Source: https://patents.google.com/patent/EP1716960A1/en
Timestamp: 2019-12-11 08:14:53
Document Index: 477251239

Matched Legal Cases: ['art, 5', 'art 4', 'art 4', 'art 4', 'art 4', 'art 4', 'art 4', 'art 45', 'art 45', 'art 45', 'art 45', 'art 45', 'art 45', 'art 45', 'art 45', 'art 45', 'art 45', 'art 45', 'art 45', 'art 45', 'art 45', 'art 45']

EP1716960A1 - Laser processing method and device - Google Patents
EP1716960A1
EP1716960A1 EP04806955A EP04806955A EP1716960A1 EP 1716960 A1 EP1716960 A1 EP 1716960A1 EP 04806955 A EP04806955 A EP 04806955A EP 04806955 A EP04806955 A EP 04806955A EP 1716960 A1 EP1716960 A1 EP 1716960A1
EP04806955A
EP1716960B1 (en
EP1716960A4 (en
Kazuhiro Hamamatsu Photonics K.K. ATSUMI
Koji Hamamatsu Photonics K.K. KUNO
Masayoshi Hamamatsu Photonics K.K. KUSUNOKI
Tatsuya Hamamatsu Photonics K.K. SUZUKI
Kenshi Hamamatsu Photonics K.K. FUKUMITSU
Fumitsugu Hamamatsu Photonics K.K. FUKUYO
2004-01-09 Priority to JP2004004304A priority Critical patent/JP4509578B2/en
2004-12-13 Priority to PCT/JP2004/018594 priority patent/WO2005065882A1/en
2006-11-02 Publication of EP1716960A1 publication Critical patent/EP1716960A1/en
2008-08-13 Publication of EP1716960A4 publication Critical patent/EP1716960A4/en
2010-03-10 Publication of EP1716960B1 publication Critical patent/EP1716960B1/en
2018-09-07 First worldwide family litigation filed litigation Critical https://patents.darts-ip.com/?family=34747111&utm_source=google_patent&utm_medium=platform_link&utm_campaign=public_patent_search&patent=EP1716960(A1) "Global patent litigation dataset” by Darts-ip is licensed under a Creative Commons Attribution 4.0 International License.
238000003672 processing method Methods 0 abstract claims description title 33
201000009310 astigmatism Diseases 0 description 13
A laser processing method which can efficiently perform laser processing while minimizing the deviation of the converging point of a laser beam in end parts of an object to be processed is provided.
This laser processing method comprises a preparatory step of holding a lens at an initial position set such that a converging point is located at a predetermined position within the object; a first processing step (S11 and S12) of emitting a first laser beam for processing while holding the lens at the initial position, and moving the lens and the object relative to each other along a main surface so as to form a modified region in one end part of a line to cut; and a second processing step (S13 and S14) of releasing the lens from being held at the initial position after forming the modified region in the one end part of the line to cut, and then moving the lens and the object relative to each other along the main surface while adjusting the gap between the lens and the main surface after the release, so as to form the modified region.
Known as a technique for processing an object to be processed whose main surface has irregularities, on the other hand, is one in which the planarity in the whole part to be processed is measured by planarity measuring means (a planarity meter comprising a projector and a reflected light receiver) as a preparation for processing, and the object is processed according to thus measured planarity (see, for example, Patent Document 2).
Though the planarity of the main surface of the object to be processed can accurately be grasped when the technique disclosed in Patent Document 2 is used, the same part must be scanned twice, i.e., before and during the actual processing, which takes time and lowers the processing efficiency.
Therefore, it is an object of the present invention to provide a laser processing method and laser processing apparatus which can efficiently perform laser processing while minimizing the deviation of the laser beam converging point in the end parts of the object.
The inventors conducted various studies in order to overcome the above-mentioned problem. First, a processing method in which a first laser beam for processing and a second laser beam for measuring the displacement of a main surface of an object to be processed are emitted to the object on the same axis was studied. Details of this study will now be explained with reference to Figs. 10(A) to 10(C).
Fig. 10(A) shows a processing preparatory phase in the case where a silicon wafer 800 secured to a dicing film 802 is processed with a laser beam emitted from a laser unit 804. The laser unit 804 includes a condenser lens 804a for converging the laser beam onto the silicon wafer 800, a lens holder 804b for holding the condenser lens 804a, and a piezoelectric actuator 804c which holds the lens holder 804b such that the latter can freely advance and retract with respect to the silicon wafer 800. The laser processing apparatus including the laser unit 804 further comprises a laser light source and the like which are not described. In the state of Fig. 10(A), irradiation with a first laser beam 806 for processing and a second laser beam 808 for measuring the displacement of a main surface 800b of the silicon wafer 800 is started, while a stage (not depicted) mounting the silicon wafer 800 is moved such that the silicon wafer 800 shifts in the direction of arrow A. The silicon wafer 800 is to be processed with the first laser beam 806 at a position corresponding to a line to cut 800a.
As the silicon wafer 800 shifts in the direction of arrow A in Fig. 10(A), the optical axis of the first laser beam 806 and second laser beam 808 reaches a position where it intersects the silicon wafer 800. The piezoelectric actuator 804c causes the lens holder 804b to advance/retract with respect to the silicon wafer 800 such that an astigmatism signal detected from reflected light of the second laser beam 808 becomes a predetermined value. Therefore, the piezoelectric actuator 804c retracts from the state of Fig. 10(B), so as to raise the lens holder 804b and condenser lens 804a. However, since the silicon wafer 800 keeps shifting in the direction of arrow A in Fig. 10(A), a time lag occurs until the lens holder 804b and condenser lens 804a rise to a predetermined position so that the converging point of the first laser beam 806 is positioned at the line to cut 800a. Also, the astigmatism signal may vary so much that the converging point of the first laser beam 806 fluctuates.
