JP5846470B2 - Laser dicing apparatus and method, and wafer processing method - Google Patents

Description

  The present invention relates to a laser dicing apparatus and method and a wafer processing method, and more particularly to a laser dicing apparatus and method and a wafer processing method for processing a wafer having a plurality of devices formed on the surface.

  As a method of dividing a wafer having a plurality of devices (semiconductor elements) formed on the surface into individual chips, a dicing method using a laser (laser dicing) is known. Laser dicing is a method in which a laser beam is incident on a wafer along a street (division planned line) to form a modified layer by multiphoton absorption inside the wafer. The laser-diced wafer is then divided into individual chips starting from the modified layer by applying external stress to the wafer. This laser dicing has the advantage that it can be divided with little chipping.

  In laser dicing, a laser beam is generally incident from the front surface side (surface side on which a circuit pattern or the like is formed) of a wafer to form a modified layer inside the wafer.

  However, the method in which the laser beam is incident from the front side has a problem that in the case of a wafer in which a metal film is formed near the street, the laser beam is reflected by the metal film and cannot be used.

  In order to solve such a problem, Patent Document 1 proposes that a modified layer is formed inside the wafer by allowing laser light to enter through the dicing tape from the back surface of the wafer. Further, Patent Document 2 proposes that a wafer is sandwiched and supported by a pair of transparent glass plates so that laser light can be incident from both front and back sides of the wafer.

  Further, in Patent Document 3, a holding means having an annular holding surface that holds and holds a region where a device is not formed, which is provided at the peripheral portion of the wafer surface, holds the wafer without touching the device formation region, It has been proposed to form a modified layer inside a wafer by making a laser beam incident through a dicing tape from the back surface of the wafer.

JP 2007-123404 A JP 2005-109045 A JP 2010-029927 A

  By the way, in laser dicing, a wafer is held by a table and laser light is incident. However, in Patent Document 1, the front side of the wafer is sucked and held by a table so that the laser light can be incident on the back surface of the wafer. It is configured to do.

  However, if the surface side of the wafer is sucked and held by the table in this way, in the case of a wafer on which a fine structure element or the like such as a single MEMS element (Micro Electro Mechanical System) is formed, the element is destroyed by the suction. There are drawbacks. Such a problem also occurs in the laser dicing apparatus of Patent Document 2 in which a wafer is sandwiched between transparent glass plates.

  On the other hand, as described in Patent Document 3, it is conceivable to support only the peripheral edge of the wafer with the holding means having an annular holding surface, but if only the peripheral edge of the wafer is supported, the wafer is bent, There is a drawback that a modified layer cannot be formed in a predetermined region.

  In general, the surface (tape surface) of a dicing tape (especially thin tape) that is attached to the back surface of a wafer is less likely to form a flat flat surface such as a hard body such as glass. Often has. In addition, there are many cases where the object is slightly rough. For this reason, when laser light is incident from the back surface of the wafer through the dicing tape, there is a problem that the laser light is not efficiently incident due to the influence of scattering on the tape surface.

  Further, in Patent Document 3, air is introduced from a blow unit into a space formed by a concave portion provided in a holding unit and a wafer, and the back surface of the wafer is pressed by a warp correction unit, thereby warping the wafer. While trying to correct waviness and undulation, there is a limit to the method of correcting such a wafer, and in principle, the wafer cannot be corrected to a completely flat state.

  Here, the wafer correction method in Patent Document 3 will be briefly described with reference to FIG. In this correction method, as shown in FIG. 8A, when the central portion of the wafer W is recessed downward relative to the peripheral portion, the space 904 formed by the concave portion 902 of the holding means 900 and the wafer W is used. , The wafer W is pressed upward, and the back surface (upper surface in the drawing) of the wafer W is pressed by the warp correction means 906. As a result, the wafer W acts in a direction in which the warpage of the wafer W is entirely canceled so as to follow the correction surface (surface on the wafer W side) 906A of the warp correction means 906, but the warpage of the wafer W is not necessarily limited. 8 is not completely eliminated. For example, as shown in FIG. 8B, only the center portion of the wafer W is in contact with the correction surface 906A, and the peripheral portion thereof is not in contact with the correction surface 906A. There may be a non-uniform gap between the means 906.

  Further, it is very difficult to maintain the wafer W in a completely flat state by controlling the pressure in the sealed space 904 regardless of whether the inside of the space 904 is positive or reduced. That is, if the pressure in the space 904 is too high, the wafer W will bend outwards too much. On the other hand, if the pressure is too low, the wafer W will be bent too much inward, and the pressure control is very delicate. It is difficult to maintain the wafer W in a completely flat state.

  As described above, in the method disclosed in Patent Document 3, it is theoretically difficult to completely correct the warpage and waviness of the wafer. For this reason, when the laser beam is incident from the back surface of the wafer, the laser beam cannot be focused at a predetermined position inside the wafer, and a modified layer by the laser beam is accurately formed inside the wafer. I can't.

  In addition, when laser light is incident from the back surface of the wafer through the glass plate while supporting the back surface of the wafer with a glass plate, an air layer is formed between the glass surface and the back surface of the wafer (the surface on which the dicing tape is adhered). When interposed, reflection occurs repeatedly at the interface between them, and the laser light is scattered outside the desired portion of the wafer, causing laser burn. The loss due to such scattered light consumes energy in the vicinity of the loss, and the laser light in the vicinity, such as surface deterioration on the glass surface and adhesion of debris to the dicing tape due to deterioration, will be consumed. You will suffer from the harmful effects of scattering.

  In addition, if the glass surface and the back surface of the wafer are not in close contact, even if the laser is turned on with a large laser power, due to the scattering effect between the glass surface and the back surface of the wafer, the wafer surface can be efficiently There is a problem that the modified layer is not formed.

