JP5141070B2 - Wafer dicing method - Google Patents

Description

  The present invention relates to a rib structure wafer dicing method in which the outer peripheral portion of the back surface of a wafer is thickened.

  A wafer on which a plurality of devices such as IC and LSI are formed on the front (front) surface side is divided into individual devices along a street using a dicing machine etc., and is widely used by being incorporated into various electronic devices. ing. In order to reduce the size and weight of the electronic device, the wafer before being divided into individual devices is formed such that the back surface is ground and the thickness is, for example, 100 μm to 50 μm.

However, if the wafer is thinned by grinding, the rigidity is lost, making it difficult to handle in subsequent processes. For example, a large warp is generated by the stress of the film formed on the front surface and the back surface of the wafer, making it difficult to carry and process itself. Furthermore, the occurrence of defects due to cracks and chips increases because the wafer end surface becomes a knife edge.
As a countermeasure, a technique is known in which a ring-shaped protective member is attached to an outer peripheral surplus region where a device on the surface of the wafer is not formed via an adhesive, and the back surface is ground while holding the protective member side in that state. (Patent Document 1). This document discloses a method of separating a device into chips by performing normal dicing on a wafer provided with a ring-shaped protective member.

Also, as a countermeasure for reinforcing the wafer, a structure (rib structure) in which the outer peripheral portion is left as a thick portion having a width of about 2 to 5 mm and only the central portion on the backside of the wafer surrounded by the thin portion (rib structure) and a manufacturing method are well known 2). As a method for thinning the central portion of the wafer, grinding and chemical etching are known. As the former, there is known a method of processing by infeed grinding using a grinding wheel having a diameter smaller than that of a wafer. As the latter, a method of etching using an alkaline solution is known.
JP 2005-123568 A JP 2003-124147 A

However, there is a problem that dicing becomes difficult if the outer peripheral portion of the back surface of the wafer is left as a thick portion and the central portion is thinned.
First, when dicing is performed from the front surface side, a gap is generated in the vicinity of the thick portion on the outer periphery of the wafer called a rib when a dicing tape is attached to the back surface. For this reason, the vibration of the wafer is increased during dicing, and dicing defects such as chipping are likely to occur.

In addition, since the wafer bends when the back side of the wafer is attracted to the stage, (1) the dicing height changes depending on the location and the processing state becomes unstable. (2) Focus adjustment becomes difficult and the marker position is changed. There is a problem that an undetectable error occurs.
On the other hand, when a dicing tape is attached to the front (front) surface of the wafer and dicing is performed from the back side, there is a problem caused by the difference between the thick part of the outer periphery and the thin part of the inner part. To do. In other words, if the dicing conditions are set according to the thin area inside the wafer, the load when processing the thick part on the outer periphery increases, and processing defects such as chipping occur near the outer periphery, possibly causing blade damage. There is a problem of growing. Furthermore, when dicing from the back side, there is no marker as a mark, so there is a problem that it is difficult to perform dicing according to the street on the front side.

  These problems become more conspicuous when the wafer is thinned and the electrodes are formed on the back surface side in order to improve the characteristics like a power device such as an IGBT (Insulated Gate Bipolar Transistor). This is because when chipping is performed on a wafer having electrodes formed on the entire back surface, sudden chipping occurs due to clogging of the blade.

In order to solve the above-mentioned problems, the inventors have found a method in which the front surface of a wafer having a rib structure is attached to a dicing tape, and two-stage dicing is performed from the back surface side. In the first step, the outer peripheral rib is partially cut by half cutting, and in the second step, full cutting is performed in accordance with the rib cutting portion.
That is, according to the present invention, a thick portion (rib) is formed along the outer periphery of the back surface, and a plurality of devices divided by streets on the front (front) surface side of the thin portion surrounded by the thick portion. It is a dicing method for a formed wafer. This method has at least two steps. In the first step, dicing with a cutting blade is performed from the back side of the wafer to partially remove the thick portion in accordance with the position of the street, and so-called half cut is performed to form a groove. Below this groove, a wafer is partially left in the thickness direction. In the second step, the thick part and the thin part are fully cut along the street in accordance with the position of the groove to separate the plurality of devices.

