JP2001009716A - Wafer thickness measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid dispersion of wafer thickness posed by an axial inclination of chuck tables when the thickness of wafers being chucked is measured with two-point in-process gauges. SOLUTION: One pair of contacts 17a and 17b of a two-point in-process gauge 17 is first put in contact with the surface of a chuck 9 carrying no wafers W to measure levels Tc0 and Tw0, and the identification number of the contact 17a or 17b that provides the greater level, and the level difference (t) as a correction value given by |Tc0-Tw0| are stored in a controller. For the computations of the thickness of the ground wafer W from the difference between new levels Tci and Twi that, during or after a grinding operation, the pair of contacts 17a and 17b of the two-point in-process gauge 17 measures again when put in contact with the surfaces of the chuck 9 and wafer W, the level Tci or Twi the number-stored contact 17a or 17b that has shown the greater initial level measures is subjected to correction, which subtracts the correction value (t) from it, before used in the difference calculation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-point system in which the thickness of a wafer vacuum-adsorbed to a chuck is applied to the surface of the wafer and the surface of the chuck in a state where the wafer is vacuum-adsorbed during or after the grinding. In a method of measuring a difference in height measured by applying a pair of contacts of an in-process gage as a thickness of a wafer, the thickness of the ground wafer caused by the inclination of the axis of the chuck is reduced. The present invention relates to a method of measuring the thickness of a wafer at the time of or after grinding the wafer, which can eliminate the variation.

[0002]

2. Description of the Related Art When a wafer is ground with a grindstone, the thickness of the wafer is measured during or / and after the grinding so as to have a target wafer thickness. JP-A-61-27
No. 4876 is formed by a plurality of equally divided frames,
A surface grinding machine that chucks a plurality of wafers to a rotary table that repeatedly rotates and stops at a constant low speed by vacuum-sucking a thin wafer by a chuck mechanism and automatically grinds the wafer. Alternatively, in a state in which the processed semiconductor wafer is vacuum-adsorbed, the upper surface of the wafer and the upper surface of the chuck are measured using an integrated two-point in-process gage, and the difference in height is measured. A method for measuring the thickness of a wafer is proposed.

[0003] Wafers are usually stored in cassettes in units of 25 wafers.
And sent to the next etching and polishing process
Therefore, as far as possible, the thickness of these 25 wafers is uniform.
And it is required to be within 1μm
You. During grinding, the thickness of the wafer (T₁) Is measured by
Confirmation of the grinding state, but the thickness of the wafer before grinding
(T₀) And grinding time (t₁Min) to the previous grinding speed
(T _o-T₁) / T₁) And calculate the target wafer thickness
(T)₁−T) t₁/ (T_o
-T₁) Is calculated from the formula, and grinding is performed
In some cases, control is performed to obtain a desired wafer thickness.
Wafer thickness measurement method using two-point in-process gage
Can measure the thickness of the wafer even during grinding, and
Grinding is terminated when the two-point in-process gauge indicates.
It is necessary to control the grinding speed and remaining grinding time.
Has advantages not required.

[0004]

However, when the axis of the chuck for chucking the wafer is inclined, especially when a plurality of wafer chuck mechanisms are used, the inclination angles are also different. As shown in (c), the thickness of the wafer measured by the inclination angle of the axis varies. The present invention provides a method for measuring the thickness of a wafer in a grinding apparatus capable of obtaining a wafer having extremely small variation in the thickness of a ground wafer obtained even if the axis of a chuck for sucking the wafer is inclined. The purpose is to:

[0005]

