JP2009152288A - Laser dicing apparatus and dicing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser dicing apparatus that prevents defective processing because of a variance of wafer thickness and flexibly cope with various kinds and small amount of wafer, and to provide a dicing method. <P>SOLUTION: The laser dicing apparatus 10 is used to form a modification area for division of a chip by applying a laser light to a wafer W. The apparatus includes an optical measuring means 56 for measuring the thickness of the wafer W by a laser light emitted from a laser oscillator 41 and an input section 52 to which a processing condition and an assumed range of the wafer thickness corresponding to the processing condition. A control section 50 determines whether the actual thickness of the wafer measured by the optical measuring means 56 is within the assumed range of the wafer thickness input by means of the input section 52, and determines that the input processing condition corresponds to the wafer to be processed. Thus, defective processing because of a variance of wafer thickness can be prevented. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a laser dicing apparatus and a dicing method for dividing a wafer into individual chips.

  As a dicing apparatus that divides a wafer into individual chips, a laser dicing apparatus that forms a modified region for dividing a chip by irradiating the wafer with laser light is known.

  In order to perform dicing with high accuracy using a laser dicing apparatus, it is preferable to adjust dicing processing conditions according to the thickness of the wafer. However, the wafer thickness generally varies within a range of about 10 μm even in the same lot. For this reason, if dicing is performed on the same lot of wafers under the same processing conditions, the modified region may not be formed properly, which may result in dicing failure such that the wafers cannot be singulated.

  In order to prevent such dicing failure, in Patent Document 1, the thickness of each wafer is measured based on the surface position (height) of the wafer, and the measured wafer from the processing condition table stored in advance. There has been proposed a laser dicing apparatus that automatically selects a processing condition corresponding to the thickness of the film.

When using the laser dicing apparatus disclosed in Patent Document 1, appropriate processing conditions for various wafer thicknesses are obtained in advance by trial and error, and a processing condition table in which the appropriate processing conditions are associated with the wafer thickness is prepared. Keep it. And before starting dicing, the thickness of the wafer is measured, and based on the measurement result, an appropriate processing condition for each wafer is automatically selected from the processing condition table. Such a laser dicing apparatus is particularly useful when dicing a large number of wafers of the same type.
JP 2007-95952 A

  The wafers to be diced are not always of the same type and quantity, but vary depending on the application of the chip, which is the final product. For example, if the chip application is a memory, the same type and a large number of wafers are subject to dicing, and if the chip application is an expensive system LSI, a large variety and a small number of wafers are generally subject to dicing. is there.

  By the way, processing conditions suitable for a wafer to be processed differ depending on the type of wafer. In other words, appropriate processing conditions depend on the type of dopant, the amount of dopant implanted (doping amount), the type of film formed on the surface of the wafer, and the like in addition to the thickness of the wafer.

  For this reason, when processing various types of wafers using the laser dicing apparatus of Patent Document 1, as many processing condition tables as the number of types of wafers are required, and the labor involved in preparing the processing condition tables is enormous. In particular, when dicing a wide variety and a small amount of wafers, a great deal of labor is required to dice a small amount of wafers, and the processing condition table is prepared, which is inefficient.

  The present invention has been made in view of such circumstances, and provides a laser dicing apparatus and a dicing method suitable for processing a wide variety and a small amount of wafers while preventing processing defects due to variations in wafer thickness. The purpose is to do.

  In order to achieve the above object, one embodiment of the present invention is a laser dicing apparatus that forms a modified region on a wafer by irradiating the wafer with laser light, and irradiates the wafer to be processed with the laser light. Laser light irradiation means, input means for inputting an assumed range of wafer thickness corresponding to the processing conditions, measurement means for measuring the thickness of the wafer to be processed, and the measurement means measured by the measurement means Processing condition determination means for determining whether the processing condition corresponds to the processing target wafer by determining whether the thickness of the processing target wafer is included in the assumed range input to the input means; The present invention relates to a laser dicing apparatus.

