WAFER GRINDING METHOD

Abstract

In a holding surface correction processing step, a shape of a holding surface is corrected by an etching mechanism in such a manner as to have a surface shape similar to that of an upper surface of a test grinding wafer having been ground in a test grinding step. As a result, at a time of a grinding step, when a holding section of a chuck table communicates with a suction source and a product wafer is held under suction on the holding surface, the holding surface becomes a substantially flat surface, and a radius part of the holding surface becomes parallel to a lower surface of a wafer grinding grindstone. Hence, it is possible to prevent partial thickness differences from being generated in the product wafer having been ground by the wafer grinding grindstone.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a wafer grinding method.

Description of the Related Art

In a wafer grinding method, inclination of a chuck table is adjusted to thereby set a holding surface of the chuck table parallel to lower surfaces of grindstones, as disclosed in Japanese Patent Laid-open No. 2008-264913 and Japanese Patent Laid-open No. 2013-119123. This is conducted for ensuring that a difference in thickness would not be generated in a radial direction of the ground wafer.

SUMMARY OF THE INVENTION

However, a minute difference in thickness may be partially generated in a circumferential direction in the ground wafer. Such a difference in thickness in the circumferential direction of the wafer is difficult to be removed by adjustment of the inclination of the chuck table.

One of the reasons for the generation of the partial minute thickness difference in the circumferential direction of the wafer is considered to lie in the self-grinding in which the chuck table is ground by a table grinding grindstone for grinding the chuck table to form a holding surface.

The self-grinding is carried out in a state in which the chuck table does not communicate with a suction source. In contrast, at a time of grinding a wafer, the chuck table is caused to communicate with the suction source, and the wafer is held under suction by the holding surface, so that the holding surface is in the state of being pressed by the atmospheric pressure.

More specifically, comparing the case of the self-grinding with the case of grinding the wafer, it is considered that the chuck table is deformed in the case of the self-grinding and that this deformation may cause the partial thickness difference to be generated in the ground wafer.

Accordingly, it is an object of the present invention to provide a wafer grinding method by which it is possible to prevent a partial thickness difference from being generated in the ground wafer.

In accordance with an aspect of the present invention, there is provided a wafer grinding method in which a chuck table mounted to a table base is made to communicate with a suction source and a wafer held under suction by a holding surface of the chuck table is ground by a wafer grinding grindstone for grinding the wafer, the wafer grinding method including a holding surface forming step of grinding an upper surface of the chuck table by use of the wafer grinding grindstone or a table griding grindstone for grinding the table in a state in which the chuck table does not communicate with the suction source, to thereby form the holding surface, a holding step of causing the holding surface to communicate with the suction source and holding a test grinding wafer under suction by the holding surface, after the holding surface forming step is carried out, a test grinding step of grinding the test grinding wafer held under suction by the holding surface in the holding step by the wafer grinding grindstone to a predetermined thickness, a distribution measuring step of measuring a thickness distribution of a whole surface of the test grinding wafer ground in the test grinding step, or an upper surface height distribution of a whole surface of an upper surface of the test grinding wafer, a holding surface correction processing step of subjecting the holding surface used in the test grinding step to correction processing in such a manner that a holding surface having a surface shape similar to that of the upper surface of the test grinding wafer having been ground is obtained, in reference to the thickness distribution or the upper surface height distribution measured in the distribution measuring step, and a grinding step of holding a product wafer under suction by the holding surface and grinding the product wafer to a predetermined thickness with the wafer grinding grindstone, after the holding surface correction processing step is carried out.

Preferably, the holding surface of the chuck table includes silicon, and, in the holding surface correction processing step, partially plasmatized etching gas is jetted from an etching gas jet nozzle to the holding surface to subject the holding surface to correction processing by atmospheric-pressure plasma etching.

Preferably, in the holding surface correction processing step, the holding surface is ground by a small-diameter grindstone having a diameter smaller than a radius of the holding surface, to thereby subject the holding surface to correction processing.

