Laser processing methods and laser processing systems

Abstract

Laser processing processes, the steps include: Irradiating a planar object (1) to be processed with laser light (L) with a first pulse waveform, while a convergence point (P) within the object (1) is localized at a first position separated by a first distance in a thickness direction of the object (1) from a laser light entry surface of the object (1) in order to form a first modified region (131) such that it becomes a cutting start point within the object (1) along a line (5) for cutting the object (1); Irradiating the object (1) with laser light (L) with a second pulse waveform, while a convergence point (P) within the object (1) is localized at a second position separated from the laser light entry surface by a second distance in the thickness direction of the object (1) in order to form a second modified region (132) such that it becomes a cutting start point within the object (1) along the line (5) to be cut, where the impulse waveform describes a relationship between impulse intensity and time, and wherein a degree of distortion of the first impulse waveform and a degree of distortion of the second impulse waveform differ from each other, and at least one of the first impulse waveform and the second impulse waveform has a peak position with a leading or lagging impulse waveform relative to a standard impulse waveform.

Description

Technical field

[0001] The present invention relates to a laser processing method and a laser processing device for cutting a planar object to be processed along a line to be cut. State of the art

[0002] A conventional technique known in the above-mentioned field is a semiconductor wafer splitting method comprising the steps of irradiating a semiconductor wafer with laser light, which is transmissible through the semiconductor wafer, along a line to be split, in order to form a modified layer in the semiconductor wafer along the line to be split; and then stretching a stretchable protective band, which is adhered to a surface of the semiconductor wafer, in order to split the semiconductor wafer along the modified layer (see, for example, patent document 1).

[0003] Patent document 1: Published Japanese patent application JP 2005-129607A

[0004] JP 2006-35 710 A discloses a laser cutting method based on the formation of a modified region within an object at the beam focus of a first laser beam. Subsequently, the object is cut by focusing a second high-energy laser beam into the modified region. The pulse characteristics of the second laser beam differ from those of the first laser beam. Irradiation with the second laser beam induces mechanical stresses in the modified region, so that the object is cut by utilizing these stresses while still being irradiated with the second laser beam.

[0005] DE 10 2005 047 124 A1 discloses a laser beam processing machine comprising path distribution means for alternately distributing a pulsed laser beam, which is oscillated by pulsed laser beam oscillation means, to a first path and a second path, and wherein a laser beam which passes through one of the paths and is converged by a converging lens, and the other laser beam which passes through the other path and is converged by the converging lens, are alternately applied or applied at different focal points which have been displaced from each other in the direction of the optical axis, with a time delay between them.

[0006] US Patent 2005 / 0226287A1 discloses a femtosecond laser-based laser processing system comprising a femtosecond laser, frequency conversion optics, beam manipulation optics, target motion control, processing chamber, diagnostic systems and system control modules, wherein the femtosecond laser-based laser processing system enables the use of thermal control in micromachining, and the system features greater output beam stability, a continuously adjustable repetition rate and temporal beam shaping capabilities.

[0007] US Patent 2005 / 0202596A1 discloses a laser processing method that can cut objects with various laminate structures with high precision, wherein an object to be processed, comprising a substrate and a laminate part arranged on the front of the substrate, is irradiated with laser light, while a light conversion point is positioned at least within the substrate to form a modified area due to multiphoton absorption at least within the substrate and to cause the modified area to form a starting point area for cutting, wherein when the object is cut along the starting point area, the object can be cut with high precision. Disclosure of the invention Problem to be solved by the invention

[0008] However, there are different types of planar objects to be machined, which differ in terms of shape, structure, material, crystal orientation, and the like, so that there are cases where modified regions that differ in their types (size, ease of generating fractures, and the like) should be formed in a single object to be machined in order to cut the object precisely along the line to be cut.

[0009] In view of such circumstances, it is an object of the present invention to provide a laser processing method and a laser processing device that can reliably form modified regions of different types in a single object to be processed. Facilities for solving the problem

[0010] The inventors conducted thorough investigations to achieve the aforementioned goal and determined that when an object is irradiated with pulse-oscillating laser light while a convergence point is localized within the object, the temperature distribution in the vicinity of the convergence point changes according to the pulse waveform. This alters the characteristics (size, ease of fracture generation, and the like) of modified regions formed near the convergence point. This occurs because, even if the laser light can be transmitted through the object, it is more readily absorbed when the object's temperature is higher, as the absorption coefficient is temperature-dependent. Based on this finding, the inventors conducted further investigations to complete the present invention.

[0011] A laser processing method according to the present invention is defined in claim 1.

[0012] This laser processing method can reliably form the first and second modified regions, whose types differ from each other, at the first and second positions, which are separated by the first and second distances in the thickness direction of the object from the laser light entry surface of the object, along the line to be cut.

[0013] Preferably, in this laser processing method, the object is cut along the line to be cut, starting from the first and second modified regions, which act as the starting points of the cut. This allows the object to be cut precisely along the line to be cut.

[0014] Another laser processing method according to the present invention is defined in claim 3.

[0015] This laser processing method can reliably form the first and second modified regions, which differ in nature, within the object along the first and second lines to be cut, respectively. There is one case where the first and second lines to be cut intersect.

[0016] Preferably, in this laser processing method, the object is cut along the first and second lines to be cut, starting from the first and second modified regions, which act as the starting points of the cut. This allows The object must be cut precisely along the first and second lines to be cut.

[0017] A laser processing device according to the present invention is defined in claim 6.

