Processing method of wafer

A processing method of a wafer includes a modified layer forming step of positioning the focal point of a laser beam with a wavelength having transmissibility with respect to the wafer to the inside of a planned dividing line and executing irradiation along the planned dividing line to form modified layers inside and a water-soluble resin coating step of coating the front surface of the wafer with a water-soluble resin before or after the modified layer forming step. The processing method also includes a dividing step of expanding a dicing tape to divide the wafer into individual device chips together with the water-soluble resin with which the front surface of the wafer is coated and a modified layer removal step of executing plasma etching and removing the modified layers that remain at the side surfaces of the device chips in a state in which the dicing tape is expanded and the front surfaces of the individual device chips are coated with the water-soluble resin.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a processing method of a wafer for dividing, into individual device chips, the wafer on which plural devices are formed on a front surface in such a manner as to be marked out by plural planned dividing lines that intersect each other.

Description of the Related Art

A wafer on which plural devices such as integrated circuits (ICs), large-scale integration (LSI) circuits, and light emitting diodes (LEDs) are formed on a front surface in such a manner as to be marked out by plural planned dividing lines that intersect each other is divided into individual device chips by a laser processing apparatus, and the device chips obtained by the dividing are used for electrical equipment such as mobile phones and personal computers.

The laser processing apparatus includes a chuck table that holds a workpiece (wafer), a laser beam irradiation unit that irradiates the workpiece held by the chuck table with a laser beam with a wavelength having transmissibility with respect to the workpiece, an X-axis feed mechanism that executes processing feed of the chuck table and the laser beam irradiation unit relatively in an X-axis direction, and a Y-axis feed mechanism that executes processing feed of the chuck table and the laser beam irradiation unit relatively in a Y-axis direction orthogonal to the X-axis direction. The laser processing apparatus positions the focal point of the laser beam to the inside of a planned dividing line of the wafer and executes irradiation to form modified layers that serve as the points of origin of dividing inside the planned dividing lines (for example, refer to Japanese Patent Laid-open No. 2012-2604). Then, a tape that supports the back surface of the wafer is expanded and the wafer is divided into the individual device chips with use of the modified layers formed inside along the planned dividing line as the points of origin of the dividing.

SUMMARY OF THE INVENTION

In the case in which modified layers that serve as the points of origin of dividing are formed along planned dividing lines and a wafer is divided into individual device chips as described above, there is a problem that, when the wafer is divided, dust is scattered from the parts that have served as the points of origin of dividing and adheres to the front surface of devices to contaminate the devices.

Further, part of the modified layers remains at the outer circumferences (sidewalls) of the device chips. Therefore, there are problems that dust is scattered from the remaining modified layers to contaminate the device chips and the atmosphere also in steps subsequent to the dividing step, and that the flexural strength of the device chips is lowered due to the remaining of the modified layers at the sidewalls of the device chips.

Thus, an object of the present invention is to provide a processing method of a wafer in which the front surface of device chips and the atmosphere are not contaminated and the flexural strength of the device chips is not lowered.

In accordance with an aspect of the present invention, there is provided a processing method of a wafer for dividing, into individual device chips, the wafer on which a plurality of devices are formed on a front surface in such a manner as to be marked out by a plurality of planned dividing lines that intersect each other. The processing method includes a modified layer forming step of positioning a focal point of a laser beam with a wavelength having transmissibility with respect to the wafer to an inside of the planned dividing line and executing irradiation with the laser beam along the planned dividing line to form modified layers inside and a water-soluble resin coating step of coating the front surface of the wafer with a water-soluble resin, before or after the modified layer forming step. The processing method includes also a frame supporting step of sticking a back surface of the wafer to a dicing tape and supporting an outer circumference of the dicing tape by a ring frame having an opening part that houses the wafer, before or after the modified layer forming step, and a dividing step of expanding the dicing tape to divide the wafer into the individual device chips together with the water-soluble resin with which the front surface of the wafer is coated. The processing method includes also a modified layer removal step of executing plasma etching and removing the modified layers that remain at side surfaces of the device chips in a state in which the dicing tape is expanded and front surfaces of the individual device chips are coated with the water-soluble resin and a water-soluble resin removal step of removing the water-soluble resin with which the front surfaces of the device chips are coated.