  The present invention has been made in view of such circumstances, and a laser dicing apparatus and method capable of accurately forming a modified layer inside a wafer without destroying a device formed on the surface of the wafer. An object of the present invention is to provide a wafer processing method.

In order to achieve the above object, the invention according to claim 1 is a laser dicing apparatus that irradiates a wafer having a plurality of devices formed on the surface thereof with a laser beam and forms a modified layer inside the wafer. And a wafer having a substantially flat holding surface that is formed so as to be able to transmit the laser beam and that holds the back surface of the wafer in close contact with a refractive liquid in order to correct warpage or undulation of the wafer. There is provided a laser dicing apparatus comprising: a table; and laser irradiation means for irradiating the laser beam from the back side of the wafer through the wafer table.

  According to the present invention, the back surface of the wafer is held in close contact with the holding surface of the wafer table formed so as to transmit laser light with the refractive liquid interposed. Thereby, the wafer is held in a flat state without bending. Then, by irradiating the laser beam from the back side of the wafer through the wafer table, the modified layer can be accurately formed inside the wafer. Further, the dicing process can be performed without touching the surface of the wafer at all. Therefore, the dicing process can be performed without destroying the device formed on the surface of the wafer.

  In particular, by introducing and interposing a refractive liquid in a minute gap between the wafer and the wafer table, the refractive liquid automatically spreads uniformly in the minute gap by capillary action. Also, the interfacial tension that acts between the interface between the refractive liquid and the holding surface of the wafer table, and the interfacial tension that acts between the interface between the refractive liquid and the wafer (the surface on which the tape is applied when the tape is applied). As a result, the wafer comes into close contact with the wafer table with no gaps uniformly across the entire surface.

  As a result, when a modified layer is formed inside the wafer by irradiating the laser beam through the wafer table, the laser beam is efficiently imaged and modified inside the wafer without significant energy loss along the path. A layer can be formed.

  Moreover, in this invention, the tape which can permeate | transmit a laser beam may be stuck to the back surface of a wafer, and it does not need to be stuck. In the former case, the surface of the tape is generally rough, and scattering tends to occur when air is present. However, when a liquid (refractive liquid) is interposed as in the present invention, a surface having a rough surface is changed, and the interfacial tension increases due to the effect of increasing the surface area, and wettability is increased. Also, since the liquid fills up the unevenness of the fine roughness, the liquid spreads uniformly over the roughened tape surface, and the refractive index distribution is further reduced and scattered. The laser beam can be transmitted more efficiently.

  As the refractive liquid, water, ethanol, isopropyl alcohol (IPA), or the like can be used. In the present invention, ethanol or IPA is preferably used, but even water (refractive index is 1.3) generally has a higher refractive index than air (refractive index 1) and is used as a refractive liquid. be able to.

  Although the wafer table transmits laser light, for example, when quartz glass is used as the wafer table, the refractive index is 1.45. Therefore, liquid rather than gas is used for these wafer tables and tapes. On the other hand, the refractive index has a close value. When the refractive index is close, reflection and scattering are reduced at that interface, and energy loss when irradiating laser light can be greatly reduced.

  In addition, if a liquid having a refractive index equivalent to that of a wafer table or tape is used as the refractive liquid, there is almost no loss of laser light at the interface, and the laser light is efficiently transmitted to form a modified layer inside the wafer. It becomes possible.

  As described above, according to the present invention, a modified layer is accurately formed at a certain depth inside the wafer while irradiating the laser beam from the back surface of the wafer without destroying the device formed on the front surface of the wafer. In addition, an improved and stable modified layer is formed inside the wafer by reducing scattering in the middle path of the laser beam, and laser burning due to scattering of the laser beam is eliminated by scattering in the middle path. It becomes possible to prevent deterioration of components and performance.

  The invention according to claim 2 provides the laser dicing apparatus according to claim 1, wherein the refractive liquid is a liquid containing isopropyl alcohol in order to achieve the object.

  According to the present invention, it is possible to suppress the generation of a watermark on a wafer.

  In addition, since isopropyl alcohol (IPA) has a lower surface tension than water, it penetrates into the gap between the back surface of the wafer (the surface to which the tape is applied when the tape is applied) and the wafer table. Further, it is possible to make the back surface of the wafer and the wafer table more closely contact each other.

  In addition to the uniform contact between the back surface of the wafer and the wafer table, and the uniform liquid between them, the refractive index variation in the laser beam path can be reduced. There is almost no in-plane uniform state.

  According to a third aspect of the present invention, there is provided the laser dicing apparatus according to the first or second aspect, wherein the holding surface is roughened to achieve the object.

  According to the present invention, it is possible to hold the wafer in close contact with a greater contact force. That is, the rough surface treatment of the wafer table increases the substantial surface area of the wafer table and increases the interfacial tension between the individual liquids that act on the large surface area. Therefore, the back surface of the wafer (the surface to which the tape is applied when the tape is applied) and the wafer table are further in close contact with each other, and there is no difference in the refractive index between the back surface of the wafer and the wafer table. It becomes possible to form a modified layer by light inside the wafer.

  According to a fourth aspect of the present invention, in order to achieve the object, a tape capable of transmitting the laser light is attached to the back surface of the wafer, and the wafer is held on the holding surface of the wafer table via the tape. The laser dicing apparatus according to any one of claims 1 to 3, wherein the laser dicing apparatus is closely held.

  According to this invention, the tape which can permeate | transmit a laser beam is stuck on the back surface of a wafer, and a wafer is hold | maintained on a wafer table via this tape. Thus, by sticking the tape to the back surface of the wafer, the tape can be easily divided into chips by expanding the tape after laser dicing.

  The invention according to claim 5 provides the laser dicing apparatus according to claim 4, wherein the wafer is mounted on a frame via the tape in order to achieve the object.

  According to the present invention, the wafer is mounted on the frame via the tape. Thereby, the wafer can be transported through the frame, and the handling can be facilitated.

