WORKPIECE MACHINING PROCESS
Patent Information
- Authority / Receiving Office
- DE · DE
- Patent Type
- Patents
- Current Assignee / Owner
- DISCO CORP
- Filing Date
- 2021-06-22
- Publication Date
- 2026-07-30
Smart Images
Figure 00000000_0000_ABST
Abstract
Description
BACKGROUND OF THE INVENTION Field of invention The present invention relates to a workpiece machining method. Description of the state of the art A semiconductor wafer or an optical device wafer, on which a gallium nitride-based compound semiconductor or the like is layered, is divided into several regions by lines, also called partition lines, arranged in a grid pattern on a front surface. The respective components are formed in these partitioned regions. The wafer is cut along the lines to divide the regions containing the circuits, thereby producing individual chips. In recent years, a laser processing method has been tested as a method for dividing a workpiece, such as the wafer described above. This method involves applying a laser beam with a transmission wavelength suitable for the workpiece, establishing a light concentration point within the areas to be divided. The laser processing method employing this technique involves applying the laser beam with a transmission wavelength suitable for the workpiece, with the light concentration point located within a surface of the workpiece, to continuously form modified layers along the paths within the workpiece. An external force is then applied along these paths, where the strength is reduced due to the formation of these modified layers, thereby dividing the workpiece (see, for example, Japanese patent JP 3 408 805 B2). US 2009 / 0039559A1 relates to a laser processing method that irradiates an object to be processed with laser light while a light convergence point is positioned within the object, thereby forming modified areas that serve as the starting point area for cutting along cutting lines 5. The entry surface for the laser light into the object is an irregular surface. DE 10 2020 203 932 A1 discusses that in a laser processing device the height of a focusing lens in a processing unit can be changed according to a change in the height of the upper surface of a wafer, thereby changing a vertical position of a focal point of a laser beam in the wafer. US 2009 / 0291544A1 relates to a wafer laser processing method for forming damaged layers along a plurality of roads inside a wafer with a component area, wherein a plurality of areas is subdivided by the plurality of roads arranged in a grid pattern on the front face and components are formed in the subdivided areas, and a peripheral excess area surrounding the component area, wherein the surface of the component area is formed higher than the surface of the peripheral excess area. SUMMARY OF THE INVENTION However, a wafer formed with components such as microelectromechanical systems (MEMS) has a structure in which the surface of a component-formed area is set several tens to several hundred micrometers higher than the surface of a peripheral border area surrounding the component area. In addition, there are also wafers where only one side of a rear surface of the component area is ground and an annular protrusion is formed in the peripheral edge area surrounding the component area to reduce the risk of damage when transporting the wafers after grinding. In the case of forming modified layers by causing a laser beam to strike the inside of the wafer which has such a step, it is necessary to process a thick part and a thin part separately, and special software is needed for control so that the laser beam can be switched on and off at freely chosen positions. Accordingly, an objective of the present invention is to provide a workpiece machining method by which machining can be easily applied inside a workpiece that has a step. According to one aspect of the present invention, a workpiece machining method is provided for machining a workpiece with a step, having a higher surface and a lower surface on one side onto which a laser beam is applied, using a laser machining device comprising a clamping table holding the workpiece, a laser beam application unit comprising a condenser lens that concentrates the laser beam with a transmission wavelength for the workpiece held on the clamping table, and a machining feed unit that places the clamping table and the laser beam application unit in a relative machining feed.The workpiece machining process comprises: a first machining step of performing a machining guide, wherein a focal point of the condenser lens is positioned inside the workpiece at a predetermined distance from the lower surface, and machining the interior of an area having the lower surface of the workpiece at a light concentration point of the laser beam refracted by the lower surface; and a second machining step of performing a machining guide, wherein the focal point of the condenser lens is positioned inside the workpiece at a predetermined distance from the higher surface, and machining the interior of an area having the higher surface of the workpiece at a light concentration point of the laser beam refracted by the higher surface.In the first processing step, the light concentration point formed by the refraction of the laser beam through the higher surface is positioned outside the area of the workpiece with the higher surface, so that the area with the higher surface of the workpiece is not processed. In the second processing step, the focal point of the condenser lens is spaced away from the lower surface and positioned outside the area with the lower surface of the workpiece, so that the laser beam is scattered and the area with the lower surface of the workpiece is not processed. The workpiece has a component area and a peripheral boundary area surrounding the component area. The component area has roads defined in a grid pattern, and components are formed in respective areas subdivided by these roads.The higher surface is a front surface of the component area and the lower surface is a front surface of the peripheral edge area. According to a further aspect of the present invention, a workpiece machining method is provided for machining a workpiece with a step, having a higher surface and a lower surface on one side, onto which a laser beam is applied, using a laser machining device comprising a clamping table holding the workpiece, a laser beam application unit comprising a condenser lens that concentrates the laser beam with a transmission wavelength for the workpiece held on the clamping table, and a machining feed unit that places the clamping table and the laser beam application unit in a relative machining feed.The workpiece machining process comprises: a first machining step of performing a machining guide, wherein a focal point of the condenser lens is positioned inside the workpiece at a predetermined distance from the lower surface, and machining the interior of an area having the lower surface of the workpiece at a light concentration point of the laser beam refracted by the lower surface; and a second machining step of performing a machining guide, wherein the focal point of the condenser lens is positioned inside the workpiece at a predetermined distance from the higher surface, and machining the interior of an area having the higher surface of the workpiece at a light concentration point of the laser beam refracted by the higher surface.In the first processing step, the light concentration point formed by the refraction of the laser beam through the higher surface is positioned outside the area of the workpiece with the higher surface, so that the area with the higher surface of the workpiece is not processed. In the second processing step, the focal point of the condenser lens is spaced away from the lower surface and positioned outside the area with the lower surface of the workpiece, so that the laser beam is scattered and the area with the lower surface of the workpiece is not processed. The workpiece has a component area and a peripheral boundary area surrounding the component area. The component area has roads defined in a grid pattern, and components are formed in respective areas subdivided by these roads.The higher