JP7321639B2 - Wafer processing method - Google Patents

Description

The present invention relates to a wafer processing method for dividing a wafer, in which a plurality of devices are formed in respective regions of a surface partitioned by dividing lines, into individual device chips.

2. Description of the Related Art In the manufacturing process of device chips used in electronic devices such as mobile phones and personal computers, first, a plurality of intersecting dividing lines (streets) are set on the surface of a wafer made of a material such as a semiconductor. Then, devices such as ICs (Integrated Circuits), LSIs (Large-Scale Integrated circuits), LEDs (Light Emitting Diodes), etc. are formed in the regions defined by the division lines.

After that, an adhesive tape called a dicing tape, which is attached to an annular frame having an opening so as to close the opening, is attached to the back surface of the wafer, and the wafer, the adhesive tape, and the annular frame are integrated. form a frame unit. Then, by processing and dividing the wafer contained in the frame unit along the planned division lines, individual device chips are formed.

A cutting device, for example, is used to divide the wafer. The cutting device includes a chuck table that holds the wafer via an adhesive tape, a cutting unit that cuts the wafer, and the like. The cutting unit includes a cutting blade having an annular grindstone portion, and a spindle penetrating through a central through hole of the cutting blade and rotating the cutting blade.

When cutting a wafer, the frame unit is placed on the chuck table, the wafer is held by the chuck table via adhesive tape, the cutting blade is rotated by rotating the spindle, and the cutting unit is moved to a predetermined height. lower into position. Then, the chuck table and the cutting unit are relatively moved along the direction parallel to the upper surface of the chuck table, and the cutting blade cuts the wafer along the dividing lines. The wafer is then divided.

After that, the frame unit is carried out from the cutting device, the adhesive tape is subjected to treatment such as irradiation with ultraviolet rays to reduce the adhesive strength of the adhesive tape, and the device chip is picked up. As a processing apparatus with high device chip production efficiency, there is known a cutting apparatus that can continuously divide a wafer and irradiate an adhesive tape with ultraviolet light (see Patent Document 1). The device chip picked up from the adhesive tape is mounted on a predetermined wiring board or the like.

Japanese Patent No. 3076179

When a wafer is cut by a cutting device to form dividing grooves along streets, defects such as chipping may be formed around the dividing grooves. If a device chip to be formed has chipping of an amount exceeding the allowable range, the performance of the device chip is impaired. Therefore, there is a demand to observe the device chips formed after cutting the wafer to check whether chipping has occurred or whether the size is within the allowable range even if chipping has occurred. be.

By the way, the adhesive tape includes, for example, a base layer formed of a vinyl chloride sheet or the like, and an adhesive layer provided on the base layer. When the wafer is cut to form dividing grooves along the streets and the back side of the formed device chips is observed, the device chips are observed through the adhesive tape. However, the adhesive tape contains a glue layer, and the glue contained in the glue layer scatters light and obstructs the field of view, so there is a problem that the back side of the device chip cannot be clearly observed.

SUMMARY OF THE INVENTION The present invention has been made in view of such problems, and its object is to provide a wafer processing method capable of clearly observing the back side of a device chip to be formed and confirming the state of the dividing grooves with high accuracy. is to provide

According to one aspect of the present invention, there is provided a wafer processing method for dividing a wafer formed in respective regions of a surface partitioned by dividing lines into individual device chips, in which a plurality of devices are accommodated. A thermocompression sheet disposing step of positioning a wafer in the opening of a frame having an opening and arranging a thermocompression bonding sheet having no glue layer on the back surface of the wafer and the outer periphery of the frame; and heating the thermocompression bonding sheet. Then, an integration step of integrating the wafer and the frame via the thermocompression sheet by thermocompression bonding, and cutting the wafer along the planned division line using a cutting device equipped with a rotatable cutting blade. a dividing step of forming dividing grooves to divide the wafer into individual device chips; Disposing a transparent plate through a liquid in a region overlapping the region thermocompressed to the wafer on the first surface, observing the back side of the device chip through the transparent plate and the thermocompression sheet, and a backside observation step of checking the state of the dividing grooves.

Preferably, in the rear surface observation step, the liquid is water and the transparent plate is a glass plate.

Further, preferably, in the back surface observation step, an image showing the back surface of the device chip is acquired by an imaging unit.

Moreover, preferably, the thermocompression-bonded sheet is either a polyolefin-based sheet or a polyester-based sheet.

Moreover, preferably, the polyolefin-based sheet is any one of a polyethylene sheet, a polypropylene sheet, and a polystyrene sheet, and the polyester-based sheet is either a polyethylene terephthalate sheet or a polyethylene naphthalate sheet.

