Patent Publication Number: US-2010119351-A1

Title: Method and system for venting load lock chamber to a desired pressure

Description:
FIELD OF THE INVENTION 
     The present invention relates, most generally, to semiconductor manufacturing systems and methods. More particularly, the invention relates to a method and system for venting a load lock chamber to a desired crossover pressure. 
     BACKGROUND 
     Today&#39;s rapidly advancing semiconductor manufacturing industry involves highly-precise operations performed upon semiconductor substrates and extremely miniaturized features formed on the semiconductor devices produced on the semiconductor substrates. In order to accurately and reliably produce the highly-miniaturized features and produce functional and reliable devices, contamination sources must be eliminated from the processing environment because even one contaminating particle can destroy the functionality of a device. 
     The semiconductor fabrication process involves a number of processing operations carried out in different processing tools. Many of these tools are high vacuum processing tools and when the semiconductor substrates undergoing the fabrication process are transferred from one high vacuum processing tool to another, they are transferred into or out of the associated load lock chamber of the high vacuum processing tool. In order to open the load lock door to the outside and transfer substrates into or out of the load lock chamber, the load lock chamber is vented to atmosphere, according to conventional technology in which the outside environment is generally considered to be at atmosphere, i.e. at 760,000 mT. 
     Particulate contamination associated with breaking vacuum, i.e., venting the load lock chamber and opening the load lock chamber door to the fabrication facility environment, can destroy semiconductor devices, especially as device features continue to shrink and the sensitivity to particle damage increases. If the venting process used to increase the load lock chamber pressure to or near atmospheric pressure is too turbulent, particle contamination may result. The crossover pressure level in the load lock when the load lock door is opened to the environment, is also very important to particle generation. For example, if the crossover pressure in the load lock is too low when the load lock door is opened to the fabrication area environment, dirty outside air could potentially stream back into the load lock and the tool and the resulting particles may cause substantial defects to the substrates. Conversely, if the crossover pressure maintained in the load lock is too high when the load lock door is opened to the environment, the resulting outward burst could similarly cause contaminating particle generation. 
     It would therefore be desirable to minimize any turbulence and particle generation associated with opening the load lock door to the fabrication area environment. 
     SUMMARY OF THE INVENTION 
     To address these and other needs, and in view of its purposes, one aspect of the invention provides a method for venting a load lock chamber in a semiconductor processing tool. The method includes detecting ambient pressure outside the tool, determining a desired load lock crossover pressure based on the detected ambient pressure and purging the load lock chamber with an inert gas until the desired load lock crossover pressure is achieved and the load lock chamber stabilizes at the desired load lock crossover pressure. The method then provides for opening an external load lock door after the load lock chamber stabilizes at the desired load lock crossover pressure. 
     According to another aspect, the invention provides a system for venting a load lock chamber of a semiconductor processing tool. The system includes a pressure sensor capable of detecting ambient pressure outside the semiconductor tool, means for determining a desired load lock crossover pressure based on the detected ambient pressure, and a venting system capable of purging the load lock chamber with an inert gas until the desired load lock crossover pressure is achieved and stabilizes in the load lock chamber. The system further includes an actuator capable of opening an external load lock door responsive to the load lock pressure stabilization in the load lock chamber. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The present invention is best understood from the following detailed description when read in conjunction with the accompanying drawing. It is emphasized that, according to common practice, the various features of the drawing are not necessarily to scale. On the contrary, dimensions of the various features may be arbitrarily expanded or reduced for clarity. Like numerals denote like features throughout the specification and drawing. 
         FIG. 1  is a front view illustrating a semiconductor processing tool with a load lock chamber disposed in an exemplary mini-environment in a semiconductor fabrication production area; 
         FIG. 2  is a flow chart illustrating one exemplary sequence of events for carrying out an aspect of the invention; and 
         FIG. 3  is a flow chart illustrating another exemplary sequence of events for carrying out an aspect of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention provides a method and system that reduces particle contamination when a load lock door is opened to the fabrication area environment, by achieving and maintaining a crossover pressure in the load lock chamber that is equal to the pressure in the fabrication environment, or represents a desired pressure difference between the load lock chamber and the fabrication area environment, when the load lock door is open. The system and method provide for accurately monitoring the pressure in the fabrication area environment or mini-environment on an ongoing or real-time basis even as the ambient pressure in the fabrication area environment drifts from atmosphere, i.e. 760,000 mT. It has been found that the ambient pressures throughout the semiconductor fabrication area may vary, sometimes significantly, from 760,000 mT. The fluctuations may be fluctuations in time and may result from changing weather, for example. The ambient pressure within the semiconductor fabrication area may also vary spatially within the semiconductor fabrication area, such as in mini-environments that may be produced when certain portions of the fabrication area are located under laminar flow hoods, or subject to other environment-affecting factors. 
