JP7068096B2 - Grinding method for workpieces - Google Patents

Description

The present invention relates to a method for grinding a workpiece.

In the semiconductor device manufacturing process, in order to obtain the desired thickness of the device, the back surface is ground and thinned at the stage of the semiconductor wafer, which is an aggregate of a large number of devices. Wafers are being machined thinner in response to the remarkable thinning of devices these days, which requires higher precision in thickness control. Therefore, the movement amount of the grinding tool is controlled while measuring the thickness of the workpiece until the workpiece is formed to the finish thickness.

As a method for measuring the thickness during grinding of the workpiece, for example, a contact-type thickness measuring method for measuring by contacting a probe as shown in Patent Document 1 and a laser as shown in Patent Document 2 are used. There is a non-contact thickness measuring method for measuring using.

A non-contact type thickness measuring method that can measure the thickness without contacting the workpiece with a probe or the like is considered to be more advantageous than the contact type in that it does not damage the workpiece and does not reduce the bending strength. Further, the non-contact thickness measuring method has an advantage that the measurement can be performed without being limited by the unevenness of the pattern or the thickness variation of the surface protection member.

Japanese Unexamined Patent Publication No. 2001-9716 Japanese Patent No. 34913337

However, at present, there is a limit to the thickness measurement range of the non-contact measuring means using a laser, and if the thickness falls below a certain thickness, the non-contact measuring means cannot measure the thickness of the workpiece. This poses a barrier to the ultra-thinning of the workpiece.

The present invention has been made in view of the above facts, and its main technical problem is to measure the thickness of the workpiece to be high in the case of grinding thinner than the measurement limit thickness of the non-contact type thickness measuring means. Do it with precision.

The grinding method according to the present invention comprises a rotatable chuck table having a holding surface for holding the protective member side of the workpiece to which the protective member is attached to the surface, and the workpiece held on the chuck table. Grinding means that rotatably support the grinding wheel, in which grinding grindstones for grinding an object are arranged in an annular shape, and measurement light is radiated toward the workpiece, and the irradiated measurement light is on the upper surface of the workpiece. The probe is brought into contact with a non-contact thickness measuring means that calculates the thickness of the workpiece from the time difference between the reflected light and the light transmitted through the workpiece and reflected on the lower surface. A non-contact grinding method for grinding the back surface of a work piece to a desired finish thickness by a grinding device equipped with at least a contact-type thickness measuring means for measuring the thickness of an object and a protective member. While measuring the thickness of the workpiece by the thickness measuring means, the chuck table was rotated, the grinding wheel was rotated, and the grinding wheel was moved toward the chuck table and held on the chuck table. Protection that calculates the thickness of the protective member by subtracting the measured value of the non-contact stone thickness measuring means from the first grinding step for grinding the back surface of the workpiece and the measured value of the contact type thickness measuring means. The chuck table is controlled while controlling the finish thickness with a value obtained by subtracting the thickness of the protective member calculated in the protective member thickness calculation step from the measured values of the member thickness calculation step and the contact type thickness measuring means. A second grinding step for grinding the back surface of the workpiece held on the chuck table by rotating the grinding wheel and moving the grinding wheel toward the chuck table. By calculating the thickness of the protective member, it is possible to control the thickness of the work piece by using the contact type thickness measuring means even in a thickness region that cannot be measured by the non-contact type thickness measuring means. This is a method for grinding a workpiece, which is characterized by the above.

The grinding method according to the present invention is used for measuring the thickness of a workpiece thinner than the measurable thickness when it is desired to grind the workpiece thinner than the thickness measurable by the non-contact thickness measuring means. The value of the sum of the thickness of the work piece measured by the non-contact thickness measuring means within the measurable range and the thickness of the work piece measured by the contact type thickness measuring means and the thickness of the protective member is used. This makes it possible to perform grinding while measuring the thickness with the same accuracy as the non-contact type thickness measuring means. Further, in this measuring method, the thickness can be measured without being limited by the unevenness of the pattern and the thickness variation of the surface protection member. By using the contact type thickness measuring means, grinding of a wider range of thickness can be performed accurately without installing a separate thickness measuring means in order to widen the measuring range of the non-contact type thickness measuring means.

In recent years, in many industries dealing with semiconductor devices, including the automobile industry, it has become necessary to store the thickness of the semiconductor wafer at the end of cutting as numerical data from the viewpoint of product quality and the like. In the conventional grinding in an ultra-thin region thinner than the measurement range of the non-contact type thickness measuring means, the thickness to be ground is determined in advance at a thickness not exceeding the measuring range of the non-contact type thickness measuring means, and the predetermined thickness is determined. After grinding to the thickness, the measurement by the non-contact thickness measuring means is stopped, and the grinding tool is moved in the grinding direction by the amount corresponding to the difference between the predetermined thickness and the finish thickness. do. In this grinding method, when grinding from the predetermined thickness to the finish thickness, it is not possible to grind while measuring the thickness data, and the degree of reliability of the thickness data depends on the accuracy of the movement of the grinding tool. Dependent. Grinding by this method in view of the fact that the amount of movement of the grinding tool does not always match the thickness of the ground wafer because the grinding tool wears during grinding and the movement control of the grinding tool may have an error. Then, the reliability of the thickness data is questionable. On the other hand, in the present invention, since the thickness measurement by the contact type thickness measuring means is used until the workpiece reaches the finished thickness, the actual thickness data at the end of grinding can be obtained.

