Integrated wafer warpage measurement

Abstract

In some examples, a wafer warpage measurement system includes a measurement unit including: a wafer support assembly for transferring rotational motion to a wafer under test supported in the measurement unit; an optical sensor; the calibration standard component is used for calibrating the optical sensor; a linear platform actuator for transmitting a direction of linear motion to the optical sensor; a wafer centering sensor for determining the centering of the wafer to be measured supported in the measuring unit; and a wafer alignment sensor for determining the alignment of the wafer under test supported in the measurement unit.

Description

This application is a divisional application of the application with application number 202080010882.3, application date January 24, 2020, and invention name “Integrated Wafer Warpage Measurement”. Priority claim

[0001] This application claims priority to U.S. Patent Application No. 62 / 796,963, filed on January 25, 2019, by Arora et al., entitled “Integrated WaferBow Measurements,” which is incorporated herein by reference in its entirety. Technical Field

[0002] The subject matter disclosed herein relates to equipment used in the semiconductor and related industries. More particularly, the present disclosure relates to integrated wafer warpage measurement, and in one example, to wafer warpage measurement using optical sensors. Background Art

[0003] The background description provided here is for the purpose of generally presenting the context of the present disclosure. No admission is made, either explicitly or implicitly, that the work of the presently designated inventors is prior art to the present disclosure to the extent that it is described in this background section and in aspects of the specification that were not determined to be prior art at the time the application was filed.

[0004] Advances in plasma processing have fueled the growth of the semiconductor industry. Typically, multiple semiconductor devices can be produced from dies cut from a single processed wafer (i.e., substrate). Because most recipes for processing wafers assume the wafer is planar, non-planar wafers (e.g., wafers with warpage) can introduce variations that can result in defective semiconductor devices.

[0005] The degree of wafer warpage generally indicates the degree of wafer stress. Highly warped wafers can cause chuck failure during photolithography. Ideally, a wafer would be perfectly flat. However, most wafers tend to have slight warpage and / or protrusions, resulting in a non-planar wafer. The non-planarity of the wafer may be due to the original shape of the wafer and / or may be due to stress (e.g., mechanical stress) from films that may have been deposited onto the wafer during one or more deposition steps. In some cases, if a wafer is too non-flat, it may be deemed unusable and may be discarded.

[0006] In certain processing steps, such as etching or deposition, understanding the wafer configuration can be important to accurately determine the amount of etching and to prevent electrodes within the processing chamber from accidentally contacting the wafer, thereby damaging the wafer and / or the electrodes. This is particularly true for processing chambers that may be sensitive to wafer warpage. In one example, a bevel etcher may be particularly sensitive to wafer warpage because the upper electrode may be very close to the wafer in order to etch along the edge (e.g., the bevel) of the wafer.

[0007] In a bevel etcher, the gap between the upper electrode and the wafer can be approximately 0.35 mm. However, wafer warpage can be as large as 0.25 mm. Therefore, if wafer warpage is not correctly identified, the upper electrode may accidentally contact the wafer, resulting in damage to the wafer and / or the upper electrode. Furthermore, because the amount of plasma that can be introduced into the process module may also depend on knowing the actual gap, failure to accurately identify the gap may lead to variations in processing.

[0008] Therefore, before etching can be performed on a wafer, measurements may have to be performed to determine the extent of wafer warpage. However, inline measurements are not typically performed during the deposition process. Therefore, it may not be possible to input the measurement data into the etching process to determine the extent of wafer warpage. Instead, a stand-alone metrology tool can be used to determine measurements of wafer warpage. However, stand-alone metrology tools are typically used to perform characteristic measurements. In other words, each wafer is not measured to determine the wafer warpage of the wafer. Instead, a sample can be taken to determine the type of wafer warpage that can characterize a group of wafers. Furthermore, because the stand-alone metrology tool is not in situ or even inline, the format of the measurement data is typically not such that the data can be easily fed to another tool, such as a bevel etcher.

[0009] One approach for implementing in-situ measurement is to include a metrology tool within the process module to measure wafer bow. In one example, wafer bow measurement can be performed while the wafer is on an electrostatic chuck within the process module, while waiting for the etching process to begin. One method for performing this measurement involves shining a light beam across the wafer and measuring the light intensity level while lowering the upper electrode of the process module to reduce the gap between the upper electrode and the wafer. Lowering the upper electrode stops when a predetermined amount of light is no longer detected. At this point, the upper electrode is determined to be in close proximity to the wafer, but not yet in contact with it.

