Patent Publication Number: US-2021193490-A1

Title: Wafer process monitoring system and method

Description:
BACKGROUND 
     Integrated circuit (IC) fabrication utilizes a variety of processing steps, including etching and depositing films (i.e., layers) on masked wafers in order to create trenches, vias, metal lines, components of passive and active electrical circuits, such as capacitors, resistors, inductors, transistors, antennas, and in general forming insulating and conducting structures in the production of integrated circuits on batches of wafers formed of semiconductor substrate material. 
     Often, processing steps are performed via automated or at least semi-automated systems in a linear assembly-line fashion. Processing steps may include cleaning, etching, rinsing, and/or depositing material on the wafers in chambers or individual tanks of solutions. Wafers may be moved into and out of processing solutions contained in different tanks, thus requiring placing the wafers on, and removing the wafers from, tank transport devices or mechanisms, as well as moving the wafers between different tank transport devices. That is, wafers may be automatically moved, transported and/or transferred multiple times during wafer processing that typically involves exposure of the wafers to high/low temperatures, temperature changes, high/low pressures, pressure changes, and different chemical agents. Thus, the wafers may incur stresses and even strains during processing of the wafers, as well as during transport/transfer of the wafers accompanying the processing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. 
         FIG. 1  illustrates a system for determining condition of wafers during processing of the wafers, according to an embodiment of the present disclosure; 
         FIG. 2A  illustrates an end view of the arms of the wafer transfer robot of  FIG. 1  in proximity to a bottom portion of the wafer lift of  FIG. 1 , according to an embodiment of the present disclosure; 
         FIG. 2B  illustrates an end view of the arms of the wafer transfer robot of  FIG. 1  in proximity to a bottom portion of the wafer lift of  FIG. 1 , according to another embodiment of the present disclosure; 
         FIG. 3A  illustrates a time series of vibrations of the wafer transfer robot as illustrated on the monitor of  FIG. 1 , according to an embodiment of the present disclosure; 
         FIG. 3B  illustrates a time series of vibrations of the wafer transfer robot as illustrated on the monitor of  FIG. 1  depicting a broken wafer being held by the wafer transfer robot, according to an embodiment of the present disclosure. 
         FIG. 3C  illustrates a time series of vibrations of the wafer transfer robot as illustrated on the monitor of  FIG. 1  depicting a wafer being missing from the wafer transfer robot, according to an embodiment of the present disclosure; and 
         FIG. 4  is a flowchart of a method for determining condition of wafers during processing of the wafers, according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. 
     Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper,” “vertical,” horizontal” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly. 
     Wafers may undergo forces, such as stresses, as well as relative molecular movement, e.g., strain, during IC fabrication steps. For example, the forces and resulting strain may be caused by exposure of the wafers to chemical processes, such as chemical baths, electric currents, high/low pressures, pressure changes, high/low temperatures, temperature changes, ion bombardment, doping, oxidation, metallization, and other fabrication processes. Many fabrication processes may be automated or semi-automated by mechanical systems or devices, including robotic or other automated devices that may subject the wafers to addition stresses and strains caused by the handling, transfer and/or transport of the wafers. 
     Wafers may suffer physical damage during or between different processing steps, such as being cracked or broken. Furthermore, wafers can become incorrectly positioned in automated devices while being transferred from one device to another device, or as a result of transporting wafers in an automated device as the device moves the wafers from one location in a processing assembly line to another location in the processing assembly line. In addition, wafers may go missing from an automated device used to hold a batch of wafers, transport the wafers, and/or transfer the wafers to other devices. 
     For example, when performing wet etch process steps on wafers using wet benches, a first mechanized automated subsystem of the wet bench may move batches of wafers into and out of different chemical solutions (also referred to as chemical baths), and a second mechanized automated subsystem may transport the batch of wafers to locations near components of the first subsystem and then transfer the batch of wafers to the components of the first subsystem and collect the wafers from the components of the first subsystem. Wafers may suffer damage while in the chemical baths, being placed in or removed from the chemical baths, during transfer of the wafers between the first and second automated subsystems, and/or during transport of the wafers by the first and/or second automated subsystems. The chemical baths are typically held in processing tanks or chambers. If one or more wafers is physically damaged, or incorrectly held or positioned within an automated system because of a faulty transfer between the automated systems, wafers may fall out (i.e., go missing) from the automated system. For example, damaged or misoriented wafers being held by components of an automated system may fall into the processing tanks or remain in the processing tanks. 