surface is a rear surface of the peripheral edge region and the lower surface is a rear surface of the component area. The above and other aims, features and advantages of the present invention and the manner of its realization will become clearer, and the invention itself will best be understood by studying the following description and the attached claim with reference to the attached drawings, which show some preferred embodiments of the invention. SHORT FIGURE DESCRIPTION Fig. 1 is a perspective view showing an exemplary embodiment of a laser processing device used in a workpiece processing method according to a first embodiment; Fig. 2 is a perspective view of a workpiece that is a target to be processed using the workpiece processing method according to the first embodiment; Fig. 3 is a sectional view of the workpiece shown in Fig. 2; Fig. 4 is a flowchart showing a sequence of the workpiece processing method according to the first embodiment; Fig. 5 is a perspective view showing a state in which the workpiece is held on a clamping table in a first processing step of the workpiece processing method shown in Fig. 4; Fig. 6 is a sectional view schematically showing a state in which a laser beam is used in the first processing step of the workpiece processing method shown in Fig. 4.Figure 4 is applied to the workpiece processing method shown in Figure 4; Figure 7 is a sectional view schematically representing a state in which the laser beam is applied in a second processing step of the workpiece processing method shown in Figure 4; Figure 8 is a perspective view of a workpiece that is a target to be processed by a workpiece processing method according to a second embodiment; Figure 9 is a sectional view of the workpiece shown in Figure 8; Figure 10 is a sectional view schematically representing a state in which a laser beam is applied in a first processing step of the workpiece processing method according to the second embodiment; and Figure 11 is a sectional view schematically representing a state in which the laser beam is applied in a second processing step of the workpiece processing method according to the second embodiment. DETAILED DESCRIPTION OF PREFERRED EXECUTION FORMS Embodiments of the present invention are described in detail below with reference to the drawings. The present invention is not intended to be limited by the content described in the following embodiments. Furthermore, the components described below include those that can be easily devised by a person skilled in the art and those that are essentially identical. Moreover, the embodiments described below can be combined as needed. In addition, various omissions, substitutions, or modifications of the embodiments are possible in areas that do not deviate from the basic concept of the present invention. <Erste Ausführungsform> A workpiece machining method according to a first embodiment of the present invention is described with reference to the drawings. First, an embodiment of a laser machining device 1, which is used in the workpiece machining method according to the first embodiment, is described. Fig. 1 is a perspective view showing an embodiment of the laser machining device used in the workpiece machining method according to the first embodiment. Fig. 2 is a perspective view of a workpiece, which is a target to be machined using the workpiece machining method according to the first embodiment. Fig. 3 is a sectional view of the workpiece shown in Fig. 2.The laser processing device 1 shown in the first embodiment is a device for applying a pulsed laser beam 21 to a workpiece 200 in order to perform laser processing of the workpiece 200. (Workpiece) The workpiece 200, the target of processing by the laser processing device 1 shown in Fig. 1, is a wafer, such as a disk-shaped semiconductor wafer or optical component wafer, having a substrate 201 made of silicon, sapphire, gallium arsenide, or the like. As shown in Fig. 1, the workpiece 200 has a component area 210 and a peripheral edge area 220 surrounding the component area 210. The component area 210 has roads 203 defined in a grid pattern on a front surface 202 of the substrate 201, and components 204 formed in respective areas subdivided by the respective roads 203. The component 204 is, for example, an integrated circuit such as an integrated circuit (IC) or a large-scale integration (LSI), an imaging sensor such as a charge-coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS), or a microelectromechanical system (MEMS). The peripheral border region 220 surrounds the component region 210 along its entire perimeter and is a region in which the components 204 are not formed on the front surface 202 of the substrate 201. Note that in the first embodiment, the front surface 202 of the substrate 201 is a surface on one side onto which a laser beam is applied. Furthermore, in the first embodiment, as shown in Figures 2 and 3, a rear surface 205 is formed on a rear side relative to the front surface 202 of the substrate 201 such that it is aligned with the component area 210 and the peripheral edge area 220, and a thickness T1 of the component area 210 is specified as greater than a thickness T2 of the peripheral edge area 220, so that a step 206, which has a front surface 211 of the component area 210, which is a higher surface, and a front surface 221 of the peripheral edge area 220, which is a lower surface, is provided on the side of the front surface 202. The front surface 211 of the component area 210 and the front surface 221 of the peripheral edge area 220 are parallel to each other and also to the rear surface 205. Note that in the first embodiment, the component area 210 is a region with a large thickness and a higher surface area. The thickness T1 is the thickness of the region with the higher surface area. Additionally, in the first embodiment, the peripheral edge region 220 is a region with a smaller thickness and a lower surface area. The thickness T2 is the thickness of the region with the lower surface area. Note that in the first embodiment, the substrate 201 of the workpiece 200 is silicon, and the components 204 are MEMS. In addition, the workpiece 200 in the first embodiment has an adhesive strip 231 attached to its rear surface 205, wherein the adhesive strip 231 is disc-shaped with a diameter larger than the outer diameter of the workpiece 200 and has a ring frame 230 attached to an outer edge portion thereof, and the workpiece 200 is supported in an opening 232 of the ring frame 230 by the adhesive strip 231. In the first embodiment, the workpiece 200 is divided into individual components 204 along the paths 203. (Laser processing device) As shown in Fig. 1, the laser processing device 1 has a clamping table 10 which holds the workpiece 200 on a holding surface 11, a laser beam application unit 20, a motion unit 30, an imaging unit 40 and a control unit 100. The clamping table 10 holds the workpiece 200 against the holding surface 11. The holding surface 11 has a disc-like shape, formed from a porous ceramic or similar material, and is connected to a vacuum suction source (not shown) via a vacuum suction line (not shown). The clamping table 10 holds the workpiece 200, which is positioned against the holding surface 11, by suction. In the first embodiment, the holding surface 11 is a flat surface parallel to horizontal directions. Several clamping sections 12 are arranged around the circumference of the clamping table 10 for clamping the ring frame 230, which supports the workpiece 200, in the opening 232. Additionally, the clamping table 10 is rotated about an axis parallel to a Z-axis direction, orthogonal to the holding surface 11 and parallel to the vertical direction, by a rotary motion unit 34 of the motion unit 30. The clamping table 10 is moved by an X-axis motion unit 31 of the motion unit 30 in an X-axis direction parallel to a horizontal direction, and by a Y-axis motion unit 32 together with the rotary motion unit 34 in a Y-axis direction parallel to a horizontal direction and orthogonal to the X-axis direction. The laser beam application unit 20 is a unit that applies a pulsed laser beam 21 to the workpiece 200 held on the clamping table 10. In the first embodiment, the