TW202111848A - Position adjustment method and position adjustment device can shorten the time required to identify the position of a condenser lens - Google Patents

Abstract

The problem to be solved in the present invention is to shorten the time required to identify the position of a condenser lens. The solution of the present invention is to provide a position adjustment method comprising: a photographing step for moving the condenser lens along an optical axis of a predetermined optical system which includes the condenser lens in the state where the pattern of the reticle is projected on the upper surface of the workpiece through the condenser lens, so to position the condenser lens at a plurality positions on the optical axis and photographing the upper surface while been positioned at each position; a calculation step for calculating the contrast value of each image obtained in the photographing step; a prediction step for performing polynomial interpolation based on the contrast value of each image calculated in the calculation step to obtain the contrast value of the image at a position where the condenser lens is positioned at a position that the condenser lens has not been positioned yet, and predicting the position of the condenser lens where the image with the maximum contrast value can be obtained; and a position adjusting step for positioning the condenser lens at the position where the image having the maximum contrast value predicted in the prediction step.

Description

Position adjustment method and position adjustment device

The present invention relates to a position adjustment method for adjusting the position of a condenser lens for condensing a laser beam, and a position adjustment device for adjusting the position of the condenser lens.

In order to divide the processed object such as a semiconductor wafer with a plurality of planned division lines arranged in a grid on the front side to produce a wafer along each planned division line, for example, a wafer having a wavelength that penetrates the processed object is used Laser beam (for example, refer to Patent Document 1).

In the state where the condensing point of the laser beam is positioned inside the workpiece, the condensing point and the workpiece are moved relative to each other, thereby forming an area along the moving path where the mechanical strength is lower than that of the condensing point. The vulnerable area is the modified area (modified layer). After forming modified regions along all the planned dividing lines, if an external force is applied to the workpiece, the workpiece will be divided with the modified region as the starting point of division.

However, when forming the modified region, the condensing point must be accurately positioned at a predetermined depth inside the workpiece. If the position of the condensing point is not accurately positioned at a predetermined depth, poor segmentation may occur, or the crack may spread out obliquely without being perpendicular to the front and back of the workpiece.

In order to accurately position the focusing point at a predetermined depth inside the workpiece, first, the front side of the workpiece is held by a chuck table so that the back surface of the workpiece is exposed upward. Next, for example, the upper surface (back surface) of the workpiece is irradiated with light from a predetermined light source, and the approximate position of the upper surface of the workpiece is determined based on the amount of reflected light reflected from the upper surface (first rough search).

After the first rough search, for a reticle with a predetermined pattern that is arranged at a position conjugate to the condensing point of the condensing lens that condenses the laser beam, irradiate light from other light sources and pass through the condensing lens. The light of the transparent marking sheet is condensed on the upper surface side of the processed object. By making the reflected light from the workpiece enter the camera and photograph the upper surface of the workpiece, the position of the upper surface can be determined more accurately than the first rough search (the second rough search).

The optical axis of the condenser lens is arranged parallel to the Z-axis direction (height direction) of the device. In the second rough search, first, the condensing lens is moved along the Z-axis direction by a large amount of movement (for example, 1.0 μm), and then it is made to stand still to photograph the upper surface of the workpiece. The image of the upper surface corresponding to each height position of the condenser lens is obtained by repeating movement, static and shooting. Then, the contrast value of the predetermined pattern of the reticle is calculated in each image, and the position of the condenser lens that can obtain the image with the largest contrast value is determined.

Next, using the position of the condenser lens of the image with the largest contrast value obtained in the second rough search as the reference position, move the condenser lens along the Z axis by a small amount within a predetermined range including the reference position The amount (for example, 0.1μm) moves (precise search). After moving, make the condenser lens still and photograph the upper surface of the workpiece.

In the precise search, the image of the upper surface corresponding to each height position of the condenser lens is also obtained by repeating movement, stillness, and shooting. Thereby, within a predetermined range including the reference position, the position of the condenser lens that can obtain the image with the maximum contrast value is determined. When the image with the maximum contrast value can be obtained, it can be considered that the condensing point is located on the upper surface. Therefore, as long as the condensing lens is lowered only a predetermined distance corresponding to the design value, the condensing point can be correctly positioned inside the workpiece. Predetermined depth. [Literature Technical Literature] [Patent Literature]

[Patent Document 1] JP 2002-192370 A

[The problem to be solved by the invention] In this way, in the ordinary laser processing process, in addition to the second rough search, a precise search is also performed, so there is a problem that it takes time to determine the position of the condenser lens. The present invention was made in view of the above-mentioned problems, and its object is to shorten the time required to determine the position of the condenser lens more than before.

