JP2006082139A - Dry polishing device and dry polish method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To implement a dry polishing device which can exert pressurization by itself ranging from an ultra-low pressure of 80 g/cm<SP>2</SP>to a high pressure of 1,500 g/cm<SP>2</SP>. <P>SOLUTION: The dry polishing device functions to polish a workpiece by rotating a polishing plate on a polishing device base by using oxide powder as abrasive grain, and is formed of an adsorbing head 16 for holding the workpiece, a ball spline 17 for vertically moving the adsorbing head 16, an air cylinder 18 for pressurizing the workpiece via the ball spline 17, a floating unit 23 for achieving floating bonding between the ball spline 17 and the air cylinder 18, and a motor for applying a rotary driving force to the ball spline 17 via a belt. Then the air cylinder 18 is arranged on the polishing base so as to be erect from the center of the workpiece. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a dry polishing apparatus and a dry polishing method in which a powder of diamond, oxide, or the like in a polishing method for a semiconductor wafer or the like is used as abrasive grains.

  As a surface polishing method for a relatively soft semiconductor substrate such as single crystal silicon, a CMP polishing method using a colloidal silica slurry is widely known. CMP is an abbreviation for chemical mechanical polishing and is a polishing method that literally uses both a chemical action and a mechanical action. The general CMP process is divided into primary and secondary polishing, which is a rough process, and tertiary polishing, which is a finishing process. In rough polishing, a polyester nonwoven fabric or foamed urethane polishing cloth and colloidal silica with a pH of about 11 Using slurry, it is processed mainly with emphasis on shape accuracy.

On the other hand, finish polishing is processed using a suede-type polishing cloth with a foam surface and a colloidal silica slurry to which amine or the like that suppresses the occurrence of microwaviness is added, and the process emphasizes surface roughness and surface cleanliness. It has been. However, in the surface polishing of a compound semiconductor such as silicon carbide having a high Mohs hardness of 7 or more, chemical action and mechanical action in CMP are difficult to occur on the workpiece. The MCP method using the mechanochemical polishing phenomenon is used. The mechanochemical polishing phenomenon is a phenomenon in which a chemical reaction or a phase transformation is induced or promoted by a mechanical stress acting on a contact point between solids. That is, it is a polishing method characterized by using a powder that is scientifically softer than the workpiece as the abrasive grain and that can cause a chemical reaction with the workpiece.・ It is said that processing proceeds by removing the minute reaction layer that occurs instantaneously at high pressure by frictional force. However, there is no specific report on what kind of abrasive grains is used and how much polishing pressure is applied to advance the processing. (See Non-Patent Document 1)
As one of the factors that determine the processing speed and accuracy in CMP and MCP, the processing pressure is raised, and as the pressurization method, the following methods are known. There are devices using a dead weight method and a method using fluid pressurization, and a method using both a dead weight method and a fluid pressurization method. The dead weight method is a simple method in which a weight is placed on the workpiece and pressed as shown in FIG. 7, and the pressure is adjusted by increasing or decreasing the weight of the weight to be placed.

  Next, a method using fluid pressurization is employed. In the air cylinder that can be said to be a representative example of the fluid pressurization method shown in FIG. 8, an air cylinder that is replaced with a dead weight type weight is disposed above the workpiece. It has a structure.

Further, as disclosed in Japanese Patent Laid-Open No. 9-38856, in the method using both the dead weight method and the fluid pressurization method, the head weight is resisted in a state where the pressure of the head's own weight is applied from above the workpiece. Then, it is pushed upward by an air cylinder so that a pressing force from above according to the difference between the head weight and the thrust of the air cylinder is applied to the workpiece. (See Patent Document 1)
Yoshiaki Matsushita, 3 others, "Ultra-precision wafer surface control technology", Science Forum, February 28, 2002, 1st edition, p.205, 214-215 Japanese Patent Laid-Open No. 9-38856

In the above-described polishing with a hard material such as silicon carbide, a high pressure of 1500 g / cm ² or more is required in a rough process where it is desired to increase the processing rate, and in a finishing process where surface accuracy is to be improved, 100 g / cm ² is required. The following low pressure is required. Based on this, the following problems are expected when the above-described pressurization method is considered.
First, in the dead weight system, it is necessary to manually replace the weight, and the weight is increased when the pressure is high, and the weight is decreased when the pressure is low. The biggest problem with this method is that a very large weight is required at high pressure. For example, a weight of about 30 kg is required to obtain a surface pressure of 1500 g / cm ² for a 2-inch wafer. Simply, when a weight of 30 kg is produced in the area of a 2-inch wafer with mild steel, a weight with a height of 188 mm is required, and it is difficult to balance the pressure on the workpiece, which is practically impossible.

