JP2001113460A - Double-side simultaneously polishing work method and device thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate a fluctuation in a polishing quantity when simultaneously polishing both surfaces of a thin plate between upper/lower rotary surface plates. SOLUTION: Upper/lower rotary surface plates 1, 2 are independently driven by separate motors 13, 18. Inverter power sources 25, 26 for driving the motors 13, 18 are controlled so that electric current values of both motors 13, 18 become the same. Polishing speeds of both surfaces are equalized without being influenced by the degradation with the lapse of time and mesh-clogging of polishing cloth installed on opposed surfaces of the rotary surface plates 1, 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a double-sided simultaneous polishing method used for manufacturing a semiconductor wafer or the like used as a material of a semiconductor device.

[0002]

2. Description of the Related Art A silicon wafer, which is a typical semiconductor wafer, is obtained by slicing a silicon single crystal manufactured by a CZ method or the like into a thin plate, performing lapping (grinding) on the thin plate for thickness adjustment, and further polishing the surface mirror surface. It is manufactured by performing polishing (polishing) for finishing. Until now, mirror finishing has been performed only on the surface on which the device is formed. However, in the case of a large-diameter wafer exceeding 8 inches, for example, 12 inches, the back surface on which no device is formed is required to have a finish comparable to the mirror surface. As a result, polishing was also required on both sides.

For double-side polishing of a silicon wafer, a double-sided simultaneous polishing apparatus of a planetary gear system is usually used. As shown in FIGS. 3 and 4, the polishing apparatus includes a pair of upper and lower rotary plates 1 and 2, a sun gear 3 disposed at the center of rotation between the rotary plates 1 and 2, and a rotary plate. 1,2
Ring-shaped internal gear 4 arranged on the outer peripheral portion between
, And a plurality of carriers 5, 5,... Which are set around the rotation center between the rotary platens 1 and 2 in mesh with the sun gear 3 and the internal gear 4.

The plurality of carriers 5, 5,... Function eccentrically to hold a circular work 6 made of a silicon wafer, and mesh with the inner sun gear 3 and the outer internal gear 4 to function as planetary gears. A polishing cloth (not shown) is mounted on each of the opposing surfaces of the rotary platens 1 and 2.

In the polishing operation, a plurality of workpieces 6,
6 and .. are held by carriers 5, 5,.
And more specifically, between the upper and lower polishing cloths, and while the polishing liquid is being supplied between the rotary platens 1 and 2, the rotary platens 1 and 2, the sun gear 3 and the internal gear 4 are rotationally driven. . The rotation directions of the rotation bases 1 and 2 are opposite directions, and the rotation directions of the sun gear 3 and the internal gear 4 are usually the same as the rotation base 2 on the lower side.

By these rotations, the plurality of carriers 5, 5,... Revolve around the sun gear 3 while rotating between the rotating bases 1, 2 rotating in opposite directions. This allows
A plurality of works 6, 6,... Are simultaneously polished on both sides.

[0007]

In such double-side polishing of a silicon wafer, the polishing amount is generally 10 to 15 μm on one side and about 25 to 30 μm on both sides. If the polishing amount is insufficient, processing distortion and processing flaws generated in the pre-processing and the like are not sufficiently removed, resulting in poor quality. Conversely, when the polishing amount is excessive, the processing accuracy deteriorates in that the variation in the wafer thickness increases. For this reason,
It is necessary to polish both sides of the wafer evenly and only to the minimum necessary. From this viewpoint, the number of rotations of the upper and lower rotating platens is the same, or the peripheral speed applied to the wafer is the same on both sides. Is generally set to.

However, in the actual polishing operation, the polishing cloth mounted on the opposing surfaces of the upper and lower rotating platens is repeatedly used, and the polishing cloth deteriorates with time and becomes clogged due to clogging.
The polishing rate changes greatly between the upper platen and the lower platen. Even if the polishing efficiency changes between the upper surface plate and the lower surface plate, there is no problem as long as the polishing amount of the upper surface plate and the polishing amount of the lower surface plate can be separately measured and controlled. However, this individual management is difficult, and the fact is that only the total machining amount (TTL) on both sides is managed. Also, it is not practical in terms of work efficiency and work cost to use a new polishing cloth every time processing is performed.

