JP7309277B2 - POSITION ADJUSTMENT METHOD AND POSITION ADJUSTMENT DEVICE - Google Patents

Description

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

In order to manufacture chips by dividing a workpiece such as a semiconductor wafer having a plurality of planned division lines arranged in a lattice pattern on the front side thereof along each planned division line, for example, the workpiece is divided into A laser beam having a penetrating wavelength is used (see, for example, Patent Document 1).

Positioning the focal point of the laser beam inside the workpiece and moving the focal point and the workpiece relative to each other, the mechanical strength is reduced compared to the area through which the focal point does not pass. A modified region (modified layer), which is a weakened region of low strength, is formed along the path of this migration. After the modified regions are formed along all the planned division lines, if an external force is applied to the work piece, the work piece is divided with the modified region as the starting point of division.

By the way, when forming the modified region, it is necessary to accurately position the focal point at a predetermined depth inside the workpiece. If the position of the focal point is not accurately positioned at a predetermined depth, poor segmentation may occur, and cracks may grow obliquely rather than perpendicularly to the front and back surfaces of the workpiece. .

In order to accurately position the focal 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 rough position of the upper surface of the workpiece is specified based on the amount of light reflected from the upper surface ( first coarse search).

After the first rough search, a reticle having a predetermined pattern, which is arranged at a position conjugate to the condensing point of a condensing lens for condensing the laser beam, is irradiated with light from another light source and condensed. The light transmitted through the reticle via the optical lens is condensed on the upper surface side of the workpiece. The position of the top surface of the workpiece is specified more accurately than in the first rough search (second rough search) by capturing an image of the top surface of the workpiece by allowing reflected light from the workpiece to enter the camera.

The optical axis of the condensing lens is arranged parallel to the Z-axis direction (height direction) of the apparatus. In the second rough search, first, the condenser lens is moved along the Z-axis direction by a relatively large amount of movement (for example, 1.0 μm) and then held still to pick up an image of the upper surface of the workpiece. By repeating movement, rest, and imaging, an image of the upper surface corresponding to each height position of the condenser lens is acquired. Then, the contrast value of the predetermined pattern on the reticle is calculated for each image, and the position of the condensing lens at which the image with the maximum contrast value is obtained is specified.

Next, with the position of the condenser lens at which the image with the maximum contrast value obtained in the second coarse search is set as a reference position, the condenser lens is moved along the Z-axis direction within a predetermined range including the reference position. It is moved by a relatively small amount of movement (for example, 0.1 μm) (precise search). After the movement, the condensing lens is stopped and the upper surface of the workpiece is imaged.

Even in the precision search, by repeating movement, stillness, and imaging, an image of the upper surface corresponding to each height position of the condenser lens is obtained. Thereby, the position of the condensing lens at which an image having the maximum contrast value is obtained within a predetermined range including the reference position is specified. When an image with the maximum contrast value is obtained, the condensing point can be considered to be located on the upper surface. A focal point can be precisely positioned at a given depth.

Japanese Patent Application Laid-Open No. 2002-192370

As described above, in the normal laser processing process, since the fine search is performed in addition to the second rough search, there is a problem that it takes time to specify the position of the condenser lens. SUMMARY OF THE INVENTION An object of the present invention is to reduce the time required to specify the position of a condenser lens compared to the conventional art.

According to one aspect of the present invention, there is provided a position adjustment method for adjusting the position of a condenser lens that condenses a laser beam, comprising: a holding step of holding a workpiece on a chuck table; A predetermined optical system including the condenser lens in a state in which the reticle is irradiated with light and the pattern of the reticle is projected through the condenser lens onto the upper surface of the workpiece held by the chuck table. an imaging step of positioning the condenser lens at a plurality of positions on the optical axis by moving the condenser lens along the optical axis of and imaging the top surface when positioned at each position; a calculating step of calculating a contrast value of each image obtained in the imaging step; a prediction step of predicting the position of the condenser lens at which an image having the maximum contrast value is obtained by polynomial interpolation of the contrast value of the image obtained when the condenser lens is positioned; a positioning step of positioning the condenser lens at a position of the condenser lens at which an image having the maximum contrast value is obtained. Preferably, in the calculating step, the calculation of the contrast value is performed over the pixels of each image. Also, preferably, the wavelength of the light emitted from the light source in the imaging step is the same as that of the laser beam.

