Method of processing a wafer

Abstract

A wafer processing method prevents damage to devices adjacent to a peripheral remaining region of a wafer. The method includes a protective member providing step of providing a protective member (14) to a front surface (2a) of the wafer; a first and second annular modification layer forming step of forming a first annular modification layer (24) and a second annular modification layer (26) along the peripheral remaining region; a division predetermined line modification layer forming step of forming a division predetermined line modification layer (28) along a division predetermined line; and a division step of grinding a back surface (2b) of the wafer to form the wafer to a predetermined thickness, and dividing the wafer into individual device chips by a crack (28') extending from the division predetermined line modification layer along the division predetermined line. In the division predetermined line modification layer forming step, a focal point of a laser light is positioned in a manner that a start point (28a) and an end point (28b) of the division predetermined line modification layer are positioned between the first and second annular modification layers.

Description

TECHNICAL FIELD

[0001] The present application relates to a processing method of a wafer which is divided into individual device chips, the wafer having a device region in which a plurality of devices are formed by division with a plurality of division- scheduled lines intersecting each other, and a peripheral remaining region surrounding the device region, on a front surface. BACKGROUND

[0002] A wafer having a device region in which a plurality of devices such as ICs, LSIs, and the like are formed by division with a plurality of division- scheduled lines intersecting each other, and a peripheral remaining region surrounding the device region, on a front surface, is divided into individual device chips, and the divided device chips are used for electronic equipment such as mobile phones, personal computers, and the like.

[0003] As a method of dividing a wafer into individual device chips, a technique has been proposed in which a condensing point of laser light having a wavelength which is transmissive to the wafer is positioned inside the wafer corresponding to the division- scheduled line, the wafer is irradiated with the laser light to form a modified layer along the division- scheduled line, and then, the wafer is divided into individual device chips by applying an external force to the wafer (for example, refer to Patent Literature 1).

[0004] As a method of applying an external force to a wafer, a technique has also been proposed in which the wafer is thinned to a desired thickness by providing a protective member on the front surface of the wafer and polishing the back surface of the wafer, and the wafer is divided into individual device chips by causing a crack to reach the front surface from the modified layer (for example, refer to Patent Literature 2).

[0005] Patent Literature 1: Japanese Patent No. 3408805

[0006] Patent Literature 2: Japanese Patent No. 4358762

[0007] However, since chamfer processing is performed on the peripheral surface of the peripheral remaining region of the wafer, it is difficult to form a modified layer in a region in which chamfer processing is performed on the extension line of the division- scheduled line. Therefore, when an external force is applied to the wafer after the modified layer is formed inside the wafer along the division- scheduled line, a crack is sometimes produced disorderly due to the fact that a modified layer is not formed in the region in which chamfer processing is performed in the peripheral remaining region, thereby causing a problem in which a device adjacent to the peripheral remaining region is damaged. SUMMARY

[0008] Therefore, an object of the present application is to provide a processing method of a wafer which can prevent damage to a device adjacent to a peripheral remaining region of a wafer.

[0009] According to the present invention, a method for processing a wafer is provided, wherein the wafer is divided into individual device chips. The wafer has a device region on its front side, which is divided by multiple intersecting predetermined dividing lines and in which multiple devices are formed, and an outer peripheral remaining region surrounding the device region. The wafer processing method includes the following steps: a protective component placement step, in which a protective component is placed on the front side of the wafer; and an annular modification layer formation step, in which a laser beam of a wavelength that is transparent to the wafer is positioned from the back side of the wafer within the inner part of the wafer corresponding to the outer peripheral remaining region, and the laser beam is irradiated onto the wafer, thereby forming a first annular modification layer along the outer peripheral remaining region and a second annular modification layer surrounding the first annular modification layer. The process includes: a layer; a process for forming a pre-defined dividing line modified layer, wherein a laser beam of wavelength that is transparent to the wafer is positioned from the back of the wafer at the interior of the wafer corresponding to the pre-defined dividing line, and the laser beam is irradiated onto the wafer, thereby forming a pre-defined dividing line modified layer along the pre-defined dividing line; and a dividing process, wherein the back of the wafer is ground to form the wafer to a predetermined thickness, and the wafer is divided into individual device chips by cracks extending from the pre-defined dividing line modified layer along the pre-defined dividing line, wherein in the process of forming the pre-defined dividing line modified layer, the laser beam of the pre-defined dividing line modified layer is positioned such that the start and end points of the pre-defined dividing line modified layer are located between the first annular modified layer and the second annular modified layer.

