Abstract:
A vacuum chamber load lock purging method and apparatus is disclosed. The purging apparatus includes a purging gas diffusion device disposed in a rear portion of a load lock chamber. The purged gas diffusion device is located proximate the vacuum door and distal from the atmospheric door such that the purge gas diffuses towards the atmospheric door during purging. The purging gas diffusion device is porous and permits a purge gas such as nitrogen to purge a load-lock chamber of oxygen or other contaminants from the load lock. The purge gas diffusion device may be tubular and is positioned in the load lock chamber in an offset channel portion in communication with and offset from a through path portion of the load lock chamber, through which a product, such as a semiconductor wafer may proceed without disruption by the diffusion device. The load lock purging system is useful, for example, in a film deposition or other process in which precisely-controlled conditions of pressure and concentration affect the integrity of the process.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates generally to load-lock chambers used in the processing of semiconductor wafers. More specifically, the present invention relates to an apparatus and methodology for purging a load-lock chamber with an inert gas.  
           [0002]    In industrial process applications, particularly in the semiconductor field, it is common to utilize a load-lock chamber in order to prevent introduction of ambient air into the processing chamber. The introduction of air contaminants could degrade the quality of the film deposition deposited on semiconductor wafers. The goal is to reduce the introduction of contaminants into the load lock, particularly oxygen and moisture, to prevent such contamination from adversely affecting processing of the semiconductor wafers.  
           [0003]    In general, a semiconductor processing system will often include load lock, a central handler chamber, and a processing chamber configured together and isolated by pneumatic gate valves. During the process, the load-lock chamber receives a semiconductor wafer. The gas in the load-lock chamber is evacuated and replaced with a gas that will permit a pressure environment to be created, which is generally the same as the process chamber. The gate valve is opened and the wafer is moved from the load-lock chamber to the processing chamber via the central handler. Following processing, the gate valve is opened and the wafer is returned to the load-lock chamber. Then the gate valve is closed and the gas within the load-lock chamber is evacuated and replaced with an inert gas, such as nitrogen, which is used to return the load lock to atmospheric pressure. The inert gas may be used to purge the load-lock chamber while the wafer is being moved into and out of the chamber.  
           [0004]    One method of introducing the purge gas to the load-lock chamber is with one or more nozzles. The use of purge gas nozzles produce turbulent flows and eddy regions that results in high concentration of oxygen and moisture within the purged region. The introduction of moisture is particularly troublesome, as it tends to adsorb on the interior surfaces of the chamber. This adsorbed moisture may then be slowly released during the chamber evacuation process, and subsequently transported to the wafer process chamber.  
           [0005]    Therefore, it would be desirable to be able to introduce a purge gas into a load-lock chamber while maintaining relatively low oxygen and moisture levels in order to reduce contamination of a semiconductor wafer during a film deposition process.  
         SUMMARY OF THE INVENTION  
         [0006]    A purging apparatus that introduces purge gas into a load-lock chamber in such a way as to minimize the introduction of moisture and oxygen during the product loading and unloading processes is disclosed. In one aspect of the invention, the purging apparatus includes a load-lock having a vacuum door and an atmospheric door and defining a load-lock chamber. A purging gas diffusion device is disposed in the load-lock chamber proximate the vacuum door and distal from the atmospheric door. The purging gas diffusion device includes a porous section. The pores in the porous section diffuse the purge gas therethrough in a purge flow that travels through the load-lock chamber in flow direction from the vacuum door to the atmospheric door.  
           [0007]    In another aspect of the invention, a method for purging a load lock is also contemplated. A method of purging a load-lock includes providing a load-lock having a vacuum door and an atmospheric door and defining a load-lock chamber, a purging gas diffusion device disposed in the load-lock chamber proximate the vacuum door and distal from the atmospheric door, the purging gas diffusion device including a plurality of pores. The method includes diffusing purge gas through the pores of the purging gas diffusing device; creating a purge gas flow within the load-lock chamber to remove ambient air and prevent entrainment of air during wafer transport.  
           [0008]    Various other features, objects and advantages of the present invention will be made apparent from the following detailed description and the drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    The drawings illustrate a preferred mode presently contemplated for carrying out the invention.  
