JP2013003317A - Image-side telecentric objective lens and laser processing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image-side telecentric objective lens which is capable of radiating a laser beam in parallel with an optical axis of the objective lens, and a laser processing apparatus including the objective lens.SOLUTION: The image-side telecentric objective lens includes a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, and a third lens group G3 having negative refractive power, which are arranged in order from the light projection side. The first lens group constitutes a positive air lens by a first negative lens and a second negative lens of which the surfaces facing each other are concave. The image-side telecentric objective lens satisfies conditions 0.9<|F1/F2|<3.5, 1.2<|F3/F2|<5.0, and 1.3<|F/Fa|<2.55 wherein F is a composite focal length of an optical system, F1 is a composite focal length of the first lens group G1, Fa is a focal length of the air lens of the first lens group G1, F2 is a composite focal length of the second lens group G2, and F3 is a composite focal length of the third lens group G3.

Description

  The present invention relates to an image-side telecentric objective lens and a laser processing apparatus that includes the image-side telecentric objective lens and performs laser processing on a workpiece such as a semiconductor wafer.

  In the semiconductor device manufacturing process, a plurality of regions are partitioned by dividing lines called streets arranged in a lattice pattern on the surface of a substantially wafer-shaped semiconductor wafer, and devices such as ICs, LSIs, etc. are partitioned in the partitioned regions. Form. Then, the semiconductor wafer is cut along the streets to divide the region in which the device is formed to manufacture individual semiconductor chips.

  In order to reduce the size and increase the functionality of an apparatus, a module structure in which a plurality of devices are stacked and bonding pads provided on the stacked devices are connected has been put into practical use. This module structure has a structure in which a through hole (via hole) is formed at a position where a bonding pad is provided in a semiconductor wafer, and a conductive material such as aluminum connected to the bonding pad is embedded in the via hole. (For example, refer to Patent Document 1.)

  The via hole provided in the semiconductor wafer described above is formed by a drill. However, the via hole provided in the semiconductor wafer has a diameter as small as 50 to 300 μm, and there is a problem that productivity is poor when drilling with a drill.

  In order to solve the above problem, a via hole reaching a bonding pad by irradiating a wafer having a plurality of devices formed on the surface of the substrate and a bonding pad formed on the device by irradiating a pulse laser beam from the back side of the substrate. A processing method for forming the film has been put into practical use. A laser processing apparatus that efficiently forms a plurality of via holes is disclosed in Patent Document 2 below. The laser processing apparatus disclosed in the following Patent Document 2 includes a scanner that deflects a laser beam oscillated by a laser beam oscillating means in an XY direction, and a laser beam deflected in the XY direction by the scanner to collect and irradiate the wafer. An objective lens including a -tan θ lens is provided, and the focal length is constant even when the incident angle θ with respect to the objective lens is changed, and irradiation is performed substantially parallel to the optical axis of the objective lens.

JP 2003-249620 A Japanese Patent Laid-Open No. 2004-230466

  Thus, the laser processing apparatus provided with the objective lens composed of the f-tan θ lens disclosed in the above-mentioned Patent Document 2 can be applied to the wafer when the diameter of the wafer becomes as large as 200 mm and the angle of view of the incident angle θ increases. The irradiated laser beam is not parallel to the optical axis of the objective lens, and the via hole cannot be formed perpendicular to the bonding pad.

  The present invention has been made in view of the above-mentioned facts, and the main technical problem thereof is an image that can irradiate a laser beam parallel to the optical axis of the objective lens without depending on the angle of view of the incident angle θ. A side telecentric objective lens and a laser processing apparatus including the image side telecentric objective lens are provided.

In order to solve the main technical problem described above, according to the present invention, an image side telecentric objective lens in which the optical axis of light incident from the light projecting side is emitted to the image side in parallel with the optical axis of the lens,
A first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, and a third lens group G3 having a negative refractive power, which are sequentially arranged from the light projecting side. In the first lens group G1, a positive air lens is constituted by a first negative lens and a second negative lens having concave surfaces facing each other, the combined focal length of the optical system being F, The combined focal length of the lens group G1 is F1, the focal length of the air lens of the first lens group G1 is Fa, the combined focal length of the second lens group G2 is F2, and the combined focal length of the third lens group G3 is F3. When
0.9 <| F1 / F2 | <3.5
1.2 <| F3 / F2 | <5.0
1.3 <| F / Fa | <2.55
An image side telecentric objective lens characterized by satisfying the following conditions is provided.

When the focal length of the first negative lens of the first lens group G1 is f11 and the focal length of the second negative lens is f12, the condition of 0.3 <f11 / f12 <7.1 is satisfied. Is set.
Further, when the distance from the aperture stop to the first negative lens of the first lens group G1 is L1, it is desirable to satisfy the condition of L1 / F <0.51.
Further, the second lens group G2 has at least five positive lenses, and the third lens group G3 has at least one negative lens.

