JP2013171906A - Laser dicing method and laser processing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser dicing method which allows for dividing of a silicon carbide substrate without performing a breaking process.SOLUTION: A laser dicing method includes a damage formation step for forming damage 50% of or deeper than the thickness of a silicon carbide substrate along a division schedule line, by irradiating the silicon carbide substrate with laser light having a wavelength of 500 nm or longer along the division schedule line, and an expanding step for applying a tensile force to the silicon carbide substrate irradiated with the laser light. The silicon carbide substrate is irradiated with the laser light so that irradiation spots tightly overlap spatially and temporally. The silicon carbide substrate is divided in the damage formation step or the expanding step.

Description

  The present invention relates to a laser dicing method for forming a silicon carbide substrate into a chip, and a laser processing apparatus used in the laser dicing method.

  Silicon carbide (silicon carbide; hereinafter abbreviated as “SiC”) is superior in voltage resistance and heat resistance compared to silicon (hereinafter abbreviated as “Si”). SiC is attracting attention as a material for semiconductor devices that support power electronics because it can reduce device power loss to about 1/10 compared to Si. However, since SiC is much harder than Si, it has not been possible to efficiently divide (dicing) the SiC substrate with a diamond blade or the like that has been conventionally used.

  On the other hand, in recent years, a laser dicing method has been proposed as a new technique for dividing a semiconductor substrate. In the laser dicing method, a laser beam is irradiated on the surface or the inside of the substrate, thereby forming damage that becomes the starting point of the division on the surface or the inside of the substrate. For example, in Patent Document 1, 1) a damage forming step of irradiating a Si substrate with laser light to form damage (dicing grooves) on the surface of the Si substrate, and 2) applying a bending force to the Si substrate, There has been disclosed a laser dicing method including a break process for dividing a Si substrate starting from damage, and 3) an expanding process for applying a tensile force to the Si substrate to widen an interval between the divided chips.

In Patent Document 1, damage is formed on the Si substrate, but a technique for forming damage on the SiC substrate is also reported. For example, Non-Patent Document 1 discloses a method of forming damage (holes) in a SiC substrate by irradiating UV pulse laser light (wavelength 193 nm, pulse width 25 nanoseconds, repetition frequency 100 Hz). In this method, even if the light intensity density per pulse of the pulse laser beam is 10 J / cm ² , the damage depth per pulse irradiation is only about 100 nm. Therefore, in order to form one damage having a depth of 10 μm, it is necessary to irradiate the same portion with pulsed laser light for about 1 second.

JP 2010-109015 A

L. Liu, C.Y.Chang, Wenhsing Wu, S.J.Pearton and F. Ren, "Circular and rectangular via holes formed in SiC via using ArF based UV excimer laser", Applied Surface Science, Vol.257, pp.2303-2307.

  When the conventional laser dicing method is applied to the division of the SiC substrate, as shown in FIG. 1, 1) the SiC substrate 11 is irradiated with the laser beam 10, and the surface of the SiC substrate 11 is aligned along the division line 12. The damage 13 is formed (damage formation step; see FIGS. 1A and 1B), 2) a force in the depth direction (bending force) is applied to the SiC substrate 11, and the SiC substrate 11 is divided starting from the damage 13 ( (Step of break; see FIG. 1C) 3) Applying a surface force (tensile force) to the SiC substrate 11 to widen the space between the divided chips (expand step; see FIG. 1D).

  As described above, when the SiC substrate 11 is divided by the conventional laser dicing method, only the shallow damage 13 can be formed even if the laser beam 10 is irradiated over a certain period of time (see FIG. 1B). For this reason, a “break process” in which a force in the depth direction (bending force) is applied to the SiC substrate 11 is essential (see FIG. 1C). On the other hand, it is not preferable to perform the break process when dividing the SiC substrate 11 from the viewpoint of simplifying the manufacturing process of the semiconductor element and reducing the manufacturing cost of the semiconductor element, and the SiC substrate without performing the break process. The establishment of a technology that can divide 11 is required.

  This invention is made | formed in view of this point, and it aims at providing the laser dicing method which can divide | segment a SiC substrate, without performing a break process. Another object of the present invention is to provide a laser processing apparatus used in the laser dicing method.

  The inventor irradiates the SiC substrate with laser light having a wavelength of 500 nm or more so that the irradiation spots are closely overlapped spatially and temporally, and damage the SiC substrate to a depth of 50% or more of the thickness of the substrate. The present inventors have found that the above-mentioned problems can be solved by forming, and have further studied to complete the present invention.

That is, the present invention relates to the following laser dicing method.
[1] A silicon carbide substrate is irradiated with a laser beam having a wavelength of 500 nm or more along a planned division line, and the silicon carbide substrate is irradiated with a laser beam having a depth of 50% or more of the thickness of the silicon carbide substrate along the planned division line. A damage forming step for forming a damage, and an expanding step for applying a tensile force to the silicon carbide substrate irradiated with the laser light, the laser light so that the irradiation spots overlap in space and time closely. The laser dicing method, wherein the silicon carbide substrate is irradiated with the silicon carbide substrate, and the silicon carbide substrate is divided in the damage forming step or the expanding step.
[2] The thickness of the silicon carbide substrate is 200 μm or less, the laser light is pulsed laser light, and the distance between centers of the laser light irradiation spots on the surface of the silicon carbide substrate is SP (μm). The laser dicing method according to [1], wherein (SP / F) <0.007, where F (kHz) is the repetition frequency of the laser beam.
[3] The laser dicing method according to [1] or [2], wherein the silicon carbide substrate is divided in the damage forming step.
[4] The laser dicing method according to [1] or [2], wherein the silicon carbide substrate is divided in the expanding step.
[5] A break process is not included between the damage forming process and the expanding process, in which a bending force is applied to the silicon carbide substrate to divide the silicon carbide substrate starting from the damage. [4] The laser dicing method according to any one of [4].
[6] The laser dicing method according to any one of [1] to [5], wherein the laser light is pulse laser light or continuous wave laser light having a pulse width of 20 nanoseconds or more.
[7] The laser dicing method according to any one of [1] to [6], wherein the wavelength of the laser beam is 10 μm or less.
[8] The laser beam is applied to the silicon carbide substrate from the surface side of the silicon carbide substrate, and the condensing point of the laser beam is within a range of 100 μm above the surface of the silicon carbide substrate to 120 μm from the surface to the inside. The laser dicing method according to any one of [1] to [7], which is located in [1].

