JP6370227B2 - Inspection method of laser beam - Google Patents

Description

  The present invention relates to a laser beam inspection method used when processing a wafer or the like.

  In order to divide a wafer with ICs and other devices formed on the front side into multiple chips, a processing method has been put into practical use that focuses the laser beam inside the wafer to form a modified layer that is the starting point of the division. (For example, refer to Patent Document 1). In this processing method, the front side of the wafer is held by a chuck table, and a laser beam having a wavelength that is difficult to be absorbed by the wafer is irradiated from the exposed back side so as to be condensed inside.

  By the way, when the modified layer is formed on the wafer by the above-described processing method, the device may be damaged by the light passing through the laser beam reaching the surface side of the wafer. In recent years, therefore, a processing method has been proposed in which generation of light leakage is suppressed by using a laser beam having a sufficiently short pulse width in order to suppress damage to the device due to light leakage (see, for example, Patent Document 2). .

JP 2002-192370 A JP 2014-104484 A

  The damage of the device due to the above-described light leakage is considered to be caused by insufficient adjustment of the laser beam irradiated to the wafer, incompatibility of processing conditions, or the like. For example, if the laser beam is appropriately adjusted so that the intensity distribution is symmetric in a plane perpendicular to the propagation direction, or if the processing conditions can be adapted, it is considered that damage to the device due to light leakage can be further reduced.

  However, on the principle of using a laser beam having a wavelength that is difficult to be absorbed by the wafer, it is difficult to adjust the laser beam visually to adapt the processing conditions. Although the irradiation region of the laser beam can be inspected and adjusted based on a device defect that actually occurs, this method has a problem in terms of time and cost required for the inspection.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a laser beam inspection method capable of inspecting the state of a laser beam in a short time and at a low cost.

  According to the present invention, the first surface of the inspection plate having the first surface and the second surface opposite to the first surface absorbs a laser beam having a wavelength that passes through the inspection plate. After performing the inspection film disposing step for forming the inspection film to be melted and the inspection film disposing step, the inspection film is made to face the holding surface of the chuck table and the inspection is performed with the chuck table. A modified layer forming step of forming a modified layer by holding the plate for irradiation and irradiating the laser beam from the second surface side so as to be condensed inside the plate for inspection, and the modification An inspection step of inspecting a state of the laser beam based on a melt mark formed on the inspection film by the laser beam that has passed through the inspection plate after performing the layer forming step, A method for inspecting a laser beam is provided.

  In the present invention, in the inspection step, when a spot-like melt mark formed in the vicinity of the melt mark immediately below the modified layer is biased with respect to the melt mark immediately below the reformed layer formed in the modified layer In addition, it is preferable to determine that the laser beam is deviated from the optical axis of the optical unit or lens of the laser beam application means for irradiating the laser beam.

  In the laser beam inspection method according to the present invention, an inspection film that absorbs and melts the laser beam is formed on the first surface of the inspection plate, so that it is irradiated from the second surface side and passes through the inspection plate. A melt mark is formed on the inspection film by the laser beam. Therefore, the state of the laser beam can be inspected based on this melting mark.

  That is, in the laser beam inspection method according to the present invention, the irradiation position of the laser beam passing through the inspection plate can be visually determined based on the melted mark only by forming the inspection film on the first surface of the inspection plate. Since it can be confirmed, the state of the laser beam can be inspected in a short time and at a low cost.

FIG. 1A is a perspective view schematically showing a test film disposing step, and FIG. 1B is a perspective view schematically showing a state in which a protective member is attached to a test plate. It is. 2A is a partial cross-sectional side view schematically showing the modified layer forming step, and FIG. 2B is an enlarged view of a part of FIG. 2A. FIG. 3A is a plan view schematically showing an example of a melt mark when the laser beam is deviated in the −Y direction with respect to the optical axis of the laser processing unit, and FIG. FIG. 3C is a plan view schematically showing an example of a melt mark when the laser beam is not deviated from the optical axis of the unit, and FIG. 3C is a diagram in which the laser beam is deviated in the + Y direction with respect to the optical axis of the laser processing unit. It is a top view which shows typically the example of the fusion mark in the case of being. It is a figure which shows typically the structural example of the processing unit which concerns on a modification.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The laser beam inspection method according to this embodiment includes an inspection film disposing step (see FIG. 1A), a modified layer forming step (see FIGS. 2A and 2B), and an inspection step (see FIG. 3A, 3B, and 3C).