         [0010]    In the drawings:  
         [0011]    [0011]FIG. 1 is a perspective view of a load lock purging system in accordance with one aspect of the present invention;  
         [0012]    [0012]FIG. 2 is a side view of the load lock purging system of FIG. 1;  
         [0013]    [0013]FIG. 3 is a top schematic view of the load lock purging system in accordance with one aspect of the present invention;  
         [0014]    [0014]FIG. 4 is a schematic side section view of the load lock purging system of claim  3 ;  
         [0015]    [0015]FIG. 4A is a schematic side section view of the load lock purging system of claim  3  with the vacuum door removed;  
         [0016]    [0016]FIG. 5 is a perspective view of an exemplary purging gas diffusion device used in one aspect of the present invention;  
         [0017]    [0017]FIG. 6 is another perspective view of the purging gas diffusion device of FIG. 5;  
         [0018]    [0018]FIG. 7 is a cross-sectional view of the purging gas diffusion device of FIG. 5; and  
         [0019]    [0019]FIG. 8 is a graph illustrating oxygen concentration data taken from a purge optimization test. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0020]    Referring now to FIG. 1, a perspective view of a load lock purging system in accordance with one aspect of the present invention is shown. The purging apparatus is identified generally by the numeral  10 . Purging apparatus  10  includes a load lock  12  which may be used in, for example, a semiconductor wafer film deposition process. The purpose of load lock  12  is to minimize the introduction of ambient air contaminants into the semiconductor tool and to balance pressures to facilitate transport of wafers between the cleanroom and the process chamber. Although load lock  12  is contemplated to be used in a semiconductor process, it is contemplated that the present invention may be used with any process in which air or moisture could degrade the quality of a film deposition. Therefore, processes involving the regulation of air content and moisture concentration is contemplated to be within the scope of the use of the present invention. Purging apparatus  10  includes an atmospheric door  14  which is connected to load lock  12  and can be opened or closed as desired to expose the interior of load lock  12  to the ambient atmosphere. Also connected to load lock  12  is a vacuum door which has been removed to facilitate understanding of the drawing. FIG. 1 shows a load lock chamber  18  partially exposed to show purging gas diffusion device  16  disposed within the load lock chamber  18  and connected to load lock  12 . Purging gas diffusion device  16  is located preferably in a horizontal position with respect to the operational position of load lock  12 , and purging gas diffusion device  16  is located proximate to the vacuum door and distal from the atmospheric door  14 . Load lock  12  may be constructed of any suitable material and aluminum is an example of one such material.  
         [0021]    Referring now to FIG. 2, a side view of the load lock purging system of FIG. 1 is disclosed. As can be seen in this view of purging apparatus  10  (now with both the vacuum door and the atmospheric door removed), the load lock chamber  18  runs the entire length of the purging apparatus  10 , and through load lock chamber  18  to facilitate moving, for example, a semiconductor wafer along through load lock chamber  18  of load lock  12  and into, for example, a process chamber. The load lock chamber is capable of having an interior pressure that is substantially equal to a vacuum condition, as during a semiconductor process.  
         [0022]    Referring now to FIG. 3, a top schematic view of the load lock purging system  10  in accordance with one aspect of the present invention is shown. In this figure, vacuum door  15  is shown closed, as would occur during the purging process. In operation, purging gas diffusion device  16  diffuses an inert gas, which preferably includes one of N 2 , Ar and He, and more preferably N 2 . However, the operation of the present invention is independent of the type of purged gas selected. The diffusion of the purged gas by the purging gas diffusion device  16  produces a purge flow having a purge flow boundary  20 . One of the benefits of the present invention is that this purge flow boundary  20  is typically of a laminar flow type. Therefore, the purged gas flows through the entire load lock chamber  18  and purges ambient air via atmospheric door exit  22 , since the atmospheric door is opened prior to purging.  
         [0023]    Referring now to FIGS. 4 and 4 a , schematic side section views of the load lock purging system  10  are shown, with FIG. 4A illustrating FIG. 4 with the vacuum door  15  removed. Here it is illustrated that load lock chamber  18  of load lock  12  includes a through-path portion  24  and an offset channel portion  26 , located in the region created by curb  27 . It is in this offset channel portion  26  into which purging gas diffusion device  16  is disposed. Preferably, the purging gas diffusion device  16  is placed such that it is substantially in the offset channel portion  26  and does not extend substantially into the through path portion  24 . This placement prevents purging gas diffusion device  16  from interfering with, for example, a semiconductor wafer as it travels through-path portion  24  of load lock chamber  18 . The placement of purging gas diffusion device  16  is important to prevent obstruction of products passing through the load-lock chamber  18  in general, and particularly through-path portion  24 . Again, for orientation purposes, since the purging of load lock chamber  18  occurs in a purging direction from vacuum door  15  to atmospheric door exit  22 , purging gas diffusion device  16  is placed such that it is at a rear section of load lock chamber  18  and proximate the vacuum door  15 . As purging gas diffusion device  16  diffuses the purge gas therethrough, purge gas proceeds from the offset channel portion  26  and generally along through-path portion  24  in the purging direction, thereby purging load lock chamber  18  with the desired purge gas. As a result, because of the placement of purging gas diffusion device  16  into offset channel portion  26  of load lock chamber  18 , a semiconductor wafer or other product may travel a long through-path portion  24  along the line indicated by  28  without purging gas diffusion device  16  interfering with the product&#39;s progress through load lock chamber  18 .  
         [0024]    Referring now to FIG. 5, a perspective view of an exemplary purging gas diffusion device used in one aspect of the present invention. Purging gas diffusion device  16  is constructed to receive a flow of purge gas and diffuse it through a porous material of which purging gas diffusion device  16  is constructed. Purge gas diffusion device includes a hollow tubular member or portion  30  for receiving a purge gas and diffusing the purge gas through the pores of the hollow tubular member.  
