JP5098665B2 - Laser processing apparatus and laser processing method - Google Patents

Description

  The present invention relates to a laser processing apparatus, and more particularly to a laser processing apparatus that divides a wafer into individual chips such as semiconductor devices and electronic components using laser light.

  Conventionally, in order to divide a wafer having a semiconductor device or electronic component formed on its surface into individual chips, a dicing machine that uses a grinding wheel called a dicing blade to form a grinding groove in the wafer and cut the wafer has been used. . The dicing blade is obtained by electrodepositing fine diamond abrasive grains with Ni, and an extremely thin one having a thickness of about 30 μm is used.

  The dicing blade was rotated at a high speed of 30,000 to 60,000 rpm and cut into the wafer, and the wafer was completely cut (full cut) or incompletely cut (half cut or semi-full cut). Half-cut is a method of cutting about half of the thickness into a wafer, and semi-full cut is a method of forming a grinding groove leaving a thickness of about 10 μm.

  However, in the case of grinding with this dicing blade, since the wafer is a highly brittle material, it becomes brittle mode processing, chipping occurs on the front and back surfaces of the wafer, and this chipping reduces the performance of the divided chips. It was. In particular, chipping generated on the back surface is a serious problem because cracks gradually progress inside.

To solve this problem, instead of cutting with a conventional dicing blade, a laser beam with a converging point is incident on the inside of the wafer, and a plurality of modified regions by multi-light absorption are formed inside the wafer. A laser dicing apparatus and a dicing method for separating and dividing into individual chips have been proposed (for example, see Patent Document 1).
JP 2004-111946 A

  However, in the laser dicing apparatus described in Patent Document 1, since the width of the modified layer in the thickness direction is small, when processing a thick workpiece (hereinafter also referred to as “workpiece”), a plurality of layers are used. It was necessary to perform the operation once, and processing took time.

  This invention is made | formed in view of such a situation, and it aims at providing the laser processing apparatus which can shorten processing time with respect to the workpiece of wide thickness.

According to a first aspect of the present invention, in order to achieve the above-mentioned object, a laser processing apparatus for dividing a wafer into individual chips by forming a modified region inside the wafer by making laser light incident from the surface of the wafer. A laser head for irradiating the wafer with laser light, the laser head comprising a laser transmitter, laser light uniform means for making the intensity distribution of the laser light uniform, and a cross-sectional shape of the laser light a laser shaping means to square the incident angle changes and laser-like condensing means for condensing the laser light into a linear shape, said laser beam condensed into a linear shape enters inclined against the wafer and means, including an incident angle changing means for tilting along the line condensed into a linear shape, a feature that you forming the modified region in the thickness direction of the wafer To provide a laser processing apparatus for.

  According to the first aspect of the present invention, first, there is provided laser light uniforming means for making the intensity distribution of the laser irradiated from the laser oscillator uniform and laser shape deforming means for making the cross-sectional shape of the laser light square. As a result, when the beam is condensed into a linear shape by the next laser beam condensing means, it is possible to prevent a difference in intensity distribution, and the laser beam can be applied to the wafer with a uniform intensity. Can be irradiated. Therefore, the modified region can be formed linearly and uniformly on the wafer.

In addition, a laser beam condensing means for condensing the laser light in a linear shape is provided. By condensing the laser beam in a linear shape, the linear laser beam can be refracted and a modified region can be formed inside. In addition, by providing the incident angle changing means, it is possible to form the modified region up to the inside of the wafer with various thicknesses. Further, the modified region can be formed in the thickness direction of the wafer by making the incident angle of the laser light oblique to the wafer.

  A second aspect of the present invention is characterized in that, in the first aspect, the laser beam uniforming unit, the laser shape deforming unit, and the laser beam condensing unit are aspherical lenses.

  According to the second aspect, since the aspherical lens is used as the laser beam uniforming unit, the laser shape deforming unit, and the laser beam condensing unit, the laser shape of the laser beam irradiated from the laser oscillator can be easily changed. be able to.

  A third aspect of the present invention is characterized in that, in the first or second aspect, the laser light uniforming means is a beam homogenizer.

