DE102014218759A1 - Machining process for a workpiece - Google Patents

Abstract

A method of processing a workpiece includes: a modification layer forming step for applying a laser beam having a wavelength such that it can be transmitted through the workpiece to thereby form modified layers within the workpiece; and a dividing step after performing the modification layer forming step for applying a laser beam having a wavelength near to an absorption edge of the workpiece and an absorption side of the absorption edge along the modified layers, thereby dividing the workpiece with the modified layers as dividing starting points.

Description

BACKGROUND OF THE INVENTION

Field of the invention

The present invention relates to a method of machining a workpiece in which a laser beam is converged to the inside of the workpiece to form thus modified layers serving as division starting points.

Description of the Related Art

In order to divide a workpiece such as a semiconductor wafer into a plurality of chips, there has been proposed a method of machining a workpiece by converging a laser beam, which is slightly absorbed in the workpiece, into the inside of the workpiece to form a modified layer (modification layer) serving as a division starting point (see, for example, U.S. Pat Japanese Patent No. 3408805 ). After the modified layers each extending along each of streets (parting lines) on the workpiece are formed inside the workpiece by the above-mentioned machining method, the workpiece is pressed along each of the streets. Alternatively, a band attached to the workpiece is widened (see, for example, the Laid-Open Patent Publication) Japanese Patent No. 2006-229021 ). By external forces applied to the workpiece by one of these methods having the modified layers formed therein, the workpiece can be divided along the streets.

SUMMARY OF THE INVENTION

Meanwhile, in the method of pressing the workpiece along each road (breaking), a blade for pressing (crushing bar) is pressed against the road, whereby a force is applied to the workpiece. Therefore, as the number of roads increases in accordance with a reduction in the chip size, the time required for splitting the work becomes longer, resulting in a decreased productivity.

On the other hand, in the method of expanding the band attached to the workpiece (band widening), external forces are exerted simultaneously on all roads for the purpose of division, which promises excellent productivity. However, if the number of roads increases in accordance with a reduction in chip size, the force applied to each road by expanding the belt is reduced, making it impossible to properly split the workpiece. This problem becomes particularly serious in the case of workpieces with a high Mohs hardness, such as GaN wafers and SiC wafers. Therefore, if the band widening is used under the above conditions, it is inevitable to apply the crushing method or a like method together, making it impossible to maintain a suitably high productivity.

In view of the foregoing discussions, it is an object of the present invention to provide a method of machining a workpiece, in which the workpiece can be divided appropriately while maintaining high productivity.

According to one aspect of the present invention, there is provided a method of machining a workpiece, comprising: a modification layer forming step of applying a laser beam having a wavelength such that it can be transmitted through the workpiece, thereby to form a modified layer ( Modification layer) within the workpiece; and a dividing step after performing the modification layer forming step for applying a laser beam having a wavelength near an absorption edge of the workpiece and an absorption side of the absorption edge along the modified layer, thereby dividing the workpiece with the modified layer as a division starting point.

In the method of machining a workpiece according to the present invention, the modification layer forming step for applying a laser beam that can be transmitted (transmissible) highly by the workpiece is performed so as to form modified layers within the workpiece, followed by A dividing step of applying a laser beam which can be absorbed to some extent in the workpiece (absorbable) along each of the modified layers. Therefore, the heat generated by the application of the absorbable laser beam causes a stress applied to each of the modified layers, whereby the workpiece can be divided appropriately. In addition, in the method for machining a workpiece according to the present invention, it is sufficient that the application of the laser beam is performed twice in the modification layer formation step and the division step. This makes it possible to maintain a sufficiently high productivity.

Therefore, according to the present invention, it is possible to provide a method of machining a workpiece, in which the workpiece can be divided appropriately while maintaining high productivity.

The above and other objects, features and advantages of the present invention and the manner in which these will be accomplished will become more apparent and the invention itself will best be understood by the following description and the appended claim with reference to the accompanying drawings in which: which show a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

1 Fig. 15 is a perspective view schematically showing a structural example of a workpiece;

2 Fig. 16 is a partially sectional side view schematically illustrating a modification layer forming step;

3 Fig. 10 is a partially sectional side view schematically illustrating a dividing step; and

4A and 4B 12 are sectional views schematically illustrating states of a workpiece to which the laser beam is applied in the dividing step.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. A dividing method according to this embodiment includes a modification layer forming step (see 2 ) and a division step (see 3 ). In the modification layer forming step, a laser beam, which can be highly transmitted through the workpiece, is applied along each of streets (parting lines) on the workpiece so as to form there a modified layer serving as a division starting point. In the dividing step, a laser beam, which can be absorbed to some degree in the workpiece, is applied along the modified layers so as to divide the workpiece with the modified layers as dividing starting points. The dividing method according to this embodiment will be described in detail below.

