JPH11267968A - Polishing method of wafer and polishing machine used therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a wafer with a small fluctuation width in thickness and flat surface. SOLUTION: In this polishing method, the thickness T0 (μm) of a wafer is measured and the wafer is polished upto the thickness T1 (μm) of a set target wafer. At first, a polishing speed S (μm/min.) and a polishing time t1 (min.) are decided so as to be (T0 -T1 )>St1 and the wafer is polished at a polishing speed S for t1 hour and then the polished wafer thickness T1 (μm) is measured and again the wafer is polishing at the polishing speed of (T0 -T1 )/t1 (μm/min.) for the time of (T1 -Tf )t1 /(T0 -T1 ) and then the wafer with target thickness Tf (μm) is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for polishing a wafer such as a bare wafer, a wafer with devices, and a magnetic disk wafer, and a polishing machine used for the method.

[0002]

2. Description of the Related Art High integration of ICs has been started from 64 Mbits to 2
It is shifting to 56 Mbit, and is expected to become 1 Gbit in the early 21st century. In order to cope with such a high integration, a multilayer structure of a device is progressing, and it is becoming difficult to focus at the time of exposure due to unevenness of the device surface. Therefore, 8 inches of the wafer, 1
Enlargement and thinning from 2 inches to 16 inches, wafer surface flatness from 1 μm to 0.5 μm, and even 0.3
μm and 0.2 μm ("Journal of the Japan Society for Precision Engineering", Vol. 62, No. 4, 199).
6 years, 486-490). Along with the demand for the flattening of the wafer, there is also a demand for uniformity of the thickness between the wafers.

Conventionally, as a method for polishing a semiconductor wafer,
The work table 2 provided on the rotating shaft 20 as shown in FIG.
1, a polishing cloth (foamed polyurethane pad, felt pad) 22 is placed, and a head 23 is placed on the upper surface of the polishing cloth.
The semiconductor wafer 25 mounted via the suction plate 24 is lowered in the Z-axis direction until the shaft 26 comes to a fixed position, and the wafer 2
5, the head 23 rotatably attached to the shaft 26 by a rotary joint is rotated by a motor (not shown) so that the shaft 26 is rotated in the opposite direction to or in the same direction as the rotation direction of the work table. Has been carried out ("Journal of the Japan Society for Abrasive Processing", Vol. 4).
2, No. 1, January 1998, pp. 18-21).

In this polishing, water, an alkaline aqueous solution, an acidic aqueous solution, or a slurry-like abrasive in which alumina oxide powder, diamond powder, or silicon oxide powder is dispersed in water is supplied between the wafer and the polishing cloth, if necessary. (C
chemical Mechanical Polish
ing). The polishing of the wafer is usually carried out by polishing the thickness T of the wafer.
₀ (usually around 300 to 640 μm), and a grinding (including polishing) amount T ₀ that becomes a target wafer thickness T _f.
−T _f (usually 10 to 20 μm), and a certain time t
₁ (minute), the wafer is roughly cut (primary polishing) at a constant grinding (polishing) speed S (μm / minute). (St ₁ = T
₀ − _Tf is set. ).

Then, the thickness of the wafer is measured, and the wafer is transferred to a finish polishing (secondary polishing) step, and is polished with a denser polishing cloth to obtain a wafer having a mirror surface. Products are classified into non-standard products and non-standard products. The thickness of the rough-cut or rough-cut wafer is determined by the height of the polishing pad 22 on the work table 21 and the upper surface of the wafer 25 adsorbed by the suction pad 24 (the lower surface of the wafer is in contact with the polishing pad). Measure the height from the work table 21,
The difference between the two is defined as the thickness of the roughly cut wafer.

However, the polishing cloth has an indented portion due to the pressing of the head during rough cutting of a large number of wafers, and a level difference is generated between the flattened portion of the polishing cloth and the accurate thickness of the wafer. Therefore, when the thickness of the wafer taken out from the working table and the chuck mechanism is measured, for example, 3
Polishing rate (S) 0.8 μm /
Target thickness 280 when roughing for 25 minutes (t ₁ )
The variation in the thickness of the wafer of μm is as wide as 278 to 284 μm.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a wafer polishing (grinding) method for providing a wafer having a small variation in thickness and a polishing disk used in the method.