         [0025]    In one embodiment, tubular member  30  is a frit made of 3/16th inch stainless steel and includes a center tubular portion  30  and end portions  32   a  and  32   b , which are connected to tubular portion  30 . Although tubular portion  30  is shown as a tube, it is contemplated that other structures having various shapes that permit the flow of gas therethrough may be suitably employed. End portion  32   a  defines a purge gas inlet  34  as well as a mounting channel  36   a . End portion  32   b  similarly includes a mounting channel  36   b  such that purging gas diffusion device  16  may be secured to the load lock  12  (of FIG. 1).  
         [0026]    Referring now to FIG. 6, another perspective view of the purge gas diffusion device  16  of FIG. 5 is shown. In FIG. 6, securing channels  36   a  and  36   b  are shown from the reverse angle to illustrate those locations adapted to receive screws or other securing mechanisms in order to secure the entire purging gas diffusion device  16 , including tubular portion  30 , to the load lock.  
         [0027]    It is contemplated that tubular portion  30  is constructed of a porous material, such that the purged gas may be diffused therethrough. In one embodiment, for example, the average pore size is substantially 100 microns, i.e., to prevent particles having an approximate diameter of 100 microns. More preferably, the average pore size for tubular portion  30  has less than 100 microns. However, any suitable pore size feasible for the particular operation is contemplated by the present invention. The pores of tubular portion  30  may also serve to filter any purge gas as it enters the load lock.  
         [0028]    Referring now to FIG. 7, a cross-sectional view of the purging gas diffusion device of FIG. 5 is shown. Purge gas diffusion device  16  is adapted to receive the purge gas such as nitrogen into purge gas inlet  34  located in end portion  32   a . Nitrogen or other purge gas enters interior chamber  31  and is diffused through the pores of tubular portion  30 . Because end portion  32   b  prevents purge gas from exiting through that end of tubular portion  30 , as the purge gas fills purge gas diffusion device  16 , purge gas will come through the pores and not through the ends of tubular portion  30 .  
         [0029]    Referring now to FIG. 8, a graph illustrating oxygen concentration data taken from a purge optimization test. The test was conducted by comparing a nozzle to the purge gas dispersing device for completeness of purging of unwanted gaseous oxygen. In the first part of the test, a spray nozzle was placed at a central location of the load lock chamber  18 . Purge gas was then sprayed through the nozzle. Oxygen concentration levels were then taken at nine locations within the load lock chamber, the locations being shown in the side legend. The locations correspond to the relative orientation positions in the load lock, with the front corresponding to the side by the atmospheric door, and with the rear corresponding to the side near the vacuum door. The locations represented are RL, RC, RR, CL, CC, CR, FL, FC and FR. They are defined as follows in a conventional manner.  
                                       RL   right left       RC   right center       RR   right right       CL   center left       CC   center center       CR   center right       FL   front left       FC   front center       FR   front right                  
 
         [0030]    Each of the test locations were approximately 161 mm away from each other and offset between 50 mm and 75 mm from the interior wall of the load lock chamber. The readings for the center nozzle (collectively  38 ), that is, when the nozzle provides the purge gas in the center of the load lock chamber, reveal oxygen concentrations exceeding 100,000 ppm ( 40 ) for all nine locations within the load lock chamber.  
         [0031]    In the next part of the experiment, a diffuser device was used and was placed in the rear (corresponding to the offset channel portion) of the load lock chamber. Purge gas was diffused through the rear diffuser and again oxygen concentration measurements were taken at the same locations in the load lock chamber. In this experiment, the rear diffuser readings (collectively  42 ) indicated oxygen concentrations of less than 0.1 PPM, for all nine chambers position locations as shown in the graph at  44 . This represents a reduction in the oxygenation concentration in parts per million by a factor of six when using a porous diffuser at a rear of the load lock chamber and generating the purge gas front from that location. Other tests revealed oxygen concentration levels in the range from about 0.1 PPM to under 100,000 PPM.  
         [0032]    A method for purging a load lock is also contemplated in the invention. A method of purging a load-lock is disclosed and includes providing a load-lock having a vacuum door and an atmospheric door and defining a load-lock chamber, a purging gas diffusion device disposed in the load-lock chamber proximate the vacuum door and distal from the atmospheric door, the purging gas diffusion device including a plurality of pores. The method includes diffusing purge gas through the pores of the purging gas diffusing device; creating a purge gas flow within the load-lock chamber to remove ambient air having at least one ambient gas; and purging the load-lock with the purge gas to create an ambient gas concentration of the ambient gas.  
         [0033]    The present invention has been described in terms of the preferred embodiment, and it is recognized that equivalents, alternatives, and modifications, aside from those expressly stated, are possible and within the scope of the appending claims.  
         [0034]    For example, suitable flow rates of the purge gas, alternative materials for the purge gas diffusion device, and optimal load lock heights are to be considered to be part of the present invention.