Wafer pre-aligner and method for pre-aligning a wafer

Abstract

The present disclosure relates to a wafer pre-aligner and a method for pre-aligning a wafer. The pre-aligner is used to pre-align a wafer having a notch. The pre-aligner includes a wafer platform having a wafer receiving surface, and a driving device. A detector is provided to detect the notch, and a memory is provided to store a notch window that defines an angular range relative to a starting position within which the notch is predicted to be located. A controller performs a pre-alignment operation in which the wafer is rotated from the starting position to an alignment position. The controller performs an operation to rotate the wafer from the starting position to the notch position detected by the detector at a maximum acceleration / deceleration value: wherein the operation is limited to a maximum speed for rotating the wafer from the starting position to the notch window, and wherein the operation is limited to a scanning speed within the notch window until the notch position is detected.

Description

Technical Field

[0001] The present invention relates to pre - alignment of semiconductor wafers. Background Art

[0002] A pre - aligner is used to identify the position of a notch on a semiconductor wafer. A robot places the wafer on the chuck of the pre - aligner. The pre - aligner rotates the wafer chuck and thus rotates the wafer to search for the notch. In the case where the notch is identified, the wafer can then be oriented to the final orientation specified by the process to be performed on the wafer.

[0003] Upon arrival at the pre - aligner, the position of the notch can be at any position relative to the pre - aligner, depending on the previous processes performed on the wafer and / or the movement operations of the robot. Thus, in some prior - art pre - aligners, when searching for the notch, the pre - aligner must scan slowly from the start of rotation (i.e., scan at a speed not greater than the scan speed, which is the maximum speed at which the pre - aligner can accurately detect the notch) until the pre - aligner detects the notch, as Figure 13 shown, Figure 13 shows a plan view of the position of the wafer relative to the corresponding acceleration - time graph and the corresponding velocity - time graph. In such a pre - aligner, the pre - aligner starts rotating along the Figure 13 velocity - time graph at position “A” and accelerates until it reaches the scan speed at the rotation at position “B”, and then maintains that scan speed until the notch is detected at position “C”. Thus, in some prior - art pre - aligners, the wafer must be scanned at a speed not greater than the scan speed until the notch is located, then the wafer is decelerated (e.g., from position “C” to position “D” in Figure 13 ), and then the wafer is moved to the final orientation (e.g., from position “D” to position “E” in Figure 13 ).

[0004] In addition, when the robot places the wafer on the chuck of the pre - aligner, the center of the wafer may not be aligned with the rotation center of the chuck of the pre - aligner. In some prior - art pre - aligners, a method is used that requires scanning approximately 360 degrees of rotation of the wafer to locate the center of the wafer.

[0005] It has been determined that such prior - art pre - aligners are slow in performing pre - alignment of wafers and significant improvements can be made. Summary of the Invention

[0006] The present invention advantageously provides a pre-aligner for pre-aligning a wafer having a notch on its peripheral edge. The pre-aligner includes: a rotation unit including: a wafer platform having a wafer receiving surface configured to receive the wafer; and a driving device configured to rotate the wafer platform about an axis. The pre-aligner further includes: a detector configured to detect the notch on the wafer when the wafer is received on the wafer receiving surface; a memory configured to store a notch window that defines a range of angles relative to a starting position at which the wafer is initially received on the wafer receiving surface, wherein the notch is predicted to be within the range of angles, the starting position corresponding to the sensing area of the detector, and a controller programmed to perform a pre-alignment operation in which the wafer is rotated from the starting position to a predetermined alignment position. The controller is programmed to perform the pre-alignment operation such that the wafer is rotated from the starting position to the notch position detected by the detector at a maximum acceleration / deceleration value: wherein, the pre-alignment operation is limited to a maximum speed for rotating the wafer from the starting position to the notch window; and wherein, the pre-alignment operation is limited to a scanning speed for rotating the wafer within the notch window before the detector detects the notch position, the scanning speed being less than the maximum speed.

[0007] The present invention advantageously provides a method including: providing a wafer platform having a wafer receiving surface configured to receive a wafer having a notch on its peripheral edge; providing a detector configured to scan the peripheral edge of the wafer to detect the notch on the wafer when the wafer is received on the wafer receiving surface; setting a notch window that defines a range of angles relative to a starting position at which the wafer is initially received on the wafer receiving surface, wherein the notch is predicted to be within the range of angles, the starting position corresponding to the sensing area of the detector; and performing a pre-alignment operation in which the wafer is rotated from the starting position to a predetermined alignment position. The pre-alignment operation is performed such that the wafer is rotated from the starting position to the notch position detected by the detector at a maximum acceleration / deceleration value: wherein, the pre-alignment operation is limited to a maximum speed for rotating the wafer from the starting position to the notch window; and wherein, the pre-alignment operation is limited to a scanning speed for rotating the wafer within the notch window before the detector detects the notch position, the scanning speed being less than the maximum speed.

[0008] The present invention advantageously provides a method that includes: providing a wafer on a wafer platform having a wafer receiving surface, the wafer having a scribe on its peripheral edge; rotating the wafer on the wafer platform from an initial position where the wafer is initially received from the wafer receiving surface until a detector detects a scribe position of the scribe relative to the initial position, the initial position corresponding to a sensing area of the detector; storing the scribe position in a memory; repeating providing, rotating, and storing for one or more successive wafers to gather and store scribe position data in the memory; setting a scribe window using the scribe position data, the scribe window defining a range of angles relative to an initial position where a subsequent wafer is initially received from the wafer receiving surface, wherein a subsequent scribe of the subsequent wafer is predicted to be located within the range of angles; and performing a pre-alignment operation on the subsequent wafer, wherein the subsequent wafer is rotated from the initial position to the scribe position of the subsequent wafer within a first shortest time period using the scribe window. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] A more complete understanding of the present invention and many of its attendant advantages will become apparent upon reference to the following detailed description, especially when considered in conjunction with the accompanying drawings, in which:

[0010] Figure 1 is a perspective view of a robot and a pre-aligner of an embodiment of the present invention.