[0010] The goal of identifying the point at which the upper electrode can come close to contacting the wafer is to determine the minimum distance between the electrode and the wafer, thereby identifying the wafer's height. Unfortunately, the measurement performed is limited to a single point. Therefore, the measured value may not reflect the actual height of the water.

[0011] Current standalone technologies are either limited by TpT (wafer point-by-point measurement) or have a measurement range of <300 microns, making them unsuitable for process control. Furthermore, standalone systems are not designed to measure hot wafers and are therefore not suitable for real-time measurement. For example, in some cases, wafer warpage compensation can be performed by using a deposition tool to deposit a film on the backside of a warped wafer, but this does not provide adequate warpage compensation in real time for high-volume manufacturing. Summary of the Invention

[0012] In some examples, optical sensors, such as distance sensors based on laser triangulation, are integrated into the front end of a substrate (e.g., wafer) processing tool, such as a deposition tool. Using a combination of linear and rotary stages, the optical sensor scans the wafer surface in the desired pattern and measures wafer warpage. Real-time wafer warpage measurements from the integrated optical sensor are used to establish process monitoring and control on the deposition tool.

[0013] In some examples, a wafer warpage measurement system includes a measurement unit comprising: a wafer support assembly for transmitting rotational motion to a wafer under test supported in the measurement unit; an optical sensor; a calibration standard for calibrating the optical sensor; a linear stage actuator for transmitting a linear motion direction to the optical sensor; a wafer centering sensor for determining the centering of the wafer under test supported in the measurement unit; and a wafer alignment sensor for determining the alignment of the wafer under test supported in the measurement unit.

[0014] In some examples, the wafer centering sensor includes an actuator for actively centering a wafer under test supported in the measurement unit.

[0015] In some examples, the wafer support assembly includes a wafer alignment chuck.

[0016] In some examples, the wafer warpage measurement system further includes a reference wafer unit.

[0017] In some examples, the reference wafer unit includes multiple slots to accommodate a series of different reference wafers.

[0018] In some examples, the series of different reference wafers provides a series of measurement control references for the wafer under test supported in the measurement cell.

[0019] In some examples, the wafer warpage measurement system further includes a plurality of measurement units and at least one reference wafer unit.

[0020] In some examples, the wafer warpage measurement system is integrated with a wafer processing tool.

[0021] In some examples, the calibration standard includes at least one pre-measured feature or facet that can be scanned by the optical sensor to detect stray wafer bow measurements over time.

[0022] In some examples, the scannable features or facets include wedge-shaped silvered diffuse optical flats to serve as a proxy for wafer thickness.

[0023] In some examples, the calibration standard includes a plurality of steps that can be scanned by the optical sensor to detect spurious wafer bow measurements over time.

[0024] In some examples, the wafer warpage measurement system further includes a temperature sensor or a humidity sensor, and wherein the selection of the reference wafer in the series of different reference wafers is based on data derived from the temperature sensor or the humidity sensor.

[0025] In some examples, the wafer bow measurement system further includes a vibration isolation mechanism or mount.

[0026] Some examples include a method of measuring wafer warpage of a wafer in a wafer processing flow including a wafer processing module, the method comprising: integrating a wafer warpage measurement system with the wafer processing module; extracting a wafer from the wafer processing flow to undergo wafer warpage measurement by the wafer warpage measurement system; adjusting parameters of the wafer processing flow based on the wafer warpage measurement derived by the wafer warpage measurement system; and placing the measured wafer back into the wafer processing flow.

[0027] In some examples, the wafer warpage measurement system used in the exemplary method includes a measurement unit comprising: a wafer support assembly for transmitting rotational motion to a wafer under test supported in the measurement unit; an optical sensor; a calibration standard for calibrating the optical sensor; a linear stage actuator for transmitting a linear motion direction to the optical sensor; a wafer centering sensor for determining centering of the wafer under test supported in the measurement unit; and a wafer alignment sensor for determining alignment of the wafer under test supported in the measurement unit.

[0028] Further scope of applicability of the present disclosure will become apparent from the detailed description, claims and drawings.The detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In the figures of the accompanying drawings, some embodiments are shown by way of example and not limitation:

[0030] Figure 1A schematic array of different types of wafer warpage is shown according to exemplary embodiments.