  The third aspect defines specific means used as the laser beam uniforming means. According to the third aspect, the beam homogenizer is preferable.

  According to a fourth aspect of the present invention, in any one of the first to third aspects, the laser beam condensing means is a cylindrical lens.

  The fourth aspect defines specific means used as the laser beam condensing means, and according to the fourth aspect, a cylindrical lens is preferable.

According to a fifth aspect of the present invention, there is provided a laser processing method in which a laser beam is incident from a wafer surface to form a modified region inside the wafer and the wafer is divided into individual chips in order to achieve the object. , A laser beam homogenization step for making the intensity distribution of the laser beam irradiated from the laser head uniform, a laser shape conversion step for making the cross-sectional shape of the laser beam a square shape, and a laser beam shape for condensing the laser beam into a linear shape and the condensing step, a incident angle changing step of the laser light condensed into a linear shape enters inclined against the wafer, and the incident angle changing step of tilting along the line condensed into a linear shape , have a, to provide a laser processing method characterized by forming the modified region in the thickness direction of the wafer.

  In the fifth aspect, the laser processing apparatus according to the first aspect is developed as a laser processing method. According to the fifth aspect, the same effect as that of the first aspect can be obtained.

  According to the present invention, the intensity distribution of the laser beam is made constant, the cross-sectional shape of the laser beam is made rectangular, and the laser beam is condensed into a linear shape, thereby making the intensity of the formed linear laser beam constant. can do. Further, by refracting the formed linear laser light, a modified region can be formed in the thickness direction inside the wafer, so that the modified region is formed in a lump on a wide thickness wafer. And processing time can be shortened, and quality can be improved.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. In each figure, the same number or symbol is attached to the same member.

  FIG. 1 is a top view schematically showing a laser processing apparatus 10 according to the present invention. The laser processing apparatus 10 includes a chuck table 12, an X guide base 15, a Y guide base 41, a Z guide base 51, an elevator 13, a standby table 14, a laser head 31, a measuring unit 16, a control unit 21, and a main body 19. Recording means 22 is provided.

  The chuck table 12 sucks and mounts the wafer W, is rotated in the arrow θ direction by a θ rotation shaft (not shown), and is processed and processed in the arrow X direction by an X table (not shown) mounted on the X guide base. Is done.

  A Y guide base 41 is provided above the chuck table 12. The Y guide base 41 is provided with two Y tables (not shown), and Z guide bases 51 and 51 are attached to the respective Y tables.

  Each Z guide base 51, 51 is provided with a Z table (not shown), and a laser head 31 is attached to each Z table via a holder 32. The two laser heads 31, 31 are Each is independently moved in the Z direction and is independently indexed and fed in the Y direction.

  The elevator 13 accommodates a cassette in which the wafers W are stored, moves up and down, and supplies the wafers W to the X guide base (standby table) 15 by a transfer device (not shown). The standby table is provided at the same height as the chuck table 12, and various processes necessary before and after processing are performed on the wafer W placed on the standby table.

  The measuring means 16 is a contact or non-contact type displacement measuring device, and measures the height of the wafer W from the amount of displacement. When a contact-type displacement measuring device is used as a measuring means, the measuring element is moved up and down in the Z direction by an air cylinder or the like, and the measuring element is retracted from the measuring surface except during measurement. Further, when a non-contact type measuring unit is used as the measuring unit, a laser displacement meter, an IR camera, or the like can be used. The measured thickness of the wafer W is sent to the control means 21 for processing.

  The control means 21 housed in the main body 19 includes a CPU, a memory, an input / output circuit unit, and the like. The control means 21 calls information necessary for processing from a database stored in the recording means 22 housed in the main body 19 and controls the operation of each part of the laser processing apparatus 10.

  In addition, the laser processing apparatus 10 includes a wafer transfer means, an operation plate, a television monitor, an indicator lamp, and the like (not shown).

  A switch and a display device for operating each part of the laser processing apparatus 10 are attached to the operation plate. The television monitor displays a wafer image captured by a CCD camera (not shown) or displays program contents and various messages. The indicator lamp displays an operation status such as processing end or emergency stop during the processing of the laser processing apparatus 10.

