JP2015226004A - Protective film coating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow for confirmation of the thickness of a protective film coated on a bump, even in a case of a wafer having bumps formed on the surface.SOLUTION: Propriety of the thickness of a protective film 32 is confirmed before dividing a wafer W by performing a tool cutting step for cutting the upper end of a bump B projecting from the surface Wa of a wafer W by means of a tool 11, and forming a flat part 20 at the upper end of the bump B, a protective film coating step for holding the back surface Wb of the wafer W on a spinner table 14, dropping a liquid resin 31 entirely on the surface Wa of a wafer W, and diffusing the liquid resin 31 entirely on the surface Wa of a wafer W by rotating the spinner table 14, thus coating a protective film 32, and a protective film thickness measurement step for measuring the thickness of the protective film 32 coated on the flat part 20 by a protective film thickness measurement means 40.

Description

  The present invention relates to a method for forming a protective film on a wafer having bumps formed on the surface thereof.

  In a workpiece such as a semiconductor wafer or an optical device wafer, devices are formed in regions partitioned by lattice streets on the surface. As a method of dividing such various wafers into individual chips for each device, a laser beam is irradiated along the street to form a laser processing groove, and then cleaved along the laser processing groove using a mechanical braking device. A method has been proposed (see, for example, Patent Document 1 below). In this method, there is a problem in that debris is generated due to concentration of thermal energy in the region irradiated with the laser beam, and the debris adheres to the surface of the device formed on the workpiece, thereby degrading the quality of the device.

  In order to solve such problems, there is a laser processing apparatus in which a protective film made of polyvinyl alcohol or the like is coated on the surface (processed surface) on which a laser beam is incident on the wafer, and the wafer is irradiated with the laser beam through the protective film. It has been proposed (see, for example, Patent Document 2 below).

  In addition, there is a type of such laser processing apparatus that includes a thickness gauge-side means for measuring the thickness of the protective film coated on the wafer. It is confirmed whether or not the thickness is formed, or whether or not the thickness of the protective film varies (see, for example, Patent Document 3 below).

JP-A-10-305420 JP 2007-2011178 A JP 2008-229706 A

  However, for wafers with a plurality of protruding electrodes called bumps formed on the surface, the bumps are formed in a spherical shape even if the protective film is coated on the surface and the thickness of the protective film is measured by means of the thickness gauge. However, since it has fine irregularities, there is a problem that a highly reliable measurement result cannot be obtained, and the thickness of the protective film covered with the bumps cannot be confirmed. Therefore, if the wafer is divided in a state where the thickness of the protective film is not within the predetermined range, debris adheres to the bumps where the protective film is thin, and after dividing the wafer into individual chips, Problems may occur when mounting each chip.

  The present invention has been made in view of the above circumstances, and it is an object of the present invention to make it possible to confirm the thickness of a protective film covered with bumps even on a wafer having bumps formed on the surface.

  The present invention relates to a protective film coating method for coating a protective film made of a resin on a surface of a wafer on which a device in which a plurality of spherical electrodes protrude from the surface is defined by a plurality of division lines formed in a lattice shape The electrode on which the surface on which the electrode is formed is exposed, the wafer is held on the holding surface of the chuck table, and the electrode protrudes from the surface of the wafer with a bite rotating about a rotation axis orthogonal to the holding surface A cutting tool step for cutting the upper end of the electrode to form a flat portion on the upper end of the electrode, and holding the back side of the wafer on which the flat portion is formed on the electrode on a spinner table. By dripping a fixed amount of liquid resin and rotating the spinner table, the liquid resin is diffused over the entire surface of the wafer, and a protective film is formed on the surface of the wafer. A protective film coating step for covering, and after performing the protective film coating step, a protective film thickness measuring means is positioned on the flat portion of the electrode to measure the thickness of the protective film formed on the flat portion of the electrode And a protective film thickness measuring step.