By performing the two-stage dicing for the thick portion in this way, the processing load at the time of full cutting can be made uniform, so that the device can be separated without causing chipping over the entire wafer surface.
Furthermore, in the present invention, when using a wafer having an electrode formed on the back surface, it is effective to form the electrode pattern by removing the back electrode facing the street on the front surface by photolithography. At this time, instead of removing the entire area facing the street, an electrode pattern including a marker for recognizing the street may be used. If the back electrode is removed in this way, the position of the street can be confirmed from the back side during dicing, and in addition, clogging of the cutting blade is reduced and sudden chipping can be prevented.

  It is also preferable to form a marker for identifying the position of the street on the front surface side by laser irradiation or the like on the back surface of the wafer and use it for alignment during dicing. According to this method, the marker can be easily formed on the back surface of the wafer without performing photolithography.

According to the dicing method of the present invention, even when processing a wafer having a thick portion on the outer peripheral portion, the processing load at the time of full cutting can be made uniform, so that the device can be produced without causing chipping over the entire wafer surface. Can be separated.
In addition, when using a wafer with electrodes on the back side, the back electrode facing the street on the front side is removed by photolithography, so that the position of the street can be confirmed from the back side, and in addition, the cutting blade is clogged. This can reduce sudden chipping. This is particularly effective in a device in which a metal electrode is formed on the back side, such as a power device such as an IGBT.

  Further, by forming a marker for identifying the position of the street on the front surface side by laser irradiation or the like on the back surface of the wafer, a marker used for alignment during dicing can be easily formed. This method is also particularly effective in power devices such as IGBTs.

As a first embodiment of the present invention, a thin power device in which an electrode is formed on the back surface is taken as an example, and the dicing method will be described with reference to the drawings.
FIG. 1 is a perspective view schematically showing the shape of a wafer according to the present invention. A plurality of devices 3 separated by streets 2 are formed on the front surface of the wafer 1. FIG. 2A is a plan view showing the back surface of the wafer 1, and FIG. 2B is a diagram showing a cross section taken along the line IIa-IIa ′ in FIG. The device 3 is formed on the surface side of the thin part 5 surrounded by the thick part 4.

  An outline of the manufacturing process of the wafer 1 will be described. First, a gate structure and a source / emitter structure are formed on the surface side of a thick wafer by a known method, and a plurality of devices separated by streets are formed. Next, the outer peripheral portion of the back surface of the wafer is masked and only the inner peripheral portion of the wafer is etched to reduce the thickness of the inner peripheral portion of the wafer. Alternatively, only the wafer inner periphery may be wheel-polished to reduce the thickness of the wafer inner periphery. Then, a metal electrode film is formed on the back surface of the thinned wafer. As a material of the metal electrode film, for example, aluminum (Al), titanium (Ti), nickel (Ni), gold (Au), or the like can be laminated and used. By the procedure as described above, the wafer 1 having a thick portion is formed along the outer periphery of the back surface.

The wafer is made of a semiconductor such as silicon. The shape of the wafer 1 has a structure in which, for example, a rib (thick portion) 4 having a width of 5 mm is formed along the outer periphery. Here, the thickness t1 of the thin portion 5 inside the wafer is 50 to 100 μm, and the thickness t2 of the rib 4 is 200 to 500 μm (FIG. 2B). The side where the rib protrudes is the back surface.
When forming an electrode on the back surface of the wafer 1, a back surface electrode pattern is formed by removing a portion facing the surface street 2 by photolithography using a double-side exposure device. As a patterning method, either (1) a method in which electrodes on both sides of the front and back surfaces are formed at once or (2) a method in which back surface electrode patterning is performed in a separate process in accordance with the front side pattern may be used.

