Wafer bearing table lifting system and method for lifting wafer bearing table

Abstract

The invention relates to a wafer bearing platform lifting system and a method for lifting a wafer bearing platform, in particular to a system and a method for realizing accurate alignment of a wafer and a photomask in a semiconductor lithography process. The system comprises a wafer bearing table, a photomask bearing table, a plurality of linear actuators, a plurality of range finders and a controller. The wafer bearing table is used for bearing a wafer, and the photomask bearing table is used for bearing a photomask. In addition, the linear actuator is used for adjusting the wafer bearing table, and the distance measuring instrument is used for measuring the height of the surface of the wafer. The controller is configured to measure the height of multiple points on the surface of the wafer, adjust the level of the wafer, calculate the distance between the wafer and the photomask, and lift the wafer bearing table to make the wafer contact with the photomask. The invention provides a semiconductor manufacturing method which improves accuracy, efficiency and user control.

Description

TECHNICAL FIELD

[0001] The present invention relates generally to semiconductor manufacturing, and more particularly, to a system and method for raising a wafer carrier in a contact lithography process. BACKGROUND

[0002] Optical lithography is a critical process in semiconductor manufacturing, where a pattern is transferred from a mask to a wafer coated with a photosensitive material. One method used in the lithography process is contact lithography, which is the direct physical contact of the mask with the wafer.

[0003] Traditional systems typically use a spring-loaded mechanism to raise the wafer carrier and bring the wafer into contact with the mask. While this mechanism is simple and cost-effective, the spring-loaded mechanism has several limitations:

[0004] 1. Limited precision: Spring-loaded systems often lack the fine control required to precisely align the wafer and mask, which is crucial for high-resolution pattern formation.

[0005] 2. Risk of damage: The force exerted by the springs can damage the sensitive surfaces of the wafer and mask, affecting the yield and quality of semiconductor devices.

[0006] 3. Wear and tear: Springs and other mechanical components wear out, requiring frequent maintenance and replacement.

[0007] 4. Lack of feedback: Traditional systems often lack feedback mechanisms for immediate adjustments, making it difficult to adapt to changes in wafer and mask characteristics.

[0008] Therefore, there is a need for an improved system and method for raising a wafer carrier in a contact lithography process to address these issues and limitations. SUMMARY

[0009] To address the aforementioned issues, the present invention proposes a system and method for raising a wafer carrier in a contact lithography process to overcome the shortcomings and limitations of traditional spring-loaded mechanisms. The wafer carrier lifting system uses a wafer carrier to carry the wafer and is connected to at least three linear actuators responsible for its vertical movement. Located above the wafer carrier are at least three range finders. In addition, there is a mask carrier to carry the mask, with its surface set as the reference point for height measurement.

[0010] A controller of the wafer carrier lift system of the present invention is configured to perform a series of steps aimed at achieving precise alignment between the wafer and the reticle. First, the controller measures the height of at least three points on the wafer surface using a distance meter. Based on these measurements, the controller adjusts the level of the wafer surface via a linear actuator. Subsequently, the controller calculates the exact distance between the wafer surface and the reticle, for example "D". The wafer carrier is then lifted by this calculated distance "D", bringing the wafer into perfect contact with the reticle.

[0011] An important advantage of the present invention is that it achieves improved precision in aligning the wafer with the reticle by using a linear actuator and a distance meter. This system not only minimizes the risk of damage to the wafer and the reticle, but also allows for immediate adjustments through a feedback loop system, ensuring higher accuracy and repeatability. Furthermore, the invention includes a feature that triggers a program to replace the wafer when the height difference between the measured points exceeds a predetermined value, adding an extra layer of quality control to the entire lithography process.

[0012] By providing a more accurate, reliable and adaptable solution for lifting the wafer carrier in contact lithography, the present invention represents a significant advancement in the field of semiconductor manufacturing.

