JP2014086612A - Laser processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser processing method capable of manufacturing a device at a lower cost than processing using a protective film material such as a water-soluble resin.
A laser processing method for performing laser processing on a wafer in which a device is formed in each region defined by a plurality of processing lines intersecting each other on the front surface, wherein the holding step holds the back side of the wafer by a holding means. Before or after performing the holding step, an ice layer forming step for forming an ice layer covering the surface of the wafer, and from the surface of the wafer held by the holding means and having the surface covered with the ice layer. A laser processing step of irradiating a wafer with a laser beam having a wavelength having an absorption property through the ice layer to form a laser processing groove along a processing target line.
[Selection] Figure 5

Description

  The present invention relates to a laser processing method for performing laser processing on a wafer in which a device is formed in each region defined by a plurality of intersecting scheduled processing lines formed on a surface.

  A wafer such as a silicon wafer or a sapphire wafer formed on the surface by dividing a plurality of devices such as IC, LSI, LED, etc. by dividing lines (processing lines) is divided into individual devices by a processing apparatus. Devices are widely used in various electronic devices such as mobile phones and personal computers.

  A dicing method using a cutting device called a dicer is widely used for dividing the wafer. In the dicing method, a wafer is cut by cutting a wafer into a wafer while rotating a cutting blade having a thickness of about 30 μm by solidifying abrasive grains such as diamond with a metal or a resin at a high speed of about 30000 rpm. Divide into

  On the other hand, in recent years, a laser processing groove is formed by irradiating a wafer with a pulsed laser beam having a wavelength that absorbs the wafer, and the wafer is cut along the laser processing groove with a braking device to form individual laser processing grooves. A method of dividing into devices has been proposed (see, for example, JP-A-2006-140311).

  Laser processing grooves formed by a laser processing apparatus can increase the processing speed compared to a dicing method using a dicer, and relatively easily process even a wafer made of a material having high hardness such as sapphire or SiC. be able to. In addition, since the processing groove can be made to have a narrow width of, for example, 10 μm or less, the amount of devices taken per wafer can be increased as compared with the case of processing by the dicing method.

  However, when the wafer is irradiated with a pulse laser beam, debris is generated due to concentration of thermal energy in the region irradiated with the pulse laser beam. When this debris adheres to the device surface, there arises a problem that the quality of the device is lowered.

  Therefore, for example, in JP 2007-201178 A, a water-soluble resin such as PVA (polyvinyl alcohol) or PEG (polyethylene glycol) is applied to the processed surface of the wafer in order to solve such problems caused by debris. There has been proposed a laser processing apparatus in which a protective film is coated and a wafer is irradiated with a pulsed laser beam through the protective film.

JP 2006-140311 A JP 2007-2011178 A

  In general, water-soluble resins such as PVA and PEG for forming a protective film are expensive, and devices processed using the protective film are also expensive. Therefore, there is a demand for a laser processing method that can manufacture a device at a lower cost. Yes.

  The present invention has been made in view of such points, and the object of the present invention is to provide a laser processing method capable of manufacturing a device at a lower cost than processing using a protective film material such as a water-soluble resin. Is to provide.

  According to the present invention, there is provided a laser processing method for performing laser processing on a wafer in which a device is formed in each region defined by a plurality of scheduled processing lines intersecting the surface, and holding the back side of the wafer by the holding means Before or after performing the holding step, an ice layer forming step for forming an ice layer covering the surface of the wafer, and from the surface of the wafer held by the holding means and having the surface covered with the ice layer. A laser processing step of forming a laser processing groove along a processing line by irradiating the wafer with a laser beam having a wavelength that absorbs the wafer through the ice layer. A method is provided.

  In the laser processing method of the present invention, since the ice layer is used as a protective film in place of the protective film material such as PVA and PEG, a device can be manufactured at a lower cost than the processing using the protective film material.

It is a surface side perspective view of a semiconductor wafer. It is a perspective view of the semiconductor wafer supported by the annular frame via the dicing tape. It is a partial cross section side view which shows a holding | maintenance step. It is a partial cross section side view which shows a pure water supply step typically. It is a partial cross section side view which shows the ice layer formation step of 1st Embodiment. It is a perspective view explaining the ice layer formation step of 2nd Embodiment. It is a partial cross section side view which shows a laser processing step. It is sectional drawing which shows a washing | cleaning step.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Referring to FIG. 1, there is shown a perspective view of a semiconductor wafer (hereinafter sometimes simply referred to as a wafer) 11 which is a kind of workpiece suitable for processing by the laser processing method of the present invention.
The wafer 11 is made of, for example, a silicon wafer having a thickness of 100 μm, and a plurality of processing lines 13 are formed in a lattice shape on the surface 11a, and each region divided by the plurality of processing lines 13 is provided in each region. A device 15 is formed.

  In carrying out the laser processing of the present invention, first, as shown in FIG. 2, the back surface 11 b of the wafer 11 is attached to the dicing tape T which is an adhesive tape, and the outer periphery of the dicing tape T is attached to the annular frame F. To do. As a result, the wafer 11 is handled in a state of being mounted on the annular frame F via the dicing tape T.

  In the laser processing method of the present invention, as shown in FIG. 3, first, the back surface 11 b side of the wafer 11 is sucked and held by the chuck table 10 of the laser processing apparatus as a holding means via the dicing tape T, and the annular frame F is clamped 12. It is clamped and fixed by.