According to the wafer grinding method of the present invention, in the holding surface correction processing step, the shape of the holding surface is corrected so as to have a surface shape similar to that of the upper surface of the test grinding wafer having been ground in the test grinding step. As a result, when the chuck table is caused to communicate with the suction source and the product wafer is held under suction by the holding surface in the grinding step, the holding surface becomes a substantially flat surface, and a radius part of the holding surface becomes parallel to the lower surface of the wafer grinding grindstone. Hence, it is possible to prevent partial thickness differences from being generated in the product wafer ground with the wafer grinding grindstone. Accordingly, it is possible to grind the product wafer to a uniform thickness.

The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially sectional side view of a grinding apparatus at a time of a holding surface forming step;

FIG. 2 is a perspective view depicting a wafer;

FIG. 3 is a perspective view depicting a chuck table and a table base;

FIG. 4 is a partially sectional side view depicting a holding step and a test grinding step;

FIG. 5 is a sectional view depicting a distribution measuring step;

FIG. 6A is a perspective view depicting a test grinding wafer having been subjected to test grinding;

FIG. 6B is a diagram depicting an upper surface height distribution of the test grinding wafer having been subjected to the test grinding;

FIG. 7 is a sectional view depicting a holding surface correction processing step;

FIG. 8 is a partially sectional side view depicting a grinding step; and

FIG. 9 is a sectional view depicting another holding surface correction processing step.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A grinding apparatus 1 depicted in FIG. 1 includes a table assembly 2 including a chuck table 20 for holding a product wafer 100 or a test grinding wafer 105 (see FIG. 2), a grinding mechanism 10 for grinding the product wafer 100 or the test grinding wafer 105, a grinding feeding mechanism 80 for performing grinding feeding of the grinding mechanism 10, and a controller 7 for controlling each of the members of the grinding apparatus 1.

The product wafer 100 depicted in FIG. 2 is a workpiece to be processed in the grinding apparatus 1, and is a circular semiconductor wafer. The product wafer 100 has an upper surface 101 which is a surface to be ground. The product wafer 100 is held on the chuck table 20 of the table assembly 2 depicted in FIG. 1, with, for example, a protective tape (not illustrated) therebetween, in such a manner that the upper surface 101 is directed upward.

In addition, not only the product wafer 100, but also the test grinding wafer 105 to be used in a test grinding step is used in the present embodiment. The test grinding wafer 105 has an upper surface 106 which is a surface to be ground. The test grinding wafer 105 may be the same wafer as the product wafer 100.

As depicted in FIG. 1, the grinding mechanism 10 includes a spindle 11 extending along a Z-axis direction, a spindle motor 12 for driving the spindle 11 to rotate, a wheel mount 13 connected to a lower end of the spindle 11, and a grinding wheel 15 detachably mounted to a lower surface of the wheel mount 13.

The spindle 11 can rotate as indicated by arrow 501 by being driven by the spindle motor 12. The wheel mount 13 is formed in a disk-like shape, is fixed to the lower end of the spindle 11, and is rotated by the rotation of the spindle 11. The wheel mount 13 supports the grinding wheel 15.

The grinding wheel 15 is formed to have a diameter substantially equal to the diameter of the wheel mount 13. The grinding wheel 15 includes an annular wheel base 16 formed from a metal material. A plurality of wafer grinding grindstones 17 having a substantially rectangular parallelepiped shape are disposed in an annular pattern on a lower surface of the wheel base 16 over the whole circumference.

The wafer grinding grindstones 17 are rotated by the rotation of the spindle 11, to thereby grind the product wafer 100 or the test grinding wafer 105 held by the holding surface 22 of the chuck table 20. In addition, the wafer grinding grindstones 17 are used also for forming the holding surface of the chuck table 20 which will be described later.

The grinding feeding mechanism 80 moves the grinding mechanism 10 having the above-described configuration, along the Z-axis direction which is a grinding feeding direction.

The table assembly 2 includes the chuck table 20 that holds the product wafer 100 or the test grinding wafer 105 by the holding surface 22, and a table base 30 that supports the chuck table 20.

As depicted in FIG. 3, the chuck table 20 has a substantially disk-shaped frame body 23, and has a holding section 21 which is formed of a porous member and is disposed in a recess provided in the frame body 23. An upper surface of the holding section 21 serves as the holding surface 22 that holds under suction the product wafer 100 or the test grinding wafer 105.

