Wafer dividing method and laser beam processing machine

FIELD OF THE INVENTION

0001The present invention relates to a method of dividing a wafer having a plurality of streets which are formed in a lattice pattern on the front surface and devices which are formed in a plurality of areas sectioned by the plurality of streets, into individual devices (chips) along the streets; and to a laser beam processing machine.

DESCRIPTION OF THE PRIOR ART

0002In the production process of a semiconductor wafer, a plurality of areas are sectioned by dividing lines called “streets” which are arranged 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 cutting this semiconductor wafer along the streets to divide it into the areas each having a device formed thereon. An optical device wafer comprising a gallium nitride-based compound semiconductor laminated on the front surface of a sapphire substrate is also cut along predetermined streets to be divided into individual optical devices such as light emitting diodes or laser diodes which are widely used in electric appliances.

0003Each of the thus obtained devices has an adhesive film for die bonding called “die attach film” which is as thick as 20 to 40 μm and made of an epoxy resin, on the rear surface thereof, and is pressure-bonded under heating to a die bonding frame for supporting the device through this adhesive film. To form the adhesive film for die bonding on the rear surfaces of the devices, as disclosed by JP-A 2000-182995, after the adhesive film is affixed to the rear surface of the semiconductor wafer and the semiconductor wafer is put on a dicing tape through this adhesive film, the semiconductor wafer is cut together with this adhesive film along the streets formed on the front surface of the semiconductor wafer by a cutting blade to form a device having the adhesive film on the rear surface.

0004Meanwhile, as a means of dividing a plate-like workpiece such as a semiconductor wafer, a laser processing method for applying a pulse laser beam of a wavelength having permeability for the workpiece with its focusing point set to the inside of the area to be divided is attempted and disclosed by Japanese Patent No. 3408805. In the dividing method using 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 surface side of the workpiece with its focusing point set to the inside to continuously form deteriorated layers in the inside of the workpiece along the streets and exerting external force along the streets whose strength has been reduced by the formation of the deteriorated layers.

0005JP-A 2004-273895 discloses a method in which an adhesive film for die boning is affixed to the rear surface of a wafer having deteriorated layers which have been formed along the streets by the above laser processing technique, the wafer is affixed to a dicing tape through this adhesive film and then, the wafer is divided into individual devices along the streets whose strength has been reduced by the formation of the deteriorated layers and at the same time, the adhesive film is divided along the outer periphery of each divided device by expanding the dicing tape.

0006When the method in which the wafer and the adhesive film affixed to the wafer are divided along the streets by expanding the dicing tape affixed to the wafer is employed, the wafer whose strength has been reduced by the formation of the deteriorated layers is divided into individual devices along the streets by expanding the dicing tape. However, since the adhesive film is sticky and elongates when tension is exerted thereto, there is a problem in that it is difficult to divide it without fail.

SUMMARY OF THE INVENTION

0007It is an object of the present invention to provide a wafer dividing method comprising the steps of affixing an adhesive film for die bonding to the rear surface of a wafer having deteriorated layers along streets, affixing the wafer to a dicing tape through this adhesive film, dividing the wafer into individual devices along the streets whose strength has been reduced by the formation of deteriorated layers by expanding the dicing tape, and at the same time, dividing the adhesive film along the outer periphery of each divided device without fail as well as a laser beam processing machine for forming a dividing groove along the outer periphery of each device in the adhesive film by applying a laser beam to the adhesive film through the space between adjacent devices in a state of the dicing tape being expanded.

0008To attain the above object, according to the present invention, there is provided a method of dividing a wafer having a plurality of streets which are formed in a lattice pattern on the front surface and devices which are formed in a plurality of areas sectioned by the plurality of streets, along the plurality of streets, comprising:

0009a deteriorated layer forming step for forming a deteriorated layer along the plurality of streets in the inside of the wafer by applying a laser beam of a wavelength having permeability for the wafer along the plurality of streets;

0010an adhesive film mounting step for mounting an adhesive film for die bonding onto the rear surface of the wafer;

0011a wafer supporting step for affixing, the adhesive film side of the wafer onto a dicing tape mounted on an annular frame to support the wafer to the annular frame through the dicing tape;

0012a first tape expanding step for dividing the wafer into individual devices along the streets which have undergone the deteriorated layer forming step, by expanding the dicing tape after the wafer supporting step;

0013a dividing groove forming step for forming a dividing groove along the outer periphery of each individual device in the adhesive film, by applying a laser beam of a wavelength having absorptivity for the adhesive film through the spaces between adjacent devices in a state of the dicing tape being expanded after carrying out the first tape expanding step; and

0014a second tape expanding step for dividing the adhesive film along the dividing grooves by further expanding the dicing tape from the state of the first tape expanding step having been carried out after the dividing groove forming step.

0015Further, according to the present invention, there is also provided a laser beam processing machine comprising:

0016a tape expanding mechanism having a frame holding means comprising an annular frame holding member for holding an annular frame supporting a dicing tape to which a wafer is affixed and a tape expanding means for expanding the dicing tape mounted on the annular frame held on the frame holding means;

0017a laser beam application means for applying a laser beam to the wafer supported to the annular frame held, through the dicing tape, on the frame holding means of the tape expanding mechanism;

0018a processing-feed means for moving the tape expanding mechanism and the laser beam application means relative to each other in a processing-feed direction;

0019an indexing-feed means for moving the tape expanding mechanism and the laser beam application means in an indexing-feed direction perpendicular to the processing-feed direction;

0020a processing-feed position detection means for detecting the processing-feed position of the tape expanding mechanism;

0021an indexing-feed position detection means for detecting the indexing-feed position of the tape expanding mechanism;

0022an image pick-up means for picking up an image of the wafer supported to the annular frame held on the frame holding means of the tape expanding mechanism through the dicing tape; and

0023a control means for obtaining the area to be processed of the wafer supported to the annular frame held on the frame holding means of the tape expanding mechanism through the dicing tape based on an image signal obtained by the image pick-up means and detection signals from the processing-feed position detection means and the indexing-feed position detection means.