[Technical means to solve the problem] According to one aspect of the present invention, a position adjustment method can be provided, which adjusts the position of the condenser lens that focuses the laser beam, and is characterized by comprising: a holding step, holding the workpiece with a chuck table; and an imaging step, After the holding step, the reticle is irradiated with light from the light source, and the pattern of the reticle is projected on the upper surface of the workpiece held by the chuck through the condensing lens. The optical axis of the predetermined optical system of the condenser lens moves the condenser lens, thereby positioning the condenser lens at a plurality of positions on the optical axis, and photographing the upper surface when positioned at each position; calculating steps, Calculate the contrast value of each image obtained in the imaging step; the prediction step, according to the contrast value of each image calculated in the calculation step, for positioning the condenser lens in the imaging step where the condenser lens has not been positioned Polynomial interpolation is performed on the contrast value of the image that can be obtained at the time of the position, thereby predicting the position of the condenser lens that can obtain the image with the largest contrast value; and the position adjustment step, positioning the condenser lens in the prediction step predicted The position of the condenser lens where the available contrast value becomes the largest image.

According to another aspect of the present invention, a position adjustment device can be provided, which adjusts the position of the condenser lens that focuses the laser beam, and is characterized by having: a chuck table, which holds the workpiece; and laser beam irradiation Unit, which has the condensing lens; pattern projection unit, which includes a reticle and a light source for irradiating light to the reticle, by irradiating the reticle with light from the light source and passing through the condensing lens to make the mark The pattern of the reticle is projected on the upper surface of the workpiece held by the chuck table; the condenser lens position adjustment unit projects the pattern of the reticle on the upper surface along the line containing the condenser The optical axis of the predetermined optical system of the lens adjusts the position of the condenser lens; the imaging unit, when the condenser lens is positioned at multiple positions on the optical axis under the state of projecting the pattern of the reticle, obtains the An image on the upper surface; and a processing unit for processing the image taken by the camera unit; wherein the processing unit includes: a calculation unit for calculating the contrast value of each image obtained by the camera unit; a memory unit for storing the calculation unit The calculated contrast value of each image; and the predicting unit, based on the contrast value of each image stored in the memory unit, for positioning the condenser lens at a position where the condenser lens has not been positioned, the imaging unit can The contrast value of the obtained image is subjected to polynomial interpolation, thereby predicting the position of the condenser lens that can obtain the image with the largest contrast value; when processing the workpiece with the laser beam, the condenser lens position adjustment unit will The condensing lens is positioned at the position of the condensing lens predicted by the predicting unit that can obtain the image with the largest contrast value.

[Efficacy of invention] In the position adjustment method of one aspect of the present invention, in a state where the pattern of the reticle is projected on the upper surface of the workpiece through the condenser lens, the condenser is moved along the optical axis of the predetermined optical system including the condenser lens The lens, thereby positioning the condenser lens at a plurality of positions on the optical axis, and photographing the upper surface of the object to be processed (imaging step).

Then, the contrast value of each image obtained in the imaging step is calculated (calculation step). After that, according to the contrast value of each image calculated in the calculation step, polynomial interpolation is performed on the contrast value of the image that can be obtained when the condenser lens is positioned at the position where the condenser lens has not been positioned in the imaging step, so as to predict the Obtain the position of the condenser lens of the image with the largest contrast value (prediction step).

After that, the condensing lens is positioned at the position of the condensing lens that can obtain the image with the largest contrast value predicted in the prediction step (position adjustment step). Therefore, compared with the conventional case where the second rough search and the precise search are used to perform the imaging step and the calculation step separately, the time required to determine the position of the condenser lens used in laser processing can be shortened.

The embodiment of one aspect of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a perspective view of a laser processing apparatus 2 that performs the position adjustment method of this embodiment. In addition, in FIG. 1, a part of the constituent elements of the laser processing apparatus 2 is shown as a functional block. In addition, the X-axis direction (processing feed direction), Y-axis direction (indexing feed direction), and Z-axis direction (height direction) used in the following description are perpendicular to each other.

