Robotic device for substrate transfer applications

A device for use in the semiconductor industry includes a robotic arm whose end effector includes electromagnetic means to hold a substrate carrier. A pushing member can move independently of a flat, spatula-like portion of the device and is configured to exert force against the substrate carrier while the spatula-like portion is retracted from the substrate carrier, after the substrate carrier has been brought to its intended position. In this manner, the position of the substrate carrier is maintained at its intended position as the spatula-like portion is retracted.

TECHNICAL FIELD

The invention relates to a robotic device, and more particularly, to an end effector suitable for transferring substrate carriers, such as those used in the semiconductor industry.

BACKGROUND

A universal aspect of automated semiconductor processing systems (including advanced research deposition and analysis systems) is some form of transfer mechanism for moving substrates into, through, and out of process/deposition/analysis chambers. Since these systems are expensive, a reasonable return on investment necessitates high system through-put, which can be achieved only if the transfer mechanism is reliable. However, the demands of most processes create challenges to maintaining reliability of the transfer mechanism. These demands can include high or low temperatures, vacuum, corrosive gases, special material requirements, motion control requirements, special sensing requirements, or a combination of the foregoing.

Transfer mechanisms, or robots, are generally designed to do a simple task, such as pick up a substrate carrier, move it, and place it in a desired location. Such simple actions are difficult in a vacuum—not just because of the obvious constraints of working in a vacuum, but also because of the significant effect that vacuum has on the tribological properties of materials. Unfortunately, the designs for robots to be used in vacuum are often derived from those designed for use in air, so that the reliability of robots in vacuum can degrade quickly. To mitigate reliability problems, several measures can be undertaken, such as avoiding contact or sliding between parts made of similar materials, using hard or wear-resistant coatings where contact does occur, and restricting movement to motions that are precise and carefully controlled to avoid collisions. Nevertheless, robotic devices having improved reliability and flexibility are desired.

SUMMARY

This invention addresses one of the challenges associated with a robot placing its load at an intended position. In semiconductor processing equipment, an intended position can be a receiving mechanism, a platen, a chuck in a process chamber, or a slot in a cassette. In prior art devices, as the robot withdraws its end effector after releasing its load, any slight contact with the load can dislodge that load from its intended position. In this invention, the robot employs a mechanism, called a pusher, to ensure that the deposited load (e.g., the carrier and its substrate) remains in its intended position while the end effector is withdrawn.

An embodiment of the invention is a device that comprises a robotic arm that includes an end effector. The end effector has (i) an electrical and/or magnetic unit (e.g., the unit may be constructed so that both electrical and magnetic modes of operation are possible) that has on and off modes, such that this unit, when it is in the on mode, provides an attractive holding force between the unit and a substrate carrier (so that the position of the substrate carrier remains fixed) and (ii) a pushing member that is configured to exert force against the substrate carrier, thereby preventing the substrate carrier from being retracted while the unit is retracted. The device further includes a motor for moving the pushing member.

One embodiment of the invention is a device that comprises a robotic arm that includes an end effector. The end effector includes (i) a spatula member whose distal end includes an electrical and/or magnetic unit having on and off modes, such that this unit, when it is in the on mode, provides an attractive holding force between the unit and a substrate carrier (so that the position of the substrate carrier remains fixed) and (ii) a pushing member that is configured to exert force against the substrate carrier, thereby preventing the substrate carrier from being retracted while the unit is retracted.

The following exemplary method can be used in conjunction with the embodiments described herein. This method includes:

(a) using the end effector to bring a selected substrate carrier to a desired position, with the attractive force holding the unit and the selected carrier together while the selected carrier is moved;

(b) moving the pushing member towards the selected carrier, so that the pushing member exerts force against the selected carrier;

(c) moving the unit away from the selected carrier, while the pushing member exerts force against the selected carrier, thereby maintaining the desired position of the selected carrier; and

(d) retracting the pushing member so that the pushing member no longer contacts the selected carrier.

Steps (a), (b), (c), and (d) are preferably carried out in that order.