[0008]

SUMMARY OF THE INVENTION One aspect of the present invention is a method for manufacturing a wafer.
Thickness T₀(Μm), and set the target wafer.
Thickness T_f(Μm)
Polishing speed S (μm / min), polishing time t₁(Minutes) and (T
₀-T_f)> St₁Polishing speed
T in degrees S (μm / min)₁Polished for hours, then polished
Wafer thickness T ₁(Μm) and polishing the wafer again
Speed (T₀-T₁) / T₁(Μm / min), (T₁-T
_f) T₁/ (T₀-T₁) Polishing for the target thickness T
_f(Μm) of the wafer,
A polishing method is provided.

According to a second aspect of the present invention, there is provided a work table supported on a rotating shaft, a polishing cloth placed on the work table, a driving mechanism capable of moving the work table in a horizontal direction, and An object of the present invention is to provide a wafer chucking mechanism having a wafer chuck mechanism supported on a rotating shaft provided at a distance, and a wafer thickness measuring device provided at a side surface of the chuck mechanism at a distance.

[0010]

The thickness of the wafer is measured in the middle of the final time of the rough cutting (first polishing) of the wafer, and the estimated roughing speed S is corrected to the actual roughing speed and the required polishing time is corrected. And the thickness of the wafer is measured directly, so it is not affected by the measurement of the thickness of the wafer due to clogging and abrasion of the polishing pad. A group of wafers having substantially the same thickness width and small variation can be obtained even with the above wafer thickness.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. 1 is a plan view of a polishing machine 1 of the present invention, FIG. 2 is a side view of a thickness measuring device, FIG. 3 is a top view of the thickness measuring device, and FIG. 4 is a portion showing a state in which the thickness of a wafer is being measured. It is sectional drawing. 1, 2, 3 and 4, 1 is a polishing machine, 2 is a rotating shaft, 2 a is a hollow part, 3 is a polishing cloth, 4 is a work table, 4 a is a polishing cloth mounting plate, 4 b is a chamber, 5 is a wafer, 6 is a chuck mechanism, 7 is a head, 8 is a hollow rotary shaft,
9 is a bearing, 10 is a bearing, 11 is a pipe, 12 is an air cylinder, 13 is a moving table of a work table, 14 is a thickness measuring device, 14a and 14b are terminals, 14c is an air cylinder, 14d is a support shaft, 14e and 14f is a joint, 14
g is a contact.

In order to polish the wafer 5 using such a polishing machine, the wafer is loaded on the loading side handling arm 17.
The wafer is sucked by the suction pad attached to a and moved onto the temporary receiving table, and the wafer 5 is sucked by the chuck mechanism.

Then, the pressure in the hollow portion 8a of the hollow rotary shaft 8 is reduced by reducing the pressure (350 to 700 mmHg) by a vacuum pump (not shown) through the pipe 11, and the pressure in the chamber 7a of the head is reduced. 6 to wafer 5
Is lowered on to adsorb wafer suction pad of the chuck mechanism 6, the wafer is moved onto the working table 4, and the thickness T ₀ of the wafer 5 after the measurement at the wall thickness measuring instrument 14 lowers the chucking mechanism 6 The wafer 5 is brought into contact with the rotating polishing pad 3 on the work table 4, and a constant pressure is applied to the wafer by the air cylinder 12. The polishing cloth 3 is a polishing cloth mounting plate 4
a is attached with an adhesive. The lower surface of the wafer is polished by the rotation of the work table 4 and the rotation of the hollow rotary shaft 8.
During the polishing (rough grinding), the thickness T _{0 of the} wafer to be polished
(Μm) and the target wafer thickness T _f (μm)
And the polishing speed S (μm / min) are input to the RAM of the CPU, and the number of rotations of the spindle rotating shaft 8 and the rotating shaft 2 of the work table 4 is set.

The polishing time t (minute) is determined by the grinding amount (wall thickness) T ₀ -T _f (μm) of the wafer 5 and the grinding speed S
(Μm / min). Conventionally, polishing was performed at that S speed for t minutes (setting is performed as St = T ₀ −T _f ). However, in this method, since the fluctuation width of the thickness of the wafer is as large as ± 4 μm, actually, the operator stops polishing many times during the polishing, measures the thickness of the wafer, calculates the polishing rate, The reality is that trial-and-error is repeated, and the fluctuation width of the thickness of the wafer is suppressed to ± 1 μm. Therefore,
Since the polishing time requires several measurements such as measurement of the thickness of the wafer and interruption of the polishing, the polishing process takes a long time, and the variation in the thickness of the wafer varies depending on the operator.

