Work processing method

Abstract

To provide a processing method of a work-piece, for forming a plurality of modified layer at a position with a difference thickness direction as well as cancelling a warpage in the case where a wafer has the warpage.SOLUTION: A processing method for a work-piece with a warpage, comprises: a mounting step of mounting the work-piece in a direction where the work-piece is warped in a mountain shape on a holding surface of a holding table containing the holding surface that adheres and holds the work-piece; a holding step of adhering and holding the work-piece in the holding table; a warpage cancel step of irradiating a laser beam along a division schedule line to a predetermined first position in a thickness direction to the work-piece to form a modified layer and a crack from the modified layer to a lower surface of the work-piece, and cancelling the warpage of the work-piece; and a modified layer formation step of forming the modified layer by irradiating the laser beam to an upper direction from the first position. In the warpage cancel step, an upper surface height position of the work-piece is detected at each time before irradiation of the laser beam to the division schedule line, and a condensing point is positioned on the basis of the upper surface height position detected.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a method for processing a workpiece having warpage, in which a plurality of planned dividing lines are set.

Background Art

[0002] Conventionally, as disclosed in, for example, Patent Document 1, it is known to form a plurality of modified layers at different positions in the thickness direction of a wafer on the same planned dividing line of the wafer.

[0003] After forming a modified layer at a position close to the condenser inside the wafer, when trying to condense a laser beam at a position far from the condenser, the condensation of the laser beam is hindered by the previously formed modified layer, making it difficult to form the modified layer.

[0004] Therefore, as disclosed in Patent Document 1, generally, the modified layers are formed in the order from a position far from the condenser to a position close to the condenser. Then, after forming a plurality of modified layers at different positions in the thickness direction for a certain planned dividing line, a plurality of modified layers are similarly formed for an adjacent planned dividing line. This is repeated, and a plurality of modified layers are formed for all the planned dividing lines.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, when the wafer has warpage, there are internal stresses due to the warpage within the wafer. There is a concern that during the formation of a plurality of modified layers at different positions in the thickness direction with respect to the same planned division line, these internal stresses are released and unexpected cracks may occur. And there was a risk that the device would be damaged if this crack reached the device.

[0007] In addition, there is also a concern that the division line of the wafer may meander due to the release of internal stress. In this case, there is a concern that the chip size after division will not be the designed size and will fall outside the allowable range and become a defective product.

[0008] In view of the above problems, the present invention proposes a novel technique for eliminating warpage and forming a plurality of modified layers at different positions in the thickness direction when the wafer has warpage.

Means for Solving the Problems

[0009] The problems to be solved by the present invention are as described above. Next, the means for solving these problems will be described.

[0010] According to one aspect of the present invention, a processing method for a workpiece having warpage, in which a plurality of planned division lines are set, a placing step of placing the workpiece on the holding surface of a holding table including a holding surface for sucking and holding the workpiece in a direction in which the workpiece warps in a mountain shape; a holding step of sucking and holding the workpiece with the holding table after performing the placing step; After performing the holding step, with the condensing point of a laser beam having a wavelength that is transmissive to the workpiece positioned at a predetermined first position in the thickness direction of the workpiece, irradiate the laser beam along the planned division line to form a modified layer along the planned division line and a crack extending from the modified layer to the lower surface of the workpiece for all the planned division lines, thereby eliminating the warpage of the workpiece (a warpage elimination step); After performing the warp elimination step, with the condensing point of the laser beam positioned inside the workpiece above the first position from the lower surface of the workpiece, the laser beam is irradiated onto the workpiece along the planned division line to form a modified layer along the planned division line, which is a modified layer formation step. comprising In the warp elimination step, before irradiating the laser beam onto each planned division line, the height position of the upper surface of the workpiece is detected each time, and based on the detected height position of the upper surface, the condensing point is positioned. This is a method for processing the workpiece.

[0011] Also, according to one aspect of the present invention, After performing the modified layer formation step, an external force is applied to the workpiece to further include a division step of dividing the workpiece along the planned division line.