According to the present invention, the thickness of a wafer vacuum-adsorbed to a chuck is applied to the surface of the wafer and the surface of the chuck in a state where the wafer is vacuum-adsorbed during or after the grinding. In a method of measuring a difference in height measured by applying a pair of contacts of a point-type in-process gauge as a thickness of a wafer, a two-point in-process gauge without first adsorbing the wafer to a chuck. The height (T _c0 , T _w0 ) is measured by applying a pair of the contacts to the surface of the chuck, and the contact number indicating the larger value of the height and the value of the difference in height t = | T _c0 −T _w0 | is stored in the controller as a correction value, and a pair of contacts of a two-point in-process gage are applied to the surface of the wafer and the surface of the chuck during or after the grinding. Measured height (T
_ci , _Twi ), when determining the thickness of the wafer from the difference ( _Twi - _Tci ), the height ( _Tci or _Tci) measured by the contact having the higher number stored above and having the number stored above. _{The present} invention provides a method of measuring the thickness of a wafer, characterized in that the height obtained by subtracting the correction value t from _wi ) is regarded as the height measured by the contact and the thickness of the ground wafer is calculated.

Before grinding the wafer, a pair of contacts of a two-point in-process gage is applied to the surface of the chuck in a state where the wafer is not attracted to the chuck, and the height (T _c0 , T _w0 ) is measured. The control device stores the number of the contact indicating the larger value of the height and the value of the difference between the heights t = | _Tc0 - _Tw0 | as a correction value, and corrects by subtracting this t thickness. In other words, the difference between the thickness t of the two-point in-process gage measurement caused by the inclination of the axis of the chuck is subtracted, and the correction is performed with the state of T _c0 = 0 and T _w0 = 0 as the origin. Grinding is performed while calculating the thickness of the processed wafer, or the thickness after grinding is calculated, so that the thickness variation between the wafers is extremely small, 1.0 μm or less.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The method of the present invention will be described below with reference to the drawings. FIG. 1 is a top view showing one example of a grinding apparatus, which includes a rough grinding zone and a finish grinding zone. FIG. 2 is a cross-sectional view of an index turntable portion of the grinding apparatus, and FIG. 3 is a front view for explaining a state in which a wafer thickness is measured using a two-point in-process gage.

In the grinding apparatus shown in FIGS. 1 and 2,
1 is a grinding device, 2 is a wafer loading cassette placed on a mounting table located at the same height as a surface of a base 3 described later, 2 'is a wafer unloading cassette,
3 is a base, 4 is a floor, 5 is a robot, 5a is a frame standing upright from the base, 6 is a temporary wafer mounting table, 7 is a wafer cleaning mechanism,
8, 8 are transport pads, 8a and 8'a are suction pads, 8
b and 8'b are handles, 8c and 8'c are shafts, 9 is an index table provided at a location where the center of the base is hollowed out,
s1 is a wafer loading / wafer unloading zone, s2 is a rough grinding zone, s3 is a finish grinding zone, 9
Reference numerals a, 9b and 9c denote chuck mechanisms, 10a and 10b are walls erected from a base, 11 is a coarse grinding wheel, 11a is a first spindle shaft, 12 is a finishing wheel, 12a is a second spindle shaft, and 13 is chuck cleaning. Mechanism, 14 is a ceramic chuck cleaner, 15 is a polishing mechanism, 15a is a chuck mechanism, 15c is a cleaning liquid supply mechanism, 15d is an air supply nozzle, 16 is a grindstone start point positioning mechanism, and 17 and 17 are two-point in-process. Gage, 17a is a chuck top contact,
17b is a wafer upper surface contact.

In FIG. 3, a is a diagram in which a difference in height is measured by applying a contact of a two-point in-process gage to the upper surface of the chuck in a state in which the wafer is not sucked, and b is a diagram showing the t during grinding.
FIG. 3C shows a two-point in-process gage contact applied to the upper surface of the chuck and the upper surface of the wafer, which hold the wafer after _one minute, to measure the height difference. FIG. 9 is a diagram showing a measurement of a height difference between the upper surface of the chuck and the upper surface of the wafer, which are brought into contact with a contact of a two-point in-process gage. In the drawing, w is a wafer, 9 is a porous ceramic plate of a chuck mechanism, 11 is a grindstone, 17 is a two-point in-process gage, 17a is a chuck top contact, 17b is a wafer top contact, 17c and 17d. Is the joint, 17e, 17
f is a terminal, 17g is an air cylinder, and 17h is a support shaft.

