JPH0661205A - Polishing method and polishing apparatus for semiconductor wafer - Google Patents

Abstract

(57) [Abstract] [Purpose] The present invention is directed to a method for polishing a semiconductor wafer, and particularly to planarization and bonding SO of a wiring layer in a device manufacturing process
A polishing method useful for thinning the Si layer of an I wafer,
By controlling the polishing amount at each position on the wafer, it can be sufficiently practically used as a method for planarizing the wiring layer.
An object of the present invention is to provide a polishing method capable of further thinning the Si layer of a wafer and enabling uniform polishing of the entire surface of the wafer, and an apparatus for carrying out the method. [Structure] A semiconductor wafer is suction-held on a holding plate, a polishing cloth attached to a polishing jig is brought into contact with a surface to be polished of the wafer, and an abrasive is passed through the polishing cloth and supplied to the contact portion. At the time of polishing the wafer by rotating at least one of the holding plate and the polishing jig, a voltage is applied between the suction portion of the wafer and the polishing jig, and the voltage between the two is applied during polishing. And / or the current is detected, and the polishing rate at each polishing position is controlled based on the obtained detection value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor wafer polishing method, and more particularly to a polishing method useful for flattening a wiring layer in a device manufacturing process and thinning a Si layer of a bonded SOI wafer. With the increase in the degree of integration of semiconductor devices,
As the number of wiring layers increases, the unevenness of the wiring layer also increases and the risk of disconnection increases. As a preventive measure, planarization of the wiring layer becomes more important.

A very useful SOI wafer for increasing various functions of a device is at least one oxidized wafer which is bonded to one another, and a Si layer on one side is polished and thinned to be used as a device forming layer. .

[0003]

2. Description of the Related Art Generally, semiconductor devices on the market do not use polishing for planarizing a wiring layer. Current devices allow wiring without polishing. However, it is fully expected that polishing will be required to planarize the wiring layer in the near future. For that purpose, for example WJPatri
ck et al. have positively considered flattening by polishing and succeeded in trial production of actual devices (Journal Electrochem. S
oc., Vol.138, No.6, p1778-1784, Jun., 1991). In this method, as shown in FIG. 1, a horizontal conductive portion 11 is formed on a substrate 10 and then a vertical conductive portion (stud or vertical interconnec) is formed thereon.
tion) 12 is formed. Next, the SiO ₂ insulating layer 13 is formed by CVD. The insulating layer 13 has a profile having irregularities according to the arrangement of the horizontal and vertical conductive portions 11 and 12 formed previously. The insulating layer 13 is polished and deleted up to the position of the broken line 14 in the figure, and the planarization (polishing) is completed when the upper portion of the vertical conductive portion 12 is exposed. For this polishing, a single-wafer polishing apparatus as shown in FIG. 2 is used. Rotating shaft 2
The polishing cloth 23 is attached to the upper surface of the surface plate 22 which rotates by 1. The wafer 26 is held by suction on the lower surface of the wafer holding plate 25 rotated by the rotating shaft 24, the lower surface of the wafer 26, which is the surface to be polished, is brought into contact with the polishing cloth 23, and an abrasive is supplied onto the polishing cloth 23 from above. The surface plate 22 and the wafer holding plate 25 are rotated to perform polishing.

The greatest drawback of the above method is that it is practically impossible to finish the polishing when the longitudinal conductive portion 12 is exposed on the entire surface to be polished of the wafer. That is, although it is possible to flatten a part of the region within the surface to be polished of the wafer, a high polishing yield cannot be obtained. Therefore, the above method has not been put to practical use.

On the other hand, thinning of the Si layer of the bonded SOI wafer is performed by the procedure shown in FIG. For example, as shown in FIG. 3A, a Si wafer 31 having a surface on which an oxide film 33 is formed by thermal oxidation and a Si wafer 32 having no oxide film are prepared, and as shown in FIG. These two
The wafers 31 and 32 are superposed in close contact with each other, and heat-treated at 900 ° C. for 30 minutes in a nitrogen atmosphere for adhesion. Next, the side of the wafer 31 having the oxide film 33 is ground to a thickness of about 3 μm as shown in FIG. 4C, and then further polished to a thickness of about 2 μm as shown in FIG. This polishing is usually performed using a single-wafer polishing apparatus as shown in FIG. 2, and the polishing amount is controlled by the polishing time. However, since it is unavoidable that the polishing amount varies depending on the position on the wafer surface, there is a problem that a high yield cannot be obtained and there is a limit in thinning the Si layer.

