KR20130008857A - Laser back-lapping apparatus and method using intra-beam v-shaped micro-crack - Google Patents

Abstract

PURPOSE: A laser back-lapping apparatus and a method using an intra-beam V-shaped micro-crack are provided to improve processing speed by extending the gap between micro cracks. CONSTITUTION: Multiple laser beams are focused on a processing object(10). Multiple light focusing points(21,22) are formed. A micro crack is generated between the light focusing points. The micro crack has a V shape. The processing object has a separation area(30). [Reference numerals] (AA) Processing direction

Description

Laser back-lapping apparatus and method using intra-beam V-shaped micro-crack generated between multiple beams

The present invention relates to a back-lapping apparatus and method using a laser, and more particularly, to a laser back-lapping apparatus and method using a V-shaped fine crack generated between multiple beams irradiated inside the object to be processed. .

For example, a semiconductor device such as a light emitting diode (LED) is manufactured by forming a semiconductor material layer and an electrode material layer on a wafer. The manufactured semiconductor device is subjected to a packaging process, which includes a polishing process for polishing the back surface to reduce the thickness of the wafer used as the substrate. This polishing process is called a back lap process or a back-grind process.

The polishing process may be a mechanical polishing method using a rotating diamond wheel. Mechanical polishing involves friction heat between the diamond wheel and the wafer which rotates at a high speed, and the heat may cause the wafer to bend or damage the semiconductor element formed on the surface. In addition, debris generated during the mechanical polishing process may cause electrical and physical damage of the semiconductor device.

Recently, in order to solve the problem of mechanical polishing, a method of separating the wafer in the thickness direction by forming a separation surface by concentrating a laser beam inside the wafer has been studied.

SUMMARY OF THE INVENTION An object of the present invention is to provide a laser back-lapping apparatus and method capable of high-speed polishing with low generation of debris and excellent separation characteristics in a back-lapping process.

Laser back-lapping method according to an aspect of the present invention comprises the steps of focusing a plurality of laser beams spaced apart from each other in the same plane inside the object to be processed to form a plurality of light collecting points; Generating fine V-shaped cracks between the plurality of light collecting points; And forming at least one of the plurality of laser beams and the object to be processed relative to each other in a machining direction to form an isolation surface due to the V-shaped microcracks inside the object.

The V-shaped fine crack may have a corn shape cut in a direction perpendicular to the separation plane.

The plurality of light collecting points may be arranged in at least one direction of the processing direction and a direction crossing the processing direction.

The laser beam may be a pulsed laser beam. The pulse width of the pulsed laser beam may be within 1 microsecond.

The object to be processed is a crystalline material, and the pulse intensity of the pulsed laser beam may be determined to have an intensity that can melt the crystal and transform it into a granular form.

Laser back-lapping apparatus according to an aspect of the present invention, the table on which the object to be processed is mounted; A light source unit emitting at least two laser beams; A focusing lens for condensing the at least two laser beams at positions spaced apart from each other in the same plane of the interior of the object, including V- between converging points in the object to be processed by the at least two laser beams; A fine crack of a shape is formed, and at least one of the laser beam and the object to be processed is relatively moved in the processing direction to form a separation surface by the V-shaped minute crack in the object.

The V-shaped fine crack may have a corn shape cut in a direction perpendicular to the separation plane.

The converging points may be arranged in at least one of the machining direction and a direction crossing the machining direction.

The light source unit may include a light source emitting a laser beam; And a light separator that separates the laser beam into a plurality of laser beams.

The laser beam may be a pulsed laser beam. The pulse width of the pulsed laser beam may be within 1 microsecond.

The object to be processed is a crystalline material, and the pulse intensity of the pulsed laser beam may be determined to have an intensity that can melt the crystal and transform it into a granular form.

According to the laser back-lapping apparatus and method according to the present invention, the following effects can be obtained.

First, back-lapping with little thermal effect is possible by forming a separation surface due to V-shaped fine cracks by multiple beams having horizontal stresses using multiple laser beams.

Second, it is possible to form a separation plane of superior quality as compared to the conventional method of forming vertical cracks by a single beam.

Third, since the interval between the fine cracks can be made wider than the conventional method, it is possible to realize a high processing speed.

Fourth, because the crack is easily propagated in the horizontal direction by the horizontal stress can be easily separated.

Fifth, since it is easily separated by an external force, back-lap processing with less occurrence of debris in the separation process is possible.

Sixth, since the debris is generated less, it is possible to reduce the defect of the semiconductor device due to foreign matter such as fine debris generated during separation when separating the substrate on which the semiconductor device is formed as a processing object.