Further, according to the present invention, in a laser processing apparatus comprising: a chuck table for holding a workpiece; and a laser beam irradiation means for irradiating a workpiece with the laser beam to the workpiece held by the chuck table.
The laser beam irradiation means includes a laser beam oscillator that oscillates a laser beam, a scanner that deflects the optical axis of the laser beam oscillated by the laser beam oscillator, and collects the laser beam whose optical axis is deflected by the scanner and holds it on the chuck table. And a condenser for irradiating the processed workpiece,
The concentrator includes a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, and a third lens having a negative refractive power, which are sequentially arranged from the light projecting side. The first lens group G1 includes a first negative lens having a concave surface and a second negative lens constituting a positive air lens, and a combined focal length of the optical system. F, the combined focal length of the first lens group G1 is F1, the focal length of the air lens of the first lens group G1 is Fa, the combined focal length of the second lens group G2 is F2, and the third lens group G3 When the combined focal length of F3 is
0.9 <| F1 / F2 | <3.5
1.2 <| F3 / F2 | <5.0
1.3 <| F / Fa | <2.55
It is constituted by an image side telecentric objective lens that satisfies the conditions of
A laser beam irradiation apparatus is provided.

The image side telecentric objective lens according to the present invention has a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, and a negative refractive power, which are sequentially arranged from the light projecting side. And the first lens group G1 is composed of a first negative lens and a second negative lens whose surfaces facing each other are concave, and the first negative lens and the second negative lens. By forming a positive air lens with a negative lens, spherical aberration occurring on the optical axis and astigmatism occurring outside the optical axis are effectively corrected, and image-side telecentricity is realized.
In addition, since the laser beam irradiation apparatus according to the present invention includes the condenser configured by the image side telecentric objective lens, the irradiated pulse laser beam is directed to the optical axis from the center to the periphery of the image side telecentric objective lens. Since it becomes parallel and the incident angle with respect to the workpiece becomes vertical, the machining hole can be formed with uniform quality. Therefore, even if the workpiece is a wafer having a diameter of, for example, 200 mm, it is possible to realize accurate and high throughput laser processing from the center to the periphery.

The perspective view of the laser processing apparatus comprised according to this invention. The block diagram of a structure of the laser beam irradiation means with which the laser processing apparatus shown in FIG. 1 is equipped. Sectional drawing of Numerical Example 1 of the image side telecentric objective lens comprised according to this invention used for the collector with which the laser processing apparatus shown in FIG. 1 is equipped. Sectional drawing of Numerical Example 2 of the image side telecentric objective lens comprised according to this invention used for the collector with which the laser processing apparatus shown in FIG. 1 is equipped. Sectional drawing of Numerical Example 3 of the image side telecentric objective lens comprised according to this invention used for the collector with which the laser processing apparatus shown in FIG. 1 is equipped. Sectional drawing of Numerical Example 4 of the image side telecentric objective lens comprised according to this invention used for the collector with which the laser processing apparatus shown in FIG. 1 is equipped. Sectional drawing of Numerical Example 5 of the image side telecentric objective lens comprised according to this invention used for the collector with which the laser processing apparatus shown in FIG. 1 is equipped. Sectional drawing of Numerical Example 6 of the image side telecentric objective lens comprised according to this invention used for the collector with which the laser processing apparatus shown in FIG. 1 is equipped. FIG. 4 is an aberration curve diagram showing spherical aberration and astigmatism of Numerical Example 1 shown in FIG. 3. FIG. 5 is an aberration curve diagram showing spherical aberration and astigmatism of Numerical Example 2 shown in FIG. 4. FIG. 6 is an aberration curve diagram showing spherical aberration and astigmatism of Numerical Example 3 shown in FIG. 5. FIG. 7 is an aberration curve diagram showing spherical aberration and astigmatism of Numerical Example 4 shown in FIG. 6. FIG. 8 is an aberration curve diagram showing spherical aberration and astigmatism of Numerical Example 5 shown in FIG. 7. FIG. 9 is an aberration curve diagram showing spherical aberration and astigmatism of Numerical Example 6 shown in FIG. 8. The block block diagram of the control means with which the laser processing apparatus shown in FIG. 1 is equipped. The top view of the semiconductor wafer as a wafer. FIG. 17 is an enlarged plan view showing a part of the semiconductor wafer shown in FIG. 16. The perspective view which shows the state which affixed the semiconductor wafer shown in FIG. 16 on the surface of the protective tape with which the cyclic | annular flame | frame was mounted | worn. FIG. 17 is an explanatory diagram showing a relationship with coordinates in a state where the semiconductor wafer shown in FIG. 16 is held at a predetermined position of the chuck table of the laser processing apparatus shown in FIG. 1. FIG. 7 is an explanatory diagram of a drilling process for drilling laser processed holes (via holes) in the semiconductor wafer illustrated in FIG. 6 using the laser processing apparatus illustrated in FIG. 1.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Preferred embodiments of an image side telecentric objective lens configured according to the present invention and a laser processing apparatus including the image side telecentric objective lens will be described below in more detail with reference to the accompanying drawings.

  FIG. 1 is a perspective view of a laser processing apparatus constructed according to the present invention. A laser processing apparatus shown in FIG. 1 includes a stationary base 2, a chuck table mechanism 3 that is disposed on the stationary base 2 so as to be movable in the X-axis direction indicated by an arrow X, and holds a workpiece. 2, a laser beam irradiation unit support mechanism 4 disposed so as to be movable in the Y-axis direction indicated by an arrow Y orthogonal to the X-axis direction, and to be movable in the Z-axis direction indicated by an arrow Z to the laser beam irradiation unit support mechanism 4. And an arranged laser beam irradiation unit 5.