0024The above tape expanding means comprises an expansion drum which is installed within the annular frame holding member and has a smaller outer diameter than the inner diameter of the annular frame and a larger inner diameter than the outer diameter of the wafer affixed to the dicing tape mounted on the annular frame, and an expansion and moving member for moving the expansion drum and the annular frame holding member relative to each other in an axial direction.

0025In the wafer dividing method according to the present invention, after the wafer is divided into individual devices along the streets where the deteriorated layer has been formed by carrying out the first tape expanding step, the step of forming a dividing groove along the outer periphery of each device in the adhesive film by applying a laser beam of a wavelength having absorptivity for the adhesive film through the spaces between adjacent divided devices is carried out and then, the second tape expanding step for dividing the adhesive film along the dividing grooves by further expanding the dicing tape from the state in which the first tape expanding step has been carried out is carried out. Therefore, as the dividing grooves are formed along the outer periphery of each device in the adhesive film when the second tape expanding step is carried out, the adhesive film can be divided along the dividing grooves without fail.

BRIEF DESCRIPTION OF THE DRAWINGS

0026<figref idref="DRAWINGS">FIG. 1</figref> is a perspective view of a semiconductor wafer to be divided into individual devices by the wafer dividing method of the present invention;

0027<figref idref="DRAWINGS">FIG. 2</figref> is a perspective view of the semiconductor wafer shown in <figref idref="DRAWINGS">FIG. 1</figref> having a protective member on the front surface;

0028<figref idref="DRAWINGS">FIG. 3</figref> is a perspective view of the principal portion of a laser beam processor for carrying out a deteriorated layer forming step in the wafer dividing method of the present invention;

0029<figref idref="DRAWINGS">FIGS. 4(</figref><i>a</i>) and <b>4</b>(<i>b</i>) are explanatory diagrams of the deteriorated layer forming step in the wafer dividing method of the present invention;

0030<figref idref="DRAWINGS">FIG. 5</figref> is an explanatory diagram showing a state where deteriorated layers are formed in the inside of the semiconductor wafer by the deteriorated layer forming step shown in <figref idref="DRAWINGS">FIGS. 4(</figref><i>a</i>) and <b>4</b>(<i>b</i>);

0031<figref idref="DRAWINGS">FIG. 6</figref> is an explanatory diagram of an adhesive film mounting step in the wafer dividing method of the present invention;

0032<figref idref="DRAWINGS">FIG. 7</figref> is an explanatory diagram of a wafer supporting step in the wafer dividing method of the present invention;

0033<figref idref="DRAWINGS">FIG. 8</figref> is a perspective view of a laser beam processing machine having a wafer dividing mechanism constituted according to the present invention to carry out a first tape expanding step, a dividing groove forming step and a second tape expanding step in the wafer dividing method of the present invention;

0034<figref idref="DRAWINGS">FIG. 9</figref> is a perspective view showing a tape expanding mechanism provided in the laser beam processing machine shown in <figref idref="DRAWINGS">FIG. 8</figref>;

0035<figref idref="DRAWINGS">FIGS. 10(</figref><i>a</i>) and <b>10</b>(<i>b</i>) are explanatory diagrams showing the first tape expanding step in the wafer dividing method of the present invention;

0036<figref idref="DRAWINGS">FIGS. 11</figref> (<i>a</i>) to <b>11</b>(<i>c</i>) are explanatory diagrams showing the dividing groove forming step in the wafer dividing method of the present invention; and

0037<figref idref="DRAWINGS">FIGS. 12</figref> (<i>a</i>) and <b>12</b>(<i>b</i>) are explanatory diagrams of the second tape expanding step in the wafer dividing method of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

0038Preferred embodiments of the present invention will be described in detail hereinunder with reference to the accompanying drawings.

0039<figref idref="DRAWINGS">FIG. 1</figref> is a perspective view of a semiconductor wafer as the wafer to be divided by the wafer dividing method of the present invention. The semiconductor wafer <b>10</b> shown in <figref idref="DRAWINGS">FIG. 1</figref> is, for example, a silicon wafer having a thickness of 150 μm, and a plurality of streets <b>101</b> are formed in a lattice pattern on the front surface <b>10</b><i>a</i>. A device <b>102</b> such as IC or LSI is formed in a plurality of areas sectioned by the plurality of streets <b>101</b> on the front surface <b>10</b><i>a </i>of the semiconductor wafer <b>10</b>. A description is subsequently given of the method of dividing this semiconductor wafer <b>10</b> into individual devices <b>102</b> (chips).

0040A protective member <b>11</b> is affixed to the front surface <b>10</b><i>a </i>of the above semiconductor wafer <b>10</b> as shown in <figref idref="DRAWINGS">FIG. 2</figref> to protect the devices <b>102</b> (protective member affixing step).