     It would be advantageous to accurately determine the condition of wafers while being processed by a wafer processing system, such as determining if one or more wafers have been damaged and/or incorrectly positioned in, or missing from, components of the system designed to transfer/transport wafers during processing, so that processing can be stopped to avoid contamination and/or damage to other wafers being processed by the system and/or to avoid damage to components of the automated system itself. 
       FIG. 1  illustrates a system  100  for determining condition of wafers during processing of the wafers, according to an embodiment of the present disclosure. The system  100  includes a wafer transfer robot  102  and one or more vibration sensors  104 . The system  100  may optionally include at least one of one or more wafer lifts  106 , one or more processing regions  108 , a processing module  110 , a monitor  112 , one or more optical sensors  114  and one or more wafer number sensors  116 . The processing region  108  may be defined by an enclosure, such as a processing container (e.g., a processing tank or a processing chamber), or any other region in which one or more processing procedures are performed on wafers. A processing region may be any region in which one or more processing parameters, such as temperature, pressure, type and concentration of processing agents, may be controlled. In one embodiment, a processing region may contain a chemical bath. In other embodiments, a processing container includes processing tanks and processing chambers of deposition systems, such as chemical vapor deposition (CVD) and physical vapor deposition (PVD) systems. For purpose of the following discussion, the one or more processing regions are one or more processing tanks ( 108 ), although the scope of the present disclosure covers any type of processing region or processing container. Each processing tank  108  may contain one or more wafer processing agents that form a chemical bath  118 . Processing agents may include any solution that is used in the processing of wafers, including ionized water for rinsing. In one embodiment, the chemical bath may be used in an IC fabrication procedure performed on semiconductor wafers, such as a wet etch, a rinse or a chemical deposition of material on the wafers. However, the scope of the present disclosure includes all types of processing procedures performed on semiconductor wafers, including processes performed on wafers formed of insulators and/or metals. 
     In one embodiment, any combination of the wafer transfer robot  102 , the one or more wafer lifts  106 , the one or more processing tanks  108 , the processing module  110 , the monitor  112 , and the optical sensor  114  may be components of wafer processing systems, such as semiconductor processing benches. For example, wet benches are used to etch semiconductor wafers in different chemical solutions, also referred to as chemical baths, and other fabrication benches are used for performing other processing procedures for manufacturing semiconductor dies, including integrated circuits, from semiconductor wafers. 
     The wafer transfer robot  102  is configured to hold one or more wafers  120 , including a batch of wafers (not shown). The wafer transfer robot  102  is also configured to place the wafers  120  on the wafer lift  106 , remove the wafers  120  from the wafer lift  106 , and transport the wafers  120  from a location near one wafer lift (e.g., wafer lift  106 ) to a location near another wafer lift (not shown) for placing the wafers  120  on, and then removing the wafers  120  from, the other wafer lift. In one embodiment, the wafer transfer robot  102  includes two arms  121  configured for holding the wafers  120 . The two arms  121  may be positioned directly opposite one another. 