[0011] Figure 2 is a flowchart of a process in which a scribe memory is used to store data that allows improvement of the performance of the pre-aligner;

[0012] Figure 3 is a flowchart of a process of a pre-alignment operation of a pre-aligner in which the performance of the pre-aligner is optimized;

[0013] Figure 4 is a schematic diagram showing a plan view of a wafer in a first starting scenario;

[0014] Figure 5 shows Figure 4 the wafer usage Figure 3 of a process of a

[0015] Figure 6 is a diagram showing another movement trajectory of the wafer usage Figure 4 of a Figure 3 process in a scenario where the maximum speed is reached after detecting a scribe during the movement trajectory;

[0016] Figure 7 is a diagram showing another movement trajectory of the wafer usage Figure 4 of a Figure 3 process in a scenario where the maximum speed is reached before detecting a scribe during the movement trajectory;

[0017] Figure 8 A schematic diagram showing a plan view of a wafer in a second starting point scenario;

[0018] Figure 9 Shows Figure 8 The movement trajectory diagram of the wafer using Figure 3 During the movement trajectory, a speed greater than the scanning speed is reached before reaching the notch window and a speed greater than the scanning speed is reached after detecting the notch;

[0019] Figure 10 A schematic diagram showing the wafer relative to the center of the wafer chuck and the reading head of the detector of the pre-aligner to determine the eccentricity and find the center of the wafer;

[0020] Figure 11 Shows an example of a common notch specification;

[0021] Figure 12 Shows an embodiment of a computer system (or controller) implementing an embodiment of the present invention; and

[0022] Figure 13 A plan view showing the position of the wafer of the related art example relative to the corresponding acceleration-time curve graph and the corresponding velocity-time curve graph. Detailed description of the invention

[0023] Embodiments of the present invention will be described below with reference to the accompanying drawings. In the following description, components having substantially the same function and arrangement are denoted by the same reference numerals, and repeated description is made only when necessary.

[0024] In semiconductor manufacturing, it is important to accurately determine the position (i.e., position and orientation) of a semiconductor wafer so as to accurately perform precise manufacturing processes on the semiconductor wafer. As the wafer is moved from one processing station to another, for example, by using a robot such as an atmospheric multi-joint robot, it is important to determine the position of the semiconductor wafer in certain processing stations. For example, a pre-aligner can be used to identify the position of a notch on the periphery of the semiconductor wafer so that the pre-aligner determines the position of the semiconductor wafer.

[0025] Figure 1A perspective view of a robot 100 including an arm member 110 and an end effector 120 is depicted. The robot 100 can be configured as a multi-joint robot having a robot arm and an end effector, the robot arm having one or more arm members rotatable relative to each other, and the end effector being rotatably mounted to one end of the robot arm. The robot 100 is configured to move the end effector in the X, Y, and Z directions, and to pivot the end effector about one or more axes (including at least the Z axis). The end effector has an upper surface 122 configured to receive, support, and transport a semiconductor wafer during manufacturing between processing stations (e.g., from a first processing station to a second processing station).

[0026] Figure 1 A scenario is depicted in which the robot 100 has transferred a semiconductor wafer W to a processing station including a pre-aligner 200. In Figure 1 the pre-aligner 200 is depicted as including a rotation unit 210 and a detection unit 240. For simplicity of depiction, Figure 1 the pre-aligner 200 in

[0027] is depicted without a housing, and such a housing can be provided to house both the rotation unit 210 and the detection unit 240. The rotation unit 210 includes a rotation motor (or drive device) 220 having a rotation shaft 222 protruding upward therefrom. The motor 220 can be, for example, an electric motor. The motor 220 is configured to rotate the rotation shaft 222 about a rotation axis 224 that extends vertically along the Z axis through the vertical center of the rotation shaft 222. A wafer platform, such as a wafer chuck 230, is mounted to the distal end of the rotation shaft 222. The wafer chuck 230 has a wafer receiving surface 232 configured to receive the semiconductor wafer W. The rotation axis 224 extends through the rotation center of the wafer platform 230 and the rotation center of the wafer receiving surface 232. The wafer receiving surface 232 supports the wafer and can be provided with a surface material that provides friction between the wafer W and the wafer receiving surface 232 to prevent the wafer W from moving relative to the wafer receiving surface 232. Alternatively, or in addition to the surface material, the wafer receiving surface 232 can be provided with suction holes, and the wafer chuck 230 can be provided with a suction device to hold the wafer W on the wafer receiving surface 232 to prevent the wafer W from moving relative to the wafer receiving surface 232.

[0028] The detection unit 240 includes a base 242, a support member 244, and a reading head 246. The base 242 supports the support member 244 and the reading head 246. The support member 244 supports the reading head 246 on the base 242. The base 242 is installed within a housing (not shown) of the pre-aligner 200. The base 242 can be mounted to the housing such that the rotation unit 210 and the detection unit 240 can move relative to each other. For example, the base 242 can be mounted to the housing such that the detection unit 240 can move linearly closer to and away from the rotation unit 210, so that the pre-aligner 200 can be used with semiconductor wafers of various diameters.

[0029] The detection unit 240 includes a detector 250 configured to sense the presence of a wafer received on the wafer receiving surface 232. In conjunction with the operation of the rotation unit 210, the detector 250 can scan the periphery of the wafer W to determine the alignment (i.e., position and orientation) of the wafer W. (The term "scan" or "scanning" as used herein includes the operation of the detector 250 on the periphery of the wafer with the wafer W rotating or not rotating.)