It is sectional drawing which shows the state of grinding of the workpiece. It is a perspective view which shows the state of grinding of the workpiece. It is explanatory drawing which simply shows the operation of the contact type thickness measuring means and non-contact type thickness measuring means. It is explanatory drawing which shows the state of the thickness measurement of the workpiece in the 1st grinding step. It is explanatory drawing which shows the state of the thickness measurement of the workpiece and the protective member in the protection member thickness calculation step. It is explanatory drawing which shows the state of the measurement of the thickness of the workpiece and the protective member in the 2nd grinding step.

The grinding device 10 shown in FIG. 1 is a device that grinds the workpiece 110 and thins it to a desired finish thickness. The grinding device 10 includes a chuck table 14 for holding the workpiece 110, a grinding means 15 for grinding the workpiece 110 held by the chuck table 14, and a non-measurement for measuring the thickness of the workpiece at the time of grinding. The contact-type thickness measuring means 12 and the contact-type thickness measuring means 13 for measuring the total thickness of the work piece and the thickness of the protective member attached to the work piece 110 at the time of the grinding. To prepare for.

The chuck table 14 has a circular suction area 140 made of a porous ceramic material on the upper surface, and as a result of the protective member 111 being sucked on the holding surface 140a which is the upper surface of the suction area 140, the protective member 111 is attached. The work piece 110 is held on the chuck table 14. An annular frame body 141 is formed around the suction area 140, and the upper surface 141a of the frame body 141 is continuously in the same plane as the upper surface 140a of the suction area 140. The chuck table 14 can be rotated about a rotation axis parallel to the ± Z direction perpendicular to the XY plane by a rotation means (not shown).

As shown in FIG. 2, the grinding means 15 includes a mount 150 at the tip of a rotating shaft parallel to the ± Z direction, and a grinding wheel 151 mounted on the mount 150. A grinding wheel 152 is fixed to the lower end of the grinding wheel 151. The grinding wheel 152 fixed to the grinding wheel 151 is arranged in an annular shape, and when the grinding wheel 151 rotates, it passes on the rotation axis of the chuck table 14. Both the non-contact type thickness measuring means 12 and the contact type thickness measuring means 13 can measure the thickness even during grinding.

As shown in FIG. 3, the non-contact thickness measuring means 12 measures the thickness T2 of the workpiece by using a laser beam without touching the upper surface 110a of the workpiece. The non-contact thickness measuring means 12 irradiates the work piece 110 with the measurement light, and the irradiated measurement light reflects the light (reflected light L1) on the upper surface 110a of the work piece and the work piece 110. The thickness T2 of the workpiece is measured from the time difference between the light transmitted and reflected by the lower surface 110b of the workpiece (transmitted light L2) and the received light.

The contact type thickness measuring means 13 includes two contacts. Two contacts by contacting one contact (reference probe 130a) with the upper surface 141a of the frame of the chuck table 14 and the other contact (variable probe 130b) with the upper surface 110a of the workpiece 110. The difference in height is measured as the total thickness T1 which is the sum of the thickness of the protective member held by the chuck table 14 and the work piece.

Hereinafter, a grinding method for grinding a workpiece using the above-mentioned grinding device 10 will be described separately for a first grinding step, a protective member thickness calculation step, and a second grinding step.

(1st grinding step)
First, the limit measurement thickness T21 of the workpiece 110 to be measured by the non-contact thickness measuring means 12 is determined. The limit measurement thickness T21 is the minimum value of the thickness measured by the non-contact type thickness measuring means 12, and is the lower limit of the measurable thickness in the specifications of the non-contact type thickness measuring means 12 or this. It is preferable that the thickness is as close as possible to and thicker than this. As shown in FIG. 4, first, the chuck table 14 is rotated and the grinding wheel 152 is rotated while measuring the thickness of the workpiece 110 having an initial thickness of T20 by the non-contact thickness measuring means 12. Further, the grinding wheel 152 is moved in a direction (−Z direction) perpendicular to the holding surface 140a of the chuck table 14, the upper surface 110a of the workpiece is ground, and the thickness of the workpiece 110 by the non-contact thickness measuring means 12 Grinding is performed until the measured value T2 of is the limit measured thickness T21. While the thickness is measured by the non-contact type thickness measuring means 12, the reference probe 130a of the contact type thickness measuring means 13 may be kept in contact with the upper surface 141a of the frame, but the variable probe 130b may be kept in contact with the upper surface 141a. Keep out of contact with the upper surface 110a of the workpiece. Further, in FIGS. 4 and later, the illustration of the grinding means 15 shown in FIGS. 1 and 2 is omitted.