In a case in which the frame supporting step is executed after the modified layer forming step, irradiation with the laser beam can be executed from a back surface side of the wafer to form the modified layers inside the planned dividing lines in the modified layer forming step. Further, in a case in which the frame supporting step is executed before the modified layer forming step, irradiation with the laser beam can be executed from a side of the dicing tape through the dicing tape to form the modified layers inside the planned dividing lines in the modified layer forming step.

Preferably, in the dividing step, the water-soluble resin is heated and softened in a case in which the dicing tape is expanded to divide the wafer into the individual device chips after the water-soluble resin solidifies. Preferably, in the dividing step, the dicing tape is expanded to divide the wafer into the individual device chips before the water-soluble resin solidifies.

According to the processing method of a wafer in accordance with the present invention, even if dust is scattered when the wafer is divided, the front surface of the wafer is shielded from the dust by the water-soluble resin, and the problem that the device chips are contaminated is solved. Further, the plasma etching is executed in the state in which the front surfaces of the device chips are protected by the water-soluble resin. Therefore, the modified layers that remain at the outer circumferences of the device chips are removed without giving damage to the device chips, and dust is not scattered in the subsequent steps. Thus, the problem that the device chips and the atmosphere are contaminated is solved. In addition, the problem that the flexural strength of the device chips lowers is also solved.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A processing method of a wafer according to an embodiment of the present invention will be described in detail below with reference to the accompanying drawings. InFIG.1, a wafer10that is a workpiece processed by the processing method of a wafer according to the present embodiment is illustrated. The wafer10is a wafer that contains silicon, sapphire, gallium arsenide, or the like as a substrate and has a circular disc shape, and plural devices12are formed on a front surface10ain such a manner as to be marked out by plural planned dividing lines14that intersect each other. The wafer10prepared in this manner is conveyed to a water-soluble resin coating apparatus20(only partly illustrated) illustrated inFIG.1and is placed and held on a spinner table18with the side of a back surface10boriented downward. The spinner table18includes a rotational drive unit that is not illustrated in the diagram and the spinner table18is rotated at high speed.

In the water-soluble resin coating apparatus20, a nozzle22that supplies a predetermined water-soluble resin24downward is disposed. The water-soluble resin24supplied from the nozzle22is a water-soluble liquid resin such as polyvinyl alcohol (PVA) or polyvinylpyrrolidone (PVP), for example.

The above-described nozzle22is positioned above the center of the spinner table18, i.e., the center of the front surface10aof the wafer10, and a predetermined amount of the water-soluble resin24is supplied downward. In addition, the spinner table18is rotated in a direction depicted by R1at, for example, 300 rpm. The water-soluble resin24is spread to the outer circumferential side of the front surface10aof the wafer10by a centrifugal force generated due to this rotation, and the whole of the front surface10aof the wafer10is coated with the water-soluble resin24as illustrated on the lower stage ofFIG.1(water-soluble resin coating step). As described later, the water-soluble resin coating step is not limited to the execution at this timing and may be executed after a modified layer forming step to be described later is executed, and it suffices that the water-soluble resin coating step is executed by the time a dividing step is executed.

Subsequently, the wafer10is conveyed to a laser processing apparatus30(only partly illustrated) illustrated inFIG.2. The laser processing apparatus30includes a holding unit including a chuck table32and a laser beam irradiation unit34that irradiates the wafer10held by the chuck table32with a laser beam LB. Further, the upper surface of the chuck table32is formed of a material having gas permeability and is connected to a suction source that is not illustrated in the diagram through the inside of the chuck table32. The laser processing apparatus30includes an X-axis feed mechanism that executes processing feed of the chuck table32and the laser beam irradiation unit34relatively in an X-axis direction, a Y-axis feed mechanism that executes indexing feed of the chuck table32and the laser beam irradiation unit34relatively in a Y-axis direction orthogonal to the X-axis direction, and a rotational drive unit that rotates the chuck table32(diagrammatic representation is omitted regarding all of them).

The wafer10conveyed to the laser processing apparatus30is placed on the upper surface of the chuck table32and is sucked and held with the side of the back surface10boriented upward. The water-soluble resin24solidifies over time and no trouble is caused even when the wafer10is held by the chuck table32. For the wafer10held by the chuck table32, an alignment step with use of an infrared irradiation unit disposed in the laser processing apparatus30and an alignment unit including an infrared camera (diagrammatic representation is omitted) is executed. Thereby, the position of the planned dividing line14formed in a predetermined direction of the front surface10ais detected, and the planned dividing line14is aligned with the X-axis direction. Information regarding the position of the detected planned dividing line14is stored in a control unit that is not illustrated in the diagram.