Therefore, as shown in Fig. 10(C), a part other than the line to cut 800a is processed with the laser in an area B until the first laser beam 806 is in focus with the line to cut 800a so as to attain a stable state. For example, assuming that the silicon wafer 800 has a thickness of 100 µm, and that a time delay of 15 mS occurs, the length of the area B is theoretically 1.5 mm when the processing speed is 100 mm/S.
Though Figs. 10(A) to 10(C) relate to the silicon wafer 800 having an ideally high planarity, there may be a case where end parts are warped upward. An example of a silicon wafer having an end part warped upward will be explained with reference to Figs. 11(A) to 11(C).
Fig. 11 (A) shows a processing preparatory phase in the case where a silicon wafer 810 secured to a dicing film 802 is processed with a laser beam emitted from a laser unit 804. This laser unit 804 is the same as that explained with reference to Figs. 10(A) to 10(C). The silicon wafer 810 has an end part warped upward. A line to cut 810a in the silicon wafer 810 is set so as to be positioned equidistantly from a main surface 810b.
As the silicon wafer 810 shifts in the direction of arrow A in Fig. 11 (A), the optical axis of the first laser beam 806 and second laser beam 808 reaches a position where it intersects the silicon wafer 810 as shown in Fig. 11(B). The piezoelectric actuator 804c causes the lens holder 804b to advance/retract with respect to the silicon wafer 810 such that an astigmatism signal detected from reflected light of the second laser beam 808 becomes a predetermined value. Therefore, the piezoelectric actuator 804c retracts from the state of Fig. 11 (B), so as to raise the lens holder 804b and condenser lens 804a. However, since the silicon wafer 810 keeps shifting in the direction of arrow A in Fig. 11 (A), a time lag occurs until the lens holder 804b and condenser lens 804a rise to a predetermined position so that the converging point of the first laser beam 806 is positioned at the line to cut 810a. Also, since an end part of the silicon wafer 810 is warped upward, the gap from the position of the dotted line C to the actual position of the main surface 810b in Fig. 11(B) causes an overshoot when the lens holder 804b and condenser lens 804a rise to the predetermined position.
Therefore, as shown in Fig. 11 (C), a part other than the line to cut 810a is processed with the laser in an area D until the first laser beam 806 is in focus with the line to cut 810a so as to attain a stable state. The length of the area D tends to be longer by the overshoot than the length of the area B in Fig. 10(C). Hence, the inventors take notice of the processing in end parts of the object to be processed. The present invention is achieved according to these findings.
The present invention provides a laser processing method for irradiating an object to be processed with a first laser beam while converging the first laser beam with a lens such that a converging point is positioned within the object, and forming a modified region within the object along a line to cut in the object; the method comprising a preparatory step of holding the lens at an initial position with respect to a main surface of the object, the initial position being set so that the converging point is located at a predetermined position within the object; a first processing step of emitting the first laser beam while holding the lens at the initial position, and moving the lens and the object relative to each other along the main surface so as to form the modified region in one end part of the line to cut; and a second processing step of releasing the lens from being held at the initial position after forming the modified region in the one end part, and then moving the lens and the object relative to each other along the main surface while adjusting a gap between the lens and the main surface so as to form the modified region.
Since the modified region is formed in one end part of the line to cut while the lens is held at the initial position, the modified region can be formed while excluding the influence of fluctuations in the shape of end parts in the object as much as possible in the laser processing method of the present invention. After the modified region is formed in one end part of the line to cut, the lens is released from being held, and the modified region is formed in the remaining part while adjusting the lens position, whereby the modified region can be formed at a predetermined position within the object.
It will be preferred in the laser processing method of the present invention if, in the second processing step, the first laser beam and a second laser beam for measuring a displacement of the main surface are converged by the lens onto the object on the same axis, and the lens is released from being held after the quantity of reflected light of the second laser beam reflected by the main surface exceeds a predetermined threshold. Since the first and second laser beams are converged by the lens so as to be emitted on the same axis, the converging point of the first laser beam can be prevented from deviating from a predetermined position within the object because of a vibration of a stage mounting the object, for example. The quantity of reflected light varies depending on the distance from the reflecting surface. Therefore, when a predetermined threshold is set to a value corresponding to the height of the main surface, and a location where the quantity of reflected light becomes the predetermined threshold is assumed to correspond to an outer edge of the main surface of the object to be processed, the lens can be released from being held.
It will also be preferred in the laser processing method of the present invention if, in the second processing step, the first laser beam and a second laser beam for measuring a displacement of the main surface are converged by the lens onto the object on the same axis, and the lens is released from being held after an amount of change in the quantity of reflected light of the second laser beam reflected by the main surface becomes a maximum value. Since the first and second laser beams are converged by the lens so as to be emitted on the same axis, the converging point of the first laser beam can be prevented from deviating from a predetermined position within the object because of a vibration of a stage mounting the object, for example. Since the quantity of reflected light varies depending on the distance from the reflecting surface, the displacement of the main surface seems to be acute in the vicinity of the location where the amount of change in the quantity of reflected light becomes an extreme value. Therefore, assuming that this location corresponds to an outer edge of the main surface of the object to be processed, the lens can be released from being held.
It will also be preferred if the laser processing method of the present invention further comprises a transition step of holding the lens so as to keep the lens from being driven toward the main surface after the second processing step. Since the lens is held so as not to be driven toward the main surface after forming the modified region, a smooth transition is possible when shifting to the processing of the next line to cut, for example.
It will also be preferred in the laser processing method of the present invention if, in the transition step, the first laser beam and a second laser beam for measuring a displacement of the main surface are converged by the lens onto the object on the same axis, and the lens is held so as to be kept from being driven after the quantity of reflected light of the second laser beam reflected by the main surface becomes smaller than a predetermined threshold. The quantity of reflected light varies depending on the distance from the reflecting surface. Therefore, when a predetermined threshold is set to a value corresponding to the height of the main surface, and a location where the quantity of reflected light becomes the predetermined threshold is assumed to correspond to an outer edge of the main surface of the object to be processed, the lens can be held so as to be kept from being driven.