Next, there is a method using fluid pressurization. If an air cylinder necessary for obtaining a surface pressure of 1500 g / cm ² is considered, when the head weight is 1 kg, the air cylinder has about 29 kgf. Thrust is required. Since the supply air pressure at the factory is about 0.5 MPa, the inner diameter of the cylinder is considered to be equivalent to 40 mm. The thrust when the rated minimum air supply source air pressure of 0.2 MPa is supplied to the air cylinder is about 13 kgf. In this case, even if the head's own weight of 1 kg is ignored, the surface pressure on the workpiece becomes 600 g / cm ² or more, and the surface pressure of 100 g / cm ² or less cannot be dealt with at all.

  Finally, a dead weight method and a method using fluid pressurization are shown. FIG. 9 shows a simplified apparatus configuration for this method. A holder 2 that holds the workpiece 1 and a head 4 that supports the holder 2 above the polishing surface plate 3 are provided. The head 4 is combined with a plate-like member 5, and a moving mechanism 6 in the vertical direction is provided. Is provided. Further, an air cylinder 7 is arranged as a pressurizing control mechanism that can urge the head 4 upward against its own weight.

  That is, the air cylinder 7 adjusts the differential pressure between the pressure to be actually pressed and the pressure applied by the head's own weight. More specifically, assuming that the head's own weight is 20 kg and the load that is originally required for the work 1 is 10 kg, the pressure applied to the air cylinder 7 in the direction against the own weight is 10 kg. Become. That is, low pressurization is realized by giving a differential pressure between its own weight and the drag force of the air cylinder 7 to the workpiece.

When high pressurization is required, it is necessary to increase the head's own weight, so it can be predicted that the same problem as the deadweight method described above will occur, but if the fluid pressurization method is used instead of the deadweight method, It can be predicted that improvement is possible. This device configuration can theoretically handle from high pressures of 1500 g / cm ² to low pressures of 100 g / cm ² or less, but the balance of the device configuration is very poor due to the relationship between power point and action point. It can be predicted that the processing accuracy will be greatly affected. Specifically, when the center of gravity of the entire head is considered, it can be predicted that the center of gravity is not on the axis extending upward from the center point of the workpiece and is on the moving mechanism 6 side. It is necessary to compensate for this misalignment by the moving mechanism 6. However, when the head load reaches about 30 kg, it is difficult to compensate completely, and it is predicted that the pressure applied to the workpiece is also biased toward the holder side. The In addition, when the load is low, it is necessary to apply an upward force to resist this pressurization. However, in the case of this device configuration, it is not possible to pressurize coaxially with the pressure from the upper side. A cylinder is arranged, and in this case, the pressure applied to the workpiece is expected to be biased to the opposite side of the holder.

In order to solve the conventional problems, a dry polishing apparatus of the present invention is a dry polishing apparatus that rotates a polishing plate on a polishing apparatus base and polishes a workpiece using oxide powder as abrasive grains. A suction head for holding a workpiece, a ball spline for moving the suction head up and down, an air cylinder for pressurizing the workpiece through the ball spline, and floating joining the ball spline and the air cylinder A floating unit, a motor for applying a rotational driving force to the ball spline via a belt,
And the air cylinder is arranged vertically from the center of the workpiece on the polishing base.

  The dry polishing method of the present invention is a dry polishing method for polishing a workpiece by rotating a polishing plate on a polishing apparatus base and using oxide powder as abrasive grains, and a suction head for holding the workpiece. A ball spline for moving the suction head up and down, an air cylinder for pressurizing a workpiece through the ball spline, a floating unit for floatingly joining the ball spline and the air cylinder, and the ball A motor for applying a rotational driving force to the spline via a belt, and the air cylinder is arranged vertically from the center of the workpiece on the polishing base, and a direction of introducing compressed air to the air cylinder And controlling the suction head to pressurize the suction head in the downward and upward directions. A.

  According to the dry polishing apparatus of the present invention, it is possible to consistently realize from the roughing process to the finishing process only by changing the processing pressure without changing the grain size of the abrasive grains and the polishing plate.

