JP6713214B2 - Device wafer processing method - Google Patents

Description

The present invention relates to a device wafer processing method.

In the step of processing a device wafer to produce a device chip or the like, the back surface side of the device wafer is ground in order to thin the device wafer having a device formed on the front surface. In the step of grinding the back surface of the device wafer, grinding debris generated from the device wafer by grinding is taken in and removed by the working liquid provided on the back surface during grinding.

Then, the device wafer is divided into individual device chips. To divide a device wafer, first, a modified layer serving as a starting point of division is formed in the device wafer along a dividing line by a laser processing device, and an external force is applied to the device wafer to cause cracks from the modified layer. It is carried out by stretching.

For the manufacturing process of the device chip and the like as described above, for example, as described in Patent Document 1, a process of simultaneously performing grinding of the back surface side of the device wafer and division into device chips is considered. ing. The modified layer is formed in advance, and then the back surface side of the device wafer is ground to thin the device wafer, and cracks are extended from the modified layer to divide the device wafer. In this way, the process can be simplified by simultaneously performing the division and the grinding.

Further, as described in Patent Document 2, instead of forming the modified layer by the laser processing apparatus, a cutting groove may be formed by the cutting apparatus to divide the device wafer. In this case, a cutting groove deeper than the thickness of the device chip at the time of completion is formed from the front surface side of the device wafer in advance, and then the device wafer is ground from the back surface side so as to remove the bottom portion of the cutting groove. Divide into device chips.

International Publication No. 03/077295 JP-A-11-40520

However, in such a process, since the grinding is performed even after the gap for separating the device chips is formed, the working liquid used in the grinding process enters the gap. Then, the machining liquid evaporates and dries between the time when the grinding is completed and the surface to be ground is cleaned, and grinding debris contained in the machining liquid adheres to the side surface of the device chip. .. Then, foreign matter such as grinding dust once fixed cannot be easily removed.

Particularly, when the device wafer is divided by grinding after forming the modified layer, the gap between the formed device chips is narrow. Therefore, the cleaning liquid cannot sufficiently enter the gap, and it becomes difficult to remove the foreign matter by cleaning. After that, the device chip is picked up and mounted on a printed circuit board or the like. At the stage of being picked up, a foreign substance is attached to the side surface of the device chip.

Then, when the foreign matter falls off when the device chip is mounted and the foreign matter settles on a printed circuit board or the like, the foreign matter may adversely affect the mounting of the device chip.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a device wafer processing method capable of suppressing mounting defects without fixing foreign matter to the side surface of a device chip.

According to one aspect of the present invention, there is provided a device wafer processing method having a surface on which a device is formed in each area defined by a plurality of intersecting dividing lines, wherein a protective member is provided on the surface of the device wafer. A protective member disposing step to be provided, and a modified layer forming step of forming a modified layer serving as a starting point of division along the division line of the device wafer before or after performing the protective member disposing step, After performing the protective member disposing step and the modified layer forming step, a grinding step of grinding the back surface of the device wafer to divide the device wafer into individual chips, and after performing the grinding step And a cleaning step of cleaning the device wafer, wherein in the modified layer forming step or the grinding step, a crack is extended from the modified layer serving as the division starting point, and in the grinding step, the device wafer is made hydrophilic. Grinding is performed while supplying the working fluid to the device wafer, and in the grinding step, before the grinding is performed while supplying the working fluid to make the device wafer hydrophilic, water contained in the working fluid is supplied. A method for processing a device wafer is provided, which comprises grinding while supplying a liquid containing water to the device wafer at a ratio higher than the ratio .

According to the device wafer processing method of one aspect of the present invention, a processing liquid that makes the device wafer hydrophilic is used in the grinding step. Then, grinding is performed while the processing liquid is supplied to the device wafer to make the device wafer (device chip) hydrophilic. Therefore, in the subsequent cleaning step, the cleaning liquid easily enters the gap between the device chips, and the foreign matter (grinding dust) that has entered the gap can be easily removed.

Therefore, according to one aspect of the present invention, there is provided a device wafer processing method capable of suppressing mounting defects without fixing foreign matter to the side surface of the device chip.

