Patent Grant
8263479
The present invention relates to a method of cutting a semiconductor substrate used for cutting a semiconductor substrate in semiconductor device manufacturing processes and the like.
As a conventional technique of this kind, Japanese Patent Application Laid-Open Nos. 2002-158276 and 2000-104040 disclose the following technique. First, an adhesive sheet is bonded to the rear face of a semiconductor wafer by way of a die-bonding resin layer, and the semiconductor wafer is cut with a blade while in a state where the semiconductor wafer is held on the adhesive sheet, so as to yield semiconductor chips. Subsequently, when picking up the semiconductor chips on the adhesive sheet, the die-bonding resin is peeled off together with the individual semiconductor chips. This can bond the semiconductor chips onto a lead frame while omitting the step of applying an adhesive to the rear faces of semiconductor chips, and so forth.
When cutting the semiconductor wafer held on the adhesive sheet with the blade in the above-mentioned technique, however, the die-bonding resin layer existing between the semiconductor wafer and adhesive sheet is needed to be cut surely without cutting the adhesive sheet. Therefore, particular care must be taken when cutting a semiconductor wafer with a blade in such a case.
In view of such circumstances, it is an object of the present invention to provide a method of cutting a semiconductor substrate which can efficiently cut a semiconductor substrate with a die-bonding resin layer.
For achieving the above-mentioned object, in one aspect, the present invention provides a method of cutting a semiconductor substrate, the method comprising the steps of irradiating a semiconductor substrate having a sheet bonded thereto by way of a die-bonding resin layer with laser light while locating a light-converging point within the semiconductor substrate, so as to form a modified region caused by multiphoton absorption within the semiconductor substrate, and causing the modified region to form a part which is intended to be cut; and expanding the sheet after the step of forming the part which is intended to be cut, so as to cut the semiconductor substrate and die-bonding resin layer along the part which is intended to be cut.
This method of cutting a semiconductor substrate irradiates the semiconductor substrate with laser light while locating a light-converging point within the semiconductor substrate, and generates a phenomenon of multiphoton absorption within the semiconductor substrate, so as to form a modified region, whereby the modified region can form a part which is intended to be cut within the semiconductor substrate along a desirable line to cut for cutting the semiconductor substrate. When the part which is intended to be cut is formed within the semiconductor substrate as such, a relatively small force can start fractures in the thickness direction of the semiconductor substrate from the part which is intended to be cut. Therefore, when the sheet bonded to the semiconductor substrate is expanded, the semiconductor substrate can be cut with a high precision along the part which is intended to be cut. Here, opposing cut sections of the cut semiconductor substrate are initially in close contact with each other, but are separated from each other as the sheet expands, whereby the die-bonding resin layer existing between the semiconductor substrate and the sheet is also cut along the part which is intended to be cut. Therefore, the semiconductor substrate and die-bonding resin layer can be cut along the part which is intended to be cut much more efficiently than in the case where the semiconductor substrate and die-bonding resin layer are cut with a blade while leaving the sheet. Also, since the opposing cut sections of the cut semiconductor substrate are initially in close contact with each other, the cut pieces of the semiconductor substrate and cut pieces of the die-bonding resin layer have substantially the same outer form, whereby the die-bonding resin is prevented from protruding from the cut sections of the semiconductor substrate.
In another aspect, the present invention provides a method of cutting a semiconductor substrate, the method comprising the steps of irradiating a semiconductor substrate having a sheet bonded thereto by way of a die-bonding resin layer with laser light while locating a light-converging point within the semiconductor substrate under a condition with a peak power density of at least 1×108 (W/cm2) at the light-converging point and a pulse width of 1 μs or less, so as to form a modified region including a molten processed region within the semiconductor substrate, and causing the modified region including the molten processed region to form a part which is intended to be cut; and expanding the sheet after the step of forming the part which is intended to be cut, so as to cut the semiconductor substrate and die-bonding resin layer along the part which is intended to be cut.
This method of cutting a semiconductor substrate irradiates the semiconductor substrate with laser light while locating a light-converging point within the semiconductor substrate under a condition with a peak power density of at least 1×108 (W/cm2) at the light-converging point and a pulse width of 1 μs or less. Therefore, the inside of the semiconductor substrate is locally heated by multiphoton absorption. This heat forms a molten processed region within the semiconductor substrate. Since the molten processed region is an example of the above-mentioned modified region, the semiconductor substrate and die-bonding resin layer can also be cut along the part which is intended to be cut much more efficiently in this method of cutting a semiconductor substrate than in the case where the semiconductor substrate and die-bonding resin layer are cut with a blade while leaving the sheet.