0041After the protective member <b>11</b> is affixed to the front surface <b>10</b><i>a </i>of the semiconductor wafer <b>10</b> by carrying out the protective member affixing step, next comes the step of forming a deteriorated layer in the inside of the wafer along the streets by applying a laser beam of a wavelength having permeability for the wafer. This deteriorated layer forming step is carried out by using a laser beam processor <b>12</b> shown in <figref idref="DRAWINGS">FIG. 3</figref> in the illustrated embodiment. The laser beam processor <b>12</b> shown in <figref idref="DRAWINGS">FIG. 3</figref> comprises a chuck table <b>121</b> for holding a workpiece, a laser beam application means <b>122</b> for applying a laser beam to the workpiece held on the chuck table <b>121</b>, and an image pick-up means <b>125</b> for picking up an image of the workpiece held on the chuck table <b>121</b>. The chuck table <b>121</b> is designed to suction-hold the workpiece and to be moved in a processing-feed direction indicated by an arrow X in <figref idref="DRAWINGS">FIG. 3</figref> and an indexing-feed direction indicated by an arrow Y by a moving mechanism that is not shown.

0042The above laser beam application means <b>122</b> has a cylindrical casing <b>123</b> arranged substantially horizontally. In the casing <b>123</b>, 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 condenser <b>124</b> for converging a pulse laser beam oscillated from the pulse laser beam oscillation means is mounted on the end of the above casing <b>123</b>.

0043The image pick-up means <b>125</b> mounted on the end portion of the casing <b>123</b> constituting the above laser beam application means <b>122</b> comprises 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.

0044To carry out the deteriorated layer forming step by using the above-described laser beam processor <b>12</b>, the protective member <b>11</b> side of the semiconductor wafer <b>10</b> is placed on the chuck table <b>121</b> of the laser beam processor <b>12</b> as shown in <figref idref="DRAWINGS">FIG. 3</figref>. The semiconductor wafer <b>10</b> is then suction-held on the chuck table <b>121</b> by a suction means that is not shown (wafer holding step). Therefore, the rear surface <b>10</b><i>b </i>of the semiconductor wafer <b>10</b> suction-held on the chuck table <b>121</b> faces up.

0045The above wafer holding step is followed by the step of forming a deteriorated layer in the inside of the semiconductor wafer <b>10</b> along the streets <b>101</b> by applying a pulse laser beam of a wavelength having permeability for the silicon wafer constituting the semiconductor wafer <b>10</b> from the rear surface <b>10</b><i>b </i>side of the semiconductor wafer <b>10</b>. To carry out the deteriorated layer forming step, the chuck table <b>121</b> suction-holding the semiconductor wafer <b>10</b> is first brought to a position right below the image pick-up means <b>125</b> by the moving mechanism that is not shown. Then, alignment work for detecting the area to be processed of the semiconductor wafer <b>10</b> is carried out by the image pick-up means <b>125</b> and the control means that is not shown. That is, the image pick-up means <b>125</b> and the control means (not shown) carry out image processing such as pattern matching, etc. to align a street <b>101</b> formed in a predetermined direction of the semiconductor wafer <b>10</b> with the condenser <b>124</b> of the laser beam application means <b>122</b> for applying a laser beam along the street <b>101</b>, thereby performing the alignment of a laser beam application position. Further, the alignment of the laser beam application position is also carried out on streets <b>101</b> formed on the semiconductor wafer <b>10</b> in a direction perpendicular to the above predetermined direction (aligning step). Although on the front surface <b>10</b><i>a</i>, on which the street <b>101</b> is formed, of the semiconductor wafer <b>10</b> faces down at this point, as the image pick-up means <b>125</b> comprises 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, an image of the street <b>101</b> can be picked up through the rear surface <b>10</b><i>b. </i>

0046After the aligning step is carried out, the chuck table <b>121</b> is moved to a laser beam application area where the condenser <b>124</b> of the laser beam application means <b>122</b> for applying a laser beam is located as shown in <figref idref="DRAWINGS">FIG. 4(</figref><i>a</i>) so as to bring one end (left end in <figref idref="DRAWINGS">FIG. 4(</figref><i>a</i>)) of the predetermined street <b>101</b> to a position right below the condenser <b>124</b> of the laser beam application means <b>122</b>. The chuck table <b>121</b> is then moved in the direction indicated by the arrow X<b>1</b> in <figref idref="DRAWINGS">FIG. 4</figref> (<i>a</i>) at a predetermined feed rate while a pulse laser beam of a wavelength having permeability for the silicon wafer is applied from the condenser <b>124</b>. When the application position of the condenser <b>124</b> reaches the other end of the street <b>101</b> as shown in <figref idref="DRAWINGS">FIG. 4(</figref><i>b</i>), the application of the pulse laser beam is suspended and the movement of the chuck table <b>121</b> is stopped. In this deteriorated layer forming step, the focusing point P of the pulse laser beam is set to a position near the front surface <b>10</b><i>a </i>(undersurface) of the semiconductor wafer <b>10</b>. As a result, a deteriorated layer <b>110</b> is exposed to the front surface <b>10</b><i>a </i>(undersurface) of the semiconductor wafer <b>10</b> and formed from the front surface <b>10</b><i>a </i>toward the inside. This deteriorated layer <b>110</b> is formed as a molten-resolidified layer.