A beam condenser36of the laser beam irradiation unit34is positioned to the processing start position of the predetermined planned dividing line14on the basis of the position information detected by the above-described alignment step, and the focal point of the laser beam LB is positioned to the inside of the planned dividing line14that extends in a first direction of the wafer10and irradiation is executed. In addition, processing feed of the chuck table32is executed in the X-axis direction, and a modified layer100is formed inside the planned dividing line14of the wafer10. After the modified layer100has been formed along the inside of the predetermined planned dividing line14that extends in the first direction, indexing feed of the chuck table32is executed in the Y-axis direction by the interval of the planned dividing lines14, and the planned dividing line14that is adjacent in the Y-axis direction and has not yet been processed is positioned directly under the beam condenser36. Then, similarly to the above-described process, the focal point of the laser beam LB is positioned to the inside of the planned dividing line14of the wafer10and irradiation is executed, and processing feed of the chuck table32is executed in the X-axis direction to form the modified layer100inside.

Similarly, processing feed of the chuck table32is executed in the X-axis direction and indexing feed of the chuck table32is executed in the Y-axis direction to form the modified layers100inside all planned dividing lines14that extend in the first direction. Subsequently, the chuck table32is rotated by 90 degrees, and the planned dividing lines14of a second direction orthogonal to the planned dividing lines14that extend in the first direction are aligned with the X-axis direction. Then, also for the inside of each planned dividing line14, the focal point of the laser beam LB is positioned to the inside and irradiation is executed similarly to the above-described process, so that the modified layers100are formed inside all planned dividing lines14formed in the front surface10aof the wafer10(modified layer forming step).

The laser processing condition in the above-described modified layer forming step is set as follows, for example.

Average output power: 1.2 W

After the modified layer forming step has been executed as described above, the wafer10is carried out from the laser processing apparatus30. Then, the side of the front surface10acoated with the water-soluble resin24is oriented upward, and the side of the back surface10bis oriented downward and is stuck to the center of a dicing tape T illustrated inFIG.3. In addition, the outer circumference of the dicing tape T is supported by a ring frame F having an opening part Fa with a size that allows housing of the wafer10. Due to this, the wafer10is supported by the ring frame F through the dicing tape T (frame supporting step). The dicing tape T is a thin sheet that is composed of, for example, polyvinyl chloride (PVC) and has a surface on which a glue layer is formed and has expandability and contractibility.

After the wafer10has been supported by the ring frame F as described above, according to need, a heater (diagrammatic representation is omitted) is positioned above the front surface10acoated with the water-soluble resin24, and the water-soluble resin24is heated through application of hot air H thereto from the upper side as illustrated inFIG.4to soften the water-soluble resin24. Subsequently, in the state in which the water-soluble resin24is softened, the wafer10is conveyed to an expanding apparatus that is not illustrated in the diagram and that expands the dicing tape T, and the dicing tape T is expanded in a radial manner (directions depicted by arrows R2) as illustrated inFIG.5. Thereby, dividing grooves110are formed along the planned dividing lines14and the wafer10is divided into individual device chips12′ together with the water-soluble resin24with which the front surface10aof the wafer10is coated (dividing step).

After the dividing step has been executed as described above, as illustrated inFIG.6, the wafer10is conveyed, in a state in which the wafer10is supported by the ring frame F, to a plasma apparatus40regarding which detailed diagrammatic representation is omitted. A well-known plasma apparatus can be used as the plasma apparatus40. For example, the plasma apparatus40includes an etching chamber that forms a sealed space, an upper electrode and a lower electrode that are disposed in the etching chamber, a gas supply unit that jets an etching gas from the upper electrode toward the lower electrode side in the etching chamber, and so forth (diagrammatic representation is omitted regarding all of them). Here, between the upper electrode and the lower electrode, the wafer10for which the dividing step has been executed is placed with the side of the front surface10aoriented upward. Then, the etching gas is supplied into the etching chamber, and high-frequency power that generates plasma is applied to the upper electrode. Thereby, the etching gas turned to plasma is generated in the space between the upper electrode and the lower electrode, and the etching gas turned to the plasma is drawn to the side of the wafer10.