In still another aspect, the present invention provides a method of cutting a semiconductor substrate, the method comprising the steps of irradiating a semiconductor substrate having a sheet bonded thereto by way of a die-bonding resin layer with laser light while locating a light-converging point within the semiconductor substrate, so as to form a modified region within the semiconductor substrate, and causing the modified region to form a part which is intended to be cut; and expanding the sheet after the step of forming the part which is intended to be cut, so as to cut the semiconductor substrate and die-bonding resin layer along the part which is intended to be cut. The modified region may be a molten processed region.
Because of the same reason as with the above-mentioned methods of cutting a semiconductor substrate, the semiconductor substrate and die-bonding resin layer can also be cut along the part which is intended to be cut much more efficiently in this method of cutting a semiconductor substrate than in the case where the semiconductor substrate and die-bonding resin layer are cut with a blade whine leaving the sheet. The modified region may be formed by multiphoton absorption or other causes.
In still another aspect, the present invention provides a method of cutting a semiconductor substrate, the method comprising the steps of irradiating a semiconductor substrate having a sheet bonded thereto with laser light while locating a light-converging point within the semiconductor substrate, so as to form a modified region within the semiconductor substrate, and causing the modified region to form a part which is intended to be cut; and expanding the sheet after the step of forming the part which is intended to be cut, so as to cut the semiconductor substrate along the part which is intended to be cut.
This method of cutting a semiconductor substrate can cut the semiconductor substrate along the part which is intended to be cut much more efficiently than in the case where the semiconductor substrate is cut with a blade while leaving the sheet.
In the step of forming the part which is intended to be cut in any of the above-mentioned methods of cutting a semiconductor substrate in accordance with the present invention, a fracture may be caused to reach a front face of the semiconductor substrate on the laser light entrance side from the part which is intended to be cut acting as a start point, a fracture may be caused to reach a rear face of the semiconductor substrate on the side opposite from the laser light entrance side from the part which is intended to be cut acting as a start point, or a fracture may be caused to reach the front face of the semiconductor substrate on the laser light entrance side and the rear face on the side opposite therefrom from the part which is intended to be cut acting as a start point.
In still another aspect, the present invention provides a method of cutting a semiconductor substrate, the method comprising the steps of irradiating a semiconductor substrate having a sheet bonded thereto by way of a die-bonding resin layer with laser light while locating a light-converging point within the semiconductor substrate, so as to form a modified region caused by multiphoton absorption within the semiconductor substrate, and causing the modified region to form a part which is intended to be cut; generating a stress in the semiconductor substrate along the part which is intended to be cut after the step of forming the part which is intended to be cut, so as to cut the semiconductor substrate along the part which is intended to be cut; and expanding the sheet after the step of cutting the semiconductor substrate, so as to cut the die-bonding resin layer along a cut section of the semiconductor substrate.
The modified region caused by multiphoton absorption can form a part which is intended to be cut within the semiconductor substrate along a desirable line to cut for cutting the semiconductor substrate in this method of cutting a semiconductor substrate as well. Therefore, when a stress is generated in the semiconductor substrate along the part which is intended to be cut, the semiconductor substrate can be cut with a high precision along the part which is intended to be cut. Then, when the sheet bonded to the semiconductor substrate is expanded, opposing cut sections of the cut semiconductor substrate are separated from each other from their close contact state as the sheet expands, whereby the die-bonding resin layer existing between the semiconductor substrate and sheet is cut along the cut sections of the semiconductor substrate. Therefore, the semiconductor substrate and die-bonding resin layer can be cut along the part which is intended to be cut much more efficiently than in the case where the semiconductor substrate and die-bonding resin layer are cut with a blade while leaving the sheet. Also, since the opposing cut sections of the cut semiconductor substrate are initially in close contact with each other, the cut pieces of the semiconductor substrate and cut pieces of the die-bonding resin layer have substantially the same outer form, whereby the die-bonding resin is prevented from protruding from the cut sections of the semiconductor substrate.
In still another aspect, the present invention provides a method of cutting a semiconductor substrate, the method comprising the steps of irradiating a semiconductor substrate having a sheet bonded thereto by way of a die-bonding resin layer with laser light while locating a light-converging point within the semiconductor substrate under a condition with a peak power density of at least 1×108 (W/cm2) at the light-converging point and a pulse width of 1 μs or less, so as to form a modified region caused by multiphoton absorption within the semiconductor substrate, and causing the modified region to form a part which is intended to be cut; generating a stress in the semiconductor substrate along the part which is intended to be cut after the step of forming the part which is intended to be cut, so as to cut the semiconductor substrate along the part which is intended to be cut; and expanding the sheet after the step of cutting the semiconductor substrate, so as to cut the die-bonding resin layer along a cut section of the semiconductor substrate.