It is a perspective view which illustrates an example of a device wafer concerning one mode of the present invention, and a protection member disposition step typically. It is a fragmentary sectional view explaining a modification layer formation step typically. 3A is a partial cross-sectional view schematically showing an example of the grinding step, and FIG. 3B is a partial cross-sectional view schematically showing another example of the grinding step. It is a fragmentary sectional view explaining a washing step typically.

An embodiment according to the present invention will be described. At the bottom of FIG. 1, a perspective view illustrating an example of the workpiece is shown. The device wafer 1, which is the workpiece, is a substrate made of a material such as silicon, SiC (silicon carbide), or another semiconductor, or a material such as sapphire, glass, or quartz.

The surface 1a of the device wafer 1 is divided into a plurality of regions by dividing lines 3 arranged in a grid pattern, and a device 5 such as an IC is formed in each region. The workpiece 1 is finally divided along the dividing line 3 to form individual device chips.

Next, a method of processing the device wafer 1 according to this embodiment will be described. In the processing method, a protective member disposing step of disposing a protective member on the surface 1a of the device wafer 1 is performed. Before or after performing the protective member disposing step, a reforming layer forming step of forming a reforming layer serving as a starting point of division along the dividing line 3 of the device wafer 1 is performed.

After performing the protective member disposing step and the modified layer forming step, a back surface 1b of the device wafer 1 is ground to perform a grinding step of dividing the device wafer 1 into individual device chips. When the crack extends from the modified layer and the crack penetrates the device wafer in the thickness direction, the device wafer 1 is divided into individual device chips.

In addition, in the grinding step, grinding is performed while supplying a processing liquid that makes the device wafer hydrophilic to the device wafer. After the grinding step is performed, a cleaning step for cleaning the device wafer is performed to wash away the grinding debris attached to the back surface of the device chip and the gap between the device chips.

Hereinafter, each step of the method for processing a device wafer according to this embodiment will be described in detail.

First, the step of disposing the protective member will be described with reference to FIG. In the protective member disposing step, the protective member 7 for protecting the surface 1a of the device wafer 1 is disposed on the surface 1a. The protective member 7 protects the surface 1a side of the device wafer 1 from an impact applied during each step or transportation, and prevents the device 5 from being damaged.

As shown in FIG. 1, the protective member 7 is attached to the surface 1a in a state where the protective member 7 has a planar shape similar to that of the device wafer 1 in advance. However, the processing method according to the present embodiment is not limited to this, and for example, after the tape-shaped protective member 7 having a width wider than the diameter of the device wafer 1 is attached to the surface 1a of the device wafer 1, The protective member 7 may be cut into the same shape as the device wafer 1.

Next, the modified layer forming step will be described with reference to FIG. The modified layer forming step is performed before or after the protective member disposing step is performed. In the modified layer forming step, the modified layer 9 is formed by irradiating a laser beam from the back surface 1b side of the device wafer 1 and focusing the laser beam to a predetermined depth inside the device wafer 1.

The laser processing apparatus 2 used in the modified layer forming step includes a chuck table 4 that holds the device wafer 1 by suction, and a processing head 6 that oscillates a laser beam. The chuck table 4 has therein a suction path (not shown) connected to a suction source (not shown), and the other end of the suction path is connected to the holding surface 4 a on the chuck table 4.

The holding surface 4a is constituted by a porous member, and the negative pressure generated by the suction source is applied to the device wafer 1 placed on the holding surface 4a through the porous member to cause the chuck table 4 to move to the device wafer. 1 is suction-held.

The processing head 6 has a function of oscillating a laser beam to focus the laser beam at a predetermined depth inside the device wafer 1, and forms the modified layer 9 at the predetermined depth. A laser beam oscillated using Nd:YAG as a medium is used as the laser beam. The laser processing apparatus 2 moves the chuck table 4 in the processing feeding direction of the laser processing apparatus 2 (for example, the direction of the arrow in FIG. 2) by the processing feeding means (not shown) powered by a pulse motor or the like. The device wafer 1 is processed and fed with the chuck table 4 being fed in the processing feed direction.