Preferably, in the integration step, the heating temperature is 120° C. to 140° C. when the polyolefin sheet is the polyethylene sheet, and the heating temperature is 160° C. when the polyolefin sheet is the polypropylene sheet. ° C. to 180° C. When the polyolefin sheet is the polystyrene sheet, the heating temperature is 220° C. to 240° C. When the polyester sheet is the polyethylene terephthalate sheet, the heating temperature is 250° C. to 270° C. °C, and the heating temperature is 160°C to 180°C when the polyester sheet is the polyethylene naphthalate sheet.

Also preferably, the wafer is made of Si, GaN, GaAs, or glass.

In the method for processing a wafer according to one aspect of the present invention, when forming the frame unit, the adhesive tape having a glue layer is not used, and the frame and the wafer are joined using a polyolefin-based sheet having no glue layer. unify. The integration step of integrating the frame and the wafer via the polyolefin-based sheet is realized by thermocompression bonding. After performing the integration process, the wafer is cut by a cutting blade to divide the wafer into individual device chips.

After that, the back side of the device chip formed by dividing the wafer is observed through the thermocompression sheet. Then, the condition of the dividing groove is checked to confirm whether chipping is formed around the dividing groove, and if chipping is formed, whether the size of the chipping exceeds the allowable range.

By the way, in the integration process, when forming the frame unit, for example, a thermocompression bonding sheet wound into a roll is pulled out and used. The surface of the thermocompression-bonded sheet is not flattened so as not to adhere to each other when wound into a roll. If the second surface of the thermocompression sheet, which is opposite to the first surface thermocompression bonded to the wafer, is not flat, the second surface of the thermocompression bonding sheet may not be flat even if the back side of the device chip is observed through the thermocompression bonding sheet. Light scattering occurs on the surface. In this case, the back side of the device chip cannot be clearly observed.

Therefore, in a wafer processing method according to an aspect of the present invention, a transparent plate is provided on the second surface of the thermocompression sheet via a liquid, and the transparent plate and the thermocompression sheet are passed through. The back surface of the device chip is observed to confirm the state of the dividing groove. Even if the second surface side of the thermocompression bonding sheet is not flat, if the transparent plate is arranged on the second surface with the liquid interposed therebetween, the liquid is formed between the second surface and the transparent plate. is filled with air and the air is expelled. Therefore, light is less likely to scatter on the second surface, and the back side of the device chip can be clearly observed, so that the presence or absence of chipping can be confirmed with high accuracy.

Therefore, according to one aspect of the present invention, there is provided a wafer processing method that enables the back side of a device chip to be formed to be clearly observed and the state of the dividing grooves to be confirmed with high accuracy.

It is a perspective view which shows a wafer typically. FIG. 4 is a perspective view schematically showing how the wafer and frame are positioned on the holding surface of the chuck table; It is a perspective view which shows typically a thermocompression-bonding sheet|seat arrangement|positioning process. It is a perspective view which shows an example of an integration process typically. It is a perspective view which shows an example of an integration process typically. It is a perspective view which shows an example of an integration process typically. FIG. 7A is a perspective view schematically showing how the thermocompression sheet is cut, and FIG. 7B is a perspective view schematically showing the formed frame unit. It is a perspective view which shows a division process typically. FIG. 4 is a perspective view schematically showing how a transparent plate is arranged on a thermocompression sheet with a liquid interposed therebetween. FIG. 10A is a perspective view schematically showing the back surface observation process, and FIG. 10B is a cross-sectional view schematically showing the back surface observation process.

An embodiment according to one aspect of the present invention will be described with reference to the accompanying drawings. First, a wafer to be processed by the wafer processing method according to the present embodiment will be described. FIG. 1 is a perspective view schematically showing a wafer 1. FIG.

The wafer 1 is made of materials such as Si (silicon), SiC (silicon carbide), GaN (gallium nitride), GaAs (gallium arsenide), or other semiconductors, or materials such as sapphire, glass, or quartz. It is a substantially disc-shaped substrate or the like made of. Examples of the glass include alkali glass, alkali-free glass, soda-lime glass, lead glass, borosilicate glass, and quartz glass.

The front surface 1a of the wafer 1 is partitioned by a plurality of dividing lines 3 arranged in a lattice. Further, devices 5 such as ICs, LSIs, and LEDs are formed in respective regions defined by dividing lines 3 on the front surface 1a of the wafer 1 . In the method for processing the wafer 1 according to the present embodiment, the wafer 1 is cut along the dividing lines 3 to be divided into individual device chips.

A wafer 1 is cut by a cutting device. Before carrying the wafer 1 into the cutting apparatus, the wafer 1, the thermocompression bonding sheet and the frame are integrated to form a frame unit. The wafer 1 is carried into the cutting device in the state of the frame unit and cut. Each formed device chip is supported by a thermocompression sheet. After that, the thermocompression sheet is expanded to widen the space between the device chips, and the device chips are picked up by a pick-up device. At this time, the thermocompression sheet also functions as a dicing tape.