In still another aspect, the present invention provides a method of cutting a semiconductor substrate, the method comprising the steps of irradiating a semiconductor substrate having a sheet bonded thereto by way of a die-bonding resin layer with laser light while locating a light-converging point with the semiconductor substrate, so as to form a modified region within the semiconductor substrate, and causing the modified region to form a part which is intended to be cut; generating a stress in the semiconductor substrate along the part which is intended to be cut after the step of forming the part which is intended to be cut, so as to cut the semiconductor substrate along the part which is intended to be cut; and expanding the sheet after the step of cutting the semiconductor substrate, so as to cut the die-bonding resin layer along a cut section of the semiconductor substrate. The modified region may be a molten processed region.
Because of the same reason as with the above-mentioned methods of cutting a semiconductor substrate, the semiconductor substrate and die-bonding resin layer can also be cut along the part which is intended to be cut much more efficiently in this method of cutting a semiconductor substrate than in the case where the semiconductor substrate and die-bonding resin layer are cut with a blade while leaving the sheet.
In still another aspect, for achieving the above-mentioned object, the present invention provides a method of cutting a semiconductor substrate having a front ace formed with a functional device along a line to cut, the method comprising the steps of irradiating the semiconductor substrate with laser light while using a rear face of the semiconductor substrate as a laser light entrance surface and locating a light-converging point within the semiconductor substrate, so as to form a modified region, and causing the modified region to form a cutting start region within the semiconductor substrate inside of the laser light entrance surface by a predetermined distance along the line to cut; attaching an expandable holding member to the rear face of the semiconductor substrate by way of a die-bonding resin layer after forming the cutting start region; and expanding the holding member after attaching the holding member, so as to cut the semiconductor substrate and die-bonding resin layer along the line to cut.
The object to be processed in this method of cutting a semiconductor substrate is a semiconductor substrate having the front face formed with a functional device. Using the rear face of such a semiconductor substrate as a laser light entrance surface, the semiconductor substrate is irradiated with laser light while locating a light-converging point within the semiconductor substrate, so as to generate multiphoton absorption or optical absorption equivalent thereto, thereby forming a cut start region caused by a modified region within the semiconductor substrate along the line to cut. Here, the rear face of the semiconductor substrate is used as the laser light entrance surface, since there will be a fear of the functional device inhibiting the laser light from entering if the front face is employed as the laser light entrance surface. When the cutting start region is formed within the semiconductor substrate as such, a fracture can start from the cutting start region naturally or with a relatively small force applied thereto, so as to reach the front and rear faces of the semiconductor substrate. Therefore, when an expandable holding member is attached to the rear face of the semiconductor substrate by way of a die-bonding resin layer and expanded after forming the cut start region, cut sections of the semiconductor substrate cut along the lines to cut are separated from each other from their close contact state as the holding member expands. As a consequence, the die-bonding resin layer existing between the semiconductor substrate and holding member is also cut along the line to cut. Therefore, the semiconductor substrate and die-bonding resin layer can be cut along the line to cut much more efficiently than in the case of cutting with a blade or the like. Also, since the opposing cut sections of the cut semiconductor substrate are initially in close contact with each other, the cut pieces of the semiconductor substrate and cut pieces of the die-bonding resin layer have substantially the same outer form, whereby the die-bonding resin is prevented from protruding from the cut sections of the semiconductor substrate.
The functional device refers to semiconductor operating layers formed by crystal growth, light-receiving devices such as photodiodes, light-emitting devices such as laser diodes, and circuit devices formed as circuits, for example.
Preferably, the method further comprises the step of grinding the rear face of the semiconductor substrate such that the semiconductor substrate attains a predetermined thickness before forming the cutting start region. When the rear face of the semiconductor substrate is ground beforehand such that the semiconductor substrate attains a predetermined thickness as such, the semiconductor substrate and die-bonding resin layer can be cut along the line to cut with a higher precision. Here, the grinding encompasses cutting, polishing, chemical etching, etc.
The modified region may include a molten processed region. When the object to be processed is a semiconductor substrate, a molten processed region may be formed upon irradiation with laser light. Since the molten processed region is an example of the above-mentioned modified region, the semiconductor substrate can be cut easily, whereby the semiconductor substrate and die-bonding resin layer can efficiently be cut along the line to cut in this case as well.
