Wafer dividing method and wafer dividing apparatus

A method of dividing, along lattice pattern-like dividing lines, a wafer which has the lattice pattern-like dividing lines and a polymer film on the front surface of a substrate and is processed to allow for division along the dividing lines, the method comprising a frame holding step for putting the wafer on the surface of an adhesive tape mounted on an annular frame; a wafer cooling step for cooling the wafer that is affixed to the surface of the adhesive tape mounted on the annular frame; and a diving step for dividing the wafer along the dividing lines by expanding the adhesive tape to which the cooled wafer is affixed.

FIELD OF THE INVENTION

The present invention relates to a method of dividing a wafer such as a semiconductor wafer along predetermined dividing lines; and to a wafer dividing apparatus.

DESCRIPTION OF THE PRIOR ART

In the production process of a semiconductor device, a plurality of areas are sectioned by dividing lines which are formed in a lattice pattern on the front surface of a substantially disk-like semiconductor wafer, and a device such as IC or LSI is formed in each of the sectioned areas. Individual devices are manufactured by dividing this semiconductor wafer along the dividing lines.

As a means of dividing a plate-like workpiece such as a semiconductor wafer, Japanese Patent No. 3408805 discloses a laser processing method for applying a pulse laser beam having permeability for the workpiece with its focal point set to the inside of the area to be divided. In the dividing method making use of this laser processing technique, the workpiece is divided by applying a pulse laser beam of an infrared range having permeability for the workpiece from one side of the workpiece with its focal point set to the inside to continuously form a deteriorated layer in the inside of the workpiece along the dividing lines and exerting external force along the dividing lines whose strength has been reduced by the formation of the deteriorated layers.

JP-A 2005-19769 discloses a dividing apparatus for dividing a workpiece by exerting external force along dividing lines whose strength has been reduced by the formation of the above deteriorated layers. This dividing apparatus comprises a frame holding means for holding an annular frame on which a protective tape having the workpiece affixed thereto is mounted, and a tape expanding means for expanding the protective tape mounted on the annular frame held on the frame holding means, and divides the workpiece which is affixed to the protective tape and whose strength has been reduced along the dividing lines, along the dividing lines, by expanding the protective tape with the tape expanding means.

To improve the mechanical strength, chemical resistance and moisture resistance of a device, a wafer having a polymer protective film made of a polyimide resin, polybenzooxazole resin or silicon-based resin on the surface of a silicon substrate having devices formed thereon has recently been implemented. A wafer having a polymer insulating film as an interlayer insulating film for devices has also been implemented.

When the wafer having a polymer protective film or an insulating film is divided by using the above dividing apparatus, the silicon substrate whose strength has been reduced along the dividing lines is divided while the polymer film or the insulating film is stretched and not divided along the dividing lines. Even when the polymer protective film or the insulating film is divided, its divided surface becomes jagged, thereby reducing the quality of each device.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a wafer dividing method and a wafer dividing apparatus, both capable of dividing the polymer film of a wafer having the polymer film formed on the front surface of a substrate, along predetermined dividing lines without fail.

To attain the above object, according to the present invention, there is provided a method of dividing, along lattice pattern-like dividing lines, a wafer which has the lattice pattern-like dividing lines and a polymer film formed on the front surface of a substrate and is processed to allow for division along the dividing lines, the method comprising:

a frame holding step for putting the wafer on the surface of an adhesive tape mounted on an annular frame;

a frame cooling step for cooling the wafer that is affixed to the surface of the adhesive tape mounted on the annular frame; and

a dividing step for dividing the wafer along the dividing lines by expanding the adhesive tape to which the cooled wafer is affixed.

The above cooling step is to cool the wafer to +5 to −20° C.

