Substrate dividing method

ES 2 639 733 T3

DESCRIPTION

Substrate division method

Technical field

The present invention relates to a substrate splitting method used to split a substrate such as a semiconductor substrate in a manufacturing step of a semiconductor device or the like.

Background of the technique

As semiconductor devices have been on the decline in recent years, there are cases where a semiconductor substrate is thinned to a thickness of several tens of microns in a semiconductor device manufacturing step. Therefore, when a thinned semiconductor substrate is cut and split with a blade, chipping and cracking occurs more than in the case where a semiconductor substrate is thicker, thus causing a problem that decreases the performance of the chips. semiconductors obtained by dividing the semiconductor substrate.

The methods of dividing semiconductor substrates that can solve this problem are those described in Japanese Patent Application Laid-Open No. SHO 64-38209 and SHO 62-4341.

In the methods described in these publications, a semiconductor substrate having a front face formed with a functional device is inscribed with a slot by a blade on the side of the front face, then an adhesive sheet is attached to the front face, to keep the semiconductor substrate and the back face of the semiconductor substrate is rectified until the pre-formed groove is exposed, thereby thinning the semiconductor substrate and splitting the semiconductor substrate.

EP1022778A1 describes a wafer splitting method and a semiconductor device manufacturing method in which grooves are formed in a wafer surface, wherein the semiconductor elements of the surface are formed, along cube dividing lines or chip separation lines on the wafer. The grooves are deeper than the thickness of a finished chip. A holding sheet is attached to that surface of the wafer on which the semiconductor elements are formed. The bottom surface of the wafer is lapped and ground to the thickness of the finished chip, thereby dividing the wafer into chips. When the wafer is divided into chips, lapping and grinding continue until the thickness of the wafer equals the thickness of the finished chip, even after the wafer has been divided into chips by lapping and grinding.

Description of the Invention

However, if the back face grinding of the semiconductor substrate is performed by surface grinding in the methods described in the above-mentioned publications, chipping and cracking may occur on the side faces of the groove formed in advance in the semiconductor substrate when the face surface-groove reaches the groove.

In view of such circumstance, it is an object of the present invention to provide a substrate splitting method that can prevent chipping and cracking from occurring and thinning and splitting a substrate.

To achieve the above-mentioned object, the substrate division method according to the present invention is defined in claim 1.

In the substrate grinding step, the substrate is ground in such a way that the substrate reaches a predetermined thickness after the starting point region for cutting is formed. Herein, even when the soil surface reaches the fracture generated from the starting point region for the cut acting as the starting point, the substrate cut surfaces cut by the fracture remain in close contact with each other, by which can prevent the substrate from chipping and cracking after grinding.

This can prevent chipping and cracking from occurring and can thin and split the substrate.

Herein, the point of convergence of light refers to a location where the laser light is converging. Grinding encompasses scraping, grinding, chemical etching, and the like. The starting point region for cutting refers to a region that becomes a starting point for cutting when the substrate is cut. Therefore, the starting point region for cutting is a part to be cut where the cut is to be made in the substrate. The starting point region for cutting can be produced by continuously forming a modified region or by intermittently forming a modified region.

The substrate encompasses semiconductor substrates such as silicon substrates and GaAs substrates.

Since the substrate can be ground after forming the functional device, for example a chip is obtained

ES 2 639 733 T3 thinned to fit a smaller size of a semiconductor device. Herein, the functional device refers to light receiving devices such as photodiodes, light emitting devices such as diodes, circuit devices formed as circuits, etc.

Preferably, the step of grinding the substrate includes a step of subjecting the back face of the substrate to chemical etching. When the back side of the substrate is chemically etched, the back side of the substrate naturally becomes smoother. Also, since the cutting surfaces of the substrate cut by the fracture generated from the starting point region for the cutting acting as the starting point remain in close contact with each other, only the edge portions on the back face of the surfaces cutting are selectively etched, to be chamfered. This can improve the transverse breaking strength of the chips obtained by splitting the substrate and prevent chipping and cracking of the chips.

Brief description of the drawings

Figure 1 is a plan view of an object to be processed during laser processing in the laser processing method according to an embodiment of the present invention;

Figure 2 is a sectional view of the object to be processed taken along the line II-II of Figure 1;

Figure 3 is a plan view of the object to be processed after laser processing by the laser processing method according to the embodiment;

Figure 4 is a sectional view of the object to be processed taken along the line IV-IV of Figure 3;

Figure 5 is a sectional view of the object to be processed taken along the line VV of Figure 3;

Figure 6 is a plan view of the object to be processed cut by the laser processing method according to the embodiment;

Figure 7 is a graph showing the relationship between electric field intensity and crack point size in the laser processing method according to the embodiment;

Figure 8 is a sectional view of the object to be processed in a first stage of the laser processing method according to the embodiment;

Figure 9 is a sectional view of the object to be processed in a second stage of the laser processing method according to the embodiment;

Figure 10 is a sectional view of the object to be processed in a third stage of the laser processing method according to the embodiment;

Figure 11 is a sectional view of the object to be processed in a fourth stage of the laser processing method according to the embodiment;

Fig. 12 is a view showing a photograph of a cut section in a part of a silicon wafer cut by the laser processing method according to the embodiment;