When forming the cutting start region in the above-mentioned methods of cutting a semiconductor substrate in accordance with the present invention, a fracture may be caused to reach the front face of the semiconductor substrate from the cutting start region acting as a start point, a fracture may be caused to reach the rear face of the semiconductor substrate from the cutting start region acting as a start point, or a fracture may be caused to reach the front and rear faces of the semiconductor substrate from the cutting start region acting as a start point.
In the following, preferred embodiments of the method of cutting a semiconductor substrate in accordance with the present invention will be explained in detail with reference to drawings.
The method of cutting a semiconductor substrate in accordance with an embodiment irradiates a semiconductor substrate with laser light while locating a light-converging point within the semiconductor substrate, so as to form a modified region caused by multiphoton absorption within the semiconductor substrate, and causes the modified region to form a part which is intended to be cut. Therefore, before explaining the method of cutting a semiconductor substrate in accordance with this embodiment, a laser processing method carried out for forming the part which is intended to be cut will be explained mainly in terms of multiphoton absorption.
A material becomes optically transparent when its absorption bandgap EG is greater than photon energy hv. Hence, a condition under which absorption occurs in the material is hv>EG. However, even when optically transparent, the material generates absorption under a condition of nhv>EG (where n=2, 3, 4, . . . ) if the intensity of laser light becomes very high. This phenomenon is known as multiphoton absorption. In the case of pulsed waves, the intensity of laser light is determined by the peak power density (W/cm2) of laser light at a light-converging point. The multiphoton absorption occurs under a condition where the peak power density is 1×108 (W/cm2) or greater, for example. The peak power density is determined by (energy of laser light at the light-converging point per pulse)/(beam spot cross-sectional area of laser light×pulse width). In the case of continuous waves, the intensity of laser light is determined by the field intensity (W/cm2) of laser light at the light-converging point.
The principle of the laser processing method in accordance with an embodiment using such multiphoton absorption will be explained with reference to
As shown in
The laser light L is relatively moved along the line to cut 5 (i.e., along the direction of arrow A), so as to shift the light-converging point P along the line to cut 5. As a consequence, the modified region 7 is formed along the line to cut 5 only within the semiconductor substrate 1 as shown in
When a start point exists in an area for cutting the semiconductor substrate 1, the semiconductor substrate 1 fractures from this start point, whereby the semiconductor substrate 1 can be cut with a relatively small force as shown in
There seem to be the following two ways of cutting a semiconductor substrate from a cutting start region acting as a start point. The first case is where an artificial force is applied to the semiconductor substrate after the cutting start region is formed, so that the semiconductor substrate fractures from the cutting start region acting as a start point, and thus is cut. This is the cutting in the case where the semiconductor substrate has a large thickness, for example. Applying an artificial force refers to exerting a bending stress or shear stress to the semiconductor substrate along the cutting start region, or generating a thermal stress by imparting a temperature difference to the semiconductor substrate, for example. The other case is where the forming of the cutting start region causes the semiconductor substrate to fracture naturally in its cross-sectional direction (thickness direction) from the cutting start region acting as a start point, thereby cutting the semiconductor substrate. This becomes possible if the cutting start region is formed by one row of the modified region when the semiconductor substrate has a small thickness, or if the cutting start region is formed by a plurality of rows of the modified region in the thickness direction when the semiconductor substrate has a large thickness. Even in this naturally fracturing case, fractures do not extend onto the front face at a portion corresponding to an area not formed with the cutting start region in the part which is intended to be cut, so that only the portion corresponding to the area formed with the cutting start region can be cleaved, whereby cleavage can be controlled well. Such a cleaving method with a favorable controllability is quite effective, since semiconductor substrates such as silicon wafers have recently been apt to decrease their thickness.
An example of the modified region formed by multiphoton absorption in this embodiment is a molten processed region which will be explained in the following.
A semiconductor substrate is irradiated with laser light while locating a light converging point therewithin under a condition with a field intensity of at least 1×108 (W/cm2) at the light-converging point and a pulse width of 1 μs or less. As a consequence, the inside of the object is locally heated by multiphoton absorption. This heating forms a molten processed region within the object. The molten processed region encompasses regions once molten and then re-solidified, regions just in a molten state, and regions in the process of being re-solidified from the molten state, and can also be referred to as a region whose phase has changed or a region whose crystal structure has changed. The molten processed region may also be referred to as a region in which a certain structure changes to another structure among monocrystal, amorphous, and polycrystal structures. For example, it means a region having changed from the monocrystal structure to the amorphous structure, a region having changed from the monocrystal structure to the polycrystal structure, or a region having changed from the monocrystal structure to a structure containing amorphous and polycrystal structures. When the object to be processed is of a silicon monocrystal structure, the molten processed region is an amorphous silicon structure, for example. The upper limit of field intensity is 1×1012 (W/cm2), for example. The pulse width is preferably 1 to 200 ns, for example.
