JP6029347B2 - Wafer processing method - Google Patents

Description

  The present invention relates to a wafer processing method, and more particularly to a wafer processing method for forming a chip having an adhesive sheet attached to the back surface.

  In a semiconductor device manufacturing process, a semiconductor device is formed by dividing a semiconductor wafer on which a plurality of semiconductor devices such as ICs and LSIs are formed into individual chips.

  The divided semiconductor devices are die-bonded to a metal substrate (lead frame), a tape substrate, or the like, and individual semiconductor chips are manufactured by dividing the metal substrate or the tape substrate. The semiconductor chip thus manufactured is widely used in various electric devices such as mobile phones and personal computers.

  In order to die-bond a semiconductor device on a substrate, an adhesive such as solder, Au-Si eutectic, resin paste or the like is supplied to the semiconductor device mounting position on the substrate, and the semiconductor device is mounted thereon and bonded. The method is used.

  In recent years, as disclosed in, for example, Japanese Patent Application Laid-Open No. 2000-182959, a method of adhering an adhesive sheet called DAF (die attach film) to the back surface of a semiconductor wafer in advance has been widely adopted.

  That is, the semiconductor wafer with the adhesive sheet attached to the back surface is formed by dividing the semiconductor wafer to which the DAF is bonded into individual chips. Thereafter, die bonding is performed on the substrate via the DAF on the back surface of the semiconductor chip, thereby minimizing the adhesive used and minimizing the mounting area of the semiconductor chip.

  In recent years, electric devices such as mobile phones and personal computers are required to be lighter and smaller, and thinner devices are required. As a technique for dividing a wafer into thinner devices, a dividing technique called a so-called first dicing method has been developed and put into practical use (for example, see Japanese Patent Application Laid-Open No. 11-40520).

  In this tip dicing method, a divided groove having a predetermined depth (a depth corresponding to the finished thickness of the device) is formed along the line to be divided from the surface of the semiconductor wafer, and then the semiconductor wafer in which the divided grooves are formed on the surface. This is a technique of grinding the back surface of the substrate and exposing a dividing groove on the back surface to divide the device chip into individual device chips. The thickness of the device chip can be reduced to 50 μm or less.

JP 2000-182959 A JP 11-40520 A JP 2005-223283 A

  However, when a DAF (adhesive sheet) is attached to a wafer once divided into device chips by the previous dicing method, so-called die shift occurs in which the device chips move. When die shift occurs, a line to be irradiated with a laser beam formed at an interval between adjacent device chips is not straight but bent, and sometimes there is no gap between device chips.

  If the line to be irradiated with the laser beam is bent, it is necessary to irradiate the laser beam following the bending, and it becomes very difficult to control the laser beam irradiation, and if there is no gap between the device chips, the laser There arises a problem that the beam cannot be irradiated.

  On the other hand, Japanese Patent Application Laid-Open No. 2005-223283 discloses a technique in which an adhesive sheet is not broken by a laser beam but is torn off by a dividing device. However, in this method, for example, when the chip size is as small as 1 mm square or less, there is a possibility that a region where the adhesive sheet is not broken is generated.

  In recent years, further reduction of the line to be divided (street reduction) has been desired in order to improve the number of chips taken per wafer, and the thickness of the cutting blade used in the tip dicing method is made thinner. There is a desire to reduce the removal area. However, when cutting with a thinner cutting blade, there are problems that meandering may occur and the processing speed cannot be increased.

  The present invention has been made in view of these points, and an object of the present invention is to provide a wafer processing method that solves the above-described problems.

