JPH0317622B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a polishing apparatus for mirror polishing a semiconductor wafer, for example, and in particular to a parallelism maintaining mechanism for keeping the surface plate and plate highly parallel. The present invention relates to a polishing device provided therein and a polishing device that aims to reduce the operating resistance of the parallelism maintaining mechanism.

(Prior Art) FIG. 8 shows a diagram of the principle of polishing using a polishing device. For example, a semiconductor wafer W is bonded to the lower surface of a plate 104 via a mounting material, wax 121, etc., and the lower surface is moved at a predetermined speed. Abrasive cloth (cloth) affixed on the horizontally rotating surface plate 101
102 with a predetermined force P, the nozzle 122
The abrasive cloth 1 is supplied with abrasive 123 from
02, and the lower surface of the semiconductor wafer W is mirror-polished.

Incidentally, with the recent increase in the degree of integration of semiconductor devices, high parallelism and high flatness are required for semiconductor wafers to be polished. Parallelism with plate 104 must be maintained.

FIGS. 9 to 12 are explanatory diagrams of various mechanisms for maintaining parallelism between the surface plate and the plate. That is, the one shown in FIG. 9 is a mechanical fixing method in which a shaft 203 integrally attached to a plate 204 is rotatably supported by a bearing 203 to prevent the plate 204 from wobbling. It is. Furthermore, the one shown in FIG. 10 is a plate following system, in which a bearing 330 is interposed between 303 and plate 304 to cause plate 304 to follow along the inclination of surface plate 301. It is. Furthermore,
The one shown in FIG. 11 is a pivot bearing system, in which the plate 4 is
04 is supported tiltably about a shaft 403, and the position of the operating center 0 of the plate 404 is lowered. (For example, JP-A-55-86120, JP-A No. 57-86120,
20436 and 60-80558). Furthermore, what is shown in FIG. 12 is an outer periphery holding method, in which the outer periphery of the plate 504 is held by rotatable rollers 540, 540 as shown.
Note that FIG. 12a is a plan view of the polishing device, and FIG. 12b is a side view of the polishing device, and 501 in the figure is a surface plate that rotates in the direction of the arrow in the figure.

(Problems to be Solved by the Invention) However, each of the conventional parallelism maintaining mechanisms described above has the following problems. That is, in the case of the mechanical fixing method shown in FIG. 9, a high-precision polishing machine is required, and the shaft 203
If the tilt of the surface plate 201 or surface runout of the surface plate 201 occurs, parallelism cannot be maintained, and in the plate following method shown in FIG. The surface plate 301 and the plate 304 are not kept parallel due to the frictional force acting on the surface plate 301. It is said that semiconductor wafers with high parallelism and flatness cannot be obtained because the distribution of the compressive force applied to the cloth (not shown) becomes uneven, causing uneven deformation of the mounting material and the polishing cloth. There's a problem. Further, in the case of the pivot bearing system shown in FIG. 11, there is a problem that not only the central part of the plate 404 is deformed and the flatness cannot be maintained, but also a high load cannot be applied to the plate 404. However, the outer periphery holding method shown in FIG. 12 is difficult to apply when the diameter of the plate 504 is small, and there is a problem that polishing cannot be performed while the plate 504 is forcibly pressurized with a hydraulic cylinder or the like. There is.

The present invention has been made in view of the above-mentioned conventional problems, and its purpose is to maintain strict parallelism between the plate and the surface plate even when frictional force acts on the polished surface, and to achieve high parallelism and high flatness. An object of the present invention is to provide a polishing device capable of performing polishing processing.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a mirror-like surface of the object to be polished by pressing the object to be polished held by a tiltable plate with a predetermined force. In a polishing device configured to perform polishing, the plate is supported via a parallelism maintaining mechanism on a shaft vertically disposed above the surface plate, and the parallelism maintaining mechanism is arranged such that its center of tilt is aligned with the object to be polished. Its feature is that it includes a spherical bearing located on the contact surface between the polishing cloth and the polishing cloth.

(Function) According to the present invention, the plate is supported by the shaft via the spherical bearing that constitutes the parallelism maintaining mechanism, and the center of tilt of the spherical bearing is on the contact surface (polishing surface) between the object to be polished and the polishing cloth. Because of the position, the thickness of the object to be polished (if the object to be polished is a semiconductor wafer, its thickness is negligible compared to the thickness of the plate).
If ignored, the operating center of the plate (tilting center)
will also be located on the polished surface.

Therefore, when the operating center of the plate is located on the polishing surface as described above, the distance L between the point of application of the frictional force F acting on the polishing surface and the operating center of the plate becomes zero (L=O), The moment M that tries to tilt the plate, which is expressed as the product of the frictional force F and the distance L, becomes zero (M=F×L=O), and even though the frictional force acts on the polished surface, the plate Parallelism with the surface plate can be strictly maintained, thereby enabling polishing with high parallelism and high flatness.