     The wafer lift  106  is configured to move the wafers  120  received from the wafer transfer robot  102  into the chemical bath  118 , and typically after a given processing time, remove the wafers  120  from the chemical bath  118 . In one embodiment, the wafer lift  106  is configured to be lowered into and raised out of the chemical bath  118  for immersing the wafers  120  into and removing the wafers  120  from the chemical bath  118 . In one embodiment, the wafer lift  106  is configured to move substantially vertically downward for being lowered into the chemical bath  118  and substantially vertically upward for being raised from the chemical bath  118 . In one embodiment, the wafer lift  106  has bottom portion  122  with inscribed slots  124 . For example, the bottom portion  122  may be a metallic, ceramic or plastic plate. The size, depth and spacing of the slots  124  are configured such that a single slot may receive a portion of an edge of a single wafer for holding the wafer temporarily in place on the wafer lift  106 . The wafer lift  106  may also include a side portion  126  that is configured to be engaged with a vertical transfer means for moving the wafer lift in a substantially vertical direction  128 . Vertical transfer means are well known in the art of wafer fabrication and may include robotic arms or other types of electrically powered devices that have components that move substantially vertically. 
     In one embodiment, the wafer transfer robot  102  is configured to be moved in any direction. Although not shown, the wafer transfer robot  102  may be attached to a robotic arm or other mechanical systems configured to move the wafer transfer robot in any direction. For example, the processing module  110  or other external computers or control modules (not shown) may execute preprogrammed code for directing motion of the wafer transfer robot  102 , as well as other components, such as the wafer lift  106 , during the processing of the wafers  120  in various chemical baths for completion of a processing fabrication cycle, for example. 
     In one embodiment, the wafer transfer robot  102  is configured to be moved in a substantially horizonal direction  130  and in a substantially vertical direction  128 . For example, and as illustrated, the wafer transfer robot  102 , holding the wafers  120 , is positioned at a location near the wafer lift  106 . The wafer transfer robot  102  may then be moved in a substantial vertically downward direction for placement adjacent to, or placement circumferentially surrounding, the wafer lift  106 . 
       FIGS. 2A and 2B  are schematics illustrating an end view of the arms  121  of the wafer transfer robot  102  in proximity to the bottom portion  122  of the wafer lift  106 , according to embodiments of the present disclosure. In one embodiment, at least one arm  121  of the wafer transfer robot  102  is configured to be moveable in a substantially horizontal direction, however the scope of the present disclosure covers a wafer transfer robot  102  including two moveable arms  121 . At least one arm  121 , or alternatively both arms  121 , are configured with a plurality of slots  202  (also referred to as grooves) for receiving a portion of an edge  204  of a wafer  120  for holding the wafer  120  in place on the wafer transfer robot  102 . 
     As illustrated by  FIG. 2A , the wafer transfer robot  102  has been previously moved in a substantial vertically downward direction for placement of the arms  121  adjacent to the wafer lift  106 . Once positioned adjacent to the wafer lift  106 , one or both of the arms  121  of the wafer transfer robot  102  are moved substantially horizontally outward  206  (i.e., away from one another), thereby enabling the wafers  120  to dislodge or fall from the wafer transfer robot  102  into position on the bottom portion  122  of the wafer lift  106 . In one embodiment, a portion of the edge  204  of the wafer  120  falls into a slot  124  ( FIG. 1 ) inscribed in the bottom portion  122  of the wafer lift  106 . Each slot  124  is configured for receiving a portion of the edge  124  of a corresponding wafer such that the corresponding wafer is fixed in an upright position on the bottom portion  122  of the wafer lift  106 . 
     Once the wafer lift  106  has received the wafers  120  from the wafer transfer robot  102 , the wafer lift  106  may be lowered in a substantially vertical downward direction for immersion of the wafers  120  in the chemical bath  118 . After a predetermined processing time, the wafer lift  106  may be raised in a substantially vertically upward direction for repositioning of the wafer lift  106  in a location near the wafer transfer robot  102 . 
     Once the wafer lift  106  is repositioned near the wafer transfer robot  102 , as illustrated by  FIG. 2B , one or both of the arms  121  of the wafer transfer robot  102  are moved substantially horizontally inward  208  (i.e., toward one another) for collecting (i.e., removing) the wafers  120  from the wafer lift  106 . In one embodiment, as one or both of the arms  121  move substantially horizontally inward  208 , the slots  202  in the arms  121  of the wafer transfer robot  102  engage the portion of edge  204  of the wafer  120 . In one embodiment, the slots  202  in the arms  121  are designed such that as the arms  121  engage portions of the edges  204  of the wafers  120 , the wafers  120  are lifted a small distance vertically upward, thereby disengaging each wafer  120  from its corresponding slot  124  in the bottom portion  122  of the wafer lift  106 . In another embodiment, the wafers  120  are disengaged from the slots  124  in the bottom portion  122  of the wafer lift  106  as the wafer transfer robot  102  is moved in a substantially vertically upward direction away from the wafer lift  106 . 
