Laser machining method and semiconductor device

Mode of execution

With the following detailed description with reference to the embodiment of the invention. The embodiment of a laser processing method, in order to the processing object by forming a modified region inside a known as multi-photon absorption phenomenon. Therefore, first note to multi-photon absorption to form a modified region of the laser processing method.

If the energy of the photon absorbed than hv of the material band gap E_G more small, the optical is transparent. Therefore, the conditions of the absorption material to produce hv>E_G. However, even if optical is transparent, if the intensity of the laser becomes very large, the material in nhv>E_G conditions (n=2, 3, 4, ...) the generation of absorption. This phenomenon is referred to as multi-photon absorption. Under the condition of the pulse wave, the intensity of the laser depends on the peak power density of the laser spot (W/cm²), for example, multi-photon absorption of the peak power density is 1 × 10⁸ (W/cm²) generated under the condition of more than. The peak power density (focal point in the laser per 1 pulse energy) ÷ (laser light beam spot cross-sectional area × pulse width) to gaining. Furthermore, in the case of continuous, the intensity of the laser depends on the electric field intensity in the focal point of the laser (W/cm²).

The use of such a multi-photon absorption of the relevant this embodiment the principle of the laser processing method, with reference to Figure 1-Figure 6 note. As shown in Figure 1, in a wafer-shaped (plate-shaped) processing the object 1 surface 3 used for cutting the object 1 of the to-be-cut line 5. Cut-off line 5 is a linearly extending an imaginary line. Related to this embodiment of the laser processing method, as shown in Figure 2, in a multi-photon absorption under the condition of producing, the focal point P aligned with the processing the object 1 L the internal laser irradiation, thereby forming a modified region 7. Furthermore, P means the focal position of laser light L. Furthermore, cut-off line 5 is not limited to the straight line shape can also be a curved linear, and is not limited to the imaginary-line can also be the processing target actual picture 1 line.

Furthermore, through making the laser L along the cut-off line 5 (i.e., to Figure 1 the direction of the-arrow A) relatively moving, the focal point P along the cut-off line 5 mobile. Therefore, as shown in Figure 3-Figure 5 is shown, the modified region 7 along the cut-off line 5 is formed on the processing object 1 internal, the regional 7 become cut off the starting point region 8. In this, the area cut off the starting point 8 means processing the object 1 is cut off when the starting point as cutting off the area of the (cutting). The cutting starting point region 8, through making the modified region 7 to form a continuous average, or, the modified region 7 formed by discontinuously formed.

The embodiment of a laser processing method is not processing the object 1 absorption laser L, so that the processing object 1 heating to form a modified region 7 of the method. The laser L through processing the object 1, in the processing the object 1 is produced in the multi-photon absorption in order to form the modified region 7. Therefore, because the processing the object 1 on the surface of the 3 laser will not be absorbed almost L, therefore, processing the object 1 surface 3 is not melted.

If in processing the object 1 is formed inside the region of the cut off the starting point 8, it is easy in order to cut off this is the starting point region 8 as a starting point a spall, so as shown in Figure 6, with a low power-cut-off processing the object 1. Therefore, in processing the object 1 surface 3 does not deviate significantly from cut-off line 5 is not necessary under the condition of the split, with high precision can be processed is cut in the object 1.