FIG. 3 is a plan view schematically showing the back electrode pattern. The electrode removal region 6 is formed by photolithography so as to face the street 2 on the front surface, and the separated back electrode 7 and marker 8 are formed. Here, the width of the electrode removal region 6 is 60 to 150 μm.
Next, a method for dicing the wafer 1 will be described with reference to the drawings. FIG. 4 is a cross-sectional view showing a process flow of the dicing method according to the present invention, and FIG. 5 is an enlarged cross-sectional view of the main part of the wafer in process B shown in FIG. First, the wafer 1 is attached to the dicing film 9 (process A). At this time, the surface of the wafer 1 is attached to the dicing film 9 and simultaneously supported by the frame 10 having a substantially donut shape. Subsequently, the first dicing (process B) is performed in which the outer peripheral rib 4 is cut and removed by a blade using the marker 8 (FIG. 3) formed on the back surface as a mark for alignment. By this step, the groove 11 is formed at a position where the extension line of the street 2 on the front surface and the rib 4 intersect.

  At this time, as shown in FIG. 5, the cutting height from the bottom surface of the wafer to the bottom of the groove is a, and the thickness of the thin portion inside the wafer is d,

It is desirable to remove the ribs 4 so as to satisfy the above. If the value of a / d is smaller than 1.05, the dicing blade may come into contact with the back surface of the thin portion inside the wafer, and chipping may occur inside the wafer near the rib. On the other hand, if a / d is larger than 1.5, chipping may occur inside the wafer due to non-uniformity in the height of the cutting area.
Subsequently, the thick portion 4 and the thin portion 5 are fully cut in accordance with the position of the groove 11 (step C), thereby separating the devices arranged across the street.

  In addition, the dicing blade width at the time of the full cut in the process C needs to be equal to or less than the dicing blade width at the time of the half cut in the process B. Further, the width of the blade used in the process B needs to be selected according to the depth and width of the groove 11. As a method for realizing this, a method in which blades having different widths are mounted on a two-spindle type dicing apparatus and processed or divided into two stages by a one-spindle type dicing apparatus can be considered.

A plurality of devices are separated from the wafer by repeating the above steps B and C for all the streets. Although the repetition order can be set arbitrarily, it is preferable to perform the process C after performing the process B for all the streets, so that the load on the wafer can be reduced.
By performing dicing using this method, satisfactory processing can be performed without causing chipping over the entire surface. The present invention is a two-stage process using blades with different widths, but this is effective in avoiding the blade from contacting the thick part of the rib in the second stage process and making the processing load uniform. .

  For comparison, a method of processing the wafer with ribs 1 from the back surface by one dicing (full cut) and a method of processing from the front surface were also examined. In the former case, chipping of about 50 to 100 μm, which is considered to be caused by load fluctuation, occurred near the boundary between the rib 4 and the thin portion 5. In the latter case, chip skipping and cracking occurred in a region close to the outer periphery, resulting in an extremely poor processing state.

A second embodiment of the present invention will be described with reference to the drawings. FIG. 6 is an explanatory view schematically showing alignment mark formation processing on the back surface of the rib structure wafer. Here, description will be made using a wafer 1 that is created in the same manner as in the first embodiment and has a metal electrode film formed on the back surface.
In this embodiment, the pattern of the structure of the street 2 and the device 3 on the front surface of the wafer 1 is recognized, and an alignment marker for alignment by laser marking is formed on a part of the back electrode. For alignment for dicing, it is sufficient to mark a few points on the wafer, which is a much lower cost and shorter process than using the double-sided exposure tool used in the first embodiment. Marking is possible.

  Specifically, when forming an alignment mark on the rib structure wafer 1, the XY stage 201 has the back surface of the rib structure wafer 1 facing the laser marker 206 and the front surface of the rib structure wafer 1 facing the CCD camera 205. put on top. That is, the surface having the rib structure step is placed on the upper surface side of the XY stage 201, and the surface on which the surface device structure such as the gate structure is formed is placed on the lower surface side of the XY stage 201.

