DIAMOND SUBSTRATE PROCESS

Abstract

Diamond substrate manufacturing process for producing a diamond substrate (34) from a diamond ingot (2) having a flat surface formed as a crystal plane on a (001) plane, the diamond substrate manufacturing process comprising: a focal point adjustment step comprising adjusting a focal point of a laser beam (LB) having a transmission wavelength for diamond to a predetermined depth inside the diamond ingot (2) from the flat surface of the diamond ingot (2), wherein the predetermined depth corresponds to a thickness of the diamond substrate (34) to be produced; After performing the focal point adjustment step, a step to form a band-shaped separation layer (22) is performed by applying the laser beam (LB) to the diamond ingot (2) while moving the diamond ingot (2) and the focal point relative to each other in a [110] direction perpendicular to a (110) plane as a further crystal plane, in order to form a band-shaped separation layer (22) extending in the [110] direction inside the diamond ingot (2) at the predetermined depth; After performing the step to form a band-shaped separation layer (22), a division step is performed by moving the diamond ingot (2) and the focal point relative to each other in a division direction parallel to the (001) plane and perpendicular to the [110] direction; a step to form a planar separating layer (24) with a repetition of the step to form a band-shaped separating layer and the division step in order to form a planar separating layer (24) parallel to the (001) plane inside the diamond ingot (2), wherein the planar separating layer (24) is composed of several band-shaped separating layers (22) arranged side by side in the division direction; and After performing the step to form a planar separation layer (24), a separation step is carried out by separating the diamond substrate (34) along the planar separation layer (24) from the diamond ingot (2).

Description

BACKGROUND OF THE INVENTION AREA OF THE INVENTION

[0001] The present invention relates to a diamond substrate manufacturing process for producing a diamond substrate from a diamond ingot having a flat surface formed as a crystal plane on a (001) plane. DESCRIPTION OF THE RELATED STATE OF THE ART

[0002] A multitude of electronic components, such as integrated circuits (ICs) and large-scale integrated circuits (LSIs), are fabricated by forming a functional layer on the top surface of a wafer-shaped semiconductor substrate, made, for example, of silicon (Si), and dividing this functional layer into numerous separate regions along a multitude of intersecting dividing lines. The semiconductor wafer, containing the multitude of components, is then divided along these dividing lines using a separating device or laser processing device to obtain individual component chips corresponding to the multitude of components. These component chips are used in electronic equipment such as mobile phones and personal computers.

[0003] In recent years, attention has been focused on the use of diamond as a material for a semiconductor substrate, as diamond is superior in terms of dielectric voltage, thermal conductivity and physical properties (see, for example, the published Japanese patent number 2008-78611 and the published Japanese patent number 2015-57824).

[0004] Further information helpful for understanding the present invention can be found in the following documents: JP 2009 - 61 462 A relates to a method for producing a substrate, wherein the method avoids loss of substrate material when separating the substrate from the substrate material. US 2018 / 0126484A1 relates to a method for creating a detachment zone in a solid material in order to detach a solid section from the solid material. SUMMARY OF THE INVENTION

[0005] However, a technique for efficiently producing a diamond substrate from a diamond ingot is still under development, and the diamond substrate is expensive and uneconomical.

[0006] It is therefore an object of the present invention to provide a diamond substrate manufacturing process that can efficiently and cost-effectively produce a diamond substrate from a diamond ingot.

[0007] In accordance with one aspect of the present invention, a diamond substrate manufacturing method for producing a diamond substrate from a diamond ingot having a flat surface formed as a crystal plane on a (001) plane is provided, wherein the diamond substrate manufacturing method includes: a focal point setting step comprising setting a focal point of a laser beam having a transmission wavelength for diamond to a predetermined depth inside the diamond ingot from the flat surface of the diamond ingot, wherein the predetermined depth corresponds to a thickness of the diamond substrate to be produced;After performing the focal point adjustment step, a step to form a band-shaped separation layer is performed by applying the laser beam to the diamond ingot with a relative movement of the diamond ingot and the focal point to each other in a

[110] direction perpendicular to a (110) plane as a further crystal plane, in order to form a band-shaped separation layer which extends inside the diamond ingot to the predetermined depth in the

[110] direction; after performing the step to form a band-shaped separation layer, a division step is performed with a relative movement of the diamond ingot and the focal point to each other in a division direction parallel to the (001) plane and perpendicular to the

[110] direction;a step to form a planar separating layer with a repetition of the step to form a band-shaped separating layer and the division step to form a planar separating layer inside the diamond ingot parallel to the (001) plane, wherein the planar separating layer is composed of a plurality of band-shaped separating layers arranged side by side in the division direction; and a separation step comprising separating the diamond substrate along the planar separating layer from the diamond ingot after performing the step to form a planar separating layer.

