Patent Publication Number: US-2023154794-A1

Title: Method of processing wafer

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a method of processing a wafer with a plurality of devices provided thereon and a method of manufacturing a plurality of packaged devices from such a wafer. 
     Description of the Related Art 
     Pieces of electronic equipment such as cellular phones or personal computers incorporate device chips. Device chips are manufactured as follows. First, a plurality of projected dicing lines are established in a grid pattern on a face side of a silicon wafer, hereinafter simply referred to as “wafer,” and devices such as an integrated circuit (IC) are constructed in respective areas demarcated on the face side of the wafer by the projected dicing lines. Then, a laser beam applying apparatus applies a pulsed laser beam having a wavelength absorbable by the wafer to the face side of the wafer, producing laser-processed slots in the wafer along the projected dicing lines to a predetermined depth from the face side. Then, a cutting apparatus further cuts into the laser-processed slots in the wafer, dividing the wafer into device chips. 
     When the pulsed laser beam is applied to the wafer to produce the laser-processed slots in the wafer, a melted substance, i.e., debris, produced from the wafer by the applied pulsed laser beam is scattered around and deposited on the face side of the wafer, tending to lower quality of the device chips. To solve this problem, there has been known in the art a technology for covering the face side of the wafer with a protective film of water-soluble resin (see, for example, JP 2006-140311A). When the pulsed laser beam is applied to the face side of the wafer that is covered with the protective film, the debris produced from the wafer is deposited on the protective film. After the wafer has been processed by the pulsed laser beam, the face side of the wafer is cleaned by pure water or the like, removing the debris together with the protective film from the wafer. Accordingly, the debris is prevented from being deposited on the face side of the wafer. 
     SUMMARY OF THE INVENTION 
     However, it has been found that when the face side of the wafer is covered with an encapsulating resin after the protective film and the debris have been removed, there are instances where the face side of the wafer and the encapsulating resin are not held together in a sufficient level of intimate contact with each other. 
     The present invention has been made in view of the above difficulty. It is an object of the present invention to increase the level of intimate contact between the face side of a wafer and an encapsulating resin covering the face side of the wafer. 
     In accordance with an aspect of the present invention, there is provided a method of processing a wafer having a plurality of devices provided in respective areas demarcated on a face side of the wafer by a plurality of intersecting projected dicing lines established on the face side. The method includes a protective film applying step of coating the face side of the wafer with a protective film agent and thereafter drying the protective film agent into a protective film covering the face side of the wafer, after the protective film applying step, a laser processing step of applying a laser beam having a wavelength absorbable by the wafer to the wafer along the projected dicing lines on the face side of the wafer, thereby producing a plurality of laser-processed slots in the wafer along the projected dicing lines, after the laser processing step, a protective film removing step of cleaning away the protective film, after the protective film removing step, a residual organic substance removing step of applying ultraviolet rays to the face side of the wafer to remove an organic substance deriving from the protective film and remaining on the face side of the wafer, and after the residual organic substance removing step, an encapsulating resin applying step of covering coverage areas corresponding to the respective devices on the face side of the wafer with an encapsulating resin. 
     The organic substance remaining on the face side of the wafer after the protective film removing step and before the residual organic substance removing step includes compounds containing nitrogen atoms. 
     In accordance with another aspect of the present invention, there is provided a method of manufacturing a plurality of packaged devices from a wafer having a plurality of devices provided in respective areas demarcated on a face side of the wafer by a plurality of intersecting projected dicing lines established on the face side. The method includes a protective film applying step of coating the face side of the wafer with a protective film agent and thereafter drying the protective film agent into a protective film covering the face side of the wafer, after the protective film applying step, a laser processing step of applying a laser beam having a wavelength absorbable by the wafer to the wafer along the projected dicing lines on the face side of the wafer, thereby producing a plurality of laser-processed slots in the wafer along the projected dicing lines, after the laser processing step, a protective film removing step of cleaning away the protective film, after the protective film removing step, a residual organic substance removing step of applying ultraviolet rays to the face side of the wafer to remove an organic substance deriving from the protective film and remaining on the face side of the wafer, and after the residual organic substance removing step, a packaged device producing step of producing a plurality of packaged devices in which coverage areas corresponding to the respective devices on the face side of the wafer are covered with an encapsulating resin. 
     The method of processing a wafer according to the aspect of the present invention includes, after the protective film removing step, the residual organic substance removing step of applying ultraviolet rays to the face side of the wafer to remove an organic substance deriving from the protective film and remaining on the face side of the wafer. Since the organic substance deriving from the protective film is removed in the residual organic substance removing step, the amount of organic substance remaining on the face side is reduced to about the same level as if the face side were not covered with the protective film. Therefore, the level of intimate contact between the face side of the wafer and the encapsulating resin becomes higher than if the residual organic substance removing step were not carried out. 
