Robotic device for substrate transfer applications

A device for use in the semiconductor industry includes a robotic arm whose end effector includes at least two prongs designed to hold a substrate carrier. A pushing member located between the prongs can move independently of the prongs and is configured to exert force against the substrate carrier while the prongs are 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 prongs are retracted. Each of the prongs may include a claw or gripping member for grasping the substrate carrier.

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.

One aspect of the invention is a device that includes a robotic arm that has an end effector. The end effector includes i) at least two prongs designed to hold a substrate carrier and ii) a pushing member that can move independently of the prongs. The pushing member is configured to exert force against the substrate carrier while the prongs are retracted from the substrate carrier, thereby preventing the substrate carrier from being retracted while the prongs are retracted. The device further includes one or more motors for moving the pushing member and the prongs.

A preferred method for use with this device includes the following steps:

(a) bringing, by using the end effector, a selected substrate carrier to a desired position, the prongs holding the selected carrier while the selected carrier is being moved;

(b) moving the pushing member towards the selected carrier, the pushing member exerting force against the selected carrier;

(c) moving the prongs away from the selected carrier, while the pushing member continues to exert force against the selected carrier and thereby maintain the desired position of the selected carrier; and

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

in which steps (a), (b), (c), and (d) are carried out in turn (in that order). The method can be carried out under harsh conditions, e.g., at elevated temperatures, under vacuum, and/or in an oxidizing atmosphere such as that used in a deposition or etching process.

Another aspect of the invention is a device that includes i) a forked member having ends that engage and hold a substrate carrier and ii) a pusher that extends between the ends of the forked member, so that the pusher can apply force against the substrate carrier as the forked member is retracted from the substrate carrier.

Yet another aspect of the invention is a device that includes i) a plurality of extension members, the extension members having respective gripping members designed to hold a substrate carrier and ii) a pushing member between two of the extension members. The pushing member can be moved independently of each of the plurality of extension members; it is used for maintaining the position of a substrate carrier that has been brought to a desired position by exerting force against the positioned carrier when the extension members are retracted.

DETAILED DESCRIPTION

A preferred embodiment of the invention is 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 or removed from the robotic device110. 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 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.

FIGS. 2A and 2Bshow in greater detail that portion of the robotic device110designated as the fork assembly200, which includes a fork205with its two prongs210that house respective motor-actuated claws215. The fork assembly200also includes a pusher220. The end effector portion of the robotic device110can be used to manipulate a substrate carrier225. The claws215are retracted inFIGS. 2A and 2B, but as is evident fromFIG. 3, when the claws are extended they can be used to grasp and restrain the substrate carrier225so that it can be moved securely from one location to another. (A substrate can be placed in the center, hollow portion of the substrate carrier225and 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. 3.)

Once the substrate carrier225has been brought to an intended position, it is released by bringing the claws215to their retracted position (seeFIGS. 2A and 2B, in which the claws are retracted). The prongs210are then pulled back from the substrate carrier225; note that the prongs slide underneath flange portions230of the substrate carrier as they are retracted from the substrate carrier. Unfortunately, even slight contact between mechanical parts under vacuum can generate high frictional forces. Thus, one could imagine that as the prongs210are withdrawn, the substrate carrier225might be unintentionally dragged along as a result of accidental contact with the prongs, thereby dislodging the substrate carrier from its intended position.

To circumvent this problem, when the claws215release the substrate carrier225, the pusher220moves towards the substrate carrier until contact occurs (or alternatively, the pusher may be brought into contact with the substrate carrier before or after the claws release the substrate carrier). The pusher220is used to apply force against the substrate carrier225while the prongs210are 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 toFIGS. 2A and 2B. 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 fork205. The pusher drive rod245is in turn fixed to a pusher guide block250, which in turn is connected to the pusher220(seeFIG. 2B, which shows the underside of the fork assembly200). As the pusher guide block250is moved forwards or backwards within a groove in the fork205, 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.

