Abstract:
Apparatus and method for measuring and controlling static charge inside vacuum equipment. In-line gas ionizers deliver gas ions to pass-through doors, load-locks, vacuum cluster vent lines, or neutralizing chambers. Static charge measurement is accomplished while the wafer or product remains in a vacuum or near-vacuum. In one embodiment, a neutralizing chamber and measurement chamber are combined. This invention has application in semiconductor, disk drive, and flat panel industries.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Application 60/793,201 filed Apr. 19, 2006 entitled “In-situ Ionizers for Vacuum Process and Metrology Equipment”. 
     
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
       [0002]    Not Applicable 
       REFERENCE TO A MICROFICHE APPENDIX 
       [0003]    Not Applicable 
       BACKGROUND OF THE INVENTION 
       [0004]    1. Field of the Invention 
         [0005]    This invention relates to static charge neutralizers, which are designed to remove or minimize static charge accumulation. Static charge neutralizers remove static charge by generating air ions and delivering those ions to a charged target. 
         [0006]    Ionizers are historically utilized inside atmospheric process equipment or metrology equipment. Prior art ionizers are designed for atmospheric environments since air ions are created from air, nitrogen, or other gases that are near the ionizing mechanism (corona electrodes, nuclear sources, X-rays, ultraviolet light, or equivalent). 
         [0007]    Process equipment and metrology equipment also operate in vacuum or near vacuum. And static charge neutralization remains necessary. The instant invention is directed toward the need for ionizers in vacuum or low pressure equipment. 
         [0008]    Examples of application fields include semiconductor, disk drive, and flat panel display. 
         [0009]    2. Description of Related Art 
         [0010]    Some process and metrology equipment operate in vacuum or close to vacuum. Examples include scanning electron microscopes, ion implanters, and low pressure chemical vapor deposition chambers. 
         [0011]    Getting a wafer, disk, substrates, or panel into the vacuum environment requires a pump down step. Returning the wafer, disk, or panel to atmospheric pressure requires a venting step with a clean gas. 
         [0012]    Both pump down and venting are time consuming, and equipment operators would like to minimize the frequency of pump down and venting cycles. 
         [0013]    One time-saving approach is to combine multiple vacuum process steps into a vacuum cluster, wherein a central vacuum robot moves product among process or metrology stations. After a single pump down, all vacuum process steps are completed. Then the wafers are returned to atmosphere. Product throughput is increased because only one pumping step and one venting step are needed. 
         [0014]    Static charge builds up in vacuum processes as well as in atmospheric processes. And since the wafers remain under vacuum for long periods of time, the wafers are at risk of static charge induced damage. 
         [0015]    A need exists to assure that wafers or products (a) enter the low pressure (or vacuum) environment with low static charge, (b) maintain low static charge, and (c) exit with low static charge. 
         [0016]    Prior art vacuum equipment attempts to remove static charge (1) before products enter the vacuum environment, and (2) after products leave the vacuum environment. Normally, the static neutralizers are positioned in an atmospheric handler that interfaces to the front of the process equipment. Hence, products pass by the ionizer as they travel in and out of the vacuum chamber. 
         [0017]    But the prior art does not offer static charge removal within the vacuum process environment. 
         [0018]    In addition, the prior art does not offer a way to measure the product&#39;s static charge while the product moves within the vacuum environment. Prior art measurement methods are done atmospherically, and the product must be removed from the vacuum environment before measurement. 
         [0019]    Further, prior art practice places ionizers near the ceiling of the atmospheric handler that interfaces to the front of the process or metrology equipment. This placement is useful from the standpoint of achieving low charges at multiple locations within the atmospheric handler. But it is geographically unfocused. It misses the opportunity to provide focused (very fast) discharge times at the product pass-through door, which separates the atmospheric handler from the vacuum equipment. 
         [0020]    Static charge control for vacuum processes could be improved by (a) adding more atmospheric ionizing capability close to the product pass-through door, (b) adding a charge measurement module inside the vacuum environment, (c) adding a low-pressure charge neutralization chamber into the vacuum cluster, (d) providing a way to introduce gas ions into the vacuum cluster itself, and (e) providing a way to introduce gas ions into the load-lock which interfaces with the vacuum cluster. 
         [0021]    A system approach is needed wherein the most productive improvements are combined as needed. 