In order to cut off this regional starting point 8 as the starting point of processing the object 1 with the cutting off of the following 2 situation. 1 situation is, forms the cutting starting point for the regional 8 later, by the processing the object 1 by force is applied, the processing object 1 in order to cut off the starting point region 8 as a starting point spall, thereby the processing the object 1 of is cut off. This is, for example, processing the object 1 when the thickness of the cutting method. The so-called artificial force is applied to, for example, for processing the object 1 along the processing the object 1 cut off the starting point region of 8 applied bending stress or shearing stress, or, for processing the object 1 produced by this given temperature difference of the thermal stress. Another situation is, forms the cutting starting point region through 8, in order to cut off the starting point region 8 as the starting point for processing the object 1 in a sectional direction (thickness direction) naturally spall, the result of the processing the object 1 of is cut off. Its in, for example, processing the object 1 under the condition of a small thickness, can be made of 1 column the modified region 7 forms the cutting starting point region to 8, in the processing the object 1 under the condition of the thickness of the, can be formed on in the direction of thickness of the multi-banked the modified region 7 forms the cutting starting point region to 8. Furthermore, in the case of natural splitting, similarly, is in the cut off, spall will not go on to cut off the starting point region not formed is 8 corresponding to the part of the surface of the part 3 on, can only cut off and formed with a cut-off starting point region 8 a portion corresponding to a part of, the sever can be well controlled. In recent years, silicon wafer, etc. processing the object 1 the thickness of the thin trend of the change, therefore, the controllability good cutting method is very effective.

Furthermore, in this embodiment of the laser processing method in the related, to form by multi-photon absorption the modified region have the following (1)-(3) circumstances.

(1) the modified region containing 1 or multiple fractures situation of area of cracks

The focal point aligned with the processing object (for example, from glass or LiTaO₃ of the piezoelectric material the) internal, the electric field intensity in the spot 1 × 10⁸ (W/cm²) the above, and the pulse width is 1 the irradiating laser   s the following conditions. Is the magnitude of the width of this pulse, to produce multi-photon absorption, and the surface of the processing object without generating additional damage, a processing object can be only the inside of the area of the crack formation conditions. In this way, the inside of the processing object by the multi-photon absorption occurs is called the optics caused by the phenomenon of damage. The optical damage the inside of the processing object of the thermal strain is generated, the processing object by the formation of cracks in the region of the inside of the. The upper limit value of electric field strength, for example 1 × 10¹² (W/cm²). Pulse width is preferably, for example 1ns -200ns. Furthermore, multi-photon absorption on the crack caused by the formation of the region, for example in section 45 session of laser thermal processing cbik collection (1998 year 12 month) section 23 page-section 28 pages of "to solid laser high-harmonic to internal indicia the glass substrate".

The inventors the electric field strength is obtained through experiments the relationship between the crack size. The experimental conditions are as follows.

(A) processing the object: PYREX (registered trademark) glass (thickness of the 700  m)

(B) laser

Light source: semiconductor laser excitation Nd: YAG laser

Wavelength: 1064 nm

Sectional area of the laser point: 3.14 × 10^-8 cm²

Oscillation form: Q switch pulse

Repetition frequency: 100kHz

Pulse width: 30ns

Output: output <1mJ/pulse

Laser quality: TEM₀₀

The polarization characteristic: linear polarized light

(C) a condensing lens

The transmission of relative laser wavelength: 60%

(D) for loading of the processing object the moving speed of the load: 100 mm/sec

Furthermore, the so-called laser quality TEM₀₀, is high pollution, can be spot light to the laser wavelength of the meaning of the degree.

Figure 7 is graph of the experimental results. HAWT for peak power density, because the laser is a pulse laser, the power density of the electric field intensity to that of the crest. By the longitudinal axis of 1 pulse laser formed in the interior of the processing object (crack) crack the size of the part. Cracks become crack region set. The size of the crack, is the shape of the crack in a maximum length of the size of the part. In order to curve the data expressed by [...] , is lens the condensation uses (C) for the magnification of 100 times, the numerical aperture (NA) 0.80 situation. On the other hand, in the curve chart of the data represented by the white dot , is lens the condensation uses (C) for the magnification of 50 times, the numerical aperture (NA) to 0.55 situation. That: the inside of the processing object from the peak power density is about 10¹¹ (W/cm²) crack to produce, the greater the peak power density, is more likely to crack.

