TW201818459A - Processing method of wafer capable of dividing the reverse side of a wafer formed of a metal film into a plurality of chips - Google Patents

Abstract

A processing method of a wafer is provided, wherein a wafer having a metal film formed on its reverse side can be easily and efficiently divided into chips. The processing method of a wafer having a front side on which elements are respectively formed in each of regions divided by intersecting a plurality of divided lines and a metal film is formed on the reverse side is characterized in that it includes a cutting step of cutting a wafer along a predetermined divided line from the front side thereof by a cutting blade to form a cutting groove that does not reach the metal film; a protective film forming step of supplying water-soluable resin to the front side of the wafer after performing the cutting step and coating the front side of the wafer and the cutting groove by a protective film made of the water-soluable resin; a laser processing step of irradiating a laser beam having a wavelength that is absorptive to the metal film from the front side of the wafer toward the cutting groove after performing the protective film forming step to cut the metal film together with the wafer; and a protective film removal step of washing the wafer to remove the protective film after performing the laser processing step.

Description

Processing method of wafer

FIELD OF THE INVENTION The present invention relates to a method for processing a wafer in which a wafer having a metal film formed on the back surface is divided into individual wafers.

BACKGROUND OF THE INVENTION A wafer such as a semiconductor wafer has a front surface of an element formed in each region divided by a plurality of intersecting division lines, and can be divided into individual elements by cutting along the division line. Wafer.

In such a wafer, there is a problem that a metal film is formed on the back surface in order to form the electrical characteristics of the device well. When the metal film is cut with a cutting blade, clogging occurs on the cutting blade. When a clogged cutter cuts a wafer, there is a problem that a crack may be formed on the wafer or the blade may be damaged.

On the other hand, when a full cut is performed on a wafer with a laser beam having an absorptive wavelength to the wafer, metal chips generated by the laser beam irradiating the metal film adhere to the side of the wafer.

Therefore, Japanese Patent Application Laid-Open No. 2015-138857 describes a method for processing a wafer with a metal film, which irradiates a laser beam having a wavelength that is absorptive to the wafer from the back side of the wafer to The metal film is cut and a cut groove is formed on the wafer, and then the wafer is cut with a cutter from the front side of the wafer until the cut groove to divide the wafer into individual element wafers. Prior Art Literature Patent Literature

Patent Document 1: Japanese Patent Laid-Open No. 2015-138857

SUMMARY OF THE INVENTION Problems to be Solved by the Invention However, when a metal film is laser-processed from the back side of a wafer, the metal film is formed on the back side of the wafer, and it is impossible to detect a predetermined division line formed on the front side. problem. In Patent Document 1, there is no description of a method for detecting a predetermined division line from the rear surface side of the wafer, but it is still necessary to remove, for example, the metal film on the outer peripheral portion of the wafer in advance and use an infrared camera from the rear surface side of the wafer The time and effort required to detect the planned division line, etc., becomes time-consuming and laborious in detecting the planned division line.

The present invention has been made in view of this problem, and an object thereof is to provide a processing method capable of easily and efficiently dividing a wafer having a metal film formed on a back surface into wafers. Means to solve the problem

According to the present invention, it is possible to provide a method for processing a wafer having a front surface in which elements are formed in respective regions defined by a plurality of intersecting predetermined division lines, and a metal film is formed on the back surface. The method for processing a circle is characterized by comprising: a cutting step of cutting the wafer along a predetermined dividing line from a front surface of the wafer with a cutter to form a cutting groove that does not reach the metal film; After the cutting step, a water-soluble resin is supplied to the front side of the wafer, and the front surface of the wafer and the cutting groove are covered with a protective film made of the water-soluble resin; the laser processing step is to implement the protective film After the forming step, a laser beam having an absorptive wavelength to the metal film is irradiated from the front side of the wafer toward the cutting groove to cut the metal film together with the wafer; and a protective film removal step is implemented in After the laser processing step, the wafer is cleaned and the protective film is removed. Invention effect

In the method of processing a wafer of the present invention, a cutting groove that does not reach the metal film is formed from the front side of the wafer, and then a laser beam is irradiated to cut the metal film together with the wafer. Since the cutting step and the laser processing step are performed from the front side of the wafer, it is possible to easily and efficiently detect a predetermined division line and divide the wafer into wafers.

