Apparatus for handling a wafer and method of handling a wafer

Abstract

Apparatus for handling a wafer, comprising: a support for supporting a wafer; an end effector for placing the wafer onto the support or for picking the wafer up from the support; and an actuator for moving the end effector in a vertical direction to place the wafer onto the support or to pick the wafer up from the support, wherein the end effector comprises a sensor, the apparatus is configured to detect an event when placing the wafer onto the support or when picking the wafer up from the support based at least in part on an output of the sensor, and the apparatus is configured to obtain positional information from the actuator when the event is detected.

Description

[0001] APPARATUS FOR HANDLING A WAFER AND METHOD OF HANDLING A WAFER

[0002] Field of the Invention

[0003] The present invention relates to an apparatus for handling a wafer and particularly, although not exclusively, to a wafer mass metrology apparatus that handles a wafer. The present invention also relates to a method of handling a wafer.

[0004] Background

[0005] Microelectronic devices are fabricated on semiconductor (e.g. silicon) wafers using a variety of techniques, for example including deposition techniques and removal techniques. Semiconductor wafers may be further treated in ways that alter their mass, for example by cleaning, ion implantation, lithography and the like. These treatment techniques typically cause a change in mass at or on the surface of the wafer. The configuration of the changes to the surface are often vital to the functioning of the device, so it is desirable for quality control purposes to assess wafers during production in order to determine whether they have the correct configuration.

[0006] WO / 2002 / 003449 discloses an apparatus and method for investigating semiconductor wafers in which changes in the mass of the wafer are determined to assess various properties of the wafer, e.g. to enable fabrication of the wafer to be monitored.

[0007] A common method of obtaining mass measurements is to use a sensitive force sensor to measure the force (weight) due to gravity. Typically, a wafer is weighed to determine the mass of the wafer before a processing step is performed on the wafer, and then after the processing step is performed the wafer is weighed again to determine the mass of the wafer after the processing step has been performed. The measurement results are then used to calculate a change in mass of the wafer caused by the processing step. This change in mass can then be correlated to the performance of the production equipment and / or the desired properties of the wafer.

[0008] When measuring the weight of the wafer, the wafer is typically loaded onto a balance pan of a weighing device, which supports the wafer during the weight measurement. Typically, the balance pan comprises a plurality of wafer support pins that contact the underside of the wafer to support the wafer.

[0009] If a wafer has a higher temperature than a measurement chamber in which the wafer is weighed, air currents (e.g. convection currents) may be generated in the air in the measurement chamber, which may affect the measured weight. In addition, the air in the measurement chamber may be heated, changing its density and pressure and therefore a buoyancy force exerted on the semiconductor wafer by the air. This may also affect the measured weight.

[0010] In the method described in W02002 / 003449, a semiconductor wafer is removed from a wafer cassette and placed on a passive thermal transfer plate that is thermally coupled to a chamber of a weighing apparatus before it is placed on a balance pan of a weighing device located in the chamber. The passive thermal transfer plate equalises the temperature of the semiconductor wafer to the temperature of the chamber to within ±0.1 °C. This reduces or prevents the issues discussed above regarding air currents and changes in the buoyancy force.

[0011] Wafers are typically transported between a wafer carrier (such as a Front Opening Unified Pod or FOUP), the passive thermal transfer plate and the balance pan of the weighing device using a robotic arm with an end effector that supports the wafer from below. In particular, the end effector can be moved in a vertical direction to place the wafer on the respective support or to pick the wafer up from the respective support. The end effector is typically on a robotic arm for moving the end effector that comprises one or more actuators for moving the end effector into a desired position.

[0012] The robotic arm is typically programmed in advance with a predetermined position or movement at which the end effector places the wafer on the respective support or picks the wafer up from the respective support. The robotic arm is configured to move to this predetermined position or to perform the predetermined movement when placing the wafer on the support or picking the wafer up from the support. The predetermined position or movement may be programmed by setting a corresponding control value or information of an actuator that moves the robotic arm.

[0013] However, the present inventors have realised that in some cases the predetermined position or movement may not correctly correspond to the actual position or movement at which the end effector places the wafer on the support or picks up the wafer from the support in practice.

[0014] For example, the predetermined position or movement may have been incorrectly set initially.

[0015] Alternatively, the predetermined position or movement may have been set correctly initially but may have become incorrect subsequently. This may happen, for example, where the end effector droops or becomes angled, where the end effector is damaged, or where there has been a change in a configuration of the apparatus.

[0016] If the predetermined position or movement with which the robotic arm is programmed is incorrect, this can lead to various problems, such as the wafer not being correctly placed on the support or picked up from the support, or the wafer being damaged by the end effector, for example.

[0017] The present invention has been devised in light of the above considerations.

[0018] Summary of the Invention

[0019] The present inventors have realised that at least some of the problems identified above can be solved by detecting an event when placing a wafer onto a support or when picking the wafer up from the support based at least in part on an output of a sensor of an end effector that carries the wafer, and obtaining positional information from an actuator that moves the end effector in a vertical direction when the event is detected. The output of the sensor may therefore be used to provide a check on the vertical positioning of the end effector by the actuator that is independent of control of the actuator. According to a first aspect of the present invention there is provided an apparatus for handling a wafer, comprising: a support for supporting a wafer; an end effector for placing the wafer onto the support or for picking the wafer up from the support; and an actuator for moving the end effector in a vertical direction to place the wafer onto the support or to pick the wafer up from the support, wherein the end effector comprises a sensor, the apparatus is configured to detect an event when placing the wafer onto the support or when picking the wafer up from the support based at least in part on an output of the sensor, and the apparatus is configured to obtain positional information from the actuator when the event is detected.

[0020] In the first aspect of the present invention, an event is detected when placing the wafer onto the support or when picking the wafer up from the support based at least in part on an output of the sensor, and positional information is obtained from the actuator when the event is detected. This may be used to provide a check on the vertical positioning of the end effector that is independent of control of the actuator, for example. For example, this may enable determination that the end effector is not being correctly vertically positioned by the actuator, for example due to the issues discussed above such as where the end effector droops or becomes angled, where the end effector is damaged, or where there has been a change in a configuration of the apparatus.

[0021] The first aspect of the present invention may have any one, or, where compatible, any combination of the following optional features.

[0022] Handling the wafer may comprise holding and / or supporting and / or transporting the wafer.

[0023] The wafer may be a semiconductor wafer, such as a silicon wafer.

[0024] The wafer may have a predetermined diameter, such as 200 mm or 300 mm. The apparatus may therefore be for handling a wafer having the predetermined diameter.

[0025] Supporting the wafer may mean supporting the weight of the wafer and / or maintaining the wafer in a predetermined orientation and position.

[0026] Typically the support supports the wafer from beneath, by contacting an underside of the wafer.

[0027] The end effector may be for supporting or holding or conveying the wafer.

[0028] The end effector may alternatively be referred to as a wafer support element, or a wafer holding element, for example.

[0029] The end effector may be lowered vertically to place the wafer onto the support or raised vertically to pick the wafer up from the support.

[0030] The end effector may be used for both placing the wafer onto the support and subsequently picking the wafer up from the support, or vice versa.

[0031] The actuator may only move the end effector in the vertical direction. Alternatively, the end effector may also move the end effector in one or more other directions.

[0032] The actuator may be controllable to move the end effector only in the vertical direction when placing the wafer on the support or picking the wafer up from the support. An actuator may be a component or part or device that produces force, torque or displacement so as to move the end effector.

[0033] The actuator may be directly connected to the end effector. Alternatively, the actuator may be indirectly connected to the end effector via one or more other components.

[0034] For example, the apparatus may comprise a robotic arm having the end effector, and the actuator may be connected to the robotic arm for moving the robotic arm in the vertical direction. By moving the robotic arm in the vertical direction, the actuator therefore moves the end effector of the robotic arm in the vertical direction.

[0035] The actuator may be controlled by a controller or processor of the apparatus.

[0036] The actuator may comprise a motor, for example a linear motor or rotary motor.

[0037] The sensor may be positioned on the end effector, and / or attached to the end effector, and / or embedded in the end effector.

[0038] The end effector may have more than one sensor, for example a first sensor of a first type and a second sensor of a different type.

[0039] The apparatus may comprise a controller or processor that is configured to detect the event when placing the wafer onto the support or when picking the wafer up from the support based at least in part on the output of the sensor.

[0040] The apparatus may be configured to determine or identify when the event has occurred.

[0041] An event may mean a thing that happens or occurs, and various different types of events are possible in the present invention as discussed below.

[0042] The event may occur before, for example immediately before, the wafer is placed on the support or picked up from the support.