For these reasons, in the actual polishing operation, variations in the polishing amount on both surfaces are unavoidable, and on the surface where the polishing amount is insufficient, processing distortion and processing flaws caused by pre-processing and the like remain. On the surface where the quality is poor and the polishing amount is excessive, the processing accuracy is deteriorated. Therefore, conventionally, it has been difficult to stably secure desired polishing quality.

An object of the present invention is to provide a double-sided simultaneous polishing method capable of equalizing the polishing amount on both the front and back surfaces irrespective of the condition of the polishing cloth and without depending on a difficult technique such as individual polishing amount control. It is to provide a device.

[0011]

Means for Solving the Problems To achieve the above object, a double-sided simultaneous polishing method of the present invention is a method for simultaneously polishing both sides of a thin plate by sandwiching the thin plate between upper and lower rotating platens. The upper and lower turntables are independently driven by separate motors, and both current values are controlled to be substantially the same.

Further, the double-sided simultaneous polishing apparatus of the present invention comprises:
Sandwiching a thin plate to be polished on both sides, and upper and lower rotary platen independently driven by separate motors, and a drive power supply unit for driving two types of motors for independently driving the upper and lower rotary platen, A power control unit that measures each current value of the two types of motors and controls the drive power supply unit so that both current values are substantially the same.

In the method and apparatus for simultaneous double-side polishing according to the present invention, the current values of the two types of motors for separately driving the upper and lower rotary platens are controlled to be substantially the same. According to this control,
Although the rotation speed of the surface plate differs between the upper surface plate side and the lower surface plate side, the polishing speed is equalized. The reason is simply that the polishing rate depends on the motor current value irrespective of the state of the polishing cloth. The details are as follows.

In the simultaneous double-side polishing, the contribution of the abrasive differs between the upper platen and the lower platen. Due to gravity, the contribution rate on the upper platen side is small, and it increases on the lower platen side. For this reason,
When the rotation speed is the same, there is a difference in the polishing rate between the upper surface plate and the lower surface plate. However, when the current value is the same, the difference in the contribution ratio of the abrasive is removed, and the polishing speed is equalized ( (See FIG. 2).

In the double-sided simultaneous polishing method and apparatus according to the present invention, the thin plate is eccentrically held in a plurality of carriers arranged around the center of rotation between the upper and lower rotating platens in terms of processing efficiency. It is preferable to rotate the plurality of carriers while rotating at a fixed position or revolving around the rotation center.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a double-sided simultaneous polishing apparatus showing one embodiment of the present invention.

The simultaneous double-side polishing apparatus according to the present embodiment comprises a pair of upper and lower rotary platens 1, which sandwich a plurality of carriers 5, 5,.
2, a center gear 7 disposed at the center of rotation between the rotary bases 1 and 2, and a plurality of holding gears 8, 8,...

A plurality of holding gears 8, 8,... Are arranged at predetermined intervals in the circumferential direction of the platen with two being one set.
The plurality of carriers 5, 5,... Are arranged around the center of rotation between the rotary platens 1, 2 and mesh with the center gear 7 on the inside, and mesh with the two holding gears 8, 8 on the outside, so that they are in a fixed position. Rotate. A plurality of workpieces 6, 6,... Made of silicon wafers are eccentrically held in a plurality of carriers 5, 5,. A polishing cloth is mounted on the facing surfaces of the rotary platens 1 and 2.

The above is the basic configuration of the double-sided simultaneous polishing apparatus. Hereinafter, a drive system of the processing apparatus will be described.

The upper rotary platen 1 is mounted on the lower surface of the rotary drive shaft 9. The rotation drive shaft 9 includes gears 10 and 11
Also, it is connected to an upper platen drive motor 13 via a speed reducer 12, whereby the rotary platen 1 is driven to rotate independently of the lower rotary platen 2. The rotary drive shaft 9 also includes a speed reducer 12 and an upper platen drive motor 1 for raising and lowering the rotary platen 1.
3 and the like.