  In the inspection film disposing step, an inspection film that absorbs and melts the laser beam is formed on the first surface of the inspection plate. In the modified layer forming step, a laser beam is irradiated from the second surface side of the inspection plate so as to be condensed inside the inspection plate, thereby forming a modified layer inside the inspection plate. To do.

  In the inspection step, the state of the laser beam is inspected based on the melting mark formed on the inspection film by the laser beam that has passed through the inspection plate. Hereinafter, the laser beam inspection method according to this embodiment will be described in detail.

  First, an inspection film disposing step for forming an inspection film on the inspection plate is performed. FIG. 1A is a perspective view schematically showing an inspection film disposing step. As shown in FIG. 1A, the inspection plate 11 used in the present embodiment is a disk-shaped semiconductor wafer, a ceramic substrate, or the like, and has a substantially flat first surface 11a and first surface 11a. It has the second surface 11b on the opposite side. However, the present invention is not limited to this, and a plate-like material having any material and shape can be used as the inspection plate-like material.

  In the inspection film disposing step, the inspection film 13 is formed on the first surface 11 a of the inspection plate 11 described above. The inspection film 13 is formed of a material that absorbs a laser beam used in a later modified layer forming step, and melts when a predetermined temperature is reached. With this inspection film 13, the irradiation position of the laser beam reaching the first surface 11 a of the inspection plate 11 can be confirmed.

  The inspection film 13 is typically a single layer structure or a laminated structure of a film made of a metal material such as titanium (Ti), tantalum (Ta), tungsten (W), aluminum (Al), tin (Sn), or the like. It is. When the inspection film 13 has a laminated structure, a laminated structure of a titanium film (for example, a thickness of 200 nm) and a tin film (for example, a thickness of 50 nm), a titanium film (for example, a thickness of 50 nm), A laminated structure with an aluminum film (for example, a thickness of 500 nm) can be employed.

  Although the formation method of the test | inspection film | membrane 13 is arbitrary, For example, plasma CVD method, a vacuum evaporation method, sputtering method etc. can be used. Similarly, the thickness of the inspection film 13 is also arbitrary. However, the thickness of the inspection film 13 needs to be thin enough to be melted by the laser beam. Note that the present invention is not limited to this, and any inspection film that absorbs and melts a laser beam can be formed.

  After performing the inspection film arrangement step, a protective member may be attached to the first surface 11a side of the inspection plate 11 on which the inspection film 13 is formed. FIG. 1B is a perspective view schematically showing a state in which a protective member is attached to the inspection plate 11. As shown in FIG. 1B, for example, a protective member 15 such as a resin tape is attached to the first surface 11a side (inspection film 13) of the inspection plate 11. An annular frame 17 is fixed to the outer peripheral portion of the protection member 15.

  Next, a modified layer forming step is performed in which the inspection plate 11 is irradiated with a laser beam to form a modified layer therein. 2A is a partial cross-sectional side view schematically showing the modified layer forming step, and FIG. 2B is an enlarged view of a part of FIG. 2A. The modified layer forming step is performed by, for example, the laser processing apparatus 2 shown in FIG.

  The laser processing apparatus 2 includes a chuck table 4 that sucks and holds the inspection plate 11. The chuck table 4 is connected to a rotational drive source (not shown) such as a motor, and rotates around a vertical axis. A moving mechanism (not shown) is provided below the chuck table 4, and the chuck table 4 is moved in the horizontal direction by the moving mechanism.

  The upper surface of the chuck table 4 is a holding surface 4 a that sucks and holds the first surface 11 a side (inspection film 13 side) of the inspection plate 11 through the protection member 15. A negative pressure of a suction source (not shown) acts on the holding surface 4a through a flow path (not shown) formed inside the chuck table 4, and a suction force for sucking the inspection plate 11 is generated. Around the chuck table 4, a plurality of clamps 6 for holding and fixing the annular frame 17 are arranged.