[0043] Alternatively, the event may occur at the moment that the wafer is placed on the support or picked up from the support.

[0044] Alternatively, the event may occur after, for example immediately after, the wafer is placed on the support or picked up from the support.

[0045] The event may occur during an operation of placing the wafer onto the support or during an operation of picking the wafer up from the support.

[0046] The event being detected based at least in part on an output of the sensor means that the output of the sensor is used to detect the event. In addition, other information may also be used to detect the event, such as the output of an additional sensor of the end effector.

[0047] The event may be detected when the output of the sensor is a first value, or when the output of the sensor is a second value, or when the output of the sensor changes or transitions from the first value to the second value or from the second value to the first value. The event may indicate that a particular stage or step of placing the wafer on the support or picking the wafer up from the support has been reached or occurred.

[0048] The apparatus obtaining the positional information from the actuator may comprise a controller or processor of the apparatus obtaining the positional information from the actuator.

[0049] The apparatus may record or report or store the positional information.

[0050] The positional information may be a position value or positional value.

[0051] The positional information of the actuator may be information or a value of the actuator that indicates a position to which the actuator has been moved, or a movement that the actuator has performed.

[0052] The positional information of the actuator may be a control value or control information of the actuator that is used to control a position or movement of the actuator.

[0053] The positional information of the actuator may indicate or correspond to a relative position of the actuator relative to a reference position.

[0054] The positional information of the actuator may be vertical positional information, or z-positional information, of the actuator.

[0055] The actuator may comprise a controller or monitor for controlling or monitoring the positional information of the actuator, and the apparatus may obtain the positional information of the actuator from the controller or monitor. For example, the controller or monitor may be an encoder of the actuator.

[0056] The apparatus obtaining the positional information from the actuator when the event is detected may mean that the apparatus obtains the positional information at the same moment in time that the event is detected, or while the event is detected.

[0057] The event that is detected may comprise one or more of: the wafer being placed onto the support; the wafer being picked up from the support; the sensor, or at least part of the end effector, being at a predetermined vertical position relative to the support; the sensor, or at least part of the end effector, being at a predetermined vertical position relative to the wafer; the wafer being present on the end effector; or the wafer not being present on the end effector.

[0058] More generally, the event may indicate a specific or predetermined stage or point or position of an operation of placing the wafer on the support or picking the wafer up from the support.

[0059] The event may occur when the sensor, or at least part of the end effector, is at a predetermined vertical position relative to the support. The event occurring may therefore indicate that the sensor, or at least part of the end effector, is at the predetermined vertical position relative to the support.

[0060] The event may indicate that placing the wafer on the surface, or picking the wafer up from the surface, has occurred, will occur, or is occurring.

[0061] Typically the event occurs each time, and at the same stage or point or position of an operation of placing the wafer on the support or picking the wafer up from the support, when the wafer is placed on the support or picked up from the support. The sensor, or at least part of the end effector, being at a predetermined vertical position relative to the support or the wafer may mean that there is a predetermined spacing in the vertical direction between the sensor, or at least part of the end effector, and the support or wafer.

[0062] By obtaining the positional information of the actuator when it is detected that the event has occurred, it may be possible to detect when the obtained positional information is different to expected positional information, or different to previous positional information when the same event previously occurred during a previous same operation of placing the wafer on the support or picking the wafer up from the support. This may indicate one or more of the issues identified above. For example, if the positional information of the actuator when the event occurs is a first value X at a first time and a different value Y at a later second time, this may indicate that the end effector is not being correctly positioned by the actuator, which may be caused by one or more of the issues identified above.

[0063] The apparatus may be configured to compare the obtained positional information of the actuator to stored positional information. For example, the stored positional information may correspond to a predetermined, or programmed, or preset, or taught positional information corresponding to the detected event.

[0064] The apparatus may be configured to determine whether or not the obtained positional information is the same as, or within a predetermined range or value of, the stored positional information. For example, if the stored positional information has a value X, the apparatus may be configured to determine if the obtained positional information is in the range of X±Y, where Y is a value, or that the obtained positional information is greater than (or greater than or equal to) X-Y and is less than (or less than or equal to) X+Y.

[0065] The stored positional information may be a predetermined or expected value, or previously obtained positional information of the actuator that was obtained when the same event previously occurred during a previous same operation of placing the wafer on the support or picking the wafer up from the support.

[0066] For example, each time that the end effector is used to place the wafer on the support or pick the wafer up from the support and the event occurs, the positional information of the actuator may be obtained and stored. By comparing the presently obtained positional information of the actuator with one or more previously obtained positional information for the same event, it may be detected or determined if there is a change in the obtained positional information. As discussed above, such a change may be indicative of the one of more of the issues discussed above.

[0067] The apparatus may be configured to monitor positional information of the actuator at which the event occurs over a plurality of operations of placing the wafer onto the support or picking the wafer up from the support.

[0068] The apparatus may be configured to detect or determine a trend in the obtained positional information over time. This may detect gradual changes in the configuration of the apparatus. For example, the end effector may have a plurality of pads on an upper surface of the end effector that are configured to contact the bottom surface of the wafer to support the wafer. These pads may become worn over time, which may mean that the z-position of the end effector at which the pads first make contact with the wafer when picking the wafer up, or the z-position of the end effector at which the pads lose contact with the wafer when placing the wafer, may change gradually over time. Wear of the pads may therefore be detected by detecting a gradual change in the positional information of the actuator obtained when the wafer presence sensor detects the presence of the wafer when picking the wafer up, or when the wafer presence sensor detects the absence of the wafer when placing the wafer, for example.

[0069] The apparatus may be configured to determine that the obtained positional information is not the same as, or is not within a predetermined range or value of, the stored positional information, or that there is a trend in the positional information based on the obtained positional information and the stored positional information.

[0070] The apparatus may be configured to perform an operation when it is determined that the obtained positional information is not the same as, or is not within a predetermined range or value of, the stored positional information, or when it is determined that there is a trend in the positional information based on the obtained positional information and the stored positional information. As mentioned above, if the positional information changes from the stored value this may indicate one or more of the issues discussed above.

[0071] Various different operations are possible for the performed operation, for example one or more of: alerting a user of the apparatus; stopping or preventing an operation of the apparatus; or informing a user of the apparatus of the obtained positional information. The controller or processor of the apparatus may perform such an operation, for example.

[0072] In some embodiments, if the obtained positional information is not the same as the stored positional information but is within a first predetermined range or value of the stored positional information, the apparatus may be configured to alert a user of the apparatus. Furthermore, when the obtained positional information is outside the first predetermined range or value of the stored positional information the apparatus may be configured to stop or prevent an operation of the apparatus. In other words, there may be different tolerances for alerting a user of the apparatus and for stopping or preventing an operation of the apparatus.

[0073] The apparatus may be configured to store the obtained positional information in a memory, for example a memory of the apparatus.

[0074] The actuator may comprise a motor, and the positional information of the actuator may be a value of a controller or monitor of the motor, for example a value of an encoder of the motor.

[0075] The positional information may be, or indicate, a z-position value (vertical position value) of the actuator, such as a z-position value of the controller, monitor or encoder.

[0076] Of course, the end effector may comprise more than one sensor, i.e. a plurality of sensors, and the outputs of one or more of the plurality of sensors may be used to detect when the event occurs.

[0077] For example, the end effector may comprise a first sensor and a second sensor, and the apparatus may be configured to detect an event when placing the wafer onto the support or when picking the wafer up from the support based at least in part on an output of the first sensor and an output of the second sensor.

[0078] The sensor may be configured to detect when the sensor, or at least part of the end effector, is at a predetermined vertical position relative to the support. Alternatively, the sensor may be configured to detect the presence (or absence) of the wafer on the end effector. Of course, both types of sensor may be present.

[0079] The sensor may be configured to have a first output when the sensor, or at least part of the end effector, is at a predetermined vertical position relative to the support and to have a different second output when the sensor, or at least part of the end effector, is at one or more other vertical positions relative to the support.

[0080] The sensor may be configured to have a first output when a wafer is present on the end effector and to have a different second output when a wafer is not present on the end effector.

[0081] The sensor may comprise: a light source; and a light detector arranged to detect light emitted from the light source.

[0082] Light may mean visible light, or non-visible light such as infrared light.

[0083] The light detector is positioned to detect light emitted from the light source.

[0084] The light detector may have a first output when it detects the light and a second output when it does not detect the light.

[0085] The apparatus may be configured such that a light path between the light source and the light detector is unobstructed when the sensor, or at least part of the end effector, is at a predetermined vertical position relative to the support; and the light path between the light source and the light detector is obstructed when the sensor, or at least part of the end effector, is at one or more other vertical positions relative to the support.