[0012] Also, according to one aspect of the present invention, In the modified layer formation step, after forming a second modified layer by irradiating along the planned division line with the condensing point of the laser beam positioned at a second position inside the workpiece above the first position, a third modified layer is formed by irradiating along the planned division line with the condensing point of the laser beam positioned at a third position inside the workpiece above the second position. This is performed for each planned division line.

[0013] Also, according to one aspect of the present invention, The workpiece has a warp that warps in a mountain shape when the back surface is facing up. In the placement step, the workpiece is placed on the holding table with the surface of the workpiece facing down. In the holding step, the surface side of the workpiece is held by the holding table. In the warp elimination step and the modified layer formation step, the laser beam is irradiated from the back surface side of the workpiece.

Advantages of the Invention

[0014] The present invention has the following advantages. That is, according to one aspect of the present invention, the focus point of the processing laser beam can be positioned at a predetermined position in the thickness direction of the workpiece, and the warp can be eliminated by ensuring that the crack reaches the lower surface of the workpiece. Further, even when the upper surface height of the workpiece varies with the elimination of the warp of the workpiece due to the formation of the modified layer, the focus point of the processing laser beam can be positioned at a predetermined position in the thickness direction of the workpiece by detecting the upper surface height of the immediately preceding workpiece. And in the modified layer forming step, since the warp has been eliminated in advance by the warp eliminating step, it is possible to prevent the occurrence of unexpected cracks during the process of forming the modified layer and the meandering of the planned dividing line. Thereby, it is possible to prevent defects such as damage to the device due to cracks and chip size defects.

Brief Description of Drawings

[0015]

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Embodiments for Carrying Out the Invention

[0016] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIGS. 1(A) and (B) show an example of a work W with warpage formed. The work W is, for example, a wafer formed of a material such as Si (silicon), SiC (silicon carbide), GaN (gallium nitride), GaAs (gallium arsenide), or other semiconductors. Or, it is a wafer formed of a complex oxide such as LT (lithium tantalate) or LN (lithium niobate). Or, the work W is a substrate or the like made of a material such as sapphire, glass, or quartz. The glass is, for example, alkali glass, non-alkali glass, soda-lime glass, lead glass, borosilicate glass, fused silica, or the like.

[0017] On the surface Wa of the work W shown in FIG. 1(A), devices D are regularly formed, and division planned lines S (streets) intersecting each other are set between the devices.

[0018] In the example of the work W shown in FIG. 1(B), a warpage is formed in which the surface Wa side shrinks and dents, and the back surface Wb side bulges. Due to such warpage, internal stress exists in the work W. Incidentally, conversely, there may be a case where a warpage is formed in which the back surface Wb side of the work W shrinks and dents, and the surface Wa side bulges.

[0019] As shown in FIG. 2, the workpiece W has its back surface Wb adhered to the expandable tape T, is fixed to the annular frame F via the expandable tape T, and is handled as a workpiece unit U. The front surface Wa of the workpiece W is exposed upward. The expandable tape T has an adhesive surface, and the workpiece and the annular frame F are adhered to the adhesive surface. The expandable tape T has expandability and can be expanded radially outward.

[0020] In addition, a protective tape may be adhered to the exposed front surface Wa of the workpiece W. Further, when a warp is formed such that the back surface Wb side of the workpiece W shrinks and dents while the front surface Wa side bulges, the front surface Wa of the workpiece W is adhered to the expandable tape T. Further, the workpiece W may be handled as a workpiece unit U integrated with the annular frame F as in the example of FIG. 2, or may be handled alone as the workpiece W. Further, the expandable tape T may not have an adhesive surface.

[0021] FIG. 3 shows an example of a laser processing apparatus for processing the workpiece W. The laser processing apparatus 10 is configured to process the workpiece W by relatively moving a laser beam irradiation mechanism 12 that irradiates a laser beam and a holding table 13 that holds the workpiece W on its upper surface.

