Abstract:
Apparatus for processing a surface of a substrate includes a chamber containing a cavity that has one side that is open, the chamber wall including a lip surrounding the open side of the cavity. Gas ports, disposed within the chamber wall and opening through the lip, emit a pressurized gas so as to create a gas cushion between the lip and the surface when the open side of the cavity is placed adjacent to the surface, thus creating a seal between the cavity and an environment external to the chamber.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application No. 60/347,726, filed Jan. 11, 2002, which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to fabrication of microelectronic devices, and specifically to a novel, miniaturized chamber for use in semiconductor wafer processing. 
     BACKGROUND OF THE INVENTION 
     The use of air bearings is well known in a variety of mechanical applications. Such bearings operate by creating a high-pressure cushion of gas between two surfaces in relative motion. The air bearing reduces the friction between the surfaces to a negligible level, and allows the surfaces to be held in very precise mutual alignment by proper control of the gas pressure. Due to the lack of friction, air bearings are generally characterized by low wear and, consequently, absence of particle generation due to such wear. For example, Anorad (Hauppauge, N.Y.) produces linear positioning stages based on high-performance air bearings. Air Bearing Technology (Hayward, Calif.) produces air bearing spindles and disk chucks, as well as ancillary equipment. 
     The use of air bearings in semiconductor processing equipment is also known in the art. For example, U.S. Pat. No. 5,898,179, whose disclosure is incorporated herein by reference, describes mechanical scanning apparatus for moving a semiconductor wafer inside a vacuum chamber, based on air bearing seals. The apparatus includes differentially-pumped integral air bearing vacuum seals that support both linear and rotary motion. The air bearing seals are produced by a combination of nozzles and vacuum grooves between the surfaces to be sealed. Gas is injected through the nozzles in order to create a high-pressure cushion between the surfaces, which also acts as a barrier to keep ambient air from entering the vacuum chamber. The gas is pumped out through the vacuum grooves in order to maintain a high vacuum within the chamber. 
     SUMMARY OF THE INVENTION 
     It is an object of some aspects of the present invention to provide improved apparatus and methods for processing a substrate under controlled atmospheric conditions, and particularly for processing semiconductor wafers and other elements used in producing microelectronic devices. 
     Preferred embodiments of the present invention provide a micro-chamber for processing of substrates such as semiconductor wafers. Rather than encompassing the entire substrate, in the manner of processing chambers known in the art, the micro-chamber covers and processes only a small area of the surface of the substrate at any one time. An air bearing seal is created between the periphery of the micro-chamber and the surface. This seal permits the micro-chamber to scan over the substrate without damage to the surface, while maintaining controlled atmospheric conditions—either vacuum or positive pressure—within the micro-chamber. By scanning the micro-chamber over the surface, typically using a linear mechanical scanner or a combination of linear and rotary scanning motions, the entire substrate can be processed. Multiple micro-chambers, each performing a different process step, may be controlled to scan the surface together (in a desired sequence) within a single processing tool. 
     Micro-chambers in accordance with preferred embodiments of the present invention can thus be used to reduce the size and increase the efficiency of wafer fabrication equipment. Because of the small volume of the micro-chambers, the quantity of chemicals and gases that they must use to carry out a given process step is typically small, thus saving on manufacturing costs and minimizing contamination and environmental pollution. Furthermore, maintaining process uniformity within the small processing volume of the micro-chamber is much easier than in a large chamber that can contain the entire wafer. As noted above, the micro-chamber can be scanned over the entire wafer, while maintaining uniform process conditions, so that the entire wafer is processed uniformly. 
     In some preferred embodiments of the present invention, a micro-chamber is used for particle removal and surface cleaning of semiconductor wafers and of other manufacturing elements, such as masks and reticles. The high-pressure gas injected into the bearing region around the micro-chamber creates an aerodynamic shearing force at the surface, which is helpful in dislodging contaminants from the surface. Within the micro-chamber, various means may be used for cleaning the surface, including (but not limited to) laser irradiation, particle bombardment, plasma generation, liquid and gaseous agents, and other means known in the art. Alternatively or additionally, micro-chambers may be used for other process steps, such as etching and passivation. 