1 shows an embodiment of a laser back-lapping method according to the invention.
2 is a perspective view showing an arrangement example of a pair of light collecting points as one embodiment of a laser back-lapping method according to the present invention;
3 is a view illustrating a process of forming a V-shaped microcracks through melting, expanding, and contracting a pair of condensing points;
4 is a view illustrating a process in which cracks start to form during a contraction process of a pair of condensing points;
FIG. 5 is a side view showing a separation surface formed by a plurality of V-shaped fine cracks. FIG.
6 is a perspective view showing a separation surface formed by a plurality of V-shaped fine cracks.
7 is a view illustrating a process of forming a vertical crack by a single beam.
FIG. 8 is a view showing a separation surface formed by a plurality of vertical cracks. FIG.
FIG. 9 is a perspective view illustrating a method of arranging a plurality of pairs of condensing points arranged in a processing direction in a direction perpendicular to the processing direction as an example of a back-lapping method according to the present invention. FIG.
10 is a plan view illustrating a method of using a plurality of light collecting points arranged in a processing direction as an example of a back-lapping method according to the present invention.
11 illustrates a laser back-lapping apparatus according to an embodiment of the present invention.

Hereinafter, embodiments of the laser back-lapping method and apparatus according to the present invention will be described in detail with reference to the accompanying drawings. In the drawings, like reference numerals refer to like elements, and the size and thickness of each element may be exaggerated for clarity of explanation.

The laser back-lapping apparatus and method according to the present invention condenses multiple laser beams inside an object to be processed and inter-beam V-shaped micro-cracks between the multiple laser beams. ) To form an inner separation surface for separating the object to be processed in the thickness direction. After the inner separation surface is formed, the object to be processed is separated along the inner separation surface by applying physical and thermal stresses to the object from the outside, thereby reducing the thickness of the object to be polished.

As shown in FIG. 1, two laser beams 11 and 12 are irradiated with a focus on the inside of the object 10. The light collecting points 21, 22 by the laser beams 11, 12 are located in the same plane inside the object 10. For example, the light collecting points 21 and 22 may be arranged in the processing direction as shown in FIG. 1. Further, for example, as shown in FIG. 2, the laser beams 11 ′ and 12 ′ may be irradiated to form the light collecting points 21 ′ and 22 ′ in a direction crossing the processing direction. In addition to this, in particular, the arrangement direction of the light collecting points 21 and 22 is not limited, and sufficient to be spaced apart from each other in the same plane. V-shaped fine cracks are formed between the two light collecting points 21 and 22 formed by the laser beams 11 and 12. When the object 10 or the laser beams 11 and 12 are relatively moved in the plane in the processing direction and the direction orthogonal thereto, the internal separation surface 30 is formed inside the object 10. Hereinafter, a process of generating V-shaped fine cracks will be described.

When the laser beams 11 and 12 are irradiated, the laser beams are collected at the light collecting points 21 and 22 inside the object 10 as shown in FIGS. 3A, 3B, and 3C. The energy of (11) and (12) is absorbed by the object to be processed 10, and melting occurs instantaneously. In this process, expansion occurs in the vicinity of the light collecting points 21 and 22, and when the laser beams 11 and 12 pass, cooling and contracting and solidification occur. According to the experiment, the size of the melting region, the expansion region, and the contraction region is in the order of the melting region <contraction region <expansion region. In the shrinking process, as illustrated in FIG. 2C, V-shaped minute cracks 40 are generated between the light collecting points 21 and 22. Hereinafter, the process of generating the V-shaped fine crack 40 will be described in more detail.

Referring to FIG. 4, the periphery (the area shown by the dashed line) of the light-converging spots 21 and 22 that are fully inflated is also softened to some extent by the influence of heat. When cooling starts, a stress is generated from the periphery of the light collecting points 21 and 22 toward the center of the light collecting points 21 and 22. Cooling takes place faster in areas farther away from the light spots 21, 22. In particular, cooling takes place faster in the opposite region than in the light incident direction. Due to the stresses directed toward the two light collecting points 21 and 22, minute cracks 41 start to be generated in the region opposite to the light incident direction between the two light collecting points 21 and 22. As the cooling proceeds, the cracks 41 become V-shaped, which are dotted by the stresses directed toward the two light collecting points 21 and 22. As the shrinkage progresses and the size of the light collecting points 21 and 22 decreases, the cracks 41 gradually increase, and when the shrinking and solidification ends, the two light collecting points 21 as shown in FIG. The V-shaped fine cracks 40 are formed between the 22.