[0006]

The present invention is sufficiently practical as a method of flattening a wiring layer by controlling the polishing amount at each position on the wafer, and the Si of an SOI wafer can be achieved.
An object of the present invention is to provide a polishing method capable of further thinning a layer and enabling uniform polishing of the entire surface of a wafer, and an apparatus for carrying out the method.

[0007]

In order to achieve the above object, the polishing method of the present invention uses a polishing cloth attached to a polishing jig by sucking and holding a semiconductor wafer on a holding plate and polishing the wafer. When polishing the wafer by rotating at least one of the holding plate and the polishing jig while bringing the polishing agent into contact with the surface and supplying the polishing agent to the contact portion through the polishing cloth, suction of the wafer A voltage is applied between the polishing part and the polishing jig to detect the voltage and / or current between them during polishing, and control the polishing rate at each polishing position based on the detected value obtained. Characterize.

A polishing apparatus for carrying out the polishing method of the present invention comprises a holding plate for sucking and holding a semiconductor wafer, and a polishing jig arranged so that a polishing cloth attached to the tip of the wafer is brought into contact with the surface to be polished of the wafer. A means for supplying a polishing agent to the contact portion through the polishing cloth, a means for applying a voltage between the suction portion of the wafer and the polishing jig, and a voltage between the two during polishing. And / or a means for detecting an electric current and a means for controlling a polishing rate according to the obtained detection value, and at least one of the holding plate and the polishing jig can rotate.

[0009]

According to the present invention, a voltage is applied between the holding plate attracting portion of the wafer and the polishing jig, the voltage and / or current between the two is detected during polishing, and based on the detected value obtained. By controlling the polishing rate at each polishing position, the entire surface of the wafer can be highly uniformly polished.

Hereinafter, the present invention will be described in more detail by way of examples with reference to the accompanying drawings.

[0011]

EXAMPLE 1 An example of flattening a wiring layer during a device manufacturing process according to the present invention will be described with reference to FIG. In this example, when the interlayer insulating film on the wafer surface is polished, polishing is performed while actually measuring the thickness of the interlayer insulating film at each polishing position, thereby obtaining a uniform desired interlayer insulating film over the entire surface of the wafer.

On the entire surface of the wafer 401, a conductive portion 402 such as a horizontal conductive portion (interconnect) and a vertical conductive portion (stud) is formed, and then an interlayer insulating film 403 is formed. The side surface and the lower surface of the wafer 401 are entirely covered with an insulating film 404 such as a thermal oxide film. The wafer holding plate 411 of the polishing apparatus is made of a conductive material such as metal, and is rotated by a rotary shaft 412 made of a similar conductive material. The wafer 401 is sucked and held on the wafer holding plate 411. This suction is performed by a usual method such as vacuum suction, a suction pad, wax, and an adhesive.
When vacuum suction is performed, a ventilation passage for vacuum evacuation is used, which passes through the inside of the rotation shaft 412 and the inside of the wafer holding plate 411 and opens to the suction surface of the wafer holding plate 411. Usually, a large number of suction openings are provided so that the wafer can be firmly held on the entire surface.

The rotary polishing jig 421 of the polishing apparatus is a cylindrical member made of a conductive material such as metal. A polishing cloth 431 is attached to a lower end surface 422 of the polishing tool 421 and the polishing agent introduced from the upper portion is internally supplied. Polishing cloth 43 through a through hole (not shown)
It is designed to supply one. As the polishing agent, one in which fine polishing abrasive grains such as colloidal silica are dispersed in a solution is generally used. The polishing cloth 431 includes a large number of through passages 432 through which polishing grains can freely pass. The specific resistance of the abrasive can be reduced to a required level by adding an electrolyte. The polishing jig 421 can move in the radial direction of the wafer 401 on the wafer holding plate 411 to polish an arbitrary radial position of the wafer 401.

The wafer 401 has an insulating film 40 on a part of the lower surface.
4 is removed, and a conductive material 40 such as a conductor paste is applied to this portion.
5 is arranged and held in a state of being electrically connected to the wafer holding plate 411. Wafer holding plate 411
A DC voltage 441 is applied between the polishing jig 412 and the polishing jig 412, and the current value corresponding to the thickness of the interlayer insulating film 403 at each position on the wafer 401 is continuously detected by the ammeter 442 during polishing. To do.