[0086] The apparatus may comprise a space or gap such that the light path between the light source and the light detector is unobstructed (not obstructed) when the sensor, or at least part of the end effector, is at a predetermined vertical position relative to the support.

[0087] Therefore, the output of the sensor changes depending on whether the sensor, or at least part of the end effector, is in the predetermined vertical position or in the one or more other vertical positions.

[0088] The end effector may comprise two prongs or forks, which extend at a distal end of the end effector.

[0089] The light source may be positioned on a first one of the two prongs or forks and arranged to direct light towards a second one of the two prongs or forks.

[0090] The light detector may be positioned on the second one of the two prongs or forks.

[0091] The end effector may comprise a plurality of wafer support pads for contacting and supporting the wafer.

[0092] The sensor may comprise a wafer mapping sensor.

[0093] The support may be a device for changing the temperature of the wafer. For example, the device may be a device for contacting the wafer and exchanging heat or thermal energy with the wafer to change the temperature of the wafer.

[0094] The device may be an active device that includes one or more powered heating or cooling devices to control a temperature of the device. Alternatively, the device may be a passive device that does not include such powered heating or cooling devices, or that does not use such powered heating or cooling devices.

[0095] The device may comprise: a surface that is configured to support the wafer and to exchange heat with the wafer; and a space that is configured to receive at least a distal part of the end effector when the end effector is used to place the wafer onto the surface.

[0096] Therefore, when the end effector is lowered towards the surface to place the wafer on the surface, the end effector is lowered into the space such that the wafer can be received on the surface.

[0097] The space may have a shape that corresponds to a shape of the end effector.

[0098] The sensor may be configured to detect when the end effector enters, exits, or is received in the space.

[0099] The sensor may be configured to detect when the end effector is at a predetermined vertical position relative to the surface.

[0100] The sensor may comprises a light source and a light detector arranged to detect light emitted from the light source; and the device may comprise a sensor gap in which a light path between the light source and light detector is positioned when the sensor, or at least part of the end effector, is at a predetermined vertical position relative to the device, so that the light path is unobstructed.

[0101] Therefore, the output of the sensor may indicate when the sensor, or at least part of the end effector, is at the predetermined vertical position relative to the device.

[0102] The device may comprise a plate having the surface on an upper face of the plate; at least part of the space may be located below the plate; and the apparatus may be configured to detect when the sensor transits up past a lower face of the plate when the end effector is being used to pick the wafer up from the surface, or the apparatus may be configured to detect when the sensor transits down past the lower face of the plate when the end effector is being used to place the wafer onto the surface. The event may be detected by the apparatus when it is detected that the sensor transits up or down past the lower face of the plate.

[0103] The support may be a pan of a weighing device for performing a weight measurement on the wafer. For example, the support may be connected to a weighing device that measures the weight of the wafer.

[0104] The apparatus may comprise a wafer carrier for carrying a plurality of wafers, and the wafer carrier may comprise the support. For example, the wafer carrier may comprise a plurality of shelves for supporting individual wafers, and each of the plurality of shelves may correspond to a support.

[0105] The support may be a wafer carrier for carrying a plurality of wafers.

[0106] For example, the wafer carrier may be a Front Opening Unified Pod or FOUP. Such a wafer carrier may be used for conveying a plurality of wafers to the apparatus, or more generally for conveying a plurality of wafers between different apparatuses in a wafer fabrication environment.

[0107] The sensor may comprise a wafer presence sensor that is configured to detect the presence of the wafer on the end effector.

[0108] An output of the wafer presence sensor may be a first value when the presence of the wafer on the end effector is detected and a second value when the presence of the wafer on the end effector is not detected.

[0109] The wafer presence sensor may comprise a wafer presence beam for detecting the presence of the wafer on the end effector.

[0110] The wafer presence beam may be directed towards the location of the wafer so that the wafer is in the wafer presence beam when the wafer is on the end effector.

[0111] An output of the wafer presence sensor may be a first value when the wafer is in the wafer presence beam and a second value when the wafer is not in the wafer presence beam.

[0112] The wafer presence sensor may comprise an emitter of the wafer presence beam that is located above the wafer when the wafer is on the end effector, and the wafer presence beam may be directed downwards towards the wafer when the wafer is on the end effector. A detector may be positioned in the support for detecting the wafer presence beam.

[0113] The wafer presence beam may be a light beam, which may be visible or non-visible light.

[0114] The wafer presence beam may be directed at a (non zero) angle to the vertical towards the wafer when the wafer is on the end effector.

[0115] The apparatus may be configured to detect when the wafer presence beam transits up past an outside edge of the (static) wafer when the end effector is being used to pick the wafer up from the support, and / or the apparatus may be configured to detect when the wafer presence beam transits down past the outside edge of the wafer when the end effector is being used to place the wafer onto the support.

[0116] Of course, various other types of wafer presence detectors can be used in embodiments of the present invention instead of the example set out above. For example, the end effector may comprise a vacuum clamping arrangement for securing the wafer to the end effector, and the apparatus may be configured to detect the presence or absence of a wafer on the end effector based on a change in flow rate or pressure of the vacuum clamping arrangement.

[0117] Alternatively, the end effector may comprise a force transducer or pressure sensor that detects when a wafer is present on the end effector.

[0118] Alternatively, the end effector may comprise one or more capacitive or inductive sensors that detect when a wafer is present on the end effector.

[0119] The apparatus may comprise a first support and a second support. The end effector may be for lowering the wafer onto the first support or for picking the wafer up from the first support, and the end effector may also be for placing the wafer onto the second support or for picking the wafer up from the second support. For example, the first support may comprise a balance pan of a weighing device of the apparatus and the second support may comprise a device for changing the temperature of the wafer of the apparatus.

[0120] The support may comprise a plurality of wafer support elements for contacting a bottom surface of the wafer to support the wafer. For example, the plurality of wafer support elements may comprise a plurality of pins or bumps.

[0121] The apparatus may be a wafer mass metrology apparatus. The apparatus may therefore be for measuring the mass of the wafer.

[0122] The apparatus may comprise a controller or processor for calculating the mass of the wafer based on a measurement output of a weighing device of the apparatus that performs a weight measurement on the wafer. For example, the controller or processor may use the gravitational field strength at the location of the apparatus, or a predetermined calibration value, to convert the measured weight value into a mass value. The controller or processor may also perform a buoyance correction to correct for the effects of buoyance on the measured weight value. For example, the apparatus may comprise one or more sensors for detecting a temperature and / or pressure and / or humidity of the air around the weighing device, in order to calculate a buoyancy force on the wafer.

[0123] The apparatus may comprise a robotic arm having the end effector. As mentioned above the actuator may therefore be for moving the robotic arm. The actuator may be part of the robotic arm, or connected to the robotic arm.

[0124] The end effector may be located at a distal end of the robotic arm.

[0125] The apparatus may comprise more than one actuator for moving the end effector. For example, the apparatus may comprise a first actuator for moving the end effector in a first horizontal direction (x direction), a second actuator for moving the end effector in a second horizontal direction (y direction) and a third actuator for moving the end effector in a vertical direction (z direction). When the event occurs, the positional information may be obtained from the actuator for moving the end effector in the vertical direction (z direction). Of course, if is not necessary to have three such actuators.

[0126] According to a second aspect of the present invention there is provided a method of handling a wafer using an apparatus that comprises: a support for supporting a wafer; an end effector for placing the wafer onto the support or for picking the wafer up from the support; and an actuator for moving the end effector in a vertical direction to place the wafer onto the support or to pick the wafer up from the support, the method comprising: detecting an event when placing the wafer onto the support or when picking the wafer up from the support based at least in part on an output of the sensor, and obtaining a positional information from the actuator when the event is detected.

[0127] The second aspect of the present invention may have any of the features of the first aspect of the present invention discussed above.

[0128] For example, the apparatus used in the second aspect of the present invention may have any of the features of the apparatus of the first aspect of the present invention discussed above. The invention includes the combination of the aspects and preferred features described except where such a combination is clearly impermissible or expressly avoided.

[0129] Summary of the Figures

[0130] Embodiments illustrating the principles of the invention will now be discussed with reference to the accompanying figures in which:

[0131] Figure 1 shows a semiconductor wafer mass metrology apparatus according to an embodiment of the present invention.

[0132] Figure 2 shows a device for changing the temperature of a wafer that can be used in embodiments of the present invention.

[0133] Figure 3 is a sectional view of a device for changing the temperature of a wafer that can be used in embodiments of the present invention.

[0134] Figures 4A to 4C show an end effector and robotic arm that can be used in embodiments of the present invention.

