JP6735372B2 - Laser dicing device - Google Patents

Description

The present invention relates to a laser dicing apparatus, and more particularly to a laser dicing apparatus that processes a wafer having a plurality of devices formed on its surface.

Conventionally, a dicing method using a laser (laser dicing) is known as a method of dividing a wafer having a plurality of devices (semiconductor elements) formed on its surface into individual chips. Laser dicing is a method of forming a modified layer by multiphoton absorption inside a wafer by injecting laser light onto the wafer along streets (planned dividing lines). 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 an advantage that it can be divided with almost no chipping.

In laser dicing, laser light is generally incident from the front surface side (the 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 of injecting laser light from the surface side has a problem that a wafer having a metal film formed near the street cannot be used because the laser light is reflected by the metal film.

In order to solve such a problem, Patent Document 1 proposes to form a modified layer inside the wafer by injecting laser light from the back surface of the wafer through the dicing tape. Further, Patent Document 2 proposes that a pair of transparent glass plates sandwich and support a wafer 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 the dicing tape to form a modified layer inside the wafer. Further, there is proposed a laser processing apparatus and a laser processing method capable of holding a work without touching a region where a device is not formed and irradiating a laser beam from the back surface 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 thereon. However, in Patent Document 1, in order to allow the laser light to be incident on the back surface of the wafer, the back surface side of the wafer is suction-held by a table It is configured to do. However, if the back surface side of the wafer is sucked and held on the table in this way, for example, in the case of a wafer on which microstructured elements such as MEMS (Micro Electro Mecanical System) are formed, the elements are destroyed by suction. There is a drawback that it will end up. Such a problem also occurs in the laser dicing device of Patent Document 2 in which a wafer is held between transparent glass plates.

On the other hand, it is also possible to support only the peripheral portion of the wafer with a table formed in an annular shape, but if only the peripheral portion is supported in this way, the wafer will bend and the modified layer cannot be formed in a predetermined region. There are drawbacks. Further, when irradiating a laser beam through the film, when the film is a thin film, the surface of the film is not a hard body such as glass, so that a flat surface is rarely formed, and there are many cases with undulations. In addition, some objects are often slightly roughened, and there is a problem that when the film surface is directly irradiated with laser light, the laser light is not efficiently incident due to the influence of the film surface.

Further, in Patent Document 3, in order to correct warpage and undulation of the work (wafer W) in [0018] in the publication relating to the Patent Document 3, the work is pressed from the back surface side to form a flat body. It is described that the warp correction means is irradiated with laser light while the back surface of the work is pressed. However, in principle, even if a wafer having a monotonic warp is positively pressed to press the work from the back side [0074], the work is not completely planarized in principle. Even if a member having a warp is pressed against a flat body and forcibly used, one point of the central portion comes into contact and the periphery remains in the same position. Therefore, as shown in FIG. Is pressed against a flat body and is not completely flattened. Therefore, when a non-uniform gap as shown in FIGS. 7A and 7B is formed between the work and the correction member, it is not possible to focus on a stable region inside the wafer, so that the inside of the wafer can be accurately measured. A modified layer cannot be formed by laser light.

Furthermore, the presence of an air layer between the glass surface and the wafer surface causes repeated reflection between the film and the glass surface, causing scattered light from the laser to enter a portion other than the desired portion 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 be adversely affected.

In addition, if the glass surface and the film surface are not in close contact, even if the laser power is increased and the laser is turned on, the influence of scattering that occurs between the glass surface and the film surface effectively reforms the inside of the wafer. There was a problem that the layer was not formed. In addition, it is very difficult to control the pressure in the sealed space and make one of the surfaces completely horizontal regardless of whether the pressure is positive or reduced. If the positive pressure is too high, the surface will bend in the protruding direction, and if the pressure is reduced, it will bend to the concave side. Its pressure control is very delicate and it is difficult to maintain a flat surface in principle.

