KR20090030301A - Laser processing method - Google Patents

Abstract

In the case of forming a plurality of rows of modified regions, in the thickness direction of a processing object, along a line to be cut, a first modified region closest to a first surface and a second modified region closest to a second surface are accurately formed. In a laser processing method, laser beams are applied by having a light collecting point inside the processing object (1), and the modified regions (M1-M6) to be starting points of cutting are formed, in the thickness direction of the processing object (1), along the line (5) to be cut on the processing object (1). Among the modified regions (M1-M6), the modified region (M6) closest to a rear surface (21) is formed by having the position of the rear surface (21) as reference, and the modified region (M1) closest to the front surface (11a) is formed by having the position of the front surface (11a) as reference. Thus, even when the thickness of the processing object (1) varies, shift of the position of the modified region (M6) and that of the position of the modified region (M1) due to changes of the thickness of the processing object (1) are suppressed.

Description

Laser processing method {LASER PROCESSING METHOD}

The present invention relates to a laser processing method for cutting a plate-shaped object to be cut along a cutting schedule line.

In the conventional laser processing method, a plurality of modified regions serving as starting points of cutting along a cutting scheduled line of the processing target are plural in the thickness direction of the processing target by aligning the light collection point inside the plate-like processing target and irradiating laser light. The method of forming heat is known (for example, refer patent document 1). In such a laser processing method, the position of the first surface on which the laser light is incident on the object to be processed is detected, and the position of the light converging point of the laser light is controlled in accordance with the detection signal, thereby from the first surface within the object to be processed. It is common to form each modified region at a position of a predetermined distance.

Patent Document 1: Japanese Patent Application Laid-Open No. 2005-150537

Problems to be Solved by the Invention

By the way, in the case where the modified object is cut in a plurality of rows in the thickness direction of the object to be processed to cut the object, the formation region of the modified region closest to the first surface and the modified region closest to the second surface opposite to the first surface, In view of the quality of the cut surface, particularly high precision is required. This is because, when these modified regions are not formed precisely at positions of a predetermined distance from the first surface and the second surface, respectively, the ends of the cut surface in the thickness direction of the object to be processed are cut, for example. This is because a so-called skirt phenomenon may be largely deviated from the cutting schedule line.

However, in the laser processing method as described above, since a plurality of rows of modified regions are formed in the thickness direction of the object to be processed based only on the position of the first surface, the thickness of the object to be processed is plural, for example, due to the difference in the grinding lot. In the case of uneven between the object to be processed, or when a part of the object is thick or thin in one object (i.e., the thickness of the object is changed), the modified region closest to the second surface is determined from the second surface. There is a possibility that the position of the distance cannot be formed with high precision.

Therefore, in the present invention, when a plurality of rows of modified regions are formed along the cutting line, in the thickness direction of the object to be processed, the first modified region closest to the first surface and the second modified region closest to the second surface are precisely determined. An object of the present invention is to provide a laser processing method which can be formed satisfactorily.

Means to solve the problem

In order to achieve the above object, in the laser processing method according to the present invention, a modified region which becomes a starting point of cutting along a cutting schedule line of the processing object by aligning a light collection point inside the plate-shaped processing object and irradiating laser light. A laser processing method for forming a plurality of rows in a thickness direction, comprising: forming a first modified region closest to a first surface among the modified regions on the basis of a position of a first surface on which a laser light is incident in a workpiece; And a step of forming a second modified region closest to the second surface among the modified regions on the basis of the position of the second surface opposite to the first surface in the object to be processed.

According to this laser processing method, the first modified region closest to the first surface among the modified regions is formed based on the position of the first surface, and the second modified region closest to the second surface among the modified regions is the second surface. It is formed based on the position of. Thus, since the position of both the 1st surface and the 2nd surface becomes a reference | standard, even if the thickness of a process object changes, the position and the 2nd surface of the 1st modified area | region which are closest to a 1st surface among the modified area | regions. The position of the second modified region closest to can be suppressed from being released due to the change in the thickness of the object. That is, in the case where a plurality of rows of modified regions are formed along the cutting scheduled line in the thickness direction of the object to be processed, the first modified region closest to the first surface and the second modified region closest to the second surface can be formed with high accuracy. It becomes possible. As a result, high quality of the cut surface can be maintained. In addition, each modified region is formed by aligning a light-converging point within the object to be processed and irradiating laser light to cause multiphoton absorption or other light absorption in the object to be processed.

Here, in the step of forming the first modified region, by detecting the reflected light reflected from the first surface, first position information about the position of the first surface is obtained, and based on the first position information, In the step of forming the first modified region on the inner side by a predetermined distance from the first surface and forming the second modified region, by detecting the reflected light reflected from the second surface, the second position with respect to the position of the second surface The positional information is acquired and a second modified region may be formed on the inside by a predetermined distance from the second surface based on the second positional information.

Moreover, in the process of forming a 1st modified area | region, the 1st position information regarding the position of a 1st surface is acquired by detecting the reflected light reflected from the 1st surface, and based on this 1st position information, In the step of forming the first modified region on the inside by a predetermined distance from one surface and forming the second modified region, the second modified region is predetermined from the second surface based on the first positional information and the thickness information on the thickness of the object to be processed. In some cases, the second modified region may be formed by the distance of.

In the step of forming the second modified region, second position information relating to the position of the second surface is obtained by detecting the reflected light reflected from the second surface, and based on the second position information, In the step of forming the second modified region on the inside by a predetermined distance from the two surfaces and forming the first modified region, the second modified region is predetermined from the first surface based on the second positional information and the thickness information on the thickness of the object to be processed. The first modified region may be formed on the inner side by the distance of.

In addition, the object to be processed may include a semiconductor substrate, and the modified region may include a molten processed region.