  The invention according to claim 6 is characterized in that, in order to achieve the above object, the surface of the tape opposite to the wafer side is subjected to a rough surface treatment. A dicing apparatus is provided.

  According to the present invention, it is possible to hold the wafer in close contact with a greater contact force.

  According to a seventh aspect of the present invention, in order to achieve the above object, the wafer table is horizontally installed with the holding surface facing upward, and the laser irradiation means is applied to the wafer table from below the wafer table. The laser dicing apparatus according to claim 1, wherein the held wafer is irradiated with laser light.

  According to the present invention, the wafer is held horizontally on the holding surface. The laser light is irradiated from below the wafer table and is incident on the wafer through the wafer table. Thereby, even if it is a large diameter wafer, a wafer can be reliably stuck to a holding surface.

  According to an eighth aspect of the present invention, in order to achieve the above object, the wafer table is installed horizontally with the holding surface facing downward, and the laser irradiation means is applied to the wafer table from above the wafer table. The laser dicing apparatus according to claim 1, wherein the held wafer is irradiated with laser light.

  According to the present invention, the wafer is held horizontally below the holding surface. The laser beam is irradiated from above the wafer table and is incident on the wafer through the wafer table. Thereby, the laser irradiation means can be installed by effectively utilizing the space above the wafer table.

  The invention according to claim 9 is characterized in that, in order to achieve the object, a laser antireflection plate is installed at a position separated from the holding surface. A laser dicing apparatus is provided.

  According to the present invention, the laser antireflection plate is installed at a position separated from the holding surface. As a result, unnecessary reflection of the laser light transmitted through the wafer can be prevented, and problems such as reflection burn can be effectively prevented.

  The invention according to claim 10 is the laser according to any one of claims 1 to 9, wherein, in order to achieve the object, the wafer is a wafer having a MEMS element formed on a surface thereof. A dicing apparatus is provided.

  According to the present invention, even if a MEMS element is formed on the surface, the wafer can be diced without touching the surface, so that the wafer can be diced without destroying the MEMS element. it can.

According to an eleventh aspect of the present invention, in order to achieve the above object, a laser dicing method for irradiating a wafer having a plurality of devices formed on the surface with laser light and forming a modified layer inside the wafer. And a wafer having a substantially flat holding surface that is formed so as to be able to transmit the laser beam and that holds the back surface of the wafer in close contact with a refractive liquid in order to correct warpage or undulation of the wafer. There is provided a laser dicing method characterized in that the wafer is held by a table and the laser beam is irradiated from the back side of the wafer through the wafer table.

  According to the present invention, the back surface of the wafer is held in close contact with the holding surface of the wafer table formed so as to transmit laser light with the refractive liquid interposed. Thereby, the wafer is held in a flat state without bending. Then, by irradiating the laser beam from the back side of the wafer through the wafer table, the modified layer can be accurately formed inside the wafer. Further, the dicing process can be performed without touching the surface of the wafer at all. Therefore, the dicing process can be performed without destroying the device formed on the surface of the wafer.

  The invention according to claim 12 provides the laser dicing method according to claim 11, wherein the refractive liquid is a liquid containing isopropyl alcohol in order to achieve the object.

  According to the present invention, it is possible to suppress the generation of a watermark on a wafer.

  According to a thirteenth aspect of the present invention, there is provided the laser dicing method according to the eleventh or twelfth aspect, wherein the holding surface is roughened to achieve the object.

  According to the present invention, it is possible to hold the wafer in close contact with a greater contact force.

  In the invention according to claim 14, in order to achieve the object, a tape capable of transmitting the laser light is attached to the back surface of the wafer, and the wafer is held on the holding surface of the wafer table via the tape. The laser dicing method according to any one of claims 11 to 13, wherein the laser dicing method is provided.

  According to this invention, the tape which can permeate | transmit a laser beam is stuck on the back surface of a wafer, and a wafer is hold | maintained on a wafer table via this tape. Thus, by sticking the tape to the back surface of the wafer, the tape can be easily divided into chips by expanding the tape after laser dicing.

  The invention according to claim 15 provides the laser dicing method according to claim 14, wherein, in order to achieve the object, the wafer is mounted on a frame via the tape.

  According to the present invention, the wafer is mounted on the frame via the tape. Thereby, the wafer can be transported through the frame, and the handling can be facilitated.

  The invention according to claim 16 is characterized in that, in order to achieve the above object, the surface opposite to the wafer side of the tape is subjected to a rough surface treatment. A dicing method is provided.

  According to the present invention, it is possible to hold the wafer in close contact with a greater contact force.

Invention, in order to achieve the above object, the wafer table is installed horizontally facing up the holding surface, the wafer held from below the front Symbol wafer table on the wafer table according to Claim 17 The laser dicing method according to claim 11, wherein the laser dicing method is provided.

  According to the present invention, the wafer is held horizontally on the holding surface. The laser light is irradiated from below the wafer table and is incident on the wafer through the wafer table. Thereby, even if it is a large diameter wafer, a wafer can be reliably stuck to a holding surface.

The invention according to claim 18, in order to achieve the above object, the wafer table, the holding surface is provided horizontally toward the bottom, from the top of the front Symbol wafer table on the wafer held by the wafer table The laser dicing method according to claim 11, wherein the laser dicing method is provided.

  According to the present invention, the wafer is held horizontally below the holding surface. The laser beam is irradiated from above the wafer table and is incident on the wafer through the wafer table. Thereby, the laser irradiation means can be installed by effectively utilizing the space above the wafer table.

  The invention according to claim 19 is characterized in that a laser antireflection plate is installed at a position spaced from the holding surface in order to achieve the object. A laser dicing method is provided.

  According to the present invention, the laser antireflection plate is installed at a position separated from the holding surface. As a result, unnecessary reflection of the laser light transmitted through the wafer can be prevented, and problems such as reflection burn can be effectively prevented.

