JP5963537B2 - Processing method of silicon wafer - Google Patents

Description

The present invention relates to a silicon wafer processing method for polishing a silicon wafer and providing a gettering layer.

  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, it is an object capable of forming a silicon wafer gettering layer with a gettering effect in a simple way to remove the grinding distortion of the silicon wafer It is to provide a processing method.

According to the present invention, there is provided a silicon wafer processing method, a holding step for holding a silicon wafer with a chuck table, and a fixed abrasive-type polishing pad containing abrasive grains while rotating the chuck table holding the silicon wafer. A polishing step of polishing the silicon wafer with the fixed-abrasive polishing pad while rotating the substrate and pressing the silicon wafer held on the chuck table and supplying an alkaline polishing liquid to the silicon wafer and the polishing pad; After the polishing step, the chuck table and the fixed abrasive polishing pad are rotated, and the silicon wafer held on the chuck table and the fixed abrasive polishing pad that presses the silicon wafer are rinsed. while supplying pure water as a liquid, sheet with the fixed abrasive type polishing pad Method for processing a silicon wafer, characterized by comprising, a gettering layer forming step to form a thin strained layer Kon'ueha gettering layer is provided.

According to the present invention, grinding strain remaining on a silicon wafer can be effectively removed by polishing the silicon wafer with a fixed abrasive polishing pad containing abrasive grains while supplying an alkaline polishing liquid. Since no distortion is generated in a silicon wafer in this state, by switching the polishing liquid of pure water as a rinsing liquid which does not cause the silicon wafer and the chemical reaction, the gettering layer fine strained to the silicon wafer Can be generated as

Since the polishing step for removing the grinding strain and the gettering layer generation step can be performed on the same chuck table, the efficiency is very good. In addition, since pure water is used as the rinsing liquid, the cleaning step of cleaning the silicon wafer after the gettering layer generation step can be omitted.

It is a perspective view of the processing apparatus suitable for implementing the processing method of the plate-shaped object 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 partial cross section side view which shows a holding | maintenance step. It is a partial cross section side view which shows the grinding | polishing formation step of 1st Embodiment. It is a partial cross section side view which shows the gettering layer production | generation step of 1st Embodiment. It is a partial cross section side view which shows the grinding | polishing formation step of 2nd Embodiment. It is a partial cross section side view which shows the gettering layer production | generation step of 2nd Embodiment.

  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. As the polishing pad 74, for example, a fixed abrasive polishing pad disclosed in WO2003 / 101668 can be suitably used. For example, from a fixed abrasive polishing pad in which abrasive grains are dispersed in foamed urethane and fixed with an appropriate bonding agent. Composed.

  As the abrasive grains, for example, GC (Green Carbide) abrasive grains having a particle diameter of 0.2 to 1.5 μm are contained in the urethane foam. GC abrasive grains may be contained in the nonwoven fabric in place of urethane foam.

  The abrasive grains only need to be higher in hardness than the work piece and capable of scratching the work piece. When the work piece is a silicon wafer, an abrasive mainly composed of a material having a Mohs hardness of 5 or more is used. Preferably, for example, abrasive grains such as diamond, alumina, ceria, CBN may be included instead of the GC abrasive grains.

  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.

  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.

  The plate-like object to be processed in the present invention is not limited to a silicon wafer, but includes a wafer such as a GaN wafer or a SiC wafer, or a plate-like object such as a glass substrate or a ceramic substrate.

  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 processing method of the plate-shaped object which concerns on embodiment of this invention is demonstrated in detail. A semiconductor wafer 11 (hereinafter sometimes abbreviated as “wafer”) 11 accommodated in the first wafer cassette 90 is pulled out of the first cassette 90 by the wafer transfer robot 94 and transferred to the temporary setting table 96 for temporary setting. The table 96 is used to center the semiconductor wafer 11.

  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 rough grinding of the back surface 11b of the semiconductor wafer 11 is performed. 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 of the first embodiment, as shown in FIG. 6, the polishing is performed with the polishing pad 74 partially covering the back surface 11 b of the wafer 11. The machining liquid supply nozzle 78 is selectively connected to the polishing liquid supply source 82 and the rinse liquid supply source 84 via the electromagnetic switching valve 80.

  In the polishing step of polishing the back surface 11 b of the wafer 11, the processing liquid supply nozzle 78 is connected to the polishing liquid supply source 82, and the polishing liquid is supplied from the processing liquid supply nozzle 78 to the back surface 11 b and the polishing pad 74 of the wafer 11. While the chuck table 50 is rotated in the direction of arrow a and the polishing pad 74 is rotated in the direction of arrow b, the polishing pad 74 is pressed against the back surface 11b of the wafer 11 to polish the back surface 11b of the wafer 11.

  This polishing step aims to remove the grinding strain generated in the grinding step, and the grinding strain generated in the grinding step is removed by the polishing step. The polishing liquid used in this polishing step includes a substance capable of performing CMP by causing a chemical reaction with the workpiece. In this embodiment in which the wafer is made of silicon, for example, an alkaline polishing liquid is used.