     The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing some preferred embodiments of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a flowchart of a sequence of a method of manufacturing a plurality of packaged devices according to a first embodiment of the present invention; 
         FIG.  2    is a perspective view of a laser processing apparatus; 
         FIG.  3    is a perspective view of a wafer unit; 
         FIG.  4    is a perspective view of a coating/cleaning assembly; 
         FIG.  5    is a side elevational view, partly in cross section, illustrating a protective film applying step; 
         FIG.  6    is an enlarged fragmentary cross-sectional view of a wafer covered with a projective film; 
         FIG.  7    is an enlarged fragmentary elevational view, partly in cross section, illustrating a laser processing step; 
         FIG.  8    is a side elevational view, partly in cross section, illustrating a protective film removing step; 
         FIG.  9    is an enlarged fragmentary cross-sectional view of the wafer after the protective film removing step; 
         FIG.  10    is a side elevational view, partly in cross section, illustrating a residual organic substance removing step; 
         FIG.  11    is an enlarged fragmentary cross-sectional view of the wafer covered with an encapsulating resin; 
         FIG.  12    is a perspective view illustrating a cutting step; 
         FIG.  13    is a flowchart of a sequence of a method of manufacturing a plurality of packaged devices according to a second embodiment of the present invention; 
         FIG.  14 A  is a side elevational view, partly in cross section, illustrating a plurality of device chips; and 
         FIG.  14 B  is a cross-sectional view of a packaged device. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.  FIG.  1    illustrates a sequence of a method of manufacturing a plurality of packaged devices  31  (see  FIG.  12   ) according to a first embodiment of the present invention. As illustrated in  FIG.  1   , the method of manufacturing a plurality of packaged devices  31  includes a protective film applying step S 10 , a laser processing step S 20 , a protective film removing step S 30 , a residual organic substance removing step S 40 , an encapsulating resin applying step S 52 , and a cutting step S 54 . In the present description, some of the steps of the method of manufacturing a plurality of packaged devices  31  may be referred to as a method of processing a wafer  11 . According to the first embodiment, the encapsulating resin applying step S 52  and the cutting step S 54  will collectively be referred to as a packaged device producing step S 50 . Each of the packaged devices  31  manufactured according to the first embodiment is also called “wafer level chip size (scale) package (WL-CSP)”. The steps of the method illustrated in  FIG.  1    will be described below. 
       FIG.  2    illustrates, in perspective, a laser processing apparatus  2  to be used in each of protective film applying step S 10 , laser processing step S 20 , protective film removing step S 30 , and residual organic substance removing step S 40 . In  FIG.  2   , the laser processing apparatus  2  is illustrated in reference to a three-dimensional coordinate system having X-, Y-, and Z-axes indicated respectively by the arrows X, Y, Z, where X-, Y-, and Z-axes are orthogonal with each other. The X-axis and the Y-axis lie on a horizontal plane, whereas the Z-axis extends vertically perpendicularly to the horizontal plane. X-axis directions, i.e., leftward and rightward directions, extend parallel to the X-axis, and Y-axis directions, i.e., forward and rearward directions, extend parallel to the Y-axis. Z-axis directions, i.e., upward and downward directions, extend parallel to the Z-axis perpendicularly to the X-axis and the Y-axis. The laser processing apparatus  2  has a base  4  supporting thereon and housing therein the components of the laser processing apparatus  2 . The laser processing apparatus  2  includes a cassette table  8  shaped as a rectangular plate for supporting a cassette  6  thereon. The cassette table  8  is disposed in a front corner of the base  4  that is oriented in one of the Y-axis directions and one of the X-axis directions. An elevator, not depicted, is disposed in the base  4  beneath the cassette table  8  for selectively lifting and lowering the cassette table  8  along the Z-axis. The cassette  6  houses therein a plurality of wafer units  21  each having a wafer  11  shaped as a circular plate having a substrate mainly made of a semiconductor material such as silicon. 
     The structure of a wafer unit  21  will be described below with reference to  FIG.  3   .  FIG.  3    illustrates, in perspective, the wafer unit  21 . As illustrated in  FIG.  3   , the wafer  11  has a face side  11   a  on which there is disposed a circuit layer  11   c  (see  FIG.  6   ) including an interlayer insulating film material with a low dielectric constant, i.e., a low-k material, and a metallization layer. A plurality of straight projected dicing lines or streets  13  are established in a grid or intersecting pattern on the face side  11   a  of the wafer  11 . Devices  15  such as ICs are formed in respective rectangular areas demarcated on the face side  11   a  of the wafer  11  by the projected dicing lines  13 . As illustrated in  FIG.  6   , the rectangular areas where the devices  15  are present are slightly thicker than areas where the projected dicing lines  13  are established. 
     As illustrated in  FIG.  3   , a circular dicing tape  17  that is larger in diameter than the wafer  11  has a central portion affixed to a reverse side  11   b  of the wafer  11 . The dicing tape  17  has a layered structure including a base layer and an adhesive or glue layer. For example, the base layer is made of a resin such as polyolefin, whereas the adhesive layer is made of an adhesive resin such as an uncured ultraviolet-curable resin. The dicing tape  17  has an outer circumferential portion to which there is affixed a surface of an annular frame  19  having a circular opening larger in diameter than the wafer  11 . The wafer  11  is thus supported on the frame  19  by the dicing tape  17 , jointly making up the wafer unit  21 . 
     As illustrated in  FIG.  2   , the laser processing apparatus  2  has a push-pull arm  10  disposed behind the cassette table  8 , i.e., spaced from the cassette table  8  in the other of the Y-axis directions. The push-pull arm  10  grips the frame  19  and delivers the wafer unit  21  out of the cassette  6  onto a pair of guide rails  12 . The guide rails  12  are disposed one on each side of a track along which the push-pull arm  10  is movable and have a function to adjust a position of the wafer unit  21  in the X-axis directions. A first delivery unit  14  is disposed on the base  4  near the guide rails  12  for delivering the wafer unit  21  from and to the guide rails  12 . 