In the present invention, the rough cutting time at the polishing rate S is set to a time t of 80 to 99.9% of t (minutes).
₁ (minute) and the target thickness T _{f in} polishing for t ₁ minute.
Insufficient grinding amount (T ₁ −T _f ) μm that does not reach the maximum polishing speed (T ₀ −T ₁ ) / t ₁ is divided into the polishing time t ₂ (min) at the measured actual polishing rate (T ₀ −T ₁ ) / t ₁ . Roughing (first polishing) is performed. The thickness of the wafer after t ₁ minute is T ₁
(Μm), the unground amount (μm) is

[0016]

(T ₁ −T _f ) (1)

The actual polishing rate (μm / min) is

[0018]

(T ₀ −T ₁ ) / t ₁ (2)

Grinding amount (μm)

## EQU3 ## St ₁ = T ₀ −T ₁ (3)

## EQU1 ## Therefore, the unground amount (T ₁ −
The time t ₂ (minutes) to remove T _f ) μm at the actual polishing rate shown by the equation (2) is:

[0021]

T ₂ = (T ₁ −T _f ) t ₁ / (T ₀ −T ₁ ) (4)

Is calculated. Therefore, after measuring the thickness T ₁ (μm) of the wafer after the _first t ₁ minute
U sent to ROM and the condition of the second roughing was (2)
At the actual polishing rate (μm / min) shown by the equation, the CPU sets the polishing time t ₂ (min) to the value shown by the equation (4).
From the RAM. After polishing for t ₂ minutes at the polishing speed shown by the equation (2), the chuck mechanism 6 is raised or the work table 4 is moved in the horizontal direction to remove the wafer 5 from the polishing cloth 3.
Roughing of wafer 5 by releasing (primary polishing)
To end. Then measure the wall thickness T ₂ of the wafer.

The wafer 5 is then brought into contact with another dense polishing cloth, and the final polishing is performed with a polishing amount of 0.01 to 0.5 μm.
m, preferably 0.1 to 0.3 μm. The measurement of the thicknesses T ₁ and T ₂ of the wafer 5 is performed by using the polishing machine 1 shown in FIG.
After the rough cutting of the wafer 5 for t ₁ minute at the S speed, the work table 4 is moved rightward on the rails, the thickness measuring device 14 is moved rightward on the moving table 13, and the thickness measuring device 14 Activate the air cylinder 14c to operate the receiving portion 14f.
The contact 14g of the terminal 14a is placed on the lower surface of the wafer 5, and the contact 14g 'of the terminal 14b is placed on the head 7 by pushing the support shaft 14d obliquely by pushing the rod 14h with the rod 14h.
Or the lower surface of the suction pad 6 'abuts the difference between the height and the thickness T ₁ of the wafer, convey it to the ROM of the CPU (see FIG. 5).

Next, the thickness measuring device 14 is moved to the left by the moving table 13 to separate it from the wafer and the chuck mechanism, and the work table 4 is also moved to the left to bring the wafer and the polishing cloth into contact again. Polishing by rotation is performed at a polishing rate represented by the equation (2) for t ₂ minutes represented by the equation (4),
After t ₂ minutes, the work table 4 is moved rightward to complete the rough cutting (primary polishing). Then measuring the thickness T ₂ of the wafer 5 in the same manner. The roughly cut wafer 5 is
The wafer is transferred to the finish polishing step, and is ground to about 0.01 to 0.5 μm with a denser polishing cloth.

Next, the thickness T _{3 of} the finish-polished wafer is measured, and the wafer is transferred to another temporary receiving table by the chuck mechanism, and is further housed in a cassette by an arm.
When the chuck mechanism newly sucks a wafer having a measured thickness T ₀ ′ (μm), the chucking rate is input to the RAM as S ′ (μm / min) using the polishing rate calculated by the above equation (2), and the grinding is performed. The amount (T ₀ ′ −T _f ) and the polishing time t are defined as (T ₀ ′ −
T _f ) / S ′ to calculate the first roughing time t
₁ (min) 80 to 99.9% of the t (usually the same rate as the previous roughing) input to RAM is set to, roughing t ₁ minute wafer is performed.