By an experiment, the inventors verified that a molten processed region was formed within a silicon wafer. The following are conditions of the experiment.
(A) Object to be processed: silicon wafer (with a thickness of 350 μm and an outer diameter of 4 inches)
(B) Laser
(C) Condenser lens
(D) Moving rate of the mount table mounting the object: 100 mm/sec
The fact that the molten processed region 13 is formed by multiphoton absorption will now be explained.
For example, at the Nd:YAG laser wavelength of 1064 nm, the laser light appears to be transmitted through the silicon substrate by at least 80% when the silicon substrate has a thickness of 500 μm or less. Since the silicon wafer 11 shown in
A fracture is generated in a silicon wafer from a cutting start region formed by a molten processed region, acting as a start point, toward a cross section, and reaches the front and rear faces of the silicon wafer, whereby the silicon wafer is cut. The fracture reaching the front and rear faces of the silicon wafer may grow naturally or as a force is applied to the silicon wafer. The fracture naturally growing from the cutting start region to the front and rear faces of the silicon wafer encompasses a case where the fracture grows from a state where the molten processed region forming the cutting start region is molten and a case where the fracture grows when the molten processed region forming the cutting start region is re-solidified from the molten state. In either case, the molten processed region is formed only within the silicon wafer, and thus is present only within the cut section after cutting as shown in
When a cutting start region is formed as follows while taking account of the crystal structure of a semiconductor substrate, its cleavage characteristic, and the like, the object can be cut with a high precision by a smaller force from the cutting start region acting as a start point.
Namely, in the case of a substrate made of a monocrystal semiconductor having a diamond structure such as silicon, it will be preferred if a cutting start region is formed in a direction extending along a (111) plane (first cleavage plane) or a (110) plane (second cleavage plane). In the case of a substrate made of a III-V family compound semiconductor of sphalerite structure such as GaAs, it will be preferred if a cutting start region is formed in a direction extending along a (110) plane.
When the substrate is formed with an orientation flat in a direction to be formed with the above-mentioned cutting start region (e.g., a direction extending along a (111) plane in a monocrystal silicon substrate) or a direction orthogonal to the direction to be formed therewith, the cutting start region extending in the direction to be formed with the cutting start region can be formed easily and accurately with reference to the orientation flat.
With reference to
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 in order to regulate the output, pulse width, and the like of the laser light L; a dichroic mirror 103 arranged so as to change the orientation of the optical axis of the laser light L by 90° while functioning to reflect the laser light L; a condenser lens 105 for converging the laser light L reflected by the dichroic mirror 103; a mount table 107 for mounting a semiconductor substrate 1 to be irradiated with the laser light L converged by the condenser lens 105; an X-axis stage 109 for moving the mount table 107 along an X axis; a Y-axis stage 111 for moving the mount table 107 along a Y axis which is orthogonal to the X axis; a Z-axis stage 113 for moving the mount table 107 along a Z-axis which is orthogonal to X and Y axes; and a stage controller 115 for controlling the movement of the three stages 109, 111, 113.
The Z axis is orthogonal to the front face 3 of the semiconductor substrate 1, and thus is the direction of focal depth of the laser light incident on the semiconductor substrate 1. Therefore, the light-converging point P of the laser light L can be positioned within the semiconductor substrate 1 by moving the Z-axis stage 113 along the Z axis. The movement of the light-converging point P along the X (Y) axis is performed by moving the semiconductor substrate 1 along the X (Y) axis by the X (Y)-axis stage 109 (111).
The laser light source 101 is Nd:YAG laser generating pulsed laser light. Other examples of the laser employable in the laser light source 101 include Nd:YVO4 laser, Nd:YLF laser, and titanium sapphire laser. For forming a molten processed region, Nd:YAG laser, Nd:YVO4 laser, and Nd:YLF laser are preferably used. Though this embodiment uses pulsed laser light for processing the semiconductor substrate 1, continuous wave laser light may also be used if it can cause multiphoton absorption.
The laser processing apparatus 100 further comprises an observation light source 117 for generating visible rays for illuminating the semiconductor substrate 1 mounted on the mount table 107, and a visible ray beam splitter 119 disposed on the same optical axis as with the dichroic mirror 103 and condenser lens 105. The dichroic mirror 103 is disposed between the beam splitter 119 and condenser lens 105. The beam splitter 119 functions to reflect about a half of the visible rays and transmit the remaining half therethrough, and is disposed so as to change the orientation of the optical axis of visible rays by 90°. About a half of the visible rays generated from the observation light source 117 are reflected by the beam splitter 119. Thus reflected visible rays pass through the dichroic mirror 103 and condenser lens 105, thereby illuminating the front face 3 of the semiconductor substrate 1 including the line to cut 5 and the like.