     The first delivery unit  14  has an arm that is of a substantially L shape as viewed in plan. The arm supports on its distal end an attracting mechanism for attracting the frame  19  under suction. The arm has a proximal end coupled to a turning mechanism including an electric motor, not depicted, for turning the arm about a predetermined pivot axis. The first delivery unit  14  is disposed in the vicinity of a coating/cleaning unit  16  housed in the base  4 . The first delivery unit  14  delivers the wafer unit  21  between the guide rails  12  and the coating/cleaning unit  16 . The coating/cleaning unit  16  will be described in detail below with reference to  FIG.  4   . 
       FIG.  4    illustrates the coating/cleaning unit  16  in perspective. The coating/cleaning unit  16  produces a protective film  23   a  (see  FIG.  6   ) on the face side  11   a  of the wafer  11  and then cleans the wafer  11  that has been processed by a laser beam with the face side  11   a  coated with the protective film  23   a . As illustrated in  FIG.  4   , the coating/cleaning unit  16  has a spinner table  18  shaped as a circular plate. The spinner table  18  has a frame of metal that is shaped as a circular plate. The frame has a circular cavity, not depicted, defined in an upper surface thereof. A circular porous plate is fixedly disposed in the circular cavity. A negative pressure generated by a suction source, not depicted, such as an ejector is transmitted to the circular porous plate through a fluid channel, not depicted, defined in the frame. 
     The upper surface of the frame lies substantially flush with an upper surface of the circular porous plate, jointly making up a substantially flat holding surface  18   a . A plurality of clamp units  18   b  (not illustrated in  FIG.  2   ) are mounted on an outer circumferential portion of the spinner table  18 . Each clamp unit  18   b  can swing like a pendulum according to centrifugal forces generated by the rotation of the spinner table  18 . The spinner table  18  is coupled to a first actuator  20  such as an electric motor disposed below the spinner table  18  for rotating the spinner table  18  about a predetermined rotational axis parallel to the Z-axis. A plurality of air cylinders  22 , each of which has a rod movable along the Z-axis, are mounted on a side surface of the first actuator  20 . 
     When the air cylinders  22  are actuated, the spinner table  18  and the first actuator  20  are moved along the Z-axis between a relatively high loading/unloading position (see  FIG.  4   ) and a relatively low working position (see  FIGS.  5 ,  8 , and  10   ). The spinner table  18  has side and bottom walls surrounded by a hollow cylindrical bottomed receptacle  24  whose inside diameter is larger than the outside diameter of the spinner table  18 . The receptacle  24  functions as a waste container. The receptacle  24  is supported on a plurality of legs  26 . The receptacle  24  has a through opening defined centrally in its bottom wall. The first actuator  20  has an output shaft extending vertically through the through opening in the bottom wall of the receptacle  24 . The through opening is covered with a hollow cylindrical cover (see  FIG.  5   ). 
     The receptacle  24  is horizontally spaced from the spinner table  18  by an annular clearance  28  in which there is disposed a coating unit  30  for coating the wafer  11  with a liquid protective film agent  23  (see  FIG.  5   ). The coating unit  30  has a first nozzle  32  for supplying the liquid protective film agent  23  to the face side  11   a  of the wafer  11  that is held under suction on the holding surface  18   a . The first nozzle  32  is fixed to a distal end of a first arm  34 . The first nozzle  32  and the first arm  34  are omitted from illustration in  FIG.  2   . The first nozzle  32  is fluidly connected to a liquid protective film agent supply source, not depicted, through a fluid channel, not depicted, defined in the first arm  34 . 
     The liquid protective film agent supply source includes a tank, not depicted, storing the liquid protective film agent  23  therein and a pump, not depicted, for sending the liquid protective film agent  23  from the tank through the fluid channel in the first arm  34  to the first nozzle  32 . The liquid protective film agent  23  includes a solvent of pure water, a water-soluble resin, a light absorbent, and an organic solution. The water-soluble resin includes polyvinylpyrrolidone, for example, though it may be any of other water-soluble resins, such as poly-N-vinylacetamide, polyoxazoline, or a copolymer of polymeric compounds, e.g., a vinyl acetate-vinylpyrrolidone copolymer, or a combination of a plurality of types of water-soluble resins. 
     The light absorbent includes a cinnamic acid derivative such as a ferulic acid or a caffeic acid or a benzophenone derivative such as polyhydroxy benzophenone or a 2-hydroxy-4-methoxy benzophonene-5-sulfonic acid, a flavone, flavonoid, or flavonol derivative such as transglycosylated rutin or transglycosylated hesperidin. The organic solution includes propylene glycol monomethyl ether (PGME), methanol, ethanol, isopropanol, acetone, or tetrahydrofuran. 
     The first arm  34  has a proximal end coupled to a reversible electric motor  36  (see  FIG.  5   ). When the reversible electric motor  36  is energized, it turns the first arm  34  between a position (see  FIG.  5   ) above a central area of the holding surface  18   a  where the first nozzle  32  applies the liquid protective film agent  23  to the wafer  11  on the holding surface  18   a  and a retracted position (see  FIG.  4   ) where the first nozzle  32  is retracted from the position above the holding surface  18   a.    
     In the annular clearance  28 , there is also disposed a cleaning unit  38  at a position that is diametrically opposite the coating unit  30  across the spinner table  18 . The cleaning unit  38  has a second nozzle  40  for supplying cleaning water  25  (see  FIG.  8   ) such as pure water to the face side  11   a  of the wafer  11  held under suction on the holding surface  18   a.    