Hereinafter, as described above, the thickness T ₁ ′ of the wafer
Was measured, and the second polishing rate and polishing time t ₂ =
(T ₁ ′ −T _f ) t ₁ / (T ₀ ′ −T ₁ ′) is set, and the second grinding is performed for t ₂ minutes at the polishing rate calculated by the equation (2). Hereinafter, even when a new wafer is supplied, rough polishing and finish polishing of the wafer are performed in the same manner.

In this wafer polishing method, a conventional CMP (Chemical Machi) is placed on the upper surface of the polishing cloth.
As in the case of the (nary polishing) method, polishing may be performed by supplying water, an aqueous solution of caustic soda, an aqueous solution of trimethyltetramine, an aqueous solution of hydrochloric acid, a slurry in which silicon oxide powder, diamond crystal powder, or glass powder is dispersed in water. Further, it is preferable to do so in cooling the wafer.

The rotating shaft 8 is driven by a motor for 10 to 500 r.
pm, preferably at a rotation speed of 50 to 200 rpm. The rotating shaft 2 of the work table 4 is driven by a motor for 10
It is rotated at a rotation speed of ５００500 rpm, preferably 50-200 rpm. The rotation direction of the rotation shaft 2 and the rotation shaft 8 of the work table may be either forward or reverse, but rotation in the reverse direction is preferable because a flatter wafer can be obtained.

The pressure of the polishing pad 3 applied to the wafer 5 is 5 to 5.
1,000 g / cm ² , preferably 20 to 800 g / c
m ² . The number of rotations of the rotating shaft may be changed stepwise in a stepwise manner depending on the polishing state of the wafer. For example,
When the flatness is 0.5 to 1 μm, the pressure is 50 to 200 g /
cm ² , the rotation speed of the rotation shaft 2 is 20 to 200 rpm, the rotation speed of the rotation shaft 8 is 30 to 200 rpm, 0.3 to 0.4 μm.
m, the pressure is 300 to 800 g / cm ² , the number of rotations of the rotating shaft 2 is 30 to 200 rpm, and the number of rotations of the rotating shaft 8 is 5
When the flatness is 0 to 200 rpm and 0.05 to 0.2 μm, the pressure is 500 to 1,000 g / cm ² , the number of rotations of the rotating shaft 2 is 50 to 200 rpm, and the number of rotations of the rotating shaft 8 is 50 to 20.
0 rpm.

As the material of the suction pad 6 'and the polishing pad 4a, a metal plate such as an alumina plate or a stainless steel plate, a polyvinyl chloride resin plate or an aluminum plate is used. This suction pad is made of a material having a high rigidity of a bending strength of 20,000 kg / cm ² or more, preferably 40,000 kg / cm ² or more.

As the polishing cloth 5, a foamed polyurethane sheet, felt or the like is used. A polishing cloth for finish polishing (secondary polishing) is smoother and smoother than a polishing cloth for rough polishing (primary polishing). FIG. 5 is a top view of the polishing machine 1 showing another mode in which a plurality of wafers can be simultaneously rough-polished and finish-polished.

In the drawing, 4 is a work table for rough polishing, 4 'is a work table for finish polishing, 4b,
4'b is a polishing cloth surface correcting device, 5 is a wafer, 6 is a chuck mechanism having five suction pads, 14 is a thickness measuring device, 15 is a plurality of chuck mechanisms, and an index table to which 6, 6 are attached. The shaft 15a is intermittently rotatable rightward. Reference numeral 16 denotes an attachment member for rotatably attaching the chuck mechanism 6 to the index table 15a, reference numeral 17 denotes a wafer loading robot, and reference numeral 17a denotes an arm. 18 and 18 are wafer storage cassettes, 19
Is a rotatable wafer temporary receiving table.