The present invention also relates to the following laser processing apparatus.
[9] A laser light source that emits laser light having a wavelength of 500 nm or more; an optical system that irradiates the silicon carbide substrate with the laser light; and at least one of the optical system and the silicon carbide substrate is moved to A drive unit that relatively moves the silicon carbide substrate, and the silicon carbide substrate is arranged so that the laser beam is closely overlapped spatially and temporally along the planned dividing line. And damaging the silicon carbide substrate to a depth of 50% or more of the thickness of the silicon carbide substrate along the division line.
[10] The thickness of the silicon carbide substrate is 200 μm or less, the laser light is pulsed laser light, and the distance between centers of the laser light irradiation spots on the surface of the silicon carbide substrate is SP (μm). The laser processing apparatus according to [9], wherein (SP / F) <0.007 when the repetition frequency of the laser beam is F (kHz).
[11] The laser processing apparatus according to [9] or [10], wherein the laser light is pulse laser light or continuous wave laser light having a pulse width of 20 nanoseconds or more.
[12] The laser processing apparatus according to any one of [9] to [11], wherein the wavelength of the laser beam is 10 μm or less.

  According to the laser dicing method and the laser processing apparatus of the present invention, the SiC substrate can be divided without performing a break process. For example, by using the laser dicing method and the laser processing apparatus of the present invention, it is possible to simplify the manufacturing process of the semiconductor element and reduce the manufacturing cost of the semiconductor element.

1A to 1D are schematic views showing a process of dividing a SiC substrate using a conventional laser dicing method. 2A to 2C are schematic views showing a process of dividing a SiC substrate using the laser dicing method of the present invention. It is a schematic diagram which shows an example of a structure of a laser processing apparatus. It is a schematic diagram for demonstrating shot pitch. 5A and 5B are photographs showing the result of dividing a 10 × 10 mm square SiC substrate. 6A and 6B are photographs showing the result of dividing a 25 × 25 mm fan-shaped SiC substrate. FIGS. 7A and 7B are photographs showing the results of dividing a 38 × 38 mm fan-shaped SiC substrate. 8A and 8B are photographs showing the result of forming damage on the SiC substrate under the condition of No. 4. 6 is a graph showing the relationship between the value of “SP / F” and the dicing characteristics in the experimental results of Example 1. 6 is a graph showing the relationship between the value of “SP / F” and the dicing characteristics in the experimental results of Example 2. 11A and 11B are photographs showing the result of forming damage on the SiC substrate by irradiating with UV pulse laser light. It is a graph which shows the relationship between the pulse energy and the depth of damage in the experimental result of a comparative example.

1. Laser dicing method of the present invention A laser dicing method of the present invention includes a damage forming step of irradiating a SiC substrate with laser light to form damage on the SiC substrate, and an expanding step of applying a tensile force to the SiC substrate irradiated with the laser light. Including. The SiC substrate is divided in either the damage forming process or the expanding process. As will be described later, in the laser dicing method of the present invention, the wavelength of the laser beam irradiated onto the SiC substrate is 500 nm or more, and the laser beam is irradiated so that the irradiation spots overlap spatially and temporally densely. It is characterized by.

  FIG. 2 is a schematic diagram showing an example of dividing a SiC substrate using the laser dicing method of the present invention. As shown in FIG. 2A, the relative position between the laser beam 100 and the SiC substrate 110 is changed while irradiating the SiC substrate 110 with the laser beam 100 having a wavelength of 500 nm or more. At this time, the condensing point of the laser beam 100 is located outside, on the surface, or inside the SiC substrate 110 and moves along the division line 120 of the SiC substrate 110. Further, the laser beam 100 is scanned so that the irradiation spots closely overlap in space and time. Here, the “irradiation spot” means a laser light irradiation region on the surface of the SiC substrate (see FIG. 4). By scanning the laser beam 100 having a wavelength of 500 nm or more in this way, as shown in FIG. 2B, the damage 130 having a depth of 50% or more of the thickness of the SiC substrate 110 is formed along the planned dividing line 120. (Damage formation process). Thereafter, as shown in FIG. 2C, a tensile force is applied to the SiC substrate 110 on which the damage 130 is formed (expanding process). With the above procedure, SiC substrate 110 can be easily cleaved along division planned line 120.

  In the laser dicing method of the present invention, it is possible to immediately move to the expanding step (see FIG. 2C) after the damage forming step (see FIGS. 2A and 2B). That is, in the laser dicing method of the present invention, it is not necessary to perform a break process (see FIG. 1C) between the damage forming process and the expanding process. Here, the “break process” means that a force (bending force) in a direction substantially perpendicular to the substrate surface is applied to the substrate to cause damage formed on the surface of the substrate to reach the back surface of the substrate. It means a process of dividing (see FIG. 1C). On the other hand, the “expanding process” means a process of dividing the substrate starting from damage formed on the substrate by applying a force (tensile force) in a direction substantially parallel to the substrate surface to the substrate (FIG. 2C). reference).