  The chuck table mechanism 3 includes a pair of guide rails 31, 31 disposed in parallel along the X-axis direction on the stationary base 2, and a machining feed direction indicated by an arrow X on the guide rails 31, 31 ( A first sliding block 32 movably arranged in the X-axis direction), a second sliding block 33 movably arranged on the first sliding block 32 in the Y-axis direction, and the first A cover table 35 supported by a cylindrical member 34 on a second sliding block 33 and a chuck table 36 as a workpiece holding means are provided. The chuck table 36 includes a suction chuck 361 formed of a porous material, and holds, for example, a disk-shaped semiconductor wafer, which is a workpiece, on the suction chuck 361 by suction means (not shown). . The chuck table 36 configured as described above is rotated by a pulse motor (not shown) disposed in the cylindrical member 34. The chuck table 36 is provided with a clamp 362 for fixing an annular frame described later.

  The first sliding block 32 has a pair of guided grooves 321 and 321 fitted to the pair of guide rails 31 and 31 on the lower surface thereof, and is parallel to the upper surface along the Y-axis direction. A pair of formed guide rails 322 and 322 are provided. The first sliding block 32 configured in this way moves in the X-axis direction along the pair of guide rails 31, 31 when the guided grooves 321, 321 are fitted into the pair of guide rails 31, 31. Configured to be possible. The chuck table mechanism 3 in the illustrated embodiment includes X-axis direction moving means 37 for moving the first sliding block 32 along the pair of guide rails 31, 31 in the X-axis direction. The X-axis direction moving means 37 includes a male screw rod 371 disposed in parallel between the pair of guide rails 31 and 31, and a drive source such as a pulse motor 372 for rotationally driving the male screw rod 371. It is out. One end of the male screw rod 371 is rotatably supported by a bearing block 373 fixed to the stationary base 2, and the other end is connected to the output shaft of the pulse motor 372 by transmission. The male screw rod 371 is screwed into a penetrating female screw hole formed in a female screw block (not shown) provided on the lower surface of the central portion of the first sliding block 32. Therefore, when the male screw rod 371 is driven forward and backward by the pulse motor 372, the first sliding block 32 is moved along the guide rails 31, 31 in the X-axis direction.

  The laser processing apparatus in the illustrated embodiment includes X-axis direction position detecting means 374 for detecting the amount of movement of the chuck table 36 in the X-axis direction, that is, the X-axis direction position. The X-axis direction position detecting means 374 moves along the linear scale 374a together with the linear scale 374a disposed along the guide rail 31 and the first sliding block 32 along the linear scale 374a. It consists of a read head 374b. In the illustrated embodiment, the reading head 374b of the X-axis direction position detecting means 374 sends a pulse signal of one pulse every 1 μm to the control means described later. The control means described later counts the input pulse signal to detect the amount of movement of the chuck table 36 in the X-axis direction, that is, the position in the X-axis direction. When the pulse motor 372 is used as the drive source of the X-axis direction moving means 37, the chuck table 36 is moved by counting the drive pulses of the control means to be described later that outputs a drive signal to the pulse motor 372. It is also possible to detect the quantity, that is, the position in the X-axis direction. When a servo motor is used as a drive source for the X-axis direction moving means 37, a pulse signal output from a rotary encoder that detects the rotation speed of the servo motor is sent to the control means described later, and the control means inputs it. By counting the pulse signals, the amount of movement of the chuck table 36 in the X-axis direction, that is, the position in the X-axis direction can also be detected.

  The second sliding block 33 is provided with a pair of guided grooves 331 and 331 which are fitted to a pair of guide rails 322 and 322 provided on the upper surface of the first sliding block 32 on the lower surface thereof. By fitting the guided grooves 331 and 331 to the pair of guide rails 322 and 322, the guided grooves 331 and 331 are configured to be movable in the Y-axis direction. The chuck table mechanism 3 in the illustrated embodiment includes a first Y for moving the second sliding block 33 in the Y-axis direction along a pair of guide rails 322 and 322 provided in the first sliding block 32. An axial movement means 38 is provided. The first Y-axis direction moving means 38 includes a male screw rod 381 disposed in parallel between the pair of guide rails 322 and 322, and a pulse motor 382 for driving the male screw rod 381 to rotate. Contains sources. One end of the male screw rod 381 is rotatably supported by a bearing block 383 fixed to the upper surface of the first slide block 32, and the other end is connected to the output shaft of the pulse motor 382. The male screw rod 381 is screwed into a through female screw hole formed in a female screw block (not shown) provided on the lower surface of the center portion of the second sliding block 33. Therefore, the second sliding block 33 is moved in the Y-axis direction along the guide rails 322 and 322 by driving the male screw rod 381 forward and backward by the pulse motor 382.