0047The processing conditions in the above deteriorated layer forming step are set as follows, for example. <ul id="ul0001" list-style="none"><li id="ul0001-0001" num="0000"><ul id="ul0002" list-style="none"><li id="ul0002-0001" num="0048">Light source: LD excited Q switch Nd:YVO4 pulse laser</li><li id="ul0002-0002" num="0049">Wavelength: 1,064 nm</li><li id="ul0002-0003" num="0050">Repetition frequency: 100 kHz</li><li id="ul0002-0004" num="0051">Average output: 1 W</li><li id="ul0002-0005" num="0052">Focusing spot diameter: 1 μm</li><li id="ul0002-0006" num="0053">Processing-feed rate: 100 mm/sec</li></ul></li></ul>

0054When the semiconductor wafer <b>10</b> is thick, as shown in <figref idref="DRAWINGS">FIG. 5</figref>, the above-described deteriorated layer forming step is carried out several times by changing the focusing point P stepwise so as to form a plurality of deteriorated layers <b>110</b>. 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 twice to form deteriorated layers <b>110</b> having a total thickness of 100 μm. In the case of a wafer <b>10</b> having a thickness of 150 μm, three deteriorated layers <b>110</b> may be formed from the front surface <b>10</b><i>a </i>to the rear surface <b>10</b><i>b </i>along the streets <b>101</b> in the inside of the semiconductor wafer <b>10</b>. The deteriorated layer <b>110</b> may be formed only in the inside so as not to be exposed to the front surface <b>10</b><i>a </i>and the rear surface <b>10</b><i>b. </i>

0055After the deteriorated layer forming step is carried out along all the streets <b>101</b> extending in the predetermined direction of the semiconductor wafer <b>10</b> as described above, the chuck table <b>121</b> is turned at 90° to carry out the above deteriorated layer forming step along streets <b>101</b> extending in a direction perpendicular to the above predetermined direction.

0056After the deteriorated layer forming step is thus carried out along all the streets <b>101</b> formed on the semiconductor wafer <b>10</b>, next comes the step of mounting an adhesive film <b>13</b> for die bonding onto the rear surface <b>10</b><i>b </i>of the semiconductor wafer <b>10</b> as shown in <figref idref="DRAWINGS">FIG. 6</figref>. The adhesive film <b>13</b> is an epoxy resin film having a thickness of 20 to 40 μm and mounted under pressure onto the rear surface <b>10</b><i>b </i>of the semiconductor wafer <b>10</b> while it is heated at 80 to 200° C.

0057Next comes the step of supporting the semiconductor wafer <b>10</b> to an annular frame F through a dicing tape T by affixing the adhesive film <b>13</b> side of the semiconductor wafer <b>10</b> having the adhesive film <b>13</b> mounted thereon to the elastic dicing tape T mounted on the annular frame F as shown in <figref idref="DRAWINGS">FIG. 7</figref>. The protective member <b>11</b> affixed to the front surface <b>10</b><i>a </i>of the semiconductor wafer <b>10</b> is then removed. A dicing tape having an adhesive film preliminary affixed to the front surface of the dicing tape T may also be used. In this case, the rear surface <b>10</b><i>b </i>of the semiconductor wafer <b>10</b> which has undergone the above deteriorated layer forming step is placed on the adhesive film of the dicing tape having the adhesive film mounted on the annular frame, and the adhesive film is mounted under pressure onto the rear surface <b>10</b><i>b </i>of the semiconductor wafer <b>10</b> while it is heated at 80 to 200° C.

0058The above wafer supporting step is followed by the first tape expanding step for dividing the semiconductor wafer <b>10</b> into individual devices along the streets <b>101</b> where the deteriorated layer <b>110</b> has been formed by expanding the dicing tape F. This first tape expanding step is carried out by using a laser beam processing machine having a wafer dividing function constituted according to the present invention and shown in <figref idref="DRAWINGS">FIG. 8</figref>. The laser beam processing machine <b>1</b> shown in <figref idref="DRAWINGS">FIG. 8</figref> comprises a stationary base <b>2</b>, a wafer dividing mechanism <b>3</b> mounted on the stationary base <b>2</b> in such a manner that it can move in a processing-feed direction indicated by an arrow X, a laser beam application unit support mechanism <b>4</b> mounted on the stationary base <b>2</b> in such a manner that it can move in an indexing-feed direction indicated by an arrow Y perpendicular to the direction indicated by the arrow X, and a laser beam application unit <b>5</b> mounted on the laser beam application unit support mechanism <b>4</b> in such a manner that it can move in a direction shown by an arrow Z.

0059The above wafer dividing mechanism <b>3</b> comprises a pair of guide rails <b>31</b> and <b>31</b> which are mounted on the stationary base <b>2</b> and arranged parallel to each other in the processing-processing-feed direction indicated by the arrow X, a sliding block <b>32</b> mounted on the guide rails <b>31</b> and <b>31</b> in such a manner that it can move in the processing-processing-feed direction indicated by the arrow X, a cylindrical member <b>33</b> mounted on the sliding block <b>32</b>, a support table <b>34</b> turnably supported by the cylindrical member <b>33</b>, and a tape expanding mechanism <b>35</b> mounted on the support table <b>34</b>.

