Wafer pre-aligner and wafer pre-alignment method

Abstract

To provide a wafer pre-aligner and a method of pre-aligning a wafer, capable of improving speed of pre-alignment for a semiconductor wafer with a notch.SOLUTION: A pre-aligner 200 includes: a wafer platform 230 such as a wafer chuck having a semiconductor wafer W receiving surface; and a drive device 220. A detector 240 is provided to detect a notch N. A memory is provided to store a notch window defining a range of angles in which the notch is predicted to be located in relation to a start position. A controller performs a pre-alignment operation where the wafer is rotated from the start position to an alignment location. The controller performs the operation such that the wafer is rotated at maximum acceleration / deceleration values from the start position to a notch location detected by the detector. The operation is limited to maximum velocity for the rotation of the wafer from the start position to the notch window. The operation is limited to scanning velocity within the notch window until the notch location is detected.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] A pre-aligner is used to locate 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, which rotates the wafer, to search for the notch. Once the notch is located, the wafer is turned to a final orientation dictated by the process to be performed on the wafer.

[0003] The position of the notch when it arrives at the prealigner may be at any position relative to the prealigner depending on previous processes performed on the wafer and / or robot movement operations. Therefore, as shown in FIG. 13, in some related art prealigners, when the prealigner searches for the notch, it must scan slowly (i.e., at or below the scan speed, which is the maximum speed at which the prealigner can accurately detect the notch) from the start of rotation until the prealigner detects the notch. FIG. 13 shows a plan view of the position of the wafer in relation to a corresponding acceleration vs. time graph and a corresponding velocity vs. time graph. In such a prealigner, the prealigner starts rotating at position "A" along the velocity vs. time graph of FIG. 13, speeds up until the rotation reaches the scan speed at position "B", and then maintains the scan speed until the notch is detected at position "C". Thus, in some related art pre-aligners, the wafer must be scanned at or below the scan speed until the notch is located, then the wafer is decelerated (e.g., from position "C" to position "D" in FIG. 13), and then the wafer is moved to its final orientation (e.g., from position "D" to position "E" in FIG. 13).

[0004] In addition, when the robot places the wafer on the pre-aligner chuck, the center of the wafer may not be aligned with the center of rotation of the pre-aligner chuck. Some related art pre-aligners use a method that requires the wafer to be rotated and scanned approximately 360 degrees to locate the wafer center. Summary of the Invention [Problem to be solved by the invention]

[0005] It has been found that such related art pre-aligners can be slow when performing wafer pre-alignment and leave room for significant improvement. [Means for solving the problem]

[0006] The present invention advantageously provides a pre-aligner for pre-aligning a wafer having a notch on its outer periphery. The pre-aligner includes a rotation unit including a wafer platform having a wafer receiving surface configured to receive a wafer, and a drive configured to rotate the wafer platform about an axis. The pre-aligner further includes a detector configured to detect a notch of the wafer when the wafer is received on the wafer receiving surface, a memory configured to store a notch window defining an angular range in which the notch is expected to be located relative to a starting position where the wafer is initially received on the wafer receiving surface and corresponding to a sensing area of ​​the detector, and a controller programmed to perform a pre-alignment operation to rotate the wafer from the starting position to a predetermined alignment position. The controller is programmed to perform the pre-alignment operation to rotate the wafer from the starting position to a notch position detected by the detector with a maximum acceleration / deceleration value. The pre-alignment operation is limited to a maximum speed when rotating the wafer from the starting position to the notch window. The pre-alignment operation is limited to a scan speed that is less than the maximum speed when rotating the wafer within the notch window until the notch position is detected by the detector.

[0007] The present invention advantageously provides a method including the steps of: providing a wafer platform having a wafer receiving surface configured to receive a wafer having a notch on its outer periphery; providing a detector configured to scan the outer periphery of the wafer to detect the notch of the wafer when the wafer is received on the wafer receiving surface; setting a notch window defining an angular range within which the notch is expected to be located relative to a start position where the wafer is initially received on the wafer receiving surface and which corresponds to a sensing area of ​​the detector; and performing a pre-alignment operation to rotate the wafer from the start position to a predetermined alignment position. The pre-alignment operation is performed to rotate the wafer with a maximum acceleration / deceleration value from the start position to a notch position detected by the detector. The pre-alignment operation is limited to a maximum speed when rotating the wafer from the start position to the notch window. The pre-alignment operation is limited to a scan speed when rotating the wafer within the notch window until the notch position is detected by the detector. The scan speed is less than the maximum speed.

[0008] The present invention advantageously provides a method including the steps of: providing a wafer having a notch on an outer periphery of the wafer on a wafer platform having a wafer receiving surface; rotating the wafer on the wafer platform from a start position at which the wafer is initially received on the wafer receiving surface and corresponding to a sensing area of ​​a detector until the detector detects a notch position of the notch relative to the start position; storing the notch position in a memory; repeating the providing, rotating and storing steps for one or more successive wafers to collect and store notch position data in the memory; setting a notch window using the notch position data to define an angular range within which a subsequent notch of the subsequent wafer is expected to be located relative to the start position at which the subsequent wafer is initially received on the wafer receiving surface; and performing a pre-alignment operation on the subsequent wafer using the notch window to rotate the subsequent wafer from the start position to the notch position of the subsequent wafer within a first shortest time. [Brief description of the drawings]