laser beam application unit 20 is a laser beam application device that applies the pulsed laser beam 21, which has a transmission wavelength for the workpiece 200, to form modified layers 207 (shown in Figs. 6 and 7) that become a starting point for fracture in the interior of the workpiece 200. The modified layer 207 refers to a region in which the density, refractive index, mechanical strength, or another physical property differs from that of the surrounding area. The modified layer 207 is, for example, a melt treatment region, a crack region, a dielectric breakdown region, a region with a modified refractive index, or a region in which these regions are mixed.In this embodiment, the modified layer 207 has a lower mechanical strength than the other parts of the substrate 201. In the first embodiment, as shown in Fig. 1, a portion of the laser beam application unit 20 is supported by a lifting element 4, which is moved in the Z-axis direction by a Z-axis motion unit 33 of the motion unit 30, the motion unit being provided on an upright wall 3 extending to a main body of the device 2. The laser beam application unit 20 comprises a laser oscillator that emits a pulsed laser for processing the workpiece 200, a condenser lens 22 for concentrating the laser beam 21 emitted by the laser oscillator onto the workpiece 200 held on the holding surface 11 of the clamping table 10, and at least one optical element that is provided on a beam path of the laser beam 21 between the laser oscillator and the condenser lens 22 and guides the laser beam 21 emitted by the laser oscillator to the condenser lens 22. The condenser lens 22 is arranged such that it faces the holding surface 11 of the clamping table 10 in the Z-axis direction, transmits the laser beam 21 oscillated by the laser oscillator, and concentrates the laser beam 21 onto a light concentration point 21-1 (shown in Fig. 6 and Fig. 7). In the first embodiment, the condenser lens 22 is also a convex lens and has a focal point 22-1 (shown in Fig. 6 and Fig. 7). The motion unit 30 moves the laser beam application unit 20 and the clamping table 10 relatively in the X-axis direction, the Y-axis direction and the Z-axis direction and about an axis parallel to the Z-axis direction. The X-axis direction and the Y-axis direction are directions parallel to the holding surface 11. The motion unit 30 comprises the X-axis motion unit 31, which is a machining feed unit for moving the clamping table 10 in the X-axis direction; the Y-axis motion unit 32, which is an index feed unit for moving the clamping table 10 in the Y-axis direction; the Z-axis motion unit 33 for moving the condenser lens 22, which is contained in the laser beam application unit 20, in the Z-axis direction; and the rotary motion unit 34 for rotating the clamping table 10 about the axis parallel to the Z-axis direction. The Y-axis motion unit 32 is a unit for positioning the clamping table 10 and the laser beam application unit 20 in a relative indexing position. In the first embodiment, the Y-axis motion unit 32 is arranged on the main body 2 of the laser processing device 1. The Y-axis motion unit 32 carries a movable plate 15, which supports the X-axis motion unit 31, movable in the Y-axis direction. The X-axis motion unit 31 is a unit for bringing the clamping table 10 and the laser beam application unit 20 into a relative processing position. The X-axis motion unit 31 is arranged on the movable plate 15. The X-axis motion unit 31 carries a second movable plate 16, which carries the rotary motion unit 34. This rotary motion unit rotates the clamping table 10 about the axis parallel to the Z-axis direction, movable in the X-axis direction. The Z-axis motion unit 33 is arranged on the vertical wall 3 and carries the lifting element 4, movable in the Z-axis direction. The X-axis motion unit 31, the Y-axis motion unit 32 and the Z-axis motion unit 33 each have a known ball screw spindle rotatable about an axis, a known pulse motor that rotates the ball screw spindle about the axis, and known guide rails that movably support the movable plate 15 or 16 in the X-axis direction or the Y-axis direction and movably support the lifting element 4 in the Z-axis direction. Additionally, the laser processing device 1 has an X-axis direction position detection unit (not shown) for detecting a position in the X-axis direction of the clamping table 10, a Y-axis direction position detection unit (not shown) for detecting a position in the Y-axis direction of the clamping table 10, and a Z-axis direction position detection unit for detecting a position in the Z-axis direction of the condenser lens 22, which is present in the laser beam application unit 20. Each position detection unit outputs a detection result to a control unit 100. The imaging unit 40 serves to image the workpiece 200 held on the clamping table 10. The imaging unit 40 comprises an imaging element, such as a charge-coupled device (CCD) or a complementary MOS imaging element (CMOS), for imaging the workpiece 200 held on the clamping table 10. In the first embodiment, the imaging unit 40 is attached to a tip of a housing of the laser beam application unit 20 and is positioned in a location aligned in the X-axis direction with the condenser lens 22 of the laser beam application unit 20. The imaging unit 40 images the workpiece 200 to obtain an image for performing an alignment between the workpiece 200 and the laser beam application unit 20 and outputs the obtained image to the control unit 100. The control unit 100 serves to control the aforementioned components of the laser processing device 1 and causes the laser processing device 1 to perform a processing operation on the workpiece 200. It should be noted that the control unit 100 is a computer comprising an arithmetic processing unit, which includes a microprocessor such as a central processing unit (CPU), a memory element with storage such as ROM or RAM, and an input / output interface.The arithmetic processing unit of the control unit 100 performs arithmetic processing according to a computer program stored in the storage device and outputs control signals via the input-output interface device to the aforementioned components of the laser processing device 1 in order to realize functions of the control unit 100. Additionally, the control unit 100 is connected to a display unit 110, which has a liquid crystal display for showing the status of a machining operation, images, and the like, and to an input unit (not shown) that is used when the operator registers machining content information and the like. The input unit has at least a touch field on the display unit 110 or an external input device such as a keyboard. (Workpiece machining process) Next, the workpiece machining process will be described. The workpiece machining process is a method for laser machining the workpiece 200 using the laser machining device 1 mentioned above to form the modified layers 207 along the paths 203, which become the starting points of a fracture inside the workpiece 200. Fig. 4 is a flowchart illustrating the sequence of the workpiece machining process according to the first embodiment. As shown in Fig. 4, the workpiece machining process has a first machining step 1001 and a second machining step 1002. Each step of the workpiece machining process is described below. (First processing step) Fig. 5 is a perspective view showing the workpiece held on the clamping table in the first machining step of the workpiece machining process shown in Fig. 4. Fig. 6 is a sectional view schematically representing the state in which a laser beam is applied in the first machining step of the workpiece machining process shown in Fig. 4. The first processing step 1001 is a step of performing a processing guide of the clamping table 10, wherein the focal point 22-1 of the condenser lens 22 inside the workpiece 200 is positioned at a predetermined distance from the front surface 221 of the peripheral edge region 220, which is the lower surface of the workpiece 200, in order to perform a processing to form the modified layers 207 inside the peripheral edge region 220 of the workpiece 200 at the light concentration point 21-1 of the laser beam 21 refracted from