Patent Publication Number: US-2023133808-A1

Title: Laser cutting method using spatial light modulator and laser cutting device

Description:
TECHNICAL FIELD 
     The present disclosure is in related to a crystal pillar laser cutting method, more particularly to a crystal pillar laser cutting method using spatial light modulator. 
     BACKGROUND 
     Crystal pillar cutting is a very common process in the semiconductor manufacturing process, and it mainly cuts the microchips from the crystal pillars. Currently, wire cutting, such as piano wire, is the main technique. There is an inconvenient point that the width of the wire cutting is wider, so that a larger cutting lane must be reserved on the crystal pillar, thus it means more material of the crystal pillar substrate is wasted. 
     Further, some components may be manufactured by silicon carbide (SiC) or gallium nitride (GaN) wafers. It is known that the cost of silicon carbide (SiC) or gallium nitride (GaN) is higher. Obviously, the more expensive material and the wider cutting lane make that of the more cost on the cutting base material. In addition, the hardness of silicon carbide is higher than others, so as to possibly generate cracks on the cutting surface. Therefore, additional grinding treatment is a must. 
     Laser cutting is another option. Although laser cutting is able to effectively decrease the width of the cutting lane, laser cutting in prior arts has the disadvantages of high cost and difficulty in cutting crystal pillar. 
     Please refer to  FIG.  1 A  and  FIG.  1 B , which illustrate a micro schematic view of the laser cutting and an energy distribution map of the laser light. As shown in  FIG.  1 B , the vertical axis represents the energy strength of the laser light, and a horizontal axis represents the position along the horizontal direction. When the laser light  11  is projected to the uncut object  10 , which is to be cut, and it seems that the laser beam is concentrated. As a matter of fact, the energy is concentrated in the center of the laser beam, and decreased outward. This kind of the distribution is normally called the Gaussian distribution. By way of the Gaussian distribution, the energy concentration positions of the object will greatly change due to heat effects affecting the physical properties of the material, such as change of refractive index. As a result, the laser has a slight offset, resulting in uneven cutting surface. 
     For cutting silicon carbide (SiC) crystal pillar, the invisible laser cutting technology or Stealth Dicing™ is adopted. The features of penetration and diffraction of the laser light are applied to let the focal points of the laser light be distributed in the object. Therefore, the positions where the focal points will be dissolved and cracked along the crystal surface, so as to achieve the purpose of cutting. On the other hand, heat effects may not be effectively released when the material in the object is dissolved, and the focus of the laser light will not be very accurate either. As a conclusion, the flatness of the cut surface is not good, and a following large-scale grinding process is a need. 
     Thus, how to over the problem of cutting silicon carbide or gallium nitride crystal pillar becomes an issue to a person having ordinary skill in the art. 
     SUMMARY 
     The present disclosure provides a laser cutting method. Different light pattern distributions are produced by phase modulations, and the laser light with the different light pattern distributions is capable of compensating heat effects of the material, so as to overcome the problem of uneven cutting surfaces. 
     A laser cutting method comprises steps of: 
     (a) emitting a laser light to a spatial light modulator that has a plurality of pixels; 
     (b) the laser light modulated by the spatial light modulator being irradiated on an uncut object, which is to be cut, for forming a focal point and cutting the uncut object; 
     (c) measuring a cutting depth of the object; 
     (d) the spatial light modulator converting a phase of each of the laser light modulated by each of the pixels to change a light pattern distribution at the focal point when the cutting depth of the object reaches a first predetermined depth; and 
     (e) repeating the step (b) to the step (d) until the cutting depth of the object reaches a second predetermined depth; 
     wherein the first predetermined depth is varied when the step (b) to the step (d) are repeated. 
     The present disclosure further provides a laser cutting method comprising steps of: 
     (a) emitting a laser light to a spatial light modulator that has a plurality of pixels; 
     (b) focusing the laser light on a plurality of focal points in an uncut object, which is to be cut, by means of the spatial light modulator; 
     wherein the spatial light modulator dynamically converts a phase of each of the laser lights modulated by each of the pixels in order to change a light pattern distribution of each of the focal points. 
