Method for processing wafer and wafer

The present invention relates to a wafer that is formed thin but is easy to handle, and a method for processing the wafer.

Wafers in which a plurality of devices such as ICs and LSIs are formed on the surface side are divided into individual devices by using a dicing device or the like, and are widely used by being incorporated into various electronic devices. Then, in order to reduce the size and weight of the electronic device, the back surface of the wafer before being divided into individual devices is ground and formed so that the thickness thereof is, for example, 100 μm to 50 μm (for example). See Patent Document 1).

<patcit num="1"><text>Japanese Unexamined Patent Publication No. 2004-319885</text></patcit>

<p> However, when the wafer becomes thin due to grinding, there is a problem that it becomes difficult to handle in the subsequent process because the rigidity is lost. For example, it becomes difficult to coat the back surface of the wafer after back surface grinding with a metal film made of gold, silver, titanium, or the like, and it becomes difficult to perform an electrical test of the device.</p><p> Therefore, an object to be solved by the present invention is to stably support a wafer thinned by grinding and to facilitate handling during subsequent processing.</p>

<p> The present invention is a method for processing a wafer having a device region on which a plurality of devices are formed and an outer peripheral surplus region surrounding the device region on the front surface, and corresponds to the device region on the back surface of the wafer. The present invention relates to a method for processing a wafer in which a recess is formed in a region and a ring-shaped reinforcing portion including an outer peripheral surplus region is formed on the outer peripheral side of the recess.</p><p> The ring-shaped reinforcing portion including the outer peripheral surplus region is formed by a back surface grinding step in which the front surface side of the wafer is held on the chuck table of the grinding device and the region corresponding to the device region on the back surface of the wafer is ground to form a recess. Although it is preferable, the recess can also be formed by dry etching, wet etching, CMP or the like.</p><p> When a recess is formed by grinding using a grinding device, the diameter of the outermost circumference of the rotating track of the grindstone portion includes the grinding portion including the rotating shaft and the wheel mounted on the rotating shaft and to which the grindstone portion is fixed. In the back surface grinding process, a chuck table that holds the wafer is used by using a grinding device that is larger than the radius of the device region and smaller than the diameter of the device region, and the diameter of the innermost circumference of the rotating track of the grindstone is smaller than the radius of the device region. It is desirable that the grindstone portion is always in contact with the rotation center of the back surface of the wafer while rotating, and is not in contact with the back surface of the outer peripheral excess region.</p><p> After forming the ring-shaped reinforcing portion on the wafer, a film forming step of forming a film on the back surface of the wafer on which the ring-shaped reinforcing portion is formed and a test step of performing a probe test of the device formed in the device region are performed. May be done.</p><p> Further, after the ring-shaped reinforcing portion is formed, or after the film forming step and the test step when the test step is performed, the surface of the wafer on which the ring-shaped reinforcing portion is formed is attached to the dicing tape to form a dicing frame. In some cases, a dividing step is performed in which the wafer is supported by the wafer, diced from the back surface side of the wafer, and divided into individual devices. In the dividing step, the back surface of the wafer on which the ring-shaped reinforcing portion is formed is attached to a dicing tape having a convex portion that is accommodated in the concave portion and absorbs the step between the concave portion and the ring-shaped reinforcing portion, and is supported by the dicing frame. Dicing may be performed from the surface side of the wafer.</p><p> Prior to the dividing step, a ring-shaped reinforcing portion separating step of cutting the wafer along the inner circumference of the ring-shaped reinforcing portion to separate the ring-shaped reinforcing portion from the device region may be performed.</p><p> Further, the present invention is a wafer provided with a device region on which a plurality of devices are formed and an outer peripheral surplus region surrounding the device region on the front surface, and a recess is formed in a region corresponding to the device region on the back surface of the wafer. The present invention relates to a wafer in which a ring-shaped reinforcing portion including an outer peripheral excess region is formed on the outer peripheral side of the recess.</p>