The laser processing apparatus 100 further comprises an image pickup device 121 and an imaging lens 123 which are disposed on the same optical axis as with the beam splitter 119, dichroic mirror 103, and condenser lens 105. An example of the image pickup device 121 is a CCD camera. The reflected light of visible rays having illuminated the front face 3 of the semiconductor substrate 1 including the line to cut 5 and the like passes through the condenser lens 105, dichroic mirror 103, and beam splitter 119, so as to be focused by the imaging lens 123 and captured by the image pickup device 121, thus yielding imaging data.
The laser processing apparatus 100 further comprises an imaging data processor 125 for inputting the imaging data outputted from the image pickup device 121, an overall controller 127 for controlling the laser processing apparatus 100 as a whole, and a monitor 129. Based on the imaging data, the imaging data processor 125 calculates focal data for positioning the focal point of visible rays generated by the observation light source 117 onto the front face 3. According to the focal data, the stage controller 115 regulates the movement of the Z-axis stage 113, so as to position the focal point of visible rays at the front face 3. Thus, the imaging data processor 125 functions as an autofocus unit. On the basis of imaging data, the imaging data processor 125 calculates image data such as enlarged images of the front face 3. The image data are sent to the overall controller 127, so as to be subjected to various processing operations, and thus processed data are transmitted to the monitor 129. As a consequence, enlarged images and the like are displayed on the monitor 129.
The data from the stage controller 115, the image data from the imaging data processor 125, etc. are fed into the overall controller 127, whereas the laser light source controller 102, observation light source 117, and stage controller 115 are regulated according to these data as well, whereby the laser processing apparatus 100 as a whole is controlled. Hence, the overall controller 127 functions as a computer unit.
A procedure by which thus configured laser processing apparatus 100 forms a part which is intended to be cut will now be explained with reference to
The light absorption characteristic of the semiconductor substrate 1 is measured by a spectrophotometer or the like which is not depicted. According to the result of measurement, a laser light source 101 generating laser light L having a wavelength to which the semiconductor substrate 1 is transparent or less absorptive is chosen (S101). Subsequently, the thickness of the semiconductor substrate 1 is measured. According to the result of measurement of thickness and the refractive index of the semiconductor substrate 1, the amount of movement of the semiconductor substrate along the Z axis is determined (S103). This is an amount of movement the semiconductor substrate 1 along the Z axis with reference to the light-converging point P of laser light positioned at the front face 3 of the semiconductor substrate 1 for locating the light-converging point P of laser light L within the semiconductor substrate 1. This amount of movement is fed into the overall controller 127.
The semiconductor substrate 1 is mounted on the mount table 107 of the laser processing apparatus 100. Then, visible rays are generated from the observation light source 117, so as to illuminate the semiconductor substrate 1 (S105). The front face 3 of the semiconductor substrate 1 including the illuminated line to cut 5 is captured by the image pickup device 121. The line to cut 5 is a desirable virtual line to cut the semiconductor substrate 1. The imaging data captured by the image pickup device 121 is sent to the imaging data processor 125. According to the imaging data, the imaging data processor 125 calculates such focal data as to position the focal point of visible rays generated by the observation light source 117 onto the front face 3 (S107).
The focal data is sent to the stage controller 115. According to the focal data, the stage controller 115 moves the Z-axis stage 113 along the Z axis (S109). As a consequence, the focal point of the visible rays from the observation light source 117 is positioned at the front face 3 of the semiconductor substrate 1. According to the imaging data, the imaging data processor 125 calculates enlarged image data of the front face 3 of the semiconductor substrate 1 including the line to cut 5. The enlarged image data is sent to the monitor 129 by way of the total controller 127, whereby an enlarged image of the line to cut 5 and its vicinity is displayed on the monitor 129.
The movement amount data determined by step S103 has been fed into the total controller 127 beforehand, and is sent to the stage controller 115. According to the movement amount data, the stage controller 115 causes the Z-axis stage 113 to move the semiconductor substrate 1 along the Z axis to such a position that the light-converging point P of laser light L is located within the semiconductor substrate 1 (S111).