  FIG. 2 is a side view schematically showing the configuration of the laser head. The present invention is not limited to these. The laser head is positioned above the wafer W so that the wafer W placed on the chuck table 12 provided in the laser processing apparatus 10 by the dicing tape T is irradiated with the laser light L.

  The laser light L oscillated from the laser oscillator 60 passes through a collimating lens 61, a plano-concave lens, a plano-convex lens, a beam homogenizer 63, and a cylindrical lens 65 constituting a beam expander 62, and is irradiated onto the wafer W.

  As shown in FIG. 2, the laser light L oscillated from the laser oscillator 60 is converted into parallel rays in the horizontal direction by the collimator lens 61, and the beam diameter is expanded by the beam expander 62. Next, the light is reflected by the mirror 66 toward the beam homogenizer 63 and passes through the beam homogenizer 63. At this time, before passing through the beam homogenizer 63 (point A in FIG. 2), the laser light L has a circular beam shape and a Gaussian distribution of beam cross-sectional intensity. Since the beam energy is averaged by passing through the beam homogenizer 63, the beam shape is square at the point B, and the beam cross-sectional intensity is transformed into a top hat distribution.

Further, the laser beam L is reflected in the direction of the wafer W by the mirror 66, the width of the laser beam L is scraped w ₀ Karakara w ₁ is the desired range diaphragm 64 (in FIG. 2 C point). Next, by passing through the cylindrical lens 65, the laser beam L can be condensed in one direction, and the cross-sectional intensity of the beam can be increased at the focal point (point D in FIG. 2).

This, by irradiating the laser light L linearly focused by the cylindrical lens 65 to the wafer W, it is possible to form a modified region in the wafer with a width of w _2, with respect to the vertical direction of the wafer W it is possible to form the modified region P having a thickness of w _f Te.

  As described above, as a laser beam uniform means for averaging the beam energy and deforming the beam profile into a square top hat distribution, in addition to the beam homogenizer as shown in FIG. 2, an aspheric lens such as a microlens array Can be mentioned.

  Further, examples of the laser beam condensing unit that condenses the laser light L in a linear shape include a uniaxial concave mirror in addition to the cylindrical lens.

  In the laser processing apparatus 10 of FIG. 2, the laser shape converting means for making the cross-sectional shape of the laser light L square is performed simultaneously with the laser light uniforming means using a beam homogenizer, but can also be performed separately. It is.

Thus, since the laser processing apparatus of the present invention is focused linearly by the laser beam focusing means, as shown in FIG. The modified region P can be formed widely. The thickness of the modified region P can be adjusted by the incident angle θ ₁ of the wafer W of the laser light L.

Therefore, the mirror 66 is arranged as an incident angle changing means so that the angle at which the laser beam L oscillated from the laser oscillator 60 is reflected can be changed. By the mirror 66 by reflecting the laser beam L, to the wafer surface, it is possible to change the incident angle theta ₁ of the laser beam L. In this case, it is necessary to adjust the inclination of the beam homogenizer 63, the aperture 64, and the cylindrical lens 65 so that the laser light L strikes the beam homogenizer 63, the aperture 64, and the cylindrical lens 65 vertically. In the present invention, the incident angle refers to the angle formed by the perpendicular of the wafer W and the laser light L, and is represented by θ ₁ in the figure. The refraction angle refers to the refraction when the laser light L enters the wafer W. The angle formed by the perpendicular of the wafer W and the laser beam L in the wafer W is indicated by θ ₂ in the figure.

  For example, for a thin wafer, the incident angle of the laser light L with respect to the wafer W is reduced. By reducing the incident angle, the portion of the wafer W that contacts the thickness direction in the wafer W is reduced, so that a modified region having a small thickness can be formed. Conversely, the incident angle of the laser beam L is increased for a thick wafer. Thereby, since the part which contacts the thickness direction of a wafer becomes large, the thick modification area | region P can be formed.