[0018] In this laser processing device, the pulse waveform of the laser light, which is pulse-oscillated by the laser light source, can be modified by the pulse waveform modification device, thereby reliably forming modified regions of different types within a single object being processed. Effect of the invention

[0019] The present invention can reliably form modified regions, the types of which differ from one another, within a single object to be processed. Brief description of the drawings Fig. Figure 1 is a top view of an object to be processed during laser processing by a laser processing method underlying the invention; Fig. 2 is a sectional view of the object, taken along line II-II of Fig. 1 is executed; Fig.Figure 3 is a top view of the object after laser processing using the laser processing method underlying the invention; Fig. Figure 4 is a sectional view of the object, taken along line IV-IV. Fig. 3 is executed; Fig. 5 is a sectional view of the object, taken along line VV from Fig. 3 is executed; Fig. Figure 6 is a top view of the object that was cut using the laser processing method underlying the invention; Fig. Figure 7 is a graphical representation showing the relationships between the peak power density and the crack size in the laser processing method underlying the invention; Fig. Figure 8 is a sectional view of the object in a first step of the laser processing method underlying the invention; Fig.Figure 9 is a sectional view of the object in a second step of the laser processing method underlying the invention; Fig. Figure 10 is a sectional view of the object in a third step of the laser processing method underlying the invention; Fig. Figure 11 is a sectional view of the object in a fourth step of the laser processing process underlying the invention; Fig. Figure 12 is a view showing a photograph of a section of a silicon semiconductor wafer that has been cut using the laser processing method underlying the invention; Fig. Figure 13 is a graphical representation showing the relationships between the laser light wavelength and the transmission within a silicon substrate in the laser processing method according to a preferred embodiment; Fig.Figure 14 is a view to explain a principle of the laser processing process according to its execution; Fig. Figure 15 is a graphical representation showing the relationships between time and pulse intensity in the laser processing process after execution; Fig. 16 is a table showing the highest temperature reached and the range exceeding the melting point for each pulse waveform; Fig. Figure 17 is a view showing photographs of a section of a silicon semiconductor wafer cut by the laser processing method according to the execution, wherein (a) and (b) refer to cases irradiated with laser light with pulse waveforms, where α = 0.34 and α = 0.76 respectively; Fig. 18 is a top view of the object that is to be processed using the laser processing method after execution; Fig.19 is a partial sectional view taken along the XIX-XIX line from Fig. 18 is executed; Fig. Figure 20 is a partial sectional view of the object to explain the laser processing procedure after execution and represents a state in which a stretchable band is attached to the object; Fig. Figure 21 is a partial sectional view of the object to explain the laser processing procedure after execution and represents a first state of irradiating the object with laser light; Fig. Figure 22 is a partial sectional view of the object to explain the laser processing procedure after execution and represents a second state of irradiating the object with laser light; Fig. Figure 23 is a partial sectional view of the object to explain the laser processing procedure after execution and represents a state in which the stretchable band is stretched; Fig.Figure 24 is a partial sectional view of the object to explain the laser processing process after execution and represents a state in which the object has been cut into semiconductor chips; Fig. 25 is a partial sectional view taken along line XXV-XXV of Fig. 22 is executed; and Fig. Figure 26 is a schematic representation showing the laser processing device according to one embodiment. Explanations of reference symbols

[0020] 1 ... object to be processed; 3 ... front surface; 5, 51, 52 ... line to be cut; 7 ... modified region; 11, 111, 112 ... silicon semiconductor wafer; 11a ... laser light entry surface; 13, 131, 132 ... molten processed region; 21 ... back surface; L ... laser light; P ... convergence point. Best ways of implementing the invention

[0021] Preferred embodiments of the present invention are explained in detail below with reference to the drawings. In the laser processing method according to the embodiment, a phenomenon known as multiphoton absorption also contributes to the formation of a modified region within an object to be processed. Therefore, a laser processing method for forming a modified region using multiphoton absorption is explained first.

[0022] A material becomes transparent when its absorption band gap E G is greater than the photon energy hv. Consequently, one condition under which absorption occurs in the material is hv > E G However, even if the material is optically transparent, it still produces absorption under a condition where nhv > E. G(where n = 2, 3, 4, ...), when the intensity of laser light becomes very high. This phenomenon is known as multiphoton absorption. For pulsed waves, the intensity of laser light is determined by the peak power density (W / cm²). 2 ) of laser light at its convergence point. Multiphoton absorption occurs under a condition where the peak power density is, for example, 1 × 10 8 (W / cm 2 ) or greater. The peak power density is determined by (energy of laser light at the convergence point per pulse) / ( beam spot cross-sectional area of ​​laser light × pulse width). For continuous wave lasers, the intensity of laser light is determined by the field intensity (W / cm²). 2 ) of laser light at the convergence point.

[0023] The principle of the laser processing method according to the execution using such multiphoton absorption is described with reference to the Fig. 1 to 6 explained. As in Fig.As shown in Figure 1, a cutting line 5 exists on a front surface 3 of a semiconductor disk-shaped (planar) object 1 to be processed. The cutting line 5 is a virtual line that extends straight. As shown in Fig. As shown in Figure 2, the laser processing method according to this embodiment irradiates object 1 with laser light L while a convergence point P is localized within it, under conditions of generating multiphoton absorption to form a modified region 7. The convergence point P is a position at which laser light L converges. The line 5 to be cut can be curved instead of straight and can be a line actually drawn on object 1, without being limited to the virtual line.