In addition, as a specific means for positioning the tilting center of the spherical bearing on the contact surface (polishing surface) between the object to be polished and the polishing cloth, it is possible to place the spherical bearing on a concave-convex spherical surface whose center of curvature is located on the polishing surface. It is conceivable to include a concavo-convex surface seat consisting of the following.

(Example) Examples of the present invention will be described below based on the accompanying drawings.

FIG. 1 is a longitudinal sectional view of the polishing apparatus according to the present invention, and in the figure, 1 is a surface plate on a disk, which is rotated horizontally around its central axis by a drive device (not shown). It is driven, and an abrasive cloth 2 having appropriate elasticity is attached to its upper surface.
Further, a shaft 3 is vertically installed above the outer circumference of the surface plate 1, and a parallelism maintaining mechanism 1 is provided at the lower end of the shaft 3.
A disk-shaped plate 4 is attached to the shaft 3 via the shaft 3 so as to be tiltable. Furthermore, this plate 4
is made of highly rigid materials such as stainless steel (SUS) and ceramics, and has many small holes 4a.
... has been drilled. Further, the shaft 3 is hollow, and a hole 3a formed through the center thereof is communicated with a vacuum pump 5 as shown in the figure, and an end of the hole 3a is connected to the parallelism maintaining mechanism 10. It opens into a space S surrounded by the plate 4. A thin plate-shaped semiconductor wafer W, which is an object to be polished, is adsorbed to the lower surface of the plate 4 by means described later, and the semiconductor wafer W is pressed onto the polishing cloth 2 with a predetermined force P. There is.

By the way, the parallelism maintaining mechanism 10 positions the operating center O of the plate 4 on the contact surface between the semiconductor wafer W and the polishing cloth 2, that is, on the polishing surface f, and is specifically constructed of a spherical bearing. has been done. This spherical bearing is a block 14 formed by assembling and integrating a member 11 and a member 12 with bolts 13.
and a block 15 in spherical contact with the block 14.
The block 14 is rotatably attached to the outer periphery of the shaft 3 via a ball bearing 16. Further, a spherical seat 15a having a radius r and whose center of curvature is located on the polishing surface f is formed on the upper part of the other block 15.
A spherical concave seat 14a having the same center of curvature and the same radius r as the spherical seat 15a formed on the lower surface of 4.
sliding contact. Therefore, the center of tilt of the spherical bearing composed of the spherical seat 15a and the spherical concave seat 14a is located on the polished surface f. and,
The plate 4 is mounted and supported on the lower part of the block 15 via a support member 18 fastened to the block 15 with bolts 17, and the lower surface of the block 15 has a plurality of plates connected to the space S. The annular grooves 19 are formed concentrically. In addition, in the figure, 20 is an oil seal.

Next, the operation of this polishing device will be explained.

The thin semiconductor wafer W is attracted to the lower surface of the plate 4 by the negative pressure drawn by the vacuum pump 5 through the small holes 4a bored in the plate 4, the space S, and the hole 3a in the shaft 3. Ru.

On the other hand, the surface plate 1 is rotated horizontally around its central axis at a constant speed by a drive mechanism (not shown), and the semiconductor wafer W is placed on the upper surface of the polishing cloth 2 stuck on the surface plate 1. is pressed with a predetermined force P. Then, relative slippage occurs between the semiconductor wafer W and the polishing cloth 2, and due to this slippage, the semiconductor wafer W is mirror-polished by the polishing cloth 2 while being supplied with abrasive from a nozzle (not shown). , a frictional force F is generated on the polished surface f. The semiconductor wafer W, the plate 4, and the parallelism maintaining mechanism 10 rotate around the shaft 3 via the ball bearing 16 due to the difference in the circumferential speed in the radial direction on the surface plate 1.

Incidentally, since the plate 4 is tiltably supported with respect to the shaft 3 via the parallelism maintaining mechanism 10 constituted by a spherical bearing, the plate 4 tilts following the tilt of the surface plate 1. In reality, an oil film of lubricating oil is formed between the spherical seat 15a and the spherical concave seat 14a of the parallelism maintaining mechanism 10, and the plate 4
The tilting is done extremely smoothly. At this time, the plate 4 is supported by the shaft 3 via a spherical bearing that constitutes a parallelism maintaining mechanism, and the center of tilt of the spherical bearing is located on the polishing surface f, so if the thickness of the semiconductor wafer W is ignored, , since the operating center O of the plate 4 is also located on the polishing surface f, the point of application of the frictional force F acting on the polishing surface f coincides with the operating center O of the plate 4, and the distance L between them is The moment M that tries to tilt the plate 4, which is expressed as the product of the frictional force F and the distance L, becomes zero (M=F×0), and the frictional force F is applied to the polished surface f. Despite this, the parallelism between the plate 4 and the surface plate 1 can be maintained strictly, and it is possible to polish the semiconductor wafer W, which is the object to be polished, with high parallelism and high flatness. Note that a resultant force Q of the load P and the frictional force F acts on the operating center 0 of the plate 4 in the direction of the arrow shown in the figure.

