Force sensing system for substrate lifting apparatus

A system and method for monitoring forces on a substrate lifting apparatus. The system includes a platen cartridge with a platen and a movable lifting portion. The movable lifting portion includes a plurality of lifting arms coupled to a plurality of lift pins. A plurality of force sensing elements are associated with respective ones of the plurality of lifting arms and the plurality of lift pins. A controller receives signals from the plurality of force sensing elements, correlates the signals to respective forces applied to said plurality of lift pins. The correlated forces may indicate to the controller that an error condition exists, such as a stuck wafer, a broken wafer, a mis-positioned wafer, or a mechanical malfunction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a non-provisional of pending U.S. provisional patent application Ser. No. 61/817,194, filed Apr. 29, 2013, the entirety of which provisional application is incorporated by reference herein.

FIELD OF THE DISCLOSURE

The disclosure relates generally to semiconductor processing systems, and more particularly to a system for monitoring forces applied to a substrate lifting apparatus used in substrate transfer operations.

BACKGROUND OF THE DISCLOSURE

During production, substrates are often handled by robotic arms that are equipped with specialized tools, or “end effectors,” that are adapted for lifting and moving the substrates between a substrate cassette or other container and a processing platen located within a process chamber. End effectors typically engage the substrates from below. As such, while an end effector can pick a substrate directly from a cassette, it typically cannot directly deposit a substrate onto the surface of the platen.

Thus, the platen often includes a set of movable pins that protrude upward through openings in the top surface of the platen. The end effector positions the substrate above the pins, the pins move upward to pick up the substrate and raise it above the end effector. Once the pins raise the substrate out of engagement with the end effector, there is sufficient distance between the substrate and the platen top surface to allow the end effector to retract from the platen. The pins can then be retracted through the openings, lowering the substrate onto the platen.

An electrostatic chuck can then be used to secure the substrate to the platen so that one or more processing steps can be performed. When processing is complete, the electrostatic chuck can release the substrate, the pins are moved upward to protrude through the openings and lift the substrate above the platen so the end effector can engage and remove the substrate from the process chamber.

As will be appreciated, problems such as substrate breakage, substrate mis-positioning, substrate sticking, and the like, can occur before, during or after the substrate transfer and/or processing operations. It would be desirable, therefore, to provide a system capable of detecting such problems so that corrective action can be taken in an efficient and cost effective manner.

SUMMARY OF THE DISCLOSURE

A system is disclosed for monitoring force on a substrate lifting apparatus. The system includes a platen cartridge having a platen and a movable lifting portion. The movable lifting portion can include a plurality of lifting arms coupled to a plurality of lift pins. A plurality of force sensing elements may be associated with respective ones of the plurality of lifting arms and the plurality of lift pins. The system may further include a controller for receiving signals from the plurality of force sensing elements, and for correlating said received signals to respective forces applied to the plurality of lift pins.

A method is disclosed for sensing forces applied to a substrate lifting apparatus. The method can include receiving, at a controller, signals from at least one force sensing element, where the received signals are representative of a force applied to a lift pin of a substrate lifting apparatus, and controlling operation of said substrate lifting apparatus based on said received signals.

A method is disclosed for operating a substrate lifting apparatus. The method can include, at a controller, sampling signals from at least one force sensing element associated with a lift pin of a substrate lifting apparatus, where the sampling occurs prior to moving the lift pin, and where the sampled signals are representative of force applied to said lift pin. The method can further include controlling movement of said lift pin based on said sampled signals.

DETAILED DESCRIPTION

FIG. 1illustrates an exemplary embodiment of a system in accordance with the present disclosure. For the sake of convenience and clarity, terms such as “front,” “rear,” “top,” “bottom,” “right,” “left,” “up,” “down,” “inwardly,” “outwardly,” “lateral” and “longitudinal” will be used herein to describe the relative placement and orientation of components of the system, each with respect to the geometry and orientation of the as it appears inFIG. 1. Said terminology will include the words specifically mentioned, derivatives thereof, and words of similar import.

