Patent Grant
7544589
The present invention relates to a method of dividing a wafer having a plurality of devices, which are formed in a plurality of areas sectioned by streets formed in a lattice pattern on the front surface thereof, and having test metal patterns which are formed on the streets along the streets.
As known to people of ordinary skill in the art, in the production process of a semiconductor device, individual semiconductor chips are manufactured by cutting a semiconductor wafer comprising devices such as IC's or LSI's which are formed in a plurality of areas sectioned by break lines called “streets” arranged in a lattice pattern on the front surface of a substantially disk-like semiconductor substrate, along the streets to divide it into the areas each having a device formed thereon.
Most of the above semiconductor wafers have a plurality of test metal patterns called “test element group (TEG)” for testing the function of each device on the streets. Before the semiconductor wafer having the test metal patterns is divided into individual semiconductor chips, the function of each device is checked by using the test metal patterns. The test metal patterns are cut and removed simultaneously at the time when the semiconductor wafers are divided. That is, when the test metal patterns remain, there is a possibility that the constitution of each device is detected from the metal patterns. Therefore, the test metal patterns are removed from the standpoint of keeping a company secret.
Meanwhile, as a means of dividing a plate-like workpiece such as a semiconductor wafer, a laser processing method in which a pulse laser beam of a wavelength having permeability to the workpiece is applied with its focal point set to the inside of the area to be divided is attempted nowadays, and disclosed by Japanese Patent No. 3408805. 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 to the workpiece from one surface 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 streets and exerting external force along the streets whose strength has been reduced by the formation of the deteriorated layers.
When the TEG is formed on the streets of the wafer, however, there is a problem in that the TEG becomes an obstacle to a laser beam, thereby making it impossible to form a deteriorated layer uniformly.
To solve the above problem, a laser beam is applied from the rear surface devoid of TEG of the wafer along the streets, thereby making it possible to form a deteriorated layer uniformly. However, there arises a problem that when the wafer having the deteriorated layers is divided by exerting external force thereto, the TEG is broken like the teeth of a saw, causes contamination and reduces the quality of devices. Further, there remains the problem that the constitution of devices can be detected from the remaining TEG, resulting in the leakage of a company secret.
It is an object of the present invention to provide a wafer dividing method capable of dividing a wafer into individual devices without being influenced by test metal patterns formed on streets and preventing the constitution of the obtained devices from being detected.
According to the present invention, there is provided a method of dividing a wafer having a plurality of devices, which are formed in a plurality of areas sectioned by streets formed in a lattice pattern on the front surface and having test metal patterns which are formed on the streets, comprising:
a metal pattern breaking step for forming a break line in the test metal patterns by holding the wafer in such a manner that its rear surface faces up and applying a pulse laser beam having permeability to the wafer from the rear surface of the wafer with its focal point set to a position near the test metal patterns along the streets;
a deteriorated layer forming step for forming a deteriorated layer along the streets above the break lines in the inside of the wafer by applying a pulse laser beam having permeability to the wafer from the rear surface of the wafer with its focal point set to a position above the break lines in the inside of the wafer along the streets; and
a dividing step for dividing the wafer into individual chips along the deteriorated layers of the wafer by exerting external force to the wafer having the deteriorated layers formed therein.
The pulse laser beam applied in the above metal pattern breaking step has a wavelength of 1,064 nm, a repetition frequency of 20 to 80 KHz and an average output of 0.05 to 0.2 W.
In the wafer dividing method of the present invention, since the plurality of test metal patterns formed on the streets are broken along the streets to form a break line in the test metal patterns by carrying out the metal pattern breaking step, even when the wafer is broken along the deteriorated layers formed by the deteriorated layer forming step, the test metal patterns are not broken like the teeth of a saw. Further, as the test metal patterns are broken and their function is destroyed by the application of a laser beam, the constitution of the devices cannot be detected from the remaining test metal patterns.
a) and 4(b) are explanatory diagrams showing the metal pattern breaking step in the wafer dividing method of the present invention;
a) to 5(c) are explanatory diagrams showing the deteriorated layer forming step in the wafer dividing method of the present invention;
a) and 7(b) are explanatory diagrams showing the dividing step in the wafer dividing method of the present invention.