It will also be preferred in the laser processing method of the present invention if, in the transition step, the first laser beam and a second laser beam for measuring a displacement of the main surface are converged by the lens onto the object on the same axis, and the lens is held so as to be kept from being driven after an amount of change in the quantity of reflected light of the second laser beam reflected by the main surface becomes a minimum value. Since the quantity of reflected light varies depending on the distance from the reflecting surface, the displacement of the main surface seems to be acute in the vicinity of the location where the amount of change in the quantity of reflected light becomes a minimum value. Therefore, assuming that this location corresponds to an outer edge of the main surface of the object to be processed, the lens can be held so as to be kept from being driven.
It will also be preferred in the laser processing method of the present invention if the line to cut includes first and second lines to cut; respective displacements of the main surface in unit time zones are successively stored in the second processing step of the first line to cut; the lens is held in the transition step of the first line to cut such that, with respect to the main surface, the lens is placed at a position based on the displacement stored in the unit time zone earlier by a predetermined number than the unit time zone where the lens is held so as to be kept from being driven in the transition step of the first line to cut; and the position where the lens is held in the transition step of the first line to cut is employed as the initial position in the preparatory step of the second line to cut. Since the position of the lens with respect to the main surface in the preparatory step of the next line to cut is set to the position based on the displacement stored in the unit time zone earlier by a predetermined number than the unit time zone corresponding to the time when the lens is held so as to be kept from being driven, the influence of fluctuations in the shape of end parts can be excluded as much as possible.
The present invention provides a laser processing apparatus for irradiating an object to be processed with a first laser beam while converging the first laser beam with a lens such that a converging point is positioned within the object, and forming a modified region within the object along a line to cut in the object; the apparatus comprising a lens for converging the first laser beam onto the object; moving means for moving the object and the lens relative to each other along a main surface of the object; holding means for holding the lens such that the lens freely advances and retracts with respect to the main surface; and control means for controlling respective behaviors of the moving means and holding means; wherein the control means controls the holding means so as to hold the lens at an initial position where the converging point is located at a predetermined position within the object; wherein, while emitting the first laser beam with the lens being held at the initial position, the control means controls the moving means so as to move the object and the lens relative to each other along the main surface, thereby forming the modified region in one end part of the line to cut; and wherein, after forming the modified region in the one end part of the line to cut, the control means controls the holding means so as to release the lens from being held at the initial position and hold the lens while adjusting a gap between the lens and the main surface, and controls the moving means so as to move the lens and the object relative to each other along the main surface, thereby forming the modified region.
Since the modified region is formed in one end part of the line to cut while the lens is held at the initial position, the laser processing apparatus of the present invention can form the modified region while excluding the influence of fluctuations in the shape of end parts in the object as much as possible. After the modified region is formed at one end part of the line to cut, the lens is released from being held, and the modified region is formed in the remaining part while adjusting the lens position, whereby the modified region can be formed at a predetermined position within the object.
It will be preferred in the laser processing apparatus of the present invention if the first laser beam and a second laser beam for measuring a displacement of the main surface are converged by the lens onto the object on the same axis, and the control means controls the holding means so as to release the lens from being held after the quantity of reflected light of the second laser beam reflected by the main surface exceeds a predetermined threshold. Since the first and second laser beams are converged by the lens so as to be emitted on the same axis, the converging point of the first laser beam can be prevented from deviating from a predetermined position within the object because of a vibration of a stage mounting the object, for example. The quantity of reflected light varies depending on the distance from the reflecting surface. Therefore, when a predetermined threshold is set to a value corresponding to the height of the main surface, and a location where the quantity of reflected light becomes the predetermined threshold is assumed to correspond to an outer edge of the main surface of the object to be processed, the lens can be released from being held.
It will also be preferred in the laser processing apparatus of the present invention if the first laser beam and a second laser beam for measuring a displacement of the main surface are converged by the lens onto the object on the same axis, and the control means controls the holding means so as to release the lens from being held after an amount of change in the quantity of reflected light of the second laser beam reflected by the main surface becomes a maximum value. Since the first and second laser beams are converged by the lens so as to be emitted on the same axis, the converging point of the first laser beam can be prevented from deviating from a predetermined position within the object because of a vibration of a stage mounting the object, for example. Since the quantity of reflected light varies depending on the distance from the reflecting surface, the displacement of the main surface seems to be acute in the vicinity of the location where the amount of change in the quantity of reflected light becomes an extreme value. Therefore, assuming that this location corresponds to an outer edge of the main surface of the object to be processed, the lens can be released from being held.
It will also be preferred in the laser processing apparatus of the present invention if, after forming the modified region in the one end part of the line to cut, the control means controls the holding means so as to release the lens from being held at the initial position and hold the lens while adjusting a gap between the lens and the main surface, and controls the moving means so as to move the lens and the object relative to each other along the main surface, thereby forming the modified region; and the control means controls the holding means so as to hold the lens such that the lens is kept from being driven toward the main surface and move the lens and the object relative to each other along the main surface. Since the lens is held so as not to be driven toward the main surface after forming the modified region, a smooth transition is possible when shifting to the processing of the next line to cut, for example.
It will also be preferred in the laser processing apparatus of the present invention if the first laser beam and a second laser beam for measuring a displacement of the main surface are converged by the lens onto the object on the same axis, and the control means controls the holding means so as to hold the lens such that the lens is kept from being driven toward the main surface after the quantity of reflected light of the second laser beam reflected by the main surface becomes smaller than a predetermined threshold. The quantity of reflected light varies depending on the distance from the reflecting surface. Therefore, when a predetermined threshold is set to a value corresponding to the height of the main surface, and a location where the quantity of reflected light becomes the predetermined threshold is assumed to correspond to an outer edge of the main surface of the object to be processed, the lens can be held so as to be kept from being driven.