[0024] Then the laser light L is moved relatively along the line 5 to be cut (i.e. in the direction of arrow A in Fig.1) to shift the point of convergence P along the line 5 to be intersected. Consequently, as in the Fig. As shown in Figures 3 to 5, the modified region 7 is formed along the line 5 to be cut within object 1 and becomes a starting point region for cutting 8. The starting point region for cutting 8 refers to a region that becomes a starting point for cutting (fracture formation) when object 1 is cut. The starting point region for cutting 8 can be created by forming the modified region 7 either continuously or intermittently.

[0025] In the laser processing method according to this design, the front surface 3 of the object 1 hardly absorbs the laser light L and does not melt.

[0026] Forming the starting point region for cutting 8 within object 1 makes it easier to create breaks starting from the starting point region for cutting 8, which acts as a starting point, thus allowing object 1 to be cut with a relatively small force, as in Fig. 6 shown. Therefore, object 1 can be cut with high accuracy without creating unnecessary breaks on the front surface 3 of object 1.

[0027] There appear to be two ways to cut object 1 starting from the initial cutting point region 8, which acts as a starting point. One is to apply an artificial force to object 1 after the initial cutting point region 8 has been formed, causing object 1 to break from this region, thus cutting it. This is the cutting method used when object 1 has a significant thickness, for example. Applying an artificial force refers to exerting a bending or shearing stress on object 1 along the initial cutting point region 8, or generating a thermal stress, for example, by applying a temperature difference to object 1.The other effect is that forming the starting point region for cutting 8 allows the object 1 to break naturally in its cross-sectional direction (thickness direction) starting from the starting point region for cutting 8, which acts as a starting point, in order to cut the object 1. This is possible if the starting point region for cutting 8 is formed by a row of the modified region 7 when the object 1 has a small thickness, or if the starting point region for cutting 8 is formed by a multitude of rows of the modified region 7 in the thickness direction when the object 1 has a large thickness.Even in this case of natural fracturing, fractures in a section corresponding to an area not formed with the starting point region for cutting 8 in the part to be cut do not extend to the front surface 3, so that only the section corresponding to the area formed with the starting point region for cutting 8 can be cleaved, thus allowing good control of the cleavage. Such a cleavage method with favorable controllability is very effective, since the object 1, like a silicon semiconductor wafer, has recently been able to reduce its thickness.

[0028] The modified region in the laser processing procedure after execution includes the following cases (1) to (3): (1) Case where the modified region is a crack region containing one or more cracks

[0029] An object to be processed (e.g., glass or a piezoelectric material made of LiTaO3) is illuminated with laser light under a condition with a field intensity of at least 1 × 10 while a convergence point is localized within it. 8 (W / cm 2 The object is irradiated at the convergence point with a pulse width of 1 µs or less. This pulse width is a condition under which a crack region can form solely within the object while generating multiphoton absorption, without causing unnecessary damage to the object's front surface. This creates a phenomenon of optical damage due to multiphoton absorption within the object. This optical damage induces thermal distortion within the object, thereby forming a crack region. The upper limit of the field intensity is, for example, 1 × 10⁻⁶. 12 (W / cm 2The pulse width is preferably, for example, 1 ns to 200 ns. The formation 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 to 28.

[0030] The inventors determined the relationship between field intensity and crack size through an experiment. The following are the conditions of the experiment. (A) Object to be processed: Pyrex (registered trademark) glass (with a thickness of 700 µm) (B) Laser Light source: Semiconductor laser, pumping Nd:YAG laser Wavelength: 1064 nm Laser light spot cross-sectional area: 3.14 x 10 -8 cm 2 Oscillation mode: Q-switched pulse Repetition frequency: 100 kHz Pulse width: 30 ns Output: Output < 1 mJ / pulse Laser light quality: TEM 00 Polarization property: linear polarization (C) Condenser lens transmission at a laser light wavelength: 60% (D) Movement speed of the mounting table that attaches the object: 100mm / sec.

[0031] The laser light quality TEM 00 This means that the convergence characteristic is so high that convergence to approximately the wavelength of laser light is possible.

[0032] Fig.Figure 7 is a graphical representation showing the results of the aforementioned experiment. The abscissa represents the peak power density. Since the laser light is pulsed, the field intensity is represented by the peak power density. The ordinate shows the size of a crack segment (crackle) formed within the object by a pulse of laser light. Crack segments cluster together to form a crack region. The crack segment size is the size of the segment that exhibits the maximum length among crack segment shapes. Data represented by black circles in the graphical representation pertain to a case where the condenser lens (C) has a 100x magnification and a numerical aperture (NA) of 0.80.On the other hand, data represented by white circles in the graphical representation refer to a case where the condenser lens (C) has a 50x magnification and a numerical aperture (NA) of 0.55. The appearance of cracks within the object can be seen from the time when the peak power density is approximately 10. 11 (W / cm 2 ) is, and these become larger as the peak power density increases.