Preferred embodiments of the wafer dividing method of the present invention will be described in more detail hereinunder with reference to the accompanying drawings.
The front surface 2a side of the semiconductor wafer 2 constituted as described above is put on a support tape 4 which is composed of a synthetic resin sheet such as a polyolefin sheet and mounted on an annular frame 3 as shown in
A description will be first given of the method of dividing the semiconductor wafer 2 along the plurality of streets 21.
First comes a metal pattern breaking step for forming a break line in the test metal patterns 23 by holding the semiconductor wafer 2 in such a manner that the rear surface 2b of the semiconductor wafer 2 faces up and applying a pulse laser beam having permeability to the semiconductor wafer 2 from the rear surface 2b of the semiconductor wafer 2 along the streets 21 with its focal point set to a position near the test metal patterns 23. This metal pattern breaking step is carried out by using a laser beam processing machine shown in
The above laser beam application means 52 applies a pulse laser beam from a condenser 522 mounted on the end of a cylindrical casing 521 arranged substantially horizontally. The illustrated laser beam processing machine 5 comprises an image pick-up means 53 mounted onto the end portion of the casing 521 constituting the above laser beam application means 52, as shown in
A description will be subsequently given of the metal pattern breaking step using the above-described laser beam processing machine 5. The semiconductor wafer 2 supported to the annular frame 3 through the support tape 4 is first placed on the chuck table 51 of the laser beam processing machine 5 shown in
The chuck table 51 suction-holding the semiconductor wafer 2 as described above is brought a position right below the image pick-up means 53 by the processing-feed mechanism that is not shown. After the chuck table 51 is positioned right below the image pick-up means 53, the image pick-up means 53 and the control means (not shown) carry out alignment work for detecting the area to be processed of the semiconductor wafer 2. That is, the image pick-up means 53 and the control means (not shown) carry out image processing such as pattern matching etc. to align a street 21 formed in a predetermined direction of the semiconductor wafer 2 with the condenser 522 of the laser beam application means 52 for applying a laser beam along the street 21, thereby performing the alignment of a laser beam application position. Although the street 21 formed on front surface 2a of the semiconductor wafer 2 positions on the underside at this point, an image of the street 21 can be picked up through the rear surface 2b as the image pick-up means 53 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. The alignment of the laser beam application position is also carried out on streets 21 formed on the semiconductor wafer 2 in a direction perpendicular to the above predetermined direction.
After the street 21 formed on the semiconductor wafer 2 held on the chuck table 51 is detected and the alignment of the laser beam application position is carried out as described above, as shown in
The processing conditions of the above metal pattern breaking step are set as follows, for example.
After the above-described metal pattern breaking step is carried out along all the streets 21 formed in the predetermined direction of the semiconductor wafer 2, the chuck table 51, therefore, the semiconductor wafer 2 is turned at 90° . The above metal pattern breaking step is then carried out along all the streets 21 formed on the semiconductor wafer 2 in a direction perpendicular to the above predetermined direction. As a result, break lines 231 are formed along the streets 21 in all the test metal patterns 23 formed on all the streets 21 of the semiconductor wafer 2.
According to experiments conducted by the inventors of the present invention, when the pulse laser beam applied in the above metal pattern breaking step had a repetition frequency of less 20 kHz and an average output of less than 0.05 W, the metal patterns 23 could not be broken. When the repetition frequency was higher than 80 kHz and the average output was higher than 0.2 W, the metal patterns 23 were destroyed and fine break lines 231 could not be formed. Therefore, the pulse laser beam applied in the metal pattern breaking step should have a repetition frequency of 20 to 80 kHz and an average output of 0.05 to 0.2 W.
