JP6483204B2 - Laser dicing apparatus and method - Google Patents

Description

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

  Conventionally, a dicing method (laser dicing) using a laser is known as a method of dividing a wafer having a plurality of devices (semiconductor elements) formed on the surface thereof into individual chips. 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 having a metal film 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, Patent Document 3 proposes that a laser beam is incident through a dicing tape to form a modified layer inside the wafer. In addition, a laser processing apparatus and a laser processing method have been proposed that can hold a workpiece without touching a region where no device is formed and irradiate a laser beam from the back side.

JP 2007-123404 A JP 2005-109045 A JP 2010-29927 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 back surface 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, when the back side of the wafer is sucked and held by the table in this way, for example, in the case of a wafer having a fine structure such as a MEMS (Micro Electro Mechanical System), the element is destroyed by the suction. There is a disadvantage that it ends up. 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, it is also conceivable to support only the peripheral edge of the wafer with an annular table, but if only the peripheral edge is supported in this way, the wafer will be bent and a modified layer cannot be formed in a predetermined region. There are drawbacks. In addition, when the laser beam is irradiated through the film, the film surface is not a hard body such as glass in the case of a thin film, and therefore, there are few cases where a clean flat surface is formed, and there are many cases where there is a general swell. In addition, depending on the object, there are many cases in which the surface is minutely rough, and there is a problem that when the laser beam is directly applied to the film surface, the laser beam is not efficiently incident due to the influence of the film surface.

  Furthermore, in Patent Document 3, in [0018] in the publication related to Patent Document 3, in order to correct the warp and undulation of the work (wafer W), the work is pressed from the back side, It is described that the laser beam is irradiated with the back surface of the work pressed against the warp correction means. However, even if the workpiece is pressed from the back side with a positive pressure on a wafer that normally has a monotonous warp [0074], in principle, the workpiece is not completely flattened. Even if a member having warpage is pressed against a flat body and forcedly used, one point of the central part comes into contact with the surrounding area, so that a part of the central part is shown in FIG. 7B. Is only pressed against a flat body and is not completely corrected to a flat surface. Therefore, when a non-uniform gap as shown in FIGS. 7A and 7B is formed between the workpiece and the correction member, it is impossible to focus on a stable region inside the wafer, so that the inside of the wafer can be accurately obtained. A modified layer cannot be formed by laser light.

  In addition, an air layer is interposed between the glass surface and the wafer surface, so that reflections occur repeatedly between the film and the glass surface, and laser scattered light enters other than the desired part of the wafer, causing laser burn. It will be. Loss due to such scattered light consumes energy in the vicinity of the loss, and this is due to laser scattering in the vicinity, such as surface deterioration on the glass surface and adhesion of debris to the film due to deterioration. Will suffer from the harmful effects of

  In addition, when the glass surface and the film surface are not in close contact, even if the laser is turned on with a large laser power, it is efficiently reformed inside the wafer due to the scattering effect between the glass surface and the film surface. There was a problem that the layer was not formed. Moreover, it is very difficult to control the pressure of the sealed space to make one surface completely horizontal, whether it is positive pressure or reduced pressure. If the pressure is too high, the surface will bend in the protruding direction, and if it is reduced in pressure, it will bend toward the concave side. The pressure control is very delicate and it is in principle difficult to maintain a flat surface.

  Furthermore, it becomes a problem in the subsequent steps. As described above, the device used in the MEMS element has a tape on the element surface, and even when trying to vacuum-suck it on the adsorption table with the element surface facing down, the element is very fragile. Or even touching. In such a case, the film surface and the glass surface are brought into close contact with each other, laser light is incident to form a modified layer in the wafer surface, the film is then peeled off from the glass surface, and the film is stretched. Must be spaced apart from the tip. In such a film, a film having a property of spreading to such an extent that the chips are separated from each other while satisfying the transmittance of the laser beam is required.

  However, there is no suitable film that has such permeability and has spreadability enough to separate the chips. First, such a film needs to be an elastic material. However, in the case of an elastic material, that is, a rubber member, there is more or less unevenness of the elastic modulus in the surface, although there are some problems. Moreover, in the case of an elastic material, it is comprised from the nonpolar material which -CH couple | bonded. There are various mechanisms with elasticity, but the most main factor with elasticity is that molecules are entangled with each other, and the degree of entanglement of the molecules changes, so that elasticity is often exhibited. That is, the density and the degree of homogeneity of the material itself change due to external stress.

