PH12015000103B1

PH12015000103B1 - Processing method for stacked substrate

Info

Publication number: PH12015000103B1
Application number: PH12015000103A
Authority: PH
Inventors: Kumazawa Satoshi
Original assignee: Disco Corp
Priority date: 2014-04-11
Filing date: 2015-04-08
Publication date: 2016-10-17
Also published as: CN104979183A; TW201546890A; TWI640038B; KR102256562B1; KR20150118024A; PH12015000103A1; CN104979183B; JP6234312B2; JP2015204314A

Abstract

Disclosed herein is a processing method for a stacked substrate composed of a first substrate and a second substrate attached through an adhesive layer to the first substrate, the stacked substrate being formed with a plurality of streets each having a predetermined width. The processing method includes a laser processed groove forming step of applying a laser beam having an absorption wavelength to the stacked substrate along the streets from the side of the second substrate, thereby forming a pair of laser processed grooves along the opposite side edges of each street so that each laser processed groove has a depth reaching the first substrate, and a cutting step of cutting the area defined between the pair of laser processed grooves in each street by using a cutting blade having a thickness smaller than the spacing between the pair of laser processed grooves after performing the laser processed groove forming step.

Description

laser-processed is performed. In the alignment step, the infrared imaging device of the imaging unit 24 is operated to image the front side 12a of the first substrate 12 through the second substrate 14, and the streets 13 extending in a first direction are made parallel to the X direction (feeding direction) shown by an arrow X in FIG. 2.

After performing the alignment step mentioned above, one end of a predetermined one of the streets 13 extending in the first direction is positioned directly below the focusing means 22 of the laser beam applying unit 18, and a laser beam having an absorption wavelength to the stacked substrate 10 is applied from the focusing means 22 to the stacked substrate 10 along the predetermined street 13 as moving the chuck table in the

X direction. That is, the laser beam is applied to the second substrate 14 constituting the stacked substrate 10 held on the chuck table so as to reach the first substrate 12 constituting the stacked substrate 10. At this time, the laser beam 1s applied along the opposite side edges of the predetermined street 13 having a width

Wl (see FIG. 1), so that a pair of laser processed grooves 17 parallel to each other are formed along the opposite side edges of the predetermined street 13 so as to have a depth reaching the first substrate 12 as shown in FIG. 4 (laser processed groove forming step).

Thereafter, the chuck table holding the stacked substrate 10 is moved stepwise in the Y direction (indexing direction) shown by an arrow Y in FIG. 4 to similarly perform the laser processed groove forming step along all of the streets 13 extending in the first direction, thereby similarly forming a pair of laser processed grooves 17 along each street 13 extending in the first direction. Thereafter, the chuck table is rotated 90 degrees to thereby rotate the stacked substrate 10 by 90 degrees, so that the remaining streets 13 extending in a second direction perpendicular to the first direction becomes parallel to the X direction. In this condition, the laser processed groove forming step is similarly performed to form a pair of laser processed grooves 17 along each street 13 extending in the second direction.

For example, the laser processed groove forming step mentioned above may be performed under the following processing conditions.

Light source : YAG pulsed laser

Wavelength : 355 nm (third harmonic by

YAG pulsed laser)

Average power : 3.0 W

Repetition frequency : 20 kHz

Focused spot diameter : 1.0 um

Work feed speed : 100 mm/second

After performing the laser processed groove forming step mentioned above, a cutting step of cutting the area defined between the pair of laser processed grooves 17 in each street 13 is performed by using a cutting blade having a thickness smaller than the spacing between the pair of laser processed grooves 17. Referring to FIG. 5A, there is shown a first preferred embodiment of the cutting step in the present invention. As shown in FIG. 5A, a cutting blade 36 mounted on the front end portion of a spindle 34 is rotated at a high speed and lowered to cut into the stacked substrate 10 from the second substrate 14 side. At the same time, the chuck table holding the stacked substrate 10 is moved in the X direction, thereby fully cutting the stacked substrate 10.

In the first preferred embodiment of the cutting step shown in FIG. 5A, a dicing tape Tl is attached to the back side 12b of the first substrate 12 constituting the stacked substrate 10, and the stacked substrate 10 is held under suction on the chuck table in the condition where the dicing tape T1 is in contact with the upper surface of the chuck table. In this condition, the cutting blade 36 being rotated is lowered to cut into the area defined between the pair of laser processed grooves 17 in the predetermined street 13 of the stacked substrate 10 until the lower end of the cutting blade 36 reaches the dicing tape T1, and the chuck table holding the stacked substrate 10 is moved in the X direction to thereby form a full-cut groove 19 along the predetermined street 13. Thereafter, this cutting step is similarly performed along all of the streets 13 extending in the first direction, thereby forming a similar full-cut groove 19 along each street 13 extending in the first direction. Thereafter, the chuck table holding the stacked substrate 10 is rotated 90 degrees to similarly perform the cutting step along all of the remaining streets 13 extending in the second direction, thereby forming a similar full-cut groove 19 along each street 13 extending in the second direction. As a result, the stacked substrate 10 is divided into a plurality of individual chips 21 corresponding to the plural devices 15 as shown in FIG. 5A.