[0030] The detector 250 includes a light source 252 and a light sensor (or optical sensor) 254. In this embodiment, the light source 252 is disposed within the base 242, and a lens 256 is disposed at the upper end of the base 242. The light sensor 254 is disposed on the reading head 246. The light sensor 254 can be, for example, a charge-coupled device (CCD) sensor. The light emitted from the light source 252 is collimated by the lens 256, and the collimated light L is received by the light sensor 254. The detection unit 240 including the reading head 246 positions the light sensor 254 in the -Z direction toward the upper surface of the wafer W, and the light sensor 254 can sense the wafer within the sensing area, such as its edge or a mark / scratch formed thereon, so as to align the semiconductor wafer for inspection and / or processing. By detecting whether the light on the sensing device of the light sensor 254 is received, the detector 250 can determine the presence or absence of the peripheral edge E of the wafer W and the presence or absence of a scratch disposed on the peripheral edge E of the wafer W.

[0031] The pre-aligner 200 is controlled by one or more controllers, and embodiments thereof will be described below with reference to Figure 12 The robot 100 can be controlled by a controller independent of the controller of the pre-aligner, or the robot 100 and the pre-aligner 200 can be controlled by one or more common controllers.

[0032] Note that an aligner such as aligner 200 will have certain operating parameters within which the aligner operates. For example, the rotation unit 210 of aligner 200 will have a maximum angular velocity (also referred to herein as the maximum speed) and a maximum angular acceleration / deceleration (also referred to herein as the maximum acceleration and maximum deceleration) that the aligner can use to rotate the wafer. Such maximum speed and maximum acceleration / deceleration values depend on the operating parameters of the motor 220 (e.g., the speed and acceleration / deceleration operating ranges). Such maximum speed and maximum acceleration / deceleration values as used herein can also depend on the operating parameters of the wafer chuck 230 (e.g., the surface friction or suction device provided therein to ensure that the wafer will remain on the wafer chuck within a certain speed and acceleration / deceleration range), and the operating parameters of the wafer chuck 230 may reduce these values below the operating parameters of the motor 220. Additionally, the aligner will have a maximum scan speed (also referred to herein as the scan speed), which is the maximum speed at which the detection unit 240 of the aligner can accurately detect the notch. Generally, the scan speed is a value less than the maximum speed of the motor 220 of the rotation unit 210.

[0033] As Figure 1 shown, the robot 100 has transferred the semiconductor wafer W to a processing station including the aligner 200 and placed the wafer on the wafer chuck 230 of the aligner 200. The motor 220 of the aligner 200 rotates the wafer chuck 230 and thus rotates the wafer W to search for the notch N using an optical sensor such as the detector 250. In the case where the notch N is identified, the wafer W is then oriented to a final orientation that is specified by the processing to be performed on the wafer W at the processing station where the aligner 200 is provided, for example. The position of the notch N when it reaches the aligner 200 can vary relative to the aligner 200 depending on the previous processing performed on the wafer W and / or the movement operations of the robot 100.

[0034] The aligner 200 is used to identify the position of the notch N on the semiconductor wafer W. It has been determined that the position of the notch N relative to the aligner 200 on which the wafer is placed is generally consistent between wafers within a certain tolerance range. In other words, when the robot 100 repeats the same overall movement of the wafer from a previous processing station to the processing station where the aligner 200 is provided, the wafers are generally positioned and oriented in a similar (within a certain tolerance range) manner between wafers. Thus, the method described herein involves using the aligner 200 to use the same as Figure 13 depicted along Figure 13The velocity-versus-time curve scans the scribe marks of successive wafers in a manner similar to that of the related art from position "A" to position "C", and stores the scribe mark positions of multiple successive wafers in a memory (also referred to herein as the scribe memory). Based on these scribe mark positions, a range of scribe mark positions can be set and stored in the scribe memory, and such data can be used to define a scribe window. The scribe window is a range of angles at which the scribe mark is predicted to be located relative to the starting position where the wafer is initially received on the wafer receiving surface, and this starting position corresponds to the sensing area of the detector 250. A numerical value of the number of stored scribe mark positions (i.e., the number of data points) used to set the scribe window can be determined such that the operator has a predetermined confidence level (e.g., 90% or 95% or 99%, etc.) at a likelihood rate that any given scribe mark of a future wafer will fall within the scribe window (e.g., the data points fall within a range of 10° to 35° from the starting point, or within a range of 5° to 15° from the starting point, or within a range of -10° to 15° from the starting point, etc.). Once the scribe window is set, the pre-aligner 200 can use the following process to scan the scribe mark of the wafer: from the starting position with the maximum acceleration / deceleration and maximum speed of the rotation unit 210 until the wafer W is rotated into the scribe window, and the maximum acceleration / deceleration and maximum speed can be used during the rotation of the wafer W after the scribe mark is detected. This can advantageously increase the speed of detecting the scribe mark and orienting the wafer to the desired alignment position, and advantageously reduce the time period for performing the alignment, thereby increasing the throughput while maintaining the alignment accuracy.

[0035] Therefore, it has been found that in the case where it is proven that the scribe mark positions of successive wafers are consistent over a certain number of wafers, the pre-aligner can be moved to the area of the expected scribe mark (i.e., the scribe window) in the optimal direction at the maximum acceleration and maximum speed instead of slow scanning, and then the pre-aligner can decelerate the rotation of the wafer to the scanning speed to detect the scribe mark within the expected area. Kinematic studies have been conducted to demonstrate the throughput advantages of using such a scribe memory, and these advantages can be easily understood through the following metaphor. If someone is looking for a lost dog, the person usually has to slowly drive through the town during the search for the dog until the person finds the dog within the town. Once the person has found the dog, the person needs to drive the dog back to its owner. In the case of the scribe memory process, the person knows that the dog usually likes to run to the butcher shop. In this case, the person can drive to the butcher shop as fast as possible, pick up the dog, and then return the dog to its owner within the fastest time period.

