JP4941636B2 - Substrate grinding method - Google Patents

Description

The present invention relates to a grinding method for reducing the thickness by grinding a substrate such as a semiconductor wafer (hereinafter abbreviated as “wafer”), and in particular, grinding with a uniform grinding load on the central portion and the outer peripheral portion of the substrate. The present invention relates to a technique for making the finish uniform and shortening processing tact.

  A semiconductor chip having an electronic circuit such as an IC or LSI formed on its surface divides a rectangular rectangular area on a surface of a substrate such as a disk-shaped wafer by a cutting line called a street, and the electronic circuit is placed in the rectangular area. After the formation, the substrate is manufactured by a process of dividing the substrate along the street.

  In such a manufacturing process, the semiconductor chip finally obtained is obtained by grinding the back surface opposite to the device surface on which the electronic circuit is formed to reduce the thickness of the substrate before being divided into semiconductor chips. A method for producing a light-weight and large-capacity semiconductor package is known (for example, Patent Document 1 and Patent Document 2).

  As a method for grinding the back surface of a wafer, for example, in Patent Document 1, a wafer mounted on a chuck table is attached to a chuck table so that a plurality of grindstone portions pass through the center of rotation of the wafer. A method of grinding by pressing is disclosed. Further, Patent Document 1 discloses that a plurality of chuck tables are arranged on a turntable, and after performing rough grinding of a wafer by a grinding unit, finish grinding is performed by another grinding unit. Further, Patent Document 2 discloses a technique for simultaneously grinding the front and back surfaces of a wafer with two opposing grinding wheels. Also in this technique, grinding is performed by pressing a grindstone disposed so that a plurality of grindstone portions pass through the center of rotation of the wafer against the surface of the wafer.

Japanese Patent Laid-Open No. 7-130692 Japanese Patent Laid-Open No. 10-256203

  In the techniques described in the above patent documents, since one surface of the wafer is always ground by one grinding unit, there is a limit to shortening the processing tact. Further, since the wafer is processed while rotating, there is a large difference in the rotational peripheral speed between the vicinity of the center and the outer edge of the wafer. In particular, in the case of a wafer having a large outer diameter, the processing load due to the grindstone is considerably higher in the outer peripheral portion than in the central portion, and as a result, there is a significant difference in the finishing of the grinding process between the central portion and the outer peripheral portion. There's a problem.

Accordingly, the present invention is to provide a uniform grinding finish by equalizing the grinding load on the central portion and the peripheral portion of the substrate, and its object is to provide a grinding method of a substrate which can shorten the processing tact.

The present invention is adsorbed and fixed to the rotatable holding table substrate, the exposed surface of the substrate to a grinding method for a substrate for grinding, rotatable Ru stone portions are arranged in a trajectory passing through the rotation center of the holding table A first cup wheel and a rotatable second cup wheel in which a grindstone portion is disposed at a position that does not pass through the center of rotation and contacts an outer peripheral portion of the exposed surface , and rotates the substrate. While grinding the first cup wheel and the second cup wheel simultaneously pressing the exposed surface of the substrate , the second cup wheel is then retracted, and the entire exposed surface of the substrate is predetermined by the first cup wheel. It is characterized by finishing to the thickness of .

In the substrate grinding method of the present invention, the first cup wheel in which the grindstone portion is disposed on the locus passing through the rotation center and the second cup in which the grindstone portion is disposed at a position in contact with the outer peripheral surface of the substrate. Since the wheel is used , the grinding speed (feeding speed to the substrate) by one cup wheel can be increased and the machining tact time can be shortened by sharing the grinding work between the first and second cup wheels. Further, since the second cup wheel is in contact with the outer peripheral surface of the substrate, there is little difference in rotational peripheral speed between the inner peripheral side and the outer peripheral side of the processing area. Therefore, the difference in processing load due to the grindstone between the inner peripheral side and the outer peripheral side of the processing area can be reduced to equalize the finishing of the grinding process.

In the present invention, since the first and second cup wheels can be driven and rotated independently of each other, the processing load of the first and second cup wheels can be appropriately set according to the situation.
For example, the entire surface of the substrate can be ground by the first cup wheel while the outer peripheral side portion of the substrate is ground by the second cup wheel. In this case, the lower end positions of the grindstones of the first and second cup wheels may be made the same.