DETAILED DESCRIPTION

Preferred embodiments of the invention are now described with respect to the figures.FIG. 1shows a robotic device110mounted within a robot chamber120(shown as a cutaway for clarity). The robot chamber120includes a viewing port130that includes transparent glass through which the robotic device110can be viewed. The robotic device110can be moved through the robot chamber120towards an adjacent load lock chamber or cassette loading chamber (not shown, but the load lock chamber would be connected to, and to the right of, the robot chamber120inFIG. 1), where a substrate carrier can be loaded onto the robotic device110or, alternatively, removed from it and inserted into a receiver in the load lock chamber. The load lock chamber is in turn connected to a process chamber (not shown, but still further to the right), such as a deposition chamber (or an etching chamber), where materials may be deposited onto (or etched away from) a substrate or wafer positioned by the robotic device110. Electrical power is supplied to the robotic device110through a ribbon cable140that passes through an electrical feedthrough150. More precisely, the portion of the ribbon cable140that is external to the robot chamber120mates with electrical pins (not shown) in the electrical feedthrough150, and the portion of the ribbon cable140within the robot chamber120likewise mates with the electrical pins, so that no mechanical feedthrough is used that might otherwise compromise the integrity of the vacuum. Alternatively, the cable140external to the robot chamber120need not be a ribbon cable. To the left of the robot chamber120is a distance sensing laser assembly160. A laser beam (not shown) directed through the glass of a second viewing port170can be used to establish the approximate position of the robotic device110.

Electromagnetic Embodiment

FIG. 2Ashows in greater detail that portion of the robotic device110designated as the assembly200, which includes a spatula205having an electromagnetic unit215at its distal end. The assembly200also includes a pusher220. The end effector portion of the robotic device110can help position a substrate carrier225using the electromagnetic unit215, which includes at least one electromagnetic coil217. (Four such coils217are shown inFIG. 2A.) When they are activated, the coils217hold the substrate carrier225as a result of the magnetic force between the coils and the substrate carrier, thereby permitting the substrate carrier225to be moved securely from one location to another. For the substrate carrier225(and the other substrate carriers described herein), a substrate can be placed in the center, hollow portion of the substrate carrier and then overlaid with a block of SiC, which can be heated with infrared radiation to heat the underlying substrate; neither the substrate nor the SiC block is shown inFIG. 2A,2B, or2C.

The substrate carrier225can then be brought to an intended position, e.g., the grooves228in the substrate carrier can mate with a receiver in a load lock chamber. At this point, the coils217can be deactivated by turning off the current supplied to them. The spatula205is then pulled back from the substrate carrier225; note that the spatula slides underneath the substrate carrier as it is retracted from the substrate carrier. (This is most easily visualized with respect toFIG. 2B, which shows the spatula205underneath, and in contact with, the substrate carrier225.) Unfortunately, even slight contact between mechanical parts under vacuum can generate high frictional forces. Thus, one could imagine that as the spatula205is withdrawn, the substrate carrier225might be unintentionally dragged along as a result of contact with the spatula, thereby dislodging the substrate carrier from its intended position.

To circumvent this problem, as the coils217are being deactivated, the pusher220is moved towards the substrate carrier until contact occurs (or alternatively, the pusher may be brought into contact with the substrate carrier before or after the coils are deactivated). The pusher220is used to apply force against the substrate carrier225while the spatula205is retracted, as shown inFIGS. 2A and 2B; doing so keeps the substrate carrier225in place (e.g., at a desired location in a process chamber or in a cassette in a load lock chamber).

Actuation of the pusher220is now described with respect toFIG. 2A. A pusher motor235is mechanically tied to various components designated collectively as the pusher drive mechanism240. The pusher drive mechanism240may include conventional components, such as one or more gears, lead screws, traveling nuts, and limit switches for constraining motion. The pusher drive mechanism240engages a pusher drive rod245, thereby pushing this rod either forwards or backwards relative to the spatula205. The pusher drive rod245is in turn fixed to a pusher guide block250(e.g., by a screw252), which in turn is connected to the pusher220(e.g., by screws253). As the pusher guide block250is moved forwards or backwards within a groove251in the spatula205, the pusher220is likewise moved forwards or backwards. In this manner, the pusher220can be made to butt up against the substrate carrier225or retracted from it. Two pusher guide brackets255help keep the pusher220in place as it is moved back and forth.