[0033] A mechanism by which the object to be processed is cut by forming a crack region is now described with reference to the Fig. 8 to 11 explained. As in Fig.As shown in Figure 8, while the convergence point P is localized within object 1, object 1 is irradiated with laser light L under a condition where multiphoton absorption occurs, in order to form a crack region 9 within it along a line to be cut. The crack region 9 is a region containing one or more cracks. The crack region 9 thus formed becomes a starting point region for cutting. A crack grows from the crack region 9, which acts as a starting point (i.e., from the starting point region for cutting, which acts as a starting point), as shown in Figure 8. Fig. 9 shown, continues and reaches the front surface 3 and the rear surface 21 of object 1, as in Fig. 10 shows how object 1 breaks and is consequently cut, as in Fig.Figure 11 shows the crack that reaches the front surface 3 and the back surface 21 of object 1, either naturally or when a force is applied to object 1. (2) Case where the modified region is a molten machined region

[0034] An object to be processed (e.g., semiconductor material such as silicon) is illuminated with laser light under a condition with a field intensity of at least 1 × 10⁻⁶ while a convergence point is located within the object. 8 (W / cm 2The object is irradiated at the convergence point with a pulse width of 1 µs or less. As a result, the interior of the object is locally heated by multiphoton absorption. This heating forms a molten processed region within the object. The molten processed region includes regions that are once melted and then resolidify, regions that are merely in a molten state, and regions that are in the process of resolidifying from the molten state. It can also be described as a region whose phase has changed or whose crystal structure has changed. Furthermore, the molten processed region can be described as a region where a particular structure changes to another structure among monocrystalline, amorphous, and polycrystalline structures.For example, this means a region that has changed from a monocrystalline to an amorphous structure, a region that has changed from a monocrystalline to a polycrystalline structure, or a region that has changed from a monocrystalline structure to a structure containing both amorphous and polycrystalline structures. If the object being processed has a monocrystalline silicon structure, the molten processed region would be, for example, an amorphous silicon structure. The upper limit of the field intensity is, for example, 1 × 10⁻⁶. 12 (W / cm 2 The pulse width is preferably, for example, 1 ns to 200 ns.

[0035] Through an experiment, the inventors demonstrated that a molten, machined region was formed within a silicon semiconductor wafer. The following are the conditions of the experiment. (A) Object to be processed: Silicon semiconductor wafer (with a thickness of 350 µm and an outer diameter of 4 inches) (B) Laser Light source: Semiconductor laser, pumping Nd:YAG laser Wavelength: 1064 nm Laser light spot cross-sectional area: 3.14 × 10 -8 cm 2 Oscillation mode: Q-switched pulse Repetition frequency: 100 kHz Pulse width: 30 ns Output: 20 µJ / pulse Laser light quality: TEM 00 Polarization property: linear polarization (C) Condenser lens Magnification: 50x NA: 0.55 Transmission at a laser light wavelength: 60% (D) Movement speed of the mounting table that attaches the object: 100 mm / sec.

[0036] Fig.Figure 12 is a view showing a photograph of a cross-section of a portion of a silicon semiconductor wafer cut by laser processing under the aforementioned conditions. A molten processed region 13 is formed within the silicon semiconductor wafer 11. The molten processed region 13, formed under the aforementioned conditions, has a thickness of approximately 100 µm.

[0037] The fact that the molten processed region 13 is formed by multiphoton absorption is now explained. Fig.Figure 13 is a graphical representation showing the relationships between the laser wavelength and the transmission within the silicon substrate. Here, the respective reflected components on the front and back surfaces of the silicon substrate have been eliminated to show only the internal transmission. The relationships are shown for silicon substrate thicknesses t of 50 µm, 100 µm, 200 µm, 500 µm, and 1000 µm.

[0038] For example, at an Nd:YAG laser wavelength of 1064 nm, the laser light appears to pass through the silicon substrate by at least 80% when the silicon substrate has a thickness of 500 µm or less. Since the in Fig.Since the silicon semiconductor wafer 11 shown in Figure 12 has a thickness of 350 µm, the molten machined region 13, which is caused by multiphoton absorption, is formed near the center of the silicon semiconductor wafer 11, i.e., in a portion located 175 µm from the front surface. The transmission in this case is 90% or more with respect to a silicon semiconductor wafer with a thickness of 200 µm, meaning that the laser light is only minimally absorbed within the silicon semiconductor wafer 11 but is essentially transmitted through it. This indicates that the molten machined region 13 is formed by multiphoton absorption. The formation of a molten processed region by multiphoton absorption is disclosed, for example, in “Ultrashort Pulse Laser Microprocessing of Silicon”, Preprints of the National Meetings of Japan Welding Society, Vol. 66 (April 2000), pp. 72-73.

[0039] A fracture is created in a silicon semiconductor wafer, originating from a cutting point region formed by a molten, machined area that acts as the starting point. The fracture propagates in a cross-sectional direction, reaching the front and back surfaces of the silicon semiconductor wafer, thus cutting the wafer. The fracture, which reaches the front and back surfaces of the silicon semiconductor wafer, can grow naturally or can grow when a force is applied to the silicon semiconductor wafer.The fracture, which naturally propagates from the initial cutting point region to the front and back surfaces of the silicon semiconductor wafer, encompasses a case where the fracture grows from a state in which the molten machined region forming the initial cutting point region is molten, and a case where the fracture grows as the molten machined region forming the initial cutting point region solidifies from the molten state. In both cases, the molten machined region is formed only within the silicon semiconductor wafer and is therefore present after cutting only within the cut section, as shown in [reference]. Fig.Figure 12 shows that if a starting point region for cutting is formed in this way by a molten machined region within the object, unnecessary fractures deviating from a starting point region for a cutting line can occur more difficult at the time of splitting, thus simplifying splitting control. The molten machined region is formed not only by multiphoton absorption but also by other absorbing effects. (3) Case where the modified region is a refractive index change region