Further, it also poses a problem in the subsequent steps. As described above, the device used in the MEMS element is very fragile even if a tape is attached to the element surface and vacuum adsorption is performed on the adsorption table with the element surface facing down, the surface is pressed. In some cases, even touching is not allowed. In such a case, the film surface and the glass surface are brought into close contact with each other, laser light is made incident to form a modified layer in the wafer surface, and then the film is peeled from the glass surface, and the film is stretched. Must be separated by tip. For such a film, a film having a property of being malleable to the extent that the chips are separated from each other while satisfying the laser beam transmittance is required.

However, there is no suitable film having such transparency while being malleable enough to separate the chips. First, such films need to be elastic materials. However, if the material is an elastic material, that is, if it is a rubber member, there is some degree of problem, and there is more or less unevenness in the elastic modulus within the surface. Further, in the case of the elastic material, it is composed of a non-polar material in which -CH is bonded. Although there are various mechanisms of elasticity, the most main factor of elasticity is that molecules are entangled with each other, and the degree of entanglement of the molecules changes, so that elasticity is often exerted. That is, the external stress changes the density and homogeneity of the material itself.

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

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. That is, the fact that the homogeneity of the material itself is likely to change in an external environment such as external stress means that the material itself is not formed homogeneously and stably, which means that the refractive index is not uniform. .. Therefore, generally, an elastic material having a uniform refractive index and having a large extensibility is basically absent, though it depends on the degree. In particular, there is almost no material capable of accurately transmitting a laser beam of laser processing for forming an image inside the substrate and pulling the film to separate the chips.

Therefore, without destroying the device formed on the front surface of the wafer, that is, without touching the front surface, a reforming layer is formed at a constant depth position accurately inside the wafer while irradiating laser light from the back surface of the wafer. In addition, by reducing the scattering in the intermediate path of the laser and forming a stable and efficient modified layer inside the wafer, the scattering of the intermediate path eliminates the laser burn due to laser scattering, and the deterioration and performance of each component due to the laser burn. While preventing the decrease, the wafer after laser irradiation is divided into chips, and technical problems to be solved in order to stably separate the chips occur, and the present invention aims to solve this problem. To do.

The present invention has been proposed to achieve the above object, and the invention according to claim 1 is a laser dicing apparatus for irradiating a laser beam on a wafer to form a modified layer inside the wafer, A film adhered to the back surface of the wafer, a wafer holding means capable of adsorbing and holding the back surface of the wafer through the film in a substantially flat manner, and removing waviness of the film, and the wafer through the film and the wafer holding means. Laser irradiating means for irradiating a laser beam on the inside of the wafer to form a modified layer inside the wafer.

According to this configuration, the film that is permeable to the laser light and is attached to the wafer is held on the substantially flat holding surface of the wafer holding means that is formed so that the laser light can be transmitted. As a result, the wafer is held in a flat state without bending with reference to the surface of the wafer held by the wafer holding means. Then, by irradiating the laser beam from the laser irradiating means through the film and the hard wafer holding means, it becomes possible to accurately form the modified layer inside the wafer. Further, the modified layer can be formed inside the wafer without touching any device formed on the wafer. In addition, after the modified layer is formed inside the wafer by laser light, each chip of the wafer attached to the film is separated from the modified layer, and the wafer is separated into the chips together with the film. This makes it possible to efficiently divide the wafer into individual pieces. Further, when the laser beam is transmitted through the film and the chips attached to the film are separated, it is possible to separate the chips together with the film, which is very efficient. As a result, it is possible to efficiently cut the wafer by processing from one side without touching the device formed on the wafer.

The invention according to claim 2 provides a laser dicing device in which the film is attached in a dicing frame.

The invention according to claim 3 provides a laser dicing apparatus in which the film has an expandability capable of being expanded to divide the wafer into chips.

According to this configuration, by expanding the film, the wafer can be divided from the modified layer into the respective chips, and the wafer can be efficiently divided into individual pieces.