It will also be preferred in the laser processing apparatus of the present invention if the first laser beam and a second laser beam for measuring a displacement of the main surface are converged by the lens onto the object on the same axis, and the control means controls the holding means so as to hold the lens such that the lens is kept from being driven toward the main surface after an amount of change in the quantity of reflected light of the second laser beam reflected by the main surface becomes a minimum value. Since the quantity of reflected light varies depending on the distance from the reflecting surface, the displacement of the main surface seems to be acute in the vicinity of the location where the amount of change in the quantity of reflected light becomes a minimum value. Therefore, assuming that this location corresponds to an outer edge of the main surface of the object to be processed, the lens can be held so as to be kept from being driven.
It will also be preferred in the laser processing apparatus of the present invention if the line to cut includes first and second lines to cut, the apparatus further comprises displacement storage means for successively storing respective displacements of the main surface in unit time zones, and the control means sets a position based on the displacement stored in the unit time zone earlier by a predetermined number than the unit time zone where the lens is held so as to be kept from being driven in the first line to cut as the initial position in the second line to cut. Since the position of the lens with respect to the main surface in the preparatory step of the next line to cut is set to the position based on the displacement stored in the unit time zone earlier by a predetermined number than the unit time zone corresponding to the time when the lens is held so as to be kept from being driven, the influence of fluctuations in the shape of end parts can be excluded as much as possible.
The laser processing method and laser processing apparatus of the present invention can efficiently carry out laser processing while minimizing the deviation of the converging point of a laser beam in end parts of an object to be processed.
[Fig. 1] Fig. 1 is a view showing the configuration of the laser processing apparatus in accordance with an embodiment of the present invention.
[Fig.2] Fig. 2 is a diagram showing a functional configuration of a control unit provided in the laser processing apparatus in accordance with the embodiment.
[Fig. 3] Fig. 3 is a view showing an object to be processed for explaining the embodiment.
[Fig. 4] Fig. 4 is a view for explaining the laser processing method in accordance with an embodiment of the present invention.
[Fig. 5] Fig. 5 is a flowchart for explaining the laser processing method in accordance with the embodiment.
[Fig. 6] Fig. 6 is a view for explaining the laser processing method in accordance with the embodiment.
[Fig. 7] Fig. 7 is a chart for explaining the laser processing method in accordance with the embodiment.
[Fig. 8] Fig. 8 is a chart for explaining the laser processing method in accordance with the embodiment.
[Fig. 9] Fig. 9 is a flowchart for explaining the laser processing method in accordance with the embodiment.
[Fig. 10] Fig. 10 is a view for explaining details of the studies led to the present invention.
[Fig. 11] Fig. 11 is a view for explaining details of the studies led to the present invention.
1...laser processing apparatus, 2... stage, 3...laser head unit, 4... optical system main part, 5... objective lens unit, 6... laser emitting apparatus, 7... control unit, S... object, R... modified region, 42...processing objective lens, 43... actuator, 13... laser head, 44... laser diode, 45...light-receiving part.
The laser head unit 3 is detachably attached to an upper end part of the optical system main part 4. The laser head unit 3 includes an L-shaped cooling jacket 11. Embedded in a vertical wall 11 a of the cooling jacket 11 is a cooling pipe 12 in a winding state, through which cooling water circulates. Attached to the front face of the vertical wall 11a are a laser head 13 which emits the processing laser beam L1 downward, and a shutter unit 14 for selectively opening and closing an optical path of the processing laser beam L1 emitted from the laser head 13. This can prevent the laser head 13 and shutter unit 14 from overheating. For example, the laser head 13 uses an Nd: YAG laser and emits a pulsed laser beam having a pulse width of 1 µs or shorter as the processing laser beam L1.
In the laser head unit 3, an adjuster 15 for adjusting the inclination of the cooling jacket 11 and the like is attached to the lower face of a bottom wall 11 b of the cooling jacket 11. The adjuster 15 is used for aligning an optical axis α of the processing laser beam L1 emitted from the laser head 13 with an axis β which is set in the optical system main part 4 and objective lens unit 5 such as to extend vertically. Namely, the laser head unit 3 is attached to the optical system main part 4 by way of the adjuster 15. When the inclination of the cooling jacket 11 or the like is adjusted by the adjuster 15 thereafter, the inclination of the laser head 13 or the like is adjusted in conformity to the movement of the cooling jacket 11. As a consequence, the processing laser beam L1 advances into the optical system main part 4 while in a state where its optical axis α coincides with the axis β. The bottom wall 11b of the cooling jacket 11, the adjuster 15, and a housing 21 of the optical system main part 4 are formed with through holes through which the processing laser beam L1 passes.
For observing the object S mounted on the stage 2, a light guide 28 for guiding an observation visible ray is attached to the housing 21 of the optical system main part 4, whereas a CCD camera 29 is disposed within the housing 21. The observation visible ray is guided by the light guide 28 into the housing 21, successively, passes through a field stop 31, a reticle 32, a dichroic mirror 33, and the like, and then is reflected by a dichroic mirror 34 disposed on the axis β. The reflected observation visible ray advances downward on the axis β and irradiates the object S. On the other hand, the processing laser beam L1 is transmitted through the dichroic mirror 34.
