Grinding and Polishing Machine

Abstract

To provide a grinding device that can process wafers (materials to be polished), plates, etc. with high parallelism, low flatness, and minimal surface irregularities by eliminating the eccentricity of the rotating shaft that occurs when the device rotates and to which the tool and material to be polished are attached, thereby eliminating vibration of the rotating body and enabling the flatness required for high yield. [Solution] The grinding device is combined with a balance unit 14 and a wafer holder 12, and is set so that the rotation axis 15 and plate 13 intersect at a right angle in a dynamic vertical state. This grinding device is equipped with passive, automatic balancing technology and has a rotation axis with low vibration. It reduces the vibration of the rotation axis using a dynamic method, passive technology, which is inexpensive to manufacture, has a simple structure, and is easy to manufacture. It is configured with what is called passive equilibrium point automatic tracking type balancing technology.

Description

[Technical Field]

[0001] This invention relates to an improvement of a grinding and polishing machine for wafer processing. [Background technology]

[0002] With the development of semiconductor technology, there is a need for higher density and finer processing, which in turn requires highly flat processing surfaces.

[0003] The conventional purposes of planarization include element isolation, planarization of interfacial insulating films, formation of metal wiring (damascene method), formation of shallow trench isolation (STI), hybrid bonding (Cu-Cu direct bonding), and improvement of processing quality of gates, connections, etc.

[0004] Conventional flattening relies on the skill of skilled technicians, and the reason for this is the eccentricity, vibration, and wobble of the rotating shaft of the equipment used, namely the wafer processing grinding and polishing machine.

[0005] The cause of eccentricity is that the spindle (motor, electric motor, etc.) used is made up of multiple parts, which are combined into a device. Assembling parts that have design tolerances results in an accumulation of errors. It is virtually impossible to align the inertial rotation axis (rotation axis affected by the center of gravity) caused by eccentricity with the geometric rotation axis (rotation axis in design).

[0006] In a typical grinding and polishing machine, the workpiece or processing tool is attached to the tip of the rotating shaft. For example, in the vertical grinding and polishing machine shown in Figure 1, the polishing tool is at the tip and the workpiece (wafer) is on the plate. When the rotating shaft is tilted, the contact force between the workpiece and the polishing tool becomes uneven, complicating the flow state of the abrasive liquid. In the uneven tip area of ​​the polishing tool caused by the tilt, pressure is concentrated in one area of ​​the wafer (workpiece), resulting in height variations on the surface.

[0007] Additionally, most rotating shafts on which wafer processing grinding and polishing tools or workpieces are attached use ball bearings or metal bearings to secure the rotating shaft. For these to rotate, a space called operating clearance (internal clearance of the bearing) is required between the rotating shaft and the bearing. The latest magnetic bearings and air bearings also have operating clearance.

[0008] Due to this structure, it has long been known that conventional rotating shafts have a planetary motion (whirling), but also a mixture of irregular rotation and conical whirling motion. Therefore, when rotating, they are in a non-parallel, non-contact state, as shown in Figure 1. For example, in the specifications of polishing machines currently in use, the wafer (polished material) and wafer holder are attached to the tip of the rotating shaft, and are set so that they come into perpendicular contact with the plate containing the polishing tool (PC).

[0009] In other words, the polishing process is carried out on the assumption that the rotating shaft to which the polishing tool is attached intersects the wafer at a right angle. When observing the dynamic state of the rotating shaft, it rotates eccentrically as shown in the lower diagram of Figure 1.

[0010] For example, in Figure 1, if a stationary spindle is rotated and the eccentricity is 10 μm, then in the case of a polishing tool 4 with a radius of 150 mm, a height difference of 5 μm will occur between the edge of polishing tool 4 and the surface of wafer 5. To avoid the effects of conical rotation, it is necessary to at least rotate the shaft and adjust it so that the geometric rotation axis 15 and the inertial rotation axis 3 coincide.

[0011] Furthermore, for high 3D integration, skilled technicians correct and adjust the processed surface to a usable flatness. As wafer materials change, it is necessary to respond to the diversification of friction pressure applied to the wafer, rotation speed of the polishing tool, and polishing materials. To maintain quality, even unskilled technicians need specifications that allow polishing in a dynamic state during the polishing process. [Prior art documents] [Non-patent literature]

[0012] [Non-Patent Document 1] Home Page: Possibility of Practical Use of "Passive Auto-Balancing Technology" 2019, 09, 17<URL:https: / / autobalancing.web.fc2.com> [Non-patent document 2] Home Page:Passive type Auto balancing System with auto Trucking Balancing Point mounting, 2024.7.14<URL:https: / / autobalancing3.web.fc2.com> Summary of the Invention [Problem to be solved by the invention]

[0013] As the industry has developed, semiconductor materials have also changed, and ever-increasing density has become necessary to reduce the width of wiring and achieve advanced multi-layer integration.