[0009] [Figure 1] FIG. 2 is a perspective view of a robot and a pre-aligner according to an embodiment of the present invention. [Diagram 2] 13 is a flow chart of a process in which a notch memory is used to store data that allows for improved performance of a pre-aligner. [Diagram 3] 13 is a flowchart of a process of a pre-alignment operation of the pre-aligner in which the performance of the pre-aligner is optimized. [Figure 4] 1 shows a schematic diagram of a wafer plan view in a first starting point scenario. [Diagram 5] 5 shows a graph of the motion profile of the wafer of FIG. 4 using the process of FIG. 3. [Figure 6] 5 shows a graph of an alternative motion profile for the wafer of FIG. 4 using the process of FIG. 3 in a scenario in which a maximum velocity is reached during the motion profile after detection of the notch. [Figure 7] 5 shows a graph of a further alternative motion profile for the wafer of FIG. 4 using the process of FIG. 3 in a scenario in which a maximum velocity is reached during the motion profile before a notch is detected. [Figure 8] FIG. 13 shows a schematic diagram of a wafer plan view in a second starting point scenario. [Figure 9] 9 shows a graph of the motion profile of the wafer of FIG. 8 using the process of FIG. 3 , which reaches a speed faster than the scan rate before reaching the notch window during the motion profile, and reaches a speed faster than the scan rate after detecting the notch. [Figure 10] 1 shows a schematic diagram of the wafer in relation to the center of the wafer chuck and the read head of the detector of the pre-aligner to determine eccentricity and find the center of the wafer. [Figure 11] An example of a conventional notch specification is shown below. [Figure 12] 1 illustrates an embodiment of a computer system (or controller) upon which embodiments of the present invention may be implemented. [Figure 13]1 shows a plan view of the position of a wafer in relation to corresponding acceleration versus time graphs and corresponding velocity versus time graphs of a related art example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. In the following description, components having substantially the same functions and configurations are designated by the same reference numerals, and duplicated descriptions will be given only when necessary.

[0011] In semiconductor manufacturing, it is important to accurately determine the placement (i.e., location and orientation) of a semiconductor wafer in order to accurately perform precise manufacturing processes on the semiconductor wafer. Because the wafer is moved between processing stations using a robot, such as an atmospheric articulated robot, it is important to determine the location of the semiconductor wafer at a particular processing station. For example, a pre-aligner may be used to identify the location of a notch on the periphery of the semiconductor wafer in order for the pre-aligner to determine the location of the semiconductor wafer.

[0012] 1 shows a perspective view of a robot 100 including an arm member 110 and an end effector 120. The robot 100 may be configured as an articulated robot having a robot arm with one or more arm members rotatable relative to one another and an end effector rotatably mounted at the end of the robot arm. The robot 100 is configured to move the end effector in the X, Y, and Z directions as well as rotate the end effector about one or more axes, including at least the Z axis. The end effector has a top surface 122 configured to receive, support, and transport semiconductor wafers between processing stations, such as from a first processing station to a second processing station, during manufacturing.

[0013] Figure 1 illustrates a scenario in which a robot 100 has transferred a semiconductor wafer W to a processing station that includes a pre-aligner 200. The pre-aligner 200 is shown in Figure 1 as including a rotation unit 210 and a detection unit 240. For ease of depiction, the pre-aligner 200 shown in Figure 1 is shown without a housing that may be provided to house both the rotation unit 210 and the detection unit 240.

[0014] The rotation unit 210 includes a rotation motor (or drive) 220 having a rotation shaft 222 protruding upward. The motor 220 may 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 a vertical center of the rotation shaft 222. A wafer platform, such as a wafer chuck 230, is attached to an end of the rotation shaft 222. The wafer chuck 230 has a wafer receiving surface 232 configured to receive a semiconductor wafer W. The rotation axis 224 extends through a center of rotation of the wafer platform 230 and a center of rotation of the wafer receiving surface 232. The wafer receiving surface 232 may comprise a surface material that supports the wafer and also prevents the wafer W from moving relative to the wafer receiving surface 232 by creating friction between the wafer W and the wafer receiving surface 232. Alternatively or in addition to this surface material, the wafer receiving surface 232 may have suction holes and the wafer chuck 230 may have a suction device for holding the wafer W on the wafer receiving surface 232 and preventing the wafer W from moving relative to the wafer receiving surface 232.

[0015] The detection unit 240 includes a base 242, a support member 244, and a read head 246. The base 242 supports the support member 244 and the read head 246. The support member 244 supports the read head 246 on the base 242. The base 242 is mounted 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 be moved relative to each other. For example, the base 242 can be mounted to the housing such that the detection unit 240 can be moved linearly toward and away from the rotation unit 210 so that the pre-aligner 200 can be used with semiconductor wafers of various diameters.

[0016] The detection unit 240 includes a detector 250 configured to sense the presence of a wafer received on the wafer receiving surface 232. 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 use of the terms "scan" or "scanning" herein includes operation of the detector 250 around the periphery of the wafer with or without rotation of the wafer W.) 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 in the base 242, and a lens 256 is provided on the top end of the base 242. The light sensor 254 is disposed on the read head 246. The light sensor 254 may 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 light L thus collimated is received by the light sensor 254. The detection unit 240 including the read head 246 has the light sensor 254 facing in the -Z direction toward the top surface of the wafer W, which can detect the wafer in a detection area, for example, the edge of the wafer or a mark / notch formed on the wafer, to align the semiconductor wafer for inspection and / or processing. The detector 250 can determine whether or not the outer periphery E of the wafer W and the notch provided on the outer periphery E of the wafer W are present by detecting whether or not light is received by the detection device on the optical sensor 254 .

