JP6837712B2 - Wafer processing method - Google Patents

Description

The present invention relates to a method for processing a wafer having a device region in which a plurality of devices are formed on the surface and an outer peripheral surplus region surrounding the device region, and a chamfered portion is formed on the outer periphery.

A semiconductor wafer in which a plurality of devices such as ICs and LSIs are formed on the front surface and has a chamfered portion on the outer periphery (hereinafter, may be simply abbreviated as a wafer) is obtained after the back surface is ground and thinned to a desired thickness. It is cut along a planned division line called a street and divided into individual chips, and the divided chips are used in various electronic devices.

As a method of dividing the wafer into individual chips, a dicing method of cutting the wafer along the street with a cutting blade having a cutting edge having a thickness of about 20 to 40 μm, or a wavelength having a wavelength that is transparent to the wafer. A method using a pulsed laser beam is common.

In the method using a pulsed laser beam having a wavelength that is transparent to the wafer, the modified layer is continuously formed inside the wafer by aligning the condensing point inside the wafer and irradiating the pulsed laser beam along the street. By applying an external force along the streets that are formed and the strength is reduced by the formation of the modified layer, the wafer is divided into individual chips of the wafer (see, for example, Japanese Patent No. 3408805). This processing method is sometimes referred to as an SD (Stealth Dicing) method.

In this SD method, in order to prevent ablation processing from occurring due to irradiation of the outer peripheral chamfered portion with a laser beam, a so-called inside-inside SD cutting method of irradiating a pulsed laser beam excluding the outer peripheral chamfered portion is characteristic. It is proposed in Kai 2013-237097.

Japanese Patent No. 3408805 Japanese Unexamined Patent Publication No. 2013-237097

However, the SD inner-inner cutting method described in Patent Document 2 has a problem that cracks do not extend along the street in the region where the modified layer is not formed on the outer peripheral portion, and the wafer is not divided neatly. For example, when the chip size is as small as 1 mm square or less, this problem occurs particularly prominently.

The present invention has been made in view of these points, and an object of the present invention is to provide a wafer processing method capable of improving the resolvability of a wafer as compared with the conventional one.

According to the present invention, a device region in which a device is formed in each region partitioned by a plurality of intersecting streets and an outer peripheral surplus region surrounding the device region are provided on the surface, and a chamfered portion is formed on the outer periphery. A method for processing a wafer, in which a focusing point of a laser beam having a wavelength that is transparent to the wafer is positioned inside the wafer, the laser beam is irradiated to the wafer along the street, and the street is inside the wafer. A laser beam irradiation step for forming a modified layer along the line, a cutting step for forming a cutting groove by cutting at least the chamfered portion on an extension of the street with a cutting blade, the laser beam irradiation step, and the cutting step. A method for processing a wafer, which comprises applying an external force to the wafer to divide the wafer into individual chips using the reforming layer and the cutting groove as a division starting point. Provided.

Preferably, the cutting step is performed after performing the laser beam irradiation step.

According to the processing method of the present invention, since a cutting groove serving as a division starting point is formed in the outer peripheral chamfered portion by a cutting blade before division, even if the chip size is small, the divisionability is higher than that of the conventional SD inner-inner cutting method. Is improved.

It is a front side perspective view of the semiconductor wafer. It is a perspective view of a wafer unit. It is a partial cross-sectional side view which shows the laser beam irradiation step. It is a partial cross-sectional side view which shows the cutting step. It is a top view explaining the cutting groove formation position. It is sectional drawing which shows the division step.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. With reference to FIG. 1, a front side perspective view of a semiconductor wafer (hereinafter, may be simply abbreviated as a wafer) 11 is shown. The wafer 11 is made of, for example, a silicon wafer having a thickness of 100 μm, and a plurality of streets (scheduled division lines) 13 are formed in a grid pattern on the surface 11a, and ICs are formed in each region partitioned by the plurality of streets 13. , LSI and other devices 15 are formed.

The wafer 11 configured in this way is provided with a device region 17 on which a plurality of devices 15 are formed and an outer peripheral surplus region 19 surrounding the device region 17 on a flat portion of the surface 11a. An arcuate chamfered portion 11e is formed on the outer peripheral portion of the wafer 11. Reference numeral 21 denotes a notch as a mark indicating the crystal orientation of the silicon wafer.

