Wafer blade contact monitor

A method and apparatus are provided for detecting contact between a wafer blade of a wafer-handling robot and a component in a wafer-handling system. The robot moves the wafer blade within the system while the wafer blade is maintained at an electrical potential, which is different from an electrical potential of the component. Contact between the wafer blade and the component is detected by sensing a change in the electrical potential of the wafer blade during the contact.

FIELD OF THE INVENTION

The present invention relates to substrate-based wafer manufacturing and processing equipment and, more specifically to robotic devices for transporting wafers within such equipment.

BACKGROUND OF THE INVENTION

Semiconductor and other substrate-based wafers are typically fabricated or processed within multi-process “cluster tool” systems. A cluster tool is a manufacturing system that includes a set of environmentally isolated process chambers or modules, which are linked by a wafer-handling interface robot and a computer communications interface. The wafer-handling robot transports each wafer between the various modules in the system. The computer communication interface controls the sequential steps. There are several types of cluster tool systems, such as vacuum cluster tools for deposition and etching, lithography tools, chemical-mechanical polishing systems, ion implant tools and wafer inspection tools.

The wafer-handling robot has one or more articulated arms that support a wafer blade for carrying each wafer within the system. For example, a typical wafer-handling robot includes a pair of frog-leg type robotic arms that provide radial and rotational movement of the wafer blade in a fixed plane within the system. This movement is coordinated by the computer communications interface to pick up and drop off wafers and to transport the wafers between the various processing modules.

The wafer blade typically includes a relatively thin and planar piece of rigid material that supports the back surface of the wafer during transport. The wafer blade can also include an upwardly extending bridge at its distal end to assist in stabilizing the wafer.

Occasionally, slight alignment drift or shift of the wafer-handling robot or its arms can cause the wafer blade to contact the housing, the frame or another component in the system. This contact can release particles that can fall onto the wafer and cause defects. Since this type of contact is intermittent in nature, the contact can be nearly impossible to reproduce and can go undetected for a very long period of time. The intermittent nature of the contact often makes trouble shooting ineffective.

Currently, the only way to determine that there might be an alignment problem is to detect poor yields and high defect counts during a subsequent inspection step. In addition, the next inspection step may not occur until after several additional processing steps. This further adds to the difficulty in detecting and troubleshooting alignment problems. Therefore, the existing approach may not detect a problem until the damage is already done, or it may not detect the problem at all.

Improved methods and apparatus are desired for detecting or troubleshooting alignment errors in wafer-handling robots.

SUMMARY OF THE INVENTION

One embodiment of the present invention is directed to a method of detecting contact between a wafer blade of a wafer-handling robot and a component in a wafer-handling system. The method includes: (a) moving the wafer blade within the system with the robot; (b) maintaining the wafer blade at an electrical potential during movement of the wafer blade, wherein the electrical potential of the wafer blade is different from an electrical potential of the component; and (c) sensing a change in the electrical potential of the wafer blade during contact of the wafer blade with the component.

Another embodiment of the present invention is directed to a wafer-handling system. The wafer-handling system includes a component, a wafer-handling robot and a contact sensor. The robot includes a robotic arm, which supports a wafer blade for transporting a wafer in the system. The wafer blade has a different electrical potential than the component. The contact sensor is electrically coupled to the wafer blade to sense a change in the electrical potential of the wafer blade during contact between the wafer blade and the component.

Another embodiment of the present invention is directed to a wafer blade contact sensor for sensing contact between a wafer blade of a wafer-handling robot and a component in a wafer-handling system. The contact sensor includes a sense wire for electrically coupling to the wafer blade and a sensor circuit, which is electrically-coupled to the sense wire. The sensor circuit generates a contact output signal in response to a change in an electrical potential of the sense wire.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIG. 1is a schematic illustration of a multi-process cluster tool system10in which the present invention is useful. However, the present invention can also be used in any other type of wafer-handling system in which a substrate wafer is transported or moved by a wafer-handling robot.

Cluster tool system10includes a wafer loading/unloading module12with load/unload ports14and16. InFIG. 1, standard Front Opening Unified Pods (FOUPs)18are “docked” at load/unload ports14and16. Pods18hold a plurality of wafers in horizontally oriented slots to be loaded into or unloaded out of cluster tool system10. Wafer loading/unloading module12includes a wafer-handling robot for transporting individual wafers to and from ports14and16and load lock chambers20and22.