  The invention according to claim 20 is the laser according to any one of claims 11 to 19, wherein, in order to achieve the object, the wafer is a wafer having a MEMS element formed on a surface thereof. A dicing method is provided.

  According to the present invention, even if a MEMS element is formed on the surface, the wafer can be diced without touching the surface, so that the wafer can be diced without destroying the MEMS element. it can.

In order to achieve the above object, the invention according to claim 21 has a plurality of devices formed on the front surface and laser light applied to the wafer mounted on the frame via the tape attached to the back surface. A laser dicing step of irradiating and forming a modified layer inside the wafer, and an expanding step of dividing the tape of the wafer subjected to the laser dicing treatment into individual chips on the tape. in the wafer processing method having, in the laser dicing, while being permeable to form the laser beam, the surface on which the tape is adhered to the wafer holding surface of wafer table having a substantially flat holding surface the closely held in a state where a refractive liquid is interposed in order to correct a warp or waviness of the wafer, the laser beam It provides a wafer processing method characterized by irradiating through the wafer table from the back side of the wafer.

  According to the present invention, the back surface of the wafer (that is, the surface on which the tape of the wafer is attached) is held in close contact with the holding surface of the wafer table formed so as to be able to transmit laser light with the refractive liquid interposed. Is done. Thereby, the wafer is held in a flat state without bending. Then, by irradiating the laser beam from the back side of the wafer through the wafer table, the modified layer can be accurately formed inside the wafer. Further, the dicing process can be performed without touching the surface of the wafer at all. Therefore, the dicing process can be performed without destroying the device formed on the surface of the wafer.

  According to the present invention, a modified layer can be accurately formed inside a wafer without destroying a device formed on the surface of the wafer.

1 is a schematic configuration diagram showing an embodiment of a laser dicing apparatus according to the present invention. A perspective view showing a wafer mounted on a dicing frame Schematic configuration diagram of laser irradiation equipment The block diagram which showed the structural example with which the reinforcement member was attached to the table board Configuration diagram showing the holding surface of the wafer table Schematic configuration diagram showing another embodiment of a laser dicing apparatus Process diagram showing the outline of the expanding process by the expanding device Diagram for explaining problems in conventional technology

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

<Constitution>
FIG. 1 is a schematic configuration diagram showing an embodiment of a laser dicing apparatus according to the present invention.

  As shown in the figure, the laser dicing apparatus 10 according to the present embodiment mainly applies laser light to the wafer table 20 that holds the wafer W, and the laser reflection preventing plate 50 and the wafer W held on the wafer table 20. And a laser irradiation device 60.

  First, the wafer W to be processed by the laser dicing apparatus 10 of the present embodiment will be described.

  The wafer W to be processed by the laser dicing apparatus 10 according to the present embodiment is a wafer W having a plurality of devices (for example, MEMS elements) formed on the surface, and is processed while mounted on the dicing frame F. The

  FIG. 2 is a perspective view showing the wafer mounted on the dicing frame.

  As shown in the figure, the wafer W is mounted on a dicing frame F via a dicing tape T.

  The dicing frame F is formed in a frame shape, and a dicing tape T is attached to the inside of the dicing frame F. The wafer W is mounted on a dicing frame F with its back surface attached to a dicing tape T.

  Here, the dicing tape T attached to the dicing frame F is formed of a material having ductility, and is formed of a material capable of transmitting laser light emitted from the laser irradiation device 60. In this example, it is made of a transparent material having ductility. It is more preferable to have air permeability.

  The wafer W mounted on the dicing frame F is held by the wafer table 20 on the surface (back surface) to which the dicing tape T is attached.

  As shown in FIG. 1, the wafer table 20 mainly includes a table plate 22 and a table plate holding frame 24 that holds the table plate 22.

  The table plate 22 is formed in a disk shape corresponding to the wafer W to be processed (in a disk shape having a larger diameter than the wafer W to be processed so that the entire surface of the wafer W to be processed can be supported). The upper and lower surfaces are both formed flat. The table plate 22 is formed of a material that can transmit laser light emitted from the laser irradiation device 60. As an example, in the present embodiment, it is made of transparent quartz glass. The table plate 22 is formed with a necessary and sufficient thickness so that the wafer W to be processed can be held without bending.

  The table plate 22 has a holding surface 22A for holding the wafer W on the upper surface side. A uniform and thin film-like refractive liquid 26 is interposed between the holding surface 22A and the surface (back surface) of the wafer W on which the dicing tape T is adhered, and the wafer W is held in close contact with the table plate 22. As will be described in detail later, examples of the refractive liquid 26 include water, ethanol, isopropyl alcohol (IPA), and the like.

  The table plate holding frame 24 is formed in an annular shape. The table plate 22 is held on the inner periphery of the table plate holding frame 24.

  The table plate holding frame 24 is rotated about its axis by a rotation drive mechanism (not shown), and is moved up and down (Z direction) by a lift drive mechanism (not shown). Moreover, while moving in the front-rear direction (Y direction) on the horizontal plane by a front-rear drive mechanism (not shown), it moves in the left-right direction (X direction) on the horizontal plane by a left-right drive mechanism (not shown).

  The table plate 22 rotates about its axis as the table plate holding frame 24 rotates. Further, the table plate holding frame 24 moves up and down as it moves up and down. Further, the table plate holding frame 24 moves in the front-rear direction when it moves in the front-rear direction, and moves left-right as it moves in the left-right direction.

  The laser antireflection plate 50 is installed below the wafer table 20. This laser antireflection plate 50 is formed in a flat plate shape having an antireflection treatment (for example, black treatment) on the upper surface portion, and is horizontally installed at a position away from the holding surface 22A of the wafer table 20 by a predetermined distance. Is done. That is, a predetermined space is formed between the holding surface 22 </ b> A of the wafer table 20 and the laser antireflection plate 50.