<p> In the wafer processing method according to the present invention, a recess is formed in a region corresponding to a device region on the back surface of the wafer, and a ring-shaped reinforcing portion including an outer peripheral surplus region is formed on the outer peripheral side of the recess to form a device region. Even if the thickness is reduced to 100 μm to 50 μm, for example, the outer peripheral side of the device region is reinforced by the ring-shaped reinforcing portion, so that the subsequent wafer can be easily handled, and no adhesive or the like is used. There is no need for complicated work such as removing the adhesive. Further, when the recess is formed by the back surface grinding step, the thickness of the device region can be made uniform.</p><p> When the film forming step and the test step are performed after the ring-shaped reinforcing portion is formed, the handling thereof is carried out in the transfer of the wafer from the step of forming the ring-shaped reinforcing portion to the film forming step and the transfer of the wafer from the film forming step to the test step. Is easy.</p><p> After the ring-shaped reinforcing portion is formed, or after the film forming step and the test step when the test step is performed, the surface of the wafer on which the ring-shaped reinforcing portion is formed is attached to the dicing tape and supported by the dicing frame. When the dividing step of dicing from the back surface side of the wafer and dividing into individual devices is performed, the wafer can be easily handled in the transfer up to the dividing step.</p><p> Further, a division step in which the back surface of the wafer is attached to a dicing tape having a convex portion that absorbs a step between the concave portion and the ring-shaped reinforcing portion, supported by a dicing frame, and diced from the front surface side of the wafer to divide into individual devices. When the above is performed, the step is absorbed by the convex portion, so that dicing can be performed in a stably supported state.</p><p> When the ring-shaped reinforcing portion separation step of cutting the wafer along the inner circumference of the ring-shaped reinforcing portion to separate the ring-shaped reinforcing portion from the device region is performed before the dividing step, the wafer is moved in the dividing step. Since the stroke is shortened, the dividing process can be performed efficiently.</p><p> In the wafer according to the present invention, since a recess is formed in a region corresponding to a device region on the back surface of the wafer and a ring-shaped reinforcing portion including an outer peripheral surplus region is formed on the outer peripheral side of the recess, a ring-shaped reinforcing portion is formed. The wafer can be easily handled in various subsequent steps.</p>

In the surface Wa of the wafer W shown in FIG. 1, a plurality of devices D are formed by being partitioned by streets S, and the portion where the devices D are formed constitutes the device region W1. Further, on the outer peripheral side of the device region W1, an outer peripheral surplus region W2, which is a region in which no device is formed, is formed, and the device region W1 is surrounded by the outer peripheral surplus region W2. When polishing the back surface Wb of the wafer W, a protective member 1 such as a tape is attached to the front surface Wa of the wafer W to protect the device D, and the state is as shown in FIG.

Next, the portion of the back surface Wb of the wafer W corresponding to the device region W1, that is, the back surface of the device region 1 is ground to obtain a desired thickness. For such grinding, for example, the grinding device 2 shown in FIG. 3 can be used.

The grinding device 2 includes a chuck table 20 for holding the wafer and a grinding unit 21 for grinding the wafer held on the chuck table 20. The grinding portion 21 is composed of a rotating shaft 22 having a vertical axis, a wheel 23 mounted on the lower end of the rotating shaft 22, and a grindstone portion 24 fixed to the lower surface of the wheel 23. The diameter of the outermost circumference of the grindstone portion 24 is larger than the radius of the device region W1 and smaller than the diameter of the device region W1, and the diameter of the innermost circumference of the rotary orbit is smaller than the radius of the device region W1. It is formed to be.

In the wafer W, the protective member 1 side is held by the chuck table 20, and the back surface Wb is exposed. Then, as the chuck table 20 rotates and the wheel 23 rotates while the grinding portion 21 descends, the rotating grindstone portion 24 comes into contact with the back surface Wb of the rotating wafer W to perform grinding. At this time, the grindstone portion 24 is controlled so as to be in constant contact with the rotation center of the back surface of the wafer W and not in contact with the back surface of the outer peripheral surplus region W2. Specifically, as shown in FIG. 4, the rotation center Wo of the wafer W is always located inside the outermost circumference 24a of the rotation orbit of the grindstone portion 24 and outside the inner circumference 24b of the rotation orbit. , The grindstone portion 24 is always in contact with the rotation center Wo. Further, the outermost circumference 24a of the rotation track is controlled so as not to come into contact with the back surface side of the outer circumference surplus region W2.

