Source: https://patents.google.com/patent/US8389384B2/en
Timestamp: 2020-01-27 21:57:18
Document Index: 34883338

Matched Legal Cases: ['art; 72', 'art; 74', 'art 16', 'art 16', 'art 16', 'art 71', 'art 16', 'art 16', 'art 71', 'art 16', 'art 16', 'art 16', 'art 73', 'art 16', 'art 73', 'art 16', 'art 16']

US8389384B2 - Laser beam machining method and semiconductor chip - Google Patents
US8389384B2
US8389384B2 US12/159,338 US15933806A US8389384B2 US 8389384 B2 US8389384 B2 US 8389384B2 US 15933806 A US15933806 A US 15933806A US 8389384 B2 US8389384 B2 US 8389384B2
US12/159,338
US20090302428A1 (en
2005-12-27 Priority to JP2005-375695 priority
2006-12-26 Application filed by Hamamatsu Photonics KK filed Critical Hamamatsu Photonics KK
2006-12-26 Priority to PCT/JP2006/325919 priority patent/WO2007074823A1/en
2009-02-09 Assigned to HAMAMATSU PHOTONICS K.K. reassignment HAMAMATSU PHOTONICS K.K. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: MURAMATSU, KENICHI, SAKAMOTO, TAKESHI
2009-12-10 Publication of US20090302428A1 publication Critical patent/US20090302428A1/en
2013-03-05 Publication of US8389384B2 publication Critical patent/US8389384B2/en
238000003672 processing method Methods 0 claims description 60
An object to be processed 1 comprising a substrate 4 and a plurality of functional devices 15 formed on a front face 3 of the substrate 4 is irradiated with laser light L while locating a converging point P within the substrate 4, so as to form at least one row of a divided modified region 72, at least one row of a quality modified region 71 positioned between the divided modified region 72 and the front face 3 of the substrate 4, and at least one row of an HC modified region 73 positioned between the divided modified region 72 and a rear face 21 of the substrate 4 for one line to cut 5. Here, in a direction along the line to cut, a forming density of the divided modified region 72 is made lower than that of the quality modified region 71 and that of the HC modified region 73.
The present invention relates to a laser processing method used for cutting an object to be processed comprising a substrate and a plurality of functional devices formed on a front face of the substrate along a line to cut, and a semiconductor chip cut by using such a laser processing method.
Conventionally known as this kind of art is a laser processing method which irradiates a wafer-like object to be processed with laser light while locating a converging point within the object, thereby forming a plurality of rows of modified regions within the object along a line to cut and using the modified regions as a cutting start point (see Patent Document 1, for example).
The laser processing method such as the one mentioned above is a technique which becomes particularly effective when the object to be processed is thick. This is because even a thick object to be processed can be cut accurately along the line to cut by increasing the number of rows of modified regions along the line to cut. Such a technique has been demanded to shorten the processing time while keeping the cutting quality.
In view of such circumstances, it is an object of the present invention to provide a laser processing method which can cut an object to be processed comprising a substrate and a plurality of functional devices formed on a front face of the substrate along a line to cut accurately in a short time even when the substrate is thick, and a semiconductor chip cut by using such a laser processing method.
For achieving the above-mentioned object, in one aspect, the present invention provides a laser processing method of irradiating an object to be processed comprising a substrate and a plurality of functional devices formed on a front face of the substrate with laser light while locating a converging point within the substrate, so as to form a modified region to become a cutting start point within the substrate along a line to cut the object; the method including the step of forming at least one row of a first modified region, at least one row of a second modified region positioned between the first modified region and the front face of the substrate, and at least one row of a third modified region positioned between the first modified region and a rear face of the substrate; wherein a forming density of the first modified region in a direction along the line to cut is lower than that of the second modified region and that of the third modified region in the direction along the line to cut.