[0022] The laser processing apparatus 10 has a rectangular parallelepiped base 11. On the upper surface of the base 11, a moving mechanism 14 is provided that processes and feeds the holding table 13 in the X-axis direction and indexing feeds it in the Y-axis direction. A vertical wall portion 16 is erected behind the moving mechanism 14, and the laser beam irradiation mechanism 12 is supported so as to face the holding table 13.

[0023] The moving mechanism 14 includes an indexing feed mechanism 20 that relatively moves the holding table 13 in the indexing feed direction (Y-axis direction) with respect to the laser beam irradiation mechanism 12, and a processing feed mechanism 21 that relatively moves it in the processing feed direction (X-axis direction).

[0024] In the movement in the indexing feed direction (Y-axis direction) by the indexing feed mechanism 20, after laser processing for a certain planned division line, the index feed of the holding table 13 is performed in order to perform laser processing for an adjacent planned division line parallel thereto.

[0025] In the movement in the machining feed direction (X-axis direction) by the machining feed mechanism 21, with the alignment between the planned division line detected by an imaging camera (not shown) and the machining head 40 of the laser beam irradiation mechanism 12 being performed, the holding table 13 is moved in the X-axis direction, thereby performing laser processing along the planned division line.

[0026] The holding table 13 is provided so as to be rotatable about the vertical axis (rotation in the θ direction). Four clamp portions 39 are provided around the holding table 13, and the annular frame F of the work unit U is clamped and fixed from four directions by the clamp portions 39.

[0027] As shown in FIG. 4, a holding plate 13b made of a porous ceramic material is provided above the holding table 13, and a horizontal holding surface 13a is formed by the upper surface of the holding plate 13b. The holding plate 13b communicates with a suction source 28 via a valve 29, and is configured to generate a negative pressure on the holding surface 13a to adsorb and hold the work W.

[0028] As shown in FIG. 3, the laser beam irradiation mechanism 12 includes an oscillator that generates a laser beam for machining, a condenser lens that condenses the laser beam generated by the oscillator onto the work held by the holding table, a mirror that guides the laser beam generated by the oscillator to the condenser lens, etc. As shown in FIG. 4, the machining laser beam 40a is irradiated from the machining head 40 onto the work W.

[0029] The height position in the thickness direction of the work W at the condensing point of the machining laser beam 40a is sequentially set to a predetermined position as will be described in detail later, and is corrected as appropriate.

[0030] As shown in FIG. 3, the laser beam irradiation mechanism 12 includes an oscillator that generates a laser beam for measuring the height position of the upper surface (back surface Wb) of the workpiece W, a condenser lens that condenses the laser beam generated by the oscillator onto the workpiece held by the holding table, a mirror that guides the laser beam generated by the oscillator to the condenser lens, etc. As shown in FIGS. 4 and 5(A)(B), measurement laser beams 51a and 52a are irradiated onto the workpiece W from the measurement heads 51 and 52, respectively.

[0031] As shown in FIG. 4, the measurement laser beam 51a is continuously irradiated, and the measurement result of the upper surface height of the workpiece is fed back to the controller at intervals of 0.5 mm, for example, in the length direction of the planned division line. By appropriately correcting the condensing point of the processing laser beam 40a using this feedback, as shown in FIG. 5(A), the condensing point of the processing laser beam 40a can be accurately positioned at a predetermined distance from the upper surface (back surface Wb) of the workpiece W, or at a predetermined distance from the lower surface (front surface Wa) of the workpiece W.

[0032] As shown in FIG. 4, the measurement heads 51 and 52 are arranged on both sides of the processing head 40 in the processing feed direction (X-axis direction). Then, as shown in FIG. 5(A), the upper surface height (height of the back surface Wb) of the workpiece W at the position immediately in front of the processing head 40 when the holding table 13 moves forward in the first direction X1 can be detected by the measurement laser beam 51a irradiated from the measurement head 51. Further, as shown in FIG. 5(B), the upper surface height (height of the back surface Wb) of the workpiece W at the position immediately in front of the processing head 40 when the holding table 13 moves backward in the second direction X2 can be detected by the measurement laser beam 52a irradiated from the measurement head 52.