Fig. 2 shows a functional configuration of the control unit 7. Functionally, as shown in Fig. 2, the control unit 7 comprises a laser emission controller 701, a stage movement controller 702, an actuator controller 703, a converging point calculator 704, an end part determiner 705, and a circular memory 706 (displacement storage means). The laser emission controller 701 is a part which outputs signals for controlling emissions of the processing laser beam L1 and rangefinding laser beam L2 to the laser head 13 of the laser head unit 3 and the laser diode 44 of the objective lens unit 5, respectively. The stage movement controller 702 is a part which outputs a control signal for controlling the movement of the stage 2 thereto. The actuator controller 703 is a part which outputs a control signal for controlling the driving of the actuator 43 of the objective lens unit 5 to the actuator 43. The actuator controller 703 is also a part which causes the circular memory 706 to store the amount of movement of the actuator 43. The amount of movement varies according to the displacement of the main surface S1 of the object, and thus can be taken as an amount indicative of the displacement of the main surface S1. The converging point calculator 704 is a part which calculates the distance between the object S and the converging point of the rangefinding laser beam L2 according to an astigmatism signal outputted from the light-receiving part 45 of the objective lens unit 5. The end part determiner 705 is a part which determines whether the processing objective lens 42 is at a position corresponding to an end part of the object S or not according to the quantity of light received by the light-receiving part 45. The circular memory 706 is one which stores the amount of movement of the actuator 43. The circular memory 706 comprises 64 channels of storage areas, and successively stores respective amounts of movement into the storage areas. Operations of the individual functional constituents will be explained later.
The laser processing method using the laser processing apparatus 1 of this embodiment will be explained more specifically. The explanation of the laser processing method will also illustrate the movement of the laser processing apparatus 1. The laser processing method in accordance with this embodiment can be divided into a preparatory step of setting an initial position of the processing objective lens 42 with respect to the wafer-like object S, and a processing step of emitting the processing laser beam L1 so as to form a modified region. Each of the preparatory step and processing step will be explained.
(Preparatory Step) First, the preparatory step of setting the initial position of the processing objective lens 42 with respect to the wafer-like object S will be explained.
Fig. 3 is a plan view of the object S. In the object S, n lines to cut C1 to Cn are set and are successively subjected to laser processing. First, the height of the stage 2 (see Fig. 1) is adjusted such that, at a point Q1 on the first line to cut C1, the converging point is located at a predetermined position within the object S. Using thus adjusted height as the initial position, the stage 2 is moved such that the processing objective lens 42 is positioned at a point X1 on an extension of the line to cut C1.
More detailed explanations will be set forth with reference to Figs. 4(A) to 4(C). Figs. 4(A) to 4(C) are views showing the cross section II-II of Fig. 3. For easier understanding, the hatching indicating the cross section is omitted in Figs. 4(A) to 4(C). As shown in Fig. 4(A), the object S is attracted and secured to the stage 2 by way of a dicing film 2a. The dicing film 2a is secured with a dicing ring (not depicted).
As shown in Fig. 4(A), the stage 2 moves such that the processing objective lens 42 is placed at a position corresponding to the point Q1 on the line to cut C1 in the object S. The actuator 43 holding the processing objective lens 42 is in a state expanded by 25 µm from the most contracted state. This amount of expansion, i.e., 25 µm, is set as one half of the maximum amount of expansion of the actuator 43, i.e., 50 µm. In this state, the stage 2 is moved up/down so that a reflected light beam of the observation visible ray is in focus. When a large error occurs as the stage 2 moves up and down, it will be preferred if the actuator 43 is moved to a desirable position while storing the astigmatism signal at this time, the actuator 43 is returned to the original position, the stage 2 is moved (roughly), and then the actuator 43 is minutely adjusted to a position corresponding to the stored astigmatism signal.
Subsequently, as shown in Fig. 4(B), the stage 2 is further raised by a predetermined distance (hereinafter referred to as processing height) from the state of Fig. 4(A), such that the distance between the surface S1 of the object S and the processing objective lens 42 is set shorter by the processing height than the distance in Fig. 4(A). Here, assuming that the focal point of the visible range and the converging point of the laser beam coincide with each other, the processing laser beam L1 is converged at a position corresponding to the value of product of the processing height from the surface S1 and the refractive index of the object S at the laser wavelength within the object S. When the object S is a silicon wafer having a refractive index of 3.6 (at a wavelength of 1.06 µm) and a processing height of 10 µm, for example, the processing laser beam L1 is converged at a position of 3.6 × 10 = 36 µm. An astigmatism signal is obtained from the reflected light beam of the rangefinding laser beam L2 in the state shown in Fig. 4(B), and the value of this astigmatism signal is employed as a reference value.
The stage 2 is moved as it is from the state shown in Fig. 4(B), and attains a wait state as shown in Fig. 4(C) when the processing objective lens 42 reaches a point X1 on the extension of the line to cut C1. The position of the processing objective lens 42 with respect to the object S in the vertical direction shown in Figs. 4(B) and 4(C) is the initial position.
Operations of the laser processing apparatus 1 in this preparatory step will be explained with reference to the flowchart shown in Fig. 5. The stage controller 702 of the control unit 7 outputs a control signal to the stage 2 such that the processing objective lens 42 moves to the point Q1 on the C1 (step SO1). In response to the output of this control signal, the stage 2 moves. Further, the actuator controller 703 of the control unit 7 outputs a control signal to the actuator 43 so as to make the latter expand by 25 µm (step S02). In response to the output of this control signal, the actuator 43 expands by 25 µm. In this state, the stage 2 is moved up/down so that the observation visible ray is in focus therewith, and a focal position of the observation visible ray is set, whereby the processing objective lens 42 and the object S attain the state explained with reference to Fig. 4(A) (step S03).
The stage movement controller 702 of the control unit 7 outputs a control signal to the stage 2 so as to make the latter rise by a predetermined processing height (e.g., 10 µm) (step S04). In response to the output of this control signal, the stage rises by 10 µm, whereby the processing objective lens 42 and the object S attain the state explained with reference to Fig. 4(B).
The laser emission controller 701 of the control unit 7 outputs a control signal to the laser diode 44 so as to make the latter emit the rangefinding laser beam L2 (step S05). In response to the output of this control signal, the laser diode 44 emits the rangefinding laser beam L2, whereas its reflected light beam reflected by the surface S1 of the object S is received by the four-divided position detecting device in the light-receiving part 45. In response to the light received, signals are outputted to the converging point calculator 704 and the end part determiner 705.
