METHOD OF PROCESSING WAFER

A method is of processing a wafer that includes on a side of a front surface a plurality of intersecting planned dividing lines and a plurality of devices formed in respective areas defined by the planned dividing lines, and a metal layer laminated on a side of a back surface. The method includes: forming a mark indicating positions of the planned dividing lines of the wafer on the back surface; and dicing the wafer from the side of the back surface using the formed mark as a reference to divide the wafer into individual chips.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application claims priority to and incorporates by reference the entire contents of Japanese Patent Application No. 2023-156475 filed in Japan on Sep. 21, 2023.

BACKGROUND

The present disclosure relates to a method of processing a wafer having a front surface on which a plurality of devices are formed and a back surface on which a metal layer is laminated.

In order to prevent foreign matter from adhering to a device during cutting, dicing by bonding a front surface side of a wafer to a tape has been widely used (see, for example, JP H6-232255 A).

In a dicing method described in JP H6-232255 A, when dicing is performed from a back surface side of a wafer, a pattern on a front surface side is detected using an infrared camera, a position of a planned dividing line is identified based on the pattern, and dicing is performed by a cutting blade along the planned dividing line.

However, in the case of a wafer including a metal layer laminated on a back surface side, it is difficult to identify a position of a planned dividing line using the infrared camera, and improvement is earnestly desired.

SUMMARY

A method according to one aspect of the present disclosure is of processing a wafer, the wafer including on a side of a front surface a plurality of intersecting planned dividing lines and a plurality of devices formed in respective areas defined by the planned dividing lines, and a metal layer laminated on a side of a back surface. The method includes: forming a mark indicating positions of the planned dividing lines of the wafer on the back surface; and dicing the wafer from the side of the back surface using the formed mark as a reference to divide the wafer into individual chips.

DETAILED DESCRIPTION

Embodiments of the present disclosure will be described in detail with reference to the drawings. The present invention is not limited by the contents described in the following embodiment. In addition, components to be described below include those that can be easily assumed by those skilled in the art and those that are substantially the same. Furthermore, configurations described below can be appropriately combined. In addition, various omissions, substitutions, or changes of the configurations can be made within a scope not departing from the gist of the present invention.

First Embodiment

A method of processing a wafer according to a first embodiment of the present disclosure will be described with reference to the drawings.FIG.1is a perspective view schematically illustrating a wafer to be processed by a method of processing a wafer according to the first embodiment.FIG.2is a flowchart illustrating a flow of the method of processing a wafer according to the first embodiment.

Wafer

The method of processing a wafer according to the first embodiment is a method of dicing (which corresponds to processing) a wafer1. The wafer1illustrated inFIG.1to be processed by the method of processing a wafer according to the first embodiment is a disk-shaped semiconductor device wafer, optical device wafer, or the like using silicon, sapphire, gallium arsenide, silicon carbide (Sic), or the like as a substrate2. In the first embodiment, the substrate2of the wafer1is made of SiC.

As illustrated inFIG.1, the wafer1includes a device area4on a front surface3of the substrate2and an outer peripheral marginal area5surrounding the device area4. The device area4includes, on the front surface3side, a plurality of intersecting planned dividing lines6and devices7formed in respective areas defined by the planned dividing lines6.

Examples of the devices7include an integration circuit such as an integrated circuit (IC) or a large scale integration (LSI), an image sensor such as a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS), an optical element such as a light-emitting diode (LED), and a memory (semiconductor storage device). The outer peripheral marginal area5surrounds the entire periphery of the device area4, and is an area where the devices7are not formed on the front surface3of the substrate2.

In addition, in the first embodiment, the wafer1includes a metal layer9laminated on a back surface8on the back side of the front surface3of the substrate2. Since the wafer1includes the metal layer9formed on the back surface8, the planned dividing lines6cannot be detected even if an image is captured by an infrared camera from the back surface8side.

Method of Processing Wafer

Next, the method of processing a wafer according to the first embodiment will be described. The method of processing a wafer according to the first embodiment is a method of dicing the wafer1to divide the wafer1into individual chips10. Note that the chips10include a part of the substrate2and the chips10formed on the front surface3of the substrate2. As illustrated inFIG.2, the method of processing a wafer according to the first embodiment includes a tape arrangement step1001, a mark formation step1002, and a dicing step1003.