After the cutting groove is formed, the front surface of the wafer and the cutting groove are covered with a protective film, so even if debris is generated in the laser processing step and the generated debris is attached to the protective film, in the subsequent protective film removing step Debris can still be removed. This makes it possible to easily and efficiently divide a wafer having a metal film formed on the back surface into wafers without causing metal chips to adhere to the side surface of the wafer.

Embodiments for Carrying Out the Invention Embodiments of the present invention will be described in detail below with reference to the drawings. 1 (A), a front perspective view of a semiconductor wafer (hereinafter sometimes referred to as a wafer) 11 is shown. FIG. 1 (B) is a cross-sectional view of the semiconductor wafer 11.

On the front surface 11 a of the wafer 11, a plurality of planned division lines 13 are formed in a grid pattern, and elements 15 such as LSIs are formed in each area defined by the planned division lines that cross. As shown in FIG. 1 (B), a metal film 21 made of copper (Cu), aluminum (Al), or the like is formed on the back surface 11b of the wafer 11.

Prior to implementing the wafer processing method according to the embodiment of the present invention, processing is performed in the form of a wafer unit 17 formed by attaching a wafer 11 to a dicing tape T having an outer peripheral portion attached to a ring frame F. .

In the method for processing a wafer according to the embodiment of the present invention, first, a cutting step is performed. The cutting step is to cut from the front side of the wafer along a predetermined division line with a cutter to form a cutting groove that does not reach the metal film.

In this cutting step, as shown in FIG. 3 (A), the back surface side of the wafer 11 is sucked and held on the work clamp table 1 of the cutting device via a dicing tape T, and the ring frame F is held by the jig 7 Clamped.

Prior to the cutting step, a conventionally known calibration can be performed. This calibration uses an imaging unit provided in the cutting device to capture the front side 11a of the wafer 11 held on the work clamp table 1 and mount it on the front end of the spindle 3. The part cutter 5 is aligned with the planned division line 13 to be cut.

After the calibration is performed, a cutting step is performed. The cutting step is to cut the wafer from the front surface 11 a of the wafer 11 along the predetermined division line 13 with a high-speed rotating cutter 5 to form a metal that does not reach the back surface 11 b formed on the wafer 11.切 槽 23。 Film 21 cutting groove 23.

This cutting step is performed one by one along the planned dividing line 13 that is elongated in the first direction when the planned dividing line 13 is indexed at every pitch on the wafer 11. Next, after the work table 1 is rotated by 90 °, the same cutting process is performed along the planned division line 13 that is elongated in the second direction orthogonal to the first direction. An enlarged cross-sectional view of the wafer 11 after the cutting step is performed is shown in FIG. 3 (B).

Although the thickness of the leftover portion at the bottom of the cutting groove 23 after the cutting step is performed is not particularly limited, considering the handling property in the subsequent steps, it is preferable to leave the leftover portion of about 30 to 50 μm.

After the cutting step is performed, a protective film forming step is performed. The protective film forming step is to supply a water-soluble resin to the front side of the wafer, and cover the front surface and the cutting groove of the wafer with a protective film made of the water-soluble resin. As an example of the protective film forming step, it is preferable to use a protective film forming apparatus provided in the laser processing apparatus 2 shown in FIG. 4. Of course, a separate protective film forming device may be used.