[0010] In Figure 3a, the upper surface in two-point-process gain of the chuck 9 in a state in which does not adsorb the wafer thickness T ₀ - height against the contact 17a of the di- and 17b (T _c0,
T _w0 ) was measured, and the number of the contact that showed the larger value of the height (here, the contact 17b side is assumed) and the value of the difference in height t = | T _c0 −T _w0 Is stored in the control device CPU as a correction value.

In FIG. 3b, the height of the wafer is measured by applying a pair of contacts of a two-point in-process gage to the surface of the wafer and the surface of the chuck before grinding, by adsorbing the wafer to the chuck. (T _c, T _w) value of is sent to the CPU, the CPU calculating unit calculates the thickness T ₀ of the grinding prior to the wafer from the value T ₀ = a (T _w -t) -T _c. Then t ₁
2 minutes after grinding for 2 minutes
The values of the heights (T _c1 , T _w1 ) measured by applying a pair of contacts of the point-type in-process gage to the CPU are transmitted to the CPU. When the thickness of the contact is determined, the correction value is obtained from the height (T _w1 ) measured by the contact having the large number stored therein and indicating the value of the large height (the contact 17b is assumed here as described above). Is deemed to be the height measured by the contact, and the thickness T _{1 of the} ground wafer is calculated as T ₁ = (T _w1 −t) −T _c1 . To obtain the remaining grinding time t ₂ , the grinding speed for t ₁ minute is calculated as (T ₀ −T ₁ ) / t _1, and the remaining grinding time t ₂ is calculated from the target wafer thickness T to t t. ₂ = (T ₁ −T) t ₁ / (T ₀ −T ₁ ) is calculated by the calculation unit, and further grinding for t ₂ minutes is performed by the CPU.
Is transmitted to the grinding device 1.

In FIG. 3c, a pair of contacts of a two-point in-process gage are applied to the surface of the wafer and the surface of the chuck when the grinding is completed for the remaining t ₂ minutes and the grinding is completed. Of the heights (T _c2 , T _w2 ) measured by
The data is transmitted to the PU, and the CPU calculation unit calculates the thickness of the wafer after grinding from this value as T ₂ = (T _w2 −t) −T _c2 and stores it. When the control based on the grinding speed and the remaining grinding time is not performed, the measurement state of FIG. 3B is continuously performed in FIG. 3, and the value of (T _w2 −t) −T _c2 is set to the target wafer thickness T ₂ . The grinding is terminated when it becomes.

The grinding of a wafer using the grinding apparatus 1 is performed as follows. Note that the target thickness of the finish-ground wafer in the example is T μm, and the amount of grinding by finish grinding is about 10 to 30 μm (therefore, the target value of the wafer thickness at the end of rough grinding is 10 to 30 μm from T _2).
This is a value obtained by subtracting μm. ). First, the two-point in-process gage 17 is held in a state where the wafer is not attracted to the chuck.
The pair of contacts 17a, 17b of each of the chucks 9a, 9
b, the height of each chuck against the surface of 9c (T _c0 ,
T _w0 ) was measured, and the number of the contact (1) indicating the chuck number and the larger value of the height at the chuck number
7a or 17b) and the height difference value t = |
T _c0 −T _w0 | is stored in the controller as a correction value for each chuck. Hereinafter, the following steps (1) to (7) are performed. In addition, in order to facilitate explanation, each chuck mechanism 9
The description will be made on the assumption that the contact 17b has a high value in each of a, 9b, and 9c, and that the difference between the heights is t.

(1) The wafer w is sucked from the wafer loading cassette 2 to the suction arm 5c of the articulated robot 5 suspended so that the suction arms 5b and 5c are on the lower side. Place on table 3.