[0135] Figures 5A to 5E show a wafer being placed on a device for changing the temperature of a wafer according to an embodiment of the present invention.

[0136] Figures 6A to 6D show a wafer being placed on a wafer support according to an embodiment of the present invention.

[0137] Figures 7A and 7B illustrate the effects of droop or angling of the end effector.

[0138] Detailed Description of the Invention

[0139] Aspects and embodiments of the present invention will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art. All documents mentioned in this text are incorporated herein by reference. FIG. 1 shows a semiconductor wafer mass metrology apparatus 1 according to an embodiment of the present invention. The semiconductor wafer mass metrology apparatus 1 is configured to measure a mass of a wafer, or a change in the mass of a wafer.

[0140] The semiconductor wafer mass metrology apparatus 1 comprises a weighing device 3 having a weighing pan 5 for receiving a semiconductor wafer and for supporting the wafer during a weight measurement performed on the wafer by the weighing device 3. The weighing device 3 is configured to provide measurement output indicative of the weight of a wafer loaded on the weighing pan 5. For example, the weighing device 3 may measure the weight of the wafer loaded on the weighing pan 5, or a change in the weight of the wafer relative to a previous measurement, or a difference between the weight of the wafer and a reference weight.

[0141] The weighing device 3 is located within a weighing chamber 7, which forms an enclosed environment around the weighing device 3. For example, the weighing chamber 7 may maintain a substantially uniform air density, air pressure and air temperature of the air around the weighing device 3. The weighing chamber 7 has an opening (not shown), e.g. a suitably sized slot in a side-wall of the weighing chamber 7, to allow a wafer to be transported into the weighing chamber 7, by an end effector of a robotic arm, and positioned on the weighing pan 5. When not in use, the opening may be covered by an openable door or covering (not shown) to allow the weighing chamber 7 to be substantially closed or sealed when performing measurements using the weighing device 3.

[0142] A temperature changing part 9 for changing a temperature of the wafer is positioned on top of the weighing chamber 7. The temperature changing part 9 may comprise a plate or block. The plate or block may be made of, or comprise, a material having a good thermal conductivity, for example aluminium.

[0143] The temperature changing part 9 preferably has a high thermal mass, so that its temperature changes slowly and little when it is supplied with heat, and / or a good lateral thermal conductivity, so that it maintains a substantially uniform temperature across its upper surface.

[0144] The temperature changing part 9 may comprise or be a thermal transfer plate, or thermal plate, or thermalisation plate.

[0145] The temperature changing part 9 is positioned directly on top of the weighing chamber 7, so that there is a good thermal contact between the temperature changing part 9 and the weighing chamber 7. The temperature changing part 9 is in direct physical contact with the weighing chamber 7. The temperature changing part 9 may be attached or fixed to the weighing chamber 7, for example using one or more bolts (not shown) and / or a thermally conductive bonding layer (not shown).

[0146] As a result of the good thermal contact between the temperature changing part 9 and the weighing chamber 7, the temperature changing part 9 may be substantially in thermal equilibrium with the weighing chamber 7 and therefore may have substantially the same temperature as the weighing chamber 7 (when a heat load on the temperature changing part 9 is low). The weighing device 3 may also be in thermal equilibrium with the weighing chamber 7 and therefore may also have substantially the same temperature as the weighing chamber 7. As such, the temperature changing part 9 may be substantially in thermal equilibrium with the weighing device 3 and therefore may have substantially the same temperature as the weighing device 3 (when a heat load on the temperature changing part 9 is low).

[0147] In use, a wafer to be measured is positioned on the temperature changing part 9 to reduce its temperature. A vacuum clamping mechanism may be provided to vacuum clamp the wafer to the temperature changing part 9 in order to achieve a good thermal contact between the temperature changing part 9 and the wafer. The temperature changing part 9 may therefore comprise a vacuum clamp for clamping a wafer to the temperature changing part 9. Thermal equilibrium between the wafer and the temperature changing part 9 may be achieved in a short time period, for example less than 0.01 °C temperature difference between the temperature changing part 9 and the wafer within 20 seconds.

[0148] The temperature changing part 9 is therefore a passive temperature changing part.

[0149] The wafer may be positioned on the temperature changing part 9 for a predetermined period of time sufficient to achieve thermal equilibrium between the wafer and the temperature changing part 9.

[0150] Typically, the temperature of the wafer is higher than the temperature of the temperature changing part 9 and the temperature of the weighing chamber 7, and therefore typically the temperature changing part 9 cools the wafer (reduces the temperature of the wafer).

[0151] After the wafer has been cooled by the temperature changing part 9, it is transported from the temperature changing part 9 into the weighing chamber 7 and positioned on the weighing pan 5 of the weighing device 3, for measurement.

[0152] The weighing device 3 is used to perform a weight measurement on the wafer. For example, the weighing device 3 may measure a weight of the wafer.

[0153] The semiconductor wafer mass metrology apparatus 1 further comprises a second temperature changing part 13.

[0154] The second temperature changing part 13 may comprise a plate or block. The plate or block may be made of, or comprise, a material having a good thermal conductivity (for example Al).

[0155] The second temperature changing part 13 may further comprise a plurality of Peltier devices 15 attached on a bottom side of the plate or block, and / or in contact with the bottom side of the plate or block. Each Peltier device 15 has a heat sink 17 attached to it, for example on the bottom side thereof. An air flow 19 can be provided in a region 21 beneath the bottom side of the plate or block in order to remove heat from the Peltier devices 15 and from the heat sinks 17. The second temperature changing part is therefore an active temperature changing part. Of course, the configuration of the air flow may be different to that shown in FIG. 1. For example, air may be blown out of the bottom of the region 21 by a fan.

[0156] Alternatively, an air flow may not be provided in other embodiments. In addition, a number of the Peltier devices 15 and / or heat sinks 17 may be different to that illustrated in FIG. 1.

[0157] The second temperature changing part 13 may include or have a temperature sensor for sensing a temperature of the second temperature changing part 13. A temperature of the second temperature changing part 13 may be controlled so that it is equal to, or within a predetermined range or value of, a target temperature. For example, the plurality of Peltier devices 15 may be operated or controlled so that the sensed temperature is equal to, or within a predetermined range or value of, a target temperature.

[0158] The second temperature changing part 13 is operated to remove a bulk of a heat load from the wafer, so that the temperature of the wafer is reduced to close to a target temperature of the wafer for when the wafer is positioned on the weighing pan 5.

[0159] In particular, the wafer is firstly loaded onto the second temperature changing part 13 to actively remove a bulk of the heat load of the wafer, so that the temperature of the wafer is closer to the target temperature of the wafer for when the wafer is positioned on the weighing pan 5. Then, the wafer is subsequently loaded on the temperature changing part 9 for equalising the temperature of the wafer to the temperature of the weighing chamber 7. Since the bulk of the heat load of the wafer has already been removed by the second temperature changing part, the thermal load on the temperature changing part 9 during the temperature equalisation is low, and the temperature of the temperature changing part 9 and the weighing chamber 7 (which have a high thermal mass) may therefore remain substantially constant during the temperature equalisation. In addition, relatively little heat has to be exchanged to bring the wafer into thermal equilibrium with the temperature changing part 9.

[0160] The arrangement illustrated in FIG. 1 is an illustrative arrangement only, and other configurations of the weighing chamber and / or temperature changing part or parts are possible in the present invention and will be apparent to the skilled person from the above disclosure and the following disclosure.

[0161] For example, in a modified version of the embodiment described above the second temperature changing part 13 or the temperature changing part 9 may be omitted, so that the temperature of the wafer is changed using only one temperature changing part, which may be the temperature changing part 9 or the second temperature changing part 13.

[0162] In addition, the positions of the temperature changing part 9 or the second temperature changing part 13 may be different to that illustrated in FIG. 1.

[0163] In other embodiments, neither of the temperature changing parts 9 and 13 may be provided, so that a wafer is loaded directly on the weighing pan 5.

[0164] The apparatus 1 is configured to perform a calculation to calculate the mass of the wafer based on the result of the weight measurement by the weighing device 3, for example using a gravitational field strength at the location of the apparatus 1 or a predetermine calibration value. The calculation may comprise performing a buoyancy correction to correct for a buoyancy force on the wafer from the air in the weighing chamber 7. For example, the weighing chamber 7 may comprise one or more sensors for detecting a temperature and / or pressure and / or humidity of the air in the weighing chamber 7, in order to calculate a buoyancy force on the wafer.