  According to this laser dicing apparatus, it is possible to know whether the processing conditions correspond to the wafer to be processed based on the measured thickness of the wafer, so that processing defects caused by variations in the thickness of the wafer are effective. Can be prevented. In addition, since it is not necessary to prepare a processing condition table in advance, it is suitable for processing a wide variety of wafers.

  The measuring means may calculate the thickness of the wafer to be processed based on the laser light applied to the wafer to be processed by the laser light irradiation means.

  In this aspect, the laser beam for forming the modified region and the laser beam for measuring the wafer thickness can be guided to the wafer by one optical system, so that the configuration of the laser dicing apparatus can be simplified.

  The processing conditions may include at least one of a scanning speed of the laser light with respect to the wafer to be processed, a focal position of the laser light, a power of the laser light, and a pulse width of the laser light. .

  In this way, by using the scanning speed of the laser beam, the focal position of the laser beam, or the power and pulse width of the laser beam as processing conditions, for example, the position where the modified region is formed, the number of layers where the modified region is formed , And the thickness of the modified region can be adjusted.

  In order to achieve the above object, one aspect of the present invention is a wafer dicing method for forming a modified region by irradiating a laser beam on a wafer to be processed based on predetermined processing conditions, It is measured in a thickness assumption range input step in which an assumed range of wafer thickness corresponding to the processing conditions is input, a thickness measurement step in which the thickness of the wafer to be processed is measured, and the thickness measurement step. And a processing condition determination step for determining whether the thickness of the wafer to be processed is included in the assumed range input in the estimated thickness range input step.

  According to the present invention, based on the measured thickness of the wafer, it can be determined whether the processing conditions correspond to the wafer to be processed, while preventing processing defects due to wafer thickness variations,・ It is possible to handle a small amount of wafers.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a configuration diagram showing an outline of a laser dicing apparatus 10 according to an embodiment of the present invention.

  As shown in FIG. 1, the laser dicing apparatus 10 includes a wafer moving unit 20 that moves the wafer W, an observation optical unit 30 that observes the surface of the wafer W, and a laser optical unit 40 that irradiates the wafer W with laser light. An input unit 52 for inputting an assumed range and processing conditions of the thickness of the wafer W, a display unit 54 for displaying a message, an astigmatism optical measuring device 56 for measuring the thickness of the wafer W, and laser dicing And a control unit 50 that controls each unit of the apparatus 10.

  The wafer moving unit 20 includes an XYZθ table 22 provided on the main body base 26 and a suction stage 24 for sucking and holding the wafer W. The XYZθ table 22 includes guide rails (not shown), and is controlled by the control unit 50 and is movable in four directions of XYZθ shown in FIG.

  Here, the three directions of XYZ are orthogonal to each other. In the embodiment shown in FIG. 1, the X direction and the Y direction are horizontal directions, and the Z direction is a vertical direction. Further, the θ direction is a rotation direction with a vertical axis (Z direction axis) as a rotation axis.

  The suction stage 24 is placed on the XYZθ table 22 and holds the dicing sheet S that holds the wafer W by suction. The wafer W can be moved in the XYZθ direction with high accuracy by such a wafer moving unit 20 having the XYZθ table 22 and the suction stage 24.

  FIG. 2 is a view showing an example of the wafer W carried into the laser dicing apparatus 10 of FIG. In the present embodiment, the wafer W is fixed on a dicing sheet S provided with a frame F on the periphery, and is carried into the laser dicing apparatus 10 integrally with the frame F and the dicing sheet S. The wafer W, the frame F, and the dicing sheet S are carried in by an arbitrary method. For example, a cassette in which the wafer is stored is moved up and down to a predetermined position by an elevator and sent to a transfer device. The wafer may be placed on the suction stage 24.

  An observation optical unit 30 shown in FIG. 1 is controlled by a control unit 50 and is an observation light source 31 that emits observation illumination light, and a half that reflects illumination light from a collimator lens 32 and passes reflected light from a wafer W. It has a mirror 33, a CCD camera 35 to which the reflected light that has passed through the half mirror 33 is incident, and an image processing device 38 that creates imaging data relating to the surface of the wafer W based on the reflected light that has entered the CCD camera 35. A collimating lens 32 is disposed between the observation light source 31 and the half mirror 33, a condensation lens 37 is disposed between the half mirror 33 and the wafer W, and between the half mirror 33 and the CCD camera 35. Condensation lens 34 is arranged in the.