[0013] In order that the manner in which the above-recited features and advantages of the present invention are obtained and utilized can be understood, a more particular description of the invention briefly summarized above will be rendered by reference to specific embodiments thereof, which are illustrated in the appended drawings. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1A A schematic diagram of one embodiment of the wafer carrier lift system of the present invention is shown;

[0015] Figure 1A A perspective view of three distance meters aimed at three wafer distance points, respectively, is shown;

[0016] Figure 2A A flowchart of one embodiment of the method of lifting the wafer carrier of the present invention is shown;

[0017] Figure 2A A flowchart of another embodiment of the method of lifting the wafer carrier of the present invention is shown;

[0018] Figure 2A A flowchart of yet another embodiment of the method of lifting the wafer carrier of the present invention is shown;

[0019] Figure 2A A flowchart of still another embodiment of the method of lifting the wafer carrier of the present invention is shown;

[0020] Figure 3AOne of the embodiments of the wafer carrier table of the present application is shown in the transition from the tilted to the adjusted horizontal state.

[0021] Figure 3A Another embodiment of the wafer carrier table of the present application is shown in the transition from the tilted to the adjusted horizontal state.

[0022] Figure 4 A schematic diagram of the structured light illuminating the reticle is shown.

[0023] SYMBOL DESCRIPTION

[0024] 100: wafer carrier table lifting system

[0025] 10: wafer

[0026] 11, 12, 13: measurement points

[0027] 110: wafer carrier table

[0028] 120: linear actuator set

[0029] 120A-120C: linear actuators

[0030] 122: motor

[0031] 124: rod body

[0032] 130: distance meter set

[0033] 130A-130C: distance meters

[0034] 140: reticle carrier table

[0035] 20: reticle

[0036] 150: controller

[0037] 30: structured light

[0038] 32: fringe pattern

[0039] 40: structured light generator

[0040] 42: light source

[0041] 44: grating

[0042] 50: camera

[0043] S110-S140, S210-S240, S315, S318, S405, S408: flowchart steps DETAILED DESCRIPTION

[0044] Reference is made to Figure 1A , Figure 1AA schematic diagram of one embodiment of a wafer chuck lift system of the present application is shown. The wafer chuck lift system 100 includes a wafer chuck 110 designed to securely hold a wafer 10. The wafer chuck 110 is typically made of a material that provides high rigidity and thermal stability, such as aluminum or ceramic composites, to ensure that its shape and dimensions are maintained under different environmental conditions. In addition, the surface of the wafer chuck 110 is engineered to provide a high degree of flatness and is typically coated with a non-reactive material to prevent any chemical reaction with the wafer 10. This ensures that the wafer 10 remains contamination free throughout the process, thereby improving the yield and quality of semiconductor devices.

[0045] The wafer chuck 110 can employ various mechanisms to secure the wafer 10, such as vacuum chucks, electrostatic chucks, or mechanical chucks. Vacuum chucks are often used because they are able to securely hold the wafer 10 without exerting excessive force that can damage the wafer 10. The vacuum is generated through a series of small holes (not shown) in the surface of the wafer chuck 110 that create a suction force to hold the wafer 10 in place.

[0046] In addition, the wafer chuck 110 is connected to a set of linear actuators 120. In this embodiment, there are three linear actuators 120, namely linear actuator 120A, linear actuator 120B, and linear actuator 120C. The linear actuators 120 are the primary means of driving the vertical movement of the wafer chuck 110, allowing the position of the wafer 10 relative to the reticle 20 to be precisely controlled. Unlike conventional spring loading mechanisms, the linear actuators 120 provide a high degree of precision and repeatability, whereas spring loading mechanisms lack fine control and can induce stress on the wafer 10 and the reticle 20.