The annular frame 7 (see FIG. 2, etc.) is made of a material such as metal, and has an opening 7a with a diameter larger than the diameter of the wafer 1 . When forming the frame unit, the wafer 1 is positioned within the opening 7a of the frame 7 and accommodated in the opening 7a.

The thermocompression sheet 9 (see FIG. 3, etc.) is, for example, a flexible resin-based sheet such as a polyolefin-based sheet or a polyester-based sheet. The thermocompression sheet 9 has a diameter larger than the outer diameter of the frame 7 and does not have a glue layer. Moreover, the thermocompression-bonded sheet 9 is a sheet having thermoplasticity.

Here, the polyolefin-based sheet is a polymer sheet synthesized using alkene as a monomer. The polyolefin-based sheet used for the thermocompression-bonding sheet 9 is, for example, a sheet transparent or translucent to visible light, such as a polyethylene sheet, a polypropylene sheet, or a polystyrene sheet.

A polyester sheet is a polymer sheet synthesized using a dicarboxylic acid (a compound having two carboxyl groups) and a diol (a compound having two hydroxyl groups) as monomers. The polyester-based sheet used for the thermocompression-bonding sheet 9 is, for example, a sheet transparent or translucent to visible light, such as a polyethylene terephthalate sheet or a polyethylene naphthalate sheet.

Since the thermocompression sheet 9 does not have a glue layer, it cannot be attached to the wafer 1 and the frame 7 at room temperature. However, the thermocompression-bonding sheet 9 has thermoplasticity, and when heated to a temperature near the melting point while being bonded to the wafer 1 and the frame 7 while applying a predetermined pressure, the sheet 9 partially melts to melt the wafer 1 and the frame 7 . can be adhered to Therefore, in the method for processing the wafer 1 according to the present embodiment, the wafer 1, the frame 7, and the thermocompression bonding sheet 9 are integrated by thermocompression bonding as described above to form a frame unit.

Next, each step of the method for processing the wafer 1 according to this embodiment will be described. First, in preparation for integrating the wafer 1, the thermocompression sheet 9, and the frame 7, a thermocompression sheet disposing process is carried out. FIG. 2 is a perspective view schematically showing how the wafer 1 and the frame 7 are positioned on the holding surface 2a of the chuck table (vacuum table) 2. FIG. As shown in FIG. 2, the process of disposing the thermocompression-bonded sheets is performed on a chuck table 2 having a holding surface 2a on its top.

The chuck table 2 has a porous member having a diameter larger than the outer diameter of the frame 7 at the center of the upper portion. The upper surface of the porous member serves as the holding surface 2a of the chuck table 2. As shown in FIG. As shown in FIG. 3, the chuck table 2 has therein an exhaust path, one end of which communicates with the porous member, and a suction source 2b is arranged on the other end of the exhaust path. The exhaust path is provided with a switching portion 2c for switching between a connected state and a disconnected state. Pressure is applied, and the object to be held is held by suction on the chuck table 2 .

In the thermocompression sheet placement step, first, the wafer 1 and the frame 7 are placed on the holding surface 2a of the chuck table 2, as shown in FIG. At this time, the wafer 1 is positioned in the opening 7a of the frame 7 with the front surface 1a side of the wafer 1 facing downward. Next, a thermocompression sheet 9 is arranged on the rear surface 1b of the wafer 1 and the outer circumference of the frame 7. As shown in FIG. FIG. 3 is a perspective view schematically showing a process of disposing a thermocompression-bonded sheet. As shown in FIG. 3, a thermocompression sheet 9 is placed over the wafer 1 and the frame 7 so as to cover them.

In addition, in the thermocompression-bonding sheet disposing process, the thermocompression-bonding sheet 9 having a larger diameter than the holding surface 2a of the chuck table 2 is used. When applying the negative pressure from the chuck table 2 to the thermocompression sheet 9 in the integration process to be performed later, if the entire holding surface 2a is not covered with the thermocompression sheet 9, the negative pressure will leak through the gap. , the thermocompression sheet 9 cannot be properly applied with pressure.

In the method for processing the wafer 1 according to the present embodiment, next, the thermocompression sheet 9 is heated, and an integration step is performed in which the wafer 1 and the frame 7 are integrated via the thermocompression sheet 9 by thermocompression bonding. do. FIG. 4 is a perspective view schematically showing an example of the integration process. In FIG. 4, broken lines indicate what can be seen through the thermocompression sheet 9 which is transparent or translucent to visible light.

In the integration process, first, the switching portion 2c of the chuck table 2 is operated to bring the suction source 2b into a communication state in which it is connected to the porous member above the chuck table 2, and the negative pressure from the suction source 2b is applied to the thermocompression bonding sheet 9. act. Then, the thermocompression sheet 9 is brought into close contact with the wafer 1 and the frame 7 by the atmospheric pressure.