[0010] Preferably, the interval between the first annular modified layer and the second annular modified layer formed in the annular modified layer forming process is set to 300 μm to 1000 μm.

[0011] According to the present invention, even if a crack extends randomly from the start or end point of the pre-defined line modification layer, the crack will be blocked by the first and second annular modification layers, thus preventing the crack from reaching the device. Therefore, the wafer processing method according to the present invention can prevent damage to devices adjacent to the remaining peripheral region of the wafer. Attached Figure Description

[0012] Figure 1 It is a perspective view showing the state of the protective component installation process.

[0013] Figure 2 (a) is a perspective view showing the state in which the wafer is held on the chuck stage. Figure 2 (b) is a three-dimensional view of the wafer being held in place by a chuck stage.

[0014] Figure 3 This is a perspective view showing the state of the ring-shaped modified layer formation process.

[0015] Figure 4 (a) is a three-dimensional view of a wafer with the first and second annular modified layers formed thereon.Figure 4 (b) is Figure 4 (a) is a cross-sectional view of the wafer.

[0016] Figure 5 (a) is a perspective view showing the state of the process of forming a modified layer with a predetermined dividing line. Figure 5 (b) is Figure 5 (a) is a top view of the wafer. Figure 5 (c) is Figure 5 An enlarged view of part A in (b). Figure 5 (d) is Figure 5 An enlarged view of part B in (b).

[0017] Figure 6 (a) is a perspective view showing the state of the cutting process. Figure 6 (b) is a three-dimensional view of the segmented wafer. Figure 6 (c) is Figure 6 (b) is a top view of the wafer.

[0018] Label Explanation

[0019] 2: Wafer; 2a: Front side of the wafer; 2b: Back side of the wafer; 4: Device; 6: Pre-defined dicing line; 8: Device region; 10: Remaining peripheral region; 14: Protective component; 24: First annular modified layer; 26: Second annular modified layer; 28: Pre-defined dicing line modified layer; 28a: Start point of the pre-defined dicing line modified layer; 28b: End point of the pre-defined dicing line modified layer; 46: Device chip. Detailed Implementation

[0020] Hereinafter, a preferred embodiment of the wafer processing method of the present invention will be described with reference to the accompanying drawings.

[0021] Figure 1 A wafer 2 processed using the wafer processing method of the present invention is shown. The wafer 2 can be formed, for example, from silicon. On the front side 2a of the disc-shaped wafer 2, a device region 8 is formed, divided by multiple predetermined dividing lines 6 in a lattice pattern, on which multiple devices 4 such as ICs and LSIs are formed, and a remaining peripheral region 10 surrounding the device region 8 is also shown. Figure 1 For convenience, a double-dotted line is used to represent the boundary 12 between the device region 8 and the remaining outer region 10, but in reality, there is no line representing the boundary 12.

[0022] In the wafer processing method of this embodiment, such as Figure 1 As shown, firstly, a protective component placement process is performed to place a protective component 14 on the front side 2a of the wafer 2. For example, a circular adhesive tape with the same diameter as the wafer 2 can be used as the protective component 14.

[0023] After the protective component installation process is performed, the focal point of the laser light with a wavelength that is transparent to the wafer 2 is positioned from the back side 2b of the wafer 2 inside the wafer 2 corresponding to the outer peripheral remaining area 10, and the laser light is irradiated onto the wafer 2 to perform the annular modification layer formation process of forming a first annular modification layer along the outer peripheral remaining area 10 and a second annular modification layer surrounding the first annular modification layer.

