FIELD OF THE INVENTION
The present invention generally relates to an apparatus through which a substrate may be transferred between a heat chamber and a second chamber, such as a central transfer chamber, to effect a semiconductor or glass substrate processing regimen. The present invention has application in a broad array of manufacturing processes, leading to improved semiconductors or flat panel display yields. Further, the invention also has application in prolonging the life of equipment used in such manufacturing processes.
Semiconductor devices are typically made in highly automated systems. Many of these systems include a central transfer chamber mounted on a monolithic platform. The central transfer chamber transfers semiconductor substrates to one or more specialized chambers or reactors located on the periphery of the transfer chamber. The specialized chambers or reactors are used to conduct the various specialized etching, chemical vapor deposition, diffusion, and annealing processes that are necessary to process the substrate. Similar such equipment is used in the manufacture of flat panel displays, as well as various optical components such as couplers, splitters, filters, array waveguide gratings, Bragg gratings, taps, attenuators, multiplexers, and de-multiplexers. Many of these processes are performed at controlled temperatures and very low pressures.
FIG. 1A illustrates a representative modular architecture 10 for processing substrates. Architecture 10 comprises a central transfer chamber 12 to which are connected load lock/cooling chambers 14A and 14B, each for transferring substrates into system 10, heating chamber 102, and processing chambers 40, 42, 44, and 46. Central transfer chamber 12, loadlock/cooling chambers 14A and 14B, heating chamber 102, and processing chambers 40, 42, 44, and 46 are sealed together for a closed environment in which the system may be operated at internal pressures considerably less than standard atmospheric pressure. For example, a representative pressure is about 10−3 Torr. Load lock/cooling chambers 14A and 14B have closable openings comprising load doors 16A and 16B, respectively, on their outside walls for transfer of substrates into system 10.
Load lock/cooling chambers 14A and 14B each contain a cassette 17 fitted with a plurality of shelves for supporting and cooling substrates. Cassettes 17 in load lock/cooling chambers 14 are mounted on an elevator assembly (not shown) to raise and lower the cassettes 17 incrementally by the height of one shelf. To load chamber 14A, load door 16A is opened and a substrate 72 is placed on a shelf in cassette 17. The elevator assembly then raises cassette 17 by the height of one shelf so that an empty shelf is opposite load door 16A. Another substrate is placed on that shelf and the process is repeated until all of the shelves of cassette 17 are filled. At that point, load door 16A is closed and chamber 14A is evacuated to the pressure in system 10.
A slit valve 20A on the inside wall of load lock/cooling chamber 14A adjacent to central transfer chamber 12 is then opened. The substrates are transferred by means of a robot 22 in central transfer chamber 12 to a heating chamber 102 where they are heated to the temperature required for processing operations described below. Robot 22 is controlled by a microprocessor control system (not shown). Robot 22 is used to withdraw a substrate from cassette 17 of load lock/cooling chamber 14A, insert the substrate onto an empty shelf in heating chamber cassette 29 and withdraw, leaving the substrate on a shelf within heating chamber 102. Typically, heating chamber cassette 29 is mounted on an elevator assembly within heating chamber 102. After loading one shelf, heating chamber cassette 29 is raised or lowered to present another empty shelf for access by robot 22. Robot 22 then retrieves another substrate from cassette 17 of load lock/cooling chamber 14A.
In like manner, robot 22 transfers all or a portion of the substrates from heating chamber cassette 29 to one of four single substrate processing chambers 40, 42, 44 and 46. Processing chambers 40, 42, 44 and 46 are adapted to deposit one or more thin layers onto the substrates. Each of the film chambers 40, 42, 44 and 46 is also fitted on its inner walls 40 a, 42 a, 44 a and 46 a, respectively, with a slit valve 41, 43, 45 and 47, respectively, for isolation of process gases.
At the end of film processing, each hot substrate is transferred to cooling cassette 17 of load lock/cooling chamber 14A, one substrate being placed onto each shelf, with the elevator mechanism raising and lowering cassette 17 to present an empty shelf to transfer robot 22 for each substrate.
Various chambers and reactors used in a typical modular architecture based system such as a cluster tool are described in the prior art. For example, U.S. Pat. No. 4,367,672, Wang, et al. discloses methods of using a plasma to selectively etch holes or trenches in a film layer on a semiconductor substrate. Similarly, U.S. Pat. No. 5,614,055, Fairburn, et al., discloses a high density plasma chemical vapor deposition and etching reactor. U.S. Pat. No. 5,865,896, Nowak et al., discloses a high density plasma chemical vapor deposition reactor with combined inductive and capacitive cooling. U.S. Pat. No. 5,108,792, Anderson, et al., discloses a double-dome reactor for semiconductor processing. U.S. Pat. No. 6,000,227 discloses a representative central transfer chamber that is cooled.