Figure 13 is a graph showing the relationships between the wavelength of laser light and the internal transmittance of a silicon substrate in the laser processing method according to the embodiment;

Figure 14 is a schematic diagram of the laser processing apparatus according to Example 1;

Figure 15 is a flow chart for explaining the laser processing method according to Example 1;

Figure 16 is a view showing the semiconductor substrate after a step of forming a starting point region for cutting according to Example 1;

Figure 17 is a view for explaining a step of bonding a protective film according to Example 1;

Figure 18 is a view for explaining a step of rectifying the semiconductor substrate according to Example 1;

Figure 19 is a view for explaining a step of bonding an expansion film according to Example 1; Figure 20 is a view for explaining a step of peeling off the protective film according to Example 1;

Figure 21 is a view for explaining a step of expanding the expansion film and collecting the semiconductor chips according to Example 1;

Fig. 22 is a view showing the chamfers formed in the edge portions on the back face side of the cutting surfaces of the semiconductor chips after the step of grinding the semiconductor substrate according to Example 1;

Figure 23A is a view for explaining a case where a fused processed region remains on a cutting surface of a semiconductor chip after the step of grinding the semiconductor substrate according to Example 1, while a fracture reaches the face. frontal before the step of rectifying the semiconductor substrate;

Fig. 23B is a view to explain a case where a fused processed region remains on a cutting surface of a semiconductor chip after the step of grinding the semiconductor substrate according to Example 1, while a fracture does not reach the front face before the step of rectifying the semiconductor substrate;

Figure 24A is a view to explain a case where a fused processed region does not remain on a cutting surface of a semiconductor chip after the step of grinding the semiconductor substrate according to Example 1, while a fracture reaches the front face before the step of rectifying the semiconductor substrate;

Figure 24B is a view for explaining a case where a fused processed region does not remain on a cutting surface of a semiconductor chip after the step of rectifying the semiconductor substrate of

ES 2 639 733 T3 according to Example 1, while a fracture does not reach the front face before the step of grinding the semiconductor substrate;

Figure 25A is a view for explaining a case where a fused processed region remains on an edge portion on the back face side of a cutting surface of a semiconductor chip after the step of rectifying the semiconductor substrate according to with Example 1, while a fracture reaches the front face before the step of grinding the semiconductor substrate;

Figure 25B is a view for explaining a case where a fused processed region remains at an edge portion on the back face side of a cutting surface of a semiconductor chip after the step of rectifying the semiconductor substrate according to with Example 1, while a fracture does not reach the front face before the step of grinding the semiconductor substrate;

Figure 26A is a sectional view of a marginal portion of the semiconductor substrate prior to the step of rectifying the semiconductor substrate according to Example 1;

Figure 26B is a sectional view of the marginal portion of the semiconductor substrate after the step of rectifying the semiconductor substrate according to Example 1;

Best embodiments of the invention

Next, a preferred embodiment of the present invention will be explained in detail with reference to the drawings. The method of dividing substrates according to this method comprises the steps of irradiating a substrate with laser light while positioning a point of convergence of light within the substrate, to form a region modified due to multiphoton absorption within the substrate, forming of thus a starting point region for cutting; and then grinding the substrate such that the substrate reaches a predetermined thickness.

First, a laser processing method carried out in the stage of forming the starting point region for cutting will be explained, a laser processing method carried out in the stage of forming the starting point region for cutting, multiphoton absorption in particular.

A material becomes optically transparent if its absorption band EG is greater than the energy of a photon hv. Therefore, the condition under which absorption occurs in the material is hv> EG. However, even when optically transparent, the material produces absorption in the condition of hv> EG (n = 2, 3, 4, ...) if the laser light intensity is very high. This phenomenon is known as multiphoton absorption. In the case of pulse waves, the intensity of the laser light is determined by the maximum power density (W / cm2) of the laser light at a point of light convergence thereof. Multiphoton absorption occurs, for example, at a maximum power density (W / cm2) of 1 x 108 (W / cm2) or higher. The maximum power density is determined by (energy per pulse of laser light at the point of convergence of the light) / (point cross-sectional area of ​​the laser light beam per pulse width). In the case of a continuous wave, the intensity of the laser light is determined by the intensity of the electric field (W / cm2) of the laser light at the point of convergence of the light.

The laser processing principle according to the embodiment using such multiphoton absorption will be explained with reference to Figures 1 to 6. Figure 1 is a plan view of a substrate 1 during laser processing; Figure 2 is a sectional view of the substrate 1 taken along the line II-II of Figure 1; Figure 3 is a plan view of substrate 1 after laser processing; Figure 4 is a sectional view of the substrate 1 taken along the line IV-IV of Figure 3; Figure 5 is a sectional view of the substrate 1 taken along the line VV of Figure 3; and Figure 6 is a plan view of cut substrate 1.

As shown in Figures 1 and 2, the front face 3 of the substrate 1 has a desirable line 5 along which the substrate must be cut to cut the substrate 1. Line 5 along which the substrate is a virtual line that extends linearly (substrate 1 can also be formed with a real line that acts as line 5 along which the substrate must be cut). In laser processing according to the present embodiment, the substrate 1 is irradiated with laser light L in such a way that a point of convergence of the light P is positioned within the semiconductor substrate 1 in a condition that causes multiphoton absorption, to form a modified region 7. Herein, the point of convergence of light is a place where the laser light L is convergent.