In the modified layer forming step, first, the device wafer 1 is placed on the chuck table 4 of the laser processing apparatus 2 with the surface 1a of the device wafer 1 facing downward. Then, a negative pressure is applied from the chuck table 4 to hold the device wafer 1 on the chuck table 4 by suction.

Next, the processing head 6 of the laser processing apparatus 2 irradiates the back surface 1b of the device wafer 1 with a laser beam. A laser beam is focused on a predetermined depth of the device wafer 1 to form a modified layer (starting point of division) 9. The device wafer 1 is processed and fed by moving the chuck table 4 while irradiating the laser beam so that the modified layer 9 is formed along the planned dividing line 3.

After the reformed layer 9 is formed along one planned dividing line 3, the device wafer 1 is indexed and fed, and the reformed layers (starting points for dividing) 9 are successively formed along the adjacent planned dividing lines 3. To do. Further, the chuck table 4 is rotated to switch the direction in which the device wafer 1 is processed and fed, and the laser beam is irradiated to form the modified layer 9 along all the planned dividing lines 3.

In the modified layer forming step, the modified layer 9 can be formed on the device wafer 1 and cracks extending from the modified layer 9 in the direction of the surface 1a can be formed depending on the processing conditions. Then, the crack can be extended to the surface 1a. When a crack extending from the modified layer 9 toward the front surface 1a is formed, the crack also extends in the back surface 1b direction. Thus, in the modified layer forming step, the crack may be extended from the modified layer 9.

Next, the grinding step will be described with reference to FIG. The grinding step is performed after the protective member disposing step and the modified layer forming step are performed. In the grinding step, the back surface 1b side of the device wafer 1 is ground, the device wafer 1 is thinned to a predetermined thickness, and the device wafer 1 is divided into individual device chips.

FIG. 3A is a partial cross-sectional view schematically illustrating the cross section of the device wafer 1 in the grinding step. In this step, the grinding device 8 is used. The grinding device 8 includes a spindle 12 that constitutes a rotary shaft that is perpendicular to the grinding wheel 14, and a disk-shaped grinding wheel 14 that is mounted on one end side of the spindle 12 and that has a grinding wheel 16 on the lower side. A rotary drive source (not shown) such as a motor is connected to the other end of the spindle 12, and when the motor rotates the spindle 12, the grinding wheel 14 mounted on the spindle 12 also rotates.

The spindle 12 has a machining liquid supply path 18 whose one end is connected to a machining liquid supply source (not shown). The other end of the processing liquid supply path 18 is opened at the lower part of the grinding wheel and serves as a processing liquid supply port 18a for supplying the processing liquid to the back surface 1b of the device wafer 1.

Further, the grinding device 8 has a chuck table 20 which faces the grinding wheel 10 and holds an object to be ground. The holding surface 20a on the chuck table 20 is composed of a porous member connected to a suction source (not shown). The chuck table 20 is rotatable about an axis substantially perpendicular to the holding surface 20a.

First, the device wafer 1 is placed on the holding surface 20 a of the chuck table 20 with the front surface 1 a of the device wafer 1 facing downward. Then, a negative pressure by the suction source is applied through the porous member to hold the device wafer 1 on the chuck table 20.

During grinding, the chuck table 20 is rotated and the spindle 12 is rotated to rotate the grinding wheel 14. While the chuck table 20 and the grinding wheel 14 are rotating, when the grinding wheel 14 is lowered and the grinding wheel 16 hits the back surface 1b of the device wafer 1, grinding of the back surface 1b is started. Then, the grinding wheel 14 is further lowered so that the device wafer 1 has a predetermined thickness.

The grinding is performed while supplying the working liquid to the back surface 1b of the device wafer 1 from the working liquid supply port 18a. Grinding of the back surface 1b produces grinding chips, but since the machining liquid supplied to the back surface 1b is caused to flow while containing the grinding chips, the grinding chips are removed from the back surface 1b.

As the grinding progresses, a force generated by the grinding acts on the inside of the device wafer 1, and a crack extends from the modified layer 9 in the thickness direction of the device wafer 1. Then, a gap is formed along the dividing line 3 and the device wafer 1 is divided into individual device chips. However, the cracks and the gaps may be formed in the modified layer forming step described above. Further, when the cracks formed in the modified layer forming step are not sufficiently expanded, the cracks may be further expanded in the grinding step.