[0033] In this way, by arranging the measurement heads 51 and 52 on both sides of the processing head 40, it becomes possible to perform measurement and processing for a certain planned division line during each of the forward and backward movements of the holding table 13.

[0034] In addition, as shown in FIG. 6(A), for example, by providing only one measurement head 53 adjacent to the processing head 40, when the holding table 13 is moved forward in the first direction X1, the upper surface height (the height of the back surface Wb) of the workpiece W may be measured while processing is performed for a certain planned division line.

[0035] Furthermore, as shown in FIGS. 6(B) and 6(C), in a configuration where an irradiation head 45 capable of selectively irradiating a processing laser beam and a measurement laser beam is provided, for example, as shown in FIG. 6(B), after the holding table 13 is moved forward in the first direction X1 and the measurement laser beam 45a is irradiated to perform measurement for a certain planned division line, the holding table 13 is moved backward in the second direction X2 to return to the original position, and as shown in FIG. 6(C), the holding table 13 is again moved forward in the first direction X1 and the processing laser beam 45b is irradiated to perform processing.

[0036] Next, a processing method using the above device configuration will be described. FIG. 7 is a flowchart showing each step of this processing method.

[0037] <Tape sticking step> As shown in FIG. 2, it is a step of sticking the back surface Wb of the workpiece W to the expandable tape T. The workpiece W is integrated with the annular frame F via the expandable tape T to form a workpiece unit U. Note that the front surface Wa of the workpiece W may be stuck to the expandable tape T. When the workpiece W is directly placed on the holding table, the tape sticking step is omitted.

[0038] <Placement step> As shown in FIG. 8, it is a step of placing the workpiece W in a direction in which the workpiece warps in a mountain shape on the holding surface 13a of the holding table 13 including the holding surface 13a for adsorbing and holding the workpiece W.

[0039] In the example of FIG. 8, the back surface Wb of the workpiece W is warped in a mountain shape so that the back surface Wb is on the upper side. As will be described in detail later, a laser beam is irradiated from the back surface Wb side of the workpiece W. Further, in the example of FIG. 8, a gap 15 is formed between the front surface Wa of the workpiece W and the holding surface 13a, and the annular frame F is shown being placed on the clamp portion 39. When the front surface Wa of the workpiece W is along the mountain shape so that the front surface Wa is on the upper side, the back surface Wb side is placed on the holding surface 13a.

[0040] <Holding step> As shown in FIG. 9, after performing the placing step, it is a step of sucking and holding the workpiece W by the holding table 13. Specifically, the valve 29 is opened to connect the holding table 13 to the suction source 28, a negative pressure is generated on the holding surface 13a, and the front surface Wa of the workpiece W is attracted to be adsorbed on the holding surface 13a. Further, the annular frame F is clamped by the clamp portion 39.

[0041] <Warp elimination step> As shown in FIG. 10(A), after performing the holding step, with the condensing point of the processing laser beam 40a having a wavelength that is transmissive to the workpiece W positioned at a predetermined first position in the thickness direction of the workpiece W, the processing laser beam 40a is irradiated along the division planned line to form a modified layer K1 along the division planned line and a crack Ka extending from the modified layer K1 to the lower surface (front surface Wa) of the workpiece W. This is performed for all the division planned lines to eliminate the warp of the workpiece W.

[0042] In the example of FIG. 10(A), the predetermined first position in the thickness direction of the workpiece W is set at a position at a distance H1 from the lower surface (front surface Wa) of the workpiece W (a position at a distance H2 from the upper surface (back surface Wb) of the workpiece W). The total distance H0 of the distance H1 and the distance H2 corresponds to the thickness of the workpiece W.

[0043] In this way, when the crack Ka reaches the lower surface (front surface Wa) of the workpiece W, the internal stress inherent in the lower surface side of the workpiece W is released, the lower surface side of the workpiece W is expanded, and the warp is eliminated. This crack Ka is formed for all the division planned lines S.

