JP2012146889A - Method for grinding wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for grinding a wafer having a circular concave portion having a predetermined depth and an annular convex portion surrounding the circular concave portion.
A wafer grinding method in which a central portion of a back surface of a wafer is ground to a first thickness with a grinding wheel to form a circular concave portion having the first thickness and an annular convex portion surrounding the circular concave portion. A second thickness obtained by adding a predetermined value to the first thickness of the outer peripheral edge region of the wafer including at least the annular convex portion on the back surface of the wafer with a grinding wheel having a diameter approximately half the diameter of the wafer. After the first grinding step and the first grinding step are performed, the center portion of the back surface of the wafer excluding the annular convex portion is ground to the first thickness with the grinding wheel, and the first portion is formed on the bottom portion. And a second grinding step for forming an annular convex portion having the second thickness surrounding the circular concave portion.
[Selection] Figure 6

Description

  The present invention relates to a wafer grinding method in which a rear surface of a wafer is ground to form a circular concave portion having a predetermined depth and an annular convex portion surrounding the circular concave portion.

  In a semiconductor device manufacturing process, a plurality of regions are partitioned by dividing lines called streets arranged in a lattice pattern on the surface of a semiconductor wafer having a substantially disk shape, and devices such as ICs and LSIs are divided into these partitioned regions. Form.

  Then, the semiconductor wafer is cut into individual semiconductor devices (semiconductor chips) by cutting the semiconductor wafer along the streets, and the divided semiconductor devices are widely used in various electric devices such as personal computers and mobile phones. Has been.

  The wafer to be divided is processed to a predetermined thickness by grinding the back surface before cutting along the street. In recent years, in order to achieve a reduction in weight and size of electrical equipment, it has been required to make the wafer thinner, for example, about 50 μm.

  Such thin wafers are difficult to handle and may be damaged during transportation. Accordingly, there is a grinding method in which only the back surface corresponding to the device region of the wafer is ground to form a circular recess, and an annular convex portion (annular reinforcing portion) is formed on the back surface of the wafer corresponding to the outer peripheral surplus region surrounding the device region. This is proposed in Japanese Patent Laid-Open No. 2007-19461.

  After grinding only the back surface corresponding to the device area of the wafer and then dicing (cutting) from the front side without removing the annular protrusion, or grinding the protective tape attached to the wafer surface during wafer grinding In the case of peeling later, a convex chuck table that fits into the circular concave portion of the ground wafer and supports the upper surface of the annular convex portion from below is used (for example, see JP 2010-16146 A).

JP 2007-19461 A JP 2010-16146 A

  Such a convex chuck table has a convex portion corresponding to the depth of the circular concave portion of the wafer to be held. There is a standard for the thickness of the wafer before grinding, for example, a constant thickness such as 700 μm. However, since the thickness of the circular recess (the grinding finish thickness of the circular recess) varies depending on the device to be manufactured, the depth of the circular recess is also manufactured. It will be different for each device.

  Therefore, when a wafer having a circular recess having a different depth is sucked and held by a chuck table having a certain level of protrusion, suction holding becomes incomplete or the wafer breaks from the boundary between the circular recess and the annular protrusion. There is a problem of end.

  On the other hand, it is possible to prepare a plurality of convex chuck tables according to the depth of the circular recess and replace the chuck table according to the depth of the circular recess at the time of cutting, but the management becomes complicated and the cost is high. There is a problem of becoming.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a wafer grinding method capable of reliably sucking and holding a wafer having circular concave portions having different thicknesses by a single chuck table. Is to provide.

  According to the present invention, a wafer grinding method for forming a circular concave portion having the first thickness and an annular convex portion surrounding the circular concave portion by grinding the central portion of the back surface of the wafer to a first thickness with a grinding wheel. A second grinding wheel having a diameter approximately equal to a half of the diameter of the wafer, the outer peripheral area of the wafer including at least the annular convex portion on the back surface of the wafer being added with a predetermined value to the first thickness. After performing the first grinding step for grinding to the thickness and the first grinding step, the grinding wheel is used to grind the center of the back surface of the wafer excluding the annular convex portion to the first thickness to the bottom. And a second grinding step for forming a circular concave portion having a thickness of 1 and an annular convex portion having the second thickness surrounding the circular concave portion, and a method for grinding a wafer is provided. .