  On the other hand, the refractive index of the material must be uniform in order for the laser light to pass through the material stably. When the refractive index is not uniform, the depth at which the laser beam forms an image varies and a stable modified layer cannot be formed.

  Here, the elastic material is a material whose degree of homogeneity changes due to external stress, and the degree of homogeneity of the material corresponds to the uniformity of the refractive index. In other words, the fact that the degree of homogeneity of the material itself is likely to change in an external environment such as external stresses means that the material itself is not homogeneously and stably formed, which means that the refractive index is not uniform. . Therefore, in general, there is almost no elastic material having a large spreading property having a uniform refractive index depending on the degree. In particular, there is almost no material that can accurately separate the laser beam for laser processing that forms an image inside the substrate and can separate the chip by pulling the film.

  Therefore, without modifying the device formed on the front surface of the wafer, that is, without touching the front surface, a modified layer is accurately formed at a certain depth inside the wafer while irradiating laser light from the back surface of the wafer. In addition, an efficient and stable modified layer is formed inside the wafer by reducing scattering along the laser path, and laser burning due to laser scattering is eliminated by scattering along the path. A technical problem to be solved in order to prevent the decrease and to divide the wafer after laser irradiation into chips and stably separate the chips is generated, and the present invention aims to solve this problem. To do.

The present invention has been proposed in order to achieve the above object, and the invention according to claim 1 forms a modified layer in the wafer by irradiating a laser beam onto a wafer having a device formed on the surface. In the laser dicing apparatus, the wafer holding means for adsorbing and holding the wafer substantially flat with respect to the back surface through a transparent film that is formed so as to transmit the laser light and is attached to the back surface of the wafer; irradiating through a substantially flat the film sandwiched backside or found before Symbol wafer holding means and said wafer holding means and the wafer of the wafer with the laser beam, the laser irradiation to form a modified layer within said wafer And a laser dicing apparatus comprising the means.

  According to this configuration, the transparent film attached to the wafer is adsorbed and held on the substantially flat holding surface of the wafer holding means formed so as to be able to transmit laser light. Thus, the wafer is held in a flat state without bending with respect to the surface adsorbed by the wafer holding means. Then, by irradiating the laser beam from the laser irradiation means through the transparent film and the transparent hard wafer holding means, the modified layer can be accurately formed inside the wafer. In addition, the modified layer can be formed inside the wafer without touching any device formed on the wafer. In addition, after forming a modified layer inside the wafer with laser light, a wafer attached to a transparent film is divided into individual chips from the modified layer, and is divided into individual chips together with the transparent film. Thereby, it becomes possible to divide a wafer into pieces efficiently. Further, when the laser beam is irradiated through the transparent film and the chip attached to the transparent film is separated, the transparent film can be separated from the transparent film, which is very efficient. As a result, it is possible to efficiently cleave the wafer by processing from one side without touching the device formed on the wafer.

According to a second aspect of the present invention, there is provided a laser dicing method in which a modified layer is formed inside the wafer by irradiating the wafer having a device formed on the surface thereof with a laser holding device capable of transmitting the laser beam. a step of substantially flat suction holding the wafer as a reference the back through the transparent film applied to the back surface of the wafer, the back surface side or found before Symbol wafer holding means of said wafer to said laser beam and And irradiating the wafer holding means and the substantially flat film sandwiched between the wafers to form a modified layer in the wafer.

  According to this configuration, a transparent film is attached to the wafer, and the wafer is held in close contact with the substantially flat holding surface of the wafer holding means formed so as to transmit laser light through the transparent film. Thus, the wafer is held in a flat state without bending with respect to the surface adsorbed by the wafer holding means. In the next step, the laser beam from the laser irradiation unit is irradiated through the transparent film and the transparent hard wafer holding unit. By this irradiation, the modified layer is accurately formed inside the wafer. After the modified layer is formed inside the wafer, it is removed from the wafer holding means at the transparent film portion, and then each chip is divided from the modified layer, and is divided into each chip together with the transparent film. Thereby, wafers are efficiently separated into individual pieces.