[0017] The pre-aligner 200 is controlled by one or more controllers, an embodiment of which is described below with respect to Fig. 12. The robot 100 may be controlled by a controller separate from that of the pre-aligner, or the robot 100 and the pre-aligner 200 may be controlled by one or more common controllers.

[0018] It should be noted that a pre-aligner such as the pre-aligner 200 has certain operating parameters within which the pre-aligner operates. For example, the rotation unit 210 of the pre-aligner 200 will have a maximum angular velocity (also referred to herein as maximum speed) and a maximum angular acceleration / deceleration (also referred to herein as maximum acceleration and maximum deceleration) at which the pre-aligner can rotate the wafer. Such maximum velocity and maximum acceleration / deceleration values ​​depend on the operating parameters of the motor 220 (e.g., the operating range of the speed and acceleration / deceleration). Such maximum velocity and maximum acceleration / deceleration values ​​as used herein may also depend on the operating parameters of the wafer chuck 230 (e.g., the surface friction or suction device provided therein that ensures that the wafer stays on the wafer chuck within a certain speed and acceleration / deceleration range), which may cause these values ​​to be below the operating parameters of the motor 220. In addition, the pre-aligner will have a maximum scanning speed (also referred to herein as scanning speed), which is the maximum speed at which the detection unit 240 of the pre-aligner can accurately detect the notch. Typically, the scanning speed is less than the maximum speed of the motor 220 of the rotating unit 210 .

[0019] As shown in Fig. 1, the robot 100 transfers a semiconductor wafer W to a processing station including a pre-aligner 200 and places the wafer on a wafer chuck 230 of the pre-aligner 200. A motor 220 of the pre-aligner 200 rotates the wafer chuck 230, thereby rotating the wafer W, to search for a notch N using an optical sensor such as a detector 250. Once the notch N is identified, the wafer W is oriented to a final orientation, e.g., in the processing station where the pre-aligner 200 is located, as defined by the process to be performed on the wafer W. The position of the notch N upon arrival at the pre-aligner 200 may vary relative to the pre-aligner 200 depending on previous processes performed on the wafer W and / or movement operations of the robot 100.

[0020] The pre-aligner 200 is used to identify the location of a notch N on a semiconductor wafer W. It has been found that the location of the notch N relative to the pre-aligner 200 on which the wafer is placed is generally consistent from wafer to wafer within some tolerance. In other words, when the robot 100 repeats the same general movement of the wafer from a previous processing station to the processing station where the pre-aligner 200 is located, the wafer is typically positioned and oriented similarly from wafer to wafer within some tolerance. Thus, the method described herein includes using the pre-aligner 200 to scan along the velocity versus time graph of FIG. 13 from position "A" to position "C" for the notch of successive wafers using a process similar to that of the related art shown in FIG. 13, and storing the notch positions of these successive wafers in a memory (also referred to herein as a notch memory). From those notch positions, a range of notch positions can be established and stored in the notch memory, and such data can be used to define a notch window. The notch window is the angular range in which the notch is expected to be located relative to a starting position where the wafer is initially received on the wafer receiving surface, which starting position corresponds to the sensing area of ​​the detector 250. The number of stored notch positions (i.e., the number of data points) used to set the notch window can be determined so that the operator has a predetermined confidence level that any given notch of a future wafer will fall within the notch window (e.g., 90% or 95% or 99% of the data points, etc., will fall within 10° to 35° from the starting point, or within 5° to 15° from the starting point, or within −10° to 15° from the starting point, etc.). Once the notch window is set, the pre-aligner 200 can scan the wafer for the notch using a process in which the maximum acceleration / deceleration and maximum velocity of the rotation unit 210 are utilized until the wafer W is rotated from the starting position to the notch window, and may also be utilized during the rotation of the wafer W after the notch is detected.This can advantageously increase the speed at which the notch can be detected and the wafer can be oriented to the desired alignment position, and can advantageously reduce the time in which the alignment is performed, thereby increasing throughput while maintaining alignment accuracy.

[0021] Thus, it has been found that if the notch location of successive wafers is known to be consistent over a number of wafers, then instead of scanning at a slower speed, the pre-aligner can move with maximum acceleration and speed in an optimal direction to the region of the expected notch (i.e., the notch window), and then the pre-aligner can slow down the wafer rotation to the scanning speed to find the notch within the expected region. Kinematic studies have been performed to demonstrate the throughput advantages of using such a notch memory, which can be easily understood by the following analogy: If a person is looking for a lost dog, he or she would normally have to drive slowly around the town searching for the dog until he or she finds it in the town. Once he or she finds the dog, he or she must drive the dog to its owner. In the case of the notch memory process, the person knows that dogs usually like to run away to the butcher. In this case, the person can drive to the butcher as fast as possible, pick up the dog, and return it to its owner in a much shorter time.

[0022] 2 illustrates a process 300 in which a notch memory is used to store data that allows for improved performance of the pre-aligner. The process 300 includes a step 302 of loading a wafer into the pre-aligner. For example, as shown in FIG. 1, the robot 100 transfers a semiconductor wafer W to a processing station that includes a pre-aligner 200. The robot 100 uses the end effector 120 to place the wafer W on the wafer receiving surface 232 of the wafer chuck 230, and then the robot 100 moves the end effector 120 away from the pre-aligner. The location of the notch N based on the position of the wafer W.