  The laser light emitted from the laser irradiation device 60 and transmitted through the wafer W enters the laser antireflection plate 50. Thereby, unnecessary reflection can be prevented and occurrence of reflection burn can be prevented.

  The laser irradiation device 60 is installed above the wafer table 20 and emits laser light vertically toward the wafer table 20.

  FIG. 3 is a schematic configuration diagram of the laser irradiation apparatus. As shown in the figure, the laser irradiation device 60 mainly includes a laser oscillation device 62, a collimator lens 64, a condenser lens 66, and an actuator 68.

  The laser oscillator 62 oscillates laser light in accordance with the processing conditions of the wafer W. The laser light oscillated from the laser oscillation device 62 is collimated by the collimator lens 64 and then condensed at the focal point P by the condenser lens 66.

  When the focal point P is set inside the wafer W and laser light is incident on the wafer W, a modified region is formed inside the wafer W. When the wafer W is moved horizontally in this state, the modified region is continuously formed along the movement locus of the focal point P, and the modified layer L is formed. At the time of division, this modified layer is formed along the street (division planned line).

  The actuator 68 slightly moves the condenser lens 66 in the optical axis direction (Z-axis direction). That is, the condenser lens 66 is held by a lens frame (not shown) and is supported so as to be movable in the optical axis direction. The condenser lens 66 is driven by the actuator 68 and moves minutely in the optical axis direction.

  By driving the actuator 68 and moving the condenser lens 66 in the optical axis direction, the position of the focal point P of the laser light is displaced in the Z direction. Thereby, the position (position in the Z direction) where the modified layer L is formed can be adjusted. Further, a plurality of modified layers L can be formed inside the wafer W by changing the position of the focal point P in the Z direction and making the wafer W enter the wafer W a plurality of times.

  The laser dicing apparatus 10 of the present embodiment is configured as described above.

  The operation of the laser dicing apparatus 10 is controlled by a control device (not shown). The control device executes a predetermined control program, controls the operation of each unit, and executes the processing of the wafer W.

<Action>
Next, a dicing method using the laser dicing apparatus 10 will be described.

  As described above, the wafer W is processed while mounted on the dicing frame F. The wafer W is mounted on the dicing frame F by attaching the back surface (the surface on which no device is formed) to the dicing tape T.

  The wafer W mounted on the dicing frame F is transferred to the lower part of the wafer table 20 by a transfer device (not shown) (for example, a robot arm). At this time, the wafer W is transported to the lower position of the wafer table 20 with the surface on which the dicing tape T is adhered facing upward, and the surface is in a non-contact state.

  The wafer W transferred to the lower position of the wafer table 20 is delivered from the transfer device to the wafer table 20. The delivery is performed by tightly holding the back surface of the wafer W with the holding surface 22A of the wafer table 20. Specifically, this is performed as follows.

  First, the wafer W is positioned. That is, the wafer W is positioned so that the center of the wafer W coincides with the center of the wafer table 20. Thereafter, the refracting liquid 26 is uniformly supplied to the back surface of the wafer W using a refracting liquid supply means (not shown) for dropping or coating the refracting liquid 26. The wafer W may be positioned after the refractive liquid 26 is supplied. Further, the refractive liquid 26 may be supplied to the holding surface 22 </ b> A of the wafer table 20 instead of the back surface of the wafer W or together with the back surface of the wafer W. Thereafter, the holding surface 22A of the wafer table 20 is pressed against the back surface of the wafer W with a predetermined pressure. As a result, the refractive liquid 26 is uniformly and thinly spread between the back surface of the wafer W and the holding surface 22 </ b> A of the wafer table 20, so that the wafer W is tightly held on the wafer table 20.

  In this way, the holding surface 22A of the wafer table 20 is held in close contact with the surface of the wafer W on which the dicing tape T is adhered with the refractive liquid 26 interposed. Thereby, the wafer W can be held in a flat state without being bent. Moreover, since the back surface of the wafer W is held in close contact via the dicing tape T, the front surface can be held in a non-contact manner.

  The transfer device that has delivered the wafer W retracts from the lower portion of the wafer table 20. Thereafter, a predetermined alignment process is performed, and dicing is started.

  Dicing is performed by making the laser beam emitted from the laser irradiation device 60 enter the wafer W along the street.

  A control device (not shown) drives the actuator 68 to adjust the position of the condenser lens 66 so that the focal point P is set at a predetermined position inside the wafer W. Then, the wafer table 20 is moved so that the emitted laser light is incident on the wafer W along the street.

  By the way, in the laser dicing apparatus 10 of the present embodiment, the wafer W to be processed is held in close contact with the lower surface of the wafer table 20. On the other hand, the laser light is incident on the upper surface of the wafer table 20.

  However, since the wafer table 20 is formed so as to transmit laser light, it can enter the wafer W even when the laser light is incident on the upper surface.

  In addition, the wafer W is held in close contact with the wafer table 20 on the surface (back surface) to which the dicing tape T is adhered. However, since the dicing tape T is also formed so as to transmit laser light, it enters the wafer W. be able to. As will be described later, the refractive liquid 26 is also capable of transmitting laser light.

  Thus, in the laser dicing apparatus 10 according to the present embodiment, the laser light is incident on the wafer W through the wafer table 20 and the dicing tape T.

  Since the wafer W is in close contact with the holding surface 22A of the wafer table 20 by interposing the refractive liquid 26 and is held without being bent, the laser beam can be accurately incident on a predetermined position. Thereby, the modified layer L can be accurately formed along the street.

  In addition, since the wafer W is held on the wafer table 20 without touching the surface, it can be processed without destroying a device (such as a MEMS element) formed on the surface.

  In addition, if the surface of the wafer W is held tightly, the holding surface 22A is burned by the laser light transmitted through the wafer W, or a melt adheres, and the smoothness of the holding surface 22A cannot be maintained. By holding the wafer W in close contact without touching the surface, it is possible to prevent such a problem from occurring. Thereby, even if it processes continuously, the wafer W can always be closely_contact | adhered and hold | maintained.