  The laser processing apparatus in the illustrated embodiment includes Y-axis direction position detection means 384 for detecting the amount of movement of the second sliding block 33 in the Y-axis direction, that is, the Y-axis direction position. The Y-axis direction position detecting means 384 moves along the linear scale 384a together with the linear scale 384a disposed along the guide rail 322 and the second sliding block 33. And a reading head 384b. In the illustrated embodiment, the reading head 384b of the Y-axis direction position detecting means 384 sends a pulse signal of one pulse every 1 μm to the control means described later. The control means described later counts the input pulse signal to detect the amount of movement of the chuck table 36 in the Y-axis direction, that is, the position in the Y-axis direction. When the pulse motor 382 is used as the drive source for the first Y-axis direction moving means 38, the chuck table is counted by counting the drive pulses of the control means to be described later that outputs a drive signal to the pulse motor 382. The amount of movement in the Y-axis direction, that is, the position in the Y-axis direction can also be detected. When a servo motor is used as a drive source for the first Y-axis direction moving means 38, a pulse signal output from a rotary encoder that detects the rotation speed of the servo motor is sent to the control means described later, and the control means By counting the pulse signals inputted, the amount of movement of the chuck table 36 in the Y-axis direction, that is, the position in the Y-axis direction can also be detected.

  The laser beam irradiation unit support mechanism 4 includes a pair of guide rails 41, 41 arranged in parallel along the indexing feed direction (Y-axis direction) indicated by an arrow Y on the stationary base 2, and the guide rails 41, 41, A movable support base 42 is provided on 41 so as to be movable in the Y-axis direction. The movable support base 42 includes a movement support portion 421 that is movably disposed on the guide rails 41, 41, and a mounting portion 422 that is attached to the movement support portion 421. The mounting portion 422 is provided with a pair of guide rails 423 and 423 extending in the Z-axis direction perpendicular to the holding surface of the chuck table 36 on one side surface. The laser beam irradiation unit support mechanism 4 in the illustrated embodiment includes second Y-axis direction moving means 43 for moving the movable support base 42 in the Y-axis direction along the pair of guide rails 41, 41. Yes. The second Y-axis direction moving means 43 includes a male screw rod 431 disposed in parallel between the pair of guide rails 41, 41, a pulse motor 432 for driving the male screw rod 431, and the like. Contains sources. One end of the male screw rod 431 is rotatably supported by a bearing block (not shown) fixed to the stationary base 2, and the other end is connected to the output shaft of the pulse motor 432. The male screw rod 431 is screwed into a female screw hole formed in a female screw block (not shown) provided on the lower surface of the central portion of the moving support portion 421 constituting the movable support base 42. For this reason, when the male screw rod 431 is driven to rotate forward and reversely by the pulse motor 432, the movable support base 42 is moved along the guide rails 41, 41 in the Y-axis direction.

  The laser beam irradiation unit 5 in the illustrated embodiment includes a unit holder 51 and laser beam irradiation means 52 attached to the unit holder 51. The unit holder 51 is provided with a pair of guided grooves 511 and 511 that are slidably fitted to a pair of guide rails 423 and 423 provided in the mounting portion 422. By being fitted to the guide rails 423 and 423, the guide rails 423 and 423 are supported so as to be movable in the Z-axis direction.

  The laser beam irradiation unit 5 in the illustrated embodiment includes a unit holder 51 and laser beam irradiation means 52 attached to the unit holder 51. The unit holder 51 is provided with a pair of guided grooves 511 and 511 that are slidably fitted to a pair of guide rails 423 and 423 provided in the mounting portion 422. By being fitted to the guide rails 423 and 423, the guide rails 423 and 423 are supported so as to be movable in the Z-axis direction.

  The laser beam irradiation unit 5 in the illustrated embodiment includes Z-axis direction moving means 53 as focusing point position adjusting means for moving the unit holder 51 along the pair of guide rails 423 and 423 in the Z-axis direction. ing. The Z-axis direction moving means 53 includes a drive source such as a male screw rod (not shown) disposed between the pair of guide rails 423 and 423 and a pulse motor 532 for rotationally driving the male screw rod. Then, the male screw rod (not shown) is driven to rotate forward and reverse by the pulse motor 532, so that the unit holder 51 and the laser beam irradiation means 52 are moved along the guide rails 423 and 423 in the Z-axis direction. In the illustrated embodiment, the laser beam irradiation means 52 is moved upward by driving the pulse motor 532 forward, and the laser beam irradiation means 52 is moved downward by driving the pulse motor 532 in reverse. Yes.

  The illustrated laser beam application means 52 includes a cylindrical casing 521 arranged substantially horizontally. In the casing 521, as shown in FIG. 2, a pulse laser beam oscillation means 6, a scanner 7 that oscillates from the pulse laser beam oscillation means 6 and deflects the optical axis of the pulse laser beam in the X axis direction and the Y axis direction, and the scanner 7 And a condenser 8 composed of an image side telecentric objective lens that condenses the laser beam whose optical axis is deflected and irradiates the workpiece held on the chuck table 36.

  The pulse laser beam oscillation means 6 is composed of a pulse laser beam oscillator 61 and a repetition frequency setting means 62 attached thereto. In the illustrated embodiment, the pulse laser beam oscillator 61 is composed of a YVO4 laser or a YAG laser oscillator, and oscillates a pulse laser beam LB having a wavelength (for example, 355 nm) that is absorptive to a workpiece such as silicon. The repetition frequency setting means 62 sets the frequency of the pulse laser beam oscillated from the pulse laser beam oscillator 61.