The machining liquid may not be supplied to the back surface 1b through the machining liquid supply passage 18 inside the spindle 12. For example, as shown in FIG. 3(B), the grinding device 8 may be provided with a machining liquid ejecting means (machining liquid ejecting nozzle) 18b above the chuck table 20 at a position apart from the spindle 12. Then, the processing liquid may be supplied to the back surface 1b of the device wafer 1 held on the chuck table 20 from the processing liquid discharger (processing liquid discharge nozzle) 18b.

In the processing method according to the present embodiment, when the device wafer 1 is thinned in the grinding step, it is divided into individual device chips. Therefore, it is not necessary to perform another step only for dividing the device chip, and the device chip manufacturing process is simplified.

On the other hand, when the gap is formed during grinding, the working liquid containing grinding dust enters the gap. After that, when the water content of the working liquid evaporates after the grinding step is completed, the grinding chips are fixed to the device chip in the gap, but the grinding chips thus fixed cannot be easily removed.

When the device chip is picked up, the grinding dust fixed in the gap moves together with the device chip while being fixed to the side surface. When the device chip is bonded to a printed circuit board or the like, if the grinding dust falls off from the side surface, there is a risk that it may enter between the device chip and the printed circuit board or the like to cause defective bonding. Therefore, it is necessary to remove the grinding dust in the gap.

In the cleaning step described later, a cleaning liquid is provided to the back surface 1b of the device wafer 1 (device chip) to clean the device wafer 1 from the back surface 1b side. However, the gap formed at the time of division is narrow, and even if an attempt is made to remove the grinding dust that has entered the gap, the cleaning liquid does not easily enter the gap.

Therefore, in the processing method according to the present embodiment, a processing liquid that makes the device wafer 1 hydrophilic is used as the processing liquid supplied to the back surface 1b of the device wafer 1 in the grinding step. When the device wafer 1 is made hydrophilic by the processing liquid, the cleaning liquid containing water as a main component easily enters the gap in the cleaning step described later. Therefore, the grinding dust present in the gap can be easily removed.

As the processing liquid for making the device wafer 1 (device chip) hydrophilic, for example, a liquid obtained by adding polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), or a surfactant to water is used. The volume concentration of PVA or the like in the working liquid is, for example, about 10% to 15%.

By the way, if only the working liquid that makes the device wafer 1 hydrophilic is used, the cost of the working liquid increases by the amount of PVA or the like consumed. Therefore, for example, the processing liquid for making hydrophilic may be provided from the time when a gap is formed in the device wafer 1.

More specifically, in the initial stage of grinding, for example, grinding is performed using a working liquid having a high water content ratio (for example, pure water) until the gap is formed, and then the device wafer 1 is made hydrophilic. Grinding may be performed by switching to a working liquid to be used. When a crack is formed in the modified layer forming step, the working fluid may be switched when the grinding wheel 16 reaches the crack. As described above, by suppressing the amount of the processing liquid used for making the device wafer 1 hydrophilic, the cost required for processing can be reduced.

Next, the cleaning step performed after the grinding step will be described with reference to FIG. FIG. 4 is a partial cross-sectional view schematically showing the device wafer (device chip) during the cleaning step. A cleaning liquid is supplied to the back surface 11b of the device chip 11 to remove grinding debris that has entered the gap 11c while cleaning the back surface 11b of the device chip 11.

As shown in FIG. 4, the cleaning device 22 includes a cleaning liquid supply unit (cleaning liquid supply nozzle) 24 and a chuck table 26 below the cleaning liquid supply unit 24. The cleaning liquid supply unit (cleaning liquid supply nozzle) 24 jets the cleaning liquid toward the object to be cleaned held on the chuck table 26. The cleaning liquid ejected from the cleaning liquid supply means 24 is a cleaning liquid such as pure water whose main component is water.

The chuck table 26 has a suction path (not shown) internally connected to a suction source (not shown), and the other end of the suction path is connected to a holding surface 26 a on the chuck table 26. The holding surface 26a is made of a porous member, and when the negative pressure generated by the suction source is applied to the device chip 11 placed on the holding surface 26a through the porous member, the chuck table 26 is moved to the device chip. Hold 11 by suction.