Referring to FIG. 6A, there is shown one of the chips 21 in enlarged cross section. In the cutting step mentioned above, the area defined between the pair of laser processed grooves 17 in each street 13 is cut by the cutting blade 36. Accordingly, there is a possibility that the second substrate 14 in each street 13 may be partially scattered away by the impact in fully cutting the stacked substrate 10, so that a chip 21A as shown in

FIG. 6B may be obtained.

Referring to FIG. 5B, there is shown a second preferred embodiment of the cutting step in the present invention. In the second preferred embodiment of the cutting step shown in FIG. 5B, the first substrate 12 of the stacked substrate 10 is not fully cut by the cutting blade 36 being rotated at a high speed, but the first substrate 12 is partially cut from the second substrate 14 side by the cutting blade 36. That is, the stacked substrate 10 is half cut from the second substrate 14 side in the area defined between the pair of laser processed grooves 17 in the predetermined street 13 extending in the first direction, thereby forming a half- cut groove 23 along the predetermined street 13.

Thereafter, this cutting step is similarly performed along all of the streets 13 extending in the first direction, thereby forming a similar half-cut groove 23 along each street 13 extending in the first direction.

Thereafter, the chuck table holding the stacked substrate

10 is rotated 90 degrees to similarly perform the cutting step along all of the remaining streets 13 extending in the second direction, thereby forming a similar half-cut groove 23 along each street 13 extending in the second direction.

After performing this cutting step shown in FIG. 5B, a dividing step is performed to divide the stacked substrate 10 into individual chips. Referring to FIG. 7, there is shown a first preferred embodiment of this dividing step. The first preferred embodiment of the dividing step is performed by using a grinding unit 38 shown in FIG. 7. The grinding unit 38 includes a spindle 40 adapted to be rotationally driven by a motor (not shown), a wheel mount 42 fixed to the lower end of the spindle 40, and a grinding wheel 44 detachably mounted on the lower surface of the wheel mount 42. The grinding wheel 44 is composed of an annular wheel base 46 and a plurality of abrasive members 48 fixed to the lower surface of the annular wheel base 46 so as to be arranged along the outer circumference of the wheel base 46.

In this grinding step, a protective tape T2 is attached to the front side of the second substrate 14 of the stacked substrate 10, and the stacked substrate 10 is held under suction on a chuck table 50 in the condition where the protective tape T2 is in contact with the upper surface of the chuck table 50, that is, the back side 12b of the first substrate 12 is exposed. In this condition, the chuck table 50 is rotated at 300 rpm, for example, in the direction shown by an arrow a, and the grinding wheel 44 is also rotated at 6000 rpm, for example, in the direction shown by an arrow b. Thereafter, a grinding unit feeding mechanism (not shown) 1s operated to bring the abrasive members 48 into contact with the back side 12b of the first substrate 12. Thereafter, the grinding wheel 44 is fed downward by a predetermined amount at a predetermined feed speed, thereby grinding the first substrate 12 until all of the half-cut grooves 23 are exposed. As a result, the stacked substrate 10 is divided into individual chips.

Referring next to FIGS. 8A and 8B, there is shown a second preferred embodiment of the dividing step in the present invention. The second preferred embodiment of the dividing step is performed by applying an external force to the stacked substrate 10 formed with the half-cut grooves 23 to thereby divide (break) the stacked substrate 10 into individual chips. As shown in FIG. 8A, the second preferred embodiment of the dividing step is performed by using a tape expanding apparatus 52. The tape expanding apparatus 52 includes an annular frame holding member 58 having an mounting surface 58a, a plurality of clamps 60 mounted on the outer circumference of the annular frame holding member 58, an expansion drum 56 provided inside the annular frame holding member 58, and a plurality of air cylinders 64 connected to the annular frame holding member 58 for vertically moving it.

In the second preferred embodiment of the dividing step shown in FIGS. 8A and 8B, the back side 12b of the first substrate 12 of the stacked substrate 10 is attached to an expansive tape T3 whose peripheral portion is supported to an annular frame F. That is, the stacked substrate 10 is attached to a central portion of the expansive tape T3 so as to be surrounded by the annular frame F. Thereafter, the annular frame F is placed on the mounting surface 58a of the annular frame holding member 58 and next fixed to the mounting surface 58a by the clamps 60. At this time, the frame holding member 58 is set at a reference position where the mounting surface 58a is at substantially the same level as that of the upper end of the expansion drum 56.