[0031] Figure 2-3 A diagram and a side view are respectively shown of an exemplary measurement unit for a wafer warpage measurement system according to an exemplary embodiment.

[0032] Figure 4 A schematic diagram of a reference wafer unit according to an exemplary embodiment is shown.

[0033] Figure 5 A schematic diagram illustrating components of a wafer warpage measurement system according to an exemplary embodiment is shown.

[0034] Figure 6 An example wafer warpage measurement system is shown according to an exemplary embodiment.

[0035] Figure 7 Pairs of measurement units according to exemplary embodiments are shown.

[0036] Figure 8 A measurement system according to an exemplary embodiment is shown.

[0037] Figure 9-10 Schematic diagrams and cross-sectional views of a calibration standard according to an exemplary embodiment are shown.

[0038] Figure 11 A schematic diagram representing operations in a noise subtraction operation is shown, according to an exemplary embodiment.

[0039] Figure 12-13 Schematic pictures and cross-sectional views are shown of some internal components of a reference wafer unit according to an exemplary embodiment.

[0040] Figure 14-15 A schematic diagram of a measuring unit according to an exemplary embodiment is shown.

[0041] Figure 16 Exemplary graphical results of a wafer warpage measurement method according to an exemplary embodiment are shown.

[0042] Figure 17 Operations in a wafer warpage measurement method according to an exemplary embodiment are illustrated.

[0043] Figure 18 Schematic illustrations and cross-sectional views are shown of aspects of a multi-step and multi-interface calibration standard according to exemplary embodiments.

[0044] Figure 19 Aspects of exemplary operations in a sampling method according to exemplary embodiments are shown.

[0045] Figure 20 An arrangement or configuration of a wafer warpage measurement system according to an exemplary embodiment is shown. DETAILED DESCRIPTION

[0046] The following description includes systems, methods, techniques, instruction sequences, and computer program products that embody illustrative embodiments of the present invention. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the exemplary embodiments. However, it will be apparent to those skilled in the art that the embodiments may be practiced without these specific details.

[0047] A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by any person of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever. The following notice applies to any data described below and in the drawings that form a part of this document: Copyright LAM Research Corporation, 2018. All rights reserved.

[0048] As a general background, semiconductors typically begin as wafer slices of purified semiconductor material. Typically these wafers are produced by heating the material, shaping it, and processing it to cut and grind it into small, smooth wafers.

[0049] During the deposition phase, the prepared wafer is cleaned, heated, and exposed to pure oxygen in a diffusion furnace. This results in a reaction that creates a uniform silicon dioxide film on the wafer surface.

[0050] During the masking phase (also known as photolithography or photomasking), the process protects one area of ​​the wafer while processing another area. After a photosensitive film is applied to a portion of the wafer, an intense light is projected onto it through a mask, exposing the film with the mask pattern.

[0051] During the etching phase, manufacturers bake the wafer to harden the remaining film pattern, then expose it to a chemical solution to etch the areas not covered by the hardened film. After this step, the film is removed, and the wafer is inspected to ensure proper image transfer. Doping, deposition, and plating phases can occur during semiconductor manufacturing.

[0052] In some examples, the wafer warpage measurement system includes an optical distance sensor (e.g., a laser triangulation sensor with a large measurement range in the ±2000 μm region) integrated with a wafer aligner and mounted at the front end of a wafer deposition tool. Other integrated arrangements are also possible. Using a combination of linear and rotary stages, the sensor measures the relative distance relative to the wafer surface and calculates or derives the wafer shape or warpage. In some examples that allow real-time applicability, the total measurement time may take less than 2 seconds. Real-time wafer warpage measurements from the integrated wafer warpage measurement system can be used to establish process monitoring and control on wafer deposition or warpage compensation tools. In some examples, the method can be applied to other wafer processing tools, such as etching, stripping and cleaning, and metrology modules.

[0053] An example wafer warpage measurement system may include a measurement unit comprising the following elements: an optical distance sensor that measures the relative distance to the wafer, the linear and rotational motion axes (or the path of sensor travel) to scan the wafer in a desired manner; and a set of sensors for monitoring the wafer and its environmental conditions (e.g., wafer temperature, ambient temperature, ambient humidity sensor, accelerometer, sensor temperature measurement, or wafer fiducial (notch) alignment sensor). Other environmental sensors or measurements are also possible. Environmental compensation factors may be applied based on the measurements made by the environmental sensors.