  The scanner 7 is constituted by a galvanometer mirror in the illustrated embodiment, and is controlled by a control means to be described later. The scanner 7 oscillates a pulse laser beam oscillated from a pulse laser beam oscillator 61 in the X-axis direction and the Y-axis direction, and is a condenser. Lead to 8. As the scanner 7, a polygon mirror or a piezo mirror can be used.

Next, the condenser 8 composed of the image side telecentric objective lens will be described with reference to FIGS.
The condenser 8 composed of the image side telecentric objective lens shown in FIGS. 3 to 8 includes a first lens group G1 having a negative refractive power and sequentially arranged from the light projecting side as the scanner 7, respectively. It consists of a second lens group G2 having a positive refractive power and a third lens group G3 having a negative refractive power. In the first lens group G1, a positive air lens G1-3 is constituted by a first negative lens G1-1 and a second negative lens G1-2 whose surfaces facing each other are concave. The second lens group G2 includes at least four positive lenses. The third lens group G3 is composed of at least one negative lens. Each lens is made of synthetic quartz.

As described above, the image-side telecentric objective lens constituted by the first lens group G1 having refractive power, the second lens group G2 having positive refractive power, and the third lens group G3 having negative refractive power is optical. The combined focal length of the system is F, the combined focal length of the first lens group G1 is F1, the focal length of the air lens G1-3 of the first lens group G1 is Fa, and the combined focal length of the second lens group G2 is F2. 3 When the combined focal length of the lens group G3 is F3,
0.9 <│F1 / F2│ <3.4 (1)
1.2 <| F3 / F2 | <5.0 (2)
1.3 <│F / Fa│ <2.55 (3)
It is important to satisfy these conditions.

When the focal length of the first negative lens G1-1 in the first lens group G1 is f11 and the focal length of the second negative lens G1-2 is f12,
0.35 <f11 / f12 <7.1 (4)
It is desirable to satisfy the following conditions.
Furthermore, when the distance from the aperture stop (scanner 7) to the first negative lens G1-1 of the first lens group G1 is L1,
L1 / F <0.51 (5)
It is desirable to satisfy the following conditions.

The image side telecentric objective lens shown in FIGS. 3 to 8 is configured as in the following numerical examples so as to satisfy the conditional expressions (1), (2), (3), (4), and (5) described above. ing. In addition, the meaning of the symbol described in the numerical Example is as follows.
m: Surface number of each lens viewed from the light projecting side of the scanner 7
ri: radius of curvature of each lens surface (mm)
di: Thickness and spacing of each lens (mm)
n: Refractive index of each lens

Numerical Example 1 of the image side telecentric objective lens shown in FIG. 3 is as follows.

Numerical Example 2 of the image side telecentric objective lens shown in FIG. 4 is as follows.

Numerical Example 3 of the image side telecentric objective lens shown in FIG. 5 is as follows.

Numerical Example 4 of the image side telecentric objective lens shown in FIG. 6 is as follows.

Numerical Example 5 of the image side telecentric objective lens shown in FIG. 7 is as follows.

Numerical Example 6 of the image side telecentric objective lens shown in FIG. 8 is as follows.

  Aberration curve diagrams of the image side telecentric objective lens shown in the numerical examples 1 to 6 are shown in FIGS. 9A shows the spherical aberration of Numerical Example 1, and FIG. 9B shows the astigmatism of Numerical Example 1. FIG. 10A shows the spherical aberration of Numerical Example 2, and FIG. 10B shows the astigmatism of Numerical Example 2. FIG. 11A shows the spherical aberration of Numerical Example 3, and FIG. 11B shows the astigmatism of Numerical Example 3. FIG. 12A shows the spherical aberration of Numerical Example 4, and FIG. 12B shows the astigmatism of Numerical Example 4. FIG. 13A shows the spherical aberration of Numerical Example 5, and FIG. 13B shows the astigmatism of Numerical Example 5. 14A shows the spherical aberration of Numerical Example 6, and FIG. 14B shows the astigmatism of Numerical Example 6. FIG. As described above, the image side telecentric objective lens in the illustrated embodiment includes the first negative lens G1-1 and the second negative lens G1-2 in which the first lens group G1 has a concave surface facing each other. Then, by forming the positive air lens G1-3 by the first negative lens G1-1 and the second negative lens G1-2, spherical aberration that occurs on the optical axis, astigmatism that occurs outside the optical axis. It effectively corrects aberrations and realizes image side telecentricity.

Here, the setting of the upper limit value and the lower limit value in the conditional expressions (1), (2), (3), (4), and (5) described above will be described.
Conditional expression (1) defines the ratio of the lens focal lengths of the first lens group G1 and the second lens group G2.
As the lower limit of conditional expression (1) (0.9 <| F1 / F2 |) is approached, the negative power of the first lens group G1 becomes strong as in Example 5 shown in FIG. Shorter). Therefore, if the area exceeds the lower limit (0.9 <| F1 / F2 |) of the conditional expression (1), the negative power of the first lens group G1 is too strong, so that the tolerance sensitivity becomes severe.
When approaching the upper limit (| F1 / F2 | <3.5) of the conditional expression (1), the negative power of the first lens group G1 becomes weaker as in the numerical example 2 shown in FIG. become longer). Accordingly, if the region exceeds the upper limit (| F1 / F2 | <3.5) of the conditional expression (1), the negative power of the first lens group G1 is weak, so that the field curvature aberration is insufficiently corrected, and the aberration performance. Gets worse. Further, since the deterioration of the aberration performance is corrected by the third lens group G3, the power of this lens becomes very large. Since the third lens group G3 has a small radius of curvature and requires a large curved surface, the flange back is shortened. Thereby, impurities such as debris by laser processing are likely to adhere.