Here, the wafer10having conveyed to the plasma apparatus40through the above-described dividing step is kept in a state in which the side of the front surface10ais protected by the water-soluble resin24and the adjacent device chips12′ are separated with the intermediary of the dividing groove110, i.e., a state in which the sidewalls that form the outer circumferences of the device chips12′ are exposed. The state in which the sidewalls of the device chips12′ are exposed is implemented through execution of heating shrink processing in which heating treatment is executed on the outer circumferential region of the dicing tape T that supports the wafer10and a tensile force S is kept, for example. Due to this, in the above-described plasma apparatus40, plasma etching is executed on the sidewalls of the device chips12′ in a state in which the front surface side of the individual device chips12′ is coated with the water-soluble resin24. As a result, the modified layers that remain at the outer circumferences of the device chips12′ are removed without etching of the front surfaces of the device chips12′ (modified layer removal step).

Subsequently, the wafer10is held on a spinner table (diagrammatic representation is omitted) of a cleaning unit50(only partly illustrated) illustrated inFIG.7and is positioned directly under a water jet nozzle52. Then, cleaning water W is jetted toward the front surface10aof the wafer10while the spinner table is rotated in a direction depicted by the arrow R2at, for example, 500 rpm. By the jetting of the cleaning water W, the film of the water-soluble resin24formed on the front surface10aof the wafer10is dissolved and removed (water-soluble resin removal step). After the water-soluble resin24has been removed from the front surface10aof the wafer10, while the spinner table is rotated at, for example, 3000 rpm, air for drying is jetted from an appropriate air jet nozzle (diagrammatic representation is omitted) to dry the front surface10aof the wafer10.

According to the above-described embodiment, even if dust is scattered from the dividing grooves110when the wafer10is divided, the dust is blocked by the water-soluble resin24with which the front surfaces of the device chips12′ are coated and contamination is prevented. Further, the modified layers that remain at the outer circumferences of the device chips12′ are removed by the plasma etching, and therefore dust is not scattered in the subsequent steps. Thus, the problem that the device chips and the atmosphere are contaminated is solved. In addition, the problem that the flexural strength of the device chips is lowered is also solved.

After the dividing step and the modified layer removal step have been executed as described above, a pick-up step of picking up the device chips12′ from the dicing tape T as illustrated inFIG.8may be executed according to need. The pick-up step can be executed by using a pick-up apparatus60illustrated inFIG.8, for example. The pick-up apparatus60includes a pick-up collet62that causes suction adhesion of the device chip12′ and conveys it and an expanding unit64that expands the dicing tape T to expand the interval between the adjacent device chips12′.

As illustrated inFIG.8, the expanding unit64includes a circular cylindrical expanding drum64a, plural air cylinders64bthat are adjacent to the expanding drum64aand extend upward at intervals in the circumferential direction, an annular holding member64cjoined to the upper end of each of the air cylinders64b, and plural clamps64ddisposed at the outer circumferential edge part of the holding member64cat intervals in the circumferential direction. The inner diameter of the expanding drum64ais larger than the diameter of the wafer10, and the outer diameter of the expanding drum64ais smaller than the inner diameter Fa of the ring frame F. Further, the holding member64ccorresponds to the ring frame F, and the ring frame F is allowed to be placed on the flat upper surface of the holding member64c.

As illustrated inFIG.8, the plural air cylinders64braise and lower the holding member64crelatively to the expanding drum64abetween a reference position (depicted by solid lines) at which the upper surface of the holding member64cis at almost the same height as the upper end of the expanding drum64aand an expanding position (depicted by two-dot chain lines) at which the upper surface of the holding member64cis located on the lower side relative to the upper end of the expanding drum64a.

The pick-up collet62illustrated inFIG.8is configured movably in the horizontal direction and the upward-downward direction. Further, suction means (diagrammatic representation is omitted) is connected to the pick-up collet62, and suction adhesion of the device chip12′ is caused by the lower surface of the tip of the pick-up collet62.