[0024] The ring-shaped modified layer formation process can be used, for example, in... Figure 3 The laser processing apparatus 16 shown in the figure is used to implement this process. The laser processing apparatus 16 includes: a chuck stage 18 for attracting and holding a wafer 2; a concentrator 20 for irradiating pulsed laser beams LB onto the wafer 2 attracted and held by the chuck stage 18; and an imaging unit (not shown) for imaging the wafer 2 attracted and held by the chuck stage 18.

[0025] like Figure 2 As shown in (a), a porous circular adsorption chuck 22 connected to an adsorption unit (not shown) is disposed at the upper end of the chuck stage 18. The chuck stage 18 generates an adsorption force on the upper surface of the adsorption chuck 22 through the adsorption unit, thereby adsorbing and holding the wafer 2 placed on the upper surface of the adsorption chuck 22.

[0026] The chuck stage 18 is configured to rotate freely about an axis extending vertically through the radial center of the suction chuck 22, and is configured to rotate along... Figure 2 The X-axis direction indicated by the middle arrow X and the Y-axis direction perpendicular to the X-axis direction ( Figure 2 The direction indicated by the middle arrow Y) can be moved forward and backward freely. Furthermore, the XY plane defined by the X-axis and Y-axis directions is essentially horizontal.

[0027] The condenser 20 has a focusing lens (not shown) that focuses the pulsed laser beam LB emitted from the laser oscillator (not shown) of the laser processing apparatus 16. The imaging unit of the laser processing apparatus 16 includes (all not shown): a conventional imaging element (CCD) that images the workpiece using visible light; an infrared irradiation unit that irradiates the workpiece with infrared light; an optical system that captures the infrared light irradiated by the infrared irradiation unit; and an imaging element (e.g., an infrared CCD) that outputs an electrical signal corresponding to the infrared light captured by the optical system.

[0028] In the process of forming a ring-shaped modified layer, such as Figure 2 As shown in (b), first, with the back side 2b of the wafer 2 facing upwards, the wafer 2 is attracted and held by the upper surface of the chuck stage 18. At this time, the radial center of the wafer 2 is aligned with the radial center of the adsorption chuck 22 (the rotation center of the chuck stage 18).

[0029] Next, the imaging unit (not shown) of the laser processing apparatus 16 is used to image the wafer 2 from above. Based on the image of the wafer 2 captured by the imaging unit, the focusing point of the pulsed laser beam LB with a wavelength that is transparent to the wafer 2 is positioned from the back side 2b of the wafer 2 inside the wafer 2 corresponding to the remaining peripheral area 10.

[0030] Furthermore, when photographing the wafer 2 using the imaging unit, the back side 2b of the wafer 2 faces upward, while the front side 2a, where the device 4 and the pre-defined dividing line 6 are formed, faces downward. However, as described above, since the imaging unit includes an infrared illumination unit, an optical system for capturing infrared light, and an imaging element (e.g., an infrared CCD) that outputs an electrical signal corresponding to the infrared light, it is possible to photograph the device 4 and the pre-defined dividing line 6 on the front side 2a through the back side 2b of the wafer 2. Thus, the focusing point of the pulsed laser beam LB can be positioned from the back side 2b of the wafer 2 within the wafer 2 corresponding to the remaining peripheral region 10.

[0031] Next, as Figure 3 As shown, while the chuck stage 18 is rotated at a predetermined speed, causing the focusing point of the pulsed laser beam LB to move relative to the wafer 2 along the outer peripheral remaining region 10, the pulsed laser beam LB is irradiated onto the wafer 2 from the concentrator 20. As a result, a first annular modified layer 24 with low intensity can be formed in the interior of the wafer 2 along the outer peripheral remaining region 10.