     The second nozzle  40  is fixed to a distal end of a second arm  42 . The second nozzle  40  and the second arm  42  are omitted from illustration in  FIG.  2   . The second nozzle  40  is fluidly connected to a cleaning water supply source, not depicted, through a fluid channel, not depicted, defined in the second arm  42 . The cleaning water supply source includes a tank, not depicted, storing the cleaning water  25  therein and a pump, not depicted, for sending the cleaning water  25  from the tank through the fluid channel in the second arm  42  to the second nozzle  40 . The second arm  42  has a proximal end coupled to a reversible electric motor  44  (see  FIG.  5   ). 
     When the reversible electric motor  44  is energized, it turns the second arm  42  between a predetermined area (see  FIG.  8   ) above the holding surface  18   a  and a retracted position (see  FIG.  4   ) where the second nozzle  40  is retracted from the area above the holding surface  18   a . In the predetermined area above the holding surface  18   a , the second arm  42  is swung by the reversible electric motor  44 , swinging the second nozzle  40  in a predetermined angular range while supplying the cleaning water  25  to the wafer  11  on the holding surface  18   a.    
     An air ejection unit  46  is disposed in the clearance  28  between the coating unit  30  and the cleaning unit  38 . The air ejection unit  46  has a third nozzle  48  for supplying air, not depicted, such as drying air to the face side  11   a  of the wafer  11  held under suction on the holding surface  18   a . The third nozzle  48  is fixed to a distal end of a third arm  50 . The third nozzle  48  and the third arm  50  are omitted from illustration in  FIG.  2   . The third nozzle  48  is fluidly connected to an air supply source, not depicted, through a fluid channel, not depicted, defined in the third arm  50 . 
     The air supply source includes an air compressor, not depicted, and a tank, not depicted, storing air under pressure supplied from the air compressor. The third arm  50  has a proximal end coupled to a reversible electric motor, not depicted. When the reversible electric motor is energized, it turns the third arm  50  between a predetermined area, not depicted, above the holding surface  18   a  and a retracted position (see  FIG.  4   ) where the third nozzle  48  is retracted from the area above the holding surface  18   a . In the predetermined area above the holding surface  18   a , the third arm  50  is swung in a predetermined angular range by the reversible electric motor, swinging the third nozzle  48  while supplying the air to the wafer  11  on the holding surface  18   a.    
     As illustrated in  FIG.  2   , a rectangular opening  4   a  that is open upwardly is defined in the base  4  forwardly of the coating/cleaning unit  16 . The rectangular opening  4   a  has a longitudinal axis extending along the X-axis. A chuck table  52  shaped as a circular plate is disposed in the rectangular opening  4   a . The chuck table  52  has a frame of metal that is shaped as a circular plate. The frame has a circular cavity, not depicted, defined in an upper surface thereof. A circular porous plate is fixedly disposed in the circular cavity. A negative pressure generated by a suction source, not depicted, such as an ejector is transmitted to the circular porous plate through a fluid channel, not depicted, defined in the frame. 
     The upper surface of the frame lies substantially flush with an upper surface of the circular porous plate, jointly making up a substantially flat holding surface  52   a  for holding the wafer unit  21  under suction thereon. A plurality of clamp units  52   b  that are actuatable by respective air actuators, not depicted, are mounted on an outer circumferential portion of the chuck table  52 . When actuated by the air actuators, the clamp units  52   b  grip the frame  19  of the wafer unit  21  held under suction on the holding surface  52   a . The chuck table  52  is coupled to a second actuator, not depicted, such as an electric motor disposed below the chuck table  52  for rotating the chuck table  52  about a predetermined rotational axis parallel to the Z-axis. 
     The second actuator is supported on an X-axis movable plate, not depicted. The X-axis movable plate is slidably supported on a pair of guide rails, not depicted, extending along the X-axis. A nut, not depicted, is mounted on a lower surface of the X-axis movable plate. A screw shaft, not depicted, extending along the X-axis and disposed between the guide rails is rotatably threaded through the nut. The screw shaft has an end coupled to a third actuator, not depicted, such as a stepping motor for rotating the screw shaft about its central axis. 
     The X-axis movable plate, the guide rails, the nut, the screw shaft, and the third actuator jointly make up a ball-screw-type processing feed unit, not depicted, for moving the chuck table  52  and the second actuator along the X-axis. When the ball-screw-type processing feed unit is actuated, the chuck table  52  is moved between a loading/unloading area A 1  near the cassette table  8  and a processing area A 2 . When the wafer  11  on the chuck table  52  is processed by a laser beam, the chuck table  52  is reciprocably moved in the processing area A 2 . 
     An image capturing unit  54  is disposed above a track along which the chuck table  52  is movable. The image capturing unit  54  has a camera including an objective lens and an image capturing device such as a charge-coupled-device (CCD) image sensor or a complementary-metal-oxide-semiconductor (CMOS) image sensor. The chuck table  52  is turned about the predetermined rotational axis parallel to the Z-axis to orient one of the projected dicing lines  13  substantially parallel to the X-axis on the basis of the result of an alignment process based on an image captured of the face side  11   a  of the wafer  11  by the image capturing unit  54 . 