[0054] An exemplary wafer warpage measurement system may further include a reference wafer unit that accommodates different reference wafers. A specific reference wafer measurement value may be subtracted (or accounted for) from the original wafer measurement value. In some examples, the reference wafer measurement may enable compensation or reduction of mechanical component noise and the effects of gravity-related wafer sag or wafer aligner fingerprints. The wafer warpage measurement system may further include an integrated calibration standard to check sensor accuracy and status. In some examples, the calibration standard is mounted next to the wafer in the measurement unit and may be measured during wafer scanning or at periodic intervals for calibration purposes. In some examples, the wafer warpage measurement system includes a controller that can communicate with the environment and optical sensors and calculate or derive the wafer warpage.

[0055] In an exemplary process flow, before and / or in post processing, the wafer is transferred to a warp metrology station of a measurement unit, which is used for notch alignment and wafer warp measurement. This measurement can be used to establish process monitoring and control in the wafer deposition tool. Some process examples can be "feedforward" based, where the pre-processed wafer warp value is fed forward to the process module of the deposition tool to control the incoming wafer warp variation. Other process examples are "feedback" based, where the pre-processing and post-measurement data can be used for operations such as process module quality assessment, wafer excursion detection (or non-compliance with specifications), compensation for process module drift over time, chamber accumulation, etc. If the target warp value is not achieved, the wafer can be rerouted back to the process module to achieve the required warp compensation.

[0056] In some examples, instead of using an optical triangulation sensor, a chromatic confocal, confocal, or interferometric based sensor, or an inductive or capacitive sensor may be used for wafer bow measurement. A combination of multiple sensors may also be used.

[0057] refer to Figure 1 , an array 100 of different types of wafer warpage is depicted. Element 102 depicts positive warpage, element 104 depicts negative warpage, and element 106 depicts a saddle shape. Different measurement schemes 108 including combinations of linear and rotational motions may be employed to measure the types of warpage depicted in the array 100. An optical sensor in a measurement unit, discussed further below, may employ one of a plurality of measurement schemes 108 to measure or derive wafer warpage. The measurement scheme 110 may include a one-dimensional (1-D) wafer scan. The measurement scheme 112 may include a two-dimensional (2-D) wafer scan including, for example, a one-dimensional scan by an optical sensor along multiple linear axes. For example, a single linear scan may be followed by a 90° rotational motion of the scanned wafer and then a second linear scan. The measurement scheme 114 may include a 2-D spiral scan including, for example, continuous rotational motion of the wafer by the measurement unit coupled to a linear motion of the optical sensor. The measurement scheme 116 may include 2-D concentric wafer scanning, for example, including rotational motion of the scanning wafer combined with spaced or intermittent linear motion of the optical sensor to produce the illustrated concentric rings of wafer bow measurement.

[0058] An exemplary method for providing metrology for substrate processing (e.g., bow-type wafer bow measurement) includes providing an optical metrology station including a plurality of optical sensors to measure spectra from a plurality of measurement locations on a substrate, measuring at least one of mass or mass variation of the substrate, generating thickness values ​​at the plurality of measurement locations of the substrate based on the spectra from the plurality of measurement locations and a learned model, and generating a spatial thickness distribution model of the substrate based on the thickness values ​​and at least one of the mass or mass variation at the plurality of measurement locations. In this regard, reference is made to commonly owned U.S. Patent Application 15 / 696,768, entitled “Systems and Methods for Combining Optical Metrology with Mass Metrology,” which is incorporated herein in its entirety.

[0059] Figure 2-3 A diagram and a side view of an exemplary measurement unit 200 for a wafer warpage measurement system are depicted, respectively. The measurement unit 200 includes a housing or support for an optical sensor 1, a calibration standard 2, a wafer 3 (which is used for wafer warpage measurement), a linear stage actuator that imparts a linear motion direction 4 to the optical sensor 1, a wafer centering sensor (e.g., an active wafer centering (AWC) sensor 5, which includes an actuator for active wafer centering), a wafer alignment sensor 6, and a wafer support assembly (e.g., a rotating stage (aligner) chuck 7 ( Figure 3 )). The linear stage can apply linear motion 4 to the optical sensor 1, and the rotary stage 7 can apply rotary motion to the wafer 3 to be measured. Figure 1 The wafer bow measurement of wafer 3 is derived using one or more of the measurement schemes 108 depicted in FIG.