the front surface 221. In the first embodiment, in the first processing step 1001, the processing content information entered by an operator at the input unit or the like is accepted by the control unit 100, the workpiece 200 is placed by the adhesive strip 231 on the holding surface 11 of the clamping table 10, and when the control unit 100 accepts the start command from an operator for the processing operation from the input unit, the laser processing device 1 starts a processing operation based on the registered processing content information. In the first processing step 1001, the laser processing device 1, as shown in Fig. 5, holds the workpiece 200 by means of the adhesive strip 231 by suction against the holding surface 11 of the clamping table 10, and the ring frame 230 is clamped by the clamping sections 12. Note that the clamping sections 12 are omitted in Fig. 5. Next, in the first processing step 1001, the motion unit 30 of the laser processing device 1 moves the clamping table 10 towards a lower side of the imaging unit 40, and the imaging unit 40 images the workpiece 200. In the first processing step 1001, the laser processing device 1 performs an alignment based on the image created by the imaging unit 40. In the first processing step 1001, the laser processing device 1, based on the processing content information, projects a pulsed laser beam 21 from the laser beam application unit 20 onto the path 203, while moving the laser beam application unit 20 and the workpiece 200 relative to the path 203 by guiding the clamping table 10. In the first embodiment, in the first processing step 1001, as shown in Fig. 6, the laser processing device 1 positions the height of the focal point 22-1 of the condenser lens 22 inside the substrate 201 of the peripheral edge region 220.In other words, the machining device 1 positions the height of the focal point 22-1 of the condenser lens 22 below the front surface 221 of the peripheral edge region 220 and above the rear surface 205, positions the focal point 22-1 of the condenser lens 22 inside the workpiece 200 at a predetermined distance from the front surface 221 of the peripheral edge region 220, and the clamping table 10 is moved into a machining guide. Additionally, in the first processing step 1001, the laser processing device 1 positions the condenser lens 22 in the Z-axis direction if a position where the distance in the Z-axis direction between a main surface 22-2 (shown by a dashed line in Fig. 6) of the condenser lens 22 and the front surface 211 of the component area 210, which is the higher surface, is equal to the focus distance of the condenser lens 22 is a just-focus (JF) position, if the deviation amount (which is a distance in the Z-axis direction) of the light concentration point 21-1 from the JF position (i.e., the front surface 211 of the component area 210, which is the higher surface) in a case where the condenser lens 22 is moved from the JF position is DF1.if a distance in the Z-axis direction between the front surface 211 of the component area 210 and the front surface 221 of the peripheral edge area 220 is Δt, and if a refractive index of the substrate 201 of the workpiece 200 r is, at such a position that it satisfies both the following expression 1 and expression 2, and directs the pulsed laser beam 21 from the laser beam application unit 20 onto the road 203. Therefore, in the first processing step 1001, as shown in Fig. 6, the focal point 22-1 of the condenser lens 22 is positioned in the peripheral edge region 220, and the laser beam 21, which is refracted at the front surface 221 of the peripheral edge region 220 and enters the substrate 201 of the workpiece 200, is concentrated at the light concentration point 21-1 within the substrate 201 of the peripheral edge region 220, thereby performing a processing operation to form the modified layer 207 inside the peripheral edge region 220 of the workpiece 200.Furthermore, in the first processing step 1001, the light concentration point 21-1 of the laser beam 21, formed by refraction at the front surface 211 of the component area 210 and entering the substrate 201 of the workpiece 200, is formed on the outside of the component area 210, being positioned on the lower side with respect to the rear surface 205 of the component area 210 of the workpiece 200, so that the component area 210 of the workpiece 200 is not processed and the modified layer 207 is not formed. In this way, in the first processing step 1001, the laser processing device 1 defines the light concentration point 21-1 of the laser beam 21 inside the substrate 201, specifically within the peripheral edge region 220 of the workpiece 200, and the modified layer 207 is formed along the path 203 inside the substrate 201, specifically within the peripheral edge region 220. In other words, in the first processing step 1001, the laser processing device 1 forms the modified layer 207 along the path 203 inside the substrate 201, specifically within the peripheral edge region 220, from the component area 210 and the peripheral edge region 220. In the first processing step 1001, when the laser processing device 1 has formed the modified layers 207 along all roads 203 inside only the substrate 201 of the peripheral edge area 220, the application of the laser beam 21 is stopped. Thus, the first processing step 1001 is a step of processing the workpiece 200 by positioning the condenser lens 22 at such a height that only the peripheral edge region 220 of the component area 210 and the peripheral edge region 220 is processed. Note that in the present invention, in the first processing step 1001, while the laser beam application unit 20 and the workpiece 200 are moved relative to each path 203, the pulsed laser beam 21 is applied at least once by the laser beam application unit 20 to all paths 203. In other words, in the present invention, in the first processing step 1001, the laser beam application unit 20 is moved relative to the workpiece 200 along each path 203 for at least one pass, applying the laser beam 21.Note that in the present invention, in the first processing step 1001, the position of the light concentration point 21-1 in the Z-axis direction may or may not be changed in each pass; in a case where the position is changed, it is desirable to change the position of the light concentration point 21-1 in the Z-axis direction sequentially from the lower side to the upper side. (Second processing step) Fig. 7 is a sectional view schematically depicting a state in which the laser beam is applied in a second processing step of the workpiece processing method shown in Fig. 4. The second processing step 1002 consists of a process of guiding the clamping table 10 while positioning the focal point 22-1 of the condenser lens 22 inside the workpiece 200 at a predetermined distance from the front surface 211 of the component area 210, which is the higher surface of the workpiece 200, and a process of forming the modified layer 207 inside the component area 210 of the workpiece 200 at the light concentration point 21-1 of the laser beam 21 refracted at the front surface 211. In the second processing step 1002, the laser processing device 1, based on the processing content information, applies the pulsed laser beam 21 from the laser beam application unit 20 to the path 203, while it moves the clamping table 10 into the processing feed and while the laser beam application unit 20 and the workpiece 200 are moved relatively along the path 203 by the X-axis motion unit 31 of the motion unit 30. In the first embodiment, in the second processing step 1002, as shown in Fig. 7, the laser processing device 1 positions the height of the focal point 22-1 of the condenser lens 22 within the substrate 201 in the component area 210 and outside the substrate 201 in the peripheral edge area 220.In other words, the laser processing device 1 places the clamping table 10 into a processing feed, positioning the height of the focal point 22-1 of the condenser lens 22 below the front surface 211 of the component area 210 and above the front surface 221 of the peripheral edge area 220, and then positioning the focal point 22-1 of the condenser lens 22 inside the workpiece 200 at