     The laser processing apparatus  2  includes a laser beam applying unit  56  disposed above the processing area A 2  in the x-axis direction. The laser beam applying unit  56  has a hollow cylindrical casing  58  whose longitudinal axis extends horizontally along the Y-axis and a beam condenser  60  including a condensing lens, etc. The casing  58  houses therein a laser oscillator, not depicted, having a laser medium made of Nd:YAG, Nd:YVO 4 , or the like. The laser oscillator includes a light source, not depicted, such as a laser diode for emitting stimulating light to the laser medium. 
     To the light source, there is electrically connected a pulse generator, not depicted, for controlling operation of the light source. The pulse generator controls laser beam pulse properties including a pulse duration, a repetitive frequency, etc. of a pulsed laser beam L (see  FIG.  7   ) emitted from the laser oscillator. The casing  58  also houses therein a wavelength converter (not depicted) having a nonlinear optical crystal for generating harmonics. 
     The laser beam L that is emitted from the laser oscillator is converted by the wavelength convertor such that the laser beam L has a main peak at a predetermined wavelength, e.g., 355 nm, absorbable by the wafer  11 . The laser beam L thus converted is emitted from the beam condenser  60  toward the holding surface  52   a  of the chuck table  52  positioned in the processing area A 2 . A ball-screw-type first Y-axis moving unit, not depicted, is coupled to the casing  58  for moving, i.e., indexing-feeding, the beam condenser  60  along the Y-axis. 
     The laser beam L applied from the beam condenser  60  to the wafer  11  on the holding surface  52   a  processes the wafer  11 . After the wafer  11  has been processed by the laser beam L, the chuck table  52  is returned from the processing area A 2  to the loading/unloading area A 1  by the processing feed unit. A second delivery unit  62  for delivering the wafer unit  21  from the chuck table  52  in the loading/unloading area A 1  to the coating/cleaning unit  16  is disposed behind the loading/unloading area A 1 . The second delivery unit  62  has an arm combined with a lifting and lowering mechanism such as an air cylinder on a distal end thereof. The lifting and lowering mechanism includes a suction mechanism on a lower end thereof for attracting the frame  19  under suction. The arm has a proximal end coupled to a ball-screw-type second Y-axis moving unit, not depicted, for moving the arm along the Y-axis. 
     An ultraviolet ray applying unit  64  is disposed below the arm of the second delivery unit  62 . The ultraviolet ray applying unit  64  has a straight arm and a head  66  shaped as a circular plate connected to a distal end of the straight arm and having a diameter substantially equal to the outside diameter of the receptacle  24 . The head  66  has a circular cavity defined therein that is exposed downwardly. The circular cavity houses therein an array of cylindrical ultraviolet lamps  68  (see  FIG.  10   ). Each of the cylindrical ultraviolet lamps  68  includes a low-pressure mercury lamp, for example. 
     Ultraviolet (UV) rays  68   a  emitted from the ultraviolet lamps  68  include those having wavelengths of 185 nm and 254 nm. The ultraviolet rays  68   a  are applied from the head  66  to the holding surface  18   a  substantially in its entirety. The arm connected to the head  66  has a proximal end connected to a ball-screw-type third Y-axis moving unit, not depicted, for moving the arm and hence the head  66  along the Y-axis. The ball-screw-type third Y-axis moving unit moves the head  66  between an irradiating position B 1  covering the coating/cleaning unit  16  and a retracted position B 2  behind the irradiating position B 1 . 
     The wafer  11  is cleaned and dried by the coating/cleaning unit  16  and then irradiated with the ultraviolet rays  68   a  by the ultraviolet ray applying unit  64 . Thereafter, the wafer  11  is delivered from the irradiating position B 1  back to the cassette  6  by the first delivery unit  14 , the guide rails  12 , and the push-pull arm  10 . 
     The laser processing apparatus  2  also has a control panel  70  for entering commands from the operator into the laser processing apparatus  2 . The control panel  70  is mounted on a casing attached to a front side of the base  4 . The control panel  70  functions as a pushbutton user interface. 
     The laser processing apparatus  2  further includes a display device  72  such as a liquid crystal display. The display device  72  displays processing conditions entered by the operator through the control panel  70 , images acquired by the image capturing unit  54 , and other information. The display device  72  may include a touch panel functioning as both a display device and an input device, providing the control panel  70  is dispensed with. The components described above of the laser processing apparatus  2  are controlled by a controller, not depicted. 
     The controller includes a computer including a processor, i.e., a processing unit, typically a central processing unit (CPU), a main storage device such as a dynamic random access memory (DRAM), and an auxiliary storage device such as a flash memory. The auxiliary storage device stores pieces of software including predetermined programs. The controller has its functions performed when the processor and other components thereof are operated according to the stored pieces of software. 
     The method of processing the wafer  11  using the laser processing apparatus  2  will be described below. First, the wafer unit  21  is delivered from the cassette  6  to the coating/cleaning unit  16  where the face side  11   a  of the wafer  11  is coated with the protective film  23   a  (protective film applying step S 10 ).  FIG.  5    illustrates the protective film applying step S 10  in side elevation, partly in cross section. In  FIG.  5   , the air ejection unit  46  is omitted from illustration. Similarly, the air ejection unit  46  is omitted from illustration in  FIGS.  8  and  10   . 