  Hereinafter, embodiments of the dry polishing apparatus of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a pressure mechanism diagram in the dry polishing apparatus of Example 1 of the present invention. The suction head 16 is made of a porous metal and can uniformly hold the back surface of the workpiece 15 by suction. The suction mechanism is connected to the ball spline 17 via an air tube 27 extending from the suction head 16 and is drawn into a vacuum pump (not shown) attached to the outside through the air tube 25. It has become. The shaft center of the ball spline 17 is hollow in order to be used as a path for this adsorption air. That is, the air tube 27 connects the suction head 16 and the ball spline 17, and the air tube 25 connects the ball spline 17 and the vacuum pump. That is, the unloading operation of the suction head 16 is performed by the air tube 25 and the air tube 27.

  Further, the ball spline 17 is slid up and down in the bush 19, so that a loading operation for pressing the suction head 16 against the polishing plate 22 and an unloading operation for lifting the suction head 16 can be performed smoothly. An air cylinder 18 is connected to the upper end of the ball spline 17 via a floating unit 23. When the air cylinder 18 moves up and down, the loading and unloading operations of the suction head 16 to the polishing plate 22, and The pressure application to the polishing plate 22 can be performed smoothly. Further, the ball spline 17 is a mechanism capable of rotating through the rotational movement of the motor 20 via the timing belt 21.

The air cylinder 18 is 40 kg which is a thrust required to realize 1500 g / cm ² which is a processing pressure necessary for processing this 2 inch size silicon carbide.
In order to obtain f, a cylinder with an inner diameter of 40 mm was selected. The pressure of the air cylinder is transmitted to the workpiece 15 via the ball spline 17, and the workpiece 15 is pressed against the polishing plate 22. It has been found that the polishing plate 22 is preferably hard to cause a mechanochemical phenomenon, and this time, a cast iron plate was used. The polishing plate 22 has a rotatable structure, and was processed by rotating at about 50 rpm, which is equivalent to the head.

  Further, the air cylinder 18 as a pressurizing unit is on an axis extending vertically upward from the center point of the work piece so that an unbalanced load is not generated on the work piece during both high pressurization and low pressurization. Arranged. Furthermore, regarding the drag mechanism from below required for realizing low pressurization, it is physically impossible to arrange them on the same axis. In the present invention, the air cylinder 18 is not loaded or pressurized. By operating in the opposite direction, that is, in the direction of pulling up the suction head 16, the weight of the head 16 and the ball spline 17 is reduced and low pressurization is realized. That is, low pressurization is realized by applying an upward biasing force.

  More specifically, the case of creating a high pressure state will be described with reference to FIG. 2, which is a schematic diagram of the air cylinder 18 of FIG. In FIG. 2A, air is supplied from the B port and air in the cylinder is discharged from the A port, so that the ball spline 17 and the suction head 16 connected to the cylinder rod 50 are moved down to the polishing plate 22. A pressed state, which is a pressed state, is created.

  Also, in order to create a low pressure state contrary to the above, as shown in FIG. 2B, a fixed amount of air is supplied from the A port and the air in the cylinder is discharged from the B port. Although the cylinder rod 50 is going to rise, the pulling thrust is set smaller than the combined load of the suction head 16 and the ball spline 17, and the head 16 and the ball spline 17 cannot be lifted. In other words, the pressure that presses the workpiece 15 against the polishing plate 22 is reduced. Such an operation principle enables a low pressure state.

The weight of the suction head and ball spline in this equipment is about 2.6 kg, the pressure on the workpiece by only its own weight is about 130 g / cm ² , and air from the supply source of about 0.2 MPa is discharged from the cylinder. A high pressure of 1500 g / cm 2 was achieved by supplying to the side, and a low pressure of 80 g / cm ² was achieved by supplying air from a supply source of about 0.02 MPa to the cylinder return side. In addition, the air cylinder 18 not only controls the air pressure on the outlet side and the return side, but also needs to play a role of loading / unloading the work piece. ), (B), and (c) as shown in FIG.