According to another aspect of the present invention, there is provided a position adjusting device for adjusting the position of a condenser lens for condensing a laser beam, comprising a chuck table for holding a workpiece, and a laser beam irradiation apparatus having the condenser lens. a unit, a reticle, and a light source for irradiating the reticle with light; by irradiating the reticle with light from the light source, the upper surface of the workpiece held by the chuck table is illuminated through the condenser lens; a pattern projection unit for projecting the pattern of the reticle using a pattern projection unit for projecting the pattern of the reticle on the upper surface; a condensing lens position adjusting unit for adjustment, and an imaging unit for obtaining an image of the upper surface when the condensing lens is positioned at a plurality of positions on the optical axis in a state where the pattern of the reticle is projected. , a processing unit that processes an image captured by the imaging unit, the processing unit includes a calculation unit that calculates a contrast value of each image obtained by the imaging unit, and a contrast value that is calculated by the calculation unit a storage unit for storing the contrast value of each image; and based on the contrast value of each image stored in the storage unit, the condenser lens is positioned at a position where the condenser lens is not positioned in the imaging unit. a prediction unit that predicts the position of the condenser lens at which an image having the maximum contrast value is obtained by polynomial interpolation of the contrast value of the image obtained in the case, and When processing, the condenser lens position adjusting unit is provided with a position adjusting device for positioning the condenser lens at a position of the condenser lens where an image with the maximum contrast value predicted by the prediction unit is obtained. be.

In the position adjustment method according to one aspect of the present invention, the reticle pattern is projected onto the upper surface of the workpiece through the condenser lens, and the light is condensed along the optical axis of the predetermined optical system including the condenser lens. By moving the optical lens, the condensing lens is positioned at a plurality of positions on the optical axis, and the upper surface of the workpiece is imaged (imaging step).

Then, the contrast value of each image obtained in the imaging step is calculated (calculation step). After that, based on the contrast value of each image calculated in the calculation step, polynomial interpolation is performed on the contrast value of the image obtained when the condenser lens is positioned at a position where the condenser lens is not positioned in the imaging step. , to predict the position of the condensing lens at which the image with the maximum contrast value is obtained (prediction step).

After that, the condenser lens is positioned at the position of the condenser lens where the image with the maximum contrast value predicted in the prediction step is obtained (position adjustment step). Therefore, the time required to identify the position of the condenser lens used in laser processing can be shortened compared to the conventional case where the imaging step and the calculation step are performed in both the second coarse search and the fine search. .

1 is a perspective view of a laser processing device; FIG. It is a figure which shows the outline|summary of a structure, such as a laser beam irradiation unit. FIG. 3A is an example of an image with relatively high contrast values, and FIG. 3B is an example of an image with relatively low contrast values. It is the graph which interpolated the contrast value between the representative values of the contrast value in each image. FIG. 5 is a flow diagram showing an example of a position adjustment method;

An embodiment according to 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 in which the position adjustment method according to this embodiment is performed. In addition, in FIG. 1, some components of the laser processing apparatus 2 are shown as functional blocks. 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, index 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.

A Y-axis moving table 10 is slidably attached to 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 . A Y-axis ball screw 12 substantially parallel to the Y-axis guide rail 8 is rotatably coupled to the nut portion of the Y-axis moving table 10 .

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 along the Y-axis guide rail 8 in the Y-axis direction.

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 . An X-axis moving table 18 is slidably attached to 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 .

An X-axis ball screw 20 substantially parallel to the X-axis guide rail 16 is rotatably coupled to the nut portion of the X-axis moving table 18 . 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 along the X-axis guide rail 16 in the X-axis direction.

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

The workpiece 11 of the present embodiment is a disk-shaped silicon wafer mainly made of silicon, but the workpiece 11 may be made of semiconductors other than silicon, ceramics, various types of glass, and the like. An adhesive tape 13 having a diameter larger than that of the workpiece 11 is attached to the surface (lower surface 11 b ) of the workpiece 11 .

An annular frame 15 made of metal is fixed to the outer peripheral portion of the adhesive tape 13 . Thereby, a frame unit 17 in which the workpiece 11 is supported by the frame 15 via the adhesive tape 13 is formed.

A portion of the upper surface of the chuck table 26 is composed of, for example, a disk-shaped porous member. It is connected to a suction source (not shown).

When the suction source is operated, negative pressure is generated on the upper surface of the porous member (part of the holding surface 26a). When the suction source is operated with the frame unit 17 placed on the upper surface of the chuck table 26, the surface (lower surface 11b) side of the workpiece 11 is suction-held by the holding surface 26a.