Moreover, it is preferable to include the process of cut | disconnecting a process object along a cutting plan line, using a modified area as a starting point of cutting | disconnection. Thereby, a process object can be cut | disconnected with high precision along a cutting schedule line.

Effects of the Invention

According to the present invention, in the case where a plurality of rows of modified regions are formed along the cutting scheduled line in the thickness direction of the object to be processed, the first modified region closest to the first surface and the second modified region closest to the second surface are precisely determined. It can form well.

1 is a plan view of an object to be processed during laser processing by the laser processing apparatus according to the present embodiment.

It is sectional drawing along the II-II line of the process target object shown in FIG.

3 is a plan view of the object to be processed after laser processing by the laser processing apparatus according to the present embodiment.

It is sectional drawing along the IV-IV line of the to-be-processed object shown in FIG.

It is sectional drawing along the V-V line of the process target object shown in FIG.

6 is a plan view of the object to be cut by the laser processing apparatus according to the present embodiment.

7 is a graph showing the relationship between the electric field strength and the magnitude of the crack spot in the laser processing apparatus according to the present embodiment.

8 is a cross-sectional view of the object to be processed in the first step of the laser machining apparatus according to the present embodiment.

9 is a cross-sectional view of the object to be processed in the second step of the laser machining apparatus according to the present embodiment.

10 is a cross-sectional view of the object to be processed in the third step of the laser machining apparatus according to the present embodiment.

11 is a cross-sectional view of the object to be processed in the fourth step of the laser machining apparatus according to the present embodiment.

It is a figure which shows the photograph of the cross section in a part of silicon wafer cut | disconnected by the laser processing apparatus which concerns on this embodiment.

FIG. 13 is a graph showing the relationship between the wavelength of laser light and the transmittance inside the silicon substrate in the laser processing apparatus in accordance with the present embodiment. FIG.

It is a front view which shows the processing target object of the laser processing method which concerns on 1st Embodiment of this invention.

FIG. 15 is a partial cross-sectional view taken along line XV-XV in FIG. 14.

16 is a flowchart showing a laser processing method according to the first embodiment of the present invention.

It is a figure for demonstrating calculation of back surface position information and surface position information in the laser processing method shown in FIG.

FIG. 18 is a partial cross-sectional view along the line XVIII-XVIII in FIG. 14 for explaining the laser processing method shown in FIG. 16.

It is a figure for demonstrating calculation of this surface position information and surface position information in the laser processing method which concerns on 2nd Embodiment of this invention.

20 is a partial cross-sectional view taken along the line XVIII-XVIII in FIG. 14 in the laser processing method by a conventional autofocus function.

It is a schematic block diagram which shows the laser processing apparatus which concerns on one Embodiment of this invention.

Explanation of the sign

31... Processing object, 5... Line to be cut, 11a... Surface (second side), 21... Back side (first side), L... Laser light, L1, L3, L5... Reflected light (reflected light reflected from the first surface), L2, L4, L6... Reflected light (reflected light reflected from the second surface), M1, M2, M3, M4, M5, M6... Modified region, P... Condensing point.

Best Mode for Carrying Out the Invention

EMBODIMENT OF THE INVENTION Hereinafter, preferred embodiment of this invention is described in detail with reference to drawings. In the laser processing method of the present embodiment, a phenomenon called multiphoton absorption is used in order to form a modified region inside the object to be processed. Therefore, the laser processing method for forming a modified region is demonstrated first.

If the energy hv of the photons is smaller than the band gap EG of the material absorption, it becomes optically transparent. Therefore, the condition under which absorption occurs in the material is hv> EG. However, even if it is optically transparent, when the intensity of the laser light is made very large, absorption occurs in the material under the condition of nhv> EG (n = 2, 3, 4,...). This phenomenon is called multiphoton absorption. In the case of a pulse wave, the intensity of the laser light is determined by the peak power density (W / cm 2) of the converging point of the laser light. For example, multi-photon absorption occurs at a peak power density of 1 × 10 ⁸ (W / cm 2) or more. . The peak power density is determined by (energy per pulse of laser light at the converging point) ÷ (beam spot cross-sectional area x pulse width of laser light). In the case of the continuous wave, the intensity of the laser light is determined by the electric field intensity (W / cm 2) of the light converging point of the laser light.

The principle of the laser processing method concerning this embodiment using such multiphoton absorption is demonstrated with reference to FIGS. As shown in FIG. 1, the cutting plan line 5 for cutting the process object 1 exists in the surface 3 of the process object 1 of wafer shape (plate shape). The line to be cut 5 is an imaginary line extending in a straight line shape. In the laser processing method which concerns on this embodiment, as shown in FIG. 2, the condensing point P is made to fit inside the process target object 1, and the laser light L is irradiated on the conditions which generate | occur | produce multi-photon absorption, and a modified area | region ( 7) form. In addition, the condensing point P is a location where the laser beam L condenses. In addition, the cutting plan line 5 may not only be a straight line but a curved line, and may be a line actually drawn on the object to be processed 1, not just an imaginary line.

Then, by moving the laser light L relatively along the cutting schedule line 5 (that is, in the direction of the arrow A in FIG. 1), the light collection point P is moved along the cutting schedule line 5. . Thereby, as shown to FIG. 3-FIG. 5, the modified area | region 7 is formed in the inside of the process target object 1 along the cutting plan line 5, and this modified area | region 7 is a starting point area | region 8 of a cutting | disconnection. ) Here, the cutting starting point region 8 means a region which becomes the starting point of cutting (dividing) when the object 1 is to be cut. This cutting origin region 8 may be formed by forming the reformed region 7 continuously, or may be formed by forming the modified region 7 intermittently.

In the laser processing method which concerns on this embodiment, since the laser beam L is hardly absorbed by the surface 3 of the processing target object 1, the surface 3 of the processing target object 1 does not melt.