The converging point calculator 704 holds the value of astigmatism signal in this state as a reference value (step S06). Subsequently, the stage movement controller 702 outputs a control signal to the stage 2 such that the processing objective lens 42 moves to a position corresponding to X1 on an extension of the line to cut C1 in the object S (step S07). The stage 2 moves in response to the output of this control signal. When the processing objective lens 42 reaches the position corresponding to X1 on the extension of the line to cut C1 in the object S, the stage movement controller 702 outputs a control signal to the stage 2 so as to make the latter stop moving (step S08).
The explanation will be set forth with reference to Figs. 6(A) to 6(C) showing the cross section II-II of Fig. 3 as with Figs. 4(A) to 4(C). For easier understanding, the hatching indicating the cross section is omitted in Figs. 6(A) to 6(C). Subsequent to the state of Fig. 4(C), Fig. 6(A) shows a state where the processing objective lens 42 has started forming a modified region on the line to cut C1. The actuator 43 is fixed at the amount of expansion set in Fig. 4(C). The processing laser beam L1 and rangefinding laser beam L2 are emitted before the state of Fig. 6(A) after the state of Fig. 4(C). The stage 2 moves such that the processing objective lens 42 shifts in the direction of arrow E in the drawing.
The rangefinding laser beam L2 is reflected less by the dicing film 2a so that the total quantity of light reflected thereby is smaller, whereas the total quantity of reflected light increases in the object S. Namely, the total quantity of reflected light beam of the rangefinding laser beam L2 detected by the four-divided position detecting device in the light-receiving part 45 (see Fig. 1) increases, whereby it can be determined that the processing objective lens 42 is located at the position intersecting the line to cut C1 in the object S when the total quantity of reflected light beam exceeds a predetermined threshold. Therefore, when the total light quantity detected by the four-divided position detecting device in the light-receiving part 45 (see Fig. 1) is greater than the predetermined threshold, the processing objective lens 42 is assumed to be located at one end of the line to cut C1 (in the state corresponding to Fig. 6(A)), the expansion amount of the actuator 43 at this time is released from being held, and the expansion amount control of the actuator 43 is started such that the astigmatism signal becomes the reference value held at step S06 at predetermined intervals (e.g., at individual sampling points). Hence, when the processing objective lens moves in the direction of arrow E in Fig. 6(A), the state shown in Fig. 6(B) is attained. As shown in Fig. 6(B), a modified region R is formed by a predetermined processing height in area F (one end part). After the modified region R is formed by a predetermined processing height in this area F, the processing objective lens 42 moves along the line to cut C1, and forms the modified region R with the processing laser beam L1. During this period, the actuator 43 is adjusted such that the astigmatism signal obtained from the reflected light beam of the rangefinding laser beam L2 becomes the above-mentioned reference value.
When the processing objective lens 42 further moves in the direction of arrow E in Fig. 6(A) from the state shown in Fig. 6(B), the processing objective lens 42 is located at the other end of the line to cut C1 as shown in Fig. 6(C). When the processing objective lens 42 reaches a position outside of the object S, a state opposite to that explained with reference to Fig. 6(A) is attained, whereby the total quantity of the reflected light beam of the rangefinding laser beam L2 detected by the four-divided position detecting device in the light-receiving part 45 (see Fig. 1) decreases. Therefore, when the total quantity of light detected by the four-divided position detecting device in the light-receiving part 45 (see Fig. 1) becomes smaller than a predetermined threshold, the processing objective lens 42 is assumed to be located at a position corresponding to one end of the line to cut C1 (in the state corresponding to Fig. 6(C)), and the amount of expansion of the actuator at this time is held. While keeping the amount of expansion of the actuator 43, the stage 2 is moved such that the processing objective lens 42 reaches the position of X2 in Fig. 6(C), so as to be ready for the processing of the next line to cut C2 (transition step).
Though the processing objective lens 42 having reached a position corresponding to one end of the line to cut C1 (Fig. 6(A)) is detected according to the fact that the total light quantity detected by the four-divided position detecting device in the light-receiving part 45 (see Fig. 1) exceeds a predetermined threshold in the foregoing explanation, this is not restrictive, whereby other criteria may also be employed. An example of such criteria will be explained with reference to Figs. 7(A) and 7(B). Fig. 7(A), whose ordinate and abscissa indicate the total light quantity detected by the four-divided position detecting device of the light-receiving part 45 (see Fig. 1) and time, respectively, is a chart recording the change in the total light quantity detected by the four-divided position detecting device of the light-receiving part 45 (see Fig. 1) in the states of Figs. 6(A) and 6(B). In this case, as mentioned above, it is determined that the processing objective lens 42 is located at a position corresponding to one end of the line to cut C1 at the time when the light quantity exceeds a predetermined threshold T1.
From the graph of Fig. 7(A), at predetermined intervals (e.g., at individual sampling points), the amount of change in difference obtained by subtracting the previous total light quantity value from the current total light quantity value is calculated. Thus obtained values are plotted in Fig. 7(B) whose ordinate and abscissa indicate the amount of change and time, respectively. In this case, a part exhibiting a positive peak seems to be a point where the change in the total light quantity is the largest, i.e., a part corresponding to the vicinity of the center of an edge (outer edge) of the object S. Therefore, the tracking of the actuator 43 can be started after the differential peak shown in Fig. 7(B) stops changing after the total light quantity shown in Fig. 7(A) becomes the threshold T1.
Though the processing objective lens 42 having reached a position corresponding to the other end of the line to cut C1 (Fig. 6(C)) is detected according to the fact that the total light quantity detected by the four-divided position detecting device in the light-receiving part 45 (see Fig. 1) becomes smaller than a predetermined threshold in the foregoing explanation, this is not restrictive, whereby other criteria may also be employed. An example of such criteria will be explained with reference to Figs. 8(A) and 8(B). Fig. 8(A), whose ordinate and abscissa indicate the total light quantity detected by the four-divided position detecting device of the light-receiving part 45 (see Fig. 1) and time, respectively, is a chart recording the change in the total light quantity detected by the four-divided position detecting device of the light-receiving part 45 (see Fig. 1) in the states of Figs. 6(B) and 6(C). In this case, as mentioned above, it is determined that the processing objective lens 42 is located at a position corresponding to one end of the line to cut C1 at the time when the light quantity becomes smaller than a predetermined threshold T2.