[0036] Figure 2 Process 300 is depicted, in which a scribe memory is used to store data that allows the performance of the pre-aligner to be improved. Process 300 includes step 302 of loading a wafer onto the pre-aligner. For example, as Figure 1As shown, the robot 100 transfers the semiconductor wafer W to a processing station including a pre-aligner 200. The robot 100 places the wafer W on the wafer receiving surface 232 of the wafer chuck 230 using the end effector 120, and then the robot 100 moves the end effector 120 away from the pre-aligner. The position of the notch N is based on the position of the wafer W.

[0037] Process 300 includes step 304, in which the wafer is scanned using the pre-aligner to find the notch position. For example, the motor 220 of the rotation unit 210 rotates the rotation shaft 222, thereby rotating the wafer chuck 230 and the wafer W thereon. During this rotation, the detector 250 of the detection unit 240 senses (or scans) the peripheral edge E of the wafer W. Light is emitted from the light source 252 and collimated by the lens 256 so that the light sensor 254 receives the collimated light L. The light sensor 254 facing the upper surface of the wafer W in the -Z direction senses the wafer within the sensing area, such as its edge or a mark / notch formed thereon. By detecting whether the light on the sensing device of the light sensor 254 is received, the detector 250 can determine the presence or absence of the peripheral edge E of the wafer W and the presence or absence of the notch N provided on the peripheral edge of the wafer W. The processor 1204 of the controller 1200 (see Figure 12 ) of the pre-aligner 200 will determine whether the notch has been detected based on the signal from the detection unit 240.

[0038] Process 300 further includes step 306, in which the position of the notch N detected in step 304 is stored in a notch memory, for example, stored in the memory 1206 of the controller 1200 depicted in Figure 12 and discussed in more detail below. The position of the notch N will include an angular value regarding the central axis of the wafer W relative to the starting position.

[0039] Process 300 also includes step 308, where the controller determines whether the scribe window confidence has been reached. This determination is based on whether a sufficient number of data points regarding scribe points on consecutive test wafers have been accumulated and stored such that the operator is confident about the likelihood of any given scribe on a future wafer falling within the scribe window. For example, if the data points collected are evenly spread around the full three hundred and sixty degrees of the wafer central axis, the operator may not be able to set a narrow scribe window with an acceptable confidence. However, if ninety-five percent of the data points collected are within a thirty-degree range from ten degrees past the starting position to forty degrees past the starting position, the operator can decide to set the scribe window within this thirty-degree range. The confidence can be set based on various parameters, such as a predetermined number of data points (e.g., at least 20 data points, at least 40 data points, etc.) having been collected and a predetermined percentage (e.g., ninety percent, ninety-five percent, etc.) of the data points falling within a predetermined range (e.g., 20 degrees, 30 degrees, etc.) of the scribe window. Thus, the operator can set the confidence based on the parameters for achieving the desired result. Setting the scribe window in this manner can be performed manually by the operator or by a processor executing an algorithm that takes into account parameters such as those described above (i.e., the minimum number of data points, the percentage of data points falling within a predetermined range).

[0040] Accordingly, in step 308, if the scribe window confidence has not been reached, process 300 loops back to step 302 and another wafer is loaded onto the pre-aligner to accumulate another data point for storage in the scribe memory. On the other hand, in step 308, if the scribe window confidence has been reached, process 300 moves to step 310.

[0041] In step 310, the set scribe window is stored in the scribe memory, e.g., stored in Figure 12 memory 1206 of. The scribe window will include a range of angular values of the central axis of wafer W relative to the starting position.

[0042] It is noted that once each step in steps 302 and 304 has been performed for each wafer processed using process 300, the pre-alignment of that wafer can start from step 304 and be completed in Figure 13 the manner shown. Figure 13 From position "C" to position "E" to complete the pre-alignment of the processed wafer in order to set the scribe window.

[0043] Once the scribe window is set, the performance of the pre-aligner can be optimized, for example, as discussed with respect to Figure 3 describing the pre-alignment operation.

[0044] Figure 3Depicts the pre - alignment operation including process 400, where process 400 includes step 402 of loading a wafer onto a pre - aligner.

[0045] In step 404, a determination is made as to whether the starting position of the wafer is within the notch window stored in the notch memory. The starting position is the angular position aligned with the sensing area of the detection unit of the pre - aligner. Thus, if the processor 1204 of the controller 1200 determines that the notch window stored in the notch memory overlaps with the starting position that will also be stored in the memory (e.g., if the notch window extends from - 5 degrees to + 30 degrees of the starting position), then process 400 proceeds to step 408 discussed below. However, if the processor 1204 of the controller 1200 determines that the starting position is not within the notch window (e.g., if the notch window extends from + 5 degrees to + 30 degrees of the starting position), then process 400 proceeds to step 406.

[0046] In step 406, the pre - aligner 200 will rotate the wafer W to the notch window using maximum acceleration / deceleration without exceeding the maximum speed value. In other words, the pre - aligner will rotate the wafer W by accelerating and / or decelerating at the maximum value so as to reach the notch window as fast as possible without exceeding the maximum speed value. Thus, if the pre - aligner 200 rotates the wafer at the maximum acceleration value and reaches the maximum speed value before reaching the notch window, the pre - aligner 200 will stop further acceleration and will start decelerating at the maximum deceleration value so as to reach the notch window at the scanning speed (e.g., see Figure 9 ). The controller 1200 can calculate whether the scanning speed is reached or exceeded when reaching the starting point of the notch window having been rotated by using the motor based on the distance from the starting position to the starting point of the notch window and the maximum acceleration value. Thus, the computer system 1200 can calculate the motion trajectory in the manner discussed in more detail below with respect to Figures 4 to 9 which is discussed in more detail.

[0047] In step 408, the pre - aligner 200 will scan the notch N using the detection unit 240. In step 408, the pre - aligner rotates the wafer W at the maximum acceleration / deceleration without exceeding the scanning speed. Thus, if the wafer W is rotating at a speed lower than the scanning speed when the notch window has been reached, the pre - aligner can rotate the wafer W at the maximum acceleration until the scanning speed is reached, at which point the pre - aligner 200 will stop further acceleration.

