Method for improving shallow pit in center of silicon wafer

Abstract

The invention discloses a method for improving a shallow pit in the center of a silicon wafer, and relates to the technical field of silicon wafer polishing, and the method comprises the following steps: S1, adjusting the vertical position of an attaching suction head, and enabling the silicon wafer to be in contact with a ceramic plate in a decelerating and pressurizing stage; s2, adjusting the size of the attaching vacuum suction force, and adapting the suction force value according to the thickness of the silicon wafer; and S3, adjusting the pressurization time, and reducing the deformation of the silicon wafer. According to the invention, the vertical position of the attaching suction head is accurately improved from 33 mm to 33.2 mm, so that the accelerated descending stage is completely finished before the silicon wafer is in contact with a ceramic plate in the descending process of the suction head with the silicon wafer, and then, the equipment enters a decelerating and pressurizing stage, and at the moment, the silicon wafer is in contact with the ceramic plate stably at a slower and more controllable speed; instantaneous stress and deformation of the silicon wafer caused by high-speed collision are avoided, enough discharge time is provided for air between the silicon wafer and the waxed ceramic plate at the slow contact speed, and positive pressure formed by air sealing is avoided.

Description

Technical Field

[0001] This invention relates to the field of silicon wafer polishing technology, and more specifically to a method for improving shallow pits in the center of silicon wafers. Background Technology

[0002] During silicon wafer fabrication, polishing is required to remove minute bumps and damaged layers from the wafer surface, ensuring uniform thickness and surface smoothness, and achieving good flatness. Before polishing, the back side of the semiconductor silicon wafer must be attached to a ceramic disk. Our process uses wax attachment. In this attachment step, a reverse suction head uses vacuum pressure to generate suction on the silicon wafer, lifting the front side upwards, rotating it 180°, lowering it, and applying pressure to attach the back side of the wafer to the ceramic plate. The existing technology has the following problems:

[0003] In existing processes, the front side of the silicon wafer will undergo a certain deformation due to the influence of vacuum suction. The higher the vacuum value, the greater the deformation. At the same time, if the pressure position of the attachment head is too low, the area in the center of contact with the attachment head will also deform under the combined effect of vacuum suction. The resulting protruding deformation is removed first during silicon wafer polishing, making the silicon wafer thinner at that location. After the silicon wafer is peeled off, the stress is restored, and a shallow pit is formed in the center of that location, affecting the quality of the silicon wafer. Summary of the Invention

[0004] The present invention provides a method for improving shallow pits in the center of silicon wafers to solve the problems mentioned in the background art.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0006] A method for improving shallow pits in the center of silicon wafers includes the following steps:

[0007] S1: Adjust the up and down position of the attachment head so that the silicon wafer contacts the ceramic plate during the deceleration and pressurization phase;

[0008] S2: Adjust the vacuum suction force for attachment, and match the suction force value according to the thickness of the silicon wafer;

[0009] S3: Adjust the pressurization time to reduce silicon wafer deformation.

[0010] A further improvement to the technical solution of the present invention is that the specific method of adjusting the upper and lower positions in step S1 is to raise the upper and lower positions from 33mm to 33.2mm so that the silicon wafer contacts the ceramic plate after the accelerated descent phase is over.

[0011] A further improvement of the technical solution of the present invention is that the method of adjusting the attachment vacuum suction in step S2 is to reduce the attachment vacuum suction from 50Pa to 45Pa.

[0012] A further improvement of the technical solution of the present invention is that when processing thin silicon wafers with a thickness less than a set threshold, the attachment vacuum suction force is further reduced to 30 Pa.

[0013] A further improvement to the technical solution of the present invention is that the method of adjusting the pressurization time in step S3 is to shorten the pressurization time from 3s to 2.5s.

[0014] A further improvement of the technical solution of the present invention is that the diameter of the attachment tip is 40mm.

[0015] A further improvement of the technical solution of the present invention is that: the silicon wafer is adsorbed onto the front of the attachment head by vacuum suction during the attachment process, and is attached to the back of the ceramic plate after being flipped 180°.

[0016] A silicon wafer attachment system for implementing the method described above includes an attachment part, a control unit, and a vacuum system. The attachment part includes a liftable and flip-up attachment head for adsorbing and attaching silicon wafers. The vacuum system is connected to the attachment head and is used to provide and control the vacuum suction force required to adsorb the silicon wafers. The control unit is electrically connected to the attachment part and the vacuum system and is used to adjust the vertical position, vacuum suction force, and pressurization time.