The wafer is placed on the temporary receiving table 19 by the loading robot, the index table 15 is rotated rightward by 120 degrees, and the chuck mechanism 6 is positioned on the temporary receiving table 19. Next, the chuck mechanism 6 is connected to the air cylinder 1.
2 (or raise the temporary support) and rotate the shaft 8
The inside of the chuck mechanism 6 is depressurized, and the wafer is sucked by the suction pad 6 ′ of the chuck mechanism 6.
To be absorbed. Then, after raising the chuck mechanism (or lowering the temporary support), the index table 15 is
It rotates rightward by 0 degrees and moves on the work table 4.
The thickness T ₀ of the wafer is measured by the thickness measuring device 14.

The chuck mechanism 6 is lowered while rotating the rotary shaft 8 to make contact with the polishing cloth placed on the work table 4, and a constant pressure is applied to the wafer by the air cylinder 12. Roughing polishing is performed by the rotation of the respective rotating shafts 2 and 8. When the rough polishing for t ₁ is completed, the work table 4 is moved to the left, and the terminal 14 of the thickness measuring device 14 provided on the index table 15 is moved.
The lower surface of the wafer and the lower surface of the head of the chuck mechanism are brought into contact with the contacts 14g, 14g on a, 14b to measure the thickness (T ₁ ) of the wafer.

After measuring the thickness T ₁ , the work table 4 is moved rightward by the transfer device 4b to resume the rough polishing and polishing of the wafer, and the polishing rate (T ₀ −
T ₁₎ / t time set t ₂ in _1, polished. t ₂
After the separation, the working table moves to the left again, measures the thickness T ₂ of the wafer. Then, after returning the work table to the right direction, the index table 15 is rotated to the right by 120 degrees, and the rough-polished wafer is placed together with the chuck mechanism 6 on the work table 4 'on which a denser polishing cloth is placed. Move.

Next, the chuck mechanism is lowered, brought into contact with the polishing cloth, and the polishing is performed by utilizing the rotation of the rotating shafts 2 and 8 while applying a constant pressure to the wafer by the air cylinder 12. After finishing polishing, the transfer device 4'b
The operating work table 4 in the right direction 'moves, after measuring the thickness T ₃ of the wafer which has been polished by the thickness measuring device 14, work table 4' to move to the left. When the chuck mechanism 6 is raised, the index table 15 is rotated rightward by 120 degrees, and then the robot arm 17 is rotated.
a, wafers 5, 5,.
.. Are held, and the polished wafers 5, 5 are stored in the storage cassettes 18, 18.

[0037]

EXAMPLE 1 Using the polishing machine 1 shown in FIG.
The pressure was reduced to Hg, a 5-inch diameter silicon wafer on the temporary receiving table was adsorbed, and the thickness T _{0 of the} wafer was measured (300 μm).
m).

The final thickness (T _f ) of the target wafer is 2
Since it is 84 μm, the grinding amount (T ₀ −T _f ) is calculated to be 16 μm. If the polishing rate S is 0.8 μm / min, the theoretical polishing time t (T ₀ −T _f ) / S is calculated to be 20 minutes. Therefore, the first polishing time is set to 0.9 in the RAM.
The time of the first polishing was set to T ₁ μm, and the second polishing rate was set to (T ₀
−T ₁ ) / t ₁ μm / min, and the polishing time t ₂ are set to (T ₁ −T _f ) t ₁ / (T ₀ −T ₁ ) in equation (4).

The upper chuck mechanism 6 holding the wafer 5 is moved onto the polishing cloth 3 on the work table 4 and descends to press the wafer against the polishing cloth.
0 rpm, the number of rotations of the rotating shaft 8 to the left is 80 rpm, the pressure of the polishing cloth on the wafer is 500 g / cm ² , and the processing speed (S)
While occasionally adding water to the upper surface of the polishing cloth at 0.8 μm / min, 1
After polishing for 8 minutes, and then moving the work table 4 rightward, the thickness T ₁ (28
6 μm), which is transmitted to the ROM, and the equation (2)
According to equation (4), the remaining second polishing rate (14 /
18) The μm / min and the polishing time t ₂ (2 × 18/14) are calculated by the ROM, the thickness measuring device 14 is retracted to the left, the work table 4 is moved to the left, and the wafer is put on the polishing cloth. And polished for t ₂ minutes.