     The present disclosure provides a laser cutting device adopted to cut an object to be cut, comprises a laser light source, a spatial light modulator, a laser cutting head, a jig, and a controller. The laser light source is adopted to emit a laser light. The spatial light modulator is disposed at a path of the laser light emitted by the laser light source and comprises a plurality of pixels. The laser cutting head comprises an autofocus system. The jig is adopted to fix an uncut object, which is to be cut. The controller electrically connects to the laser light source, the spatial light modulator and the laser cutting head. Wherein the laser light reflected by the pixels of the spatial light modulator passes through the laser light head to the object. Wherein the controller detects a cutting depth of the object through the autofocus system of the laser cutting head. Wherein the controller controls each of the pixels of the spatial light modulator in order to convert a phase of each of the laser light reflected by each of the pixels when the cutting depth of the object reaches a first predetermined depth. Wherein the controller controls the jig or the laser cutting head to move when the cutting depth reaches a second predetermined depth. 
     The accompanying drawings are incorporated in and constitute a part of this application and, together with the description, serve to explain the principles of the disclosure in general terms. Like numerals refer to like parts throughout the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objects, spirits, and advantages of the preferred embodiments of the present disclosure will be readily understood by the accompanying drawings and detailed descriptions, wherein: 
         FIG.  1 A  illustrates a micro schematic view of the laser cutting; 
         FIG.  1 B  illustrates an energy distribution map of the laser light; 
         FIG.  2 A  illustrates a flow chart of a first preferred embodiment of the laser cutting method of the present disclosure; 
         FIG.  2 B  illustrates a schematic view of a laser cutting device; 
         FIG.  2 C  illustrates a schematic view of a spatial light modulator; 
         FIG.  2 D  illustrates a schematic structural view of a controller of the present disclosure; 
         FIG.  3 A  and  FIG.  3 B  illustrate schematic views of the light pattern distributions at different cutting depths; 
         FIG.  3 C  illustrates a schematic view of the cutting depths, and is represented by the cross-section of the laser light and the object. 
         FIG.  4 A  illustrates a flow chart of a second embodiment of the laser cutting method of the present disclosure; 
         FIG.  4 B  illustrates a schematic view of the laser light of the second embodiment of the present disclosure; 
         FIG.  5    illustrates a schematic view of a water-guided laser of the present disclosure; 
         FIG.  6 A  to  FIG.  6 D  illustrate schematic views of laser cutting processes of the present disclosure; 
         FIG.  7 A  illustrates a cutting plane view of a traditional invisible laser cutting technology or Stealth Dicing™ in prior arts; and 
         FIG.  7 B  illustrates a cutting plane view of the cutting method of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In order to describe in detail the technical content, structural features, achieved objectives and effects of the instant application, the following detailed descriptions are given in conjunction with the drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the application and not to limit the scope of the instant application. 
     The present disclosure provides a laser cutting method, and it adopts a spatial light modulator to modulate a plurality of phases of laser lights, so as to control the energy concentration positions of the laser lights, and overcome the problem of uneven cutting surfaces. The laser cutting method is adopted to use a laser cutting device  100 . Please refer to  FIG.  2 B , which illustrates a schematic view of a laser cutting device. The laser cutting device  100  has a laser light source  110 , a beam expander  120 , a spatial light modulator  130 , a plurality of reflection mirrors  101 , a laser cutting head  140 , a jig  210 , and a controller  160 . 
     With reference to  FIG.  2 A , which illustrates a flow chart of a first preferred embodiment of the laser cutting method of the present disclosure. A step (S 11 ) is of emitting a laser light  111  to a spatial light modulator  130  that has a plurality of pixels  131 . That is, a laser light source  110  emits the laser light  111 , then to a beam expander  120 . Continuously, a laser light  111   a  expanded by the beam expander  120  is irradiated on the spatial light modulator  130 . 
     Referring to  FIG.  2 C , which illustrates a schematic view of the spatial light modulator. The spatial light modulator  130  is an LCOS (Liquid Crystal On Silicon) device, and has a plurality of pixels  131 . It is able to control a phase of each of the laser lights reflected by each of the pixels  131 . A laser light  111   b  is reflected by the LCOS device. Because of converting the phases, the energy concentration positions of the laser lights  111   b  may be varied. That means light pattern distributions of focal points are changed. 
     Please refer to  FIG.  2 A  and  FIG.  2 B . A step (S 12 ) is of the laser light  111   b  modulated by the spatial light modulator  130  being irradiated on an uncut object  10 , which is to be cut, for forming a focal point and cutting the uncut object  10 . The laser light  111   b  modulated by the spatial light modulator  130  is reflected by the reflection mirrors  101  in order to adjust directions, and then passes through the laser cutting head  140  with an autofocus system. The laser cutting head  140  with the autofocus system mainly helps the laser light  111   b  to focus onto the object  10  and measures cutting depths. For the embodiment, the object ( 10 ), which is to be cut, is a crystal pillar, such as silicon carbide or gallium nitride. 