     Once the wafer transfer robot  102  has moved a sufficient vertically upward distance (e.g., a sufficient distance to clear all lifts  106  and other components that may be attached to the processing tanks  108 , the wafer transfer robot  102  may be moved in a substantially horizontal direction  130  for placement in a location near another wafer lift corresponding to another processing tank for performing a next processing procedure on the wafers  120  of the wafer transfer robot  102 . 
     When wafers are processed with liquids, gases or solids, including conventional semiconductor processes, they may be subject to stresses and resultant strains causes by exposure to high/low temperatures, rapid temperature changes, high/low pressures, rapid pressure changes, various chemical compounds and/or vibrations. The vibrations may be purposely induced, e.g., vibration of chemical baths as part of a processing step, or induced by transfer of wafers from one mechanical transport/transfer system to another mechanical transport/transfer system. For example, the wafers  120  may be subject to stresses/strains incurred as the wafers  120  are transported by the wafer lift  106  into and out of the chemical baths  118 , and by the transfer of the wafers  120  from the wafer transport robot  102  to the wafer lift  106  and/or by the collection of the wafers  120  by the wafer transfer robot  102  from the wafer lift  106 . These stresses/strains, singly or in any combination, may change the condition of one or more of the wafers  120 , such as causing a wafer  120  to crack or break. If a wafer breaks into one or more portions, some of the portions may fall from the wafer transfer robot  102  into the chemical bath  118 , or all of the portions may fall from the wafer transfer robot  102  resulting in the wafer transfer robot  102  having one or more missing wafers. Furthermore, a cracked or broken wafer, and on some occasions, an uncracked, unbroken wafer (i.e., an intact wafer) may not, upon collection by the wafer transfer robot  102  from the wafer lift  106 , be held properly by the wafer transport robot  102 . 
     For example, a wafer may be held incorrectly by the wafer transfer robot  102  when a portion of the edge  204  of the wafer  120  to be engaged by the slot  202  of the wafer transfer robot  102  upon collection of the wafer  120  from the wafer lift  106  is not received by the slot  202  or any slot, or is received by an incorrect slot. An incorrect slot is a slot that has received portions of the edges  204  of two or more wafers, for example, or is a slot on one arm  121  of the wafer transfer robot  102  that receives a portion of the edge  204  of a wafer that is not directly opposite a slot on the other opposite arm that has received a portion of the opposite edge of the wafer. 
     These wafer conditions, such as cracked, broken, incorrectly held wafers, or missing wafers, may affect the subsequent processing of the wafers held by the wafer transfer robot  102  as they are transferred to other wafer lifts for subsequent processing, or may affect a subsequent processing of a new batch of wafers due to the existence of wafers or portions of wafers that have fallen or remained in the chemical bath  118 . 
     In accordance with embodiments described herein, one or more vibration sensors  104  are attached to the wafer transfer robot  102 . In one embodiment, the vibration sensor  104  is attached to one arm  121  of the wafer transfer robot  102 , or alternatively, one vibration sensor  104  is attached to each arm  121  of the wafer transfer robot  102 . 
     The vibration sensor  104  is configured to detect vibrations of the wafer transfer robot  102 . Although the vibration sensor  104  may detect vibrations of the wafer transfer robot  102  any time during operation of the wafer transfer robot  102 , the vibrations detected after the wafer transfer robot  102  removes (i.e., collects) the wafers  120  from the wafer lift  106  may be particularly of interest. In one embodiment, the vibration sensor  104  is an inertial-based motion detector for detecting motion, such as vibrational motion. In some embodiments, the vibration sensor  104  includes an accelerometer, gyroscope components, one or more other suitable components, or a combination thereof. 