The laser light L travels relatively along the line 5 along which the substrate must be cut (in the direction of the arrow A), to move the point of convergence of the light P along the line 5 along which the substrate is to be cut. This forms the modified region 7 along the line 5 along which the substrate must only cut into the substrate 1 as shown in Figures 3 to 5 and the modified region 7 forms a starting point region 8 for cutting (part to be cut). In the laser processing method according to the present embodiment, no modified region 7 is formed by heating the substrate 1 causing the substrate 1 to absorb the laser light L. Instead, the laser light L is transmitted through the semiconductor substrate 1, to generate multiphoton absorption within the semiconductor substrate 1, thereby forming the modified region 7. Therefore, the laser light L is hardly absorbed by the face. front 3 of the semiconductor substrate 1, whereby the front face 3 of the semiconductor substrate 1 does not melt.

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If there is a starting point at a location to cut when substrate 1 is cut, substrate 1 fractures from this starting point and thus can be cut with a relatively small force as shown in Figure 6. This makes it possible to cut substrate 1 without generating unnecessary fractures on the front face 3 of substrate 1.

It appears that there are the following two ways to cut the substrate from the starting point region for the cut acting as the starting point. The first case is where, after forming the starting point region for cutting, an artificial force is applied to the substrate, so that the substrate is fractured from the starting point region for cutting which acts as the starting point , through which the substrate is cut. This is the cut in the case where the substrate has a great thickness, for example. The application of an artificial force encompasses the application of bending stress and shear stress throughout the region of starting point for cutting the substrate, and the exercise of a temperature difference on the substrate to generate thermal stress, for example. The other case is where a starting point region for cutting is formed, such that the substrate naturally fractures in a transverse direction (thickness direction) of the substrate from the starting point region for cutting acting as a point. start, through which the substrate is cut. This is achieved, for example, by forming the starting point region for cutting by a single row of modified regions when the substrate has a small thickness and by a plurality of rows of modified regions aligned in the thickness direction when the substrate has a great thickness. Even in the case of natural fracturing, the fractures do not extend to the front face at a location not formed with the starting point region for cutting in the part to be cut, so only the part corresponding to the location formed with the Starting point region for cutting may fracture. Therefore, the fracture can be well regulated. Such a fracturing method with favorable controllability is quite efficient, since semiconductor substrates such as silicon wafers have recently been able to become thinner.

The modified region formed by multiphoton absorption in this example includes the following cases (1) to (3). Cases (1) and (3) do not refer to the present invention:

(1) Case where the modified region is a fissure region that includes one or a plurality of fissures

A substrate (for example, glass or a piezoelectric material made from LiTaO3) is irradiated with laser light while a point of convergence of light is positioned within it under a condition with an electric field intensity of at least 1 x 108 (W / cm2) at the point of convergence of the light and a pulse width of 1 ps or less. This pulse width is a condition under which a crack region can be formed only within the substrate while generating multiphoton absorption without causing unnecessary damage to the substrate. This generates a phenomenon of optical damage due to multiphoton absorption within the substrate. This optical damage induces thermal distortion within the substrate, thereby forming a crack region within it. The upper limit of electric field strength is 1 x 1012 (W / cm2), for example. The pulse width is preferably 1 ns to 200 ns, for example. The formation of a fissure region due to multiphoton absorption is described, for example, in Internal Marking of Glass Substrate by Solid-state Laser Harmonics, Proceedings of the 45^to Laser Material Processing Conference (December 1998), pp. 23-28.

The inventors determined the relationship between the intensity of the electric field and the magnitude of the crack by means of an experiment. The conditions for the experiment are as follows:

(A) Substrate: Pyrex glass (registered trademark) (having a thickness of 700 pm) (B) Laser

Light source: Nd: YAG laser pump semiconductor laser

Wavelength: 1064 nm

Point cross-sectional area of ​​laser light: 3.14 x 10-8 cm2

Oscillation mode: Q-switch pulse Repetition frequency: 100 kHz Pulse width: 30 ns

Output: output <1 mJ / pulse

Laser light quality: TEM00

Polarization characteristics: linear polarization (C) Light convergence lens

Transmittance with respect to the wavelength of laser light: 60% (D) Travel speed of a mounting table mounting the substrate: 100 mm / sec

Herein, the quality of laser light that is TEM00 indicates that the convergence of the light is so high that the light can converge to about the wavelength of laser light.

The Fi gure 7 is a graph showing the results of the above experiment. The abscissa indicates the maximum power density. Since laser light is pulse laser light, its electric field intensity is

ES 2 639 733 T3 represented by the maximum power density. The ordinate indicates the size of a part of the fissure (fissure point) formed within the substrate processed by a pulse of laser light. the fissure points meet, to form a fissure region. The size of a crack point refers to that part of the crack point dimensions that produces the maximum length. The data indicated with black circles in the graph refer to a case in which the light convergence lens (C) has a magnification of x 100 and a numerical aperture (NA) of 0.80. On the other hand, the data indicated with white circles in the graph refer to a case in which the light convergence lens (C) has a magnification of x 50 and a numerical aperture (NA) of 0.55. It is observed that crack points begin to occur within the substrate when the maximum power density reaches about 1011 (W / cm2) and become larger as the maximum power density decreases.