In this laser processing method, the forming density of the first modified region in a direction along the line to cut is lower than that of the second modified region and that of the third modified region in this direction. This can reduce the time required for forming the first, second, and third modified regions as compared with the case where the forming density of the first modified region is equal to that of the second modified region and that of the third modified region. Meanwhile, the second modified region, which is positioned between the first modified region and the front face of the substrate, and the third modified region, which is positioned between the first modified region and the rear face of the substrate, are more influential on the cutting quality of the object than is the first modified region. However, since the forming densities of the second and third modified regions in the direction along the line to cut are made higher than the forming density of the first modified region in the direction along the line to cut, the cutting quality of the object can be prevented from deteriorating. Because of the foregoing, this laser processing method can cut an object to be processed comprising a substrate and a plurality of functional devices formed on the front face of the substrate along a line to cut accurately in a short time even when the substrate is thick.
The functional devices herein refer to semiconductor operating layers formed by crystal growth, light-receiving devices such as laser diodes, circuit devices formed as circuits, and the like, for example. The forming density of the modified region in the direction along the line to cut (hereinafter simply referred to as “forming density of the modified region”) refers to the ratio at which the modified region is distributed per unit length in the direction along the line to cut.
The first, second, and third modified regions can be formed in any order. The first, second, and third modified regions are formed by generating multiphoton absorption or other kinds of absorption within the substrate by irradiating the substrate with the laser light while locating the converging point within the substrate.
When irradiating the substrate with the laser light while using the rear face of the substrate as a laser light entrance surface and locating the converging point within the substrate in the above-mentioned laser processing method, it will be preferred if the second modified region is formed such that an end part on the front face side of the second modified region and the front face of the second modified region are separated from each other by a distance of 5 μm to 20 μm. When the second modified region is formed as such, even a multilayer part formed on the line to cut in the front face of the substrate, if any, can be cut accurately along the line to cut together with the substrate.
Preferably, the third modified region is formed such that a fracture along the line to cut occurs from the third modified region to the rear face of the substrate. When the third modified region is formed as such, the fracture generated from the third modified region to the rear face of the substrate proceeds smoothly toward the front face of the substrate through the first and second modified regions at the time of expanding an expandable tape attached to the rear face of the substrate, for example, whereby the object can be cut accurately along the line to cut.
The above-mentioned laser processing method encompasses a case where the substrate is a semiconductor substrate, while the first, second, and third modified regions include a molten processed region. When the substrate is a semiconductor substrate, a modified region including a molten processed region may be formed as the first, second, and third modified regions.
The above-mentioned laser processing method may further comprise the step of cutting the object into the functional devices along the line to cut. Because of the reason mentioned above, the object can be cut accurately in a short time into the functional devices even when the substrate is thick.
In another aspect, the present invention provides a laser processing method of irradiating an object to be processed comprising a substrate and a plurality of functional devices formed on a front face of the substrate with laser light while locating a converging point within the substrate, so as to form a modified region to become a cutting start point within the substrate along a line to cut the object; the method including the step of forming at least one row of a first modified region, at least one row of a second modified region positioned between the first modified region and the front face of the substrate, and at least one row of a third modified region positioned between the first modified region and a rear face of the substrate; wherein, when forming the first modified region, the laser light is moved relative to the object along the line to cut at a rate faster than that at the time of forming the second and third modified regions.
This laser processing method can make the forming density of the first modified region lower than that of the second modified region and that of the third modified region. Therefore, this laser processing method can cut an object to be processed comprising a substrate and a plurality of functional devices formed on the front face of the substrate along a line to cut accurately in a short time even when the substrate is thick as with the former laser processing method.
In still another aspect, the present invention provides a semiconductor chip comprising a substrate and a functional device formed on a front face of the substrate; wherein a side face of the substrate is formed with at least one row of a first modified region, at least one row of a second modified region positioned between the first modified region and the front face of the substrate, and at least one row of a third modified region positioned between the first modified region and a rear face of the substrate; and wherein a forming density of the first modified region in a direction orthogonal to a thickness direction of the substrate is lower than that of the second modified region and that of the third modified region in the direction orthogonal to the line to cut.
Since this semiconductor chip is considered to be one cut by using the above-mentioned laser processing methods, the side face of the substrate formed with the first, second, and third modified regions is a high-precision cut section in which irregularities are suppressed.
FIG. 20 is a view for explaining the laser processing method in accordance with the first embodiment, in which (a) is a state where an expandable tape is attached to the object, and (b) is a state where the protective tape is irradiated with UV rays;
FIG. 22 is a partial sectional view of the object taken along the line XXII-XXII of FIG. 19( b);
FIG. 26 is a partial sectional view of the object taken along the line XXVI-XXVI of FIG. 23( b).