In carrying out the wafer processing method of the present invention, as shown in FIG. 2, the back surface 11b of the wafer 11 is attached to the dicing tape T whose outer peripheral portion is mounted on the annular frame F, and the wafer 11 is attached to the dicing tape T. The wafer unit 23 is supported by the annular frame F through the wafer unit 23 and is introduced into the laser processing apparatus and the cutting apparatus.

In the wafer processing method of the embodiment of the present invention, first, as shown in FIG. 3, the back surface 11b side of the wafer 11 is sucked and held by the chuck table 12 of the laser processing apparatus via the dicing tape T to expose the front surface 11a. Then, the annular frame F of the wafer unit 23 is clamped and fixed by the clamp 14 arranged on the chuck table 12 (holding step).

After sucking and holding the wafer 11 on the chuck table 12 in this way, a conventionally known alignment step for detecting the street 13 of the wafer 11 to be laser-machined is performed. After performing the alignment step, as shown in FIG. 3, the focusing point of the pulsed laser beam LB having a wavelength that is transparent to the wafer 11 is positioned inside the wafer 11 along the street 13 by the condenser 16. By processing and feeding the chuck table 12 in the direction of the arrow X1, the laser beam irradiation step of irradiating the wafer 11 with the pulsed laser beam LB along the street 13 to form the modified layer 25 inside the wafer 11 is performed. ..

In this laser beam irradiation step, the modified layer 25 is formed along the street 13 at least in the device region 17, and the wafer 11 is laser-processed in the modified layer non-formed region 27 including the chamfered portion 11e in the outer peripheral surplus region 19. It is preferable that the irradiation condition of the laser beam is set to a value that is not set.

However, the laser beam irradiation step of the present invention is not limited to this, and in the case of a workpiece such as an optical device wafer which is particularly hard to break, the laser beam is irradiated from one end to the other end of the street 13 to the inside. The modified layer 25 may be formed on the surface.

A similar reforming layer is formed inside the wafer 11 along all the streets 13 extending in the first direction while indexing and feeding the chuck table 12 in the direction orthogonal to the machining feed direction indicated by the arrow X1 by the pitch of the street 13. 25 is formed.

Next, after rotating the chuck table 12 by 90 °, a similar modified layer 25 is formed inside the wafer 11 along all the streets 13 extending in the second direction orthogonal to the first direction.

The laser processing conditions of the laser beam irradiation step are set as follows, for example.

Light source: LD excitation Q-switch Nd: YVO4 pulsed laser Wavelength: 1064 nm
Repeat frequency: 100kHz
Pulse output: 10 μJ
Focused spot diameter: 1 μm
Processing feed rate: 100 mm / s

After performing the laser beam irradiation step or before performing the laser beam irradiation step, at least the chamfered portion 11e on the extension line of the street 13 is cut with a cutting blade to form a cutting groove serving as a division starting point. ..

This cutting step may be performed before the laser beam irradiation step is performed, but it is preferable that the cutting step is performed after the laser beam irradiation step because the cutting groove does not interfere with the formation of the modified layer.

In this cutting step, as shown in FIG. 4, the chuck table 18 of the cutting apparatus sucks and holds the wafer 11 via the dicing tape T, and the clamp 22 arranged on the chuck table 18 sucks and holds the wafer 11 and the annular frame F of the wafer unit 23. Clamp and fix.

Next, after performing a conventionally known alignment step for detecting the street 13 to be cut, the cutting blade 20 rotating at high speed in the direction of arrow A is moved in the direction of arrow Z1 on an extension line on which the modified layer 25 is formed. A cut is made in the modified layer non-forming region 27, and a cutting groove 29 serving as a division starting point is formed by a half-cut chopper cut. The modified layer non-formed region 27 may be fully cut, or the modified layer non-formed region 27 may be formed with a chopper traverse cut to form a cutting groove 29.

This cutting step is carried out for the modified layer non-forming regions 27 at both ends of the modified layer 25 corresponding to all the planned division lines 13 extending in the first direction. Next, after rotating the chuck table 18 by 90 °, the modified layer non-forming regions 27 at both ends of the modified layer 25 corresponding to all the streets 13 extending in the second direction orthogonal to the first direction are formed. This is carried out to form a cutting groove 29 as shown in FIG.