     In the protective film applying step S 10 , the reverse side  11   b  of the wafer  11  is held under suction on the holding surface  18   a  with the dicing tape  17  interposed therebetween so that the face side  11   a  is exposed upwardly. Then, the spinner table  18  is rotated about its central axis at a predetermined speed ranging from 10 rpm to 100 rpm, for example. The first nozzle  32  is placed above the position above the central area of the holding surface  18   a , and then applies the liquid protective film agent  23  to the face side  11   a  of the wafer  11 . The liquid protective film agent  23  applied to the face side  11   a  is spread radially outwardly over the face side  11   a  in its entirety under centrifugal forces. Thereafter, the first nozzle  32  stops applying the liquid protective film agent  23  to the face side  11   a , while the spinner table  18  continues to rotate to dry the applied protective film agent  23  into a protective film  23   a  having a substantially uniform thickness ranging from 0.5 μm to 10 μm, for example, on the face side  11   a .  FIG.  6    illustrates the wafer  11  covered with the protective film  23   a  in enlarged fragmentary cross section. 
     After the protective film applying step S 10 , the wafer unit  21  is delivered to the chuck table  52  in the loading/unloading area A 1  and held under suction on the holding surface  52   a  thereof. The image capturing unit  54  captures an image of the face side  11   a  of the wafer  11 , and the alignment process is carried out by performing pattern matching, etc. based on the captured image. On the basis of the result of the alignment process, the chuck table  52  is slightly turned to orient one of the projected dicing lines  13  substantially parallel to the X-axis. Thereafter, the chuck table  52  is moved from the loading/unloading area A 1  to the processing area A 2  where the chuck table  52  is positioned directly below the laser beam applying unit  56 . The focused spot of the laser beam L emitted from the beam condenser  60  is positioned at one end of the projected dicing line  13  on the face side  11   a , and the chuck table  52  is moved in one of the X-axis directions to apply the laser beam L to the face side  11   a  along the projected dicing line  13  (laser processing step S 20 ). 
       FIG.  7    illustrates the laser processing step S 20  in enlarged fragmentary cross section. The laser beam L applied to the face side  11   a  performs an ablation process on the wafer  11 , partly removing the protective film  23   a  and the circuit layer  11   c  along the projected dicing line  13  thereby to produce a laser-processed slot  11   d  in the semiconductor substrate to a predetermined thickness. The laser beam L is applied to process the wafer  11  under the following processing conditions, for example.
         Laser medium: Nd:YAG   Wavelength: 355 nm   Average output power: 0.1 W to 100 W (typically, 0.5 W to 15 W)   Repetitive frequency: 20 kHz to 50000 kHz   Focused spot diameter: 1.0 μm to 100 μm (typically, 30 μm to 60 μm)   Pulse duration: 10 fs to 500 ns   Processing feed speed: 20 mm/s to 5000 mm/s (typically, 100 mm/s to 1000 mm/s)       

     After the laser beam L has been applied to the wafer  11  along the X-axis from one end to the other of a projected dicing line  13 , the beam condenser  60  is indexing-fed a predetermined distance along the Y-axis. Then, the laser beam L is applied to the wafer  11  along the X-axis from one end to the other of a next projected dicing line  13  that is disposed adjacent to the previous projected dicing line  13  in one of the Y-axis directions. After the laser beam L has been applied to the wafer  11  along all the projected dicing lines  13  that extend along one direction, the chuck table  52  is turned 90 degrees. Then, the laser beam L is applied to the wafer  11  along all the projected dicing lines  13  that extend perpendicularly to the one direction. In this manner, laser-processed slots  11   d  are produced in the wafer  11  along all the projected dicing lines  13  on the face side  11   a.    
     In the laser processing step S 20 , a melted substance produced from the wafer  11  by the applied laser beam L is scattered around as debris  27  and deposited on the upper surface of the protective film  23   a . After the laser processing step S 20 , the wafer unit  21  is delivered to the coating/cleaning unit  16  where the protective film  23   a  is cleaned away with cleaning water  25  (see  FIG.  8   ) (protective film removing step S 30 ).  FIG.  8    illustrates the protective film removing step S 30  in side elevation, partly in cross section. In the protective film removing step S 30 , the holding surface  18   a  holds the reverse side  11   b  of the wafer  11  under suction thereon. Then, while the second nozzle  40  is being swung in the predetermined angular range, the second nozzle  40  ejects the cleaning water  25  to the face side  11   a  and the spinner table  18  is rotated at a predetermined speed of 300 rpm, for example. 
     The protective film  23   a  is dissolved by the cleaning water  25  and removed from the face side  11   a  under centrifugal forces. At this time, the debris  27  is also removed together with the protective film  23   a  from the face side  11   a . After the wafer  11  has been cleaned for a predetermined period of time, the second nozzle  40  stops ejecting the cleaning water  25  to the wafer  11 . Then, the spinner table  18  is rotated at a predetermined speed of 2000 rpm, for example, for a predetermined period of time, thereby drying the wafer  11 . 
       FIG.  9    illustrates the wafer  11  after the protective film removing step S 30  in enlarged fragmentary cross section. The protective film  23   a  and the debris  27  are removed substantially entirely from the wafer  11  in the protective film removing step S 30 . However, a close examination conducted by the present applicant has revealed that a layer of organic substance deriving from the protective film  23   a  and having a thickness in the range from about several nm to several tens nm remains on the face side  11   a  of the wafer  11  after the protective film removing step S 30 . 