     According to an embodiment of the present disclosure, the vibration sensor  104  detects the vibrations of the wafer transfer robot  102  and generates signals based on the detected vibrations. The scope of the present disclosure covers vibration sensors that include a microprocessor or CPU that processes the detected vibrations to generate electrical signals, such as current, voltage or magnetic signals, and other vibration sensors that may not include a processor, but may include components formed of materials, such as piezoelectric materials, that generate electrical signals from their vibrational motion. 
     The processing module  110  may include one or more processors, CPUs, microcontrollers, memory, ADC/DAC units and associated logic circuitry and/or firmware for digital and/or analog signal processing. In one embodiment, the processing module  110  is configured to receive the signals from the vibration sensor  104  and process the signals. For example, the processing module  110  may process the signals for display on the monitor  112  as a time series or a frequency spectrum. The processing module  110  may alternatively, or in addition to displaying the processed signals, compare the processed signals or patterns of the processed signals in the frequency and/or time domain with signals or patterns of signals stored in a memory. Each signal or signal pattern stored in memory may be associated with a corresponding cause of the signal, also stored in memory. 
     For example,  FIG. 3A  illustrates a time series of vibrations of the wafer transfer robot  102  as illustrated on the monitor  112 , according to an embodiment of the present disclosure. From t=0 to t=t 1 , the wafer transfer robot  102  is being moved to be positioned for collecting wafers  120  from the wafer lift  106 , at t=t 1  the wafer transfer robot  102  collects the wafers  120  from the wafer lift  106 , and for times greater than t=t 1  the wafer transfer robot  102  is being moved away from the wafer lift  106 . The spike in the vibrations at t=t 1  indicate the collection (i.e., removal) of the wafers  120  from the wafer lift  106 , and the smaller vibrations occurring for times greater than t=t 1  indicate the damping of the initial vibration caused by the collection event at t=t 1 .  FIG. 3A  does not indicate that any of the wafers are broken, cracked, missing or held incorrectly by the wafer transfer robot  102 . 
       FIG. 3B  illustrates a time series of vibrations of the wafer transfer robot  102  as illustrated on the monitor  112  depicting a broken wafer being held by the wafer transfer robot  102 , according to an embodiment of the present disclosure. The collection event is indicated by the spike in the vibrations at t=t 1 , however, the pattern of spikes at time t&gt;t 1  indicate that a wafer being held by the wafer transfer robot  102  is broken. 
       FIG. 3C  illustrates a time series of vibrations of the wafer transfer robot  102  as illustrated on the monitor  112  depicting a wafer being missing from the wafer transfer robot  102 , according to an embodiment of the present disclosure. The collection event is indicated by the spike in the vibrations at t=t 1 , however, the pattern of spikes at t&gt;t 1  indicate that a wafer is missing from the wafer transfer robot  102  after the wafer transfer robot  102  has collected the wafers  120  from the wafer lift  106 . Thus, it is likely that the missing wafer, or at least portions of the missing wafer, may be in the chemical bath  118  of the processing tank  108  corresponding to the wafer lift  106 . 
     Although the processing module  110  may process the signals received from the vibration sensor  104  for display as a time series, the processing module  110  may generate a frequency spectrum of the time series and analyze the frequency spectrum or a combination of the frequency spectrum and the time series. In other embodiments, the processing module  110  may analyze the processed signals in conjunction with signals or signal patterns stored in the memory of the processing module  110  to determine the condition of the wafers being processed and/or being held by the wafer transfer robot  102 . 
     Referring back to  FIG. 1 , the vibration sensor  104  may be communicatively coupled to the processing module  110  via a wired connection  132 . However, the scope of the present disclosure includes wireless communication between the sensor  104  and the processing module  110 . 
