JP2009123875A - Laser dicing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser dicing method working a wafer, even in an acceleration/deceleration moving block and having a shorter work time and higher productivity, as compared to those of conventional types. <P>SOLUTION: In the laser dicing method, a laser beam L is made incident from a surface of the wafer W. A reforming region P is formed inside the wafer W and the wafer W is divided into individual chips, the wafer W is laser-diced, while an oscillation frequency of the laser beam L is controlled, based on moving speed of a chuck table 12 on which the wafer W is placed and which moves in an X direction, which is a working direction. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a laser dicing method, and more particularly to a laser dicing method in which a laser beam is used to divide individual chips such as semiconductor devices and electronic components from a wafer.

  Conventionally, in order to divide a wafer having a semiconductor device or electronic component formed on its surface into individual chips, a dicing machine that uses a grinding wheel called a dicing blade to form a grinding groove in the wafer and cut the wafer has been used. . The dicing blade is obtained by electrodepositing fine diamond abrasive grains with Ni, and an extremely thin one having a thickness of about 30 μm is used.

  The dicing blade was rotated at a high speed of 30,000 to 60,000 rpm and cut into the wafer, and the wafer was completely cut (full cut) or incompletely cut (half cut or semi-full cut). Half-cut is a method of cutting about half the thickness into a wafer, and semi-full cut is a method of forming a grinding groove leaving a thickness of about 10 μm.

  However, when grinding with this dicing blade, since the wafer is a highly brittle material, it becomes brittle mode processing and chipping occurs on the front and back surfaces of the wafer, and this chipping is a factor that degrades the performance of the divided chips. It was. In particular, chipping generated on the back surface has been a serious problem because cracks gradually progress inside.

To solve this problem, instead of cutting with a conventional dicing blade, a laser beam with a focused point is incident on the inside of the wafer, and a plurality of modified regions due to multiphoton absorption are formed inside the wafer and separated. A laser dicing apparatus and a dicing method for dividing into individual chips have been proposed (for example, Patent Document 1).
JP 2004-111946 A

  When the modified region is formed using a laser dicing apparatus as described in Patent Document 1, the width of the modified region formed in the wafer varies depending on the pulse width (oscillation frequency) of the laser. . Therefore, depending on the modified region to be formed. Since the quality after dicing is affected, there is a correlation between the laser pulse width and the dicing quality. Therefore, during processing, high processing quality is ensured by appropriately setting the relative speed with the wafer according to the oscillation frequency.

  Currently, the laser-side oscillation frequency is not changed linearly, and processing is performed using the oscillation frequency set before processing. Therefore, it is necessary to keep the wafer moving speed constant during processing. For this reason, in the wafer acceleration / deceleration movement section where the movement speed is not constant, the wafer cannot be processed and a section that does not contribute to the processing occurs. Therefore, the wafer movement section is longer than the actual processing distance. It was. For this reason, the processing time becomes longer, which has been a factor in reducing productivity.

  In other words, in the current laser dicing apparatus, the wafer is located on the drive axis (X axis) that moves linearly, and the laser light source is located on the movement axis (Y axis) orthogonal thereto. Dicing can be performed by irradiating a laser beam from a laser light source on the Y axis while the object on the X axis moves linearly. Conventionally, the linear movement of the wafer consists of “stop”, “acceleration”, “speed settling”, “constant speed move”, “post-settling”, “deceleration”, “stop”, laser light source and wafer When the two are orthogonal to each other (during processing), it is necessary that the object is “moving at constant speed”. Therefore, in the conventional method, during the movement of the wafer, the processing cannot be performed between “stop” and “speed settling”, and “post-settling” and “stop”, the processing time becomes long, and the production A decline in sex was observed.

  The present invention has been made in view of such circumstances, and it is possible to process a wafer even in the acceleration / deceleration movement section of the wafer. The purpose is to provide.

  In order to achieve the above object, the present invention provides a laser dicing method in which a laser beam is incident from the surface of a wafer to form a modified region inside the wafer, and the wafer is divided into individual chips. A laser dicing method comprising: laser dicing the wafer while controlling the oscillation frequency of the laser light on the basis of a moving speed of a chuck table on which the wafer is placed and moved in the processing direction X direction. provide.

  According to the first aspect, the oscillation frequency of the laser beam is controlled in accordance with the moving speed of the chuck table on which the wafer is placed. Therefore, regardless of the moving speed of the chuck table, the modified region formed in the wafer can be formed with a uniform width by controlling the oscillation frequency. Then, by dividing the wafer, chips can be formed with the same quality.