[0060] Figure 4 A schematic diagram of a reference wafer unit 400, described further below, is depicted. The reference wafer unit 400 may include multiple slots (not shown) to accommodate a range of different reference wafers, e.g., of varying wafer thickness, wafer warpage, stress, rigidity / flexibility, and crystal orientation to provide a range of measurement control references for different types of wafers 3 under test.

[0061] Figure 5 A schematic diagram of components of a wafer warpage measurement system 500 is depicted. In this example, the system 500 includes two stacked measurement units 200 and a reference wafer unit 400. Figure 6-8 In some exemplary embodiments, the wafer warpage measurement system 500 may be integrated with or mounted to a deposition tool or module 600. Figure 6, an exemplary wafer warpage measurement system 500 is shown mounted near a side port 602 of an exemplary deposition module 600. The measurement system 500 may include one or more measurement units 200 and, if desired, a reference wafer unit 400. A series of one or more wafer boat loaders 604 may be used to introduce wafers into the interior of the deposition module 600 where they may be accessed (or pre-measured) for wafer warpage measurement by the warpage measurement unit 200.

[0062] Other installation positions of the measuring system 500 or the measuring unit 200 are possible. For example, Figure 7 , a pair of measurement cells 200 are shown mounted at designated integrated metrology module (IMM) ports 702 of a deposition module 600. Figure 8 In FIG. 5 , the measurement system 500 is installed at the wafer loader position.

[0063] Return Reference Figure 2 And in some example measurement units and systems, a calibration standard 2 is provided. A schematic diagram and a cross-sectional view of an exemplary calibration standard 902 are shown in FIG. Figure 9-10 The illustrated calibration standard 902 has a structure that can be detected by an optical sensor (e.g. Figure 2 The calibration standard 902 here comprises a wedge-shaped silvered diffuse optical flat surface that can be placed in close proximity to a wafer (e.g., Figure 2 3) Positioning of the chip in the Figure 10 As more clearly shown in FIG, the exemplary optical plane 902 is generally tilted downward from left to right in the view to a drop or depth 1002. Other configurations or tilts of the calibration standard 2 or optical plane 902 are possible. In some examples, the pre-measured (or known) optical depth 1002 of the optical standard 2 or optical plane 902 can serve as a proxy for the perpendicularity of the wafer thickness or wafer warp and be used to calibrate or check that the optical sensor reports such values ​​accordingly. The calibration standard 2 or optical plane 902 can be scanned during the wafer scanning operation or can be scanned at other times (e.g., when the deposition module 600 or measurement unit 200 is available). The exemplary calibration operation described above seeks to ensure that the measurement unit 200 performs within the desired measurement specifications.

[0064] refer to Figure 18In some examples, a multi-step standard 1802 is provided. As shown, a standard 1804 may include multiple flat steps rather than a wedge shape. Another example standard 1806 includes multiple interfaces. In some examples of this nature, the standard may be made of an optically transparent material that includes multiple interfaces. Light from the sensor is reflected at each interface and focused at a different point on the detector, so the thickness of each interface can be measured in a single operation. This can be used for sensor calibration. Additionally, the interfaces may have anti-reflection coatings to avoid multiple re-reflections between interfaces.

[0065] In some cases, wafer warpage measurements may be affected by noise or environmental conditions at a particular time. These factors may negatively impact making accurate wafer warpage measurements. Some examples herein seek to subtract or compensate for such noise or environmental conditions. For example, wafer warpage at any given time may depend on how the wafer is held on the aligner lift pins in an electrostatic chuck (ESC). A "reference" wafer measurement may be obtained by a reference wafer unit (e.g., Figure 4 The reference wafer is typically subject to the same noise as the processed wafer, so once the noise to which the reference wafer is subject can be determined, its size or effect can be subtracted from the corresponding measurements obtained from processed wafers of the same type. In the present example, such wafer referencing operation can filter out or minimize two sources of potential measurement uncertainty, namely the deformation effects of the lift pins and the effects of gravity causing the wafer to sag in the central region not supported by the pins. In a further example, systematic z-axis noise from moving mechanical components such as the linear stage 4, the rotary stage 7, etc. can be eliminated in a similar manner. One or more reference wafers, each having specific characteristics suitable for the corresponding processed wafer, can be stored in the reference wafer unit 400 in association with the measurement unit 200, for example as Figure 5 shown.