[0165] The apparatus 1 may comprise a controller or processor 22 that is configured to calculate the mass of the wafer. The controller or processor 22 may also, or alternatively, control one or more operations of the apparatus 1. The wafer may be picked up from a wafer carrier 18 that holds a plurality of wafers W for loading on the second temperature changing part 13. For example, the wafer carrier may be a FOUP as described above. The wafer carrier 18 may comprise a plurality of shelves, each of which is configured to support a wafer W in the wafer carrier 18, The wafer carrier 18, or a shelf in the wafer carrier 18, may be an example of a support.

[0166] To pick a wafer up from a shelf of the wafer carrier 18 the end effector may be inserted into the wafer carrier 18, for example through a door on a side of the wafer carrier 18, beneath the wafer and then raised vertically to pick the wafer up from the shelf. Conversely, to place a wafer on a shelf of the wafer carrier 18 the end effector carrying the wafer may be positioned above the shelf and then lowered vertically to place the wafer on the self.

[0167] FIG. 2 is an example of a device 23 for changing the temperature of a wafer that can be used in embodiments of the present invention. The device 23 can be used as the temperature changing part 9 or the second temperature changing part 13 in the semiconductor wafer mass metrology apparatus 1 described above, for example.

[0168] The device 23 comprises a plate or block 24. The plate or block 24 is made of, or comprises, a material having a high thermal mass and high thermal conductivity. The plate or block 24 may be made of, or comprise, a metal, such as aluminium.

[0169] As illustrated in FIG. 2, the plate or block 24 has a surface 25 that is configured to support a wafer when the wafer is placed on the plate or block 24 on the surface 25. The surface 25 is an upper surface of the plate or block 24, and therefore an upper surface of the device 23.

[0170] The surface 25 is configured to contact the wafer to support the wafer and to exchange heat or thermal energy with the wafer to change the temperature of the wafer. In other words, the surface 25 is for performing heat transfer with the wafer to change the temperature of the wafer.

[0171] The device 23 may be for changing the temperature of a wafer having a predetermined diameter, for example 200mm, or 300mm, or 450mm. The surface 25 may therefore be configured to support a wafer having the predetermined diameter.

[0172] As illustrated in FIG. 2, the plate or block 24 comprises a cut out 27 that is configured to receive an end effector of a robotic arm when the end effector is used to lower the wafer onto the surface 25 while supporting the wafer from beneath.

[0173] The cut out 27 is formed in a top surface of the plate or block 24 of the thermal transfer plate 23, such as the surface 25, such that the end effector can be lowered into the cut out 27 from the top surface when the end effector is used to lower the wafer onto the surface 25 while supporting the wafer from beneath.

[0174] The cut out 27 is configured, for example positioned and / or shaped and / or sized to receive the end effector when the end effector is used to lower the wafer onto the surface 25.

[0175] In particular, the cut out 27 is positioned lower in the plate or block 24 than the surface 25, so that the end effector can be lowered into the cut out 27 when lowering the wafer onto the surface 25 so that the end effector is received in the cut out 27 when the wafer is placed on the surface 25. In particular, the cut out 27 is located below the surface 25 in the plate or block 24.

[0176] The cut out 27 extends into the plate or block 24 from the surface 25 and is accessible and / or open to the end effector from the surface 25.

[0177] The cut out 27 has an open side at a side of the device 23.

[0178] The cut out 27 also extends to a side of the plate or block 24 and is accessible and / or open to the end effector at the side of the plate or block 24.

[0179] As shown in FIG. 2, the surface 25 extends over or above part of both longitudinal sides of the cut out 27 so that a groove or trench 28 is formed along part of both longitudinal sides of the cut out 27.

[0180] This means that an area of an opening of the cut out 27 formed in the surface 25 is smaller than an area of a main body of the cut out 27 below the surface 25.

[0181] The groove or trench 28 allows the end effector to be withdrawn laterally from the cut out 27 via the open side of the cut out 27 even though a distal end of the end effector is a widest part of the end effector, as discussed below.

[0182] A minimum width of a main part of the cut out 27 below the surface 25 is larger than a maximum width of the end effector received in the cut out 27. This enables the end effector to be withdrawn laterally from the cut out 27.

[0183] When the end effector is received in the cut out 27, the end effector is below the surface 25. In other words, when the end effector is received in the cut out 27 the end effector is lower in the plate or block 24 than the surface 25. In such an arrangement the end effector does not protrude above the surface 25,

[0184] The cut out 27 is configured, for example shaped and / or positioned, so that once the end effector has been received in the cut out 27, the end effector can be withdrawn laterally from the device 23 while the wafer is supported by the surface 25.

[0185] The device 23 may further comprise or be provided with a vacuum clamp for clamping the wafer to the device 23. For example, the device 23 may comprise a groove or channel 29 in the surface 25 from which air can be sucked, for example by one or more pumps, so as to create a low pressure between the device 23, and / or the surface 25 of the device 23, and the wafer so as to clamp the wafer to the surface 25.

[0186] FIG. 3 is a sectional view of a device 31 for changing the temperature of a wafer that can be used in embodiments of the present invention. The device 31 corresponds to the device 23 illustrated in FIG. 2 with the minor difference that the single groove or channel 29 of FIG. 2 is replaced with a double or looped groove or channel 33. Otherwise, the features of the device 31 discussed below may also be present in the device 23 described above the devices 23 and 31 may be considered to be the same device.

[0187] As illustrated in FIG. 3, the device 31 comprises a sensor gap or space 35 which is located below the surface 25. In particular, the surface 25 is provided on an upper face of a plate 36, and the sensor gap or space 35 is provided below a lower face 38 of the plate 36. The purpose of the sensor gap or space 35 is discussed below.

[0188] Of course, in other embodiments the device 23 or 31 may be formed from a single plate or piece of material with the sensor gap or space 35 embedded in the body of the plate or piece of material. In other words it is not necessary for the device 23 or 31 to include the separate plate 36.

[0189] Figures 4A to 4C show an end effector and robotic arm that can be used in embodiments of the present invention. As shown in FIG. 4A, the end effector 37 comprises two prongs or forks 39 at a distal part of the end effector 37. The end effector 37 is configured to contact an underside of the wafer to support the weight of the wafer from beneath, so that the wafer can be carried by the end effector 37. The end effector 37 may comprise a plurality of wafer contact pads on an upper surface of the end effector 37 for contacting the underside of the wafer. For example, the end effector 37 may comprise three or more such wafer contact pads.

[0190] A proximal end of the end effector 37 opposite to the two prongs or forks 39 is configured to be attached to a robotic arm, so that the end effector 37 can be moved by the robotic arm to move the wafer.

[0191] FIG. 4B shows the end effector 37 attached to a robotic arm 41. In this example, the robotic arm 41 comprises two linear arm segments. A first arm segment 43 is rotatably mounted at its first end to another part of the robotic arm 41. A second arm segment 45 is rotatably mounted at its first end to a second end of the first arm segment 43. The end effector 37 is attached to a second end of the second arm segment 45.

[0192] As shown in FIG. 40, the first arm segment 43 is connected to an actuator 47 that is configured to move the first arm segment upwards and downwards in the vertical direction.

[0193] The robotic arm 41 can therefore be used to move the end effector 37 to different positions, including different vertical positions.

[0194] As shown in FIG. 4A, the end effector 37 further comprises a first sensor arrangement 40. The first sensor arrangement 40 comprises a light source 49 and a light detector 51 . The light source 49 is attached to a first one of the two prongs or forks 39 and is arranged to direct light towards a second one of the two prongs or forks 39. The light detector 51 is attached to the second one of the two prongs or forks 39 and is arranged to detect light emitted by the light source 49.

[0195] The light may be visible light, for example laser light, or may be non-visible light, for example infrared light.

[0196] The first sensor arrangement 40 therefore detects whether or not the light path between the light source 49 and the light detector 51 is obstructed.

[0197] The light source 49 and the light detector 51 are arranged so that when the end effector 37 is received in a predetermined vertical position in the cut out 27 in the device 23 or 31 , the light path between the light source 49 and the light detector 51 is positioned in the sensor gap or space 35 described above and is therefore not obstructed. Therefore, when the end effector 37 is supporting a wafer and is used to lower the wafer onto the surface 25 of the device 23 or 31 , the light path between the light source 49 and light detector 51 will be obstructed while the wafer is passing through the plate 36 and entering the cut out 27 until the end effector 37 is positioned in the predetermined vertical position in the cut out 27, at which point the light path will be positioned in the sensor gap or space 35 and therefore will not be obstructed.

[0198] Therefore, the output of the first sensor arrangement 40 can be used to detect when the end effector 37 is at a predetermined vertical position relative to the surface 25. In particular, by detecting when the light detector 51 detects the light from the light source 49 while the end effector 37 is being lowered into the cut out 27, the predetermined vertical position of the end effector 37 relative to the surface 25 can be detected. This predetermined vertical position is a position at which the first sensor arrangement 40 transits down past the lower face 38 of the plate 36 such that the light path is positioned in the sensor gap or space 35.