1 . . . object to be processed; 3 . . . front face; 4 . . . substrate; 4 a . . . cut section (side face); 5 . . . line to cut; 15 . . . functional device; 21 . . . rear face; 24 . . . fracture; 25 . . . semiconductor chip; 71 . . . quality modified region; 71 a . . . front-side end part; 72 . . . divided modified region; 73 . . . HC modified region; 73 a . . . front-side end part; 74 . . . auxiliary HC modified region; L . . . laser light; P . . . converging point
A material becomes transparent when its absorption bandgap EG is greater than photon energy hv. Consequently, a condition under which absorption occurs in the material is hν>EG. However, even when optically transparent, the material generates absorption under a condition of nhν>EG (where n=2, 3, 4, . . . ) if the intensity of laser light becomes very high. This phenomenon is known as multiphoton absorption. In the case of pulsed waves, the intensity of laser light is determined by the peak power density (W/cm2) of laser light at its converging point. The multiphoton absorption occurs under a condition where the peak power density is 1×108 (W/cm2) or greater, for example. The peak power density is determined by (energy of laser light at the converging point per pulse)/(beam spot cross-sectional area of laser light×pulse width). In the case of continuous waves, the intensity of laser light is determined by the field intensity (W/cm2) of laser light at the converging point.
An object to be processed (e.g., glass or a piezoelectric material made of LiTaO3) is irradiated with laser light while locating a converging point therewithin under a condition with a field intensity of at least 1×108 (W/cm2) at the converging point and a pulse width of 1 μs or less. This magnitude of pulse width is a condition under which a crack region can be formed only within the object while generating multiphoton absorption without causing unnecessary damages on the front face of the object. This generates a phenomenon of optical damage by multiphoton absorption within the object. This optical damage induces a thermal distortion within the object, thereby forming a crack region therewithin. The upper limit of field intensity is 1×1012 (W/cm2), for example. The pulse width is preferably 1 ns to 200 ns, for example. The forming of a crack region by multiphoton absorption is disclosed, for example, in “Internal Marking of Glass Substrate with Solid-state Laser Harmonics”, Proceedings of the 45th Laser Materials Processing Conference (December, 1998), pp. 23-28.
The inventors have tried to expand the laser light L in order to restrain the laser light L from affecting the front face 3 of the silicon wafer 11. In one technique therefor, the laser light L emitted from the laser light source is expanded by a predetermined optical system, so as to widen the skirt of the Gaussian distribution, thereby relatively raising the laser intensity of light components in a peripheral part of the laser light L (those corresponding to L1 to L3 and L6 to L8 in FIG. 15). When thus expanded laser light L is transmitted through the silicon wafer 11, the molten processed region 13 is formed near the converging point P, and the microcavity 14 is formed at a part corresponding to the molten processed region 13 as explained above. Namely, the molten processed region 13 and the microcavity 14 are formed at respective positions on the optical axis (dash-dot line in FIG. 15) of the laser light L. The position at which the microcavity 14 is formed corresponds to a location where light components in the peripheral part of the laser light L (those corresponding to L1 to L3 and L6 to L8 in FIG. 15) are theoretically converged.
The spherical aberration of a lens converging the laser light L seems to cause light components in the center part of the laser light L (those corresponding to L4 and L5 in FIG. 15) and light components in the peripheral part of the laser light L (those corresponding to L1 to L3 and L6 to L8 in FIG. 15) to converge at respective locations different from each other in the thickness direction of the silicon wafer 11 as in the foregoing. The first hypothesis assumed by the inventors lies in that the difference in converging positions may have some effects.
The second hypothesis assumed by the inventors lies in that, since the portion where light components in the peripheral part of the laser light L (those corresponding to L1 to L3 and L6 to L8 in FIG. 15) are converged is a theoretical laser-converging point, the light intensity is so high in this portion that minute structural changes occur, thereby forming the microcavity 14 whose periphery does not substantially change its crystal structure, whereas the portion formed with the molten processed region 13 is thermally affected so much that it is simply molten and re-solidified.