After performing the laser beam irradiation step and the cutting step, an external force is applied to the wafer 11 to divide the modified layer 25 into individual chips at the division starting point.

This division step will be described in detail with reference to FIG. As shown in FIG. 6A, the annular frame F of the wafer unit 23 is placed on the mounting surface 36a of the frame holding member 36 of the frame holding means 32 of the dividing device 30, and the frame holding member 36 is mounted by the clamp 38. Clamp and fix. At this time, the frame holding member 36 is positioned at a reference position where the mounting surface 36a is substantially the same height as the upper end of the expansion drum 40.

Next, the air cylinder 46 constituting the drive means 44 is driven, and the frame holding member 36 connected to the piston rod 48 is pulled down to the expansion position shown in FIG. 6 (B). As a result, the annular frame F fixed on the mounting surface 36a of the frame holding member 36 is also pulled down, so that the dicing tape T attached to the annular frame F abuts on the upper end edge of the expansion drum 40 and mainly has a radius. Expanded in the direction.

As a result, a tensile force acts radially on the wafer 11 attached to the dicing tape T. When a tensile force acts radially on the wafer 11 in this way, the wafer 11 is broken along the street 13 with the modified layer 25 and the cutting groove 29 formed along the street 13 as the starting points of division, and the wafer 11 is broken along the street 13 to the individual chips 31. It is divided.

In the wafer processing method of the present embodiment, the modified layer 25 is formed inside the wafer 11 along each street 13 of the wafer 11, and the cutting groove 29 is formed in the modified layer non-formed region 27. Therefore, when the dividing step is performed, the wafer 11 is surely divided into individual chips 31.

Further, since the modified layer 25 is not formed in the modified layer non-formed region 27 including the chamfered portion 11e in the outer peripheral surplus region 19 of the wafer 11, the wafer unit 23 is cut from the laser processing apparatus after performing the laser beam irradiation step. Since the modified layer non-forming region 27 serves as a reinforcing portion to some extent when transferred to the apparatus, the handling property of the wafer unit 23 is good, and the wafer 11 is prevented from cracking starting from the modified layer 25 during handling. ..

11 Semiconductor wafer (wafer)
11e Chamfering section 13 Street (planned division line)
15 Device 16 Concentrator 17 Device area 19 Outer peripheral surplus area 20 Cutting blade 23 Wafer unit 25 Modified layer 27 Modified layer non-formed area 29 Cutting groove 30 Dividing device 31 Chip

Claims (4)

A wafer processing method in which a device region in which a device is formed in each region partitioned by a plurality of intersecting streets and an outer peripheral surplus region surrounding the device region are provided on the surface, and a chamfered portion is formed on the outer circumference. There,
A focusing point of a laser beam having a wavelength that is transparent to the wafer is positioned inside the wafer, and the wafer is irradiated with the laser beam along the street to form a modified layer along the street inside the wafer. Laser beam irradiation step and
A cutting step of forming a cutting groove by cutting at least the chamfered portion on the extension line of the street with a cutting blade.
After performing the laser beam irradiation step and the cutting step, an external force is applied to the wafer to divide the wafer into individual chips with the modified layer and the cutting groove as the starting point of division.
A wafer processing method characterized by being equipped with. A wafer having a device region in which a device is formed in each region partitioned by a plurality of intersecting streets and an outer peripheral surplus region surrounding the device region on a flat portion of the surface and a chamfered portion formed on the outer circumference. It ’s a processing method,
A focusing point of a laser beam having a wavelength that is transparent to the wafer is positioned inside the wafer, and the wafer is irradiated with the laser beam along the street to form a modified layer along the street inside the wafer. Laser beam irradiation step and
A cutting step of forming a cutting groove by cutting at least the chamfered portion on the extension line of the street with a cutting blade.
After performing the laser beam irradiation step and the cutting step, an external force is applied to the wafer to divide the wafer into individual chips with the modified layer and the cutting groove as the starting point of division.
A wafer processing method characterized by being equipped with. The wafer processing method according to claim 1 or 2 , wherein the cutting step is performed after the laser beam irradiation step is performed. The wafer processing method according to any one of claims 1 to 3, wherein the cutting groove is formed by lowering the cutting blade positioned above the chamfered portion and bringing it into contact with the chamfered portion.