0060The above sliding block <b>32</b> has, on the undersurface, a pair of to-be-guided grooves <b>321</b> and <b>321</b> to be fitted to the above pair of guide rails <b>31</b> and <b>31</b> and can move along the pair of guide rails <b>31</b> and <b>31</b> in the processing-feed direction indicated by the arrow X by fitting the to-be-guided grooves <b>321</b> and <b>321</b> to the pair of guide rails <b>31</b> and <b>31</b>, respectively. The wafer dividing mechanism <b>3</b> in the illustrated embodiment has a processing-feed means <b>38</b> for moving the sliding block <b>32</b> along the pair of guide rails <b>31</b> and <b>31</b> in the processing-feed direction indicated by the arrow X. The processing-feed means <b>38</b> comprises a male screw rod <b>381</b> arranged between the above pair of guide rails <b>31</b> and <b>31</b> parallel to them and a drive source such as a pulse motor <b>382</b> for rotary-driving the male screw rod <b>381</b>. The male screw rod <b>381</b> is, at its one end, rotatably supported to a bearing block <b>383</b> fixed on the above stationary base <b>2</b> and is, at the other end, transmission-coupled to the output shaft of the above pulse motor <b>382</b>. The male screw rod <b>381</b> is screwed into a threaded through-hole formed in a female screw block (not shown) projecting from the undersurface of the center portion of the sliding block <b>32</b>. Therefore, by driving the male screw rod <b>381</b> in a normal direction or adverse direction with the pulse motor <b>382</b>, the sliding block <b>32</b> is moved along the guide rails <b>31</b> and <b>31</b> in the processing-feed direction indicated by the arrow X.

0061The wafer dividing mechanism <b>3</b> in the illustrated embodiment comprises a processing-processing-feed position detection means <b>384</b> for detecting the processing-feed position of the above tape expanding mechanism <b>35</b> mounted above the above sliding block <b>32</b>. The processing-feed position detection means <b>384</b> comprises a linear scale <b>384</b><i>a </i>which is arranged along the guide rail <b>31</b> and a read head <b>384</b><i>b </i>which is mounted on the sliding block <b>32</b> and moves along the linear scale <b>384</b><i>a </i>together with the sliding block <b>32</b>. The read head <b>384</b><i>b </i>of this processing-feed position detection means <b>384</b> supplies one pulse signal for every 1 μm to a control means which will be described later in the illustrated embodiment. The control means counts the input pulse signals to detect the processing-feed position of the tape expanding mechanism <b>35</b> mounted above the sliding block <b>32</b>. When the pulse motor <b>382</b> is used as a drive source for the above processing-feed means <b>38</b>, the processing-feed position of the tape expanding mechanism <b>35</b> mounted above the sliding block <b>32</b> can be detected by counting the drive pulses of the control means described later for outputting a drive signal to the pulse motor <b>382</b>. When a servo motor is used as a drive source for the above processing-feed means <b>38</b>, pulse signals outputted from a rotary encoder for detecting the revolution of the servo motor are supplied into the control means described later and the control means counts the pulse signals input, thereby making it possible to detect the processing-feed position of the tape expanding mechanism <b>35</b> mounted above the sliding block <b>32</b>.

0062In the cylindrical member <b>33</b> mounted on the above sliding block <b>32</b> to support the support table <b>34</b>, a pulse motor (not shown) is installed and the support table <b>34</b> is so constituted as to be turned suitably.

0063A description will be subsequently given of the tape expanding mechanism <b>35</b> mounted on the above support table <b>34</b> with reference to <figref idref="DRAWINGS">FIG. 9</figref>.

0064The tape expanding mechanism <b>35</b> shown in <figref idref="DRAWINGS">FIG. 9</figref> comprises a frame holding means <b>36</b> for holding the above annular frame F and a tape expanding means <b>37</b> for expanding the dicing tape T mounted on the annular frame F held on the frame holding means <b>36</b>. The frame holding means <b>36</b> is composed of an annular frame holding member <b>361</b> and a plurality of clamps <b>362</b> as a fixing means arranged around the frame holding member <b>361</b>. The top surface of the frame holding member <b>361</b> serves as a placing surface <b>361</b><i>a </i>for placing the annular frame F, and the annular frame F is placed on this placing surface <b>361</b><i>a</i>. The annular frame F placed on the placing surface <b>361</b><i>a </i>is fixed on the frame holding member <b>361</b> by the clamps <b>362</b>. The frame holding means <b>36</b> constituted as described above is supported by the tape expanding means <b>37</b> in such a manner that it can move in the vertical direction.

0065The tape expanding means <b>37</b> comprises an expansion drum <b>371</b> arranged within the above annular frame holding member <b>361</b>. This expansion drum <b>371</b> has a smaller outer diameter than the inner diameter of the annular frame F and a larger inner diameter than the outer diameter of the semiconductor wafer <b>10</b> on the dicing tape T affixed to the annular frame F. The expansion drum <b>371</b> has a support flange <b>371</b><i>a </i>at the lower end. The tape expanding means <b>37</b> in the illustrated embodiment has support means <b>372</b> which can move the above annular frame holding member <b>361</b> in the axial direction (vertical direction). This support means <b>372</b> is composed of a plurality of air cylinders <b>373</b> installed on the above support flange <b>371</b><i>a</i>, and their piston rods <b>373</b><i>a </i>are connected to the undersurface of the above annular frame holding member <b>361</b>. The support means <b>372</b> composed of the plurality of air cylinders <b>373</b> moves the annular frame holding member <b>361</b> in the vertical direction to a standard position where the placing surface <b>361</b><i>a </i>becomes substantially flush with the upper end of the expansion drum <b>371</b>, a first expansion position where the placing surface <b>361</b><i>a </i>is positioned below the upper end of the expansion drum <b>371</b> by a predetermined distance and a second expansion position where the placing surface <b>361</b><i>a </i>is positioned below the first expansion position by a predetermined distance. Therefore, the support means <b>372</b> composed of the plurality of air cylinders <b>373</b> functions as an expanding and moving means for moving the annular frame holding member <b>361</b> relative to the expansion drum <b>371</b> in the axial direction (vertical direction).

