JP5907797B2 - Wafer processing method - Google Patents

Description

  The present invention relates to a wafer processing method for providing a gettering effect to a wafer having a plurality of devices formed on its surface.

  A grinding apparatus is widely used to thin a wafer such as a semiconductor device wafer or an optical device wafer to a predetermined thickness. The grinding apparatus has a grinding wheel including abrasive grains such as diamond and CBN (Cubic Boron Nitride), and the wafer is ground with this grinding wheel to thin the wafer to a predetermined thickness.

  However, when the wafer is ground with a grinding wheel, grinding distortion is generated in the wafer. When grinding distortion is generated in the wafer, the bending strength of the wafer is lowered and the risk of breakage increases. Therefore, for example, polishing such as dry polishing and CMP (Chemical Mechanical Polishing) as disclosed in JP-A-2002-183111 is applied to the ground wafer to remove grinding distortion.

  However, there is a problem that the gettering effect is lost in the wafer from which the grinding distortion is removed. With the gettering effect, during the manufacturing process of semiconductor device wafers, optical device wafers, etc., the impurities mainly consisting of heavy metals contained in these wafers are supplemented in regions other than the device regions where the wafer devices are formed, The effect is to protect the device from contamination by impurities.

  Grinding strain is used as a site for trapping impurities in regions other than the device formation region. The gettering effect does not contaminate the device with impurities, and defects such as generation of crystal defects and deterioration of electrical characteristics are suppressed, and device characteristics are stabilized and performance is improved (for example, Japanese Patent Laid-Open No. Hei 10-2010). 70099 and JP-A-2005-93869).

  Therefore, as a method of imparting a gettering effect to a wafer from which grinding strain has been removed, a method of immersing the wafer in a liquid mixed with abrasive grains and applying ultrasonic waves to form a strained layer on the back surface of the wafer is a special feature. This is proposed in Japanese Unexamined Patent Publication No. 2006-303223.

JP 2002-183111 A JP 10-70099 A Japanese Patent Laying-Open No. 2005-93869 JP 2006-303223 A

  However, the method disclosed in Patent Document 4 described above has a problem that it is uneconomical because diamond abrasive grains for imparting a gettering effect are required.

  The present invention has been made in view of these points, and an object of the present invention is to provide a wafer processing method that can impart a gettering effect to a wafer more economically than in the past.

  According to the present invention, there is provided a wafer processing method for imparting a gettering effect to a wafer having a plurality of devices formed on the surface, wherein the grinding means supplies the grinding fluid to the grinding means and the wafer while the back surface of the wafer is applied by the grinding means. A grinding step for grinding and thinning to a predetermined thickness, a polishing step for polishing the back surface of the wafer after performing the grinding step, and removing grinding distortion generated in the grinding step, and a grinding step generated by the grinding step After the processing waste separation step for separating the processing waste from the processed waste liquid and the polishing step, the processing waste separated in the processing waste separation step is sprayed to the back surface of the wafer under high pressure to cause distortion on the back surface of the wafer. And a strained layer forming step of forming a layer.

  The processing scrap generated by the grinding of the wafer is mainly composed of wafer scraps from which the wafer has been crushed, abrasive grains degrown from the grinding wheel, and a bonding agent for the grinding wheel. In the wafer processing method of the present invention, since a strain layer is formed on the back surface of the wafer with these processing scraps, no abrasive grains are required to form the strain layer. Therefore, it is more economical than before. Further, since the processing waste liquid generated by grinding is reused, there is an effect that it is environmentally friendly.

It is a perspective view of the processing apparatus suitable for implementing the processing method of the wafer of this invention. It is a back side perspective view of a polish unit. It is a surface side perspective view of a semiconductor wafer. It is a back surface side perspective view of the semiconductor wafer by which surface protection tape was stuck on the surface. It is a perspective view which shows a grinding | polishing step. It is a perspective view which shows a distortion layer formation step.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Referring to FIG. 1, there is shown a perspective view of a processing apparatus 2 suitable for carrying out the processing method of the present invention. The processing device 2 includes a device housing 4 having a substantially rectangular parallelepiped shape. A column 6 is erected on the upper right end of the device housing 4.