Conditional expression (2) defines the ratio of the lens focal lengths of the second lens group G2 and the third lens group G3.
When approaching the lower limit (1.2 <| F3 / F2 |) of the conditional expression (2), the negative power of the third lens group G3 becomes strong as shown in Numerical Example 2 shown in FIG. Shorter). Therefore, in the region exceeding the lower limit (1.2 <| F3 / F2 |) of the conditional expression (2), the negative power of the third lens group G3 is too strong, so that the tolerance sensitivity becomes severe.
As the upper limit (<| F3 / F2 | <5.0) of conditional expression (2) is approached, the role of the third lens group G3 as a field flattener becomes smaller as in Numerical Example 3 shown in FIG. Therefore, when the region exceeds the upper limit (<| F3 / F2 | <5.0) of the conditional expression (2), the role of the third lens group G3 as a field flattener is small, and the field curvature aberration is increased. Aberration performance deteriorates.

Conditional expression (3) defines the ratio of the combined focal length F of the optical system to the focal length Fa of the air lens G1-3 of the first lens group G1.
As the lower limit (1.3 <| F / Fa |) of the conditional expression (3) is approached, the aberration correction effect decreases as shown in the aberration curve diagram (FIG. 14) of Numerical Example 6 shown in FIG. Therefore, if the region exceeds the lower limit (1.3 <| F / Fa |) of conditional expression (3), a sufficient aberration correction effect cannot be obtained, and correction of various aberrations occurring in the second lens group G2 is difficult. It becomes.
When approaching the upper limit (| F / Fa | <2.55) of the conditional expression (3), the second negative lens G1-2 of the first lens group G1 is nearly concentric as in Numerical Example 4 shown in FIG. Strong curved lens shape. Therefore, if the region exceeds the upper limit (| F / Fa | <2.55) of the conditional expression (3), a strong curved lens shape close to concentricity with almost no power is required. Therefore, the so-called Z coefficient indicating the difficulty of centering becomes too small, making it difficult to process.

Conditional expression (4) defines the ratio between the focal length f11 of the first negative lens G1-1 and the focal length f12 of the second negative lens G1-2 in the first lens group G1.
When approaching the lower limit (0.3 <f11 / f12) of the conditional expression (4), the second negative lens G1-2 of the first lens group G1 is strongly concentric as shown in Numerical Example 4 shown in FIG. It becomes a lens shape. Accordingly, when the region exceeds the lower limit (0.3 <f11 / f12) of the conditional expression (4), the second negative lens G1-2 in the first lens group G1 has almost no power and has a lens shape close to concentricity. Become. For this reason, the so-called Z coefficient indicating the difficulty of centering becomes too small, making it difficult to process.
When the upper limit (f11 / f12 <7.1) of the conditional expression (4) is approached, the first negative lens G1-1 of the first lens group G1 has a strong curvature close to concentricity as in Numerical Example 5 shown in FIG. It becomes a lens shape. Accordingly, when the region exceeds the upper limit (f11 / f12 <7.1) of the conditional expression (4), it is difficult to process the first negative lens G1-1 of the first lens group G1. Further, the difference from the lower limit value is that the tolerance sensitivity becomes strict because the second negative lens G1-2 having a negative power is disposed at a position where the light beam spreads relatively.

Conditional expression (5) defines the ratio of the distance L1 from the aperture stop (scanner 7) to the first negative lens G1-1 of the first lens group G1 with respect to F as the combined focal length of the optical system. .
In this case, the closer the scanner 7 is to the first negative lens G1-1 in the first lens group G1, the easier it is to correct aberrations because light rays pass through lower positions with respect to different angles of view. Furthermore, the aperture of the first negative lens G1-1 can be reduced. Therefore, the scanner 7 should be as close to the first negative lens G1-1 as the arrangement allows. For this reason, there is no lower limit.
If the region exceeds the upper limit (L1 / F <0.51) of the conditional expression (5), it is difficult to correct the aberration because the light passes through a higher position unless the power of the first lens group G1 is reduced. Therefore, it is necessary to make the power of the first lens group G1 as small as possible, and the correction of the field curvature aberration becomes insufficient, and the aberration performance deteriorates.

  Referring back to FIG. 1, the laser processing apparatus in the illustrated embodiment includes an imaging unit 11 that is disposed at a front end portion of the casing 521 and detects a processing region to be laser processed by the laser beam irradiation unit 52. Yes. The imaging unit 11 includes, in addition to a normal imaging device (CCD) that captures an image with visible light, an infrared illumination unit that irradiates a workpiece with infrared rays, an optical system that captures infrared rays emitted by the infrared illumination unit, An image sensor (infrared CCD) that outputs an electrical signal corresponding to the infrared rays captured by the optical system is used, and the captured image signal is sent to a control means to be described later.