[0023] The process 300 includes a step 304 of scanning the wafer using the pre-aligner to locate 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 detects (or scans) the outer edge E of the wafer W. Light is emitted from the light source 252, and the light is collimated by the lens 256, so that the collimated light L is received by the light sensor 254. The light sensor 254, which faces in the -Z direction toward the top surface of the wafer W, detects the wafer within the detection area, for example, the edge of the wafer or a mark / notch formed on the wafer. The detector 250 can determine the presence or absence of the outer edge E of the wafer W and the presence or absence of the notch N provided on the outer edge of the wafer W by detecting the reception or non-reception of light by the detection device on the light sensor 254. The processor 1204 of the controller 1200 (see FIG. 12) of the pre-aligner 200 determines whether a notch is detected based on the signal from the detection unit 240.

[0024] Process 300 further includes a step 306 in which the position of notch N detected in step 304 is stored in a notch memory, such as memory 1206 of controller 1200 shown in FIG. 12 and discussed in more detail below. The position of notch N includes an angle value about the central axis of wafer W relative to a starting position.

[0025] The process 300 further includes a step 308 in which the controller determines whether a notch window confidence level has been reached. This determination is based on whether a sufficient number of data points for the notch points of successive test wafers have been accumulated and stored so that the operator has confidence that any given notch of future wafers will likely fall within the notch window. For example, if the collected data points are evenly distributed across the entire 360 ​​degrees of the central axis of the wafer, the operator may not be able to set a narrow notch window with an acceptable level of confidence. On the other hand, if 95% of the collected data points are within a 30 degree range that extends from 10 degrees past the start position to 40 degrees past the start position, the operator may decide to set the notch window to that 30 degree range. The confidence level can be set based on various parameters, such as, for example, that a predetermined number of data points are collected (e.g., a minimum of 20 data points, a minimum of 40 data points, etc.) and that a predetermined percentage of the data points (e.g., 90 percent, 95 percent, etc.) fall within a notch window of a predetermined range (e.g., 20 degrees, 30 degrees, etc.). This allows an operator to set the confidence level based on parameters that will achieve a desired result. Setting such a notch window can be done manually by an operator or by a processor running an algorithm that takes into account such parameters (i.e., minimum number of data points, percentage of data points falling within a predetermined range).

[0026] Thus, in step 308, if the notch window confidence level has not been reached, the process 300 loops back to step 302 where another wafer is loaded into the pre-aligner to collect another data point in the notch memory. On the other hand, if in step 308 the notch window confidence level has been reached, the process 300 proceeds to step 310.

[0027] In step 310, the set notch window is stored in a notch memory, for example memory 1206 of Figure 12. The notch window includes a range of angle values ​​about the central axis of the wafer W relative to a starting position.

[0028] Notably, once each of steps 302 and 304 have been performed for each wafer processed using process 300, pre-alignment of that wafer can proceed from step 304 and be completed in the manner shown in FIG. 13 from position "C" to position "E" to complete pre-alignment of the processed wafer to set the notch window.

[0029] Once the notch window is set, the performance of the pre-aligner can be optimized, for example, as discussed with respect to FIG. 3 which illustrates the pre-alignment operation.

[0030] FIG. 3 shows a pre-alignment operation that includes a process 400 that includes a step 402 of loading a wafer into a pre-aligner.

[0031] In step 404, it is determined whether the starting position of the wafer is within a notch window stored in the notch memory. The starting position is an angular position that coincides 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 (also stored in the memory) (e.g., the notch window extends from −5 degrees from the starting position to +30 degrees from the starting position), the process 400 proceeds to step 408, described below. However, if the processor 1204 of the controller 1200 determines that the starting position is not within the notch window (e.g., the notch window extends from +5 degrees from the starting position to +30 degrees from the starting position), the process 400 proceeds to step 406.

[0032] In step 406, the pre-aligner 200 rotates the wafer W to the notch window using the maximum acceleration / deceleration without exceeding the maximum velocity value. In other words, the pre-aligner rotates the wafer W by accelerating and / or decelerating at the maximum value to reach the notch window as fast as possible without exceeding the maximum velocity value. Thus, if the pre-aligner 200 is rotating the wafer at the maximum acceleration value and reaches the maximum velocity value before reaching the notch window, the pre-aligner 200 stops further acceleration and starts decelerating at the maximum deceleration value to reach the notch window at the scan velocity (see, for example, FIG. 9). Based on the distance from the starting position to the start of the notch window and the maximum acceleration value, the controller 1200 can calculate whether the rotation using the motor will reach or exceed the scan velocity by the time the start of the notch window is reached, which allows the computer system 1200 to calculate the motion profile in a manner described in more detail below with respect to FIGS. 4-9. Hereinafter, the time required for moving the wafer W from the starting position to the starting point of the notch window using the maximum acceleration / deceleration without exceeding the maximum velocity value will be referred to as the first shortest time.

[0033] In step 408, the pre-aligner 200 performs a scan to look for the notch N using the detection unit 240. During step 408, the pre-aligner rotates the wafer W using the maximum acceleration / deceleration without exceeding the scan speed. Thus, if the wafer W is rotating below the scan speed when the notch window is reached, the pre-aligner can rotate the wafer W using the maximum acceleration until it reaches the scan speed, at which point the pre-aligner 200 stops further acceleration.