1) Damage formation step In the damage formation step, the SiC substrate is irradiated with laser light having a wavelength of 500 nm or more to form damage to the SiC substrate at a depth of 50% or more (preferably 75% or more) of the thickness of the SiC substrate. (See FIGS. 2A and 2B). Hereinafter, the laser light irradiation conditions in the damage forming step will be described.

[wavelength]
One feature of the laser dicing method of the present invention is that the wavelength of the laser light applied to the SiC substrate is 500 nm or more.

  In the laser dicing method of the present invention, damage is formed using multiphoton absorption. Thereby, damage is formed even inside the SiC substrate, and damage having a depth of 50% or more of the thickness of the SiC substrate can be formed in the SiC substrate. The processing mechanism of the laser dicing method of the present invention is not limited to this, but is presumed to be “processing by thermal effect”. That is, when the SiC substrate is irradiated with laser light having a wavelength of 500 nm or more, an interband transition of electrons of the SiC substrate occurs due to multiphoton absorption (substantially two-photon absorption or three-photon absorption). Due to the heat released when the excited electrons relax, the temperature of the irradiated region rises locally. As a result, it is considered that SiC is decomposed and melted, a volume explosion occurs, and damage is formed at the irradiated site.

  In the laser dicing method of the present invention, in order to realize the desired processing, it is necessary to avoid the occurrence of one-photon one absorption. The band gap (Eg) of SiC is about 3 eV, which is 413 nm when converted into a wavelength. Therefore, in order to avoid the occurrence of one-photon-one absorption, laser light having a wavelength exceeding 413 nm may be irradiated. In consideration of the absorption skirt, impurity level, and the like, it is preferable to irradiate a laser beam having a wavelength of 500 nm or more in order to surely avoid the occurrence of one-photon one absorption.

  By irradiating the SiC substrate with a laser beam having a wavelength of 500 nm or more, absorption due to electronic transition can be avoided. On the other hand, if the SiC substrate is irradiated with laser light having a wavelength of 10 μm or more, absorption due to vibration transition occurs, and there is a possibility that desired processing cannot be performed. Therefore, it is preferable that the wavelength of the laser beam irradiated to the SiC substrate is 10 μm or less.

[Oscillation method]
The laser beam applied to the SiC substrate may be a pulsed laser beam or a continuous wave (CW) laser beam. From the viewpoint of forming damage with a large aspect ratio (damage with a depth of 50% or more of the thickness of the SiC substrate), pulsed laser light having a pulse width of 20 nanoseconds or more (more preferably 100 nanoseconds or more) or continuous oscillation Laser light (pulse width: infinite) is preferably irradiated. By irradiating pulsed laser light or continuous wave laser light having a pulse width of 20 nanoseconds or more in this way, the aspect ratio of damage formed can be increased. This is considered to be because the peak output is reduced by increasing the pulse width, and as a result, the probability of occurrence of multiphoton absorption is also reduced. Therefore, damage with a large aspect ratio can be more efficiently formed when a pulse laser beam having a pulse width of 100 nanoseconds is irradiated than a pulse laser beam having a pulse width of 20 nanoseconds. On the other hand, when a pulse laser beam having a pulse width of less than 20 nanoseconds is irradiated, the aspect ratio of damage formed may be reduced.

[Spatial and temporal intervals of irradiation spots]
One feature of the laser dicing method of the present invention is that the laser beam is irradiated so that the irradiation spots are closely overlapped spatially and temporally.

  When the laser beam applied to the SiC substrate is a pulsed laser beam, the distance between the centers of irradiation spots of the pulse laser beam on the SiC substrate surface (hereinafter referred to as “shot pitch”; see FIG. 4) is such that the irradiation spot is spatially dense. If it overlaps, it will not specifically limit, For example, what is necessary is just about 0-10 micrometers. Further, the repetition frequency of the pulse laser beam is not particularly limited as long as the irradiation spots overlap closely in time, and may be, for example, 1 kHz to 10 MHz. By irradiating the laser beam so that the irradiation spots overlap closely in space and time in this way, damage suitable for dicing can be formed. The reason will be described below.

The following three are considered as damage formed by laser light irradiation.
i) Bond breakage Chemical bonds are partially broken within and between SiC molecules.
ii) Amorphous region While the irradiated region has a crystalline structure, it has an amorphous structure.
iii) Lattice defects Si atoms or C atoms are missing from the crystal lattice, are substituted for each other, or are substituted with other atoms (O atoms or H atoms).

  When i) bond breakage, ii) amorphous regions, and iii) lattice defects are generated, the following complex processes are involved.

  First, heat is generated locally at the laser beam irradiation site due to the multiphoton absorption of SiC. The heat breaks chemical bonds within and between SiC molecules (bond breakage), and a part of the broken bonds recombine to change the atomic arrangement (amorphous regions and lattice defects). In this case, after the temperature rises until the chemical bond can be broken by the i-th pulse laser beam, the progress of the chemical process and the temperature decrease due to cooling naturally occur. From the viewpoint of forming damage suitable for dicing, it is preferable that the temperature of the irradiated region does not decrease until the chemical process (damage formation process) is completed. Therefore, the position interval between the irradiation spot of the i-th pulse laser beam and the irradiation spot of the i + 1-th pulse laser beam and the time interval between the i-th pulse laser beam and the i + 1-th pulse laser beam are important. These are defined by the shot pitch SP and the repetition frequency F of the pulse laser beam.

  In addition, when heat is locally generated at the laser beam irradiation site, stress distortion occurs in the process of cooling the laser beam irradiation site. The above three types of damage (particularly amorphous regions) are also formed by this stress strain. Also in this case, it is the shot pitch SP and the repetition frequency F of the pulse laser beam that define the formation efficiency of these damages.