The holding surface 22 is formed by grinding the upper surface of the holding section 21 of the chuck table 20, in a holding surface forming step which will be described later. For example, the holding surface 22 is formed in the shape of a conical surface with the center as a vertex, as depicted in FIG. 1. In addition, a frame body surface 24 which is an upper surface of the frame body 23 surrounds the holding surface 22, and is formed to be flush with the holding surface 22.

In the present embodiment, the holding section 21 is a porous member including silicon. Hence, the holding surface 22 which is the upper surface of the holding section 21 also includes silicon. Note that the holding section 21 is not limited to the porous member including silicon and may be a dense body of silicon provided with a plurality of through-holes. In this case, also, the holding surface 22 is a surface including silicon. In addition, the chuck table 20 formed of the dense body of silicon provided with the plurality of through-holes may have the holding section 21 and the frame body 23 formed as one body.

In addition, as depicted in FIG. 1, the holding section 21 is connected to a suction source 201 through a suction valve 35. The holding section 21 communicates with the suction source 201, and a suction force from the suction source 201 is transmitted to the holding surface 22 which is the upper surface of the holding section 21, whereby the chuck table 20 can hold under suction the product wafer 100 or the test grinding wafer 105 by the holding surface 22. Thus, in the present embodiment, the chuck table 20 (the holding section 21) communicates with the suction source 201, whereby the product wafer 100 or the test grinding wafer 105 can be held by the holding surface 22.

As depicted in FIG. 3, the chuck table 20 includes an annular flange 25 which is fixed to a lower part of the frame body 23 and has an outside diameter greater than that of the frame body 23. The annular flange 25 is formed with a plurality of through-holes 26 for passing screws 300 which are male screws therethrough, at predetermined intervals in the circumferential direction.

The table base 30 is a disk-shaped body configured to support the chuck table 20 by a support surface 31 which is an upper surface thereof. The support surface 31 of the table base 30 is formed with a suction groove 32, and a suction port 33 which penetrates the table base 30. The suction groove 32 and the suction port 33 are configured to be opposed to a bottom surface 27 of the chuck table 20 supported on the support surface 31.

The suction groove 32 and the suction port 33 are used for transmitting the suction force from the suction source 201 to the holding section 21, via a table suction channel 29 (see FIG. 1) which penetrates the frame body 23 of the chuck table 20 and communicates with the holding section 21. In the present embodiment, the suction port 33 is provided in the suction groove 32 at the center of the support surface 31.

Further, the support surface 31 of the table base 30 is formed with a plurality of screw holes (female screws) 34 at positions corresponding to the through-holes 26 of the chuck table 20. When the bottom surface 27 of the chuck table 20 is put in contact with the support surface 31 of the table base 30, and screws 300 are inserted into the through-holes 26 from above the annular flange 25 and put into screw engagement with the screw holes 34 of the table base 30, the chuck table 20 is thereby fixed to the table base 30. With each of the screws 300 fastened with a predetermined torque pressure, the bottom surface 27 of the chuck table 20 is put into close contact with the support surface 31 of the table base 30.

In addition, as depicted in FIG. 1, the grinding apparatus 1 includes a table rotating mechanism 91. The table assembly 2 including the chuck table 20 is rotated around a table rotational axis 301 by the table rotating mechanism 91, as indicated by arrow 502.

Besides, the grinding apparatus 1 includes an inclination adjusting mechanism 93. The inclination adjusting mechanism 93 is for adjusting the inclination of the table assembly 2 including the chuck table 20 (the inclination of the table rotational axis 301). The inclination adjusting mechanism 93 adjusts the inclination of the table rotational axis 301 in such a manner that, for example, a radius part of the holding surface 22 of the chuck table 20 (or of the wafer held on the holding surface 22) becomes parallel to the lower surfaces of the wafer grinding grindstones 17.

Further, the grinding apparatus 1 includes a table moving mechanism 95. The table moving mechanism 95 relatively moves the chuck table 20 of the table assembly 2 and the wafer grinding grindstones 17 of the grinding mechanism 10 in a Y-axis direction which is a direction parallel to the holding surface 22. In the present embodiment, the table moving mechanism 95 moves the table assembly 2 including the chuck table 20 in the Y-axis direction, relative to the grinding mechanism 10.

In addition, as depicted in FIG. 4, the grinding apparatus 1 includes a thickness measuring mechanism 60 that has a first height measuring unit 61, a second height measuring unit 62, and a calculation section 63.