     Specifically, a layer made of compounds containing nitrogen atoms (N) and represented by molecular formulas C 4 H 8 NO, C 5 H 8 NO, C 7 H 10 NO, C 8 H 12 NO, etc. and having a thickness ranging from approximately several nm to several tens nm remains on the face side  11   a  of the wafer  11 . The compounds containing nitrogen atoms are thought to derive from polyvinylpyrrolidone or the like referred to above that is used as the water-soluble resin. In addition, compounds represented by molecular formulas C 2 H 3 O, C 4 H 5 O, etc. as well as the compounds containing nitrogen atoms remain on the face side  11   a  of the wafer  11 . The present applicant has found that when a layer of organic substance deriving from the protective film  23   a  and having a thickness ranging from approximately several nm to several tens nm remains on the face side  11   a  of the wafer  11 , the face side  11   a  of the wafer  11  and an encapsulating resin  29  (see  FIG.  11   ) are not held together in a sufficient level of intimate contact with each other, compared with when such a layer of organic substance does not remain on the face side  11   a.    
     It is considered that when an organic substance containing nitrogen atoms remains on the face side  11   a , the angle of contact of the encapsulating resin  29  with the face side  11   a  is smaller than when an organic substance containing nitrogen atoms does not remain on the face side  11   a . However, the present applicant has found that regardless of the smaller angle of contact, the level of intimate contact of the encapsulating resin  29  with the face side  11   a  is lower than when an organic substance containing nitrogen atoms does not remain on the face side  11   a  due to some action between the organic substance containing nitrogen atoms and the encapsulating resin  29 . According to the present embodiment, after the protective film removing step S 30 , the face side  11   a  of the wafer  11  is irradiated with ultraviolet rays  68   a  emitted from the ultraviolet lamps  68  (see  FIG.  10   ) to remove the layer of organic substance deriving from the protective film  23   a  and remaining on the face side  11   a  (residual organic substance removing step S 40 ). 
       FIG.  10    illustrates the residual organic substance removing step S 40  in side elevation, partly in cross section. In the residual organic substance removing step S 40 , the head  66  of the ultraviolet ray applying unit  64  is placed in the irradiating position B 1 . Then, the face side  11   a  of the wafer  11  whose reverse side  11   b  has been held under suction on the spinner table  18  that is kept still is irradiated in its entirety with the ultraviolet rays  68   a  emitted from the ultraviolet lamps  68 . For example, the ultraviolet rays  68   a  have an illuminance level of 50 (W/m 2 ) or higher and are applied to the face side  11   a  for an exposure time of  30  ( s ) or longer. According to the present embodiment, the illuminance level is set to a value ranging from  50  (W/m 2 ) to  70  (W/m 2 ), and the exposure time is set to 120 (s). The face side  11   a  of the wafer  11  is spaced from the ultraviolet lamps  68  by a distance of approximately 2 cm. 
     An example of mechanism for removing the residual organic substance from the face side  11   a  will be described below. When the ultraviolet rays  68   a  are applied to the face side  11   a  of the wafer  11  in a clean room atmosphere containing oxygen, those ultraviolet rays  68   a  which have the wavelength of 185 nm react with oxygen molecules (O 2 ), generating ozone (O 3 ). Furthermore, those ultraviolet rays  68   a  which have the wavelength of 254 nm react with the ozone, generating active oxygen. The generated active oxygen decomposes the organic substance made up of carbon (C), hydrogen (H), nitrogen (N), etc. into carbon dioxide (CO 2 ), carbon monoxide (CO), water (H 2 O), nitrogen dioxide (NO 2 ), etc. The ultraviolet rays  68   a  which have the wavelength of 254 nm may react directly with the organic substance, decomposing it into a volatile substance, or may be involved in other reaction processes. At any rate, the application of the ultraviolet rays  68   a  is effective to reduce the organic substance deriving from the protective film  23   a  that remains on the face side  11   a  after the protective film removing step S 30  and before the residual organic substance removing step S 40  to about the same level as if the face side  11   a  were not covered with the protective film  23   a.    
     After the residual organic substance removing step S 40 , the wafer unit  21  is taken out of the laser processing apparatus  2 , and coverage regions  15   a  (see  FIG.  11   ) corresponding to the face sides of the respective devices  15  are covered with the encapsulating resin  29  (encapsulating resin applying step S 52 ). The face sides of the devices  15  are positioned at the face side  11   a  of the wafer  11 . In the encapsulating resin applying step S 52 , a dispenser, not depicted, supplies the face side  11   a  with a liquid resin for encapsulation. The liquid resin for encapsulation includes, for example, a bisphenol-A-type epoxy resin, a bisphenol-F-type epoxy resin, a novolak-type epoxy resin, an aliphatic-type epoxy resin, a glycidylamine-type epoxy resin, or the like. 
     After the liquid resin for encapsulation supplied to the face side  11   a  has been pressed against the face side  11   a  until the liquid resin is spread over the face side  11   a  in its entirety, a thermosetting process is performed to set the liquid resin, covering the face side  11   a  with the encapsulating resin  29 .  FIG.  11    illustrates the wafer  11  covered with the encapsulating resin  29  in enlarged fragmentary cross section. When the face side  11   a  is encapsulated all together by the encapsulating resin  29 , the encapsulating resin  29  finds its way into the circuit layer  11   c  and the laser-processed slots  11   d  as well as the face sides of the devices  15 . Therefore, the face sides of the devices  15  and the four sides thereof are encapsulated by the encapsulating resin  29 . 