By such control, only the region corresponding to the device region W1 of the back surface Wb is ground, and as shown in FIGS. 5 and 6, a recess W3 is formed in the back surface Wb, and a portion corresponding to the outer peripheral surplus region W2. A ring-shaped reinforcing portion W4 having the same thickness as before grinding remains in the back surface grinding process (back surface grinding process). Moreover, while the wafer W is rotating, the grindstone portion 24 is controlled so as not to always contact the rotation center Wo and the back surface side of the outer peripheral surplus area W2, so that the chuck table 20 is reciprocated in the horizontal direction. It is not necessary, and the recess W3 and the ring-shaped reinforcing portion W4 can be formed only by rotating the chuck table 20 and the grindstone portion 24 at a fixed position. For example, the width of the ring-shaped reinforcing portion W4 may be about 2 to 3 mm. Further, it is desirable that the thickness of the ring-shaped reinforcing portion W4 is several hundred μm. On the other hand, the thickness of the device region W1 can be reduced to about 30 μm.

After the back surface grinding process, the street S shown in FIG. 1 is diced by cutting or the like to separate it and divided into individual devices D. Before that, gold, silver, and titanium are applied to the back surface Wb of the wafer W. A metal film consisting of such materials may be formed and an electrical test of each device D may be performed.

When forming a metal film on the back surface Wb, for example, the reduced pressure film forming apparatus 3 shown in FIG. 7 can be used. The vacuum film forming apparatus 3 is provided with a holding portion 32 that electrostatically holds the wafer W inside the chamber 31, and a sputter source 34 made of metal is an exciting member at an opposite position above the holding portion 32. It is arranged in a state of being supported by 33. A high frequency power supply 35 is connected to the sputter source 34. Further, one side of the chamber 31 is provided with an introduction port 36 for introducing a sputter gas, and the other side is provided with a decompression port 37 communicating with a decompression source.

Since the protective member 12 side is electrostatically held by the holding portion 32, the back surface of the wafer W is held facing the sputtering source 34. Then, high-frequency power of about 40 kHz is added to the sputter source 34 magnetized by the exciting member 33, and the inside of the chamber 31 is 10 from the decompression port 37.^-2Pa ~ 10^-4When the pressure is reduced to about Pa to create a reduced pressure environment and argon gas is introduced from the introduction port 36 to generate plasma, the argon ions in the plasma collide with the sputtering source 34 and the particles are ejected to the back surface of the wafer W. A metal film 6 is formed as shown in FIG. The metal film 6 has a thickness of, for example, about 30 to 60 nm. When the ring-shaped reinforcing portion W4 is masked, the metal film 6 is formed only in the recess W3 (film forming step). The film forming step is performed in a state where the back side of the device region W1 is thinned by grinding, but since the ring-shaped reinforcing portion W4 is formed on the wafer W, the wafer W can be easily handled in the film forming step. .. In the film forming step, vapor deposition, CVD, or the like may be used.

After the film forming step is completed, as shown in FIG. 9, the protective member 1 attached to the surface Wa of the wafer W is peeled off. Then, as shown in FIG. 10, the back surface side on which the metal film 6 is formed is held by the holding table 50, and the holding table 50 is connected to the ground to connect the wafer W to the ground via the metal film 6. .. Then, by bringing the probe 51 into contact with the device D on the front surface side, the electrical characteristics of each device are tested (test step). Since the ring-shaped reinforcing portion W4 is formed on the wafer W, the wafer W can be easily handled in the test process.

After the metal film 6 is formed on the back surface side by the film forming step and the wafer W has undergone the test step, the front surface Wa is then attached to the dicing tape T as shown in FIG. The dicing tape T is attached to the ring-shaped dicing frame F, the wafer W is supported by the dicing frame via the dicing tape T, and the back surface on which the metal film 6 is formed is exposed.

The wafer W supported by the dicing frame F is diced by cutting along a street S (see FIG. 1) formed on the surface, and is divided into individual devices D. Such dicing is also realized by irradiating the street S with a laser beam, but here, for example, a case where the street S is cut by using the cutting device 4 shown in FIG. 12 will be described.

The cutting device 4 has a chuck table 40 that holds the wafer 1 and a cutting means 41 that acts on the wafer 1 held by the chuck table 40 to perform cutting. The chuck table 40 is connected to the drive source 400 and is rotatable. The drive source 400 is fixed to the moving base 401, and the moving base 401 can be moved in the X-axis direction by the cutting feed means 42. The cutting feed means 42 is composed of a ball screw 420 arranged in the X-axis direction, a pulse motor 421 connected to one end of the ball screw 420, and a pair of guide rails 422 arranged in parallel with the ball screw 420. A nut (not shown) provided at the bottom of the moving base 401 is screwed into the ball screw 420. The ball screw 420 is driven by the pulse motor 421 to rotate, and the moving base 401 is guided by the guide rail 422 to move in the X-axis direction.