Actuation of the claws215is now described with respect toFIGS. 2A and 2C. InFIG. 2Ccomponents related to operation of the claws215are visible, whereas for clarity certain components unique to operation of the pusher220have been removed from view. A claw motor260is mechanically tied to various components designated collectively as the claw drive mechanism265. The claw drive mechanism265may include conventional components, such as one or more gears, lead screws, traveling nuts, and limit switches for constraining motion. The claw drive mechanism265engages a claw drive rod270, thereby pushing this rod either forwards or backwards relative to the fork205. The claw drive rod270is in turn fixed to a claw guide block275, which is secured by two clamps280. The claw guide block275is in turn secured to a beam285, whose motion is constrained by guide members287located on both sides of the beam.

When the beam285moves forwards, two links290rotate to allow the proximal ends of levers294to move in an outward direction, so that the claws215at the distal ends of the levers are deployed from out of their respective prongs210(as the levers rotate about respective pivots296), thereby permitting the claws215to grasp a carrier225. Specifically, two springs298acting between the fork205(not shown inFIG. 2C) and respective levers294urge the two rotating links290(each having 3 arms) to maintain contact with pins297that are attached to the beam285and extend below the beam. (Each spring298fits within a notch in a respective lever294and a hole in the fork205).

Conversely, the claws215are retracted when the claw drive rod270is moved backward. Specifically, as the beam285is retracted, the pins297contact the rotating links290, causing them to rotate. This in turn causes the levers294to rotate inward, which compresses the springs298. Note that the rotating links290are constrained in one direction by respective adjustable stops299, so that the claws215do not extend too far inward when they are deployed; motion of the rotating links290is constrained in the other direction by a sensor in the claw drive mechanism265, so that the claws215do not rotate out of the prongs210when they are retracted.

Movement of the fork assembly200is now described with respect toFIGS. 4A and 4B.FIG. 4Ashows the fork assembly200in combination with other components designed to permit the fork assembly to move back and forth throughout the robot chamber120(see alsoFIG. 1). An exploded view of the same is shown inFIG. 4B, which shows the fork assembly200, an upper carriage block320, a rail325, and a lower carriage block330. When these components are assembled, the fork 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 fork 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 fork assembly200, thereby holding together the upper carriage block and the fork 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 carrier225has been brought to an intended location, the pusher220is used to apply force against the substrate carrier while the prongs210are 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 prongs210are being retracted. One way to accomplish this is to synchronize the motion of the fork assembly200(with its prongs210) 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 fork assembly) 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 fork assembly200retreats along the rail325at the same speed that the pusher220moves forward relative to the fork 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 fork assembly200and its prongs210(along with the upper carriage block320and the lower carriage block330) are pushed away from the substrate carrier.

The various parts of the robotic device110may be machined from stock materials. The fork205may be advantageously made of molybdenum, since it is thermally and mechanically stable. Alternatively, the fork205could be made from a ceramic material such as Macor® (although ceramics are more brittle), or the fork 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 fork assembly200, such as the claws215and the pusher220, can be made of stainless steel, for example. The substrate carrier225is preferably fabricated from HAYNES® 230® alloy, which is 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 device110described 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 device110designed 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: prongs210having a length between 20 and 60-100 mm and a width between 6 and 12 mm; a fork assembly200whose range of motion is between 200 mm and 600 mm; a substrate carrier having a width and a length of 40-60 mm; and claws215whose hooked portion (the portion that contacts the substrate carrier) has a length of 1-3 mm. A larger device designed for manufacturing applications may have, for example: prongs210having a length between 300 and 350 mm and a width between 25 and 40 mm; a fork assembly200whose range of motion is between 600 mm and 1000 mm; a substrate carrier having a width and a length of 300-350 mm; and claws215whose hooked portion (the portion that contacts the substrate carrier) has a length of 2-6 mm. In either case, the range of motion of the pusher220is preferably comparable to that of the length of the prongs210.