[0048] In step 410, a determination is made as to whether notch N has been detected. The processor 1204 of the controller 1200 will determine whether notch N has been detected based on the signal from the detection unit 240. If it is determined that notch N has not been detected, the process 400 will loop back to step 408, and the pre-aligner 200 will continue to scan for notch N using the detection unit 240. It should be noted that if notch N is not detected within the notch window because the detection unit 240 fails to detect notch N or because the starting point is located after the position of the notch within the notch window, the process will continue to scan for notch N at the scan speed until notch N is detected, even if this requires the wafer W to rotate a full circle or more.

[0049] In step 410, if it is determined that notch N has been detected, the process 400 proceeds to step 412, where the pre-aligner 200 will rotate the wafer W to the desired alignment position (e.g., a predetermined alignment position) using maximum acceleration / deceleration without exceeding the maximum speed value. In other words, the pre-aligner will rotate the wafer W by accelerating and / or decelerating at the maximum value in order to reach the desired alignment position as quickly as possible and within the shortest possible time period without exceeding the maximum speed value. Thus, if the pre-aligner 200 rotates the wafer at the maximum acceleration value and reaches the maximum speed value before reaching the desired alignment position, the pre-aligner 200 will stop further acceleration and will begin decelerating at the maximum deceleration value in order to reach and stop at the desired alignment position (e.g., see Figure 9 ). It should be noted that the direction of rotation from the detection of the notch to the desired alignment position can be a continuation of the direction during the notch scan (i.e., counterclockwise in the example shown in Figures 4 to 9 ), or the direction can be reversed, depending on which direction will result in the shortest time period to reach the desired alignment position.

[0050] The following Figures 4 to 9 depicts Figure 3 various possible scenarios of the process 400. Figure 4 A schematic diagram depicting a plan view of the wafer W1 is shown, and Figure 5 depicts Figure 4 the movement trajectory diagram of the wafer W1 using the process 400. Figure 6 depicts Figure 4 an alternative movement trajectory diagram of the wafer W1 using the process 400 in the following scenario: reaching the maximum speed V after the detection of the notch during the movement trajectory max . Figure 7 depicts Figure 4 another alternative movement trajectory diagram of the wafer W1 using the process 400 in the following scenario: reaching the maximum speed V before the detection of the notch during the movement trajectory max .Figure 8 A schematic diagram depicting a plan view of the wafer W2, and Figure 9 depicts Figure 8 a movement trajectory diagram of the use process 400 of the wafer W2, where during the movement trajectory, a speed greater than the scanning speed is reached before reaching the notch window, and a speed greater than the scanning speed is reached after detecting the notch.

[0051] The present disclosure relates to finding notches and notch windows, and provides a new technique using a memory storing such parameters, which allows the pre-aligner to memorize the approximate position (or position range) of the notch over time. This technique will reduce the maximum and average alignment times.

[0052] The movement trajectory formed using the algorithms set forth herein will allow the pre-aligner to accelerate and decelerate to the notch window stored in the memory, where the notch is most likely to occur. When within the notch window, the pre-aligner will search for the notch at the scanning speed. Once the pre-aligner detects the notch, the pre-aligner can determine how far the wafer must be rotated to reach the desired position. To reach the desired alignment position, the pre-aligner can utilize the maximum acceleration and maximum speed values, as scanning is not required during this movement. It should be noted that to find the edge, a minimum distance must be rotated.

[0053] Accordingly, the present disclosure provides the following process, wherein: (i) using the maximum acceleration / deceleration to reach the notch window and enter the notch window at the scanning speed; (ii) scanning at the scanning speed until the notch is reached; (iii) using the maximum acceleration / deceleration to move the wafer to the predetermined alignment position. This process will also take into account the maximum speed to limit the rotational speed during movement outside the notch window. The movement trajectory can be customized according to how much scanning is required.

[0054] The first possible scenario involves the following situation: The wafer is placed on the pre-aligner such that the detector 250 is already within the notch window, and the notch is directly clockwise of the detector 250. For example, Figure 4 depicts such a scenario, where a schematic diagram of the plan view of the wafer W1 is shown. Figure 4 The starting point x0 in Figure 4 represents the angular position aligned with the sensing area of the detector 250 of the pre-aligner. As w1 shown, the notch window has a starting point x w2 . Figure 4 The notch position x n and the desired or predetermined alignment position x d are shown in

[0055] Figures 5 to 7 respectively show Figure 4The movement trajectory of the wafer W1 during the usage process 400, where the notch position is x n close enough to the starting point x0 such that the wafer does not reach the scanning speed before the notch is detected when rotating with the maximum acceleration. There exist movement trajectories in the following situations Figure 5 and 6 : The notch appears before reaching the range Δx, where Δx is the distance required to stop and reach the scanning speed V S ; and there exist movement trajectories in the situation where the notch appears after reaching the range Δx Figure 7 . Figure 6 Depicts Figure 4 an alternative movement trajectory diagram of the wafer W1 during the usage process 400 in the following scenario: During the movement trajectory, during the process of moving to the desired alignment position x d , after the notch is detected at the notch position x n , the maximum speed V max is reached.

[0056] Therefore, the movement trajectory is subdivided as follows: (i) Before reaching the notch, with the initial maximum acceleration; and continue to move forward with the maximum acceleration / deceleration until the desired alignment position is reached without exceeding the maximum speed. Since the controller 1200 can determine how far the desired alignment position is from the detected notch position, the controller 1200 can calculate whether the rotating unit 210 can accelerate all the way to the maximum speed and continue to move forward at that speed before decelerating, as shown in Figure 6 ; or whether it is necessary to accelerate to a speed lower than the maximum speed and start decelerating before reaching the maximum speed, as shown in Figure 5 .