According to the present invention, there is also provided a wafer dividing apparatus for dividing a wafer which is put on an adhesive tape mounted on an annular frame so as to cover its inner opening, along predetermined dividing lines, the apparatus comprising:

a frame holding means having a holding surface for holding the annular frame;

a wafer pressing member having a pressing surface to be applied to the wafer mounting area of the adhesive tape mounted on the annular frame supported by the wafer holding means;

a moving means for moving the wafer pressing member from a relief position below the holding surface of the frame holding means to a pressing position above the holding surface of the frame holding means;

a cooling chamber formed above the holding surface of the frame holding means; and

a cooling means for cooling the inside of the cooling chamber.

The above moving means moves the wafer pressing member from the relief position to the pressing position at a rate of 10 to 1,000 mm/sec, preferably 50 to 150 mm/sec.

The above cooling means cools the inside of the cooling chamber to +5 to −20° C.

According to the present invention, since the wafer affixed to the surface of the adhesive tape mounted on the annular frame is cooled and divided along the dividing lines by expanding the adhesive tape to which the cooled wafer is affixed, the polymer film formed on the front surface of the substrate is also cooled, whereby the polymer film is divided along the dividing lines surely without being stretched.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the wafer dividing method and the wafer dividing apparatus of the present invention will be described in detail hereinunder with reference to the accompanying drawings.

FIG. 1is a perspective view of a semiconductor wafer to be divided into individual devices by the wafer dividing method of the present invention, andFIG. 2is an enlarged sectional view of the principal portion of the semiconductor wafer shown inFIG. 1. In the semiconductor wafer2shown inFIG. 1andFIG. 2, a plurality of dividing lines21are formed in a lattice pattern on the front surface of a semiconductor substrate20such as a silicon substrate. And, a device22such as IC or LSI is formed in a plurality of areas sectioned by the plurality of dividing lines21formed in a lattice pattern on the front surface20aof the semiconductor substrate20, and a protective film23(polymer film) made of a polymer such as a polyimide resin, polybenzooxazole resin or silicon-based resin is formed on these devices22, as shown inFIG. 2.

An embodiment of the method of dividing the above semiconductor wafer2into individual devices along the dividing lines21will be described hereinunder.

In the illustrated embodiment, first comes the step of forming a deteriorated layer along the dividing lines21in the inside of the semiconductor substrate20by applying a pulse laser beam of a wavelength having permeability for the semiconductor substrate20of the semiconductor wafer2along the dividing lines21to reduce the strength of the semiconductor substrate20along the dividing lines21. This deteriorated layer forming step is carried out by using a laser beam processing machine3shown inFIG. 3. The laser beam processing machine3shown inFIG. 3comprises a chuck table31for holding a workpiece, a laser beam application means32for applying a laser beam to the workpiece held on the chuck table31, and an image pick-up means33for picking up an image of the workpiece held on the chuck table31. The chuck table31is designed to suction-hold the workpiece and to be moved in the processing-feed direction indicated by an arrow X and the indexing-feed direction indicated by an arrow Y inFIG. 3by a moving mechanism that is not shown.

The above laser beam application means32has a cylindrical casing321arranged substantially horizontally. In the casing321, there is installed a pulse laser beam oscillation means (not shown) which comprises a pulse laser beam oscillator composed of a YAG laser oscillator or YVO4 laser oscillator and a repetition frequency setting means. A condenser322for converging a pulse laser beam oscillated from the pulse laser beam oscillation means is attached to the end of the above casing321.

The image pick-up means33mounted on the end portion of the casing321constituting the above laser beam application means32is constituted by an infrared illuminating means for applying infrared radiation to the workpiece, an optical system for capturing infrared radiation applied by the infrared illuminating means, and an image pick-up device (infrared CCD) for outputting an electric signal corresponding to infrared radiation captured by the optical system, in addition to an ordinary image pick-up device (CCD) for picking up an image with visible radiation in the illustrated embodiment. An image signal is supplied to a control means that is not shown.

The deteriorated layer forming step which is carried out by using the above laser beam processing machine3will be described with reference toFIGS. 3 to 5.