  A second aspect of the present invention is the method according to the first aspect, wherein when the moving speed of the chuck table is fast, the oscillation frequency of the laser light is increased, and when the moving speed of the chuck table is slow, the oscillation frequency of the laser light is decreased. It is characterized by that.

  According to the second aspect, when the moving speed of the chuck table is high, the oscillation frequency of the laser beam is increased, and when the moving speed of the chuck table is low, the moving speed of the chuck table is reduced by decreasing the oscillation frequency. Even if it changes, the modified regions can be formed at equal intervals, so that chips can be formed with the same quality.

  According to the present invention, since the oscillation frequency of the laser beam can be controlled in accordance with the moving speed of the wafer, the modified region formed in the wafer can be formed with a uniform width. Therefore, the divided chips can be formed with the same quality. Conventionally, processing could not be performed until the moving speed of the wafer became uniform. However, according to the present invention, laser dicing can be performed even when the moving speed of the wafer is accelerated or decelerated. Thus, the processing time can be shortened. Further, in the present invention, since the oscillation frequency is controlled according to the moving speed of the wafer, the width in which the modified region is formed can be prevented from being extremely widened, and a high quality chip can be obtained. Can be formed.

  Hereinafter, a preferred implementation of the laser dicing method according to the present invention will be described with reference to the accompanying drawings.

  First, a laser dicing apparatus used in the laser dicing method of the present invention will be described. FIG. 1 is a diagram schematically showing the configuration of a laser dicing apparatus.

  The laser dicing apparatus 10 includes a chuck table 12, an X guide base 15, a Y guide base 41, a Z guide base 51, an elevator 13, a standby table 14, a laser head 31, a measuring means 16, a control means 21, and a main body 19. Recording means 22 is provided.

  The chuck table 12 sucks and mounts the wafer W, is rotated in the arrow θ direction by a θ rotation shaft (not shown), and is processed and processed in the arrow X direction by an X table (not shown) mounted on the X guide base. Is done.

  A Y guide base 41 is provided above the chuck table 12. Two Y tables (not shown) are provided on the Y guide base 41, and Z guide bases 51 and 51 are attached to the respective Y tables.

  Each Z guide base 51, 51 is provided with a Z table (not shown), and a laser head 31 is attached to each Z table via a holder 32. The two laser heads 31, 31 are Each is independently moved in the Z direction and is independently indexed and fed in the Y direction.

  The elevator 13 accommodates the cassette in which the wafer W is stored, moves up and down, and supplies the wafer W to the standby table 14 by a transfer device (not shown). The standby table is provided at the same height as the chuck table 12, and each process necessary before and after processing is performed on the wafer W placed on the standby table.

  The measuring means 16 is a contact or non-contact type displacement measuring device, and measures the height of the wafer W from the amount of displacement.

  The control means 21 housed in the main body 19 includes a CPU, a memory, an input / output circuit unit, and the like. The control means 21 calls information necessary for processing from the database stored in the recording means 22 housed in the main body 19 and controls the operation of each part of the laser dicing apparatus 10.

  In the present invention, the control means 21 controls the moving speed of the chuck table and the oscillation frequency of the laser beam. By controlling the oscillation frequency according to the moving speed of the chuck table, the modified region can be formed at a predetermined interval, and even when moving the chuck table on which the wafer is mounted, the quality is equivalent. Thus, a modified region can be formed. Specifically, when the moving speed of the chuck table is fast, the laser beam oscillation frequency is increased, and when the moving speed is slow, the oscillation frequency is decreased to equalize the intervals between the reformed regions to be formed. Can do.

  As a method of controlling the oscillation frequency of the laser beam and the moving speed of the chuck table, load detecting means for detecting the power value of the motor for moving the chuck table is provided, and the control unit is configured to detect the laser beam based on the detected power value. Controls the oscillation frequency.

  FIG. 2 is a diagram showing a configuration diagram of an embodiment applied to a dicing apparatus used in the dicing method of the present invention. The motor 61 is a motor that drives the chuck table 12 in the X-axis direction. The high frequency motor driver 62 generates a drive signal for the motor 61 in accordance with the control signal. The wattmeter 63 is a wattmeter that detects the power value of the high-frequency motor driver 62, and the oscillation frequency control unit 64 sends a signal for controlling the oscillation frequency of the laser light L to the laser head 31 based on this power value.