(2) The index turntable 9 is rotated by 120 degrees, the wafer on the temporary table is attracted to the transfer pad 8, and the transfer pad is rotated to turn the wafer into an index turntable. The wafer is transferred to the chuck mechanism a of the loading / wafer unloading zone s1, during which the wafer is sucked from the wafer loading cassette to the suction arm of the articulated robot 5.
This is placed on a temporary table.

(3) The index turntable 9 is rotated by 120 degrees to set the chuck mechanism a to a coarse grinding zone s2.
After the chuck mechanism b is moved to the wafer loading / wafer unloading zone s1, the two-point in-process gauge 17 is moved to the rough grinding zone s2.
One contact 17a is applied to the surface of the chuck 9a to measure the height (T _ci ), and the other contact 17b is applied to the upper surface of the wafer to measure the height (T _wi ), and the value is used as an electric signal. The data is transmitted to the RAM of the control device CPU. The arithmetic unit of the control device CPU calculates the thickness (T ₀ ) of the wafer before grinding by the following equation and stores the thickness in the control device. T ₀ = (T _wi −t) −T _ci Then, the first spindle 10 a is lowered to press the grindstone 11 against the wafer, and the rough grinding of the wafer is performed while rotating the chuck mechanism a and the first spindle. During that time, one of the contacts 17 of the two-point in-process gage 17
a is applied to the surface of the chuck 9a to measure the height (T ' _ci ), the other contact 17b is applied to the upper surface of the wafer to measure the height (T' _wi ), and the value is used as an electrical signal to control the controller. Send to CPU RAM. The thickness (T ₁ ) of the wafer ground by the calculation unit of the control unit CPU is expressed by the following equation: T ₁ =
Constantly calculated by _{(T 'wi -t) -T'} ci. When the software of the grinding speed is included, the grinding speed is calculated from the formula (T ₀ −T ₁ ) / t, and the remaining grinding time t ₂ is calculated as (T ₁ −T + 1).
0) Calculate as t ₁ / (T ₀ −T ₁ ). Further, one contact 17a of the two-point in-process gage 17 is attached to the chuck 9a.
Measure the height (T '' _ci ) against the surface of the
7b is applied to the upper surface of the wafer to measure the height (T ″ _wi ), and the grinding is continued (theoretically, t ₂ minutes), and the thickness of the ground wafer is calculated by the formula (T ″ _wi −t). ) -T '' After _ci at being calculated a desired thickness T _2, and ends the rough grinding by increasing the 1st spindle axis.

In the meantime, the wafer on the temporary table 3 is transferred to the chuck mechanism b of the wafer loading / unloading zone s1 of the index table 9 by the transfer pad 8, and the multi-joint robot 5 is used. Then, the wafer in the wafer loading cassette 2 is placed on the temporary table 3.

(4) The index turntable 9 is rotated by 120 degrees to move the chuck mechanism a to the finishing grinding zone s3, and to move the chuck mechanism b to the coarse grinding zone s2.
Wafer loading / wafer unloading with chuck mechanism c
After moving to the loading zone s1, the shaft of the second spindle 10b is lowered to press the grindstone 12 against the wafer, and the chuck mechanism a and the spindle shaft are rotated to finish grind the wafer. Raise the second spindle to finish grinding. During the finish grinding, the height of the chuck and the height of the wafer are measured using a two-point in-process gauge during the finish grinding, and the correction value t is measured.
Is calculated in consideration of the above, and when the desired finish grinding thickness T μm is reached, finish grinding is finished. (The same applies to the following steps.) During this time, the first spindle 10a is lowered to press the grindstone 11 against the wafer, and the chuck mechanism b and the spindle are rotated to roughly grind the wafer. ,
Raise the first spindle shaft. In this rough grinding, the height of the chuck and the height of the wafer are measured using the in-process gauge during the rough grinding as described above, and the correction value t is set.
Is calculated in consideration of the above. (The same applies to the following steps.) On the other hand, the wafer on the temporary table 3 is transferred to the chuck mechanism c of the wafer loading / wafer unloading zone s1 of the index turntable by the transport pad 8 on the left side. , Using an articulated robot 5
The wafer in the loading cassette 2 is placed on the temporary table 3.