When the object 10 and the laser beams 11 and 12 are intermittently irradiated with relative movement in the processing direction and a plane perpendicular to the process direction through the above-described process, the object to be processed (as shown in FIGS. 5 and 6) Inside of 10) an inner separation surface 30 is formed by a plurality of V-shaped fine cracks 40. By separating the workpiece 10 in the vertical direction on the basis of the internal separation surface 30, the same effect as polishing can be obtained.

As the laser beam, a pulsed laser beam may be employed. The pulsed laser beam may have a pulse width of 1 microsecond or less. The pulse energy of the pulsed laser beam is greater than 10 micro-joule (μJ) orders, the peak pulse power is greater than 10 ² watt (W) orders, and the pulse intensity is 1 GW / The order of cm 2 or more, but the scope of the present invention is not limited thereto.

The condition of the pulsed laser beam may be determined such that energy absorption may occur inside the object 10. Energy absorption is expected to occur, for example, by multiphoton absorption or equivalent processes, but the scope of the invention is not limited by the energy absorption mechanism itself.

The condition of the pulsed laser beam may be appropriately selected according to the conditions such as material properties and processing speed of the object to be processed 10. The object to be processed 10 may be a substrate made of a transparent material. The object to be processed 10 may be a sapphire substrate, a glass substrate, a crystalline or amorphous silicon substrate, or the like, and may be a substrate of various materials. In addition, the object to be processed 10 may be a wafer on which the semiconductor element (1 of FIG. 5) is formed on the substrate.

As an example, when the material of the object 10 is a crystalline material, a pulse that is enough to break down the crystal, that is, the crystalline may be converted into a granular form by melting, expanding, and solidifying processes. The condition of the pulsed laser beam can be determined to have an intensity. The spacing (FIG. 1: A) between the light collecting points 21 and 22 is not particularly limited and may be appropriately selected within a range of several micrometers to several hundred micrometers.

For example, an internal separation surface due to V-shaped fine cracks could be formed inside the crystalline silicon substrate using a laser beam having the following conditions.

Laser power: varies within the range of 0.5 to 3 W

Pulse width: 250 ns

Pulse repetition frequency: 80 kHz

Spot diameter of condensing point: 2 μm

7 illustrates a process of forming an inner separation surface using a single beam as a comparative example. Referring to FIG. 7, when one laser beam 101 is focused inside the object to be processed, the object is locally melted at the light collecting point 102, and an expansion, shrinkage, and solidification process occurs. Since the left and right regions of the light collecting point 102 are first contracted during the shrinking process, a crack 103 is generated at the center of the light collecting point 102, and when the shrinking is completed, the crack 103 grows in the vertical direction to vertical crack 104. Is formed. When intermittently irradiating the object to be processed and the laser beam 101 in the processing direction through the above-described process, as shown in FIG. 8, the inner separation surface of the object 10 by the vertical crack 104 is shown. 130 is formed.

Now, the effect of the processing method using the V-shaped inter-beam v-shape micro-crack between the condensing points by the multiple beams according to the present invention is formed vertically inside the condensing points by the single beam. It demonstrates compared with the processing method using an intra-beam vertical micro-crack.

First, according to the processing method according to the invention it is possible to form a crack of excellent quality compared to the comparative example. The quality of the cracks for so-called back-lapping can be determined by how easily the separation process can be carried out. According to the processing method according to the present invention, the fine crack 40 is formed between the multiple beams (inter-beam), the shape is V-shaped, and in three-dimensional view, the cone shape extending in the light incident direction Close to Therefore, the V-shaped fine crack 40 has a stress in the horizontal direction and the separation surface 30 direction, so that the crack can be easily grown in the horizontal direction. In contrast, the vertical crack 104 of the comparative example formed inside the single beam is formed in the vertical direction. Therefore, the growth of the crack in the horizontal direction is not easy as compared with the V-shaped fine crack 40 according to the present invention. Therefore, the V-shaped fine crack 40 by the processing method according to the present invention can be seen that the quality is superior to the vertical crack 104 of the comparative example.