Subsequently, laser light L is generated from the laser light source 101, so as to illuminate the line to cut 5 in the front face 3 of the semiconductor substrate 1. Since the light-converging point P of laser light L is located within the semiconductor substrate 1, a molten processed region is formed only within the semiconductor substrate 1. Then, the X-axis stage 109 and Y-axis stage 111 are moved along the line to cut 5, whereby the molten processed region formed along the line to cut 5 forms a part which is intended to be cut along the line to cut 5 (S113).
The foregoing completes the forming of the part which is intended to be cut by the laser processing apparatus 100, whereby the part which is intended to be cut is formed within the semiconductor substrate 1. When the part which is intended to be cut is formed within the semiconductor substrate 1, a relatively small force can start fractures in the thickness direction of the semiconductor substrate 1 from the part which is intended to be cut.
The method of cutting a semiconductor substrate in accordance with this embodiment will now be explained. Here, a silicon wafer 11 which is a semiconductor wafer is used as the semiconductor substrate.
First, as shown in
Subsequently, as shown in
After forming the part which is intended to be cut 9, sheet expanding means 30 pulls the periphery of the adhesive sheet 20 outward as shown in
Here, opposing cut sections 25a, 25a of neighboring semiconductor chips 25, 25 are initially in close contact with each other, but are separated from each other as the adhesive sheet 20 expands, whereby the die-bonding resin layer 23 in close contact with the rear face 17 of the silicon wafer 11 is cut along the part which is intended to be cut 9.
There are cases where the sheet expanding means 30 is disposed on a stage for mounting the silicon wafer 11 when forming the line to cut 9, and not. In the case where the sheet expanding means 30 is not disposed on the stage, transfer means transfers the silicon wafer 11 mounted on the stage onto another stage provided with the sheet expanding means 30 after forming the part which is intended to be cut 9.
After the expanding of the adhesive sheet 20 is completed, the adhesive sheet 20 is irradiated with UV rays from the rear face side as shown in
Subsequently, as shown in
In the method of cutting the silicon wafer 11, the molten processed region 13 formed by multiphoton absorption yields the line to cut 9 within the silicon wafer 11 along a desirable line to cut for cutting the silicon wafer 11 as in the foregoing. Therefore, when the adhesive sheet 20 bonded to the silicon wafer 11 is expanded, the silicon wafer 11 is cut along the part which is intended to be cut 9 with a high precision, whereby the semiconductor chips 25 are obtained. Here, the opposing cut sections 25a, 25a of the neighboring semiconductor substrates 25, 25 are initially in close contact with each other, but are separated from each other as the adhesive sheet 20 expands, whereby the die-bonding resin layer 23 in close contact with the rear face 17 of the silicon wafer 11 is cut along the part which is intended to be cut 9. Therefore, the silicon wafer 11 and die-bonding resin layer 23 can be cut along the part which is intended to be cut 9 much more efficiently than in the case where the silicon wafer 11 and die-bonding resin layer 23 are cut with a blade without cutting the base 21.
Also, since the opposing cut sections 25a, 25a of the neighboring semiconductor chips 25, 25 are initially in close contact with each other, the cut individual semiconductor chips 25 and cut pieces of the die-bonding resin layer 23 have substantially the same outer form, whereby the die-bonding resin is prevented from protruding from the cut sections 25a of the semiconductor chips 25.
Though the foregoing method of cutting the silicon wafer 11 relates to a case where fractures starting from the part which is intended to be cut 9 are not generated in the silicon wafer 11 before the adhesive sheet 20 is expanded as shown in
When a stress is generated in the silicon wafer 11 along the part which is intended to be cut 9 after forming the part which is intended to be cut 9, so as to cut the silicon wafer 11 along the part which is intended to be cut 9 as such, semiconductor chips 25 cut with a very high precision can be obtained. When the adhesive sheet 20 bonded to the silicon wafer 11 is expanded, the opposing cut sections 25a, 25a of the neighboring semiconductor substrates 25, 25 are separated from each other from their close contact state as the adhesive sheet 20 expands, whereby the die-bonding resin layer 23 in close contact with the rear face 17 of the silicon wafer 11 is cut along the cut sections 25a in this case as well. Therefore, the silicon wafer 11 and die-bonding resin layer 23 can also be cut along the part which is intended to be cut 9 much more efficiently by this cutting method than in the case where the silicon wafer 11 and die-bonding resin layer 23 are cut with a blade without cutting the base 21.
When the silicon wafer 11 becomes thinner, there is a case where fractures 15 started from the part which is intended to be cut 9 reach the front face 3 and rear face 17 of the silicon wafer 11 as shown in
When the part which is intended to be cut 9 caused by the molten processed region 13 is formed near the front face 3 within the silicon wafer 11 such that a fracture 15 reaches the front face 3 as shown in
Results of an experiment in a case using “LE-5000 (product name)” available from Lintec Corporation as the adhesive sheet 20 will now be explained.