1 FIG. 15 is a perspective view schematically showing a structural example of a workpiece in this embodiment. FIG. As in 1 is shown is a workpiece 11 for example, a circular disc-shaped semiconductor wafer. A top surface 11a of the workpiece 11 is in a middle component area 13 and a circumferential excess area 15 that the component area 13 surrounds, split. The component area 13 is further by roads (dividing lines) 17 , which are arranged in a grid pattern, divided into several areas, wherein a component 19 , such as an IC, is formed in each of the multiple regions. An outer circumference 11c of the workpiece 11 is bevelled so that it has an arcuate cross-sectional shape. Before the method of machining a workpiece according to this embodiment is performed, a guard tape is previously formed 21 on the aforementioned workpiece 11 attached, with a top surface 21a of the protective tape 21 in contact with the top surface 11a of the workpiece 11 is arranged (see 2 Etc.). In addition, an annular frame will be previously 23 on an outer peripheral portion of the protective tape 21 attached.

In the method of processing a workpiece according to this embodiment, first, a modification layer forming step is performed, in which a laser beam is taken along each of the streets 17 of the aforementioned workpiece 11 is applied so that there is formed a modified layer, which serves as a division starting point. 2 Fig. 16 is a partially sectional side view schematically illustrating the modification layer forming step.

The modification layer forming step is performed by using an in 2 shown laser beam processing apparatus 2 carried out. The laser beam processing device 2 has a holding table (clamping table) 4 on, on which the workpiece 11 is held by suction. jam 6 for tight clamping of the annular frame 23 that the workpiece 11 are on a perimeter of the holding table 4 arranged. The holding table 4 is connected to a rotating mechanism (not shown) such as a motor and is rotated about a vertical axis. In addition, a moving mechanism (not shown) is below the holding table 4 provided and becomes the holding table 4 moved in horizontal directions by the movement mechanism. A surface of the holding table 4 is as a holding surface 4a provided on which the workpiece 11 is held by suction, with the side of the top surface 11a (the side of the protective tape 21 ) points downwards. A negative pressure of a suction source (not shown) is provided by one within the holding table 4 formed channel (not shown) on the holding surface 4a applied, whereby a suction force for sucking the workpiece 11 is produced. A first laser beam machining head 8th is above the holding table 4 arranged. The first laser beam machining head 8th is constructed such that a laser beam L1 oscillated by a first laser beam oscillator (not shown) enters the inside of the workpiece 11 , sucking on the holding table 4 held, is converged.

In the modification layer forming step, a back surface is first formed 21b of the protective tape 21 with the holding surface 4a of the holding table 4 brought into contact and applied the negative pressure of the suction on this. As a result, the workpiece becomes 11 on the holding table 4 through the interposed protective tape 21 kept under suction. In this state, the side of the back surface is 11b of the workpiece 11 exposed on the upper side. Subsequently, the holding table 4 moved and rotated so that the first laser beam machining head 8th to the street 17 of the edit object. After alignment, the laser beam L1 from the first laser beam machining head 8th towards the side of the back surface 11b of the workpiece 11 radiated and become at the same time the holding table 4 and the first laser beam machining head 8th in a first direction parallel to the road 17 of the machining object in relative motion (machining feed) brought. It should be noted that in 2 only the holding table 4 is moved.

The wavelength of the first laser beam processing head 8th emitted laser beam L1 is such a wavelength that this little in the workpiece 11 absorbed (that is transmitted by this) is. When the laser beam L1 with such a wavelength in the interior of the workpiece 11 is converged, a workpiece area in the vicinity of a convergence point P1 can be modified by multiphoton absorption. Therefore, when the laser beam L1 is applied simultaneously with the above-mentioned relative movement (machining feed), a modified film is formed 25 along the road 17 formed the machining object. If the workpiece 11 For example, a pulsed YAG or YVO4 laser beam oscillator is used as the first laser beam oscillator, a laser beam L1 having a wavelength of 1064 nm oscillates at an output power of 0.25 W, and the laser beam L1 converges so that an application spot diameter of approximately 1 micron is obtained. This allows the formation of modified layers 25 with high quality. If the workpiece 11 For example, if a 4H SiC wafer with n conductivity is used, a pulsed YVO4 laser beam oscillator is used as the first laser beam oscillator, a laser beam L1 having a wavelength of 532 nm is oscillated at an output power of 0.9 W, and the laser beam L1 is converged in that an application spot diameter of approximately 1 μm is obtained. This allows the formation of modified layers 25 with high quality.