Here, the molten processed region 13 is as stated in the above (2), whereas the microcavity 14 is one whose periphery does not substantially change its crystal structure. When the silicon wafer 11 has a silicon monocrystal structure, the periphery of the microcavity 14 mostly keeps the silicon monocrystal structure.
The first embodiment of the present invention will now be explained. FIG. 17 is a plan view of the object to be processed in the laser processing method in accordance with this embodiment, whereas FIG. 18 is a sectional view of a part of the object taken along the line XVIII-XVIII of FIG. 17.
As shown in FIGS. 17 and 18, the object 1 comprises a substrate 4 made of silicon having a thickness of 30 μm and an outer diameter of 6 inches, and a multilayer part 16 which is formed on the front face 3 of the substrate 4 while including a plurality of functional devices 15. The functional devices 15 have an interlayer insulating film 17 a laminated on the front face 3 of the substrate 4, a wiring layer 19 a arranged on the interlayer insulating film 17 a, an interlayer insulating film 17 b laminated on the interlayer insulating film 17 a so as to cover the wiring layer 19 a, and a wiring layer 19 b arranged on the interlayer insulating film 17 b. The wiring layer 19 a and the substrate 4 are electrically connected to each other by a conductive plug 20 a penetrating through the interlayer insulating film 17 a, whereas the wiring layers 19 a and 19 b are electrically connected to each other by a conductive plug 20 b penetrating through the interlayer insulating film 17 b.
Thus constructed object 1 is cut into the functional devices 15 (cut into thin square sheet-like chips each having a size of 5 mm×5 mm here when seen two-dimensionally) as follows. First, as shown in FIG. 19( a), a protective tape 22 is attached to the object 1 so as to cover the multilayer part 16. Subsequently, as shown in FIG. 19( b), the object 1 is fixed onto a mount table (not depicted) of a laser processing apparatus such that the rear face 21 faces up. Here, the protective tape 22 keeps the multilayer part 16 from coming into direct contact with the mount table, whereby each functional device 15 can be protected.
Then, lines to cut 5 are set like grids (see broken lines in FIG. 17) at intervals of 5 mm so as to pass between the functional devices 15, adjacent to each other, and the substrate 4 is irradiated with laser light L under a condition generating multiphoton absorption while using the rear face 21 as a laser light entrance surface and locating a converging point P within the substrate 4. At the same time, the mount table is shifted, so as to move the laser light L relative to the object 1 along the lines to cut 5.
The relative movement of the laser light L along the lines to cut 5 is performed six times for each line to cut 5 with respective different distances from the rear face 21 to the converging point P, so that one row of a quality modified region (second modified region) 71, three rows of divided modified regions (first modified regions) 72, and two rows of HC (half cut) modified regions (third modified regions) 73 are formed row by row along the line to cut 5 within the substrate 4 successively from the front face 3 side. Each of the modified regions 71, 72, 73 is a molten processed region since the substrate 4 is a semiconductor substrate made of silicon, but may include cracks.
When forming the quality modified region 71 and HC modified regions 73, the rate at which the laser light L is moved relative to the object 1 along the line to cut 5 (hereinafter simply referred to as “moving rate of laser light L”) is 300 mm/sec. When forming the divided modified regions 72, in contrast, the moving rate of laser light L is 600 mm/sec. The repetition frequency of the light source for the laser light L is fixed at 80 kHz.
Consequently, as shown in FIG. 22, the forming interval in the divided modified regions 72 formed by pulsed irradiation with the laser light L is greater than the forming interval in the quality modified region 71 and HC modified regions 73 formed by pulsed irradiation with the laser light L. Namely, the forming density of the divided modified regions 72 is lower than that of the quality modified region 71 and that of the HC modified regions 73.
When forming the quality modified region 71, one row of the quality modified region 71 is formed such that the distance from the front face 3 of the substrate 4 to the front-side end part 71 a of the quality modified region 71 becomes 5 μm to 20 μm. When forming the divided modified regions 72, three rows of the divided modified regions 72 are formed in series in the thickness direction of the substrate 4. When forming the HC modified regions 73, two rows of the HC modified regions 73 are formed as shown in FIG. 19( b), so as to generate a fracture 24 along the line to cut 5 from the HC modified regions 73 to the rear face 21 of the substrate 4. (Depending on the forming condition, the fracture 24 may also occur between the divided modified region 72 and HC modified region 73 that are adjacent to each other.)