Immediately after starting expanding the adhesive sheet 20, the silicon wafer 11 was cut along the part which is intended to be cut 9, whereby the opposing cut sections 25a, 25a of neighboring semiconductor chips 25 were in close contact with each other as shown in
When the expanding of the adhesive sheet 20 was completed as such, the die-bonding resin layer 23 was cut into the individual semiconductor chips 25 as shown in
When made of a nonelastic material and the like, the die-bonding resin layer 23 is not left on the base 21 of the adhesive sheet 20 between the semiconductor chips 25, 25 separated from each other as shown in
The adhesive sheet 20 comprising the base 21 and UV-curable resin layer 22 may be bonded to the rear face 17 of the silicon wafer 11 by way of the UV-curable resin layer 22 as shown in
The method of cutting the silicon wafer 11 by using the adhesive sheet 20 comprising the base 21 and UV-curable resin layer 22 is not limited to the case where no fractures starting from the part which is intended to be cut 9 occur in the silicon wafer 11 before expanding the adhesive sheet 20 as explained with reference to
In the following, a preferred second embodiment of the method of cutting a semiconductor substrate in accordance with the present invention will be explained more specifically.
On the front face 3 of a silicon wafer (semiconductor substrate) 11 to become an object to be processed, a plurality of functional devices 215 are patterned into a matrix in directions parallel and perpendicular to an orientation flat 16 as shown in
First, as shown in
Subsequently, using a laser processing apparatus, a cutting start region is formed within the silicon wafer 11. Namely, as shown in
Next, the silicon wafer 11 having the protective film 18 bonded thereto is removed from the mount table 19, and a die-bonding-resin-attached film 220 (e.g., “LE-5000 (product name)” available from Lintec Corporation) is bonded to the rear face 17 of the silicon wafer 11 as shown in
Subsequently, as shown in
Next using a vacuum collet or the like, the semiconductor chips 25 are successively picked up as shown in
In the foregoing method of cutting the silicon wafer 11, the silicon wafer 11 having the front face 3 formed with the functional devices 215 is used as an object to be processed, and is irradiated with laser light L while using its rear face 17 as a laser light entrance surface and locating the light-converging point P within the silicon wafer 11. This generates multiphoton absorption within the silicon wafer 11, thereby forming the cutting start regions 8 caused by the molten processed regions 13 within the silicon wafer 11 along the lines to cut 5. Here, the rear face of the semiconductor substrate is used as the laser light entrance surface, since there will be a fear of the functional devices inhibiting the laser light from entering if the front face is used as the laser light entrance surface. When the cutting start regions 8 are formed within the silicon wafer 11 as such, fractures can start from the cutting start regions 8 naturally or with a relatively small force applied thereto, so as to reach the front face 3 and rear face 17 of the silicon wafer 11. Therefore, when the expandable film 221 is bonded to the rear face 17 of the silicon wafer 11 by way of the die-bonding resin layer 223 and expanded after forming the cutting start regions 8, the cut sections 25a, 25a of the silicon wafer 11 cut along the lines to cut 5 are separated from each other from their close contact state. As a consequence, the die-bonding resin layer 223 existing between the silicon wafer 11 and expandable film 221 is also cut along the lines to cut 5. Therefore, the silicon wafer 11 and die-bonding resin layer 223 can be cut along the lines to cut 5 much more efficiently than in the case cut with a blade or the like.
Since the cut sections 25a, 25a of the silicon wafer 11 cut along the lines to cut 5 are initially in close contact with each other, the cut pieces of silicon wafer 11 and cut pieces of die-bonding resin layer 223 have substantially the same outer form, whereby the die-bonding resin is prevented from protruding from the cut sections 25a of the pieces of the silicon wafer 11.
Further, before forming the cutting start regions 8 within the silicon wafer 11, the rear face 17 of the silicon wafer 11 is ground such that the silicon wafer 11 attains a predetermined thickness. When the silicon wafer 11 is thinned to a predetermined thickness as such, the silicon wafer 11 and die-bonding resin layer 223 can be cut along the lines to cut 5 with a higher precision.
As explained in the foregoing, the method of cutting a semiconductor substrate in accordance with the present invention can efficiently cut the semiconductor substrate together with a die-bonding resin layer.
| Number | Date | Country | Kind |
|---|---|---|---|
| P2002-351600 | Dec 2002 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP03/11624 | 9/11/2003 | WO | 00 | 11/30/2005 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2004/051721 | 6/17/2004 | WO | A |
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