a predetermined distance from the front surface 211 of the component area 210. Additionally, the laser processing device 1 brings a position where the distance in the Z-axis direction between the main surface 22-2 of the condenser lens 22 and the front surface 211 of the component area 210, which is the higher surface, is equal to the focus distance of the condenser lens 22, is a Just-Focus (JF) position, and if the deviation amount (which is the distance in the Z-axis direction) of the light concentration point 21-1 from the JF position in a case where the condenser lens 22 is moved from the JF position is DF2, the pulsed laser beam 21 from the laser beam application unit 20 onto the road 203 by positioning the position in the Z-axis direction of the condenser lens 22 at such a position that both of the following expressions 3 and 4 are satisfied. Therefore, in the second processing step 1002, as shown in Fig. 7, the focal point 22-1 of the condenser lens 22 is positioned closer to the side of the laser beam application unit 20 than the front surface 221 of the peripheral edge region 220 (spaced apart from it), which is the lower surface. In the second processing step 1002, the focal point 22-1 of the condenser lens 22 is positioned closer to the side of the laser beam application unit 20 than the peripheral edge region 220 of the workpiece 200, causing the laser beam 21 to be scattered, and the peripheral edge region 220 of the workpiece 200 is not processed, so that the modified layer 207 is not formed inside the peripheral edge region 220. Additionally, in the second processing step 1002, as shown in Fig.Figure 7 shows that the focal point 22-1 of the condenser lens 22 is positioned inside the component area 210, and the laser beam 21, refracted at the front surface 211 of the component area 210 and entering the substrate 201 of the workpiece 200, is concentrated at the light concentration point 21-1 inside the substrate 201 of the component area 210, thereby performing a process to form the modified layer 207 inside the component area 210 of the workpiece 200. Thus, in the second processing step 1002, the laser processing device 1 defines the light concentration point 21-1 of the laser beam 21 inside the substrate 201 only in the component area 210 of the workpiece 200 and forms the modified layer 207 along the path 203 inside the substrate 201 only in the component area 210. In other words, in the second processing step 1002, the laser processing device 1 forms the modified layer 207 along the path 203 inside only the component area 210 from the component area 210 and the peripheral edge area 220. The second processing step 1002 is thus a step of processing the workpiece 200 by positioning the condenser lens 22 at such a height that only the component area 210, consisting of component area 210 and the peripheral edge area 220, is processed. Furthermore, in the first embodiment, in the first processing step 1001 and in the second processing step 1002, the modified layers 207 are formed at positions where the position in the Z-axis direction is the same. Note that in the present invention, in the second processing step 1002, while the laser beam application unit 20 and the workpiece 200 are moved relatively along the path 203, the pulsed laser beam 21 is applied at least once by the laser beam application unit 20 to all paths 203.In other words, in the second processing step 1002 of the present invention, the laser beam 21 is applied by moving the laser beam application unit 20 by at least one pass along each path 203 relative to the workpiece 200. Note that in the second processing step 1002 of the present invention, the position in the Z-axis direction of the light concentration point 21-1 could or could not be changed in each pass; if the position is changed, it is desirable to position the position in the Z-axis direction of the light concentration point 21-1 sequentially from the lower side to the upper side. Furthermore, the modified layers 207 formed in the first processing step 1001 are not shown in Fig. 7. In the second processing step 1002, when the laser processing device 1 has formed the modified layers 207 along all the paths 203 inside only the substrate 201 in the component area 210, the application of the laser beam 21 is completed. In the second processing step 1002, when the laser processing device 1 stops holding the workpiece 200 by suction through the clamping table 10 and releases the clamping of the ring frame 230 by the clamping sections 12, the processing operation, i.e., the workpiece processing method, is completed. The workpiece 200, with the modified layers 207 as starting points for breaking, is broken by widening the adhesive strip 231 or similar means in order to be divided into individual components 204. In this way, in the workpiece machining process according to the first embodiment, in the first machining step 1001 and in the second machining step 1002, if the aforementioned expression 1, expression 2, expression 3 and expression 4 are satisfied, taking into account the thicknesses T1 and T2 of the workpiece 200, the distance Δt in the Z-axis direction between the front surface 211 of the component area 210 and the front surface 221 of the peripheral edge area 220, and the refractive index r of the substrate 201 of the workpiece 200, the height of the condenser lens 22 is determined such that in the first machining step 1001 the modified layers 207 are formed only in the interior of the peripheral edge area 220 and in the second machining step 1002 the modified layers 207 are formed only in the interior of the component area 210. As described above, the workpiece machining method according to the first embodiment comprises the first machining step 1001 of machining the workpiece 200 by positioning the condenser lens 22 at such a height that only the peripheral edge region 220 is machined, and the second machining step 1002 of machining the workpiece 200 by positioning the condenser lens 22 at such a height that only the component area 210 is machined.Furthermore, the workpiece machining method according to the first embodiment satisfies expression 1 and expression 2 in the first machining step 1001 and satisfies expression 3 and expression 4 in the second machining step 1002, whereby the height of the condenser lens 22 is set to such a height that in the first machining step 1001 the modified layers 207 are formed only in the interior of the peripheral edge region 220 and that in the second machining step 1002 the modified layers 207 are formed only in the interior of the component region 210. Therefore, the workpiece machining method according to the first embodiment can form the modified layers 207 inside the substrate 201 of the workpiece 200, which has the step 206, by repeatedly applying the pulsed laser beam 21 over the peripheral edge region 220 and the component area 210, without having to perform ON / OFF control of the laser beam using special software in either the first machining step 1001 or the second machining step 1002. As a result, the workpiece machining method according to the first embodiment achieves such an effect that the machining to form the modified layers 207 inside the substrate 201 of the workpiece 200, which has the step 206, can be carried out simply. <Zweite Ausführungsform> A workpiece machining method according to a second embodiment of the present invention is described with reference to the drawings. Fig. 8 is a perspective view of a workpiece as an object to be machined by the workpiece machining method according to the second embodiment. Fig. 9 is a sectional view of the workpiece shown in Fig. 8. Fig. 10 is a sectional view that schematically represents a state in which a laser beam is applied in a first machining step of the workpiece machining method according to the second embodiment. Fig. 11 is a sectional view that schematically represents a state in which a laser beam is applied in a second machining step of the workpiece machining method according to the second embodiment. Note that in the description of the second embodiment, the parts in Figs. 8, 9, 10, and 11 are not shown.11, which are identical to those of the first embodiment, are designated