[0057] The total movement time can be subdivided as follows:

[0058] The time required to reach the notch during the initial acceleration process;

[0059] The time required to reach the desired alignment position. This depends on the distance of the desired position from the notch, because it determines whether there is enough space to accelerate from the intermediate speed V int all the way to the maximum speed before cruising (shown in parentheses) and decelerating, or whether the wafer can only accelerate to a certain lower speed V before decelerating;

[0060] Δt full = Δt1 + Δt2 + Δt f : The total movement time.

[0061] To solve for the speed V in the Δt2 term above, a system of three equations and three unknowns is developed as follows:

[0062] Describe how the wafer accelerates from an intermediate speed to the peak speed;

[0063] 0 = V 2 + 2(-α)x down : Describe how the wafer decelerates from the peak speed to zero; and

[0064] x up + x down = x desired - x notch : The distance covered during acceleration and deceleration is equal to the distance from the notch to the desired alignment position.

[0065]

[0066] Repeat this process for the different trajectories detailed below; however, use slightly modified equations.

[0067] Another possibility when the wafer is placed such that the sensor is within the window of the notch is that the notch is not within the Δx range. Figure 7 The movement trajectory in this case is shown, which is similar to Figure 5 the movement trajectory, except that the pre-aligner must cruise at the scanning speed until the notch is found.

[0068] For Figure 7 the movement trajectory, the total movement time can be subdivided as follows:

[0069] The time required to reach the scanning speed;

[0070]

[0071] The time required to reach the desired alignment position. This depends on the distance of the desired alignment position from the notch, as it determines whether there is enough space to accelerate from the intermediate speed V int all the way to the maximum speed, or whether the wafer can only accelerate to a certain lower speed V before decelerating; and

[0072] Δt full = Δt1 + Δt2 + Δt3 + Δt f : The total movement time.

[0073] The second possible scenario involves the case where the wafer is placed on the pre-aligner such that the detector 250 is initially outside the notch window. For example, Figure 8 such a scenario is depicted in, which shows a schematic diagram of the plan view of the wafer W2. Figure 8The starting point x0 therein also represents the angular position aligned with the sensing area of the detector 250 of the pre-aligner. As Figure 8 shown, the notch window also has a starting point x w1 and an end point x w2 . Figure 8 The notch position x n and the desired or predetermined alignment position x d are shown in Figure 9 . Figure 8 The movement trajectory of the wafer W2 in

[0074] using the process 400 is shown. Figure 8 The breakdown of the movement trajectory related to the scenario shown in

[0075] is as follows: w The time required to reach the starting point of the notch window x. This depends on the distance of the notch from the initial starting position, as it determines whether there is enough space to accelerate to the maximum speed before cruising (shown in parentheses) and decelerating, or whether the wafer can only accelerate to a certain lower speed V before decelerating;

[0076] The time required to cruise from the edge of the window to the notch at the scanning speed;

[0077] The time required to reach the desired alignment position. This depends on the distance of the desired alignment position from the notch, as it determines whether there is enough space to accelerate from the scanning speed to the maximum speed before cruising (shown in parentheses) and decelerating, or whether the wafer can only accelerate to a certain lower speed V before decelerating; and

[0078] Δt full = Δt1 + Δt2 + Δt3 + Δt f : The total movement time.

[0079] Due to the fact that the controller 1200 of the pre-aligner will know the position of the notch window after a period of time, and the detector 250 can scan in both directions, the pre-aligner 200 will be able to realize that if the notch distance from the initial position exceeds 180° in the clockwise direction, the wafer can be rotated counterclockwise and the same movement trajectory scenario as described above can be used.

[0080] Various detected notch positions, average notch positions, and notch windows (ranges), in addition to being stored in the memory 1206 of the controller 1200, can also be stored in the non-volatile memory (e.g., ROM1208) on the board within the pre-aligner. In this way, if the system is powered on again, it can retain the historical record of such data.

[0081] It should be noted that if the notch is not found within the notch window as expected, the process can continue scanning at the scanning speed until the notch is detected. If the notch position is shown to be consistent within a certain range on some number of wafers, a notch memory implementation is preferably used.

[0082] It should be noted that as the pre-aligner rotates the wafer, the center of the wafer does not have to be placed at the center of the wafer chuck of the pre-aligner. Thus, in order to find the wafer center, the eccentricity caused by the offset can be discovered. The present disclosure utilizes a least squares approximation to identify the center of the wafer, which has significantly fewer required rotations (e.g., 90 degrees) compared to other methods that may require scanning approximately 360 degrees of rotation to locate the center of the wafer.

[0083] Figure 10 A schematic diagram of the wafer W3 relative to the center of the wafer chuck and the reading head of the detector of the pre-aligner is shown. Figure 10 Shown are the wafer W3, the center C1 (e.g., the center of rotation of the wafer chuck 230), and the reading head 246 of the detector 250 of the pre-aligner 200. The pre-aligner rotates the wafer W3 by an angle θ. The center C2 of the wafer W3 does not have to be placed at the center C1 of the wafer chuck. The eccentricity is defined by the radius r and the offset angle β. As the wafer rotates, the magnitude of the vector p is measured for varying angles θ. For a given wafer radius R, the eccentricity can be found.

[0084]

[0085]

[0086] Thus, the two equations have three unknowns r, and β. In addition, β is a continuously fluctuating value that varies with the angle. Finally, the reading head 246 will have a certain measurement width such that the position of the vector p in the direction orthogonal to the pixels of the reading head is uncertain. The expected eccentricity is preferably not greater than 2 mm. Given a wafer radius of 150 millimeters, the maximum expected value of R*cos(β) is:

[0087] 150 – 150*cos(atan(2 / 150)) = 13 microns.