Various chambers and vacuum systems are commercially available. A representative commercial embodiment of a vacuum system is the AKT processing system which is available from AKT, Inc., located in Santa Clara, Calif. An exemplary processing chamber is an AKT 1600 PECVD Chamber, and an exemplary thermal anneal chamber is a rapid thermal anneal chamber, such as a lamp heated thermal anneal chamber. These chambers are available from Applied Materials, Inc.
Unique Problems Associated with Glass Substrate Processing
The fabrication of devices, such as plates for use in solar cells and video and computer monitors, makes use of glass substrates. Often, thin film transistors are etched onto the glass substrates. The fabrication of such devices is done in a system that uses many of the same processes and chambers used to fabricate semiconductor devices. For instance, U.S. Pat. No. 5,512,320, Turner et al., discloses a representative system for processing glass substrates. U.S. Pat. Nos. 5,441,768, Law et al., 5,861,107, Law et al., and 5,928,732 Law et al., disclose methods for plasma-enhanced chemical vapor deposition on substrates such as glass. U.S. Pat. No. 5,607,009, Turner et al., discloses a heater chamber with an elevator assembly for heating glass substrates.
One product that relies on processing of glass substrates is flat panel displays. The manufacture of a flat panel display begins with a clean glass substrate. Transistors are formed on the flat panel using film deposition and selective etching techniques. Sequential deposition, photolithography and selective etching of film layers on the substrate create individual transistors on the substrate. These transistors, as well as metallic interconnects, liquid crystal cells and other devices formed on the substrate are then used to create active matrix display screens for flat panel displays.
Although the flat panel display is typically manufactured using the same processes as those used in semiconductor device fabrication, the glass used as the flat panel display substrate is different from a semiconductor substrate in certain aspects that affect processing and system design. In semiconductor fabrication, individual devices are formed on the wafer, and the wafer is diced to form multiple individual integrated circuits. Thus, the creation of some defective devices on the semiconductor wafer is tolerated, because the die bearing these defective devices are simply discarded once the substrate is cut into individual integrated circuits. In contrast, in a flat panel display, individual defective devices must not be removed. Therefore, the number of defective devices created on the flat panel substrate must approach zero. If a substrate is sufficiently large to allow multiple displays to be formed on a single substrate, a defect in any one of the flat panel displays being formed on the flat panel substrate renders the entire substrate useless. Thus, it is important that error rates are minimized in flat panel display fabrication systems.
An objective common to both semiconductor and glass substrate processing is the need to avoid, to the extent possible, exposing the substrate to contamination sources. Accordingly, conventional processing systems provide a closed environment in which the various chambers are sealed together. This presents special problems. For instance, in a typical semiconductor or glass substrate processing scheme, a heat chamber within the cluster tool system is used to subject the substrate to a very high temperature. Yet prior art apparatuses that couple a heat chamber to a central transfer chamber in a closed environment have not adequately addressed the heat problems that arise when a heat chamber is coupled to a central transfer chamber.
One drawback of prior art cluster tool systems, or other modular system architectures that have a heat chamber and/or another high temperature process chamber coupled to a central transfer chamber, is that thermal energy flows from the heat chamber or high temperature process chamber to the central transfer chamber at a significant rate. A reason for this significant flow of thermal energy is that the apparatus used to couple the heat chamber or high temperature process chamber to the central transfer chamber in prior art cluster tool systems, or other modular system architectures, is made of machined aluminum or aluminum alloys. Aluminum and aluminum alloys have a high thermal conductivity coefficient. Central transfer chamber exposure to excessive thermal energy raises the ambient temperature of the central transfer chamber. This temperature rise has a deleterious effect on moving parts within the central transfer chamber, such as the robot arm, and significantly reduces the lifetime of such parts.
As discussed above, prior art apparatuses used to couple a heat chamber or other high temperature process chamber to a central transfer chamber lose a considerable amount of thermal energy through the aperture used to ultimately connect the heat chamber or other high temperature process chamber to the transfer chamber. This heat loss causes a cold spot to arise within the heat chamber or other high temperature process chamber. This cold spot is undesirable because many of the processes carried out in a heat chamber or other high temperature process chamber require that the temperature be uniform across the entire substrate. If one section of the heat chamber or other high temperature process chamber has a cold spot, it is difficult to maintain substrate temperature uniformity.