  The laser processing apparatus in the illustrated embodiment includes a control means 20 shown in FIG. The control means 20 is configured by a computer, and a central processing unit (CPU) 201 that performs arithmetic processing according to a control program, a read-only memory (ROM) 202 that stores control programs and the like, and a read / write that stores arithmetic results and the like. A random access memory (RAM) 203, a counter 204, an input interface 205, and an output interface 206 are provided. Detection signals from the X-axis direction position detection unit 374, the Y-axis direction position detection unit 384, the imaging unit 11, and the like are input to the input interface 205 of the control unit 20. A control signal is output from the output interface 206 of the control means 20 to the pulse motor 372, the pulse motor 382, the pulse motor 432, the pulse motor 532, the pulse laser beam oscillation means 6 of the pulse laser beam irradiation means 52, the scanner 7, and the like. .

The laser processing apparatus in the illustrated embodiment is configured as described above, and the operation thereof will be described below.
FIG. 16 shows a plan view of a semiconductor wafer 30 as a workpiece to be laser processed. A semiconductor wafer 30 shown in FIG. 16 is divided into a plurality of regions by a plurality of division lines 301 arranged in a lattice pattern on a surface 300a of a silicon substrate 300 having a thickness of 100 μm, for example, and IC, LSI are divided into the divided regions. Each of the devices 302 is formed. All the devices 302 have the same configuration. A plurality of bonding pads 303 (303a to 303j) are formed on the surface of the device 302 as shown in FIG. The bonding pads 303 (303a to 303j) are made of aluminum in the illustrated embodiment. In the illustrated embodiment, 303a and 303f, 303b and 303g, 303c and 303h, 303d and 303i, and 303e and 303j have the same position in the X direction. The design value data of the X and Y coordinate values of the bonding pads 303 (303a to 303j) formed in each device 302 is stored in the random access memory (RAM) 203. Further, design value data of the X and Y coordinate values of the center S (see FIG. 16) of the semiconductor wafer 30 is stored in the random access memory (RAM) 203.

An embodiment of laser processing in which a laser processing hole (via hole) is formed in the bonding pad 303 (303a to 303j) of each device 302 formed on the semiconductor wafer 30 using the laser processing apparatus described above will be described.
As shown in FIG. 18, the semiconductor wafer 30 has a surface 300 a attached to a protective tape 50 made of a synthetic resin sheet such as polyolefin and attached to an annular frame 40. Accordingly, the back surface 300b of the semiconductor wafer 30 is on the upper side. In this way, the semiconductor wafer 30 supported on the annular frame 40 via the protective tape 50 places the protective tape 50 side on the chuck table 36 of the laser processing apparatus shown in FIG. Then, by operating a suction means (not shown), the semiconductor wafer 30 is sucked and held on the chuck table 36 via the protective tape 50. Therefore, the semiconductor wafer 30 is held with the back surface 300b facing upward. The annular frame 40 is fixed by a clamp 362.

  As described above, the chuck table 36 that sucks and holds the semiconductor wafer 30 is positioned directly below the imaging unit 11 by the processing feed unit 37. When the chuck table 36 is positioned immediately below the imaging means 11, the semiconductor wafer 30 on the chuck table 36 is positioned at the coordinate position shown in FIG. In this state, an alignment process is performed to determine whether or not the grid-like division planned lines 301 formed on the semiconductor wafer 30 held on the chuck table 36 are arranged in parallel to the X-axis direction and the Y-axis direction. . That is, the semiconductor wafer 30 held on the chuck table 36 is imaged by the imaging means 11, and image processing such as pattern matching is executed to perform alignment work. At this time, the surface 300a on which the division line 301 of the semiconductor wafer 30 is formed is positioned on the lower side. However, the imaging unit 11 corresponds to the infrared illumination unit, the optical system for capturing infrared rays, and infrared rays as described above. Since the image pickup device is provided with an image pickup device (infrared CCD) that outputs an electrical signal, the division planned line 301 can be picked up from the back surface 300 b of the semiconductor wafer 30. Thus, the semiconductor wafer 30 on the chuck table 36 on which the alignment process has been performed is positioned at the coordinate values shown in FIG.

  Next, a drilling step of drilling laser processed holes (via holes) in the bonding pad 303 (303a to 303j) portion formed in each device 302 of the semiconductor wafer 30 is performed. In the punching step, first, the X-axis direction moving means 37 and the first Y-axis direction moving means 38 are operated to move the chuck table 36, and the semiconductor shown in FIG. 19 stored in the random access memory (RAM) 203 is stored. The coordinate value of the center S of the wafer 30 is positioned immediately below the condenser 8 of the laser beam irradiation means 52 as shown in FIG. Then, the control unit 20 operates the pulse laser beam oscillation unit 6 of the pulse laser beam irradiation unit 52 and controls the scanner 7, and the random access memory (RAM) is connected to the random access memory (RAM) from the condenser 8 constituted by the image side telecentric objective lens described above. ) A pulse laser beam is irradiated to the coordinate value of each bonding pad 303 (303a to 303j) formed in each device 302 stored in 203. Then, for example, 100 shots of a pulse laser beam are applied to each bonding pad 303 (303a to 303j). As a result, as shown in FIG. 20B, the processing holes 304 are formed in one bonding process in all bonding pads 303a to 303j (processing positions) provided in the device 302 formed in the semiconductor wafer 30. can do.

