JP2008258412A - Method for singulating silicon wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a silicon chip singulated in a state that a die attach film is stuck to a rear face in the case of singulating a silicon wafer by a DBG method. <P>SOLUTION: A protection material is stuck to a circuit forming surface of a silicon wafer, the silicon wafer is ground from a surface opposed to the protection material sticking surface, a die attach film is stuck to the ground surface of the silicon wafer, a wafer holding material is stuck on the die attach film, the protection material is removed, the silicon wafer is diced to a singulated chip so that a cutting edge arrives from the circuit forming surface side of the silicon wafer at the wafer holding material, a protection material is stuck to a circuit forming surface of the chip, the wafer holding material is ground until the die attach film appears, a holding tape is stuck to the die attach film, the chip is transferred to the holding tape together with the die attach film, and then the protection material is removed from the chip. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a silicon wafer singulation method, and more particularly, to a silicon wafer singulation method suitable for use in a prior dicing method.

  Silicon wafers used in semiconductor devices are becoming larger and thinner in order to improve the productivity of semiconductor devices. As a processing method for dividing such a silicon wafer having a large diameter and a thin shape without damaging the wafer, a dicing before grinding (DBG) method (hereinafter simply referred to as a DBG method) is widely used. Yes.

In the DBG method, when a silicon wafer is singulated, the silicon wafer is half-cut from the circuit forming surface side and half-cut from the back surface side of the silicon wafer before grinding the silicon wafer to a desired thickness dimension. This is a silicon wafer singulation method in which a silicon wafer is singulated at the same time by grinding to a position and adjusting the silicon wafer to a predetermined thickness. Silicon chips separated by the DBG method are bonded to a wiring substrate such as a lead frame by using an adhesive and are formed in a semiconductor device. As described above, the silicon chip separated by the DBG method is mounted by attaching an adhesive to the joint surface with the wiring board.
JP 2000-294522 A

  With the miniaturization of semiconductor devices, silicon wafers have also become more finely divided. Therefore, in the method of separating silicon wafers by the DBG method, since it is necessary to individually apply an adhesive to each silicon chip, the work of uniformly applying the adhesive to the bonding surface of the silicon chip is very difficult. There is a problem that it is complicated.

  In addition, some semiconductor devices have a product in which silicon chips are stacked and mounted. In such products, since silicon chips need to be stacked flat, a method of bonding using a double-sided adhesive film such as a die attach film instead of an adhesive has come to be used. However, in the conventional DBG method, even if it is possible to divide the silicon wafer, it is impossible to divide the silicon wafer with the die attach film attached. Therefore, it is necessary to affix the die attach film to each individual silicon wafer, but the operation of adhering the die attach film to the silicon chip is extremely inefficient.

  In the DBG method, the silicon wafer is adjusted to a desired thickness by grinding to be singulated, but by grinding, a fractured layer is formed on the ground surface of the silicon wafer and strain remains. End up. Since the bending strength of the silicon chip is lowered by this residual strain, there is a case where a polishing process is performed after the grinding process to remove the residual strain (stress relief). However, since this polishing process polishes the surface of the separated silicon chip, contamination accumulates in the groove between the silicon chips supported by the holding sheet, and the polishing process is performed accurately. There is also a problem that the chip cannot be peeled off and a chip is peeled off by the polishing process, resulting in a decrease in yield.

  Therefore, the present invention can provide a silicon chip that is separated with a die attach film attached to the back surface when the silicon wafer is separated by the DBG method, and without reducing the yield. An object of the present invention is to provide a silicon wafer singulation method capable of easily polishing a silicon wafer.

  The present invention includes a step of grinding the silicon wafer from a surface opposite to the surface to which the first protective material is pasted after pasting the first protective material to the circuit forming surface of the silicon wafer; A step of attaching a die attach film to the ground surface, then bonding a wafer holding material on the die attach film and removing the first protective material, and the wafer holding material from the circuit forming surface side of the silicon wafer. Dicing the silicon wafer into individual chips so that the cutting blade reaches the edge, and attaching a second protective material to the circuit forming surface of the chip over all the chips held by the wafer holding material; And after grinding the wafer holding material until the die attach film appears, affixing a holding tape to the die attach film, A step of transferring the chip to the holding tape, is a silicon wafer singulation method comprising that and a step of removing the second protective material from the tip.

  In addition, the step of grinding the silicon wafer includes a step of grinding the silicon wafer and a step of polishing after the grinding. Such a polishing step is preferably performed by dry polishing. As a result, even if the silicon chip is polished to improve the bending strength, contamination accumulation in the groove formed between the silicon chips can be prevented, and an efficient and highly accurate polishing process is performed. be able to.

  Further, a bare silicon wafer is used as the wafer holding material. As a result, since the equipment used for polishing the silicon wafer and the silicon wafer processing method can be applied as they are, a large-scale equipment investment is unnecessary, and the operator's work burden can be reduced. In addition, improvement in the processing accuracy of silicon wafers can be expected.