Tape Arrangement Step

FIG.3is a perspective view illustrating the wafer after the tape arrangement step of the method of processing a wafer illustrated inFIG.2. The tape arrangement step1001is a step of arrangement a tape11on the front surface3of the wafer1. In the tape arrangement step1001of the first embodiment, as illustrated inFIG.3, a central portion of the tape11having a disk shape whose diameter is larger than t the wafer1is bonded to the front surface3of the wafer1, and a frame12having a ring shape whose inner diameter is larger than an outer diameter of the wafer1is bonded to an outer edge portion of the tape11.

Note that the tape11in the first embodiment is an adhesive tape including a base material layer made of a resin having non-adhesiveness and flexibility, and a glue layer laminated on the base material layer and made of a resin having adhesiveness and flexibility, the glue layer being bonded to the wafer1and the frame12. However, in the present disclosure, the tape11may be a sheet that does not include a glue layer but includes only a base material layer which is made of a thermoplastic resin, exhibits an adhesive force by heating, and is thermocompression-bonded to the wafer1and the frame12.

In the first embodiment, in the tape arrangement step1001, the front surface3of the wafer1is bonded to the tape11equipped with the frame12in the outer edge portion, so that the wafer1is supported by the frame12to expose the metal layer9on the back surface8side of the wafer1.

Processing Apparatus

The mark formation step1002of the method of processing a wafer illustrated inFIG.2is performed by a processing apparatus30illustrated inFIG.4. Next, the processing apparatus30will be described.FIG.4is a perspective view illustrating a configuration example of the processing apparatus that performs the mark formation step of the method of processing a wafer illustrated inFIG.2.

The processing apparatus30illustrated inFIG.4is a laser processing apparatus that holds the wafer1on a holding table42of a holding unit40and forms marks13indicating positions of the planned dividing lines6of the wafer1on the metal layer9laminated on the back surface8side. As illustrated inFIG.4, the processing apparatus30includes the holding unit40, a laser beam irradiation unit50, a moving unit60, an upper imaging unit70, a lower imaging unit80, and a control unit100.

As illustrated inFIG.4, the holding unit40includes: a table base41moved by the moving unit60in an X-axis direction parallel to the horizontal direction and a Y-axis direction parallel to the horizontal direction and orthogonal to the X-axis direction; and the holding table42provided on the table base41so as to be rotatable about an axis parallel to a Z-axis direction along the vertical direction.

In the first embodiment, the table base41includes: a lower plate411moved in the X-axis direction and the Y-axis direction by the moving unit60and is parallel to the horizontal direction; a side plate412that is erected from an outer edge of the lower plate411; and an upper plate413that has an outer edge continuous with an upper end of the side plate412, is parallel to the lower plate411, and has, at the center, a circular hole having the same diameter as a holding portion44to be described later.

The holding table42holds the wafer1on a holding surface441and is supported by the upper plate413so as to be rotatable about the axis. As illustrated inFIG.6, the holding table42includes: an annular base43that has a ring shape, is supported by the upper plate413so as to be rotatable about the axis parallel to the Z-axis direction, and has an opening at the center; and the holding portion44that has a disk shape, is attached inside the opening of the annular base43and is made of a transparent material.

The holding portion44is made of the transparent material that is transparent, such as quartz glass, borosilicate glass, sapphire, calcium fluoride, lithium fluoride, or magnesium fluoride, and has an upper surface serving as the holding surface441that holds the wafer1. That is, the holding table42includes the holding surface441. In the first embodiment, the front surface3side of the wafer1is placed on the holding surface441of the holding portion44with the tape11interposed therebetween. A suction groove connected to a vacuum suction source is formed in the holding surface441of the holding portion44.

When the holding surface441is sucked by the vacuum suction source, the holding table42sucks and holds the wafer1placed on the holding surface441onto the holding surface441with the tape11interposed therebetween. Since the holding portion44is made of the transparent material in the first embodiment, at least a part of the holding surface441of the holding table42is made of the transparent material.

The moving unit60includes: an X-axis moving unit61which is a processing feed unit; a Y-axis moving unit62which is an indexing feed unit; and a rotary moving unit63which rotates the holding table42about the axis parallel to the Z-axis direction.