The coils217and their actuation are now described with respect toFIGS. 2B and 2C.FIG. 2Bshows two coils217, with two other coils being hidden underneath the substrate carrier225. Electrical current flows through the coils217so that the coils act as magnets; the two coils shown inFIG. 2Bare magnets whose top ends have opposite polarities, e.g., north and south. The two other coils (which are not visible inFIG. 2B) have polarities such that coils that are at diagonals to each other have the same polarity. When the coils217are activated, magnetic flux lines from the electromagnets pass through the substrate carrier225, and the magnetic force keeps the substrate carrier in contact with the spatula205. The substrate carrier in this embodiment is made of magnetic material, such as martensitic stainless steel. Current may be supplied to the coils217through one or more wires257. The wiring to the coils217may be either in parallel or series, provided that the desired polarities are produced.

The construction of an individual coil217is illustrated inFIG. 2C. The wires forming the coil217may be 23 gauge copper wire insulated with, for example, GE varnish that forms a sheath around the wire. The wire257may be wound around a bobbin258that surrounds a pole piece259. The pole pieces259may be made from material such as soft iron or silicon iron.

Shunted Magnet Embodiments

FIG. 3shows another embodiment in which magnetic force is used to hold a substrate carrier.FIG. 3Ashows in greater detail that portion of a robotic device (similar to the robotic device110) designated as the assembly200a, which includes a spatula205ahaving a magnet unit218at its distal end. The assembly200aalso includes a pusher220a. The end effector of this embodiment can help position a substrate carrier225ausing the magnet unit218, which is activated mechanically as described below. When the magnet unit218is activated, the substrate carrier225ais held as a result of the magnetic force between a magnet262(shown inFIG. 3C) in the unit218and the substrate carrier, thereby permitting the substrate carrier225ato be moved securely from one location to another.

The substrate carrier225acan then be brought to an intended position, e.g., the grooves228ain the substrate carrier can mate with a receiver in a load lock chamber. At this point, the magnet unit218can be deactivated. The spatula205ais then pulled back from the substrate carrier225a; note that the spatula slides underneath the substrate carrier as it is retracted from the substrate carrier. (This is most easily visualized with respect toFIG. 3B, which shows the spatula205aunderneath, and in contact with, the substrate carrier225a.)

As with the previously described embodiment, to reduce the risk of dislodging the substrate carrier225afrom its intended position as the spatula205ais withdrawn, the pusher220ais moved towards the substrate carrier until contact occurs (e.g., the pusher may be brought into contact with the substrate carrier before, during, or after deactivation of the magnet unit218). The pusher220ais used to apply force against the substrate carrier225awhile the spatula205ais retracted (seeFIGS. 3A and 3B); doing so keeps the substrate carrier225ain place (e.g., at a desired location in a process chamber or in a cassette in a load lock chamber).

Actuation of the pusher220ais now described with respect toFIG. 3A. A pusher motor235ais mechanically tied to various components designated collectively as the pusher drive mechanism240a. The pusher drive mechanism240amay include conventional components, such as one or more gears, lead screws, traveling nuts, and limit switches for constraining motion. The pusher drive mechanism240aengages a pusher drive rod245a, thereby pushing this rod either forwards or backwards relative to the spatula205a. The pusher drive rod245ais in turn fixed to a pusher guide block250a(e.g., by one or more screws252a), which in turn is connected to the pusher220a(e.g., by one or more screws253a). As the pusher guide block250ais moved forwards or backwards within a slot251ain the spatula205a, the pusher220ais likewise moved forwards or backwards. In this manner, the pusher220acan be made to butt up against the substrate carrier225aor retracted from it. Two pusher guide brackets255ahelp keep the pusher220ain place as it is moved back and forth.