After the formation of the modified layer 25 along the road 17 of the processing object, the radiation of the laser beam L1 is stopped and becomes the holding table 4 and the first laser beam machining head 8th in a second direction perpendicular to the road 17 of the processing object in relative motion (Einteilungszuführung) brought. As a result, the first laser beam machining head becomes 8th to an adjacent street 17 aligned. After this alignment, a modified layer similar to the aforementioned modified layer becomes 25 along the adjacent street 17 educated. This process is repeated to the modified layers 25 along all the roads 17 , which extend in the first direction, form, after which the holding table 4 is rotated by 90 degrees about the vertical axis and a modified layer 25 along each of the streets 17 formed in a second direction perpendicular to the first direction is formed. If the modified layers 25 each along all roads 17 have been formed, the modification layer forming step is completed.

After the modification layer forming step, a dividing step for applying a laser beam along the modified layers 25 so as to get the workpiece 11 to share. 3 is a partially sectioned side view schematically illustrating the division step. As in 3 is shown in the dividing step, one of the first laser beam machining head 8th different second laser beam machining head 10 used. The second laser beam machining head 10 Brings a laser beam L2 oscillated by a second laser beam oscillator (not shown) onto the workpiece 11 on the holding table 4 is held by suction.

In the division step, the holding table 4 initially moved and rotated about the second laser beam machining head 10 to the modified layer 25 align the division object. After alignment, the laser beam L2 from the second laser beam machining head 10 towards the side of the back surface 11b of the workpiece 11 radiated and become at the same time the holding table 4 and the second laser beam machining head 10 in a first direction parallel to the modified layer 25 of the division object into relative movement (machining feed). It should be noted that in 3 only the holding table 4 is moved.

A wavelength of the second laser beam machining head 10 emitted laser beam L2 is a wavelength near to an absorption edge (absorption optical edge) of the workpiece 11 and on the absorption side of the absorption edge where the absorptivity (or absorbency) is higher than at the absorption edge. Here, the absorption edge (optical absorption edge) denotes a wavelength (or energy) at which the absorption coefficient in abruptly changes an absorption spectrum. When the laser beam L2 with such a wavelength on the workpiece 11 is applied, the laser beam L2 in the workpiece 11 absorbed, creating a workpiece area around each modified layer 25 is heated around. The application of the laser beam L2 is performed simultaneously with the relative movement (machining feed), whereby the workpiece 11 along the modified layer 25 can be shared.

4A and 4B are sectional views, the states of the workpiece 11 to which the laser beam L2 is applied in the division step schematically illustrate. It should be noted that the 4A and 4B show a cross section perpendicular to the in 3 shown cross-section is. As in 4A is shown, when the laser beam L2 on the workpiece 11 is applied, a workpiece area around the modified layer 25 warmed around. The area heated by the laser beam L2 is thermally expanded, so that a stress around the modified layer 25 is generated around. As a result, as in 4B shown is a crack 27 that differs from the modified layer 25 towards the top surface 11a and the back surface 11b extends, trained and the workpiece 11 thus with the modified layer 25 divided as a division starting point.

If the workpiece 11 is a silicon wafer, for example, a CW laser beam oscillator is used as the second laser beam oscillator, and a laser beam L2 having a wavelength of 1080 to 1100 nm is oscillated at an output power of 100 to 120W. The laser beam L2 is formed so that an application spot diameter of approximately 0.8 mm at the back surface 11b of the workpiece 11 is obtained. This allows an advantageous division of the workpiece 11 , If the workpiece 11 is a 4H-SiC wafer with n conductivity, a CW laser beam oscillator is used as the second laser beam oscillator, and a laser beam L2 having a wavelength of 1080 to 1100 nm is oscillated at an output power of 130W. The laser beam L2 is formed so that an application spot diameter of approximately 1 mm at the back surface 11b of the workpiece 11 is obtained. This allows an advantageous division of the workpiece 11 ,

Here, when a laser beam L2 having a wavelength at which the absorption degree in the workpiece 11 is too high, the workpiece is used 11 only on the side of the back surface 11b heated so that it is impossible to cover the area around the modified layer 25 around suitable to warm. In consideration of this, in this embodiment, a laser beam L2 having a wavelength close to the absorption edge of the workpiece 11 used. This ensures that the workpiece area around the modified layer 25 around in its entirety is suitably heated, thereby providing an advantageous division of the workpiece 11 is possible. Therefore, in this embodiment, the wavelength is close to the absorption edge of the workpiece 11 a wavelength that ensures that the laser beam is partially in the workpiece 11 absorbed (partially by the workpiece 11 is transmitted) and that the area around the modified layer 25 around in its entirety can be heated appropriately.

