JP2006303223A - Processing method of wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a processing method of a wafer in which a gettering sink effect is sustained while ensuring flexural strength. <P>SOLUTION: The processing method of the wafer for imparting the gettering sink effect to the wafer having a plurality of devices formed on the surface comprises a step for forming a predetermined amount of a strained layer on the rear surface of the wafer by immersing the rear surface of the wafer into liquid mixed with abrasive grains and contained in a processing tub, and imparting an ultrasonic wave to the liquid mixed with abrasive grains so that the mixed abrasive grains act on the rear surface of the wafer. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a wafer processing method for providing a gettering sink effect to a wafer such as a semiconductor wafer having a plurality of devices formed on the surface thereof.

  In the semiconductor device manufacturing process, a large number of rectangular areas are defined by planned cutting lines called streets arranged in a lattice pattern on the surface of a semiconductor wafer having a substantially disk shape, and each of the rectangular areas includes IC, LSI, etc. Form the device. Individual semiconductor chips are formed by cutting the semiconductor wafer formed with a large number of devices along the streets. In order to reduce the size and weight of the semiconductor chip, the semiconductor wafer is usually cut along the streets to cut the individual rectangular regions, and the back surface of the semiconductor wafer is ground to a predetermined thickness. Forming.

  The grinding of the back surface of the semiconductor wafer is usually performed by pressing a grinding wheel formed by fixing diamond abrasive grains with an appropriate bond such as a resin bond against the back surface of the semiconductor wafer while rotating at high speed. When the back surface of the semiconductor wafer is ground by such a grinding method, a processing strain layer composed of microcracks of about 1 μm is generated on the back surface of the semiconductor wafer, and particularly when the thickness of the semiconductor wafer is ground to 100 μm or less, the processing strain is generated. The bending strength of the semiconductor chips individually divided by the layers is considerably reduced.

As a countermeasure for removing the processing strain layer generated on the back surface of the ground semiconductor wafer, polishing such as polishing, wet etching, or dry etching is performed on the back surface of the ground semiconductor wafer. (For example, refer to Patent Document 1 and Patent Document 2).
JP 2002-28311 A JP 2001-85385 A

Thus, according to the study by the present inventors, DRAM (Dynamic
In the case of a wafer in which a device including a memory element such as a Random Access memory or a flash memory is formed, the memory function can be achieved by removing the processing strain layer generated by grinding by polishing or etching after grinding the back surface of the wafer. It turned out to be reduced. In the wafer manufacturing process, metal atoms such as copper (Cu) contained in the semiconductor are present on the back side of the wafer. However, when the processing strain layer generated on the back surface of the wafer is removed, the gettering sink effect due to the processing strain layer disappears and the contained metal atoms such as copper (Cu) move to the vicinity of the device. This may be due to adversely affecting the memory function.

  The present invention has been made in view of the above facts, and a main technical problem thereof is to provide a wafer processing method capable of maintaining the gettering sink effect and ensuring the bending strength.

In order to solve the main technical problem, according to the present invention, a wafer processing method for providing a gettering sink effect to a wafer having a plurality of devices formed on a surface thereof,
Immerse the back surface of the wafer in the liquid contained in the treatment tank and mixed with abrasive grains, and apply the ultrasonic waves to the liquid mixed with abrasive grains to make the abrasive particles mixed in the liquid act on the back surface of the wafer, A strain layer forming step of forming a predetermined amount of strain layer on the back surface of the wafer;
A method for processing a wafer is provided.

  Further, according to the present invention, before performing the strain layer forming step, the back surface of the wafer is formed by grinding the back surface of the wafer to form the wafer to a predetermined thickness. And a processing strain layer removing step of removing the processing strain layer generated on the wafer.