According to the present invention, a wafer is sucked and held in a flat state on a substantially flat holding surface of a wafer holding means via a transparent film attached to the wafer, and a laser beam is irradiated through the film and the wafer holding means. As a result, the modified layer can be accurately formed inside the wafer at a certain depth position without destroying the device formed on the wafer. After forming the modified layer inside the wafer, there is an advantage that the transparent film to which the wafer is attached can be 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 a first embodiment of the present invention. FIG. 3 is a perspective view showing a wafer mounted on a dicing frame. The schematic block diagram of a laser irradiation device. The top view of the table board which formed the concentric circle shape or the groove|channel of a spiral shape in the holding surface. The schematic block diagram which shows Example 2 of a laser dicing apparatus. The process drawing which shows the outline of the expansion process by an expander. FIG. 4 is a diagram for explaining one of the problems in the conventional technique, (a) is a diagram showing that the wafer is bent when only supporting the peripheral portion of the wafer, and (b) is a straightening member for straightening. FIG. 6 is a view showing that a non-uniform gap is formed between the wafer and the correction member.

The present invention, without destroying the device formed on the surface of the wafer, that is, without touching the surface, while irradiating the laser beam from the back surface of the wafer, a modified layer at a certain depth position accurately inside the wafer. In addition, a stable reformed layer is formed inside the wafer by reducing the scattering in the intermediate path of the laser and eliminating the laser burning due to the laser scattering due to the scattering of the intermediate path, and the deterioration of each part due to the laser burning. In order to prevent the performance deterioration and to divide the wafer after laser irradiation into chips and stably separate the chips, the wafer is irradiated with laser light and a modified layer is formed inside the wafer. In a laser dicing apparatus to form, a film adhered to the back surface of the wafer, and a wafer holding means capable of sucking and holding the back surface of the wafer through the film substantially flatly and removing the undulations of the film, and the film and the wafer holding Laser irradiation means for irradiating the wafer with laser light through the means to form a modified layer inside the wafer.

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.
<Structure>
FIG. 1 is a schematic configuration diagram of a laser dicing apparatus according to this 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 is composed of.

First, the wafer W to be processed by the laser dicing apparatus 10 of this embodiment will be described. The 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 being mounted on the dicing frame F.

FIG. 2 is a perspective view showing the wafer W mounted on the transparent film T and mounted. 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 attached to the inside thereof. The back surface of the wafer W is attached to the transparent film T and mounted on the dicing frame F.

Here, the transparent film T attached to the dicing frame F is a brittle film that is easily torn off, and at the same time, is formed of a material capable of transmitting the laser light emitted from the laser irradiation device 60. In this embodiment, it is made of a transparent material. In addition, it is more preferable to have air permeability. Further, the transparent film T has the property of becoming more brittle when irradiated with ultraviolet light, warmed to a required temperature, or cooled to a required low temperature. Therefore, before the extract band tape stuck on the transparent film T is radially stretched as described later, the transparent film T is irradiated with ultraviolet light, warmed to a required temperature, or cooled to a required low temperature. The brittleness increases, and it becomes possible to more efficiently divide the wafer into individual pieces.

The wafer W mounted on the dicing frame F is held on 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 (a disk shape having a diameter larger than that of 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 made of a material that can transmit the 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 and permeable so that a flat surface can be defined. For example, a resin such as acrylic or transparent vinyl chloride may be used. Silicon and the like are opaque to visible light, but transparent to light in the infrared region. Therefore, the bare silicon wafer and germanium have a refractive index of about 4.0, and are extremely high-refraction materials. The use of such a high-refractive-index material makes it 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 upper surface side of the table plate 22 is a holding surface 22A for holding the wafer W. The holding surface 22A and the surface (rear surface) of the wafer W to which the transparent film T is attached are held in a state of being completely adhered. There are various methods for holding this. For example, a vacuum suction groove may be formed on the outer peripheral portion of the table, and the groove may be sucked by vacuum to bring the table and the transparent film T attached to the wafer W into close contact.

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 liquid is attached by the interfacial tension acting between the liquid and the solid surface. For example, when a uniform and thin film 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, isopropyl alcohol (IPA), and the like.