[0040] An object to be processed (e.g., glass) is illuminated with laser light under a condition with a field intensity of at least 1 x 10 while a convergence point is located within the object. 8 (W / cm 2The object is irradiated at the convergence point with a pulse width of 1 ns or less. If multiphoton absorption is generated within the object with a very short pulse width, the energy caused by multiphoton absorption is not converted into thermal energy, thus inducing a continuous structural change within the object, such as ion valence change, crystallization, or orientational polarization, thereby forming a refractive index change region. The upper limit of the field intensity is, for example, 1 x 10⁻⁶. 12 (W / cm 2 The pulse width is, for example, preferably 1 ns or less, more preferably 1 ps or less. The formation of a refractive index change region by multiphoton absorption is disclosed, for example, in "Forming of Photoinduced Structure within Glass by Femtosecond Laser Irradiation", Proceedings of the 42nd Laser Materials Processing Conference (November 1997), pp. 105 to 111.

[0041] Even if cases (1) to (3) above are explained as modified regions, the formation of starting point regions for cutting as follows, taking into account the crystal structure of a semiconductor disk-like object to be processed, its cleavage characteristics and the like, makes it possible to cut the object with less force and favorable accuracy starting from the starting point regions for cutting.

[0042] The laser processing method will now be explained after it has been carried out.

[0043] When the laser light L, which can be transmitted through the silicon semiconductor disk 11, is pulse-oscillated under the conditions set forth in the aforementioned “(2) case where the modified region is a molten machined region,” while the convergence point P is localized within the silicon semiconductor disk 11, a high temperature is locally reached at the convergence point P. The absorption coefficient is temperature-dependent and thus increases at the convergence point P, causing the laser light L to begin to be absorbed. This reduces the laser light L that travels to the opposite side of the convergence point P from the laser light entry surface 11a of the silicon semiconductor disk 11, causing the portion on the laser light entry surface 11a side of the convergence point P to locally reach a high temperature along the optical axis Z of the laser light L.As a consequence, the temperature-dependent absorption coefficient in this part increases, causing the laser light L to be absorbed. This raises the temperature in this part above its melting point, thus forming the molten processed region 13. The molten processed region is formed not only by the multiphoton absorption of the laser light L, but also by the absorption of laser light L resulting from the temperature dependence of the absorption coefficient. In actual processing, phenomena such as processing with laser light absorption due to the temperature dependence of the absorption coefficient and processing with multiphoton absorption are assumed to overlap. This occurs when a semiconductor material, such as silicon, is irradiated with laser light under a field intensity of at least 1 x 10⁻⁶. 8 (W / cm 2) at the convergence point P therein and a pulse width of 1 µs or less, a modified region containing a molten machined region can be formed as set out in the aforementioned “(2) case where the modified region is a molten machined region”.

[0044] The length R in the optical axis Z-direction of the portion where the temperature exceeds the melting point due to the absorption of laser light L is referred to as the "melting point exceeding the melting point region". A waveform based on a Gaussian beam profile of laser light, as shown in [reference], is used as an index for the pulse waveform of laser light L. Fig.As shown in Figure 15, if α is the degree of deformation of the Gaussian jet profile, then α = 1 in the Gaussian jet profile. If α is less than 1, the resulting jet profile has a leading tip position compared to the case where α = 1. If α is greater than 1, the resulting jet profile has a lagging tip position compared to the case where α = 1.

[0045] As in the Fig. 15 and Fig.As shown in Figure 16, when the silicon semiconductor disk 11 was irradiated with laser light L using pulse waveforms where α = 0.1, α = 1.0, and α = 1.9, the highest temperatures reached in the vicinity of the convergence point P were 14,500 K, 17,000 K, and 9,900 K, respectively, while the regions exceeding the melting point extended by 28.0 µm, 27.5 µm, and 27.0 µm. The laser irradiation conditions were a sampling rate of 300 mm / s, a repetition frequency of 80 kHz, a pulse width of 150 nm, and a pulse energy of 6.5 µJ. Although these values ​​were determined by simulations, multiphoton absorption phenomena are difficult to reproduce in simulation results and are therefore not considered here. Therefore, the actual processing is not limited by the aforementioned values.

[0046] In general, the highest temperature reached in the vicinity of the convergence point P is higher when irradiated with laser light with a pulse waveform where 0.7 ≤ α ≤ 1.3 (hereinafter referred to as the "standard pulse waveform") than with a pulse waveform where α < 0.7 (hereinafter referred to as the "leading pulse waveform") or a pulse waveform where α > 1.3 (hereinafter referred to as the "lagging pulse waveform"). This results in a steeper temperature gradient for the surroundings, so that a long fracture in the thickness direction of the silicon semiconductor wafer 11 originating from the molten machined region 13 can more easily occur.

[0047] On the other hand, the area exceeding the melting point is larger when irradiated with the laser light L using the led pulse waveform than with the standard pulse waveform or the delayed pulse waveform. This increases the size of the molten processed region 13 (in particular, the size in the thickness direction of the silicon semiconductor wafer 11).

[0048] In contrast, the highest temperature reached in the vicinity of the convergence point P is lower when the area exceeding the melting point is smaller when irradiated with laser light L using the delayed pulse waveform compared to the standard pulse waveform or the led pulse waveform. This makes it more difficult to create fractures in the thickness direction of the silicon semiconductor wafer 11 starting from the molten processed region 13 and to reduce the size of the molten processed region 13.