When the starting point region 8 for cutting is formed inside the object 1, cracking tends to occur with the starting point region 8 as the starting point. As shown in FIG. 6, the processing target object is relatively small. (1) can be cut. Therefore, it becomes possible to cut | disconnect the process object 1 with high precision, without generating unnecessary cracking on the surface 3 of the process object 1.

The following two methods can be considered for the cutting | disconnection of the process object 1 which made this cutting origin region 8 the starting point. One is, after forming the starting point region 8 for cutting, an artificial force is applied to the processing target object 1, whereby the processing target object 1 is divided by the starting point region for cutting 8 and the processing target object 1 is formed. This is the case. This is the cutting in the case where the thickness of the object 1 is large, for example. The application of an artificial force may, for example, apply bending stress or shear stress to the object 1 along the cutting origin region 8 of the object 1 or give a temperature difference to the object 1. To generate thermal stress. The other is to form the starting point region 8 for cutting, thereby naturally splitting toward the cross-sectional direction (thickness direction) of the object 1, starting from the starting point region 8 for cutting, and consequently the processing object 1 This is the case. This is possible, for example, when the thickness of the object to be processed 1 is small by forming the starting point region 8 for cutting by one row of the modified regions 7, and when the thickness of the object to be processed 1 is large, The cutting origin region 8 is formed by the modified region 7 formed in a plurality of rows in the thickness direction. Moreover, also in this case of naturally splitting, in the part to cut off, a crack does not advance to the surface 3 of the part corresponding to the site | part which is not formed in the cutting origin region 8, and a cutting origin region 8 Since only the part corresponding to the site | part which formed () can be cleaved, the cleaving can be controlled well. In recent years, since the thickness of the processing object 1, such as a silicon wafer, tends to become thin, such a cleaving method with such controllability is very effective.

By the way, in the laser processing method which concerns on this embodiment, there exist a case of following (1)-(3) as a modified area | region.

(1) When the modified region is a crack region including one or a plurality of cracks

The focusing point is aligned inside the object to be processed (for example, a piezoelectric material made of glass or LiTaO ₃ ), the electric field strength at the focusing point is 1 × 10 ⁸ (W / cm 2) or more, and the pulse width is 1. The laser light is irradiated under the condition of or less. The magnitude of the pulse width is a condition in which a crack region can be formed only inside the object to be processed without causing unnecessary damage to the surface of the object while continuing to absorb multiphotons. As a result, a phenomenon called optical damage due to multiphoton absorption occurs inside the object to be processed. This optical damage causes thermal deformation inside the object to be processed, whereby a crack region is formed inside the object. As an upper limit of electric field intensity, it is 1 * 10 <^12> (W / cm <2>), for example. As for pulse width, 1 micrometer-200 micrometers are preferable, for example. In addition, the formation of the crack region by multiphoton absorption is described, for example, in "The glass substrate by solid laser harmonics" on pages 23 to 28 of the 45th Laser Thermal Processing Society Proceedings (December 1998). Internal marking ”.

The inventors obtained the relationship between the electric field strength and the crack size by experiment. Experimental conditions are as follows.

(A) Object to be processed: Pyrex (registered trademark) glass (700 μm thick)

(B) laser

Light source: semiconductor laser excitation Nd: YAG laser

Wavelength: 1064nm

Laser light spot cross section: 3.14 × 10 ^-8 cm 2

Oscillation form: Q switch pulse

Repetition frequency: 100 Hz

Pulse width: 30 Hz

Output: output <1mJ / pulse

Laser light quality: TEM ₀₀

Polarization Characteristics: Linearly Polarized

(C) condensing lens

Transmittance for Laser Light Wavelength: 60 Percent

(D) Movement speed of the mounting table on which the object to be processed is placed: 100 mm / sec

In addition, the laser light quality of TEM ₀₀ means that the light collecting property is high and the light can be collected up to the wavelength of the laser light.

7 is a graph showing the results of the experiment. The abscissa is the peak power density, and since the laser light is pulsed laser light, the electric field strength is represented by the peak power density. The vertical axis | shaft has shown the magnitude | size of the crack part (crack spot) formed in the inside of a to-be-processed object by 1 pulse of laser light. Crack spots gather to form a crack area. The size of the crack spot is the size of the portion that becomes the maximum length of the shape of the crack spot. Data represented by black circles in the graph is a case where the magnification of the condensing lens C is 100 times and the numerical aperture NA is 0.80. On the other hand, the data represented by the white circle in the graph is a case where the magnification of the condensing lens C is 50 times and the numerical aperture NA is 0.55. From the peak power density of about 10 ¹¹ (W / cm 2), crack spots are generated inside the object to be processed, and as the peak power density increases, the crack spots also increase.

Next, the cutting mechanism of the object to be processed by forming the crack region will be described with reference to FIGS. 8 to 11. As shown in FIG. 8, in the condition which multiphoton absorption generate | occur | produces, the converging point P is made to fit inside the process target object 1, a laser beam L is irradiated, and the crack area | region 9 is built in along a cutting plan line. Form. The crack area 9 is an area including one or a plurality of cracks. The crack region 9 thus formed becomes a starting point region for cutting. As shown in FIG. 9, a crack grows further from the crack area | region 9 (namely, from a cut origin area | region), and as shown in FIG. 3) and the back surface 21 are reached, and as shown in FIG. 11, the process object 1 is cut | disconnected as the process object 1 splits. The cracks reaching the front 3 and back 21 of the object 1 may grow naturally, or may grow by applying a force to the object 1.

