Robot assembly

A robot assembly, including a central hub, has two arms arranged for independent rotation about the hub. Two carriers, oriented 180.degree. apart from each other, are coupled to an end of each of the arms. A drive is provided for rotating the arms in opposite directions to extend one or the other of said carriers radially from said central hub, and for rotating the arms in the same direction to effect rotation of the carriers.

BACKGROUND OF THE INVENTION 
1. TECHNICAL FIELD 
The present invention relates to robotics. More particularly, the present 
invention relates to a robot assembly for the simultaneous manipulation of 
multiple objects, for example semiconductor wafers. 
2. Description of the Prior Art 
The use of robot arms is a well established manufacturing expedient in 
applications where human handling is inefficient and/or undesired. For 
example, in the semiconductor arts robot arms are used to handle wafers 
during various process steps. Such process steps include those which occur 
in a reaction chamber, e.g. etching, deposition, passivation, etc., where 
a sealed environment must be maintained to limit the likelihood of 
contamination and to ensure that various specific processing conditions 
are provided. 
Current practice includes the use of robot arms to load semiconductor 
wafers from a loading port into various processing ports within a multiple 
chamber reaction system. The robot arm is then employed to retrieve the 
wafer from a particular port after processing within an associated process 
chamber. The wafer is then shuttled by the robot arm to a next port for 
additional processing. When all processing within the reaction system is 
complete, the robot arm returns the semiconductor wafer to the loading 
port and a next wafer is placed into the system by the robot arm for 
processing. Typically, a stack of several semiconductor wafers is handled 
in this manner during each process run. 
In multiple chamber reaction systems it is desirable to have more than one 
semiconductor wafer in process at a time. In this way, the reaction system 
is used to obtain maximum throughput. In the art, a robot arm used in a 
reaction system must store one wafer, fetch and place another wafer, and 
then fetch and place the stored wafer. Although this improves use of the 
reaction system and provides improved throughput, the robot arm itself 
must go through significant repetitive motion. 
One way to overcome the inefficiency attendant with such wasted motion is 
to provide a robot arm having the ability to handle two wafers at the same 
time. Thus, some equipment manufacturers have provided a robot arm in 
which the two carriers are rotated about a pivot by a motor with a belt 
drive at the end of the arm. In this way, one wafer may be stored on one 
carrier while the other carrier is used to fetch and place a second wafer. 
The carriers are then rotated and the stored wafer may be placed as 
desired. Such mechanism is rather complex and requires a massive arm 
assembly to support the weight of a carrier drive located at the end of an 
extendible robot arm. For example, three drives are usually required for a 
system incorporating such a robot arm: one drive to rotate the arm, one 
drive to extend the arm, and one drive to rotate the carriers. Thus, any 
improvement in throughput as is provided by such a multiple carrier robot 
arm comes at a price of increased cost of manufacture, increased weight 
and power consumption, and increased complexity and, thus, reduced 
reliability and serviceability. 
Another approach to providing a multiple carrier robot arm is to place two 
robot arms coaxially about a common pivot point. Each such robot arm 
operates independently of the other and improved throughput can be 
obtained through the increased handling capacity of the system, i.e. two 
arms are better than one. However, it is not simple to provide two robot 
arms for independent operation about a common axis. Thus, multiple drives 
and rigid shafts must be provided, again increasing the cost of 
manufacture and complexity while reducing reliability. 
SUMMARY OF THE INVENTION 
The present invention is a robot assembly, including a central hub having 
two arms. Each arm is arranged for rotation relative to the hub. Two 
carriers, spaced apart from each other, are provided for handling various 
objects, such as semiconductor wafers. Each carrier is coupled to an end 
of each of the arms. A drive is provided for rotating the arms in opposite 
directions from each other to extend one or the other of the carriers 
radially from the central hub, and for rotating both arms in the same 
direction to effect rotation of the carriers about the hub. In the 
preferred embodiment, one drive is used for rotation of one arm and a 
second drive is used for rotation of the other arm. By synchronizing drive 
operation the arms can be rotated in the same or opposite directions.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention is best understood by referring to the Drawings in 
connection with review of this Description. The present invention is a 
robot assembly adapted to handle multiple objects. In the preferred 
embodiment, the invention finds application in a reaction system, as is 
used in the manufacture of semiconductors. For example, the present 
invention is useful for inserting and withdrawing wafers through a 
reaction chamber port. 