[0032] Next, the chuck stage 18 is moved to position the focal point of the pulsed laser beam LB radially outward from the first annular modified layer 24. Then, while rotating the chuck stage 18 at a predetermined speed to move the focal point of the pulsed laser beam LB relative to the wafer 2 along the outer peripheral remaining region 10, the pulsed laser beam LB is irradiated onto the wafer 2 from the concentrator 20. This allows a second annular modified layer 26 with low intensity to be formed along the outer peripheral remaining region 10 within the wafer 2.

[0033] By reference Figure 4 (a) and Figure 4 (b) can be understood that the diameter of the second annular modified layer 26 is larger than the diameter of the first annular modified layer 24, and the second annular modified layer 26 surrounds the first annular modified layer 24. The spacing between the first annular modified layer 24 and the second annular modified layer 26 (the radial spacing of the wafer 2) can be set, for example, to 300 μm to 1000 μm.

[0034] Such a ring-shaped modified layer formation process can be carried out, for example, under the following conditions.

[0035] wafer diameter: 200mm

[0036] Diameter of the device area: 190mm

[0037] The remaining area on the outer perimeter ranges from 190mm to 200mm.

[0038] Diameter of the first annular modified layer: 193 mm

[0039] Diameter of the second annular modified layer: 194 mm

[0040] Wavelength of pulsed laser light: 1342nm

[0041] Repetition frequency: 90kHz

[0042] Average output: 0.6W

[0043] The rotational speed of the chuck table is 0.5 revolutions per second.

[0044] After the ring-shaped modified layer formation process, a focal point of laser light with a wavelength that is transparent to the wafer 2 is positioned from the back surface 2b of the wafer 2 inside the wafer 2 corresponding to the dicing predetermined line 6, and the laser light is irradiated onto the wafer 2 to perform the dicing predetermined line modified layer formation process, which forms a dicing predetermined line modified layer along the dicing predetermined line 6. The dicing predetermined line modified layer formation process can also be performed using the laser processing apparatus 16 described above.

[0045] In the process of forming the pre-defined dividing line modification layer, firstly, with the wafer 2 held in place by the upper surface of the chuck stage 18, the pre-defined dividing line 6 is aligned with the X-axis direction based on an image of the wafer 2 captured by the imaging unit of the laser processing apparatus 16, and the concentrator 20 is positioned above the pre-defined dividing line 6 aligned with the X-axis direction. Next, the focusing point of a pulsed laser beam LB with a wavelength transparent to the wafer 2 is positioned from the back surface 2b of the wafer 2 within the wafer 2 corresponding to the pre-defined dividing line 6, between the first annular modification layer 24 and the second annular modification layer 26.

[0046] Next, as Figure 5 As shown in (a), while the chuck stage 18 is moved along the X-axis at a predetermined feed speed, causing the focusing point of the pulsed laser beam LB to move relative to the wafer 2 along the predetermined slitting line 6, the pulsed laser beam LB is irradiated onto the wafer 2 from the concentrator 20. This allows a low-intensity slitting line modification layer 28 to be formed inside the wafer 2 along the predetermined slitting line 6. If, during the formation of the slitting line modification layer 28, the focusing point of the pulsed laser beam LB reaches between the first annular modification layer 24 and the second annular modification layer 26, the irradiation of the pulsed laser beam LB is stopped.

[0047] In the process of forming the modified layer along the predetermined dividing line, such as Figure 5 (b) and Figure 5 As shown in (d), it is important to position the focal point of the laser beam LB in such a way that the starting point 28a and the ending point 28b of the pre-defined line modified layer 28 are located between the first annular modified layer 24 and the second annular modified layer 26.