Secondly, on the use of the crack region is formed to carry out processing of the cut-off mechanism of the object, with reference to Figure 8-Figure 11 to note. As shown in Figure 8, in the multi-photon absorption occurs under the condition of, the focal point P aligned with the processing the object 1 to illuminate the inside of the laser L, thus the formation of cracks in the predetermined line along the to-be-cut area 9. Crack region 9 comprises 1 or more of the area of the cracks. The crack area so formed 9 become a starting point region is cut off. As shown in Figure 9, in order to crack crack region 9 as a starting point (i.e., in order to cut off the starting point region as a starting point) to grow further, as shown in Figure 10, the crack reaches the processing the object 1 surface 3 and the back 21, as shown in Figure 11, processing the object 1 spall, so that the processing the object 1 is cut off. Arrival for processing the object 1 surface 3 and the back 21 of the crack, the situation of the natural growth, will have to processing the object 1 of the growth of applied forces.

(2) the modified region is a fusing treatment area of the

The focal point aligned with the processing object (for example, silicon as semiconductor material of) internal, the electric field intensity in the spot 1 × 10⁸ (W/cm²) the above, the pulse width for the 1   s the following conditions to illuminate the laser. In this way, the inside of the processing object by the multi-photon absorption of the local heating. Because of the heating in the inside of the processing object forming a fusing treatment area. The so-called fusing treatment area, is molten and then solidified area, in the area of the molten state, or is in a self-molten state to begin the state of the re-solidification of the regional, can also be referred to as phase change of the area or the area of the crystalline structure changes. Furthermore, so-called fusing treatment area, in the single crystal structure, an amorphous structure, more crystalline in structure, can also be changed to a structure in the area of the structure. In other words, for example, mean from list changed into the non-crystalline structure of the area of the amorphous structure, since the single-crystal structure change the area of a plurality of crystalline structure, since the single-crystal structure comprising the amorphous structure of the crystalline structure and the area of the structure. As a processing object of the silicon single crystalline structure, fusing treatment area for example, amorphous silicon structure. The upper limit value of electric field strength, for example 1 × 10¹² (W/cm²). Pulse width is preferably, for example 1ns -200ns.

The inventors confirmed through the experiment the internal of the silicon wafer forming the melt processing region. The experimental conditions are as follows.

(A) object to be processed: silicon wafer (thickness 350 the  m, outer diameter 4 went)

(B) laser

Light source: semiconductor laser excitation Nd: YAG laser

Wavelength: 1064 nm

Sectional area of the laser point: 3.14 × 10^-8 cm²

Oscillation patterns: Q switch pulse

Repetition frequency: 100kHz

Pulse width: 30ns

Output: the 20  J/pulse

Laser quality: TEM₀₀

The polarization characteristic: linear polarized light

(C) a condensing lens

Magnification: 50 times

N.A. : 0.55

The transmission of relative laser wavelength: 60%

(D) for loading of the processing object the moving speed of the load: 100 mm/sec

Figure 12 is diagram of the above said under the condition of being severed by laser processing of the silicon wafer of a portion of the cross-sectional photograph. The silicon wafer 11 is formed inside of the fusing treatment area 13. Furthermore, the above-mentioned conditions to form the fusing treatment area 13 in the thickness direction is about the size of a on the 100  m.

Note fusing treatment area 13 formed through a plurality of photon absorption. Figure 13 is graph of the wavelength of laser said internal the silicon substrate by the relationship between the transmittance. The removal of the silicon substrate and the rear surface side of the surface side of the respective reflecting component, that only internal transmittance. Respectively the thickness of the silicon substrate for t the 50  m, the 100  m, the 200  m, the 500  m, 1000 the various   m expressed above-mentioned relationship.

For example, in Nd: YAG laser with a wavelength of 1064 nm, the thickness of the silicon substrate 500 the following situation   m, the silicon substrate can be known through the internal laser of 80% or more. The Figure 12 of the silicon wafer shown in 11 the thickness of the the 350  m, the produced by multi-photon absorption of the fusing treatment area 13 is formed on the silicon wafer 11 in the vicinity of the center, i.e., counting from the surface of a 175 of a portion where the   m. If at this moment the transmission of to the thickness is 200 the silicon wafer   m as a reference, is 90% or more, therefore, the laser almost all through, only a very few a part of the silicon wafer 11 is absorbed inside. This result implies that: in the laser is in the silicon wafer 11 is absorbed inside, fusing treatment area 13 and non-formed on the silicon wafer 11 internal (i.e., fusing treatment area is not formed by a laser caused by the heat and form of the usually), fusing treatment area 13 is formed by multi-photon absorption. Multi-photon absorption is caused by the formation of the melt processing region, for example, recorded in the whole country of Japan of the general assembly of the welding Institute lecture SUMMARY section 66 integrates (2000 years 4 months) section 72 page-section 73 pages of "using picosecond (picosecond) pulse laser silicon processing characteristic evaluation" in.