According to the present invention, the backside of a wafer is immersed in a liquid contained in a processing tank and mixed with abrasive grains, and ultrasonic waves are applied to the liquid mixed with abrasive grains to remove the abrasive grains mixed into the liquid from the wafer. Since a predetermined amount of a strained layer is formed on the back surface of the wafer, the gettering sink effect can be maintained and the bending strength can be ensured.
In the wafer processing method according to the present invention, the back surface of the wafer is ground to form a predetermined thickness, and after the processing strain layer removal step is performed to remove the grinding processing strain, the strain layer formation step is performed. Therefore, a predetermined amount of the strained layer can be formed without variation. Therefore, a chip having a stable gettering sink effect and bending strength can be obtained.

  Preferred embodiments of a wafer processing method according to the present invention will be described below in more detail with reference to the accompanying drawings.

  FIG. 1 shows a perspective view of a semiconductor wafer as a wafer to be processed according to the present invention. A semiconductor wafer 2 shown in FIG. 1 is made of a silicon wafer, and a plurality of streets 21 are formed in a lattice shape on the surface 2a, and devices 22 are formed in a plurality of regions partitioned by the plurality of streets 21. Has been. As shown in FIG. 2, the protective member 3 is stuck to the surface 2a of the semiconductor wafer 2 configured as described above (protective member sticking step).

  If the protective member 3 is attached to the front surface 2a of the semiconductor wafer 2 by performing the protective member attaching step, the grinding step of grinding the back surface 2b of the semiconductor wafer 2 to form the semiconductor wafer 2 to a predetermined thickness. To implement. This grinding process is performed by the grinding apparatus 4 shown in FIG. That is, the protective member 3 side of the semiconductor wafer 2 is placed on the chuck table 41 of the grinding apparatus 4 (therefore, the back surface 2b of the semiconductor wafer 2 is on the upper side), and the semiconductor wafer is placed on the chuck table 41 by suction means (not shown). 2 is adsorbed and held. Then, while rotating the chuck table 41 at, for example, 300 rpm, the grinding wheel 43 provided with the grinding wheel 42 is rotated at 6000 rpm to contact the back surface 2b of the semiconductor wafer 2 until a predetermined thickness, for example, 100 μm is reached. Grind. When the grinding process is performed in this manner, a work strain layer having a thickness of about 1 μm is generated on the back surface 2b of the semiconductor wafer 2 by grinding.

  If the grinding process mentioned above is implemented, the process distortion layer removal process of removing the process distortion layer produced | generated on the back surface 2b of the semiconductor wafer 2 will be implemented. This processing strain layer removing step is performed by, for example, the polishing apparatus 5 shown in FIG. That is, the protection member 3 side of the semiconductor wafer 2 subjected to the above-described grinding process is placed on the chuck table 51 of the polishing apparatus 5 (therefore, the back surface 2b of the semiconductor wafer 2 is on the upper side), and suction means (not shown) Thus, the semiconductor wafer 2 is sucked and held on the chuck table 51. Then, while rotating the chuck table 51 at, for example, 300 rpm, a polishing tool 53 including a polishing wheel 52 in which abrasive grains such as zirconia oxide are dispersed in a flexible member such as felt and fixed with an appropriate bonding agent is rotated at, for example, 6000 rpm. By contacting the back surface 2b of the semiconductor wafer 2, the back surface 2b of the semiconductor wafer 2 is polished. As a result, the processing strain layer generated on the back surface 2b of the semiconductor wafer 2 is removed by performing the above-described grinding process. The processing strain layer removing step may be performed by polishing, wet etching, dry etching, or the like.

  When the processing strain layer removing step is performed as described above, a strain layer forming step for forming a predetermined amount of strain layer on the back surface 2b of the semiconductor wafer 2 from which the processing strain layer has been removed is performed. This strained layer forming step is performed by, for example, the strained layer forming apparatus 6 shown in FIG. A strain layer forming apparatus 6 shown in FIG. 5 includes a base 61, a support side plate 62 attached to the rear side surface of the base 61, an ultrasonic transmitter 63 disposed on the base 61, A processing tank 64 disposed on the sonic wave transmitter 63, a temporary placement table 65 for temporarily placing a wafer as a workpiece, and a temporary placement table 65 for holding a wafer as a workpiece and the treatment bath 64 It consists of a workpiece holding means 66 that moves between them. The ultrasonic transmitter 63 oscillates an ultrasonic wave of 20 kHz to 10 MHz. The processing tank 64 contains a liquid 67 mixed with abrasive grains. The abrasive grains mixed in the liquid may be diamond abrasive grains having a particle diameter of about 2 μm, for example, and water can be used as the liquid. On the temporary placing table 65, the semiconductor wafer 2 carried by the carrying means (not shown) after the above-described processing strain layer removing step is placed with the protective member 3 facing upward.