[0044] In this warp elimination step, immediately before the processing laser beam is irradiated onto each planned division line, the height position of the upper surface of the workpiece (the height of the back surface Wb) is detected each time, and the condensing point is positioned based on the detected upper surface height position.

[0045] That is, in the formation of the modified layer K1, as shown in FIGS. 5(A) and 5(B), the height of the upper surface of the workpiece W (the height of the back surface Wb) at the position immediately before the processing head 40 is fed back by the irradiation of the measurement laser beams 51a and 52a from the measurement heads 51 and 52, and the position of the condensing point of the processing laser beam is corrected.

[0046] Thereby, even when a large warp is formed in the workpiece W, the condensing point of the processing laser beam can be positioned at a predetermined position in the thickness direction of the workpiece W, and the warp can be eliminated by reliably causing the crack Ka to reach the lower surface (front surface Wa) of the workpiece W.

[0047] Further, even when the height of the upper surface of the workpiece W (the height of the back surface Wb) fluctuates as the warp of the workpiece W is eliminated by the formation of the modified layer K1, the condensing point of the processing laser beam can be positioned at a predetermined position in the thickness direction of the workpiece by detecting the height of the upper surface of the immediately preceding workpiece W (the height of the back surface Wb).

[0048] In the formation of the modified layer K1, as shown in FIG. 5(A), the workpiece W is fed in the first direction X1, and after the modified layer K1 is formed for a certain planned division line, the workpiece W is index-fed (in the Y-axis direction (FIG. 1)), and as shown in FIG. 5(B), the workpiece W is fed in the second direction X2, and the modified layer K1 is formed for the adjacent planned division line. After the modified layer K1 is formed for all the planned division columns extending in the X-axis direction, the workpiece W is rotated by 90 degrees, and the modified layer K1 is similarly formed for all the planned division lines orthogonal to the planned division lines where the modified layer K1 has already been formed.

[0049] <Modified layer formation step> As shown in Fig. 10(B), after performing the warpage elimination step, the processing laser beam 40a is irradiated along the planned division line with the condensing point of the processing laser beam 40a positioned inside the workpiece W above the first position from the lower surface (surface Wa) of the workpiece W, thereby forming modified layers K2 and K3 along the planned division line.

[0050] In the example of Fig. 10(B), after forming the second modified layer K2 by irradiating along the planned division line with the condensing point of the laser beam positioned at a second position inside the workpiece above the first position, the third modified layer K3 is formed by irradiating along the planned division line with the condensing point of the laser beam positioned at a third position inside the workpiece above the second position. In this way, cracks Ka to Kc formed by each of the modified layers K1, K2, and K3 are formed from the surface Wa to the back surface Wb of the workpiece W. As shown in Fig. 10(B), the modified layers are formed such that the tip portions of the cracks Ka to Kc formed by each of the modified layers K1, K2, and K3 are connected to each other, or are close to each other until almost connected. Alternatively, the modified layers may be formed such that a gap is formed between the tip portions of the cracks Ka to Kc and they are not connected.

[0051] Note that the two modified layers K2 and K3 may be sequentially formed for one planned division line, or the modified layer K3 may be formed for all the planned division lines after the modified layer K2 is formed for all the planned division lines. According to the configurations shown in Figs. 4, 5(A), and 5(B), the modified layer K2 can be formed on the forward path and the modified layer K3 can be formed on the return path.

[0052] Also, the laser beam may be branched and a plurality of condensing points may be positioned in the optical axis direction, so that a plurality of layers of modified layers are formed in one processing feed. Also, the number of layers for forming the modified layers is not particularly limited.

[0053] In the modification layer formation step described above, since the warpage has been eliminated in advance by the warpage elimination step, unexpected cracks are prevented from occurring during the process of forming the modification layer, and the division planned line is prevented from meandering. As a result, it is possible to prevent defects such as damage to the device due to cracks and chip size defects.

[0054] <Dividing step> As shown in FIGS. 11(A) and 11(B), after the modification layer formation step is performed, an external force is applied to the workpiece W and it is divided along the division planned line.