Four clamps 28 for fixing the frame 15 are provided around the chuck table 26 . The frame 15 is fixed by each clamp 28 when the workpiece 11 is held by the holding surface 26a.

A rotary drive source (not shown) such as a motor is connected to the lower portion of the table base 24 . When the rotary drive source is operated, the chuck table 26 rotates about a straight line substantially parallel to the Z-axis direction as a rotation axis. Further, 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 having side surfaces substantially perpendicular to the X-axis direction is provided in a region adjacent to one side of the horizontal movement mechanism 6 in the Y-axis direction. A vertical movement mechanism (collecting lens position adjustment unit) 32 is arranged on the side surface of the support structure 30 .

The vertical movement mechanism 32 has a pair of Z-axis guide rails 34 . A pair of Z-axis guide rails 34 are fixed to the side surfaces of the support structure 30 in a manner generally parallel to the Z-axis direction. A flat Z-axis moving table 36 is slidably attached to the 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 rail 34 is rotatably coupled to the nut portion of the Z-axis moving table 36 .

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

A support 40 is fixed to the surface side of the Z-axis moving table 36, and a part of the laser beam irradiation unit 42 is supported by the support 40. As shown in FIG. The laser beam irradiation unit 42 includes, for example, a laser oscillator 42a (see FIG. 2) fixed to the base 4, a cylindrical housing 44 supported by the support 40, and a housing 44 at the end in the Y-axis direction. and an irradiation head 46 provided.

Here, the configuration of the laser beam irradiation unit 42 and the like will be described with reference to FIGS. 1 and 2. FIG. FIG. 2 is a diagram showing an overview of the configuration of the laser beam irradiation unit 42 and the like. In addition, in FIG. 2, some components are indicated by functional blocks.

Although the adhesive tape 13 and the frame 15 of the frame unit 17 are omitted in FIG. 2, the adhesive tape 13 side of the frame unit 17 is held by the holding surface 26a. That is, the workpiece 11 is suction-held by the holding surface 26a with the upper surface 11a exposed.

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

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

In addition to the laser beam irradiation unit 42 , the laser processing apparatus 2 is 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 emits light having a wavelength different from that of the laser beam, for example.

A condensing lens 54a is provided near the light source 52, and a reticle 54b is provided on the side opposite to the light source 52 with respect to the condensing 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 approximately in the center of one surface of the quartz plate.

Further, at four locations around the cross-shaped pattern, patterns having a substantially L-shape are provided, which are arranged in four-fold rotational symmetry about the intersection point of the cross (the upper surface of the reticle 54b in FIG. 2). A).

The cross and L-shaped patterns are made of metal (for example, chromium (Cr)) so as to partially shield one surface of the quartz plate from light. Light emitted from the light source 52 passes through the quartz plate, but does not pass through the cross and L-shaped patterns. Therefore, when the reticle 54b is irradiated with light from the light source 52 through the condenser lens 54a, a shadow of a predetermined pattern is projected behind the reticle 54b.

A collimator lens 54c is provided on the opposite side of the reticle 54b from the condenser lens 54a, with its optical axis coaxial with the optical axis of the condenser lens 54a. The light transmitted through the reticle 54b is emitted as parallel light from the collimating lens 54c.

A half mirror 54d is provided on the side opposite to the reticle 54b with respect to the collimating lens 54c. The half mirror 54d transmits a portion (eg, half) of the light transmitted through the collimating lens 54c and reflects the other portion (eg, the remaining half).

A dichroic mirror 54e is provided on the side opposite to the collimating lens 54c with respect to the half mirror 54d. The dichroic mirror 54e reflects the light from the light source 52 that has passed through the half mirror 54d and guides it to the condenser lens 46a.

The light from the light source 52 that has entered the condenser lens 46a is applied to the upper surface 11a. In this manner, 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, when light is emitted from the light source 52, a predetermined pattern of the reticle 54b is projected onto the upper surface 11a through the condenser lens 46a.

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

The camera unit 56 includes, for example, a CMOS (Complementary Metal Oxide Semiconductor) image sensor, a CCD (Charge Coupled Device) image sensor, or the like. When the camera unit 56 captures an image of the upper surface 11a, an image of a predetermined pattern of the reticle 54b illuminated on the upper surface 11a is obtained. The acquired image is processed by the processing unit 64 (see FIG. 1), which will be described later.

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

Therefore, the laser beam and the light from the light source 52 are each incident on the condenser lens 46a. As a result, the focal point of the laser beam and the focal point of the light from the light source 52 are positioned at approximately the same position in the Z-axis direction.