In this deteriorated layer forming step, the semiconductor wafer2is first placed on the chuck table31of the laser beam processing machine3shown inFIG. 3in such a manner that the rear surface20bof the semiconductor substrate20faces up, and suction-held on the chuck table31. The chuck table31suction-holding the semiconductor wafer2is brought to a position right below the image pick-up means33by the moving mechanism that is not shown.

After the chuck table31is positioned right below the image pick-up means33, alignment work for detecting the area to be processed of the semiconductor wafer2is carried out by the image pick-up means33and the control means that is not shown. That is, the image pick-up means33and the control means (not shown) carry out image processing such as pattern matching, etc. to align a dividing line21formed in a predetermined direction of the semiconductor wafer2with the condenser322of the laser beam application means32for applying a laser beam along the dividing line21, thereby performing the alignment of a laser beam application position. The alignment of the laser beam application position is also carried out on dividing lines21formed on the semiconductor wafer2in a direction perpendicular to the above predetermined direction. Although the front surface20ahaving the dividing lines21formed thereon of the semiconductor substrate20faces down at this point, as the image pick-up means33comprises an infrared illuminating means, an optical system for capturing infrared radiation and an image pick-up device (infrared CCD) for outputting an electric signal corresponding to the infrared radiation as described above, images of the dividing lines21can be picked up through the rear surface20bof the semiconductor substrate20.

After the dividing line21formed on the semiconductor wafer2held on the chuck table31is detected and the alignment of the laser beam application position is carried out as described above, the chuck table31is moved to a laser beam application area where the condenser322of the laser beam application means32for applying a laser beam is located as shown inFIG. 4(a) so as to bring one end (left end inFIG. 4(a)) of the predetermined dividing line21to a position right below the condenser322of the laser beam application means32. The chuck table31is then moved in the direction shown by the arrow X1inFIG. 4(a) at a predetermined processing-feed rate while a pulse laser beam of a wavelength having permeability for the semiconductor substrate20such as a silicon substrate is applied from the condenser322. When the application position of the condenser322of the laser beam application means32reaches the other end (right end inFIG. 4(b)) of the dividing line21as shown inFIG. 4(b), the application of the pulse laser beam is suspended and the movement of the chuck table31is stopped. In this deteriorated layer forming step, the focal point P of the pulse laser beam is set to a position near the front surface20a(undersurface) of the semiconductor substrate20. As a result, a deteriorated layer210is formed from the front surface20a(undersurface) toward the inside of the semiconductor substrate20. This deteriorated layer210is formed as a molten and re-solidified layer.

The processing conditions in the above deteriorated layer forming step are set as follows, for example.Light source: LD excited Q switch Nd:YVO4 laserWavelength: pulse laser beam having a wavelength of 1,064 nmRepetition frequency: 50 kHzAverage output: 3 WFocal spot diameter: 1 μmProcessing-feed rate: 100 mm/sec

When the semiconductor substrate20is thick, as shown inFIG. 5, the above-described deteriorated layer forming step is carried out a plurality of times by changing the focal point P stepwise so as to form a plurality of deteriorated layers210. For example, as the thickness of the deteriorated layer formed once under the above processing conditions is about 50 μm, the above deteriorated layer forming step is carried out three times to form deteriorated layers210having a total thickness of 150 μm. In the case of a semiconductor substrate20having a thickness of 300 μm, six deteriorated layers210may be formed in the inside of the semiconductor substrate20from the front surface20ato the rear surface20balong the dividing lines21.

After the deteriorated layer210is formed in the inside of the semiconductor wafer2along all the dividing lines21by the above-described deteriorated layer forming step, one side of the wafer is put on the surface of an adhesive tape which is mounted on an annular frame (wafer supporting step). That is, as shown inFIG. 6, the rear surface20bof the semiconductor substrate20of the semiconductor wafer2is put on the surface of the adhesive tape5whose peripheral portion is mounted on the annular frame4so as to cover its inner opening41. The adhesive tape5has an acrylic resin adhesive layer having a thickness of about 5 μm on the surface of a 70 μm-thick sheet backing made of polyvinyl chloride (PVC) in the illustrated embodiment.