     After the encapsulating resin applying step S 52 , the encapsulating resin  29  and the wafer  11  are cut along the projected dicing lines  13  by a cutting apparatus  80  (see  FIG.  12   ) (cutting step S 54 ).  FIG.  12    illustrates the cutting step S 54  in perspective. The cutting apparatus  80  has a chuck table  82  having a holding surface for holding the wafer unit  21  under suction thereon. The chuck table  82  is movable along the X-axis by a ball-screw-type X-axis moving unit, not depicted. 
     The cutting apparatus  80  also includes a cutting unit  84  disposed above the chuck table  82 . The cutting unit  84  has a spindle housing  86  whose longitudinal axis extends along the Y-axis. A cylindrical spindle  88  has a portion rotatably housed in the spindle housing  86 . The spindle  88  has a proximal end. A rotary actuator, not depicted, such as an electric motor is provided near the proximal end of the spindle  88 . The spindle  88  has a distal end portion protruding from the spindle housing  86 . A cutting blade  90  having an annular cutting edge is mounted on the protruding distal end portion of the spindle  88 . 
     In the cutting step S 54 , an alignment process is carried out on the wafer  11  on the chuck table using an image capturing unit, not depicted, to orient one of the projected dicing lines  13  substantially parallel to the X-axis. Since terminals or the like, not depicted, that are in a predetermined positional relation to the projected dicing lines  13  are exposed on the upper surface of the encapsulating resin  29 , the positions of the projected dicing lines  13  can be identified from an image captured of the upper surface of the encapsulating resin  29 . Then, the cutting blade  90  is rotated about its central axis in a predetermined direction D, and the lower end of the rotating cutting blade  90  is positioned between the holding surface of the chuck table  82  and the dicing tape  17 . While cutting water such as pure water is being supplied to the cutting blade  90 , the chuck table  82  is processing-fed in a predetermined direction E so that the cutting blade  90  rotating in the direction D cuts the wafer  11  by way of down milling. In this fashion, the cutting blade  90  cuts the wafer  11  and the encapsulating resin  29  along the projected dicing lines  13  to divide the wafer  11  into a plurality of packaged devices  31 . 
     According to the first embodiment, inasmuch as the organic substance deriving from the protective film  23   a  is removed in the residual organic substance removing step S 40 , the amount of organic substance remaining on the face side  11   a  is reduced to about the same level as if the face side  11   a  were not covered with the protective film  23   a . Therefore, the level of intimate contact between the face side  11   a  and the encapsulating resin  29  becomes higher than if the residual organic substance removing step S 40  were not carried out. As a result, both the prevention of the debris  27  from being deposited on the face side  11   a  and the increase in the level of intimate contact between the face side  11   a  and the encapsulating resin  29  are achieved. 
     A second embodiment of the present invention will be described below.  FIG.  13    illustrates a sequence of a method of manufacturing a plurality of packaged devices  39  (see  FIG.  14 B ) according to the second embodiment. The method according to the second embodiment has the protective film applying step S 10 , the laser processing step S 20 , the protective film removing step S 30 , the residual organic substance removing step S 40  that are identical to those of the method according to the first embodiment. Consequently, these steps will not be described below. According to the second embodiment, after the residual organic substance removing step S 40 , the cutting apparatus  80  cuts the wafer  11  into device chips  33  (see  FIG.  14 A ) (cutting step S 56 ).  FIG.  14 A  illustrates the device chips  33  in side elevation, partly in cross section. 
     After the cutting step S 56 , the reverse side of a device chip  33  that is positioned at the reverse side  11   b  of the wafer  11  is placed on an upper surface of a wiring board  37 , and the device  15  of the device chip  33  is electrically connected to the wiring board  37  by metal wires  35 . Thereafter, a coverage region  15   a , four sides of the device  15 , the metal wires  35 , the lower surface of the wiring board  37 , etc. are encapsulated by the encapsulating resin  29  (encapsulating resin applying step S 58 ). In this manner, a packaged device  39  is produced. 
       FIG.  14 B  illustrates the packaged device  39  in cross section. The other device chips  33  are similarly processed into respective packaged devices  39 . According to the second embodiment, the cutting step S 56  and the encapsulating resin applying step S 58  are collectively referred to as the packaged device producing step S 50 . According to the second embodiment, inasmuch as the organic substance deriving from the protective film  23   a  is removed in the residual organic substance removing step S 40 , the amount of organic substance remaining on the face side  11   a  is reduced to about the same level as if the face side  11   a  were not covered with the protective film  23   a . Therefore, the level of intimate contact between the face side  11   a  and the encapsulating resin  29  becomes higher than if the residual organic substance removing step S 40  were not carried out. As a result, both the prevention of the debris  27  from being deposited on the face side  11   a  and the increase in the level of intimate contact between the face side  11   a  and the encapsulating resin  29  are achieved. 
     The structure, method, etc. according to the above embodiments may be changed or modified appropriately without departing from the scope of the present invention. For example, according to the second embodiment, the face sides of the device chips  33  and surfaces of the wiring boards  37  may be electrically connected by electrically conductive members such as solder balls, not depicted, rather than the metal wires  35 . An encapsulating resin, also called an underfill, such as an epoxy resin, is interposed between each of the device chips  33  and a corresponding wiring board  37 . Since the amount of organic substance remaining on the face side of the device chip  33  has been reduced in the residual organic substance removing step S 40 , the level of intimate contact between the device chip and the encapsulating resin is increased. 
     The present invention is not limited to the details of the above described preferred embodiments. The scope of the invention is defined by the appended claims and all changes and modifications as fall within the equivalence of the scope of the claims are therefore to be embraced by the invention.