[0047] In this embodiment, the linear actuator set 120 is powered by electricity, but in other embodiments, it can be powered by air pressure or hydraulic pressure. Electrically powered linear actuator sets 120 are generally preferred because of their ease of control and convenience of integration with digital control systems. The linear actuators 120A, 120B, 120C of the linear actuator set 120 are typically driven by a motor 122 in a screw drive fashion to cause a rod 124 to extend and retract to produce linear motion. The motor 122 in the linear actuators 120A, 120B, 120C of the linear actuator set 120 can be selected to vary depending on the speed and torque required. Common choices include stepper motors, servo motors. The screw drive can be of various types, such as ball screw or lead screw. In this embodiment, sensors (not shown) in the linear actuators 120A, 120B, 120C of the linear actuator set 120 constantly monitor the position of the rods 124 and communicate this information to the controller 150. This allows the controller 150 to immediately adjust the position of the linear actuators 120A, 120B, 120C of the linear actuator set 120 to ensure that the wafer carrier 110 is uniformly raised and aligned with the reticle 20 (to be described later). Note that the linear actuator set 120 and its rods 124 are shown schematically and are not drawn to scale.

[0048] The linear actuators included in the linear actuator set 120 are at least three in number (three in this embodiment) and are not collinear, namely linear actuator 120A, linear actuator 120B, linear actuator 120C. They are responsible for the vertical movement of the wafer carrier 110 and are arranged in a triangular or other polygonal fashion (triangular in this embodiment). These linear actuators 120 are pre-positioned so that the linear actuators 120A, 120B, 120C can be individually raised or lowered to provide a precisely adjusted height at different positions of the wafer carrier 110 in the horizontal plane, thereby ensuring uniform and flat contact of the wafer 10 surface with the reticle 20.

[0049] Next, referring to Figure 1A , Figure 1A is shown as a perspective view of three range finders aiming at three points on the wafer surface. Above the wafer carrier 110, there is provided a range finder set 130 (in this embodiment, three range finders) that are not collinear and are capable of measuring the height of the wafer 10 surface. The range finders 130 are arranged in a triangular or other polygonal fashion (triangular in this embodiment). The range finders 130 are pre-positioned so that the range finders 130 can be individually aimed at different positions of the wafer carrier 110 in the horizontal plane, thereby ensuring uniform and flat contact of the wafer 10 surface with the reticle 20. Figure 1AThe distance measuring devices 130 are arranged in a triangular or polygonal pattern (triangular in this embodiment). The distance measuring devices 130 can be laser distance measuring devices, capacitive distance measuring devices, or any other type of distance measuring device that can provide accurate distance measurements. In this embodiment, the distance measuring devices 130 are laser distance measuring devices. The distance measuring devices 130 are communicatively coupled to the controller 150, which processes the distance measurement data in real time. The distance measurement data is used to calculate the exact distance between the surface of the wafer 10 and the mask 20. In this embodiment, the distance measuring devices 130 correspond to the linear actuators 120, i.e., the number of distance measuring devices 130 corresponds to the number of linear actuators 120 and are positioned directly above the linear actuators 120. In this embodiment, the distance measuring devices 130A, 130B, 130C correspond to the linear actuators 120A, 120B, 120C.

[0050] The distance measuring devices 130 work in conjunction with the mask carrier 140, which carries the mask 20. In addition, the distance and level between the distance measuring devices 130 and the mask carrier 140 are pre-adjusted and calibrated so that the surface of the mask carrier 140 is level and serves as a reference level, which is usually set to zero, for measuring the height of the points on the surface of the wafer 10. In addition, the level of the wafer carrier 110 and the distance between the wafer carrier 110 and the mask carrier 140 are also pre-determined and precisely calibrated.

[0051] In addition, the wafer carrier lifting system 100 also includes a controller 150, which is responsible for controlling the measurement of the distance measuring devices 130 and the lifting of the linear actuators 120, and is also configured to manage the calculation and control of the lifting of the wafer carrier 110.