The first height measuring unit 61 can be disposed on the upper side of the frame body surface 24 of the chuck table 20, and is used for measuring the height of the frame body surface 24 (namely, the height of the holding surface 22).

The second height measuring unit 62 is used for measuring the height of the wafer (the product wafer 100 or the test grinding wafer 105) held on the holding surface 22, by making contact with the upper surface of the wafer. The calculation section 63 can calculate the thickness of the wafer, in reference to the difference between the measured height of the wafer and the measured height of the holding surface 22.

Note that the second height measuring unit 62 can be moved along the radial direction of the wafer, and can also measure the height distribution of the upper surface of the wafer. In addition, when the wafer is not held on the holding surface 22 of the chuck table 20, the second height measuring unit 62 can measure the height and the height distribution of the holding surface 22, by making contact with the holding surface 22.

The controller 7 of the grinding apparatus 1 includes a central processing unit (CPU) for performing arithmetic processing according to a control program, and a storage medium such as a memory, and the like. The controller 7 controls each of the above-mentioned members of the grinding apparatus 1, and performs overall control of the constituent elements of the grinding apparatus 1. For example, the controller 7 controls each of the above-mentioned members of the grinding apparatus 1, to carry out the wafer grinding method according to the present embodiment.

The wafer grinding method according to the embodiment of the present invention will be described below. The wafer grinding method is a wafer grinding method in which the chuck table 20 mounted to the table base 30 is caused to communicate with the suction source 201, and the product wafer 100 held under suction by the holding surface 22 of the chuck table 20 is ground by the wafer grinding grindstones 17 for grinding the wafer.

(Holding Surface Forming Step)

In this step, in a state in which the chuck table 20 does not communicate with the suction source 201, the upper surface of the chuck table 20 (the upper surfaces of the holding section 21 and the frame body 23) is ground by use of the wafer grinding grindstones 17 of the grinding apparatus 1, to thereby form the holding surface 22.

Specifically, as depicted in FIG. 1, the controller 7 closes the suction valve 35, to establish a state in which the communication between the holding section 21 of the chuck table 20 and the suction source 201 is interrupted.

Thereafter, the controller 7 causes the table moving mechanism 95 to dispose the table assembly 2 including the chuck table 20 at a processing position on the lower side of the grinding mechanism 10. At this processing position, the wafer grinding grindstones 17 of the grinding wheel 15 of the grinding mechanism 10 pass through the center of the holding section 21 of the chuck table 20. In addition, the controller 7 sets the inclination of the table rotational axis 301, which is the rotational axis of the chuck table 20, to a predetermined value by use of the inclination adjusting mechanism 93.

Then, while rotating the wafer grinding grindstones 17 and the chuck table 20, the controller 7 causes the grinding feeding mechanism 80 to lower the grinding mechanism 10, to bring the wafer grinding grindstones 17 into contact with the upper surfaces of the holding section 21 and the frame body 23 of the chuck table 20, and thereby to grind these surfaces with the wafer grinding grindstones 17. This grinding is carried out in such a manner that the upper surface of the holding section 21 becomes the holding surface 22 having the shape of a conical surface with a center having a predetermined height as a vertex, and becomes flush with the frame body surface 24 which is the upper surface of the frame body 23. As a result, a holding surface 22 that has a radius part parallel to the lower surfaces of the wafer grinding grindstones 17 is formed.

(Holding Step)

Next, a holding step is carried out. In this step, the holding surface 22 of the chuck table 20 formed in the holding surface forming step is caused to communicate with the suction source 201, and the test grinding wafer 105 (see FIG. 2) is held under suction by the holding surface 22.

Specifically, the controller 7 disposes the table assembly 2 including the chuck table 20 at a predetermined holding position spaced from the lower side of the grinding mechanism 10, by the table moving mechanism 95. Next, the controller or an operator mounts the test grinding wafer 105 on the holding surface 22 of the chuck table 20 in such a manner that the upper surface 106 of the wafer is directed upward. Thereafter, the controller 7 opens the suction valve 35, to cause the holding section 21 of the chuck table 20 to communicate with the suction source 201. As a result, as depicted in FIG. 4, the test grinding wafer 105 is held under suction by the holding surface 22 which is the upper surface of the holding section 21.