Next, the thermocompression bonding is performed by heating the thermocompression bonding sheet 9 while sucking the thermocompression bonding sheet 9 with the suction source 2b. Heating of the thermocompression-bonding sheet 9 is performed, for example, by a heat gun 4 arranged above the chuck table 2 as shown in FIG.

The heat gun 4 includes a heating means such as a heating wire and a blowing mechanism such as a fan, and can heat and jet air. While applying a negative pressure to the thermocompression bonding sheet 9 , the heat gun 4 supplies hot air 4 a to the thermocompression bonding sheet 9 from above to heat the thermocompression bonding sheet 9 to a predetermined temperature. It is thermo-compressed.

Moreover, the heating of the thermocompression bonding sheet 9 may be performed by another method, for example, by pressing the wafer 1 and the frame 7 from above with a member heated to a predetermined temperature. FIG. 5 is a perspective view schematically showing another example of the integration process. In FIG. 5, the dashed lines indicate what can be seen through the thermocompression sheet 9 that is transparent or translucent to visible light.

In the integration step shown in FIG. 5, for example, a heat roller 6 having an internal heat source is used. In the integration step shown in FIG. 5 as well, first, a negative pressure is applied to the thermocompression bonding sheet 9 by the suction source 2b, and the thermocompression bonding sheet 9 is brought into close contact with the wafer 1 and the frame 7 by the atmospheric pressure.

After that, the heat roller 6 is heated to a predetermined temperature and placed on one end of the holding surface 2 a of the chuck table 2 . Then, the heat roller 6 is rotated to roll the heat roller 6 on the chuck table 2 from the one end to the other end. Then, the thermocompression sheet 9 is thermocompression bonded to the wafer 1 and the frame 7 . At this time, if the heat roller 6 applies a force in the direction of pushing down the thermocompression bonding sheet 9, the thermocompression bonding is performed with a pressure higher than the atmospheric pressure. Incidentally, it is preferable to coat the surface of the heat roller 6 with a fluororesin.

Further, the thermocompression bonding of the thermocompression bonding sheet 9 may be performed by using an iron-like pressing member having an internal heat source and a flat bottom plate instead of the heat roller 6 . In this case, the pressing member is heated to a predetermined temperature to serve as a hot plate, and the thermocompression bonding sheet 9 held on the chuck table 2 is pressed from above by the pressing member.

Heating of the thermocompression-bonding sheet 9 may be performed by other methods. FIG. 6 is a perspective view schematically showing still another example of the integration process. In FIG. 6, the dashed lines indicate what can be seen through the thermocompression sheet 9 which is transparent or translucent to visible light. In the integration step shown in FIG. 6, the thermocompression bonding sheet 9 is heated using an infrared lamp 8 arranged above the chuck table 2 . The infrared lamp 8 can irradiate infrared rays 8a having a wavelength that at least the material of the thermocompression bonding sheet 9 absorbs.

In the integration step shown in FIG. 6 as well, first, a negative pressure is applied to the thermocompression sheet 9 by the suction source 2b to bring the thermocompression sheet 9 into close contact with the wafer 1 and the frame 7. As shown in FIG. Next, the infrared lamp 8 is operated to irradiate the thermocompression sheet 9 with infrared rays 8a to heat the thermocompression sheet 9 . Then, the thermocompression sheet 9 is thermocompression bonded to the wafer 1 and the frame 7 .

When the thermocompression bonding sheet 9 is heated to a temperature near its melting point by any method, the thermocompression bonding sheet 9 is thermocompression bonded to the wafer 1 and the frame 7 . After the thermocompression bonding sheet 9 is thermocompression bonded, the switching portion 2c is operated to release the state of communication between the porous member of the chuck table 2 and the suction source 2b, and the adsorption by the chuck table 2 is released.

Next, the thermocompression sheet 9 protruding from the outer circumference of the frame 7 is cut and removed. FIG. 7A is a perspective view schematically showing how the thermocompression bonding sheet 9 is cut. For cutting, an annular cutter 10 is used as shown in FIG. 7(A). The cutter 10 has a through hole and is rotatable around a rotating shaft that passes through the through hole.

First, the annular cutter 10 is positioned above the frame 7 . At this time, the rotating shaft of the cutter 10 is aligned with the chuck table 2 in the radial direction. Next, the cutter 10 is lowered to sandwich the thermocompression sheet 9 between the frame 7 and the cutter 10 to cut the thermocompression sheet 9 . Then, cut marks 9 a are formed on the thermocompression sheet 9 .

Further, the cutter 10 is made to go around the opening 7a of the frame 7 along the frame 7, so that a predetermined area of the thermocompression bonding sheet 9 is surrounded by the cut marks 9a. Then, the thermocompression sheet 9 is removed from the area on the outer peripheral side of the cut mark 9a so as to leave the area of the thermocompression sheet 9. As shown in FIG. Then, unnecessary portions of the thermocompression bonding sheet 9 including the region protruding from the outer periphery of the frame 7 can be removed.