[0052] Please also refer to Figure 2A , Figure 2A The flowchart shown is an embodiment of the method for lifting the wafer carrier 110 of the present application. First, as shown in step S110, the controller 150 starts the distance measuring devices 130 to measure the height of at least three points on the surface of the wafer 10, for example, three points, i.e., the distance measuring devices 130A, 130B, 130C measure the height of the measurement points 11, 12, 13, which are arranged in a triangular pattern in this embodiment. In other embodiments, if the number of distance measuring devices 130 exceeds three, the measurement points will be arranged in a polygonal pattern. Then, as shown in step S120, the level of the surface of the wafer 10 is adjusted according to the measurement results. For example, if the measurement point 11 is higher than the measurement point 12, the linear actuators 120A, 120B are adjusted to lower the wafer carrier 110, and vice versa. Figure 1AFor example, the distances between the original distance meters 130A, 130B, and 130C and the measurement points 11-13 on the wafer 10 surface are Zl, Z2, and Z3, respectively. The distances Zl, Z2, and Z3 are adjusted to be equal to ensure that the wafer 10 surface is level. As shown in FIG. 1, the distances Zl, Z2, and Z3 are measured by the distance meters 130A, 130B, and 130C, respectively. Figure 3A In this step S120, the controller 150 operates the linear actuators 120A, 120B, and 120C to adjust the distances Zl, Z2, and Z3 to be equal to ensure that the wafer 10 surface is level. After the wafer 10 surface is leveled, the height of the leveled wafer 10 surface is measured again in step S130. The controller 150 calculates the distance between the leveled wafer 10 surface and the mask 20, for example, "D" (as shown in FIG. 2), according to the measurement results. Then, the wafer stage 110 is raised by the calculated distance "D" to allow the wafer 10 to be in contact with the mask 20 in step S140. Figure 1A

[0053] In addition, in the above embodiment, the controller 150 first adjusts the wafer 10 surface to be level (i.e., step S120) and then raises the wafer stage 110 (i.e., step S140). However, in other embodiments, the controller 150 can raise the wafer stage 110 while adjusting the wafer 10 surface to be level. This simultaneous operation allows more efficient use of time and resources. Please refer to Figure 2A Figure 2A A flowchart of another embodiment of the wafer stage raising method of the present application is shown. First, in step S210, the controller 150 starts the distance meters 130 to measure the distances between the measurement points 11, 12, and 13 on the wafer 10 surface and the distance meters 130A, 130B, and 130C, respectively, Zl, Z2, and Z3.

[0054] Then, in step S220, the controller 150 calculates the distances between the measurement points 11, 12, and 13 on the wafer 10 surface and the mask 20, Dl, D2, and D3 (as shown in FIG. 3), according to the measurement results. Figure 3A ​​The distances Dl, D2, D3 between the measurement points 11, 12, 13 and the reticle 20 can be determined from the distances Zl, Z2, Z3 measured after the distances of the distance meters 130A, 130B, 130C from the zero point are known. Since the surface of the reticle carrier 140 is pre-set to be horizontal and serves as the reference level point, i.e. the zero point, and the distances of the distance meters 130A, 130B, 130C from the zero point are known, the distances Dl, D2, D3 between the measurement points 11, 12, 13 and the reticle 20 can be determined after the distances Zl, Z2, Z3 are measured. Subsequently, in step S230, the controller 150 operates the linear actuators 120A, 120B, 120C of the linear actuator set 120 to ascend by the distances Dl, D2, D3, respectively, so as to make the surface of the wafer 10 adhere to the reticle 20 (as in step S240), while achieving the purposes and results of adjusting the level and lifting the wafer 10.

[0055] Next, please refer to Figure 2A , Figure 2A The flowchart shown is another embodiment of the method of the present application for lifting the wafer carrier. In this embodiment, the wafer carrier 110 and the reticle carrier. In this embodiment, the controller 150 also performs step S315: determining whether the wafer 10 should be replaced according to the height measurements taken at multiple points on the surface of the wafer 10. This step S315 is to maintain the quality and integrity of the lithography process, because a wafer 10 with a surface that has significant height variations can cause misalignment of the pattern or other defects.

[0056] The controller 150 first evaluates the three height measurements obtained from the three distance meters 130A, 130B, 130C. These different position measurements are compared to evaluate the height difference between the points on the surface of the wafer 10. If this difference exceeds a predetermined value, i.e. the flatness of the surface of the wafer 10 exceeds the allowable predetermined value range, the controller 150 triggers a process to replace the wafer 10. The predetermined value is usually set according to empirical data and quality control standards, and the predetermined value serves as a threshold value. If the predetermined value is set too low, it can lead to frequent replacement of the wafer 10, reducing production and increasing costs. Conversely, if the predetermined value is set too high, it can compromise the quality of the final product. Therefore, the predetermined value is usually determined through rigorous testing and statistical analysis to ensure optimal performance.