In the protective film coating method of the present invention, the protective film coating step is performed after the bite cutting step is performed. Therefore, the flat film formed on the upper end of the electrode protruding from the surface of the wafer is coated with a protective film having no thickness variation. be able to. Then, by carrying out the protective film thickness meter side step, the thickness of the protective film coated on the flat portion of the electrode can be accurately measured, and whether or not the thickness of the protective film is within a predetermined range Can be confirmed.
As described above, since it is possible to check the thickness of the protective film coated on the electrode before dividing the wafer into individual chips, it is possible to prevent debris from adhering to the electrode when the wafer is divided. .

It is a perspective view which shows an example of a wafer. It is a side view showing a cutting tool step. (A) is a side view which shows the wafer before a cutting tool step implementation, (b) is a side view which shows the wafer by which the flat part was formed in the bump by the cutting tool step. It is sectional drawing which shows a protective film coating step. It is sectional drawing which shows a protective film thickness meter side step. It is a block diagram which shows a protective film thickness meter side means.

  The wafer W shown in FIG. 1 is an example of a workpiece, and the surface Wa is a spherical electrode protruding from the surface Wa in each region partitioned by a plurality of grid-like division lines S. A device D on which bumps B are formed is formed. On the surface Wa of the wafer W, for example, a Low-K film is laminated. The device D is not formed on the back surface Wb which is the surface opposite to the front surface Wa of the wafer W. Hereinafter, a protective film coating method for coating the surface Wa of the wafer W with a protective film made of resin will be described with reference to the accompanying drawings.

Cutting Tool Step First, cutting using a cutting tool at the upper end of the bump B protruding from the surface Wa of the wafer W (hereinafter referred to as “cutting tool cutting”) is performed using the cutting tool 1 shown in FIG. The cutting tool 1 has a column 2 extending in the Z-axis direction, and a chuck table 3 having a holding surface 3 a for holding the wafer W, and a wafer W held on the chuck table 3 on the front side of the column 2. The cutting tool 4 includes a cutting tool 4 for cutting the tool, and a lifting / lowering means 12 that includes a motor 13 and moves the cutting tool 4 up and down in the Z-axis direction. The chuck table 3 may be configured to be rotatable, but is not rotated during cutting of the cutting tool.

  The cutting tool 4 is connected to a spindle 5 having a shaft center perpendicular to the holding surface 3 a of the chuck table 3 (Z-axis direction), a spindle housing 6 that rotatably surrounds the spindle 5, and one end of the spindle 5. And a bite tool 9 detachably attached to the lower end of the spindle 5 via a mount 8 and a bite tool 10 detachably attached to the bite wheel 9. The bite tool 10 has a configuration in which a bite 11 is fixed to one end of a prismatic shank. The motor 7 rotates the spindle 5 at a predetermined rotation speed, thereby rotating the bite wheel 9 at a predetermined rotation speed. Can be made.

  When cutting the upper end of the bump B in the cutting tool 1, the back surface Wb side of the wafer W is placed on the holding surface 3a of the chuck table 3, and the surface Wa side of the wafer W is exposed upward, The wafer W is sucked and held on the chuck table 3 by a suction source (not shown).

  The lifting / lowering means 12 lowers the cutting tool 4 in the Z-axis direction approaching the wafer W held on the chuck table 3 to position the cutting tool 11 at a predetermined height position, and the spindle 5 is rotated by the motor 7. The bite wheel 9 is rotated in the direction of arrow A, for example.

  While moving the chuck table 3 in the horizontal direction, the upper ends of the bumps B protruding from the surface Wa of the wafer W are scraped by the rotating cutting tool 11 and the heights thereof are made uniform to form a flat surface. That is, the upper ends of the plurality of bumps B curved in a spherical shape shown in FIG. 3A are scraped off by the cutting tool 11 shown in FIG. 2 to flatten the upper ends of the bumps B as shown in FIG. Part 20 is formed. By forming the flat portion 20 on the upper ends of all the bumps B and aligning the height thereof, the flat surface 21 made of the flat portion 20 can be formed.