(Test Grinding Step)

Next, a test grinding step is carried out. In this step, the test grinding wafer 105 held under suction by the holding surface 22 in the holding step is ground by the wafer grinding grindstones 17 to a predetermined thickness.

Specifically, the controller 7 causes the table moving mechanism 95 to dispose the table assembly 2 including the chuck table 20 with the test grinding wafer 105 held thereon under suction at the above-mentioned processing position on the lower side of the grinding mechanism 10. In this processing position, the wafer grinding grindstones 17 of the grinding mechanism 10 pass through the center of the holding surface 22 of the chuck table 20.

Then, while rotating the wafer grinding grindstones 17 of the grinding mechanism 10 and the chuck table 20, the controller 7 causes the grinding feeding mechanism 80 to lower the grinding mechanism 10, to bring the wafer grinding grindstones 17 into contact with the radius part of the upper surface 106 of the test grinding wafer 105 held on the holding surface 22, and to grind the upper surface 106 with the wafer grinding grindstones 17. In this instance, the controller 7 measures the thickness of the test grinding wafer 105 being ground, with the thickness measuring mechanism 60, and carries out this test grinding until the thickness of the test grinding wafer 105 becomes the predetermined thickness.

(Distribution Measuring Step)

Next, a distribution measuring step is carried out. In this step, the thickness distribution in the whole surface of the test grinding wafer 105 having been ground in the test grinding step is measured.

In this step, a non-contact thickness measuring mechanism 70 as depicted in FIG. 5 is used. The non-contact thickness measuring mechanism 70 is provided in the grinding apparatus 1, and includes a non-contact thickness measuring unit 71, and a moving unit 72 that moves the non-contact thickness measuring unit 71 in a horizontal direction and a vertical direction.

The non-contact thickness measuring unit 71 is for measuring the thickness of the wafer (the product wafer 100 or the test grinding wafer 105) held on the chuck table 20 in a non-contact manner. The non-contact thickness measuring unit 71, for example, applies measurement light having such a wavelength as to be transmitted through the wafer to the wafer from above the wafer, receives the upper surface reflected light reflected on the upper surface of the wafer and the lower surface reflected light passing through the wafer and reflected on the lower surface of the wafer, and measures the thickness of the wafer by spectral interference.

Then, the controller 7 measures the thickness distribution of the whole surface of the test grinding wafer 105 having been ground in the test grinding step, by use of the non-contact thickness measuring mechanism 70 in the distribution measuring step.

Specifically, while causing the table rotating mechanism 91 to rotate the chuck table 20 gradually and while causing the moving unit 72 to move the non-contact thickness measuring unit 71 in the radial direction of the test grinding wafer 105 gradually, the controller 7 causes the non-contact thickness measuring unit 71 to measure the thickness of the test grinding wafer 105 by. As a result, the controller 7 can calculate the thickness distribution of the whole surface of the test grinding wafer 105.

Note that, in measuring the thickness distribution of the test grinding wafer 105, the controller 7 may cause the inclination adjusting mechanism 93 to control the inclination of the chuck table 20, thereby setting that part of the upper surface 106 of the test grinding wafer 105 which is located on the lower side of the non-contact thickness measuring mechanism 70 (the part of which the thickness is to be measured) into a horizontal state.

(Holding Surface Correction Processing Step)

Next, a holding surface correction processing step is carried out. In this step, in reference to the thickness distribution measured in the distribution measuring step, the holding surface 22 used in the test grinding step is subjected to correction processing, in such a manner that a holding surface 22 having a surface shape similar to that of the upper surface 106 of the test grinding wafer 105 having been subjected to grinding is obtained.

Specifically, the controller 7 first determines the height distribution of the upper surface 106 of the test grinding wafer 105 having been subjected to the test grinding step, in reference to the thickness distribution of the test grinding wafer 105 measured in the distribution measuring step.

FIG. 6A depicts the height distribution of the upper surface 106 of the test grinding wafer 105 having been subjected to the test grinding step (upper-surface height distribution). In this figure, the upper height distribution is expressed by use of contour lines L. As depicted in this figure, the upper surface 106 of the test grinding wafer 105 obtained after the grinding has minute height differences (corresponding to the thickness differences of the test grinding wafer 105) partially generated in the circumferential direction and the radial direction.