The laser processing device 2 includes a base 4 that supports each component. A horizontal movement mechanism (processing feed mechanism, indexing feed mechanism) 6 is arranged on the upper surface of the base 4. The horizontal movement mechanism 6 includes a pair of Y-axis guide rails 8 fixed to the upper surface of the base 4 and substantially parallel to the Y-axis direction.

The Y-axis moving table 10 is slidably mounted on the Y-axis guide rail 8. A nut portion (not shown) is provided on the lower surface side of the Y-axis moving table 10. The Y-axis ball screw 12 substantially parallel to the Y-axis guide 8 is coupled to the nut portion of the Y-axis moving table 10 in a rotatable manner.

A Y-axis pulse motor 14 is connected to one end of the Y-axis ball screw 12. When the Y-axis ball screw 12 is rotated by the Y-axis pulse motor 14, the Y-axis moving table 10 moves in the Y-axis direction along the Y-axis guide 8.

A pair of X-axis guide rails 16 that are substantially parallel to the X-axis direction are provided on the upper surface of the Y-axis moving table 10. The X-axis moving table 18 is slidably mounted on the X-axis guide rail 16. A nut portion (not shown) is provided on the lower surface side of the X-axis moving table 18.

The X-axis ball screw 20 substantially parallel to the X-axis guide 16 is coupled to the nut portion of the X-axis moving table 18 in a rotatable manner. An X-axis pulse motor 22 is connected to one end of the X-axis ball screw 20. When the X-axis ball screw 20 is rotated by the X-axis pulse motor 22, the X-axis moving table 18 moves in the X-axis direction along the X-axis guide rail 16.

A cylindrical table base 24 is provided on the upper surface side of the X-axis moving table 18. The chuck table 26 is provided on the upper part of the table base 24. This chuck table 26 is used to hold the workpiece 11.

The workpiece 11 in this embodiment is a silicon wafer that has a disc shape and is mainly formed of silicon, but the workpiece 11 may be formed of semiconductors other than silicon, ceramics, various glasses, and the like. An adhesive film 13 having a larger diameter than the workpiece 11 is attached to the front surface (lower surface 11 b) of the workpiece 11.

In addition, a ring frame 15 made of metal is fixed to the outer peripheral portion of the adhesive film 13. Thereby, a frame unit 17 that supports the workpiece 11 to the frame 15 through the adhesive film 13 is formed.

A part of the upper surface of the chuck table 26 is composed of, for example, a porous member in the shape of a disc. This porous member interacts with a suction source such as an ejector through a suction path (not shown) formed inside the chuck table 26. (Not shown) connection.

When the suction source is operated, a negative pressure is generated on the upper surface (part of the holding surface 26a) of the porous member. If the suction source is operated in a state where the frame unit 17 is placed on the upper surface of the chuck table 26, the front (lower surface 11b) side of the workpiece 11 will be sucked and held by the holding surface 26a.

In addition, four jigs 28 for fixing the frame 15 are provided around the chuck table 26. When the workpiece 11 is held by the holding surface 26 a, the frame 15 is fixed by the jigs 28.

A rotation drive source (not shown) such as a motor is connected to the lower part of the table base 24. When the rotation drive source is operated, the chuck table 26 rotates with a straight line substantially parallel to the Z-axis direction as the rotation axis. In addition, the table base 24 and the chuck table 26 are moved in the X-axis direction and the Y-axis direction by the horizontal movement mechanism 6 described above.

A columnar support structure 30 is provided in a region adjacent to one side of the horizontal movement mechanism 6 in the Y-axis direction, and the support structure 30 has a side surface that is substantially perpendicular to the X-axis direction. A vertical movement mechanism (condenser lens position adjustment unit) 32 is arranged on the side surface of the support structure 30.

The vertical movement mechanism 32 includes a pair of Z-axis guide rails 34. A pair of Z-axis guide rails 34 are fixed to the side surface of the support structure 30 in a manner substantially parallel to the Z-axis direction. The flat Z-axis moving table 36 is slidably mounted on a pair of Z-axis guide rails 34.

A nut portion (not shown) is provided on the back side of the Z-axis moving table 36 (that is, on the Z-axis guide rail 34 side). A Z-axis ball screw (not shown) substantially parallel to the Z-axis guide 34 is coupled to the nut portion of the Z-axis moving table 36 in a rotatable manner.