The position of the focal point in the Z-axis direction is adjusted by moving the position of the condensing 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 movement mechanism 32, the condenser lens 46a is positioned at a predetermined position on the optical axis 54f of the condenser lens 46a while the pattern of the reticle 54b is projected onto the upper surface 11a. Then, the camera unit 56 acquires an image of the upper surface 11a. In this manner, the vertical movement mechanism 32 positions the condenser lens 46a at a plurality of different positions on the optical axis 54f, and the camera unit 56 obtains an image of the upper surface 11a at each position.

In addition, since the reticle 54b is arranged at a position conjugate with the light-condensing point of the condenser lens 46a, the closer the light-condensing point of the condenser lens 46a is to the upper surface 11a, the clearer the pattern of the reticle 54b becomes. Imaged at 56 .

Therefore, if the upper surface 11a on which the pattern of the reticle 54b is projected is imaged by the camera unit 56, and the position of the condenser lens 46a is adjusted so that the pattern of the reticle 54b becomes the clearest, the focal point of the laser beam can be determined. It can be positioned on the top surface 11a.

In this embodiment, the chuck table 26, the vertical movement mechanism 32 (see FIG. 1), the laser beam irradiation unit 42, the pattern projection unit 50, the camera unit 56 and the processing section 64 (see FIG. 1) determine the position of the condenser lens 46a. A position adjusting device 58 is configured to adjust the .

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

The top of the base 4 is covered with a cover (not shown) that can accommodate each component. A touch panel type display 60 serving as a user interface is provided on the side surface of this cover.

For example, various conditions applied when processing the workpiece 11 are input to the laser processing device 2 via the display 60 . 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 each connected to the control section 62 . The control unit 62 controls each component described above in accordance with a series of steps necessary for processing the workpiece 11, imaging, and the like.

The control unit 62 is typically configured by a computer including a processing device such as a CPU (Central Processing Unit) and a storage device such as a flash memory. The functions of the control unit 62 are realized by operating the processing device and the like according to the software stored in the storage device.

The control unit 62 has a processing unit 64 that processes the image of 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 configured by a program stored in a storage device.

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

FIG. 3A is an example of an image with relatively high contrast values, and FIG. 3B is an example of an image with relatively low contrast values. In FIGS. 3A and 3B, the black areas correspond to the pattern of the reticle 54b.

In FIGS. 3A and 3B, squares indicated by thin lines and crosshairs positioned inside the squares are grids for indicating the center position of the imaging area of the camera unit 56. It is a line and is not subject to contrast value calculation.

In this embodiment, the calculation of the contrast value is performed over the entire pixels of each image. As a result, the calculation unit 66 calculates the representative value of the contrast values in each image (for example, the maximum value of the contrast values in each image). For example, the maximum contrast value of the image shown in FIG. 3A is greater than the maximum contrast value of the image shown in FIG. 3B.

The calculated representative value of the contrast value of each image is stored in the storage unit 68 . The storage unit 68 of the present embodiment is part of the storage area of the storage device of the control unit 62, but unlike the storage device of the control unit 62, the storage unit 68 is a storage device dedicated to storing contrast values. may

A prediction unit 70 is connected to the storage unit 68 . The prediction unit 70 of this embodiment is configured by a program stored in a storage device. Based on each representative value of the contrast value of each image stored in the storage unit 68, the prediction unit 70 predicts the contrast of the image obtained when the condenser lens 46a is positioned at a position where the condenser lens 46a is not positioned. Polynomial interpolation of values. Thereby, the prediction unit 70 predicts the position of the condenser lens 46a in the Z-axis direction at which an image having the maximum contrast value is obtained.

FIG. 4 is a graph obtained by interpolating contrast values between representative values of 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 contrast value. In addition, in FIG. 4, the representative value of the contrast value of each image is indicated by a dot.

In the graph shown in FIG. 4, the predictor 70 calculated polynomials between representative values using spline interpolation. However, the prediction unit 70 may employ Lagrange interpolation, Newtonian interpolation, etc., in addition to spline interpolation.

Based on the created polynomial, the prediction unit 70 calculates the position of the condenser lens 46a in the Z-axis direction, that is, the Z-coordinate (Z _M ) at which an image with the maximum contrast value (C _MAX ) is obtained. When the workpiece 11 is processed with a laser beam, the controller 62 controls the operation of the vertical movement mechanism 32 so that the condenser lens 46a is positioned at the calculated Z coordinate (Z _M ).