FIG. 2 shows actual measurement results of the flatness of the surface of a semiconductor wafer W polished by the polishing apparatus according to the present invention described above, in comparison with actual measurement results when polished by a conventional apparatus. In addition, FIG. 2a shows the actual measurement results of the semiconductor wafer W in the x-x direction, and FIG. 2b shows the actual measurement results in the Y-
The actual measurement results in the Y direction are shown, and the solid line a in the figure
When polished with the device of the present invention, the broken line b is the 10th
The dashed line c shows the actual measurement results when polishing was performed using a conventional device employing the plate following method shown in the figure, and when polishing was performed using the conventional device employing the pivot bearing method shown in FIG. 11, respectively. Also, the actual measurement is load 370
g/cm ² and the number of rotations of the surface plate was 40 rpm, and a waxless method was used to bond the semiconductor wafer W to the plate.

As is clear from the results shown in FIG. 2, according to the apparatus of the present invention, the flatness of the semiconductor wafer W can be maintained extremely high over its entire surface.

Next, a modified embodiment of the present invention is shown in FIG. still,
In FIG. 3, the same elements as shown in FIG. 1 are given the same reference numerals, and explanations thereof will be omitted.

In this modified embodiment, the parallelism maintaining mechanism 10
An annular soft elastic body 21 (specifically, an O-ring) made of rubber or the like is interposed between the uneven face seats 14a and 15a of the spherical bearing blocks 14 and 15 that constitute the bearing. That is, the spherical seat 15a of the block 15
An annular groove 15b is formed on the surface of the groove 15b, and the soft elastic body 21 is fitted into the groove 15b. The hardness of the soft elastic body 21 is preferably a value such that the uneven surface seats 14a, 15a are deformed to such an extent that they do not come into direct metal contact with each other.

By providing the soft elastic body 21, the operating resistance of the spherical bearing constituting the parallelism maintaining mechanism 10 can be significantly reduced for the following reason. That is, the force R and displacement l applied to the soft elastic body 21 are as shown by the straight line d in FIG.
Block 1, which has a proportional relationship and constitutes a spherical bearing
The required sliding distance between the concavo-convex face seats 14a and 15a of No. 4 and 15 is actually very small. Therefore, as shown in FIG. 4, the necessary force to further displace the soft elastic body 21, which is balanced by a certain displacement lo and a certain force Ro, by Δl is ΔR. As mentioned above, the uneven surface seats 14 of the blocks 14 and 15 forming the spherical bearing
Since the necessary sliding distance between a and 15a is actually very small, the uneven surface seats 14a and 15a
The displacement Δl of the soft elastic body 21 interposed between becomes almost zero (Δl=0), and the force ΔR proportional to this displacement Δl also becomes almost zero (ΔR=0), resulting in The operating resistance of the spherical bearing corresponding to this force ΔR is significantly reduced.

Next, O, which is generally commercially available as a soft elastic material,
The results of various tests conducted on a polishing device that uses a ring (hereinafter referred to as an elastic body interposed device) and a device that does not use a ring (hereinafter referred to as a sliding type device) are shown below.

First, we pressed the spherical surface of the spherical bearing with our hands and grasped the operating resistance of the spherical bearing with our hands.As a result, we found that with a sliding type device, intermittent movement was felt and there was a feeling of catching, whereas with an elastic body Smooth movement was felt with the interventional device. In addition, as a result of calculating the slipping rotation rate defined by the following formula = plate rotation speed / surface plate rotation speed x 100 (%) for both devices, the value for the sliding type device is 36%. In contrast, the rate for the elastic body-mediated device was 89%. Incidentally, as the spherical bearing approaches the ideal state, the number of rotations of the plate approaches the number of rotations of the surface plate, and the value of the rotation rate becomes higher. In the elastic body-interposed type, the resistance of the bearing is significantly reduced by using an O-ring, so that the number of rotations of the plate approaches the number of rotations of the surface plate.

When the rotation rate becomes low, the surface precision deteriorates, and the semiconductor wafer may become a spherical surface with a convex center. Therefore, lowering the bearing resistance and increasing the rolling rate is effective in making the polishing amount of the semiconductor wafer uniform.