(5) By rotating the index turntable 9 by 120 degrees, the chuck mechanism a is used for the wafer loading / wafer unloading zone s1, the chuck mechanism b is used for the finish grinding zone s3 and the chuck mechanism c. After moving to the coarse grinding zone s2, the wafer finished and ground by the transport pad 8 on the right side is transferred to the cleaning mechanism, and the wafer is cleaned. The wafer that has been subjected to finish grinding and washing is adsorbed to the chuck and placed on the chuck mechanism 15a of the polishing machine 15,
The polishing pad 15b is pressed against the wafer surface, and a chuck mechanism,
The polishing is performed by rotating the polishing pad, and the surface of the polished wafer is cleaned with a cleaning liquid sprayed from the cleaning mechanism 15c.
Then, air is blown from the air supply nozzle 15d to dry the wafer, and the wafer is sucked by the suction arm of the articulated robot 5 and stored in the unloading cassette 2 on the right side.
Then, the transfer pad 8 on the left side is rotated to transfer the wafer on the temporary mounting table 3 to the chuck mechanism a of the wafer loading / unloading zone of the index turntable. Is moved to the left, the wafer is sucked from the wafer loading cassette to the suction arm of the articulated robot, and the wafer is placed on the temporary table. During this time, the second spindle shaft is lowered to move the grindstone to the wafer. To finish grinding the wafer by rotating the chuck mechanism b and the spindle shaft, then raise the second spindle shaft, and
The second spindle is lowered to press the grindstone against the wafer, the chuck mechanism c and the spindle are rotated to roughly grind the wafer, and then the first spindle is raised.

(6) The index turntable is set to 1
The chuck mechanism b is rotated by 20 degrees, the chuck mechanism b is used as a wafer loading / wafer unloading zone, the chuck mechanism c is used as a finish grinding zone, and the chuck mechanism a is used as a rough grinding zone.
Then, the wafer, which has been finish-ground by the transfer pad, is transferred to the cleaning mechanism, and the wafer is cleaned. After that, the articulated robot is moved to the right to finish-grind and clean the arm of the robot. The wafer is sucked, placed on the chuck mechanism of the polishing machine, the polishing pad is pressed against the wafer surface, the chuck mechanism and the polishing pad are rotated to perform polishing, and the polished wafer surface is washed, dried, and dried. The wafer is sucked by the suction arm of the articulated robot and stored in an unloading cassette. Then, the wafer on the temporary mounting table is rotated by rotating a transfer pad to load the wafer on an index table. The robot is transferred to a chuck mechanism b of a wafer unloading zone, while the articulated robot is moved to the left, and a wafer loading cassette is attached to a suction arm of the articulated robot. The Toyori wafer is adsorbed, placed it on the provisional table, it presses the first second grindstone lowers the spindle axis to the wafer during chucking mechanism c
Then, the finish grinding of the wafer is performed by rotating the spindle shaft, then the second spindle shaft is raised, and the first spindle shaft is lowered to press the grindstone against the wafer, and the chuck mechanism a and the spindle The shaft is rotated to roughly grind the wafer, and then the first spindle shaft is raised.