[0199] Similarly, the same predetermined vertical position can be detected when the end effector 37 is being used to pick up the wafer from the surface 25 by detecting when the first sensor arrangement 40 transits up past the lower face 38 of the plate 36 such that the light path becomes obstructed.

[0200] The output of the first sensor arrangement 40 therefore provides detection of a specific vertical position of the end effector 37 relative to the surface 25 that is independent of the control of an actuator for controlling the vertical position of the end effector 37, such as the actuator 47 in FIG. 4G.

[0201] The predetermined vertical position is a position that the end effector 37 moves through each time that the end effector 37 is used to place a wafer on the surface 25 or to pick a wafer up from the surface 25.

[0202] Positional information (for example a positional value or control value) of an actuator for moving the end effector 37 in the vertical direction, for example the actuator 47 in FIG. 4C, can also be obtained at the same time that the first sensor arrangement 40 detects that the end effector 37 is at the predetermined vertical position relative to the surface 25. For example, a value of an encoder of the actuator can be obtained. The positional information can be stored in a memory 50 of the apparatus, for example a memory 50 coupled to the controller or processor 22. The positional information may be a relative vertical or z position value for the actuator, for example.

[0203] When performing repeated movements of the end effector 37 to place different wafers on the surface 25, and subsequently pick them up from the surface 25, the positional information can be monitored to check for any variation in the positional information over the repeated movements or relative to the immediately preceding positional information. If the obtained positional information changes over time, this may mean that the end effector 37 is not being correctly positioned vertically relative to the surface 25 by the actuator, for example because of droop or angling of the end effector, or because of damage to the end effector, or because of a change in the configuration of the apparatus, for example. As mentioned above, this may lead to incorrect placement of the wafer or damage to the wafer or end effector 37, for example.

[0204] If such variation in the obtained positional information is detected, one or more different operations may be performed, for example by the controller or processor 22. For example, the apparatus may raise an alarm to warn an operator of the apparatus of an issue, or further operation of the apparatus may be prevented.

[0205] Therefore, the first sensor arrangement 40 may be used to provide an independent indication of the vertical position of the end effector 37 relative to the surface 25 that can be used to check that the end effector 37 is being correctly positioned by the robotic arm 41.

[0206] In addition, or alternatively, the end effector may comprise a different sensor to the first sensor arrangement 40 described above. For example, as illustrated in FIGS. 5A to 5E, the end effector 37 may comprise a wafer presence sensor 53 that is configured to detect when a wafer is present on the end effector. For example, the wafer presence sensor 53 may be an optical sensor.

[0207] The wafer presence sensor 53 may comprise a light source 54 and a light detector 56 that detects a light beam 59 (wafer presence beam) emitted by the light source 54. The light may be visible light, or non- visible light. The light source 54 and light detector 56 are positioned such that the light beam 59 is interrupted by the wafer W when the wafer W is on the end effector 37. Therefore, the wafer presence sensor 53 can detect when a wafer is on the end effector 37. The wafer presence sensor 53 may have a first output when the light beam 59 is not interrupted and a second output when the light beam 59 is detected.

[0208] In this example, the light source 54 is positioned above the wafer when the wafer is on the end effector 37, and the light detector 56 is embedded in a surface of the end effector 37 below the wafer when the wafer is on the end effector.

[0209] Of course, the positions of the light source 54 and light detector 56 may be switched relative to that illustrated in FIG. 5, and / or the absolute positions may be different to those illustrated in FIG. 5.

[0210] FIGS. 5A to 5E show a wafer W being placed on a device for changing the temperature of a wafer according to an embodiment of the present invention. For example, the device may be the device 23 or 31 described above. The device 23, 31 is illustrated schematically and in a simplified form in FIGS. 5A to 5E so not all features of the device 23, 31 are illustrated in FIGS. 5A to 5E.

[0211] In particular, FIGS, 5A to 5E show the end effector 37 passing through the plate 36 of the device. The plate 36 has a predetermined thickness / depth, and the cut out 27 extends through the plate 36 and is at least partly located below the plate 36 in a portion of the device 23, 31 below the plate 36. The cut out 27 is not illustrated in FIGS. 5A to 5E.

[0212] In this arrangement, the end effector 37 comprises both the first sensor arrangement 40 described above and the wafer presence sensor 53 mentioned above. Outputs of both these sensors are used to detect when the end effector 37 is in a predetermined vertical position relative to the surface 25 of the device in this embodiment.

[0213] However, in practice only the output of the first sensor arrangement 40 is needed to detect when the end effector 37 is in the predetermined vertical position relative to the surface 25 in this embodiment, so in other embodiments the wafer presence sensor 53 may be omitted and / or an output of the wafer presence sensor 53 may not be used for detecting that the end effector 37 is in the predetermined vertical position relative to the surface 25

[0214] In this arrangement, an output of the first sensor arrangement 40 is set to “0” when the light path between the light source 49 and light detector 51 is not obstructed, and is set to “1” when the light path is obstructed.

[0215] Furthermore, in this arrangement an output of the wafer presence sensor is set to “1” when the presence of a wafer on the end effector 37 is detected, and is set to “0” when the presence of a wafer on the end effector 37 is not detected.

[0216] An amplifier is used to perform a logical OR operation on the outputs of the first sensor arrangement and the wafer presence sensor, such that an output of the amplifier is “1” when the output of either the first sensor arrangement or the wafer presence sensor is “1” and is “0” when the output of either the first sensor arrangement or the wafer presence sensor is “0”.

[0217] Table 1 below shows the outputs of the first sensor arrangement, the wafer presence sensor and the amplifier for each of the arrangements illustrated in FIGS. 5A to 5E. In addition, Table 1 further shows a value of an encoder of an actuator that moves the robotic arm and therefore the end effector 37 in the vertical direction (z direction), for example the actuator 47 in FIG. 4G.

[0218] TABLE 1

[0219] FIGS. 5A to 5E show the end effector being lowered through the plate 36 into the cut out 27 of the device 23 or 31.

[0220] FIG. 5A shows the end effector positioned above the surface 25 of the plate 36. In this arrangement the light path between the light source 49 and the light detector 51 is unobstructed by the plate 36 and the output of the first sensor arrangement 40 is therefore “0”.

[0221] FIG. 5B shows a first transition point where the end effector 37 is starting to be lowered through the surface 25 into the cut out 27 in the plate 36. In this position, the light path between the light source 49 and the light detector 51 is starting to be blocked by the plate 36, such that an output of the first sensor arrangement 40 is in transition between “0” and “1”.

[0222] In FIG. 50 the end effector is passing through the cut out 27 in the plate 36, such that the light path is obstructed by the plate 36 and the output of the first sensor arrangement 40 is “1”.

[0223] FIG. 5D shows a second transition point where the end effector 37 is finishing being lowered through the cut out 27 in the plate 36 into the cut out 27 below the plate 36 and is passing the lower face 38 of the plate 36. When the end effector 37 is positioned in the cut out 27 below the plate 36 as illustrated in FIG. 5E, the light path is located in the sensor gap or space 35 of the device such that the light path is not blocked and the output of the first sensor arrangement is “0”. FIG. 5D therefore shows a position in which the light path between the light source 49 and the light detector 51 is starting to be unblocked, such that an output of the first sensor arrangement 40 is in transition between “1” and “0”.

[0224] Furthermore, in FIGS. 5A and 5B the wafer presence detector 53 detects the presence of the wafer on the end effector 37 and therefore has the output “1”. In particular, the wafer presence beam 59 of the wafer presence sensor 53 is incident on the wafer W on the surface of the end effector 37.

[0225] In FIG. 5C the wafer presence sensor 53 is in transition between detecting the wafer and not detecting the wafer. In particular, a lower edge of the wafer W is just passing through the wafer presence beam 59 so that the wafer will no longer be in the wafer presence beam. In FIG. 50 the output of the wafer presence sensor 53 is therefore in transition between “1” and “0”.

[0226] In FIGS. 5D and 5E the wafer presence sensor 53 does not detect the wafer since there is a suitable separation between the end effector 37 and the wafer, and therefore an output of the wafer presence sensor 53 is “0”.

[0227] As shown in Table 1 , an output of the amplifier is therefore “1” for FIGS. 5A to 50, “0” in FIG. 5E and in transition in FIG. 5D.