The incident angle of the laser beam L is preferably 0 ° or more because the optical axis is obliquely incident on the wafer W. Specifically, when the object is a silicon single crystal, when the incident angle is 0 °, the depth direction w _f is 0, and when the incident angle is 22 °, w _f is about 10% of w ₁ and 38 °. In this case, w _f is about 20% of w _{1 and} at 50 °, w _f is about 30% of w ₁ .

  As described above, in the laser processing apparatus of the present invention, a modified region having a wide width in the depth direction can be formed, so that the number of scans can be reduced. In the conventional laser processing apparatus, since the modified region is formed starting from the condensing point, the thickness of the modified layer in the depth direction has a limit. Therefore, in order to form the modified region in the depth direction, it is necessary to scan a single processing line a plurality of times while shifting the focal position. However, in the present invention, this problem can be solved.

  However, when a sufficient modified region cannot be formed by one scan, it can be performed a plurality of times.

  The modified region P is formed in the thickness direction of the wafer W, and the wafer W is naturally cleaved from the modified region P as a starting point, or is cleaved from the modified region P as a starting point by applying a slight external force. . In this case, the wafer W is easily divided into chips without causing chipping on the front and back surfaces.

  As described above, by changing the incident angle of the laser beam L to the wafer W corresponding to each thickness of the wafer W, an optimum modified region is formed for each thickness of the wafer W, and the wafer W is cleaved. can do. Therefore, since the modified region can be formed in the depth direction by one scan, the modified region can be formed by batch or several scans on a wide thickness wafer. Can be shortened. In addition, since the modified region is formed in the thickness direction of the wafer W, it is possible to reduce the occurrence of defects and the like due to chip breaking failure.

It is the top view which showed typically the structure of the laser processing apparatus which concerns on this invention. It is the side view which showed the structure of the laser head typically.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Laser processing apparatus, 12 ... Chuck table, 13 ... Elevator, 14 ... Standby table, 15 ... X guide base, 16 ... Measuring means, 19 ... Main body, 21 ... Control means, 22 ... Recording means, 31 ... Laser head, 32 ... Holder, 41 ... Y guide base, 51 ... Z guide base, 60 ... Laser oscillator, 61 ... Collimating lens, 62 ... Beam expander, 63 ... Beam homogenizer, 64 ... Shrinking, 65 ... Cylindrical lens, 66 ... Mirror, L ... Laser beam, P ... Modified region, T ... Dicing tape, W ... Wafer, [theta] ₁ ... incident angle, [theta] ₂ ... refractive angle

Claims (5)

In a laser processing apparatus that makes a laser beam incident from the surface of a wafer to form a modified region inside the wafer, and divides the wafer into individual chips,
A laser head for irradiating a laser beam toward the wafer is provided,
The laser head
A laser transmitter,
Laser light uniform means for uniforming the intensity distribution of the laser light;
Laser shape conversion means for making the cross-sectional shape of the laser beam a square,
A laser beam condensing means for condensing the laser beam in a line;
A incident angle changing means for the laser light condensed into a linear shape enters inclined against the wafer, comprising the incident angle changing means for tilting along the line condensed into a linear shape, a
Laser processing apparatus characterized that you forming the modified region in the thickness direction of the wafer.   2. The laser processing apparatus according to claim 1, wherein the laser beam uniforming unit, the laser shape converting unit, and the laser beam condensing unit are aspherical lenses.   3. The laser processing apparatus according to claim 1, wherein the laser beam uniforming means is a beam homogenizer.   4. The laser processing apparatus according to claim 1, wherein the laser beam condensing means is a cylindrical lens. In a laser processing method in which a laser beam is incident from the wafer surface to form a modified region inside the wafer, and the wafer is divided into individual chips.
A laser light uniform process for making the intensity distribution of the laser light emitted from the laser head uniform,
A laser shape conversion step of making the cross-sectional shape of the laser beam a square,
A laser beam condensing step for condensing the laser light in a linear form;
A incident angle changing step of the laser light condensed into a linear shape enters inclined against the wafer, possess the incident angle changing step of tilting along the line condensed into a linear shape, a
A laser processing method, wherein a modified region is formed in a thickness direction of the wafer .

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