According to the present invention, there is provided a method for processing a wafer having a plurality of intersecting scheduled lines, wherein a condensing point of a laser beam having a wavelength transparent to the wafer is positioned inside the wafer and the laser beam is divided. Irradiation along the planned line to form a modified layer along the planned division line inside the wafer, and the surface of the wafer is protected before or after the modified layer forming step is performed. After performing the protective member disposing step for disposing the member, the reforming layer forming step, and the protective member disposing step, the back surface of the wafer is pressed by a grinding means including a grinding wheel to grind the wafer. A grinding step for dividing the wafer into individual chips using the modified layer as a starting point for dividing the modified layer, and after performing the grinding step, on the back surface of the wafer An adhesive sheet that is cured by irradiation with external lines is attached, the back surface of the wafer is covered with the adhesive sheet, and an adhesive sheet is attached on the adhesive sheet, and the protective member disposed on the surface of the wafer is removed from the wafer. After performing the sheet sticking step to be removed and the sheet sticking step, the ultraviolet ray irradiation lamp made of LED is used to irradiate the surface of the wafer with ultraviolet rays to prevent the adhesive sheet from being deteriorated by heating. An ultraviolet irradiation step for breaking the adhesive sheet along the chip by curing and shrinking the adhesive sheet between the chips, and after performing the ultraviolet irradiation step, each of the adhesive sheets adhered to the back surface A wafer processing method comprising: a pickup step for picking up a chip from the adhesive sheet.

  Preferably, the wafer processing method further includes an expansion step of expanding an adhesive sheet to expand an interval between adjacent chips before performing the ultraviolet irradiation step.

  Preferably, the protective member is composed of an expandable adhesive sheet, and the wafer processing method is such that after the grinding step is performed, the protective member is expanded and the interval between adjacent chips is performed before the sheet adhering step is performed. The method further includes an expansion step of expanding

  According to the processing method of the present invention, since the wafer is divided into individual device chips starting from the modified layer formed on the wafer, the removal region between the chips can be substantially eliminated, and street reduction is possible.

  In addition, since the wafer is thinned by grinding and the wafer is divided into individual device chips by pressing during grinding, it is not necessary to perform a separate division step, and the process can be simplified.

  Since an adhesive sheet that cures when exposed to ultraviolet rays is used, an area where the adhesive sheet is not broken because the adhesive sheet breaks along the chip when the adhesive sheet between the chips is cured and shrinks when irradiated from the surface of the wafer. Can reduce the risk of occurrence.

It is a perspective view which shows a mode that a surface protection tape is stuck on the surface of a semiconductor wafer. It is sectional drawing of the semiconductor wafer of the state by which the surface protection tape was stuck on the surface. It is a block diagram of a laser beam irradiation unit. It is sectional drawing which shows the modified layer formation step in the processing method of the wafer of 1st Embodiment. It is a perspective view which shows a grinding step. It is sectional drawing of the wafer after implementation of a grinding step. It is sectional drawing explaining a sheet sticking step. It is sectional drawing which shows an ultraviolet irradiation step. It is sectional drawing which shows a pick-up step. It is a longitudinal cross-sectional view which shows the expansion step in the processing method of the wafer of 2nd Embodiment. It is sectional drawing which shows the ultraviolet irradiation step of 2nd Embodiment. It is sectional drawing which shows the pick-up step of 2nd Embodiment. It is sectional drawing which shows the surface protection tape sticking step of 3rd Embodiment. It is sectional drawing which shows the modified layer formation step of 3rd Embodiment. It is sectional drawing which shows the grinding step of 3rd Embodiment. It is sectional drawing which shows the expansion step of 3rd Embodiment. It is sectional drawing which shows the sheet | seat sticking step of 3rd Embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Referring to FIG. 1, a front side perspective view of a semiconductor wafer 11 to be processed by the processing method of the present invention is shown. A semiconductor wafer (hereinafter sometimes abbreviated as a wafer) 11 is made of, for example, a silicon wafer having a thickness of 700 μm, and a plurality of division lines (streets) 13 are formed in a lattice shape on the surface 11a. A device 15 such as an IC or an LSI is formed in each region partitioned by the plurality of division lines 13.

  The wafer 11 configured as described above includes a device region 17 in which the device 15 is formed and an outer peripheral surplus region 19 surrounding the device region 17 on the surface 11a. A notch 21 is formed on the outer periphery of the wafer 11 as a mark indicating the crystal orientation of the silicon wafer.