[0228] The final column in T able 1 shows the value of the encoder of the actuator for each of the arrangements illustrated in FIGS. 5A to 5E. In this embodiment, the value of the encoder of the actuator is obtained when the output of the amplifier is in the “transitioning” stage where the output of the amplifier is transitioning from “1” to “0”. This corresponds to the moment that the first sensor arrangement 40 passes the lower face 38 of the plate 36 as illustrated in FIG. 5D. This may correspond to a predetermined vertical position of the end effector 37 relative to the surface 25. The detection of this position may be an example of an event. Therefore, in the table above, the value of the encoder “-12000” is obtained. The obtained value may be stored in a memory.

[0229] The obtained value of the encoder may be compared to a predetermined or expected value of the encoder when the end effector 37 is in the vertical position relative to the surface 25 illustrated in FIG. 5D. For example, a value of the encoder when the end effector 37 is in this vertical position may be set in advance, or predetermined in advance. As discussed above, the obtained value of the encoder may differ from this predetermined or expected value for reasons such as droop or angling of the end effector 37, or damage to the end effector, or a change to a configuration of the apparatus. Alternatively, or in addition, the obtained value of the encoder may be compared to a previously obtained value of the encoder when the end effector 37 was previously in the same vertical position relative to the surface 25. It may then be determined whether the two obtained values of the encoder are the same, or within a predetermined range or value of each other. As discussed above, the obtained value of the encoder may change over time for reasons such as droop or angling of the end effector 37, or damage to the end effector 37, or a change to a configuration of the apparatus.

[0230] When it is determined that the obtained value of the encoder differs from the predetermined or expected value of the encoder, or from the previously obtained value of the encoder, the apparatus, for example the controller or processor 22, may be configured to perform one or more operations.

[0231] For example, the controller or processor 22 may be configured to alert a user of the apparatus to the difference, for example by providing a visual and / or audible alert. Alternatively, or in addition, the controller or processor 22 may be configured to stop or prevent further operation of the apparatus.

[0232] Of course, it is not essential to provide both the first sensor arrangement 40 and the wafer presence sensor 53 in this embodiment. Instead, only the first sensor arrangement 40 may be provided. In this case the amplifier is also not necessary. Instead, it may be detected that the end effector 37 is in the predetermined vertical position relative to the surface 25 when the output of the first sensor arrangement 40 is transitioning between “1” and “0”, which corresponds to the arrangement illustrated in FIG. 5D. In this case, it is also not essential for the output of the first sensor arrangement 40 to be either “1” or “0”, and other outputs may be used instead.

[0233] Of course, in other embodiments the device 23 or 31 may be formed from a single plate or piece of material with the cut out 27 and the sensor gap or space 35 provided in the body of the single plate or piece of material. In other words, it is not necessary for the device 23 or 31 to include the separate plate 36. In this case, the output of the first sensor arrangement will transition from “1” to “0” when the first sensor arrangement transits down past the upper surface of the sensor gap or space 35.Similar considerations apply when the end effector 37 is instead being used to pick up the wafer from the surface 25. In particular, during such a pick up operation the outputs of the first sensor arrangement 40 and the wafer presence sensor 53 will be the same as those illustrated in Table 1 for the arrangements illustrated in FIGS. 5A to 5E, so the same value of the encoder will be obtained.

[0234] Figures 6A to 6D show a wafer W being placed on a wafer support according to an embodiment of the present invention using the same end effector 37 described above. For example, the wafer support may be the weighing pan 5 illustrated in FIG. 1 , or a shelf of the wafer carrier 18 illustrated in FIG. 1 .

[0235] As shown in FIGS. 6A to 6D, the wafer support 55 comprises a plurality of wafer support pins 57 that are configured to contact the underside of a wafer W when the wafer W is lowered onto the wafer support 55 using the end effector 37. For example, there may be three of the wafer support pins 57.

[0236] T able 2 below shows the outputs of the first sensor arrangement 40, the wafer presence sensor 53 and the amplifier for each of the arrangements illustrated in FIGS. 6A to 6D. In addition, Table 2 further shows the value of the encoder of the actuator that moves the robotic arm and therefore the end effector 37 in the vertical direction, for example the actuator 47 in FIG. 4G.

[0237] TABLE 2

[0238] FIG. 6A shows the end effector 37 positioned above the wafer support pins 57 of the wafer support 55. In this arrangement the wafer W is supported by the end effector 37 and the presence of the wafer W is detected by the wafer presence beam 59 of the wafer presence sensor 53. The output of the wafer presence sensor 53 is therefore “1”.

[0239] In FIG. 6B the wafer W has been lowered by the end effector 37 so that the wafer W is in contact with the wafer support pins 57 but is also still in contact with the end effector 37. In this arrangement the wafer is still at least partly supported by the end effector 37 and the presence of the wafer W is still detected by the wafer presence beam 59 of the wafer presence sensor 53. The output of the wafer presence sensor 53 is therefore still “1”.

[0240] In FIG. 60 the end effector 37 has been further lowered so that the wafer W is supported by the wafer support pins 57 and is not supported by the end effector 37. In this position the bottom edge of the wafer W is just passing through the wafer presence beam 59 of the wafer presence sensor 53. Therefore, the output of the wafer presence sensor 53 is transitioning from “1” to “0”.

[0241] In FIG. 6D the end effector 37 has been further lowered. In this position the presence of the wafer W is not detected by the wafer presence sensor 53 and the output of the wafer presence sensor 53 is therefore “0”.

[0242] In all of the arrangements illustrated in FIGS. 6A to 6D the light path between the light source 49 and the light detector 51 is unobstructed. The output of the first sensor arrangement is therefore “0” for all of FIGS. 6A to 6D.

[0243] As shown in Table 2, an output of the amplifier is therefore “1” for FIGS. 6A and 6B, “0” in FIG. 6D and in transition in FIG. 6C.

[0244] The final column in T able 2 shows the value of the encoder of the actuator for each of the arrangements illustrated in FIGS. 6A to 6D. In this embodiment, the value of the encoder of the actuator is obtained when the output of the amplifier is in the “transitioning” stage where the output of the amplifier is transitioning from “1” to “0”. This corresponds to the moment that the wafer W is sufficiently separated from the top surface of the end effector 37 that the bottom edge of the wafer W has just passed through the wafer presence beam 59 of the wafer presence sensor 53, as illustrated in FIG. 60. This may correspond to an event that is being detected. Therefore, in the table above, the value of the encoder 4500” is obtained. The obtained value may be stored in a memory.

[0245] The obtained value of the encoder may be compared to a predetermined or expected value of the encoder when the bottom edge of the wafer W has just passed through the wafer presence beam 59 of the wafer presence sensor 53. For example, such a value of the encoder may be set in advance, or predetermined in advance. As discussed above, the obtained value of the encoder may differ from this predetermined or expected value for reasons such as droop or angling of the end effector, or damage to the end effector 37, or a change in a configuration of the apparatus, for example.

[0246] Alternatively, or in addition, the obtained value of the encoder may be compared to a previously obtained value of the encoder when it was previously detected that the bottom edge of the wafer W has just passed through the wafer presence beam 59 of the wafer presence sensor 53. It may then be determined whether the two obtained values of the encoder are the same, or within a predetermined range or value of each other. As discussed above, the obtained value of the encoder may change over time for reasons such as droop or angling of the end effector, or damage to the end effector, or a change of a configuration of the apparatus.

[0247] When it is determined that the obtained value of the encoder differs from the predetermined or expected value of the encoder, or from the previously obtained value of the encoder, the apparatus, for example the controller or processor 22, may be configured to perform one or more operations discussed above with respect to FIG. 5.

[0248] Similar considerations apply when the end effector 37 is instead being used to pick up the wafer from the support 55. In particular, during such a pick up operation the outputs of the first sensor arrangement 40 and the wafer presence sensor 53 will be the same as those illustrated in T able 2 for the arrangements illustrated in FIGS. 6A to 6D.

[0249] Of course, it is not essential to provide both the first sensor arrangement 40 and the wafer presence sensor 53 in this embodiment. Instead, only the wafer presence sensor 53 may be provided. In this case the amplifier is also not necessary. Instead, it may be detected that the end effector is in the predetermined vertical position relative to the wafer support 55 when the output of the wafer presence sensor 53 is transitioning between “1” and “0”, which corresponds to the arrangement illustrated in FIG. 6C. In this case, it is also not essential for the output of the wafer presence sensor to be either “1” or “0”, and other outputs may be used instead.

[0250] In addition, in other embodiments a different type of wafer presence sensor may be provided instead of the wafer presence sensor 53 described above. For example, the end effector may comprise one or more of a force transducer, pressure sensor, capacitive sensor or inductive sensor for detecting the presence of a wafer on the end effector.