The table plate holding frame 24 is rotated around an axis by a rotation drive mechanism (not shown) and is moved up and down in the vertical direction (Z direction) by an elevation drive mechanism (not shown). The front-rear drive mechanism (not shown) moves in the front-back direction (Y direction) on the horizontal plane, and the left-right drive mechanism (not shown) moves left-right direction (X direction) in the horizontal plane. The table plate 22 rotates about its axis when the table plate holding frame 24 rotates. Further, as the table plate holding frame 24 moves up and down, it moves up and down. Further, when the table plate holding frame 24 moves in the front-rear direction, it moves back and forth, and when it moves in the left-right direction, it moves left and right.

The laser antireflection plate 50 is installed below the wafer table 20. The laser antireflection plate 50 is formed in a flat plate shape whose upper surface is subjected to antireflection treatment of laser light (for example, black treatment), and is horizontally installed at a position apart from the holding surface 22A of the wafer table 20 by a predetermined distance. To be done. That is, a predetermined space is formed between the holding surface 22A 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 reflection burn or the like can be prevented.

The laser irradiation device 60 is installed above the wafer table 20 and vertically emits laser light 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 according to the processing conditions of the wafer W. The laser light oscillated from the laser oscillating device 62 is collimated by the collimator lens 64 and then focused on 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 horizontally moved 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, the modified layer is formed along the street (division 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 movably supported in the optical axis direction, and is driven by this actuator 68 to make a minute movement in the optical axis direction. The position of the focal point P of the laser light is displaced in the Z direction by driving the actuator 68 and slightly moving the condenser lens 66 in the optical axis direction. Thereby, the position (the 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 making the laser light enter the control device a plurality of times.

Here, the surface of the wafer table 20 on which the laser light is incident is preferably a mirror surface. The laser light is more likely to enter the wafer table 20 when the mirror surface is used. On the other hand, the surface of the wafer table 20 on the side that contacts the film is preferably not a mirror surface, as compared with the surface on the side on which the laser light is incident. This is because when it is a mirror surface, the surface area for the liquid becomes small and the wettability becomes poor. That is, if the surface portion of the wafer table 20 has roughness, the surface area of the wafer table surface increases, and the liquid spreads evenly on the wafer table 20. One of the methods of roughening the wafer table 20 is a texturing (by facing) method. As shown in FIG. 4, a small groove 23 is formed in the glass wafer table 20 in a concentric or spiral shape. The refracting liquid spreads uniformly along the groove 23. The groove 23 for texturing may have a groove width of about 0.2 mm and a pitch of about 0.4 mm, and a groove width of 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 groove may be formed on the entire surface of the wafer table 20 corresponding to the diameter of the wafer.

In addition to texturing, there is a method of simply roughening the surface. For example, #2000 of GC abrasive grains may be used and the surface may be lapped for about 20 minutes. Alternatively, #500 abrasive grains may be used. Other than GC, the surface may be roughened by using abrasive grains such as WA. By doing so, the surface becomes frosted glass, and in the air, it is scattered due to the roughness of the surface and becomes cloudy. The surface roughness may be Ra of 0.1 mm or less, but it is not limited to this, and it is better that the liquid is buried in the gaps of the roughness so that the interfacial tension increases and the surface area is large.

Although quartz glass is used as the material of the wafer table 20, a silicon wafer or the like may be used instead. Quartz glass or the like has an absorption band in the infrared light 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 it has a good transmittance at the wavelength selected by the laser light and can make the flat surface a mirror surface. Further, it is necessary that the wafer table 20 has a uniform thickness and hardly bends. Further, in the case of bending independently, it is necessary to eliminate the bending as much as possible by using an outer peripheral fixed end such as attaching a rim to the outer peripheral portion.

The laser dicing device 10 of this embodiment is configured as described above. The operation of the laser dicing device 10 is controlled by a control device (not shown). The control device executes a predetermined control program to control the operation of each unit and execute the processing of the wafer W.
<Action>
Next, a dicing method using the laser dicing device 10 will be described. As described above, the wafer W is processed while being mounted on the dicing frame F. The back surface (surface on which no device is formed) of the wafer W is attached to the transparent film T and mounted on the dicing frame F. 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 conveyed to the lower position of the wafer table 20 with the surface on which the transparent film T is attached facing upward and the surface not contacting.