The lower rotary platen 2 is mounted on the upper surface of the rotary drive shaft 14. The rotary drive shaft 14 has a hollow structure having a through hole at the center, and is connected to a lower platen drive motor 18 via gears 15 and 16 and a speed reducer 17 to rotate the rotary platen 2 upward. It is driven to rotate independently of the surface plate 1.

The center gear 7 is connected to a rotary drive shaft 19 that passes through the rotary drive shaft 14. Rotary drive shaft 19
Is connected to a gear drive motor 22 via a belt 20 and a speed reducer 21 to drive the center gear 7. The reduction gear 21 is also provided with a rotary drive shaft 22,
22. Are connected by belts 23 and 24.
.. Are driven synchronously at the same peripheral speed as the center gear 7.

An upper surface plate drive motor 13 which is a drive source of the upper rotating surface plate 1 is driven at an arbitrary speed by an inverter power supply 25. On the other hand, the lower platen drive motor 18, which is the drive source of the lower rotary platen 2, is driven at an arbitrary speed by the inverter power supply 26. The sequence controller 27, which is a control unit for these power supplies, controls the inverter power supplies 25, 2 to rotate the turntables 1, 2 at a preset number of rotations.
6 is controlled, and the current values of the motors 13 and 18 are transferred from the inverter power supplies 25 and 26 to the inverter power supplies 25 and 26.
Then, one of the inverter power supplies 25 and 26 is precisely controlled so that the smaller current value matches the larger current value.

Next, a description will be given of a double-sided simultaneous polishing method using the above processing apparatus.

The upper rotating platen 1 is lifted and separated from the lower rotating platen 2. Carriers 5, 5,... And works 6, 6,... Are set at fixed positions on the lower rotary platen 2. By lowering the upper rotating platen 1 to its original position and combining it with the lower rotating platen 2, the workpieces 6, 6,... Are sandwiched between the upper and lower polishing cloths.

While the polishing liquid is supplied between the rotary platens 1 and 2, the motors 13 and 18 are driven by the inverter power supplies 25 and 26.
To rotate the rotary platens 1 and 2 in the opposite direction at the set speed. Also, the gear drive motor 22 is driven to drive the center gear 7 and the holding gears 8, 8,... At the same peripheral speed. Thus, the carriers 5, 5,... Do not revolve between the upper and lower rotary platens 1, 2 rotating in opposite directions, that is, rotate at fixed positions. Thus, the workpieces 6, 6,... Held by the carriers 5, 5,. Thereby, both surfaces of each work are mirror-finished, and the total polishing amount of both surfaces is controlled to a predetermined value.

Here, a sequence controller 27 which is a control unit of the inverter power supplies 25 and 26 is provided with
Each of the current values 18 is taken in from the inverter power supplies 25 and 26 and compared, and one of the inverter power supplies 25 and 26 is precisely controlled so that the larger current value matches the smaller current value. As a result, the same amount of current flows through the motors 13 and 18.

Since the loads of the motors 13 and 18 are not the same, if the current values of the motors 13 and 18 are the same, the rotational speeds of the upper and lower rotary platens 1 and 2 will be different. On the other hand, the polishing rates of the workpieces 6, 6,... Are uniform on both surfaces regardless of the temporal deterioration or clogging of the upper and lower polishing cloths. Since the total polishing amount on both surfaces is controlled to a predetermined value, the polishing amount on both surfaces is equalized by equalizing the polishing speed on both surfaces. The reason why the polishing speed is equalized by making the motor currents the same on the upper surface plate side and the lower surface plate side is as described above.

In such motor current control, it is not necessary to completely match the motor currents on both sides. The current value may be controlled within a range of ± 5%. The reason why the small current value is made to coincide with the large current value is to improve the productivity by increasing the polishing rate. However, it is also possible to make the large current value coincide with the small current value.