Furthermore, in order to melt processing a silicon wafer formed by the areas of the cut-off point as a starting point to the sectional direction of the area of a spall, the spall the surface and the back of the silicon wafer, the result of the silicon wafer is cut off. The surface and the back of the silicon wafer of the spall, the situation of the natural growth, there are also the silicon wafer of the growth of applied forces. Furthermore, since the splitting of the natural growth to cut off the starting point region of the silicon wafer in the case of surface and the back, and any one of the following situation: the starting point region forms the cutting splits from the melt processing region is molten state to begin growth of to; cut off the starting point region in the self-formation of the melt processing region is molten state to begin the re-solidification, the growth of the crack. However, regardless of the in the any kind of situation, fusing treatment area are formed in only the inside of the silicon wafer, after cutting off the cut-off surface, is as shown in Figure 12, only in the internally formed with a fusing treatment area. As mentioned above, if the inside of the processing object by the fusing treatment area to form the cut-off starting point region, when the cut off, it is difficult to deviate the zone line of cut off the starting point of the crack is not necessary, so the cut off control is facilitated.

(3) the modified region is the refractive index of the region of variation

The focal point aligned with the processing object (such as glass) internal, the electric field intensity in the spot 1 × 10⁸ (W/cm²) the above, and the pulse width 1ns the following conditions to illuminate the laser. When the pulse width is extremely short, the multi-photon absorption occurs in the inside of the processing object, is produced by multi-photon absorption will not change the energy of the heat energy, the inside of the object to be processed caused by ion valence state change, such as crystallization or directional polarization changes in the permanent structure, thereby forming a refractive index change region. The upper limit of electric field intensity value for example to 1 × 10¹² (W/cm²). Is preferably, for example, pulse width 1ns the following, more preferably 1ps the following. Multi-photon absorption of the refractive index change caused by the formation of the region, for example, recorded in the Japanese paragraph 42 laser thermal processing cbik theses on session (1997 years 11 month) section 105 page-section 111 pages of "use of femtosecond (femtosecond) laser irradiation to the glass inside the light-induced structure is formed".

The above, as to form by multi-photon absorption the modified region, the (1)-(3) circumstances, however, taking into account the processing of the wafer-crystalline structure of the object, and to its rational manner that it forms the cutting starting point region, the starting point can be in order to cut off this area as the starting point in order to more small strength and accurately cut off the object to be processed.

In other words, in the structure of diamonds silicon and so on of a single crystalline semiconductor by under the condition of the substrate, preferably along the (111) surface (section 1 the cleavage plane), (110) surface (section 2 cleavage plane) forms the cutting starting point in the direction of the area. Furthermore, in the structure of the GaAs sphalerite III-V group compound semiconductor by under the condition of a substrate, preferably along the (110) surface of the starting point region forms the cutting direction. Furthermore, the sapphire (Al₂ O₃) having a hexagonal crystal, such as the crystalline structure of the case of the base plate, preferably the (0001) surface as a main surface (surface C) along (1120) (A surface) face or the (1100) face in the direction of (M surface) is formed on the region cut off the starting point.

Furthermore, if the substrate should be formed on the cut off along the region of the direction of the starting point (for example, in the single crystal silicon substrate surface in the direction along (III)), or and should form a cut-off starting point region is formed on the vertical direction of the direction (orientation   flat) directional plane, through the directional plane as a reference, can be easily and correctly formed on the substrate should be forms the cutting starting point region along the direction of the area of the cut-off point.