The wafer W transferred to the lower position of the wafer table 20 is transferred to the wafer table 20 from the transfer position. The delivery is performed by holding the back surface of the wafer W in close contact with the holding surface 22A of the wafer table 20. Specifically, it is performed as follows.

First, the wafer W is positioned. That is, the wafer W is positioned so as to coincide with the center thereof. After that, the contact liquid 26 is dropped or a contact liquid supply means (not shown) is used to uniformly supply the contact liquid 26 to the back surface of the wafer W. The wafer W may be positioned after the contact liquid 26 is supplied. Further, the contact liquid 26 may be supplied to the holding surface 22A of the wafer table 20 instead of the back surface of the wafer W or together with the back surface of the wafer W. Then, 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 contact liquid 26 spreads uniformly between the back surface of the wafer W and the holding surface 22A of the wafer table 20 in the form of a thin film, and the wafer W is held in close contact with the wafer table 20.

In this manner, the holding surface 22A 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. As a result, the wafer W can be held in a flat state without being bent. Further, since the back surface of the wafer W is closely held 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. After that, a predetermined alignment process is performed and dicing is started. The dicing is performed by making laser light emitted from the laser irradiation device 60 incident on the wafer W along the streets. A control device (not shown) drives the actuator 68 and adjusts the position of the condenser lens 66 so that the focus 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 closely held on 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 be able to transmit the laser light, even when the laser light is incident on the upper surface, the wafer table 20 can be incident on the wafer W. Further, the surface (back surface) of the wafer W on which the transparent film T is adhered is held in close contact with the wafer table 20, but since the transparent film T is also formed so as to be able to transmit laser light, it is incident on the wafer W. be able to. As will be described later, the contact liquid 26 that can transmit the laser beam is also used.

As described above, 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 also 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 being bent, so that the laser light 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 waviness of the transparent film T, and the interface of the wafer W is sandwiched by the hard work table surface. The part becomes a flat surface, and the incidence efficiency of laser light is further improved.

Further, by making the thickness of the wafer table 20 constant, the surface of the wafer W can be traced with the wafer table 20 as a reference. That is, even if the initial wafer W is a wafer W having a warp or a thickness unevenness, the surface of the wafer W on the laser incident side is attracted by a plane, and as a result, the wafer table 20 surface and the laser By accurately making the position constant, the work distance from the laser position to the laser condensing part inside the wafer W can be kept constant.

Then, 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 through the wafer table 20 and the transparent film T is almost the same. It will be constant. As a result, the modified layer can be stably formed at a constant depth position regardless of the weight of the wafer W.

Conventionally, when the surface of the wafer W is flattened on the side opposite to the laser irradiation side, undulations are left on the surface of the wafer W on the laser irradiation side due to variations in the thickness of the wafer W, and the wafer W surface is changed to a constant depth. In order to form a quality layer, the laser position was adjusted by autofocus along the undulation, but by using the laser irradiation side as the reference surface, a constant depth position was obtained without autofocus. It is possible to form the modified layer L on the. Thereby, the modified layer L can be accurately formed along the street.

Further, since the wafer W is held on the wafer table 20 without touching the surface, the wafer W can be processed without destroying the device (MEMS element or the like) formed on the surface. Further, when the surface of the wafer W is held in close contact, the holding surface 22A is burned by the laser beam transmitted through the wafer W or a melt is attached, so that 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. As a result, even if the wafer W is continuously processed, the wafer W can be always held flat and in close contact.