Thereafter, the air cylinders 64 are operated to lower the frame holding member 58 to an expansion position shown in FIG. 8B. Accordingly, the annular frame

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FF fixed to the mounting surface 58a of the frame holding member 58 is also lowered, so that the expansive tape T3 supperted to the annular frame F abuts against the upper end of the expansion drum 56 and is expanded mainly in the radial direction of the expansive tape T3. As a result, a tensile force is radially applied to the stacked substrate 10 attached to the expansive tape T3.

When the tensile force is radially applied to the stacked substrate 10 as mentioned above, the stacked substrate 10 is broken along the half-cut grooves 23 functioning as a division start point, thereby obtaining individual chips 21B as shown in FIG. 8B.

While the stacked substrate processing method described above is applied to the first substrate 12 having the plural devices 15 separated from each other by the plural crossing streets 13 formed on the front side 12a of the first substrate 12, the stacked substrate processing method according to the present invention is applicable not only to such a patterned substrate, but also to an unpatterned workpiece and a workpiece to be divided in one direction.

The present invention is not limited to the details of the above described preferred embodiments. The scope of the invention is defined by the appended claims and all changes and modifications as fall within the equivalence of the scope of the claims are therefore to be embraced by the invention.

. .

PROCESSING METHOD FOR STACKED SUBSTRATE CTE

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a processing method for a stacked substrate composed of a first x substrate and a second substrate attached through an adhesive layer to the first substrate, wherein the stacked substrate is divided into individual chips by the method. ; Description of the Related Art

In a fabrication process for a MEMS (Micro Electro

Mechanical Systems) device such as an acceleration sensor and a pressure sensor, a plurality of streets (division lines) are formed on a wafer to define a plurality of regions where a plurality of MEMS devices are provided, thereby forming a device wafer (first substrate).

Thereafter, the device wafer is cut along the streets by using a cutting apparatus as disclosed in Japanese Patent

Laid-Open No. 2008-307646, for example, so that the device wafer is divided into individual chips corresponding to the plural MEMS devices.

In many MEMS devices, a protective cover called a cap is provided to protect a MEMS structure. The MEMS

IR lo ,

E device with such a protective cover is manufactured by attaching a cover plate (second substrate) to the device wafer (first substrate) to form a stacked wafer (stacked substrate) and next dividing the stacked wafer along the streets.

In the case of using such a stacked substrate composed of a first substrate and a second substrate attached through an adhesive layer to the first substrate and then dividing the stacked substrate by using a cutting blade, a dicing tape is attached to the first substrate of the stacked substrate, and the stacked substrate is next held through the dicing tape on a chuck table of a cutting apparatus under suction. In this condition, the cutting blade is lowered to cut into the stacked substrate from the second substrate side, thereby dividing the stacked substrate into individual chips (see

Japanese Patent Laid-Open No. 2006-228816, for example) .

SUMMARY OF THE INVENTION

In the case of cutting the stacked substrate by using the cutting blade to divide the stacked substrate into the individual chips as mentioned above, there is a problem such that when the adhesive strength of the adhesive layer is insufficient, the first substrate may be separated from the adhesive layer. If the first substrate is separated in any area other than the streets to be cut away, the chips in this area become poor and an improvement is therefore desired.

It is therefore an object of the present invention to provide a stacked substrate processing method which can reduce the production of poor chips due to the separation of the first substrate without depending on the type of the workpiece.

In accordance with an aspect of the present invention, there is provided a processing method for a stacked substrate composed of a first substrate and a second substrate attached through an adhesive layer to said first substrate, said stacked substrate being formed with a plurality of streets each having a predetermined width, said processing method including a laser processed groove forming step of applying a laser beam having an absorption wavelength to the stacked substrate along the i streets from a side of the second substrate, thereby forming a pair of laser processed grooves along opposite side edges of each street so that each laser processed groove has a depth reaching the first substrate; and a j cutting step of cutting an area defined between the pair of laser processed grooves in each street by using a

- cutting blade having a thickness smaller than a spacing i between the pair of laser processed grooves after performing the laser processed groove forming step.

In the laser processed groove forming step of the processing method according to the present invention, the ] laser processed grooves reaching the first substrate are ’ formed along each street by applying a laser beam, so that no physical load is applied to the stacked substrate.

Accordingly, even when the adhesive layer in the stacked substrate has an insufficient adhesive strength, there is no possibility that the first substrate may be separated.