A mechanism by which the substrate is cut after formation of a crack region in laser processing according to the present embodiment will be explained with reference to Figures 8 to 11. As shown in Figure 8, substrate 1 is irradiated with laser light L while positioning the point of convergence of light P within substrate 1 in a condition where multiphoton absorption occurs, to form a fissure region 9 within it along the line along which the substrate is to be cut. The fissure region 9 is a region that includes one or a plurality of fissure points. The fissure region 9 forms a starting point region for cutting. As shown in Figure 9, the crack grows further while using the crack region 9 as the starting point (ie, using the starting point region for cutting as the starting point). As shown in Figure 10, the crack reaches the front face 3 and the rear face 21 of the substrate 1. As shown in Figure 11, the substrate 1 is broken, to be cut. The crack that reaches the front face and the back face of the substrate can naturally grow or grow when a force is applied to the substrate.

(2) Case where the modified region is a fused processed region

A substrate (for example, a semiconductor material such as silicon) is irradiated with laser light while a point of convergence of light is positioned within it under a condition with an electric field intensity of at least 1 x 108 (W / cm2 ) at the point of convergence of the light and a pulse width of 1 ps or less. As a consequence, the interior of the substrate is locally heated by multiphoton absorption. This heating forms a molten processed region within the substrate. The melt processed region refers to a region once melted and then re-solidified, a region just in the molten state, or a region in the process of re-solidification from its molten state, and can also be defined as a phase change region. or a region that has changed its crystal structure. The fused processed region can also be considered as a region in which a certain structure has been transformed into another structure in single crystal, amorphous and polycrystalline structures. That is, it refers to a region in which a single crystal structure has transformed into an amorphous structure, a region in which a single crystal structure has transformed into a polycrystalline structure, and a region in which a single crystal structure has transformed into a structure that includes an amorphous structure and a polycrystalline structure, for example. When the substrate is a silicon single crystal structure, the molten processed region is an amorphous silicon structure, for example. The upper limit of electric field strength is 1 x 1012 (W / cm2), for example. The pulse width is preferably 1 ns to 200 ns, for example.

Through an experiment, the inventors have verified that a fused processed region is formed within a silicon wafer.

The conditions for the experiment are as follows:

(A) Substrate: silicon wafer (having a thickness of 350 pm and an outside diameter of 10.2 cm (4 inches)) (B) Laser

Light source: Nd: YAG laser pump semiconductor laser

Wavelength: 1064 nm

Point cross-sectional area of ​​laser light: 3.14 x 10-8 cm2

Oscillation mode: Q-switch pulse Repetition frequency: 100 kHz Pulse width: 30 ns Output: 20 pJ / pulse

Laser light quality: TEM00

Polarization characteristics: linear polarization (C) Light convergence lens

Magnification: x50

AN: 0.55

Transmittance with respect to the wavelength of laser light: 60% (D) Travel speed of a mounting table mounting the substrate: 100 mm / sec

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Fig. 12 is a view showing a photograph of a cut section in a part of a silicon wafer cut by laser processing under the above-mentioned conditions. A fused processed region 13 is formed within a silicon wafer 11. The size of the melt processed region 13 formed under the above-mentioned conditions is about 100 µm in the thickness direction.

The fact that the fused processed region 13 is formed by multiphoton absorption will be explained. Figure 13 is a graph showing the relationships between laser light wavelength and transmittance within the silicon substrate. Herein, the respective reflective components on the front face side and the back face side of the silicon substrate are eliminated, whereby only the transmittance within it is depicted. The aforementioned relationships are shown in the cases where the thickness t of the silicon substrate is 50 pm, 100 pm, 200 pm, 500 pm and 1000 pm, respectively.

For example, it is observed that the laser light transmits through the silicon substrate by at least 80% at 1064 nm, where the wavelength of the Nd: YAG laser is located, when the silicon substrate has a thickness of 500 pm or less. Since the silicon wafer 11 shown in Figure 12 has a thickness of 350 pm, the melted processed region 13 due to multiphoton absorption is formed near the center of the silicon wafer, that is, in a separate part of the face. frontal by 175 pm. The transmittance in this case is 90% or greater with reference to a silicon wafer having a thickness of 200 pm, whereby the laser light is only slightly absorbed within the silicon wafer 11 and is transmitted substantially through the herself. This means that the fused processed region 13 is not formed by absorption of laser light within the silicon wafer 11 (ie, it is not formed by conventional heating with laser light), but by multiphoton absorption. The formation of a melted processed region by multiphoton absorption is described, for example, in Processing Characteristic Evaluation of Silicon by Picosecond Laser, pre-publication of the National Meeting of the Welding Society of Japan, No. 66 (April 2000), pp 72-73.

Herein, a fracture is generated in the transverse direction while using a fused processed region as a starting point, whereby the silicon wafer is cut when the fracture reaches the front face and the back face of the silicon wafer. . The fracture that reaches the front face and the back face of the silicon wafer can naturally grow or grow when a force is applied to the silicon wafer. The fracture grows naturally from the starting point region to cut to the front face and the back face of the silicon wafer in any of the cases where the fracture grows from the molten processed region in a molten state and in which the fracture grows from the molten processed region in the re-solidification process from the molten state. In either of these cases, the fused processed region is formed only within the silicon wafer. In the cutting section after cutting, the fused processed region is formed only within it as shown in Figure 12. When a fused processed region is formed within the substrate, unnecessary fractures that deviate from a line along the along which the substrate must be cut are difficult to occur at the time of fracture, which facilitates fracture control.