The above metal pattern breaking step is followed by the deteriorated layer forming step for forming a deteriorated layer along the streets 21 above the break lines 231 in the inside of the semiconductor wafer 2 by applying a pulse laser beam having permeability to the semiconductor wafer 2 from the rear surface 2b of the semiconductor wafer 2 along the streets 21 with its focal point set to a position above the break lines 231 in the inside of the semiconductor wafer 2.
That is, the chuck table 51 is moved to a laser beam application area where the condenser 522 of the laser beam application means 52 for applying a laser beam is located to bring one end (left end in
The processing conditions in the above deteriorated layer forming step are set as follows, for example.
After the above deteriorated layer forming step is carried out along all the streets 21 formed in the predetermined direction of the semiconductor wafer 2, the chuck table 51, therefore, the semiconductor wafer 2 is turned at 90°. The above deteriorated layer forming step is carried out along all the streets 21 formed on the semiconductor wafer 2 in a direction perpendicular to the above predetermined direction. As a result, deteriorated layers 24 are formed along all the streets 21 above the break lines 231 formed in the test metal patterns 23 on all the streets 21 in the inside of the semiconductor wafer 2.
The above deteriorated layer forming step is followed by a dividing step for dividing the semiconductor wafer 2 along the deteriorated layers 24 as the dividing start points by exerting external force to the semiconductor wafer 2. This dividing step is carried out by using a dividing apparatus 6 shown in
The tape expanding means 62 has an expansion drum 621 arranged in the inside of the above annular frame holding member 611. This expansion drum 621 has a smaller inner diameter than the inner diameter of the annular frame 3 and a larger outer diameter than the outer diameter of the semiconductor wafer 2 put on the support tape 4 mounted on the annular frame 3. The expansion drum 621 has a support flange 622 at the lower end. The tape expanding means 62 in the illustrated embodiment has a support means 63, which can move the above annular frame holding member 611 in the vertical direction. This support means 63 comprises a plurality of air cylinders 631 installed on the above support flange 622, and their piston rods 632 are connected to the undersurface of the above annular frame holding member 611. The support means 63 comprising the plurality of air cylinders 631 moves the annular frame holding member 611 in the vertical direction between a standard position where the placing surface 611a becomes substantially flush with the upper end of the expansion drum 621 and an expansion position where the placing surface 611a is positioned below the upper end of the expansion drum 621 by a predetermined distance. Therefore, the support means 63 comprising the plurality of air cylinders 631 functions as an expanding and moving means for moving the frame holding member 611 relative to the expansion drum 621 in the vertical direction.
The dividing step which is carried out by using the above constituted dividing apparatus 6 will be described with reference to
The following dividing methods may be employed besides the above dividing method.
That is, a method in which the semiconductor wafer 2 put on the support tape 4 (the deteriorated layer 24 is formed along the streets 21) is placed on a soft rubber sheet, and the top surface of the semiconductor wafer 2 is pressed with a roller to divide the semiconductor wafer 2 along the streets 21 whose strength has been reduced by the formation of the deteriorated layers 24 may be employed. Alternatively, a method in which an ultrasonic wave as a longitudinal wave (compressional wave) having a frequency of about 28 kHz is applied along the streets 21 whose strength has been reduced by the formation of the deteriorated layers, a method in which a pressing member is applied along the streets 21 whose strength has been reduced by the formation of the deteriorated layers 24 or a method in which a heat shock is given by applying a laser beam along the streets 21 whose strength has been reduced by the formation of the deteriorated layers 24 may be employed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-191914 | Jun 2005 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 7446020 | Nakamura | Nov 2008 | B2 |
| 20050009301 | Nagai et al. | Jan 2005 | A1 |
| 20080057680 | Watanabe | Mar 2008 | A1 |
| 20080124898 | Kobayashi | May 2008 | A1 |
| Number | Date | Country |
|---|---|---|
| 3408805 | Mar 2003 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20070004179 A1 | Jan 2007 | US |