     The monitor  112  may be communicatively coupled to the processing module  110  via either a wired connection  134  or wirelessly. In one embodiment, when the processing module  110  determines that the condition of wafers  120  being held by the wafer transfer robot  102  includes at least one wafer being cracked, broken, held incorrectly, and/or missing, the processing module  110  generates an alert signal for display on the monitor  112 . The alert signal alerts an operator, thereby allowing the operator to halt the current fabrication processing steps such that missing wafers may be removed from processing tanks, broken and/or cracked wafers may be removed from the wafer transfer robot  102  and incorrectly held wafers may be adjusted such they are correctly held by the wafer transfer robot  102 . Furthermore, the operator may decide, based on the alert signal and the type of wafer condition(s) determined by the processing module  110  and/or after inspecting one or more the processing tanks for missing wafers, to discard all wafers currently being processed and start a new processing cycle with new wafers. 
     The one or more optical sensors  114  may be communicatively coupled to the processing module  110  via either a wired connection  136  or wirelessly. The optical sensor  114  may be positioned for capturing images of at least one of the chemical baths contained within the one or more processing tanks. In another embodiment, the optical sensor  114  may be configured to capture additional images of the wafer lift  106  and/or the wafer transfer robot  102 . In one embodiment, the optical sensor  114  is a charge coupled device. The processing module  110  is configured to process the captured images and/or send the captured images to the monitor  112  for display. 
     The optical sensors  114  may be used by an operator of the system  100 , in combination with the analysis of the vibrations of the wafer transfer robot  102 , to determine the condition of the wafers  120  being held by the wafer transfer robot  102 . For example, optical sensors  114  have limited resolution, and captured images of the inside of processing tanks that may not be sufficiently illuminated may be difficult to interpret. Furthermore, some chemical baths comprise chemical compounds that may be opaque or partially opaque to light and/or the opacity of some chemical baths may change during the processing of wafers. Furthermore, imaging of the chemical baths may also be hindered by reflection of imaging light from the surface of the chemical baths. In addition, the surface of the baths may have ripples, adding to the difficulty of imaging items, such as wafers or portions of wafers that may be submersed in the baths. 
     Although optical imaging methods for determining the condition of wafers or the systems for processing the wafers may not always be sufficient and accurate, in accordance with the disclosed embodiments, images captured of the baths contained in the processing tanks may be used in combination with the detected vibrations of the wafer transfer robot  102 . For example, results from the optical imaging sensor  114  may be used to assist in training, by associating wafer conditions, such as broken, cracked, missing and/or incorrectly held wafers as determined via an analysis of the detected vibrations and as verified via captured images, with the corresponding vibration signals for creating a table of vibrational signals or patterns of vibration signals in time or frequency space having the corresponding wafer conditions. The table may be stored in a memory of the processing module  110  or a memory external to the processing module  110 . In another embodiment, the captured images may be used in combination with the vibrational signals to determine the condition of the wafers  120  on the wafer transfer robot  102  when the vibrational signals are not by themselves determinant of the condition (i.e., state) of the wafers  120 . 
     One or more wafer count sensors  116  may be configured to detect a number of wafers held by the wafer transfer robot  102  and generate a corresponding wafer count signal. In one embodiment, the wafer count sensor  116  is attached to the wafer transfer robot  102 , such as one or both arms  121  of the wafer transfer robot  102 . The wafer count sensor  116  may include one or more pressure sensors, mechanical sensors and/or electro-mechanical sensors for detecting the presence of a wafer in a corresponding slot of the arm  121  and generating a corresponding wafer count signal. The wafer count sensor  116  may be communicatively coupled to the processing module  110  via wired or wireless connections. The processing module  110  is further configured to receive the wafer count signal from each wafer count sensor  116  and process the wafer count signal(s) for determining the number of the wafers being held by the wafer transfer robot  102 . The processing module  110  and monitor  112  may be configured to display the determined number of wafers on the monitor  112  and/or use the determined number of wafers in combination with an analysis of the vibrations of the wafer transfer robot  102  and/or the captured images to determine the condition of the wafers  120  held by the wafer transfer robot  102 , and/or for creating a table of vibrational signals or patterns of vibration signals in time or frequency space having the corresponding wafer conditions. 