     The invention provides for detecting ambient pressure outside of the semiconductor processing tool and determining a desired crossover pressure based on the detected ambient pressure, purging the load lock chamber until the desired crossover pressure is achieved in the load lock chamber, and opening the external load lock door after the load lock chamber has stabilized at the desired crossover pressure. 
       FIG. 1  shows a load lock chamber in conjunction with a semiconductor processing tool. Load lock chamber  2  forms part of semiconductor tool  4  and allows for semiconductor substrates, i.e. wafers, to be loaded into semiconductor tool  4  through load lock door  6 . In some embodiments, an automated external substrate transport system may be directly coupled to or near load lock chamber  2 . Semiconductor tool  4  may be any of various processing equipment tools used in the semiconductor manufacturing industry. Semiconductor tool  4  may be a high-vacuum tool in which substrates are processed in near-vacuum conditions, or at very low pressures. Semiconductor tool  4  may be an etching tool, a deposition tool, a photolithography tool, a metrology tool, a cleaning system, an analytical tool or any of various other tools used in semiconductor device fabrication industry. 
     After the semiconductor substrates are introduced to load lock chamber  2 , an additional door or doors, in conjunction with internal transport mechanisms, transfer the substrates internally from load lock chamber  2  to other portions of semiconductor tool  4  for processing. Conventional pumping and venting systems may be used in conjunction with load lock chamber  2 . In the illustrated embodiment, semiconductor tool  4  is located within optional mini-environment  8  which is a discrete environment within environment  12  of a semiconductor fabrication area. According to other exemplary embodiments, semiconductor tool  4  may be situated within environment  12  and not within any mini-environment within the fabrication area. According to one exemplary embodiment, mini-environment  8  may be produced by laminar flow hood  10  and defined by walls  14  which may be rigid impermeable walls, flexible plastic sheets, permeable dividers or other conventional devices used to produce mini-environments within a semiconductor fabrication area. 
     In the illustrated embodiment, pressure sensor  16  is disposed within load lock chamber  2  and pressure sensor  18  is located external to semiconductor tool  4 . It should be noted that additional pressure sensors may be used in other exemplary embodiments and in particular that the external pressure sensor  18  need not be in contact with semiconductor tool  4  and may be disposed in various other locations within mini-environment  8  or within environment  12  of the semiconductor fabrication area. According to yet another exemplary embodiment, external pressure sensor  18  may not be used. Pressure sensors  16  and  18  may be any of various suitable conventional pressure sensors available in the art and capable of detecting both high-vacuum pressures and also pressures in the range of atmospheric pressure. 
       FIG. 2  illustrates a flow chart that shows an exemplary sequence of operations according to an aspect of the invention. At step  101 , a signal is sent to vent the load lock chamber and open the load lock door, typically to load or unload substrates to be or which have been processed. In other exemplary embodiments, the signal may be sent to vent the load lock chamber and open the load lock door for other purposes such as for testing or maintenance procedures. The signal may be sent automatically, such as when processing of substrates in semiconductor tool  4  is complete and it is desired to unload the wafers from semiconductor tool  4  via load lock chamber  2 , or when an external delivery of substrates arrives at semiconductor tool  4  and is acknowledged and queued for being processed in the tool. Such signals may alternatively be sent manually. 
     At step  103 , the pressure outside the semiconductor tool, P out , is measured. This may be accomplished using conventional pressure detectors/sensors such as pressure sensor  18  shown in  FIG. 1  or various other suitable pressure detectors that may be located proximally or distally external to semiconductor tool  4  and load lock chamber  2 . In various exemplary embodiments, multiple pressure sensors may be used and the pressure measured by each of the pressure sensors averaged to determine a mean P out . According to the exemplary embodiment in which the outside pressure is sensed responsive to a signal requesting the load lock chamber to be opened, i.e. step  101 , a real-time pressure is obtained. In one embodiment, pressure sensor  18  may detect the ambient pressure P out  substantially continuously and the most recently recorded measured pressure will be used as P out . In various embodiments P out  may be stored in a memory which may be in a processor, and referenced for calculation in subsequent step  107 . 
     At step  105 , the load lock chamber is vented responsive to the signal sent at step  101 . Conventional systems may be used to vent the load lock chamber such as by purging with nitrogen or another inert gas. Various suitable purging/venting systems are available in the art and may be used. The pressure in the load lock chamber is increased and, at step  107 , the load lock pressure, P LL , is allowed to reach and stabilize at a desired crossover pressure that is determined based on P out . The crossover pressure is the pressure in load lock chamber  2  at which load lock door  6  is opened. The desired crossover pressure may be the same or different than P out , the pressure measured outside semiconductor tool  4  and which may be saved in memory. In one exemplary embodiment, the desired crossover pressure will be a pressure identical to the detected pressure outside producing no pressure gradient when load lock door  6  is opened and in other exemplary embodiments, the desired crossover pressure may be up to 100,000 millitorr greater than or less than the outside detected pressure, P out . According to one exemplary embodiment, the crossover pressure, i.e. the pressure at which the load lock chamber is allowed to stabilize before load lock chamber door  6  opens, may be 20,000-30,000 millitorr greater than P out  and in yet another exemplary embodiment, the crossover pressure may be 20,000-30,000 millitorr less than P out . 