(2) When the reformed region is a molten processed region

The laser beam is placed under the condition that the focusing point is aligned inside the object to be processed (for example, a semiconductor material such as silicon), and the electric field strength at the focusing point is 1 × 10 ⁸ (W / cm 2) or more and the pulse width is 1 dB or less. Investigate As a result, the inside of the object to be processed is locally heated by multiphoton absorption. By this heating, a molten processed region is formed inside the object to be processed. The melt processing region is a region that is once remelted after melting, a region that is certainly in a molten state, or a region that is restocked from a molten state, and may be referred to as a phase changed region or a region in which the crystal structure is changed. The molten processed region may also be referred to as a region in which a structure is changed to another structure in a single crystal structure, an amorphous structure, and a polycrystalline structure. That is, for example, a region changed from a single crystal structure to an amorphous structure, a region changed from a single crystal structure to a polycrystalline structure, and a region changed from a single crystal structure to a structure including an amorphous structure and a polycrystalline structure. If the workpiece is a silicon single crystal structure, the molten processed region is, for example, an amorphous silicon structure. As an upper limit of electric field intensity, it is 1 * 10 <^12> (W / cm <2>), for example. As for pulse width, 1 micrometer-200 micrometers are preferable, for example.

The inventors confirmed by experiment that a molten processed region was formed inside a silicon wafer (semiconductor substrate). Experimental conditions are as follows.

(A) Object to be processed: Silicon wafer (thickness 350 µm, outer diameter 4 inches)

(B) laser

Light source: semiconductor laser excitation Nd: YAG laser

Wavelength: 1064 nm

Laser light spot cross section: 3.14 × 10 ^-8 cm 2

Oscillation form: Q switch pulse

Repetition frequency: 100 Hz

Pulse width: 30 Hz

Output: 20 μJ / pulse

Laser light quality: TEM ₀₀

Polarization Characteristics: Linearly Polarized

(C) condensing lens

Magnification: 50 times

N.A .: 0.55

Transmittance for Laser Light Wavelength: 60 Percent

(D) Moving speed of the mounting table on which the object to be processed is placed: 100 mm / sec

It is a figure which shows the photograph of the cross section in a part of silicon wafer cut | disconnected by the laser processing on the said conditions. The molten processed region 13 is formed inside the silicon wafer 11. In addition, the magnitude | size of the thickness direction of the molten process area | region 13 formed by the said conditions is about 100 micrometers.

It is explained that the molten processed region 13 is formed by multiphoton absorption. 13 is a graph showing the relationship between the wavelength of laser light and the internal transmittance of a silicon substrate. However, the reflection component of each of the front side and the back side of the silicon substrate was removed, and only the internal transmittance was shown. The above relationship was shown for the thickness t of the silicon substrate for each of 50 µm, 100 µm, 200 µm, 500 µm and 1000 µm.

For example, at 1064 nm which is the wavelength of an Nd: YAG laser, when the thickness of a silicon substrate is 500 micrometers or less, it turns out that 80% or more of laser light transmits inside a silicon substrate. Since the thickness of the silicon wafer 11 shown in FIG. 12 is 350 micrometers, the molten process area | region 13 by multiphoton absorption is formed in the vicinity of the center of the silicon wafer 11, ie, the part of 175 micrometers from the surface. Since the transmittance in this case is 90% or more with reference to a silicon wafer having a thickness of 200 μm, the laser light is absorbed within the silicon wafer 11 only a few and most of them are transmitted. This is because laser light is absorbed inside the silicon wafer 11 and the molten processed region 13 is formed inside the silicon wafer 11 (that is, the molten processed region is formed by normal heating by laser light). This means that the molten processed region 13 is formed by multiphoton absorption. Formation of the molten processed region by multiphoton absorption is described, for example, by "picosecond pulse lasers" on pages 72 to 73 of the 66th edition of the Proceedings of the Japan Welding Society (April 2000). Evaluation of processing characteristics of silicon ”.

In addition, the silicon wafer generates cracks in the cross-sectional direction starting from the cutting origin region formed by the molten processed region, and the cracks are cut as a result by reaching the front and back surfaces of the silicon wafer. This crack reaching the front and back of the silicon wafer may grow naturally, or may grow when a force is applied to the silicon wafer. In the case where the cracks naturally grow from the cutting starting point region to the front and back surfaces of the silicon wafer, the cracks grow from the molten state in which the molten processed region forming the starting point region is melted, and the cutting starting region is formed. There are cases where cracks grow when remelting from the state in which the molten processed region is molten. In either case, the molten processed region is formed only inside the silicon wafer, and the molten processed region is formed only inside the cut surface after cutting, as shown in FIG. 12. In this way, when the starting point region for cutting is formed inside the object to be processed by the molten processing region, the cleaving control is facilitated because unnecessary splitting off the starting point region line during cleaving hardly occurs. Incidentally, the formation of the molten processed region may be caused not only by multiphoton absorption but also by other absorption effects.

(3) the modified region is a refractive index change region

The condensing point is set inside the object to be processed (for example, glass), and the laser light is irradiated under the condition that the electric field strength at the condensing point is 1 × 10 ⁸ (W / cm 2) or more and the pulse width is 1 ㎱ or less. When the pulse width is extremely short and multiphoton absorption is caused inside the workpiece, the energy due to the multiphoton absorption does not change to thermal energy, and permanent structure changes such as ion valence change, crystallization, or polarization orientation do not occur inside the workpiece. Is caused to form a refractive index change region. As an upper limit of electric field intensity, it is 1 * 10 <^12> (W / cm <2>), for example. The pulse width is preferably, for example, 1 m or less, more preferably 1 ps or less. The formation of the refractive index change region by multiphoton absorption is described, for example, by the femtosecond laser irradiation on pages 105 to 111 of the 42nd Laser Thermal Processing Proceedings (Nov. 1997). Formation of a broad-night structure for glass interior ”.