  In the wafer processing method of the present invention, in order to protect the device 15 formed on the surface 11a of the semiconductor wafer 11, a surface protection tape 23 is attached to the surface 11a of the wafer 11 as shown in FIG. Instead of the surface protective tape 23, a protective member made of glass or silicon wafer or the like may be disposed on the surface 11a of the wafer 11.

  The surface protection member disposing step may be performed before the back surface 11b of the wafer 11 is ground, and the surface protection tape 23 is applied to the surface 11a of the wafer 11 after performing a modified layer forming step described later. You may make it stick. FIG. 2 shows a cross-sectional view of the wafer 11 in a state where the surface protection tape 23 is adhered to the surface 11 a of the wafer 11.

  In the wafer processing method of the first embodiment of the present invention, first, a laser beam having a wavelength that is transmissive to the wafer 11 is irradiated along the planned dividing line 13 by a laser processing apparatus, and is scheduled to be divided inside the wafer 11. A modified layer forming step for forming a modified layer along the line 13 is performed.

  Referring to FIG. 3, a block diagram of the laser beam irradiation unit 12 of the laser processing apparatus is shown. The laser beam irradiation unit 12 includes a laser beam generation unit 14 and a condenser 16 serving as a processing head.

  The laser beam generation unit 14 includes a laser oscillator 18 that oscillates a YAG laser or a YVO4 laser, a repetition frequency setting unit 20, a pulse width adjustment unit 22, and a power adjustment unit 24.

  The pulse laser beam adjusted to a predetermined power by the power adjusting means 24 of the laser beam generating unit 14 is reflected by the mirror 26 of the condenser 16 and further condensed by the condenser objective lens 28 to be chucked by the laser processing apparatus. The semiconductor wafer 11 held on the table 30 is irradiated. In the modified layer forming step of the present embodiment, preferably, as shown in FIG. 4, a pulse laser beam is irradiated from the back surface 11 b side of the wafer 11.

  Before performing this modified layer forming step, an alignment step for aligning the light collector 16 and the planned dividing line 13 of the wafer 11 is performed. In this specification, the alignment step is a well-known step. The description is omitted.

  In FIG. 4, the chuck table 30 that holds the wafer 11 is omitted. In the modified layer forming step, the chuck table 30 is processed and fed by irradiating the interior of the wafer 11 with a pulsed laser beam having a wavelength that is transmissive to the wafer 11 from the condenser 16 with the focal point P aligned. As a result, the modified layer 25 along the division line 13 is formed inside the wafer 11.

  In the present embodiment, the modified layer 25 is formed on the back surface 11b side of the wafer 11 from the ground finish thickness t1. When the modified layer forming step is performed, cracks often occur from the modified layer 25 to the surface 11a side of the wafer 11.

  While indexing and feeding the chuck table 30, the modified layer 25 is formed one after another along the planned division line 13 extending in the first direction. Next, after the chuck table 30 is rotated by 90 degrees, a similar modified layer 25 is also formed along the planned division line 13 extending in the second direction orthogonal to the first direction. The modified layer 25 is formed as a melt rehardened layer. The modified layer 25 is a region where the density, refractive index, mechanical strength, and other physical characteristics are different from the surroundings.

  The processing conditions in this modified layer forming step are set as follows, for example.

Light source: LD excitation Q switch Nd: YVO 4 pulse laser Wavelength: 1064 nm
Repetition frequency: 100 kHz
Pulse output: 10μJ
Processing feed rate: 100 mm / sec

  After performing the modified layer forming step and the protective member disposing step of disposing a protective member on the front surface 11a of the wafer 11, a grinding step of grinding the back surface 11b of the wafer 11 is performed. In this grinding step, as shown in FIG. 5, the surface protection tape 23 attached to the front surface 11a of the wafer 11 is sucked and held by the chuck table 32 of the grinding device, and the back surface 11b of the wafer 11 is exposed.