[0088] Assuming the effect of the angle β is small, the cos(β) term is linearized as follows:

[0089]

[0090] It can be rewritten as:

[0091]

[0092] This is an equation with two unknowns. We can generate N equations with N subsequent rotation angles to perform a least-squares approximation as follows:

[0093]

[0094] X * A = b;

[0095] where X is N×2, A is 2×1, and b is N×1;

[0096] X T * X * A = X T * b;

[0097] A = (X T * X) -1 * X T * b.

[0098] To account for errors in the variables R and p, we re - consider the above equation as follows:

[0099]

[0100] For the ideal radius, we expect p to have a sinusoidal component as well as a steady - state value:

[0101]

[0102]

[0103] We group these steady - state terms together as follows:

[0104] a = - p o - δp + R + δR

[0105] Thus,

[0106]

[0107] This is an equation with three unknowns. We can generate N equations with N subsequent rotation angles to perform a least - squares approximation as follows:

[0108]

[0109] X * A = b;

[0110] where X is N×3, A is 3×1, and b is N×1;

[0111] X T * X * A = X T * b;

[0112] A = (X T*X) -1 *X T *b。

[0113] In this way, we considered any change in the steady-state offset and extracted the pure eccentricity of the wafer.

[0114] Figure 11 The scratch specifications regarding the polished single-crystalline silicon wafer specifications from the 2017 Semiconductor Equipment & Materials Institute (SEMI) M1 draft document are depicted. It should be noted that the pins shown in the Figure 11 sketch can be used to align the scratched wafer within the fixture during use. The pins can also be used to index the scratched wafer during the process of testing the scratch size and dimensional tolerances. Figure 11 The scratch sizes shown in assume that the diameter of the alignment pins is 3 mm. The scratch sizes are for illustrative purposes only and are not intended to limit the scope of the claims described herein.

[0115] Figure 12 An embodiment of a computer system (or controller) 1200 for implementing an embodiment of the present invention is shown. Although the computer system 1200 is depicted for a particular device or apparatus, it is contemplated that other devices or apparatuses (e.g., network elements, servers, etc.) may deploy the illustrated hardware and components of the computer system 1200. The computer system 1200 is programmed (e.g., via computer program code or instructions) to provide the functions described herein and includes a communication mechanism such as a bus 1202 for transferring information between other internal and external components of the computer system 1200. One or more processors 1204 for processing information are coupled to the bus 1202 to perform a set of operations on the information specified by the computer program code.

[0116] The computer system 1200 also includes a memory 1206 coupled to the bus 1202. The memory 1206 (e.g., random access memory (RAM) or other dynamic storage device) stores information including processor instructions. The memory 1206 is also used by the processor 1204 to store transient values during the execution of the processor instructions. The computer system 1200 also includes a read-only memory (ROM) 1208 or other static storage device coupled to the bus 1202 for storing static information that is not changed by the computer system 1200, including instructions. The ROM 1208 or a separate memory connected to the bus 1202 may be provided as non-volatile memory. The computer system 1200 includes a communication interface 1216 that allows the computer system 1200 to communicate with other devices or apparatuses (e.g., network elements, servers, internal or external robot controllers, etc.).

[0117] Information including a user input instruction is provided from the user interface 1210 to the bus 1202 for use by the processor 1204. The user interface 1210 is, for example, a keyboard including alphanumeric keys operated by a human user, a display device, a pointing device (e.g., a mouse, or a trackball, or cursor direction keys).

[0118] The rotation unit 1212 (e.g., the rotation unit 210, including a motor 220, and any associated sensors for detecting the rotational position of the wafer chuck 230, and any devices (e.g., a suction device) disposed on the wafer chuck 230 for holding the wafer, etc.) can communicate with the processor 1204 via the bus 1202 to send and receive data, operation instructions / commands, or other information therebetween. The processor 1204 can use the operation instructions / commands to control the operation of the drive device rotation unit 1212 to control the rotation (e.g., start, stop, direction (e.g., clockwise, counterclockwise), speed, etc.) of the output shaft (e.g., the output shaft 222) of the motor 220.

[0119] It should be noted that the computer system 1200 can be additionally connected to a robot (e.g., the robot 100) for moving wafers. In such an arrangement, the robot can communicate with the processor 1204 via the bus 1202 to send and receive data, operation instructions / commands, or other information therebetween. In such an arrangement, the processor 1204 can use the operation instructions / commands to control the operation of the robot to control the actuation of the robot. Alternatively, the computer system 1200 can communicate with a separate controller of the robot via the communication interface 1216 to cooperate with the robot to load wafers onto the pre-aligner and retrieve wafers from the pre-aligner.

[0120] The detection unit 1214 (e.g., the detection unit 240) can communicate with the processor 1204 via the bus 1202 to send and receive data, operation instructions / commands, or other information therebetween. The processor 1204 can use the operation instructions / commands to control the operation of the detection unit 1214 to control the operation of the detection unit 1214 in combination with the operation of the rotation unit 1214.

[0121] The computer system 1200 can be disposed on the housing of the pre-aligner 200, or can be connected to other components of the pre-aligner 200 in a wired manner, or the computer system 1200 can be disposed at a remote location that communicates with other components of the pre-aligner 200 in a wired or wireless manner.

[0122] It should be noted that the exemplary embodiments depicted and described herein illustrate the preferred embodiments of the present invention and are not intended to limit the scope of the claims in any way. Given the foregoing teachings, various modifications and variations of the present invention are possible. Accordingly, it is to be understood that within the scope of the appended claims, the present invention may be practiced in other ways than as specifically described herein.