The above wafer supporting step may be carried out before the above deteriorated layer forming step. In this case, the front surface20aof the semiconductor substrate20of the semiconductor wafer2is put on the surface of the above adhesive tape5mounted on the annular frame4(therefore, the rear surface20bof the semiconductor substrate20of the semiconductor wafer2faces up). Then, the above deteriorated layer forming step is carried out in a state where the semiconductor wafer2is mounted on the above adhesive tape5mounted on the annular frame4.

After the above deteriorated layer forming step and the wafer supporting step, next comes the step of cooling the semiconductor wafer2affixed to the surface of the adhesive tape5mounted on the annular frame4and the step of dividing the semiconductor substrate20and the protective film23along the dividing lines21by expanding the adhesive tape5to which the cooled semiconductor wafer2is affixed.

A description is subsequently given of a wafer dividing apparatus for carrying out the wafer cooling step and the dividing step with reference toFIG. 7andFIG. 8.

FIG. 7is a perspective view of the wafer dividing apparatus constituted according to the present invention, andFIG. 8is a sectional view of the wafer dividing apparatus shown inFIG. 7.

The wafer dividing apparatus6shown inFIG. 7andFIG. 8has a rectangular parallelepiped housing60which is open at the top. A frame holding means7for holding the above annular frame4is installed on top of this housing60. The frame holding means7is composed of a plate-like holding member71and clamps72arranged in each of four corner portions of the holding member71. The holding member71has an opening711with the same diameter as the diameter of the opening41of the above annular frame4at the center, a cooling gas introduction port712and a cooling gas exhaust port713. The holding member71thus formed has a top surface functioning as a holding surface714for holding the above annular frame4. The frame holding means7constituted as described above fixes the annular frame4on the holding surface714of the holding member71by the clamps72to hold the annular frame4.

In the above housing60, there are installed a wafer pressing member8which acts on the wafer affixing area of the adhesive tape5mounted on the annular frame4held on the above frame holding means7and a moving means9for moving this wafer pressing member8from a relief position shown inFIG. 8below the holding surface714of the holding member71to a pressing position above the holding surface714. The wafer pressing member8is circular with an outer diameter smaller than the diameter of the opening711formed in the above holding member71and its top surface serves as a pressing surface81. An annular groove82is formed in the peripheral portion of the top surface of the wafer pressing member8and a plurality of expansion aid rollers83are fitted in this annular groove82. The expansion aid rollers83reduce friction resistance which is generated when the wafer pressing member8is moved up to the pressing position to expand the adhesive tape5. An air escape hole84open to the pressing surface81is desirably formed in the center portion of the wafer pressing member8. The above moving means9is composed of an air cylinder mechanism as shown inFIG. 8in the illustrated embodiment, and the above wafer pressing member8is connected with the upper end of its piston rod91. When the wafer pressing member8is at the relief position, the pressing surface81is positioned 5 mm below the holding surface714of the holding member71in the illustrated embodiment. When the wafer pressing member8is at the pressing position, the pressing surface81is positioned 20 mm above the holding surface714of the holding member71in the illustrated embodiment.

The wafer dividing apparatus6in the illustrated embodiment has a cover10for forming a cooling chamber above the holding surface714of the holding member71constituting the above frame holding means7. This cover10is rectangular parallelepiped and is open at the bottom, and one side thereof is connected with the holding member71of the frame holding means7by hinges11as shown inFIG. 7. The cover10constituted as described above is placed on the top of the holding member71as shown inFIG. 8to form a cooling chamber100above the holding surface714of the holding member71. The cover10preferably has a heat insulating structure.