The X-axis moving unit61is installed on an apparatus body31. The X-axis moving unit61moves a moving table32on which the Y-axis moving unit62is installed in the X-axis direction, thereby relatively moving the holding table42and the laser beam irradiation unit50in the X-axis direction. The X-axis moving unit61moves the holding table42in the X-axis direction over a loading and unloading area where the wafer1is loaded onto and unloaded from the holding table42and a processing area where the wafer1held by the wafer1is subjected to laser processing.

The Y-axis moving unit62is installed on the moving table32moved in the X-axis direction by the X-axis moving unit61. The Y-axis moving unit62moves the lower plate411of the table base41of the holding unit40in the Y-axis direction, thereby relatively moving the holding table42and the laser beam irradiation unit50in the Y-axis direction.

The X-axis moving unit61and the Y-axis moving unit62each include a known ball screw provided so as to be rotatable about an axis, a known motor that rotates the ball screw about the axis, and a known guide rail that supports the moving table32or the table base41so as to be movable in the X-axis direction or the Y-axis direction.

The rotary moving unit63rotates the holding table42about the axis parallel to the Z-axis direction. The rotary moving unit63rotates the holding table42about the axis within a range of more than 180 degrees and less than 360 degrees. The rotary moving unit63includes a motor631fixed to the side plate412of the table base41, a pulley632connected to an output shaft of the motor631, and a belt633that is wound around and attached to the outer periphery of the annular base43of the holding table42and is rotated about the axis by the pulley632.

When the motor631is rotated, the rotary moving unit63rotates the holding table42about the axis via the pulley632and the belt633. In addition, in the first embodiment, the rotary moving unit63can rotate the holding table42by 220 degrees in both one direction about the axis and the other direction opposite to the one direction.

The laser beam irradiation unit50is a processing unit that condenses and emits a pulsed laser beam to the wafer1held on the holding surface441of the holding table42to perform the laser processing on the metal layer9of the wafer1. In the first embodiment, as illustrated inFIG.4, a part of the laser beam irradiation unit50is disposed at a distal end of a support column34whose proximal end portion is supported by an upright column33erected from the apparatus body31.

The laser beam irradiation unit50includes an oscillator that emits a laser beam with a wavelength having absorbability with respect to the metal layer9, and a condenser lens that condenses the laser beam emitted from the oscillator and irradiates the wafer1with the laser beam.

The upper imaging unit70is fixed to the distal end of the support column34. In the first embodiment, the upper imaging unit70is disposed at a position aligned with the condenser lens of the laser beam irradiation unit50in the X-axis direction. The upper imaging unit70includes a plurality of imaging elements that capture images of the wafer1held on the holding table42from above. The imaging element is, for example, a charge-coupled device (CCD) imaging element or a complementary MOS (CMOS) imaging element. The upper imaging unit70captures an image of the wafer1held by the holding portion44of the holding table42and outputs the obtained image to the control unit100.

The lower imaging unit80captures an image of the front surface3of the wafer1held on the holding table42through the holding portion44of the holding table42. The lower imaging unit80captures an image of the front surface3side of the wafer1held by the holding portion44of the holding table42from below the wafer1through the holding portion44.

The lower imaging unit80is disposed adjacent to the moving table32in the Y-axis direction and adjacent to the upright column33in the X-axis direction. The lower imaging unit80is disposed to be movable in the Z-axis direction by a Z-axis moving unit64provided on an upright column35erected from the apparatus body31. In the first embodiment, the lower imaging unit80is attached to a distal end of a horizontal extension member65whose proximal end portion is movable in the Z-axis direction by the Z-axis moving unit64.

The Z-axis moving unit64includes a known ball screw provided so as to be rotatable about an axis, a known motor that rotates the ball screw about the axis, and a known guide rail that supports the lower imaging unit80so as to be movable in the Z-axis direction.

The lower imaging unit80enters between the lower plate411and the upper plate413of the table base41moved by the Y-axis moving unit62and is arranged below the holding portion44of the holding table42. The lower imaging unit80includes an imaging element that captures an image of the wafer1held on the holding table42from below through the holding portion44. The imaging element is, for example, a charge-coupled device (CCD) imaging element or a complementary MOS (CMOS) imaging element. The lower imaging unit80captures an image of the wafer1held on the holding table42and outputs the obtained image to the control unit100.