[0055] The dividing device 80 shown in FIGS. 11(A) and 11(B) includes a frame holding mechanism 81 that holds the annular frame F of the workpiece unit U, a drive mechanism 84 that raises and lowers the frame holding mechanism 81, and a cylindrical expansion drum 83 that abuts against the expandable tape T of the workpiece unit U from below.

[0056] As shown in FIG. 11(A), when the frame holding mechanism 81 holds the annular frame F and the drive mechanism 84 lowers the frame holding mechanism 81, as shown in FIG. 11(B), the expandable tape T is held by the expansion drum 83 from below and expands.

[0057] When the expandable tape T expands, an external force that spreads in the radial direction acts on the workpiece W attached to the expandable tape T, and due to this external force, starting from the modification layer, the workpiece W is divided into chips C. After division, the expandable tape T is heat-shrunk to maintain the interval between the chips C.

[0058] In addition to expanding and dividing the expandable tape T as described above, after forming the modification layer, the back surface of the wafer may be ground and divided into chips.

[0059] Alternatively, by increasing the number of layers of the modified layer, many cracks may be formed to achieve a divided state. After expanding the expandable tape T to increase the interval between chips, heat shrinkage may be performed to maintain the interval between chips.

Explanation of Signs

[0060] 10 Laser processing apparatus 12 Laser beam irradiation mechanism 13 Holding table 13a Holding surface 13b Holding plate 14 Moving mechanism 40 Processing head 40a Processing laser beam 51 Measuring head 52 Measuring head 51a Measuring laser beam 52a Measuring laser beam 80 Dividing device C Chip D Device F Annular frame K1 Modified layer K2 Modified layer K3 Modified layer Ka Crack Kb Crack Kc Crack S Predetermined dividing line T Expandable tape U Work unit W Workpiece Wa Surface Wb Back surface X1 First direction X2 Second direction

Claims

1. A method for processing a workpiece having warpage, in which a plurality of planned division lines are set, comprising: a placing step of placing the workpiece on a holding surface of a holding table including the holding surface for sucking and holding the workpiece in a direction in which the workpiece warps in a mountain shape; a holding step of sucking and holding the workpiece with the holding table after performing the placing step; after performing the holding step, with the condensing point of a laser beam having a wavelength that is transmissive to the workpiece positioned at a predetermined first position in the thickness direction of the workpiece, irradiating the laser beam along the planned division line to form a modified layer along the planned division line and a crack extending from the modified layer to the lower surface of the workpiece, and performing this for all the planned division lines to eliminate the warpage of the workpiece (a warpage elimination step); after performing the warpage elimination step, with the condensing point of the laser beam positioned inside the workpiece above the first position from the lower surface of the workpiece, irradiating the workpiece with the laser beam along the planned division line to form a modified layer along the planned division line (a modified layer formation step); and in the warpage elimination step, before irradiating the laser beam for each planned division line, detecting the upper surface height position of the workpiece each time, and positioning the condensing point based on the detected upper surface height position. A method for processing a workpiece.

2. After performing the modified layer formation step, further comprising a dividing step of applying an external force to the workpiece to divide it along the planned division line, The method for processing a workpiece according to claim 1, characterized in that.

3. In the modified layer formation step, after forming a second modified layer by irradiating along the planned division line with the condensing point of the laser beam positioned at a second position inside the workpiece above the first position, irradiating along the planned division line with the condensing point of the laser beam positioned at a third position inside the workpiece above the second position to form a third modified layer, and performing this for each planned division line. The method for processing a workpiece according to claim 1 or claim 2, characterized in that...

4. The workpiece has a warpage that warps in a mountain shape when the back surface is facing up, In the placing step, the workpiece is placed on the holding table with the surface of the workpiece facing down, In the holding step, the holding table holds the surface side of the workpiece, In the warp elimination step and the modified layer formation step, the laser beam is irradiated from the back surface side of the workpiece. The method for processing a workpiece according to claim 1 or claim 2, characterized in that...

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