     Referring to  FIG.  5   , which illustrates a schematic view of a water-guided laser of the present disclosure. For the preferred embodiment, the step (S 11 ) further comprises that of: launching a water column  156 ′ toward a direction of the uncut object  10 . The step (S 12 ) further comprises that of: the laser light  111   b ′ being irradiated on the object  10  by total reflection in the water column  156 ′ for cutting the object  10 . As it can be seen, the laser cutting head  140  further comprises a focusing lens  151  and a water jacket  152  below the focusing lens  151 , wherein the water jacket  152  has a transparent window  153 , a water inlet  154  and a nozzle  155 . The transparent window  153  is disposed on an upper lateral surface of the water jacket  152 , and faces the focusing lens  151 . The nozzle  155  is disposed at a lower side surface of the water jacket  152 . Further, The nozzle  155  is on a vertical projection plane same as the transparent window  153 . The water inlet  154  is disposed on a lateral surface of the water jacket  152 , liquid  156  is injected into the water jacket  152  through the water inlet  154 . Besides, the liquid  156  is injected into the water jacket  152  under a certain pressure, so that the liquid  156  is sprayed out from the nozzle  155  to form a water column  156 ′ in order to cut/pound the object  10 . 
     The laser light  111   b  is emitted to the water jacket  152  by means of the focusing lens  151  and the transparent window  153 , and then leaves the water jacket  152  with the liquid  156  from the nozzle  155 . In the meantime, the laser light  111   b ′ may not leave from the water column  156 ′, since it is reflected by an inner surface in the water column  156 ′. Namely, the laser light  111   b ′ is irradiated on the object  10  by total reflection in the water column  156 ′, that also effectively promotes a focus effect of the laser light  111   b ′. In addition, the water column  156 ′ is capable of lowering down the temperature while the object  10  is being cut. The dust generated by cutting the object  10  is wiped out simultaneously, so as to maintain the cleanliness of a cutting path. 
     According to  FIG.  2 A  and  FIG.  2 B , as soon as the laser light  111   b  is irradiated on the object  10 , the work of cutting is started. Thus, a step (S 13 ) is of measuring a cutting depth of the object ( 10 ). By way of the autofocus system, the light reflected by the laser light  111   b  from the object to be cut  10  can be measured for the cutting depth. A step (S 14 ) is being processed while a first predetermined depth is reached, and it is of the spatial light modulator  130  converting a phase of each of the laser light  111   b  modulated by each of the pixels  131  to change a light pattern distribution at the focal point. Continuously, a step (S 15 ) of repeating the step (S 12 ) to the step (S 14 ) until the cutting depth of the object  10  reaching a second predetermined depth is executed. It is to be noted, every cycle of executing the step (S 12 ) to the step (S 14 ) is using a different first predetermined depth, which means the first predetermined depth will be varied by a new cycle of executing the step (S 12 ) to the step (S 14 ). It is to be noted, every cycle of executing from the step (S 12 ) to the step (S 14 ) is using a different first predetermined depth, which means a new cycle of executing from the step (S 12 ) to the step (S 14 ) will be a new first predetermined depth. 
     With reference to  FIG.  1 B ,  FIG.  3 A ,  FIG.  3 B , and  FIG.  3 C ,  FIG.  3 A  and  FIG.  3 B  illustrate schematic views of the light pattern distributions at different cutting depths, wherein a vertical axis represents energy strength, and a horizontal axis represents position along a horizontal direction.  FIG.  3 C  illustrates a schematic view of the cutting depths, and is represented by the cross-section of the laser light and the object  10 . According to the step (S 12 ) and the step (S 14 ), the light pattern distribution in  FIG.  1 B  is used to cut the object  10 . Therefore, corresponding to  FIG.  3 C , the energy concentration positions are located on a vertical line  21   a . When the cutting depth reaches a first predetermined depth L 1 , the spatial light modulator  130  may remodulate the laser light  111   b  in order to make the light pattern distributions of the laser light  111   b  be as  FIG.  3 A . Consequently, the object  10  is being cut, and then the energy concentration positions are distributed on a vertical line  21   b , corresponding to  FIG.  3 C . When the cutting depth reaches another first predetermined depth L 2 , the spatial light modulator  130  may remodulate the laser light  111   b  in order to make the light pattern distributions of the laser light  111   b  be as  FIG.  3 B . Consequently, the object  10  is being cut, and then the energy concentration positions are distributed on a vertical line  21   c , corresponding to  FIG.  3 B . When the cutting depth reaches more another first predetermined depth L 3 , a total cutting depth is equal to a second predetermined depth L 4 . It seems that the second predetermined depth L 4  is the same as the thickness of the object  10 , that is to say the laser light  111   b  penetrates through the object by cutting. Therefore, the laser cutting head  140  with the autofocus system or the cut object  10  can be moved along a cutting path, wherein moving the cut object  10  must be through a jig  210 . If continuous cutting the object  10  is a need, the three first predetermined depths L 1 ˜L 3  may be recut. 