Next, note the embodiment of the invention. Figure 14 is plan view, Figure 15 is part of the profile of this embodiment of the laser processing method of processing object along the processing object XV-XV-line shown in Figure 14.

As shown in Figure 14 and Figure 15 shows, in this embodiment, processing the object 1 has, for example, is formed by silicon thickness is 300 the substrate   m 4, and includes a plurality of function element 15 and is formed on the substrate 4 surface 3 of the laminate 16. Functional element 15 has: laminated on the substrate 4 surface 3 of the interlayer insulating film 17a, is disposed in the interlayer insulating film 17a of the wiring layer 19a, in order to cover the wiring layer 19a laminated on the interlayer insulating film 17a the interlayer insulating film 17b, and, disposed in the interlayer insulating film 17b of the wiring layer 19b. Wiring layer 19a and the base plate 4 by the penetrated through the interlayer insulating film 17a bushing (plug) 20a the conductivity of the incoming call is connected with the; wiring layer 19b and the wiring layer 19a through the interlayer insulating film by 17b conductive bushing 20b incoming call connection.

As a functional element 15, can be cited for example, is formed by crystal growth of semiconductor movement level , a light receiving element photodiode and the like, light-emitting element of the laser diode and the like, formed of a circuit element of the circuit, such as semiconductor devices.

Furthermore, a plurality of function element 15 in the base plate 4 of the directional plane 6 and a direction parallel to the vertical direction and arranged in a matrix shape is formed on; the interlayer insulating film 17a, 17b in order to cover the substrate 4 surface 3 all the way across the adjacent function element 15, 15 is formed between the.

Such as the above-mentioned the processing the object 1 by the following mode according to each functional element 15 to cut-off. First of all, as shown in Figure 16 (a) shows, the processing the object 1 so as to cover the laminate 16 way of a protective tape 22. Furthermore, as shown in Figure 16 (b) shows, the base plate 4 of the back 21 towards the above, the processing the object 1 is fixed on the laser processing apparatus (not shown) on load. At this moment, since the protective tape 22 avoids the laminate 16 directly in contact with the loading platform, the protection of the functional element can be 15.

Furthermore, in order to through adjacent functional element 15, 15 way between, the cut-off line 5 is set into a lattice shape (with reference to Figure 14 the dashed-line), to the back 21 as laser incidence plane the focal point P aligned with the base plate 4 of the internal, multiple photon absorption conditions of irradiation of the laser beams L, at the same time, the focal point P movement of the stage along the cut-off line 5 is scanned.

In this embodiment, the 1 line cut-off 5 to 6 times along the to-be-cut line 5 the focal point of the scanning of the P, and, the alignment change each scanning of the position of the focal distance of the P 21 of the distance, thus on the base plate 4 along the inside of the cutting line 5 from the surface 3 side in order in every 1 column form: 1 list of quality reformed region 71 ; 3 cut in the modified region 72 ; and, 2 of the HC (half-cutting (half   cut)) the modified region 73. The modified region 71, 72, 73 in the cut-off processing the object 1 is cut off at the time of the starting point. Furthermore, because the base plate of this embodiment 4 is composed of a semiconductor substrate of silicon, so the modified region 71, 72, 73 is a fusing treatment area. Furthermore, the modified region 71, 72, 73 and the above-mentioned the modified region 7 similarly, can be formed by continuously forming the modified region, and also can be formed by discontinuously at predetermined intervals to form the modified region is formed.

So, as each modified region 71, 72, 73 in order to distance the base plate 4 of the back 21 far in the past, the way each time to form a row, so that in forming the modified region 71, 72, 73, the, -the back of the laser incident face 21 which the focal point of the laser L does not exist between the modified region P, therefore, has been formed will not take place the modified region caused by the scattering of the laser L, adsorption, and the like. Therefore, the modified region can be 71, 72, 73 along the to-be-cut line 5 precision formed in the base plate 4 of the internal. Furthermore, the base plate 4 on the back surface of 21 as the laser incident face, even when the laminate 16 the cut-off line 5 on the part of the reflected laser L (for example, TEG) under the condition of, can also be on the base plate 4 along the inside of the line to cut reliably form 5 of the modified region 71, 72, 73.