The processing conditions in the drilling step are set as follows, for example.
Light source: LD excitation Q switch Nd: YVO4
Wavelength: 355nm
Average output: 4W
Repetition frequency: 50-100kHz
Condensing spot diameter: φ50μm

  As described above, the image-side telecentric objective lens in the above-described embodiment includes the first negative lens G1-1 and the second negative lens G1-2 in which the first lens group G1 has a concave surface facing each other. By constructing and forming the positive air lens G1-3 by the first negative lens G1-1 and the second negative lens G1-2, spherical aberration occurring on the optical axis, non-occurrence occurring outside the optical axis Astigmatism is effectively corrected and image side telecentricity is realized. In the image side telecentric objective lens shown in FIG. 3, when the combined focal length F of the optical system is 307.7 mm, the angle of view is 21.0 degrees, the Petzval radius is about 110000 mm, the telecentric angle (perpendicular to the surface of the workpiece) (The difference angle) can be within ± 0.1 degrees. Thus, the irradiated pulse laser beam is parallel to the optical axis from the center to the periphery of the image side telecentric objective lens, and the incident angle with respect to the semiconductor wafer 30 as the workpiece is vertical, so that the processing hole can be formed with uniform quality. 304 can be formed. Therefore, even with a semiconductor wafer having a diameter of 200 mm, it is possible to realize accurate and high-throughput laser processing from the center to the periphery.

2: stationary base 3: chuck table mechanism 31: guide rail 36: chuck table 37: X-axis direction moving means 374: X-axis direction position detecting means 38: first Y-axis direction moving means 384: Y-axis direction position detecting Means 4: Laser beam irradiation unit support mechanism 41: Guide rail 42: Movable support base 43: Second Y-axis direction moving means
5: Laser beam irradiation unit 51: Unit holder 52: Laser beam irradiation means 53: Z-axis direction moving means 6: Pulse laser beam oscillation means 7: Scanner 8: Condenser 11: Imaging means 20: Control means 30: Semiconductor wafer 301: Division Scheduled line 302: Device 303: Bonding pad 304: Processing hole 40: Ring frame 50: Protective tape

Claims (7)

An image side telecentric objective lens in which the optical axis of light incident from the light projecting side is emitted to the image side in parallel with the optical axis of the lens,
A first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, and a third lens group G3 having a negative refractive power, which are sequentially arranged from the light projecting side. In the first lens group G1, a positive air lens is constituted by a first negative lens and a second negative lens having concave surfaces facing each other, the combined focal length of the optical system being F, The combined focal length of the lens group G1 is F1, the focal length of the air lens of the first lens group G1 is Fa, the combined focal length of the second lens group G2 is F2, and the combined focal length of the third lens group G3 is F3. When
0.9 <│F1 / F2│ <3.5
1.2 <│F3 / F2│ <5.0
1.3 <│F / Fa│ <2.55
An image-side telecentric objective lens characterized by satisfying the following conditions. When the focal length of the first negative lens of the first lens group G1 is f11 and the focal length of the second negative lens is f12,
0.3 <f11 / f12 <7.1
The image side telecentric objective lens according to claim 1, wherein the following condition is satisfied. When the distance from the aperture stop to the first negative lens of the first lens group G1 is L1,
L1 / F <0.51
The image side telecentric objective lens according to claim 1 or 2, wherein the following condition is satisfied.   The image-side telecentric objective lens according to claim 1 or 2, wherein the second lens group G2 has at least five positive lenses, and the third lens group G3 has at least one negative lens. In a laser processing apparatus comprising: a chuck table for holding a workpiece; and a laser beam irradiation means for irradiating a workpiece with a laser beam to the workpiece held on the chuck table.
The laser beam irradiation means includes a laser beam oscillator that oscillates a laser beam, a scanner that deflects the optical axis of the laser beam oscillated by the laser beam oscillator, and collects the laser beam whose optical axis is deflected by the scanner and holds it on the chuck table. And a condenser for irradiating the processed workpiece,
The concentrator includes a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, and a third lens having a negative refractive power, which are sequentially arranged from the light projecting side. The first lens group G1 includes a first negative lens having a concave surface and a second negative lens constituting a positive air lens, and a combined focal length of the optical system. F, the combined focal length of the first lens group G1 is F1, the focal length of the air lens of the first lens group G1 is Fa, the combined focal length of the second lens group G2 is F2, and the third lens group G3 When the combined focal length of F3 is
0.9 <│F1 / F2│ <3.5
1.2 <│F3 / F2│ <5.0
1.3 <│F / Fa│ <2.55
It is constituted by an image side telecentric objective lens that satisfies the conditions of
The laser beam irradiation apparatus characterized by the above-mentioned. When the focal length of the first negative lens of the first lens group G1 is f11 and the focal length of the second negative lens is f12,
0.3 <f11 / f12 <7.1
The laser beam irradiation apparatus of Claim 5 which satisfies the conditions of. When the scanner is an aperture stop and the distance to the first negative lens in the first lens group G1 is L1,
L1 / F <0.51
The laser beam irradiation apparatus according to claim 5 or 6, which satisfies the following condition.

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