As mentioned above, although the case of (1)-(3) was demonstrated as a modified area | region, when the starting point area | region of cutting | disconnection is formed in consideration of the crystal structure of a wafer-like process object, its cleavage property, etc., it will cut | disconnect the following. It is possible to cut the object to be processed more precisely with a smaller force using the starting point area as a starting point.

That is, in the case of a substrate made of a single crystal semiconductor having a diamond structure such as silicon, it is preferable to form a starting point region for cutting in the direction along the (111) plane (first cleaved plane) or the (110) plane (second cleaved plane). Moreover, in the case of the board | substrate which consists of a group III-V compound semiconductor of a galvanic light structure, such as GaAs, it is preferable to form a cutting origin region in the direction along the (110) plane. In the case of a substrate having a hexagonal crystal structure such as sapphire (A1 ₂ 0 ₃ ), the (0001) plane (A plane) or (1100) plane (A plane) or (1100) plane ( It is preferable to form a cut origin region in the direction along M plane).

Further, orientation is performed on the substrate along a direction perpendicular to the direction in which the above-mentioned cutting origin region should be formed (for example, a direction along the (111) plane in a single crystal silicon substrate) or a direction in which the cutting origin region should be formed. By forming an orientation flat, it is possible to easily and accurately form the cutting origin region along the direction in which the cutting origin region is to be formed on the substrate by referring to the orientation flat.

Next, preferable embodiment of this invention is described.

[First Embodiment]

As shown in FIG. 14 and FIG. 15, the processing target 1 includes a silicon wafer 11 and a plurality of functional elements 15, which will be referred to as a “surface” hereinafter. The functional element layer 16 formed in 11a is provided, and the thickness is set to about 300 micrometers. The functional element 15 is, for example, a semiconductor operating layer formed by crystal growth, a light receiving element such as a photodiode, a light emitting element such as a laser diode, or a circuit element formed as a circuit, and the like, and orientation of the silicon wafer 11. Many are formed in matrix form in the direction parallel to and perpendicular to the flat 6. Such a workpiece 1 is a discrete device which is cut along a cutting schedule line 5 (see a broken line in FIG. 14) set in a lattice shape so as to pass between neighboring functional elements 15. ) And so on.

When cutting this process object 1, a process tape is first attached to the surface of the function element layer 16, and the process object is processed to the stage of a laser processing apparatus in the state which protected the function element layer 16 with a protection tape. Secure the protective tape holding (1). Subsequently, the laser beam is irradiated under the condition that the condensation point is made inside the silicon wafer 11 from the back surface (hereinafter also referred to simply as the "back surface") 21 of the object 1, A reformed region serving as a starting point of cutting is formed along each cutting scheduled line 5 (backside incident machining). Here, six rows of modified regions are formed along the respective cutting scheduled lines 5 in the thickness direction of the object to be processed 1. Subsequently, the protective tape fixed to the stage is spaced apart from the object to be processed 1. The expand tape is attached to the back surface 21 of the silicon wafer 11, the protective tape is peeled off from the surface of the functional element layer 16, and then the expanded tape is expanded. As a result, the modified region is used as the starting point for cutting, and the object to be processed 1 is precisely cut for each of the functional elements 15 along the cutting scheduled line 5 so that a plurality of semiconductor chips are separated from each other. In addition, the modified region may include a crack region or the like in addition to the molten processed region.

By the way, the object to be processed 1 may have irregular thicknesses between a plurality of objects to be processed 1 due to, for example, a difference in grinding lot, or may be uneven at the time of grinding in one object to be processed 1. There is a case where a part becomes thick or thin (when the thickness of the processing object 1 changes). Specifically, in the processing target object 1 having a thickness of 300 µm, the thickness may vary by ± 10 µm or more between the plurality of processing targets 1, and the thickness of a part of the processing target 1 is further increased. May deviate by ± 5 µm or more.

However, in the general autofocus function, the thickness of the object to be processed 1 is regarded as constant, and only the displacement amount of the back surface 21, which is the laser light incident surface, is measured, whereby the position of the light collection point of the laser light is moved from the back surface 21 to a predetermined position. To control. Therefore, as shown in FIG. 20 conventionally, the modified area | region which is closest to the surface 11a among the formed modified area | region M is formed so that the process object 1 may protrude from this process object 1, or the process object In the thin part (1), it may be formed in the back surface 21 side, without reaching to the deep position of the to-be-processed object 1 in some cases.

Therefore, in the laser processing method of this embodiment, the 1st modification closest to the back surface (1st surface) 21 among the modification areas formed in multiple rows along the cutting plan line 5 of the to-be-processed object 1 in the thickness direction. A region is formed on the basis of the position of the back surface 21, and a second modified region closest to the surface (second surface) 11a is formed on the basis of the position of the surface 11a. Hereinafter, the formation of this modified region will be described in more detail.

[Height set]

First, the laser beam for distance measurement is irradiated on the back surface 21 of the object to be processed 1, for example, while the focus of the reticle image is aligned, and the reflected light of the distance laser light reflected on the back surface 21 is reflected. Is detected as a voltage value, and the detected voltage value is stored (S1 in FIG. 16).

[Trace]

Subsequently, the cutting schedule line 5 is arranged so that the voltage value maintains the voltage value by setting the height while detecting the reflected light of the distance measuring laser light that is reflected from the back surface 21 as the voltage value while irradiating the distance measuring laser light. Along the cut-out line 5, the displacement of the back surface 21 along the cutting plan line 5 is acquired, and the displacement of this back surface 21 is memorized as back surface position information (first position information). That is, back surface position information is calculated | required as the relative distance of the thickness direction from the back surface 21 to the back surface 21 position set high.