  In FIG. 3A, a sequence during loading and high pressurization will be described. In the case of a loading operation in which the workpiece 15 is pressed onto the polishing plate 22, the compressed air supplied from the air supply source 36 enters the precision regulator 35 and is supplied to the B port of the air cylinder 18 via the electromagnetic valve 34. . As a result, the cylinder rod 50 in the air cylinder 18 is pushed out in the direction of pressing against the polishing plate 22. The operation mechanism of the air cylinder 18 is very simple. The cylinder rod 50 is pushed out toward the side opposite to the port through which air enters, and the air is discharged from the port on the side to be pushed out. That is, in the loading operation in which the suction head 16 is pressed against the polishing plate 22, air is supplied from the B port of the air cylinder 18, and air is simultaneously discharged from the opposite A port. The air discharged from the A port is guided to the electromagnetic valve 33 while adjusting the discharge amount by the speed controller 32, that is, adjusting the air discharge amount to adjust the speed of the cylinder pushing operation. By controlling the amount of air discharged by the speed controller 32, loading onto the polishing plate 22 is performed slowly, and it is possible to prevent the suction head 16 and the polishing plate 22 from colliding violently and damaging each other.

  Then, in order to shift to the high pressure mode, the precision regulator 35 is pressurized to a predetermined amount of air in a state where loading is completed, that is, in a state where the suction head 16 and the polishing plate 22 are in contact with their own weight. Adjust it.

Next, the sequence in the low pressure mode will be described with reference to FIG. By switching the switch for controlling the air supply direction of the electromagnetic valve 34, the air supplied to the B port of the air cylinder 18 is shut off. Further, since the air supply direction is switched by the electromagnetic valve 34, the air is guided to the A port of the air cylinder 18 through the path to the electromagnetic valve 33. As a result, the cylinder rod 50 in the air cylinder 18 moves in a direction in which the workpiece is pulled up from the polishing plate 22. To explain with a specific example, the suction head 16 and the ball spline 17 of this time have a weight of about 2.6 kg, and 1.6 kg (80 g) when the air amount is adjusted so that the pulling force of the air cylinder 18 becomes 1 kg. / cm ² ).

Next, the unloading sequence is as shown in FIG. 3 (c). As shown in FIG. 3 (c), the electromagnetic valve 34 is switched in the same manner as in the reduced pressure mode, and the electromagnetic valve is shut off from the air entering the cylinder B port. 33 is switched, and the air supplied via the precision regulator 35 is shut off. The compressed air is supplied from the air supply source 36 to the A port of the cylinder 18 with the air discharge amount controlled via the speed controller 32. In other words, the air pressure from the air supply source 36 is supplied directly to the A port of the air cylinder 18 without being reduced by the precision regulator 35 as in the case of low pressurization, and is generally not attenuated. Is 0.5 MPa, the lifting thrust exerted by the air cylinder 18 is about 550 N about −56 kg (2800 g / cm ² ) from the cylinder thrust table (not shown), and the workpiece 15 is pulled up from the polishing plate 22. It will be. That is, unloading is performed.

  4 and 5 show the results of measuring the pressure actually applied to the workpiece using this pneumatic control system. FIG. 4 shows the relationship between the supply air pressure at the time of low pressurization and the pressure applied to the workpiece, and FIG. 5 shows that at the time of high pressurization. It can be seen that the pressurization of the workpiece smoothly changes with respect to the supply air pressure at both the low pressurization and the high pressurization.

It is the result of having performed the grinding | polishing experiment of a 2-inch polycrystalline silicon carbide board | substrate using the grinding | polishing apparatus manufactured based on this invention. A chromium oxide powder having a particle diameter of 2 μm was used as the abrasive grains, and cast iron was used for the polishing plate. In the case of normal mechanical polishing, the processing rate W can be empirically expressed by the following equation. W = f · v · t Here, f is the product of the friction coefficient μ between the workpiece and abrasive grains and the processing pressure p, and v and t are the relative sliding speed and time. That is, the processing pressure and the processing rate are in a proportional relationship. However, as can be seen from FIG. 6 as a result of this experiment, the processing rate is rapidly increased by setting the processing pressure to 1500 g / cm ² . This rapid increase phenomenon is not due to the mechanical action, but it is considered that the mechano polishing phenomenon described above, that is, the solid-phase reaction is intensified with this pressure as a boundary. Further, it can be said that the processing rate and the surface roughness Ra are in a trade-off relationship with respect to the change of the processing pressure. As a result, in order to remove the work-affected layer generated in the previous process of the slicing process, in the roughing process, polishing is quickly performed at a high pressure of 1500 g / cm ² , and in a finishing process that requires processing accuracy. It is possible to improve the processing accuracy by reducing the polishing pressure to 100 g / cm ² or less.