In some substrate processing applications, ion beam implanters utilize a rotating platen device1, a non-limiting exemplary illustration of which is shown inFIG. 1. The rotating platen device1may be disposed within a process chamber (not shown) and may be configured to hold a substrate in a desired position during one or more implanting steps. The rotating platen device1may include a platen2and a base portion4, which can be controllably rotatable with respect to each other so that during processing the substrate can be held at a desired angle with respect to an incident ion beam.

As can be seen inFIG. 1, a plurality of lift pins8may be axially movable so as to protrude above a top surface10of the platen2. In the illustrated embodiment, three lift pins8are provided in a triangular arrangement. It will be appreciated, however, that this is not critical and that different numbers of pins, in different arrangements, may be used as desired.

FIG. 2shows a side view of the platen2in which an exemplary substrate12is held a distance “D” above the top surface10by the lift pins8. The pins8are shown in the extended position. For clarity the base portion4is not shown in this and further views. The distance “D” can be selected to be larger than the vertical dimension of an associated end effector. Thus, when the lift pins8are in the extended position, the end effector can be inserted between the substrate12and the top surface10of the platen2to either engage or disengage the substrate.

The position of the lift pins8can be controlled so that once they have engaged the substrate12, they can be retracted into the platen2to bring the substrate down into contact with the top surface10of the platen. The retracted position of the pins8is shown inFIG. 3. The substrate12can then be secured to the platen2using an electrostatic clamp (not shown) or other appropriate technique, thus permitting the substrate to be tilted and/or rotated to a desired orientation for undergoing one or more implant processes.

Once processing is completed, the platen2may be rotated so that the substrate12is returned to a horizontal orientation. The electrostatic clamp can then be de-energized, and the lift pins8can again be moved to their extended position to raise the substrate12above the top surface10of the platen2(FIG. 2), thus permitting the end effector to extend beneath the substrate. The lift pins8may once again be retracted toward the platen2, lowering the substrate12back onto the end effector so that it may transport the substrate back out of the process chamber.

As previously mentioned, during substrate handling and processing operations a variety of error conditions can be experienced, including the presence of broken or mis-positioned substrates on the platen, substrates that stick to the platen after the electrostatic clamp is de-energized, malfunctioning lift pins, and the like. The disclosed lifting arrangement, therefore, includes a force sensing feature associated with one or more of the lift pins8to assure that substrate12transfers onto and off the platen2are completed in a safe and efficient manner, and to allow corrective action to be taken if an error condition is sensed.

Referring toFIG. 4, a platen cartridge14can include a cartridge base16, a platen support18and a movable lifting portion20configured to raise and lower the lift pins8with respect to the platen cartridge. The movable lifting portion20includes a plurality of lifting arms22, each of which is associated with a respective lift pin8. The lifting arms22are coupled at proximal ends24to a central hub26which, in turn, is coupled to a central lifting post28. Thus arranged, by extending and retracting the central lifting post28in and out of the platen cartridge14, the lift pins8can be selectively configured in the extended and retracted position shown inFIGS. 2 and 3.FIG. 4shows the movable lifting portion20in the retracted position associated with the pin placement ofFIG. 2, whileFIG. 5shows the movable lifting portion20in the extended position associated with the pin placement ofFIG. 3.

FIG. 5shows the platen cartridge14with the platen support18removed. As will be appreciated, selective movement of the central lifting post28(i.e., rotation, axial extension/retraction) may be achieved using any of a variety of appropriate actuating mechanisms disposed ion the platen cartridge14, including servo motors and the like.