An ultrasonic cutter may be used for cutting the thermocompression-bonded sheet, and a vibration source for vibrating the annular cutter 10 at a frequency in the ultrasonic band may be connected to the cutter 10 . When cutting the thermocompression sheet 9, the thermocompression sheet 9 may be cooled and hardened to facilitate cutting. As described above, the frame unit 11 in which the wafer 1 and the frame 7 are integrated via the thermocompression sheet 9 is formed. FIG. 7B is a perspective view schematically showing the formed frame unit 11. As shown in FIG.

It should be noted that the thermocompression sheet 9 is preferably heated to a temperature below its melting point when performing the thermocompression bonding. This is because if the heating temperature exceeds the melting point, the thermocompression-bonded sheet 9 may melt and become unable to maintain its shape. Also, the thermocompression-bonded sheet 9 is preferably heated to a temperature equal to or higher than its softening point. This is because thermocompression bonding cannot be properly performed unless the heating temperature reaches the softening point. That is, the thermocompression sheet 9 is preferably heated to a temperature above its softening point and below its melting point.

Furthermore, some thermocompression sheets 9 may not have a clear softening point. Therefore, when the thermocompression bonding is performed, the thermocompression sheet 9 is preferably heated to a temperature higher than or equal to a temperature lower than the melting point by 20° C. and a temperature lower than the melting point.

Further, for example, when the polyolefin sheet used as the thermocompression sheet 9 is a polyethylene sheet, the heating temperature is preferably 120.degree. C. to 140.degree. Further, when the polyolefin sheet is a polypropylene sheet, the heating temperature is preferably 160.degree. C. to 180.degree. Furthermore, when the polyolefin sheet is a polystyrene sheet, the heating temperature is preferably 220.degree. C. to 240.degree.

Furthermore, for example, when the polyester sheet used as the thermocompression sheet 9 is a polyethylene terephthalate sheet, the heating temperature is set to 250.degree. C. to 270.degree. When the polyester sheet is a polyethylene naphthalate sheet, the heating temperature is 160.degree. C. to 180.degree.

Here, the heating temperature refers to the temperature of the thermocompression bonding sheet 9 during the integration process. For example, a heat source such as a heat gun 4, a heat roller 6, an infrared lamp 8, etc., has been put to practical use with a model capable of setting the output temperature. In some cases, the temperature of 9 does not reach the set output temperature. Therefore, in order to heat the thermocompression sheet 9 to a predetermined temperature, the output temperature of the heat source may be set higher than the melting point of the thermocompression sheet 9 .

Next, in the method for processing the wafer 1 according to the present embodiment, a dividing step is performed in which the wafer 1 in the state of the frame unit 11 is cut by a cutting blade to be divided. A division process is implemented with the cutting apparatus shown, for example in FIG. FIG. 8 is a perspective view schematically showing the dividing step.

The cutting device 12 includes a cutting unit 14 that cuts the workpiece, and a chuck table (not shown) that holds the workpiece. The cutting unit 14 includes a cutting blade 18 having an annular grindstone portion, and a spindle (not shown) whose tip side is passed through a central through hole of the cutting blade 18 and rotates the cutting blade 18 . The cutting blade 18 includes, for example, an annular base having the through hole in the center, and an annular grindstone portion provided on the outer peripheral portion of the annular base.

The proximal end of the spindle is connected to a spindle motor (not shown) housed inside the spindle housing 16, and the cutting blade 18 can be rotated by operating the spindle motor.

When the cutting blade 18 cuts the workpiece, heat is generated due to friction between the cutting blade 18 and the workpiece. In addition, when the workpiece is cut, chips are generated from the workpiece. Therefore, in order to remove the heat and chips generated by cutting, cutting water such as pure water is supplied to the cutting blade 18 and the workpiece while the workpiece is being cut. The cutting unit 14 includes, for example, a cutting water supply nozzle 20 that supplies cutting water to the cutting blade 18 or the like on the side of the cutting blade 18 .

When cutting the wafer 1 , the frame unit 11 is placed on the chuck table, and the wafer 1 is held on the chuck table via the thermocompression sheet 9 . Then, the chuck table is rotated to align the dividing line 3 of the wafer 1 with the processing feed direction of the cutting device 12 . Also, the relative positions of the chuck table and the cutting unit 14 are adjusted so that the cutting blade 18 is disposed above the extension line of the dividing line 3 .

The cutting blade 18 is then rotated by rotating the spindle. Then, the cutting unit 14 is lowered to a predetermined height position, and the chuck table and the cutting unit 14 are relatively moved along the direction parallel to the upper surface of the chuck table. Then, the grindstone portion of the rotating cutting blade 18 comes into contact with the wafer 1 and cuts the wafer 1 to form dividing grooves 3 a along the dividing lines 3 in the wafer 1 .