FIG. 2A is a table showing the relationship between the number of rotations of the rotary platen and the polishing rate (the amount of polishing in the same time), and FIG. 2B shows the current of the motor driving the rotary platen. 5 is a table showing a relationship between a value and a polishing rate (amount of polishing within the same time).
The solid line in the chart indicates the polishing speed on one side when the polishing cloth is new (up and down the same), the broken line indicates the polishing rate on the lower side when the lower polishing cloth is old, and the dashed line indicates that the upper polishing cloth is old. The upper polishing rate at each time is shown.

As can be seen from FIGS. 2 (a) and 2 (b), the polishing rate increases with an increase in the number of rotations. However, at any number of rotations, the polishing rate is affected by the condition of the polishing cloth. Especially large. In other words, the relationship between the number of revolutions and the polishing rate is affected by the state of the polishing cloth, and the polishing rate varies greatly depending on the state of the polishing cloth and further with the arrangement position even at the same number of revolutions. On the other hand, the relationship between the current value of the motor and the polishing speed is not affected by the state and the arrangement position of the polishing cloth. If the current value is the same, the polishing speed becomes the same.

Accordingly, by controlling the current values of the respective motors for driving the upper and lower platens to be the same, the polishing speed on both surfaces is equalized, and as a result, the polishing amount is also equalized.

In the above-described embodiment, the plurality of carriers are rotated at fixed positions between the upper and lower stools, but using a general planetary gear type polishing apparatus as shown in FIGS.
It is also possible to revolve around the center of rotation between the upper and lower platens.

[0034]

As described above, the double-sided simultaneous polishing method and apparatus of the present invention controls the respective current values of the two types of motors for separately driving the upper and lower rotating platens to be substantially the same. Since the polishing rate is equalized on the upper and lower platens, it can be easily combined with management of the total polishing amount on both the front and back surfaces without depending on difficult technologies such as individual polishing on the front and back surfaces. The amount of polishing on both sides can be equalized by appropriate current control, and a desired polishing quality can be stably secured.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a double-sided simultaneous polishing apparatus showing an embodiment of the present invention.

FIG. 2A is a chart showing a relationship between a rotation speed of a rotating platen and a polishing speed, and FIG. 2B is a chart showing a relationship between a current value of a motor for driving the rotating platen and a polishing speed.

FIG. 3 is a schematic diagram of a general double-sided simultaneous polishing apparatus.

FIG. 4 is a diagram showing an arrow AA in FIG. 3;

[Explanation of symbols]

 1, 2 rotation platen 3 sun gear 4 internal gear 5 carrier 6 work 7 center gear 8 holding gear 9, 14, 19 rotation drive shaft 10, 11, 15, 16 gear 12, 17, 21 reduction gear 13, 18 fixed Board drive motor 20,23,24 Belt 22 Gear drive motor 25,26 Inverter power supply 27 Sequence controller

Claims (4)

[Claims] 1. A method of simultaneously polishing both surfaces of a thin plate with a thin plate sandwiched between the upper and lower rotary platens, wherein the upper and lower rotary platens are independently driven by separate motors, and both current values are substantially reduced. A double-sided simultaneous polishing method characterized by the same control. 2. The thin plate is eccentrically held in a plurality of carriers arranged around a center of rotation between upper and lower rotating platens, and the plurality of carriers are rotated at a fixed position or revolved around the center of rotation. The double-sided simultaneous polishing method according to claim 1, wherein the substrate is rotated while rotating. 3. An upper and lower rotary platen, which sandwich a thin plate to be polished on both sides and are independently driven by separate motors, and two types of motors for independently driving the upper and lower rotary platens, respectively. A double-sided simultaneous polishing process comprising a drive power supply unit and a power supply control unit that measures each current value of two types of motors and controls the drive power supply unit so that both current values are substantially the same. apparatus. 4. A plurality of carriers which are arranged around a rotation center between the upper and lower rotating platens, each holding the thin plate eccentrically, and while rotating the plurality of carriers at a fixed position or revolving around the rotation center. The double-sided simultaneous polishing apparatus according to claim 1, further comprising a carrier driving mechanism that rotates.