[0049] Fig.Figure 17 is a view showing photographs of a section of the silicon semiconductor wafer 11 cut by the laser processing method after execution, where (a) and (b) refer to cases irradiated with laser light L with pulse waveforms, where α = 0.34 and α = 0.76, respectively. It is evident that the size of the molten processed region 13 is larger when irradiated with laser light L with the pulse waveform where α = 0.34 (i.e., led pulse waveform) ((a) in the drawing) than when irradiated with the pulse waveform where α = 0.76 (i.e., standard pulse waveform) ((b) in the drawing). It is also evident that when irradiated with laser light L with the pulse waveform where α = 0.76 (i.e.,Standard pulse waveform) ((b) in the drawing) longer breaks 24 in the thickness direction of the silicon semiconductor wafer 11 starting from the molten machined region 13 occur than in the pulse waveform where α = 0.34 (i.e., led pulse waveform) ((a) in the drawing).

[0050] The cutting of the planar object 1 using the laser processing method will now be explained.

[0051] As in the Fig. 18 and Fig.As shown in Figure 19, the object 1 comprises a silicon semiconductor wafer 111 with a thickness of 100 µm, a silicon semiconductor wafer 112 with a thickness of 50 µm, which is placed on the silicon semiconductor wafer 111, and a functional device layer 16 formed on the silicon semiconductor wafer 112 and containing a plurality of functional devices 15. A number of functional devices 15, including examples of semiconductor operating layers formed by crystal growth, light receiving devices such as laser diodes, and switching devices formed as circuits, are arranged like a matrix in directions parallel and perpendicular to an alignment flat 6 of the silicon semiconductor wafers 111, 112.

[0052] The object 1 constructed in this way is cut into the functional devices 15. First, as in Fig.20 shows a stretchable band 23 attached to the back surface 21 of the object 1 and the object 1 is attached to a mounting table (not shown) of a laser processing device such that the functional device layer 16 points upwards.

[0053] The following describes how in Fig. As shown in Figure 21, the laser light L pulse oscillates with a standard pulse waveform while the front surface 3 of the object 1 is used as the laser light entry surface and the convergence point P is located within the silicon semiconductor disk 111, and the mounting table is moved to scan the convergence point P along intersecting lines 5, which resemble grid lines (see dashed lines in Figure 21). Fig.18) are set up, which run between the adjacent functional devices 15, 15. In the silicon semiconductor disk 111, the convergence point P is scanned twice along each line 5 to be cut, while it is located at respective positions with different distances to the front surface 3, in order to form two rows of molten machined regions 131 within the silicon semiconductor disk 111 one after the other along the line 5 to be cut starting from the side of the back surface 21.

[0054] The following will be described as in Fig.Figure 22 shows that the laser light L pulse oscillates with a delayed pulse waveform while the front surface 3 of object 1 is used as the laser light entry surface and the convergence point P is located within the silicon semiconductor wafer 112, and the mounting table is moved to scan the convergence point P along the lines 5 to be cut. On the silicon semiconductor wafer 112, the convergence point P is scanned once along each line 5 to be cut, forming a series of molten machined regions 132 within the silicon semiconductor wafer 112 along the line 5 to be cut.

[0055] As in the Fig. 22 and Fig.As shown in Figure 25, the molten machined regions 131 within the silicon semiconductor wafer 111 are formed by irradiation with the laser light L with the standard pulse waveform and are thus larger in the thickness direction of the object 1 than the molten machined region 132 within the silicon semiconductor wafer 112, which is formed by irradiation with the laser light L with the delayed pulse waveform, while fractures 24 are generated in the thickness direction of the object 1. The molten machined regions 131, 132 may contain cracks mixed in.

[0056] The elastic band 23 is then stretched, as shown in Fig. 23 shown to cut the object 1 along the lines to be cut 5 starting from the melted machined regions 131, 132, which act as cutting start points, and a large number of semiconductor chips 25 obtained by cutting are separated from each other.

[0057] As explained above, the laser processing method according to this embodiment can form the molten processed regions 131, which have a larger size in the thickness direction of the object 1 and can easily generate the fractures 24 in the thickness direction of the object 1, within the silicon semiconductor disk 111 by irradiating them with the laser light L with the standard pulse waveform, and the molten processed region 132, which has a smaller size and can hardly generate the fractures 24 in the thickness direction of the object 1, can be formed within the silicon semiconductor disk 112 by irradiating them with the laser light L with the delayed pulse waveform.If the pulse waveform of the laser light L is modified in this way according to the structure of object 1 and the like, in order to form the molten machined regions 131, 132 of different types within object 1, the object 1 can be cut precisely along the lines 5 to be cut starting from the molten machined regions 131, 132, which act as cutting start points.

[0058] If the object 1 contains a silicon semiconductor disk 113 with a thickness of 120 µm, it can be irradiated with the laser light L with a pre-leaded waveform to form a molten machined region 133 of an even larger size in the thickness direction of the object 1 within the silicon semiconductor disk 113, thereby enabling the object 1 to be cut precisely along the lines 5 to be cut.

[0059] The laser processing device will now be explained in detail.

[0060] As in Fig. As shown in Figure 26, the laser processing device 100, which forms the modified region 7 such that it becomes a cutting start point within the planar object 1, comprises a laser light source 101 for pulse oscillation of the laser light L, a laser light source control device 102 for controlling the laser light 101 to regulate the output, pulse width and similar properties of the laser light L, a cold light mirror 103 which operates to reflect the laser light L and is arranged to change the direction of the optical axis of the laser light L by 90°, and a condenser lens 105 which converges the laser light reflected by the cold light mirror 103 into the object 1 and forms the modified region 7 at the convergence point P of the laser light L.