[0048] Next, the chuck stage 18 is indexed relative to the condenser 20 along the Y-axis by an interval in the Y-axis direction of the predetermined dividing lines 6. Then, by alternately repeating the irradiation of the laser beam LB and the indexing feed, a predetermined dividing line modification layer 28 is formed along all predetermined dividing lines 6 aligned with the X-axis direction. Next, the chuck stage 18 is rotated 90 degrees, and then the irradiation of the laser beam LB and the indexing feed are alternately repeated, thereby forming a predetermined dividing line modification layer 28 along all predetermined dividing lines 6 perpendicular to the predetermined dividing lines 6 where the predetermined dividing line modification layer 28 was previously formed.

[0049] Such a process of forming a modified layer along a predetermined dividing line can be carried out, for example, under the following conditions.

[0050] Wavelength of pulsed laser light: 1342nm

[0051] Repetition frequency: 90kHz

[0052] Average output: 0.6W

[0053] Chuck table feed rate: 500 mm / s

[0054] After the process of forming the pre-defined dividing line modification layer, the following dividing process is performed: the back side 2b of the wafer 2 is ground to form the wafer 2 to a specified thickness, and the wafer 2 is divided into individual device chips by using cracks extending from the pre-defined dividing line modification layer 28 along the pre-defined dividing line 6.

[0055] For example, the segmentation process can use Figure 6 A portion of the grinding apparatus 30 is shown in (a) and (b) to implement this process. The grinding apparatus 30 includes: a chuck stage 32 that attracts and holds the wafer 2; and a grinding unit 34 that grinds the wafer 2 attracted and held by the chuck stage 32. The chuck stage 32, which attracts and holds the wafer 2 on its upper surface, is configured to rotate freely about an axis extending in the vertical direction.

[0056] The grinding unit 34 includes a spindle 36 extending in the up-and-down direction, and a circular plate-shaped wheel mounting seat 38 fixed to the lower end of the spindle 36. An annular grinding wheel 42 is fixed to the lower surface of the wheel mounting seat 38 by means of bolts 40. A plurality of grinding stones 44 arranged in a ring shape are fixed to the outer peripheral portion of the lower surface of the grinding wheel 42 at intervals in the circumferential direction.

[0057] Referring to Figure 6 (a) to Figure 6 (c), in the dividing process, first, the back surface 2b of the wafer 2 is made to face upward, and the wafer 2 is held by suction against the upper surface of the chuck table 32. Next, the chuck table 32 is caused to rotate counterclockwise at a prescribed rotational speed (for example, 300 rpm) as viewed from above. Also, the spindle 36 is caused to rotate counterclockwise at a prescribed rotational speed (for example, 6000 rpm) as viewed from above. Next, after the spindle 36 is caused to descend so that the grinding stones 44 come into contact with the back surface 2b of the wafer 2, the spindle 36 is caused to descend at a prescribed grinding feed rate (for example, 1.0 μm / s). Thus, the back surface 2b of the wafer 2 is ground, and the wafer 2 is formed to a prescribed thickness.

[0058] When the wafer 2 is ground, pressing force resulting from the grinding feed acts on the wafer 2, and therefore the dividing-predestined-line cracks 28' extend from the dividing-predestined-line modification layer 28 toward the dividing-predestined line 6 in the thickness direction of the wafer 2. Thus, as shown in Figure 6 (b) and Figure 6 (c), the wafer 2 is divided into individual device chips 46 by the dividing-predestined-line cracks 28'. Also, in order to improve the strength against folding, it is preferable that the dividing-predestined-line modification layer 28 be removed by grinding, leaving only the dividing-predestined-line cracks 28'.

[0059] Also, when the wafer 2 is ground, there is a concern that cracks will extend disorderly from the start point 28a or the end point 28b of the dividing-predestined-line modification layer 28. However, in the present embodiment, the start point 28a and the end point 28b of the dividing-predestined-line modification layer 28 are located between the first annular modification layer 24 and the second annular modification layer 26, and when the wafer 2 is ground, the first and second annular cracks 24', 26' extend from the first and second annular modification layers 24, 26 in the thickness direction of the wafer 2, and therefore the disorderly cracks extending from the start point 28a and the end point 28b of the dividing-predestined-line modification layer 28 are blocked by the first and second annular modification layers 24, 26 and the first and second annular cracks 24', 26', and do not reach the devices 4. Thus, according to the present embodiment, damage to the devices 4 adjacent to the outer-peripheral remaining region 10 of the wafer 2 can be prevented.