Claims

1. A pre-aligner for pre-aligning a wafer, the wafer having a notch on its peripheral edge, the pre-aligner comprising: A rotation unit, comprising: a wafer platform having a wafer receiving surface configured to receive the wafer; and a driving device configured to rotate the wafer platform about an axis; A detector configured to detect the notch on the wafer when the wafer is received on the wafer receiving surface; A memory configured to store a notch window that defines a range of angles relative to a starting position where the wafer is initially received on the wafer receiving surface, wherein the notch is predicted to be located within the range of angles, the starting position corresponding to the sensing area of the detector; and A controller programmed to perform a pre-alignment operation in which the wafer is rotated from the starting position to a predetermined alignment position; wherein the controller is programmed to perform the pre-alignment operation such that the wafer is rotated from the starting position to the notch position detected by the detector at a maximum acceleration / deceleration value; wherein the pre-alignment operation is limited to a maximum speed for rotating the wafer from the starting position to the notch window; and wherein the pre-alignment operation is limited to a scan speed for rotating the wafer within the notch window before the detector detects the notch position, the scan speed being less than the maximum speed.

2. The pre-aligner according to claim 1, wherein, The controller is programmed to further perform the pre-alignment operation such that the wafer is rotated from the notch position detected by the detector to the predetermined alignment position at the maximum acceleration / deceleration value, wherein the pre-alignment operation is limited to the maximum speed for rotating the wafer from the notch position detected by the detector to the predetermined alignment position.

3. The pre-aligner according to claim 1, wherein, The controller is programmed to minimize the time period for moving from the starting position to the notch position detected by the detector.

4. The pre-aligner according to claim 1, wherein, The controller is programmed to minimize the time period for moving from the starting position to the predetermined alignment position.

5. The pre-aligner according to claim 1, wherein, The controller is programmed to use a least squares approximation to determine the eccentricity between the center of the wafer at the predetermined alignment position and the rotation center of the wafer platform having the wafer receiving surface.

6. The pre-aligner according to claim 1, further comprising a non-volatile memory configured to store the notch window.

7. A method for pre-aligning a wafer, comprising: Providing a wafer platform having a wafer receiving surface configured to receive a wafer, the wafer having a notch on its peripheral edge; Providing a detector configured to scan the peripheral edge of the wafer to detect the notch on the wafer when the wafer is received on the wafer receiving surface; Setting a notch window that defines a range of angles relative to a starting position where the wafer is initially received on the wafer receiving surface, wherein the notch is predicted to be located within the range of angles, the starting position corresponding to the sensing area of the detector; and And Perform a pre-alignment operation in which the wafer is rotated from the starting position to a predetermined alignment position during the pre-alignment operation. Wherein the pre-alignment operation is performed such that the wafer is rotated from the starting position to the notch position detected by the detector at a maximum acceleration / deceleration value. Wherein the pre-alignment operation is limited to a maximum speed for rotating the wafer from the starting position to the notch window. And Wherein the pre-alignment operation is limited to a scanning speed for rotating the wafer within the notch window before the detector detects the notch position, and the scanning speed is less than the maximum speed.

8. The method according to claim 7, wherein, The pre-alignment operation is also performed such that the wafer is rotated from the notch position detected by the detector to the predetermined alignment position at the maximum acceleration / deceleration value, wherein the pre-alignment operation is limited to the maximum speed for rotating the wafer from the notch position detected by the detector to the predetermined alignment position.

9. The method according to claim 7, wherein, The notch window is set by: Performing notch detection on a predetermined number of consecutive wafers to collect notch position data relative to the starting position. Determining an angular range within which a predetermined percentage of the notch position data falls. And Setting the notch window to the angular range.

10. The method according to claim 7 further comprises: Using a least squares approximation to determine the eccentricity between the center of the wafer at the predetermined alignment position and the rotation center of the wafer platform having the wafer receiving surface.

11. The method according to claim 7 further comprises: Store the notch window in a memory.

12. The method according to claim 7 further comprises: Store the notch window in a non-volatile memory.

13. A method for pre-aligning a wafer, comprising: Providing a wafer on a wafer platform having a wafer receiving surface, the wafer having a notch on its peripheral edge. Rotating the wafer on the wafer platform from an initial starting position of receiving the wafer from the wafer receiving surface until a detector detects a notch position of the notch relative to the starting position, the starting position corresponding to a sensing area of the detector. Storing the notch position in a memory. Repeating the providing, rotating, and storing for one or more consecutive wafers to collect and store notch position data in the memory. Using the notch position data to set a notch window that defines a range of angles relative to the starting position at which the wafer receiving surface initially receives subsequent wafers, wherein subsequent notches of the subsequent wafers are predicted to be located within the range of angles. And Performing a pre-alignment operation on the subsequent wafer, wherein the subsequent wafer is rotated from the starting position to the notch position of the subsequent wafer within a first shortest time period using the notch window.

14. The method according to claim 13, wherein Performing the pre-alignment operation on the subsequent wafer, wherein the subsequent wafer is rotated from the starting position to a predetermined alignment position within a second shortest time period using the notch window.

15. The method according to claim 13, Among them, Perform the pre - alignment operation on the subsequent wafer such that the subsequent wafer is rotated from the starting position to the notch position detected by the detector at a maximum acceleration / deceleration value: wherein, the pre - alignment operation is limited to a maximum speed for rotating the subsequent wafer from the starting position to the notch window; and wherein, the pre - alignment operation is limited to a scanning speed for rotating the subsequent wafer within the notch window before the detector detects the notch position, and the scanning speed is less than the maximum speed.

16. The method according to claim 15, wherein, Also perform the pre - alignment operation such that the subsequent wafer is rotated from the notch position detected by the detector to a predetermined alignment position at the maximum acceleration / deceleration value, wherein the pre - alignment operation is limited to the maximum speed for rotating the subsequent wafer from the notch position detected by the detector to the predetermined alignment position.

17. The method according to claim 13, wherein, The notch window is set by: determining an angular range within which a predetermined percentage of the notch position data falls; and setting the notch window to the angular range.

18. The method according to claim 13 further comprises: Use least - squares approximation to determine the eccentricity between the center of the subsequent wafer at the predetermined alignment position and the rotation center of the wafer platform having the wafer receiving surface.

19. The method according to claim 13, further comprising storing the notch window in a memory.

20. The method according to claim 13, further comprising: Store the notch window in a non - volatile memory.

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