Back position information = displacement of back side 21

= Relative distance in the thickness direction from the back surface 21 to the back surface 21 position set in height

At this time, the laser beam for distance measurement is scanned, and the thickness (thickness information) of the object to be processed 1 is optically measured by a thickness measuring device along the cut line 5. Specifically, as shown in FIG. 17A, the light L1 from the rear surface 21 and the object 1 are transmitted through the line 5 to be cut and reflected from the surface 11a. The reflected light L2 is received by the line sensor 50. The distance from the front surface 11a to the rear surface 21, that is, the object to be processed is determined by the light-receiving positions of the reflected light L1 and L2 in the line sensor 50 and the refractive index of the object to be processed 1 previously obtained. Calculate the thickness of 1).

Then, the above-mentioned backside positional information is added to the calculated thickness of the object 1 to be processed and stored as surface positional information (second positional information) along the cutting schedule line 5. That is, surface positional information is calculated | required as the relative distance of the thickness direction from the surface 11a to the position of the back surface 21 set high (S2 in FIG. 16).

If surface positional information =, the positional information + thickness of the workpiece 1

= Relative distance in thickness direction from surface 11a to the back surface 21 position set height

In addition, here, the measuring system of the back surface 21 and the measuring system of the thickness of the process target object 1 are comprised by two axes. Moreover, the displacement of the back surface 21 and the thickness of the process target object 1 are acquired in association with the coordinate of the direction along the cutting plan line 5. Therefore, the measuring system of the back surface 21 and the thickness measuring system of the object to be processed 1 are constituted by two axes, and the back surface position information and the surface position information are synthesized on the coordinates from the distance D1 between the respective measuring systems. Is accurately obtained.

Alternatively, as shown in FIG. 17B, the thickness of the object 1 may be measured by interfering the reflected light L3 from the back surface 21 and the reflected light L4 from the surface 11a. Also in this case, the measuring system of the back surface 21 and the thickness measuring system of the object 1 are constituted by two axes, and the displacement of the back surface 21 and the thickness of the object 1 to be cut off the line to be cut. It is obtained in association with the coordinates of the direction. Therefore, the back surface position information and the surface position information are synthesize | combined on the coordinate from the distance D2 between each measurement system, and the back position position information and the surface position information are calculated | required with high precision.

[Formation of modified region]

Subsequently, as shown in FIG. 18 (a), inside the object 1, the laser beam is irradiated with a focusing point on the inner side (upper side) by 10 μm from the surface 11 a, and is to be cut. Scan along line 5. Specifically, in the inside of the object 1, the focusing point is moved to a position on the rear surface 21 side by 10 µm from the surface position information to irradiate the laser light with an output of 0.72 W, and the stored surface position information is stored. It reproduces with a position adjustment element (actuator using a piezo element in this embodiment), and scans along the cutting plan line 5, controlling a condensing point position. Thereby, the modified area | region (2nd modified layer) M1 is formed along the cutting plan line 5 inside 10 micrometers from this surface 11a with respect to the surface 11a (S3 in FIG. 16). Specifically, the modified region M1 along the cutting schedule line 5 is formed at the position on the rear surface 21 side by 10 µm from the surface position information.

Subsequently, as shown in FIG. 18 (b), inside the object 1, the laser beam is irradiated by cutting the laser light at an inner side (upper side) by 25 µm from the surface 11a. Scan along line 5. Specifically, in the inside of the object 1, the focusing point is moved to the position on the rear surface 21 side by 25 µm from the surface position information to irradiate the laser light with an output of 1.20 W, and the surface position information memorized is stored. It scans along the cutting | disconnection plan line 5, regenerating by a piezo element and continuing to control a condensing point position. As a result, the modified region M2 is formed along the cut schedule line 5 on the inside of the surface 11a by 25 µm from the surface 11a (S4 in FIG. 16). Specifically, the modified region M2 along the cutting scheduled line 5 is formed at the position on the rear surface 21 side by 25 µm from the surface position information.

Subsequently, inside the object 1, the laser beam is irradiated with the focusing point on the inner side (upper view) by 35 µm from the surface 11a, and scanned along the cutting schedule line 5. Specifically, inside the object 1, the focusing point is moved to a position on the rear surface 21 side by 35 µm from the surface position information to irradiate the laser light with an output of 1.20 W, and the surface position information memorized is stored. It scans along the cutting | disconnection plan line 5, regenerating by a piezo element and continuing to control a condensing point position. As a result, the modified region M3 is formed along the cut schedule line 5 on the inside of the surface 11a by 35 μm from the surface 11a (S5 in FIG. 16). Specifically, the modified region M3 along the cutting schedule line 5 is formed at the position on the rear surface 21 side by 35 µm from the surface position information.

Subsequently, in the inside of the object 1, laser beams are irradiated with a light converging point on the inner side (upper view) by 45 µm from the surface 11a, and scanned along the cutting schedule line 5. Specifically, in the inside of the object 1, the focusing point is moved to a position on the rear surface 21 side by 45 µm from the surface position information, and the laser beam is irradiated at an output of 1.20 W, and the surface position information memorized is stored. It scans along the cutting | disconnection plan line 5, regenerating by a piezo element and continuing to control a condensing point position. As a result, the modified region M4 is formed along the cut schedule line 5 on the inner side of the surface 11a by 45 µm from the surface 11a (S6 in FIG. 16). Specifically, the modified region M4 along the cutting scheduled line 5 is formed at the position on the rear surface 21 side by 45 µm from the surface position information.