  Furthermore, since the laser light is incident on the back surface of the wafer W, the modified layer L can be accurately and reliably formed at a predetermined position without being affected by the device formed on the front surface.

  When the laser beam is incident on the wafer W along the street and the processing is completed, the wafer W is transferred from the wafer table 20 to the transfer device, and is transferred to the next process by the transfer device.

<Refractive liquid>
Next, the refractive liquid 26 used in this embodiment will be described.

  In the present embodiment, as described above, the wafer W is held in close contact with the holding surface 22A of the wafer table 20 with the refractive liquid 26 interposed on the surface (back surface) to which the dicing tape T is attached, The laser light is incident from the back side of the wafer W through the refractive liquid 26. For this reason, the liquid used as the refractive liquid 26 may be any liquid that can transmit at least laser light. For example, water, ethanol, isopropyl alcohol (IPA), or the like can be used. Of these liquids, ethanol and IPA are preferred. Ethanol and IPA have a lower surface tension than water and high wettability with respect to the wafer table 20 and the dicing tape T. For this reason, these liquids (that is, ethanol and IPA) are uniformly and thinly formed between the surface (back surface) of the wafer W on which the dicing tape T is adhered and the holding surface 22A of the wafer table 20. Therefore, the wafer W can be held tightly in a state of higher adhesion.

  In particular, in the present embodiment, an embodiment using IPA as the refractive liquid 26 is suitable. IPA has higher volatility than other liquids, and can suppress the occurrence of a watermark on the wafer W. It is also possible to prevent organic contamination of the wafer table 20 and its peripheral part. In addition, the aspect using the liquid mixture (For example, the liquid mixture of IPA, water, or ethanol) of IPA and another liquid instead of IPA is also preferable.

  In the present embodiment, it is preferable to use a liquid having a refractive index comparable to that of the dicing tape T as the refractive liquid 26. According to this aspect, the difference in refractive index at the interface with the dicing tape T can be eliminated, and the transmittance of laser light can be improved. For example, when the dicing tape T is made of a polyolefin-based polyethylene film (refractive index: about 1.54), for example, dichlorotoluene (refractive index: 1.546) can be preferably used as the refractive liquid 26. As the liquid having a predetermined refractive index, for example, a refractive index standard solution manufactured by Kyoto Electronics Industry, a contact liquid (refractive liquid) manufactured by Shimadzu Corporation, a Cargill standard refractive solution manufactured by Moritex, etc. can be used.

  In the present embodiment, as described above, the table plate 22 of the wafer table 20 is made of transparent quartz glass, but is not limited thereto, and may be made of, for example, silicon. Moreover, according to the aspect in which the wafer W and the table plate 22 are made of the same material, the laser light can be transmitted without being affected by refraction by using the refracting liquid 26 having the same refractive index as that of the material. The rate can be further improved.

  Further, quartz glass or the like used as a material for the table plate 22 has an absorption band in the infrared light region, and the transmittance may be reduced. In such a case, the table plate 22 may not be made of quartz glass but may be made of a transparent resin material such as acrylic.

  As described above, the material of the table plate 22 preferably has a transmittance at a wavelength selected by the laser light, and more preferably a material that can be mirror-finished as described later.

  In the present embodiment, as described above, the table plate 22 is formed with a necessary and sufficient thickness so that the wafer W to be processed can be held without bending. The table plate 22 is also required to have a uniform thickness.

  Thus, by making the thickness of the table plate 22 of the wafer table 20 uniform and eliminating the bending, the wafer adhered from the position of the objective lens of the laser irradiation device 60 via the wafer table 20 and the dicing tape T. The distance to the surface is almost constant. As a result, the modified layer can be stably formed at a certain depth regardless of the weight of the wafer W.

  When the table plate 22 is bent by itself, as shown in FIG. 4, for example, on the outer peripheral portion of the laser beam incident surface (surface opposite to the holding surface 22A) 22B of the table plate 22 An annular rim member 30 may be provided along the same. In this way, by reinforcing the outer peripheral portion of the table plate 22 with a reinforcing member such as the rim member 30, it is possible to suppress the bending of the table plate 22.

  As shown in FIG. 4, when the annular rim member 30 is provided on the laser light incident surface 22 </ b> B of the table plate 22, the refractive liquid 26 is placed between the laser light incident surface 22 </ b> B and the objective lens position of the laser irradiation device 60. It is also possible to intervene. In this case, the refracting liquid 26 on the laser light incident surface 22B does not flow outward by the rim member 30, and the objective lens of the laser irradiation device 60 and the laser light incident surface 22B are filled with the refracting liquid. The numerical aperture of the lens can be further increased, and the light can be efficiently condensed inside the wafer W.

  In the configuration example shown in FIG. 4, a plurality of suction holes (not shown) are formed on the outer peripheral portion of the lower surface of the table plate holding frame 24 (the surface on the dicing frame F side). By being vacuum-sucked through the suction holes, it is held in close contact with the table plate holding frame 24.

  In the present embodiment, the holding surface 22A of the wafer table 20 is preferably roughened. Further, instead of the holding surface 22A of the wafer table 20, or together with the holding surface 22A of the wafer table 20, the surface to be held of the dicing tape T attached to the wafer W (the surface opposite to the wafer W) is rough. Surface treatment may be performed. In this way, by subjecting at least one of the holding surface 22A of the wafer table 20 and the held surface of the dicing tape T to a rough surface treatment, a minute space is formed between them, which is caused by capillary action. The refractive liquid 26 spreads efficiently without gaps. As a result, the contact area between the surface subjected to the rough surface treatment and the refractive liquid 26 is increased, and the wafer W is held in close contact with a larger contact force. As will be described later, when the wafer W is not directly mounted on the dicing frame F but directly held by the wafer table 20, the back surface of the wafer W may be roughened.