[0060] Then, after the wafer 2 is divided into individual device chips 46, the rectangular device chips 46 whose outer periphery is defined only by the division- scheduled line cracks 28' are carried to the next process, and the chips 46 whose outer periphery includes the first annular crack 24' (arc-shaped portion) and the portion outside the first annular crack 24' are discarded Figure 6 the portion shown by the gray in (c) (the chip including the first annular crack 24' (arc-shaped portion) in the outer periphery and the portion outside the first annular crack 24').

[0061] As described above, in the wafer processing method of the present embodiment, the disorderly cracks extending from the start point 28a and the end point 28b are blocked by the first and second annular modification layers 24, 26 and the first and second annular cracks 24', 26', and thus do not reach the devices 4, so that damage to the devices 4 adjacent to the outer peripheral remaining region 10 of the wafer 2 can be prevented.

[0062] Further, in the case where the annular modification layer is one, in order to prevent damage to the devices 4 due to the disorderly cracks extending from the start point 28a and the end point 28b, it is necessary to precisely align the start point 28a and the end point 28b on the circumference of the annular modification layer. However, it is difficult to precisely align the start point 28a and the end point 28b on the circumference of the annular modification layer, and thus if the annular modification layer is one, it is likely that the devices 4 are damaged due to the disorderly cracks. In this regard, in the wafer processing method of the present embodiment, the first and second annular modification layers 24, 26 are formed at intervals in the radial direction of the wafer 2, and thus it is possible to easily position the start point 28a and the end point 28b between the first and second annular modification layers 24, 26, so that it is possible to block the disorderly cracks by the first and second annular modification layers 24, 26 and the first and second annular cracks 24', 26', and thus it is possible to reliably prevent damage to the devices 4.

Claims

1. A wafer processing method of dividing a wafer into individual device chips, the wafer having a device region in which a plurality of devices are formed by a plurality of division- scheduled lines intersecting each other, and a peripheral remaining region surrounding the device region on a front surface, wherein the wafer processing method comprises the steps of: a protective member attaching step of attaching a protective member to the front surface of the wafer; a ring-shaped modified layer forming step of irradiating laser light to the wafer from a back surface of the wafer with a focus point of the laser light of a wavelength having a transmittance to the wafer positioned inside the wafer corresponding to the peripheral remaining region, forming a first ring-shaped modified layer along the peripheral remaining region and a second ring-shaped modified layer surrounding the first ring-shaped modified layer; a division-scheduled line modified layer forming step of irradiating laser light to the wafer from the back surface of the wafer with a focus point of the laser light of a wavelength having a transmittance to the wafer positioned inside the wafer corresponding to the division-scheduled line, forming a division-scheduled line modified layer along the division-scheduled line; and a dividing step of grinding the back surface of the wafer to form the wafer into a prescribed thickness, and dividing the wafer into individual device chips by a crack extending from the division-scheduled line modified layer along the division-scheduled line, wherein in the division-scheduled line modified layer forming step, the focus point of the laser light is positioned in a manner that a start point and an end point of the division-scheduled line modified layer formed along the division-scheduled line are positioned between the first ring-shaped modified layer and the second ring-shaped modified layer, and the cracks extending from the start point and the end point of the division-scheduled line modified layer, respectively, are blocked by the first ring-shaped modified layer and the second ring-shaped modified layer.

2. The wafer processing method according to claim 1, wherein a gap between the first ring-shaped modified layer and the second ring-shaped modified layer formed in the ring-shaped modified layer forming step is set to 300 μm to 1000 μm. ​ ​ ​ ​ ​ ​ ​

Images