[0017] Due to the adoption of the above technical solution, the technical progress achieved by this invention compared to the prior art is as follows:

[0018] 1. This invention provides a method for improving the shallow pit in the center of a silicon wafer. By precisely raising the vertical position of the attachment head from 33mm to 33.2mm, it ensures that the accelerated descent phase of the head carrying the silicon wafer is completely completed before the silicon wafer contacts the ceramic plate. Subsequently, the equipment enters the deceleration and pressurization phase, at which time the silicon wafer contacts the ceramic plate smoothly at a slower and more controllable speed, avoiding the instantaneous stress and deformation caused by high-speed collisions. The slow contact speed provides sufficient time for the air between the silicon wafer and the waxed ceramic plate to be expelled, preventing the air from being trapped and forming positive pressure.

[0019] 2. This invention provides a method for improving shallow pits in the center of silicon wafers. For standard thickness silicon wafers, the vacuum suction force is reduced from the conventional 50 kPa to 45 kPa. While ensuring reliable adsorption, the source of suction force that causes the silicon wafer center to bulge is directly reduced. For thinner silicon wafers, the suction force is further reduced significantly to 30 kPa, which greatly reduces adsorption deformation. For thicker silicon wafers, the suction force is maintained or slightly higher than the original level. The optimal balance is achieved between preventing deformation and ensuring process stability. While ensuring production safety, the initial deformation introduced by the vacuum adsorption step is minimized.

[0020] 3. This invention provides a method for improving shallow pits in the center of silicon wafers. By shortening the pressurization time from 3.0 seconds to 2.5 seconds, the pressurization time is reduced, which decreases the duration of the silicon wafer under mechanical pressure after being removed from vacuum suction. This limits the duration the silicon wafer is held in a non-flat deformed state, allowing the silicon wafer to release external stress more quickly and rebound more rapidly using its own elasticity to restore a free and flat state. This effectively prevents the solidification of deformation, thereby reducing the depth of the shallow pit or even completely eliminating it. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the method flow of the structure of the present invention;

[0022] Figure 2 This is a schematic diagram of the process flow of the structure of the present invention;

[0023] Figure 3 This is a schematic diagram of the silicon wafer orientation of the structure of the present invention;

[0024] Figure 4 This is a schematic diagram of a silicon wafer before the improvement of this invention;

[0025] Figure 5 This is a schematic diagram of the improved silicon wafer according to the present invention;

[0026] Figure 6 This is a system structure block diagram of the present invention. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to embodiments:

[0028] Example 1

[0029] like Figure 1-6 As shown, this invention provides a method for improving shallow pits in the center of silicon wafers. This embodiment is performed on a standard silicon wafer mounting device. The device mainly includes a loading section, a ceramic plate processing section, a mounting section, a cooling section, and a unloading section. The mounting section is the core component for performing this method. It has a mounting suction head with a vacuum system. The suction head can perform rising, rotating 180°, falling, and pressurizing actions under the control of a control unit, which is a PLC or an industrial PC. The mounting suction head uses the negative pressure generated by the vacuum holes on its surface to adhere to the front side of the silicon wafer, i.e., the side that will be polished in the future. After adhering, the suction head rises and rotates to press the back side of the silicon wafer onto a ceramic plate that has been coated with a wax layer.

[0030] In this embodiment, when adjusting the up and down position, the operator accesses the motion parameter setting menu of the attachment part through the human-machine interface of the device and finds the up and down position or similar named parameter item. This parameter defines the endpoint height of the attachment head's accelerated ascent. Its value directly affects the height of the head at the end of the descent phase. This parameter value is increased from the commonly used 33mm in the original technology to 33.2mm, ensuring that the accelerated descent phase of the attachment head carrying the silicon wafer ends before the silicon wafer contacts the ceramic plate. Subsequently, the head enters the deceleration and pressurization phase at a slower pressurization speed. In this phase, the silicon wafer slowly and smoothly contacts the ceramic plate. This soft landing method allows sufficient time for the air between the silicon wafer and the ceramic plate to be completely expelled, avoiding the formation of positive pressure due to air closure, thereby eliminating the possibility of bulging deformation on the front side of the silicon wafer due to residual air.

[0031] When adjusting the attachment vacuum suction, the operator accesses the vacuum system parameter setting menu on the equipment HMI, finds the attachment vacuum or similar parameter item, and for standard thickness silicon wafers: reduce the vacuum suction value from the commonly used 50kPa in the original technology to 45kPa; for thinner silicon wafers: because thinner wafers are more easily deformed, further reduce the vacuum suction to 30kPa; for thicker silicon wafers: because of their greater weight, too low a vacuum suction can easily cause the wafer to fall off, so the vacuum suction can be maintained at 50kPa or slightly higher.