(3) Case in which the modified region is a region of refractive index change (not related to the invention).

A substrate (for example glass) is irradiated with laser light while a point of convergence of light is positioned within it in a condition with an electric field intensity of at least 1 x 108 (W / cm2) at the point of convergence light and a pulse width of 1 ns or less. When multiphoton absorption is generated within the substrate with a very short pulse width, the energy caused by multiphoton absorption is not transformed into thermal energy, so that a permanent structural change is induced such as ionic valence change, crystallization or orientation of polarization within the substrate, whereby a region of refractive index change is formed. The upper limit of electric field strength is 1 x 1012 (W / cm2), for example. The pulse width is preferably 1 ns or less, more preferably 1 ps or less, for example. The formation of a region of change of the refractive index by multiphoton absorption is described, for example, in Formation of Photoinduced Structure within Glass by Femtosecond Laser Irradiation, Proceedings of the 42^to Laser Materials Processing Conference (November 1997), pp. 105-111.

The cases of (1) to (3) are explained as modified regions formed by multiphoton absorption in the above. When a starting point region for cutting is formed as follows in view of the crystalline structure of the substrate, its cleavage property and the like, the substrate can be cut with less force and higher precision while using the point region. starting point for cutting as the starting point.

That is, in the case of a substrate made of a monocrystalline semiconductor having a diamond structure such as silicon, the starting point region for cutting is preferably formed in a direction along the (111) plane (first plane cleavage) or plane (110) (second cleavage plane). In the case of a substrate made of a III-V family compound semiconductor having a zinc-like structure such as GaAs, the starting point region for cutting is preferably formed in a direction along the plane ( 110). In the case of a substrate having a hexagonal crystal structure such as sapphire (Al2O3), a starting point region for cutting is preferably formed in a direction along plane (1120) (plane A) or plane (1100 ) (M-plane) while using the (0001) (C-plane) plane as the principal plane.

When the substrate is formed in a planar orientation along a direction to be formed with the point region of

ES 2 639 733 T3 starting for cutting (for example, in a direction along the plane (111) in the single crystal silicon substrate) or a direction orthogonal to the direction to be formed with the starting point region for cutting , the starting point region for cutting extending along the direction to be formed with the starting point region for cutting can be formed in the substrate easily and precisely with reference to the planar orientation.

Hereinafter, the present invention will be explained more specifically with reference to Examples.

Example 1

Example 1 of the substrate division method according to the present invention will be explained. Example 1 relates to a case where substrate 1 is a silicon wafer (having a thickness of 350 pm and an outer diameter of (10.2 cm (4 inches)) (substrate 1 will be referred to as Hereinafter the semiconductor substrate 1 in Example 1), while the front face 3 of the semiconductor substrate 1 is formed with a plurality of functional devices in a device manufacturing process.

First, before explaining a step of forming a starting point region for cutting within the semiconductor substrate 1, a laser processing apparatus employed in the step of forming a starting point region for cutting will be explained. referring to Figure 14. Figure 14 is a schematic diagram of laser processing apparatus 100.

The laser processing apparatus 100 comprises a laser light source 101 for generating laser light L; A laser light source controller 102 for controlling the laser light source 101 to regulate the output, pulse width, etc., of the laser light L and the like; a dichroic mirror 103, arranged to change the orientation of the optical axis of the laser light L by 90 ° having a function of reflecting the laser light L; a light convergence lens 105 for converging the laser light L reflected by the dichroic mirror 103; a mounting table 107 for mounting a semiconductor substrate 1 irradiated with the converging laser light L by the light converging lens 105; an X-axis stage 109 for moving the mounting table 107 in the direction of the X-axis; a Y-axis stage 111 for moving the mounting table 107 in the Y-axis direction orthogonal to the X-axis direction; a Z-axis step 113 for moving the mounting board 107 in the Z-axis direction orthogonal to the X and Y-axis directions; and a stage controller 115 to control the movement of these three stages 109, 111 and 113.

The direction of the Z axis is a direction orthogonal to the front face 3 of the semiconductor substrate 1 and thus becomes the focal depth direction of the laser light L incident on the semiconductor substrate 1. Therefore, move the stage 113 of the Z axis in the direction of the Z axis can position the convergence point of the light P of the laser light L inside the semiconductor substrate 1. This movement of the point of convergence of the light P in the direction of the X (Y) axis is effected by moving the semiconductor substrate 1 in the direction of the X (Y) axis by step 109 (111) of the X (Y) axis.

The laser light source 101 is a Nd: YAG laser that generates pulsed laser light. Other types of lasers usable as the 101 laser light source include the Nd: YVO4 laser, Nd: YLF laser, and titanium sapphire laser. For the formation of a fused processed region, the Nd: YAG laser, Nd: YVO4 laser and Nd: YLF laser are preferably employed. Although pulse laser light is used to process semiconductor substrate 1 in Example 1, continuous wave laser light can be used as long as multiphoton absorption can occur.