  As an alternative embodiment, in the first grinding step, the entire back surface of the wafer may be ground with a grinding wheel and thinned to the second thickness.

  According to the present invention, since the circular concave portion of the wafer is formed at a predetermined depth, a wafer having circular concave portions having different thicknesses can be reliably sucked and held by one convex chuck table, and different steps (high It is unnecessary to prepare a plurality of convex chuck tables with Further, since the annular convex portion is also thinned in the first grinding step, a grinding apparatus provided with another grinding wheel for thinning the annular convex portion becomes unnecessary.

1 is a perspective view of a grinding apparatus suitable for carrying out the wafer grinding method of the present invention. 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 the protective tape was stuck on the surface. It is a perspective view which shows a 1st grinding step. It is explanatory drawing of 1st Embodiment of a 1st grinding step. 6A is a side view of the wafer before the first grinding step is performed, and FIG. 6B is a side view of the wafer after the first grinding step of the first embodiment. It is explanatory drawing of 2nd Embodiment of a 1st grinding step. FIG. 8A is a side view of the wafer before the first grinding step is performed, and FIG. 8B is a side view of the wafer after the first grinding step of the second embodiment. It is a perspective view which shows a 2nd grinding step. It is explanatory drawing of a 2nd grinding step. It is a longitudinal cross-sectional view of the wafer after 2nd grinding step implementation. It is a longitudinal cross-sectional view of the state which mounted | worn the wafer which has a circular recessed part and an annular convex part to the annular frame via the dicing tape. It is a longitudinal cross-sectional view of a state in which a wafer having a circular concave portion and an annular convex portion is sucked and held by a convex chuck table.

  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 grinding apparatus 2 suitable for carrying out the wafer grinding method of the present invention. Reference numeral 4 denotes a housing (base) of the grinding device 2, and a column 6 is erected on the rear side of the housing 4. A pair of guide rails 8 extending in the vertical direction are fixed to the column 6.

  A grinding unit (grinding means) 10 is mounted along the pair of guide rails 8 so as to be movable in the vertical direction. The grinding unit 10 includes a housing 12 and a support portion 14 that holds the housing 12, and the support portion 14 is attached to a moving base 16 that moves in the vertical direction along the pair of guide rails 8. .

  The grinding unit 10 includes a spindle 18 rotatably accommodated in a housing 12, a mounter 20 fixed to the tip of the spindle 18, and a plurality of grinding wheels 24 screwed to the mounter 20 and arranged in an annular shape (see FIG. 4), and a servo motor 26 that rotationally drives the spindle 18.

  The grinding device 2 includes a grinding unit feed mechanism 32 that includes a ball screw 28 that moves the grinding unit 10 in the vertical direction along a pair of guide rails 8 and a pulse motor 30. When the pulse motor 30 is driven, the ball screw 28 rotates and the moving base 16 is moved in the vertical direction.

  A recess 4a is formed on the upper surface of the housing 4, and a chuck table mechanism 34 is disposed in the recess 4a. The chuck table mechanism 34 has a chuck table 36 and is moved in the Y-axis direction between a wafer attachment / detachment position A shown in FIG. 1 and a grinding position B facing the grinding unit 10 by a moving mechanism (not shown). 38 and 40 are bellows. On the front side of the housing 4, an operation panel 42 on which an operator of the grinding device 2 inputs grinding conditions and the like is disposed.

  Referring to FIG. 2, a front side perspective view of a semiconductor wafer 11 whose back surface is ground by the grinding device 2 is shown. The semiconductor wafer 11 is made of, for example, a silicon wafer having a thickness of 700 μm, and a plurality of streets 13 are formed in a lattice shape on the surface 11a, and ICs are formed in a plurality of regions partitioned by the plurality of streets 13, respectively. A device 15 such as an LSI is formed.