[0014] To achieve high yields and low production costs, it is necessary to reduce the working hours of skilled workers. At the same time, it is also necessary to make it possible for unskilled technicians to perform the work. This was developed using polishing machine technology that eliminates the eccentricity of the tip of the rotating shaft, eliminates vibration of the rotating body, and eliminates vibration of the polishing tool, making it possible to process surfaces with low flatness and surface irregularities. [Means for solving the problem]

[0015] We will manufacture a polishing machine equipped with the passive, self-balancing technology described below and with a rotating shaft that generates little vibration.

[0016] The new technology required is to prepare a rotating shaft that does not rotate eccentrically or vibrate, and then to set this rotating shaft vertically.

[0017] The rotational speed of a rotating shaft commonly used in the past is generally between 0 < conventional operating speed ω < ωC. When a critical speed ωC is encountered, self-centering action and gyroscopic action are used as vibration reduction methods. To eliminate this shaking, the technique of attaching a compensating weight to the opposite side of the center of gravity has long been known as a static solution, but it is well known that this method does not actually eliminate shaking.

[0018] There are dynamic methods that can be used to address this issue, and although active methods are available, they are expensive and require complex control, so they should be avoided if possible. Passive technology is the most desirable method for reducing vibrations in the rotating shaft, as it is inexpensive to manufacture, has a simple structure, and is easily manufactured. The physical phenomenon used in this invention has been known for over 100 years.

[0019] The mechanism by which this system works is an eccentrically rotating shaft, i.e., a whirling rotation, and some ingenuity is required for this shaft.

[0020] A balancing structure was devised for the rotating shaft, and a patent utilizing this physical phenomenon was granted around 1870. Since then, many researchers have published various papers on the practical application of passive, fully automated mechanisms, and most recently, around 1945, E.L. Thearle presented a basic shape that he believed could be put to practical use.

[0021] The key technology required to put this physical phenomenon into practical use is the technology to passively and fully automatically set the balancer (moving body) to the optimal position. This technology is called passive automatic balance point tracking balancing technology.

[0022] This physical phenomenon can be simply outlined as shown in Figure 2 by EL. Thearle. It consists of three elements: the steel balls of the balancer, the eccentric container, and the flexible rotating shaft that holds the container (an elastic body such as a spring that has a restoring force).

[0023] To explain the movement of the physical phenomenon we will use, if the container has an eccentric center of gravity, an imbalance will occur as it rotates. This will cause the entire container to whirl. At this time, centrifugal force is generated on the balls in the container. The balls will move in a straight line on the opposite side of the center of gravity due to the resultant force P of the centrifugal force and the drag force toward the central axis of rotation, and the tangential force of this force.

[0024] When the balls reach a position where the resultant centrifugal force acting on the balls and the centrifugal force acting on the center of gravity are balanced, the tangential force P acting on the balls becomes zero, and the balls come to a halt. After that, they maintain stable rotation. This much has been solved through past research; the only remaining challenge is the technology to set the balls in the designated positions.

[0025] When the balls start to rotate, they need to move to the optimal position and stop. To achieve this, we set up a separation wall that divides the balls into two locations, as shown in Figure 3 of the basic structure.

[0026] In the standard functional configuration, balls with masses equal to the centrifugal force generated when the center of gravity is shifted by the container during rotation are placed in two chambers. This means that the centrifugal forces in three directions are equal. The process of moving to the optimal position is as shown in Figure 4, starting from the top left and resulting in stable rotation as shown in the bottom right. A balancing load may be added to adjust the centrifugal force. In theory, the space between the ball and the adjusting load is opened 120 degrees, stopping vibration. In other words, the flexible shaft 7., a material with the restoring force (elasticity) that supports the container, rotates around the inertial rotation axis 3., but once stable, it stabilizes around the geometric rotation axis 15.

[0027] The position of the dividing wall that divides the balls into two parts is determined by the purpose of the product and controls the movement of the balls. In this invention, the dividing wall position shown in Figure 4 is considered appropriate.

[0028] The fully automatic balancing device explained above is combined with a wafer holder (which has already been developed by the company that produces wafer polishers) as shown in Figure 6, and is set up so that the rotating shaft moves and intersects Plate 13 at a right angle. Naturally, the wafer holder does not shake, so it rotates parallel to and in close contact with Plate 13. The technology for installing the rotating shaft so that it intersects Plate 13 at a right angle is still in use today, so there is no need to explain it again.

[0029] There are spindles that use magnetic bearings in combination with conventional bearings, for example. [Effects of the Invention]

[0030] ·Spindle vibration is eliminated by aligning the geometric rotation axis with the dynamic inertial rotation axis. - The flatness is reduced, allowing for high-precision circuit production. - Improved 3D stacking accuracy leads to improved yields. - The tilt angle between the workpiece (wafer, etc.) and the processing tool is almost eliminated, making it easy to adjust the parallelism This allows unskilled workers to participate in production. [Brief explanation of the drawings]