Polishing is performed as follows, for example. Wafer 4
01 is adsorbed and held on the wafer holding plate 411, and the polishing cloth 431 having an area of 1 to 4 cm ² is pressed against the wafer 401 while rotating the wafer holding plate 411. The polishing agent is supplied to the polishing cloth 431 via the polishing jig 421. A DC voltage is applied between the polishing jig 421 and the polishing plate 411.
By adding an appropriate electrolyte to the polishing agent, most of the applied voltage can be applied to the interlayer insulating film 403.

When the polishing of the interlayer insulating film 403 progresses and the conductive portion 402 is exposed, the polishing agent and the conductive portion 402 are electrically connected to each other and a current flows, which is detected by the ammeter 442. At this time, polishing is temporarily stopped and the polishing jig 421
Are moved to the outside of the wafer 401 in the radial direction, and then polishing is restarted. On the same radius of the wafer 401, the relative speed between the rotating wafer 401 and the polishing cloth 431 is substantially constant, and the distribution of the polishing speed is very small. In this way, the polishing jig 421 is gradually moved outward from the vicinity of the center of the wafer 401 to polish the entire wafer 401. Polishing cloth 4
The polishing agent supplied onto the wafer 401 via 31 flows toward the outside of the wafer 401 from the polishing position due to the centrifugal force generated by the rotation of the wafer 401. Therefore, by moving the polishing position from the inside to the outside of the wafer, it is possible to prevent the polishing agent from being supplied to the polishing completed portion of the wafer 401. When the polishing agent is supplied to the polishing-completed portion, a current flows through the conductive portion 402 exposed there, which makes it difficult to control the polishing currently in progress.

The polishing jig 4 is used without rotating the wafer 401.
When only 21 is rotated for polishing, as shown in FIG. 5, a fluid 462 such as pure water is supplied from a fluid supply port 461 arranged above the central portion of the wafer 401, and the wafer 40
By forming the flow 463 outward on one surface, it is possible to prevent the supply of the polishing agent to the polishing-completed portion. As the fluid 462 for this purpose, liquid and gas that do not contaminate the wafer and the polishing apparatus are used.

In order to perform the polishing, at least one of the polishing plate and the polishing jig may be rotated, but the rotation of both is most advantageous for uniformly polishing the entire surface of the wafer. In particular, rotating the polishing jig makes the polishing rate uniform within the polishing cloth area and facilitates the control of the polishing amount at the same radial position on the wafer. Also, when polishing is performed by rotating the polishing plate and stopping the polishing jig,
As shown in FIG. 6, it is desirable that the width W of the polishing cloth mounting surface 422 of the polishing jig be smaller on the outer side (W2) than on the inner side (W1) in the wafer radial direction. As a result, it is possible to reduce the difference in the polishing rate due to the difference in the peripheral speed of the polishing plate within the area of the polishing cloth, that is, to make the polishing rate within the area of the polishing cloth more uniform.

By increasing or decreasing the polishing rate according to the magnitude of the current value detected at each polishing position, the entire surface of the wafer can be uniformly polished. That is, in the region where the detected current value is small (large), (1) the polishing pressure increases (decreases),
The polishing speed can be increased (decreased) by (2) increasing (decreasing) the rotating speed of the polishing jig and / or (3) increasing (decreasing) the rotating speed of the wafer holding plate.

The interlayer insulating film was planarized by the method of the present invention by the method shown in FIG. 5 and compared with the planarization by the conventional single-wafer polishing apparatus shown in FIG.

<Preparation of test wafer> S with a diameter of 150 mm
W with a diameter of 2 μm and a height of 0.5 μm on the i-wafer 601
(Tungsten) Stud (vertical conduction part) 602 1
The stud pattern shown in FIG. 7 was formed by forming the stud pattern at intervals of 0 mm. CVD-SiO ₂ was deposited thereon to a thickness of 1 μm.

<Polishing Conditions> Polishing according to the present invention: Polishing is started from the center of the wafer, a DC voltage is applied between the wafer holding plate and the polishing jig, and the current value between the two exceeds a predetermined value. The polishing is temporarily stopped at this point, the polishing jig is moved to the outer side in the radial direction of the wafer, and the polishing is restarted. During polishing,
Pure water is supplied to the center of the wafer to form a water flow from the center to the outside on the wafer polishing surface. Conventional Polishing The polishing apparatus shown in FIG. 2 simply adjusts the polishing amount by polishing time.