  Damage can also be formed by chemical effects without heat. For example, a reaction intermediate having a certain lifetime such as excited electrons, ionized electrons, cations, and light absorption points (color center) is generated by the i-th pulse laser beam. When these reaction intermediates are further excited by the (i + 1) th pulse laser beam, these reaction intermediates acquire large electron energy and promote the formation of damage. In order to excite the reaction intermediate in this way, the irradiation spot of the i-th pulse laser beam and the irradiation spot of the i + 1-th pulse laser beam overlap in position, and the i-th pulse laser beam and The time interval with the (i + 1) th pulse laser beam must be shorter than the lifetime of these reaction intermediates. Therefore, also in this case, it is the shot pitch SP and the repetition frequency F of the pulse laser beam that define the excitation efficiency of the reaction intermediate.

  As described above, from the viewpoint of forming damage suitable for dicing, it is preferable that the shot pitch of the pulsed laser light is somewhat short, and it is preferable that the repetition frequency of the pulsed laser light is somewhat large. Specifically, when the thickness of the SiC substrate is 200 μm or less, when the shot pitch of the pulse laser light on the SiC substrate surface is SP (μm) and the repetition frequency of the pulse laser light is F (kHz), 0 < It is preferable to adjust the shot pitch and the repetition frequency so as to satisfy (SP / F) <0.007. By adjusting the shot pitch and repetition frequency of the pulse laser beam in this way, each chip can be surely divided only by the damage forming step and the expanding step, as shown in the examples described later. Even when the SiC substrate is irradiated with continuous wave laser light, SP = 0 and F = ∞, and therefore it can be said that (SP / F) <0.007 is satisfied.

[Others]
In the laser dicing method of the present invention, the type of laser used as the laser light source is not particularly limited as long as laser light having a wavelength of 500 nm or more can be emitted. Examples of such lasers include Ho lasers, Er lasers, various semiconductor lasers, and the like.

  The position of the condensing point of the laser beam is not particularly limited, and may be any of the outside, the surface, or the inside of the SiC substrate. From the viewpoint of improving the processing efficiency and reducing the damage width, it is preferable that the position of the condensing point of the laser light is located within a range of 100 μm above the surface of the SiC substrate to 120 μm inside from the surface. Here, “the position of the laser beam condensing point” means the position of the condensing point (lens offset) when it is assumed that the refractive index of the SiC substrate is the same as that of air.

If the laser light is pulsed laser light, it is preferable the light intensity density per pulse at the condensing position of the pulsed laser beam is in the range of 1~5000J / cm ^2. If the light intensity density per pulse is less than 1 J / cm ² , damage may not be sufficiently induced. On the other hand, when the light intensity density per pulse exceeds 5000 J / cm ^2, a large amount of debris may be generated, and the processing quality may be deteriorated. On the other hand, when the laser beam is a continuous wave laser beam, the light intensity density at the condensing position of the laser beam is preferably in the range of 1 × 10 ^{7 to} 5 × 10 ⁹ W / cm ² . When the light intensity density is less than 1 × 10 ⁷ W / cm ² , damage may not be sufficiently induced. On the other hand, when the light intensity density is more than 5 × 10 ⁹ W / cm ^2, a large amount of debris may be generated and the processing quality may be deteriorated.

  As described above, in the laser dicing method of the present invention, the SiC substrate is divided in either the damage forming process or the expanding process. In the former case, the SiC substrate is divided by naturally forming a dividing surface that reaches the back surface from the surface of the SiC substrate, triggered by the formation of damage by laser light irradiation. Whether or not the SiC substrate is divided in the damage forming step can be confirmed by observing the vicinity of the division line using a microscope from the front surface side with light applied from the back surface side of the SiC substrate. That is, in the case where the SiC substrate is divided, light passes through the planned dividing line, so that it can be confirmed that the SiC substrate is divided.

2) Expanding Step In the expanding step, a tensile force is applied to the SiC substrate that has been damaged in the damage forming step (see FIG. 2C). As described above, “applying a tensile force” means applying a force in a direction substantially parallel to the substrate surface. When the SiC substrate is divided in the damage forming process, the space between the divided chips is expanded by the expanding process. On the other hand, when the SiC substrate is not divided in the damage forming step, the expanding step divides the SiC substrate starting from the damage, and at the same time widens the interval between the divided chips.

  The method for applying a tensile force to the SiC substrate is not particularly limited. For example, a dicing tape may be attached to the back surface of the SiC substrate and the dicing tape may be stretched. In this case, a dicing tape may be affixed before the damage formation step, or a dicing tape may be affixed after the damage formation step.

  Means for carrying out the laser dicing method of the present invention is not particularly limited. For example, the laser dicing method of the present invention can be implemented using the laser processing apparatus of the present invention described below.

2. Laser processing apparatus of the present invention The laser processing apparatus of the present invention is an apparatus used in the laser irradiation step of the laser dicing method of the present invention. That is, the laser processing apparatus of the present invention irradiates a SiC substrate with a laser beam having a wavelength of 500 nm or more along a planned division line and so that irradiation spots closely overlap in space and time. Is a device that forms damage on the SiC substrate at a depth of 50% or more of the thickness of the SiC substrate. The laser processing apparatus of the present invention is characterized in that the wavelength of the laser beam irradiated on the SiC substrate is 500 nm or more and that the laser beam is irradiated so that the irradiation spots overlap closely in space and time. .

  The laser processing apparatus of the present invention includes at least a laser light source that emits laser light that irradiates a SiC substrate, an optical system that irradiates a SiC substrate with laser light emitted from the laser light source, an optical system (laser light), and SiC. And a drive unit that relatively moves the substrate. Hereinafter, each component will be described.