Referring to FIG. 4, there is shown a perspective view of a laser processing apparatus 2 provided with a protective film forming apparatus and suitable for performing a laser processing step in an embodiment of the present invention. An operation panel 4 is provided on the front side of the laser processing device 2 for an operator to input instructions to the device such as processing conditions. A display screen 6 such as a CRT is provided on the upper part of the device, which can display a guide screen for the operator and an image captured by a camera unit described later.

A plurality of wafer units 17 shown in FIG. 2 are housed in the cassette 8, and the cassette 8 is placed on a cassette elevator 9 that can be moved up and down. Behind the cassette 8 placed on the cassette lifter 9 are provided for carrying out the wafer unit 17 before laser processing from the cassette 8, and carrying out the processed wafer unit 17 into the cassette 8.入 设备 10。 Into the device 10.

Between the cassette 8 and the loading / unloading device 10, a temporary area 12 which is a region where the wafer unit 17 to be loaded / unloaded is temporarily placed is provided, and the wafer unit 17 is arranged on the temporary area 12 Alignment device 14 aligned at a certain position.

Reference numeral 30 denotes a protective film forming device. This protective film forming device 30 also doubles as a cleaning device for cleaning the processed wafer. In the vicinity of the temporary area 12, a transfer device 16 having a winding arm is arranged, and the rotating arm is a frame F that sucks the wafer unit 17 and carries it.

The wafer unit 17 carried out to the temporary area 12 is sucked by the transfer facility 16 and transferred to the protective film forming apparatus 30. As described later in detail, the protective film forming apparatus 30 applies a water-soluble liquid resin to the processed surface of the wafer 11 to cover the protective film.

The wafer 11 that has been covered with a protective film on the processing surface is transferred to the work clamp table 18 by being adsorbed by the conveyance device 16, is attracted to the work clamp table 18, and is fixed by a plurality of fixing devices (clamps) 19. The frame F is fixed and held on the work clamp table 18.

The work chuck 18 is configured to be rotatable and can move back and forth in the X-axis direction. Above the movement path in the X-axis direction of the work chuck 18, a laser processing for detecting the wafer 11 is arranged. Alignment unit 20 of the cutting path.

The calibration unit 20 includes a camera unit 22 that captures the front side of the wafer 11, and can detect a cutting path for laser processing by image processing such as pattern matching based on the image obtained by shooting. The image acquired by the imaging unit 22 is displayed on the display unit 6.

A laser beam irradiation unit 24 is provided on the left side of the calibration unit 20 so as to irradiate the wafer 11 held on the work table 18 with a laser beam. The laser beam irradiation unit 24 is movable in the Y-axis direction.

Referring to FIG. 5, a partial cross-sectional side view of the protective film forming apparatus 30 is shown. The protective film forming apparatus 30 includes a turntable mechanism 34 and a liquid receiving mechanism 36 arranged to surround the turntable mechanism 34.

The turntable mechanism 34 includes a turntable (holding table) 38, a support member 40 that supports the turntable 38, and an electric motor 42 that rotationally drives the turntable 38 through the support member 40. When the electric motor 42 is rotationally driven, the turntable 38 is rotated in the direction of arrow A.

The rotary table 38 has a suction holding portion formed of a porous material, and the suction holding portion is a negative pressure suction device which is not shown in the drawing. Therefore, the turntable 38 sucks and holds the wafer on the suction holding portion by placing a wafer on the suction holding portion and applying a negative pressure with a negative pressure suction device (not shown).

The rotary table 38 is provided with four jigs 44 of a pendulum type. When the rotary table 38 is rotated, these clamps 44 are caused to swing by the centrifugal force and clamp the annular frame F shown in FIG. 2.

The liquid receiving mechanism 36 is composed of a liquid receiving container 46 and a cover member 48 attached to the support member 40. The liquid receiving container 46 includes a cylindrical outer side wall 46a, a bottom wall 46b, and an inner side wall 46c.