  According to the silicon wafer singulation method according to the present invention, the silicon wafer and the die attach film can be singulated at the same time in a state where the die attach film is adhered to the silicon wafer. Further, since the back side of the silicon wafer, which is likely to cause chipping of the silicon wafer during grinding, is supported by the die attach film and is ground, it is possible to prevent the occurrence of chipping when polishing the silicon wafer. Furthermore, since the equipment used in the conventional DBG process can be applied as it is, it is economical because it is not necessary to make a large-scale equipment investment.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a silicon wafer singulation method according to the present invention will be described below with reference to the drawings. FIG. 1 is a flowchart showing a process sequence of a silicon wafer singulation method according to this embodiment. 2-16 is explanatory drawing which shows the state of the silicon wafer in each process.

  First, as shown in FIG. 2, a circuit (not shown) is formed on one side of the silicon wafer 10 having a predetermined size (step 1). Next, as shown in FIG. 3, a back grind protective tape 20 (hereinafter referred to as BG protective tape 20), which is a first protective material, is attached to the circuit forming surface 12 of the silicon wafer 10 (step 2). The BG protective tape 20 protects circuits and circuit components formed on the silicon wafer 10 when a chuck table (not shown) of the grinding (polishing) device 30 sucks and holds the silicon wafer 10 during back grinding. Is. Next, as shown in FIG. 4, the surface of the silicon wafer 10 facing the surface to which the BG protective tape 20 is attached is ground by a back grindstone 32 (step 3). In this way, the back grinding process is performed by the back grindstone 32 until the thickness of the silicon wafer 10 reaches the design dimension.

When the plate thickness dimension of the silicon wafer 10 reaches the design dimension, the grinding process is terminated, and then a polishing process for polishing the ground surface is performed as shown in FIG. 5 (step 4). In this polishing step, polishing is performed using a polishing apparatus 30 that uses a polisher grindstone 34. Dry polishing is preferably used for the polishing step.
By polishing the ground surface of the silicon wafer 10 with the polisher grindstone 34 in this way, residual strain on the ground surface of the silicon wafer 10 generated during grinding can be removed. Since the bending strength of the silicon wafer 10 can be improved by removing the residual strain of the silicon wafer 10, damage during handling of the silicon wafer 10 can be greatly reduced, and the yield is improved.

After the polishing process is completed, the die attach film 40 is attached to the polishing surface 14 of the silicon wafer 10 as shown in FIG. 6 (step 5). The die attach film 40 is made of a thermoplastic material, and the thickness of the die attach film 40 is 15 to 40 micrometers.
After the die attach film 40 is attached to the polished surface 14 of the silicon wafer 10, bare silicon 50, which is a wafer holding material, is attached to the die attach film 40 as shown in FIG. 7 (step 6). The bare silicon 50 in this embodiment is the same as the silicon wafer 10 used in step 1. The die attach film 40 and the bare silicon 50 are attached by superimposing the bare silicon 50 after the die attach film 40 is heated to 120 to 150 ° C. to give adhesiveness.

  After the bare silicon 50 is attached to the die attach film 40, it is naturally cooled or forcedly cooled to room temperature, and then the BG protective tape 20 as the first protective material is peeled off and removed as shown in FIG. (Step 7). Next, as shown in FIG. 9, dicing is performed from the circuit forming surface side of the silicon wafer 10 with a dicing saw 60 that is a cutting blade (step 8). The dicing process is performed such that the cutting edge of the dicing saw 60 reaches a part of the bare silicon 50. Although the silicon wafer 10 and the die attach film 40 are separated into individual pieces by the dicing process, since the die attach film 40 is preliminarily attached to the bare silicon 50, each of the separated silicon chips 16 is dicing. The same position as the plane position in the front can be maintained, and the arrangement of the silicon chips 16 is not disturbed.

  After the dicing process is completed, a back grind protective tape 70 (hereinafter referred to as BG protective tape 70), which is a second protective material, is applied to the circuit forming surface 12 of the silicon wafer 10 (silicon chip 16) as shown in FIG. (Step 9). This BG protective tape 70 can be the same as the BG protective tape 20 used in the first protective material. After the BG protective tape 70 is applied, the bare silicon 50 is ground by back grinding as shown in FIG. 11 (step 10). In this embodiment, since bare silicon 50 made of the same material as the silicon wafer 10 is used as a wafer holding material, a grinding (polishing) apparatus 30 used in a normal DBG method can be used. Further, the grinding wheel of the grinding (polishing) device 30 is convenient because the back grinding wheel 32 used in step 4 can be used and the same grinding method as in step 4 can be applied, and the burden on the operator is very small. .