Secondly, according to the machining method according to the invention it is possible to realize a faster machining speed than the comparative example. Referring to FIG. 5, the plurality of V-shaped fine cracks 40 are cracked in the direction of the separation surface 30, and when the external force is applied, the cracks easily progress in the direction of the separation surface 30 to be adjacent to each other. It may be connected to other fine cracks 40. This means that it can be easily separated along the separating face 30. However, referring to FIG. 8, the vertical crack 104 of the comparative example is cracked in a direction orthogonal to the separation plane 130, and the separation along the separation plane 130 is performed by the V-shaped microcracks according to the present invention. It is a relatively difficult form compared to 40). This can be easily understood by comparing the shape of the separation surface 30 of FIG. 5 formed by the processing method according to the present invention and the separation surface 130 of FIG. 8 formed by the comparative example. Easy propagation of cracks in the machining direction means that the distance between cracks can be increased. That is, the distance A1 between the V-shaped fine cracks 40 shown in FIG. 5 can be made wider than the distance A2 between the vertical cracks 104 shown in FIG. 8. Therefore, according to the processing method according to the present invention, in order to form the separation surface 30 on the object 10 can be formed fewer cracks than the comparative example can increase the processing speed.

Third, according to the processing method according to the present invention can be easily cut because the crack is easily propagated in the horizontal direction by the horizontal stress, and the cross-sectional quality of the object to be processed after the cutting is very excellent compared to the comparative example to increase the yield. .

Fourth, according to the processing method according to the present invention, since it is easily separated by an external force, the possibility or amount of debris in the separation process is also less than in the comparative example. Therefore, when cutting the board | substrate with which the semiconductor element was formed as a process object, the defect of a semiconductor element by the foreign material, such as a fine piece generate | occur | produced at the time of cutting | disconnection, can be reduced.

In the above-described embodiment, a case in which the separation surface 30 is formed inside the object 10 by using a pair of laser beams 11 and 12 has been described, but the scope of the present invention is limited thereto. It is not. For example, as shown in FIG. 9, the first focusing points 21 and 22 are formed inside the object 10 by a pair of first laser beams 11 and 12. The second condensing point at a position spaced apart from the first condensing points 21 and 22 in the interior of the object 10 in a direction orthogonal to the machining direction using the pair of second laser beams 13 and 14. 23) 24 may be formed. According to such a structure, the number of reciprocating processes for forming the separation surface 30 can be reduced, and the processing speed can be improved. In the above-described embodiment, the case of forming two pairs of light collecting points 21, 22, 23, and 24 has been described. However, referring to the present specification, a plurality of laser beam pairs may be used if necessary. Those skilled in the art will readily understand.

As described above, when two pairs of condensing points 21, 22, 23, 24 are simultaneously formed, between condensing points 21, 23 and adjacent condensing points 22, 24, V-shaped fine cracks 42 may occur. The process of generating the V-shaped fine cracks 42 is the same as the process of generating the V-shaped fine cracks 40 between the light collecting points 21 and 22 and the light collecting points 23 and 24. Do. In this case, it will be appreciated by those skilled in the art that the distance between the first condensing points 21 and 22 and the second condensing points 23 and 24 can be widened, so that the processing speed can be improved. This effect also applies to the case where each of the first light collecting points 21 and 22 and the second light collecting points 23 and 24 is arranged in a direction perpendicular to the processing direction, as shown in FIG. In this case, a V-shaped fine crack 40 is formed between each of the first light collecting points 21 and 22 and the second light collecting points 23 and 24, and the light collecting points 22 adjacent to each other are formed. The V-shaped fine cracks 42 can be formed between the 23.

In the above-described embodiment, a case in which even-numbered condensing points are paired has been described, but the scope of the present invention is not limited thereto. For example, when three condensing points are formed, two V-shaped fine cracks may be formed between the condensing points. That is, the plurality of laser beams are focused at positions spaced apart from each other in the same plane inside the object by forming a plurality of focusing points to generate a plurality of V-shaped fine cracks between the plurality of focusing points, It is possible to form the separation surface due to the V-shaped fine cracks. Afterwards, by separating the workpiece 10 in the vertical direction on the basis of the separation surface, the thickness of the workpiece 10 may be adjusted with little damage to the semiconductor device due to the debris, unlike mechanical back-lapping. In addition, since the laser beam having a very short pulse width is used, the energy of the laser beam is locally absorbed only in the inside of the object 10, so that back-lapping with little thermal effect is possible.

11 illustrates a laser back-lepping apparatus according to an embodiment of the present invention. Referring to FIG. 11, a laser back-lapping apparatus according to an embodiment of the present invention uses a light source unit 200 that emits two laser beams 11 and 12, and two laser beams 11 and 12. It may include a focusing lens 240 for condensing the inside of the object 10.