FIG. 5further shows a plurality of sensing elements30associated with each of the lifting arms22. Only two of the three sensing elements20are visible inFIG. 5, the third being obscured by the presence of one of the lift pins8. As will be described in greater detail, these sensing elements30can be used to detect forces applied to the lifting arms22via the lift pins8. It will be appreciated that the sensing elements30may be disposed on the lift pins8, or that more than one sensing element may be provided for each lift pin and/or lifting arm22. The sensing elements30may be used to sense and recognize the weight of a substrate12supported by the lift pins8, as well as to sense and recognize any unexpected forces applied to any of the lift pins which may be indicative of a system malfunction or error condition. For example, the sensing elements30may be used to detect whether the substrate12is positioned correctly on the platen2by comparing measurements between the three sensing elements, as will be described in greater detail later.

In one embodiment, the sensing elements30may comprise strain gauges, such as wire mesh strain gauges, piezoelectric strain gauges, semiconductor strain gauges and the like. In other embodiments the sensing elements30may be force sensitive resistors, optical displacement sensors, and the like. An associated sensor electronics and control system interface32is shown inFIG. 6. The sensor electronics and control system interface32may condition signals received from the sensing elements30so that they can be correlated to representative force values for each of the lift pins8.

In the illustrated embodiment, the sensing elements30are coupled to appropriate amplification circuitry34, which in one embodiment includes op-amps. The amplified signals may then be processed by an analog to digital (AD) converter36, and sent to a controller38. In the illustrated embodiment, the controller38is a programmable multi-axis controller (PMAC) capable of high speed sampling of the sensing elements30and of controlling the movable lifting portion20. The controller38may be configured to compare signal samples from the sensing elements30with one or more predetermined values and/or predetermined ranges to determine if an out of range condition exists for any or all of the sensing elements30. In one embodiment the controller38may have memory39connected thereto for storing a variety of predetermined values associated with the sensing elements30. In other embodiments the memory39may store operational history relating to the sensors30and the movable lifting portion20.

The controller38may be configured to stop, or to signal stoppage, of a substrate transfer operation if an error condition is observed. In one embodiment, an error condition is a condition in which a signal representative of a force value near to, or outside of, a predetermined value or range, is obtained from at least one of the sensing elements30.

The motion controller38may stop movement of the robot arm/end effector if it senses an error condition. This can prevent undesired contact between the end effector and the substrate12when the substrate is determined, for example, to be mis-positioned. The motion controller38may interface with an implanter control computer40, which can provide supervisory functions and an operator interface. In some instances, the motion controller38can signal the implanter control computer40if any error conditions, or any other issues, are detected with the lift mechanism, in order to coordinate with other implanter subsystems.

The sensor elements30may be sampled any of a variety of points before, during and/or after substrate transfer operations occur. Examples of such samplings are described below.

Unloaded Force in Range—Prior to performing an implant, all sensing elements30should detect force below a lower threshold value. Force detected above the threshold value may indicate a mechanical failure or an instrumentation problem.

Substrate on Lift Pins—When the substrate12is placed onto, or taken off, the platen2, the lift pins8are raised to unload/load end effector. Once the lift pins8are in the extended position, all sensing elements30should detect force within a predetermined range on each lift pin.

Substrate Broken—When lift pins8are configured in the extended position, all sensing elements30should detect force above a threshold value. A lower than threshold value may indicate a substrate breakage condition.

Substrate Off Center—Once the lift pins8are configured in the extended position, the sensing elements30should detect force on the lift pins8that is the same, within a predetermined threshold value. A higher than threshold difference may indicate the substrate is off center with respect to the lift pins8and the platen2.

Foreign Object on Substrate—Once the lift pins8are configured in the extended position, the sensing elements30should detect force on each lift pin8below a predetermined threshold. A higher than threshold value may indicate that a foreign object is on the substrate12.

Equal Forces on Arms—When placing the substrate12onto the lift pins8, force should be monitored for all lift pins8. If force on any single lift pin8is determined to exceed a predetermined threshold value, further lifting can be stopped. A higher than threshold value may indicate a mechanical failure.