  The illumination light emitted from the observation light source 31 reaches the wafer W through the collimating lens 32, the half mirror 33 and the condensation lens 37, and is reflected on the surface of the wafer W. The reflected light on the surface of the wafer W enters the CCD camera 35 through the condensation lens 37, the half mirror 33, and the condensation lens 34. The CCD camera 35 converts the incident reflected light into an electrical signal, and the image processing device 38 creates imaging data of the wafer W by processing the electrical signal and sends it to the control unit 50. The control unit 50 displays the surface image of the wafer W on the television monitor 36 based on the imaging data sent from the image processing device 38.

  The laser optical unit 40 includes a laser oscillation device 41 that oscillates laser light, a collimator lens 42 that aligns the oscillated laser light with parallel light, a condensation lens 46 that condenses the laser light, and a condensation lens 46 that is controlled by the control unit 50. An actuator 47 for fine movement on the optical axis, a half mirror 44 for extracting laser light reflected on the surface of the wafer W to an astigmatism optical measuring device 56 described later, and the laser light extracted by the half mirror 44 are condensed. A cylindrical lens 48 is provided.

The laser oscillation device 41 is controlled by the control unit 50, and the power and pulse width of the laser light oscillated from the laser oscillation device 41 are adjusted according to the dopant type, the doping amount, the wafer thickness, and the like of the wafer to be processed. . For example, laser light having a pulse width of 1 μs or less and a peak power density at the focal point of 1 × 10 ⁸ (W / cm ² ) or more is oscillated from the laser oscillation device 41.

  The laser light oscillated by the laser oscillation device 41 is condensed inside the wafer W through an optical system such as a collimating lens 42, a half mirror 44, and a condensation lens 46. In addition, the Z direction position (vertical direction position) of the focal point of the laser beam is adjusted by moving the condensation lens 46 in the Z direction by the actuator 47.

  In the present embodiment, a piezoelectric element is used as the actuator 47. The piezoelectric element has a hollow cylindrical shape, the upper end is fixed to the main body (not shown) of the laser optical unit 40, and the lower end is joined to a lens frame (not shown) that holds the condensation lens 46. . The piezoelectric element expands and contracts according to the applied voltage, and the condensation lens 46 slightly moves in the optical axis direction according to the expansion and contraction of the piezoelectric element.

  Here, the modified region formed in the wafer W by the laser beam oscillated by the laser oscillation device 41 will be described. FIGS. 3A and 3B are diagrams showing a modified region formed near the focal point inside the wafer.

  As shown in FIG. 3A, the modified region P is formed in the vicinity of the focal point by the laser light L1 incident on the inside of the wafer W from the laser oscillation device 41. The modified region P is a region where the wafer W has been altered by multiphoton absorption being induced in the vicinity of the focal point, and includes a crack region, a melting region, a refractive index change region, and the like.

  By scanning the laser beam L1 with respect to the wafer W a plurality of times, as shown in FIG. 3B, the modified region P can be formed in multiple layers. With the modified region P formed in a multilayer shape as a trigger, the wafer W is naturally cleaved or cleaved by applying a slight external force.

  An input unit 52 shown in FIG. 1 is a user interface for inputting processing conditions related to dicing of the wafer W by the laser dicing apparatus 10 and an assumed range of the thickness of the wafer W corresponding to the processing conditions. The processing conditions input via the input unit 52 and the assumed range of the thickness of the wafer W are sent to the control unit 50.

  The processing conditions include, for example, the scanning speed of the laser beam with respect to the wafer W, the incident height of the laser beam, the focal position of the laser beam, the power and pulse width of the laser beam, and the properties of the wafer to be processed (dopant Seed, dope amount, surface film type, etc.). Further, the assumed range of the wafer thickness means an allowable wafer thickness range in which processing defects do not occur under the input processing conditions.