<Evaluation of Polishing Result> Each of the above 10 wafers was polished under the above polishing conditions, and the peripheral portion was within 15 mm (see FIG. 7).
CVD on stud in area 603)
After -SiO ₂ is entirely removed, it counted the number of studs that are not removed. The result is shown in FIG. Almost 100% of the studs remain when polished by the present invention, whereas 70% of the studs are removed by polishing by the conventional method.

As described above, according to the present invention, the interlayer insulating film can be polished extremely uniformly over the entire surface of the wafer. In this embodiment, an example in which the polishing is controlled by the current value is shown, but the same control can be performed by using the potential difference.

[Embodiment 2] An example of thinning the Si layer of a bonded SOI wafer according to the present invention will be described with reference to FIG. In this example, when the Si layer on the wafer surface is polished, polishing is performed while actually measuring the thickness of the Si layer at each polishing position, so that the desired thin film S that is uniform over the entire wafer surface is obtained.
Get the i-layer.

The bonded SOI wafer 501 is prepared by performing the steps up to the grinding shown in FIG. 3C by the procedure already described with reference to FIG. In FIG. 9, the same objects as those in FIG. 3 are designated by the same reference numerals. That is, SOI
Wafer 501 has Si layer 3 ground to about 3 μm
1, the support-side wafer 32, and the insulating film 33 interposed therebetween, and the structure is substantially formed.

Polishing is performed using the same polishing apparatus and polishing agent as in Example 1. However, an AC voltage 541 is applied between the wafer holding plate 411 and the polishing jig 421, and the current is detected by the AC ammeter 542. SOI wafer 501
Are held in a state of being electrically connected to the wafer holding plate 411. Polishing is performed as follows, for example.

The SOI wafer 501 is attached to the wafer holding plate 411.
The wafer holding plate 411 is rotated, and the polishing cloth 431 having an area of 1 to 4 cm ² is held by the wafer 50.
Press on 1. The polishing agent is supplied to the polishing cloth 431 via the polishing jig 421. An alternating voltage 541 is applied between the polishing jig 421 and the polishing plate 411. By adding a suitable electrolyte to the polishing agent, most of the applied voltage can be applied to the Si layer 31 and the supporting-side wafer 32. If the resistance value of Si of the supporting side wafer 32 is made small, a substantial voltage is applied to the Si layer 31 to be polished.

As the polishing of the Si layer 31 progresses and becomes thinner,
The resistance value due to the Si layer 31 decreases and the current value increases.
A reference current value corresponding to a desired Si layer thickness is previously obtained by an experiment. When the current value reaches this reference value during polishing, the polishing is temporarily stopped, the polishing jig 421 is moved to the outer side in the radial direction of the wafer 401, and then the polishing is restarted. Wafer 5
On the same radius of 01, the relative speed between the rotating wafer 501 and the polishing cloth 431 is substantially constant, and the distribution of the polishing speed is very small. In this way, the polishing jig 421 is gradually moved outward from the vicinity of the center of the wafer 501 to polish the entire wafer 501. The polishing agent supplied onto the wafer 501 via the polishing cloth 431 flows from the polishing position toward the outside of the wafer 501 due to the centrifugal force generated by the rotation of the wafer 501. Therefore, by moving the polishing position from the inside of the wafer to the outside, the polishing agent is removed from the wafer 501.
Can be prevented from being supplied to the polishing-completed portion. When the polishing agent is supplied to the polishing-completed portion, a current flows through the conductive portion 402 exposed there, which makes it difficult to control the polishing currently in progress.

The wafer 501 is not rotated and the polishing jig 4 is used.
When only 21 is rotated to perform polishing, a fluid such as pure water is supplied to the central portion of the wafer 501 as shown in FIG. 5 to form a flow outward on the surface of the wafer 501. It is possible to prevent the polishing agent from being supplied to the polishing-completed portion. Liquids and gases that do not contaminate the wafer and the polishing apparatus are used as the fluid for this purpose.