with the same reference numerals as above and descriptions thereof are omitted. A workpiece 200-2, as an object to be machined by the workpiece machining process according to the second embodiment, has a rear surface 205 of a substrate 201 as a surface on the side where a laser beam 21 is applied. The workpiece 200-2, as the object to be machined by the workpiece machining process according to the second embodiment, is a wafer generally referred to as TAIKO (registered trademark), in which the rear surface 205 of a component area 210 is ground, as shown in Figs. 8 and 9, a circular recess 208 is formed on the side of the rear surface 205 in the component area 210, and an annular projection 209 is formed, in which a peripheral edge region 220 is thicker than the component area 210.Therefore, in the second embodiment, the workpiece 200-2 has a step 206-2 on the side of the rear surface 205, which has a rear surface 222 of the peripheral edge region 220, which is a higher surface, and a rear surface 212 of the component area 210, which is a lower surface. It should be noted that in the second embodiment, the component area 210 is a region with a small thickness and a lower surface area. The thickness T2 of the component area 210 is the thickness of the region with the lower surface area. Furthermore, in the second embodiment, the peripheral edge area 220 is a region with a large thickness and a higher surface area. The thickness T1 of the peripheral edge area 220 is the thickness of the region with the higher surface area. In the second embodiment, the workpiece 200-2 also has an adhesive strip 231 attached to its front surface 202. The adhesive strip 231 has a disc-like shape with a diameter larger than the outer diameter of the workpiece 200-2 and a ring frame 230 attached to a circumferential edge portion thereof. The workpiece 200-2 is supported in an opening 232 of the ring frame 230 by the adhesive strip 231. In the second embodiment, the side of the front surface 202 of the workpiece 200-2 is held by suction against a holding surface 11 of a clamping table 10 by the adhesive strip 231. As in the first embodiment, the workpiece machining method according to the second embodiment comprises a first machining step 1001 and a second machining step 1002. The first machining step 1001 of the workpiece machining method according to the second embodiment is a step of moving the clamping table 10 into a machining feeder, wherein the focal point 22-1 of a condenser lens 22 is positioned inside the workpiece 200 at a predetermined distance from the rear surface 212 of the component area 210, which is the lower surface of the workpiece 200-2, and a machining operation to form a modified layer 207 inside the component area 210 of the workpiece 200-2 at a light concentration point 21-1 of a laser beam 21 refracted at the rear surface 212. In the second embodiment, a laser processing device 1, as shown in Fig. 10, positions the height of the focal point 22-1 of the condenser lens 22 within the substrate 201 of the component area 210 in the first processing step 1001. In other words, the laser processing device 1 places the clamping table 10 into a processing feed while the height of the focal point 22-1 of the condenser lens 22 is positioned below the rear surface 212 of the component area 210 and above the front surface 202, and while the focal point 22-1 of the condenser lens 22 is positioned inside the workpiece 200, spaced a predetermined distance from the rear surface 212 of the component area 210. Additionally, in the second embodiment, in the first processing step 1001, if a position where the distance in the Z-axis direction between a main surface 22-2 of the condenser lens 22 and the rear surface 222 of the peripheral edge region 220, which is the higher surface, is equal to the focus distance of the condenser lens 22, is a just-focus position (JF), if the deviation amount (which is a distance in the Z-axis direction) of the light concentration point 21-1 from the JF position (that is, from the rear surface 222 of the peripheral edge region 220, which is the higher surface) in a case where the condenser lens 22 is moved from the JF position, is DF1, if the distance in the Z-axis direction between the rear surface 222 of the peripheral edge region 220 and the rear surface 212 of the component area 210 Δt is, and if the refractive index of the substrate 201 and the workpiece 200 r is,a pulsed laser beam 21 is applied from a laser beam application unit 20 onto a road 203, while the position in the Z-axis direction of the condenser lens 22 is positioned such that both the aforementioned expression 1 and expression 2 are satisfied, as in the first embodiment. Therefore, in the second embodiment, in the first processing step 1001, as shown in Fig. 10, a light concentration point 21-1 of a laser beam 21 refracted at the rear surface 222 of the peripheral edge region 220 and entering the substrate 201 of the workpiece 200 is positioned on the lower side with respect to the front surface 202 of the peripheral edge region 220 of the workpiece 200 and is formed outside the peripheral edge region 220, so that the peripheral edge region 220 of the workpiece 200 is not processed and a modified layer 207 is not formed therein. In addition, in the second embodiment, in the first processing step 1001, as shown in Fig. 10, the focal point 22-1 of the condenser lens 22 is positioned within the component area 210, and the laser beam 21, which is refracted at the rear surface 212 of the component area 210 and enters the substrate 201 of the workpiece 200, is concentrated on the light concentration point 21-1 inside the substrate 201 of the component area 210, thereby performing a processing operation to form the modified layer 207 inside the component area 210 of the workpiece 200. In the second embodiment, the laser processing device 1, in the first processing step 1001, defines the light concentration point 21-1 of the laser beam 21 inside the substrate 201 only in component area 210 of the workpiece 200-2 and forms the modified layer 207 along the path 203 inside the substrate 201 only in component area 210. In other words, in the second embodiment, the laser processing device 1, in the first processing step 1001, forms the modified layer 207 along the path 203 inside only component area 210 from component area 210 and the peripheral edge area 220. In the second embodiment, the first processing step 1001 is therefore a step of processing the workpiece 200 by positioning the condenser lens 22 at such a height that only the component area 210 from the component area 210 and the peripheral edge area 220 is processed. A second processing step 1002 of the workpiece processing method according to the second embodiment is a step of moving the clamping table 10 into a processing position while the focus point 22-1 of the condenser lens 22 is positioned inside the workpiece 200 at a predetermined distance from the rear surface 222 of the peripheral edge region 220, which is the higher surface of the workpiece 200-2, and of processing to form the modified layer 207 inside the peripheral edge region 220 of the workpiece 200-2 at the light concentration point 21-1 of the laser beam 21 refracted at the rear surface 222. In the second embodiment, in the second processing step 1002, as shown in Fig. 11, the laser processing device 1 positions the height of the focal point 22-1 of the condenser lens 22 inside the substrate 201 of the peripheral edge region 220 and outside the substrate 201 of the component area 210. In other words, the laser processing device 1 moves the clamping table 10 into a processing guide while positioning the height of the focal point 22-1 of the condenser lens 22 below the rear surface 222 of the peripheral edge region 220 and above the rear surface 212 of the component area 210, and positions the focal point 22-1 of the condenser lens 22 inside the workpiece 200-2, spaced a predetermined distance from the rear surface 222 of the peripheral edge region 220. Additionally, in the second embodiment, in the second processing step 1002, if a position in which the distance in the Z-axis direction between the main surface 22-2 of the condenser