The dry polishing apparatus according to the present invention enables consistent polishing from the roughing process to the finishing process by changing the processing pressure without changing the grain size of the abrasive grains and the polishing plate, and increases the processing rate. A pressurizing mechanism for applying high pressure that is not used in ordinary polishing of 1500 g / cm ² required for the process and an ultra-low pressurization of 80 g / cm ² that is used in the stage of improving the surface roughness. It is useful as semiconductor surface polishing.

1 is an overall configuration diagram of a dry polishing apparatus in Embodiment 1 of the present invention. The schematic diagram of the air cylinder of the dry-type polishing apparatus in Example 1 of this invention The figure for demonstrating the pressurization sequence of the dry-type grinding | polishing apparatus in Example 1 of this invention. The figure which shows the pressurization change of the low pressurization mode of the dry-type polishing apparatus in Example 2 of this invention. The figure which shows the pressurization change of the high pressurization mode of the dry-type polishing apparatus in Example 2 of this invention. The figure which shows the relationship between the processing rate and surface average roughness of the dry-type polishing apparatus in Example 3 of this invention Overall configuration diagram of a conventional deadweight polishing machine Overall configuration diagram of conventional fluid pressurization polishing machine Main part configuration diagram of conventional polishing equipment

Explanation of symbols

1 Work
2 Holder 3 Polishing surface plate 4 Head 5 Plate-like member 6 Moving mechanism 7 Air cylinder 15 Workpiece 16 Adsorption head 17 Ball spline 18 Air cylinder 19 Bush 20 Motor 21 Timing belt 22 Polishing plate 23 Floating unit 24 Joint 25 Air tube 26 Fitting 27 Air tube 32 Speed controller 33 Solenoid valve 34 Solenoid valve 35 Precision regulator 36 Air supply source 50 Cylinder rod

Claims (7)

A dry polishing apparatus for rotating a polishing plate on a polishing apparatus base to polish a workpiece using oxide powder as abrasive grains,
A suction head for holding the workpiece;
A ball spline for moving the suction head up and down;
An air cylinder for pressurizing the workpiece through the ball spline;
A floating unit for floatingly joining the ball spline and the air cylinder;
A motor for applying a rotational driving force to the ball spline via a belt;
A dry polishing apparatus, wherein the air cylinder is arranged vertically from the center of the workpiece on the polishing base. By energizing the pressure based on the weight of the suction head and the ball spline and the compressed air of the air cylinder, the processing pressure applied to the workpiece is set in the range of 1500 g / cm ² to 80 g / cm ^2. The dry polishing apparatus according to claim 1, wherein: The pressure direction of the air cylinder is urged in a direction to press the workpiece against the polishing plate at a high pressure, and urged in a direction to pull up the workpiece from the polishing plate at a low pressure, 2. The dry polishing apparatus according to claim 1, wherein a difference between the pressurization and the weight of the suction head and the ball spline is pressurized. A loading operation for pressing the suction head against the polishing plate by urging in the pressurizing direction at the time of the low pressurization and an unloading operation for lifting the suction head from the polishing plate are performed. The dry polishing apparatus according to claim 1. Pressure during the loading operation, downward 1.6Kg (80g / ^cm 2), the pressure during the unloading operation, to claim 1, characterized in that the upward 56Kg (2800g / cm ²⁾ The dry polishing apparatus described. A dry polishing method for polishing a workpiece by rotating a polishing plate on a polishing apparatus base and using oxide powder as abrasive grains,
A suction head for holding the workpiece;
A ball spline for moving the suction head up and down;
An air cylinder for pressurizing the workpiece through the ball spline;
A floating unit for floatingly joining the ball spline and the air cylinder;
A motor for applying a rotational driving force to the ball spline via a belt;
The air cylinder is arranged vertically from the center of the workpiece on the polishing base, and the direction of compressed air introduced into the air cylinder is controlled so that the suction head is in a downward direction and an upward direction. A dry polishing method characterized by pressurizing and energizing. By energizing the pressure based on the weight of the suction head and the ball spline and the compressed air of the air cylinder, the processing pressure applied to the workpiece is set in the range of 1500 g / cm ² to 80 g / cm ^2. The dry polishing method according to claim 6, wherein:

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