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 light is incident on the wafer W along the streets 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 band, the expand process.
<Contact liquid>
Next, the contact 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 in a state where the surface (rear surface) to which the transparent film T is attached has the contact liquid 26 interposed therebetween, and the laser Light is incident from the back surface side of the wafer W via the contact liquid 26. Therefore, the liquid used as the contact liquid 26 may be any liquid that can transmit at least laser light, and for example, water, ethanol, isopropyl alcohol (IPA) or the like can be used. Among these liquids, ethanol and IPA have lower surface tension than water and have high wettability with respect to the wafer table 20 and the transparent film T. Therefore, these liquids (that is, ethanol and IPA) form a uniform and thin film between the surface (rear surface) of the wafer W to which the transparent film T is attached and the holding surface 22A of the wafer table 20. It is easy to spread as a whole, and it becomes possible to hold the wafer W in close contact with the wafer W in a state of higher adhesion.

Particularly in this embodiment, a mode in which IPA is used as the contact liquid 26 is suitable. IPA has higher volatility than other liquids, and can prevent the occurrence of watermarks on the wafer W. Further, it is also possible to prevent organic substances from contaminating the wafer table 20 and its peripheral portion. In addition, it is also preferable to use a mixture of IPA and another liquid (for example, a mixture of IPA and water or ethanol) instead of IPA.

Further, in the present embodiment, a mode in which a liquid having a predetermined refractive index is used as the contact liquid 26 other than the above liquids is also suitable. Specifically, a liquid having a refractive index similar to that of the transparent film T is used as the contact liquid 26. As a result, the difference in refractive index at the interface with the contact liquid 26 can be eliminated, and the transmittance of laser light can be improved. For example, when the transparent film T is a polyolefin-based polyethylene film (refractive index: about 1.54), dichlorotoluene (refractive index: about 1.546) can be preferably used as the contact liquid 26. The liquid having a predetermined refractive index as described above is generally referred to as a contact liquid or a refraction liquid. For example, a refractive index standard liquid manufactured by Kyoto Electronics Manufacturing Co., Ltd., a contact liquid (refraction liquid) manufactured by Shimadzu Corporation, or Moritex. Cargill standard refraction liquid etc. can be used.

Further, when a liquid for compensating the refractive index is dropped on the glass surface, the transparent film T and the glass surface are ringed, and the refractive liquid spreads evenly over the glass surface, so that a uniform refractive index distribution is obtained within the wafer W surface. Obtainable. Further, a rim may be attached to the outer peripheral portion of the wafer table 20 so that the refracting liquid is interposed between the surface of the wafer table 20 and the objective lens. The refraction 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 refraction liquid, the numerical aperture of the objective lens can be further increased. Therefore, it becomes possible to focus light efficiently inside the wafer W.

Further, in the present embodiment, as described above, the table plate 22 of the wafer table 20 is made of transparent quartz glass, but the present invention is not limited to this, 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. According to the aspect in which the wafer W and the table plate 22 are made of the same material as described above, the transmittance of the laser light can be further improved by making the refractive index of the material and the refractive index of the contact liquid 26 similar. Is possible.

In addition, 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 held surface of the transparent film T adhered to the wafer W (the surface opposite to the wafer W) is It may be roughened. Thus, 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 the roughening treatment, a minute space is formed between them, and a capillary phenomenon occurs. The contact liquid 26 spreads efficiently without a gap. As a result, the contact area between the roughened surface and the contact liquid 26 increases, 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 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 that the laser beam can be transmitted is such that the back surface side of the wafer W has the contact liquid 26 interposed therebetween. Closely held. As a result, the wafer W is held in a flat state without bending. Then, by irradiating the laser beam from the back surface side of the wafer W through the wafer table 20, it becomes possible to accurately form the modified layer inside the wafer W. 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, and Alternatively, the wafer W may be placed on the upper surface of the wafer 20 and closely held. In this case, as shown in the figure, the laser irradiation device 60 is installed below the wafer table 20, and is configured to emit laser light from below to above. Even if the wafer W has a large diameter, the holding surface 22</b>A 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 to closely hold the wafer W. Therefore, the wafer W can be securely brought into close contact with the holding surface 22A, and the wafer W can be held flat.