  Two pairs of guide rails 8 and 10 extending in the vertical direction are provided on the inner peripheral surface of the column 6. A rough grinding unit 12 is mounted on one guide rail 8 so as to be movable in the vertical direction (Z-axis direction) by a rough grinding unit feed mechanism 14, and a finish grinding unit 16 is a finish grinding unit on the other guide rail 10. The feed mechanism 18 is mounted so as to be movable in the vertical direction.

  The rough grinding unit 12 includes a unit housing 20, a spindle 22 rotatably accommodated in the unit housing 20, a wheel mount 24 fixed to the tip of the spindle 22, and a detachable attachment to the tip of the wheel mount 24. A rough grinding wheel 26 having a rough grinding wheel and a motor 32 for rotating the spindle 22 are included.

  The finish grinding unit 16 includes a unit housing 34, a spindle 36 rotatably accommodated in the unit housing 34, a wheel mount 38 fixed to the tip of the spindle 36, and a finish detachably attached to the wheel mount 38. A finish grinding wheel 40 having a grinding wheel and a motor 46 for rotating the spindle 36 are included.

  The processing device 2 includes a turntable 48 that is disposed on the front side of the column 6 so as to be substantially flush with the upper surface of the device housing 4. The turntable 48 is formed in a relatively large-diameter disk shape, and is rotated in a direction indicated by an arrow 49 by a rotation driving mechanism (not shown). On the turntable 48, four chuck tables 50 are arranged so as to be rotatable in a horizontal plane, being spaced apart from each other by 90 degrees in the circumferential direction.

  The four chuck tables 50 arranged on the turntable 48 have a wafer carry-in / out area A, a rough grinding area B, a finish grinding area C, a polishing area D, when the turntable 48 is appropriately rotated. And sequentially moved to the wafer carry-in / carry-out area A.

  A polishing unit 52 is disposed in the polishing region D. As shown in FIG. 2, the polishing unit 52 includes a stationary block 54 fixed on the apparatus housing 4, and an X-axis moving block 56 that is attached to the stationary block 54 and can be moved in the X-axis direction by the X-axis moving mechanism 58. And a Z-axis moving block 60 mounted on the X-axis moving block 56 and movable in the Z-axis direction by the Z-axis moving mechanism 62.

  A unit housing 64 is disposed in the Z-axis moving block 60, and a spindle 66 is rotatably accommodated in the unit housing 64. A wheel mount 68 is fixed to the tip of the spindle 66, and a grinding wheel 70 is detachably attached to the wheel mount 68 with a screw 69.

  The polishing wheel 70 includes a base 72 attached to the wheel mount 68 and a polishing pad 74 attached to the base 72. The polishing pad 74 is made of, for example, polyurethane, felt, nonwoven fabric, or the like.

  On the front side of the housing 4 of the processing apparatus 2, a first cassette 90 for stocking the wafer before processing and a second cassette 92 for stocking the processed wafer are detachably mounted.

  Reference numeral 94 denotes a wafer transfer robot, which transfers the wafer accommodated in the first cassette 90 to the temporary placement table 96 and also transfers the processed wafer cleaned by the spinner cleaning unit 100 to the second cassette 92. .

  A wafer transport unit 98 transports a wafer from the temporary placement table 96 to the chuck table 50 positioned in the wafer carry-in / out area A, or sucks the processed wafer from the chuck table 50 and transports it to the spinner cleaning unit 100. And is movable in the X-axis direction, the Y-axis direction, and the Z-axis direction.

  The spinner cleaning unit 100 has a rotatable spinner table 102. The spinner cleaning unit 100 further includes a cleaning water supply nozzle 104 that supplies cleaning water to the processed wafer held by the spinner table 102.