[0057] Once the height difference exceeding the predetermined value is detected, step S318 is performed, and the controller 150 initiates a series of automated actions to replace the wafer 10. This can involve withdrawing the wafer carrier 110 from its original position and activating a robotic arm (not shown) or other automated mechanism to remove the problematic wafer 10 and replace it with a new wafer 10. The controller 150 can also mark this event in the system log for quality control and traceability.

[0058] By identifying and replacing problematic wafers 10 at an early stage of the process through step S315, the controller 150 helps prevent potentially more costly corrections of downstream problems. It also improves yield by ensuring that only wafers 10 that meet quality standards proceed to later stages of manufacturing. Note that in Figure 2A the case where the flatness of the wafer 10 surface does not exceed the predetermined range of allowable values through step S315, the wafer can be subjected to a process step of adjusting the surface to bring it into contact with the mask. Since this is the same as the steps S220, S230, S240 shown in Figure 2A , they will not be described again.

[0059] Next, refer to Figure 2A , Figure 2A , which is a flowchart illustrating yet another embodiment of the method of raising the wafer carrier 110 of the present application. In this embodiment, the distance-measuring instrument set 130 is also configured to first measure the level of the surface of the wafer carrier 110 (step S405) to add more precision to the lithography process. The level of the surface of the wafer carrier 110 serves as a reference for all subsequent operations, including the alignment of the wafer 10 with the mask 20. In step S408, based on the three measurement data obtained from the three distance-measuring instruments 130A, 130B, 130C of the distance-measuring instrument set 130, the controller 150 is configured to use the three corresponding linear actuators 120A, 120B, 120C of the linear actuator set 120 to adjust the level of the surface of the wafer carrier 110.

[0060] Steps S405 and S408 do not necessarily have to be performed every time the wafer carrier 110 is raised. These two steps are usually performed when the wafer carrier 110 is initially set up, or when the wafer carrier 110 has undergone thermal drift or mechanical wear due to prolonged use, to ensure that the level of the wafer carrier 110 does not affect the quality of the lithography process. Note that in Figure 4 the remaining steps are the same as those shown in ​ , and will not be described again.

[0061] Furthermore, in one embodiment, once the flatness of the wafer 10 surface is determined and the height measurement is completed, the wafer stage lift system 100 assists the retraction of the distance meter set 130 to avoid any potential interference with the subsequent lithography process steps. In this embodiment, the distance meter set 130 is mounted on a precision retractable mechanism (not shown) that is actuated by the command of the controller 150. The controller 150 initiates the retraction mechanism immediately after the measurement cycle is completed to move the distance meter set 130 to a predetermined safe position (not shown) to ensure that they do not obstruct the exposure area or cause any form of contamination or optical interference during the sensitive lithography exposure process. The safe position is carefully selected to avoid interference with the lithography process. The retraction mechanism can include a series of actions including vertical and lateral movements to accommodate different forms of lithography processes.

[0062] Referring to ​ In one embodiment, after the step S140 is performed, the deformation of the mask 20 is measured. If the deformation of the mask 20 is greater than a predetermined range, the wafer stage 110 is adjusted by the linear actuator set 120 to make the deformation of the mask 20 less than the predetermined range. In detail, a structured light 30 is projected on the surface of the mask 20 to form a plurality of fringe patterns 32 on the mask 20. The structured light 30 is generated by a structured light generator 40 including a light source 42 and a grating 44. The structured light 30 is the fringe pattern 30 formed by the light emitted from the light source 42 passing through the grating 44. Therefore, the structured light 30 can form the plurality of fringe patterns 32 on the surface of the mask 20. In addition, the structured light 30 can be a grid or a dot array pattern light source in addition to the fringe pattern.