In forming the modified region 71, 72, 73 after, as shown in Figure 17 (a) shows, in the processing the object 1 of the base plate 4 on the back surface of 21 with a expansion 23. Furthermore, as shown in Figure 17 (b) shows, the protective tape 22 illuminate the ultraviolet ray, in order to reduce the device to, and as shown in Figure 18 (a) shown in, from the processing of object 1 of the laminate 16 peeled off protective tape 22.

The protective strip 22 then, as shown in Figure 18 (b) shows, with the 23 expansion, to the modified region 71, 72, 73 as a starting point a spall, thereby the substrate 4 and laminate 16 along the cutting line 5 at the same time cut off, the cut-off of the respective semiconductor chips 25 (semiconductor device) are separated from each other.

In this, the modified region 71, 72, 73 carry out detailed description of the forming method. Figure 19 is floorplan, Figure 20 is part of the profile of said formed with the modified region 71, 72, 73 of the processing the object 1 of a part of processing the object 1 along line XX-XX shown in Figure 19.

Quality reformed region 71 through the irradiation of the laser beams L is selectively switching continuous oscillation and of pulse oscillation is formed. Oscillation of the laser L, L is, for example, by controlling the laser power supply controller (not shown) of the switches. When the oscillation of the pulse laser L, compared with the continuous oscillation of the laser L of its energy is more than the processing threshold value, can be on the base plate 4 of the modified region forming quality of the positively 71. Therefore, the laser-cut line along the L 5 RP to a desired part of the pulse oscillation, by making the laser L along its desired part of the part other than RP (predetermined portion) continuously oscillated RC, can be on the base plate 4 along the inside of the RP that is part of the modified region forming quality of the 71.

Furthermore, because the RC along the prescribed part continuously oscillated laser L, therefore, low energy does not exceed the processing threshold value, compared with the prescribed part of the RC pulse oscillation of the laser L situation, can reduce the laser L to the laminate 16 for the damage. Therefore, the cutting base plate 4 and laminate 16 time, can improve the cut-off line 5 on the RC a prescribed part of the laminate 16 cutting precision. Therefore, as shown in Figure 18 (b) shows, the use of this embodiment of the laser processing method for manufacturing the semiconductor chip 25 in, the base plate 4 (side) the cut area 4a, and laminate 16 (side) the cut area 16a become concavo-convex is inhibiting the cutting section of the high-precision.

Furthermore, in this embodiment, as shown in Figure 19 and Figure 20 shows, the metal along the M-cut line 5 a prescribed part of the laminate is RC 16 inner. RC along the prescribed part of the base plate 4 of the internal, in the above-mentioned laminate the 16 generated on the point of view of the damage, preferably does not form a quality reformed region 71. If the metal film is arranged in the laminate M 16 inner, the laminate is 16 damage on. The following is considered to be the facts of the reasons for the damage. Sometimes because the used to make the laser L of the condensing lens of the impact of the like is poor, a part of the laser L is assembled in component M on the metal film. In this case, reflected by the metallic film M laser L, modified area because the reflected light and formed in the base plate 4, laminate 16 internal, or the substrate 4 with the laminate 16 interface. In particular in the base plate 4 on the back surface of 21 under the condition of the incident surface, the incident distance far from the one side of the modified region is formed, is vulnerable to the effects of the aberrations of the lens. Furthermore, laminate 16 as compared with the substrate 4 is used for forming the modified region of the energy necessary for the threshold value to be low, the laminate 16 easily formed inside the modified region. However, in the laminate 16 on the cause of the damage produced is not limited to these.