The light source unit 200 may include a light source 210 that emits the laser beam 1, an optical separator 220, and a reflection mirror 230. The optical separator 220 splits the laser beam 1 emitted from the light source 210 into two laser beams 11 and 12. The optical separator 220 may be, for example, a half mirror. In addition, the optical splitter 220 may be a diffractive optical element (DOE). In addition, other suitable optical elements capable of separating light may be employed as the optical separator 220. The laser beams 11 and 12 split by the optical separator 220 travel in different optical paths, are reflected by the reflection mirror 230, and are incident to the focusing lens 240. The focusing lens 240 focuses the laser beams 11 and 12 at positions spaced apart from each other in the same plane inside the object 10. That is, the light collecting points 21 and 22 formed by the focusing lens 240 are arranged in the processing direction or the direction crossing the inside of the processing object 10. The specification and position of the focusing lens 240 may be appropriately selected and adjusted such that the focusing points 21 and 22 are located in the same plane inside the object 10. The formation positions of the light collecting points 21 and 22 can be adjusted by moving the focusing lens 240 in the optical axis direction. 11 shows an optical configuration in which the laser beams 11 and 12 are focused by one focusing lens 240, but the scope of the present invention is not limited thereto. For example, two focusing lenses may be provided that focus each of the laser beams 11 and 12 at a predetermined position inside the object 10. The light source unit 200 and the focusing lens 240 may be moved in the processing direction as one unit. In addition, the object to be processed 10 may be mounted on the table 300 which is movable in the processing direction.

In FIG. 11, a laser processing apparatus including a light source unit 200 having a structure in which one laser beam 1 is divided into two is described, but the scope of the present invention is not limited thereto. For example, although not shown in the drawings, a light source unit having two light sources emitting the laser beams 11 and 12 may be employed. In addition, as the optical separator 220, for example, a plurality of semi-transmissive mirrors are employed and the transmittance of the semi-transmissive mirror is appropriately selected, or the diffraction optical element having a three-dimensional or higher diffraction order is employed to narrow the laser beam 1. It may be separated into more than two to focus the light to be spaced apart from each other in the same plane of the inside of the object 10 by using one or a plurality of focusing lens 240. In addition, it will be understood by those skilled in the art, referring to the present specification, that a plurality of light source units 200 shown in FIG. 11 may be provided as necessary.

While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined by the appended claims.

1, 11, 12, 13, 14, 101 ... laser beam 10 ... working object
19 ... Light incidence 21, 22, 23, 24, 102 ...
30, 130 ... separated surface 40, 41 ... fine crack
104 Vertical crack 200 Light source unit
210 ... light source 220 ... light separator
230 ... reflective mirror 240 ... focusing lens
300 ... table

Claims (13)

Focusing the plurality of laser beams apart from each other in the same plane inside the object to form a plurality of condensing points;
Generating fine V-shaped cracks between the plurality of light collecting points; And
And moving the at least one of the plurality of laser beams and the object to be processed in a machining direction to form a separation surface by the V-shaped microcracks inside the object to be processed. The method of claim 1,
The V-shaped fine crack is a laser back-lapping method, characterized in that the corn (corn) cut in a direction perpendicular to the separation plane. The method of claim 1,
And the plurality of condensing points are arranged in at least one of the machining direction and a direction crossing the machining direction. The method according to any one of claims 1 to 4,
And the laser beam is a pulsed laser beam. The method of claim 4, wherein
And a pulse width of the pulsed laser beam is within 1 microsecond. The method of claim 5, wherein
The object to be processed is a crystalline material,
And the pulse intensity of the pulsed laser beam is determined to have an intensity that can melt the crystal and transform it into a granular form. A table on which a processing object is mounted;
A light source unit emitting at least two laser beams;
And a condenser lens for condensing the at least two laser beams at positions spaced apart from each other in the same plane inside the object to be processed.
The V-shaped fine crack is formed between the light-converging points in the object to be processed by the at least two laser beams, and the at least one of the laser beam and the object is relatively moved in the processing direction to form the interior of the object. Laser back-lapping apparatus, characterized in that for forming a separation surface by the V-shaped fine cracks. The method of claim 7, wherein
The V-shaped microcracks are laser back-lapping apparatus, characterized in that the shape of the corn (corn) cut in a direction perpendicular to the separation plane. The method of claim 7, wherein
And the converging points are arranged in at least one of the machining direction and a direction crossing the machining direction. The method of claim 7, wherein
The light source unit,
A light source emitting a laser beam;
And a light separator for separating the laser beam into a plurality of laser beams. The method according to any one of claims 7 to 10,
And the laser beam is a pulsed laser beam. The method of claim 11,
And a pulse width of the pulsed laser beam is within 1 microsecond. 13. The method of claim 12,
The object to be processed is a crystalline material,
And the pulse intensity of the pulsed laser beam is determined to have an intensity that can melt the crystal and transform it into a granular form.

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