  The laser light source emits laser light having a wavelength of 500 nm or more. As described above, the type of laser used as the laser light source is not particularly limited as long as laser light having a wavelength of 500 nm or more can be emitted. Examples of such lasers include Ho lasers, Er lasers, various semiconductor lasers, and the like.

  The optical system irradiates the SiC substrate with laser light emitted from the laser light source so that the focal point is located at a desired position. Usually, the optical system includes a telescope optical system that optimizes the beam diameter of the laser light, a condensing lens that condenses the laser light at a desired position, and the like.

  The drive unit moves at least one of the optical system (laser light) and the SiC substrate to relatively move the optical system and the SiC substrate. Thereby, it is possible to irradiate the laser beam along the planned dividing line of the SiC substrate so that the irradiation spots are closely overlapped spatially and temporally. As a result, it is possible to form damage with a high aspect ratio along the planned dividing line of SiC. The drive unit may move the stage on which the SiC substrate is placed, may move the optical system, or may move both the stage and the optical system.

  In addition, as will be described in an embodiment described later, the laser processing apparatus has a stage on which a SiC substrate to be processed is placed, an automatic aiming system for positioning a condensing point at a desired position, and the like. May be.

  As described above, the laser dicing method and the laser processing apparatus according to the present invention irradiate the surface of the SiC substrate with a high aspect ratio by irradiating the laser beam having a wavelength of 500 nm or more so that the irradiation spots overlap spatially and temporally densely. The damage of the ratio (depth of 50% or more of the thickness of the SiC substrate) can be formed with high accuracy and high speed. Therefore, the laser dicing method and the laser processing apparatus of the present invention can divide the SiC substrate with high accuracy and high speed only by the expanding process without performing the breaking process.

3. Features of the present invention (1) Wavelength As described above, one feature of the laser dicing method of the present invention is that the SiC substrate is irradiated with laser light having a wavelength of 500 nm or more. On the other hand, even if a laser beam having a wavelength of 500 nm or more is irradiated to a substance other than SiC, damage with a high aspect ratio cannot be formed with high accuracy and high speed as when SiC is irradiated.

As an example, a case where a laser beam having a wavelength of 500 nm or more is irradiated onto a typical difficult-to-work material such as quartz or sapphire will be described. In this case, since the band gap of these transparent dielectric materials is as large as 5 to 9 eV, 3-photon absorption or 4-photon absorption occurs only with light having a wavelength of 500 nm or more, and an interband transition of electrons can be induced only. In order to induce three-photon absorption or four-photon absorption with laser light having a long pulse width (nanosecond to microsecond), it is necessary to irradiate pulse laser light having a very large peak output (GW / cm ² or more). is there. However, when such intense light is condensed and irradiated, other nonlinear processes (dielectric breakdown) are always induced before three-photon absorption or four-photon absorption occurs, so that the shape of damage is greatly disturbed. Therefore, even if quartz or sapphire is irradiated with laser light having a wavelength of 500 nm or more, only a very disordered shape can be formed.

  In metal processing, a carbon dioxide laser (non-polarized light with a wavelength of 10 μm) may be irradiated. However, even with this method, high aspect ratio damage cannot be formed with high accuracy and high speed. In other words, since this method is a hot-melt process performed by directly exciting metal lattice vibrations, it is not possible to form damage with a high aspect ratio or to perform high-precision processing (with a spatial resolution of μm level). Can not.

(2) Shot pitch and repetition frequency The laser dicing method of the present invention is also characterized in that the laser beam is irradiated so that the irradiation spots overlap closely in space and time.

Table 1 is a table showing various characteristics of SiC, sapphire, quartz, and single crystal Si.

  In the conventional laser processing method that processes Si, glass, sapphire, etc. using multiphoton absorption, the skilled person knows that the intensity of the laser beam is increased in order to process a harder material or a material having a higher melting point. It was common sense for me. Further, from the viewpoint of improving the processing speed, it has been common knowledge for those skilled in the art to increase the shot pitch to some extent (for example, 1 to several μm).

  As shown in Table 1, since SiC is very hard and has a high melting point, SiC cannot be processed appropriately even if SiC is irradiated with laser light as in the conventional case. In particular, since SiC has a very high thermal conductivity, even if the same amount of heat as that in the past is applied locally, a large amount of heat escapes from the point, and therefore SiC cannot be processed appropriately. In such a case, a person skilled in the art generally increases the output of the laser beam. However, if the output of the laser beam is extremely increased, the chemical modification of SiC (change to carbide or burnt-like material) and the desired processing shape will be clarified to the extent that clearly deviates from the desired processing shape. SiC breaks down to a range deviating from the above, and the processing quality is significantly reduced. For this reason, with the conventional laser processing method, it is not possible to perform precision processing as required in the semiconductor field for SiC.

  On the other hand, the present inventor has considered a means for increasing the amount of supplied heat more than the amount of heat that escapes without excessively increasing the output of the laser light, considering that the thermal conductivity is very high. The inventor of the present invention invented a method for precisely processing SiC, which is difficult to process, by paying attention to unique parameters such as shot pitch and repetition frequency.

4). Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the scope of the present invention is not limited thereto.

  FIG. 3 is a schematic diagram showing a configuration of a laser processing apparatus according to an embodiment of the present invention.

  As shown in FIG. 3, the laser processing apparatus 200 includes a laser light source 210, a telescope optical system 220, a condenser lens 230, a stage 240, an AF camera 250, an XY stage controller 260, a Z controller 270, and a computer 280.