Substrate Sticking—After de-energizing the electrostatic clamp, force on the lift pins8can be monitored while moving the lifting pins from the retracted position to the extended position. If the force sensed for any single lifting arm22exceeds a predetermined threshold value, further lifting can be stopped. A higher than threshold force on one lift pin8and a lower than threshold force on one or both of the remaining lift pins8can indicate that the substrate12is sticking to the platen2.

FIG. 7is a flow diagram illustrating a method for operating the disclosed system prior to performing one or more implant processes on the substrate12. At step100, the substrate12is positioned in a transport chamber. At this point the substrate is supported by an end effector and the lift pins8are in the retracted position. The controller38may sample the sensing elements30to determine whether the upload force on the lift pins8is within a predetermined range. The predetermined range may be a force range that indicates the lift pins8are unobstructed and functional.

At step110, the substrate12is moved from the transport chamber to the process chamber by the end effector. The lift pins8remain in the retracted position. At step120, the substrate12is positioned in the process chamber, and is supported by the end effector. The lift pins8are moving upward from the retracted position to the extended position to engage the substrate12, while the controller38samples the sensing elements30to verify whether equal forces are being experienced by all of the lift pins8. At step130, the substrate12is supported by the lift pins8, and the end effector is retracted back to the transport chamber. The lift pins8are in the extended position. The controller38may sample the sensing elements30to verify that the force on the lift pins8is representative of the weight of the substrate12, that the substrate12is centered on the lift pins8, that no foreign material is located on the platen or substrate12, and/or that the substrate is not broken.

At step140, the substrate12is still supported by the lift pins8in the process chamber, the end effector remains in the transport chamber, and the lift pins are moving downward from the extended position to the retracted position so as to engage the substrate12with the platen2. At step150, the substrate12is supported by the platen2and the lift pins8are in the retracted position. The controller38may sample the sensing elements30to verify that the unload forces on the lift pins8are within a predetermined range. The predetermined range may be a force range that indicates the lift pins are unobstructed and functional. At step160, the substrate12is secured to the platen2by an electrostatic clamp. At step170the substrate12is moved by the rotating platen device1into a position appropriate for undergoing one or more processing steps, such as an ion implant process.

FIG. 8is a flow diagram illustrating exemplary system validations that can be performed after to the substrate12has undergone one or more implant processes. At step200, the substrate12is positioned within the process chamber, and is secured to the platen2by the electrostatic clamp. The lift pins8are in the retracted position. At step210, the electrostatic clamp is released, and the lift pins8are moving from the retracted position to the extended position. The controller38samples the sensing elements30to verify that the substrate12is not sticking to the platen2. At step220, the substrate12is supported by the lift pins8. The controller38may sample the sensing elements30to verify that the substrate12is engaged with the lift pins8, that the substrate is centered on the lift pins8, that no foreign material is on the substrate, and that the substrate is not broken.

At step230, the substrate12remains supported by the lift pins8, and the end effector is moved into position beneath the substrate12. The lift pins8are in the extended position. At step240, the substrate12is in the processing chamber, and the lift pins8are moving from the extended position to the retracted position to transfer support of the substrate12to the end effector. At step250, the substrate is supported by the end effector, and the end effector is moving the substrate12to the transport chamber. The lift pins8are in the retracted position. The controller38may sample the sensing elements30to verify that the unloading force is within a predetermined range. At step260the substrate is returned to the cassette.

The disclosed system adds security and information regarding the substrate's condition and position. In addition the disclosed system can be used to monitoring the condition of the platen, enabling a user to determine, for example, whether foreign material (e.g., broken substrate pieces) reside on the platen, or whether a problem exists with the movable lifting portion20and/or any of its components.

The disclosed system is configured for handling a variety of substrates, which in an exemplary embodiment includes silicon wafers. It will be appreciated by those of ordinary skill in the art that this particular configuration is disclosed by way of example only, and that the below-described arrangement may be similarly implemented in virtually any type of substrate handling configuration. All such embodiments are contemplated and may be implemented without departing from the scope of the present disclosure.