The present invention allows two objects, such as semiconductor wafers, to 
be handled simultaneously for either insertion, withdrawal, or rotation, 
such that one wafer may be stored on the robot assembly while the other is 
placed. This unique feature allows increased throughput during wafer 
processing when contrasted with prior art robot assemblies which must go 
through an entire manipulation cycle to effect wafer storage. In this way, 
the reaction chamber is continuously used to process a wafer, i.e. there 
is no `dead-time` while a processed wafer is replaced in the stack and a 
`fresh` wafer is fetched, as with prior art systems. The present invention 
provides similar advantages when used in a daisy-chain type processing 
arrangement, i.e. multiple reaction chambers used sequentially for a 
series of processing steps. 
In FIG. 1, a robot assembly 2 is shown in plan view in the context of a 
reaction system 3. The robot assembly 2 is arranged centrally within the 
reaction system 3 for movement of a semiconductor wafer 13 to and from the 
reaction chambers 7, 9, and 11. It should be noted that although the 
exemplary embodiment of the invention discloses a robot assembly centrally 
located within a reaction system, with the reaction system including three 
reaction chambers, the present invention is intended for many different 
applications. Thus, the exemplary embodiment should not be considered 
limiting the scope of the invention. That is, the present invention is 
readily adapted for use with any wafer handling application, including 
reaction systems having any number of reaction chambers and any sort of 
orientation for the robot assembly. 
The robot assembly 2 includes a first arm 6 and a second arm 8 arranged 
such that one end of each arm is coupled to a central hub 4. Each arm may 
be rotated independently of the other arm in either a clockwise or a 
counter-clockwise fashion about hub 4. Thus, the arms may be rotated in 
both a similar and in an opposite direction. "Rotation may be accomplished 
by any motive source 40, such as an electrically operated motor or 
motors." 
The motive source should be configured to rotate arm 6 and arm 8 reversibly 
in either opposing directions or in the same direction. In the preferred 
embodiment of the invention, the arms are rotatable independently and 
coaxially about the hub and the motive source is a magnetically coupled 
motor of the type described in pending U.S. patent application Ser. No. 
644,852, filed 22 Jan. 1991, now U.S. Pat. No. 5,227,708, which is a 
continuation of U.S. patent application Ser. No. 424,771, filed 20 Oct. 
1989, now abandoned. Both applications are assigned to Applied Materials, 
Inc., assignee of the present application. 
The arms 6/8 each include a pivot (28 and 29, respectively) provided at an 
end of the arm opposite the end coupled to hub 4. The arms are pivotally 
coupled to struts 24/25. The struts, in turn, are coupled by pivots 18/19, 
to a first wafer carrier 10. Each strut may include a meshing gear 14/15 
at an end within the carrier 10 to maintain the carrier 10 in rigid radial 
alignment with the hub 4 as the struts are pivoted during operation of the 
robot assembly. In some embodiments of the invention a figure-eight belt 
may be substituted for the meshing gear 14/15, if desired. 
The arms and linkage shown in FIG. 1 form a compound articulated mechanism 
which is sometimes referred to in the mechanical arts as a frog-leg 
mechanism. In FIG. 1, the carrier 10 is shown in a partially extended 
position, for example delivering or retrieving a wafer from a reaction 
chamber. 
A second wafer carrier 12 is also shown in FIG. 1, in which arms 6/8 are 
joined to struts 36/37 at pivots 34/35 located at one end of the struts. 
The struts 36/37 are also joined at pivots 20/21, located at the other end 
of the struts, to the carrier 12. As discussed more fully below, the 
carrier 12 is linked to the arms 6/8 in an identical manner to that for 
the carrier 10, such that the two carriers are maintained 180.degree. 
apart from each other about the axis of the hub 4. 
FIG. 2 is a detailed top plan view of robot assembly 2 showing one carrier 
10 in a partially extended position and another carrier 12 in a partially 
retracted position. Arrows in the Fig. show relative motion of arms 6 and 
8 about the hub 4. The carrier 10 is coupled to the arms 6/8 by the struts 
24/25. The struts 24/25 are configured for rotation in concert with the 
arms 6/8 by operation of pivots 18/19 at the carrier 10 and pivots 28/29 
at the arms 6/8. 
The carrier 12 is pivotably coupled to struts 36/37 at pivots 20/21. Struts 
36/37 are in turn pivotably coupled to the arms 6/8 at pivots 34/35. 