[0066] Figure 11A schematic diagram representing the operations in an exemplary noise subtraction operation 1110 is shown in . The wafer warpage measurement data of the process wafer may include noise or background factors, which are generally shown in area 1102 of the data input graph. The noise 1102 may be caused, for example, by one or more of the elements described above. At this point, the level of any noise, or even its existence, may not yet be determined. Measurements taken on a corresponding reference wafer that is subject to the same noise as the process wafer can be used to determine the presence of noise and deduce the noise level. The presence of noise and its level are shown by area 1104 of the intermediate reference wafer graph. As shown, the noise level can be subtracted from the data input data to obtain an accurate data output graph. The data output graph 1106 is more representative of the actual wafer warpage measurement. Schematic diagrams and cross-sectional views depicting the internal components of the exemplary reference wafer unit 400 are shown in . Figure 12-13 . Reference wafer unit 400 may include reference wafer slot 1202 for supporting one or more reference wafers 1302. Temperature and humidity sensors 1304 and 1306 may be included in exemplary reference wafer unit 400. In some examples, temperature and humidity sensors 1304 and 1306 may operate in conjunction with other sensors discussed further below. In some examples, noise generated by temperature and humidity may also be excluded or compensated.

[0067] In some examples, the temperature of the wafer can change the stress in the wafer film and substrate and affect the wafer warpage. To this end, in some examples, a series of non-contact optical sensors are placed below the wafer in the measurement unit 200 for wafer temperature measurement. Depending on the temperature of the wafer and certain deposited film and substrate properties, temperature compensation can be applied to the wafer warpage measurement. A schematic diagram of the measurement unit 200 including an exemplary temperature sensor 1402 is shown in FIG. Figure 14-15 The reference or handling wafer 1302 located above the sensor for warpage measurement is Figure 15 An example warpage measurement is shown in Figure 16 16. The change in wafer warpage (warpage variable) is shown on the y-axis of the graph 1600 relative to the wafer temperature plotted on the x-axis.

[0068] Therefore, in some examples, ambient humidity and temperature compensation is provided. Ambient humidity and temperature sensors are added to measurement unit 200 and reference wafer unit 400. This arrangement can be used to minimize measurement uncertainty or noise associated with these environmental conditions. In a further example, sensor temperature compensation can be provided. For example, the temperature of an optical or distance sensor can affect its linearity. Therefore, a temperature sensor can be installed next to the sensor to assess the extent of linear drift. This arrangement can be used to minimize measurement uncertainty associated with sensor temperature.

[0069] Some examples of the measurement unit 200 and / or reference wafer unit 400 include vibration compensation. Any vibration in these components may affect the uncertainty of the wafer bow measurement. Exemplary vibration isolation mechanisms may include one or more of an isolation mount (e.g., to minimize floor vibration), an O-ring (e.g., to isolate front-end vibration), an accelerometer (e.g., to flag measurements during high vibration), and an anti-vibration mount (e.g., to minimize seismic vibration).

[0070] Other examples can include specific wafer placement in the measurement unit 200 or reference wafer unit 400. For example, eccentricity or incorrect wafer placement on the lift pins can affect warp measurements. An AWC mechanism can be added to the measurement unit 200 to address this source of error (or noise). AWC can ensure that the measured process or reference wafer is concentric with the lift pins.

[0071] The present disclosure also includes method embodiments. The operations in the exemplary wafer warpage measurement method 1770 are Figure 17 One or more operations included in method 1700 are shown and may be performed in the order shown or in another order. An output of method 1700 may include action 1702, which includes an exemplary use case.

[0072] Exemplary action 1702 may include process monitoring and control. As previously described, the wafer may have positive or negative warp, or include a saddle shape. In a feedforward process, pre-processed wafer warp values ​​(warp measurements) are fed forward to the processing module to control incoming wafer warp variations. In a feedback process, pre-processed wafer warp values ​​and post-measurement increments may be used in operations including process module quality analysis, offset detection, compensation for process module drift over time, chamber accumulation, and other operations. If a target value or specification for a process wafer is not achieved at a given processing stage, the wafer may be rerouted back to the process module to receive adjusted warp compensation to achieve the desired target or specification. Further warp measurements in a process step may provide feedforward for process control in subsequent process steps.

[0073] Other actions 1702 may include wafer stress measurement. When performing wafer stress assessment, in addition to known parameters (such as Young's modulus, Poisson's ratio, etc.), three parameters are generally required: wafer thickness, wafer film thickness, and radius of curvature or warp. Wafer thickness can be measured in any of the following ways. For example, relative measurements are taken at the aligner pin locations before and after wafer placement, with the height delta between the two locations representing the wafer thickness. Another example includes taking a relative measurement between two distance sensors mounted at the same location, with one sensor above the wafer and the other below the wafer. In some examples, sensors based on near-infrared spectral interferometry can be used for wafer thickness measurement.