After performing cutting along one planned division line 3, the chuck table and the cutting unit 14 are moved in the index feed direction perpendicular to the processing feed direction, and the wafer 1 is similarly cut along the other planned division line 3. Carry out cutting. After cutting along all the planned dividing lines 3 along one direction, the chuck table is rotated around the axis perpendicular to the holding surface, and similarly along the planned dividing lines 3 along the other direction. to cut the wafer 1. When the wafer 1 is cut along all the dividing lines 3 of the wafer 1, the dividing process is completed.

The cutting device 12 may include a cleaning unit (not shown) near the cutting unit 14 . The wafer 1 cut by the cutting unit 14 may be transported to the cleaning unit and cleaned by the cleaning unit. For example, the cleaning unit includes a cleaning table that holds the frame unit 11 and a cleaning water supply nozzle that can reciprocate above the frame unit 11 .

The cleaning table is rotated around an axis perpendicular to the holding surface, and while the cleaning liquid such as pure water is being supplied to the wafer 1 from the cleaning water supply nozzle, the cleaning water supply nozzle is reciprocated along a path passing above the center of the holding surface. When moved, the front surface 1a side of the wafer 1 can be cleaned.

When the dividing process is performed, the wafer 1 is divided into individual device chips. The formed device chip is supported by the thermocompression sheet 9 . When cutting the wafer 1, the cutting unit 14 is set at a predetermined height so that the height position of the lower end of the cutting blade 18 is lower than the back surface 1b of the wafer 1 in order to divide the wafer 1 reliably. It is positioned as Therefore, when the wafer 1 is cut, the thermocompression bonding sheet 9 is also cut, and cutting debris originating from the thermocompression bonding sheet 9 is generated.

When an adhesive tape is used instead of the thermocompression sheet 9 for the frame unit 11, cutting waste is generated due to the glue layer of the adhesive tape. In this case, the cutting waste is taken in by the cutting water jetted from the cutting water supply nozzle 20 and spread over the surface 1 a of the wafer 1 . Cutting debris originating from the glue layer is likely to reattach to the surface of the device 5, and it is not easy to remove it in a cleaning process or the like of the wafer 1 performed after cutting. Adhesion of shavings derived from the adhesive layer causes a problem of deterioration in the quality of the formed device chip.

On the other hand, in the method of processing the wafer 1 according to the present embodiment, the thermocompression sheet 9 having no glue layer is used instead of the adhesive tape having the glue layer on the frame unit 11 . Even if shavings originating from the thermocompression bonding sheet 9 are generated and taken into the cutting water and diffused on the surface of the wafer, the shavings do not adhere to the wafer 1 and are more reliably removed in the subsequent washing process. be done. Therefore, deterioration in quality of the device chip due to the shavings is suppressed.

Further, when the wafer 1 is cut by the cutting device 12 to form the dividing grooves 3a along the dividing lines 3, defects such as chipping may be formed in the device chips around the dividing grooves 3a. If a device chip has chipping of an amount that exceeds the allowable range, the performance of the device chip is compromised. Therefore, after the division step is performed, the formed device chips are observed to confirm whether chipping has occurred or whether the chipping has a size within an allowable range even if chipping has occurred.

When checking the presence or absence of chipping on the back side of the device chip, the back side is observed through the thermocompression sheet 9 . For example, when an adhesive tape provided with an adhesive layer is used instead of the thermocompression sheet 9 for the frame unit 11, the back side is observed through the adhesive tape.

However, since the adhesive tape includes a glue layer, and the glue contained in the glue layer obstructs the field of view, the back side of the device chip cannot be clearly observed. On the other hand, in the method for processing the wafer 1 according to the present embodiment, the frame unit 11 uses the thermocompression sheet 9 that does not contain the glue layer, so the glue layer does not obstruct the field of view.

However, in the above-described integration process, when forming the frame unit 11, for example, the thermocompression bonding sheet 9 wound in a roll shape is pulled out and used. The surface of the thermocompression-bonding sheet 9 is not flattened so as not to adhere to each other when wound into a roll. If the second surface of the thermocompression bonding sheet 9 opposite to the first surface thermocompression bonded to the wafer 1 is not flat, the second surface of the thermocompression bonding sheet 9 may not be flat even if the back side of the device chip is observed through the thermocompression bonding sheet 9 . Light scattering occurs on the surface of the device chip, and the back side of the device chip cannot be observed clearly.

The thermocompression sheet 9 has, for example, unevenness of about 10 to 20 μm on the second surface, and the unevenness causes light scattering. Therefore, in the method for processing the wafer 1 according to the present embodiment, when performing the back surface observation step of observing the back surface side of the device chip, the first surface of the second surface of the thermocompression bonding sheet 9 is observed. A transparent plate is disposed in a region overlapping with the region thermally bonded to the wafer 1 of . At this time, a liquid is provided between the thermocompression sheet 9 and the transparent plate. The back surface observation step will be described below.