A Z-axis pulse motor 38 is connected to one end of the Z-axis ball screw. When the Z-axis ball screw is rotated by the Z-axis pulse motor 38, the Z-axis moving table 36 moves in the Z-axis direction along the Z-axis guide 34.

A supporting tool 40 is fixed on the front side of the Z-axis moving table 36, and a part of the laser beam irradiation unit 42 is supported by the supporting tool 40. The laser beam irradiation unit 42 includes, for example, a laser oscillator 42a (refer to FIG. 2), which is fixed to the base 4; a cylindrical housing 44, which is supported by the supporting tool 40; and an irradiation head 46, which is provided in the housing 44 The end in the Y-axis direction.

Here, the configuration of the laser beam irradiation unit 42 and the like will be described with reference to FIGS. 1 and 2. FIG. 2 is a diagram showing the outline of the configuration of the laser beam irradiation unit 42 and the like. In addition, in FIG. 2, some of the constituent elements are shown as functional blocks.

In addition, in FIG. 2, the adhesive film 13 and the frame 15 of the frame unit 17 are omitted, but the adhesive film 13 side of the frame unit 17 is held by the holding surface 26 a. That is, the workpiece 11 is sucked and held by the holding surface 26a in a state where the upper surface 11a is exposed.

The laser oscillator 42a has a laser medium such as Nd:YAG. The laser oscillator 42a generates a pulsed laser beam having a wavelength (for example, 1064 nm) that penetrates the workpiece 11, and emits the laser beam to the mirror 42b.

The mirror 42b reflects the laser beam emitted from the laser oscillator 42a to the irradiation head 46. The illuminating head 46 is provided with a condenser lens 46a. The condensing point of the laser beam is positioned, for example, at a predetermined depth of the workpiece 11 held by the holding surface 26a by the condenser lens 46a.

In addition to the laser beam irradiation unit 42, the laser processing device 2 is also provided with a pattern projection unit 50 that projects a predetermined pattern of light onto the workpiece 11. The pattern projection unit 50 has a light source 52. The light source 52 irradiates light having a wavelength different from that of a laser beam, for example.

A condenser lens 54a is provided in the vicinity of the light source 52, and a reticle 54b is provided on the side opposite to the light source 52 with respect to the condenser lens 54a. The reticle 54b is, for example, a plate made of plate-shaped quartz, that is, a quartz plate, and a cross-shaped pattern is provided in the approximate center of one surface of the quartz plate.

Furthermore, 4 locations around the cross-shaped pattern are arranged symmetrically rotated four times around the intersection of the cross and each has a substantially L-shaped pattern (refer to the upper surface of the reticle 54b in FIG. 2 A).

The cross and L-shaped patterns are formed of metal (for example, chromium (Cr)) in a state where one surface of the quartz plate is partially shielded from light. The light emitted from the light source 52 penetrates the quartz plate, but does not penetrate the cross and L-shaped patterns. Therefore, if light is irradiated from the light source 52 to the reticle 54b through the condenser lens 54a, the shadow of the predetermined pattern will be projected behind the reticle 54b.

On the side opposite to the condenser lens 54a with respect to the reticle 54b, a collimator lens 54c is provided so that the optical axis and the optical axis of the condenser lens 54a are coaxial. The light penetrating the reticle 54b is emitted as parallel light from the collimator lens 54c.

A half mirror 54d is provided on the side opposite to the reticle 54b with respect to the collimator lens 54c. The half mirror 54d transmits a part (for example, half) of the light passing through the collimator lens 54c, and reflects the other part (for example, the remaining half).

A dichroic mirror 54e is provided on the side opposite to the collimator lens 54c with respect to the half mirror 54d. The dichroic mirror 54e reflects the light from the light source 52 penetrating the half mirror 54d and guides the light to the condenser lens 46a.

The light from the light source 52 incident on the condenser lens 46a irradiates the upper surface 11a. In this way, the light source 52, the condenser lens 54a, the collimator lens 54c, the condenser lens 46a, etc. constitute a predetermined optical system.

The optical axis of the condenser lens 46a is located on the optical axis 54f of this predetermined optical system. Therefore, if light is irradiated from the light source 52, the predetermined pattern of the reticle 54b can be projected onto the upper surface 11a through the condenser lens 46a.

The light irradiated from the condenser lens 46 a to the upper surface 11 a is reflected by the upper surface 11 a, and enters the camera unit (imaging unit) 56 via the dichroic mirror 54 e and the half mirror 54 d.

