# Patent

## Title
Method of cutting laminate, apparatus for manufacturing laminate, method of manufacturing laminate, and laminate

## Abstract

A device such as an MEMS device is fabricated by cutting a laminate of a semiconductor substrate and a glass substrate. Grooves are formed in the glass substrate, and the semiconductor substrate and the glass substrate are laminated together such that the groove faces the semiconductor substrate. The laminated substrates are irradiated with a laser along the groove from the side of the glass substrate. In this way, the laminate is cut into elements.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a divisional application of and claims parent benefit under 35 U.S.C. § 120 to application Ser. No. 11/245,048, filed Oct. 7, 2005, now pending, which is a continuation-in-part of U.S. patent application Ser. No. 10/968,139 filed on Oct. 20, 2004, now pending, and claims priority benefit to Japanese Application Nos. 2004-168312 and 2005-167235, filed Jun. 7, 2004 and Jun. 7, 2005, the contents being incorporated by reference.


BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of cutting a laminate, an apparatus for manufacturing the laminate, a method of manufacturing the laminate, and the laminate itself. In more detail, the present invention relates to a method of cutting a laminate formed of substrates of different types of laminated materials. More particularly, the present invention relates to a method of cutting a laminate formed of substrates of respective materials, the corresponding transmittance or absorptance properties of which, with respect to irradiation by a laser beam, being different from each other.
2. Description of the Related Art
A device comprising a laminate including a plurality of substrates of different types of materials has recently been developed. Highly technical devices, such as micro-electronics-mechanical-system (MEMS) devices, are configured as a laminate of a substrate formed of silicon, and a substrate of lithium tantalate (LiTaO3), sapphire, or heat-resistant glass, etc, superposed together. In fabricating such a device, the laminate composed of a plurality of substrates of different types of materials is cut into separate devices (chips).
In a conventional method, a semiconductor wafer is cut into separate semiconductor chips by rotating a wheel containing diamond abrasive grains at high speed. The wheel containing the diamond abrasive grains can be used also for separating the laminate of a plurality of substrates formed of different types of materials into individual devices.
In fabricating a device having a fine mechanism such as a MEMS device, however, an attempt to separate the laminate into individual devices using the wheel containing diamond abrasive grains poses the problem that the contact between the wheel and the laminate at the time of cutting operation causes the laminate to vibrate and often damages the fine mechanism of the device.
In the case where a device having a fine mechanism such as a MEMS device is fabricated, therefore, some measure is required to prevent the vibration of the laminate, and a cutting method using a laser is one choice. In the cutting method using the laser, however, the material is required to absorb the laser light, and therefore the combinations of the lasers and the materials to be cut are limited.
In the case where the laminate including a plurality of substrates of different types of material is separated into individual devices, therefore, it is necessary to use a plurality of lasers having wavelengths suitable for a plurality of materials, respectively. Japanese Unexamined Patent Publication (Kokai) No. 2003-37218, for example, discloses a method of cutting a multilayer substrate with a dual laser irradiation, in which a first laser is focussed on a first substrate, and a second laser is focussed on a second substrate.
In the case where the laminate including a plurality of substrates of different types of material is separated into individual devices, therefore, as many laser oscillators as there are stacked substrates are required, thereby leading to the problem of an expensive, bulky dicing apparatus.
For cutting a laminate formed of silicon having the thickness of several hundred μm and pyrex glass having the thickness of several hundred μm, such as a MEMS device recently developed, a YAG laser (laser wavelength λ of 1.064 μm) can be used as a laser capable of cutting the silicon efficiently. As a laser capable of cutting glass, on the other hand, an ultraviolet laser (laser wavelength λ of 0.35 μm) typically including the excimer laser and the THG-YAG laser or an infrared laser (laser wavelength λ of 5 μm or more) typically including the CO2 laser are available. The ultraviolet laser, however, requires a long time for cutting, and for example, several hours or longer to cut one line of 100 mm. The use of the infrared laser, on the other hand, results in the laser irradiation width of at least 1 mm in the cutting operation, and adversely affects the internal circuits in an application to a small device.