Thus, in this embodiment, the prediction unit 70 predicts the position of the condenser lens 46a at which an image having the maximum representative value (C _MAX ) of the contrast values is obtained. Therefore, compared to the conventional case of acquiring an image and calculating the representative value of the contrast value in both the second coarse search and the fine search, the acquisition of the image and the calculation of the representative value of the contrast value can reduce the time required for

Next, a position adjustment method for adjusting the position of the condenser lens 46a using the position adjustment device 58 (see FIG. 2) will be described. FIG. 5 is a flow diagram showing an example of a position adjustment method. First, the frame unit 17 is placed on the chuck table 26 so that the adhesive tape 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 with the holding surface 26a (holding step (S10)). After the holding step (S10), the rough position of the upper surface 11a of the workpiece 11 is identified based on the amount of reflected light (first rough search), as in the conventional art.

Next, light is emitted from the light source 52 to the reticle 54b, and the pattern of the reticle 54b is projected onto the upper surface 11a of the workpiece 11 through the condenser lens 46a. In this state, by moving the condenser lens 46a along the optical axis 54f, the condenser lens 46a can be positioned at a plurality of different positions on the optical axis 54f. The upper surface 11a is imaged by the camera unit 56 (imaging step (S20)).

As a result, an image of the upper surface 11a corresponding to each position of the condenser lens 46a is obtained. After the imaging step (S20), the calculation unit 66 calculates a representative value of contrast values of each image obtained in the imaging step (S20) (calculation step (S30)). A representative value of the contrast value of each image is stored in the storage unit 68 .

After the calculation step (S30), the prediction unit 70 determines the contrast value of the image obtained when the condenser lens 46a is positioned at a position where the condenser lens 46a is not positioned, based on the representative value of the contrast value of each image. is polynomially interpolated. Thereby, the prediction unit 70 predicts the position of the condenser lens 46a at which an image with the maximum contrast value is obtained (prediction step (S40)).

After the prediction step (S40), the vertical movement mechanism 32 is operated to move the condenser lens 46a to the position (Z _M ) of the condenser lens 46a where an image with the maximum predicted contrast value (C _MAX ) is obtained. is positioned (position adjustment step (S50)).

In this way, by performing the imaging step (S20) and the calculating step (S30) once each, the position of the condenser lens 46a at which an image with the maximum contrast value (C _MAX ) is obtained in the prediction step (S40) can be predicted.

Therefore, compared to the conventional case of acquiring a plurality of images and calculating the representative value of the contrast value of each image in both the second coarse search and the fine search, the imaging step (S20 ) and the calculation step (S30) can be shortened.

Specifically, when both the second coarse search and the fine search are performed as in the conventional art, the imaging step (S20) and the calculation step (S30) in the second coarse search and the imaging step in the fine search (S20) and the calculation step (S30) required about 4 to 5 seconds. However, in the position adjustment method of this embodiment, the time from the imaging step (S20) to the prediction step (S40) can be shortened to about half of the conventional time (that is, about 2 seconds to 2.5 seconds).

In addition, the position (Z _M ) of the focal point at which an image with the maximum contrast value predicted in the present embodiment is obtained is the representative value of the contrast values identified by the conventional second coarse search and fine search. There was only a shift of about 0.2 μm with respect to the position of the focal point. That is, the usefulness of the position adjustment method of this embodiment was confirmed.

In addition, the structures, methods, and the like according to the above-described embodiments can be modified as appropriate without departing from the scope of the present invention. In the above-described embodiment, the light source 52 that emits light with a wavelength different from the wavelength of the laser beam was used.

However, the light source 52 may irradiate the condensing lens 54a with light having the same wavelength as that of the laser beam that the laser beam irradiation unit 42 irradiates the workpiece 11 with a lower output than the laser beam irradiation unit 42 does.

As a result, the deviation between the position of the focal point of the laser beam from the laser beam irradiation unit 42 and the position of the focal point of the light from the light source 52 (that is, the position of the focal point caused by the chromatic aberration in the condenser lens 46a positional deviation) can be eliminated.

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

In addition, the calculator 66 described above calculates the differential value (contrast value) of the pixel values over the entire image, and the maximum value of the contrast value is used as the representative value of the contrast value. However, the calculator 66 may calculate the differential value (contrast value) only in a partial area of the image including the boundary between the pattern and the non-pattern of the reticle 54b. In this case, the maximum value of the contrast values in the partial area is used as the representative value of the contrast values.