(Protective member thickness calculation step)
When the measured value T2 of the thickness of the workpiece 110 by the non-contact thickness measuring means 12 reaches the limit measured thickness T21, as shown in FIG. 5, the workpiece 110 is contacted while continuing grinding. The reference probe 130a of the formula thickness measuring means 13 is brought into contact with the upper surface 141a of the frame body, and the variable probe 130b is brought into contact with the upper surface 110a of the workpiece. And the thickness T3 of the protective member 111 are combined, and the measurement of the total thickness T1 is started. Then, the limit measurement thickness T21 of the workpiece 110 measured by the non-contact thickness measuring means 12 is subtracted from the measured value T10, and the thickness T3 of the protective member 111 is calculated by T3 = T10-T21. Immediately after the measured value T2 of the thickness of the workpiece 110 by the non-contact thickness measuring means 12 becomes the limit measurement thickness T21, the thickness of the workpiece 110 by the non-contact thickness measuring means 12 Stop the measurement.

(Second grinding step)
After the protective member thickness calculation step, the grinding of the workpiece 110 is continued, and the protective member 111 calculated in the protective member thickness calculation step from the current total thickness T1 measured by the contact type thickness measuring means 13. As shown in FIG. 6, the current thickness T2 of the workpiece 110 is the desired finish thickness, while subtracting the thickness T3 of the workpiece and measuring the current thickness T2 of the workpiece as T2 = T1-T3. Grind until T22. That is, the direction (−Z direction) perpendicular to the holding surface 140a of the chuck table 14 while rotating the chuck table 14 and the grinding wheel 152 until the current thickness T2 of the workpiece 110 reaches the desired finish thickness T22. ), The grinding wheel is moved to grind the upper surface 110a of the workpiece. At this time, the thickness T3 of the protective member 111 keeps a constant value, and the value of T1 decreases due to thinning by grinding. Therefore, the current thickness T2 = T1-T3 of the workpiece 110 is always T1. Decrease by the same amount. If the change in the value of the total thickness T1 is read by the contact-type thickness measuring means 13, the current thickness T2 of the workpiece 110 can be indirectly obtained by calculation. As a result, in a thickness region below the measurable range of the non-contact type thickness measuring means 12, grinding is possible while measuring the thickness T2 of the workpiece with the same measurement accuracy as the non-contact type measuring means 12. ..

10: Grinding device 110: Work piece 110a: Work piece upper surface 110b: Work piece lower surface 111: Protective member 12: Non-contact thickness measuring means
L1: Reflected light L2: Transmitted light 13: Contact type thickness measuring means 130a: Reference probe 130b: Variable probe 14: Chuck table 140: Suction area 140a: Holding surface 141: Frame body 141a: Frame body top surface 15: Grinding means 150 : Mount 151: Grinding wheel 152: Grinding wheel T1: Total thickness T2: Thickness of workpiece T3: Thickness of protective member T10: Total thickness (measured value at the step of calculating protective member thickness)
T11: Total thickness (measured value at the second grinding step)
T20: Initial thickness T21: Limit measurement thickness T22: Desired finish thickness

Claims (1)

A rotatable chuck table having a holding surface for holding the protective member side of the workpiece to which the protective member is attached to the surface, and
A grinding means that rotatably supports a grinding wheel in which a grinding wheel for grinding a workpiece held on the chuck table is arranged in an annular shape, and a grinding tool.
The object is irradiated with the measurement light toward the workpiece, and the light received by the irradiated measurement light between the light reflected on the upper surface of the workpiece and the light transmitted through the workpiece and reflected on the lower surface is the subject. Non-contact thickness measuring means for calculating the thickness of the workpiece,
By a grinding device provided with at least a contact-type thickness measuring means for contacting a probe and measuring the thickness including the workpiece and the protective member.
A grinding method that grinds the back surface of a work piece to a desired finish thickness.
While measuring the thickness of the workpiece with the non-contact thickness measuring means, the chuck table is rotated, the grinding wheel is rotated, and the grinding wheel is moved toward the chuck table and held on the chuck table. The first grinding step for grinding the back surface of the workpiece, and
A protective member thickness calculation step for calculating the thickness of the protective member by subtracting the measured value of the non-contact stone thickness measuring means from the measured value of the contact type thickness measuring means.
While controlling the finish thickness with a value obtained by subtracting the thickness of the protective member calculated in the protective member thickness calculation step from the measured value of the contact type thickness measuring means, the chuck table is rotated and the grinding is performed. A second grinding step for rotating the grindstone and moving the grinding wheel toward the chuck table to grind the back surface of the workpiece held on the chuck table is provided.
By calculating the thickness of the protective member, the thickness of the work piece can be controlled by using the contact type thickness measuring means even in a thickness region that cannot be measured by the non-contact type thickness measuring means. A method for grinding a workpiece, which is characterized by being possible.

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