0066Returning to <figref idref="DRAWINGS">FIG. 8</figref>, the above laser beam application unit support mechanism <b>4</b> comprises a pair of guide rails <b>41</b> and <b>41</b> which are mounted on the stationary base <b>2</b> and arranged parallel to each other in the indexing-feed direction indicated by the arrow Y and a movable support base <b>42</b> mounted on the guide rails <b>41</b> and <b>41</b> in such a manner that it can move in the direction indicated by the arrow Y. This movable support base <b>42</b> consists of a movable support portion <b>421</b> movably mounted on the guide rails <b>41</b> and <b>41</b> and a mounting portion <b>422</b> mounted on the movable support portion <b>421</b>. The mounting portion <b>422</b> is provided with a pair of guide rails <b>423</b> and <b>423</b> extending parallel to each other in the direction indicated by the arrow Z on one of its flanks. The laser beam application unit support mechanism <b>4</b> in the illustrated embodiment has an indexing-feed means <b>43</b> for moving the movable support base <b>42</b> along the pair of guide rails <b>41</b> and <b>41</b> in the indexing-feed direction indicated by the arrow Y. This indexing-feed means <b>43</b> comprises a male screw rod <b>431</b> arranged between the above pair of guide rails <b>41</b> and <b>41</b> in parallel with them and a drive source such as a pulse motor <b>432</b> for rotary-driving the male screw rod <b>431</b>. The male screw rod <b>431</b> is, at its one end, rotatably supported to a bearing block (not shown) fixed on the above stationary base <b>2</b> and is, at the other end, transmission-coupled to the output shaft of the above pulse motor <b>432</b>. The male screw rod <b>431</b> is screwed into a threaded through-hole formed in a female screw block (not shown) projecting from the undersurface of the center portion of the movable support portion <b>421</b> constituting the movable support base <b>42</b>. Therefore, by driving the male screw rod <b>431</b> in a normal direction or adverse direction with the pulse motor <b>432</b>, the movable support base <b>42</b> is moved along the guide rails <b>41</b> and <b>41</b> in the indexing-feed direction indicated by the arrow Y.

0067The laser beam processing machine <b>1</b> in the illustrated embodiment has an indexing-feed position detection means <b>433</b> for detecting the indexing-feed position of the movable support base <b>42</b> of the above laser beam application unit support mechanism <b>4</b>. This indexing-feed position detection means <b>433</b> is composed of a linear scale <b>433</b><i>a </i>which is arranged along the guide rail <b>41</b> and a read head <b>433</b><i>b </i>which is mounted on the movable support base <b>42</b> and moves along the linear scale <b>433</b><i>a</i>. The read head <b>433</b><i>b </i>of the indexing-feed position detection means <b>433</b> supplies one pulse signal for every 1 μm to the control means described later in the illustrated embodiment. Then, the control means described later counts the input pulse signals to detect the indexing-feed position of the laser beam application unit <b>5</b>. When the pulse motor <b>432</b> is used as a drive source for the above indexing-feed means <b>43</b>, the indexing-feed position of the laser beam application unit <b>5</b> can be detected by counting the drive pulses of the control means described later for outputting a drive signal to the pulse motor <b>432</b>. Further, when a servo motor is used as a drive source for the above indexing-feed means <b>43</b>, pulse signals outputted from a rotary encoder for detecting the revolution of the servo motor are supplied into the control means later described and the control means counts the pulse signals input, thereby making it possible to detect the indexing-feed position of the laser beam application unit <b>5</b>.

0068The laser beam application unit <b>5</b> in the illustrated embodiment comprises a unit holder <b>51</b> and a laser beam application means <b>52</b> secured to the unit holder <b>51</b>. The unit holder <b>51</b> has a pair of to-be-guided grooves <b>511</b> and <b>511</b> to be slidably fitted to the pair of guide rails <b>423</b> and <b>423</b> on the above mounting portion <b>422</b> and is supported in such a manner that it can move in the direction indicated by the arrow Z by fitting the to-be-guided grooves <b>511</b> and <b>511</b> to the above guide rails <b>423</b> and <b>423</b>, respectively.

0069The above laser beam application means <b>52</b> comprises a casing <b>521</b> mounted on the unit holder <b>51</b>, a pulse laser beam oscillation means (not shown) installed in the casing <b>521</b> and a condenser <b>522</b> which is mounted on the end of the casing <b>521</b> and applies a pulse laser beam oscillated by the pulse laser beam oscillation means to the workpiece held on the above tape expanding mechanism <b>35</b>.

0070An image pick-up means <b>6</b> for detecting the area to be processed by the laser beam application means <b>52</b> is mounted to the end portion of the casing <b>521</b> constituting the laser beam application means <b>52</b>. This image pick-up means <b>6</b> comprises illuminating means for illuminating the workpiece, an optical system for capturing the area illuminated by the illuminating means, and an image pick-up device (CCD) for picking up an image captured by the optical system. An image signal is supplied to the unshown control means.

0071The laser beam application unit <b>5</b> in the illustrated embodiment comprises moving means <b>53</b> for moving the unit holder <b>51</b> along the pair of guide rails <b>423</b> and <b>423</b> in the direction indicated by the arrow Z. The moving means <b>53</b> includes a male screw rod (not shown) arranged between the pair of guide rails <b>423</b> and <b>423</b> and a drive source such as a pulse motor <b>532</b> for driving the male screw rod. By driving the unshown male screw rod in a normal direction or adverse direction with the pulse motor <b>532</b>, the unit holder <b>51</b> and the laser beam application means <b>52</b> are moved along the guide rails <b>423</b> and <b>423</b> in the direction indicated by the arrow Z. In the illustrated embodiment, the laser beam application means <b>52</b> is moved up by driving the pulse motor <b>532</b> in the normal direction and moved down by driving the pulse motor <b>532</b> in the adverse direction.