  In the present embodiment, the laser light incident surface 22B of the wafer table 20 is preferably a mirror surface. The mirror surface is easier for the laser beam to enter the wafer table 20.

  On the other hand, the holding surface 22A of the wafer table 20 is preferably roughened as described above, and is preferably not a mirror surface as compared with the laser light incident surface 22B on the opposite side. This is because the mirror surface has a small surface area with respect to the liquid and poor wettability. That is, the holding surface 22A of the wafer table 20 has a larger surface area when the surface thereof is rough, and the refractive liquid 26 spreads uniformly on the holding surface 22A of the wafer table 20. One method for roughening the holding surface 22A of the wafer table 20 is a texturing (by facing) method. For example, as shown in FIG. 5, a small groove 32 is formed concentrically or spirally on the holding surface 22 </ b> A of the glass wafer table 20 so that the refractive liquid 26 spreads uniformly along the groove 32. become.

  Depending on the refractive liquid and the material of the wafer table 20 (table plate 22), the textured grooves may be about 0.4 mm with a groove width of about 0.2 mm and about 0.2 mm with a groove width of 0.1 mm. It may be a groove formed on the entire surface corresponding to the wafer diameter on the holding surface 22A of the table 20.

  In addition to the texturing, there is a method of simply roughening the holding surface 22A of the wafer table 20. For example, GC abrasive grain # 2000 may be used and the holding surface 22A may be lapped for about 20 minutes. Moreover, you may use the abrasive grain about # 500. The holding surface 22A may be roughened by using abrasive grains such as WA other than GC. By doing so, the holding surface 22A becomes on the ground glass and is scattered in the air due to surface roughness and becomes cloudy. The surface roughness should be 0.1 mm or less in terms of Ra, but is not limited to this, and it is better that the liquid is buried in the roughness gap so that the interfacial tension is increased and the surface area is increased.

  Thus, by roughening the holding surface 22A of the wafer table 20 by a method such as texturing, a liquid (refractive liquid 26) for compensating the refractive index is dropped on the holding surface 22A, and the back surface of the wafer W (dicing tape). When the holding surface 22 </ b> A is ringed between the surface T and the holding surface 22 </ b> A, the refracting liquid 26 spreads uniformly over the holding surface 22 </ b> A, and a uniform refractive index distribution can be obtained within the surface of the wafer W.

  As described above, according to the laser dicing apparatus 10 of the present embodiment, the rear surface side of the wafer W has the refractive liquid 26 interposed on the holding surface 22A of the wafer table 20 formed so as to be able to transmit laser light. Is held in close contact. Thereby, the wafer W is held in a flat state without bending. Then, the modified layer can be accurately formed inside the wafer W by irradiating the laser light from the back side of the wafer W through the wafer table 20. Further, the dicing process can be performed without touching the surface of the wafer W at all. Therefore, the dicing process can be performed without destroying the device formed on the surface of the wafer W.

<Other embodiments>
In the above embodiment, the wafer W is held in close contact with the lower surface of the horizontally placed wafer table 20, but as shown in FIG. 6, a holding surface 22A is formed on the upper surface of the wafer table 20, Alternatively, the wafer W may be placed on the upper surface 20 and held in close contact therewith. In this case, as shown in the figure, the laser irradiation device 60 is installed at a position below the wafer table 20 and emits laser light from below to above. Even if the wafer W has a large diameter, the holding surface 22A is formed on the upper surface of the wafer table 20 and the wafer W is placed on the upper surface of the wafer table 20 and held in close contact therewith. The wafer W can be securely adhered to the holding surface 22A, and the wafer W can be held flat.

  The wafer W diced by the laser dicing apparatus 10 is then divided into chips by applying external stress. This process is performed by, for example, an expanding apparatus.

  FIG. 7 is a process diagram showing an outline of the expanding process by the expanding apparatus.

  The laser-diced wafer W is placed on the peeling table 110 with the surface facing up, as shown in FIG. The dicing frame F is fixed at a predetermined position by a frame fixing mechanism (not shown).

  When the wafer W is placed on the peeling table 110 and the dicing frame F is fixed, a ring 112 arranged so as to surround the periphery of the peeling table 110 is shown in FIG. It is pushed up by the lifting mechanism that does not. As a result, the dicing tape T attached to the back side of the wafer W is expanded (expanded) radially. When the dicing tape T is expanded, external stress is applied to the wafer W, and the wafer W is divided from the modified layer L as a starting point. Since the modified layer L is formed along the street, the wafer W is divided along the street. Since the street is set between individual chips, the wafer W is divided into individual chips.

  Thus, the laser-diced wafer W is divided into individual chips by applying external stress.

  Here, in order to verify the effect of the present invention, the result of an evaluation experiment on the degree of adhesion of the wafer W will be described. In this evaluation experiment, the evaluation apparatus having the configuration shown in FIG. 6, that is, the configuration in which the holding surface 22A is formed on the upper surface of the wafer table 20 and the wafer W is placed and held on the upper surface of the wafer table 20 was used. . The wafer table 20 was made of quartz glass, and a polyolefin-based transparent film was used for the dicing tape T adhered to the wafer W. Further, IPA was used as the refractive liquid 26.

  First, when the surface (back surface) of the 12-inch wafer W on which the dicing tape T is attached is placed on the holding surface 22A of the wafer table 20 without any interposition, the warpage of the wafer W is measured. Warpage of about 0.07 mm occurred.