Another effect of equalizing the polishing amount on the semiconductor wafer surface due to the reduction in bearing resistance will be explained.

In an ideal situation, the surface plate and plate are parallel and in close contact, but the abrasive cloth attached to the surface plate may not be affixed evenly to the surface plate, or the abrasive cloth itself may be too thick. The plate may not be in close contact with the surface plate partially due to uneven surfaces or the bottom portion is worn out as the polishing process progresses, resulting in a loss of parallelism. In such a situation, the load applied to the plate from the polishing shaft is resolved by the plate's own weight, but with sliding type devices, it is difficult to quickly adjust the posture due to the friction of the sliding surface, and this often occurs. This results in non-uniformity in the polishing amount of semiconductor wafers.

However, as mentioned above, in an elastic body-interposed device, for example, when an O-ring is used, the resistance of the bearing is significantly reduced, so the attitude adjustment of the plate is performed extremely quickly, and the plate is always positioned slightly above the surface plate. Despite the unevenness of the plate, it adheres closely to this, and the parallelism of the plate to the surface plate is safely maintained. As a result, the uniformity of the polishing amount of the semiconductor wafer is significantly improved. On the other hand, in the case of a sliding type device, uneven polishing may be performed such that the polishing allowance of the semiconductor wafer is 5 μm on one side of the diameter and 15 μm on the other.

In FIG. 5, i and j are elastic body interposed devices;
g and h indicate actual measured values of the polishing amount of a semiconductor wafer in the case of a sliding type device without an elastic body such as an O-ring.

Incidentally, the present invention can also be applied to a polishing apparatus of a type that applies a dead load W ₀ as shown in FIG.
In addition, considering that machining of spherical bearings is difficult and that the working distance of spherical bearings is actually very short, the parallelism maintaining mechanism 10 is constructed of cones that fit into each other as shown in FIG. Consists of a conical bearing 30 composed of a concave surface 30a and a conical convex surface 30b,
The conical uneven surfaces 30a and 30b of the conical bearing 30
A soft elastic body 21 may be interposed between them. Furthermore,
Although a semiconductor wafer has been specifically discussed as the object to be polished, the apparatus of the present invention can of course be applied to an apparatus for processing any other object to be polished.

(Effects of the Invention) As is clear from the above description, according to the present invention, a parallelism maintaining mechanism is provided that positions the operating center of the plate of the polishing device on the polishing surface, so that the moment that tends to tilt the plate is constantly suppressed. Despite the frictional force acting on the polished surface,
The parallelism between the plate and the surface plate can be strictly maintained, thereby achieving the effect that polishing with high parallelism and high flatness can be performed.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal cross-sectional view of a polishing apparatus according to the present invention, Fig. 2 is a graph showing the actual measurement results of the flatness of the surface of a semiconductor wafer polished by the same polishing apparatus, and Fig. 3 is a diagram showing a modified embodiment of the present invention. A partially cutaway side view of such a polishing device, FIG. 4 is a diagram showing the relationship between force applied to a soft elastic body and displacement, and FIG. 5 is a polishing amount of a semiconductor wafer polished by the polishing device shown in FIG. 3. FIGS. 6 and 7 are longitudinal cross-sectional views showing another embodiment of the present invention, FIG. 8 is a diagram explaining the principle of polishing using a polishing device, and FIGS. 9 to 12 The figure shows conventional examples of various mechanisms for maintaining parallelism between the surface plate and the plate. 1...Surface plate, 2...Abrasive cloth, 3...Shaft, 4...
Plate, 10... Parallelism maintenance mechanism, 14, 15
...Block, 14a...Spherical concave seat, 15a...
... Spherical seat, 21 ... Soft elastic body, 30 ... Conical bearing.

Claims (1)

[Claims] 1. The object to be polished, which is held on a tiltable plate, is pressed with a predetermined force onto an abrasive cloth attached to a surface plate that rotates at a predetermined speed. In a polishing device designed to mirror-polish a surface,
The plate is supported by a shaft vertically disposed above the surface plate via a parallelism maintaining mechanism, and the tilting center of the parallelism maintaining mechanism is positioned on the contact surface between the object to be polished and the polishing cloth. A polishing device characterized in that it includes a spherical bearing. 2. The polishing device according to claim 1, wherein the spherical bearing has a concave-convex seat made of a concave-convex spherical surface whose center of curvature is located on the contact surface between the object to be polished and the polishing cloth. . 3. The polishing device according to claim 2, wherein a soft elastic body such as rubber is interposed between the uneven surface seats. 4. The polishing device according to claim 3, wherein the soft elastic body is constituted by an O-ring.