In addition, the processing apparatus30includes an X-axis direction position detection unit (not illustrated) configured to detect a position of the holding table42in the X-axis direction and a Y-axis direction position detection unit (not illustrated) configured to detect a position of the holding table42in the Y-axis direction. Each of the X-axis direction position detection unit and the Y-axis direction position detection unit can be configured using a linear scale parallel to the X-axis direction or the Y-axis direction and a reading head. The X-axis direction position detection unit and the Y-axis direction position detection unit output the positions of the holding table42in the X-axis direction and the Y-axis direction to the control unit100, respectively.

Note that the position of the holding table42in each axis direction detected by each position detection unit is determined with a predetermined reference position of the processing apparatus30as a reference. That is, the respective positions in the processing apparatus30according to the first embodiment are determined with the predetermined reference positions as the references.

The control unit100controls each of the above-described components of the processing apparatus30to cause the processing apparatus30to perform a processing operation on the wafer1. Note that the control unit100is a computer that includes an arithmetic processing device including a microprocessor such as a central processing unit (CPU), a storage device including a memory such as a read only memory (ROM) or a random access memory (RAM), and an input/output interface device. In the arithmetic processing device of the control unit100, the arithmetic processing device performs arithmetic processing according to a computer program stored in the storage device and outputs a control signal for controlling the processing apparatus30to the above-described components of the processing apparatus30via the input/output interface device.

In addition, the processing apparatus30is connected to a display unit (not illustrated), which is connected to the control unit100and configured using a liquid crystal display device or the like that displays a state of the processing operation, an image, and the like, and an input unit which is connected to the control unit100and used when an operator registers processing content information or the like. In the first embodiment, the input unit includes at least one of a touch panel provided on the display unit and an external input device such as a keyboard.

Mark Formation Step

FIG.5is a plan view of the wafer after the mark formation step of the method of processing a wafer illustrated inFIG.2as viewed from the back surface side.FIG.6is a plan view of another example of the wafer illustrated inFIG.5as viewed from the back surface side. The mark formation step1002is a step of forming the marks13indicating the positions of the planned dividing lines6of the wafer1on the back surface8.

In the first embodiment, in the mark formation step1002, in the processing apparatus30, a processing condition is registered in the control unit100by the operator, and the front surface3side of the wafer1before being subjected to cutting after the tape arrangement step1001is placed on the holding surface441of the holding table42positioned in the loading and unloading area with the tape11interposed therebetween. In the first embodiment, the processing apparatus30starts the processing operation, that is, the mark formation step1002when the control unit100receives an instruction to start the processing operation from the operator in the mark formation step1002.

In the first embodiment, in the mark formation step1002, when the processing apparatus30starts the processing operation, the control unit100causes the front surface3side of the wafer1to be sucked and held onto the holding surface441with the tape11interposed therebetween to expose the back surface8of the wafer1upward. In the first embodiment, in the mark formation step1002, the control unit100of the processing apparatus30controls the X-axis moving unit61and the Y-axis moving unit62to position the lower imaging unit80below the wafer1held by the holding portion44of the holding table42.

In the first embodiment, in the mark formation step1002, the control unit100of the processing apparatus30causes the lower imaging unit80to capture an image of the wafer1from below through the holding portion44and the tape11, acquires the image obtained by the capturing, and detects the planned dividing lines6from the acquired image. In the first embodiment, in the mark formation step1002, the control unit100of the processing apparatus30controls the X-axis moving unit61and the Y-axis moving unit62such that the condenser lens of the laser beam irradiation unit50and a position at which the mark13determined in the processing condition is to be formed on the back surface8based on positions of the detected planned dividing lines6face each other in the Z-axis direction.

In the first embodiment, in the mark formation step1002, the control unit100of the processing apparatus30controls the X-axis moving unit61to move the holding table42in the X-axis direction and causes the laser beam irradiation unit50to irradiate the position on the back surface8where the mark13determined in the processing condition is to be formed with a laser beam. Then, the metal layer9at the position irradiated with the laser beam on the back surface8of the wafer1is subjected to ablation to form the mark13as a groove. In this manner, in the mark formation step1002of the first embodiment, the processing apparatus30forms the marks13based on the planned dividing lines6detected by imaging of the lower imaging unit80.