  The workpiece holding means 66 includes a suction pad 661, a support means 662 for supporting the suction pad 661, a moving block 664 to which the support means 662 is attached via a support arm 663, and the moving block 664. It comprises moving means 665 for moving along a pair of guide rails 621 and 621 disposed in the horizontal direction on the front surface of the support side plate 62. The suction pad 661 is connected to suction means (not shown), and sucks and holds a wafer as a workpiece on the lower surface thereof. The support means 662 is an air cylinder in the illustrated embodiment, and a suction pad 661 is attached to the tip of the piston rod 662a. The moving block 664 includes a pair of guided grooves 664 a and 664 a that are fitted to the pair of guide rails 621 and 621, and the guided grooves 664 a and 664 a are guided by fitting to the guide rails 621 and 621. The rails 621 and 621 are supported so as to be movable. The moving means 665 includes a male screw rod 655a disposed in parallel between the pair of guide rails 621 and 621, and a drive source such as a pulse motor 655b for rotationally driving the male screw rod 655a. One end of the male screw rod 655a is rotatably supported by a bearing block 655c fixed to the support side plate 62, and the other end is connected to the output shaft of the pulse motor 655b. The male screw rod 655a is screwed into a through female screw hole 664b formed in the moving block 664. Accordingly, the moving block 664 is moved along the guide rails 621 and 621 by driving the male screw rod 655a forward and backward by the pulse motor 655b.

A strain layer forming step performed using the strain layer forming apparatus 6 configured as described above will be described with reference to FIGS. 5 and 6.
The semiconductor wafer 2 on which the above-described processing strain layer removing step has been performed is placed on the temporary placement table 65 with the protective member 3 facing upward by a conveying means (not shown). When the semiconductor wafer 2 is placed on the temporary placement table 65, the moving means 665 of the workpiece holding means 66 is activated to position the suction pad 661 above the temporary placement table 65, and the support means 662 is further activated. Then, the suction pad 661 is lowered by a predetermined amount. Then, a suction means (not shown) is operated, and the semiconductor wafer 2 placed on the temporary placement table 65 is sucked and held by the suction pad 661. If the semiconductor wafer 2 is sucked and held by the suction pad 661, the support means 662 is operated to raise the suction pad 661 by a predetermined amount, and the moving means 665 is further operated to position the suction pad 661 above the processing bath 64. Then, the support means 662 is operated to lower the suction pad 661 by a predetermined amount, and the back surface 2b of the semiconductor wafer 2 sucked and held by the suction pad 661 is mixed with abrasive 67 contained in the processing tank 64. Immerse in.

  Next, the ultrasonic transmitter 63 is operated to apply an ultrasonic wave of 20 kHz to 10 MHz to the liquid 67 mixed with abrasive grains accommodated in the treatment tank 64. As a result, abrasive grains mixed in the liquid move and act on the back surface 2b of the semiconductor wafer 2, so that a predetermined amount of strain layer is formed on the back surface 2b of the semiconductor wafer 2 (strain layer forming step). The time for applying the ultrasonic wave to the liquid 67 mixed with abrasive grains may be several minutes.

  As described above, when a predetermined amount of the strained layer is formed on the back surface 2b of the semiconductor wafer 2, the support means 662 is operated to raise the suction pad 661 that sucks and holds the semiconductor wafer 2 by a predetermined amount. Then, the moving means 665 is operated to position the suction pad 661 above the temporary placement table 65, and the support means 662 is further operated to lower the suction pad 661 by a predetermined amount. Next, the semiconductor wafer 2 suctioned and held by the suction pad 661 is placed on the temporary placement table 65 by releasing the suction holding by the suction pad 661.