  In the present invention, a wafer is sucked and held in a flat state on a substantially flat holding surface of a wafer holding means through a transparent film attached to the wafer, and laser light is irradiated through the film and the wafer holding means. As a result, the modified layer can be accurately formed in the wafer at a constant depth without destroying the device formed on the wafer. After the modified layer is formed inside the wafer, there is an advantage that the transparent film with the wafer attached is removed from the wafer holding means, and the wafer can be singulated stably and efficiently.

1 is a schematic configuration diagram of a laser dicing apparatus according to Embodiment 1 of the present invention. The perspective view which shows the wafer of the state mounted in the dicing frame. The schematic block diagram of a laser irradiation apparatus. The top view of the table board which formed the concentric or spiral groove | channel on the holding surface. The schematic block diagram which shows Example 2 of a laser dicing apparatus. Process drawing which shows the outline of the expansion process by an expanding apparatus. It is a figure for demonstrating one of the problems in a prior art, (a) is a figure which shows that a wafer will bend when only the peripheral part of a wafer is supported, (b) is corrected with a correction member. The figure which shows that a non-uniform clearance gap is made between a wafer and a correction member.

In the present invention, the device formed on the front surface of the wafer is not destroyed, that is, without touching the front surface. In addition, an improved and stable modified layer is formed inside the wafer by reducing scattering in the laser halfway path, and laser burning due to laser scattering is eliminated by scattering along the halfway path, resulting in deterioration of each part due to laser burning. In order to prevent performance degradation and to divide the wafer after laser irradiation into chips and stably separate the chips, the wafer with the device formed on the surface is irradiated with laser light. In a laser dicing apparatus that forms a modified layer inside, it is formed so that it can transmit laser light and is transparently attached to the back surface of the wafer. Through substantially a wafer holding means for holding flat adsorb the wafer relative to the back surface through the Irumu, a substantially flat film sandwiched laser beam to the wafer holding means and said wafer holding means and the wafer from the back side of the wafer And laser irradiation means for forming a modified layer in the wafer.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.
<Configuration>
FIG. 1 is a schematic configuration diagram of a laser dicing apparatus according to the present embodiment. As shown in the figure, the laser dicing apparatus 10 mainly includes a wafer table 20 that holds a wafer W, a laser antireflection plate 50, and a laser irradiation apparatus 60 that irradiates the wafer W held on the wafer table 20 with laser light. It consists of

  First, the wafer W to be processed by the laser dicing apparatus 10 of this embodiment will be described. A wafer W to be processed by the laser dicing apparatus 10 is a wafer W having a plurality of devices (for example, MEMS elements) formed on the surface thereof, and is processed while mounted on the dicing frame F.

  FIG. 2 is a perspective view showing the wafer W in a mounted state that is stuck on the transparent film T. FIG. As shown in the figure, the wafer W is mounted on a small dicing frame F via a transparent film (dicing tape) T. The small dicing frame F is formed in a frame shape, and the transparent film T is stuck inside the frame. The wafer W is attached to the dicing frame F with its back surface attached to the transparent film T.

  Here, the transparent film T attached to the dicing frame F is a film having brittleness that is easy to tear, and at the same time, is formed of a material that can transmit laser light emitted from the laser irradiation device 60. In this embodiment, it is made of a transparent material. It is more preferable to have air permeability. Further, the transparent film T has a characteristic of becoming more brittle when irradiated with ultraviolet light, heated to a required temperature, or cooled to a required low temperature. For this reason, before extending the extended tape attached on the transparent film T radially as described later, the transparent film T is irradiated with ultraviolet light, heated to a required temperature, or cooled to a required low temperature. The brittleness increases, and the wafer can be separated into more efficient pieces.

  The wafer W mounted on the dicing frame F is held by the wafer table 20 on the surface (back surface) to which the transparent film 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 this embodiment, it is made of transparent quartz glass. This is not limited to quartz glass, but may be any member that is permeable and hard enough to define a plane. For example, a resin such as acrylic or transparent vinyl chloride may be used. Silicon or the like is opaque in visible light, but transparent in light in the infrared region. Therefore, bare silicon wafers and germanium have a refractive index close to 4.0 and are extremely high refractive materials. By using such a high refractive material, it becomes possible to reduce the width of the depth of focus in the wafer.

  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. The holding surface 22 </ b> A and the surface (back surface) to which the transparent film T of the wafer W is attached are held in a state of being completely adhered. There are various holding methods. For example, a vacuum suction groove may be formed on the outer periphery of the table, and the table and the transparent film T attached to the wafer W may be brought into close contact with each other by vacuum suction at the groove.