[0034] In step 410, it is determined whether the notch N is detected. The processor 1204 of the controller 1200 determines whether the notch is detected based on the signal from the detection unit 240. If it is determined that the notch N is not detected, the process 400 loops back to step 408, and the pre-aligner 200 continues scanning for the notch N using the detection unit 240. Note that if the notch N is not detected within the notch window because the detection unit 240 fails to detect the notch N or the starting point is within the notch window past the notch location, the process continues scanning for the notch N at the scan speed until the notch N is detected, even if this requires rotating the wafer W one or more times.

[0035] If it is determined in step 410 that the notch N is detected, the process 400 continues to step 412 where the pre-aligner 200 rotates the wafer W to the desired alignment position (e.g., a predetermined alignment position) using a maximum acceleration / deceleration rate without exceeding a maximum velocity value. In other words, the pre-aligner rotates the wafer W by accelerating and / or decelerating at a maximum value in order to reach the desired alignment position as fast as possible and in the shortest possible time without exceeding the maximum velocity value. Thus, if the pre-aligner 200 is rotating the wafer W at a maximum acceleration value and reaches the maximum velocity value before reaching the desired alignment position, the pre-aligner 200 stops further acceleration and starts decelerating at a maximum deceleration value in order to reach and stop at the desired alignment position (see, for example, FIG. 9 ). Note that the direction of rotation from notch detection to the desired alignment position may continue in the direction during the scan looking for the notch (i.e., counterclockwise in the examples shown in Figures 4-9 below), or it may be reversed, depending on which direction will reach the desired alignment position in the shortest time. Hereinafter, this shortest time will be referred to as the second shortest time.

[0036] 4-9 below illustrate various possible scenarios of the process 400 of FIG. 3. FIG. 4 shows a schematic diagram of a top view of the wafer W1, and FIG. 5 shows a graph of the motion profile of the wafer W1 of FIG. 4 using the process 400. FIG. 6 shows the maximum velocity V during the motion profile after the notch is detected. max 7 shows a graph of an alternative motion profile for the wafer W1 of FIG. 4 using process 400 in a scenario where the wafer W1 reaches a maximum velocity V during the motion profile before the notch is detected. max 4 using process 400 in a scenario in which the notch window is reached. Figure 8 shows a schematic diagram of a top view of wafer W2, and Figure 9 shows a graph of a motion profile for wafer W2 of Figure 8 using process 400 in which a speed faster than the scan rate is reached during the motion profile before reaching the notch window, and a speed faster than the scan rate after the notch is detected.

[0037] The present disclosure, which involves finding the notch and notch window and utilizing memory to store such parameters, provides a novel technique that allows the prealigner to remember the approximate location (or range of locations) of the notch over time, which will reduce maximum and average alignment times.

[0038] The motion profile created using the algorithm described herein allows the pre-aligner to accelerate and decelerate to a notch window stored in memory where the notch is most likely to be present. Within the notch window, the pre-aligner searches for the notch at a scanning speed. Once the pre-aligner detects the notch, it can immediately determine how much further the wafer needs to be rotated to reach the desired position. The pre-aligner can utilize the maximum acceleration and maximum velocity values ​​to reach the desired alignment position, since no scanning is required during this operation. Note that it needs to rotate a minimum distance to find the edge.

[0039] Thus, the present disclosure provides a process to: (i) enter the notch window at the scan velocity using maximum acceleration / deceleration until the notch window is reached; (ii) scan at the scan velocity until the notch is reached; (iii) bring the wafer to a pre-defined alignment position using maximum acceleration / deceleration. This process also considers maximum speed to limit the rotation speed during operation outside the notch window. The motion profile can be adjusted depending on how many more scans are required.

[0040] A first possible scenario involves a situation where the wafer is placed in the pre-aligner such that the detector 250 is already within the notch window and the notch is immediately clockwise from the detector 250. For example, such a scenario is illustrated in Figure 4. Figure 4 shows a schematic diagram of a top view of a wafer W1. Starting point x in Figure 4 0 represents the angular position that coincides with the sensing area of ​​the prealigner detector 250. As shown in FIG. window is the starting point x w1 and end point x w2 Notch position x n and the desired or predetermined alignment position x d is shown in Figure 4.

[0041] 5-7 each show the notch position x such that when the wafer is rotated using maximum acceleration, the scan velocity is not reached before the notch is detected. n is the starting point x 0 4 using process 400, the notch appears before reaching range Δx, which is the distance required to reach the scan velocity from rest, while the motion profile of FIG 7 exists when the notch appears after reaching range Δx. FIG 6 shows a graph of an alternative motion profile for wafer W1 of FIG 4 using process 400 in a scenario where the maximum velocity Vmax is reached during the motion profile after the notch is detected at notch position xn while moving to the desired alignment position xd.

[0042] Thus, analyzing these motion profiles is as follows: (i) Take initial maximum acceleration until reaching the notch, then continue with maximum acceleration / deceleration to the desired alignment position without exceeding 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 up to the maximum speed and continue at that speed before decelerating, as shown in FIG. 6, or whether it needs to accelerate to a speed less than the maximum speed and start decelerating before reaching the maximum speed, as shown in FIG. 5.

[0043] The total travel time can be analyzed as follows:

[0044]

number

[0045] : is the time required to reach the notch during the initial acceleration.

[0046]

number

[0047] : is the time required to reach the desired alignment position. This depends on how far the desired position is from the notch, because this allows for intermediate speed V before cruising (shown in brackets) and deceleration. int t , which determines whether there is enough space to accelerate from V to the maximum velocity, or whether the wafer can only accelerate to some lower velocity V before decelerating.