  After the polishing step, a gettering layer generation step for generating a gettering layer on the back surface of the wafer is performed. In the gettering layer generation step, as shown in FIG. 7, the electromagnetic switching valve 80 is switched to connect the machining liquid supply nozzle 78 to the rinse liquid supply source 84, and the rinse liquid is supplied from the machining liquid supply nozzle 78 to the back surface 11 b of the wafer 11. While the chuck table 50 is rotated in the direction of arrow a and the polishing pad 74 is rotated in the direction of arrow b while being supplied to the polishing pad 74, the polishing pad 74 is pressed against the back surface 11 b of the wafer 11 to the back surface 11 b of the wafer 11. A gettering layer is generated.

  The rinse liquid is composed of only a substance that does not cause a chemical reaction with the workpiece, and is adjusted so that the abrasive grains of the polishing pad act extremely mechanically. In this embodiment, pure water is used as the rinse liquid, for example.

  By switching the liquid supplied from the machining liquid supply nozzle 78 from an alkaline polishing liquid to a rinse liquid such as pure water, a strain layer finer than the grinding strain is formed on the back surface 11b of the wafer 11, and this functions as a gettering layer. . The rinsing liquid may be any liquid that does not cause a chemical reaction with the wafer 11. For example, a surfactant may be supplied instead of pure water.

  When pure water is supplied as the rinsing liquid, it is possible to omit the cleaning step of cleaning the wafer 11 after the gettering layer is formed on the back surface 11b of the wafer 11 in the gettering layer forming step. Of course, a cleaning step may be performed.

  When the workpiece is the silicon wafer 11, an aqueous alkaline solution adjusted to about Ph9 to 13 is preferable as the polishing liquid. More preferably, it is an alkaline aqueous solution of Ph10-11.

  Referring to FIG. 8, a partially sectional side view showing a polishing step according to the second embodiment of the present invention is shown. In the polishing step of this embodiment, polishing is performed with the polishing pad 74 covering the entire back surface of the wafer 11.

  In this embodiment, a fluid supply path 67 is formed through the spindle 66, the wheel mount 68 and the polishing wheel 70. The fluid supply path 67 is selectively connected to the polishing liquid supply source 82 and the rinse liquid supply source 84 via the electromagnetic switching valve 80.

  In the polishing step of the present embodiment, the chuck table 50 is rotated in the direction of arrow a while supplying the alkaline polishing liquid from the fluid supply path 67 with the polishing pad 74 covering the entire back surface 11b of the wafer 11. The polishing pad 74 is pressed against the back surface 11b of the wafer 11 while rotating the polishing pad 74 in the direction of the arrow b, and the back surface 11b of the wafer 11 is polished. By this polishing step, the grinding distortion generated in the grinding step is removed.

  Subsequent to the polishing step, a gettering layer generation step is performed in which the polishing liquid is switched to the rinse liquid. In this gettering layer generation step, as shown in FIG. 9, the fluid supply path 67 is connected to a rinse liquid supply source 84 to supply pure water as a rinse liquid to the back surface 11b and the polishing pad 74 of the wafer 11, The polishing pad 74 is pressed against the back surface 11b of the wafer 11, the chuck table 50 is rotated in the direction of arrow a, and the polishing pad 74 is rotated in the direction of arrow b to generate a gettering layer.

  Similar to the first embodiment described above, by switching the supplied liquid from alkaline polishing liquid to pure water, a strain layer finer than the grinding strain is formed on the back surface 11b of the wafer 11, and this functions as a gettering layer. . Instead of pure water, a surfactant may be supplied.

  By covering the entire back surface 11b of the wafer 11 with the polishing pad 74, the polishing is accelerated by the processing heat, and the polishing can be performed in a short time. In addition, it is possible to reduce the thickness variation of the wafer 11 after polishing.

  When the plate-like workpiece is a silicon wafer, it is preferable to carry out while supplying an alkaline aqueous solution as a polishing liquid as described above. However, the plate-like workpiece is a glass, oxide substrate, SiC wafer, or GaN wafer. In such a case, it is preferable to carry out the polishing step while supplying an acidic polishing liquid.

  In the processing method of the present invention, the first processing (polishing step) for removing grinding strain and the second processing (gettering layer generation step) opposite to the first processing for generating a gettering layer are performed. It can be carried out on the same processing tool by changing the polishing liquid to a rinsing liquid. In other words, it can be carried out on the same machining axis and machining chamber, and the process can be greatly labor-saving.

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 liquid supply nozzle 80 Electromagnetic switching valve 82 Polishing liquid supply source 84 Rinse liquid supply source

Claims (1)

A method for processing a silicon wafer ,
A holding step for holding the silicon wafer on a chuck table;
While rotating the chuck table holding the silicon wafer , the fixed abrasive-type polishing pad containing abrasive grains is rotated to press the silicon wafer held on the chuck table, and an alkaline polishing liquid is applied to the silicon wafer and the silicon wafer. A polishing step of polishing the silicon wafer with the fixed abrasive polishing pad while supplying to the polishing pad;
After performing the polishing step, the chuck table and the fixed abrasive polishing pad are rotated, and a rinse solution is applied to the silicon wafer held on the chuck table and the fixed abrasive polishing pad that presses the silicon wafer. A gettering layer generating step of forming a thin strained layer on a silicon wafer with the fixed abrasive polishing pad while providing pure water as a gettering layer;
A method for processing a silicon wafer , comprising:

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