     There is therefore provided, in accordance with a preferred embodiment of the present invention, apparatus for processing a surface of a substrate, including: 
     a chamber, including a chamber wall defining a cavity having one side that is open, the chamber wall including a lip surrounding the open side of the cavity; and 
     gas ports disposed within the chamber wall and opening through the lip, the gas ports being adapted to emit a pressurized gas so as to create a gas cushion between the lip and the surface when the open side of the cavity is placed adjacent to the surface, thus creating a seal between the cavity and an environment external to the chamber. 
     Preferably, the apparatus includes a vacuum manifold for evacuating the chamber while the gas cushion maintains the seal between the cavity and the environment, wherein the vacuum manifold is disposed within the chamber wall and opens through the lip between the gas ports and the cavity. 
     In a preferred embodiment, the gas ports are adapted to emit the pressurized gas so as to create an aerodynamic shear force, which is effective to dislodge contaminants from the surface. 
     Preferably, the apparatus includes means disposed within the chamber for applying a manufacturing process to an area of the surface adjacent to the open side of the cavity. Most preferably, the means for applying the manufacturing process include means for cleaning the surface. Additionally or alternatively, the means for applying the manufacturing process include an inlet port, which is adapted to convey at least one of a gas, a vapor, a liquid and a stream of frozen particles into the cavity, and/or a radiation guide, which is adapted to direct radiation toward the area of the surface adjacent to the open side of the cavity. Typically, the substrate includes a semiconductor wafer, and the manufacturing process includes a process for fabricating microelectronic devices on the wafer. 
     Preferably, the apparatus includes a motion device, which is coupled to scan the chamber over the surface while maintaining the seal between the lip and the surface. Most preferably, the motion device includes a rotation mechanism, which is adapted to rotate the substrate about a rotation axis, and a translation mechanism, which is adapted to translate the chamber over the surface in a radial direction relative to the rotation axis. 
     There is also provided, in accordance with a preferred embodiment of the present invention, a method for processing a surface of a substrate, including: 
     placing a chamber that contains a cavity having one side that is open so that the open side of the cavity is adjacent to the surface; and 
     directing a flow of a gas through a lip of the chamber surrounding the open side of the cavity so as to create a gas cushion between the lip and the surface, thus creating a seal between the cavity and an environment external to the chamber. 
     In a preferred embodiment, placing the chamber includes placing multiple chambers at respective positions adjacent to the surface, and directing the flow of the gas includes sealing each of the chambers against the surface, and applying the manufacturing process includes operating each of the chambers to apply a respective portion of the process. Preferably, operating each of the chambers includes operating at least first and second ones of the chambers to apply successive, first and second steps of the process, respectively. 
     There is additionally provided, in accordance with a preferred embodiment of the present invention, apparatus for processing a surface of a substrate, including: 
     a plurality of chambers, each such chamber including a chamber wall defining a cavity having one side that is open, the chamber wall including a lip surrounding the open side of the cavity; 
     gas ports disposed within the chamber wall and opening through the lip of each chamber, the gas ports being adapted to emit a pressurized gas so as to create a gas cushion between the lip and the surface when the open side of the cavity is placed adjacent to the surface, thus creating a seal between the cavity and an environment external to the chambers; and 
     means disposed within each chamber for applying a respective portion of a manufacturing process to an area of the surface adjacent to the open side of the cavity. 