For example, a silicon wafer absorbs light having a wavelength of less than 1100 nm (absorption edge: 1100 nm (≈ 1.13 eV)). Therefore, if a silicon wafer is used as the workpiece 11 is used, preferably a laser beam L2 having a wavelength of approximately 1000 to 1100 nm used. In addition, an n-type conductivity 4H-SiC wafer absorbs light having a wavelength greater than 1080 nm (absorption edge: 1080 nm (≈1.15 eV)). Therefore, if a 4H-SiC n-type conductivity wafer becomes the workpiece 11 is used, preferably a laser beam L2 having a wavelength of approximately 1080 to 1200 nm used.

However, the workpiece can 11 have multiple absorption edges. For example, the n-type 4H SiC wafer has absorption edges at 480 nm (≈ 2.55 eV), 440 nm (≈ 2.9 eV), and 360 nm (≈ 3.35 eV) in addition to the above-mentioned absorption edge This light absorbs and absorbs at a wavelength of 440 to 480 nm and light having a wavelength that is equal to or less than 360 nm. If a workpiece 11 With multiple absorption edges in this manner, any one of the absorption edges may be used as a reference for determining the wavelength of the laser beam L2. For example, for the n-type 4H-SiC wafer, a laser beam L2 having a wavelength of approximately 440 to 480 nm and a laser beam L2 having a wavelength of approximately 340 to 360 nm may also be used.

After the application of the laser beam L2 along the modified layer 25 of the division object, the radiation of the laser beam L2 is stopped and becomes the holding table 4 and the second laser beam machining head 10 in a second direction perpendicular to the modified layer 25 in relative motion (Einteilungszuführung) brought. As a result, the second laser beam machining head becomes 10 to an adjacent modified layer 25 aligned. After this alignment, the laser beam L2 becomes along the adjacent modified layer 25 applied. This process is repeated to the Laser beam L2 along all modified layers 25 , which extend in the first direction, apply, after which the holding table 4 rotated 90 degrees about the vertical axis and the laser beam L2 along each of the modified layers 25 being applied in the second direction perpendicular to the first direction is applied. When the laser beam L2 along all the modified layers 25 applied and the workpiece 11 divided, the division step is completed.

As described above, in the method for machining a workpiece according to this embodiment, the modification layer forming step for applying the laser beam L1 that can be highly transmitted is performed to the modified layers 25 within the workpiece 11 followed by the dividing step of applying the laser beam L2, which can be absorbed to some degree. This ensures that the heat generated by the application of the absorbable laser beam L2, a voltage around each modified layer 25 is exercised around, causing the workpiece 11 can be divided appropriately. In addition, in the method of processing the workpiece according to this embodiment, it is sufficient that the application of the laser beams L1 and L2 is performed in the modification layer forming step and the dividing step, and therefore sufficiently high productivity can be maintained. Therefore, according to the present invention, it is possible to provide a method for machining a workpiece, in which the workpiece 11 can be divided appropriately while maintaining high productivity.

It should be noted that the present invention is not limited to the above-described embodiment and various modifications are possible in the practice of the invention. For example, in the division step described above, the laser beam L2 is propagated along all the modified layers 25 , which extend in the first direction, applied, after which the laser beam L2 along each of the modified layers 25 , which extend in the second direction, is applied. However, this does not limit the method of machining a workpiece according to the present invention. For example, a structure may be used in which the laser beam L2 is propagated along all the modified layers 25 is applied, which extends in the second direction, after which the laser beam L2 along each of the modified layers 25 , which extend in the first direction, is applied.

In addition, although in the above-described embodiment, the modification layer forming step and the dividing step using the laser beam processing apparatus 2 which are the first laser beam machining head 8th and the second laser beam machining head 10 This does not limit the machining apparatus to be used in the method for machining a workpiece according to the present invention. For example, the modification layer forming step and the dividing step may each be performed by using two laser beam processing apparatuses each having the first laser beam machining head 8th and the second laser beam machining head 10 have to be performed.

In addition, although the silicon wafer and the SiC wafer (4H-SiC wafer) are examples of the workpiece in the above embodiment 11 are called, they limit the workpiece 11 as the processing object in the present invention. A GaN wafer, a sapphire wafer, and the like may also be used as the workpiece 11 be used.

The present invention is not limited to the details of the preferred embodiment described above. The scope of the invention is defined by the appended claims, and all changes and modifications which come within the equivalence of the scope of the claims are therefore intended to be embraced by the invention.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• JP 3408805 [0002]
• JP 2006-229021 [0002]

Claims (1)

A method of machining a workpiece, comprising: a modification layer forming step for applying a laser beam having a wavelength such that it can be transmitted through the workpiece to thereby form a modified layer within the workpiece; and a dividing step after performing the modification layer forming step for applying a laser beam having a wavelength near to an absorption edge of the workpiece and an absorption side of the absorption edge along the modified layer, thereby dividing the workpiece with the modified layer as a division starting point.

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