       BRIEF SUMMARY OF THE INVENTION 
       [0022]    In the following text, four types of ionizers will be recited. They are (1) a manifold ionizer, (2) a neutralizing ionizer, (3) a cluster ionizer, and (4) a load-lock ionizer. All of these four ionizers are a type of in-line gas ionizer. An in-line gas ionizer is defined as an ionizer that receives compressed air or gas at its inlet, ionizes the inlet gas within an enclosed chamber, and delivers ionized gas from the outlet. 
         [0023]    The present invention implements static charge measurements and static charge removal on products within the vacuum environment and within the atmospheric environment. This is accomplished by adding any one, any two, any three, any four, or all of the following five structures to vacuum process or metrology equipment. 
         [0024]    The first structure is an atmospheric manifold, which transports air (or gas) ions from a manifold ionizer into an atmospheric environment. An atmospheric manifold is installed proximal to the product pass-through door and blows ions toward the center of the pass-through door. This atmospheric manifold may be on the atmospheric side of the pass-through door, the vacuum cluster side of the pass-through door, or in-between the atmospheric and cluster sides. Atmospheric manifolds may be configured as loops, but other shapes are acceptable. 
         [0025]    The second structure is a charge measurement module, which attaches to the vacuum cluster with a hermetic seal. It measures the accumulated static charge on the product. This measurement module may utilize the principle of an electrostatic field meter. Electrostatic field measurement is desirable because no contact is required. As the robot moves the product past an electrostatic field meter, charge is quantified. Alternately, charge measurement can be based on a Faraday Cup. A Faraday Cup is desirable due to simplicity. Basically, a Faraday Cup is a first cup within a second cup wherein the two cups are electrically isolated. A Faraday Cup can also measure product charge without making contact. Other measurement principles are applicable, and remain within the scope of this invention. 
         [0026]    Regardless of measurement principle, the wafer or product is moved by a vacuum robot from any vacuum station into the charge measurement module. The wafers remain in vacuum during charge measurement. 
         [0027]    When the product to be measured is conductive or dissipative, the vacuum robot should have non-conductive pickup contact points. Otherwise, the charge could be grounded prior to measurement. 
         [0028]    The third structure is a neutralizing module that attaches to the vacuum cluster with a hermetic seal. The neutralizing module receives gas ions from a neutralizing ionizer while a connected neutralizing pump (a vacuum pump) maintains low pressure. Inside the neutralizing module, a flow of ionized gas neutralizes charge on the wafer or product. An isolation valve between the neutralizing module and the vacuum cluster is closed during neutralization. 
         [0029]    The fourth structure is a cluster ionizer that is inserted into the vacuum cluster vent line, and that is capable of ionizing argon. A cluster ionizer is used to introduce gas ions into the vacuum cluster during venting or during the process itself. In addition to static charge control, reduced preventative maintenance cycles are targeted. 
         [0030]    The fifth structure is a load-lock ionizer that is connected to the load-lock and that is capable of ionizing argon. A load-lock ionizer is used to introduce gas ions into the load-lock during pump down or venting. The load-lock pump (vacuum pump) operates during pump down, and may also operate during a portion of the venting period. In addition to static charge control, reduced preventative maintenance cycles are targeted. 
         [0031]    Objects of this inventions are: 
         [0000]    (1) provide a system approach to control static charge for vacuum equipment, (2) enable rapid charge removal as a product leaves or enters the atmospheric handler through a pass-through door; (3) provide a module to measure charge on a product while that product remains inside the vacuum environment; (4) provide a way to remove charge that accumulates inside the vacuum cluster environment, (5) provide a way to remove charge that accumulates inside the load-lock, (6) reduce particle buildup inside the vacuum cluster, and (7) reduce particle buildup inside the load-lock. 
     
     
       BRIEF SUMMARY OF THE FIGURES 
         [0032]      FIG. 1  is a top-view planar diagram of a vacuum cluster with process or metrology modules attached. The vacuum cluster is interfaced with an atmospheric handler. A charge measurement module is positioned on one side on the vacuum cluster, and a charge measurement meter is connected to the charge measurement module. An atmospheric manifold is positioned inside the wafer handler. 
           [0033]      FIG. 2  is a modification of  FIG. 1 . This figure shows a cluster pump used to pump the vacuum cluster down to vacuum at the beginning of each processing cycle. A cluster vent line is also shown. The cluster vent line is used to return the vacuum cluster to atmospheric pressure at the conclusion of the process cycle. 
           [0034]      FIG. 3  shows a cluster ionizer disposed between a pressurized gas source and the vacuum cluster. 