One of the reasons thereof is considered to be that, for example, when the chuck table 20 is caused to communicate with the suction source 201 and the test grinding wafer 105 is held under suction by the holding surface 22 in the test grinding step, the holding surface 22 is pressed by the atmospheric pressure, whereby a deformation (a part which is not flat) is partially generated in the holding surface 22 formed in the holding surface forming step, and a part which is not parallel to the lower surfaces of the wafer grinding grindstones 17 is generated in the radius part of the holding surface 22. In other words, it is considered that the thickness differences (height differences) are generated in the test grinding wafer 105 having been subjected to grinding, because the test grinding has been carried out by holding the test grinding wafer 105 on the holding surface 22 which is not flat.

In view of this, in the holding surface correction processing step, the controller 7 subjects the holding surface 22 to correction processing such that the holding surface 22 will become a substantially flat surface when the product wafer 100 is held under suction later. In other words, as depicted in FIG. 6B, the holding surface 22 is subjected to correction processing in conformity with the upper-surface height distribution H of the test grinding wafer 105, whereby the shape of the holding surface 22 is corrected into a surface shape similar to that of the upper surface 106 of the test grinding wafer 105 (a shape having an upper-surface height distribution similar to that of the upper surface 106). As a result, the holding surface 22 can be made to be a substantially flat surface when the chuck table 20 is caused to communicate with the suction source 201 and the product wafer 100 is held under suction by the holding surface 22.

This correction processing is carried out by use of, for example, an etching mechanism 40 provided in the grinding apparatus 1, as depicted in FIG. 7. The etching mechanism 40 includes a jet nozzle (etching gas jet nozzle) 41 for jetting etching gas, a lifting unit 42 for lifting the jet nozzle 41 up and down along the Z-axis direction, and a horizontal moving unit 43 for moving the jet nozzle 41 and the lifting unit 42 in horizontal directions. In the present embodiment, plasmatized etching gas (SF₆ or CF₄) is jetted from the jet nozzle 41.

In the holding surface correction processing step, the controller 7 first causes the table moving mechanism 95 to dispose the table assembly 2 including the chuck table 20 at a correction processing position (which may be the same as the holding position) spaced from the processing position on the lower side of the grinding mechanism 10. Thereafter, the controller 7 or an operator detaches the test grinding wafer 105 from the holding surface 22 of the chuck table 20.

Next, the controller 7 controls the lifting unit 42 and the horizontal moving unit 43 of the etching mechanism 40, to dispose the jet nozzle 41 on the holding surface 22 of the chuck table 20. Then, while causing the horizontal moving unit 43 and the lifting unit 42 to change the position of the jet nozzle 41 in conformity with the upper-surface height distribution of the test grinding wafer 105, the controller 7 jets partially plasmatized etching gas from the jet nozzle 41 to the holding surface 22, whereby the holding surface 22 is subjected to correction processing by atmospheric-pressure plasma etching.

Owing to such correction processing, the shape of the holding surface 22 is corrected to have a surface shape similar to that of the upper surface 106 of the test grinding wafer 105. In other words, the holding surface 22 comes to have the height distribution as depicted in FIG. 6A.

(Grinding Step)

Next, a grinding step for the product wafer 100 which is a workpiece is carried out. In this step, the product wafer 100 is held under suction by the holding surface 22 and the product wafer 100 is ground to a predetermined thickness by the wafer grinding grindstones 17, after the holding surface correction processing step.

Specifically, the controller 7 causes the table moving mechanism 95 to dispose the table assembly 2 including the chuck table 20 at the above-mentioned predetermined holding position. Next, the controller 7 or an operator mounts the product wafer 100 on the holding surface 22 of the chuck table 20 in such a manner that the upper surface 101 of the product wafer 100 is directed upward. Thereafter, the controller 7 opens the suction valve 35, to thereby cause the holding surface 22 to communicate with the suction source 201. As a result, the product wafer 100 is held under suction by the holding surface 22, as depicted in FIG. 8.