[0063] Then, the change of the fringe patterns 32 on the surface of the mask 20 is detected by a camera 50 to determine whether the mask 20 is deformed. In detail, the change of the fringe patterns 32 is transmitted to the controller 150 by the camera 50 to determine the deformation of the mask 20 to determine whether the wafer 10 and the mask 20 are in good contact. When the wafer 10 and the mask 20 are not in good contact, the deformation of the mask 20 makes the fringe patterns 32 greater than a predetermined range. Then, the controller 150 can calculate the adjustment of the linear actuator set 120 to adjust the height of the wafer stage 110 to make the wafer 10 accurately contact the mask 20 to ensure the accuracy of the subsequent exposure.

[0064] Although the present application has been disclosed with reference to the preferred embodiments, it is not intended to limit the application. Any person skilled in the art can make some changes and modifications without departing from the spirit and scope of the application. Therefore, the scope of protection of the present application is defined by the appended claims.

Claims

1. A wafer carrier lifting system, characterized in that: For contact lithography, the wafer stage lift system includes: a wafer carrying platform configured to stably carry a wafer; a plurality of linear actuators operatively connected to the wafer stage to facilitate vertical movement of the wafer stage, the plurality of linear actuators being arranged in a non-linear arrangement; a plurality of rangefinders, each disposed to measure the height of a plurality of measurement points on the wafer surface of the wafer, wherein each measurement point corresponds to each linear actuator; a mask carrying platform for carrying a mask; a controller operatively connected to the linear actuator and the rangefinder, the controller being configured to: receiving altitude measurement data from the rangefinder; processing the height measurement data to determine the adjustment required to adjust the level of the wafer stage; and Calculating the distance between the wafer surface and the photomask according to the height measurement data; Controlling the linear actuator to adjust the position of the wafer carrier according to the processed height measurement data to achieve contact between the wafer and the photomask; a structured light generator, projecting a structured light onto the mask to generate a structured light pattern; and a photographing device, adapted to photograph the structured light pattern on the mask; The controller calculates the deformation of the mask according to the change of the structured light pattern, and further adjusts the position of the linear actuator according to the calculated mask deformation to reduce the deformation of the mask.

2. The wafer carrying platform lifting system according to claim 1, characterized in that: The linear actuator includes three linear actuators arranged in a triangle.

3. The wafer carrying platform lifting system according to claim 1, characterized in that: Each linear actuator includes a motor and a screw drive mechanism, and the screw drive mechanism is a ball screw or a lead screw.

4. The wafer carrying platform lifting system according to claim 1, characterized in that: The rangefinder is a laser rangefinder.

5. A method for raising a wafer carrier, characterized in that: For use in a contact lithography process, the method comprises: Measuring the height of a wafer at a plurality of measurement points using a plurality of distance meters, wherein the measurement points are located on a wafer surface of the wafer; processing the measured heights to determine height differences at various measurement points on the wafer surface of the wafer; adjusting positions of a plurality of linear actuators connected to the wafer stage according to the determined height difference to adjust the level of the wafer stage, wherein the plurality of linear actuators are arranged in a non-linear manner; Calculating the distance between the wafer surface and a photomask based on the measured height data; and Raising the wafer carrier by the calculated distance so that the wafer contacts the photomask; Projecting a structured light onto the mask through a structured light generator to generate a structured light pattern; photographing the structured light pattern on the mask using a photographing device; and A controller calculates the deformation of the mask according to the change of the projected structured light pattern, and further adjusts the position of the linear actuator according to the calculated mask deformation to reduce the deformation of the mask.

6. The method for raising the wafer carrier according to claim 5, wherein: The method further includes evaluating the height measurement data to determine whether the wafer should be replaced based on the surface flatness of the wafer exceeding a predetermined value range.

7. The method for raising the wafer carrier according to claim 5, wherein: The method further includes returning the rangefinder to a safe position after the wafer carrier is adjusted to a level.

8. The method for raising the wafer carrier according to claim 5, wherein: The rangefinder is a laser rangefinder.

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