  In FIG. 5, the grinding unit 34 includes a spindle 36 that is rotationally driven, a wheel mount 38 that is fixed to the tip of the spindle 36, and a grinding wheel 40 that is detachably attached to the wheel mount 38 with a plurality of screws 42. Contains. The grinding wheel 40 is configured by a plurality of grinding wheels 46 fixed to a free end of an annular base 44.

  In this grinding step, while rotating the chuck table 32 in the direction of arrow a at 300 rpm, for example, the grinding wheel 40 is rotated in the same direction as the chuck table 32, that is, in the direction of arrow b at 6000 rpm, for example. Is operated so that the grinding wheel 46 is pressed against the back surface 11 b of the wafer 11.

  Then, the cutting wheel 40 is ground and fed by a predetermined amount at a predetermined grinding feed speed, and the back surface 11b of the wafer 11 is ground to finish the wafer 11 to a finished thickness t1. At the time of this grinding, a predetermined pressing force is applied to the wafer 11 by grinding feed. Therefore, the wafer 11 is divided into a modified layer 25 formed inside and a crack extending from the modified layer 25 to the surface side of the wafer 11. As shown in FIG. 6, it is divided into individual device chips 27.

  After carrying out the grinding step, an adhesive sheet called DAF (die attach film) is stuck on the back surface 11b of the wafer 11, and further a sheet sticking step for sticking an adhesive sheet thereon is carried out.

  That is, as shown in FIG. 7, a DAF 29 that is cured by irradiation of ultraviolet rays is attached to the back surface 11b of the wafer 11, and an adhesive sheet T is further attached thereon. Then, the outer peripheral portion of the pressure-sensitive adhesive sheet T is attached to the annular frame F.

  The pressure-sensitive adhesive sheet T is preferably a pressure-sensitive adhesive sheet having an adhesive layer that is not cured by irradiation with ultraviolet rays, and is preferably a pressure-sensitive adhesive sheet having expandability. Furthermore, in this sheet sticking step, the surface protection tape 23 is peeled from the surface 11 a of the wafer 11.

  After performing the sheet sticking step, as shown in FIG. 8, the ultraviolet ray 48 is irradiated to the surface 11 a of the wafer 11, and the ultraviolet ray is guided to the DAF 29 through the crack 31 between the adjacent device chips 27. DAF 29 is cured. When the DAF 29 is thus cured by irradiation with ultraviolet rays, the DAF 29 is broken along the device chip 27.

  After performing the ultraviolet irradiation step, as shown in FIG. 9, the pickup step of picking up the device chip 27 with the DAF 29 attached to the back surface from the adhesive sheet T by the pickup collet 50 is performed.

  According to the wafer processing method of the present embodiment, since the wafer 11 is divided into the individual device chips 27 using the modified layer 25 formed on the wafer by the pressing force during grinding as the division starting point, it is necessary to perform a separate division step. Therefore, the process can be simplified. Furthermore, the removal area between chips can be almost eliminated, and street reduction is possible.

  Furthermore, since DAF which is cured by ultraviolet irradiation is used as the DAF 29, by irradiating ultraviolet rays from the surface 11a side of the wafer 11, the DAF 29 between the chips 27 is cured and contracted so that the DAF is along the chips 27. Since it breaks, the possibility that a region where the DAF 29 is not broken can be reduced.

  Next, a wafer processing method according to the second embodiment of the present invention will be described. In the wafer processing method of the second embodiment, the protective member disposing step described with reference to FIGS. 1 and 2, the modified layer forming step described with reference to FIGS. 3 and 4, and FIGS. The grinding step described with reference to 6 and the sheet sticking step described with reference to FIG. 7 are the same as those in the first embodiment described above.

  In the present embodiment, an expansion step for expanding the adhesive sheet T in the radial direction is performed before the ultraviolet irradiation step. In this expansion step, for example, an expanding device 52 as shown in FIG. 10 is used.

  The expanding device 52 includes a frame holding unit 54 that holds the annular frame F and an expansion drum 60 that extends the adhesive sheet T attached to the annular frame F held by the frame holding unit 54.