  Reference numeral 82 denotes a drainage port for discharging a drainage liquid containing machining waste generated by machining, and the drainage port 82 is connected to the machining waste separation unit 78. The machining waste separation unit 78 has a function of separating the machining waste from the waste liquid. Furthermore, the processing waste separation unit 78 has a built-in high-pressure pump that supplies the separated processing waste to the processing waste injection nozzle 88 at a high pressure. The processing waste jet nozzle 80 is configured to be rotatable.

  Referring to FIG. 3, a perspective view of a semiconductor wafer 11 to be processed by the processing method of the present invention is shown. A semiconductor wafer 11 shown in FIG. 3 is made of, for example, a silicon wafer having a thickness of 700 μm. A plurality of division lines (streets) 13 are formed in a lattice shape on the surface 11a, and a plurality of division lines 13 are formed. A device 15 such as an IC or an LSI is formed in each of the areas partitioned by.

  The semiconductor wafer 11 thus configured includes a device region 17 in which the semiconductor device 15 is formed, and an outer peripheral surplus region 19 that surrounds the device region 17. A notch 21 is formed on the outer periphery of the semiconductor wafer 11 as a mark indicating the crystal orientation of the silicon wafer.

  In the processing method of the present invention, before the back surface 11b of the semiconductor wafer 11 is ground, the surface 11a of the semiconductor wafer 11 has a surface to protect the semiconductor device 15 formed on the surface 11a as shown in FIG. A protective tape 23 is attached.

  Therefore, the front surface 11a of the semiconductor wafer 11 is protected by the surface protection tape 23, and the back surface 11b is exposed as shown in FIG. Instead of the surface protection tape 23, a support plate may be attached to the surface of the semiconductor wafer 11.

  Next, the wafer processing method according to the embodiment of the present invention will be described in detail. The wafer 11 accommodated in the first wafer cassette 90 is pulled out from the first cassette 90 by the wafer transfer robot 94 and transferred to the temporary placement table 96, and the semiconductor wafer 11 is centered by the temporary placement table 96. The

  Next, the semiconductor wafer 11 adsorbed by the wafer transport unit 98 is transported to the chuck table 50 positioned in the wafer carry-in / out area A, and is sucked and held by the chuck table 50 with the surface protection tape 23 facing down.

  After the semiconductor wafer 11 is sucked and held by the chuck table 50, the turntable 48 is rotated 90 degrees in the clockwise direction indicated by the arrow 49, and the semiconductor wafer 11 held on the chuck table 50 faces the rough grinding unit 12. Position in grinding area B.

  In the rough grinding of the semiconductor wafer 11, the grinding wheel 26 is rotated in the same direction as the chuck table 50 at, for example, 6000 rpm while rotating the chuck table 50 at, for example, 300 rpm with respect to the semiconductor wafer 11 positioned in this way. The grinding unit feeding mechanism 14 is operated to bring the grinding wheel for rough grinding into contact with the back surface 11 b of the semiconductor wafer 11.

  Then, the grinding wheel 26 is ground and fed by a predetermined amount at a predetermined grinding feed speed, and the rear surface 11b of the semiconductor wafer 11 is roughly ground. This rough grinding is performed while supplying a grinding fluid to the grinding wheel and the wafer 11. The wafer 11 is ground to a desired thickness while measuring the thickness of the wafer 11 with a contact or non-contact thickness gauge.

  When the rough grinding is finished, the turntable 48 is further rotated 90 degrees in the clockwise direction, and the wafer 11 after the rough grinding is positioned in the finish grinding region C. In this finish grinding, the grinding wheel 40 is rotated at, for example, 6000 rpm in the same direction as the chuck table 50 while rotating the chuck table 50 at, for example, 300 rpm, and the finish grinding unit feed mechanism 18 is operated to perform a grinding wheel for finish grinding. Is brought into contact with the back surface of the wafer 11.