M as a metal film can be cited for test element group (TEG) the metal wiring, such as metal. Furthermore, the metal film can be also M film because of heat and. Furthermore, also can be used for low dielectric constant film (low-k film), and the like to replace the metal film M insulating film, provided in the laminate and 16 the inner. The insulating film can also be stripped because of heat and the film. As the low dielectric constant film can be cited, for example, than the permittivity 3.8 (SiO₂ the permittivity of the) smaller film.

Furthermore, as shown in Figure 19, the cut-off line 5 crossing portion of CP, preferably make the laser L pulse oscillation. Therefore, quality reformed region 71 reliably along the to-be-cut line 5 crossing portion of the CP formed in the base plate 4 of the internal. Therefore, the cutting base plate 4 and laminate 16 time, can prevent the cut-off line 5 on the crossing portion of debris, such as CP (chipping). Therefore, it can further improve the base plate 4 and laminate 16 cutting precision.

Furthermore, as shown in Figure 20, preferably in the base plate 4 of the surface 3 and quality reformed region 71 of the side surface 71a is at the distance of 5 the circular m-20   m position, or, on the substrate 4 surface 3 and quality reformed region 71 of the side end portion on the back surface 71b is at the distance of [5 + (base plate 4 of the thickness) × 0.1] µm-[ 20 + (base plate 4 of the thickness) × 0.1] µm position, to form a 1 column quality reformed region 71. In this, for example, if the as with the expansion of the expansion of the film 23 on the base plate 4 of the back 21 and expansion, the base plate 4 and laminate 16 along the cut-off line 5 is cut off. At this time, if in the above-mentioned position is formed with quality reformed region 71, can be laminate 16 (in the interlayer insulating film 17a, 17b) of the high-precision cutting. Furthermore, even if the base plate 4 the thickness is 300 the relatively thick thickness of such   m the circumstances, can still carry on the base plate 4 and laminate 16 high-precision cutting.

Furthermore, the truncated the modified region 72 is formed, in the base plate 4 in the direction of thickness of the continuous way on, for example, for forming 3 cut in the modified region 72. Furthermore, the modified region HC 73 is formed, as shown in Figure 16 (b) shows, by forming for example 2 HC included in the upgraded area 73, along the cutting line 5 of the spall 24 self-HC the modified region 73 to the base plate 4 of the back 21 is. Furthermore, in accordance with different forming conditions, sometimes the adjacent cut-off the modified region 72 and HC the modified region 73 also occurred between the frame 24. If the expanding band 23 on the base plate 4 of the back 21 and expansion, in the thickness direction through the continuously formed on the 3 cut in the modified region 72, since the base plate 4 to the laminate 16 crack is smoothly performed, its result, the good precision can be along the to-be-cut line 5 cut off the base plate 4 and laminate 16.

Furthermore, as long as it can make the spall self-base plate 4 smoothly to the laminate 16 carry out, the cut-off the modified region 72 will not defines in 3 column. In general, if the substrate 4 thin it is necessary to reduce the cut-off the modified region 72, the row number of, if the base plate 4 to increase the thickness of the cut in the modified region 72, the row number of. Furthermore, as long as it can make the spall self-base plate 4 smoothly to the laminate 16 carry out, the cut-off the modified region 72 can also be the form of the separated from each other. Furthermore, as long as it can reliably make the spall 24 self-HC the modified region 73 of the base plate 4 on the back surface of 21, the modified region HC 73 can also be a 1 column.

The above embodiments of the invention suitable for a detailed explanation, but the invention is not limited to the above-mentioned embodiment.

For example, in the above-mentioned embodiment, the modified region forming quality of the 71 with selectively switching the pulse oscillation with the continuous oscillation, but in the form other modified region can also be selectively switching pulse oscillation and continuous oscillation. Other modified region as, for example, can be cited cut-off the modified region 72, HC the modified region 73, and the like. Wherein the cutting accuracy from the viewpoint of improving, the side adjacent the device is in the quality of the modified region 71 is, preferably selectively switching pulse oscillation and continuous oscillation.

Furthermore, processing the object 1 can also be a GaAs wafer or thickness of the 100   m the following silicon wafer. At this moment, the processing the object 1 along the line to cut the inside of the 5 form 1 in the modified region, can be in a very high precision for processing the object 1 is cut off.

