1. Field of the Invention
The present invention relates to an apparatus and method for transferring objects in a processing system. More specifically, the present invention relates to a robot blade made of a dielectric or semi-conducting material that reduces particulate contamination and substrate contact on a blade surface.
2. Background of the Related Art
Modern semiconductor processing systems typically integrate a number of process chambers on a single platform to perform several sequential processing steps without removing the substrate from a highly controlled processing environment. Once the cluster tool has been configured with the requisite number of chambers and auxiliary equipment for performing certain process steps, the system will typically process a large number of substrates by moving the substrates through the chambers using a robot disposed in the system. The robot provides both lateral and rotational movement of a substrate on a robot blade to retrieve, transfer, and deliver substrates from one location within the system to another. Two examples of robots include a frog-leg type robot and a polar type robot. FIG. 1 illustrates a frog-leg type robot 2 having blades 4a and 4b. FIG. 2 illustrates a polar-type robot 6 having a blade 8 supporting a substrate 12.
To increase throughput rates of substrates in a processing system, the trend is to increase the speeds at which substrates are moved in the system by the robot. However, increased speeds add complexity to the substrate handling systems and have resulted in several challenges. First, increased speeds have decreased the acceptable tolerances which are required to maintain repeatability and quality of substrate handling. The desire for speed and increased throughput rates are balanced against the possibility of damaging substrates or the films formed thereon. Typically, the substrate is held in place on a robot blade by the substrate weight and frictional contact with the blade. If a robot moves a robot blade too abruptly, or rotates the blade too fast, then the substrate may slide off the blade, potentially damaging the substrate, the chamber, and/or the robot.
One solution that addresses this problem and enables faster blade movement has been to use a clamping device, typically referred to as a gripper, to secure the substrate on the robot blade. FIGS. 3 and 4 are a top view and cross sectional view, respectively, showing a typical robot blade 10 connected to a robot 2 and having a pair of extendable substrate grippers 13a, 13b associated therewith. When a substrate 12 is received on a robot blade, the grippers 13a, 13b are extended from lateral shoulder 14 to secure a substrate between the grippers and a lateral shoulder 16. As the grippers are extended, the substrate 12 slides along a first vertical support 18 and a second vertical support 20 and into engagement with the lateral shoulder 16. The vertical supports 18, 20 are typically beveled as shown in FIGS. 5 and 6 to reduce the contact area between the substrate 12 and the respective vertical support as the substrate slides across the vertical supports into position. The movement of the substrate 12 across the vertical supports 18, 20 can generate particles which can accumulate on the edge of a substrate 12 or on the robot blade 10. Particles typically accumulate in area 17 between the lateral shoulders 14, 16 and their respective vertical supports 18, 20 as shown in FIGS. 5 and 6. If particles adhere to or are otherwise received on a substrate, the particles can cause defects on the substrate, thereby reducing the device yield of the substrate. Particles can also be transferred to other locations within a processing system and can compromise the integrity of system components such as vacuum chucks and electrostatic chucks.
In addition to holding a substrate on a blade, increasing automated substrate transfer speeds challenge acceptable tolerances related to blade deflection. Blade deflection refers to the stiffness of the blade and the associated droop of the blade experienced during movement within the system. During substrate handling, the blade deflects due to forces acting on the blade and the substrate. For example, when a substrate is loaded on the blade, the blade deflection can change depending on the speed of substrate movement, substrate mass, wear of robot/blade components, and chamber temperature. The amount of deflection can be critical because substrates are typically stored in cassettes in a stacked configuration and it is important to accurately maintain the position of the blade as the blade enters the cassette, retrieves a substrate, and exits the cassette. The same accurate positioning is needed to control delivery of a substrate into and out of a processing chamber. As the robot speed increases, the amount of blade deflection is desirably reduced to provide tighter tolerances to ensure that the blade and/or substrate will not be damaged during movement or placement within the system.
Another problem encountered in the transfer of substrates in a processing system is electrostatic charge that can build up on a substrate and, if not discharged, can cause a substrate to adhere to a robot blade. Typically, an electrostatic charge can be created on a substrate surface as a result of processing or as a result of being held to a support member on an electrostatic chuck. Another source of an electrostatic charge includes substrate cassettes which support substrates during transfer within a fabrication. While an electrostatic charge is beneficial for holding the substrate temporarily during a processing step, a residual build up of an electrostatic charge on a substrate may cause an attraction of the substrate to the robot blade or otherwise hinder efficient transfer of the substrate from chamber to chamber. In addition, an electrostatic charge can also attract particles to the substrate, causing contamination of the substrate and subsequent yield loss.
The robot is typically grounded. While it is desirable to reduce the electrostatic charge on a substrate, current blades made of aluminum or other highly conductive material can cause arcing between a conductive blade and a substrate when dissipating an electrostatic charge through the grounded robot. Arcing can cause defects in the delicate patterns developed on a substrate. Thus, while it is preferable to reduce the electrostatic charge on the substrate, the charge should not be discharged through a highly conductive electrical path which can cause arcing.
There remains a need for a robot blade that reduces the risk of contamination in substrate processing, reduces the blade deflection, and dissipates at least some of the electrostatic charge which may build up on a substrate.
The present invention generally provides a robot blade which provides a plurality of semi-conductive or conductive contacts disposed at least partially above the surface of the blade to support a substrate above the blade. The contacts are preferably located inwardly from the edge of the blade and toward the center of the blade to provide a collection area on the blade for particles to accumulate. The blade is preferably made of a ceramic, such as semi-conductive alumina or other semi-conductive material to provide an electrical flow path through the contact(s) to discharge any electrical charge which may build up on the substrate during processing.
In one aspect, the invention provides a robot blade, comprising a body having a blade surface and a plurality of conductive or semi-conductive contacts disposed at least partially on the blade surface. In another aspect, the invention provides a substrate processing system, comprising a chamber, a robot disposed in the chamber and a robot blade connected to the robot, the robot blade comprising a body having a blade surface and a plurality of conductive or semi-conductive contacts disposed at least partially on the blade surface. In another aspect, the invention provides a method of moving a substrate, comprising supporting a substrate on a plurality of at least semi-conductive contacts disposed on a blade surface, engaging a substrate with at least one biasing member, and moving the substrate in a processing system.