  As described above, the semiconductor wafer 2 that has been subjected to the strain layer forming process and returned to the temporary placement table 65 is transported to a cutting device as a dicing device, for example, by a transport unit (not shown). Then, the semiconductor wafer 2 is cut along the streets 21 by a cutting device and divided into individual semiconductor chips.

Experimental example 1

The back surface of a 600 μm-thick semiconductor wafer was ground to a thickness of 100 μm, and microcracks of about 1 μm were formed by observation with a transmission electron microscope. The semiconductor wafer thus formed was cut along the streets with a cutting device to produce semiconductor chips of 10 mm length and 10 mm width. The semiconductor chip manufactured in this way is the gettering sink described above.
sink) effect was obtained, but the bending strength was 600 MPa.

Experimental example 2

  The back surface of a semiconductor wafer having a thickness of 600 m is ground to form a thickness of 100 μm, and after the processing strain layer removal step described above is performed to remove the grinding strain, the strain layer formation step described above is performed and the semiconductor is formed. Microcracks of about 0.2 μm were formed on the back surface of the wafer by observation with a transmission electron microscope. The semiconductor wafer thus formed was cut along the streets with a cutting device to produce semiconductor chips of 10 mm length and 10 mm width. The semiconductor chip manufactured in this way has a gettering sink effect equivalent to that of the semiconductor chip manufactured according to Experimental Example 1. In addition, the semiconductor chip manufactured according to Experimental Example 2 had a bending strength of 900 MPa.

As described above, the semiconductor chip manufactured according to the present invention (Experimental Example 2) has the same gettering sink effect as the semiconductor chip manufactured according to the conventional method (Experimental Example 1). The bending strength was 1.5 times.
In the wafer processing method according to the present invention, the back surface of the wafer is ground to a predetermined thickness, and after the processing strain layer removing step is performed to remove the grinding processing strain, the strain layer described above is used. Since the forming step is performed, a predetermined amount of the strained layer can be formed without variation. Therefore, a chip having a stable gettering sink effect and bending strength can be obtained.

The perspective view of the semiconductor wafer processed by the processing method of the wafer by this invention. The perspective view which shows the state which affixed the protection member on the surface of the semiconductor wafer shown in FIG. Explanatory drawing of the grinding process in the processing method of the wafer by this invention. Explanatory drawing of the process distortion layer removal process in the processing method of the wafer by this invention. The perspective view of the distortion layer forming apparatus for implementing the distortion layer formation process in the processing method of the wafer by this invention. Explanatory drawing of the distortion layer formation process in the processing method of the wafer by this invention.

Explanation of symbols

2: Semiconductor wafer 21: Street 22: Device 3: Protection member 4: Grinding device 41: Grinding device chuck table 42: Grinding wheel 43: Grinding wheel 5: Polishing device 51: Polishing device chuck table 52: Polishing wheel 53: Polishing tool 6: Strain layer forming device 63: Ultrasonic transmitter 64: Treatment tank 65: Temporary table 66: Workpiece holding means 661: Suction pad 662: Support means 662
665: moving means 67: liquid mixed with abrasive grains

Claims (2)

A wafer processing method for providing a gettering sink effect to a wafer having a plurality of devices formed on a surface,
Immerse the back surface of the wafer in the liquid contained in the treatment tank and mixed with abrasive grains, and apply the ultrasonic waves to the liquid mixed with abrasive grains to make the abrasive particles mixed in the liquid act on the back surface of the wafer, A strain layer forming step of forming a predetermined amount of strain layer on the back surface of the wafer;
A method for processing a wafer.   Before performing the strain layer forming step, a grinding step for grinding the back surface of the wafer to form the wafer to a predetermined thickness, and a processing strain layer generated on the back surface of the wafer by performing the grinding step are performed. The wafer processing method according to claim 1, wherein a processing strain layer removing step of removing is performed.

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