After forming the modified regions 71, 72, 73, an expandable tape 23 is attached to the rear face 21 of the substrate 4 of the object 1 as shown in FIG. 20( a). Subsequently, the protective tape 22 is irradiated with UV rays as shown in FIG. 20( b), so as to lower its adhesive force, and the protective tape 22 is peeled off from the multilayer part 16 of the object 1 as shown in FIG. 21( a).
After peeling off the protective tape 22, the expandable tape 23 is expanded as shown in FIG. 21( b), so as to generate fractures from the modified regions 71, 72, 73 acting as start points, thereby cutting the object 1 into the functional devices 15 along the lines to cut 5 and separating thus cut semiconductor chips 25 from each other.
As explained in the foregoing, the moving rate of laser light L (600 mm/sec) at the time of forming the divided modified regions 72 is faster than the moving rate of laser light L (300 mm/sec) at the time of forming the quality modified region 71 and HC modified regions 73 in the above-mentioned laser processing method. Consequently, the forming density of the divided modified regions 72 is lower than that of the quality modified region 71 and that of the HC modified regions 73. This can reduce the time required for forming all the modified regions 71, 72, 73 for one line to cut 5 as compared with the case where the forming density of the divided modified regions 72 is equal to that of the quality modified region 71 and that of the HC modified regions 73.
Specifically, while it took about 1.0 sec to form all the modified regions 71, 72, 73 for one line to cut 5 when the moving rate of laser light L was fixed at 300 mm/sec, the above-mentioned laser processing method required only about 0.5 sec. While it took about 342 sec to form all the modified regions 71, 72, 73 within the substrate 4 when the moving rate of laser light L was fixed at 300 mm/sec, the above-mentioned laser processing method required only about 256.5 sec.
Meanwhile, the quality modified region 71 and HC modified regions 73 are more influential on the cutting quality of the object 1 than are the divided modified regions 72. The multilayer part 16 formed on the front face 3 of the substrate 4 can be cut accurately along the line to cut 5 together with the substrate 4 when the quality modified region 71 is formed such that the distance from the front-side end part 71 a of the modified region 71 to the front face 3 of the substrate 4 is 5 μm to 20 μm, for example. When the HC modified regions 73 are formed such that the fractures 24 along the line to cut 5 occur from the HC modified regions 73 to the rear face 21 of the substrate 4, the fractures 24 proceed smoothly toward the front face 3 of the substrate 4 through the divided modified regions 72 and quality modified region 71 at the time of expanding the expandable tape 23, for example, whereby the object 1 can be cut accurately along the line to cut 5.
Since the forming density of the quality modified region 71 and HC modified regions 73, which are more influential on the cutting quality of the object 1, is higher than that of the divided modified regions 72 in the above-mentioned laser processing method, the cutting quality of the object 1 can be prevented from deteriorating.
Since the modified regions 71, 72, 73 are formed row by row successively from the side remote from the rear face 21 of the substrate 4 in the above-mentioned laser processing method, no modified region exists between the rear face 21 acting as the laser light entrance surface and the converging point P of laser light L when forming each of the modified regions 71, 72, 73. Therefore, the laser light L is prevented from being scattered, absorbed, and so forth by modified regions which have already been formed. Hence, the modified regions 71, 72, 73 can be formed accurately within the substrate 4 along the line to cut 5.
Since the rear face 21 of the substrate 4 is used as the laser light entrance surface, the above-mentioned laser processing method can reliably form the modified regions 71, 72, 73 within the substrate 4 along the lines to cut 5 even if a member (e.g., TEG) reflecting the laser light L exists on the line to cut 5 in the multilayer part 16.
In the semiconductor chips 25 cut by using the foregoing laser processing method, cut sections (side faces) 4 a of the substrate 4 formed with the modified regions 71, 72, 73 and cut sections 16 a of the multilayer part 16 become high-precision cut sections in which irregularities are suppressed as shown in FIG. 21( b).
The second embodiment of the present invention will now be explained. The laser processing method of the second embodiment differs from that of the first embodiment in that its laser light entrance surface is the front face 3 of the substrate 4 instead of the rear face 21 of the substrate 4.