[0074] When performing thin film stress assessment, wafer bow and thickness measurements performed by measurement unit 200 (e.g., as part of an integrated wafer measurement system 500) can be combined with optical thickness measurements or mass measurements converted to thickness based on thin film properties. Some examples may include an integrated measurement system 500 in which separate optical thickness metrology sensors are mounted at locations on the front side and / or underside of the wafer being measured and utilize one or more motion-controlled axes to perform film thickness measurements.

[0075] For effective wafer temperature compensation, accurate wafer temperature measurement is generally required. In this regard, non-contact optical sensors generally require film and substrate emissivity calibration to accurately measure wafer temperature. For example, silicon wafers are transparent in IR, and the emissivity value varies depending on the film thickness. Alternatively, the wafer temperature can be measured using a contact-based probe embedded in the aligner pin. One advantage of this arrangement is that it provides accurate wafer temperature measurement without additional particles. The wafer temperature can also be measured using a combination of a contact probe embedded in the aligner pin and a non-contact temperature sensor (e.g., an IR camera), where the non-contact sensor can be calibrated in real time based on the measurement values ​​obtained by the contact probe (e.g., emissivity calibration). Based on the calibration points, a wafer temperature non-uniformity map can be generated across the entire wafer. Some examples include a thermal stabilization station. A thermal stabilization station can be added to the measurement unit 200 or system 500, which allows the process wafer or reference wafer to be thermally stabilized before measurement.

[0076] refer to Figure 19 , illustrating exemplary operations in a sampling method 1900 in schematic outline. The exemplary operations may be included in or used in conjunction with the wafer warpage, wafer measurement, or wafer alignment methods described herein. The number and positions of measurement locations 1902 can be optimized by synchronizing rotation, linear stage speed, sensor trigger rate during wafer scanning. For example, the measurement locations 1902 can be adjusted by the distance between points, by the number of points in a defined area, or to a suitable custom combination to minimize measurement error. The exemplary spiral scan depicted on the left shows a variable distance between measurement locations 1902. The exemplary spiral scan on the right shows a mixture of combinations, including, in some cases, equal distances between measurement locations 1902.

[0077] refer to Figure 20, shows an arrangement or configuration 2000 of a wafer warpage measurement system. Wafer warpage measurement is performed in parallel with robot movement to minimize the impact on wafer throughput in a wafer processing module. In configuration 1, the inner diameter (ID) of the robot end effector (EE) can be larger than the outer diameter (OD) of the aligner pins. Configuration 2 includes optimized movement between the aligner pins and the robot using the existing EE, wherein during pickup, the wafer is oriented so that there are no obstructions between the aligner pins and the robot EE.

[0078] In an exemplary measurement mode, the robot pick time is >3 seconds and the wafer bow measurement time is <2 seconds, i.e., the duration is shorter, thereby minimizing throughput, or at least not affecting the time aspect or interfering with wafer pick. By synchronizing the motion, the wafer bow measurement can be completed while the robot is in motion and before the robot picks up the wafer.

[0079] In some cases, additional benefits can be provided. For example, in terms of cost, the aligner wafer elevator is no longer required. The same robot can be used to place, pick up, and lift the wafer. From a throughput perspective, warpage measurement is performed in parallel with the robot movement, that is, during the robot movement to pick up the wafer. Because the movements (including raising and lowering) are performed by the same robot, it can also provide reduced wafer pick and place times.

[0080] Some examples of wafer warpage measurement systems therefore provide real-time, accurate wafer warpage measurement that is independent of the wafer and environmental conditions. Some example systems or methods may also be used or integrated in wafer thickness measurement systems, wafer alignment systems, and wafer stress. The exemplary system may be used as both a wafer aligner and a wafer warpage measurement system. Active compensation for wafer temperature, ambient temperature, and humidity (among other factors) may result in improved and more reliable metrology performance. Warpage measurement may be used for process monitoring and control (feedforward or feedback) of deposition tools. The wafer warpage measurement described herein may be combined with film thickness / mass metrology and may measure film stress.