     For another embodiment, the plurality of first predetermined depths L 1 ˜L 3  may be different depths, such as 1 mm of the first predetermined depth L 1 , 1.5 mm of the first predetermined depth L 2  and 2 mm of the first predetermined depth L 3 . The total depth of all the first predetermined depths is equal to a second predetermined depth. Further, before reaching the second predetermined depth, different combinations of the first predetermined depths can be used for cutting at different cutting points. The number of the aforesaid first predetermined depth is three, but not limit thereto. Persons who are skilled in the art may be able to set different number of the first predetermined depth. 
     In a period of cutting a depth, the spatial light modulator  130  modulates the laser light  111   b  in order to change the energy concentration positions. This is to let the laser light  111   b  avoid a heat affected zone of the object  10 , so as to decrease the refractive index of the laser light due to the heat-affected zone, and improve the flatness of a cutting surface. 
     Besides, a similar concept can be applied to the field of the invisible laser cutting technology or Stealth Dicing™. Following will be the descriptions as an embodiment. Please refer to  FIG.  4 A , which illustrates a flow chart of a second embodiment of the laser cutting method of the present disclosure. A step (S 21 ) is of emitting a laser light to a spatial light modulator that has a plurality of pixels. The spatial light modulator for the embodiment is LCOS device, which is the same as the first embodiment, and it will be no longer described any further. Then a step (S 22 ) is of the laser light being focused on a plurality of focal points in an uncut object, which is to be cut, via the spatial light modulator, wherein the spatial light modulator dynamically converts a phase of each of the laser lights modulated by each of the pixels in order to change a light pattern distribution of each of the focal points. The uncut object is a transparent substance at this embodiment. The so-called transparent substance means that the transmittance of the transparent substance is greater than 80% corresponding to the wavelength of the laser light. Definitely, persons skilled in the art may choose substances, which are with worse transmittance, to be uncut objects. That is the uncut object, which is to be cut, can be transparent or non-transparent substance. 
     With respect to  FIG.  4 B , which illustrates a schematic view of the laser light of the second embodiment of the present disclosure. The laser light  111   b  penetrates through the laser cutting head  140  with the autofocus system and then projects on/in the object  10 , which is to be cut. For the embodiment, the laser light  111   b  will focus on the focal points F 1 , F 2  and F 3 , wherein the focal point F 1  is on the surface of the object  10 . The light pattern distributions of the focal points F 1 , F 2  and F 3  are not the same, such as the light pattern distributions of  FIGS.  1 B,  3 A and  3 B . Accordingly, different light pattern distributions may avoid different heat-affected zones generated by different focal points when dissolving the focal points F 1 , F 2  and F 3 . Following is to rotate the object  10 , which is being cut. After rotating the object  10  a circle, the dissolved portions of the focal points F 1 , F 2  and F 3  form a cross section, thus the cut object  10  is taken apart and left from the uncut portion of the object  10 , so that the cutting is finished. It is to be noted that the cross section is neater, since different light pattern distributions may avoid different heat-affected zones generated by different focal points. 
     Further, according to the embodiment in  FIG.  4 B , the focal point F 1  is located on the surface of the object  10 , but it is not limited thereto. Another option is all the focal points F 1 , F 2  and F 3  are under the surface of the object  10 . 