           [0035]      FIG. 4  is a top-view planar diagram of a vacuum cluster with process or metrology modules attached. The vacuum cluster receives wafers (or products) from an atmospheric handler. A charge measurement module is positioned on one side of the vacuum cluster, and a measurement meter is connected to the charge measurement module. An atmospheric manifold is positioned between the atmospheric handler and the load-lock. 
           [0036]      FIG. 5  shows a vacuum cluster with a neutralizing module connected. The neutralizing module receives gas ions from a neutralizing ionizer. A neutralizing pump maintains a low pressure within the neutralizing module. 
           [0037]      FIG. 6  shows a vacuum cluster with a combined charge measurement and neutralizing module. A measurement meter receives signals that contain charge information. Gas ions are delivered by a neutralizing ionizer. A neutralizing pump maintains a low pressure within the combined module. 
           [0038]      FIG. 7  shows an atmospheric manifold disposed at the wafer (or product) pass-through door. The atmospheric manifold receives gas ions from a manifold ionizer. The atmospheric manifold can be positioned on either side of the pass-through door. 
           [0039]      FIG. 8  shows a load-lock ionizer providing air, nitrogen or argon ions to a load-lock through a load-lock ion delivery line. 
       
    
    
     DETAILED DESCRIPTION 
       [0040]      FIG. 1  shows the basic structural elements of vacuum cluster  27  architecture. Vacuum cluster  27  architecture is applicable when multiple vacuum processing steps are performed sequentially. 
         [0041]    A systems approach to static charge control in a vacuum cluster  27 , based on five inter-related structural elements, is the core of this invention. The five structural elements are:
       (a) an atmospheric manifold  3  connected to a manifold ionizer  7  [see  FIG. 7 ],   (b) a charge measurement module  5  connected to a measurement meter  24  [see  FIG. 1 ],   (c) a neutralizing chamber  14  connected to a neutralizing ionizer  15  [see  FIG. 5 ],   (d) a load-lock  26  connected to a load-lock ionizer  33  [see  FIG. 8 ], and   (e) a vacuum cluster  27  connected to a cluster ionizer  44  [see  FIG. 3 ].       
 
         [0047]    Contributions from any one, any two, any three, any four, or all five structural elements are combined to provide a system which provides the static charge control necessary. Any of the five elements is included, depending on where and how static charge is generated. 
         [0048]    Not all five structural elements are required for every static charge control system. For example, an operator who believes that incoming wafers are uncharged may elect to omit an atmospheric manifold near the pass-through door  21 , and still remain within the scope of this invention. In contrast, an operator who receives a FOUP  2  [front opening universal pod] of wafers  9  (or product) from a spin-rinse-dryer will probably incorporate an atmospheric manifold  3  into his static charge control system. 
         [0049]    In a similar way, if the charge measurement chamber  5  indicates that charge buildup inside the vacuum cluster  27  is sufficiently low to prevent product damage, the neutralizing module  14  may not be used. Charge removal by the atmospheric manifold  3  upon return to atmosphere may suffice. 
         [0050]    In cases where a FOUP of charged wafers is received from a spin-rinse-dryer (or any prior charging step) and charges accumulate inside the vacuum cluster  27 , all five structural elements are appropriately incorporated into the invented system. 
         [0051]    Optional system control software interfaces with the five structural elements, and embeds decision making capability. Additional atmospheric sensors for balance, swing, or discharge time may also be integrated into system control software. 
         [0052]    System control software is particularly useful when one vacuum cluster  27  is utilized for multiple product lines. Input from the charge measurement chamber  5  may automatically activate the neutralizing module  14  for product A and omit a neutralization step for product B. Where a single product is run and historical data show repeatable charging levels, preset values obviate the need for optional system control software. 
         [0053]    Refer to  FIG. 1 . In a typical wafer processing scenario, the atmospheric handler  1  receives wafers  9  (or product) from a FOUP  2 , and passes the wafers  9  through a pass-through door  21  into the load-lock  26  of the vacuum cluster  27 . Process or metrology stations  6  are positioned and sealed onto the vacuum cluster  27  using prior art hermetic sealing technology. Each process or metrology station  6  is isolated from the vacuum cluster  27  during use with a prior art isolation valve. 
         [0054]    Refer to  FIG. 2 . The vacuum cluster  27  is pumped down through cluster evacuation line  40  by the cluster pump  41 . Then all processing steps are performed by the process or metrology stations  6  as the vacuum robot  4  moves the wafers  9  (or product) among process or metrology stations  6 . After processing, the wafers are transferred back into the load-lock  26 , vented to atmospheric pressure, and returned to the atmospheric handler  1 . The vacuum cluster  27  normally remains at vacuum because the pump down time for a vacuum cluster  27  can be long. However, the vacuum cluster  27  can be brought to atmospheric pressure with a cluster gas  43  through cluster vent line  42 . 