[0081] Although an embodiment has been described with reference to specific exemplary embodiments, it is apparent that various modifications and changes can be made to these embodiments without departing from the broader scope of the subject matter of the present invention. Therefore, the description and drawings are to be considered illustrative rather than restrictive. The drawings forming a part thereof show, by way of illustration and not limitation, specific embodiments in which the subject matter may be practiced. The illustrated embodiments are described in sufficient detail to enable those skilled in the art to practice the teachings disclosed herein. Other embodiments can be utilized and derived therefrom so that structural and logical replacements and changes can be made without departing from the scope of the present disclosure. Therefore, this detailed description should not be understood as limiting, and the scope of the various embodiments is limited only by the appended claims and the full scope of equivalents to which these claims are assigned.

[0082] These embodiments of the subject matter of the present invention may be referred to herein individually and / or collectively as the term "the present invention," which is for convenience only and is not intended to voluntarily limit the scope of this application to any single invention or inventive concept, if more than one is in fact disclosed. Thus, although specific embodiments have been illustrated and described herein, it should be understood that any arrangement calculated to achieve the same purpose may be substituted for the specific embodiments shown. This disclosure is intended to cover all modifications or variations of the various embodiments. Combinations of the above embodiments, as well as other embodiments not specifically described herein, will be apparent to those skilled in the art upon reading the above description.

Claims

1. A wafer warpage measurement system comprising: A measuring unit comprising: a wafer support assembly for transmitting rotational motion to a wafer under test supported in the measurement unit; Optical sensors; a calibration standard for calibrating the optical sensor; a linear stage actuator for transmitting a linear motion direction to the optical sensor; a wafer centering sensor for determining the centering of the wafer under test supported in the measurement unit; and A wafer alignment sensor is used to determine the alignment of the wafer under test supported in the measurement unit.

2. The wafer warpage measurement system according to claim 1, wherein: The wafer centering sensor includes an actuator for actively centering the wafer under test supported in the measurement unit. 3 . The wafer warpage measurement system of claim 1 , wherein the wafer support assembly comprises a wafer alignment chuck. The wafer warpage measurement system according to claim 1 , further comprising a reference wafer unit. 5 . The wafer warpage measurement system of claim 4 , wherein the reference wafer unit comprises a plurality of slots to accommodate a series of different reference wafers.

6. The wafer bow measurement system of claim 5, wherein the series of different reference wafers provide a series of measurement control references for the wafer under test supported in the measurement unit. 7 . The wafer warpage measurement system according to claim 4 , further comprising a plurality of measurement units and at least one reference wafer unit.

8. The wafer warpage measurement system of claim 1, wherein the wafer warpage measurement system is integrated with a wafer processing tool.

9. The wafer bow measurement system of claim 1 , wherein the calibration standard includes at least one pre-measured feature or facet that can be scanned by the optical sensor to detect stray wafer bow measurements over time.

10. The wafer warpage measurement system of claim 9, wherein the scannable feature or facet comprises a wedge-shaped silvered diffuse optical flat to serve as a proxy for wafer thickness.

11. The wafer bow measurement system of claim 1 , wherein the calibration standard comprises a plurality of steps that can be scanned by the optical sensor to detect spurious wafer bow measurements over time.

12. The wafer warpage measurement system of claim 5 , wherein the wafer warpage measurement system further comprises a temperature sensor or a humidity sensor, and wherein selection of a reference wafer in the series of different reference wafers is based on data derived from the temperature sensor or the humidity sensor.

13. The wafer bow measurement system of claim 1, further comprising a vibration isolation mechanism or mount.

14. A method of measuring wafer warpage of a wafer in a wafer processing flow including a wafer processing module, the method comprising: integrating a wafer warpage measurement system with the wafer processing module; extracting a wafer from the wafer processing flow to perform wafer warpage measurement by the wafer warpage measurement system; adjusting parameters of the wafer processing flow based on wafer warpage measurements derived by the wafer warpage measurement system; and The wafer under test is placed back into the wafer processing flow.

15. The method of claim 14, wherein the wafer warpage measurement system comprises: A measuring unit comprising: a wafer support assembly for transmitting rotational motion to a wafer under test supported in the measurement unit; Optical sensors; a calibration standard for calibrating the optical sensor; a linear stage actuator for transmitting a linear motion direction to the optical sensor; a wafer centering sensor for determining the centering of the wafer under test supported in the measurement unit; and A wafer alignment sensor is used to determine the alignment of the wafer under test supported in the measurement unit.

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