  The astigmatism optical measurement device 56 measures the position (height) of the surface of the wafer W based on the laser beam reflected by the surface of the wafer W, and calculates the thickness of the wafer W. The thickness of the wafer W is measured at a predetermined location or a plurality of locations along the dicing street before the modified region P is formed along the dicing street. As a result, it is possible to determine the suitability of the processing conditions before the modified region is processed and formed on the wafer W, and the yield can be improved. When the thickness of the wafer W is acquired by the astigmatism optical measurement device 56, the control unit 50 controls the laser oscillation device 41 so that the power of the laser beam and the pulse width are set so as not to damage the wafer. Adjusted.

  FIGS. 4A to 4C are diagrams showing the principle of measuring the position of the surface of the wafer W by the astigmatism optical measuring device 56. The laser light reflected on the surface of the wafer W is condensed into the condensation lens 46 and A state of passing through the cylindrical lens 48 and reaching the quadrant photodiode 56A of the astigmatism optical measurement device 56 and a cross-sectional shape of the laser light incident on the quadrant photodiode 56A are shown. For simplification of description, the half mirror 44 (see FIG. 1) is omitted in FIGS.

  FIG. 4A shows a case where the distance between the wafer W and the condensation lens 46 is standard, and the cross-sectional shape of the laser light reaching the quadrant photodiode 56A is a perfect circle. On the other hand, FIG. 4B shows a case where the distance between the wafer W and the condensation lens 46 is relatively long, and the cross-sectional shape of the laser light reaching the quadrant photodiode 56A is an ellipse stretched in the vertical direction. FIG. 4C shows a case where the distance between the wafer W and the condensation lens 46 is relatively short, and the cross-sectional shape of the laser light reaching the quadrant photodiode 56A is an ellipse stretched in the horizontal direction.

  Thus, the cross-sectional shape of the laser light received by the four-divided photodiode 56A depends on the distance between the wafer W and the condensation lens 46. The astigmatism optical measurement device 56 measures the surface position of the wafer W by utilizing this property.

  Since the surface position of the wafer W measured in this way is based on the surface of the suction table 24 shown in FIG. 1, in order to obtain the thickness of the wafer W, the wafer W, the suction table 24, It is necessary to consider the thickness of the dicing tape S disposed between the two. Therefore, the astigmatism optical measuring device 56 stores the thickness of the dicing tape S in advance, and subtracts the thickness of the dicing tape S from the measured value of the surface position of the wafer W to thereby determine the thickness of the wafer W. Is calculated. The calculated thickness of the wafer W is sent from the astigmatism optical measurement device 56 to the control unit 50, and is used for determination of processing conditions described later.

  In addition, the astigmatism optical measurement device 56 measures the position of the surface of the wafer W using the four-division photodiode 56A during the modified region forming process, and obtains uneven shape information on the surface of the wafer W. Get in real time. The uneven shape information is sent to the control unit 50 and used to control the actuator 47.

  The control unit 50 includes a CPU, a memory, an input / output circuit unit, and the like, and appropriately controls each unit of the wafer moving unit 20, the observation optical unit 30, and the laser optical unit 40 based on processing conditions input via the input unit 52. Control.

  Further, the control unit 50 determines whether or not the actual thickness of the wafer W measured by the astigmatism optical measurement device 56 is included in the assumed range of the thickness of the wafer W input via the input unit 52. To do.

  When it is determined that the thickness of the wafer W to be processed measured by the astigmatism optical measurement device 56 is included in the assumed range of the thickness of the wafer W input via the input unit 52, this input The controller 50 controls each part of the laser dicing apparatus 10 so that the wafer W is diced based on the processing conditions input via the part 52. On the other hand, when it is determined that the thickness of the wafer W measured by the astigmatism optical measurement device 56 is not included in the assumed range of the thickness of the wafer W input via the input unit 52, the control unit A message 50 prompts the display unit 54 to re-enter the processing conditions and the assumed range of the thickness of the wafer W.