Next, as shown in FIG. 4, the wafer W is held by the spinner table 14 and the protective film is applied to the surface Wa of the wafer W by using the resin supply means 30 for dropping the liquid resin forming the protective film. Coating. The spinner table 14 includes a holding unit 15 having a holding surface 15 a that holds the wafer W, a support unit 16 that rotatably supports the holding unit 15 from below, a motor 17 connected to the support unit 16, and a holding unit 15. At least a frame placing portion 18 on which an annular frame F is placed, and a clamp portion 19 for clamping the frame F placed on the frame placing portion 18.

  When a protective film is coated on the front surface Wa of the wafer W, first, the tape T is attached to the lower part of the annular frame F opened at the center, and the back surface Wb side of the wafer W is attached to the tape T exposed from the center. By sticking, the frame F and the wafer W are integrally formed via the tape T. Thereafter, the tape T adhered to the back surface Wb side of the wafer W is placed on the holding surface 15 a of the holding unit 15 and the frame F is placed on the frame mounting unit 18. And the clamp part 19 hold | maintains so that the wafer W may not move by the holding surface 15a of the holding | maintenance part 15, pressing down the upper part of the flame | frame F. FIG.

  Next, the motor 17 rotates the support portion 16 and rotates the spinner table 14 in the direction of arrow A, for example, from the resin supply means 30 positioned on the upper side of the wafer W to a central region on the surface Wa of the wafer W. The liquid resin 31 is dropped. As the liquid resin 31, for example, a water-soluble liquid resin such as PVA (polyvinyl alcohol) is used. The liquid resin 31 dropped on the surface Wa of the wafer W flows from the central region of the surface Wa of the wafer W to the outer peripheral side due to the centrifugal force generated by the rotation of the spinner table 14, and stagnates on the entire surface Wa of the wafer W. Diffuse without. In this way, as shown in FIG. 5, the protective film 32 covering the surface Wa and the bumps B of the wafer W is coated.

(3) Protective film thickness meter side step After performing the protective film coating step, the protective film 32 coated on the flat part 20 of the bump B using the protective film thickness meter side means 40 as shown in FIG. Measure the thickness. The protective film thickness meter-side means 40 is a measuring instrument that measures the thickness of the protective film 32 from above the wafer W in a non-contact state. As shown in FIG. 6, the protective film thickness gauge side means 40 is based on the light emitting unit 42 that irradiates the measuring light 41 to the wafer W, the light receiving unit 43 that receives the reflected light of the measuring light 41, and the reflected light. And at least a calculation unit 44 for calculating the thickness of the protective film 32. The light emitting unit 42 includes a light emitting element 421 that emits a laser beam and a light projecting lens 422 that collects the laser beam. On the other hand, the light receiving unit 43 includes a light receiving lens 432 that collects the reflected light reflected by the protective film 32 and the flat part 20, and a light receiving position detection element 431 that detects a position where the collected reflected light is received. .

  As shown in FIG. 6, the protective film thickness gauge side means 40 is positioned above the bump B protruding from the surface Wa of the wafer W, and the measurement light 41 with the incident angle α is irradiated from the light emitting portion toward the bump B. A part of the measurement light 41 irradiated toward the bump B is reflected on the upper surface of the protective film 32 to become reflected light 411. On the other hand, the remaining light that has not been reflected on the upper surface of the protective film 32 passes through the protective film 32 and is reflected on the upper surface of the flat portion 20 of the bump B to become reflected light 412. The calculation unit 44 calculates the thickness t of the protective film 32 by the following formula based on the distance H between the position 45 where the reflected light 411 is received and the position 46 where the reflected light 412 is received in the light receiving position detection element 431. t = H / 2sin α

  Since there is no variation in the film thickness of the protective film 32 coated on the flat portion 20 of the bump B, the thickness of the protective film 32 can be measured.