[0008] Preferably, the division step includes the step of moving the diamond ingot and the focal point relative to each other in the division direction by a preset division amount, so that any adjacent of the several band-shaped separation layers come into contact with each other.

[0009] In accordance with the diamond substrate manufacturing process of the present invention, the diamond substrate can be efficiently produced from the diamond ingot at low cost.

[0010] The above and other tasks, features and advantages of the present invention and the manner of its implementation will become clearer by studying the following description and the attached claims with reference to the attached drawings, which show a preferred embodiment of the invention, and the invention itself will be best understood by this. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of a diamond ingot; Fig. 2A is a perspective view showing a step towards the formation of a band-shaped separation layer; Fig. 2B is a side view showing the Fig. 2A represents the step shown for the formation of the band-shaped separation layer; Fig. 2C is a cross-sectional view of the diamond ingot in the state in which several band-shaped discontinuities are formed to create a planar discontinuity layer inside the diamond ingot; Fig. 3A is a perspective view depicting a state in which the diamond ingot is positioned under a separating device; Fig. 3B is a perspective view that shows a separation step using the in Fig. 3A represents the separating device shown; and Fig. 3C is a perspective view showing a diamond substrate that has been separated from the diamond ingot, and also showing a remaining diamond ingot obtained by the separation step. DETAILED DESCRIPTION OF THE PREFERRED EXECUTION FORM

[0011] With reference to the drawings, a preferred embodiment of the diamond substrate manufacturing process in accordance with the present invention will now be described. Fig. 1 represents a diamond ingot 2 to which the diamond substrate manufacturing process is applicable in accordance with the present invention. As in Fig. As shown in Figure 1, the diamond ingot 2 has a substantially cylindrical shape. That is, the diamond ingot 2 has a substantially circular first end face 4 as a flat surface formed on a (001) plane as a crystal plane, a substantially circular second end face 6 opposite the first end face 4, and a substantially cylindrical surface 8 formed to connect the first end face 4 and the second end face 6. The cylindrical surface 8 of the diamond ingot 2 is formed with an alignment plane 10 which, viewed from the side, has a rectangular shape. The alignment plane 10 is parallel to a (110) plane as another crystal plane. Fig. 1 An arrow P indicates a

[110] direction perpendicular to the (110) plane.

[0012] In the preferred embodiment, a focal point adjustment step is first performed to adjust the focal point of a laser beam, which has a transmission wavelength for diamond, inside the diamond ingot 2 to a predetermined depth from the flat surface (i.e., in the preferred embodiment, the first end surface 4) of the diamond ingot 2, wherein the predetermined depth corresponds to the thickness of a diamond substrate to be produced. The focal point adjustment step can be performed using a laser processing device 12, part of which is Fig. 2A is shown.

[0013] As in Fig. As shown in Figure 2A, the laser processing device 12 includes a holding table 14 for holding the diamond ingot 2 and a focusing means or condenser 16, which applies a pulsed laser beam LB to the diamond ingot 2 held on the holding table 14, wherein the pulsed laser beam LB has a transmission wavelength suitable for diamond. The holding table 14 is rotatable about its vertical axis. The holding table 14 is also rotatable in the direction indicated by an arrow X in Fig. 2A as well as in the direction shown by an arrow Y in Fig. The Y-direction shown in Figure 2A is movable back and forth, with the Y-direction being perpendicular to the X-direction in an XY-plane. The XY-plane defined by the X-direction and the Y-direction is a substantially horizontal plane. The holding table 14 is connected from a processing area in the laser processing device 12 to a cutting device 26 (see Figure 2A). Fig. 3A) movable, which is described below.