The description will be continued with reference toFIG.8. In the pick-up step, first, the wafer10divided into the individual device chips12′ is oriented upward, and the ring frame F is placed on the upper surface of the holding member64clocated at the reference position. Subsequently, the ring frame F is fixed by the plural clamps64d. Subsequently, the holding member64cis lowered to the expanding position and thereby a radial tensile force acts on the dicing tape T. Thereupon, the interval between the device chips12′ stuck to the dicing tape T expands as depicted by the two-dot chain lines inFIG.8.

Subsequently, the pick-up collet62is positioned above the device chip12′ of the pick-up target and is lowered, and suction adhesion of the upper surface of the device chip12′ is caused by the lower surface of the tip of the pick-up collet62. Subsequently, the pick-up collet62is raised, and the device chip12′ is separated from the dicing tape T to be picked up (see the upper stage of the right side ofFIG.8). Subsequently, the picked-up device chip12′ is conveyed to a tray or the like that is not illustrated in the diagram, or is conveyed to a predetermined conveyance position of the next step. Then, such pick-up work is sequentially executed for all device chips12′, so that the pick-up step is completed. If the water-soluble resin removal step has been executed in advance as described above, the water-soluble resin24has been removed from the device chip12′ picked up in the pick-up step as depicted on the upper stage of the right side ofFIG.8. Thus, the device chip12′ can be conveyed to a bonding step as it is, and bonding processing can be executed.

In the above-described embodiment, the water-soluble resin removal step is executed before the pick-up step is executed. However, the present invention is not limited thereto. After the modified layer removal step by plasma etching is executed, the pick-up step may be executed without executing the water-soluble resin removal step, so that the device chip12′ may be picked up with the water-soluble resin24left on the front surface (see the lower stage of the right side ofFIG.8). In this case, in the next or subsequent step, the water-soluble resin removal step of removing the water-soluble resin24is executed immediately before the device chips12′ are wired to a substrate or the like, for example. This allows the front surfaces of the device chips12′ to be kept clean until immediately before the next step in the period from the pick-up step to the next step.

In the above-described embodiment, the frame supporting step is executed after the modified layer forming step, and irradiation with the laser beam LB is executed from the back surface side of the wafer directly to form the modified layer100inside the planned dividing line14in this modified layer forming step. However, the frame supporting step may be executed before the modified layer forming step. In this case, for example, as illustrated inFIG.9, the side of the front surface10aof the wafer10is oriented upward, and the side of the back surface10bis oriented downward and is stuck to the center of the dicing tape T. In addition, the outer circumference of the dicing tape T is supported by the ring frame F having the opening part Fa with a size that allows housing of the wafer10(frame supporting step). Subsequently, the front surface10aof the wafer10is positioned directly under the nozzle22of the water-soluble resin coating apparatus20. Then, the water-soluble resin24is supplied to the front surface10aof the wafer10held by the ring frame F, and the ring frame F is rotated in a direction depicted by an arrow R3. Thereby, the front surface10acan be evenly coated with the water-soluble resin24as depicted on the lower stage ofFIG.9.

In the case in which the frame supporting step is executed before the modified layer forming step as described above, as illustrated inFIG.10, the wafer10is conveyed to the laser processing apparatus30, and a chuck table that is not illustrated in the diagram is caused to hold the wafer10in such a manner that the side of the back surface10bof the wafer10supported by the ring frame F through the dicing tape T, i.e., the side of the dicing tape T, is oriented upward. Then, irradiation with the laser beam LB is executed from the side of the dicing tape T through the dicing tape T, so that the modified layers100can be formed inside all planned dividing lines14formed in the front surface10aof the wafer10, similarly to the process described based onFIG.2.

In all of the above-described respective embodiments, the water-soluble resin coating step is executed before the modified layer forming step is executed. However, as described above, it suffices that the water-soluble resin coating step is executed before the dividing step, in which dust and so forth are scattered, is executed. Therefore, the water-soluble resin coating step may be executed after the modified layer forming step is executed and immediately before the dividing step is executed. In a case in which, after the modified layer forming step is executed, the water-soluble resin coating step is executed and the dividing step is executed, it is convenient that the water-soluble resin coating step is executed immediately before the dividing step is executed and the dividing step is executed before the water-soluble resin24with which the front surface10aof the wafer10is coated solidifies. This can favorably divide the wafer10into the individual device chips12′ without heating and softening the water-soluble resin24.