Cluster tool system10further includes a plurality of substrate processing stations24. Each processing station24has a processing chamber entrance26for providing access to the station. A further wafer-handling robot30interfaces with load lock chambers20and22and process stations24along a predefined substrate travel path.FIG. 1shows robot30transporting a wafer32into one of the processing stations24.

Robot30has a hub40and a pair of articulated arms42that support a wafer blade44for carrying wafer32within system10. Each arm42has a proximal section45, an elbow46and a distal, wrist section47. Elbow joint46connects wrist section47to proximal section45and has a bearing for allowing relative movement. The distal end of wrist section47is attached to wafer blade44.

In one embodiment, wafer blade44is formed of a relatively thin, rigid material and has a substantially planar top surface for carrying wafer32. Wafer blade44can also include an upwardly extending bridge50at its distal end for preventing wafer32from slipping off the distal end.

Robot30, arms42and wafer blade44can have a variety of different configurations in alternative embodiments of the present invention. For example, robot30can have a single arm42, a pair of arms as shown inFIG. 1or multiple pairs of arms for separately carrying multiple wafers at the same time. Also, each arm42can have any number of articulated sections. The configuration shown inFIG. 1is provided as an example only.

During operation of cluster tool system10, occasional, slight alignment drift or shift can cause the bottom or edges of wafer blade44or wafer32to contact the frame, housing or another component within system10. Contact by wafer blade44or wafer32can release particles that can fall onto the wafer and cause defects.

This type of contact is often intermittent in nature making it nearly impossible to reproduce and allowing the problem to go undetected for a very long period of time. In one embodiment of the present invention, this contact is detected by sensing a change in the electrical potential of wafer blade44(or current though the blade) during the contact. In many wafer-handling systems, the frame, housing and other components in the system are electrically grounded, whereas the wafer blades have a floating electrical potential due to electrical isolation by one or more of the elements in the robotic arm or bearings. Contact with a grounded component within system10can therefore cause a change in the electrical potential of wafer blade44if the wafer blade is electrically conductive. In one embodiment, wafer blade44is constructed of titanium. However, any other electrically conductive material can be used. Alternatively, wafer blade44can be formed of an electrically non-conductive material, with electrically conductive material being positioned at typical contact points along the blade.

Controller34controls cluster tool system10, including robot30through control signals36. Controller34can also monitor the electrical potential of wafer blade44or a signal from a separate contact monitor, which indicates when contact occurs. Control signals36can include one or more drive signals for controlling movement of robot30and the operation of various other elements in system10, and can include associated power signals for providing power to the elements of system10. In one embodiment, controller34cuts power to robot30when unwanted contact is detected so the area of contact can be more easily and immediately determined.

For example, controller34can include one or more interlocked loops38. Each interlocked loop38is a series electrical circuit having one or more normally closed relays, which are operated by one or more sensors within the system. For example, these sensors can detect whether an access panel or hood in system10is open or whether one of the processing stations24has an operating error. If such an error condition is detected, the sensor opens the respective relay contacts, which brakes interlock loop38. In one embodiment of the present invention, interlock loop38includes an additional relay contact that is controlled by a contact sensor, as described in more detail below. If contact is detected, the contact sensor opens the relay contacts to break interlock loop38.

Controller34detects the open-circuit condition on interlock loop38and modifies the control signals36accordingly. For example, controller34can stop movement or operation of any of the elements in system10, such as robot30, or cut-off power to any of the elements.

FIG. 2is a diagram, which schematically illustrates a contact sensor60coupled to robot30according to one embodiment of the present invention. Contact sensor60senses a change in the electrical potential wafer blade44during contact (shown by arrow64) with a component62in system10(shown inFIG. 1) Contact sensor60has a sense wire68, which is electrically attached to distal, wrist section47or to wafer blade44.

As with many of the other components in system10, component62is electrically grounded through an electrical connection to ground terminal GND. Wafer blade44has a floating electrical potential. Although robot30is typically grounded, certain elements along arms42can be electrically isolating. For example, the bearings in elbow joints46can provide an electrical isolation between proximal section45and distal, wrist section47, which is represented by dashed line66. Therefore, distal, wrist section47also has a floating electrical potential. If wrist section47is electrically conductive and coupled to wafer blade44, sense line68can be attached to wrist section47rather than having to be attached directly to wafer blade44where space may be limited.