[0048]

number

[0049] :Total travel time.

[0050] The above Δt 2 To solve for the velocity V in terms of , a system of three equations and three unknowns was constructed as follows:

[0051]

number

[0052] : Shows the wafer accelerating from an intermediate speed to a peak speed.

[0053]

number

[0054] : Represents the wafer decelerating from peak velocity to zero.

[0055]

number

[0056] : The distance covered during acceleration and deceleration is equal to the distance from the notch to the desired alignment position.

[0057]

number

[0058] This process is repeated for the various profiles detailed below, with minor modifications to the equations.

[0059] Another possibility when the wafer is positioned such that the sensor is located within the window of the notch is that the notch is not located within the range Δx. The motion profile for this case is shown in Figure 7 and is similar to that of Figure 5, except that the pre-aligner must cruise at the scan speed until the notch is found.

[0060] The total movement time of the kinetic profile in Figure 7 can be analyzed as follows.

[0061]

number

[0062] : the time required to reach the scanning speed.

[0063]

number

[0064]

number

[0065] : the time required to reach the desired alignment position. This depends on how far the desired alignment position is from the notch, because this allows for intermediate speed V before cruising (shown in brackets) and deceleration. int t , which determines whether there is enough space to accelerate from V to the maximum velocity, or whether the wafer can only accelerate to some lower velocity V before decelerating.

[0066]

number

[0067] :Total travel time.

[0068] A second possible scenario involves a situation in which the wafer is placed in the pre-aligner such that the detector 250 is initially located outside the notch window. For example, such a scenario is illustrated in FIG. 8. FIG. 8 shows a schematic diagram of a top view of wafer W2. Starting point x in FIG. 0 represents the angular position that coincides with the sensing area of ​​the prealigner detector 250. As shown in FIG. 8, the notch window again begins at x w1and end point x w2 Notch position x n and the desired or predetermined alignment position x d is shown in Figure 8. Figure 9 shows the motion profile of wafer W2 of Figure 8 using process 400.

[0069] Analysis of the motion profile for the scenario shown in FIG. 8 is as follows:

[0070]

number

[0071] :Notch window x w This depends on how far the notch is from its initial starting position, as this determines whether there is enough space to accelerate to maximum velocity before cruising (shown in brackets) and decelerating, or whether the wafer can only accelerate to some lower velocity V before decelerating.

[0072]

number

[0073] : the time required to cruise from the edge of the window to the notch at the scan speed.

[0074]

number

[0075] : the time required to reach the desired alignment position. This depends on how far the notch is from the desired alignment position, as this determines whether there is enough space to accelerate from the scan speed to the maximum speed before cruising (shown in brackets) and decelerating, or whether the wafer can only accelerate to some lower speed V before decelerating.

[0076]

number

[0077] :Total travel time.

[0078] Because the pre-aligner controller 1200 knows the position of the notch window after a period of time, and because the detector 250 is capable of scanning in both directions, the pre-aligner 200 can recognize that if the notch is more than 180° clockwise from the initial position, the wafer can be rotated counterclockwise and the same motion profile scenario as detailed above can be used.

[0079] The various detected notch positions, average notch position, and notch window (range) can be stored in the memory 1206 of the controller 1200 as well as in an on-board non-volatile memory (e.g., ROM 1208) in the prealigner, allowing a history of such data to be maintained in case the system is power cycled.

[0080] However, if the notch is not found within the notch window as expected, the process can continue scanning at the scan rate until the notch is detected. A notch memory implementation is preferably used when the notch location has been shown to be within a certain range consistently over a number of wafers.

[0081] It should be noted that when the pre-aligner rotates the wafer, the center of the wafer may not necessarily be located at the center of the pre-aligner's wafer chuck. Therefore, the eccentricity due to this offset can be determined to find the wafer center. In the present disclosure, a least squares approximation is used to locate the wafer center with significantly fewer rotations (e.g., 90 degrees) required compared to other methods that may require a scan through approximately 360 degrees of rotation to locate the wafer center.

[0082] FIG. 10 shows a schematic diagram of wafer W3 in relation to the center of the wafer chuck and the read head of the detector of the pre-aligner. FIG. 10 shows wafer W3, center C1 (e.g., center of rotation of wafer chuck 230), and read head 246 of detector 250 of pre-aligner 200. The pre-aligner rotates wafer W3 by angle θ. Center C2 of wafer W3 may not necessarily be located at center C1 of the wafer chuck. Eccentricity is defined by radius r and offset angle φ. As the wafer is rotated, the magnitude of vector p is measured for varying angles θ. For a given wafer radius R, eccentricity can be determined.

[0083] r*cos(θ+φ)+R*cos(β)=p r*sin(θ+φ)-R*sin(β)=0 Thus, two equations are provided with three unknowns r, φ, and β. Furthermore, β is a constantly varying value as a function of angle. Finally, the readhead 246 has some measurement width, which leads to uncertainty in the position of vector p in the direction perpendicular to the readhead pixels. The expected eccentricity is preferably 2 mm or less. Given a wafer radius of 150 mm, the expected maximum value of R*cos(β) is:

[0084] 150-150*cos(atan(2 / 150))=13 microns Assuming that the effect of the angle β is small, the term cos(β) can be linearized as follows:

[0085] r*cos(θ+φ)=pR This can also be rewritten as follows:

[0086] r*sin(φ)*cos(θ)+r*cos(φ)*sin(θ)=pR This is a single equation with two unknowns. The subsequent N rotation angles may generate N equations, allowing a least-squares approximation:

[0087] [cos(θ)sin(θ)]*[r*sin(φ)r*cos(φ)] T ={pR} X*A=b Here, X is N×2, A is 2×1, and b is N×1.