  Moreover, if the lower end position of the grindstone of the second cup wheel is set lower than the lower end position of the grindstone of the first cup wheel, the outer peripheral portion of the substrate is ground only by the second cup wheel, The portion to be ground by the first cup wheel is only the central portion that is not ground by the second cup wheel. Therefore, unlike the case where the first cup wheel grinds the entire surface of the substrate, a large difference in rotational peripheral speed does not occur between the center of the processing area and the outer peripheral side, so that the processing load difference due to the grindstone is further reduced. Thus, the finish of the grinding process can be made even more uniform. In this case, if the ground area of the exposed surface of the substrate by the first and second cup wheels is made substantially the same, it is theoretically possible to process with half the tact of the conventional one.

  In the above aspect, since the grindstone of the second cup wheel precedes the grindstone of the first cup wheel, when the grinding process by the first and second cup wheels is finished simultaneously, There is a step at the boundary. In order to avoid this, the second cup wheel is retracted at the final stage of the grinding process, and the entire exposed surface is ground by the first cup wheel and finished to a predetermined thickness.

  In the present invention, it is desirable to measure at least an area where the second cup wheel is ground by a measurement terminal for measuring the thickness of the substrate being processed. Thereby, while performing the position control of the second cup wheel, it is possible to obtain the timing for retracting the second cup wheel, and it is also possible to measure the thickness of the finish by the first cup wheel. The measuring terminal can be a contact type or a non-contact type, and as a measuring means equipped with the measuring terminal, a method of supplying water to the object and reflecting the water through the ultrasonic wave with the object, Any type of device that detects the displacement of the measurement terminal from the capacitance value of the built-in capacitor can be used.

According to the present invention, the first drivable and rotate independently, so that grinding the board by the second cup wheel, by equalizing the grinding load uniformly grinding finishing to the central portion and the peripheral portion of the substrate In addition, it is possible to obtain an effect such that the machining tact time can be shortened.

Hereinafter, an embodiment in which the present invention is applied to a grinding method for grinding and thinning a semiconductor wafer will be described with reference to the drawings.
[1] Semiconductor Wafer FIGS. 1A and 1B are a perspective view and a side view, respectively, of a disk-shaped semiconductor wafer (hereinafter abbreviated as a wafer) 1 which is a substrate to be ground in this embodiment. Yes. The wafer 1 is a silicon wafer or the like and has a thickness of about 600 to 700 μm. A large number of rectangular semiconductor chips 3 are partitioned on the surface of the wafer 1 by lattice-like streets 2, and electronic circuits such as ICs and LSIs are formed on the surface of the semiconductor chips 3. Further, a V-shaped orientation notch 4 is formed on the side surface of the wafer 1.

  The wafer 1 is ground and thinned to a target thickness (for example, about 50 to 100 μm), and then cut and divided along the street 2 to be separated into a large number of semiconductor chips 3. When grinding, a protective tape 5 is attached to the surface on which the electronic circuit is formed for the purpose of protecting the electronic circuit. The protective tape 5 is peeled off after finishing the grinding process. FIG. 2 shows a grinding apparatus for thinning the wafer 1. Hereinafter, the grinding apparatus 10 will be described.

[2] code 11 in the grinding apparatus Figure 2 is a base on which various mechanisms are mounted, the base 11 is mainly a rectangular portion with a horizontal upper surface, one longitudinal end portion (FIG. 2 Wall portion 12 standing perpendicular to the upper surface. In FIG. 2, the longitudinal direction, the width direction, and the vertical direction of the base 11 are shown as a Y direction, an X direction, and a Z direction, respectively. The wall 11 side of the base 11 from the substantially middle portion in the longitudinal direction is a grinding area 10A, and the opposite side supplies the wafer 1 before grinding to the grinding area 10A, and collects the wafer 1 after grinding. It is set as the collection area 10B.

  In the grinding area 10A on the upper surface of the base 11, a disk-shaped turntable 13 whose rotation axis is parallel to the Z direction and whose upper surface is horizontal is rotatably provided. The turntable 13 is rotated in the direction of arrow R by a rotation drive mechanism (not shown). A plurality of (in this case, three) disk-shaped chuck tables (holding tables) whose rotation axis extends in the same Z direction as that of the turntable 13 and whose upper surface is horizontal are provided on the outer peripheral portion of the turntable 13. 14 is rotatably provided at equal intervals in the circumferential direction.