0072The laser beam processing machine <b>1</b> in the illustrated embodiment comprises the control means <b>20</b>. The control means <b>20</b> is composed of a computer which comprises a central processing unit (CPU) <b>201</b> for carrying out arithmetic processing based on a control program, a read-only memory (ROM) <b>202</b> for storing the control program etc., a read/write random access memory (RAM) <b>203</b> for storing data on the X and Y coordinate values of the start point and the end point for applying a pulse laser beam to the workpiece and the results of operations, a counter <b>204</b>, an input interface <b>205</b> and an output interface <b>206</b>. Detection signals from the processing-feed position detection means <b>384</b>, the indexing-feed position detection means <b>433</b> and the image pick-up means <b>6</b> are supplied to the input interface <b>205</b> of the control means <b>20</b>. Control signals are supplied to the pulse motor <b>382</b>, the pulse motor <b>432</b>, the pulse motor <b>532</b> and the laser beam application means <b>52</b> from the output interface <b>206</b> of the control means <b>20</b>.

0073The first tape expanding step (for dividing the semiconductor wafer <b>10</b> into individual devices along the streets <b>101</b> where the deteriorated layer <b>110</b> has been formed by expanding the above dicing tape F) which is carried out by using the laser beam processing machine <b>1</b> constituted as described above will be described with reference to <figref idref="DRAWINGS">FIGS. 10(</figref><i>a</i>) and <b>10</b>(<i>b</i>).

0074That is, the annular frame F supporting the semiconductor wafer <b>10</b> (the deteriorated layer <b>110</b> has been formed along the streets <b>101</b>) through the dicing tape T is placed on the placing surface <b>361</b><i>a </i>of the frame holding member <b>361</b> constituting the frame holding means <b>36</b> and fixed on the frame holding member <b>361</b> by the clamps <b>362</b> as shown in <figref idref="DRAWINGS">FIG. 10(</figref><i>a</i>). At this point, the frame holding member <b>361</b> is situated at the standard position shown in <figref idref="DRAWINGS">FIG. 10</figref> (<i>a</i>). The annular frame holding member <b>361</b> is then lowered to the first expansion position shown in <figref idref="DRAWINGS">FIG. 10(</figref><i>b</i>) by activating the plurality of air cylinders <b>373</b> as the support means <b>372</b> constituting the tape expanding means <b>37</b>. Therefore, the annular frame F fixed on the placing surface <b>361</b><i>a </i>of the frame holding member <b>361</b> is also lowered, whereby the dicing tape T mounted on the annular frame F is brought into contact with the upper edge of the expansion drum <b>371</b> and expanded as shown in <figref idref="DRAWINGS">FIG. 10(</figref><i>b</i>) (first tape expanding step). As a result, tensile force acts radially on the semiconductor wafer <b>10</b> supported on the dicing tape T trough the adhesive film <b>13</b>. When tensile force thus acts radially on the semiconductor wafer <b>10</b> supported on the dicing tape T through the adhesive film <b>13</b>, the semiconductor wafer <b>10</b> is divided into individual devices <b>102</b> along the streets <b>101</b> whose strength has been reduced by the formation of the deteriorated layers <b>110</b>. However, the adhesive film <b>13</b> is sticky and elongates when tensile force acts on the adhesive film <b>13</b>, thereby making it difficult to divide it without fail. Since the adhesive film <b>13</b> is not divided but elongates, the space S is formed between adjacent devices <b>102</b> as described above.

0075Next comes the step of forming diving grooves in the adhesive film <b>13</b> along the outer periphery of each device <b>102</b> by applying a laser beam to the adhesive film <b>13</b> through the spaces S between adjacent devices <b>102</b> in a state where the dicing tape F has been expanded by carrying out the above first tape expanding step.

0076To carry out this dividing groove forming step, the tape expanding mechanism <b>35</b> which keeps the dicing tape F expanded by carrying out the above first tape expanding step is brought to a position right below the image pick-up means <b>6</b> by the processing-feed means <b>38</b>. After the tape expanding mechanism <b>35</b> is positioned right below the image pick-up means <b>6</b>, alignment work for detecting the area to be processed of the adhesive film <b>13</b> mounted on the rear surface <b>10</b><i>b </i>of the semiconductor wafer <b>10</b> is carried out by the image pick-up means <b>6</b> and the control means <b>20</b>. That is, the image pick-up means <b>6</b> and the control means <b>20</b> carry out image processing such as pattern matching, etc. to align the space S between adjacent devices <b>102</b> obtained by dividing along the street <b>101</b> formed in the predetermined direction of the semiconductor wafer <b>10</b> with the above condenser <b>522</b>, thereby performing the alignment of a laser beam application position. Further, the alignment of the laser beam application position is also carried out on the spaces S between adjacent devices <b>102</b> obtained by dividing along streets <b>101</b> formed on the semiconductor wafer <b>10</b> in a direction perpendicular to the above predetermined direction.

0077After the alignment work for detecting the area to be processed of the adhesive film <b>13</b> on the rear surface <b>10</b><i>b </i>of the semiconductor wafer <b>10</b>, the control means <b>20</b> stores the X and Y coordinate values of the area to be processed in the random access memory (RAM) <b>203</b>. The X and Y coordinate values of the area to be processed can be obtained based on detection signals from the processing-feed position detection means <b>384</b> and the indexing-feed position detection means <b>433</b>.