  Next, as shown in FIG. 4, the wafer 11 is surrounded by the ring-shaped bank member 14, pure water 18 is supplied from the pure water supply nozzle 16, and the pure water stored in the ring-shaped bank member 14 is stored in the wafer 11. Immerse in 18

  Next, as shown in FIG. 5, cooling air 21 cooled to, for example, about 10 ° C. below the freezing point is ejected from the cooler nozzle 20 to freeze the pure water 18 in the ring-shaped bank member 14 to form an ice layer 22, The surface 11 a of the wafer 11 is covered with the ice layer 22.

Referring to FIG. 6, there is shown a perspective view illustrating a second embodiment of the ice layer forming step. In this embodiment, the ring-shaped bank member 14 that surrounds the wafer 11 is placed on the dicing tape T before the holding step. Then, the ring-shaped bank member 14 is filled with pure water, and the wafer 11 is immersed in the pure water.
In this state, the pure water is frozen in a freezer and the surface 11a of the wafer 11 is covered with an ice layer. In carrying out the laser processing, a holding step of taking out the wafer 11 whose surface 11a is covered with an ice layer from the freezer and holding it on the chuck table 10 is carried out.

  After covering the surface 11a of the wafer 11 with the ice layer 22 in this way, the atmosphere in the processing chamber is set to 0 ° C. or lower so that the ice layer 22 does not melt, and laser processing is performed. In this laser processing, as shown in FIG. 7, a laser beam oscillated from a laser oscillator of a laser beam irradiation unit (not shown) is passed through an ice layer 22 to the surface 11a side of the wafer 11 by a condenser (laser head) 24. Irradiation is performed and the chuck table 10 is processed and fed in the direction indicated by the arrow X 1, thereby forming a laser processing groove along the planned processing line 13 on the surface 11 a of the wafer 11.

  Laser processing grooves are formed one after another along the planned processing line 13 extending in the first direction while indexing and feeding the wafer 11 in the Y-axis direction orthogonal to the X1 direction. Next, after the chuck table 10 is rotated 90 degrees, a similar laser processing groove is formed along the processing line 13 that extends in a second direction orthogonal to the first direction.

  The processing conditions for the laser processing step are set as follows, for example.

Light source: LD excitation Q switch Nd: YVO 4 pulse laser Wavelength: 355 nm (third harmonic of YVO 4 pulse laser)
Output: 3.0W
Repetition frequency: 20 kHz
Condensing spot diameter: φ1μm
Processing feed rate: 100 mm / sec

  After performing the laser processing step, a cleaning step for melting the ice layer 22 is performed. This cleaning step is performed by, for example, a spinner cleaning apparatus 30 as shown in FIG. The spinner cleaning device 30 has a spinner table 32. The spinner table 32 is connected to an output shaft 36 of a motor 34 and is rotated by the motor 34. The clamp 38 attached to the spinner table 32 clamps and fixes the annular frame F by the centrifugal force by which the spinner table 32 is rotated.

  Reference numeral 40 denotes a cleaning water receiving container, and the spinner table 32 is accommodated in the cleaning water receiving container 40. Reference numeral 42 denotes a cleaning nozzle which is rotated by the motor 44 between the operating position shown in FIG. 8 and the retracted position retracted from the spinner table 32. The cleaning nozzle 42 is connected to a pure water supply source (not shown).

  A drying nozzle 46 is rotated by a motor 48 between a retracted position shown in FIG. 8 and an operating position positioned on the spinner table 32. The drying nozzle 46 is connected to an air supply source (not shown).

In the cleaning step, after the ring-shaped bank member 14 is removed, the wafer 11 covered with the ice layer 22 is sucked and held via the dicing tape T in the room temperature atmosphere by the spinner table 32 of the spinner cleaning device 30.
The spinner table 32 is rotated by the motor 34 while the pure water 43 is jetted from the jet nozzle 42a of the cleaning nozzle 42 positioned at the operating position, and the wafer 11 is spin cleaned. By this spin cleaning, debris generated by the laser processing together with the ice layer 22 is removed. You may make it wash | clean by supplying warm water from the washing nozzle 42. FIG.

  After the spin cleaning, the cleaning nozzle 42 is rotated to the retracted position, and then the drying nozzle 46 is positioned at the operating position, and the spinner table 32 is rotated by the motor 34 while air is ejected from the drying nozzle 46 to thereby clean the wafer 11 after cleaning. Spin dry.

  In the laser processing method of the above-described embodiment, the ice layer 22 is used as a protective film instead of the protective film material made of a water-soluble resin such as PVA, PEG, etc. Therefore, the device 15 is less expensive than laser processing using the protective film material. Can be manufactured. By using pure water as the water for forming the ice layer 22, the residue of the protective film on the device 15 does not become a problem, and the cleaning time can be shortened as compared with the conventional method using the protective film material.

DESCRIPTION OF SYMBOLS 10 Chuck table 11 Semiconductor wafer 14 Ring-shaped bank member 15 Device 16 Pure water supply nozzle 18 Pure water 20 Cooler nozzle 21 Cooling air 22 Ice layer 24 Condenser (laser head)
30 Spinner cleaning device 32 Spinner table 42 Cleaning nozzle 46 Drying nozzle

Claims (1)

A laser processing method for performing laser processing on a wafer in which a device is formed in each region divided by a plurality of processing lines intersecting the surface,
A holding step for holding the back side of the wafer by holding means;
Before or after performing the holding step, an ice layer forming step of forming an ice layer covering the surface of the wafer;
A laser beam having a wavelength that absorbs the wafer from the surface of the wafer that is held by the holding means and whose surface is coated with the ice layer is irradiated to the wafer through the ice layer, and the laser is processed along the planned processing line. A laser processing step for forming a processing groove;
A laser processing method comprising:

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