  The semiconductor wafer 11 configured as described above includes a device region 17 in which the 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.

  A protective tape 23 is attached to the surface 11a of the semiconductor wafer 11 by a protective tape attaching process. Therefore, the front surface 11a of the semiconductor wafer 11 is protected by the protective tape 23, and as shown in FIG. 3, the back surface 11b is exposed, and is sucked and held by the chuck table 36 of the grinding apparatus 2 with the back surface 11b facing upward.

  Hereinafter, the grinding method of the present invention will be described in detail with reference to FIGS. Referring to FIG. 4, a perspective view showing a first embodiment of the first grinding step of the grinding method of the present invention is shown. FIG. 5 is an explanatory diagram thereof.

  In the grinding method of the present invention, a grinding wheel 22 having a diameter approximately half of the diameter of the wafer 11 is used. Therefore, the diameter of the grinding wheel 24 arranged in an annular shape is also approximately ½ of the diameter of the wafer 11.

  For example, when grinding the wafer 11 having a diameter of 200 mm, it is preferable that the diameter of the grinding wheel 22, that is, the diameter of the grinding wheel 24 arranged in an annular shape is in the range of 95 to 99 mm.

  FIG. 6A shows a side view of the wafer 11 before performing the first grinding step. The grinding method of the present invention is performed by grinding the back surface of the wafer 11 corresponding to the device region 17 of the wafer 11. A grinding method for forming a circular concave portion having a thickness t1 of 1 and an annular convex portion having a second thickness t2 surrounding the circular concave portion.

  In the first grinding step, as shown in FIGS. 4 and 5, the chuck tape 36 sucks and holds the protective tape 23 side of the wafer 11, and a part of the grinding wheel 24 arranged in an annular shape is removed from the outer periphery of the wafer 11. The grinding wheel 24 is brought into contact with the back surface 11b of the wafer 11 so as to protrude. In FIG. 5, P <b> 1 is the center of the chuck table 36, and P <b> 2 is the center of the grinding wheel 24.

  In the first grinding step according to the first embodiment, while the chuck table 36 is not moved in the Y-axis direction, the grinding wheel 22 is rotated in the arrow b direction at, for example, 6000 rpm while rotating in the arrow a direction, for example, at 6000 rpm. Then, the cutting unit feed mechanism 32 is driven to grind the region including the back surface 11b of the wafer 11 corresponding to the outer peripheral surplus region 19 of the wafer 11 at a predetermined grinding feed speed.

  As shown in FIG. 6, while measuring the thickness of the wafer 11 in the ground portion with a contact-type or non-contact-type thickness measurement gauge, a second thickness measuring device t2 is obtained by adding a predetermined value h to the first thickness t1. Grind wafer 11 until

  In the first embodiment of the first grinding step of the present invention, the grinding wheel 24 does not contact the center portion of the wafer 11, so that the back surface 11b of the wafer 11 after the completion of the first grinding step is shown in FIG. As shown in FIG. 5, the circular recess 25 that is an unground region remains.

  This first grinding step may be performed while moving the chuck table 36 in the Y-axis direction at a low speed, as shown in the second embodiment of FIG. According to the first grinding step of this embodiment, since the chuck table 36 is moved under the same conditions as the first grinding step of the first embodiment described above except that the chuck table 36 is moved in the Y-axis direction, As shown in FIG. 8B, the wafer 11 is uniformly ground to a second thickness t2 obtained by adding a predetermined value h to the first thickness t1.

  In the grinding method of the present invention, after the first grinding step described above is performed, the second grinding step is performed. In this second grinding step, as best shown in FIG. 10, the outer periphery of the grinding wheel 24 arranged in an annular shape is in contact with the boundary line 48 between the device region 17 and the outer peripheral surplus region 19 of the wafer 11, and the chuck table. It is set to pass through the center P1 of 36.