[0061] The laser processing device 100 further comprises a mounting table 107 for mounting the object 1, which is irradiated with the laser light L converged by the condenser lens 105; an X-axis stage 109 for moving the mounting table 107 along the X-axis; a Y-axis stage 111 for moving the mounting table 107 along the Y-axis orthogonal to the X-axis; and a Z-axis stage 113 for moving the mounting table 107 along the Z-axis orthogonal to the X- and Y-axes; and a stage control device 115 for controlling movements of the three stages 109, 111, 113.

[0062] Moving the convergence point P along the X(Y) axis is accomplished by causing the X(Y) axis stage 109 (111) to move the object 1 along the X(Y) axis. The Z-axis is orthogonal to the front surface 3 of the object 1 and is thus a direction of the focal length of the laser light L incident on the object 1. Therefore, moving the Z-axis stage 113 along the Z-axis can locate the convergence point P of the laser light L at a desirable position within the object 1.

[0063] Laser light source 101 is an Nd:YAG laser that produces pulsed laser light. Other examples of lasers that can be used with laser light source 101 include Nd:YVO4, Nd:YLF, and titanium-sapphire lasers.

[0064] The laser processing device 100 further comprises an observation light source 117, which generates visible beams for illuminating the object 1 mounted on the mounting table 107, and a beam splitter 119, which is mounted on the same optical axis as the cold mirror 103 and the condenser lens 105, for the visible beams. The cold mirror 103 is arranged between the beam splitter 119 and the condenser lens 105. The beam splitter 119 operates to reflect approximately half of the visible beams and transmit the remaining half through it, and is arranged to change the direction of the optical axis of the visible beams by 90°.The beam splitter 119 reflects approximately half of the visible rays generated by the observation light source 117, while such reflected visible rays pass through the cold light mirror 103 and the condenser lens 105 to illuminate the front surface 3 of the object 1, which contains the lines 5 and similar features to be cut.

[0065] The laser processing device 100 further comprises an image acquisition device 121 and an imaging lens 123, which are arranged on the same optical axis as the beam splitter 119, the cold light mirror 103, and the condenser lens 105. An example of the image acquisition device 121 is a CCD camera. After illuminating the front surface 3, which contains the lines 5 and similar features to be cut, the reflected light of visible rays passes through the condenser lens 105, the cold light mirror 103, and the beam splitter 119 to be converged by the imaging lens 123. The image thus formed is then captured by the image acquisition device 121 to become imaging data.

[0066] The laser processing device 100 further comprises an image data processor 125 for inputting the image data output by the image acquisition device 121, an overall control unit 127 for controlling the laser processing device 100 as a whole, and a monitor 129. Based on the image data, the image data processor 125 calculates focus data for positioning the focal point of visible rays generated by the observation light source 129 on the front surface 3 of the object 1. Based on the focus data, the step control unit 115 controls the movement of the Z-axis step 113 to position the focal point of visible rays on the front surface 3 of the object 1. Thus, the image data processor 125 functions as an autofocus unit. The image data processor 125 calculates image data, such as magnified images of the front surface 3, based on the image data.The image data is sent to the central control unit 127 for various processing steps. The processed data is then sent to the monitor 129. As a result, enlarged images and similar content are displayed on the monitor 129.

[0067] The overall control unit 127 receives data from the step control unit 115, image data from the imaging data processor 125, and similar components, and controls the laser processing device 100 as a whole by also controlling the laser light source control unit 102, the observation light source 117, and the step control unit 115 according to this data. Thus, the overall control unit 127 operates as a single computer unit.

[0068] The laser processing device 100 further comprises a pulse waveform modification device 150 for changing the pulse waveform of the laser light L, which has been pulse-oscillated by the laser light source 101. The pulse waveform modification device 150 is, for example, constructed as follows. The pulse waveform modification device 150 has a pulse waveform modulator 151, such as an EO modulator, and a pulse waveform control device 152 for controlling the pulse waveform modulator 151 with a signal from the laser light source control device 102. For irradiation with the laser light L with the standard pulse waveform, the laser light L emitted by the laser light source 101 is transmitted through the pulse waveform modulator 151, while the pulse waveform remains unchanged.For irradiation with the laser light L with the led pulse waveform, the pulse waveform control device 152 delays the timing of the release of the pulse waveform modulator 151 relative to the laser emission start time. For irradiation with the laser light L with the delayed pulse waveform, the pulse waveform modulator 151 is released before the laser emission start time and is closed during laser pulse emission. Other methods for controlling the pulse waveform include (1) a method in which two lasers are used and superimposed with timings that are changed according to the pulse waveforms to be produced, and (2) a method that provides lasers for emitting respective pulse waveforms. Method (2) can be implemented, for example, by using Nd:YAG and Nd:YVO4 lasers for the standard waveform and the led waveform, respectively.

[0069] The laser processing device 100 constructed in this way can reliably form the modified regions 7 of different types within a single object 1, since the pulse waveform modification device 150 can change the pulse waveform of the laser light L pulse-oscillated by the laser light source 101.

[0070] The present invention is not limited to the aforementioned embodiments.

[0071] For example, even if the object 1 has a substantially fixed thickness along the lines 5 to be cut, the pulse waveform of the irradiating laser light L at the lines 5 to be cut can be changed if the thickness of the object 1 changes along the lines 5 to be cut.