The laser light source 210 emits laser light having a wavelength of 500 nm or more. The laser light source is, for example, a pulse laser beam having a wavelength of 500 nm to 10 μm, a pulse width of 20 nanoseconds or more, a repetition frequency of 1 kHz to 10 MHz, a light intensity density of 1 to 5000 J / cm ² per pulse, or a wavelength of 500 nm to 10 μm, a light intensity. A continuous wave laser beam having a density of 1 × 10 ^{7 to} 5 × 10 ⁹ W / cm ² is emitted.

  The telescope optical system 220 optimizes the beam diameter of the laser light emitted from the laser light source 210 in order to obtain a preferable processing shape.

  The condensing lens 230 condenses the laser light that has passed through the telescope optical system 220. For example, the condensing lens 230 is an objective lens for a microscope.

  Stage 240 has a mounting table on which SiC substrate 110 to be processed is mounted, and a drive mechanism that can move the mounting table. The drive mechanism can move the mounting table in the X-axis or Y-axis direction or rotate the X-axis or Y-axis as a center. The SiC substrate 110 on the stage 240 is moved in the XY-axis direction along the planned division line by this drive mechanism.

  AF camera 250 is a camera for acquiring a surface profile of a processed part of SiC substrate 110. The acquired profile is output to the computer 280.

  Based on an instruction from the computer 280, the XY stage controller 260 moves the stage 240 in the XY axis direction so that the condensing position of the laser light is along the planned dividing line of SiC 110.

  Based on an instruction from the computer 280, the Z controller 270 moves the condensing lens 230 in the Z-axis direction so that the condensing position of the laser light matches a desired position.

  The computer 280 is connected to the laser light source 210, the AF camera 250, the XY stage controller 260, and the Z controller 270, and comprehensively controls these units. For example, the computer 280 controls the AF camera 250 and the XY stage controller 260 to acquire the surface profile of the SiC substrate 110. In addition, computer 280 controls XY stage controller 260 and Z controller 270 to scan the laser beam along the planned division line of SiC substrate 110.

  Next, a procedure for dividing SiC substrate 110 using laser processing apparatus 200 will be described.

  First, damage from the surface to the inside is formed in the SiC substrate 110 by the laser processing apparatus 200 shown in FIG. 3 (damage formation step). Specifically, first, SiC substrate 110 with dicing tape 140 attached to the back surface is placed on a stage 240 and a surface profile of SiC substrate 110 is acquired by AF camera 250 and XY stage controller 260. Next, laser light is emitted from the laser light source 210 to irradiate the SiC substrate 110 with the laser light. At this time, based on the surface profile acquired in advance, the stage 240 is moved in the XY axis direction (horizontal direction) to scan the division planned line with the laser light (see FIG. 2A). In addition, the laser beam is scanned so that the irradiation spots overlap closely in space and time. Thereby, the damage of the depth of 50% or more of the thickness of SiC substrate 110 can be formed along the division | segmentation planned line of SiC substrate 110 (refer FIG. 2B).

  Next, the dicing tape 140 is stretched by an expanding device (not shown), and a tensile force is applied to the damaged SiC substrate 110 (expanding process). When the SiC substrate 110 is divided in the damage forming process, the space between the divided chips is expanded by the expanding process. On the other hand, when the SiC substrate 110 is not divided in the damage formation process, the expansion process divides the SiC substrate 110 starting from the damage, and widens the interval between the divided chips simultaneously (see FIG. 2C).

  By the above procedure, the SiC substrate can be divided (diced) only by the damage forming step and the expanding step without interposing the break step.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail with reference to an Example, this invention is not limited by these Examples.

[Example 1]
As a processing object, a SiC substrate cut into a predetermined shape from a SiC single crystal substrate (thickness 150 μm) having a diameter of 3 inches was prepared. The SiC substrate was cut into a 10 × 10 mm square, the substrate was divided into 9 grids (only the sectoral part was used; 25 × 25 mm), and the substrate was divided into four equal parts (fan shape; 38 × 38 mm).

A SiC substrate with a dicing tape affixed to the back surface is placed on the stage, and the SiC substrate is irradiated with pulsed laser light (wavelength 1064 nm, pulse width 190 nanoseconds) from the surface side of the SiC substrate to damage the SiC substrate from the surface to the inside. Was formed (damage formation step). At this time, the stage was moved in the XY axis direction (horizontal direction), and damage was formed along the planned dividing line of the SiC substrate. The condensing point was set at a position of 100 μm inside from the surface of the SiC substrate. The irradiation spot diameter (1 / e ² width) on the substrate surface was 5.8 μm. The pulse energy of the pulse laser beam was changed within a range of 133 to 500 μJ. The moving speed of the stage was changed within a range of 20 to 70 mm / second. The repetition frequency of the pulse laser beam was changed within the range of 40 to 150 kHz (see Table 2).

  Next, the dicing tape affixed to the back surface of the SiC substrate was evenly stretched to divide (chip) the SiC substrate along the planned dividing line (expanding process). Thereafter, for each SiC substrate, the ratio (hereinafter referred to as “dicing characteristic”) of the number of actually divided division lines to the total number of division planned lines (in units of the length of one side of each chip). Calculated. In each SiC substrate, 80 to 90% of the actually divided division lines are divided in the damage forming process (confirmed by irradiating light before the expanding process), and the remaining 10 to 10%. 20% was divided in the expanding process.

  FIG. 5 is a photograph showing a result of dividing a 10 × 10 mm square SiC substrate. 5A is a photograph showing the result of No. 1, and FIG. 5B is a photograph showing the result of No. 2 (see Table 2). In the example shown in FIG. 5A, 24 of the 40 scheduled division lines are divided, so the dicing characteristic is 60%. In the example shown in FIG. 5B, 40 of the 40 scheduled division lines are divided, so that the dicing characteristic is 100%.