Namely, as shown in FIG. 23( a), the expandable tape 23 is attached to the rear face 21 of the substrate 4. Subsequently, as shown in FIG. 23( b), the object 1 is fixed onto a mount table (not depicted) of a laser processing apparatus such that the multilayer part 16 faces up.
Then, lines to cut 5 are set like grids (see broken lines in FIG. 17) so as to pass between the functional devices 15, 15 adjacent to each other, and the substrate 4 is irradiated with laser light L under a condition generating multiphoton absorption while using the rear face 21 as a laser light entrance surface and locating a converging point P within the substrate 4. At the same time, the mount table is shifted, so as to move the laser light L relative to the object 1 along the lines to cut 5.
The relative movement of the laser light L along the lines to cut 5 is performed six times for each line to cut 5 with respective different distances from the front face 3 to the converging point P, so that four rows of divided modified regions (third modified regions) 72, one row of an auxiliary HC modified region (first modified region) 74, and one row of an HC modified region (second modified region) 73 are formed row by row along the line to cut 5 within the substrate 4 successively from the rear face 21 side.
Consequently, as shown in FIG. 26, the forming interval in the auxiliary HC modified region 74 formed by pulsed irradiation with the laser light L is greater than the forming interval in the divided modified regions 72 and HC modified region 73 formed by pulsed irradiation with the laser light L. Namely, the forming density of the auxiliary HC modified region 74 is lower than that of the divided modified regions 72 and that of the HC modified region 73.
When forming the HC modified region 73, one row of the HC modified region 73 is formed such that the distance from the front face 3 of the substrate 4 to the front-side end part 73 a of the HC modified region 73 becomes 30 μm to 80 μm. Before forming the HC modified region 73, one row of the auxiliary HC modified region 74 is formed as shown in FIG. 23( b), so as to generate a fracture 24 along the line to cut 5 from the auxiliary HC modified region 74 to the front face 3 of the substrate 4. (Depending on the forming condition, the fracture 24 may also occur between the divided modified region 72 and auxiliary HC modified region 74 that are adjacent to each other.)
After forming the modified regions 72, 73, 74, the expandable tape 23 is expanded as shown in FIG. 24( a). In this state, as shown in FIG. 24( b), a knife edge 41 is pressed against the rear face 21 of the substrate 4 through the expandable tape 23 and moved in the direction of arrow B. This causes such a stress in the object 1 as to open the fractures 74, so that the fractures 24 extend toward the multilayer part 16 and divided modified regions 72, whereby the object 1 is cut along the line to cut 5.
Since the expandable tape 23 attached to the rear face 21 of the substrate 4 is in the expanded state here, the semiconductor chips 25 obtained by cutting will be separated from each other immediately after the object 1 is cut as shown in FIG. 25.
As explained in the foregoing, the moving rate of laser light L (600 mm/sec) at the time of forming the auxiliary modified region 74 is faster than the moving rate of laser light L (300 mm/sec) at the time of forming the divided modified regions 72 and HC modified region 73 in the above-mentioned laser processing method. Consequently, the forming density of the auxiliary HC modified region 74 is lower than that of the divided modified regions 72 and that of the HC modified region 73. This can reduce the time required for forming all the modified regions 72, 73, 74 for one line to cut 5 as compared with the case where the forming density of the divided modified regions 74 is equal to that of the divided modified regions 72 and that of the HC modified region 73.
Since the forming density of the auxiliary HC modified region 74 is lower than that of the HC modified region 73, the fractures 24 are hard to reach the front face 3 of the substrate 4 at the time when the auxiliary HC modified region 74 is formed. This can restrain molten reservoirs from being formed by the converging point P of laser light L located at the fractures 24 when forming the HC modified region 73. As a result, dust can be prevented from being generated by the forming of molten reservoirs at the time when cutting the object 1 along the line to cut 5.
When the HC modified region 73 is formed such that the distance between the front-side end part 73 a of the HC modified region 73 and the front face 3 of the substrate 4 becomes 30 μm to 80 μm, the straightforwardness of the fractures 24 occurring from the auxiliary HC modified region 74 to the HC modified region 73 can be improved. Further, when the HC modified region 73 is formed such that the fractures 24 along the line to cut 5 occur from the modified region 73 to the front face 3 of the substrate 4, the straightforwardness of the line to cut 5 can be improved.