The laser processing apparatus 100 further comprises an observation light source 117 for generating a visible light beam to irradiate the semiconductor substrate 1 mounted on the mounting table 107 and a visible light beam splitter 119 arranged on the same optical axis. than that of the dichroic mirror 103 and the light convergence lens 105. The dichroic mirror 103 is arranged between the beam splitter 119 and the light convergence lens 105. The beam splitter 119 has a function of reflecting approximately half of a visual light beam and transmitting the remaining half therethrough, and is arranged so as to change the orientation of the optical axis of the visual light beam by 90 °. About one-half of the visible light beam generated from observation light source 117 is reflected by beam splitter 119, and thus, the reflected visible light beam is transmitted through dichroic mirror 103 and convergence lens 105 of light, to illuminate the front face 3 of the semiconductor substrate 1 including the line 5 along which the substrate must be cut and the like.

The laser processing apparatus 100 further comprises an image pickup device 121 and an imaging lens 123 which are arranged in the same optical axis as that of the beam splitter 119, the dichroic mirror 103 and the convergence lens 105 of the light. An example of the image acquisition device 121 is a CCD camera. The reflected light from the visual light beam that has illuminated the front face 3 including the line 5 along which the substrate must be cut and the like is transmitted through the light convergence lens 105, the dichroic mirror 103, and the beam splitter 119 and forms an image by means of the imaging lens 123, while the image thus formed is captured by the image pickup device 121, to produce imaging data.

The laser processing apparatus 100 further comprises an imaging data processor 125 for inputting the imaging data emitted from the imaging device 121, a

ES 2 639 733 T3 global controller 127 for controlling the laser processing apparatus 100 as a whole and a monitor 129. According to the imaging data, the imaging data processor 125 calculates the focal point data for positioning the focal point of the visible light generated from the observation light source 117 on the front face 3. According to the focal point data, the stage controller 115 controls the movement of the Z-axis stage 113 so that the visible light focal point is positioned on the front face 3. Therefore, the stage processor 125 Imaging data functions as an autofocus unit. Also, according to the imaging data, the imaging data processor 125 calculates the imaging data such as an enlarged image of the front face 3. The image data is sent to the global controller 127 , subjected to various types of processing therein, and then sent to monitor 129. As a result, an enlarged image is displayed on monitor 129.

Data from stage controller 115, image data from imaging data processor 125 and the like are input to global controller 127. According to this data also, global controller 127 regulates laser light source controller 102 , observation light source 117 and stage controller 115, thereby controlling laser processing apparatus 100 as a whole. Therefore, the global controller 127 functions as a control unit.

With reference to Figures 14 and 15, a step of forming a starting point region for cutting will be explained in the case using the aforementioned laser processing apparatus 100. Figure 15 is a flow chart for explaining the step of forming a starting point region for cutting.

The light absorption characteristics of the semiconductor substrate 1 are determined by a spectrophotometer or the like, which is not shown. According to the measurement results, a laser light source 101 is chosen which generates laser light L having a wavelength at which the semiconductor substrate 1 is transparent or shows low absorption (S101). Subsequently, the thickness of the semiconductor substrate 1 is measured. According to the result of the measurement of the thickness and the refractive index of the semiconductor substrate 1, the amount of movement of the semiconductor substrate 1 in the direction of the Z axis is determined (S103). This is an amount of movement of the semiconductor substrate 1 in the direction of the Z axis with reference to the convergence point of the light P of the laser light L positioned on the front face 3 of the semiconductor substrate 1 so that the convergence point of the light P from the laser light L is positioned within the semiconductor substrate 1. This amount of movement will be input to the global controller 127.

The semiconductor substrate 1 is mounted on the mounting table 107 of the laser processing apparatus 100. Subsequently, visible light is generated from the observation light source 117, to illuminate the semiconductor substrate 1 (S105). The front illuminated face 3 of the semiconductor substrate 1 including the line 5 along which the substrate is to be cut is captured by the image pickup device 121. The line 5 along which the substrate must be cut is a desirable virtual line to cut the semiconductor substrate 1. Herein, in order to avoid obtaining semiconductor chips by dividing the semiconductor substrate 1 into the functional devices formed on its front face 3, the line 5 along which the substrate is to be cut is fixed as a grid running between the functional devices adjacent to each other. The imaging data captured by the imaging device 121 is sent to the imaging data processor 125. According to the imaging data, the imaging data processor 125 calculates said focal point data in which the focal point of the visible light of the observation light source 117 is positioned on the front face 3 (S107).

The focal point data is sent to stage controller 115. According to the focal point data, the stage controller 115 moves the Z-axis stage 113 in the direction of the Z-axis (S109). As a consequence, the visible light focal point of the observation light source 117 is located on the front face 3 of the semiconductor substrate 1. According to the imaging data, the imaging data processor 125 calculates the enlarged imaging data of the front face 3 of the semiconductor substrate 1 which includes the line 5 along which the substratum. The enlarged image data is sent to the monitor 129 via the global controller 127, whereby an enlarged image of the line 5 along which the substrate is to be cut and its vicinity is displayed on the monitor 129.

The momentum data determined in step S103 has been input into the global controller 127 beforehand and sent to the stage controller 115. According to the momentum data, the stage controller 115 causes the Z-axis stage 113 to move the substrate 1 in the direction of the Z-axis to a position where the convergence point of the light P of the light laser L is positioned within the semiconductor substrate 1 (S111).