The brief contact64with component62causes the electrical potential of wafer blade44and wrist sections47to briefly drop toward the potential of ground terminal GND. This also causes a brief and slight current flow from contact sensor60toward ground terminal GND, through wrist section48, wafer blade44and component62. Contact sensor60detects this potential or current change and generates an output signal indicative of the contact. In one embodiment, contact sensor60is attached to arm42. However, contact sensor60can be positioned anywhere on robot30or anywhere internal or external to the system.

FIGS. 3A and 3Bare diagrams that schematically illustrate contact sensor60in greater detail according to one embodiment of the present invention. Contact sensor60includes a housing80, an internal battery82, sensor circuitry84, contact indicators86and sense line68. Battery82provides electrical power to sensor circuitry84and contact indicators86. Sensor circuitry84monitors the electrical potential on or current flow through sense line68and generates a contact output signal88when a change is detected. Output signal88drives contact indicators86.

Contact indicators86can include any indicator that is capable of being visually perceived by a human operator or received by a receiver positioned elsewhere in the system. In one embodiment, contact indicators86include two visible light emitting diodes (LEDs)90and91and one infrared light emitting diode92, which are positioned within a clear plastic dome94in housing80. Visible LEDs90and91allow a human operator to observe cluster tool system10(shown inFIG. 1) during operation and detect when and where contact may occur. Infrared LED92can be used to transmit the contact output signal from contact sensor60to a receiver positioned elsewhere within system10(shown inFIG. 1) or external to the system. In one embodiment, infrared LED92is modulated to transmit the contact output signal.

Other types of contact indicators can be used, such as an audible indicator. Also, the contact output signal can be transmitted by any other wireless method, such as a radio frequency (RF) signal, or by a direct wire.

FIG. 4is a schematic diagram illustrating sensor circuitry84according to one embodiment of the present invention. In this embodiment, electrical circuitry84forms a transmitter for transmitting an infrared signal100to a remote receiver (shown inFIG. 2) and for driving visible LEDs90and91. The component values shown inFIG. 4are provided as examples only. Any suitable values can be used.

Sensor circuit84has an input circuit102for sensing the change in electrical potential on sense line68and generating a corresponding pulse on node N1. Input circuit102includes N-channel transistors M1and M2, bias resistors R1-R4and capacitor C1. Sense wire68forms a sensor input, which is coupled to the gate of N-channel transistor M1. Transistor M1has a source coupled to ground terminal GND and a drain coupled to bias resistor R2and the gate of transistor M2. Bias resistor R1is coupled between the gate of transistor M1and voltage supply terminal VDD. Bias resistor R2is coupled between the drain of transistor M1and voltage supply terminal VDD. Bias resistor R3is coupled between the drain of transistor M2and voltage supply terminal VDD. The source of transistor M2is coupled to node N1. Bias resistor R4and capacitor C1are coupled between node N1and voltage supply terminal VDD.

When sense wire68has a floating electrical potential (during normal operation), bias resistor R1pulls the gate of transistor M1high, which turns M1on. Transistor M1therefore pulls the gate of transistor M2low, turning off transistor M2. With transistor M2off, resistor R4pulls node N1low.

When wafer blade44(shown inFIGS. 1 and 2) contacts an electrically grounded component within the system, the electrical potential on sense wire68briefly goes low, turning off transistor M1. Bias resistor R2briefly pulls the gate of transistor M2high causing transistor M2to turn on briefly and charge node N1. A pulse is therefore formed on node N1during contact. Since the contact causes a relatively noisy signal to be generated on sense wire68, capacitor C1filters the noise to generate a more defined pulse on node N1.

The pulse on node N1is supplied to modulator104. Modulator104is configured to generate a modulated set (or burst) of pulses on output88for each pulse received on node N1. In the embodiment shown inFIG. 4, modulator104includes a “555” type Integrated Circuit Timer106, which is commercially available from a variety of sources. For example, timer106can include the LMC555 CMOS Timer from National Semiconductor Corporation. Other types of timer circuits can also be used.

The standardized pin numbers of the “555” type timer circuit106are provided in FIG.4. Node N1is coupled to reset input108(pin4) of timer106. Resistors R5and R6and capacitor C2set the duration, frequency and number of pulses generated on output88for each pulse received on reset input108. In one embodiment, timer circuit106generates a one-second burst of pulses on output88. However, any other time duration can also be used.