  When the thickness of the protective film 32 measured by the protective film thickness meter side means 40 is outside the predetermined thickness range, a small amount of liquid resin 31 is removed from the wafer W by the resin supply means 30 shown in FIG. The protective film is coated again by dropping on the surface Wa. Alternatively, after the surface Wa of the wafer W is once cleaned with cleaning water, the same operation as in the protective film coating step described above may be performed to newly coat the surface Wa of the wafer W with a protective film. After the protective film is coated on the surface Wa of the wafer W in this way, the same operation as the above-described protective film thickness gauge side step is performed again, and the protective film thickness gauge side means 40 performs the operation on the flat portion 20 of each bump B. The thickness of the protective film coated on the surface is measured, and the thickness of the protective film is confirmed again.

  On the other hand, when the thickness of the protective film 32 measured by the protective film thickness meter side means 40 is within a predetermined thickness range, the wafer W is divided into chips for each device D. For example, the wafer W is fully cut by irradiating a laser beam along the division line S of the wafer W shown in FIG. Alternatively, the wafer W is divided by irradiating a laser beam along the planned division line S of the wafer W, performing a half-cut to form a division groove on the wafer W, and cutting with, for example, a blade along the division groove. Alternatively, for example, the wafer W may be cleaved along the division grooves using a braking device.

As described above, in the protective film coating method according to the present invention, a cutting tool step is performed to cut the upper end of the bump B protruding from the surface Wa of the wafer W with the cutting tool 11 and form the flat portion 20 on the upper end of the bump B. After that, the protective film coating step is performed, and the liquid resin 31 is dropped on the surface Wa of the wafer W, and the surface Wa of the wafer W is coated with the protective film 32, so that the flat portion formed on the upper end of the bump B 20 can be coated with a protective film 32 having no thickness variation. Thereafter, by carrying out the protective film thickness gauge side step, the protective film thickness gauge side means 40 can accurately measure the thickness of the protective film 32 covered by the flat portion 20 of the bump B. It is possible to confirm whether the thickness of the protective film 32 covered on the side surface as well as the upper end of B is good.
Therefore, there is no problem that debris adheres to the bumps B when the wafer W is irradiated with a laser beam, and it is possible to prevent problems from occurring when mounting individual chips after the wafer W is divided.

1: Bit cutting device 2: Column 3: Chuck table 3a: Holding surface 4: Tool cutting means 5: Spindle 6: Spindle housing 7: Motor 8: Mounter 9: Tool wheel 10: Tool tool 11: Tool 12: Lifting device 13 : Motor 14: Spinner table 15: Holding part 15a: Holding surface 16: Supporting part 17: Motor 18: Frame mounting part 19: Clamping part 20: Flat part 21: Flat surface 30: Resin supply means 31: Liquid resin 32: Protective film 40: Protective film thickness gauge side means 41: Measuring light 42: Light emitting part 421: Light emitting element 422: Light projecting lens 43: Light receiving part 431: Light receiving position detecting element 432: Light receiving lens 44: Calculation part W: Wafer Wa: Front side Wb: Back side S: Scheduled line D: Device B: Bump

Claims (1)

A protective film coating method for coating a protective film made of a resin on the surface of a wafer on which a device in which a plurality of spherical electrodes protrude from the surface is formed by a plurality of division lines formed in a lattice shape,
The surface on which the electrode is formed is exposed, the wafer is held on the holding surface of the chuck table, and the upper end of the electrode protruding from the surface of the wafer is cut with a cutting tool rotating about a rotation axis orthogonal to the holding surface. A cutting tool step for forming a flat portion at the upper end of the electrode;
The back side of the wafer having the flat portion formed on the electrode is held on a spinner table, and a predetermined amount of liquid resin is dropped on the central area of the front surface of the wafer and the spinner table is rotated. A protective film coating step for diffusing the entire surface of the wafer and coating the surface of the wafer with a protective film;
A protective film thickness measuring step for measuring the thickness of the protective film formed on the flat part of the electrode by positioning a protective film thickness measuring means on the flat part of the electrode after performing the protective film covering step; A protective film coating method comprising:

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