The camera unit 56 includes, for example, a CMOS (Complementary Metal Oxide Semiconductor) image sensor or a CCD (Charge Coupled Device) image sensor. The camera unit 56 photographs the upper surface 11a, thereby obtaining an image of a predetermined pattern of the reticle 54b irradiated on the upper surface 11a. The acquired image is processed by the following processing unit 64 (refer to FIG. 1).

In addition, the dichroic mirror 54e is arranged on the optical path between the reflecting mirror 42b and the condenser lens 46a. As described above, the dichroic mirror 54e is configured to reflect the light from the light source 52 but penetrate the laser beam.

Therefore, the laser beam and the light from the light source 52 are respectively incident on the condenser lens 46a. Thereby, the condensing point of the laser beam and the condensing point of the light from the light source 52 are located at substantially the same position in the Z-axis direction.

The position of the focusing point in the Z-axis direction is adjusted by moving the position of the focusing lens 46a in the Z-axis direction along the optical axis 54f. In this embodiment, the position of the condenser lens 46 a in the Z-axis direction is adjusted by moving the housing 44 and the irradiation head 46 by the vertical movement mechanism 32.

By moving the vertical moving mechanism 32, the condenser lens 46a is positioned at a predetermined position of the condenser lens 46a on the optical axis 54f in a state where the pattern of the reticle 54b is projected onto the upper surface 11a. Then, the image of the upper surface 11a is obtained by the camera unit 56. In this way, the condenser lens 46a is positioned at a plurality of different positions on the optical axis 54f by the vertical moving mechanism 32, and the image of the upper surface 11a at each position is obtained by the camera unit 56.

In addition, the reticle 54b is arranged at a position conjugate to the condensing point of the condenser lens 46a. Therefore, the closer the condensing point of the condenser lens 46a is to the upper surface 11a, the more clearly the reticle can be photographed by the camera unit 56 Pattern of sheet 54b.

Therefore, as long as the camera unit 56 photographs the upper surface 11a on which the pattern of the reticle 54b is projected, and adjusts the position of the condenser lens 46a so that the pattern of the reticle 54b becomes the clearest, the laser beam can be condensed The point is located on the upper surface 11a.

In this embodiment, the chuck table 26, the vertical movement mechanism 32 (refer to FIG. 1), the laser beam irradiation unit 42, the pattern projection unit 50, the camera unit 56 and the processing unit 64 (refer to FIG. 1) constitute the condenser The position adjustment device 58 adjusts the position of the lens 46a.

Here, returning to FIG. 1, other constituent elements of the laser processing apparatus 2 will be described. An alignment camera unit 48 fixed to the housing 44 is provided in the vicinity of the irradiation head 46. The camera unit 48 for alignment includes, for example, a CMOS image sensor or a CCD image sensor.

The upper part of the base 4 is covered by the cover (not shown) which can accommodate each component. A touch panel type display 60 serving as a user interface is provided on the side of the cover.

For example, various conditions applied when the workpiece 11 is processed are input to the laser processing apparatus 2 through the display 60. In addition, the images generated by the alignment camera unit 48 and the camera unit 56 are displayed on the display 60.

Components such as the horizontal movement mechanism 6, the vertical movement mechanism 32, the laser beam irradiation unit 42, the alignment camera unit 48, the pattern projection unit 50, the camera unit 56, the display 60, and the like are connected to the control unit 62, respectively. The control unit 62 controls each of the above-mentioned constituent elements in accordance with a series of steps required for processing and imaging of the workpiece 11.

The control unit 62 is typically composed of a computer including a processing device such as a CPU (Central Processing Unit) and a memory device such as a flash memory. The function of the control unit 62 is realized by operating the processing device and the like in accordance with the software stored in the memory device.

The control unit 62 has a processing unit 64 that performs image processing and the like on the upper surface 11a on which the predetermined pattern of the reticle 54b is displayed. The processing unit 64 of this embodiment includes a calculation unit 66 which is composed of a program stored in a memory device.

The calculation unit 66 of this embodiment performs edge detection processing and the like on the image. By edge detection, the calculation unit 66 calculates the difference between the pixel values of adjacent pixels in each image obtained by the camera unit 56, that is, the differential value (hereinafter, referred to as the contrast value in this embodiment).