     After the load lock chamber achieves and stabilizes at the desired crossover pressure, the load lock door is opened at step  109 , and the transfer of wafers into or out of the load lock chamber from outside semiconductor tool  4 , may take place at step  111 . 
     According to the exemplary sequence in  FIG. 3 , the outside pressure, P out , is detected prior to the signal sent at step  101  to vent the load lock chamber and open the load lock door. In one embodiment, pressure sensor  18  may detect the ambient pressure P out  substantially continuously and the most recently recorded measured pressure value will be recorded and used as P out . According to this exemplary embodiment, P out  may be recorded and stored in memory or a controller or processor and accessed when the signal is sent at step  101  to vent the load lock chamber and open the load lock door. According to another exemplary embodiment, a single sensor such as pressure sensor  16  disposed within load lock chamber  2 , may be used. According to this embodiment, when load lock door  6  is opened to the environment, the pressure P out  is measured by pressure sensor  16 . This may take place, for example, during the loading of a first production run. According to one exemplary embodiment, the signal sent at step  101  may be a signal to vent the load lock chamber at the conclusion of the same first production run or for a second or subsequent production run. According to this exemplary embodiment, the load lock chamber is vented at step  105  responsive to the signal sent at step  101  and the stored value of P out  is accessed and used to determine the desired crossover pressure at step  107 . At step  107 , the load lock pressure, P LL , is allowed to achieve and stabilize at the desired crossover pressure based on P out . According to this exemplary embodiment, the P out  value used may be the most recently measured P out  value at step  103 . Once the crossover pressure is achieved, the load lock door is opened at step  109  and wafer transfer into or out of the load lock may take place at step  111 . 
     According to the aforementioned exemplary embodiments, the desired crossover pressure, P crossover , may be determined based on P out . Conventional input means may be used to receive an input and determine a crossover pressure to be achieved and stabilized in the load lock before door opening, by comparison to P out . The input is indicative of a mathematical relationship between P out  and the desired load lock pressure, P crossover . The input may indicate that the desired crossover pressure, P crossover , equals outside pressure P out . In one embodiment P crossover  may be expressed as a percentage less than or greater than P out , e.g., P crossover =P out ×1.01. According to another exemplary embodiment, the crossover pressure may be expressed as a pressure differential. For example, the input may be “plus 20,000 millitorr” indicating that the desired crossover pressure is the measured outside pressure P out , plus 20,000 millitorr, i.e. “P crossover =P out +20,000 millitorr.” For example, if P out  measured at step  101  equals 750,000 millitorr and the input for desired crossover pressure is “plus 20,000 millitorr” the crossover pressure that the load lock is allowed to achieve and stabilize at, i.e. the crossover pressure, before the door may open, will be 770,000 millitorr. Conversely, if the desired crossover pressure is expressed as: P crossover =P out −10,000 millitorr, the crossover pressure, according to this exemplary embodiment, will be 740,000 millitorr. 
     According to various exemplary embodiments, conventional components may be used to carryout the aforementioned method. For example, a conventional memory may be used to store either or both of the measured P out  and the input mathematical relationship between P out  and P crossover . A processor with input means may be used to receive the desired crossover pressure relationship and conventional processing means may be used to derive the crossover pressure based on the input mathematical relationship between P out  and P crossover  once P out  is detected/measured. The system may further include a controller that provides P crossover  to the load lock chamber and directs the load lock door to open when P crossover  is achieved. The system may further include conventional mechanical features such as a conventional actuator that opens the load lock door once the desired crossover pressure has been achieved. 
     The preceding merely illustrates the principles of the invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements which, although not explicitly described or shown herein, embody the principles of the invention and are included within its spirit and scope. Furthermore, all examples and conditional language recited herein are principally intended expressly to be only for pedagogical purposes and to aid the reader in understanding the principles of the invention and the concepts contributed by the inventors to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents and equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure. 
     This description of the exemplary embodiments is intended to be read in connection with the figures of the accompanying drawing, which are to be considered part of the entire written description. In the description, relative terms should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description and do not require that the apparatus be constructed or operated in a particular orientation. Terms concerning attachments, coupling and the like, such as “connected” and “interconnected,” refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise. 
     Although the invention has been described in terms of exemplary embodiments, it is not limited thereto. Rather, the appended claims should be construed broadly, to include other variants and embodiments of the invention, which may be made by those skilled in the art without departing from the scope and range of equivalents of the invention.