Subsequently, as shown in FIG. 18C, inside the object 1, the laser beam is irradiated and cut at a light converging point on the inner side (downward) by 25 μm from the rear surface 21. Scan along the scheduled line 5. Specifically, in the inside of the object 1, the focusing point is moved to a position on the surface 11a side by 25 µm from the backside positional information to irradiate the laser light with an output of 1.20W, and the backside positional information memorized is stored. It scans along the cutting | disconnection plan line 5, regenerating by a piezo element and continuing to control a condensing point position. Thereby, the modification area | region M5 is formed along the cutting | disconnection plan line 5 inside 25 micrometers from this back surface 21 with respect to the back surface 21 (S7 in FIG. 16). Specifically, the modified region M5 along the cutting schedule line 5 is formed at the position on the surface 11a side by 25 µm from the rear surface position information.

Finally, in the inside of the object 1, laser beams are irradiated to the inside (downward) by 15 µm from the rear surface 21, and irradiated with a laser beam, and scanned along the cut line 5. Specifically, in the inside of the object 1, the focusing point is moved to a position on the surface 11a side by 10 µm from the backside positional information to irradiate the laser light with an output of 0.68 W, and the backside positional information memorized is stored. It scans along the cutting | disconnection plan line 5, regenerating by a piezo element and continuing to control a condensing point position. Thereby, the modified area | region (2nd modified layer) M6 is formed along the cutting plan line 5 inside 15 micrometers inside from this back surface 21 with respect to the back surface 21 (S8 in FIG. 16). Specifically, the modified region M6 along the cutting scheduled line 5 is formed at the position on the surface 11a side by 15 µm from the rear surface position information.

Here, among the modified regions M1 to M6 formed in a plurality of rows in the thickness direction in the interior of the object 1, the modified regions M5 and M6 are modified regions for forming a half cut on the upper surface, so-called half cut SD. It is called. This half cut ensures separation by expanding the expand tape, so half cut SD is a very important factor. Moreover, the modified area | region M1 closest to the surface 11a among the modified area | regions M1-M6 formed in multiple rows is a modified area | region which affects especially the quality of the cut surface after cutting | disconnection, and is called so-called quality SD. Quality SD is for precisely cutting the functional element layer 16, and is a very important factor for maintaining the quality when cutting the object 1.

Therefore, in the present embodiment, as described above, the modified regions M5 and M6 are cut inside the object 1 by the predetermined distance from the back surface 21 on the basis of the back surface 21. While forming along the predetermined line 5, the modification area | region M1 is formed along the predetermined | prescribed cutting line 5 inside the predetermined distance from this surface 11a with respect to the surface 11a. In this way, since the positions of both the rear surface 21 and the surface 11a are used as a reference, even if the thickness of the object 1 is changed irregularly, the positions of the modified regions M5 and M6 and the positions of the modified region M6 The separation due to the change in the thickness of the object 1 can be suppressed. Therefore, according to the present embodiment, in the case where a plurality of rows of modified regions are formed along the cutting scheduled line 5 in the thickness direction of the object 1, the modified region M6 and the modified region M6 closest to the rear surface 21 are formed. The modification region M5 adjacent to and the modification region M1 closest to the surface 11a can be formed with high accuracy.

In addition, in this embodiment, since the modified regions M5 and M6 are formed with high accuracy, the following effects are obtained. That is, since the modified regions M5 and M6 are too close to the back surface 21, the half cuts are twisted and the deterioration is suppressed. In addition, since the modified regions M5 and M6 are too far from the rear surface 21, the elongation of the cracks generated from the modified regions M5 and M6 becomes insufficient, and half cuts are also prevented from being formed.

In addition, as described above, since the modified region M1 is formed with high accuracy, the following effects are obtained. That is, since the modified region M1 is too close to the surface 11a, the irradiated laser light protrudes from the object to be processed 1, and a hole is drilled in the surface 11a, so that the strength of the cutout of the object 1 is processed. Suppresses weakening. In addition, the so-called skirt phenomenon in which the edge part of the surface 11a side largely deviates from the cutting | disconnection plan line 5 in a cut surface by the modified area | region M1 too far from the surface 11a is prevented from occurring. In addition, in this embodiment, the functional element 15 is formed in the surface 11a which is the surface on the opposite side to the surface on which laser light is incident for back surface incident processing. Therefore, the said effect of preventing generation of a skirt phenomenon is Especially notable.

In addition, according to the present embodiment, the positional deviation of the modified region due to the thickness variation and unevenness present in the object 1 can be corrected, and the distance from the surface 11a and the rear surface 21 can be corrected. It is possible to perform multi-stage processing in which the quality of the modified region depending on the distance is the best and the cutting surface quality after the cutting is the best.

In addition, although the thickness of the process target object 1 can also be measured by the contact-type thickness meter, in this case, when there exists a foreign material between the process target object 1 and a stage, or when it sticks with an expand tape, Air may mix between the processing object 1, and the position of the processing object 1 which contacted does not necessarily become a position which shows the thickness of the processing object 1. Therefore, in this embodiment, the measuring device which uses a transmission laser is used, and the thickness of the process target object 1 is measured accurately.

Incidentally, in the present embodiment, as described above, the modified regions M2, M3, and M4 are formed based on the surface 11a, but are not limited to the present embodiment, and the modified regions M2, M3, and M4 are the rear surfaces. It may be formed based on (21).

Second Embodiment

Next, the laser processing method concerning 2nd Embodiment of this invention is demonstrated. The laser processing method according to the second embodiment differs from the laser processing method according to the first embodiment in the autofocus function as shown in FIG. 19 without measuring the thickness of the object 1. The reflected light L5 on the back surface 21 and the reflected light L6 on the surface 11a were respectively detected using the optical system.

Specifically, in the laser processing method according to the present embodiment, the reflected light L5 reflected from the rear surface 21 and the reflected light L6 transmitted through the object 1 and reflected from the surface 11a are respectively detected. By directly acquiring the displacement of the surface 11a and the displacement of the back surface 21, respectively, the back surface position information and the surface position information are directly obtained.