In the case where a member, in which a silicon member and glass member are joined to each other, is cut, the following problems are encountered.
First, in the case where the silicon member side is irradiated with a laser beam so as to conduct laser beam machining, as the laser beam is absorbed by the silicon layer, it is possible to cut the silicon layer. However, the glass member transmits the laser beam. Therefore, cutting is stopped on the joining face on which the glass member and the silicon member are joined to each other.
On the other hand, in the case where the glass member side is irradiated with a laser beam, the laser beam penetrates the glass member and reaches the silicon face. In this case, as the silicon member is cut, the glass member can be machined while being penetrated by the laser beam. However, a problem is caused in that cracks are generated on the joining interface of the glass member and the silicon member.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method of cutting a laminate, an apparatus for manufacturing the laminate, a method of manufacturing the laminate and the laminate itself, the method being capable of cutting a laminate formed of a plurality of substrates of different types of laminated materials at low manufacturing cost with high quality.
According to the present invention, there is provided a method of cutting a laminate of the present invention comprising the steps of: forming a groove on one of the first and the second substrates; putting one substrate, on which the groove is formed, upon the other substrate so that the groove can be directed to the other substrate; and condensing and irradiating a laser beam onto the first and the second substrate from one substrate side, on which the groove is formed, along the groove, so that the laminate composed of the first and the second substrate can be cut.
According to another aspect of the present invention, there is provided a laminate in which a first plate member made of a semiconductor and a second plate member made of glass are put on each other, and the second plate member has a groove on the side which is directed to the first plate member.
According to still another aspect of the present invention, there is provided an apparatus for manufacturing a laminate having a mechanism for cutting a laminate formed of a first and a second substrate, wherein a groove is formed on one of the substrates, and the substrates are put upon each other so that the groove formed on one of the substrates can be directed to the other substrate. The apparatus for manufacturing a laminate comprises: a laser beam source; a laser beam condensing optical system; a table on which the laminate is put; and a moving mechanism for relatively moving the laser beam source and the table, wherein the laminate is put on the table so that the one substrate, on which the groove is formed, can be directed to the laser beam source, and the laminate is cut when the laser beam source is relatively moved with respect to the table and the laser beam is irradiated along the groove.
According to still another aspect of the present invention, there is provided a method of manufacturing a laminate of the present invention comprising: a step of forming a groove on one of the first and the second substrate; a step of laminating the first and the second substrate on each other so that the groove on one substrate can be directed to the other substrate; and a step of moving the laser beam source relative to the laminate while a laser beam is being irradiated to the laminate along the groove.
Due to the above-mentioned features, the laminate composed of the first and the second substrates, which are laminated on each other, can be positively cut by using a single laser beam.
The laminate formed of a plurality of substrates of different types of laminated materials can be cut at one time by irradiating a single laser beam. Accordingly, it is possible to effectively obtain an apparatus capable of cutting a laminate with high quality. Therefore, a dicing apparatus including a single laser can be made compact and the manufacturing cost can be reduced.
As the groove is formed on the joining face on which the glass member and the silicon member are joined to each other, the generation of cracks on the joining face, on which the glass member and the silicon member are joined to each other, can be suppressed.



BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1(A) to 1(C) are diagrams showing a method of cutting a laminate according to the present invention;
FIG. 2 is a perspective view showing a first substrate and a second substrate before being laminated together;
FIG. 3 is a perspective view showing a laminate comprising the first substrate and the second substrate;
FIG. 4 is a top perspective view of a part of the laminate, as seen from the second substrate side;
FIG. 5 is a diagram showing an example in which a groove is formed in the second substrate;
FIG. 6 is a diagram showing another example in which a groove is formed in the second substrate;
FIG. 7 is a perspective view showing a dicing apparatus for irradiating a laser onto the laminate;
FIGS. 8(A) and 8(B) are a plan view and a sectional view showing a portion of the suction table shown in FIG. 7.
FIG. 9 is an enlarged sectional view showing the laminate upon the laser irradiation; and
FIG. 10 is a plan view showing a part of the laminate cut by the laser irradiation.



DESCRIPTION OF THE PREFERRED EMBODIMENTS
The preferred embodiments of the present invention are described below with reference to the drawings. FIGS. 1(A) to 1(C) are diagrams showing a method of cutting a laminate according to the present invention.
In FIG. 1(A), a laminate 10 comprising a first substrate 12 and a second substrate 14 is prepared. The second substrate 14 has grooves 16. An explanation is made below with reference to an example in which a plurality of MEMS devices are fabricated, but the present invention is not limited to this example. The laminate 10 has circuits and fine mechanisms formed therein corresponding to a plurality of MEMS devices, and is cut into individual MEMS devices separated from each other. The grooves 16 are formed along a cutting line for separating the laminate into MEMS devices.
The first substrate 12 is formed of a semiconductor, i.e. constitutes a silicon wafer formed with circuits and fine mechanisms. The second substrate 14 is formed of pyrex glass, and the grooves 16 are formed in the second substrate 14. The substrate 14 formed with the grooves 16 are superposed on the first substrate 12 such that the grooves 16 faces the first substrate 12.
In the embodiment, the first substrate 12 is formed of silicon and the second substrate 14 is formed of glass, but the first substrate 12 and the second substrate 14 are not limited to these materials, and other materials may be used. The first substrate 12 is formed of a material capable of absorbing the laser and the second substrate 14 is formed of a material which transmits the laser. The grooves 16 are formed in the substrate made of a material which transmits the laser.
The first substrate 12 and the second substrate 14 are joined or bonded to each other. The first substrate 12 and the second substrate 14 are preferably bonded to each other by an anode junction.
In FIG. 1(B), a laser 18 is irradiated onto the first substrate 12 and the second substrate 14 along the grooves 16 from the side of the second substrate 14 having the grooves 16. The laser is first transmitted through the second substrate 14 and is irradiated onto the first substrate 12. The first substrate 12 absorbs the laser, and the surface portion 12A of the first substrate 12 is melted or evaporated. In this way, the first substrate 12 begins to be cut.
As shown in FIG. 1C, the silicon particles of the melted or evaporated portion 12A of the first substrate 12 are scattered and directed toward the inner surface of the grooves 16 of the second substrate 14. As a result, the second substrate 14 is cut at the position of the grooves 16. Also, the surface portion 12A of the first substrate 12 continues to be melted until the first substrate 12 is cut off. Thus, the laminate 10 including the first substrate 12 and the second substrate 14 is cut into separate individual MEMS devices.
FIG. 2 is a perspective view showing the first substrate 12 and the second substrate 14 before being laminated together. A plurality of grooves 16 are formed in parallel to each other in each of two orthogonal directions on the surface of the second substrate 14. The grooves 16 are formed along the cutting lines for separating the laminate 10 into individual MEMS devices. In this embodiment, the first substrate 12 is formed of a silicon wafer having a diameter of 4 inches and a thickness of 500 μm. The second substrate 14 is formed of an anode juncture glass having a diameter of 4 inches and a thickness of 400 μm. The depth of the grooves 16 is 200 μm.
FIG. 3 is a perspective view showing the laminate 10 including the first substrate 12 and the second substrate 14. The second substrate 14 is superposed on and joined to the first substrate 12 such that the grooves 16 face the first substrate 12. The grooves 16 are located in the joining surface between the first substrate 12 and the second substrate 14. FIG. 4 is a top perspective view of a part of the laminate 10, seen from the second substrate 14 side.