[0032] When adjusting the pressurization time, the operator locates the pressurization time or holding time parameter on the equipment's HMI and shortens this parameter value from the original 3.0 seconds to 2.5 seconds. After the silicon wafer contacts the ceramic plate, the vacuum suction will be turned off, and the attachment head will continue to press down using an internal spring or other buffer mechanism to apply pressure to the silicon wafer, ensuring that the wax on its back adheres tightly to the ceramic plate. The duration of this pressure holding time is the pressurization time. If the pressurization time is too long, the silicon wafer will remain in a non-flat deformed state under mechanical pressure after it is removed from the vacuum suction. This state is fixed, and after polishing, the stress release will form shallow pits. Appropriately shortening the pressurization time can reduce the holding time of the silicon wafer in the deformed state, allowing it to recover its free state more quickly, thereby helping to reduce shallow pits.

[0033] Example 2

[0034] like Figure 1-6 As shown, based on Example 1, the present invention provides a technical solution: using the above-mentioned optimized parameter combination to attach and subsequently polish a batch of standard thickness silicon wafers, and using a surface flatness measuring instrument such as FlatMaster to inspect the polished silicon wafers.

[0035] In this embodiment, the result is as follows Figure 4 , Figure 5As shown, compared with silicon wafers processed using the original parameters, silicon wafers processed using the method of the present invention have a smooth surface flatness curve and no obvious shallow pit defects are observed in the central region, which confirms the effectiveness and excellent effect of the present invention.

[0036] The working principle of this method for improving shallow pits in the center of silicon wafers will be explained in detail below.

[0037] like Figure 1-6 As shown, by synergistically optimizing three core process parameters—the descent termination height of the attachment nozzle, the magnitude of the vacuum suction force, and the mechanical pressurization time—the elastic deformation of the silicon wafer during adsorption and pressing is fundamentally reduced. Raising the nozzle position ensures the silicon wafer only contacts the ceramic plate during the equipment's deceleration phase, achieving a soft landing. Precisely adjusting the vacuum suction force based on the wafer thickness minimizes adsorption deformation. Shortening the pressurization time limits the duration the wafer is held under mechanical pressure, promoting a faster recovery to its natural state. These three measures work together to effectively avoid central shallow pit defects caused by stress concentration and residue, thereby significantly improving the overall flatness of the polished silicon wafer.

[0038] The present invention has been described in detail above. However, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, any modifications or improvements that do not depart from the spirit of the present invention are within the scope of protection of the present invention.

Claims

1. A method for improving shallow pits in the center of silicon wafers, characterized in that: Includes the following steps: S1: Adjust the up and down position of the attachment head so that the silicon wafer contacts the ceramic plate during the deceleration and pressurization phase; S2: Adjust the vacuum suction force for attachment, and match the suction force value according to the thickness of the silicon wafer; S3: Adjust the pressurization time to reduce silicon wafer deformation.

2. The method for improving shallow pits in the center of silicon wafers according to claim 1, characterized in that: The specific method for adjusting the vertical position in step S1 is as follows: the vertical position is increased from 33mm to 33.2mm so that the silicon wafer contacts the ceramic plate after the accelerated descent phase is over.

3. The method for improving shallow pits in the center of silicon wafers according to claim 1, characterized in that: The method for adjusting the attachment vacuum suction in step S2 is to reduce the attachment vacuum suction from 50Pa to 45Pa.

4. The method for improving shallow pits in the center of silicon wafers according to claim 3, characterized in that: When processing thin silicon wafers with a thickness less than the set threshold, the attachment vacuum suction is further reduced to 30 Pa.

5. The method for improving shallow pits in the center of silicon wafers according to claim 1, characterized in that: The method for adjusting the pressurization time in step S3 is to shorten the pressurization time from 3s to 2.5s.

6. The method for improving shallow pits in the center of silicon wafers according to claim 1, characterized in that: The diameter of the attachment tip is 40mm.

7. The method for improving shallow pits in the center of silicon wafers according to claim 1, characterized in that: During the attachment process, the silicon wafer is adsorbed onto the front of the attachment head by vacuum suction, and after being flipped 180°, it is attached to the back of the ceramic plate.

8. A silicon wafer mounting system for implementing the method as described in any one of claims 1 to 7, characterized in that: The device includes an attachment part, a control unit, and a vacuum system. The attachment part includes an attachment head that can be raised, lowered, and flipped for adsorbing and attaching silicon wafers. The vacuum system is connected to the attachment head and is used to provide and control the vacuum suction force required to adsorb the silicon wafers. The control unit is electrically connected to the attachment part and the vacuum system and is used to adjust the up and down position, vacuum suction force, and pressurization time.

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