  The chuck table 14 is of a generally known vacuum chuck type, and the wafer 1 placed on the upper surface is sucked and held on the chuck table 14. Each chuck table 14 is independently rotated in one direction or both directions by a rotation driving mechanism (not shown) provided in the turntable 13.

  As shown in FIG. 2, in a state where two chuck tables 14 are arranged in the X direction on the wall 12 side, a pair of rough grinding is disposed above the chuck tables 14 in order from the upstream side in the rotation direction of the turntable 13. The first grinding unit 20A and a pair of second grinding units 20B for finish grinding are respectively disposed. Each chuck table 14 is rotated intermittently by the turntable 13 so that the rough grinding position below the first grinding unit 20A, the finish grinding position below the second grinding unit 20B, and the most supply / recovery area 10B. It is positioned at each of the three positions with the attachment and detachment position approaching.

  Since the first and second grinding units 20A and 20B have the same configuration, they will be described with common reference numerals. The first and second grinding units 20A and 20B are attached to the wall portion 12 of the base 11 so as to be movable up and down in the Z direction via a slider 31 and a guide rail 32, and are moved up and down by a lift drive mechanism 33. As shown in FIGS. 3 and 4, the first and second grinding units 20 </ b> A and 20 </ b> B have a flange at the tip of the spindle 22 when the spindle 22 incorporated in the cylindrical housing 21 is driven to rotate by a motor 23. The cup wheel 25 fixed via 24 rotates, and a large number of grindstones 26 arranged and fixed in an annular shape over the entire circumference on the outer peripheral portion of the lower surface of the cup wheel 25 grind the workpiece. The outer diameter of the circular grinding locus of the grindstone 26 is approximately equal to the diameter of the wafer 1.

The pair of first grinding units 20A are not arranged symmetrically with respect to the chuck table 14 (wafer 1) but are offset. Specifically, as shown in FIG. 5, the left grinding unit 20 </ b> A is arranged so that the contour line of the cup wheel (hereinafter referred to as “first cup wheel”) 25 passes through the rotation center bO of the chuck table 14. The right grinding unit 20 </ b> A is arranged such that a cup wheel (hereinafter referred to as “second cup wheel”) 25 is in contact with a portion on the outer peripheral side of the wafer 1. With this configuration, when the back surface of the wafer 1 is pressed with the grindstone 26 of the second cup wheel 25 while rotating the wafer 1 together with the chuck table 14, only the outer peripheral grinding region b2 on the back surface is ground. Further, when the back surface of the wafer 1 is pressed with the grindstone 26 of the first cup wheel 25, the grinding region b1 or the grinding regions b1 and b2 in the central portion of the wafer 1 are ground.

  In the case where only the central grinding area b1 is ground by the first cup wheel 25, it is desirable that the grinding area b1 and the grinding area b2 are substantially the same. For this purpose, A: B = 7: 3 may be satisfied, where A is the radius of the grinding region b1 at the center and B is the radial length of the grinding region b2 on the outer peripheral side.

  Since the second grinding unit 20B is also configured in the same manner as the first grinding unit 20A, the same reference numerals are given and description thereof is omitted. Since the 1st grinding unit performs rough grinding and the 2nd grinding unit 20B performs finish grinding, the particle size of the abrasive grain contained in the grindstone 26 used for both differs. The grindstone 26 of the first grinding unit 20A is used for rough grinding, and those having a grain size of, for example, about 20 to 60 μm are used. Further, the grindstone 26 of the second grinding unit 20B is used for finish grinding, and those having a grain size of, for example, more than 0 μm and 3 μm or less are used.

  The wafer 1 is ground to a predetermined thickness by the first grinding unit 20A at the rough grinding position and by the second grinding unit 20B at the finish grinding position. However, as shown in FIG. A thickness measuring device 40 for measuring the thickness of the wafer 1 is disposed in the vicinity of each grinding position. The wafer 1 is ground to a predetermined thickness while the thickness is measured one by one by the thickness measuring device 40 at each grinding position.

  Two thickness measuring devices 40 are provided for each chuck table 14. The thickness measuring device 40 is supported by a stand (not shown) provided on the upper surface of the base 11, and includes a measurement terminal 40a that is rotated in the vertical direction by a built-in drive mechanism. And the front-end | tip part of the measurement terminal 40a is pressed by the to-be-measured object by rotating the measurement terminal 40a below with a drive mechanism. The measuring terminal 40a of one thickness measuring device is pressed on the upper surface by the turntable 13, and the measuring terminal 40a of the other thickness measuring device is pressed on the outer peripheral portion of the back surface of the wafer 1, that is, the grinding region b2. . Therefore, the thickness of the wafer 1 can be calculated by subtracting the measured values of the two thickness measuring devices 40.