Further, there is a limit on the depth of a laser processed groove that can be formed by applying a laser beam. In the case that the stacked substrate is thick, a plurality of passes of application of the laser beam are required. Accordingly, in the case of fully cutting such a thick stacked substrate by performing only laser processing, the productivity is greatly reduced.

In the present invention, however, a pair of laser processed grooves are first formed along the opposite side edges of each street so as to reach the first substrate. In the next step, the area defined between the pair of laser processed grooves is cut by the cutting blade to fully cut the stacked substrate, thereby dividing the stacked substrate into individual chips.

Alternatively, the stacked substrate is half cut and next subjected to a dividing step. Accordingly, the stacked substrate can be processed without a reduction in productivity and without the separation of the first substrate in any area other than the streets, so that the production of poor chips due to the separation of the first substrate can be reduced.

The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing some preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a stacked substrate;

FIG. 2 is a perspective view showing a laser processed groove forming step in the present invention;

FIG. 3 is a block diagram of a laser beam generating unit;

FIG. 4 is a sectional view showing the laser processed groove forming step;

FIG. 5A is a sectional view showing a first preferred embodiment of a cutting step in the present invention;

FIG. 5B is a sectional view showing a second preferred embodiment of the cutting step;

FIG. 6A is a sectional view of a chip obtained by dividing the stacked substrate in the first preferred embodiment of the cutting step shown in FIG. 5A;

FIG. 6B is a sectional view of such a chip in the case that a second substrate constituting the stacked substrate has been partially scattered in each street in the cutting step shown in FIG. 5A;

FIG. 7 is a partially sectional side view showing a dividing step by grinding; and

FIGS. 8A and 8B are sectional views showing a dividing step by tape expanding.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment of the present invention will now be described in detail with reference to the drawings. Referring to FIG. 1, there is shown a stacked substrate 10 in cross section. The stacked substrate 10 is composed of a first substrate 12 and a second substrate 14 attached through an adhesive layer 16 to the first substrate 12. An example of the stacked substrate 10 is composed of a device wafer having a plurality of devices and a cover substrate such as a silicon substrate attached to the device wafer. The first substrate 12 has a front side 12a and a back side 12b.

Referring to FIG. 2, there is shown a laser processed groove forming step in perspective. A plurality of crossing streets (division lines) 13 are formed on the front side 12a of the first substrate 12 to thereby define a plurality of rectangular separate regions where a plurality of devices 15 are formed. Reference numeral 18 denotes a laser beam applying unit constituting a laser processing apparatus (not shown). The laser beam applying unit 18 includes a casing 19, a laser beam generating unit 20 (see FIG. 3) contained in the casing 19, and focusing means 22 for focusing a laser beam generated by the laser beam generating unit 20 and applying the laser beam to the stacked substrate 10.

An imaging unit 24 is mounted on the casing 19 of the laser beam applying unit 18. The imaging unit 24 includes an ordinary imaging device such as CCD for imaging a workpiece by using visible light, infrared light applying means for applying infrared light to the stacked substrate 10, and an infrared imaging device such as infrared CCD for outputting an electrical signal corresponding to the infrared light. An image signal output from the imaging unit 24 is transmitted to control means (not shown).

As shown in FIG. 3, the laser beam generating unit 20 includes a laser oscillator 26, repetition frequency setting means 28, pulse width adjusting means 30, and power adjusting means 32. The repetition frequency setting means 28 and the pulse width adjusting means 30 are connected to the laser oscillator 26. Examples of the laser oscillator 26 include a YAG pulsed laser and a YVO4 pulsed laser. The power of a pulsed laser beam oscillated from the laser oscillator 26 is adjusted to a predetermined power by the power adjusting means 32. The pulsed laser beam thus adjusted in power is transmitted to the focusing means 22 and applied from the focusing means 22 to the stacked substrate 10.

Referring back to FIG. 2, the first substrate 12 constituting the stacked substrate 10 is held under suction on a chuck table (not shown) included in the laser processing apparatus. Prior to performing the laser processed groove forming step in the stacked substrate processing method according to this preferred embodiment, an alignment step of detecting the streets 13 to be

Claims

WHAT IS CLAIMED IS:

1. A processing method for a stacked substrate composed of a first substrate and a second substrate attached through an adhesive layer to said first substrate, said stacked substrate being formed with a plurality of streets each having a predetermined width, said processing method comprising: a laser processed groove forming step of applying a laser beam having an absorption wavelength to said stacked substrate along said streets from a side of said second substrate, thereby forming a pair of laser processed grooves along opposite side edges of each street so that each laser processed groove has a depth reaching said first substrate; and a cutting step of cutting an area defined between said pair of laser processed grooves in each street by using a cutting blade having a thickness smaller than a spacing between said pair of laser processed grooves after performing said laser processed groove forming step.