FIG. 5 is a diagram showing an example in which the grooves 16 are formed in the second substrate 14. The grooves 16 are formed in the surface of the second substrate 14 using a wheel 20 containing diamond abrasive grains. The wheel 20 is rotated in the direction as indicated by arrow, and moved relative to the second substrate 14 along the cutting line. The wheel 20 preferably has a peripheral cutting edge having a V-shaped cross section, so that the grooves 16 are formed to have a V-shaped cross section.
FIG. 6 is a diagram showing another example of forming grooves 16 in the second substrate 14. The grooves 16 are formed in the surface of the second substrate 14 by etching with a mask 22. The grooves 16 are preferably but not necessarily formed to have a V-shaped cross section. This is also the case with the example shown in FIG. 5.
FIG. 7 is a perspective view showing a dicing apparatus for irradiating a laser beam to the laminate 16. FIG. 8(A) is a plan view showing a portion of the stage shown in FIG. 7, and FIG. 8(B) is a partially sectional view of the stage. The dicing apparatus 24 includes: a base 26; an XY stage 28 (Reference numeral 28a is an X stage, and reference numeral 28b is a Y stage.) arranged on the base 26; a rotary (θ) stage 29; a suction table 31 arranged on the rotary stage 29, for sucking and holding the laminate 10; a laser head 30 for irradiating a laser beam 18 toward the laminate 10 put on the suction table 31; a vacuum pump 33; and an infrared ray camera 37. As shown by the arrows in the drawing, the X stage 28a and the Y stage 28b can be respectively moved in the direction X and the direction Y which are perpendicular to each other. The rotary (θ) stage 29 can be rotated in the direction of arrow θ and restricts an inclined position of the suction table 31.
The suction table 31 has vacuum suction holes 32, and the laminate 10 is held on the suction table 31 by the action of vacuum introduced from the vacuum suction holes 32. The vacuum suction holes 32 are formed at positions shifted from the cutting lines 34 of the laminate 10. Therefore, even after the laminate 10 has been divided into the individual MEMS devices, the individual MEMS devices can be held on the suction table 31 by the action of vacuum introduced from the vacuum holes 32. The vacuum suction holes 32 on the suction table 31 are connected to the vacuum pump 33 by a well known means.
On the suction face of the suction table 31 for sucking and holding the laminate 10, the lattice-shaped release grooves 35 corresponding to the cutting lines 34 of the laminate 10 are formed, that is, the lattice-shaped release grooves 35 corresponding to the grooves 16 on the second substrate 14 of the laminate 10 are formed. When the laminate 10 is put on the suction table 31, while being monitored with the infrared ray camera 37 for alignment which is arranged in an upper portion of the suction table 31, the laminate 10 is aligned at a predetermined position on the suction table 31 so that the lattice-shaped grooves 16 on the laminate 10 can coincide with predetermined cutting lines and also can coincide with the release grooves 35 on the suction table 31. Concerning the infrared ray camera 37, for example, a common camera, in which infrared rays, the wave-length of which is 2 μm, are used, can be used.
In the embodiment of the dicing apparatus shown in FIG. 7, the alignment position A of the laminated body 10 is different from the working position B which is an optical axis position at which the laser beam 18 is irradiated by the laser beam head 30. Of course, these positions A and B may be equal to each other.
FIG. 9 is an enlarged sectional view showing a laminate at the time of irradiation of a laser beam. FIG. 9 is similar to FIG. 1(B). In FIG. 9, when the laser beam 18 is irradiated onto the first substrate 12 and the second substrate 14 from the second substrate 14 side, on which the grooves 16 are formed, along the grooves 16, first, the laser beam is transmitted through the second substrate 14 and irradiated onto the first substrate 12. The first substrate 12 absorbs the laser beam, and the surface portion 12A of the first substrate 12 is melted or vaporized. Cutting of the first substrate 12 is started in this way.