It should be noted that, although the arms 6/8 are each shown having two 
pivots, one for each carrier/strut, the arms could readily be configured 
such that the carriers/struts share a single pivot point on each arm. Such 
arrangement is shown in FIG. 3, in which arms 6/8 are arranged to pivot 
about the hub 4 at one end of the arms. The other end of each arm includes 
a single pivot point 40/42, respectively. The arms are coupled at the 
pivots points 40/42 to two struts each, one strut for each carrier. Thus, 
the arm 6 is coupled to one strut 24 (for carrier 10) and to another strut 
36 (for carrier 12) at pivot 40. While the arm 8 is coupled to one strut 
22 (for carrier 10) and to another strut 37 at pivot 42. 
Operation of the present invention is shown in FIGS. 4a, 4b, and 4c. In 
FIG. 4a, the robot assembly 2 is shown undergoing rotational motion of 
both carriers 10/12 simultaneously about the hub 4, as is indicated by the 
arrow in the Figure. In preparation for this rotational motion, the arms 
6/8 are independently rotated clockwise or counterclockwise about the hub 
4 until they are 180.degree. apart, at which point the carriers 10/12 are 
equidistant from the hub 4. Rotation of the carriers is then effected by 
rotating both arms 6/8 in the same direction, e.g. clockwise. This 
rotational force is coupled to the carriers 10/12 through associated 
struts 24/25 and 36/37. 
FIG. 4b shows operation of the robot assembly in which the first carrier 10 
is retracted and the second carrier 12 is extended. As is indicated by the 
arrows, respective counter-clockwise/clockwise motion of the arms 6/8 
about the hub 4 exerts a pulling force on the struts 24/25, drawing one 
carrier 10 toward the hub 4. At the same time, the arms 6/8 exert a 
pushing force on the struts 36/37 forcing the other carrier 12 away from 
the hub 4. 
FIG. 4c shows operation of the robot assembly in which second carrier 12 is 
retracted and the first carrier 10 is extended. As is indicated by the 
arrows, respective clockwise/counter-clockwise motion of the arms 6/8 
about the hub 4 exerts a pulling force on the struts 36/37, drawing one 
carrier 12 toward the hub 4. At the same time, the arms 6/8 exert a 
pushing force on the struts 24/25 forcing the other carrier 10 away from 
the hub 4. 
The present invention is useful for manipulating multiple objects. As 
described above, a preferred embodiment of the invention finds application 
in a reaction system for processing semiconductor wafers. In FIG. 1, a 
carrier 10 is shown in an extended position, while the other carrier 12 is 
shown in a retracted position. Thus, one carrier 12 may be used to store a 
semiconductor wafer, while a carrier 10 is, for example, withdrawing a 
semiconductor wafer 13 from a reaction chamber 11. 
In operation, the robot arm fetches a wafer from a stack of wafers and 
places the wafer in a reaction chamber. The robot arm then fetches a 
second wafer while the first wafer remains in the reaction chamber. After 
sufficient processing time has elapsed, the first wafer is withdrawn from 
the reaction chamber and the robot arm now carries two wafers, one 
processed and one fresh. The carriers, when positioned as shown in FIG. 
3a, are then rotated, such that a fresh wafer on one carrier is placed 
into the reaction chamber, while a processed wafer on the other carrier is 
returned to the stack of wafers. The robot arm then loads another fresh 
wafer from the stack of wafers and returns to the reaction chamber. The 
process just described is repeated as required. Additionally, the robot 
arm of the present invention is readily adapted for use in daisy-chain 
processes where wafers are moved sequentially through a series of reaction 
chambers as part of a process flow. 
In contrast, prior art robot assemblies require that, for the operation 
described above, a first wafer is removed from the reaction chamber by the 
robot assembly and returned to a stack of wafers for storage. The robot 
assembly is then used to fetch a second wafer and place it in a reaction 
chamber. During the interval between storage of the first wafer and 
placing a the second wafer into the reaction chamber, the reaction chamber 
is idle. This deadtime seriously degrades throughput in the reaction 
system. The present invention therefore reduces handling and the number of 
steps involved in moving a wafer within a reaction system and replacing 
the wafer with a fresh wafer, thus increasing throughput (by eliminating 
unnecessary and wasted robot assembly motion). 
Although the invention is described herein with reference to the preferred 
embodiment of the robot assembly, one skilled in the art will readily 
appreciate that applications, other than those involving the handling of 
semiconductor wafers in a reaction system, and other manipulation 
schedules, and geometries, etc. may be substituted for those set forth 
herein without departing from the spirit and scope of the present 
invention. For example, it is not necessary to have independent coaxial 
motion of the arms about the hub. Rather, various motions may be provided 
without departing from the spirit and scope of the invention. Accordingly, 
the invention should only be limited by the Claims included below.