Next, the work table and the thickness measuring instrument were moved rightward to measure the thickness T _{2 of the} wafer.
It was 4.1 μm. Then, the chuck mechanism 6 is moved onto a work table on which a denser polishing cloth is placed, and is lowered to abut the wafer and the polishing cloth supplied with water on the upper surface,
Finish polishing was performed. After finishing polishing,
The thickness T ₃ of the wafer was measured, 284.05μm
Met.

The wafer is transferred onto the temporary receiving table, and the reduced pressure of the hollow rotary shaft 8 is returned to the atmosphere, whereby the wafer is placed in the temporary receiving table. The roughness (R
max) is primary polishing 30 nm, finish polishing 2
nm.

Next, a new wafer (thickness T
₀ ′) is adsorbed by the chuck mechanism, and the processing speed (T ₀ −T _f ) / (t ₁ + t ₂ ) calculated by the above equation (2) is reduced to the first processing speed (S ′) during rough cutting and polishing. )age,
After calculating the theoretical processing time t calculated from the equation (1), the value of 0.9 t was set as the first polishing time, and rough polishing was performed in the same manner as in the previous step. The distribution of the thickness (T ₂ ) of 100 wafers that were roughly cut and polished was 284.0 ± 0.1 μm.

Comparative Example 1 In Example 1, the processing time during rough polishing was 2 hours.
A polished wafer was obtained in the same manner as above except that the wafer was polished by setting it so that it was rough-cut once in a processing time of (T ₀ −T _f ) / S (20 minutes). . 1
The thickness distribution of the 00 rough-polished wafers was 284.0 ± 1 μm.

[0044]

According to the present invention, it is possible to obtain a polished wafer having a stable thickness, a small fluctuation width, and more excellent flatness. Further, since the operator does not need to measure the thickness of the wafer many times and set the polishing speed and the polishing time, the polishing time can be reduced.

[Brief description of the drawings]

FIG. 1 is a plan view in which a part of a plane polishing machine of the present invention is cut away.

FIG. 2 is a side view of a thickness measuring instrument.

FIG. 3 is a top view of the thickness measuring instrument.

FIG. 4 is a partial cross-sectional view showing a state where the thickness of a wafer is being measured.

FIG. 5 is a top view of a polishing machine showing another embodiment of the present invention.

FIG. 6 is a plan view in which a part of a conventional flat polishing machine is cut away.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Polishing machine 2 Rotating shaft 3 Polishing cloth 4 Work table 5 Wafer 6 Chuck mechanism 6 'Suction pad 7 Head 8 Hollow rotating shaft 12 Air cylinder 14 Wall thickness measuring device

Claims (5)

[Claims] In a method of measuring a wafer thickness T ₀ (μm) and polishing the wafer to a set target wafer thickness T _f (μm), first, a polishing rate S (μm / min), The polishing time t ₁ (min) is set so that (T ₀ −T _f )> St _1, and the wafer is polished at the polishing rate S (μm / min) for t ₁ hour, and then the thickness T of the polished wafer ₁ (μm), and the wafer was again polished at a polishing rate (T ₀ −T ₁ ) / t ₁ .
A method for polishing a wafer, characterized in that a wafer having a target thickness _Tf (μm) is obtained by polishing for a time of (T ₁ −T _f ) t ₁ / (T ₀ −T ₁ ). 2. The wafer polishing method according to claim 1, wherein the value of St ₁ / (T ₀ −T _f ) is 0.8 or more and 0.99 or less. 3. A work table supported on a rotary shaft, a polishing cloth placed on the work table, a drive mechanism capable of moving the work table in a horizontal direction, and a space above the polishing cloth. Chuck mechanism for the wafer,
A wafer polishing machine having a wafer thickness measuring device provided separately on a side surface of the chuck mechanism. 4. The wafer polishing machine according to claim 3, wherein the wafer chuck mechanism accommodates a rigid suction pad supported on a rotatable hollow rotary shaft in a head. 5. A wafer thickness measuring device is a two-terminal type thickness measuring device, one terminal of which is a lower surface of a suction pad of a chuck mechanism for sucking a wafer or a lower surface of a head containing a suction pad. 5. The wafer polishing machine according to claim 4, wherein the other terminal abuts on the lower surface of the wafer sucked by the suction pad and calculates the thickness of the wafer based on a difference in height between the two terminals. .