The magnet unit218and the movement of its magnet mount261and magnet262are now described. As seen inFIGS. 3C and 3D, when the magnet unit218is activated or in the “on” position, the magnet262(which can be made of Nd2Fe14B, for example, and can be epoxied or otherwise secured to the magnet mount261), is positioned between two pole pieces263(e.g., made of soft iron) and directly underneath the substrate carrier225a(which is likewise made of a magnetic material). The magnetic attractive force between the magnet262and the substrate carrier225ais sufficiently strong to hold the substrate carrier in place. This “on” position occurs when the magnet mount261(and the magnet262to which it is attached) is extended distally. As shown inFIG. 3E, on the other hand, when the magnet mount261is retracted, the magnet262is partially surrounded by a shunt264and is far enough away from the substrate carrier225athat there is no significant attractive force between the magnet and the substrate carrier; in this case, the magnet unit218is in the “off” position. Thus, the magnet mount261can be retracted or extended (as suggested by the double arrowhead inFIG. 3B), leading to the magnet unit218being deactivated or activated, respectively.

The magnet mount261can be extended or retracted with a magnet mount motor260as follows. The magnet mount motor260is mechanically tied to various components designated collectively as the magnet mount motor mechanism265. The motor mechanism265may include conventional components, such as one or more gears, lead screws, traveling nuts, and limit switches for constraining motion. The motor mechanism265engages a magnet mount drive rod270, thereby pushing this rod either forwards or backwards relative to the spatula205a. The drive rod270is in turn fixed to a magnet mount guide block275by one or more screws281. As the drive rod270is moved forwards or backwards, the magnet mount guide block275moves within the slot251ain the spatula205a. The magnet mount261is likewise moved forwards or backwards, since the drive rod270is tied to the guide block275, and the guide block275is in turn tied to a magnet mount connector285that extends along the underside of the spatula205aand is fixed to the magnet mount261(seeFIGS. 3D and 3E). Limits switches in the pusher drive mechanism240aand the magnet mount motor mechanism265ensure that the pusher guide block250aand the magnet mount guide block275do not run into each other.

Other shunted magnet embodiments, which are not shown, are also contemplated. For example, the spatula may be embedded with one or more permanent magnets surrounded by a retractable sleeve made of mu-metal. When the sleeve surrounds the magnet(s), the magnetic field is effectively screened from the substrate carrier, so that it can be easily moved. On the other hand, when the sleeve is retracted, the magnetic field is able to interact with the substrate carrier, thereby fixing its location. In yet another shunted magnet embodiment, blocks of magnetic material separated by a block of non-magnetic material may be constructed so that the magnet can be turned on and off, in analogy with how magnetic bases are constructed (e.g., those used on optical tables).

Electrostatic Embodiment

In the embodiment shown inFIG. 4, electrostatic force is used to hold a substrate carrier. This embodiment is essentially identical to the electromagnetic embodiment described above in connection withFIG. 2, except at its distal end. An assembly200bincludes a spatula205bhaving an electrostatic plate219(e.g., made of copper encapsulated with an insulator); alternatively, multiple electrodes may be embedded in the spatula. The assembly200balso includes a pusher220b. The end effector portion of this embodiment can help position a substrate carrier225b(which may include a dielectric plate or coating290). When high voltage is applied to the electrostatic plate219(e.g., through a wire292that is tied to a voltage supply at the proximal end of the robotic device), an electrostatic force arises between the electrostatic plate219and the substrate carrier225bdue to redistribution of charge within that portion of the substrate carrier closest to the spatula205. The substrate carrier225bis held in place as a result of this force, thereby permitting it to be moved securely from one location to another, like the substrate carrier225described above in connection with the electromagnetic embodiment. (When the voltage to the electrostatic plate219is turned off, the attractive force is eliminated.) Similarly, the pusher220bcan be used like the pusher220ofFIG. 2to reduce the risk of dislodging the substrate carrier225bfrom its intended position as the spatula205bis withdrawn. The pusher220bcan be actuated like its counterpart220ofFIG. 2.

Additional Mechanical Details

Movement of the assembly200(and likewise, assemblies200aand200b) is now described with respect toFIGS. 5A and 5B.FIG. 5Ashows the assembly200in combination with other components designed to permit the assembly to move back and forth throughout the robot chamber120(see alsoFIG. 1). An exploded view of the same is shown inFIG. 5B, which shows the assembly200, an upper carriage block320, a rail325, and a lower carriage block330. When these components are assembled, the assembly200can move along and over the rail325.