  FIG. 6 is a photograph showing the result of dividing a 25 × 25 mm fan-shaped SiC substrate. 6A is a photograph showing the result of No. 10 (dicing characteristic 0%), and FIG. 6B is a photograph showing the result of No. 11 (dicing characteristic 99%).

  FIG. 7 is a photograph showing the result of dicing a 38 × 38 mm fan-shaped SiC substrate. 7A is a photograph showing the result of No. 14 (dicing characteristic 0%), and FIG. 7B is a photograph showing the result of No. 17 (dicing characteristic 98%).

  Moreover, about each SiC substrate, the division surface was observed after division | segmentation, and the depth of the damage formed in the damage formation process was measured. FIG. 8A is a photograph of a cross section of a SiC substrate irradiated with laser light under the conditions of Experiment No. 4. In this experiment, a SiC substrate having a thickness of 350 μm was used to show the cross-sectional shape of the damage before the division. FIG. 8B is a photograph of the divided surface of No. 4 substrate (thickness 150 μm) after expansion.

Table 2 shows laser processing conditions, damage depth, and calculated dicing characteristics.

FIG. 9 is a graph showing the relationship between the “SP / F” value and the dicing characteristics. From this graph, it can be seen that when the value of “SP / F” is less than 0.007 (7 × 10 ⁻³ ), the dicing characteristics rapidly increase.

  From the above results, it can be seen that by the laser dicing method of the present invention, the SiC substrate can be divided only by the damage forming step and the expanding step without interposing the break step. It can also be seen that in the laser dicing method of the present invention, the SiC substrate can be diced regardless of the size of the SiC substrate.

[Example 2]
As a processing object, a SiC substrate cut out in a predetermined shape from a SiC single crystal substrate (thickness 130 μm) having a diameter of 3 inches was prepared. As the SiC substrate, a substrate cut into a 10 × 10 mm square and a substrate obtained by dividing the substrate into nine grids (using only a fan-shaped portion; 25 × 25 mm) were prepared.

A SiC substrate with a dicing tape affixed to the back surface is placed on the stage, and the SiC substrate is irradiated with pulsed laser light (wavelength 1064 nm, pulse width 190 nanoseconds) from the surface side of the SiC substrate to damage the SiC substrate from the surface to the inside. Was formed (damage formation step). At this time, the stage was moved in the XY axis direction (horizontal direction), and damage was formed along the planned dividing line of the SiC substrate. The condensing point was adjusted to the position of 80 μm inside from the surface of the SiC substrate. The irradiation spot diameter (1 / e ² width) on the substrate surface was 5.8 μm. The pulse energy of the pulse laser beam was 180 μJ. The moving speed of the stage was changed within a range of 30 to 55 mm / second. The repetition frequency of the pulse laser beam was changed within a range of 60 to 110 kHz (see Table 3).

  Next, the dicing tape affixed to the back surface of the SiC substrate was evenly stretched to divide (chip) the SiC substrate along the planned dividing line (expanding process). Thereafter, dicing characteristics were calculated for each SiC substrate in the same procedure as in Example 1. Moreover, about each SiC substrate, the division surface was observed after division | segmentation, and the depth of the damage formed in the damage formation process was measured. In each SiC substrate, 80 to 90% of the actually divided division lines were divided in the damage forming process, and the remaining 10 to 20% were divided in the expanding process.

Table 3 shows laser processing conditions, damage depth, and calculated dicing characteristics.

FIG. 10 is a graph showing the relationship between the “SP / F” value and the dicing characteristics. From this graph, it can be seen that when the value of “SP / F” is less than 0.007 (7 × 10 ⁻³ ), the dicing characteristics rapidly increase. In particular, paying attention to the experimental results of No. 4, it can be seen that appropriate dicing cannot be performed only with a small shot pitch, and proper dicing can be performed when the shot pitch is small and the repetition frequency is large.

  From the above results, it can be seen that by the laser dicing method of the present invention, the SiC substrate can be divided only by the damage forming step and the expanding step without interposing the break step.

  In Example 1 and Example 2, SiC substrates having thicknesses of 150 μm and 130 μm were divided, respectively. Further, the thickness of these SiC substrates has an error of about ± 10%. From these, in the laser dicing method of the present invention, it is suggested that the SiC substrate can be divided only by the damage forming step and the expanding step if the thickness of the SiC substrate is 200 μm or less.

[Reference example]
As a reference example, the result of investigating whether deep damage can be formed in a SiC substrate by irradiating pulsed laser light having different pulse widths is shown.

  As a processing object, a SiC substrate cut out in a 10 × 10 mm square shape from a SiC single crystal substrate (thickness 150 μm) having a diameter of 3 inches was prepared.

The SiC substrate was placed on the stage, and the SiC substrate was irradiated with pulsed laser light (wavelength 1064 nm, pulse width 30 nanoseconds or 200 nanoseconds) from the surface side of the SiC substrate to form damage on the SiC substrate from the surface to the inside. . At this time, the stage was moved in the XY axis direction (horizontal direction), and damage was formed along the planned dividing line of the SiC substrate. The focal point was adjusted to the position of 20 μm inside (when the pulse width was 30 nanoseconds) or 100 μm inside (when the pulse width was 200 nanoseconds) from the surface of the SiC substrate. The irradiation spot diameter (1 / e ² width) on the substrate surface was 5.4 μm (when the pulse width was 30 nanoseconds) or 5.8 μm (when the pulse width was 200 nanoseconds).

Thereafter, each SiC substrate was divided along another planned division line orthogonal to the planned division line, and the depth of damage formed by laser light irradiation was measured for each SiC substrate. Table 4 shows the laser processing conditions and the depth of damage.