[0031] [Figure 1] A front view showing the dynamic state of a rotating shaft with a grinding tool attached. [Figure 2] Functional diagram of a physical phenomenon shown by El. Thearle. [Figure 3] A perspective view showing the structure of the proposed auto-balancer [Figure 4] Flow diagram showing the behavior of the proposed auto-balancer (perspective view) [Figure 5] Wafer polishing tool configuration [Figure 6] Diagram showing the bearing structure of the proposed polishing / grinding machine [Figure 7] The internal state of the balancer in Figure 6 [Figure 8] A pendulum-shaped weight that engages with the main shaft of a polishing or grinding machine. DETAILED DESCRIPTION OF THE INVENTION

[0032] An embodiment of this invention is assembled as shown in Figure 7. The purpose of this automatic balancing system is to install it on a conventional grinding / polishing machine to prevent the rotating part from shaking. The system functions by interfering with the damper, rotating shaft, and balancer NIT 14. This outline shows passive automatic balancing technology. The rotating part, or spindle, is assembled around the electric motor 20. The upper part is equipped with a unit 26., which is required for adjusting the geometric rotation axis up and down and for setting the center of the geometric rotation axis. A bearing unit 17 is also provided to handle the thrust received by the rotating shaft. A coupling 25 is attached to the lower part, sandwiching the electric motor 20. Below this is the balancer unit 14., the heart of the system, and unit 12., which contains the equipment related to polishing and grinding, attached closely to this unit. This spindle is fixed to the spindle motor mounting frame 18 using a damper with a restoring force such as a coil spring 19. The spindle is adjusted so that the rotation axis generated during rotation intersects with the wafer and the plate (flat plate on which the polishing tool is placed) 13 at right angles. The most important element of this equipment is that the three components, for example, the machine's Plate 13, the object to be polished (such as a wafer), and the polishing tool, are set in the required state and set up to operate.

[0033] To bring the wafer into parallel contact with the polishing tool, a technique is required to rotate the shaft while aligning the vertical axis with the geometric rotation axis 15., which intersects the wafer at a right angle. Fine adjustments are made using a balancer unit 14. equipped with passive automatic balance point tracking balancing technology and a geometric rotation axis position adjustment unit 26.

[0034] When mounted, the contact surface can be imagined as shown in Figures 2 and 6. A highly parallel state occurs when the dynamic vertical axis coincides with the geometric rotation axis that intersects the wafer at a right angle. This eliminates the problem of polishing torque caused by tilting or eccentricity of the rotation axis as shown in Figure 1, and the contact force becomes uniform, simplifying the flow state of the grinding and abrasive fluid. With uniform friction torque, the pressure is dispersed at the tip of the polishing tool, making it smooth. [Example]

[0035] In Example 1, the heart of the balancer system is the balancer unit 14. The component diagram clearly shows the relationship between the tip of the rotating shaft on which the workpiece 5 (wafer, etc.), wafer holding unit 12, and balancer unit 14 are integrated. Inside the balancer, a balance adjustment load 10 is installed to equalize the centrifugal force in three directions. Additionally, a balancer 8 that tracks the equilibrium point is installed in each chamber formed by separation walls 11. In this example, two pendulum-type balancers (Figure 8) were used. The installation location is the rotating shaft, but it is expected to become a geometrical rotating shaft. [Explanation of symbols]

[0036] 1. Hard abrasive tools 2. Soft abrasive tools (synthetic fibers, etc.) 3. Inertial rotation axis (eccentric rotation axis) 4. Polishing tools 5. Wafer 6. Slurry (abrasives, etc.) 7. Flexible shaft (spring material, etc.) 8. Balancer (Steel ball, etc.) 9. Container (Rotor case) 10. Balance Adjustment Load 11. Separator (separation wall, etc.) 12. Wafer holder 13.Plate) 14. Balancer Unit 15. Geometric rotation axis 16. Spindle housing 17. Thrust bearing 18. Spindle mounting frame 19. Coil spring 20. Electric motor 21. Thrust bearing part 22. Radial bearings 23. Status Coil 24. Rotor 25. Coupling 26. Geometric rotation axis position adjustment UNIT 27. Ball bearings 28. Weight [Industrial Applicability]

[0037] -3D advanced multi-layer integrated LSI can be easily realized. - It allows for faster polishing, opening up the possibility of developing fixed abrasives. -There is potential for the development of metal-free liquid polishing technology. - Contributes to the development of environmentally friendly abrasives, such as those that do not require wastewater treatment. For example, porous, honeycomb-structured diamond grinding wheels can be used. -Development of high-speed spindle shaft: It can be used not only for polishing and grinding equipment but also for drilling precision holes required for printed circuit boards including semiconductors. -Highly flat, so it can be used to process solar cell components for satellites. It becomes possible to manufacture large diameter reflectors.

Claims

[Claim 1] A grinding / polishing device that uses a planetary motion (whirling) rotating body with a center of gravity separate from the axis of rotation, a freely moving weight attached to the rotating axis, and a device utilizing the physical phenomenon in which the freely moving weight automatically moves to the opposite side as the shaft rotates (called a passive equilibrium point automatic tracking balancing device), which is integrated with the workpiece or processing tool at the tip of the rotating shaft of the grinding / polishing machine and rotates, thereby suppressing tool vibration with its balancing function. Note that this includes devices in which the tool and workpiece rotate in opposite directions.

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