  The frame holding unit 54 includes an annular frame holding member 56 and a plurality of clamps 58 as fixing means disposed on the outer periphery of the frame holding member 56. An upper surface of the frame holding member 56 forms a mounting surface 56a on which the annular frame F is mounted, and the annular frame F is mounted on the mounting surface 56a.

  The annular frame F placed on the placement surface 56 a is fixed to the frame holding member 56 by a clamp 58. The frame holding unit 54 configured as described above is moved in the vertical direction by the drive unit 62. The drive unit 62 includes a plurality of air cylinders 64, and the piston rod 66 of the air cylinder 64 is connected to the lower surface of the frame holding member 56.

  The drive unit 62 composed of a plurality of air cylinders 64 is configured so that the annular frame holding member 56 is positioned at a reference position where the mounting surface 56 a is substantially flush with the upper end of the expansion drum 60 and from the upper end of the expansion drum 60. Move up and down between the expansion positions below the fixed amount.

  In this expansion step, as shown in FIG. 10A, the annular frame F that supports the wafer 11 via the adhesive sheet T is placed on the placement surface 56 a of the frame holding member 56, and the frame is clamped by the clamp 58. The holding member 56 is fixed. At this time, the frame holding member 56 is positioned at a reference position where the placement surface 56 a is substantially the same height as the upper end of the expansion drum 60.

  Next, the air cylinder 64 is driven and the frame holding member 56 is moved downward by about 15 mm and lowered to the extended position shown in FIG. As a result, the annular frame F fixed on the mounting surface 56a of the frame holding member 56 is also lowered, so that the adhesive sheet T adhered to the annular frame F abuts on the upper end edge of the expansion drum 60 and mainly. Expanded radially.

  As a result, a radial tensile force acts on the wafer 11 and the DAF 29 adhered to the adhesive sheet T, the distance between the device chips 27 is expanded, and the DAF (die attach film) 29 is stretched. In the present embodiment, it is possible to prevent the DAF 29 from being broken by the expansion by performing the expansion step at room temperature (about 5 to 35 ° C.).

  After performing the expansion step, as shown in FIG. 11, an ultraviolet irradiation step of irradiating the surface 11a of the wafer 11 with ultraviolet rays from the ultraviolet lamp 48 is performed. The ultraviolet irradiation lamp 48 is preferably composed of an LED. Since the LED generates little heat, the DAF 29 can be prevented from being altered by heating.

  When this ultraviolet irradiation step is performed, the space between the device chips 27 is widened, so ultraviolet light is irradiated to the ultraviolet curable DAF 29 through the widened space, and the irradiated portion 33 is cured and contracted, so that the DAF 29 becomes a device. It is broken along the tip 27.

  In this embodiment, since the ultraviolet irradiation step is performed after the expansion step is performed, the DAF 29 between the device chips 27 can be reliably cured and contracted, and can be broken along the device chip 27.

  After performing the ultraviolet irradiation step, as shown in FIG. 12, the pickup step of picking up the device chip 27 having the DAF 29 attached to the back surface from the adhesive sheet T by the pickup collet 50 is performed.

  Next, a wafer processing method according to a third embodiment of the present invention will be described with reference to FIGS. In the present embodiment, first, as shown in FIG. 13, a protective member disposing step is performed in which the surface protective tape 23 is attached to the surface 11 a of the wafer 11 and the outer peripheral portion of the surface protective tape 23 is attached to the annular frame F. To do. The surface protective tape 23 of this embodiment needs to be a surface protective tape having expandability.

  Next, similarly to the modified layer forming step of the first embodiment described with reference to FIGS. 3 and 4, as shown in FIG. 14, the modified layer 25 along the scheduled division line 13 is formed inside the wafer 11. Form. Similar to the first embodiment, the modified layer 25 is formed on the back surface 11b side of the wafer 11 from the ground finish thickness t1.