Fig. 3(A) is an example of an image with a higher contrast value, and Fig. 3(B) is an example of an image with a lower contrast value. In FIG. 3(A) and FIG. 3(B), the area shown in black corresponds to the pattern of the reticle 54b.

In addition, in FIGS. 3(A) and 3(B), the four corners represented by thin lines and the crosshairs located inside the four corners, respectively, are the grid lines used to show the center position of the imaging area of the camera unit 56 and are not used as The calculation object of the comparison value.

In this embodiment, the contrast value is calculated for the overall pixels of each image. In this way, the calculation unit 66 can be used to calculate the representative value of the contrast value in each image (for example, the maximum value of the contrast value in each image). For example, the maximum value of the contrast value of the image shown in Fig. 3(A) is greater than the maximum value of the contrast value of the image shown in Fig. 3(B).

The calculated representative value of the contrast value of each image is stored in the memory 68. The memory portion 68 of this embodiment is a part of the memory area of the memory device of the control portion 62, but the memory portion 68 may be different from the memory device of the control portion 62, and be a memory device that specifically stores the contrast value.

A prediction unit 70 is connected to the storage unit 68. The prediction unit 70 of this embodiment is composed of a program stored in a memory device. The prediction unit 70 performs polynomial interpolation on the contrast value of the image that can be obtained when the condenser lens 46a is positioned at the position where the condenser lens 46a has not been positioned according to the representative values of the contrast values of the images stored in the memory unit 68 . Thereby, the predicting unit 70 predicts the position in the Z-axis direction of the condenser lens 46a that can obtain the image with the largest contrast value.

Figure 4 is a graph obtained by interpolating the contrast values between the representative values of the contrast values in each image. The horizontal axis is the position in the Z-axis direction (that is, the Z coordinate), and the vertical axis is the comparison value. In addition, dots in FIG. 4 represent the representative values of the contrast values of each image.

In the graph shown in FIG. 4, spline interpolation is used, and the prediction unit 70 calculates the polynomial between the representative values. However, the prediction unit 70 is not limited to the spline interpolation method, and may also use Lagrange interpolation, Newtonian interpolation, or the like.

The prediction unit 70 calculates the position of the condenser lens 46a in the Z-axis direction, that is, the Z coordinate (Z _M ) _{, of the image with the largest contrast value (C MAX) based on the created polynomial.} When processing the workpiece 11 with a laser beam, the control unit 62 controls the operation of the vertical movement mechanism 32 to thereby position the condenser lens 46a at the calculated Z coordinate (Z _M ).

In this way, in this embodiment, the predicting unit 70 predicts the position of the condenser lens 46a _{that can obtain the image where the representative value of the contrast value becomes the largest (C MAX ).} Therefore, compared with the conventional case of obtaining images and calculating the representative value of the contrast value by both the second rough search and the precise search, the time required for obtaining the image and calculating the representative value of the contrast value can be shortened.

Next, the position adjustment method of adjusting the position of the condenser lens 46a using the position adjustment device 58 (refer to FIG. 2) is demonstrated. Fig. 5 is a flowchart showing an example of a position adjustment method. First, the frame unit 17 is placed on the chuck table 26 so that the adhesive film 13 is in contact with the holding surface 26a.

Then, the suction source is operated to suck and hold the lower surface 11b side of the workpiece 11 by the holding surface 26a (holding step (S10)). After the holding step (S10), as in the past, the approximate position of the upper surface 11a of the workpiece 11 is determined based on the amount of reflected light (first rough search).

Next, the reticle 54b is irradiated with light from the light source 52, and the pattern of the reticle 54b is projected on the upper surface 11a of the workpiece 11 through the condenser lens 46a. In this state, the condensing lens 46a is moved along the optical axis 54f, thereby positioning the condensing lens 46a at a plurality of different positions on the optical axis 54f, and the camera unit 56 is used to photograph the processed position when positioned at each position The upper surface 11a of the object 11 (imaging step (S20)).

Thereby, an image of the upper surface 11a corresponding to each position of the condenser lens 46a can be obtained. After the imaging step (S20), the calculation unit 66 calculates the representative value of the contrast value of each image obtained in the imaging step (S20) (calculation step (S30)). The representative value of the contrast value of each image is stored in the memory 68.