A hole 47 into which the support member 40 can be inserted is provided in a central portion of the bottom wall 46b, and the inner side wall 46c is formed to protrude upward from the periphery of the hole 47. The cover member 48 is formed in a disc shape, and includes a cover portion 48 a protruding downward from an outer peripheral edge thereof.

The cover member 48 thus constructed is positioned so that the cover portion 48a overlaps the outside of the inner side wall 46c constituting the liquid receiving container 46 with a gap when the turntable 38 is positioned at the working position shown in FIG. 5.

The protective film forming apparatus 30 is provided with a protective film agent discharge device 50 that discharges a liquid protective film agent composed of a water-soluble resin onto the wafer 11 before being processed and held on the turntable 38. The protective film agent discharge device 50 is a liquid protection of a liquid protective film agent by a substantially L-shaped support arm 52 formed at the front end of the support arm 52 and discharging toward the processing surface of the pre-processed wafer 11 held on the turntable 38. The film supply nozzle 54 and an electric motor 56 that can swing forward and reverse by swinging the arm 52 are configured. The protective film agent supply nozzle 54 is connected to the protective film agent supply source 58 through the arm 52.

The protective film forming device 30 is also a cleaning device that also cleans the wafer 11 after laser processing. Therefore, the protective film forming apparatus 30 includes a washing water supply device 60 for washing the processed wafer 11 held on the turntable 38.

As best shown in FIG. 9, the washing water supply device 60 includes a substantially L-shaped arm 62, a front end of the arm 62, and a processing surface of the processed wafer 11 held on the turntable 38. A washing water nozzle 64 for supplying washing water, and an electric motor 66 that can swing forward and reverse by swinging the arm 62 are configured. The washing water nozzle 64 is connected to the protective film agent supply source 68 through the arm 62.

After the cutting step is performed, a water-soluble resin is supplied to the front surface 11 a and the cutting groove 23 of the wafer 11 in the protective film forming apparatus 30 shown in FIG. 5, and the front surface 11 a and cutting of the wafer are covered with the protective film 25. The protective film formation step of the groove 23 will be described in detail.

The wafer unit 17 having the cutting groove 23 formed by the cutter 5 is transferred to the turntable 38 of the protective film forming apparatus 30 by the winding operation of the wafer transfer device 16, and the wafer 11 is sucked and held on the turntable 38. At this time, as shown in FIG. 5, the washing water nozzle 64 is positioned at a standby position separated from above the turntable 38.

The rotary stage 38 is rotated in the direction of arrow A at a low speed, for example, 30 to 50 rpm, and a liquid protective film agent made of a water-soluble resin is dropped on the wafer 11 while swinging the liquid protective film agent supply nozzle 54. .

Since the turntable 38 is rotating, the dropped liquid protective film agent will diffuse on the processing surface of the wafer 11, and the surface tension of the liquid protective film agent can be used to form a protective film on the processing surface of the wafer 11. 25.

When the protective film forming step is performed, as shown in FIG. 6, a protective film 25 made of a water-soluble resin is formed on the front surface 11 a of the wafer 11 and the cutting groove 23. After the protective film formation step has been performed, the suction and holding of the turntable 38 is released, and the wafer unit 17 is transferred to the work clamp table 18 by the wafer transfer equipment 16 so as to be sucked by the work clamp table 18 as shown in FIG. 7. The wafer 11 having the cut groove 23 formed thereon is subjected to a laser processing step.

Before the laser processing step is performed, the processing area of the wafer 11 attracted and held on the work clamp table 18 is moved directly below the camera unit 22, and the processing area of the wafer 11 is captured by the camera unit 22.

In addition, image processing such as pattern matching of the condenser 28 of the laser beam irradiation unit 24 for irradiating the laser beam with the alignment of the predetermined division line 11 extending in the first direction is performed, and laser is performed. Calibration of beam irradiation position.