  After the modified layer forming step, the back surface 11b of the wafer 11 is ground by the grinding wheel 40 in the same manner as the grinding step of the first embodiment described with reference to FIG. 11 is thinned to a ground finish thickness t1, and the wafer 11 is divided into individual device chips 27 using the modified layer 25 as a division starting point by a pressing force during grinding.

  After performing the grinding step, an expanding step for expanding the surface protection tape 23 in the direction of arrow A is performed as shown in FIG. 16 using an expanding device 52 as shown in FIG. When this expansion step is performed, the surface protection tape 23 is expanded in the radial direction, so that the distance between the device chips 27 is expanded.

  After carrying out the expansion step, as shown in FIG. 17, DAF 29 that is cured by irradiation of ultraviolet rays is adhered to the back surface 11b of the wafer 11, and the adhesive sheet T is further adhered to the DAF 29, and the outer peripheral portion of the adhesive sheet T is annularly formed. Adhere to frame F. Then, the surface protection tape 23 is peeled off from the surface 11a of the wafer 11 and the annular frame F to obtain a state as shown in FIG.

  After the sheet sticking step, the DAF 29 between the device chips 27 is cured by irradiating the surface 11a of the wafer 11 with ultraviolet rays from the ultraviolet lamp 48 in the same manner as the ultraviolet irradiation step of the second embodiment shown in FIG. An ultraviolet irradiation step of contracting and breaking along the device chip 27 is performed.

  After the ultraviolet irradiation step, the pickup step of picking up the device chip 27 with the DAF 29 attached to the back surface from the adhesive sheet T is performed in the same manner as the pickup step of the second embodiment shown in FIG.

DESCRIPTION OF SYMBOLS 11 Semiconductor wafer 11a Front surface 11b Back surface 12 Laser beam irradiation unit 13 Scheduled division line 14 Laser beam generation unit 15 Device 16 Condenser 23 Surface protection tape 25 Modified layer 27 Device chip 29 DAF (adhesive sheet)
34 grinding unit 40 grinding wheel 46 grinding wheel 48 ultraviolet lamp 50 pickup collet 52 expanding device

Claims (3)

A method for processing a wafer having a plurality of intersecting scheduled lines,
A condensing point of a laser beam having a wavelength that is transmissive to the wafer is positioned inside the wafer, and the laser beam is irradiated along the planned division line, so that a modified layer is formed along the planned division line inside the wafer. A modified layer forming step for forming
Before or after performing the modified layer forming step, a protective member disposing step of disposing a protective member on the surface of the wafer;
After performing the modified layer forming step and the protective member disposing step, the back surface of the wafer is pressed and ground by a grinding means including a grinding wheel to thin the wafer to a predetermined thickness and A grinding step for dividing the wafer into individual chips at the division starting point;
After carrying out the grinding step, an adhesive sheet that is cured by irradiation of ultraviolet rays is attached to the back surface of the wafer, the back surface of the wafer is covered with the adhesive sheet, and an adhesive sheet is attached to the adhesive sheet, and the surface of the wafer A sheet sticking step for removing the protective member disposed on the wafer from the wafer;
After carrying out the sheet adhering step, ultraviolet rays are irradiated from the surface of the wafer using an ultraviolet irradiation lamp made of LED, and the adhesive sheet between adjacent chips is cured while preventing deterioration of the adhesive sheet due to heating. An ultraviolet irradiation step for breaking the adhesive sheet along the chip by shrinking , and
After performing the ultraviolet irradiation step, a pickup step of picking up individual chips having an adhesive sheet attached to the back surface from the adhesive sheet;
A wafer processing method characterized by comprising:   The wafer processing method according to claim 1, further comprising an expanding step of expanding the pressure-sensitive adhesive sheet to expand a space between adjacent chips before performing the ultraviolet irradiation step. The protective member is composed of an expandable adhesive sheet,
2. The wafer according to claim 1, further comprising an expanding step of expanding the protective member to expand a distance between adjacent chips after performing the grinding step and before performing the sheet adhering step. Processing method.

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