     The present invention will be more fully understood from the following detailed description of the preferred embodiments thereof, taken together with the drawings in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic, sectional, side view of a micro-chamber used in cleaning a semiconductor wafer, in accordance with a preferred embodiment of the present invention; 
     FIG. 2 is a schematic top view of a wafer processing tool that uses a number of micro-chambers, in accordance with a preferred embodiment of the present invention; and 
     FIG. 3 is a schematic side view of a wafer processing tool that uses a micro-chamber, in accordance with another preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 is a schematic, sectional, side view of apparatus  20  for applying a manufacturing process to a surface  21  of a substrate  22 . In the present example, substrate  22  is a semiconductor wafer, and the process applied is a cleaning process, which is intended to remove a particle  24  from the surface. For this purpose, a micro-chamber  26  is positioned over the surface. The chamber comprises a wall, which defines a cavity  33  between the chamber wall and surface  21 . The wall may comprise substantially any suitable material, including ceramic, plastic, metal or quartz. Typically, only a small area of surface  21 , preferably on the order of 1″ square, is contained within chamber  26  at any given time. In operation of apparatus  20 , chamber  26  does not contact surface  21 , but rather floats over the surface on an air bearing seal  28 , typically at a height between 5 and 20 μm from the surface. This seal is formed by flow of pressurized gas through a pressure manifold  30 , which has multiple openings (of which two are shown in the figure) in a lip  31  of chamber  26 , adjacent to surface  21 . Optionally, when it is necessary to maintain a vacuum in cavity  33 , a vacuum manifold  32  sucks out the pressurized gas that is used to form seal  28 , so that the gas does not enter the cavity. Typically, the openings of pressure manifold  30  in lip  31  comprise nozzles, while vacuum manifold  32  comprises grooves in the lip, as described in the above-mentioned U.S. Pat. No. 5,898,179. Alternatively, other types of gas flow configurations may be used. The spacing between lip  31  and surface  21  at seal  28  is determined by the balance of the pressure of the gas emitted through manifold  30  against the weight of chamber  26 . Additionally or alternatively, mechanical or magnetic force may be used to press the chamber more firmly against the surface. A mechanically- or magnetically-supported micro-chamber can thus be positioned below substrate  22 , as shown in FIG. 3, rather than above it. 
     Chamber  26  also comprises means for applying a desired manufacturing process to surface  21 . In the embodiment shown in FIG. 1, these means comprise a waveguide  34  for conveying radiation to the location of particle  24 , along with an inlet tube  36  for process gases and an outlet tube  38  for evacuating cavity  33  and removing contaminants therefrom. Preferably, outlet tube  36  and vacuum manifold  32  are coupled to a pump or pumping system that is capable of pumping cavity  33  down to a pressure of about 10 −8  torr. Because of the small volume of cavity  33 , the chamber can be pumped down rapidly by a relatively small vacuum pump. Alternatively, the cavity may be pressurized for carrying out process steps requiring high pressure, such as wafer cleaning by frozen particle bombardment. 
     Preferably, inlet tube  36  is used to introduce a reactive or inert gas or a vapor, which cooperates with laser radiation injected through waveguide  34  in cleaning surface  21 . Exemplary methods for surface cleaning processes of this sort are described in PCT Patent Application PCT/IL99/00701, in U.S. Pat. No. 4,987,286 and in U.S. patent application Ser. No. 09/721,167, which is assigned to the assignee of the present patent application. These three documents are incorporated herein by reference. Alternatively, chamber  26  may be used to apply other cleaning processes, as are known in the art, using only one or two of the means shown in the figure (waveguide  34  and tubes  36  and  38 ). Further alternatively, other processing means may be used for cleaning surface  21 , such as a plasma generator or a source of very cold or frozen particles for bombarding surface  21 . Substantially any cleaning process known in the art may be applied in this manner to surface  21 , with the possible exception of processes based on immersion of substrate  22  in a solvent bath. Not only wafers may be cleaned in this manner, but also masks, reticles and other items having flat surfaces. 
     Pressure manifold  30  and vacuum manifold  32  are also capable of serving as processing means, for applying manufacturing processes to surface  21 , in addition to their functions in creating air bearing seal  28 . On the one hand, vacuum manifold  32  may be designed to provide sufficient suction so that a separate outlet tube  38  is not required to evacuate cavity  33 . On the other hand, the gas flow created in the area of seal  28  by the pressure manifold and, optionally, by the vacuum manifold creates strong aerodynamic shear forces, which are themselves useful in dislodging particle  24  and other contaminants from the surface. 