Next, the supply / recovery area 10B will be described.
In the center of the supply / recovery area 10B, a two-bar link type transfer robot 60 that moves up and down is installed. Around the transfer robot 60, a supply cassette 61, an alignment table 62, a swing arm type supply arm 63, a recovery arm 64 having the same structure as the supply arm 63, a spinner A cleaning device 65 and a recovery cassette 66 are arranged.

  The cassette 61, the alignment table 62 and the supply arm 63 are means for supplying the wafer 1 to the chuck table 14, and the recovery arm 64, the cleaning device 65 and the cassette 66 are configured to remove the wafer 1 from the chuck table 14 after grinding the back surface. It is a means to collect. The cassettes 61 and 66 accommodate a plurality of wafers 1 in a stacked state, and are set at predetermined positions on the base 11.

  When one wafer 1 is taken out from the supply cassette 61 by the transfer robot 60, the wafer 1 is placed on the alignment table 62 with the back side to which the protective tape 5 is not attached facing upward, Here, it is determined at a certain position. Next, the wafer 1 is picked up and picked up from the alignment table 62 by the supply arm 63 and placed on the chuck table 14 waiting at the attachment / detachment position.

  On the other hand, the back surface is ground by the first and second grinding units 20A and 20B, and the wafer 1 on the chuck table 14 positioned at the attachment / detachment position is picked up and taken up by the recovery arm 64, transferred to the cleaning device 65, and washed with water. Dried. The wafer 1 cleaned by the cleaning device 65 is transferred and accommodated in the collection cassette 66 by the transfer robot 60.

Next, the operation of grinding the back surface of the wafer 1 by the grinding apparatus 10. In this grinding, only the grinding region b1 is ground by the first cup wheel 25, and only the grinding region b2 is ground by the second cup wheel 25. First, one wafer 1 accommodated in the supply cassette 61 is moved to the positioning table 62 and positioned by the transfer robot 60, and then the supply arm 63 waits at the attachment / detachment position, and the vacuum apparatus is operated. The wafer 1 is placed on the chuck table 14 with the back side facing up. As a result, the wafer 1 is attracted and held on the chuck table 14. At this time, the measurement terminal 40a of the thickness measuring device 40 on the rough grinding side and the finish grinding side is rotated upward so as not to interfere with the moving chuck table 14.

  Next, the turntable 13 rotates in the direction of the arrow R in FIG. 2, and the chuck table 14 holding the wafer 1 stops at the rough grinding position. Then, the measurement terminal 40 a of the thickness measuring device 40 is rotated downward, and one measurement terminal 40 a is pressed against the grinding region b 1 of the wafer 1 and the other measurement terminal 40 a is pressed against the upper surface of the turntable 13. At this time, the next chuck table 14 is positioned at the attachment / detachment position, and the wafer 1 to be ground next is set on the chuck table 14 as described above.

Next, the chuck table 14 at the rough grinding position is rotated to rotate the wafer 1, while the second cup wheel 25 of the first grinding unit 20A for rough grinding is slowly lowered at a predetermined speed while rotating. The grindstone 26 is pressed against the back surface of the wafer 1 to start rough grinding of the grinding region b2. Next, the first cup wheel 25 is slowly lowered at a predetermined speed, and the grindstone 26 is pressed against the back surface of the wafer 1 to start rough grinding of the grinding region b1.
The rotational speed of the cup wheel 25 is 3000 to 6000 RPM.

  Grinding of the back surface of the wafer 1 proceeds by the first and second cup wheels 25, and the thickness of the wafer 1 measured by the thickness measuring device 40 is thicker by a predetermined dimension than the set thickness after rough grinding. Then, the second cup wheel 25 is raised. As a result, the first cup wheel 25 starts to grind the entire surface of the wafer 1. Then, when the thickness of the wafer 1 reaches the set thickness, the first cup wheel 25 is raised to finish the grinding. By the whole surface grinding by the first cup wheel 25, the step generated at the boundary between the grinding regions b1 and b2 disappears.