From the graph of Fig. 8(A), at predetermined intervals (e.g., at individual sampling points), the amount of change in difference obtained by subtracting the previous total light quantity value from the current total light quantity value is calculated. Thus obtained values are plotted in Fig. 8(B) whose ordinate and abscissa indicate the amount of change and time, respectively. In this case, a part exhibiting a negative peak seems to be a point where the change in the total light quantity is the largest, i.e., a part corresponding to the vicinity of the center of an edge (outer edge) of the object S. Therefore, the amount of expansion/contraction of the actuator 43 can be fixed at that corresponding to this part.
The amount of expansion/contraction of the actuator 43 is stored in the circular memory 706 (see Fig. 2) during period G (in the case where the amount of expansion/contraction of the actuator 43 is fixed at the time when the total light quantity becomes smaller than the threshold T2) or period H (in the case where the amount of expansion/contraction of the actuator 43 is fixed at the time when the amount of change in the total light quantity attains a negative peak) in Fig. 8(A). Since the circular memory comprises 64 channels, an average value of the amounts of expansion/contraction of the actuator 43 stored in the first 5 channels of the memory may be determined, for example, and the amount of expansion/contraction of the actuator 43 may be fixed so as to become thus determined average value. In this case, the actuator 43 is fixed at a position corresponding to the main surface height of the object corresponding to the initial quarter of the period G or H in Fig. 8(A), which is more suitably set as the initial position for the next line to cut C2.
Operations of the laser processing apparatus 1 in this processing step will be explained with reference to the flowchart shown in Fig. 9. Here, the stage 2 and processing objective lens 42 of the laser processing apparatus 1 are assumed to be in the state explained with reference to Fig. 4(C).
The laser emission controller 701 of the control unit 7 outputs control signals to the laser head 13 and laser diode 44 so as to make them emit the processing laser beam L 1 and the rangefinding laser beam L2, respectively (step S11). In response to the output of the control signals, the processing laser beam L1 and the rangefinding laser beam L2 are emitted.
The stage controller 702 of the control unit 7 outputs a control signal to the stage 2 so as to move the processing objective lens 42 in the direction of arrow E in Fig. 6(A) (step S 12). In response to the output of this control signal, the stage 2 starts moving.
According to the signal outputted from the light-receiving part 45, the end part determiner 705 of the control unit 7 determines whether the processing objective lens 42 is located at an end part of the object S or not (step S13). When it is determined that the processing objective lens 42 is located at an end part of the object S, the end part determiner 705 outputs an instruction signal to the actuator controller 703 so as to make the latter start the expansion/contraction of the actuator 43 such that the astigmatism signal equals the held reference value. The actuator controller 703 outputs the control signal to the actuator 43 so as to make the latter start expanding/contracting in order for the astigmatism signal to equal the held reference value (step S14). In response to the output of this control signal, the actuator 43 expands/contracts according to the displacement of the surface S1 of the object S, and holds the processing objective lens 42 such that the converging point of the rangefinding laser beam L2 is located at the reference position. Therefore, the modified region R is formed at a position corresponding to the displacement of the surface S1 of the object S (see Fig. 6(B)).
According to the signal outputted from the light-receiving part 45, the end part determiner 705 determines whether the processing objective lens 42 is located at the other end part of the object S or not (step S15). When it is determined that the processing objective lens 42 is located at the end part of the object S, the end part determiner 705 outputs an instruction signal to the actuator controller 703 so as to make the latter stop the expansion/contraction of the actuator 43. In response to the output of this instruction signal, the actuator controller 703 outputs a control signal to the actuator 43 so as to make the latter stop expanding/contracting and attain a held state (step S16). In response to the output of this control signal, the actuator 43 stops expanding/contracting. When the processing objective lens 42 is located at the point X2 on an extension of the line to cut C1, the stage movement controller 702 outputs a control signal to the stage 2 so as to make the latter stop moving (step S 17). Thereafter, an average value of the amounts of expansion/contraction of the actuator 43 stored in the first 5 channels of the circular memory 706 among the amounts of expansion/contraction of the actuator 43 stored in the circular memory 706 is calculated, and the amount of expansion/contraction of the actuator 43 is fixed so as to become this average value (step S 18).
Since this embodiment starts laser processing by emitting the processing laser beam L1 while holding the processing objective lens 42 at the initial position, the influence of fluctuations in the shape of end parts in the object S can be excluded as much as possible.
After forming a modified region in an end part of the object S while holding the processing objective lens 42 at the initial position, the processing objective lens 42 is released from being held, and then the modified region is formed while adjusting the distance between the processing objective lens 42 and the object S to a fixed value, whereby the modified region can stably be formed at a position separated by a predetermined distance from the surface S1 of the object S.
After forming the modified region, the processing objective lens 42 is held so as to be kept from being driven toward the main surface S1 of the object S, whereby a smooth transition is possible when shifting to the processing of the next line to cut.
In the preparatory step of the next line to cut, the position of the processing objective lens 42 with respect to the main surface S 1 is set to the position based on the amount of expansion/contraction of the actuator 43 stored before a predetermined time from the time when the processing objective lens 42 is held so as to be kept from being driven, the influence of fluctuations in the shape of end parts in the object S can be excluded as much as possible.