Subsequently, the laser light L is generated from the laser light source 101, to irradiate the line 5 along which the substrate is to be cut at the front face 3 of the semiconductor substrate 1. Next, the X-axis stage 109 and the Y-axis stage 111 move along line 5 along which the substrate is to be cut, to form a fused processed region on line 5 along which the substrate must be cut, thereby forming a starting point region for cutting within the semiconductor substrate 1 at line 5 along which the substrate must be cut (S113).

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This completes the step of forming a starting point region for cutting, thereby forming the starting point region for cutting within the semiconductor substrate 1. When the starting point region for cutting is formed within the semiconductor substrate 1, a fracture is generated in the thickness direction of the semiconductor substrate 1 from the starting point region for cutting which acts as a starting point naturally or with a relatively small force exerted on it.

In Example 1, the starting point region for cutting is formed in a position near the side of the front face 3 within the semiconductor substrate 1 in the above-mentioned step of forming a starting point region for cutting and is generates a fracture in the thickness direction of the semiconductor substrate 1 from the starting point region for cutting which acts as the starting point. FIG. 16 is a view showing the semiconductor substrate 1 after the starting point region for cutting is formed. As shown in Figure 16, the fractures 15 generated from the starting point region for cutting that acts as a starting point are formed as a grid along the lines to be cut and reach only the front face 3 of the substrate. semiconductor 1 but not its back face 21. That is, the fractures 15 generated in the semiconductor substrate 1 separate a plurality of functional devices 19 formed as a matrix on the front face of the semiconductor substrate 1 from each other. The cutting surfaces of the semiconductor substrate 1 cut by the fractures 15 are in close contact with each other.

Herein, the starting point region for cutting is formed in a position near the side of the front face 3 within the semiconductor substrate 1 means that a modified region such as a fused processed region that constitutes a starting point region Part for cutting is formed to move from the center position in the direction of the thickness of the semiconductor substrate 1 (i.e., half thickness position) towards the front face 3. That is, it refers to a case where the center position of the width of the modified region in the thickness direction of the semiconductor substrate 1 is shifted towards the front face 3 from the center position in the thickness direction of the semiconductor substrate 1 and it is not limited to the case where the entire modified region is located on the side of the front face 3 from the central position in the thickness direction of the semiconductor substrate 1.

The step of rectifying the semiconductor substrate 1 will be explained with reference to Figures 17 to 21. Figures 17 to 21 are views for explaining the respective steps including the step of rectifying the semiconductor substrate. In Example 1, the semiconductor substrate 1 is thinned from a thickness of 350 µm to a thickness of 50 µm.

As shown in Figure 17, a protective film 20 is attached to the front face 3 of the semiconductor substrate after the starting point region for cutting is formed. The protective film 20 is used to protect the functional devices 19 formed on the front face 3 of the semiconductor substrate 1 and which hold the semiconductor substrate 1. Subsequently, as shown in Figure 18, the back face 21 of the semiconductor substrate 1 is subjected to surface grinding and then etching, whereby the semiconductor substrate 1 is thinned to a thickness of 50 pm. As a consequence, that is, due to the grinding of the rear face 21 of the semiconductor substrate 1, the rear face 21 reaches the fractures 15 generated from the starting point region for cutting which acts as a starting point, whereby the substrate semiconductor 1 is divided into semiconductor chips 25 having the respective functional devices 19. Examples of chemical etching include wet etching (HF ^ HNO3) and plasma etching (HBrCl2).

Then, as shown in Figure 19, an expansion film 23 is attached to cover the back faces of all semiconductor chips 25. Next, as shown in Figure 20, the protective film 20 attached to cover the functional devices of all semiconductor chips 25 is detached. Subsequently, as shown in Figure 21, the expansion film 23 is expanded, so that the semiconductor chips 25 are separated from each other, and a circular metal suction plate 27 collects the semiconductor chips 25.

As explained above, the substrate splitting method according to Example 1 can rectify the rear face 21 of the semiconductor substrate 1 after forming the functional devices 19 on the front face 3 of the semiconductor substrate 1 in the manufacturing process of the device. Also, due to the following effects respectively exhibited by the step of forming a starting point region for cutting and the step of rectifying the semiconductor substrate, the semiconductor chips 25 thinned to respond to the smaller size of semiconductor devices can be obtained with a favorable performance.

That is, the step of forming a starting point region for cutting can avoid unnecessary fractures and deviating melting from a desirable line along which the substrate must be cut to cut the semiconductor substrate 1 and thus avoid unnecessary fractures and melting occur in the semiconductor chips 25 obtained by dividing the semiconductor substrate 1.

The step of forming a starting point region for cutting does not melt the front face 3 of the semiconductor substrate 1 at the line along which the substrate is to be cut and thus can narrow the gap between the functional devices 19 adjacent to each other, thus making it possible to increase the number of semiconductor chips 25 separated from a semiconductor substrate 1.

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On the other hand, the step of grinding the semiconductor substrate subjects the rear face 21 of the semiconductor substrate 1 to surface grinding in such a way that the semiconductor substrate 1 reaches a predetermined thickness after the starting point region for cutting within is formed. semiconductor substrate 1. Herein, even if the back face 21 reaches the fractures 15 generated from the starting point region for cutting acting as the starting point, the cutting surfaces of the semiconductor substrate 1 cut by the fractures 15 are in close contact. with each other, whereby the semiconductor substrate 1 can be prevented from chipping and cracking due to surface grinding. Therefore, the semiconductor substrate 1 can be made thinner and divided, while preventing chipping and cracking from occurring.