  Next, the evaluation was performed on the case where the wafer W in which the warp as described above occurred was held in close contact with the holding surface 22A of the wafer table 20 with the refractive liquid 26 interposed. Specifically, IPA was dropped evenly on the holding surface 22 </ b> A of the wafer table 20 by a dropper for 10 or more drops. The dripping amount at that time is about 30 mg. Thereafter, the wafer W is pressed against the wafer table 20. When the peeling force required when peeling the wafer W from the wafer table 20 was measured after the interface IPA was sufficiently applied at the time of pressing, a peeling force of about 2 N was required per chip. Further, the wafer W was completely adhered to the holding surface 22A of the wafer table 20, and the warpage of the wafer W almost disappeared and became 0.01 mm or less.

  Even when water or ethanol is used as the refracting liquid 26 instead of IPA, the wafer W can be tightly held on the holding surface 22A of the wafer table 20 without being bent. However, when IPA was used, the generation of watermarks could be suppressed compared to when water or ethanol was used.

  From the above results, it is possible to reliably attach the wafer W to the holding surface 22A of the wafer table 20 by interposing the refractive liquid 26, and the refractive liquid 26 is preferably IPA.

  In the above embodiment, the wafer W mounted on the dicing frame F is held in close contact with the wafer table 20 and laser dicing is performed. However, the wafer W is not mounted on the dicing frame F, but directly on the wafer table 20. The laser dicing can also be performed by holding. Moreover, it is possible to adopt a configuration in which laser dicing is performed by attaching only a tape (dicing tape) that can transmit laser light to the back surface without mounting on the dicing frame F.

  DESCRIPTION OF SYMBOLS 10 ... Laser dicing apparatus, 20 ... Wafer table, 22 ... Table board, 22A ... Adsorption surface, 24 ... Table board holding frame, 26 ... Refraction liquid, 50 ... Laser antireflection plate, 60 ... Laser irradiation apparatus, 62 ... Laser oscillation Apparatus 64 ... Collimator lens 66 ... Condenser lens 68 ... Actuator 110 ... Release table 112 ... Ring W ... Wafer T ... Dicing tape F ... Dicing frame

Claims (21)

In a laser dicing apparatus that irradiates a wafer having a plurality of devices formed on the surface with laser light and forms a modified layer inside the wafer,
A wafer table having a substantially flat holding surface that is formed so as to transmit the laser light and that holds the back surface of the wafer in close contact with a refractive liquid in order to correct warpage or waviness of the wafer; ,
Laser irradiation means for irradiating the laser beam from the back side of the wafer through the wafer table;
A laser dicing apparatus comprising:   The laser dicing apparatus according to claim 1, wherein the refractive liquid is a liquid containing isopropyl alcohol.   The laser dicing apparatus according to claim 1, wherein the holding surface is roughened.   The tape which can permeate | transmit the said laser beam is affixed on the back surface of the said wafer, The said wafer is closely_contact | adhered to the holding surface of the said wafer table via the said tape, The Claims 1-3 characterized by the above-mentioned. The laser dicing apparatus according to any one of claims.   The laser dicing apparatus according to claim 4, wherein the wafer is mounted on a frame via the tape.   6. The laser dicing apparatus according to claim 4, wherein a surface of the tape opposite to the wafer side is roughened.   The wafer table is horizontally installed with the holding surface facing upward, and the laser irradiation unit irradiates the wafer held by the wafer table with laser light from below the wafer table. The laser dicing apparatus according to any one of claims 1 to 6.   The wafer table is horizontally installed with the holding surface facing downward, and the laser irradiation unit irradiates the wafer held on the wafer table with laser light from above the wafer table. Item 7. The laser dicing apparatus according to any one of Items 1 to 6.   The laser dicing apparatus according to claim 1, wherein a laser antireflection plate is installed at a position separated from the holding surface.   The laser dicing apparatus according to claim 1, wherein the wafer is a wafer having a MEMS element formed on a surface thereof. In a laser dicing method in which a wafer having a plurality of devices formed on the surface is irradiated with laser light and a modified layer is formed inside the wafer,
A wafer table having a substantially flat holding surface that is formed so as to transmit the laser light and that holds the back side of the wafer in close contact with a refractive liquid in order to correct warping or waviness of the wafer. A laser dicing method characterized by holding the wafer and irradiating the laser beam from the back side of the wafer through the wafer table.   The laser dicing method according to claim 11, wherein the refractive liquid is a liquid containing isopropyl alcohol.   The laser dicing method according to claim 11, wherein the holding surface is roughened.   14. The tape according to claim 11, wherein a tape capable of transmitting the laser beam is attached to the back surface of the wafer, and the wafer is held in close contact with the holding surface of the wafer table via the tape. The laser dicing method according to any one of the above.   The laser dicing method according to claim 14, wherein the wafer is mounted on a frame via the tape.   16. The laser dicing method according to claim 14, wherein a surface of the tape opposite to the wafer side is roughened. The wafer table is installed horizontally with the holding surface facing up ,
Laser dicing method according to any one of claims 11 to 16 from below the front Symbol wafer table and then irradiating a laser beam to the wafer held on the wafer table. The wafer table is installed horizontally with the holding surface facing down ,
Laser dicing method according to any one of claims 11 to 16 from above the front Symbol wafer table and then irradiating a laser beam to the wafer held by the wafer table.   The laser dicing method according to any one of claims 11 to 18, wherein a laser antireflection plate is installed at a position separated from the holding surface.   The laser dicing method according to claim 11, wherein the wafer is a wafer having a MEMS element formed on a surface thereof. Laser dicing, in which a plurality of devices are formed on the front surface, and a laser beam is irradiated to a wafer mounted on a frame via a tape attached to the back surface to form a modified layer inside the wafer. In a wafer processing method comprising: a step and an expanding step of dividing the tape of the wafer subjected to the laser dicing process into individual chips on the tape,
In the laser dicing step, the surface of the wafer that has the tape attached to the holding surface of a wafer table that is formed to transmit the laser light and has a substantially flat holding surface is warped or undulated. A wafer processing method, wherein the wafer is held in close contact with a refractive liquid in order to correct , and the laser beam is irradiated from the back side of the wafer through the wafer table.

Images