     Alternatively, the processing means shown in FIG. 1 may be used for processes other than cleaning of surface  21 , and chamber  26  may also comprise other means for processing substrate  22 , which are not shown in the figures. For example, a plasma or chemical source may be provided for etching and/or passivation of surface  21 . Heating and/or cooling may also be provided. 
     FIG. 2 is a schematic top view of apparatus  50  for processing substrate  22  using micro-chambers  26 , in accordance with a preferred embodiment of the present invention. In this example, three micro-chambers, labeled C 1 , C 2  and C 3 , are used to process different areas of the substrate simultaneously. Each of the micro-chambers is mounted on a translation arm  54 , which is controlled by a mechanical actuator  52 , such as a motor (labeled M 1 , M 2  and M 3 , respectively). Substrate  22  is mounted on a rotating chuck or stage, which rotates the substrate about a central rotation axis. Actuators  52  and translation arms  54  move micro-chambers over the surface of substrate  22  in radial directions. This combination of rotational and translational motions enables the micro-chambers to scan conveniently over the entire surface. 
     Each of micro-chambers  26  comprises its own processing means, which may be of various types, as described above. All of the micro-chambers may be configured to carry out the same process step, such as wafer cleaning, wherein the use of multiple micro-chambers is useful in increasing process throughput. Alternatively, the different micro-chambers may carry out different steps, typically a number of steps in succession. Thus, for example, C 1  may be used to perform a first step, beginning from the outer periphery of substrate  22  and progressing radially inward in a spiral pattern, followed by C 2  with a second step, and C 3  with the final step. A greater or smaller number of micro-chambers may likewise be used. 
     A variety of multi-step processes may be performed in this manner. For example, C 1  may be used to apply a cleaning solvent to substrate  22 , followed by a rinse with isopropyl alcohol (IPA) in C 2 . Finally, C 3  may heat the substrate while applying a vacuum to remove any remaining contaminants from the surface. An advantage of this arrangement is that it allows both the wet and dry cleaning steps to be performed in the same processing station, without requiring a robot to transfer the substrate from one station to the next between steps. This approach not only saves valuable space in the plant, but also provides more effective cleaning, since particles loosened (but not removed) in C 1  and C 2  are vacuumed off the substrate immediately in C 3 , before they have had a chance to cool and harden. Laser cleaning may also be integrated in this process. 
     As another example, apparatus  50  may be used in a multi-step passivation/oxidation process, wherein substrate  22  is first exposed to a hot oxidizing gas (typically oxygen) in the first micro-chamber, followed by passivation (typically with nitrogen or hydrogen) in the second micro-chamber. Micro-chamber implementations of other multi-step processes will be apparent to those skilled in the art and are considered to be within the scope of the present invention. As a further alternative (not shown in the figures), one or more micro-chambers may be held stationary, while substrate  22  is rotated or translated beneath them. For example, a micro-chamber having a length approximately equal to the radius of the substrate may be held in a fixed position while the substrate rotates beneath the micro-chamber, thus scanning the micro-chamber over the entire surface. 
     FIG. 3 is a schematic side view of apparatus  60  for processing substrate  22 , in accordance with a preferred embodiment of the present invention. In this embodiment, micro-chamber  26  is positioned to process a lower surface of substrate  22 . The substrate is supported and rotated by a set of driving wheels  62 , since a rotation stage or chuck beneath the substrate would interfere with the movement of micro-chamber  26 . A translation stage  64  moves the micro-chamber in a radial direction and, optionally, in a tangential direction, as well. The micro-chamber is mounted on a spring  66 , which presses it upwards toward the substrate. (In the embodiments described above, in which the micro-chamber is mounted above the substrate, the weight of the micro-chamber presses it against the substrate, and spring  66  is not generally needed.) The upward force exerted by spring  66  works against the downward pressure created by gas flow through pressure manifold  30  (FIG. 1) to maintain air bearing seal  28  between the micro-chamber and the substrate. 
     It will be appreciated that the preferred embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.