The close contact of the cutting surfaces on the semiconductor substrate 1 is also effective in preventing grinding dust caused by surface grinding from entering the fractures 15 and prevents contamination of the semiconductor chips 25 obtained by dividing the semiconductor substrate 1 with grinding powder. Similarly, the close contact of the cutting surfaces on the semiconductor substrate 1 is effective to reduce detachment of the semiconductor chips 25 caused by surface grinding compared to the case where the semiconductor chips 25 are spaced from each other. That is, as the protective film 20, one with a low holding power can be used.

Since the back face 21 of the semiconductor substrate 1 is subjected to chemical etching, the back faces of the semiconductor chips 25 obtained by dividing the semiconductor substrate 1 can be made smoother. Furthermore, since the cutting surfaces of the semiconductor substrate 1 caused by the fractures 15 generated from the starting point region for cutting acting as a starting point are in close contact with each other, only the edge portions of the surfaces of cut on the back face side are selectively etched as shown in Figure 22, thereby forming the chamfers 29. Therefore, the transverse breaking strength of the semiconductor chips 25 obtained by dividing the semiconductor substrate 1 can be improved, and chipping and cracking can be prevented from occurring in the semiconductor chips 25.

The relationship between the semiconductor chip 25 and the fused processed region 13 after the step of rectifying the semiconductor substrate includes those shown in Figures 23A through 25B. The semiconductor chips 25 shown in these drawings have their respective effects explained below, and therefore can be used in accordance with various purposes. Figures 23A, 24A and 25A show the case in which the fracture 15 reaches the front face 3 of the semiconductor substrate 1 before the step of rectifying the semiconductor substrate, while Figures 23B, 24B and 25b show the case in which the fracture 15 does not reach the front face 3 of the semiconductor substrate 1 before the step of grinding the semiconductor substrate. Even in the case of Figures 23B, 24B and 25B, the fracture 15 reaches the front face 3 of the semiconductor substrate 1 after the step of rectifying the semiconductor substrate.

In the semiconductor chip 25 having the fused processed region 13 that remains within the contact surface as shown in Figures 23A and 23B, the cutting surface is protected by the fused processed region 13, thereby improving resistance to the transverse breakage of the semiconductor chip 25.

The semiconductor chip 25 in which the fused processed region 13 does not remain within the cutting surface as shown in the Figures. 24A and 24B is effective in the case where the fused processed region 13 does not favorably influence the semiconductor device.

In the semiconductor chip 25 in which the fused processed region 13 remains in an edge part on the back face side of the cutting surface as shown in Figures 25A and 25B, the edge part is protected by the region 13 processed melt, whereby chipping and cracking can be prevented from occurring in the edge part as in the case where the edge part of the semiconductor chip 25 is chamfered.

The rectilinearity of the cutting surface obtained after the step of grinding the semiconductor substrate is further improved in the case where the fracture 15 does not reach the front face 3 of the semiconductor substrate 1 before the step of grinding the semiconductor substrate as shown. in Figures 23B, 24B and 25B than in the case where the fracture 15 reaches the front face 3 of the semiconductor substrate 1 before the step of grinding the semiconductor substrate as shown in Figures 23A, 24A and 25A.

Whether or not the fracture reaches the front face 3 of the semiconductor substrate 1 depends not only on the depth of the fused processed region 13 from the front face 3, but also on the size of the fused processed region 13. That is, when the fused processed region 13 becomes smaller, the fracture 15 does not reach the front face 3 of the semiconductor substrate 1 even if the depth of the fused processed region 13 from the front face 3 is small. The size of the fused processed region 13 can be controlled by the output of the pulse laser light in the step of forming a starting point region for cutting, for example, and becomes larger and smaller as the output of pulse laser light is higher and lower, respectively.

In view of a predetermined thickness of the semiconductor substrate 1 thinned in the step of grinding the semiconductor substrate, it is preferred that the marginal parts (outer peripheral parts) of the semiconductor substrate 1 are rounded at least to the predetermined thickness by beveling beforehand (for example , before the stage of

ES 2 639 733 T3 form a starting point region for cutting). Figures 26A and 26B are respective sectional views of a marginal part of the semiconductor substrate 1 before and after the step of rectifying the semiconductor substrate according to Example 1. The thickness of the semiconductor 1 shown in Figure 26A before the step of rectifying the semiconductor substrate is 350 pm, while the thickness of the semiconductor 1 shown in Figure 26B after the step of rectifying the semiconductor substrate is 50 pm . As shown in Figure 26A, a plurality of rounded portions (seven here) are formed in advance in the marginal part of the semiconductor substrate 1 by beveling with a thickness of 50 pm each, that is, the marginal part of the semiconductor substrate 1 has a wavy shape. As a consequence, the marginal part of the semiconductor substrate 1 after the step of rectifying the semiconductor substrate 1 reaches a rounded state by beveling as shown in Figure 26B, whereby chipping and cracking can be prevented from occurring in the marginal part, and handling can be facilitated due to improved mechanical strength.

Industrial applicability

As explained above, the present invention can thin and split the substrate while preventing chipping and cracking from occurring.