  Subsequently, the wafer 1 having been subjected to the rough grinding is transferred to the finish grinding position by rotating the turntable 13 in the R direction. Here, the chuck table 14 is rotated in the same manner as described above, and the finish grinding first step is performed. By using the 2 grinding unit 20B, the back surface of the wafer 1 is finish ground. At this time, the finish grinding side thickness measuring device 40 is operated in the same manner as in the above rough grinding, and finish grinding is performed while measuring the thickness of the wafer 1 one by one. The wafer 1 that has been set in the attach / detach position in advance is transferred to the rough grinding position, and the wafer 1 is roughly ground in parallel with the preceding finish grinding while the thickness is measured in the same manner as described above. Further, the wafer 1 to be processed next is set on the chuck table 14 moved to the attachment / detachment position.

  When both the finish grinding and the rough grinding, which have been performed in parallel, are finished, the turntable 13 is rotated and the wafer 1 after the finish grinding is transferred to the attachment / detachment position. As a result, the subsequent wafer 1 is transferred to the rough grinding position and the finish grinding position, respectively. The wafer 1 on the chuck table 14 positioned at the attachment / detachment position is transferred to the cleaning device 65 by the recovery arm 64, and is washed with water and dried. The wafer 1 cleaned by the cleaning device 65 is transferred and accommodated in the collection cassette 66 by the transfer robot 60.

The above is a cycle in which the wafer 1 is cleaned and recovered by finishing it to a desired thickness while measuring the thickness by the thickness measuring device 40. According to the grinding processing apparatus 10 of the present embodiment, while the turntable 13 is intermittently rotated as described above, rough grinding is performed on the wafer 1 at the rough grinding position, and finish grinding is performed at the finish grinding position in parallel. As a result, the plurality of wafers 1 are efficiently ground.

In the grinding apparatus 10 having the above-described configuration, the grinding region b1 at the center is ground by the first cup wheel 25 in which the grindstone 26 is disposed on the locus passing through the rotation center bO of the chuck table 14, and the second cup wheel 25 is used. Since the grinding region b2 on the outer peripheral side is ground, the grinding process is shared by the first and second cup wheels 25. Therefore, it is possible to increase the grinding speed by the first and second cup wheels 25 and shorten the processing tact. In particular, in the above embodiment, there is no large difference in rotational peripheral speed between the vicinity of the center of the processing area and the outer peripheral side as in the case where one cup wheel grinds the entire surface of the wafer 1 from the beginning. The difference in load can be further reduced to make the grinding finish even more uniform.

It is the (a) perspective view and (b) side view of the semiconductor wafer by which the back surface is ground by one Embodiment of this invention. 1 is an overall perspective view of a grinding apparatus according to an embodiment. FIG. 2 is a perspective view of a grinding unit provided in the grinding apparatus shown in FIG. 1. (B) It is a side view. FIG. 2 is a side view of a grinding unit provided in the grinding apparatus shown in FIG. 1. It is a top view which shows the grinding area | region by the 1st, 2nd cup wheel. It is a top view which shows arrangement | positioning of the 1st, 2nd cup wheel with respect to a turntable.

Explanation of symbols

1 ... Wafer (substrate)
10 ... grinding apparatus 14 ... chuck table (holding table)
DESCRIPTION OF SYMBOLS 40 ... Thickness measuring device 40a ... Measurement terminal 25 ... 1st, 2nd cup wheel 26 ... Grinding wheel (grinding stone part)
bO ... Center of rotation

Claims (3)

A substrate grinding method by adsorbing and fixing a substrate to a rotatable holding table and grinding the exposed surface of the substrate,
A rotatable first cup wheel in which a grindstone portion is disposed on a trajectory passing through the rotation center of the holding table, and a grindstone portion that does not pass through the rotation center and is in contact with an outer peripheral side portion of the exposed surface. Using a rotatable second cup wheel arranged, and grinding while pressing the first cup wheel and the second cup wheel simultaneously on the exposed surface of the substrate while rotating the substrate ,
Next, the second cup wheel is retracted, and the entire exposed surface is finished to a predetermined thickness by the first cup wheel . By sending the second cup wheel to the substrate side ahead of the first cup wheel, the center portion of the exposed surface is ground by the first cup wheel, and the second cup wheel The substrate grinding method according to claim 1 , wherein the outer peripheral portion of the exposed surface is ground. The substrate grinding method according to claim 2 , wherein a grinding area of the exposed surface of the substrate by the second cup wheel is substantially half of a total grinding area.

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