Furthermore, the modified region 71, 72, 73 is not limited to the processing the object 1 of a multi-photon absorption. The modified region 71, 72, 73 can also be the processing the object 1 with inside the multi-photon absorption to form the light absorption of the equivalent.

Furthermore, although in this embodiment the use of silicon semiconductor wafer to as the processing object 1, the material of the semiconductor wafer, however, is not limited to this. As the material of the semiconductor wafer, for example, can be cited: silicon outside of the element of group IV semiconductor, a IV group element such as the SiC compound semiconductor, containing III-V group element compound semiconductor, containing II-VI group element compound semiconductor, and, doped with various dopants for semiconductor.

The following, the present embodiment of a laser processing method to a detailed description of the embodiment, but the invention is not limited to the embodiment. Figure 21 (a) and 21 (b) is the embodiment of the laser processing method in the plan view of the processing object. Figure 22 is diagram, corresponding to Figure of the said Figure 21 (b) of the processing object shown in the cut area of the base plate 4a of the photograph 20.

First of all, along the bit for function element 15, 15 between the cut line of 5 the desired part of the RP, pulse oscillation of the laser L, so as to the quality of the formed inside of the object of the modified region 71. On the other hand, along the cut-off line 5 a prescribed part of the RC continuously oscillated laser L, so as to the inside of the object does not form a quality reformed region 71. Furthermore, the back surface of the base plate 21 to the incidence plane of the laser. Secondly, along the cut-off line 5 forming truncations the modified region 72 and HC the modified region 73. The result, as shown in Figure 21 (a) shown in, while along the to-be-cut line 5 RC a prescribed part of the laminate 16 M comprises a metal film, but not to the laminate by laser 16 damage.

In forming the modified region 71, 72, 73 after, on the processing object with expansion, the expansion by the expanding device with expansion cut off the object to be processed (with reference to Figure 21 (b)). As shown in Figure 21 (b) shows, the cut area 16a to the concavo-convex, it has already been confirmed by the cut off of the fact that with high precision. Photographing the object to be processed is cut off of the cut area of the base plate 4a of the photographs, shown in Figure 22 in. As shown in Figure 22, along the cut-off line 5 a prescribed part of the RC and into the interior of the processing object is not formed with a quality reformed region 71.

Then note in the above-mentioned embodiment to form a modified region 71, 72, 73 of the laser processing condition. The pulse width of the laser L 180ns, the irradiation position of the laser L interval (pulse interval) is the 4  m, the frequency of the laser L is a 75kHz. Furthermore, the object to be processed is loaded with the loading of the mobile speed is 300 mm/s. Furthermore, since as the back side of the incident surface 21 of the distance to the focal point P (focal point position), the energy of the laser L, and the relationship between the energy unit time as shown in table 1 is shown.

Table 1

On the other hand, Figure 23 (a) and 23 (b) is an example of the laser processing method in the plan view of the processing object. Figure 24 is diagram of said Figure 23 (b) of the processing object shown in the cut area of the base plate 104a of the photo.

First of all, along the bit for function element 115,115-cut line between the 105 illuminate the laser, so as to form the inside of the object of the modified region 171,172,173. Furthermore, the back surface of the base plate 121 of the incidence plane of the laser. In this case, as shown in Figure 23 (a) is shown, along the cutting line 105 to illuminate the laser, thus comprising the metal film 100M the laminate 116 generated on the damage of the film peeling.

In forming the modified region 171,172,173 later, on the processing object with expansion, expansion by the expanding device with expansion to cut off the object to be processed (with reference to Figure 23 (b)). As shown in Figure 23 (b) shows, the cut area 116a on concave-convex, recognizing that the cut-off the lack of precision. Shooting such cut off of the base plate of the processing object 104a of the photographs show in Figure 24. As shown in Figure 24, the inside of the object to be processed along the to-be-cut line 105 is formed with the modified region 171.