Further, the chuck table 26 is rotatable about an axis substantially perpendicular to the holding surface 26a, and is rotated during the cleaning step so that the cleaning liquid provided on the chuck table 26 is spun in the outer peripheral direction by a centrifugal force. ..

In the cleaning step, first, the surface 11a of the plurality of device chips 11 is directed downward while keeping the state in which the plurality of device chips 11 are integrated by the protective member 7, and the surface 11a of the chuck table 26 is placed on the holding surface 26a. Put on. The chuck table 26 sucks and holds the plurality of device chips 11 by using the negative pressure acting from the suction source.

Next, in a state where the chuck table 26 is rotated around an axis perpendicular to the holding surface 26a, the cleaning liquid is ejected from the cleaning liquid supply means 24 toward the back surface 11b side of the device chip 11 held by the holding surface 26a. Let Since the device chip 11 is made hydrophilic by the above-described grinding step, the cleaning liquid ejected to the back surface 11b side can easily enter the gap 11c.

When the cleaning liquid enters the gap 11c, the grinding dust remaining in the gap 11c is removed by the cleaning liquid. That is, since no grinding dust remains in the gap 11c, no grinding dust adheres to the side surface of the device chip 11 even when the device chip 11 is picked up. Further, even when the device chip 11 is bonded to the printed circuit board or the like, since grinding dust does not enter between the device chip 11 and the printed circuit board or the like, the occurrence of defective bonding is suppressed.

It should be noted that the present invention is not limited to the description of the above embodiment and can be implemented with various modifications. For example, in the above embodiment, the case where the modified layer is formed in the device wafer by the laser processing apparatus and divided into individual device chips in the grinding step has been described, but the present invention is not limited to this. For example, a cutting blade is cut from the surface 1a side of the device wafer 1 along the planned dividing line 3 to form a cutting groove deeper than the thickness of the completed device chip 11.

Then, even when the front surface 1a side of the device wafer 1 is protected by the protection member 7 and the back surface 1b side of the device wafer 1 is ground to remove the bottom of the cutting groove to divide into individual device chips, Depending on the width of the groove, it may be difficult to remove the grinding dust that has entered the cutting groove. Even in such a case, by using the processing liquid that makes the device wafer hydrophilic in the grinding step, the cleaning liquid can easily enter the cutting groove in the cleaning step to remove grinding debris and the like.

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

1 Device Wafer 1a Front Surface 1b Back Surface 3 Divided Line 5 Device 7 Protective Member 9 Modified Layer 11 Device Chip 11a Front Surface 11b Back Surface 11c Gap 2 Laser Processing Device 4 Chuck Table 4a Holding Surface 6 Processing Head 8 Grinding Machine 10 Grinding Wheel 12 Spindle 14 Grinding Wheel 16 Grinding Wheel 18 Machining Liquid Supply Path 18a Machining Liquid Supply Port 18b Machining Liquid Discharging Means 20 Chuck Table 20a Holding Surface 22 Cleaning Device 24 Cleaning Liquid Supplying Means 26 Chuck Table 26a Holding Surface

Claims (1)

A method of processing a device wafer having a surface on which a device is formed in each region partitioned by a plurality of planned dividing lines that intersect,
A protective member disposing step of disposing a protective member on the surface of the device wafer,
Before or after performing the protective member disposing step, a modified layer forming step of forming a modified layer as a starting point of division along the division line of the device wafer,
After performing the protective member disposing step and the modified layer forming step, a grinding step of grinding the back surface of the device wafer to divide the device wafer into individual chips,
A cleaning step of cleaning the device wafer after performing the grinding step,
In the modified layer forming step or the grinding step, a crack is extended from the modified layer serving as the division starting point,
In the grinding step, grinding is performed while supplying a processing liquid for making the device wafer hydrophilic to the device wafer ,
In the grinding step, before the grinding is performed while supplying the processing liquid that makes the device wafer hydrophilic, to the device wafer, a liquid containing water at a ratio higher than the ratio of water contained in the processing liquid is used. A method for processing a device wafer, which comprises performing grinding while supplying the same to the device wafer.