The wafer dividing apparatus6in the illustrated embodiment comprises a cooling means12for cooling the inside of the above cooling chamber100. The cooling means12in the illustrated embodiment comprises a cooling gas feed means121, cooling gas feed pipes122and123for connecting the cooling gas feed means121to the cooling gas introduction port712formed in the holding member71of the above frame holding means7and cooling gas exhaust pipes124and125for connecting the cooling gas exhaust port713formed in the holding member71to the cooling gas feed means121. The above cooling gas feed means121supplies a +5 to −20° C. cooling gas. The above cooling gas feed pipes122and123are interconnected by a connection pipe126installed in the side wall of the housing60. The above cooling gas exhaust pipes124and125are interconnected by a connection pipe127installed in the side wall of the housing60.

The wafer dividing apparatus6in the illustrated embodiment is constituted as described above, and the wafer cooling step and the dividing step which are carried out by using this wafer dividing apparatus6will be described hereinunder.

First, the cover10of the dividing apparatus6is opened by turning it upward with the hinge11as its pivot, as shown inFIG. 7. At this point, the wafer pressing member8is at the relief position shown inFIG. 8. After the cover10is opened, the annular frame4supporting the semiconductor wafer2through the adhesive tape5as shown inFIG. 6is placed on the holding surface714of the holding member71constituting the frame holding means7(seeFIG. 9). Then, the annular frame4is fixed on the holding member71by the clamps72(frame holding step).

After the above frame holding step, the cover10is closed as shown inFIG. 9.

Thereafter, the cooling means12is activated to introduce a cooling gas into the cooling chamber100through the cooling gas feed pipes122and123and the cooling gas introduction port712. As a result, the semiconductor wafer2exposed to the cooling chamber100is cooled (wafer cooling step). The cooling gas introduced into the cooling chamber100is returned to the cooling means12from the cooling gas exhaust port713through the cooling gas exhaust pipes124and125. In this cooling step, the cooling chamber100is cooled to +5 to −20° C.

Then, the moving means9which is composed of the air cylinder mechanism is activated to carry out the dividing step for moving the wafer pressing member8up to the pressing position, as shown inFIG. 10. As a result, the pressing surface81of the wafer pressing member8is brought into contact with the wafer affixing area51of the adhesive tape5mounted on the annular frame4to thrust up the adhesive tape5, whereby the adhesive tape5is expanded. Therefore, tensile force acts radially on the semiconductor wafer2to which the adhesive tape5is affixed. When tensile force is exerted radially to the semiconductor wafer2as described above, the semiconductor substrate20of the semiconductor wafer2is divided along the deteriorated layers210because the strength of the semiconductor substrate20of the semiconductor wafer2is reduced along the deteriorated layers210formed along the dividing lines21. Simultaneously with the division of the semiconductor substrate20of the semiconductor wafer2along the deteriorated layers210, the protective film23(polymer film) formed on the front surface20aof the semiconductor substrate20is also divided along the dividing lines21where the deteriorated layer210has been formed to obtain individual devices200as shown inFIG. 11. Since the semiconductor wafer2(semiconductor substrate20and the protective film23) is cooled to +5 to −20° C. at this point, the protective film23is divided along the dividing lines21surely without being stretched. In the above dividing step, the speed for moving the wafer pressing member8from the relief position to the pressing position may be 10 to 1,000 mm/sec, preferably 50 to 150 mm/sec. Since the escape hole84is formed in the center portion of the wafer pressing member8in the illustrated embodiment, when the wafer pressing member8is moved up in the above dividing step, air does not gather in the space between the pressing surface81and the adhesive tape5, whereby the adhesive tape5can be expanded smoothly.

In the illustrated embodiment, the semiconductor substrate20and the protective film23of the semiconductor wafer2where the deteriorated layers210have been formed are divided at the same time along the dividing lines21formed in a lattice pattern by using the dividing apparatus6. The dividing apparatus6may be used to carry out the step of dividing only the protective film23formed on the front surface20aof the semiconductor substrate20. That is, after the above deteriorated layer forming step, the semiconductor substrate20is divided along the dividing lines21where the deteriorated layer210has been formed by exerting external force to the semiconductor wafer2and then, the dividing step is carried out by using the dividing apparatus6to divide the protective film23formed on the front surface20aof the semiconductor substrate20, thereby obtaining individual devices200.