  As another method, there is a method in which a transparent liquid is interposed between the table and the transparent film T attached to the wafer W, and the attachment is performed by interfacial tension acting between the liquid and the solid surface. For example, when a uniform and thin film-like contact liquid 26 is interposed between the table plate 22 and the transparent film T, the wafer W is held in close contact with the table plate 22. As will be described in detail later, examples of the contact liquid 26 include water, ethanol, and isopropyl alcohol (IPA).

  The table plate holding frame 24 is rotated about its axis by a rotation driving mechanism (not shown) and is moved up and down (Z direction) by a lifting driving 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 around the axis when 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. The laser antireflection plate 50 is formed in a flat plate shape having a laser beam antireflection treatment (for example, black processing) 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. As a result, 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 device 60. 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 collimator lens 64.

  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 region 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). In other words, 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 slightly moves in the optical axis direction. By driving the actuator 68 to slightly move 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. In addition, 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 allowing the laser beam to enter the control device a plurality of times.

  Here, it is desirable that the surface of the wafer table 20 on which the laser light is incident is a mirror surface. The mirror surface is easier for the laser beam to enter the wafer table 20. On the other hand, the surface of the wafer table 20 on the side in contact with the film should not be a mirror surface compared to the surface on the side on which the laser light is incident. This is because the mirror surface has a small surface area with respect to the liquid and poor wettability. That is, when the surface portion of the wafer table 20 has roughness, the surface area of the wafer table surface increases, and the liquid spreads uniformly over the wafer table 20. One of the methods for roughening the wafer table 20 is a texturing (by facing) method. As shown in FIG. 4, concentric or spiral grooves 23 are formed in a small groove 23 on a glass wafer table 20. The refractive liquid spreads uniformly along the groove 23. The texturing grooves 23 may be about 0.2 mm, a width of about 0.4 mm, a width of about 0.1 mm, and a pitch of about 0.2 mm depending on the refractive liquid and the material of the wafer table 20. The grooves may be formed on the entire surface of the wafer table 20 corresponding to the wafer diameter.

  In addition to texturing, there is a simple method of roughing the surface. For example, GC abrasive grain # 2000 may be used and the surface may be lapped for about 20 minutes. Moreover, you may use the abrasive grain about # 500. Other than GC, the surface may be roughened by using abrasive grains such as WA. By doing in this way, the surface becomes ground glass, and it is scattered in the air due to the rough surface and becomes cloudy. The surface roughness may 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.

  In addition, as a material of the wafer table 20, there is also quartz glass, but other than that, a silicon wafer or the like may be used. Quartz glass or the like has an absorption band in the infrared region, and the transmittance may decrease. In such a case, a transparent resin material such as acrylic may be used instead of quartz glass. Any material can be used as long as the transmittance is good at the wavelength selected by the laser beam and the plane can be mirror-finished. Further, the thickness of the wafer table 20 should be uniform and hardly bend. Moreover, when bending independently, it is necessary to eliminate bending as much as possible as an outer periphery fixed end, such as attaching a rim to the outer periphery.

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 transparent film 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, an arm of a robot). At this time, the wafer W is transported to the lower position of the wafer table 20 with the surface on which the transparent film T is adhered facing upward and the surface being in a non-contact state.

  The wafer W transferred to the lower position of the wafer table 20 is delivered to the wafer table 20 from the transfer position. 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, it is positioned so as to coincide with the center of the wafer W. Thereafter, the adhesion liquid 26 is uniformly supplied to the back surface of the wafer W by dropping the adhesion liquid 26 or using an adhesion liquid supply means (not shown). The wafer W may be positioned after supplying the contact liquid 26. Further, the contact 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. Thereby, the contact 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, and the wafer W is held in close contact with the wafer table 20.

  In this way, the holding surface 22 </ b> A of the wafer table 20 is held in close contact with the surface of the wafer W to which the transparent film T is attached with the contact 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 transparent film 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 has the surface (rear surface) to which the transparent film T is adhered is held in close contact with the wafer table 20, but the transparent film T is also formed so as to be able to transmit laser light, and therefore enters the wafer W. be able to. As will be described later, the contact liquid 26 is also capable of transmitting laser light.