[0014] During the focal point adjustment step, the diamond ingot 2 is attached to the upper surface of the holding table 14 using a suitable adhesive (for example, an epoxy resin adhesive) in the state where the first end face 4 of the diamond ingot 2 is facing upwards. This means that the adhesive is inserted between the second end face 6 of the diamond ingot 2 and the upper surface of the holding table 14. Alternatively, several suction holes can be formed on the upper surface of the holding table 14, and a suction force can be applied to the surface of the holding table 14 via these holes to hold the diamond ingot 2 under a vacuum. Subsequently, an imaging unit (not shown) belonging to the laser processing device 12 is actuated to image the surface of the diamond ingot 2 held on the holding table 14.In accordance with an image of the diamond ingot 2 as captured by the imaging unit, the holding stage 14 is rotated and moved to align the diamond ingot 2 to a predetermined orientation and also to adjust the position of the diamond ingot 2 on the XY plane relative to the focusing means 16. By adjusting the orientation of the diamond ingot 2 to the predetermined orientation, the alignment plane 10 is set, as shown in . Fig. 2A is shown, arranged parallel to the Y direction, such that the

[110] direction is perpendicular to the (110) plane and parallel to the X direction. A focal point positioning means belonging to the laser processing device 12 (not shown) is then actuated to move the focusing means 16 in a vertical direction, thereby positioning the focal point FP of the pulsed laser beam LB inside the diamond ingot 2, as shown in Fig. Figure 2B shows a flat surface set to a predetermined depth (for example, 200 µm) from the first end surface 4, where the predetermined depth corresponds to the thickness of a diamond substrate to be produced. As described above, the pulsed laser beam LB has a transmission wavelength suitable for diamond.

[0015] After performing the focal point adjustment step, a step to form a band-shaped separation layer is carried out in order to form a band-shaped separation layer by applying the laser beam LB to the diamond ingot 2 while moving the diamond ingot 2 and the focal point FP relative to each other in the

[110] direction perpendicular to the (110) plane.

[0016] During the execution of the step to form a band-shaped separation layer, the holding table 14, which holds the diamond ingot 2, is moved in the X-direction parallel to the

[110] direction, which is perpendicular to the (110) plane, at a predetermined feed rate in the X-direction in the preferred embodiment. Simultaneously, the pulsed laser beam LB, which has a transmission wavelength suitable for diamond, is applied to the diamond ingot 2 from the focusing means 16. As a result, as shown in Fig. As shown in Figure 2C, a band-shaped separation layer 22 is formed at the predetermined depth inside the diamond ingot 2 such that it extends in the X-direction, i.e., in the

[110] -direction, in which the band-shaped separation layer 22 is composed of a modified section 18, where the crystal structure has been disrupted by the application of the pulsed laser beam LB, and several cracks 20 that extend isotropically from the modified section 18. While the holding stage 14, as mentioned above, is moved in the X-direction relative to the focusing means 16 during the step of forming a band-shaped separation layer, the focusing means 16 can be moved in the X-direction relative to the holding stage 14.

[0017] After the step of forming a band-shaped separation layer has been carried out, a division step is performed to move the diamond ingot 2 and the focal point FP relative to each other in a division direction parallel to the (001) plane and perpendicular to the

[110] direction. In the preferred embodiment, the holding stage 14 is moved by a predetermined division amount Li in the Y direction perpendicular to the

[110] direction. As a variation, the focusing means 16 can be moved in the Y direction relative to the holding stage 14.

[0018] A step to form a planar separating layer is then performed to form a planar separating layer inside the diamond ingot 2 by repeatedly performing the step to form a band-shaped separating layer and the division step parallel to the (001) plane. This means that by repeating the step to form a band-shaped separating layer and the division step, several similar band-shaped separating layers 22 are formed such that they are arranged side by side in the Y-direction, thereby forming a planar separating layer 24, which, as shown in Fig. 2C, is composed of several band-shaped separation layers 22, with the planar separation layer 24, which is formed inside the diamond ingot 2, exhibiting reduced strength. While the cracks 20, as shown in Fig. As shown in Figure 2C, where the multiple band-shaped separating layers 22 are spaced apart from each other, the division value Li is preferably set during the division step such that the cracks 20 of the adjacent band-shaped separating layers 22 come into contact with each other. In this case, the adjacent band-shaped separating layers 22 can be connected to each other, so that the strength of the planar separating layer 24 can be further reduced. As a result, the separation of a diamond substrate from the diamond ingot 2 during a subsequent separation step can be facilitated.