  A laser processing unit (laser beam irradiation means) 8 is disposed above the chuck table 4. The laser processing unit 8 condenses the laser beam L 1 pulse-oscillated by a laser oscillator (not shown) inside the inspection plate 11 sucked and held by the chuck table 4. The laser oscillator is configured to be able to oscillate a laser beam L1 having a wavelength that is difficult to be absorbed by the inspection plate 11 (wavelength that passes through the inspection plate 11).

  In the modified layer forming step, first, the inspection plate 11 is so formed that the inspection film 13 formed on the first surface 11a side of the inspection plate 11 and the holding surface 4a of the chuck table 4 face each other. (And the protection member 15) are placed on the chuck table 4. If the negative pressure of the suction source is applied in this state, the inspection plate 11 is sucked and held by the chuck table 4 with the second surface 11b side exposed upward.

  Next, the chuck table 4 is moved and rotated to position the laser processing unit 8 in an arbitrary processing region. Thereafter, the chuck table 4 is moved in the horizontal direction while irradiating the laser beam L1 from the laser processing unit 8 toward the inspection plate 11. Thereby, multiphoton absorption is generated in the vicinity of the condensing point of the laser beam L1, and the linear modified layer 19 can be formed.

  Since the laser beam L1 is difficult to be absorbed by the inspection plate 11, the laser beam L2 that has not been absorbed in the vicinity of the condensing point is on the first surface 11a side of the inspection plate 11 as shown in FIG. Exit. In this embodiment, since the inspection film 13 is provided on the first surface 11a of the inspection plate 11, the laser beam L2 that has passed through the inspection plate 11 is absorbed by the inspection film 13 and becomes heat. Change. As a result, a melting mark 21 is formed in a part of the inspection film 13.

  After performing the modified layer forming step, an inspection step for inspecting the state of the laser beam L1 based on the melted mark 21 formed on the inspection film 13 by the laser beam L2 is performed. In this inspection step, for example, the state of the laser beam L1 is determined by visually observing the melting mark 21 in a plane.

  FIG. 3A is a plan view schematically showing an example of the melt mark 21 when the laser beam L1 is shifted in the −Y direction with respect to the optical axis of the laser processing unit 8, and FIG. FIG. 3C is a plan view schematically showing an example of the melt mark 21 when the laser beam L1 is not deviated from the optical axis of the laser processing unit 8. FIG. It is a top view which shows typically the example of the fusion mark 21 in case the laser beam L1 has shifted | deviated to + Y direction.

  As shown in FIGS. 3 (A), 3 (B), and 3 (C), immediately below the modified layer 19, a linear melt mark corresponding to the modified layer 19 (melting immediately below the modified layer). Scar) 21a is formed. On the other hand, a spot-like melting mark (spot-like melting mark) 21b caused by the laser beam scattered in the modified layer 19 is formed in the vicinity of the melting mark 21a.

  In the present embodiment, the state of the laser beam L1 is determined based on the positional relationship between the melting marks 21a and 21b. Specifically, as shown in FIGS. 3A and 3C, when the melted trace 21b is biased to one side of the melted trace 21a serving as a boundary, various optical units (mirrors) of the laser processing unit 8 are used. , Prism, etc.) (not shown) and the laser beam L1 is determined to be deviated from the optical axis of the lens (not shown).

  On the other hand, as shown in FIG. 3 (B), when the melted traces 21b are distributed substantially evenly on both sides of the melted trace 21a serving as the boundary, various optical units (mirrors, prisms, etc.) It is determined that the laser beam L1 is not shifted from the optical axis of the lens (not shown) or the lens (not shown).

  As described above, in the laser beam inspection method according to the present embodiment, since the inspection film 13 that absorbs and melts the laser beam L2 is formed on the first surface 11a of the inspection plate 11, the second surface 11b side. A melted mark 21 is formed in the inspection film 13 by the laser beam L2 irradiated from above and passing through the inspection plate 11. Therefore, the state of the laser beam L1 can be inspected based on the melting mark 21.

  That is, in the laser beam inspection method according to the present embodiment, the irradiation position of the laser beam L2 passing through the inspection plate 11 is melted only by forming the inspection film 13 on the first surface 11a of the inspection plate 11. Since it can confirm visually based on the mark 21, the state of the laser beam L1 can be inspected in a short time and at low cost.

  In addition, this invention is not limited to description of the said embodiment. For example, the laser processing unit (laser beam irradiation means) 8 of the laser processing apparatus 2 described above can be changed to an arbitrary laser processing unit. FIG. 4 is a diagram schematically illustrating a configuration example of a laser processing unit according to a modification.