When all of the bare silicon 50 is ground by the back grinding process, the die attach film 40 under the bare silicon 50 appears, and the silicon chip 16 can be obtained in a state where the die attach film 40 is singulated (FIG. 12). . In this grinding process, since the polishing surface 14 side of the silicon wafer 10 (silicon chip 16) that is likely to be chipped is held by the die attach film 40, chipping of the silicon wafer 10 can be prevented and the yield can be improved. improves.
When the die attach film 40 appears on the ground surface, the back grinding process is terminated, and the silicon chip 16 and the die attach separated into pieces corresponding to the silicon chip 16 are formed on the dicing tape 80 as a holding tape as shown in FIG. The film 40 is transferred (step 11), and the BG protective tape 70 is peeled off and removed from the silicon chips 16, 16,... As shown in FIG.

  The silicon chip 16 transferred to the dicing tape 80 and the die attach film 40 separated into pieces are individually picked up by a pickup device 90 which is a conveying means as shown in FIG. 15, and as shown in FIG. Is adhered by the die attach film 40 (step 13).

The silicon wafer singulation method according to the present invention has been described in detail above based on the embodiments. However, the present invention is not limited to the above embodiments, and the scope of the invention is not changed. Of course, even if various modifications are made, it belongs to the technical scope of the present invention.
For example, in the above-described embodiment, a mode is described in which a grinding surface polishing step (step 4) by dry polishing that removes residual strain on the surface of the silicon wafer 10 is performed after the grinding step of the silicon wafer 10 in step 3. However, if there is no residual strain due to the grinding process (step 3) on the surface of the silicon wafer 10 or if the residual strain does not significantly affect the bending strength, a polishing process for polishing the ground surface of the silicon wafer 10 Can be omitted.

  In the embodiment described above, an example in which bare silicon 50 is used as a wafer holding material has been described, but the wafer holding material may be formed of other materials. It is. In short, since the wafer holding material is ground by back grinding, a material that can be easily ground by the grinding device 30 is preferable. For example, in addition to a ceramic wafer holding material such as alumina, a synthetic resin wafer holding material such as an epoxy resin may be used. Further, it is more preferable that the wafer holding material is made of an inexpensive material.

It is a flowchart which shows the process order of the isolation | separation method of the silicon wafer in this embodiment. It is explanatory drawing which shows a silicon wafer. It is explanatory drawing which shows the state which affixed BG protective tape on the circuit formation surface of a silicon wafer. It is explanatory drawing which shows the state which is carrying out the back grinding of the silicon wafer. It is explanatory drawing which shows the state which grind | polishes the grinding surface of a silicon wafer. It is explanatory drawing which shows the state which affixed the die attach film on the grinding | polishing surface of the silicon wafer. It is explanatory drawing which shows the state which piled up the bare silicon on the die attach film. It is explanatory drawing which shows the state which removed the BG protective tape from the silicon wafer. It is explanatory drawing which shows the state which has diced the silicon wafer and the die attach film. It is explanatory drawing which shows the state which affixed BG protective tape on the circuit formation surface of the diced silicon wafer. It is explanatory drawing which shows the state which backgrinds bare silicon. It is explanatory drawing which shows the state which grinding of bare silicon was completed. It is explanatory drawing which shows the state which affixed the dicing tape on the grinding | polishing surface of bare silicon. It is explanatory drawing which shows the state which has removed the BG protective tape from the circuit formation surface of a silicon chip. It is explanatory drawing which shows the state which has picked up the silicon chip. It is explanatory drawing which shows the state which has adhere | attached the silicon chip on the semiconductor substrate with the die attach film.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Silicon wafer 12 Circuit formation surface 14 Polishing surface 16 Silicon chip 20, 70 BG protective tape 30 Grinding (polishing) device 32 Back grindstone 34 Polisher grindstone 40 Die attach film 50 Bare silicon 60 Dicing saw 80 Dicing tape 90 Pickup device K Wiring board

Claims (4)

After pasting the first protective material on the circuit forming surface of the silicon wafer, grinding the silicon wafer from the surface facing the surface on which the first protective material is pasted;
Attaching a die attach film to the ground surface of the silicon wafer, then bonding a wafer holding material on the die attach film, and removing the first protective material;
Dicing the silicon wafer into individual chips so that a cutting blade reaches the wafer holding material from the circuit forming surface side of the silicon wafer;
Attaching a second protective material to the circuit forming surface of the chip across all the chips held by the wafer holding material;
After grinding the wafer holding material until the die attach film appears, attaching a holding tape to the die attach film, and transferring the chip together with the die attach film to the holding tape;
And a step of removing the second protective material from the chip.   2. The silicon wafer singulation method according to claim 1, wherein the step of grinding the silicon wafer includes a step of grinding the silicon wafer and a step of polishing after the grinding.   3. The silicon wafer singulation method according to claim 2, wherein the polishing step is performed by dry polishing.   The silicon wafer individualization method according to claim 1, wherein a bare silicon wafer is used as the wafer holding material.

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