[0019] For example, the step to form a planar separating layer can be carried out under the following processing conditions, where the point “number of passes” means the number of repetitions with an application of the pulsed laser beam LB in the diamond ingot 2 to the same position. Wavelength of the pulsed laser beam: 1064 nm Average power consumption: 1.0 W Repetition rate: 30 kHz Feed speed: 350 mm / s Number of runs: 2 Allocation amount: 50

[0020] After performing the step to form a planar separation layer, a separation step is carried out to separate a diamond substrate from the diamond ingot 2 along the planar separation layer 24. The separation step can be carried out using a separation device 26, part of which is Fig. Figure 3A illustrates the separation device 26. It includes an arm 28 extending in a substantially horizontal direction and a motor 30 connected to the front end of the arm 28. The arm 28 is movable in the vertical direction. A disc-shaped suction element 32 is connected to the lower surface of the motor 30 so that it is rotatable about its vertical axis. That is to say, the suction element 32 is configured to be rotated about its vertical axis by the motor 30. The suction element 32 has a lower surface that serves as a suction holding surface for holding a workpiece under a vacuum. Furthermore, the suction element 32 includes an ultrasonic vibration application means (not shown) for applying an ultrasonic vibration to the lower surface of the suction element 32.

[0021] The separation step will now be taken with reference to the Fig. 3A to 3C are described in more detail. During the separation step, the holding table 14, which holds the diamond ingot 2, is first moved to the position below the suction element 32 of the separation device 26. Then, the arm 28 is lowered to bring the lower surface of the suction element 32 into contact with the first end surface 4 of the diamond ingot 2, i.e., the surface closer to the planar separation layer 24 formed inside the diamond ingot 2. Accordingly, the first end surface 4 of the diamond ingot 2 is attracted to the lower surface of the suction element 32 by a vacuum. The ultrasonic vibration application device is then activated to apply an ultrasonic vibration to the lower surface of the suction element 32. Simultaneously, the motor 30 is actuated to rotate the suction element 32. As a result, a diamond substrate 34, as described in Fig.Figure 3C shows the diamond ingot 2 being separated along the planar separation layer 24. The diamond substrate 34 has a separation surface 36 with a roughness of [value missing]. The separation surface 36 of the diamond substrate 34 is flattened by using a suitable flattening device.

[0022] After the diamond substrate 34 is removed, the diamond ingot 2 exhibits a parting surface 38 with a certain roughness. The parting surface 38 of the diamond ingot 2 is also flattened to obtain a flat surface. Subsequently, the focal point adjustment step, the step to form a band-shaped parting line, the division step, the step to form a planar parting line, and the separation step can be repeated in a similar manner to produce several similar diamond substrates 34 from the diamond ingot 2. Accordingly, the diamond substrate 34 can be produced efficiently and at low cost from the diamond ingot 2.

[0023] The present invention is not limited to the details of the preferred embodiment described above. The scope of protection of the invention is defined by the attached claims, and all modifications and adaptations that fall within the equivalent scope of protection of the claims are therefore included in the invention.

Claims

[1] A diamond substrate manufacturing method for manufacturing a diamond substrate (34) from a diamond ingot (2) having a flat surface formed on a (001) plane as a crystal plane, the diamond substrate manufacturing method comprising: a focus adjustment step comprising adjusting a focus of a laser beam (LB) having a transmission wavelength for diamond to a predetermined depth inside the diamond ingot (2) from the flat surface of the diamond ingot (2), the predetermined depth corresponding to a thickness of the diamond substrate (34) to be produced; after performing the focus adjustment step, a step of forming a band-shaped separation layer (22) by applying the laser beam (LB) to the diamond ingot (2) while moving the diamond ingot (2) and the focus relative to each other in a [110] direction perpendicular to a (110) plane as another crystal plane, to thereby form a band-shaped separation layer (22) extending in the [110] direction inside the diamond ingot (2) at the predetermined depth; after performing the step of forming a band-shaped separation layer (22), a dividing step comprising moving the diamond ingot (2) and the focal point relative to each other in a dividing direction parallel to the (001) plane and perpendicular to the [110] direction; a step of forming a planar separation layer (24) comprising repeating the step of forming a band-shaped separation layer and the dividing step to thereby form a planar separation layer (24) parallel to the (001) plane inside the diamond ingot (2), wherein the planar separation layer (24) is constructed with a plurality of band-shaped separation layers (22) arranged side by side in the dividing direction; and after carrying out the step of forming a planar separation layer (24), a separation step comprising separating the diamond substrate (34) along the planar separation layer (24) from the diamond ingot (2). [2] The diamond substrate manufacturing method according to claim 1, wherein the dividing step includes a step of moving the diamond ingot (2) and the focal point relative to each other in the dividing direction by a preset dividing amount so that any adjacent ones of the plurality of band-shaped layers (22) come into contact with each other.

Images