  As shown in FIG. 4, the laser processing unit (laser beam irradiation means) 12 according to the modification includes a laser oscillator 14, a prism 16, a spatial light modulator 18, a driving device 20, a control device 22, lenses 24 and 26, and a mirror 28. , And an objective lens 30.

  The laser oscillator 14 includes, for example, a laser medium such as Nd: YAG, and is configured to be able to pulse-oscillate a laser beam L having a wavelength that is difficult to be absorbed by the inspection plate 11 (wavelength that passes through the inspection plate 11). Has been. The laser beam L oscillated by the laser oscillator 14 is reflected by the first reflecting surface 16 a of the prism 16 and then input to the spatial light modulator 18.

  The spatial light modulator 18 modulates the phase of the laser beam L using a phase modulation hologram indicated by a plurality of pixels arranged two-dimensionally. As a phase modulation hologram, a CGH (Computer Generated Hologram) obtained based on calculation may be used.

  In FIG. 4, the laser processing unit 12 using the reflective spatial light modulator 18 is illustrated, but a transmissive spatial light modulator may be used. When a transmissive spatial light modulator is used, the prism can be omitted.

  The driving device 20 sets the phase modulation amount of each pixel included in the spatial light modulator 18. Thereby, the spatial light modulator 18 shows a hologram for phase modulation. The control device 22 is, for example, a computer, and controls the operation of the drive mechanism 20 to display an appropriate hologram on the spatial light modulator 18. With this control device 22, a hologram for condensing the laser beam L at a plurality of positions inside the inspection plate 11 can be displayed on the spatial light modulator 18.

  The laser beam L output from the spatial light modulator 18 is reflected by the second reflecting surface 16 b of the prism 16 and enters the objective lens 30 through the lenses 24 and 26 and the mirror 28. The lenses 24 and 26 are arranged so that the spatial light modulator 18 and the objective lens 30 are in an imaging relationship with each other, and an image of the laser beam L in the spatial light modulator 18 is formed on the objective lens 30. .

  The objective lens 30 focuses the incident laser beam L at a plurality of positions inside the inspection plate 11. By using this laser processing unit 12, the modified layer 19 can be formed simultaneously at a plurality of positions.

  In addition, the configurations, methods, and the like according to the above-described embodiments can be appropriately modified and implemented without departing from the scope of the object of the present invention.

DESCRIPTION OF SYMBOLS 11 Inspection board 11a 1st surface 11b 2nd surface 13 Test | inspection film | membrane 15 Protective member 17 Frame 19 Modified layer 21 Melting trace 21a Melting trace (melting trace just under a modified layer)
21b Melt marks (spotted melt marks)
L, L1, L2 Laser beam 2 Laser processing device 4 Chuck table 4a Holding surface 6 Clamp 8, 12 Laser processing unit (laser beam irradiation means)
DESCRIPTION OF SYMBOLS 14 Laser oscillator 16 Prism 16a 1st reflective surface 16b 2nd reflective surface 18 Spatial light modulator 20 Drive apparatus 22 Control apparatus 24,26 Lens 28 Mirror 30 Objective lens

Claims (2)

An inspection plate that absorbs a laser beam having a wavelength that passes through the inspection plate and melts it on the first surface of the inspection plate having a first surface and a second surface opposite to the first surface. An inspection film disposing step for forming a film;
After performing the inspection film disposing step, the inspection film is made to face the holding surface of the chuck table, the inspection plate is held by the chuck table, and the laser beam is emitted from the second surface side. A modified layer forming step of forming a modified layer inside the inspection plate by irradiating the inner surface of the inspection plate so as to collect light,
An inspection step of inspecting the state of the laser beam based on the melt mark formed on the inspection film by the laser beam that has passed through the inspection plate after the modified layer forming step is performed. A method for inspecting laser beams.   In the inspection step, when the spot-like melt mark formed in the vicinity of the reformed layer immediately below the modified layer is biased with respect to the melted mark immediately below the modified layer, the laser beam The laser beam inspection method according to claim 1, wherein the laser beam is determined to be deviated from the optical axis of the optical unit or lens of the laser beam irradiation means for irradiating the laser beam.