Note that, in the first embodiment, in the mark formation step1002, as illustrated inFIG.5, the processing apparatus30forms the mark13in the outer peripheral marginal area5of the back surface8of the wafer1and on an extension line of the center in the width direction of the planned dividing lines6. In addition, in the first embodiment, in the mark formation step1002, the processing apparatus30forms the marks13on the extension lines of centers in the width direction of the planned dividing lines6every predetermined number of the planned dividing lines6. In addition, in the present disclosure, in the mark formation step1002, the processing apparatus30may form the marks13on the extension lines of the centers in the width direction of all the planned dividing lines6in the outer peripheral marginal area5of the back surface8of the wafer1.

In addition, in the present disclosure, in the mark formation step1002, as illustrated inFIG.6, the processing apparatus30may form cross-shaped marks13at intersections among the planned dividing lines6in the device area4on the back surface8of the wafer1. In this manner, in the present disclosure, in the mark formation step1002, the marks13may be formed in the cross shape and formed at positions corresponding to the intersections among the planned dividing lines6.

In addition, in the present disclosure, the marks13are formed on the extension lines of the centers in the width direction of every predetermined number of the planned dividing lines6in the outer peripheral marginal area5on the back surface8of the wafer1or at the positions corresponding to the intersections among the planned dividing lines6in the mark formation step1002, and thus, are formed in areas that correspond to the planned dividing lines6and are to be removed in the dicing step1003.

Dicing Step

FIG.7is a perspective view schematically illustrating the dicing step of the method of processing a wafer illustrated inFIG.2. The dicing step1003is a step of dicing the wafer1from the back surface8side using the marks13formed in the mark formation step1002as references to divide the wafer1into the individual chips10.

In the first embodiment, in the dicing step1003, a cutting apparatus90illustrated inFIG.7sucks and holds the front surface3side of the wafer1on a holding surface of a holding table (not illustrated) with the tape11interposed therebetween, and clamps the frame12with a clamp unit (not illustrated) around the holding table. In the first embodiment, in the dicing step1003, the cutting apparatus90captures an image of the back surface8side of the wafer1held on the holding surface of the holding table with an imaging unit (not illustrated), and detects the marks13from the image obtained by the capturing.

In the first embodiment, in the dicing step1003, the cutting apparatus90performs alignment for aligning a cutting blade92of a cutting unit91and the planned dividing line6of the wafer1based on positions of the detected marks13, an interval between the planned dividing lines6, and the like. In the first embodiment, in the dicing step1003, as illustrated inFIG.7, the cutting apparatus90performs cutting on the wafer1along the planned dividing lines6to divide the wafer1into the individual chips10by causing the cutting blade92rotating about an axis to be cut into the planned dividing line6of the wafer1until reaching the tape11while relatively moving the cutting blade92of the cutting unit91and the wafer1along the planned dividing lines6.

In the first embodiment, in the dicing step1003, when the cutting is performed on all the planned dividing lines6of the wafer1, the cutting apparatus90retracts the cutting unit91from the wafer1and moves the holding table to the loading and unloading area. In the first embodiment, in the dicing step1003, the cutting apparatus90stops the suction and holding of the holding table positioned in the loading and unloading area, releases the clamping of the frame12by the clamp unit, and ends the processing operation, that is, the dicing step1003.

In the method of processing a wafer according to the first embodiment described above, the marks13indicating the planned dividing lines6are formed on the metal layer9laminated on the back surface8of the wafer1before the dicing step1003.

For this reason, in the method of processing a wafer according to the first embodiment, the positions of the planned dividing lines6can be identified even if the front surface3side of the wafer1is bonded to the tape11to prevent foreign matter from adhering to the devices7, and the metal layer9is formed on the back surface8side of the wafer1.

As a result, in the method of processing a wafer according to the first embodiment, the cutting can be easily performed on the planned dividing lines6even in the wafer1in which the front surface3side of the wafer1is bonded to the tape11in order to prevent foreign matter from adhering to the devices7and the metal layer is laminated on the back surface8side.

According to the present disclosure, it is possible to easily process a planned dividing line even in a wafer including a metal layer laminated on a back surface side.