  Thus, in the laser dicing apparatus 10 of the present embodiment, the laser light is incident on the wafer W through the wafer table 20 and the transparent film T and through the hard transparent table. The wafer W is brought into close contact with the holding surface 22A of the wafer table 20 by interposing the contact liquid 26, for example, and is held without bending, so that the laser beam can be accurately incident on a predetermined position. Further, since the wafer W is in close contact with the hard transparent wafer table 20 via the transparent film T, there is no subtle surface undulation of the transparent film T, and the interface of the wafer W is sandwiched by the hard work table surface. The portion becomes flat, and the laser beam incidence efficiency is further improved.

  Further, by making the thickness of the wafer table 20 constant, the surface of the wafer W is copied based on the wafer table 20. That is, even if the initial wafer W is a wafer W having warpage or thickness unevenness, the surface of the wafer W on the laser incident side is planarly adsorbed. By making the position exactly constant, the work distance from the laser position to the laser condensing part inside the wafer W can be kept constant.

  And, by making the thickness of the wafer table 20 uniform and eliminating the bending, the distance from the objective lens position of the laser irradiation unit to the surface of the wafer W attached via the wafer table 20 and the transparent film T is almost all. It becomes constant. As a result, the modified layer can be stably formed at a certain depth regardless of the weight of the wafer W.

  Conventionally, when the wafer W surface is flattened on the side opposite to the laser irradiation side, waviness remains on the surface of the wafer W due to the thickness variation of the wafer W on the laser irradiation side, and the wafer W surface is modified to a certain depth from the surface. In order to form a quality layer, the laser position was adjusted by autofocusing along the undulation, but by using the laser irradiation surface side as a reference surface, a constant depth position can be obtained without applying autofocusing. Thus, the modified layer L can be formed. 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 process is completed, the wafer W is transferred from the wafer table 20 to the transfer device, and is transferred to the next process of the extra process.
<Contact liquid>
Next, the adhesion liquid 26 used in this embodiment will be described. In this embodiment, as described above, the wafer W is held in close contact with the holding surface 22A of the wafer table 20 with the adhesive liquid 26 interposed between the surface (back surface) to which the transparent film T is adhered, and the laser W Light is incident from the back side of the wafer W through the contact liquid 26. For this reason, the liquid used as the contact 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. Among these liquids, ethanol and IPA have a lower surface tension than water and high wettability to the wafer table 20 and the transparent film T. For this reason, these liquids (that is, ethanol and IPA) become a uniform and thin film between the surface (back surface) of the wafer W on which the transparent film T is adhered and the holding surface 22A of the wafer table 20. It becomes easy to spread as a whole, and it becomes possible to hold the wafer W in close contact with a higher adhesiveness.

  In particular, in this embodiment, an embodiment in which IPA is used as the adhesion 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. An embodiment using a mixture of IPA and another liquid (for example, a mixed solution of IPA and water or ethanol) is preferable instead of IPA.

  In the present embodiment, a mode in which a liquid having a predetermined refractive index is used as the adhesion liquid 26 in addition to the above liquid is also suitable. Specifically, a liquid having a refractive index comparable to that of the transparent film T is used as the adhesion liquid 26. Thereby, the difference in refractive index at the interface with the contact liquid 26 can be eliminated, and the transmittance of the laser beam can be improved. For example, when the transparent film T is made of a polyolefin-based polyethylene film (refractive index: about 1.54), for example, dichlorotoluene (refractive index: about 1.546) can be preferably used as the adhesion liquid 26. Such a liquid having a predetermined refractive index is generally referred to as a contact liquid or a refractive liquid. For example, a refractive index standard liquid manufactured by Kyoto Electronics Industry, a contact liquid (refractive liquid) manufactured by Shimadzu Corporation, or Moritex Corporation. Cargill's standard refraction liquid made by the company can be used.

  Moreover, when a liquid for compensating the refractive index is dropped on the glass surface, when the transparent film T and the glass surface are ringed, the refractive liquid spreads uniformly throughout the glass surface, and a uniform refractive index distribution is obtained in the wafer W surface. Can be obtained. Further, a rim may be attached to the outer peripheral portion of the wafer table 20, and a refractive liquid may be interposed between the surface of the wafer table 20 and the objective lens. The refractive liquid on the wafer table 20 does not flow down to the outside by the rim, and by filling the space between the objective lens and the wafer table (glass) 20 with the refractive liquid, the numerical aperture of the objective lens can be further increased. Thus, the light can be efficiently condensed inside the wafer W.