In order to perform the polishing, at least one of the polishing plate and the polishing jig may be rotated, but rotating both is most advantageous for uniformly polishing the entire surface of the wafer. In particular, rotating the polishing jig makes the polishing rate uniform within the polishing cloth area and facilitates the control of the polishing amount at the same radial position on the wafer. Also, when polishing is performed by rotating the polishing plate and stopping the polishing jig,
As shown in FIG. 6, it is desirable that the width W of the polishing cloth mounting surface 422 of the polishing jig be smaller on the outer side (W2) than on the inner side (W1) in the wafer radial direction. As a result, it is possible to reduce the difference in the polishing rate due to the difference in the peripheral speed of the polishing plate within the area of the polishing cloth, that is, to make the polishing rate within the area of the polishing cloth more uniform.

The Si layer of the bonded SOI wafer was thinned according to the present invention by the method shown in FIG. 9 and compared with the thinning by the conventional single-wafer polishing apparatus shown in FIG.

<Preparation of test wafer> S with a diameter of 150 mm
The i wafer was subjected to the grinding shown in FIG. 3C to prepare an SOI wafer having a Si layer thickness of 3 μm.

<Polishing Conditions> Polishing according to the present invention: Polishing is started from the center of the wafer, an AC voltage is applied between the wafer holding plate and the polishing jig, and the current value between the two exceeds a predetermined value. The polishing is temporarily stopped at this point, the polishing jig is moved to the outer side in the radial direction of the wafer, and the polishing is restarted. During polishing,
Pure water is supplied to the center of the wafer to form a water flow from the center to the outside on the wafer polishing surface. Conventional Polishing The polishing apparatus shown in FIG. 2 simply adjusts the polishing amount by polishing time.

<Evaluation of Polishing Results> Aiming at a Si layer thickness of 1 μm, 10 wafers each were polished under each of the polishing conditions described above, and the Si layer thickness after polishing at one point in the central portion of the wafer and four points in the peripheral portion Was measured. The result is shown in FIG. In the case of polishing according to the present invention, the average thickness of the Si layer is 0.95 μm, and the variation in thickness is 0.05 μm, whereas in the conventional polishing, the average thickness of the Si layer is 1.10 μm. Variation was 0.5 μm on average. As described above, according to the present invention, it is possible to make the film more uniform and thinner than the conventional method.

In this embodiment, the polishing is controlled by the current value, but the same control can be performed by using the potential difference.

[0037]

As described above, according to the present invention,
By controlling the polishing amount at each position on the wafer, the entire surface of the wafer can be uniformly polished, which is sufficiently practical as a method for planarizing the wiring layer, and the Si layer of the SOI wafer can be further thinned.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a polishing method for planarizing an interlayer insulating film in a device manufacturing process by a conventional method.

FIG. 2 is a layout view showing an apparatus and a method for polishing a wafer by a conventional method.

FIG. 3 is a cross-sectional view showing an example of a manufacturing process of a bonded wafer.

FIG. 4 is a layout view showing an example of a polishing apparatus and a polishing method for planarizing an interlayer insulating film in a device manufacturing process according to the present invention.

FIG. 5 is a layout view showing another example of a polishing apparatus and a polishing method for flattening an interlayer insulating film in a device manufacturing process according to the present invention.

FIG. 6 is a diagram showing an example of a polishing cloth mounting surface shape in the polishing apparatus of the present invention.

FIG. 7 is a plan view showing an arrangement pattern of studs on a test wafer used for a polishing test.

FIG. 8 is a graph showing a result of polishing the wafer of FIG.

FIG. 9 shows a bonded SOI wafer according to the present invention as S.
It is a layout showing an example of a polishing device and a polishing method for thinning the i layer.

FIG. 10 is a graph showing a polishing result of a bonded SOI wafer.

[Explanation of symbols]