The cutting means 41 has a configuration in which a cutting blade 412 is attached to the tip of a spindle 411 rotatably supported by the housing 410, and the housing 410 is supported by the support portion 413.

An alignment means 43 for detecting the street of the wafer is fixed to the side portion of the housing 410. The alignment means 43 is provided with an infrared camera 430 that captures the wafer 1, and based on the image acquired by the infrared camera 430, the street to be cut is determined by processing such as pattern matching with the key pattern stored in advance. It can be detected (aligned).

The cutting means 41 and the alignment means 43 can be moved in the Z-axis direction by the cutting feed means 44. The notch feeding means 44 includes a ball screw 441 arranged in the Z-axis direction on one surface of the wall portion 440, a pulse motor 442 for rotating the ball screw 441, and a guide rail 443 arranged in parallel with the ball screw 441. A nut (not shown) inside the support 413 is screwed into the ball screw 441. The support portion 413 is driven by the pulse motor 442 and moves up and down in the Z-axis direction guided by the guide rail 443 as the ball screw 441 rotates, and the cutting means 41 supported by the support portion 413 also moves in the Z-axis direction. It is configured to go up and down.

The cutting means 4 can be moved in the Y-axis direction by the indexing feed means 45. The indexing feed means 45 includes a ball screw 450 arranged in the Y-axis direction, a moving base 451 formed integrally with the wall portion 440 and having an internal nut screwed onto the ball screw 450, and a pulse motor for rotating the ball screw 450. It is composed of a 452 and a guide rail 453 arranged in parallel with the ball screw 450, and a nut (not shown) inside the moving base 451 is screwed into the ball screw 450. The moving base 451 is driven by the pulse motor 452 and is guided by the guide rail 453 as the ball screw 450 rotates, and moves in the Y-axis direction. Along with this, the cutting means 41 also moves in the Y-axis direction. It is composed.

The wafer W supported by the dicing frame F via the dicing tape T is suction-held on the chuck table 40 with its back surface Wb side exposed. Then, as the chuck table 40 moves in the + X direction, the wafer 1 is positioned directly under the infrared camera 430, and the infrared camera 430 transmits the metal film 6 and the wafer W to image the surface Wa of the wafer W. The street S is detected by the alignment means 43 based on the image, and the street S and the cutting blade 412 are aligned in the Y-axis direction.

Then, the chuck table 40 is further moved in the + X direction by the cutting feed means 42, the cutting means 41 is lowered by the cutting feed means 44 while rotating the cutting blade 412 at high speed, and the cutting blade 412 is moved toward the detected street. Make a cut and cut the street.

The indexing feed means 45 indexes and feeds the cutting means 41 at intervals of the streets to perform the same cutting in sequence, and after all the streets in the same direction have been cut, the chuck table 40 is rotated 90 degrees to perform the same cutting. As a result, the wafer W is divided into individual devices D (division process). When cutting each street, if the ring-shaped reinforcing portion W4 on the extension line of the street S is also cut, it is not necessary to remove the ring-shaped reinforcing portion W4 later.

Before the dividing step, the ring-shaped reinforcing portion W4 may be cut slightly inside along the inner circumference of the ring-shaped reinforcing portion W4 to remove the ring-shaped reinforcing portion W4 as shown in FIG. 13 (ring-shaped reinforcing portion W4). Part separation process). Such a ring-shaped reinforcing portion separating step is realized, for example, by cutting along the inner circumference of the ring-shaped reinforcing portion W4 while rotating the wafer W supported by the dicing frame F via the dicing tape T. In this way, if the ring-shaped reinforcing portion W4 is removed before the dividing step, only the device region W1 needs to be cut in the dividing step, and the ring-shaped reinforcing portion W4 does not need to be cut. Therefore, the wafer W The moving stroke of the chuck table 40 (see FIG. 12) for holding the wafer can be shortened, and the dividing process can be efficiently performed.