(7) The index turntable is set to 1
By rotating the chuck mechanism 20 degrees, the chuck mechanism c becomes a wafer loading / wafer unloading zone, the chuck mechanism a becomes a finish grinding zone, and the chuck mechanism b becomes a rough grinding zone.
Then, the wafer, which has been finish-ground by the transfer pad, is transferred to the cleaning mechanism, and the wafer is cleaned. After that, the articulated robot is moved to the right to finish-grind and clean the arm of the robot. The wafer is sucked and stored in a cassette for unloading, and then the wafer on the temporary table is index-turned by rotating the transfer pad.
To the chuck mechanism c of the wafer loading / wafer unloading zone. On the other hand, the articulated robot is moved to the left, and the wafer is transferred from the wafer loading cassette to the suction arm of the articulated robot. The wafer is placed on a temporary mounting table, during which the second spindle shaft is lowered to press the whetstone against the wafer, and the chuck mechanism a and the spindle shaft are rotated to finish grind the wafer. The second spindle shaft is raised, and the first spindle shaft is lowered to press the grindstone against the wafer, and the chuck mechanism b and the spindle shaft are rotated to roughly grind the wafer. Raise the spindle axis.

(8) Hereafter, rotation of the index turntable, finish grinding and cleaning of the coarsely ground wafer, polishing of the wafer, storage of the polished wafer in a cassette for unloading, and loading of a new wafer The steps (5) to (7) of the wafer loading / unloading zone transfer to the chuck mechanism and the rough grinding of the wafer are repeated.

When a polishing process for eliminating crushing scratches on the wafer grinding surface by the polishing machine is not necessary, the wafer cleaned and dried by the cleaning mechanism 7 is unloaded by the articulated robot 5.
It is transported and stored in the loading cassette 2.

[0024]

According to the present invention, one contact of the two-point in-process gage is applied to the surface of the chuck to measure the height, and the other contact is applied to the upper surface of the wafer to measure the height. Is measured and the thickness of the ground wafer is calculated from the difference in height in consideration of the thickness correction value due to the inclination of the axis of the chuck. Without being affected by the vertical fluctuation of the bull and the inclination of the axis of the chuck, the swing width of the thickness of each ground wafer is 0.5 μm for a silicon wafer having a diameter of 200 μm.
0.8 μm for silicon wafers of 300 μm diameter or less
Less than the following.

[Brief description of the drawings]

FIG. 1 is a top view of a wafer grinding apparatus.

FIG. 2 is a sectional view of a wafer grinding apparatus.

FIG. 3 is a front view showing a state in which the thickness of a wafer is measured.

FIG. 4 shows the inclination of the axis of the chuck when the in-process
FIG. 6 is a diagram for explaining a cause of a measurement error when measuring the thickness of a wafer by using a method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Grinding apparatus 9 Chuck 17 Two-point in-process gage 17a Contact 17b Contact w Wafer

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Motoo Yoshida 3009 Kamiyori, Atsugi-shi, Kanagawa Prefecture F-term in the Semiconductor Division, Okamoto Machine Tool Works, Ltd. AC01 AC02 AC05 BA07 BB09 CB01 DA17

Claims (1)

[Claims] 1. A two-point in-process gage is applied to the surface of a wafer and the surface of a chuck while the thickness of the wafer vacuum-adsorbed to the chuck is being ground during vacuum processing or after vacuum processing. In a method of measuring a difference in height measured by applying a pair of contacts as a thickness of a wafer, a pair of contacts of a two-point in-process gage is first attached to the chuck in a state where the wafer is not attracted to the chuck. The height (T _c0 , T _w0 ) measured on the surface was measured, and the contact number indicating the larger value of the height and the value of the difference in height t
= | T _c0 −T _w0 | is stored in the controller as a correction value, and a pair of contacts of a two-point in-process gage are applied to the surface of the wafer and the surface of the chuck during or after the grinding. Difference (T _ci , T _wi ) between the measured heights (T _ci , T _wi )
When determining the thickness of the wafer from _wi− T _ci ), the height obtained by subtracting the correction value t from the height (T _ci or T _wi ) measured by the contact having the large number stored with the above number. A method for measuring the thickness of a wafer, comprising calculating a thickness of a ground wafer by regarding the height as a height measured by the contact.