[0251] FIGS. 7A and 7B illustrate droop or angling of the end effector 37 described above. As illustrated in

[0252] FIGS. 7A and 7B, the end effector 37 may comprise a pivot point 61 about which the end effector 37 can be pivoted. The pivot point 61 may be used for the purposes of levelling the end effector 37 once the end effector has been attached to the robotic arm, for example.

[0253] FIG. 7A shows the end effector 37 in a level (horizontal arrangement). In contract, FIG. 7B shows the end effector 37 pivoted around the pivot point 61 so that the end effector 37 is not level. This non-level arrangement is referred to as droop of the end effector, or angling of the end effector. As illustrated in FIG. 7B, droop of the end effector changes a vertical position and / or orientation of at least a distal end of the end effector 37 and the distal edge of the wafer W. For example, in FIG. 7B the edge of the wafer is lower in the vertical direction by an amount Az compared to FIG. 7A.

[0254] Such droop or angling of the end effector will also change the vertical position of the first sensor arrangement 40, which may be located at or adjacent to a distal end of the end effector 37. Therefore, a positional value of the actuator at which the first sensor arrangement 40 is at the predetermined vertical position relative to the support will be different for the horizontal arrangement of the end effector 37 illustrated in FIG. 7A and the drooped or angled arrangement of the end effector 37 illustrated in FIG. 7B. Therefore, a change in the positional value of the actuator for the same detected event during different placing or picking operations may be used to detect such drooping or angling of the end effector.

[0255] Such droop of the end effector 37 may lead to damage of wafers when loading wafers onto a support and / or when picking up wafers from the support.

[0256] In the present invention, it may be possible to detect such droop of the end effector 37 based on checking or monitoring of the control value of the actuator when an event is detected during placing of the wafer on the support or picking the wafer up from the support.

[0257] The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

[0258] While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

[0259] For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

[0260] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0261] Throughout this specification, including the claims which follow, unless the context requires otherwise, the word “comprise” and “include”, and variations such as “comprises”, “comprising”, and “including” will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0262] It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” one particular value, and / or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent “about,” it will be understood that the particular value forms another embodiment. The term “about” in relation to a numerical value is optional and means for example + / - 10%.

Claims

Claims:

1. An apparatus for handling a wafer, comprising: a support for supporting a wafer; an end effector for placing the wafer onto the support or for picking the wafer up from the support; and an actuator for moving the end effector in a vertical direction to place the wafer onto the support or to pick the wafer up from the support, wherein the end effector comprises a sensor, the apparatus is configured to detect an event when placing the wafer onto the support or when picking the wafer up from the support based at least in part on an output of the sensor, and the apparatus is configured to obtain positional information from the actuator when the event is detected.

2. The apparatus according to claim 1, wherein the event comprises: the wafer being placed onto the support; the wafer being picked up from the support; the sensor, or at least part of the end effector, being at a predetermined vertical position relative to the support; the sensor, or at least part of the end effector, being at a predetermined vertical position relative to the wafer; the wafer being present on the end effector; or the wafer not being present on the end effector.

3. The apparatus according to claim 1 or claim 2, wherein the event occurs when the sensor, or at least part of the end effector, is at a predetermined vertical position relative to the support.

4. The apparatus according to any of the preceding claims, wherein the apparatus is configured to compare the obtained positional information of the actuator to stored positional information.

5. The apparatus according to claim 4, wherein the stored positional information is: predetermined or expected positional information; or previously obtained positional information of the actuator when the event was previously detected.

6. The apparatus according to claim 4 or claim 5, wherein: the apparatus is configured to perform an operation when it is determined that the obtained positional information is not the same as, or not within a predetermined range or value of, the stored positional information, or when it is determined that there is a trend in the positional information based on the obtained positional information and the stored positional information.

7. The apparatus according to claim 6, wherein the operation comprises one or more of:alerting a user of the apparatus; stopping or preventing an operation of the apparatus; or informing a user of the apparatus of the obtained positional information.

8. The apparatus according to any of the preceding claims, wherein the apparatus is configured to store the obtained positional information in a memory.

9. The apparatus according to any of the preceding claims, wherein the actuator comprises a motor, and the positional information is a value of an encoder of the motor.

10. The apparatus according to any of the preceding claims, wherein the positional information is vertical positional information, or z-positional information, of the actuator.

11. The apparatus according to any of the preceding claims, wherein: the end effector comprises a first sensor and a second sensor; and the apparatus is configured to detect an event when placing the wafer onto the support or when picking the wafer up from the support based at least in part on an output of the first sensor and an output of the second sensor.

12. The apparatus according to any of the preceding claims, wherein: the sensor is configured to detect when the sensor, or at least part of the end effector, is at a predetermined vertical position relative to the support; or the sensor is configured to detect the presence of the wafer on the end effector.

13. The apparatus according to any of the preceding claims, wherein the sensor comprises: a light source; and a light detector arranged to detect light emitted from the light source.

14. The apparatus according to claim 13, wherein: a light path between the light source and the light detector is unobstructed when the sensor, or at least part of the end effector, is at a predetermined vertical position relative to the support; and the light path between the light source and the light detector is obstructed when the sensor, or at least part of the end effector, is at one or more other vertical positions relative to the support.

15. The apparatus according to claim 13 or claim 14, wherein: the end effector comprises two prongs; the light source is positioned on a first one of the two prongs and is arranged to direct light towards a second one of the two prongs; and the light detector is positioned on the second one of the two prongs.

16. The apparatus according to any of the preceding claims, wherein the sensor comprises a wafer mapping sensor.

17. The apparatus according to any of the preceding claims, wherein the support is a device for changing the temperature of the wafer.

18. The apparatus according to claim 17, wherein the device comprises: a surface that is configured to support the wafer and to exchange heat with the wafer; and a space that is configured to receive at least a distal part of the end effector when the end effector is used to place the wafer onto the surface.

19. The apparatus according to claim 18, wherein: the sensor comprises a light source and a light detector arranged to detect light emitted from the light source; and the device comprises a sensor gap in which a light path between the light source and light detector is positioned when the sensor, or at least part of the end effector, is at a predetermined vertical position relative to the device, so that the light path is unobstructed.

20. The apparatus according to claim 18 or claim 19, wherein: the device comprises a plate having the surface on an upper face of the plate; at least part of the space is located below the plate; and the apparatus is configured to detect when the sensor transits up past a lower face of the plate when the end effector is being used to pick the wafer up from the surface, or the apparatus is configured to detect when the sensor transits down past the lower face of the plate when the end effector is being used to place the wafer onto the surface.

21. The apparatus according to any of claims 1 to 16, wherein the support is a pan of a weighing device for performing a weight measurement on the wafer.

22. The apparatus according to any of claims 1 to 16, wherein: the apparatus comprises a wafer carrier for carrying a plurality of wafers, and wherein the wafer carrier comprises the support; or the support is a wafer carrier for carrying a plurality of wafers.

23. The apparatus according to any of the preceding claims, wherein the sensor comprises a wafer presence sensor that is configured to detect the presence of the wafer on the end effector.

24. The apparatus according to claim 23, wherein the wafer presence sensor comprises a wafer presence beam for detecting the presence of the wafer on the end effector.

25. The apparatus according to claim 24, wherein the wafer presence beam is directed downwards towards the wafer when the wafer is on the end effector.

26. The apparatus according to claim 24 or claim 25, wherein the apparatus is configured to detect when the wafer presence beam transits up past an outside edge of the wafer when the end effector is being used to pick the wafer up from the support, and / or the apparatus is configured to detect when the wafer presence beam transits down past the outside edge of the wafer when the end effector is being used to place the wafer onto the support.

27. The apparatus according to any of the preceding claims, wherein: the apparatus comprises a first support and a second support; the end effector is for placing the wafer onto the first support or for picking the wafer up from the first support; and the end effector is also for placing the wafer onto the second support or for picking the wafer up from the second support.

28. The apparatus according to any of the preceding claims, wherein the support comprises a plurality of wafer support elements for contacting a bottom surface of the wafer to support the wafer.

29. The apparatus according to any of the preceding claims, wherein the apparatus is a wafer mass metrology apparatus.

30. The apparatus according to any of the preceding claims, wherein the apparatus comprises a robotic arm having the end effector.

31. A method of handling a wafer using an apparatus that comprises: a support for supporting a wafer; an end effector for placing the wafer onto the support or for picking the wafer up from the support; and an actuator for moving the end effector in a vertical direction to place the wafer onto the support or to pick the wafer up from the support, the method comprising: detecting an event when placing the wafer onto the support or when picking the wafer up from the support based at least in part on an output of the sensor, and obtaining positional information from the actuator when the event is detected.

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