0078Then, as shown in <figref idref="DRAWINGS">FIGS. 11(</figref><i>a</i>) to <b>11</b>(<i>c</i>), the semiconductor wafer <b>10</b> mounted on the dicing tape T held on the frame holding means <b>36</b> of the tape expanding mechanism <b>35</b> through the annular frame F is moved to a laser beam application area where the condenser <b>522</b> is located so as to bring the space S between adjacent devices <b>102</b> obtained by dividing along the predetermined street <b>101</b> to a position right below the condenser <b>522</b>. At this point, the semiconductor wafer <b>10</b> should be positioned such that one end (left end in <figref idref="DRAWINGS">FIG. 11(</figref><i>a</i>)) of the space S formed along the street <b>101</b> is located right below the condenser <b>522</b>. Thereafter, the control means <b>20</b> sends a control signal to the laser beam application means <b>52</b> to apply a pulse laser beam of a wavelength having absorptivity for the adhesive film from the condenser <b>522</b> and at the same time, controls the processing-feed means <b>38</b> to move the tape expanding mechanism <b>35</b> in the direction indicated by the arrow X<b>1</b> in <figref idref="DRAWINGS">FIG. 11</figref> (<i>a</i>) at a predetermined processing-feed rate. Then, when the other end of the space S formed along the street <b>101</b> reaches a position right below the condenser <b>522</b> as shown in <figref idref="DRAWINGS">FIG. 11(</figref><i>b</i>), the application of the pulse laser beam is suspended and the movement of the tape expanding mechanism <b>35</b> is stopped. As a result, the pulse laser beam is applied to the adhesive film <b>13</b> through the space S between adjacent devices <b>102</b> obtained by dividing along the predetermined street <b>101</b> to form a dividing groove <b>130</b> along the space S between adjacent devices <b>102</b> in the adhesive film <b>13</b> as shown in <figref idref="DRAWINGS">FIG. 11(</figref><i>c</i>) (dividing groove forming step).

0079The processing conditions of the dividing groove forming step are set as follows, for example. <ul id="ul0003" list-style="none"><li id="ul0003-0001" num="0000"><ul id="ul0004" list-style="none"><li id="ul0004-0001" num="0080">Light source: LD excited Q switch Nd:YVO4 pulse laser</li><li id="ul0004-0002" num="0081">Wavelength: 355 nm</li><li id="ul0004-0003" num="0082">Repetition frequency: 100 kHz</li><li id="ul0004-0004" num="0083">Average output: 1 W</li><li id="ul0004-0005" num="0084">Focusing spot diameter: 5 μm</li><li id="ul0004-0006" num="0085">Processing-feed rate: 100 mm/sec</li></ul></li></ul>

0086After the dividing groove forming step for forming a dividing groove <b>130</b> along the space S between adjacent devices <b>102</b> in the adhesive film <b>13</b> by applying a pulse laser beam to the adhesive film <b>13</b> through the space S between adjacent devices <b>102</b> obtained by dividing along the predetermined street <b>101</b>, the control means <b>20</b> activates the indexing-feed means <b>43</b> to move the tape expanding mechanism <b>35</b> a distance corresponding to the interval between the above spaces S in the direction indicated by the arrow Y in <figref idref="DRAWINGS">FIG. 8</figref> to further carry out the above dividing groove forming step. After the dividing groove forming step is carried out by applying a pulse laser beam to the adhesive film <b>13</b> through the spaces S between adjacent devices <b>102</b> formed in the predetermined direction, the tape expanding mechanism <b>35</b> is turned at 90° to carry out the dividing groove forming step for applying a pulse laser beam to the adhesive film <b>13</b> through the spaces S between adjacent devices <b>102</b> formed in a direction perpendicular to the above predetermined direction. As a result, the dividing groove <b>130</b> is formed along all the spaces S between adjacent devices <b>102</b> in the adhesive film <b>13</b>.

0087After the above dividing groove forming step, next comes a second tape expanding step for dividing, along the outer periphery of each device <b>102</b>, the adhesive film <b>13</b> in which the dividing grooves <b>130</b> have been formed along the outer periphery of each device <b>102</b> by further expanding the dicing tape T from the state in which the above first expanding step has been carried out. In this second tape expanding step, the annular frame holding member <b>361</b> is lowered to the second expansion position shown in <figref idref="DRAWINGS">FIG. 12(</figref><i>b</i>) by activating the plurality of air cylinders <b>373</b> as the support means <b>372</b> constituting the tape expanding means <b>37</b> from the state in which the above dividing groove forming step shown in <figref idref="DRAWINGS">FIG. 12</figref> (<i>a</i>) has been carried out. Therefore, as the annular frame F fixed on the placing surface <b>361</b><i>a </i>of the frame holding member <b>361</b> is also lowered, as shown in <figref idref="DRAWINGS">FIG. 12(</figref><i>b</i>), the dicing tape T mounted on the annular frame F is brought into contact with the upper edge of the expansion drum <b>371</b> and further expanded (second tape expanding step). As a result, tensile force further acts on the adhesive film <b>13</b> affixing to the dicing tape T to divide the adhesive film <b>13</b> along the dividing grooves <b>130</b> formed along the outer periphery of each device <b>102</b>. Since the dividing grooves <b>130</b> are formed along the outer periphery of each device <b>102</b> in the adhesive film <b>13</b> when the second tape expanding step is carried out as described above, the adhesive film <b>13</b> is divided along the dividing grooves <b>130</b> without fail.