  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 the same material as the wafer W. For example, when the wafer W is made of silicon, the table plate 22 is also made of silicon. Thus, according to the aspect which comprises the wafer W and the table board 22 with the same raw material, the transmittance | permeability of a laser beam is further improved by making the refractive index of the raw material and the refractive index of the contact | adherence liquid 26 comparable. Is possible.

  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 (the surface opposite to the wafer W) of the transparent film T adhered to the wafer W is provided. The surface may be roughened. In this way, by subjecting at least one of the holding surface 22A of the wafer table 20 and the held surface of the transparent film T to a rough surface treatment, a minute space is formed between them, which is caused by capillary action. The contact liquid 26 spreads efficiently without a gap. As a result, the contact area between the roughened surface and the contact liquid 26 is increased, and the wafer W is held in close contact with a greater 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.

  As described above, according to the laser dicing apparatus 10 of the present embodiment, the holding surface 22A of the wafer table 20 formed so as to be able to transmit laser light is in a state where the back surface side of the wafer W has the adhesion liquid 26 interposed therebetween. Hold tightly. 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 beam 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.

  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. 5, 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. 6 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. Thereby, the transparent film T stuck on the back surface side of the wafer W is radially expanded (stretched). When the transparent film T is expanded, an 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. In addition, when an expanding tape (not shown) is pasted on the transparent film T and radially expanded at the portion of the expanding tape, it can be divided into individual chips more efficiently and stably.

  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. 5, that is, the configuration in which the holding surface 22 </ b> A 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 as the transparent film T attached to the wafer W. Further, IPA was used as the contact liquid 26.

  First, when the surface (back surface) of the 12-inch wafer W on which the transparent film T is adhered 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, evaluation was performed on the case where the wafer W in which the above-described warpage occurred was held in close contact with the holding surface 22A of the wafer table 20 with the contact 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 per chip was required. Further, the wafer W was completely adhered to the holding surface 22A of the wafer table 20, and the warpage of the wafer W was almost eliminated and became 0.01 mm or less.

  Even when water or ethanol is used as the contact liquid 26 instead of IPA, the wafer W can be closely 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, the wafer W can be securely adhered to the holding surface 22A of the wafer table 20 by interposing the adhesion liquid 26, and IPA is suitable as the adhesion liquid 26. 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. It can also be held and laser dicing can be performed. 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.

  The present invention can be variously modified without departing from the spirit of the present invention, and the present invention naturally extends to the modified ones.

  Without destroying the device formed on the wafer surface, the wafer is irradiated with laser light to form a modified layer at a certain depth inside the wafer, and scattering in the laser path is reduced. It is possible to widely apply to wafer dicing using laser light, which eliminates laser burn, prevents deterioration of each component and performance degradation due to laser burn, and it is essential to stably divide the wafer after laser irradiation into chips. It is.

DESCRIPTION OF SYMBOLS 10 Laser dicing apparatus 20 Wafer table 22 Table board 22A Holding surface 23 Groove 24 Table board holding frame 26 Adhesive liquid 50 Laser antireflection plate 60 Laser irradiation apparatus 62 Laser oscillation apparatus 64 Collimator lens 66 Condenser lens 68 Actuator 110 Peeling table 112 Ring W Wafer T Transparent film F Dicing frame

Claims (2)

In a laser dicing apparatus that forms a modified layer inside the wafer by irradiating a wafer having a device formed on the surface with laser light,
Wafer holding means for adsorbing and holding the wafer substantially flat with respect to the back surface through a transparent film formed so as to transmit the laser light and attached to the back surface of the wafer;
Irradiating through a substantially flat the film sandwiched backside or found before Symbol wafer holding means and said wafer holding means and the wafer of the wafer with the laser beam, the laser irradiation to form a modified layer within said wafer Means,
A laser dicing apparatus comprising: In the laser dicing method of forming a modified layer inside the wafer by irradiating the wafer having a device formed on the surface with laser light,
The wafer holding means capable of transmitting the laser beam, the step of adsorbing and holding the wafer substantially flat with respect to the back surface through a transparent film attached to the back surface of the wafer;
A step of irradiating through a substantially flat the film sandwiched backside or found before Symbol wafer holding means and said wafer holding means and the wafer of the wafer with the laser beam, to form a modified layer within the wafer ,
A laser dicing method comprising: