in close contact with the chuck table, thereby forming a modified layer; A processing method comprising:

2. 2. The processing method according to claim 1, wherein the workpiece is a wafer having a plurality of devices formed on its surface and partitioned by dividing lines, and the modified layer forming step forms the modified layer inside the dividing lines.

3. 2. The processing method according to claim 1, wherein the workpiece is an ingot, and in the modified layer forming step, a modified layer is formed over the entire interior area of ​​the ingot, the thickness of which corresponds to the thickness of the wafer to be produced from the ingot.

Images