Back position information = displacement of back side 21

= Relative distance in the thickness direction from the back surface 21 to the back surface 21 position set in height

Surface positional information = displacement of the surface 11a =

Relative distance in the thickness direction from the surface 11a to the back surface 21 position set height

Thus, even with the laser processing method of this embodiment, even if the effect similar to the said embodiment, ie, even if the thickness of the process target object 1 changes irregularly, the position of modified area | region M5, M6 and the position of modified area | region M6 are processed. The effect of suppressing the separation due to the change in the thickness of the object 1 is exhibited. As a result, in the case where a plurality of rows of modified regions are formed along the cutting scheduled line 5 in the thickness direction of the object 1, the modified region M6 closest to the rear surface 21 and the modified region adjacent to the modified region M6. The modified region M1 closest to M5 and the surface 11a can be formed with high accuracy.

Next, the laser processing apparatus which concerns on one Embodiment of this invention is demonstrated.

As shown in FIG. 21, the laser processing apparatus 100 changes the direction of the optical axis of the laser light source 101 which pulses a laser beam (machining laser beam) L, and the optical axis of the laser beam L to 90 degrees. And a dichroic mirror 103 arranged so as to be condensed, and a condenser lens 105 for condensing the laser light L. Moreover, the laser processing apparatus 100 X-mounts the mounting base 107 for mounting the process target object 1 to which the laser beam L condensed by the condensing lens 105 is irradiated, and the mounting base 107. , The stage 111 for moving in the Y, Z-axis direction, the laser light source controller 102 for controlling the laser light source 101 to adjust the output of the laser light L, the pulse width, and the like, and the stage 111. The stage control part 115 which controls the movement of) is provided.

According to the laser processing apparatus 100, the optical axis of the laser light L irradiated from the laser light source 101 is changed by 90 ° in the dichroic mirror 103, and the mounting table 107 is mounted on the condenser lens 105. The light is condensed inside the object 1 of the image. At the same time, the stage 111 is moved, and the object to be processed 1 is moved relative to the laser beam L along the cutting schedule line 5. As a result, a modified region is formed in the object 1 along the cutting scheduled line 5.

In addition, the laser processing apparatus 100 is not limited to this embodiment, The laser beam L from the laser light source 101 is guided to the condensing lens 105 without using the dichroic mirror 103. You may shine. In addition, the movement of the laser light L should just move the laser light L with respect to the process target 1. In particular, in the Z-axis direction, the focus position of the laser light L can be changed by moving the position of the condenser lens 105 instead of moving the mounting table 107.

As mentioned above, although preferred embodiment of this invention was described, this invention is not limited to the said embodiment.

For example, in the said embodiment, although it is what is called trace processing which forms a modified area | region by scanning a laser beam after measuring the displacement etc. of the surface 11a of the process target object 1, the displacement etc. of the surface 11a are not shown. What is called real-time processing may be sufficient as measuring and forming a modified region.

Moreover, in irradiation of the distance measuring laser light which permeate a process object and the distance measuring laser light reflected without permeation, you may use a some laser light source, and you may irradiate by changing a wavelength from one laser light source.

Moreover, in the said embodiment, although it is set as back surface incidence process which injects a laser beam from the back surface 21 side which opposes the surface 11a in which the functional element 15 was formed, it injects a laser beam from the surface 11a side. Of course, processing may be sufficient.

In addition, although the object 1 provided with the silicon wafer 11 is used as a process object, even if it is not the silicon wafer 11, For example, semiconductor compound materials, such as gallium arsenide, piezoelectric material, sapphire, etc. The material which has crystallinity may be sufficient.

According to the present invention, in the case where a plurality of rows of modified regions are formed along the cutting scheduled line in the thickness direction of the object to be processed, the first modified region closest to the first surface and the second modified region closest to the second surface are precisely determined. It can form well.

Claims (6)

Laser processing for forming a plurality of rows of modified regions which are the starting point of cutting along the cutting scheduled line of the processing object in the thickness direction of the processing object by aligning a light collecting point inside the plate-shaped processing object and irradiating laser light. As a method, Forming a first modified region closest to the first surface among the modified regions on the basis of the position of the first surface on which the laser light is incident in the object to be processed; And a step of forming a second modified region closest to the second surface among the modified regions on the basis of the position of the second surface facing the first surface in the object to be processed. Way. The method according to claim 1, In the step of forming the first modified region, first position information regarding the position of the first surface is obtained by detecting the reflected light reflected from the first surface, and based on the first position information, Forming the first modified region inward by a predetermined distance from the first surface, In the step of forming the second modified region, second position information relating to the position of the second surface is obtained by detecting the reflected light reflected from the second surface, and based on the second position information. And forming the second modified region inwardly by a predetermined distance from the second surface. The method according to claim 1, In the step of forming the first modified region, first position information regarding the position of the first surface is obtained by detecting the reflected light reflected from the first surface, and based on the first position information, Forming the first modified region inward by a predetermined distance from the first surface, In the step of forming the second modified region, the second modified region is formed on the inner side by a predetermined distance from the second surface based on the first positional information and the thickness information on the thickness of the object to be processed. The laser processing method characterized by the above-mentioned. The method according to claim 1, In the step of forming the second modified region, second position information relating to the position of the second surface is obtained by detecting the reflected light reflected from the second surface, and based on the second position information, Forming the second modified region inward by a predetermined distance from the second surface, In the step of forming the first modified region, the first modified region is formed on the inner side by a predetermined distance from the first surface based on the second positional information and the thickness information on the thickness of the object to be processed. The laser processing method characterized by the above-mentioned. The method according to claim 1, The processing object includes a semiconductor substrate, and the modified region includes a melt processing region. The method according to claim 1, And cutting the object to be processed along the cut schedule line, using the modified region as a starting point for cutting.

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