A laser processing method for irradiating an object to be processed with a first laser beam while converging the first laser beam with a lens such that a converging point is positioned within the object, and forming a modified region within the object along a line to cut in the object; the method comprising:
a preparatory step of holding the lens at an initial position with respect to a main surface of the object, the initial position being set so that the converging point is located at a predetermined position within the object;
a first processing step of emitting the first laser beam while holding the lens at the initial position, and moving the lens and the object relative to each other along the main surface so as to form the modified region in one end part of the line to cut; and
a second processing step of releasing the lens from being held at the initial position after forming the modified region in the one end part, and then moving the lens and the object relative to each other along the main surface while adjusting a gap between the lens and the main surface so as to form the modified region.
A laser processing method according to claim 1, wherein, in the second processing step, the first laser beam and a second laser beam for measuring a displacement of the main surface are converged by the lens onto the object on the same axis, and the lens is released from being held after the quantity of reflected light of the second laser beam reflected by the main surface exceeds a predetermined threshold.
A laser processing method according to claim 1, wherein, in the second processing step, the first laser beam and a second laser beam for measuring a displacement of the main surface are converged by the lens onto the object on the same axis, and the lens is released from being held after an amount of change in the quantity of reflected light of the second laser beam reflected by the main surface becomes a maximum value.
A laser processing method according to claim 1, further comprising a transition step of holding the lens so as to keep the lens from being driven toward the main surface after the second processing step.
A laser processing method according to claim 4, wherein, in the transition step, the first laser beam and a second laser beam for measuring a displacement of the main surface are converged by the lens onto the object on the same axis, and the lens is held so as to be kept from being driven after the quantity of reflected light of the second laser beam reflected by the main surface becomes smaller than a predetermined threshold.
A laser processing method according to claim 4, wherein, in the transition step, the first laser beam and a second laser beam for measuring a displacement of the main surface are converged by the lens onto the object on the same axis, and the lens is released from being held after an amount of change in the quantity of reflected light of the second laser beam reflected by the main surface becomes a minimum value.
A laser processing method according to claim 4, wherein the line to cut includes first and second lines to cut;
wherein respective displacements of the main surface in unit time zones are successively stored in the second processing step of the first line to cut;
wherein the lens is held in the transition step of the first line to cut such that, with respect to the main surface, the lens is placed at a position based on the displacement stored in the unit time zone earlier by a predetermined number than the unit time zone where the lens is held so as to be kept from being driven in the transition step of the first line to cut; and
wherein the position where the lens is held in the transition step of the first line to cut is employed as the initial position in the preparatory step of the second line to cut.
A laser processing apparatus for irradiating an object to be processed with a first laser beam while converging the first laser beam with a lens such that a converging point is positioned within the object, and forming a modified region within the object along a line to cut in the object; the apparatus comprising:
a lens for converging the first laser beam onto the object;
moving means for moving the object and the lens relative to each other along a main surface of the object;
wherein the control means controls the holding means so as to hold the lens at an initial position where the converging point is located at a predetermined position within the object;
wherein, while emitting the first laser beam with the lens being held at the initial position, the control means controls the moving means so as to move the object and the lens relative to each other along the main surface, thereby forming the modified region in one end part of the line to cut; and
wherein, after forming the modified region in the one end part of the line to cut, the control means controls the holding means so as to release the lens from being held at the initial position and hold the lens while adjusting a gap between the lens and the main surface, and controls the moving means so as to move the lens and the object relative to each other along the main surface, thereby forming the modified region.
A laser processing apparatus according to claim 8, wherein the first laser beam and a second laser beam for measuring a displacement of the main surface are converged by the lens onto the object on the same axis; and
wherein the control means controls the holding means so as to release the lens from being held after the quantity of reflected light of the second laser beam reflected by the main surface exceeds a predetermined threshold.
wherein the control means controls the holding means so as to release the lens from being held after an amount of change in the quantity of reflected light of the second laser beam reflected by the main surface becomes a maximum value.
A laser processing apparatus according to claim 8, wherein, after forming the modified region in the one end part of the line to cut, the control means controls the holding means so as to release the lens from being held at the initial position and hold the lens while adjusting a gap between the lens and the main surface, and controls the moving means so as to move the lens and the object relative to each other along the main surface, thereby forming the modified region; and
wherein the control means controls the holding means so as to hold the lens such that the lens is kept from being driven toward the main surface and move the lens and the object relative to each other along the main surface.
A laser processing apparatus according to claim 11, wherein the first laser beam and a second laser beam for measuring a displacement of the main surface are converged by the lens onto the object on the same axis; and
wherein the control means controls the holding means so as to hold the lens such that the lens is kept from being driven toward the main surface after the quantity of reflected light of the second laser beam reflected by the main surface becomes smaller than a predetermined threshold.
wherein the control means controls the holding means so as to hold the lens such that the lens is kept from being driven toward the main surface after an amount of change in the quantity of reflected light of the second laser beam reflected by the main surface becomes a minimum value.
A laser processing apparatus according to claim 11, wherein the line to cut includes first and second lines to cut;
wherein the apparatus further comprises displacement storage means for successively storing respective displacements of the main surface in unit time zones; and
wherein the control means sets a position based on the displacement stored in the unit time zone earlier by a predetermined number than the unit time zone where the lens is held so as to be kept from being driven in the first line to cut as the initial position in the second line to cut.
EP04806955A 2004-01-09 2004-12-13 Laser processing method and device Active EP1716960B1 (en)
JP2004004304A JP4509578B2 (en) 2004-01-09 2004-01-09 Laser processing method and laser processing apparatus
PCT/JP2004/018594 WO2005065882A1 (en) 2004-01-09 2004-12-13 Laser processing method and device
EP1716960A1 true EP1716960A1 (en) 2006-11-02
EP1716960A4 EP1716960A4 (en) 2008-08-13
EP1716960B1 EP1716960B1 (en) 2010-03-10
ID=34747111
EP04806955A Active EP1716960B1 (en) 2004-01-09 2004-12-13 Laser processing method and device
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JP (1) JP4509578B2 (en)
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AT (1) AT460247T (en)
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WO (1) WO2005065882A1 (en)
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