By the way, in the above-described embodiment, the workpiece 11 whose upper surface 11a is not mirror-finished is used. However, there are workpieces 11 that are so-called mirror wafers with mirror-finished upper surfaces 11a, and workpieces 11 that have upper surfaces 11a provided with resin films, resin sheets, or the like through which the laser beam and light from the light source 52 are respectively transmitted. may be used.

REFERENCE SIGNS LIST 11 workpiece 11a upper surface 11b lower surface 13 adhesive tape 15 frame 17 frame unit 2 laser processing device 4 base 6 horizontal movement mechanism (processing feed mechanism, indexing feed mechanism)
8 Y-axis guide rail 10 Y-axis movement table 12 Y-axis ball screw 14 Y-axis pulse motor 16 X-axis guide rail 18 X-axis movement table 20 X-axis ball screw 22 X-axis pulse motor 24 Table base 26 Chuck table 26a Holding surface 28 Clamp 30 support structure 32 vertical movement mechanism (collecting lens position adjustment unit)
34 Z-axis guide rail 36 Z-axis movement table 38 Z-axis pulse motor 40 Support tool 42 Laser beam irradiation unit 42a Laser oscillator 42b Mirror 44 Housing 46 Irradiation head 46a Collecting lens 48 Alignment camera unit 50 Pattern projection unit 52 Light source 54a Collection Optical lens 54b Reticle 54c Collimating lens 54d Half mirror 54e Dichroic mirror 54f Optical axis 56 Camera unit (imaging unit)
58 position adjustment device 60 display A upper surface

Claims (4)

A position adjustment method for adjusting the position of a condenser lens that condenses a laser beam,
a holding step of holding the workpiece on the chuck table;
After the holding step, the reticle is irradiated with light from the light source, and the light is condensed while projecting the pattern of the reticle onto the upper surface of the workpiece held by the chuck table through the condensing lens. By moving the condenser lens along the optical axis of a predetermined optical system including the lens, the condenser lens can be positioned at a plurality of positions on the optical axis, and the top surface when positioned at each position. an imaging step of imaging;
a calculating step of calculating a contrast value of each image obtained in the imaging step;
Based on the contrast value of each image calculated in the calculating step, polynomial interpolation is performed on the contrast value of the image obtained when the collecting lens is positioned at a position where the collecting lens is not positioned in the imaging step. a prediction step of predicting the position of the condenser lens at which an image having the maximum contrast value is obtained;
a position adjustment step of positioning the condenser lens at a position of the condenser lens where an image having the maximum contrast value predicted in the prediction step is obtained;
a processing step of adjusting the position of the condensing lens in the position adjusting step and then irradiating the work piece with the laser beam through the condensing lens to process the work piece with the laser beam; A position adjustment method comprising: 2. The position adjusting method according to claim 1, wherein in said calculating step, the contrast value is calculated for all pixels of each image. 3. The position adjustment method according to claim 1, wherein the wavelength of the light emitted from the light source in the imaging step is the same as that of the laser beam. A position adjustment device that adjusts the position of a condenser lens that condenses a laser beam,
a chuck table for holding a workpiece;
a laser beam irradiation unit having the condenser lens;
a reticle and a light source for irradiating the reticle with light; by irradiating the reticle with light from the light source, the reticle is placed on the upper surface of the workpiece held by the chuck table via the condenser lens; a pattern projection unit for projecting a pattern of
a condenser lens position adjustment unit for adjusting the position of the condenser lens along the optical axis of a predetermined optical system including the condenser lens, with the pattern of the reticle projected onto the upper surface;
an imaging unit for obtaining an image of the upper surface when the condenser lens is positioned at a plurality of positions on the optical axis with the pattern of the reticle projected;
and a processing unit that processes the image captured by the imaging unit,
The processing unit
a calculation unit that calculates a contrast value of each image obtained by the imaging unit;
a storage unit that stores the contrast value of each image calculated by the calculation unit;
Based on the contrast value of each image stored in the storage unit, polynomial interpolation is performed on the contrast value of the image obtained when the condenser lens is positioned at a position where the condenser lens is not positioned in the imaging unit. a prediction unit that predicts the position of the condenser lens at which an image with the maximum contrast value is obtained;
When processing the workpiece with the laser beam, the focusing lens positioning unit moves the focusing lens to the position where the image with the maximum contrast value predicted by the prediction unit is obtained. A positioning device for positioning a lens.

Images