The wafer W that has been subjected to the dicing process by the laser dicing apparatus 10 is then subjected to external stress and divided into chips. This process is performed by, for example, an expanding device. FIG. 6 is a process diagram showing the outline of the expanding process by the expanding device. The laser-diced wafer W is placed on the peeling table 110 with the surface thereof facing upward, as shown in FIG. Further, 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 peripheral portion of the peeling table 110 is illustrated as shown in FIG. Not lifted and lifted by the lifting mechanism. As a result, the transparent film T attached to the back side of the wafer W is radially expanded. Then, as the transparent film 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 streets, the wafer W is divided along the streets. Since the street is set between individual chips, the wafer W is divided into individual chips. In this way, the laser-diced wafer W is divided into individual chips by applying external stress. If an expanding tape (not shown) is attached on the transparent film T and the expanding tape is radially expanded, the chips can be divided more efficiently and stably.

Here, in order to verify the effect of the present invention, the result of an evaluation experiment on the adhesion of the wafer W will be described. In this evaluation experiment, an evaluation device having the configuration shown in FIG. 5, that is, a 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 is made of quartz glass, and the transparent film T attached to the wafer W is a polyolefin transparent film. Further, IPA was used as the contact liquid 26.

First, when the surface (rear surface) of the 12-inch wafer W to which the transparent film T was attached was placed on the holding surface 22A of the wafer table 20 without any intervention, the warp of the wafer W was measured, A warp of about 0.07 mm occurred. Next, a case was evaluated in which the wafer W having the above-described warpage was held in close contact with the holding surface 22A of the wafer table 20 with the contact liquid 26 interposed. Specifically, a dozen drops of IPA were evenly dropped onto the holding surface 22A of the wafer table 20 with a dropper. The amount dropped at that time is about 30 mg. Then, 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 IPA on the interface was sufficiently absorbed at the time of pressing, a peeling force of about 2N was required for each chip. Further, the wafer W completely adhered to the holding surface 22A of the wafer table 20, and the warp of the wafer W was almost eliminated, which was 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 held in close contact with the holding surface 22A of the wafer table 20 without bending. However, when IPA was used, the generation of watermarks could be suppressed more than when water or ethanol was used.

From the above results, it is possible to reliably bring the wafer W into close contact with the holding surface 22A of the wafer table 20 by interposing the contact liquid 26, and the contact liquid 26 is preferably IPA. In the above embodiment, the wafer W mounted on the dicing frame F is closely held by 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 is also possible to hold and perform laser dicing. Alternatively, the dicing frame F may not be mounted, and only the tape (dicing tape) capable of transmitting the laser light may be attached to the back surface to perform the laser dicing.

The present invention can be variously modified without departing from the spirit of the present invention, and it goes without saying that the present invention extends to the modified ones.

Without destroying the devices formed on the surface of the wafer, the wafer is irradiated with laser light to form a modified layer at a certain depth position inside the wafer, and scattering in the intermediate path of the laser is reduced. It can be widely applied to wafer dicing using laser light, which is essential to eliminate laser burning, prevent deterioration of each component and performance deterioration due to laser burning, and stably divide the wafer after laser irradiation into chips. Is.

10 Laser dicing device 20 Wafer table 22 Table plate 22A Holding surface 23 Groove 24 Table plate holding frame 26 Contact liquid 50 Laser antireflection plate 60 Laser irradiation device 62 Laser oscillator 64 Collimator lens 66 Condenser lens 68 Actuator 110 Stripping table 112 Ring W Wafer T Transparent film F Dicing frame

Claims (3)

In a laser dicing apparatus that irradiates a laser beam on a wafer to form a modified layer inside the wafer,
A film adhered to the back surface of the wafer,
Substantially flat adsorb hold back surface of the wafer through the film, and the wafer holding means capable of removing the waviness of the film,
Laser irradiation means for irradiating the wafer with laser light through the film and the wafer holding means, and a laser irradiation means for forming a modified layer inside the wafer,
A laser dicing device comprising: The laser dicing apparatus according to claim 1, wherein the film is attached inside a dicing frame. The laser dicing apparatus according to claim 1, wherein the film has an expandability capable of being expanded to divide the wafer into chips.