  From the above results, if the pulse width of the laser light applied to the SiC substrate is a typical nanosecond level pulse width (20 nanoseconds or more), damage with a depth of 50% or more of the thickness of the SiC substrate is formed. Thus, it is suggested that the problems of the present invention can be solved.

[Comparative example]
In the comparative example, an example in which the UV pulse laser beam is irradiated onto the SiC substrate is shown.

  As a processing object, a SiC substrate cut into a predetermined shape from a SiC single crystal substrate (thickness 150 μm) having a diameter of 3 inches was prepared. As the SiC substrate, a substrate cut into a 10 × 10 mm square was prepared.

A SiC substrate with a dicing tape affixed to the back is placed on a stage, and the SiC substrate is irradiated with UV pulse laser light (wavelength 355 nm, pulse width 25 nanoseconds) from the surface side of the SiC substrate, and the SiC substrate is directed from the surface to the inside. Damage formed. At this time, the stage was moved in the XY axis direction (horizontal direction), and damage was formed along the planned dividing line of the SiC substrate. The condensing point was adjusted to the surface of the SiC substrate. The irradiation spot diameter (1 / e ² width) on the substrate surface was 6.28 μm. The pulse energy of the pulse laser beam was changed within a range of 5 to 17 μJ. The moving speed of the stage was 18 mm / second. The repetition frequency of the pulse laser beam was 60 kHz.

  Thereafter, each SiC substrate was divided along another planned division line orthogonal to the planned division line, and the depth of damage formed by laser light irradiation was measured for each SiC substrate.

  FIG. 11A is a photograph of a cross section of a SiC substrate irradiated with laser light under a condition where the pulse energy is 5 μJ. FIG. 11B is a photograph of a cross section of the SiC substrate irradiated with laser light under a condition where the pulse energy is 17 μJ. FIG. 12 is a graph showing the relationship between pulse energy and damage depth. From this graph, it can be seen that even if the pulse energy is increased, the depth of damage only increases to about 60 μm (saturates).

  From the above results, it can be seen that even when laser light having a wavelength of less than 500 nm is irradiated, damage having a high aspect ratio cannot be formed, and the SiC substrate cannot be divided.

  The laser dicing method and the laser processing apparatus of the present invention can divide the SiC substrate without performing a break process. For example, by using the laser dicing method and the laser processing apparatus of the present invention, it is possible to simplify the manufacturing process of the semiconductor element and reduce the manufacturing cost of the semiconductor element.

10,100 Laser light 11,110 SiC substrate 12,120 Scheduled division line 13,130 Damage 140 Dicing tape 200 Laser processing device 210 Laser light source 220 Telescope optical system 230 Condensing lens 240 Stage 250 AF camera 260 XY stage controller 270 Z Controller 280 Computer

Claims (12)

Irradiate a laser beam having a wavelength of 500 nm or more to the silicon carbide substrate along the planned division line, and form damage to the silicon carbide substrate along the planned division line with a depth of 50% or more of the thickness of the silicon carbide substrate. Damage forming process to
An expanding step of applying a tensile force to the silicon carbide substrate irradiated with the laser light,
The laser beam is applied to the silicon carbide substrate so that irradiation spots closely overlap in space and time,
The silicon carbide substrate is divided in the damage forming step or the expanding step.
Laser dicing method. The silicon carbide substrate has a thickness of 200 μm or less,
The laser beam is a pulsed laser beam,
When the distance between the centers of the laser light irradiation spots on the surface of the silicon carbide substrate is SP (μm) and the repetition frequency of the laser light is F (kHz), (SP / F) <0.007. ,
The laser dicing method according to claim 1.   The laser dicing method according to claim 1, wherein the silicon carbide substrate is divided in the damage forming step.   The laser dicing method according to claim 1, wherein the silicon carbide substrate is divided in the expanding step.   2. The laser according to claim 1, wherein the laser does not include a break step of dividing the silicon carbide substrate from the damage by applying a bending force to the silicon carbide substrate between the damage forming step and the expanding step. Dicing method.   The laser dicing method according to claim 1, wherein the laser light is pulse laser light or continuous wave laser light having a pulse width of 20 nanoseconds or more.   The laser dicing method according to claim 1, wherein a wavelength of the laser light is 10 μm or less. The laser beam is applied to the silicon carbide substrate from the surface side of the silicon carbide substrate,
2. The laser dicing method according to claim 1, wherein the condensing point of the laser light is located within a range of 100 μm above the surface of the silicon carbide substrate to 120 μm inside from the surface. A laser light source that emits laser light having a wavelength of 500 nm or more;
An optical system for irradiating the silicon carbide substrate with the laser beam;
A drive unit that moves at least one of the optical system and the silicon carbide substrate and relatively moves the optical system and the silicon carbide substrate;
The silicon carbide substrate is irradiated with the laser light along the planned division line so that the irradiation spots closely overlap in space and time, and the silicon carbide substrate is applied to the silicon carbide substrate along the planned division line. Forming a damage with a depth of 50% or more of the thickness of the carbide substrate;
Laser processing equipment. The silicon carbide substrate has a thickness of 200 μm or less,
The laser beam is a pulsed laser beam,
When the distance between the centers of the laser light irradiation spots on the surface of the silicon carbide substrate is SP (μm) and the repetition frequency of the laser light is F (kHz), (SP / F) <0.007. ,
The laser processing apparatus according to claim 9.   The laser processing apparatus according to claim 9, wherein the laser light is pulse laser light or continuous wave laser light having a pulse width of 20 nanoseconds or more.   The laser processing apparatus according to claim 9, wherein a wavelength of the laser light is 10 μm or less.