lens 22 and the rear surface 222 of the peripheral edge region 220, which is the higher surface, is equal to the focus distance of the condenser lens 22, is the Just-Focus (JF) position, and if the deviation amount (which is the distance in the Z-axis direction) of the light concentration point 21-1 from the JF position in the case in which the condenser lens 22 is moved from the JF position is DF2, the pulsed laser beam 21 is applied from the laser beam application unit 20 to the road 203, while the position in the Z-axis direction of the condenser lens 22 is positioned at such a position that both the aforementioned expression 3 and expression 4 are satisfied, as in the first embodiment. Therefore, in the second embodiment, in the second processing step 1002, as shown in Fig. 11, the focal point 22-1 of the condenser lens 22 is positioned inside the peripheral edge region 220, and the laser beam 21, refracted at the rear surface 222 of the peripheral edge region 220 and entering the substrate 201 of the workpiece 200, is concentrated on the light concentration point 21-1 inside the substrate 201 of the peripheral edge region 220, thereby carrying out the processing to form the modified layer 207 inside the peripheral edge region 220 of the workpiece 200. In the second embodiment, in the second processing step 1002, as shown in Fig. 11, the focal point 22-1 of the condenser lens 22 is positioned closer to the side of the laser beam application unit 20 than the rear surface 212 of the component area 210 (spaced apart from it), which is the lower surface. In the second embodiment, in the second processing step 1002, the focal point 22-1 of the condenser lens 22 is positioned closer to the side of the laser beam application unit 20 than the component area 210 of the workpiece 200, causing the laser beam 21 to be scattered and the component area 210 of the workpiece 200 to remain unprocessed, so that the modified layer 207 is not formed inside the component area 210. In the second embodiment, the laser processing device 1, in the second processing step 1002, defines the light concentration point 21-1 of the laser beam 21 inside the substrate 201, specifically within the peripheral edge region 220 of the workpiece 200-2, and forms the modified layer 207 along the path 203 inside the substrate 201, specifically within the peripheral edge region 220. In other words, in the second embodiment, the laser processing device 1, in the second processing step 1002, forms the modified layer 207 along the path 203 inside only the peripheral edge region 220, encompassing the component area 210 and the peripheral edge region 220.In this way, in the second embodiment, the second processing step 1002 is a step to process the workpiece 200-2, while the condenser lens 22 is positioned at such a height that only the peripheral edge region 220 from the component area 210 and the peripheral edge region 220 is processed. Furthermore, in the second embodiment, in the first processing step 1001 and in the second processing step 1002, the modified layers 207 are formed at positions where the positions in the Z-axis direction are the same. In addition, in the present invention, also in the second embodiment, the laser beam 21 is applied in the first processing step 1001 and in the second processing step 1002, while the laser beam application unit 20 is moved along each path 203 relative to the workpiece 200 for at least one pass.In the second embodiment of the present invention, the position in the Z-axis direction of the light concentration point 21-1 could also be changed for each pass in the first processing step 1001 and in the second processing step 1002; if the position is changed, it is desirable to position the position in the Z-axis direction of the light concentration point 21-1 sequentially from the lower side to the upper side. Furthermore, the modified layers 207 formed in the first processing step 1001 are not shown in Fig. 11. In addition, in the workpiece machining process according to the second embodiment, in the first machining step 1001 and the second machining step 1002, if the aforementioned expressions 1, 2, 3 and 4 are satisfied, taking into account the thicknesses T1 and T2 of the workpiece 200-2, the distance Δt in the Z-axis direction between the rear surface 222 of the peripheral edge region 220 and the rear surface 212 of the component region 210, and the refractive index r of the substrate 201 of the workpiece 200, the height of the condenser lens 22 is determined such that in the first machining step 1001 the modified layers 207 are formed only in the interior of the component region 210 and in the second machining step 1002 the modified layers 207 are formed only in the interior of the peripheral edge region 220. The workpiece machining method according to the second embodiment comprises the first machining step 1001 of machining the workpiece 200 while positioning the condenser lens 22 at such a height that only the component area 210 is machined, and the second machining step 1002 of machining the workpiece 200 while positioning the condenser lens 22 at such a height that only the peripheral edge area 220 is machined.Furthermore, the workpiece machining method according to the second embodiment satisfies expression 1 and expression 2 in the first machining step 1001 and expression 3 and expression 4 in the second machining step 1002, whereby the height of the condenser lens 22 is set to such a height that in the first machining step the modified layers 207 are formed only in the interior of the component area 210 and that in the second machining step 1002 the modified layers 207 are formed only in the interior of the peripheral edge area 220. Therefore, the workpiece machining method according to the second embodiment can form the modified layers 207 inside the substrate 201 of the workpiece 200-2 with the stage 206-2 by repeatedly applying the pulsed laser beam 21 over the peripheral edge region 220 and the component area 210, without having to control the laser beam ON / OFF using special software, both in the first machining step 1001 and in the second machining step 1002. As a result, the workpiece machining method according to the second embodiment has such an effect that machining to form the modified layers 207 inside the substrate 201 of the workpiece 200-2, which has the stage 206-2, can be carried out simply, as in the first embodiment. (First example) A workpiece machining process is described according to a first example. In the first example, a disk-shaped workpiece 200-2 with a thickness T1 of 200 µm, a thickness T2 of 100 µm, a distance Δt of 100 µm, a silicon substrate 201 (that is, with a refractive index of about 4), an outer diameter of six inches, a width of each lane 203 of 200 µm, and a component 204 of 7 mm × 3.7 mm was subjected to the workpiece machining process according to the second embodiment by performing the first machining step 1001, wherein DF1 is sequentially set to -120 µm and -110 µm, and the second machining step 1002, wherein DF2 is sequentially set to -44 µm, -31 µm, and -10 µm.In the first example, the formation of the modified layers 207 in the first processing step 1001 was only achieved in the component area 210, and the formation of the modified layers 207 in the second processing step 1002 was only achieved in the interior of the peripheral edge area 220. It should be noted that the present invention is not limited to the embodiments described above. In other words, the present invention can be carried out with various modifications in such areas as do not deviate from the core of the invention. It should be noted that, in the present invention, the sequence in which the first processing step 1001 and the second processing step 1002 are carried out is not limited to the sequence described in the exemplary embodiments, provided that the modified layers 207 necessary for processing can be formed. The present invention is not limited to the details of the preferred embodiments described above. The scope of the invention is defined by the accompanying claim, and all changes and modifications that fall within the equivalent scope of the claim are therefore included in the invention.