         [0055]    An atmospheric manifold  3  can be placed at any of three positions. Sometimes, two or more atmospheric manifolds  3  are used.  FIG. 1 ,  FIG. 2 , and  FIG. 3  show the atmospheric manifold  3  positioned on the atmospheric handler  1  side of the pass-through door  21 . This is the first of the three positions. 
         [0056]      FIG. 4  shows the atmospheric manifold  3  positioned on the vacuum cluster  27  side of the pass-through door  21 . This is the second of the three positions. 
         [0057]    The atmospheric manifold  3  may also be positioned inside an extension zone which connects the pass-through door  21  to the load-lock  26 . This is the third of the three positions. 
         [0058]    Refer to  FIG. 7 . When a wafer  9  (or product) is transported through the pass-through door  21  along wafer path  10 , the atmospheric manifold  3  blows ionized manifold gas through the manifold nozzles  11  toward the wafer  9  (or product). Because the atmospheric manifold  3  is close to the wafer  9  (or product), excess charge is quickly and effectively removed from the wafer  9 . 
         [0059]      FIG. 7  further shows that the atmospheric manifold  3  receives manifold gas ions from a manifold ionizer  7  through a manifold ion line  8 . Compressed manifold gas  22  is transported to the manifold ionizer  7  through the manifold gas delivery line  23 . The manifold ionizer  7  converts a fraction of the manifold gas  22  to manifold gas ions. Manifold gas ions impinge upon both the top and bottom of the wafer  9  as the atmospheric robot  17  moves the wafer  9  through the pass-through door  21 . 
         [0060]    For an atmospheric manifold  3  near the pass-through door  21 , air or nitrogen are appropriate choices for manifold gas  22 . 
         [0061]    A loop-shaped atmospheric manifold  3  which conforms to the shape of the pass-through door  21  is an efficient design. For example, if the pass-through door  21  is rectangular, the atmospheric manifold is substantially rectangular and encircles the pass-through door  21 . Manifold nozzles  11  on the inner perimeter of the loop-shaped atmospheric manifold  3  guide the manifold gas ions inward toward the center of the atmospheric manifold  3 . 
         [0062]    Atmospheric manifold  3  volumes are minimized in an effort to reduce air ion recombination. Also, the manifold ion line  8  between the manifold ionizer  7  and the atmospheric manifold  3  is minimized. 
         [0063]    Open-ended (as opposed to-loop shaped) atmospheric manifolds may also be used to gain shorter discharge times via air entrainment. In this design, ions are transported from a manifold ionizer  7  through multiple tubes. For enhanced performance, an air entrainment port (open to atmosphere) may be positioned on each tube. The exit openings of the tubes are directed toward the center of the pass-through door  21  where the wafer  9  (or product) passes. 
         [0064]    Refer to  FIG. 8 . Load-lock gas  36  is delivered to a load-lock ionizer  33  that converts a fraction of the load-lock gas  36  into load-lock gas ions. The load-lock ionizer  33  operates during transition periods between atmospheric pressure and vacuum. The load-lock ionizer  33  may be located within the load-lock  26 . Alternately, the load-lock ionizer  33  may be located outside of the load-lock  26 . When installed outside, and load-lock gas ions are delivered to the load-lock  26  through a load-lock ion delivery line  34 . The load-lock pump  35  may or may not be operating when gas ions are being delivered. 
         [0065]    Load-lock  26  ionization is useful for two reasons. First, static charges on wafers  9  or products are neutralized. Second, ionization helps clean the load-lock  26  walls during pump down and venting. Wall cleaning is advantageous because it mitigates an established contamination mechanism. 
         [0066]    Consider the case, where wafers  9  from a high-particle-content vacuum process step are returned to the load-lock  26 . Some of the particles are carried from the process by the wafer  9  into the load-lock  26 . The venting step dislodges particles from the wafer  9 , and the dislodged particles are deposited onto the load-lock  26  walls. Here, they are poised to contaminate the next lot of incoming wafers  9  during pump-down. Over time, particles within the load-lock  26  accumulate to problematic levels. The prior art solution is to frequently withdraw the equipment from service and do a preventative maintenance cleaning. 