When the calibration of the planned division line 11 extended in the first direction is completed, after the work clamp table 18 is rotated by 90 °, the planned division in the direction orthogonal to the planned division line 13 extended in the first direction is planned. Line 13 also performs the same calibration.

After the calibration is performed, the work clamp table 18 is moved, and the processing start position of the predetermined division plan line 13 extended in the first direction is positioned directly below the condenser 28, and the light collected by the unit 24 is irradiated with a laser beam. The condenser 28 condenses the bottom of the cutting groove 23 formed on the front surface 11 a of the wafer 11 via a protective film 25.

The laser processing step is performed in such a way that the condenser 28 condenses the pulsed laser beam LB on the bottom of the cutting groove 23 via the protective film 25, and sets the work clamp 18 at a predetermined feed rate The processing feed (for example, 100 mm / s) is performed, and the wafer 11 is cut and the metal film 21 is cut by ablation processing along a predetermined division line 13 extending in the first direction.

The work table 18 is fed in increments of every pitch of the predetermined division line 13, and a laser processing step is performed to cut off the leftover portion of the wafer 11 and the metal film 21. After finishing the laser processing step along the planned division line extending in the first direction, after rotating the work table 18 by 90 °, the same planned ablation processing is performed on the planned division line 13 extended in the second direction. To cut the leftover portion of the wafer 11 and the metal film 21, and divide the wafer 11 into individual element wafers.

The laser processing conditions in the laser processing step of the present embodiment are set as follows, for example.

Light source: YAG pulsed laser Wavelength: 355nm (third harmonic of YAG laser) Average output: 3.0W Repetition frequency: 20kHz Feed rate: 100mm / sec

An enlarged sectional view of the wafer 11 after the laser processing step is shown in FIG. 8. By performing the laser processing step, the cutting groove 23 formed by the cutting tool along the predetermined division line 13 is formed to form a cutting groove 23 formed by the laser processing, and the wafer 11 is formed along the predetermined division line 13. Cut off.

After the laser processing step has been performed, a protective film removing step of cleaning the wafer 11 and removing the protective film 23 is performed. The wafer unit 17 that has completed the laser processing step is transferred to the turntable 38 of the protective film forming apparatus 30 by the transfer device 32, and is sucked and held on the turntable 38. At this time, as shown in FIG. 9, the liquid protective film agent supply nozzle 54 is positioned at a standby position separated from above the turntable 38.

In the protective film removing step, the wafer 11 is supplied with the washing water from the washing water nozzle 64 connected to the washing water supply source 68 toward the protective film 25 of the wafer 11 held on the turntable 38. Rotate at a low speed (for example, 800 rpm) in the direction of arrow A to dissolve the protective film 25 on the wafer 11 and the cutting groove 23 in water. As the washing water, for example, pure water can be used.

As an alternative embodiment, in the protective film removing step, the rotary table 38 of the protective film forming apparatus 30 is used to attract and hold the wafer 11 on which the protective film 25 is formed, and the washing water nozzle 64 is connected to the washing water supply. The source 60 and an air source (not shown) use a two-fluid washing water composed of pure water and air to spray the wafer 11 from the washing water nozzle 64 while rotating to clean the wafer 11 and remove the protective film 25. can. An enlarged cross-sectional view of the wafer 11 after the protective film removal step is performed is shown in FIG. 10.

According to the method of processing a wafer according to the above embodiment, first, a cutting groove 23 that does not reach the metal film 21 is formed from the front surface 11 a of the wafer 11 along the planned division line 13, and then the wafer is irradiated toward the bottom of the cutting groove 23. 11 A laser beam having an absorptive wavelength to cut the metal film 21 and the wafer 11 together. Since the cutting step and the laser processing step are performed from the front surface 11 a side of the wafer 11, it is possible to easily and efficiently detect the planned division line 13 and divide the wafer into individual wafers.