Next, the controller 7 causes the table moving mechanism 95 to dispose the table assembly 2 including the chuck table 20 with the product wafer 100 held thereon under suction at the above-mentioned processing position. Then, while rotating the wafer grinding grindstones 17 of the grinding mechanism 10 and the chuck table 20, the controller 7 causes the grinding feeding mechanism 80 to lower the grinding mechanism 10, to bring the wafer grinding grindstones 17 into contact with the radius part of the upper surface 101 of the product wafer 100 held by the holding surface 22, and to grind the upper surface 101 with the wafer grinding grindstones 17. In this instance, the controller 7 measures the thickness of the product wafer 100 being ground, by use of the thickness measuring mechanism 60, and carries out the grinding until the thickness of the product wafer 100 becomes a predetermined thickness.

As has been described above, in the present embodiment, in the holding surface correction processing step, the shape of the holding surface 22 is corrected to be a surface shape similar to that of the upper surface 106 of the test grinding wafer 105 having been ground in the test grinding step. As a result, when the holding section 21 of the chuck table 20 is caused to communicate with the suction source 201 and the product wafer 100 is held under suction by the holding surface 22 during the grinding step, the holding surface 22 becomes a substantially flat surface, and the radius part of the holding surface 22 becomes parallel to the lower surfaces of the wafer grinding grindstones 17. Hence, it is possible to restrain partial thickness differences from being generated in the product wafer 100 ground by the wafer grinding grindstones 17. Accordingly, it is possible to grind the product wafer 100 to a uniform thickness.

Note that, in the above-described distribution measuring step, the thickness distribution of the whole surface of the test grinding wafer 105 having been ground in the test grinding step is measured. With regard to this, in the distribution measuring step in the present embodiment, the height distribution of the whole surface of the upper surface 106 of the test grinding wafer 105 having been ground in the test grinding step may be measured.

In this case, after the test grinding step, the controller 7 or an operator detaches the test grinding wafer 105 from the chuck table 20, and holds the test grinding wafer 105 on an unillustrated flat table including a height measuring unit such as the second height measuring unit 62 of the thickness measuring mechanism 60. Then, while rotating the table with the test grinding wafer 105 held thereon gradually and while moving the height measuring unit gradually in the radial direction, the controller 7 causes the height measuring unit to measure the height of the upper surface 106 of the test grinding wafer 105. As a result, the controller 7 can determine the height distribution (upper-surface height distribution) of the whole surface of the upper surface 106 of the test grinding wafer 105.

In this case, in the holding surface correction processing step, in reference to the upper-surface height distribution measured in the distribution measuring step, the controller 7 subjects the holding surface 22 used in the test grinding step to correction processing in such a manner that a holding surface 22 having a surface shape similar to that of the upper surface 106 of the test grinding wafer 105 having been ground is obtained.

Thus, in the distribution measuring step, the thickness distribution of the whole surface of the test grinding wafer 105 having been ground in the test grinding step or the height distribution of the whole surface of the upper surface 106 may be measured. In addition, in the holding surface correction processing step, in reference to the thickness distribution and the upper-surface height distribution measured in the distribution measuring step, the holding surface 22 used in the test griding step may be subjected to correction processing such that a holding surface 22 having a surface shape similar to that of the upper surface 106 of the test grinding wafer 105 having been ground is obtained.

In addition, the grinding apparatus 1 may include a holding surface correction grinding mechanism 50 as depicted in FIG. 9, in place of or in addition to the etching mechanism 40 depicted in FIG. 7. The holding surface correction grinding mechanism 50 has a small-diameter grindstone unit 51, a lifting unit 52 that lifts the small-diameter grindstone unit 51 up and down along the Z-axis direction, and a horizontal moving unit 53 that moves the small-diameter grindstone unit 51 and the lifting unit 52 horizontally. The small-diameter grindstone unit 51 has a small-diameter grindstone 511, and a motor 512 for rotating the small-diameter grindstone 511. The small-diameter grindstone 511 has a diameter smaller than the radius of the holding surface 22 of the chuck table 20.