         [0067]    Installing a load-lock ionizer  33  into the load-lock  26  neutralizes particles which accumulate on the load-lock  26  walls. This is advantageous because neutral particles are easier to remove from a surface than charge particles. A short-duration rough pumping (turbulent) step after activating the load-lock ionizer  33  minimizes particle accumulation and reduces the frequency of preventative maintenance cleaning. Wafers may or may not be inside the load-lock  26  during the short-duration rough pumping, which is accomplished with a load-lock pump  35 . 
         [0068]    When a load-lock ionizer  33  is connected to a load-lock  26 , at least one shut-off valve  20  is recommended. The purpose is to prevent leakage of the compressed load-lock gas into the vacuum environment when the load-lock ionizer  33  is not in use or when high vacuum is sought. 
         [0069]    As wafers  9  move toward processing, they leave the load-lock  26  and enter the vacuum cluster  27 . Then, the vacuum cluster  27  is pumped down to vacuum, and a vacuum robot  4  moves the wafer  9  among process or metrology stations  6 . The process or metrology stations  6  perform a variety of process steps or measurements. 
         [0070]    Refer to  FIG. 2 . After any process step, the accumulated static charge on the wafer  9  can be measured by moving the wafer  9  to the charge measurement module  5 . Signals from the charge measurement module  5  are transmitted to the measurement meter  24  through signal lines  25 . No return to atmospheric condition is needed for the static charge measurement. 
         [0071]    The charge measurement module  5  typically employs the principle of a Faraday Cup or an electrostatic field meter. Both Faraday Cups and electrostatic field measurement principles are within the prior art. But neither Faraday Cups nor electrostatic field sensors have been configured as modules that are hermetically sealed to a vacuum cluster  27 . Other measurement principles are within the scope of this disclosure providing that the charge measurement can be performed in a vacuum environment. 
         [0072]      FIG. 5  shows a neutralizing module  14 . The neutralizing module  14  receives neutralizing gas ions from a neutralizing ionizer  15  through a neutralizing ion delivery line  30 . Pressurized neutralizing gas  32  is supplied to the neutralizing ionizer  15  via a neutralizing gas line  31 , and neutralizing gas ions are produced by the neutralizing ionizer  15 . A charged wafer  9  (or product) is placed into the neutralizing module  14  with the vacuum robot  4 , and an isolation valve is closed. The stream of neutralizing gas ions from the neutralizing ionizer  15  impinge upon the wafer  9 , and are evacuated by the neutralizer pump  13 . A shut-off valve  20  is recommended to avoid neutralizing gas  32  leakage when the neutralizing module  14  is not in use. 
         [0073]    Typically, the internal volume of the neutralizing module  14  is small, the flow of neutralizing gas is minimal, and pressure within the neutralizing module  14  remains low. These conditions are useful to re-establish vacuum quickly after the neutralization operation. The neutralizing module  14  must be returned to vacuum before the valve between the neutralizing module  14  and the vacuum cluster  27  is re-opened. 
         [0074]    Low pressure inside the neutralizing module  14  is obtained by exposing the neutralizing module  14  to a throttled neutralizing pump line  16  while the flow of neutralizing gas ions proceeds. The neutralizing pump line  16  is evacuated by the neutralizer pump  13 . 
         [0075]    An neutralizing ionizer  15  that can ionize argon gas is employed in those processes where argon gas is used for venting. Experiments have shown that commercially available in-line gas ionizers can ionize argon. Performance of the neutralizing ionizer  15  for argon can be augmented by operating at higher voltages. Argon is a common venting choice. 
         [0076]    In  FIG. 6 , the charge measurement module  5  and the neutralizing module  14  are integrated into a combined module  37  that (a) measures static charge and (b) removes static charge. This approach only uses one position on the vacuum cluster  27 , and saves time by allowing two operations at one location. It also permits real-time interaction between the charge measurement module and charge neutralization. 
         [0077]    Note that the wafer  9  or product is not returned to atmospheric pressure for either charge measurement or charge neutralization. 
         [0078]    The instant invention also allows the entire vacuum cluster  27  to be neutralized with cluster gas ions from the cluster ionizer  44  through cluster vent line  42 . Cluster gas  43  (often argon) is plumbed to the inlet of the cluster ionizer  44 . 
         [0079]    Although the vacuum cluster  27  is normally maintained at vacuum, a periodic flush with ionized cluster gas is useful for cleaning. Again, the goal is less frequent preventative maintenance cleanings. 
         [0080]    The cluster ionizer  44  also has process applications. Since argon is also used for sputtering, ionizing the sputtering gas is practical.