  In the present invention, the power value of the motor 61 is always detected by the wattmeter 63. The oscillation frequency control unit 64 reads this power value, and feedback-controls the oscillation frequency of the laser light L according to this power value. By controlling the oscillation frequency by such a method, the oscillation frequency of the laser beam L can be controlled in accordance with the moving speed of the wafer W, and a stable modified region P can be formed. Chips can be divided with less chipping.

  FIG. 3 shows an example of movement characteristics of the chuck table. FIG. 3A shows the speed characteristics of the method of the present invention, and FIG. 3B shows the speed characteristics of the conventional method. As can be seen from FIG. 3, in the conventional method, processing is performed only when the moving speed of the chuck table (wafer) is constant, but in FIG. 3, processing is also performed in the case of acceleration and deceleration. Therefore, the processing time can be shortened. For example, when the chuck table acceleration is 0.25 G, the constant speed is 300 mm / s, the settling distance is 25 mm, and the constant speed distance is 204 mm, the conventional method takes 1.092 seconds. The time can be reduced to 0.802 seconds.

  In addition, the laser dicing apparatus 10 includes a wafer transfer means, an operation plate, a television monitor, an indicator lamp, and the like (not shown).

  On the operation plate, switches for operating each part of the laser dicing apparatus 10 and a display device are attached. The television monitor displays a wafer image captured by a CCD camera (not shown) or displays program contents and various messages. The indicator lamp displays an operating status such as processing end, emergency stop, etc. during processing of the laser dicing apparatus 10.

  FIG. 4 is a side view for explaining the configuration of the laser head 31. The laser head 31 is positioned above the wafer W so as to irradiate the laser light L onto the wafer W placed on the chuck table 12 provided on the base 11 of the laser dicing apparatus 10.

  The laser head 31 includes a laser oscillator 31A, a collimating lens 31B, a mirror 31C, a condensation lens 31D, and the like. As shown in FIG. 4, laser light oscillated from the laser oscillator 31A is parallel to the collimating lens 31B in the horizontal direction. And is reflected in the vertical direction by the mirror 31C and condensed by the condensation lens 31D.

  When the condensing point of the laser light L is set inside the thickness direction placed on the chuck table 12, the energy of the laser light L transmitted through the surface of the wafer W is concentrated at the condensing point, and the condensing inside the wafer is performed. Modified regions such as a crack region, a melting region, and a refractive index change region due to multiphoton absorption are formed in the vicinity of the point.

  Further, the laser head 31 has a tilt mechanism (not shown) so that the laser head 31 can be irradiated at an arbitrary angle with respect to the laser light L.

  FIG. 5 is a conceptual diagram illustrating a modified region formed in the vicinity of a condensing point inside the wafer. FIG. 5A shows a state in which the modified region P is formed at the condensing point of the laser beam L incident on the inside of the wafer W. FIG. In this state, the wafer W is moved in the horizontal direction, and the modified region P is continuously formed, whereby the continuous modified region P is formed as shown in FIG.

  In this state, the wafer W is cleaved naturally along the modified regions P, P,... By applying the slight external force from the modified region P as a starting point. In this case, the wafer W is easily divided into chips without causing chipping on the front and back surfaces. If the widths of the modified regions P, P,... Are different, there is a partial difference when dividing into chips, which is not preferable. Therefore, in the present invention, by adjusting the moving speed of the chuck table and the oscillation frequency of the laser light, the width of the modified regions P, P,... Is adjusted to form the modified region P.

  The measuring means 16 is attached to the side surface of the laser head 31 and is moved in the Y direction and the Z direction by the Y table and the Z table in the same manner as the laser head 31.

  The measuring means 16 is provided with a contact-type displacement measuring device. The displacement measuring device is moved up and down in the Z direction by an air cylinder, and the measuring element is retracted from the measuring surface except during measurement.

  In the laser dicing apparatus used in the laser dicing method of the present invention, when laser dicing the wafer W, the wafer W is usually used for dicing via a dicing tape T having an adhesive on one side as shown in FIG. And is transported in this state during the laser dicing process.

  As the measurement means, a non-contact type measurement means such as a laser displacement meter or an IR camera can also be used.

  Next, the laser dicing method of the present invention will be described. In the laser dicing apparatus 10, first, the wafer W attached to the dicing tape T shown in FIG. 6 and mounted on the frame F is stored in the cassette, and the cassette is set in the elevator 13 (step S1).