After the calculation step (S30), the predicting unit 70 performs polynomial interpolation on the contrast value of the image that can be obtained when the condenser lens 46a is positioned at the position where the condenser lens 46a has not been positioned according to the representative value of the contrast value of each image . Thereby, the predicting unit 70 predicts the position of the condenser lens 46a where the image with the largest contrast value can be obtained (prediction step (S40)).

After the prediction step (S40), the vertical moving mechanism 32 is operated to position the condenser lens 46a at the predicted _{position (Z M} ) of the condenser lens 46a _{that can obtain the image with the largest contrast value (C MAX} ) (position adjustment) Step (S50)).

In this way, by performing the imaging step (S20) and the calculation step (S30) once each, the position of the condenser lens 46a _{that can obtain the image with the maximum contrast value (C MAX) can be predicted in the prediction step (S40 ).}

Therefore, compared to the conventional case where multiple images are obtained by both the second rough search and the precise search and the representative value of the contrast value of each image is calculated, the imaging step (S20) and the calculation step (S30) can be shortened. The time required.

Specifically, when both the second rough search and the precise search are performed as in the past, the imaging step (S20) and calculation step (S30) in the second rough search and the imaging step (S20) and calculation in the precise search Step (S30) takes about 4 seconds to 5 seconds. However, the position adjustment method of the present embodiment can shorten the imaging step (S20) to the prediction step (S40) to about half of the previous (that is, about 2 seconds to 2.5 seconds).

_{In addition, the position (Z M} ) of the condensing point of the image that can obtain the maximum contrast value predicted in this embodiment is the maximum converging point compared with the representative value of the contrast value determined in the second rough search and precise search in the past. The position of the light spot has a deviation of only about 0.2μm. That is, the usefulness of the position adjustment method of this embodiment can be confirmed.

In addition, the structure, method, etc. of the above-mentioned embodiment can be suitably changed and implemented in the range which does not deviate from the objective of this invention. In the above-mentioned embodiment, the light source 52 that irradiates light having a wavelength different from that of the laser beam is used.

However, the light source 52 may also irradiate light of the same wavelength as the laser beam that the laser beam irradiating unit 42 irradiates to the workpiece 11 to the condenser lens 54a at a lower output than the laser beam irradiating unit 42.

Thereby, the misalignment between the condensing point position of the laser beam from the laser beam irradiation unit 42 and the condensing point position of the light from the light source 52 (that is, caused by the chromatic aberration in the condenser lens 46a can be eliminated) The position of the focusing point is misaligned).

In addition, in the above-described embodiment, the condenser lens position adjustment unit that adjusts the position of the condenser lens 46 a is the vertical movement mechanism 32. However, the condensing lens position adjustment unit is not limited to the vertical movement mechanism 32 as long as it can move the position of the condensing point in the Z-axis direction with respect to the holding surface 26 a of the chuck table 26. The condenser lens position adjustment unit may also be a lens moving mechanism that moves the condenser lens 46 a in the Z-axis direction with respect to the irradiation head 46.

In addition, the calculation unit 66 calculates the differential value (contrast value) of the pixel value for the entire image, and uses the maximum value of the contrast value as the representative value of the contrast value. However, the calculation unit 66 may also calculate the differential value (contrast value) only in a partial area of the image including the boundary between the pattern of the reticle 54b and the non-pattern. In this case, use the maximum value of the contrast value in the partial area as the representative value of the contrast value.

In addition, in the above-mentioned embodiment, the to-be-processed object 11 whose upper surface 11a is not mirror-finished is used. However, it is also possible to use a so-called mirror wafer to be processed 11 on which the upper surface 11a is mirror-finished, or the upper surface 11a is provided with a resin film, a resin sheet, etc. through which the light from the laser beam and the light source 52 respectively penetrate. The processed object 11.

11: processed objects 11a: upper surface 11b: lower surface 13: Adhesive film 15: frame 17: Frame unit 2: Laser processing device 4: Abutment 6: Horizontal movement mechanism (processing feed mechanism, indexing feed mechanism) 8: Y-axis guide 10: Y-axis moving stage 12: Y-axis ball screw 14: Y-axis pulse motor 16: X axis guide 18: X axis moving stage 20: X axis ball screw 22: X-axis pulse motor 24: Workbench abutment 26: Chuck table 26a: Keep the face 28: Fixture 30: Supporting structure 32: Vertical movement mechanism (condenser lens position adjustment unit) 34: Z axis guide 36: Z-axis mobile stage 38: Z-axis pulse motor 40: Support tool 42: Laser beam irradiation unit 42a: Laser oscillator 42b: mirror 44: shell 46: Irradiation head 46a: Condenser lens 48: Camera unit for alignment 50: Pattern projection unit 52: light source 54a: Condenser lens 54b: marking sheet 54c: collimating lens 54d: half mirror 54e: Two-color mirror 54f: Optical axis 56: Camera unit (camera unit) 58: Position adjustment device 60: display A: Upper surface