Claims
A workpiece machining method for machining a workpiece (200) with a step (206) having a higher surface (211) and a lower surface (221) on one side onto which a laser beam (21) is applied, using a laser machining device (1) comprising a clamping table (10) holding the workpiece (200), a laser beam application unit (20) comprising a condenser lens (22) that focuses the laser beam (21) with a transmission wavelength for the workpiece (200) held on the clamping table (10), and a machining feed unit (31) that places the clamping table (10) and the laser beam application unit (20) in a relative machining feed, wherein the workpiece machining method comprises: a first machining step of performing a machining feed, wherein a focal point (22-1) of the condenser lens (22) is located inside the workpiece (200),a processing step, wherein the focal point (22-1) of the condenser lens (22) is positioned at a predetermined distance from the lower surface (221), and the interior of an area (220) having the lower surface (221) of the workpiece (200) is processed at a light concentration point (21-1) of the laser beam (21) refracted by the lower surface (221); and a second processing step, wherein the focal point (22-1) of the condenser lens (22) is positioned inside the workpiece (200) at a predetermined distance from the higher surface (211), and the interior of an area (210) having the higher surface (211) of the workpiece (200) is processed at a light concentration point (21-1) of the laser beam (21) refracted by the higher surface (211).wherein in the first processing step the light concentration point (21-1) formed by refraction of the laser beam (21) through the higher surface (211) is formed outside the area (210) with the higher surface (211) of the workpiece (200), so that the area (210) with the higher surface (211) of the workpiece (200) is not processed, and wherein in the second processing step the focal point (22-1) of the condenser lens (22) is spaced from the lower surface (221) and is positioned outside the area (220) with the lower surface (221) of the workpiece (200), so that the laser beam (21) is scattered and the area (220) with the lower surface (221) of the workpiece (200) is not processed, wherein the workpiece (200) has a component area (210) and a peripheral edge area (220) which the surrounding the building element area (210), wherein the building element area (210) contains roads (203) which are defined in a grid pattern,and structural elements (204) which are formed in respective areas subdivided by the respective roads (203), wherein the higher surface (211) is a front surface (211) of the structural element area (210) and the lower surface (221) is a front surface (221) of the peripheral edge area (220). Workpiece machining method for machining a workpiece (200-2) with a step (206-2) having a higher surface (222) and a lower surface (212) on one side onto which a laser beam (21) is applied, using a laser machining device (1) comprising a clamping table (10) holding the workpiece (200-2), a laser beam application unit (20) comprising a condenser lens (22) that focuses the laser beam (21) with a transmission wavelength for the workpiece (200-2) held on the clamping table (10), and a machining feed unit (31) that places the clamping table (10) and the laser beam application unit (20) in a relative machining feed, wherein the workpiece machining method comprises: a first machining step of performing a machining feed, wherein a focal point (22-1) of the condenser lens (22) is located inside the workpiece (200-2),a processing step, wherein the focal point (22-1) of the condenser lens (22) is positioned at a predetermined distance from the lower surface (212), and the interior of a region (210) having the lower surface (212) of the workpiece (200-2) is processed at a light concentration point (21-1) of the laser beam (21) refracted by the lower surface (212); and a second processing step, wherein the focal point (22-1) of the condenser lens (22) is positioned inside the workpiece (200) at a predetermined distance from the higher surface (222), and the interior of a region (220) having the higher surface (222) of the workpiece (200-2) is processed at a light concentration point (21-1) of the laser beam (21) refracted by the higher surface (222).wherein in the first processing step the light concentration point (21-1) formed by refraction of the laser beam (21) through the higher surface (222) is formed outside the area (220) with the higher surface (222) of the workpiece (200-2), so that the area (220) with the higher surface (222) of the workpiece (200-2) is not processed, and wherein in the second processing step the focal point (22-1) of the condenser lens (22) is spaced from the lower surface (212) and is positioned outside the area (210) with the lower surface (212) of the workpiece (200-2), so that the laser beam (21) is scattered and the area (210) with the lower surface (212) of the workpiece (200-2) is not processed, wherein the workpiece (200-2) has a component area (210) and a peripheral has a perimeter area (220) surrounding the building element area (210), wherein the building element area (210) includes roads (203),which are defined in a grid pattern, and has building elements (204) formed in respective areas subdivided by the respective roads (203), wherein the higher surface (222) is a rear surface (222) of the peripheral edge area (220) and the lower surface (212) is a rear surface (212) of the building element area (210).