  Next, a dicing method using the above-described laser dicing apparatus 10 will be described with reference to FIG. FIG. 5 is a flowchart showing a process of forming the modified region on the wafer W.

  First, processing conditions and an assumed range of wafer thickness corresponding to the processing conditions are input via the input unit 52 (S10 in FIG. 5). The input to the input unit 52 may be manually input directly by the user or may be input via a computer or the like.

  Next, a cassette containing the wafer W, the dicing sheet S carrying the wafer and the frame F (hereinafter also simply referred to as “wafer W”) is set in the elevator (S12). The cassette containing the wafer W is carried to a predetermined position by the elevator and is carried to a standby table (not shown) (S14). Various processes necessary before processing are performed on the standby table, and for example, surface cleaning of the wafer W, position confirmation of alignment marks, and the like are performed. Thereafter, the wafer W is transferred to the suction table 24 and sucked and held by the suction table 24. Then, the wafer W is conveyed to a predetermined processing position by the XYZθ table 22 while being held by the suction table 24 (S16).

  Next, the thickness of the wafer W on the suction table 24 is measured (S18). Specifically, the laser light is irradiated from the laser oscillation device 41 to the wafer W, and the reflected light from the wafer W is analyzed by the astigmatism optical measurement device 56, whereby the thickness of the wafer W on the suction table 24 is measured. Is required. The measurement of the thickness of the wafer W may be performed at a predetermined location, or may be performed at a plurality of locations along the dicing street.

  The thickness of the wafer W measured in this way is sent to the control unit 50 (S20).

  Then, the controller 50 determines whether or not the measured thickness of the wafer W is included in the assumed range of the thickness of the wafer W input in S10 (S22). When it is determined that the measured thickness of the wafer W is included in the assumed range of the wafer thickness input in S10 (YES determination in S22), dicing is performed under the processing conditions input in S10. (S24).

  The wafer W that has been diced is stored in the cassette again and taken out from the laser dicing apparatus 10 (S26).

  On the other hand, when it is determined that the thickness of the wafer W measured in S18 is not included in the assumed thickness range of the wafer input in S10 (NO determination in S22), the processing conditions and the wafer thickness are determined. The user is prompted to re-enter the expected range via the display unit 54 (S28). When the re-input of the processing conditions and the assumed range of the wafer thickness is performed, the process proceeds to S22 again, and the thickness of the wafer W measured in S18 becomes the assumed range of the thickness of the wafer re-input in S28. It is determined whether it is included. S28 and S22 are repeated until it is determined that the thickness of the wafer W measured in S18 is included in the assumed range of the thickness of the wafer re-input in S28.

  As described above, according to the present embodiment, the thickness of the wafer W is measured by the astigmatism optical measurement device 56, and whether the processing conditions input via the input unit 52 correspond to the wafer W is determined. Since the determination can be made, it is possible to effectively prevent a processing defect caused by the variation in the thickness of the wafer W. In addition, since it is not necessary to prepare a processing condition table in advance, it is suitable for processing a wide variety of wafers.

  Further, according to the present embodiment, the power and pulse width of the laser light oscillated by the laser oscillation device 41 are appropriately adjusted according to the application of the laser light. Specifically, when forming the modified region P, the laser oscillation device 41 is controlled by the control unit 50 to irradiate the laser beam so that the peak power density at the focal point becomes relatively high. On the other hand, when measuring the position of the surface of the wafer W, the laser oscillation device 41 is controlled by the control unit 50 to irradiate the laser beam so that the peak power density at the focal point is relatively low. As a result, the modified region P can be stably formed, and the surface position of the wafer W can be measured without damaging the wafer W.

  Although the embodiments of the present invention have been described in detail, the present invention is not limited to the above examples, and various improvements and modifications may be made without departing from the scope of the present invention. .