Figure 1 is a perspective view of a laser processing device. Fig. 2 is a diagram showing the outline of the configuration of the laser beam irradiation unit and the like. Fig. 3(A) is an example of an image with a higher contrast value, and Fig. 3(B) is an example of an image with a lower contrast value. Figure 4 is a graph obtained by interpolating the contrast values between the representative values of the contrast values in each image. Fig. 5 is a flowchart showing an example of a position adjustment method.

11: processed objects

11a: upper surface

11b: lower surface

13: Adhesive film

15: frame

17: Frame unit

2: Laser processing device

4: Abutment

6: Horizontal movement mechanism (processing feed mechanism, indexing feed mechanism)

8: Y-axis guide

10: Y-axis moving stage

12: Y-axis ball screw

14: Y-axis pulse motor

16: X axis guide

18: X axis moving stage

20: X axis ball screw

22: X-axis pulse motor

24: Workbench abutment

26: Chuck table

26a: Keep the face

28: Fixture

30: Supporting structure

32: Vertical movement mechanism (condenser lens position adjustment unit)

34: Z axis guide

36: Z-axis mobile stage

38: Z-axis pulse motor

40: Support tool

42: Laser beam irradiation unit

44: shell

46: Irradiation head

48: Camera unit for alignment

60: display

62: Control Department

64: Processing Department

66: Computing Department

68: Memory Department

70: Forecast Department

Claims (2)

A position adjustment method is to adjust the position of the condenser lens that condenses the laser beam, which is characterized by: In the holding step, the processed object is held by the chuck table; In the imaging step, after the holding step, the reticle is irradiated with light from the light source, and the pattern of the reticle is projected on the upper surface of the workpiece held by the chuck through the condenser lens, Moving the condenser lens along the optical axis of the predetermined optical system including the condenser lens, thereby positioning the condenser lens at a plurality of positions on the optical axis, and photographing the upper surface when positioned at each position; The calculation step is to calculate the contrast value of each image obtained in the imaging step; The prediction step is to perform polynomial interpolation on the contrast value of the image that can be obtained when the condenser lens is positioned at the position where the condenser lens has not been positioned in the imaging step according to the contrast value of each image calculated in the calculation step , Thereby predicting the position of the condenser lens that can obtain the image with the largest contrast value; and In the position adjustment step, the condenser lens is positioned at the position of the condenser lens predicted by the predicting step where the image with the largest contrast value can be obtained. A position adjustment device that adjusts the position of a condenser lens that condenses a laser beam, and is characterized by having: The chuck table, which holds the processed objects; A laser beam irradiation unit, which has the condenser lens; The pattern projection unit includes a reticle and a light source for irradiating light to the reticle, and the pattern of the reticle is projected on the card by irradiating the light from the light source on the reticle through the condenser lens The upper surface of the object to be processed held by the tray; The condenser lens position adjustment unit adjusts the position of the condenser lens along the optical axis of the predetermined optical system including the condenser lens in a state where the pattern of the reticle is projected on the upper surface; An imaging unit, when the condenser lens is positioned at a plurality of positions on the optical axis in a state where the pattern of the reticle is projected, images of the upper surface are obtained respectively; and The processing unit processes the images taken by the camera unit; Among them, the processing unit includes: The calculation part calculates the contrast value of each image obtained by the camera unit; The memory part memorizes the contrast value of each image calculated by the calculation part; and The predicting unit, based on the contrast value of each image stored in the memory unit, performs polynomial interpolation on the contrast value of the image obtained by the imaging unit when the condensing lens is positioned at a position where the condensing lens has not been positioned. This predicts the position of the condenser lens that can obtain the image with the largest contrast value; When processing the workpiece with the laser beam, the condenser lens position adjusting unit positions the condenser lens at the position of the condenser lens predicted by the predicting unit that can obtain the image with the largest contrast value.

Images