10 ... Semiconductor substrate 11 ... Horizontal conductive section 12 ... Vertical conductive section (stud or vertical interconnec)
13) ... SiO ₂ insulating layer by CVD 14 ... Polishing end position 21 ... Rotating shaft 22 ... Rotating platen 23 ... Polishing cloth 24 ... Rotating shaft 25 ... Rotating wafer holding plate 26 ... Wafer 31 ... Si wafer 32 ... Si wafer 33 ... Oxide film by thermal oxidation 401 ... Si wafer 402 ... Conductive part such as lateral conducting part (interconnect) and vertical conducting part (stud) 403 ... Interlayer insulating film 404 ... Insulating film such as thermal oxide film 405 ... Conductive material such as a conductive paste disposed on a part of the lower surface of the wafer 401 411 ... Wafer holding plate of the polishing apparatus (made of a conductive material such as metal) 412 ... Rotating shaft of the wafer holding plate 411 (of metal or the like) 421 ... Rotary polishing jig of polishing apparatus (made of conductive material such as metal) 422 ... Lower end surface of polishing jig 421 (polishing cloth mounting surface) W ... Width of polishing cloth mounting surface 422 of polishing jig 421 ... Polishing cloth 432 ... Many through passages through which abrasive grains can freely pass 441 ... Applied between wafer holding plate 411 and polishing jig 412 DC voltage 442 ... Ammeter 461 ... Fluid supply port 462 disposed above the central portion of the wafer 401 ... Fluid such as pure water 463 ... Direction of flow outward on the surface of the wafer 401 501 ... Bonded SOI wafer 541 ... AC voltage 542 ... AC voltmeter 601 ... Wafer 602 ... W stud

Claims (14)

[Claims] 1. A semiconductor wafer is suction-held on a holding plate,
At least one of the holding plate and the polishing jig is rotated while the polishing cloth attached to the polishing jig is brought into contact with the surface to be polished of the wafer, and the polishing agent is passed through the polishing cloth and supplied to the contact portion. Thus, when polishing the wafer, a voltage is applied between the suction part of the wafer and the polishing jig, the voltage and / or the current between the two is detected during polishing, and the obtained detected value is obtained. A method of polishing a semiconductor wafer, which comprises controlling a polishing rate at each polishing position based on the polishing rate. 2. The polishing method according to claim 1, wherein polishing debris is removed to the outside of the wafer by supplying a fluid to a substantially central portion of a surface to be polished of the held wafer. 3. The polishing method according to claim 1, wherein a polishing jig is used, in which the width of the surface on which the polishing cloth is mounted is smaller on the outer side than on the inner side in the radial direction of the wafer. 4. The polishing position is sequentially moved from the inner side to the outer side in the radial direction of the wafer to perform polishing, and when the detected current value is equal to or higher than a reference value or the detected voltage value is equal to or lower than a reference value, the polishing position is set. 4. The polishing method according to claim 1, wherein the polishing is controlled so as to be moved to the outside in the radial direction of the wafer. 5. The surface to be polished of the wafer has an outermost surface layer made of an insulator and a conductor layer thereunder, and a DC voltage is applied as the voltage. The polishing method according to claim 1. 6. The surface to be polished of the wafer has an outermost layer made of a semiconductor and an insulating layer thereunder, and an alternating voltage is applied as the voltage. The polishing method according to item 1. 7. When the wafer holding plate is rotated to polish a specific radius of the wafer, the contact pressure of the polishing cloth is increased at a position where the detected current value is small or the detected voltage value is large on the radius. 7. The polishing method according to claim 1, wherein the contact pressure is reduced at a position where a detected current value is large or a detected voltage value is small. 8. The polishing method according to claim 1, wherein the wafer holding plate and the polishing jig are rotated in the same direction. 9. When polishing a specific radius of the wafer, the rotation speed of the polishing jig is increased at a position where the detected current value is small or the detected voltage value is large on the radius to increase the detected current value. 9. The polishing method according to claim 8, wherein the rotation speed is reduced at a position where the detected voltage value is small. 10. A liquid having a low specific resistance such as pure water, a coating agent, or a gas such as air is used as a fluid supplied to the central portion of the held wafer. The polishing method according to any one of 1. 11. A holding plate for adsorbing and holding a semiconductor wafer, a polishing jig arranged so that a polishing cloth attached to a tip of the semiconductor wafer is brought into contact with a surface to be polished of the wafer, and the contact portion for transmitting the polishing cloth. A means for supplying an abrasive to the wafer, a means for applying a voltage between the suction portion of the wafer and the polishing jig, and a means for detecting the voltage and / or current between the two during polishing. And a means for controlling a polishing rate according to a detected value, wherein at least one of the holding plate and the polishing jig can rotate. 12. The polishing apparatus according to claim 1, further comprising means for supplying a fluid to a substantially central portion of a surface to be polished of the held wafer. 13. The polishing apparatus according to claim 11, wherein a width of a surface of the polishing jig on which the polishing cloth is mounted is smaller on the outer side than on the inner side in the wafer radial direction. 14. The polishing apparatus according to claim 11, further comprising means for moving a polishing position in a radial direction of the wafer.