[0088] X T *X*A=X T *b A=(X T *X) -1 *X T *b To account for the variables R and the error in p, the above equation can be reconsidered as follows:

[0089] r*sin(φ)*cos(θ)+r*cos(φ)*sin(θ)=pR For the full radius case, p is assumed to have a sinusoidal component in addition to its steady-state value.

[0090] r*sin(φ)*cos(θ)+r*cos(φ)*sin(θ)=pR o +δp+p s -R-δR r*sin(φ)*cos(θ)+r*cos(φ)*sin(θ)-p o -δp+R+δR=p s These stationary terms are summarized as follows:

[0091] a=-p o -δp+R+δR This means: r*sin(φ)*cos(θ)+r*cos(φ)*sin(θ)+a=p s This is a single equation with three unknowns. N subsequent rotation angles may generate N equations, allowing a least-squares approximation:

[0092] [cos(θ)sin(θ)1]*[r*sin(φ)r*cos(φ)a] T ={p s} X*A=b Here, X is N×3, A is 3×1, and b is N×1.

[0093] X T *X*A=X T *b A=(X T *X) -1 *X T *b In this way, any variations in the steady-state offset were taken into account and the pure eccentricity of the wafer was extracted.

[0094] FIG. 11 shows notch specifications taken from the 2017 Semiconductor Equipment and Materials Association (SEMI) M1 draft document for specifications for polished monocrystalline silicon wafers. Note that the pin shown in the schematic diagram in FIG. 11 can be used to position the notched wafer in a fixture during use. The pin can also be used to reference the notched wafer during testing for notch dimensions and dimensional tolerances. The notch dimensions shown in FIG. 11 assume a 3 mm diameter for this positioning pin. These notch dimensions are for illustrative purposes and are not intended to limit the scope of the claims that follow.

[0095] 12 illustrates an embodiment of a computer system (or controller) 1200 upon which an embodiment of the present invention may be implemented. Although computer system 1200 is illustrated with respect to a particular device or equipment, it is contemplated that other devices or equipment (e.g., network elements, servers, etc.) may deploy the hardware and components of the illustrated computer system 1200. Computer system 1200 is programmed (e.g., via computer program code or instructions) to provide the functionality described herein and includes a communication mechanism, such as a bus 1202, for passing information between other internal and external components of computer system 1200. One or more processors 1204 are coupled to bus 1202 for processing information and performing a series of operations on the information as specified by the computer program code.

[0096] The computer system 1200 also includes a memory 1206 coupled to the bus 1202. The memory 1206, such as a 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 temporary values ​​during 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 including instructions that are not changed by the computer system 1200. The ROM 1208 or a separate memory connected to the bus 1202 may be provided as a non-volatile memory. The computer system 1200 includes a communication interface 1216 that allows the computer system 1200 to communicate with other devices or equipment (e.g., network elements, servers, internal or external robot controllers, etc.).

[0097] Information including user input instructions is provided to bus 1202 for use by processor 1204 from a user interface 1210, such as a keyboard including alphanumeric keys operated by a human user, a display device, and a pointing device (such as a mouse or trackball or cursor direction keys).

[0098] The rotation unit 1212 (e.g., the rotation unit 210 including the motor 220 and any associated sensors for detecting the rotational position of the wafer chuck 230, as well as any devices (e.g., suction devices) provided on the wafer chuck 230 for holding the wafer) can communicate with the processor 1204 via the bus 1202 to send and receive data, operational instructions / commands, or other information therebetween. The processor 1204 can control the operation of the drive rotation unit 1212 using the operational instructions / commands to control the rotation (e.g., start, stop, direction (e.g., clockwise, counterclockwise), speed, etc.) of the output shaft (e.g., the rotating shaft 222) of the motor 220.

[0099] It should be noted that the computer system 1200 may further be connected to a robot (e.g., robot 100) used to move the wafer. In such a configuration, the robot may communicate with the processor 1204 via the bus 1202 to send and receive data, operation instructions / commands, or other information therebetween. In such a configuration, the processor 1204 may control the operation of the robot using the operation instructions / commands to control the operation of the robot. Alternatively, the computer system 1200 may communicate with a separate controller of the robot via the communication interface 1216 to work in conjunction with the robot to load and unload wafers from the pre-aligner.

[0100] The detection unit 1214 (e.g., detection unit 240) may communicate with the processor 1204 via the bus 1202 to send and receive data, operational instructions / commands, or other information therebetween. The processor 1204 may control the operation of the detection unit 1214 using the operational instructions / commands to control the operation of the detection unit 1214 in conjunction with the operation of the rotation unit 1214.

[0101] The computer system 1200 may be provided on the housing of the prealigner 200 or in wired connection to other components of the prealigner 200, or the computer system 1200 may be provided in wired or wireless communication with other components of the prealigner 200 at a remote location.

[0102] It should be noted that the exemplary embodiments shown and described herein represent preferred embodiments of the present invention and are not meant to limit the scope of the claims in any way. Numerous modifications and variations of the present invention are possible in light of the above teachings. It should therefore be understood that within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described herein.