     According to an embodiment of the present disclosure, the wafer count sensor  116  includes a plurality of wafer sensors, at least one slot  202  on the arm  121  of the wafer transfer robot  102  includes a wafer sensor for detecting whether the slot  202  contains (i.e., is engaged with) a portion of an edge  204  of a respective wafer. In one embodiment, a wafer sensor is attached to a portion of each slot  202  on the arm  121  of the wafer transfer robot  102 . The electro-mechanical sensor may include a piezoelectric material that generates the count signal when the piezoelectric material is stressed by the force of the wafer against the sensor, thereby causing a strain in the piezoelectric material that results in generation of the count signal. 
       FIG. 4  is a flowchart of a method  400  for determining condition of wafers during processing of the wafers, according to an embodiment of the present disclosure. The wafers may be processed by any know semiconductor processing system, including a semiconductor processing bench. Benches are configured for performing one or more processing procedures on batches of semiconductor wafers. The processing procedures may include, but are not limited to, wet etch, rinsing and/or cleaning, for example. However, the scope of the present disclosure covers any type of wafer processing procedures that involve mechanical transfer of wafers to and from processing chambers or processing tanks and/or mechanical transfer of wafers between wafer transport/transfer systems and devices. 
     A bench may include at least one processing region, such as a processing tank, and a corresponding wafer lift. For the purpose of the following discussion, the one or more processing regions are one or more processing tanks, although the scope of the present disclosure covers any type of processing region or processing container. Each processing tank is configured to perform one or more processing steps, also referred to as processing procedures, on one or more wafers. For example, a processing tank may contain a chemical bath or other fluid agent used to perform a particular processing step or procedure. Each wafer lift is configured for moving the wafers into a corresponding processing tank and moving the wafers out of the corresponding processing tank. In one embodiment, the wafer lift moves the wafer in a substantially vertical direction. The system further includes a wafer transfer robot and a vibration sensor attached to the wafer transfer robot. The wafer transfer robot is configured for holding the wafers, transferring the wafers to at least one wafer lift and removing the wafers from at least one wafer lift. According to one embodiment, the wafer transfer robot is configured to move the wafers from one wafer lift to another wafer lift. In one embodiment, the wafer transfer robot is configured to move in a substantially vertical direction for placing the wafers on, and/or removing the wafers from, a wafer transfer lift, and move in a substantial horizontal direction for moving the wafers from a location near a first wafer transfer lift to a location near a second wafer transfer lift. The wafer transfer robot may then move in a substantially vertical direction for placing the wafers on, and/or removing the wafers from, the second wafer transfer lift. 
     In step  402  of the method, vibrations of the wafer transfer robot  102  are detected. In one embodiment, one or more vibration sensors  104  detect the vibrations of the wafer transfer robot  102 . According to another embodiment, the wafer transfer robot  102  includes at least two arms  121  configured for holding wafers  120 , placing wafers on the wafer lift  106  and removing wafers from the wafer lift  106 . At least one arm is moveable with respect to the other arm for placing wafers on and removing wafers from the wafer lift  106 . In one embodiment, at least one vibration sensor  104  is attached to at least one arm  121  of the wafer transfer robot  102 . 
     In step  404 , signals are generated based upon the vibrations. In one embodiment, the vibration sensor  104  is configured to generate the signals based on the detected vibration of the wafer transfer robot  102 . The signals may be electrical signals, such a current, voltage, magnetic or electromagnetic signals. The signals may be analog or digital signals, any may represent, for example, an analog or digital time series of the detected vibrations or an analog or digital frequency spectrum of the detected vibrations. In one embodiment, the vibration sensor  104  is a electromechanical sensor that may include gyroscopic components, piezoelectric components and/or accelerometer components, for example. 