Accordingly, there is a need in the art for an improved apparatus for coupling two chambers in a closed environment. In particular, there is a need in the art for an apparatus that couples two chambers and minimizes the amount of heat that is transferred between the two chambers. Such an apparatus would be particularly useful for connecting a heat chamber or other high temperature process chamber to a central transfer chamber in the closed environment of a cluster tool system or other modular architecture used to process glass substrates.
SUMMARY OF THE INVENTION
The present invention provides an improved apparatus for connecting a heat chamber or another high temperature process chamber to a second chamber, such as a central transfer chamber, in a closed environment suitable for modular architecture based substrate processing in such a manner that heat transfer from the heat chamber or another high temperature process chamber to the second chamber is minimized. The apparatus of the present invention includes a thermally isolating interface, which has a reduced thermal conductivity coefficient, that abuts the second chamber. This thermally isolating interface reduces the amount of heat that is transferred from the heat chamber or other high temperature process chamber to the second chamber. Furthermore, in some embodiments of the present invention, the thermally isolating interface includes one or more recesses so that the surface area between the thermally isolating interface and the second chamber is minimized. Reduction in this surface area, in turn, minimizes thermal transfer between the heat chamber or other high temperature process chamber and the second chamber. Thus, the apparatus of the present invention prolongs the life of moving parts in the second chamber, such as the robot arm.
In some embodiments of the present invention, the apparatus includes a heating device to prevent heat loss from the second chamber. In many substrate processing regimens, maintenance of a uniform temperature within the second chamber is an important requirement. The inclusion of a heating device in the apparatus of the present invention prevents heat loss through the aperture to the second chamber. Furthermore, the inclusion of a heating device in the apparatus of the present invention lowers the potential temperature differential across large substrates that pass through the apparatus. The reduction in temperature differential across the substrate potentially reduces stress on the substrate, particularly in processing regiments that require the substrate to pass into the second chamber several times.
One embodiment of the present invention provides an apparatus through which a substrate may be transferred between a first chamber, such as a heat chamber or other high temperature process chamber, and a second chamber, such as a central transfer chamber. The first chamber is maintained at a high temperature relative to the temperature maintained within the second chamber. The apparatus comprises: (i) a passageway for receiving the substrate and (ii) a thermally isolating interface that reduces heat transfer from the first chamber to the second chamber. The thermally isolating interface has a hole in the face of the interface that abuts a port into the second chamber. The hole has dimensions such that the substrate is transferrable through the interface, thereby allowing for substrate transfer between the first chamber and the second chamber.
In some embodiments of the present invention, the thermally isolating interface is composed of a material having a thermal conductivity coefficient less than that of aluminum, which is about 1536 Btu inch/(hr)(ft2)(° F.). In yet other embodiments, the thermally isolating interface is composed of a material having a thermal conductivity coefficient of less than 1200 Btu inch/(hr)(ft2)(° F.). In still other embodiments of the present invention, the thermally isolating interface is composed of an austenitic, martensitic steel, or ferritic steel. In one aspect of the present invention, the thermally isolating interface is composed of stainless steel. In one embodiment in accordance with this aspect of the invention, the thermally isolating interface is composed of a stainless steel having a thermal conductivity coefficient of about 106 Btu inch/(hr)(ft2)(° F.).
In some embodiments of the present invention, the face of the thermally isolating interface includes one or more recesses such that an enclosed volume is defined within the recess when the face abuts the port of the second chamber. In some embodiments, this enclosed volume remains empty or is occupied by an insulating material. In general, whatever occupies the enclosed volume has a thermal conductivity coefficient of less than that of aluminum. For example, in one embodiment, the enclosed volume is simply air, which has a thermal conductivity of 0.18 Btu inch/(hr)(ft2)(° F.). Because whatever occupies the enclosed volume has a thermal conductivity less than that of aluminum, the enclosed volume is referred to herein as a thermally isolating volume.
The present invention contemplates a large number of different shaped recesses all of which are in accordance with the present invention. For example, in one embodiment, the recess is beveled. In other embodiments, the shape of the recess is best described in terms of the shape of a cross section of the recess. The shape of the cross section of some recesses in accordance with these embodiments is alternatively defined by a sawtooth pattern, a repeating pattern, a curve or a polynomial equation.
In selected embodiments of the present invention, the passageway through which the substrate is passed includes a heating element for maintaining the passageway at a temperature that is proximate to the temperature of the heat chamber and/or another high temperature process chamber such as a chemical vapor deposition (CVD) chamber. In some embodiments, this heating element is a coil wrapped around a ceramic base. Further, in some embodiments the heat from the heating element is distributed by a distribution mechanism such as a reflective surface. In a preferred embodiment, this reflective surface is a parabolic mirror.