Claims

1. 1. A pre-aligner for pre-aligning a wafer having a notch on its outer periphery, comprising: a rotation unit including a wafer platform having a wafer receiving surface configured to receive the wafer and a drive configured to rotate the wafer platform about an axis; a detector configured to detect the notch in the wafer when the wafer is received on the wafer receiving surface; a memory configured to store a notch window that defines an angular range within which the notch is expected to be located relative to a starting position at which the wafer is initially received on the wafer receiving surface, the starting position corresponding to a sensing area of ​​the detector; and a controller programmed to perform a pre-alignment operation to rotate the wafer from the starting position to a predetermined alignment position; the controller is programmed to perform the pre-alignment operation to rotate the wafer from the starting position to a notch position detected by the detector at a maximum acceleration / deceleration value; the pre-alignment motion is limited to a maximum speed in rotating the wafer from the starting position to a notch window; the pre-alignment motion is scan rate limited as the wafer is rotated within the notch window until the notch position is detected by the detector; the scanning speed is less than the maximum speed; Prealigner.

2. the controller is further programmed to perform the pre-alignment operation to rotate the wafer from the notch position detected by the detector to the predetermined alignment position at the maximum acceleration / deceleration value; the pre-alignment operation is limited to the maximum speed when rotating the wafer from the notch position detected by the detector to the predetermined alignment position. The prealigner according to claim 1 .

3. the controller is programmed to minimize a time of movement from the start position to the notch position detected by the detector. The prealigner according to claim 1 .

4. the controller is programmed to minimize a time of movement from the start position to the predetermined alignment position; The prealigner according to claim 1 .

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

6. and a non-volatile memory configured to store the notch window. The prealigner according to claim 1 .

7. providing a wafer platform having a wafer receiving surface configured to receive a wafer having a notch on its outer periphery; providing a detector configured to scan the outer periphery of the wafer when the wafer is received on the wafer receiving surface to detect the notch of the wafer; setting a notch window that defines an angular range within which the notch is expected to be located relative to a starting position at which the wafer is initially received on the wafer receiving surface, the starting position corresponding to a sensing area of ​​the detector; performing a pre-alignment operation to rotate the wafer from the starting position to a predetermined alignment position; the pre-alignment operation is performed to rotate the wafer from the starting position to a notch position detected by the detector with a maximum acceleration / deceleration value; the pre-alignment motion is limited to a maximum speed in rotating the wafer from the starting position to a notch window; the pre-alignment motion is scan rate limited in rotating the wafer within the notch window until the notch position is detected by the detector; the scanning speed is less than the maximum speed; method.

8. The pre-alignment operation is further performed to rotate the wafer from the notch position detected by the detector to the predetermined alignment position at the maximum acceleration / deceleration value; the pre-alignment operation is limited to the maximum speed when rotating the wafer from the notch position detected by the detector to the predetermined alignment position. The method of claim 7.

9. The notch window is performing notch detection on a predetermined number of consecutive wafers to collect notch position data relative to the starting position; determining an angle range that includes a predetermined percentage of the notch position data; Setting the notch window to the angle range It is set by The method of claim 7.

10. determining an eccentricity between a center of the wafer at the predetermined alignment position and a center of rotation of the wafer platform having the wafer receiving surface using a least squares approximation; The method of claim 7.

11. storing the notch window in a memory. The method of claim 7.

12. storing the notch window in a non-volatile memory. The method of claim 7.

13. providing a wafer having a notch on a wafer platform having a wafer receiving surface; rotating the wafer on the wafer platform from a start position where the wafer is initially received on the wafer receiving surface and corresponding to a sensing area of ​​a detector until the detector detects a notch position of the notch relative to the start position; storing the notch locations in a memory; repeating the providing, rotating and storing steps for one or more successive wafers so as to collect and store notch position data in the memory; using the notch position data to set a notch window that defines an angular range within which a subsequent notch of the subsequent wafer is expected to be located relative to the starting position at which the subsequent wafer is initially received on the wafer receiving surface; performing a pre-alignment operation on the subsequent wafer, in which the subsequent wafer is rotated from the starting position to a notch position of the subsequent wafer using the notch window within a first minimum time; A method for providing the above.

14. a pre-alignment operation is performed on the subsequent wafer, the pre-alignment operation using the notch window to rotate the subsequent wafer from the starting position to a predetermined alignment position within a second minimum time period; The method of claim 13.

15. the pre-alignment operation is performed on the subsequent wafer to rotate the subsequent wafer from the starting position to the notch position detected by the detector with a maximum acceleration / deceleration value; the pre-alignment motion is limited to a maximum speed in rotating the subsequent wafer from the starting position to the notch window; the pre-alignment motion is scan rate limited in rotating the subsequent wafer within the notch window until the notch position is detected by the detector; the scanning speed is less than the maximum speed; The method of claim 14.

16. the pre-alignment operation is further performed to rotate the subsequent wafer from the notch position detected by the detector to the predetermined alignment position at the maximum acceleration / deceleration value; the pre-alignment operation is limited to the maximum speed when rotating the subsequent wafer from the notch position detected by the detector to the predetermined alignment position. The method of claim 15.

17. The notch window is determining an angle range that includes a predetermined percentage of the notch position data; setting the notch window to the angular range; is set by The method of claim 13.

18. determining an eccentricity between a center of the subsequent wafer at the predetermined alignment position and a center of rotation of the wafer platform having the wafer receiving surface using a least squares approximation; The method of claim 14.

19. storing the notch window in a memory. The method of claim 13.

20. storing the notch window in a non-volatile memory. The method of claim 13.

Images