     Regarding to  FIG.  7 A  and  FIG.  7 B , which illustrate a cutting plane view of a laser stealth dicing in prior arts and a cutting plane view of the cutting method of the present disclosure.  FIG.  7 A  adopts a conventional multi-focus and same-phase laser light to engage cutting. When dissolving the material of the object  10 , the heat effects will affect the focal points of the laser light, the conventional multi-focus and same-phase laser light may not be able to let the focal lights arrange in order. As shown in  FIG.  7 A , the cutting surface is not neat, and the arrangement of the blast points FA, which are the focal points of the laser light, of the cutting surface is confused and disordered. On the contrary,  FIG.  7 B  uses the present disclosure to engage cutting. It seems that the flatness of the cutting surface is greatly improved, and the blast points FB of the cutting surface are arranged orderly. 
     In accordance with  FIG.  2 D , which is a schematic structural view of a controller of the present disclosure. The laser cutting method of the present disclosure is through a controller  160 . The controller  160  is electrically connected with a laser light source  110 , the spatial light modulator  130 , the laser cutting head  140 , and the jig  210 . The controller  160  is a PLC (Programmable Logic Controller) module or a computing device with control programs, and further has an input interface  161 , which is adopted to input a control instruction. The controller  160  receives the control instructions to order the laser light source  110  and the spatial light modulator  130 . In addition, the input interface  161  is a keyboard or a touch panel. 
     Furthermore, the controller  160  controls the output power of the laser light source  110  and the pixels of the spatial light modulator  130 . In a preferred embodiment, the control instructions include a plurality of first cutting depths and second cutting depths. Hence, the controller  160  computes control parameters according to the first cutting depths and the second cutting depths in order to modulate the output power of the laser light source  110  and the pixels of the spatial light modulator  130 . In addition, the laser cutting head  140  and the jig  210  can be controlled by the controller as well, so as to adjust the positions where the laser lights irradiate on, also named cutting positions, on/in the object  10 . For more descriptions about the controller  160 , it controls the movement of the laser cutting head  140  to adjust the cutting positions, or the movement or rotation of the jig  210  to change the positions of the object  10 . 
     Referring to  FIG.  6 A  to  FIG.  6 D , which illustrate schematic views of the laser cutting processes of the present disclosure. The laser cutting method is basically applied to a cutting apparatus that is adopted to cut the uncut object  10 . The cutting apparatus has a laser cutter and the jig  210 . To remain a neat view,  FIG.  6 A  to  FIG.  6 D  only illustrate the laser cutting head  140  with the autofocus system in the cutting apparatus. The jig  210  is a clamping tool in order to fix the object  10 , and also makes it beneath the laser cutting head  140  with the autofocus system. Another useful function for the jig  210  is to rotate the object  10  while in the laser cutting processes. As to the embodiment of  FIG.  6 A  to  FIG.  6 D , the object  10  is a cylinder. 
     Please firstly refer to  FIG.  6 A . The uncut object  10  fixed by the jig  210  is under the laser cutting head  140  with the autofocus system. The laser light  111   b , penetrating through the laser cutting head  140  with the autofocus system, projects on the uncut object  10 . As shown in  FIG.  6 B , the laser light  111   b  is modulated by the spatial light modulator  130 , so as to pierce through the object  10  based on different light pattern distributions for forming the cutting depths. For the embodiment, the cutting depth is equal to the radius of the object  10 . 
     With respect to  FIG.  6 C , when the cutting depth reaches the second predetermined cutting depth, the jig  210  rotates the object  10  with an axis C as the axis of rotation. In the meantime, the laser light  111   b  is continuously dissolving the material, along a radius direction, of the object  10  until the object  10  rotates one cycle (360°). Referring to FIG.  6 D, the radius material of the object  10  is cut, and a cut portion  10 ′ is leaving from the object  10 . 
     The laser cutting method is to let the laser light, modulated by the spatial light modulator  130 , irradiate on the uncut object  10  under the condition of different light pattern distributions. It can be seem that in  FIG.  7 B , the laser cutting processes with different light pattern distributions will greatly improve the flatness of the cutting surface. 
     The laser cutting method of the present disclosure adopts a multi-phase laser light for cutting, and the cutting path is narrower. Therefore. the fragments generated in the cutting processes is not easily splashed, and can further overcome the shortcomings of the uneven cutting surface of the traditional invisible laser cutting technology or Stealth Dicing™. 
     Although the disclosure has been disclosed and illustrated with reference to particular embodiments, the principles involved are susceptible for use in numerous other embodiments that will be apparent to a person having ordinary skill in the art. This disclosure is, therefore, to be limited only as indicated by the scope of the appended claims.