Silicon particles in the portion 12A of the first substrate 12, which has been melted and vaporized, are spouted or dispersed toward the inner face of the grooves 16 of the second substrate 14 as illustrated by the arrows in the drawing. Therefore, the thus dispersed silicon particles are attached to the inner face of the grooves 16 of the second substrate 14 and are formed into a film 36. Although the laser beam 18 is transmitted through the second substrate 14, the film 36, which has been attached to the inner face of the grooves 16 of the second substrate 14, absorbs the laser beam. Therefore, the temperature of the film 36 is raised, and the temperature of the inner face of the grooves 16 of the second substrate 14 coming into contact with the film 36 is raised, and stress is given to the inner face of the grooves 16. As a result, the second substrate 14 is cut at the position of the grooves 16. The surface portion 12A of the first substrate 12 is successively melted and vaporized. Finally, the first substrate 12 is completely cut off. In this way, the laminate 10, which is composed of the first substrate 12 and the second substrate 14, is cut off, and the individual MEMS devices are divided from each other. In this connection, in order to simplify the explanations, it is illustrated in the drawing that the film thickness is uniform. However, it is unnecessary that the thickness of the film 36 is uniform or that the film 36 is continuously formed.
In this connection, as the grooves 16 are provided on the second substrate 14, silicon particles of the portion 12A on the first substrate 12, which is melted and vaporized, can be dispersed toward the inner face of the grooves 16 of the second substrate 14. In the case where no grooves 16 are provided, it is impossible for the silicon particles, which are spouting out, to be released. Therefore, a high stress is generated on the joining face on which the silicon member and the glass member are joined to each other. Accordingly, there is a possibility that undesirable defects such as interface separation or micro-cracks in the material are caused. When the grooves 16 are provided, the occurrence of the above defects can be avoided.
FIG. 10 is a plan view showing a portion of the laminate 10 which has been cut by means of laser beam irradiation. In FIG. 10, reference numeral 16S is a side edge of the opening portion of the grooves 16. Reference numeral 38 is a cutting portion made by means of laser beam irradiation. The laminate 10 is divided into the individual MEMS devices (chips) 40 at the cutting portion 38.
As described above, the portion 12A on the surface of the first substrate 12 continues to be melted and vaporized by means of laser beam irradiation, and finally the first substrate 12 is perfectly cut off. At this time, the melted and vaporized silicon particles reach a lower face of the first substrate 12, that is, an upper face of the suction table 31. However, in this embodiment, as described before, the lattice-shaped release grooves 35 are formed on the upper face of the suction table 31 along the cutting lines 34 of the laminate 10. Therefore, even if the melted and vaporized silicon particles reach the upper face of the suction table 31, these particles are absorbed by the release grooves 35. Therefore, the suction table 31 itself is not affected by these particles.
In this embodiment, concerning the laser beam 18, the pulse YAG laser beam (the laser beam wave-length λ=1064 nm) was used, and the laser beam 18 is irradiated from the second substrate 14 side of the laminate 10 which was put on the suction table 31. The laser beam 18 was irradiated under the following working condition. The pulse width of the laser beam 18 is 0.1 ms, the pulse repetition is 300 times/sec, the pulse energy is 40 mJ/pulse, and the feed speed of the stage XY 28 is 120 mm/min. In this case, the laser beam 18 was adjusted so that the laser beam 18 could be condensed in the neighborhood of the joining face of the first substrate 12 and the second substrate 14. As a result, as shown in FIG. 10, both the first substrate 12 and the second substrate 14 were excellently cut, that is, the laminate 10 was positively cut. The laminate 10 was cut at high speed in such a manner that the feed speed of the stage XY 28 was 120 mm/min.
It should be understood, by those skilled in the art, that the foregoing description relates to only a preferred embodiment of the disclosed invention, and that various changes and modifications may be made to the invention without departing the sprit and scope thereof.
INDUSTRIAL APPLICABILITY
As explained above, according to the present invention, when a laser beam (for example, YAG laser beam) capable of machining one material among a plurality of materials is used, a laminate including two or more materials can be easily cut. Therefore, the dicing apparatus can be simplified and the manufacturing cost can be reduced. When a groove is provided on the material joining face along the cutting line, the material joining face can be prevented from being separated and the device can be prevented from being damaged.