In the above dividing step, the case of dicing from the back surface side of the wafer W has been described, but in the dividing step, dicing may be performed from the front surface side. In this case, as shown in FIG. 14, a dicing tape T1 having a convex portion 7 having a height corresponding to the depth of the concave portion W3 formed on the back surface of the wafer W is used, and the convex portion 7 is the concave portion of the wafer W. The back surface of the wafer W is attached so as to be accommodated in W3, and the state shown in FIGS. 15 and 16 is obtained. That is, the convex portion 7 plays a role of absorbing the step between the concave portion W3 and the ring-shaped reinforcing portion W4, and the outer diameter of the convex portion 7 is preferably slightly smaller than the outer diameter of the concave portion W3. The convex portion 7 may be a member different from the dicing tape T1.

Next, it can be divided into individual devices D by, for example, the cutting device 4 shown in FIG. Here, since the wafer W is diced in a state where the surface Wa on which the street S is formed is exposed, the camera used for imaging at the time of alignment does not need to be an infrared camera. Further, the ring-shaped reinforcing portion W4 may be removed in the same manner as described above before dicing.

In the above example, the case where the division step is performed after passing through the film forming step and the test step has been described, but the dividing step may be performed without going through the film forming step and the test step. In that case as well, both dicing from the back surface and dicing from the front surface are possible. It is also possible to remove the ring-shaped reinforcing portion before the dividing step.

Further, as a method of forming a recess in a region corresponding to a device region on the back surface of the wafer and forming a ring-shaped reinforcing portion including an outer peripheral surplus region on the outer peripheral side of the recess, a portion of the back surface other than the recess to be formed is formed. A method of forming a recess by performing plasma etching with a fluorine-based gas or wet etching with a fluorine-based etching solution on the unmasked part to form a ring-shaped reinforcing part, or a recess by CMP. There is also a method of forming a ring-shaped reinforcing portion.

<figref num="1">It is a perspective view which shows the wafer and the protective member.</figref><figref num="2">It is a perspective view which shows the state which the protective member was attached to the surface of a wafer.</figref><figref num="3">It is a perspective view which shows an example of the back surface grinding process.</figref><figref num="4">It is explanatory drawing which shows the positional relationship between the rotary trajectory of a grindstone part and a wafer in a back surface grinding process.</figref><figref num="5">It is a perspective view which shows the wafer which the recess and the ring-shaped reinforcing part were formed, and the protective member was attached.</figref><figref num="6">It is sectional drawing which shows the wafer which the recess and the ring-shaped reinforcing part were formed, and the protective member was attached.</figref><figref num="7">It is sectional drawing which shows typically an example of the vacuum film formation apparatus.</figref><figref num="8">It is sectional drawing which shows the wafer which the metal film was formed on the back surface, and the protective member was attached to the front surface.</figref><figref num="9">It is a perspective view which shows the state which the protective member is peeled off from the wafer.</figref><figref num="10">It is a perspective view which shows an example of a test process.</figref><figref num="11">It is a perspective view which shows the state which the wafer is supported by the dicing frame through the dicing tape.</figref><figref num="12">It is a perspective view which shows an example of a cutting apparatus.</figref><figref num="13">It is a perspective view which shows the state which removes the ring-shaped reinforcing part from a wafer.</figref><figref num="14">It is a perspective view which shows the state which attaches the wafer to the dicing tape which formed the convex part.</figref><figref num="15">It is a perspective view which shows the state which the wafer is attached to the dicing tape which formed the convex part.</figref><figref num="16">It is sectional drawing which shows the state which the wafer is attached to the dicing tape which formed the convex part.</figref>

Code description

W: Wafer Wa: Front surface S: Street D: Device W1: Device area W2: Outer peripheral excess area Wb: Back surface W3: Recessed part W4: Ring-shaped reinforcing part T, T1: Dying tape F: Frame 1: Protective member 2: Grinding device 20: Chuck table 21: Grinding part 22: Rotating shaft 23: Wheel 24: Grinding part 3: Decompression film forming device 31: Chamber 32: Holding part 33: Exciting member 34: Spatter source 35: High frequency power supply 36: Inlet port 37: Decompression port 4: Cutting device 40: Chuck table 400: Drive source 401: Moving base 41: Cutting means 410: Housing 411: Spindle 412: Cutting blade 413: Support 42: Cutting feed means 420: Ball screw 421: Pulse motor 422 : Guide rail 43: Alignment means 430: Infrared camera 44: Cutting feed means 440: Wall part 441: Ball screw 442: Pulse motor 443: Guide rail 45: Indexing and feeding means 450: Ball screw 451: Moving base 452: Pulse motor 453: Guide rail 50: Holding table 51: Probe 6: Metal film 7: Convex part