     In step  406 , the signals are processed for determining a condition of the wafers  120  held by the wafer transfer robot  102 . In one embodiment, the signals are processed by a processing module  110 , including, for example, microprocessors, CPUs, microcontrollers, memory, analog/digital converters and digital logic and processing circuitry. Although the scope of the present disclosure covers detecting vibrations, generating signals, and processing the signals at any or all times during operation of the wafer transfer robot  102  and/or system components for processing the wafers  120 , according to one embodiment the signals are processed for determining the condition of the wafers  120  held by the wafer transfer robot  102  directly after removal of the wafers  120  from the wafer lift  106  by the wafer transfer robot  102 . According to another embodiment of the present disclosure, the signals are processed for determining the condition of the wafers  120  held by the wafer transfer robot  102  during the period of time including removal of the wafers  120  from a first wafer lift by the wafer transfer robot  102 , movement of the wafer transfer robot  102  to a location near a second wafer lift, and placement of the wafers  120  on a second wafer lift by the wafer transfer robot  102 . 
     In one embodiment, the condition of the wafers  120  may include one or more wafers being cracked, broken, held incorrectly by the wafer transfer robot  102 , and/or missing from the wafer transfer robot  102 . 
     If the method determines that the condition of the wafers  120  include one or more wafers being cracked, broken, held incorrectly by the wafer transfer robot  102 , and/or missing from the wafer transfer robot  102 , then in step  408 , the processing of wafers, including operation of the wafer lift  106  and wafer transfer robot  102  is stopped, and an operator may check the processing tank  108  for any wafers, or portions of wafers, that are missing from the wafer transfer robot  102 , adjust positioning of any incorrectly held wafers on the wafer transfer robot  102 , remove and/or replace nay cracked or broken wafers from the wafer transfer robot  102 , replace any contaminated chemical baths  118  or other solutions held in the processing tanks  108 , and/or replace all the wafers being currently processed with a new batch of wafers and repeating one or more of the processing procedures. 
     The present disclosure provides a system and method for determining condition of wafers during processing of the wafers. The wafers may be processed by semiconductor benches or other systems or components for performing processing procedures on wafers for the fabrication of integrated circuits, for example. The system and method of the present disclosure is not limited to wafer processing but may also be used with any systems that processing objects that are transported and/or transferred by automatic or semi-automatic mechanical systems between various chambers or tanks in which processing procedures are performed. 
     In one embodiment, a system includes a wafer lift, a wafer transfer robot, a vibration sensor attached to the wafer transfer robot and a processing module communicatively coupled to the vibration sensor. The wafer lift is configured to move at least one wafer into a chemical bath for performing a processing step on the at least one wafer and remove the at least one wafer from the chemical bath. The wafer transfer robot is configured to hold the at least one wafer, place the at least one wafer on the wafer lift, and remove the at least one wafer from the wafer lift. The vibration sensor is configured to detect vibration of the wafer transfer robot during holding or removing of the at least one wafer by the wafer transfer robot and generate signals based upon the vibration. The processing module is configured to process the signals for determining a condition of the at least one wafer. 
     In another embodiment, a system for use with a semiconductor bench is provided. The semiconductor bench includes at least one semiconductor processing tank and at least one wafer lift. Each semiconductor processing tank contains a chemical bath and each wafer lift is configured for moving wafers into the chemical bath of a corresponding semiconductor processing tank and moving the wafers out of the chemical bath. The system includes a wafer transfer robot configured to hold at least one wafer, place the at least one wafer on a wafer lift and remove the at least one wafer from the wafer lift. The system also includes a vibration sensor attached to the wafer transfer robot and configured to detect vibration of the wafer transfer robot after the wafer transfer robot removes the at least one wafer from the wafer lift, generate signals based upon the vibration, and send the signals to a processing module for determining a condition of the at least one wafer held by the wafer transfer robot after removal from the wafer lift. 
     In yet another embodiment, a method for determining condition of wafers during processing of the wafers by a wafer processing system is provided. The method includes processing one or more of the wafers in a processing tank, removing the one or more wafers from the processing tank utilizing a wafer lift, receiving the one or more wafers at a wafer transfer robot, detecting vibrations of the wafer transfer robot, generating signals based upon the vibrations and processing the signals for determining a condition of the one or more wafers held by the wafer transfer robot. 
     The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. 
     Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.