## Claims

1. A method of manufacturing a laminate comprising first and second substrates, comprising:
forming a plurality of grooves, in a lattice configuration, in the first surface of the second substrate;
laminating the first and second substrates to each other with the first surface and the grooves of the second substrate facing the first substrate and with a second surface of the second substrate, opposite the first surface thereof, exposed; and
radiating the laminate with a laser beam directed onto the exposed second surface of the second substrate while moving the laser beam along each of the plurality of the grooves, said laser beam being transmitted through the second substrate and absorbed by the first substrate, cutting both the first and second substrates in respective cutting paths aligned with corresponding grooves.

2. The method of manufacturing a laminate according to claim 1, wherein a plurality of grooves are formed in the first surface of the second substrate, in a lattice shape, to form a plurality of devices.

3. The method of manufacturing a laminate according to claim 1, wherein the laminate is placed with an exposed surface of the first substrate on a surface of a suction table having release grooves therein and positioning the laminate on the suction table while monitoring the alignment of the grooves in the first surface of the second substrate with the release grooves in the surface of the table by passing an infrared beam therethrough, so that the grooves in the first surface of the second substrate of the laminate correspond to the release grooves formed in the table.

4. A method of manufacturing a laminate according to claim 2, wherein the laminate is placed with the exposed surface of the first substrate on a surface of a suction table having plural release grooves therein and positioning the laminate on the suction table while monitoring the alignment of the plurality of grooves in the first surface of the second substrate with corresponding release grooves in the surface of the table by passing an infrared beam therethrough, so that the grooves formed in the first surface of the second substrate of the laminate correspond to respective release grooves in the table thereby to form the plurality of devices from the laminate when the laminate is cut along the respective cutting paths.

5. The method of manufacturing a laminate according to claim 3, further comprising applying suction to at least one suction hole aligned with a solid portion of the exposed surface of the first substrate so as to retain the laminate on the suction table.

6. The method of manufacturing a laminate according to claim 4, further comprising applying suction to at least one suction hole aligned with a solid portion of the exposed surface of the first substrate so as to retain the laminate on the suction table.

7. A method of cutting a laminate comprising a first substrate and a transparent, second substrate having a first surface and a second, exposed surface, comprising:
radiating a laser beam, having a wavelength suitable for cutting material of the first substrate but not suitable for cutting material of the second substrate, onto the second, exposed surface of the second substrate;
wherein a groove is formed in the first surface of the second substrate, and the first and second substrates are laminated such that the first surface of the second substrate having the groove faces the first substrate; and
while radiating the laser beam onto the second, exposed surface of the second substrate, moving the laser beam, relatively to the laminate, toward and along the groove, said laser beam being transmitted through said second substrate and absorbed by said first substrate, so as to heat the first substrate and cause material thereof to travel to and collect on an inner surface of the groove, the collected material being further heated by the laser beam passing through the second substrate along the groove to heat and produce stress on the inner surface of the groove, thereby to cut both the first and the second substrates along the groove.

8. The method of manufacturing a laminate according to claim 7, comprising:
placing the laminate with an exposed surface of the first substrate on a surface of a suction table having a release groove therein and positioning the laminate on the suction table while monitoring alignment of the groove in the first surface of the second substrate with the release groove in the surface of the table by passing an infrared beam therethrough, so that the groove in the first surface of the second substrate of the laminate corresponds to the release groove in the table.

9. A method of manufacturing a laminate according to claim 7, wherein the laminate is placed with an exposed surface of the first substrate on a surface of a suction table having plural release grooves therein and positioning the laminate on the suction table while monitoring alignment of the grooves in the first surface of the second substrate with corresponding ones of plural release grooves in the surface of the table by passing an infrared beam therethrough, so that the grooves in the first surface of the second substrate of the laminate correspond to the respective release grooves in the table, thereby to cut both the first and second substrates and form the plurality of devices from the laminate.

10. The method of manufacturing a laminate according to claim 8, further comprising applying suction to at least one suction hole aligned with a solid portion of the exposed surface of the first substrate so as to retain the laminate on the suction table.

11. The method of manufacturing a laminate according to claim 9, further comprising applying suction to at least one suction hole aligned with a solid portion of the exposed surface of the first substrate so as to retain the laminate on the suction table.

12. A method of cutting a laminate comprising a transparent, second substrate having a first surface having a plurality of grooves therein in a lattice configuration and laminated to a surface of a first substrate, comprising:
irradiating a laser beam through a second exposed surface of the second substrate and through and along each groove onto the surface of the first substrate, the laser beam being transmitted through the second substrate and absorbed by the first substrate, so as to heat and thereby cut the first substrate, causing particles of the first substrate to travel to and collect on the inner surface of each groove of the second substrate; and
heating the particles collected on the inner surface of the groove by irradiating same with the laser beam passing through the second substrate and along each groove, to stress the second substrate and thereby cut both the first and second substrates of the laminate into a plurality of devices.