FIG. 9 is a perspective view schematically showing how the transparent plate 22 is arranged on the thermocompression sheet 9 with the liquid 24 interposed therebetween. As shown in FIG. 9, in the back surface observation step, first, the first surface 9b side of the thermocompression sheet 9 that is thermocompression bonded to the wafer 1 faces downward, and the second surface 9c opposite to the first surface 9b is observed. side up. Next, the liquid 24 is dropped onto the thermocompression sheet 9 to apply the liquid 24 to the second surface 9c.

A disk-shaped transparent plate 22 having a diameter equal to or greater than the diameter of the wafer 1 is arranged above the frame unit 11 . At this time, the position of the transparent plate 22 is aligned above the area of the second surface 9c of the thermocompression bonding sheet 9 that overlaps the area of the first surface 9b that is thermocompression bonded to the wafer 1 . Next, the transparent plate 22 is lowered and placed on the thermocompression bonding sheet 9 with the liquid 24 interposed therebetween.

In the backside observation step, the backside of the device chip is then observed through the transparent plate 22 and the thermocompression sheet 9 to confirm the state of the dividing grooves 3a. FIG. 10A is a perspective view schematically showing the back surface observation process, and FIG. 10B is a cross-sectional view schematically showing the back surface observation process.

FIG. 10A schematically shows a perspective view of the imaging unit 26 and the frame unit 11, and an example of an image 28 captured and acquired by the imaging unit 26. FIG. In the perspective view of the frame unit 11 in FIG. 10(A), the parts of the frame unit 11 that are visible through the transparent plate 22 and the thermocompression sheet 9 are indicated by broken lines.

When the transparent plate 22 is not arranged on the second surface 9c of the thermocompression sheet 9, light is scattered on the second surface due to the uneven shape of the second surface 9c. This is because the difference in refractive index between the air and the thermocompression sheet 9 is large, and light is diffusely reflected in a complex manner due to the uneven shape of the second surface 9c. For example, even when the transparent plate 22 is arranged on the second surface 9c of the thermocompression sheet 9 without the liquid 24 interposed therebetween, an air layer is formed between the thermocompression sheet 9 and the transparent plate 22. , the light is scattered at the second surface 9c.

In contrast, in the wafer processing method according to the present embodiment, the transparent plate 22 is arranged on the second surface 9 c of the thermocompression bonding sheet 9 with the liquid 24 interposed therebetween. In this case, as shown in FIG. 10B, air between the thermocompression sheet 9 and the transparent plate 22 is eliminated by the liquid 24, and the gap between the thermocompression sheet 9 and the transparent plate 22 is filled with the liquid 24. Here, the difference in refractive index between the liquid 24 and the thermocompression sheet 9 is smaller than the difference in refractive index between the air and the thermocompression sheet 9 . Therefore, the second surface 9c, which is the interface between the liquid 24 and the thermocompression sheet 9, is less likely to scatter light.

The transparent plate 22 is, for example, a transparent plate-like object such as a glass plate, a quartz plate, an acrylic plate, or the like. The transparent plate 22 has, for example, a flattened main surface. The liquid 24 is, for example, pure water, water mixed with a surfactant, silicone oil, glycerin, or the like. When the liquid 24 is sandwiched between the second surface 9c of the thermocompression sheet 9 and the transparent plate 22, the liquid 24 quickly fills the space between the two and eliminates the air present in the space. In addition, it is preferable that the liquid is highly wettable to the thermocompression sheet 9 .

As illustrated in FIG. 10A, the image 28 captured by the imaging unit 26 is a clear image. In the image 28, the dividing grooves 3a formed in the dividing step and the back surfaces 5a of the individual device chips formed by dividing the wafer 1 by the dividing grooves 3a are shown. Also, when a defect such as chipping 5b is formed at the end of the device chip around the dividing groove 3a, the defect such as chipping 5b is clearly captured in the image .

In the wafer processing method according to the present embodiment, defects such as chipping 5b formed in the device chip can be evaluated in detail, so the quality of the formed device chip can be accurately determined. Furthermore, if the defects can be evaluated in detail, it will be advantageous in selecting processing conditions for the wafer 1 in which the defects are less likely to occur.

Individual device chips that have been subjected to the back surface observation process and determined to be non-defective are then picked up from the frame unit 11 by a pick-up device and mounted on a predetermined mounting target for use. The pickup device includes, for example, an expansion mechanism that expands the thermocompression sheet 9 radially outward inside the opening 7a of the frame 7. As shown in FIG. When the expansion mechanism expands the thermocompression sheet 9 to widen the space between the individual device chips, the device chips can be easily picked up.