  For example, a laser beam for forming the modified region and a laser beam for measuring the thickness of the wafer may be oscillated from separate laser light sources. In this case, both the modified region forming laser beam and the wafer thickness measuring laser beam reach the wafer W through a common optical system (for example, the collimating lens 42 and the condensation lens 46). It is preferable. Simplify the configuration of the laser dicing equipment by consolidating the optical system that guides the laser beam for forming the modified region to the wafer and the optical system that guides the laser beam for measuring the wafer thickness into the wafer. can do. In particular, since the optical system that guides the laser light is relatively expensive, the manufacturing cost of the laser dicing apparatus can be reduced.

  In the above-described embodiment, the astigmatism optical measurement device 56 is used to acquire the thickness of the wafer and the uneven surface shape information of the wafer surface, but the present invention is not limited to this. For example, the thickness of the wafer may be obtained based on the phase difference of the laser light reflected on the upper and lower surfaces of the wafer to be processed. Further, the thickness of the wafer and the uneven surface shape information on the wafer surface may be acquired by an arbitrary contact type measurement method or non-contact type measurement method, and a known measurement method such as a knife edge method may be used.

  Further, in the above-described embodiment, when it is determined that the actual measured thickness of the wafer is not included in the input range of the assumed wafer thickness, the processing conditions and the assumed range of the thickness of the wafer A message prompting re-input is displayed, but the processing conditions may be automatically adjusted according to the measured thickness of the wafer. Thereby, it is possible to flexibly cope with wafers having various thicknesses, and it is possible to appropriately form a modified region corresponding to the thickness of the wafer.

  In addition, an indicator lamp may be provided that displays an operation status of the dicing apparatus 10 (for example, during processing, processing end, emergency stop, etc.).

The block diagram of the laser dicing apparatus which concerns on one Embodiment of this invention The perspective view which shows the wafer carried in into the laser dicing apparatus shown in FIG. Wafer cross section showing modified layer formed inside wafer Conceptual diagram showing the relationship between the distance between the wafer-condensation lens and the cross-sectional shape of the laser beam received by the four-division photodiode Flowchart showing a dicing method using the laser dicing apparatus shown in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Laser dicing apparatus, 20 ... Wafer moving part, 22 ... XYZ (theta) table, 24 ... Adsorption stage, 30 ... Observation optical part, 31 ... Observation light source, 32 ... Collimating lens, 33 ... Half mirror, 34, 37 ... Condensation lens 35 ... CCD camera, 36 ... TV monitor, 38 ... image processing device, 40 ... laser optical unit, 41 ... laser oscillation device, 42 ... collimating lens, 44 ... half mirror, 46 ... condensation lens, 47 ... actuator, 48 ... Cylindrical lens, 50 ... control unit, 52 ... input unit, 54 ... display unit, 56 ... astigmatic optical measuring device, 56A ... four-division photodiode

Claims (4)

A laser dicing apparatus that forms a modified region on the wafer by irradiating the wafer with laser light,
Laser light irradiation means for irradiating the wafer to be processed with the laser light;
Input means for inputting an assumed range of wafer thickness corresponding to the processing conditions;
Measuring means for measuring the thickness of the wafer to be processed;
Whether the processing condition corresponds to the processing target wafer by determining whether the thickness of the processing target wafer measured by the measuring unit is included in the assumed range input to the input unit A laser dicing apparatus comprising processing condition determination means for determining   The said measurement means calculates the thickness of the said wafer to be processed based on the laser beam irradiated with respect to the said wafer to be processed by the said laser beam irradiation means. Laser dicing equipment.   The processing conditions include at least one of a scanning speed of the laser light with respect to the wafer to be processed, a focal position of the laser light, a power of the laser light, and a pulse width of the laser light. The laser dicing apparatus according to claim 1, wherein the apparatus is a laser dicing apparatus. A wafer dicing method for forming a modified region by irradiating a laser beam to a wafer to be processed based on predetermined processing conditions,
A thickness assumption range input step in which an assumed range of the thickness of the wafer corresponding to the processing conditions is input;
A thickness measuring step for measuring the thickness of the wafer to be processed;
And a processing condition determination step of determining whether the thickness of the wafer to be processed measured in the thickness measurement step is included in the assumed range input in the assumed thickness range input step. Dicing method.

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