In this case, the controller 7 may subject the holding surface 22 of the chuck table 20 to correction processing by use of this holding surface correction grinding mechanism 50 in the correction processing step. In this case, in the holding surface correction processing step, after the test grinding wafer 105 is detached from the holding surface 22, the controller 7 controls the lifting unit 52 and the horizontal moving unit 53 of the holding surface correction grinding mechanism 50, to dispose the small-diameter grindstone unit 51 on the holding surface 22 of the chuck table 20. Then, while causing the lifting unit 52 and the horizontal moving unit 53 to change the position of the small-diameter grindstone unit 51 in conformity with the upper-surface height distribution (see FIGS. 6A and 6B) of the test grinding wafer 105, the controller 7 subjects the holding surface 22 to, for example, partial grinding with the small-diameter grindstone 511 of the small-diameter grindstone unit 51, thereby to subject the holding surface 22 to correction processing.

Owing to such correction processing, like in the case where the etching mechanism 40 is used, the shape of the holding surface 22 is corrected to have a surface shape similar to that of the upper surface 106 of the test grinding wafer 105.

Note that, in a case where the holding surface 22 is subjected to correction processing by use of the holding surface correction grinding mechanism 50, the holding surface 22 (the holding section 21) of the chuck table 20 may include silicon, or may be formed of other blank materials (an alumina-based porous ceramic or the like).

In addition, when the holding surface is subjected to correction processing in the holding surface correction processing step, the controller 7 may cause the inclination adjusting mechanism 93 to control the inclination of the chuck table 20, to thereby set that part of the holding surface 22 which is located on the lower side of the etching mechanism 40 or the holding surface correction grinding mechanism 50 into a horizontal state.

Besides, in the above-described embodiment, in the holding surface forming step, the holding surface 22 of the chuck table 20 is formed by use of the wafer grinding grindstones 17 of the grinding mechanism 10. With regard to this, in the holding surface forming step, table grinding grindstones 18 (see FIG. 1) for grinding the table which are grindstones for grinding the chuck table 20 may be used in place of the wafer grinding grindstones 17. In this case, in the holding surface forming step, an operator attaches a table grinding wheel 19 including the table grinding grindstones 18 to the wheel mount 13, in place of the grinding wheel 15.

Hence, in the holding surface forming step in the present embodiment, the holding surface 22 may be formed by grinding the upper surface of the chuck table 20 including the holding section 21 by use of the wafer grinding grindstones 17 or the table grinding grindstones 18 of the grinding mechanism 10, in a state in which the chuck table 20 does not communicate with the suction source 201.

The present invention is not limited to the details of the above described preferred embodiment. The scope of the invention is defined by the appended claims and all changes and modifications as fall within the equivalence of the scope of the claims are therefore to be embraced by the invention.

Claims

1. A wafer grinding method in which a chuck table mounted to a table base is made to communicate with a suction source and a wafer held under suction by a holding surface of the chuck table is ground by a wafer grinding grindstone for grinding the wafer, the wafer grinding method comprising: a holding surface forming step of grinding an upper surface of the chuck table by use of the wafer grinding grindstone or a table griding grindstone for grinding the table in a state in which the chuck table does not communicate with the suction source, to thereby form the holding surface;a holding step of causing the holding surface to communicate with the suction source and holding a test grinding wafer under suction by the holding surface, after the holding surface forming step is carried out;a test grinding step of grinding the test grinding wafer held under suction by the holding surface in the holding step by the wafer grinding grindstone to a predetermined thickness;a distribution measuring step of measuring a thickness distribution of a whole surface of the test grinding wafer ground in the test grinding step, or an upper surface height distribution of a whole surface of an upper surface of the test grinding wafer;a holding surface correction processing step of subjecting the holding surface used in the test grinding step to correction processing in such a manner that a holding surface having a surface shape similar to that of the upper surface of the test grinding wafer having been ground is obtained, in reference to the thickness distribution or the upper surface height distribution measured in the distribution measuring step; anda grinding step of holding a product wafer under suction by the holding surface and grinding the product wafer to a predetermined thickness with the wafer grinding grindstone, after the holding surface correction processing step is carried out.

2. The wafer grinding method according to claim 1, wherein the holding surface of the chuck table includes silicon, and,in the holding surface correction processing step, partially plasmatized etching gas is jetted from an etching gas jet nozzle to the holding surface to subject the holding surface to correction processing by atmospheric-pressure plasma etching.

3. The wafer grinding method according to claim 1, wherein, in the holding surface correction processing step, the holding surface is ground with a small-diameter grindstone having a diameter smaller than a radius of the holding surface, to thereby subject the holding surface to correction processing.