[0072] If the thickness of object 1 varies between a portion extending along a line 51 to be cut and a portion extending along a line 52 to be cut, the pulse waveform of the irradiating laser light L can be modified between them to form a modified region 71 in the portion extending along line 51 to be cut and a modified region 72, whose nature differs from that of modified region 71, in the portion extending along line 52 to be cut. As a result, object 1 can be cut precisely along the lines 51 and 52 to be cut, starting from the modified regions 71 and 72, which act as the initial cutting points. The lines 51 and 52 to be cut may or may not intersect, for example, to be substantially perpendicular to each other.

[0073] If the thickness of object 1 is less than 100 µm, object 1 is preferably irradiated with laser light L with the delayed pulse waveform along the lines 5 to be cut. This enables processing without damage (melted markings) to the front surface 3 and the back surface 21 of object 1.

[0074] If the object 1 is a (111) semiconductor wafer, a (110) semiconductor wafer, a (100) semiconductor wafer rotated by 45°, or the like, in which the cleavage direction of the object 1 and the direction of the line 5 to be cut in the object 1 are not aligned, the line 5 to be cut, which is not aligned with the cleavage direction, is preferably irradiated with the laser light L with the leading pulse waveform. This increases the size of the modified region 7 (in particular the size in the thickness direction of the object 1), whereby the object 1 can be precisely cut along the line 5 to be cut against the cleavage direction.

[0075] If the object 1 is an inclined semiconductor disk or similar, where the direction of the cleavage plane of the object 1 is not aligned with its thickness direction, the object 1 is also preferably irradiated with the laser light L with the leading pulse waveform. This increases the size of the modified region 7 (in particular the size in the thickness direction of the object 1), thereby enabling the object 1 to be precisely cut in its thickness direction.

[0076] Even if the front surface 3 of object 1 is the laser light entry surface in the aforementioned embodiments, the rear surface 21 of object 1 can also be the laser light entry surface.

[0077] Even though the molten machined regions 13 are formed within the silicon semiconductor disk 11 in the aforementioned embodiments, other modified regions 7, such as crack regions and refractive index change regions, can be formed within the object 1, which is made of other materials, such as glass and dielectric materials. Commercial usability

[0078] The present invention can reliably form modified regions, the types of which differ from one another, within a single object to be processed.

Claims

Laser processing method comprising the steps of: irradiating a planar object (1) to be processed with laser light (L) with a first pulse waveform, while a convergence point (P) within the object (1) is localized at a first position separated by a first distance in a thickness direction of the object (1) from a laser light entry surface of the object (1) to form a first modified region (131) such that it becomes a cutting start point within the object (1) along a line (5) for cutting the object (1);Irradiating the object (1) with laser light (L) with a second pulse waveform, while a convergence point (P) within the object (1) is localized at a second position separated from the laser light entry surface by a second distance in the thickness direction of the object (1) to form a second modified region (132) such that it becomes a cutting start point within the object (1) along the line (5) to be cut, wherein the pulse waveform describes a relationship between a pulse intensity and time, and wherein a degree of distortion of the first pulse waveform and a degree of distortion of the second pulse waveform differ from each other, and at least one of the first pulse waveform and the second pulse waveform has a peak position with a leading or lagging pulse waveform relative to a standard pulse waveform. Laser processing method according to claim 1, wherein the object (1) is cut along the line (5) to be cut starting from the first and second modified region (131, 132) which act as cutting start points. Laser processing method comprising the steps: Irradiating a planar object (1) to be processed with laser light (L) with a first pulse waveform, while a convergence point (P) is localized within the object (1) to form a first modified region (131) such that it becomes a cutting start point within the object (1) along a first line (5) for cutting the object (1);Irradiating the object (1) with laser light (L) with a second pulse waveform, while a convergence point is localized within the object (1) to form a second modified region (132) such that it becomes a cutting start point within the object (1) along a second line (5) for cutting the object (1), wherein the pulse waveform describes a relationship between a pulse intensity and time, and wherein a degree of distortion of the first pulse waveform and a degree of distortion of the second pulse waveform differ from each other, and at least one of the first pulse waveform and the second pulse waveform has a peak position with a leading or lagging pulse waveform relative to a standard pulse waveform. Laser processing method according to claim 3, wherein the first and the second line (5) to be cut intersect each other. Laser processing method according to claim 3, wherein the object (1) is cut along the first and second line to be cut (5) starting from the first and second modified region (131,132) which act as cutting start points. Laser processing device (100) for forming a modified region (131, 132) such that it becomes a starting point for cutting within a planar object (1) to be processed, the device comprising: a mounting table (107) for mounting the object (1); a laser light source (101) for pulse oscillating laser light (L); a pulse waveform changing device (150) for changing a pulse waveform of the laser light (L) pulsed by the laser light source (101) from a first pulse waveform to a second pulse waveform;and a condenser lens (105) for converging the laser light (L) pulse-oscillated by the laser light source (101) into the object (1) mounted on the mounting table (107) and for forming the modified region (131, 132) at a convergence point (P) of the laser light (L), wherein the pulse waveform describes a relationship between a pulse intensity and time, and wherein a degree of distortion of the first pulse waveform and a degree of distortion of the second pulse waveform differ from each other, and at least one of the first pulse waveform and the second pulse waveform has a peak position with a leading or lagging pulse waveform relative to a standard pulse waveform.

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