The upper carriage block320includes two drive motors335, which when run together provide the torque necessary to drive the upper carriage block, the lower carriage block330, and the assembly200along a gear rack338of the rail325. The upper carriage block320includes two translational rollers340athat run within a groove345ain the rail325. A pin (not shown) extends between a pinhole350in the upper carriage block320and the assembly200, thereby holding together the upper carriage block and the assembly.

The lower carriage block330includes a translational roller340band centering rollers355, all of which run along a groove345bwithin the underside of the rail325. Pins and screws that fit within pin holes360and screw holes365, respectively, permit the lower carriage block330to be fixed precisely to the upper carriage block320.

As mentioned previously, once the substrate carrier225(or225a,225b) has been brought to an intended location, the pusher220is used to apply force against the substrate carrier while the spatula205is retracted. Otherwise, the substrate carrier225might be unintentionally dislodged from its intended location (e.g., within a cassette in a load lock chamber or a deposition chamber). Preferably, the pusher220is in contact with the substrate carrier225for the entire time that the spatula205is being retracted. One way to accomplish this is to synchronize the motion of the assembly200(with its spatula205) and the motion of the pusher220, so that the distal end of the pusher extends away from the end effector (located at the distal end of the assembly200) at the same speed that the end effector is retracted from the substrate carrier225. To this end, the actions of the pusher motor235and the drive motors335may be coordinated using a motion controller (not shown) to control the respective movements of the pusher motor and drive motors, so that the assembly200retreats along the rail325at the same speed that the pusher220moves forward relative to the assembly. That is, the net effect is that the pusher220does not move with respect to the rail325(which is generally fixed) or the substrate carrier225(which is to be kept stationary at an intended location). Alternatively, the drive motors335may simply be turned off, and the pusher220(driven by the pusher motor235) may push against the substrate carrier225, so that the assembly200and its spatula205(along with the upper carriage block320and the lower carriage block330) are pushed away from the substrate carrier.

The various parts of the robotic device110(and the other robotic device embodiments described herein) may be machined from stock materials. The spatula205(and205a,205b) may be advantageously made of molybdenum, since it is thermally and mechanically stable. Alternatively, the spatula could be made from a ceramic material such as Macor® (although ceramics are more brittle), or it could be made out of more compliant materials, such as plastic (e.g., polyimide), if the substrate carrier were made of a relatively soft material. Other parts in the assembly, such as the pusher220(or220a,220b), can be made of stainless steel, for example. The substrate carrier225(and225a) is preferably fabricated from a magnetic material, and the substrate carrier225bis preferably made from HAYNES® 230® alloy. The substrate carriers225,225a, and225bare preferably designed to withstand oxidation (e.g., from oxygen or air) even at high temperatures (e.g., at 100° C., 150° C., 200° C., or greater), which are conditions encountered by the robotic devices described herein. At such high temperatures and under vacuum, oil-based lubricants are not recommended; rather, solid lubricants such as MoS2or WS2(e.g., Dicronite® coating) may be applied to parts such as gear surfaces to reduce friction.

The dimensions of the various parts disclosed herein may be selected in view of the intended application. A robotic device designed for use in a research environment (e.g., for transferring small wafers having a diameter of 20-30 mm) would be smaller than one designed for use in a manufacturing setting (e.g., for transferring wafers having a diameter of 300 mm). A smaller, research-oriented device may have, for example: an assembly (200,200a,200b) whose range of motion is between 200 mm and 600 mm, and a substrate carrier (225,225a,225b) having a width and a length of 20-60 mm. A larger device designed for manufacturing applications may have, for example: an assembly whose range of motion is between 600 mm and 1000 mm, an end effector whose width is less than 500 mm, and a substrate carrier having a width and a length of 300-500 mm. In either case, the range of motion of the pusher (220,220a,220b) is preferably at least that of the minimum lateral dimension of the substrate carrier.