  Then, the grinding wheel 40 is ground and fed by a predetermined amount at a predetermined grinding feed speed, and the back surface of the wafer 11 is ground. This finish grinding is also performed while supplying the grinding liquid to the grinding wheel and the wafer 11. While measuring the thickness of the wafer 11 with a contact-type or non-contact-type thickness measurement gauge, the wafer 11 is finished to a desired thickness, for example, 50 μm.

  The chuck table 50 holding the wafer 11 for which finish grinding has been completed is positioned in the polishing region D facing the polishing unit 52 by rotating the turntable 48 90 degrees in the clockwise direction, and a polishing step is performed. The

  In the polishing step, as shown in FIG. 5, while supplying the polishing liquid 77 from the polishing liquid supply nozzle 76, the wafer 11 is rotated while the chuck table 50 is rotated in the arrow a direction and the polishing pad 74 is rotated in the arrow b direction. The back surface 11b of the wafer 11 is polished by pressing the polishing pad 74 against the back surface 11b. By this polishing step, the grinding distortion generated in the grinding step is removed.

  In this polishing step, the grinding distortion is removed by polishing the back surface 11b of the wafer 11 while supplying a polishing liquid containing abrasive grains to the semiconductor wafer 11. As the polishing liquid, for example, an alkaline polishing liquid containing colloidal silica particles (primary particle diameter of about 5 to 100 nm) is used.

  As another embodiment of the polishing step, a fixed abrasive pad in which abrasive grains are dispersed is used, and the back surface 11b of the wafer 11 is polished while supplying an alkaline solution containing no abrasive grains as a polishing liquid to the semiconductor wafer 11. Grinding distortion may be removed.

  In the wafer processing method of the present invention, after the polishing step is performed, a strain layer forming step of forming a strain layer on the back surface 11b of the wafer 11 in the polishing region D is performed. Before performing this strained layer forming step, the spindle 66 of the polishing unit 52 shown in FIG. 2 is moved in the Z-axis direction to raise the polishing pad 74 from the back surface 11 b of the wafer 11.

  Then, the processing waste separated from the waste liquid by the processing waste separation unit 78 is sprayed from the processing waste injection nozzle 80 onto the back surface 11b of the wafer 11 at a high pressure as shown in FIG. A strain layer forming step of forming a strain layer by impact of debris is performed. When this strained layer forming step is performed, a gettering effect can be imparted to the wafer 11.

  The processing waste ejected from the processing waste injection nozzle 80 is mainly composed of wafer waste from which the wafer 11 has been crushed, abrasive grains degrown from the grinding wheel, and a bonding agent for the grinding wheel. Since a strain layer is formed on the back surface 11b of the wafer 11 with these processing scraps, no separate abrasive grains such as diamond are required. Therefore, the gettering effect can be imparted to the wafer 11 more economically than in the past.

DESCRIPTION OF SYMBOLS 11 Semiconductor wafer 12 Rough grinding unit 15 Device 16 Finish grinding unit 23 Surface protection tape 48 Turntable 50 Chuck table 52 Polishing unit 74 Polishing pad 78 Processing waste separation unit 80 Processing waste injection nozzle

Claims (1)

A wafer processing method for providing a gettering effect to a wafer having a plurality of devices formed on a surface,
A grinding step of grinding the back surface of the wafer with the grinding means and reducing the thickness to a predetermined thickness while supplying a grinding liquid to the grinding means and the wafer;
After performing the grinding step, a polishing step for polishing the back surface of the wafer to remove the grinding distortion generated in the grinding step;
A processing waste separation step for separating processing waste from the processing waste liquid generated in the grinding step;
After performing the polishing step, a strain layer forming step of forming the strain layer on the back surface of the wafer by spraying the work waste separated in the work scrap separating step on the back surface of the wafer at a high pressure;
A wafer processing method characterized by comprising:

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