  In this state, while rotating the chuck table 36 in the direction indicated by the arrow a at 300 rpm, for example, the grinding wheel 24 is rotated in the direction indicated by the arrow b at 6000 rpm, for example, and the cutting unit feed mechanism 32 is driven to 24 is brought into contact with the back surface 11 b of the wafer 11. Then, the grinding wheel 22 is ground and fed downward by a predetermined amount at a predetermined grinding feed speed.

  While measuring the thickness of the wafer 11 with a contact-type or non-contact-type thickness measurement gauge, the wafer 11 is ground to a first thickness t1, for example, 30 μm. When the second grinding step is completed, as shown in FIG. 11, a circular recess 44 having a first thickness t1 is formed on the back surface 11b of the wafer 11, and an annular protrusion having a second thickness t2 surrounding the circular recess 44 is formed. A portion (annular reinforcing portion) 46 is formed.

  Since the second thickness measurement t2 is a thickness obtained by adding a predetermined value h to the first thickness t1, the depth h of the circular recess 44 is always a constant predetermined value, and the thickness t2 of the annular protrusion 46 is a circular recess. 44 varies according to the grinding amount, that is, the thickness t1 of the circular recess 46.

  The wafer 11 ground by the grinding method of the present invention is attached to a dicing tape (adhesive tape) 50 whose outer peripheral portion is attached to the annular frame 52 prior to the cutting of the wafer 11. The dicing tape 50 is attached so as to go around not only the annular convex portion 46 but also the circular concave portion 44.

  Referring to FIG. 13, there is shown a longitudinal sectional view of an example of the chuck table 54 of the cutting apparatus. The chuck table 54 includes a rotating shaft 56 in which a vacuum suction path 58 is formed, and a frame body 60 mounted and fixed on the rotating shaft 56. The frame body 60 is made of a metal such as SUS and has a circular convex portion 62 having a predetermined height h. A circular concave portion 64 for mounting is formed in the circular convex portion 62, and a disc-shaped porous adsorption portion 68 made of porous ceramic or the like is disposed in the circular concave portion 64.

  A vacuum suction path 66 that communicates with the mounting circular recess 64 is formed in the frame 60, and the vacuum suction path 66 is connected to a vacuum suction source (not shown) via a vacuum suction path 58 of the rotating shaft 52.

  The wafer 11 ground by the grinding method of the present invention has a circular concave portion 44 having a predetermined depth h and an annular convex portion 46 surrounding the circular concave portion 44, so that the wafer 11 is formed on the circular convex portion 62 of the chuck table 54. When the wafer 11 is mounted on the chuck table 54 so as to fit the circular recess 44, the circular recess 44 is supported by the porous suction portion 68 of the chuck table 54, and the annular protrusion 46 is supported by the frame body 60. Therefore, the wafer 11 can be reliably sucked and held by connecting the porous suction portion 68 to a vacuum suction source.

2 Grinding device 10 Grinding means (grinding unit)
DESCRIPTION OF SYMBOLS 11 Semiconductor wafer 13 Street 15 Device 17 Device area | region 19 Peripheral surplus area | region 22 Grinding wheel 24 Grinding wheel 36 Chuck table t1 1st thickness t2 2nd thickness h Predetermined value (depth of circular recessed part)
44 circular recess 46 annular protrusion

Claims (2)

A method of grinding a wafer by grinding a central portion of a back surface of a wafer to a first thickness with a grinding wheel to form a circular concave portion having the first thickness and an annular convex portion surrounding the circular concave portion,
The outer peripheral edge region of the wafer including at least the annular convex portion on the back surface of the wafer is ground to a second thickness obtained by adding a predetermined value to the first thickness with a grinding wheel having a diameter approximately half the diameter of the wafer. A first grinding step;
After carrying out the first grinding step, the central portion of the wafer back surface except the annular convex portion is ground to the first thickness with the grinding wheel and the circular concave portion having the first thickness at the bottom and the circular shape A second grinding step for forming an annular convex portion having the second thickness surrounding the concave portion;
A method for grinding a wafer, comprising:   2. The wafer grinding method according to claim 1, wherein in the first grinding step, the entire back surface of the wafer is ground with the grinding wheel to reduce the thickness to the second thickness. 3.

Images