Since the protective film 25 is formed on the front surface of the wafer 11 and the bottom and sides of the cutting groove 23 after the cutting groove 23 is formed, even if debris is generated in the laser processing step, the generated debris is adhered to the protective film. 25, and debris can be removed in a subsequent protective film removal step. Therefore, the metal can not be adhered to the side surface of the wafer, but can be easily and efficiently divided on the wafer 11 on which the metal film 21 is formed on the back surface.

1.18‧‧‧Work clamp

2‧‧‧laser processing equipment

3‧‧‧ Spindle

4‧‧‧ operation panel

5‧‧‧ Cutter

6‧‧‧display

7, 44‧‧‧ fixture

8‧‧‧ cassette

9‧‧‧ Cassette Lift

10‧‧‧ Move in and out of equipment

11‧‧‧ wafer

11a‧‧‧front

11b‧‧‧Back

12‧‧‧Temporary area

13‧‧‧ divided scheduled line

14‧‧‧Alignment equipment

15‧‧‧device

16‧‧‧ transport equipment

17‧‧‧ Wafer Unit

19‧‧‧ fixed equipment

20‧‧‧ Calibration unit

21‧‧‧metal film

22‧‧‧ Camera Unit

23‧‧‧ cutting groove

24‧‧‧laser beam irradiation unit

25‧‧‧ protective film

27‧‧‧ cut off the trench

28‧‧‧ Concentrator

30‧‧‧ protective film forming device

32‧‧‧ transport equipment

34‧‧‧Rotary table mechanism

36‧‧‧Liquid receiving agency

38‧‧‧Turntable

40‧‧‧ support member

42, 56, 66‧ electric motors

46‧‧‧Liquid receiving container

46a‧‧‧outer wall

46b‧‧‧ bottom wall

46c‧‧‧ inside wall

47‧‧‧hole

48‧‧‧ cover member

48a‧‧‧ cover

50‧‧‧ Protective film agent discharge device

52, 62‧‧‧ Arm

54‧‧‧ protective film supply nozzle

58, 68‧‧‧ Protective film supply source

60‧‧‧Washing water supply equipment

64‧‧‧washing water nozzle

A‧‧‧arrow

F‧‧‧ ring frame

LB‧‧‧Pulse laser beam

T‧‧‧Cutting Tape

FIG. 1 (A) is a front perspective view of a semiconductor wafer, and FIG. 1 (B) is a sectional view thereof. FIG. 2 is a perspective view of a wafer unit obtained by supporting a wafer on a ring frame through a dicing tape. FIG. 3 (A) is a partial cross-sectional side view showing a cutting step, and FIG. 3 (B) is an enlarged cross-sectional view showing a wafer after the cutting step is performed. FIG. 4 is a perspective view of a laser processing apparatus. FIG. 5 is a sectional view showing a protective film forming step. FIG. 6 is an enlarged cross-sectional view of the wafer after the protective film forming step is performed. Fig. 7 is a partial cross-sectional side view showing a laser processing step. FIG. 8 is an enlarged cross-sectional view of a wafer after a laser processing step is performed. FIG. 9 is a sectional view showing a protective film removing step. FIG. 10 is an enlarged cross-sectional view of the wafer after the protective film removing step is performed.

Claims (1)

A method for processing a wafer having a front surface of an element formed in each region defined by a plurality of intersecting predetermined division lines and a metal film formed on the back surface. The method includes: a cutting step of cutting a wafer along a predetermined dividing line with a cutter from a front surface of the wafer to form a cutting groove that does not reach the metal film; a protective film forming step, after the cutting step is performed, A water-soluble resin is supplied on a round front side, and a front surface of the wafer and the cutting groove are covered with a protective film made of the water-soluble resin; a laser processing step, after the protective film forming step is performed, the metal A laser beam having an absorptive wavelength of the film is irradiated from the front side of the wafer toward the cutting groove to cut the metal film together with the wafer; and a protective film removing step, after performing the laser processing step, washing Clean the wafer to remove the protective film.