Output88is coupled to LED driver circuit110. LED driver circuit110includes bias resistors R7-R10, N-channel transistors M3-M5and LEDs90-92. Output88is coupled to the gates of transistors M3-M5. Bias resistor R7is coupled between output88and ground terminal GND. Bias resistors R8-R10are coupled between the drains of transistors M3-M5, respectively, and voltage supply terminal VDD. LEDs92,90and91are coupled between the sources of transistor M3-M5, respectively, and voltage supply terminal GND.

When modulator104generates a burst of pulses on output88, each pulse briefly turns on transistors M3-M5, thereby pulsing LEDs90-92on and off with each pulse on output88. Visible LEDs90and91therefore generate a visible indication that contact has occurred, whereas LED92generates a one-time modulated IR burst100that can be detected by a remote receiver. The modulation frequency of the IR signal burst can be set such that the signal does not interfere with other IR transmitters and receivers in the system.

The transmitter circuit shown inFIG. 4is provided as an example only. Any type of transmitter or circuit can be used for generating a signal indicative of contact by the wafer blade in alternative embodiments of the present invention.

FIG. 5is a schematic diagram illustrating a receiver200that can be used for receiving the IR signal100according to one embodiment of the present invention. Again, the component values shown inFIG. 5are provided as examples only. Any suitable values can be used. Receiver200includes input circuit202and decoder circuit204. Input circuit202includes IR receiving transistor206, resistors R11-R13, capacitor C3and inverting amplifier207. IR receiving transistor206is coupled in series with resistor R11, between power and ground supply terminals VCC and GND, for generating a modulated voltage on the inverting input of inverting amplifier207in response to IR signal100. Capacitor C3and resistor R2filter the modulated signal. Inverting amplifier207amplifies the modulated signal to provide a strong set of pulses on node N2, which can be decoded by decoder circuit204.

In the embodiment shown inFIG. 5, decoder circuit204includes a “567” type tone decoder circuit208, which is commercially available from a variety of sources such as National Semiconductor Corporation. Again, the standardized pin numbers for the “567” type tone decoder are provided in FIG.5. Node N2is coupled to signal input210(pin3) of tone decoder208. Timing resistor R14, time capacitor C4, output filter capacitor C5and loop filter capacitor C6are coupled to tone decoder208are coupled to the tone decoder and have values that are selected to set the center frequency, bandwidth and output delay of the tone decoder. When the appropriate modulated signal is received on signal input210, tone decoder208generates a logic low signal on output212. Otherwise, output212is normally high.

The low signal on output88indicates contact by the wafer blade and can be used in any manner to detect and respond to the contact. In the embodiment shown inFIG. 5, output212is coupled to a relay220, which is coupled within one of the interlock loops38of the cluster tool system. Interlock loop38can further include additional relays, such as relays230that are controlled by other components in the system. Relay220has a diode D1and an inductor L1, which are coupled between output212and diode D2. Diode D2is coupled to voltage supply terminal VCC. Relay220has a pair of contacts222, which have a normally closed state224. When tone decoder208generates a low signal pulse on output212, current flows through inductor L1and generates a magnetic field that momentarily pulls contacts222into an open state226(shown in dashed lines). This breaks interlock loop38causing the robot to stop moving the wafer blade immediately after contact is detected. This allows the problem to be pinpointed in the system and corrected before any further wafers are contaminated. With the wafer blade stopped, the operator of the system can observe the position of the wafer blade at the instant contact occurs so that troubleshooting can be performed more easily.

In this manner, the contact sensor can monitor the wafer blade for contact while production is running. This reduces troubleshooting time to near zero, and can result in avoidance of yield loss due to particle defects or other damage.

Also, the wafers themselves can occasionally contact components within the system. However, wafer substrates are typically formed of an electrically non-conductive material. Contact by the wafer itself can be easily tested in this system by placing an electrically conductive wafer on the wafer blade and monitoring the contact sensor's output. The electrically conductive wafer would conduct current from the contact point to the wafer blade during contact. Other applications can also be used. For example, the contact sensor can be configured as a portable monitor that can be placed on the robot while adjustments are made and then removed, with the LEDs or other indicators announcing contact.

Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. The term “coupled” used in the specification and the claims can include a direct connection or a connection through one or more additional components.