  When it is necessary to input processing data such as wafer size and index amount, the setting is performed by inputting from an operation panel (not shown) at this point. After the setting, the machining is started by operating the machining start instruction, and the elevator 13 starts moving.

  The wafer W mounted on the frame F is transferred from the elevator 13 moved to a predetermined height by a transfer device (not shown), and is transferred onto the standby table 14 (step 2).

  On the standby table 14, various processes required before processing, such as cleaning the surface of the wafer W, checking the size and chipping of the wafer W, or checking the position of the alignment mark, are performed.

  After the processing on the standby table 14 is completed, the wafer W is transferred by a transfer device (not shown) and placed on the chuck table 12 located at the origin position, and the chuck table 12 is moved in the X direction by the X table. Then, it moves to the processing position below the Y guide base 41 (step S3).

  The thickness of the wafer W on the chuck table 12 moved to the processing position is measured by the measuring means 16, and the measured value of the thickness of the wafer W is sent to the control means 21 and processed (step 4).

  The value of the thickness of the wafer W sent to the control means 21 is collated with a database stored in the recording means 22 and measured from the modified region forming conditions corresponding to each thickness of the wafer W described in the database. A modified region forming condition suitable for the thickness of the wafer W thus selected is selected (step S5).

  The modified region forming strip is composed of the number of modified regions to be formed, the position of the modified region to be formed, the thickness of the modified region to be formed, the speed at which the laser beam is moved, and the shape of the laser beam. In the database, each condition is described according to the assumed thicknesses of all the wafers W.

  The selected modified region forming conditions are set in the laser dicing apparatus 10 by the control means 21, and laser dicing is started based on the set conditions (step S7).

  When laser dicing is started, the power value of the high frequency motor driver 62 is detected by the wattmeter 63 according to the drive signal of the motor 61 that drives the chuck table 12 as described above. Then, the oscillation frequency control unit 64 controls the oscillation frequency of the laser light L to form the modified region P to be formed (step 8).

  After the laser dicing is completed, the chuck table returns to the origin position, and the wafer W laser-diced by the transfer device is returned to the standby table 14 (step S9).

  On the standby table 14, various processes necessary for processing such as expanding the wafer W, cleaning the wafer W, or checking the wafer surface are performed.

  After the processing on the standby table 14 is completed, the wafer W is returned to the cassette by the transfer device, and after the processing of all the wafers W is completed, the elevator 13 moves to the cassette removal position and finishes the processing (step S10). ).

  Thereby, by controlling the oscillation frequency based on the moving speed of the chuck table 12, the reforming region P can be stably formed even if the moving speed of the chuck table is not constant.

  In the present invention, an apparatus having a configuration like the laser dicing apparatus 10 shown in FIG. 1 is described. However, the present invention is not limited to this, and any apparatus capable of performing dicing using laser light may be used. Can also be suitably used.

It is the top view which showed the structure of the laser dicing apparatus typically. It is a figure which shows the structure of the Example of this invention. It is a figure which shows the movement characteristic of a chuck table (wafer). It is the side view which showed the structure of the measurement means. It is a conceptual diagram showing the modified layer formed in the wafer inside. It is the perspective view which showed the wafer mounted in the flame | frame.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Laser dicing apparatus, 11 ... Base, 12 ... Chuck table, 13 ... Elevator, 14 ... Standby table, 15 ... X guide base, 16 ... Measuring means, 19 ... Main body, 21 ... Control means, 22 ... Recording means, 31 ... Laser head, 31A ... Laser oscillator, 31B ... Collimating lens, 31C ... Mirror, 31D ... Condensation lens, 32 ... Holder, 41 ... Y guide base, 51 ... Z guide base, 61 ... Motor, 62 ... High frequency motor driver, 63 ... Watt meter, 64 ... Oscillation frequency controller, F ... Frame, L ... Laser light, P ... Modified region, T ... Dicing tape, W ... Wafer

Claims (2)

In a laser dicing method in which a laser beam is incident from the surface of a wafer to form a modified region inside the wafer, and the wafer is divided into individual chips.
A laser dicing method, wherein the wafer is laser-diced while controlling the oscillation frequency of the laser beam based on a moving speed of a chuck table on which the wafer is placed and moved in the X direction which is a processing direction.   The oscillation frequency of the laser beam is increased when the moving speed of the chuck table is fast, and the oscillation frequency of the laser beam is decreased when the moving speed of the chuck table is slow. Laser dicing method.

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