Further, the pick-up device may be provided with a bar-shaped push-up mechanism for pushing up individual device chips from the thermocompression bonding sheet 9 side of the frame unit 11, and an auxiliary mechanism for facilitating pick-up of the device chips is provided at the tip of the push-up mechanism. You may prepare. The auxiliary mechanism includes, for example, blowholes for blowing air onto the thermocompression-bonding sheet 9, a heating mechanism for heating the thermocompression-bonding sheet 9, a cooling mechanism for cooling the thermocompression-bonding sheet 9, and an ultrasonic wave for applying ultrasonic waves to the thermocompression-bonding sheet 9. Any of the sonic oscillators.

It should be noted that the present invention is not limited to the description of the above embodiments, and can be implemented with various modifications. For example, in the above embodiment, the case where the polyester-based sheet that can be used for the thermocompression-bonded sheet 9 is, for example, a polyethylene sheet, a polypropylene sheet, or a polystyrene sheet, but one aspect of the present invention is not limited thereto. For example, other materials may be used for the polyolefin-based sheet, such as copolymers of propylene and ethylene, olefin-based elastomers, and the like.

Further, for example, in the above-described embodiment, the polyester-based sheet that can be used as the thermocompression-bonded sheet 9 is, for example, a polyethylene terephthalate sheet or a polyethylene naphthalate sheet, but one aspect of the present invention is limited to this. not. For example, other materials may be used for the polyester-based sheet, such as a polytrimethylene terephthalate sheet, a polybutylene terephthalate sheet, a polybutylene naphthalate sheet, or the like.

Furthermore, in the above-described embodiment, the case where the liquid 24 is dropped onto the second surface 9c of the thermocompression sheet 9 to apply the liquid 24 to the second surface 9c in the back surface observation step has been described. One aspect is not limited to this. That is, in the back surface observation step, the liquid 24 may be applied to the surface of the transparent plate 22 facing the second surface 9c.

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

REFERENCE SIGNS LIST 1 wafer 1a front surface 1b back surface 3 dividing line 3a dividing groove 5 device 5a back surface of device chip 5b chipping 7 frame 7a opening 9 polyolefin sheet 9a cut mark 9b first surface 9c second surface 11 frame unit 2 chuck table 2a Holding surface 2b Suction source 2c Switching part 4 Heat gun 4a Hot air 6 Heat roller 8 Infrared lamp 8a Infrared rays 10 Cutter 12 Cutting device 14 Cutting unit 16 Spindle housing 18 Cutting blade 20 Cutting water supply nozzle 22 Transparent plate 24 Liquid 26 Imaging unit 28 Image

Claims (7)

A wafer processing method for dividing a wafer in which a plurality of devices are formed in respective regions of a surface partitioned by dividing lines into individual device chips,
a thermocompression sheet disposing step of positioning a wafer in an opening of a frame having an opening for housing the wafer, and disposing a thermocompression bonding sheet having no adhesive layer on the back surface of the wafer and the outer circumference of the frame;
an integration step of heating the thermocompression bonding sheet and integrating the wafer and the frame through the thermocompression bonding sheet by thermocompression bonding;
a dividing step of cutting the wafer along the dividing lines by using a cutting device having a rotatable cutting blade to form dividing grooves and dividing the wafer into individual device chips;
On the second surface opposite to the first surface of the thermocompression bonding sheet thermocompression bonded to the wafer, a liquid is applied to a region of the first surface that overlaps the region of the thermocompression bonding to the wafer. a backside observation step of providing a transparent plate, observing the backside of the device chip through the transparent plate and the thermocompression sheet, and confirming the state of the dividing groove;
A wafer processing method comprising: 2. The method of processing a wafer according to claim 1, wherein in said back surface observation step, said liquid is water and said transparent plate is a glass plate. 2. The method of processing a wafer according to claim 1, wherein in said back surface observation step, an image showing the back surface of said device chip is acquired by an imaging unit. 2. The wafer processing method according to claim 1, wherein said thermocompression sheet is either a polyolefin sheet or a polyester sheet. The polyolefin-based sheet is either a polyethylene sheet, a polypropylene sheet, or a polystyrene sheet,
5. The wafer processing method according to claim 4, wherein said polyester sheet is either a polyethylene terephthalate sheet or a polyethylene naphthalate sheet. In the integration step,
When the polyolefin sheet is the polyethylene sheet, the heating temperature is 120° C. to 140° C. When the polyolefin sheet is the polypropylene sheet, the heating temperature is 160° C. to 180° C. When is the polystyrene sheet, the heating temperature is 220 ° C. to 240 ° C.,
The heating temperature is 250° C. to 270° C. when the polyester sheet is the polyethylene terephthalate sheet, and the heating temperature is 160° C. to 180° C. when the polyester sheet is the polyethylene naphthalate sheet. 6. The method of processing a wafer according to claim 5. 2. The method of processing a wafer according to claim 1, wherein said wafer is made of any one of Si, GaN, GaAs and glass.

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