For example, the number of rows of divided modified regions 72 is not limited to 3 (in the first embodiment) or 4 (in the second embodiment), but may be any number as long as fractures can proceed smoothly in the thickness direction of the substrate 4. In general, the number of rows of divided modified regions 72 decreases and increases as the substrate 4 is thinner and thicker, respectively. The divided modified regions 72 may be separated from each other as long as fractures can proceed smoothly in the thickness direction of the substrate 4. In the first embodiment, the number of rows of HC modified regions 73 may be 1 as long as the fracture 24 can reliably occur from the HC modified region 73 to the rear face 21 of the substrate 4.
Though the above-mentioned embodiments relate to cases where the multilayer part 16 is formed on the line to cut 5 in the front face 3 of the substrate 4, there are cases where no multilayer part 16 is formed on the line to cut 5 in the front face 3 of the substrate 4.
1. A laser processing method of irradiating an object to be processed comprising a substrate and a plurality of functional devices formed on a front face of the substrate with laser light while locating a converging point within the substrate, so as to form a modified region serving as a cutting start point within the substrate along a cutting line used to cut the object;
the method including the step of forming at least one row of a first modified region, at least one row of a second modified region positioned between the first modified region and the front face of the substrate, and at least one row of a third modified region positioned between the first modified region and a rear face of the substrate;
wherein a forming density per one row of the first modified region extending in a cutting line direction along the cutting line is lower than that per one row of the second modified region extending in the cutting line direction and that per one row of the third modified region extending in the cutting line direction.
2. A laser processing method according to claim 1, wherein, when irradiating the substrate with the laser light while using the rear face of the substrate as a laser light entrance surface and locating the converging point within the substrate, the second modified region is formed such that an end part on the front face side of the second modified region and the front face of the second modified region are separated from each other by a distance of 5 μm to 20 μm.
4. A laser processing method according to claim 1, wherein, when irradiating the substrate with the laser light while using the front face of the substrate as a laser light entrance surface and locating the converging point within the substrate, the second modified region is formed such that an end part on the front face side of the second modified region and the front face of the second modified region are separated from each other by a distance of 30 μm to 80 μm.
8. A laser processing method of irradiating an object to be processed comprising a substrate and a plurality of functional devices formed on a front face of the substrate with laser light while locating a converging point within the substrate, so as to form a modified region serving as a cutting start point within the substrate along a cutting line used to cut the object;
wherein, when forming a row of the first modified region extending in a cutting line direction along the cutting line, the laser light is moved relative to the object along the cutting line at a rate faster than that at the time of forming a row of the second modified region extending in the cutting line direction and that at the time of forming a row of the third modified region extending in the cutting line direction.
9. A laser processing method of irradiating an object to be processed comprising a substrate and a plurality of functional devices formed on a front face of the substrate with laser light while locating a converging point within the substrate, so as to form a modified region serving as a cutting start point within the substrate along a cutting line used to cut the object;
the method including the step of forming at least three rows of modified regions extending in a cutting line direction along the cutting line;
wherein, when forming a row of a modified region extending in a the cutting line direction from among modified regions positioned between a modified region closest to the front face of the substrate and a modified region closest to the rear face of the substrate, the laser light is moved relative to the object along the cutting line at a rate faster than that at the time of forming a row of the modified region extending in the cutting line direction located closest to the front face of the substrate and that at the time of forming a row of the modified region extending in the cutting line direction located closest to the rear face of the substrate.
US12/159,338 2005-12-27 2006-12-26 Laser beam machining method and semiconductor chip Active 2029-03-05 US8389384B2 (en)
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EP2070635A1 (en) 2009-06-17 Laser processing method
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:SAKAMOTO, TAKESHI;MURAMATSU, KENICHI;REEL/FRAME:022224/0741;SIGNING DATES FROM 20080701 TO 20080707
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:SAKAMOTO, TAKESHI;MURAMATSU, KENICHI;SIGNING DATES FROM 20080701 TO 20080707;REEL/FRAME:022224/0741