  The CCD camera 205 images the front surface side of the rib structure wafer 1 placed on the XY stage 201 and outputs an image signal to the monitor 230. The monitor 230 displays an image of the front surface side of the rib structure wafer 1 taken by the CCD camera 205. Then, while viewing the image of the front surface of the rib-structured wafer 1 displayed on the monitor 230, the XY stage 201 is adjusted so that a desired position (point to be marked) becomes the center of the image.

Specifically, for example, as shown in FIG. 6, the center position P of the adjacent chips C1 to C4 of the surface device structure unit is adjusted to be the center of the image. Further, for example, when an alignment mark is previously formed on the front surface of the rib structure wafer 1, the position is adjusted so as to be the center of the image. Regardless of which position is the center, adjustment is made so that the positional relationship with the street that divides the device becomes clear. Then, a laser is irradiated from the laser marker 206 at that position, and an alignment mark (irradiation trace) for adjusting the cutting position is formed on the metal electrode film on the back surface side of the rib structure wafer 1. At this time, for example, a YLF2ω laser or a YAG2ω laser can be used as the type of laser emitted from the laser marker 206. Moreover, the irradiation energy density of a laser shall be 0.2-4.0J / cm < ² >, for example.

  In addition, as a marking method, instead of laser irradiation, a dent made of a pointed hard material, marking with ink, or the like may be used.

  In the present invention, a rib-structured wafer can be cut without causing defects such as chipping, and thus can be used for dicing processing of a wafer that is formed to be thin.

It is a perspective view which shows typically the shape of the wafer which concerns on this invention. (A) is a top view which shows the back surface of a wafer, (b) is a figure which shows the IIa-IIa 'cross section in (a). It is a top view which shows a back surface electrode pattern typically. It is sectional drawing which shows the process flow of the wafer dicing method by this invention. The broken lines in the figure are hide lines representing the shapes of the thick and thin portions. It is sectional drawing to which the principal part of the wafer in the process B of FIG. 4 was expanded. It is a conceptual diagram of the alignment marking method to the back surface metal electrode film by the 2nd Example of this invention.

Explanation of symbols

1 Wafer 2 Street 3 Device 4 Rib (Thick part)
5 Thin-walled portion 6 Electrode removal area 7 Back electrode 8 Marker 9 Dicing film 10 Dicing frame 201 XY stage 205 CCD camera 206 Laser marker 230 Monitor

Claims (3)

A wafer dicing method in which a thick part is formed along the outer periphery of the back surface, and a plurality of devices divided by streets are formed on the surface side of the thin part surrounded by the thick part,
A first step of forming a groove by partially removing the thick portion according to the position of the street by dicing with a cutting blade from the back side of the wafer;
A second step of separating the plurality of devices by fully cutting the thick part and the thin part according to the position of the groove ;
Forming an electrode pattern by forming an electrode on the back surface of the wafer, removing an area of the electrode facing the street, and forming a groove of the first process in accordance with the area; A wafer dicing method. A wafer dicing method in which a thick part is formed along the outer periphery of the back surface, and a plurality of devices divided by streets are formed on the surface side of the thin part surrounded by the thick part,
A first step of forming a groove by partially removing the thick portion according to the position of the street by dicing with a cutting blade from the back side of the wafer;
A second step of separating the plurality of devices by fully cutting the thick part and the thin part according to the position of the groove;
A wafer dicing method comprising: forming a marker corresponding to the street on a metal electrode film on a back surface side of the wafer, and forming the groove in the first step using the marker as a mark . 3. The marker according to claim 2, wherein the marker is formed on the metal electrode film on the back surface side at a position corresponding to a street that images the front surface side of the wafer and separates adjacent chips of the surface device structure portion. A wafer dicing method .

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