Abstract:
A cleaning device for use in the production of semiconductor components comprises two feed devices with which a fluid medium is guided across a respective surface of an object to be cleaned so that different faces of the object are simultaneously cleaned. At least two gas feeding devices, having one means each for directing a gas flow onto the surface of the object to be cleaned, open into a cleaning chamber supplying a pressurized cleaning gas. At least two extraction means are connected to the outside of the cleaning chamber for discharging the gas fed to the cleaning chamber. The object can be introduced into the cleaning chamber through at least one gap. At least two ionization means are used to ionize the gas and the particles that are present in the cleaning chamber. One ionization means each is mounted between a direction means and an extraction means.

Description:
BACKGROUND 
     1. Field 
     The exemplary embodiment described herein relates to a cleaning apparatus and a cleaning method for the production of semiconductor elements, such as electronic chips, memory elements and the like. According to a further aspect, the exemplary embodiments also relate to an apparatus for storing objects from semiconductor production. 
     2. Brief Description of Related Developments 
     Exposure masks (also known as reticles) are used in the fabrication of electronic components, such as for example chips or memory modules, to produce defined structures on substrates of the components by means of photochemical processes. Since these structures include interconnects in the micrometer or even nano range, and even tiny amounts of impurities on the substrate and/or exposure mask leads to scrap, i.e. products which do not satisfy the quality requirements, an extremely high level of cleanness is required. Therefore, components of this type are produced under clean and ultraclean room conditions. To protect the exposure masks from mechanical damage and soiling, they are stored and handled in cassettes or in magazines which are sealed in an airtight manner. 
     Relatively large particles can easily be detected and removed. The problems are caused by smaller particles, for example with dimensions of 10 μm to 20 μm, which it has hitherto only been possible to remove with a very high level of outlay. For this purpose, cleaning methods have been developed in which a liquid was used to wash the semiconductor production means or the corresponding components or their starting products. On the one hand, these cleaning methods entail a relatively high level of structural outlay in terms of the equipment required to carry them out. On the other hand, the washing liquids used have to be reprocessed or replaced by fresh liquids. Furthermore, the fact that the cleaned objects are wet immediately after the process and therefore have to be dried before they can be reused or processed further may be unsatisfactory. 
     However, it has been found that, despite these measures, it is not possible to avoid soiling of the exposure masks to a sufficient extent. Moreover, known cleaning apparatus have the drawback of requiring a relatively large footprint in semiconductor factories. This is disadvantageous in particular because relatively expensive installations for producing clean room conditions have to be installed in the factories, and the costs of these installations rise proportionally to the size of the factory. 
     U.S. Pat. No. 5,967,156 has disclosed a surface treatment apparatus in which different cleaning agents, namely an aerosol and another reagent, are discharged from two nozzles onto a single surface of a substrate, which is disadvantageous in process engineering terms. According to U.S. Pat. No. 5,967,156, the reagent is extracted at a distance from the cleaning point without exploiting any geometry of the suction operation. 
     U.S. Pat. No. 5,857,474 has disclosed an apparatus and a corresponding method for washing a surface of a semiconductor product with frozen water which is supplied from a water supply nozzle and a gas supply for blowing the ice particles formed off the surface of the semiconductor product, which represents a combination of the drawbacks which have been outlined. 
     U.S. Pat. No. 6,055,742 has disclosed a reticle cleaning apparatus, in which a gas supply device is provided in the upper region of a cleaning chamber and a gate device and a conveyor device for supplying the reticles are also provided. Since an apparatus of this type—for design reasons since the reticles are secured in the cleaning chamber—can only be used to clean one side of a reticle, this has the drawback of a large footprint if a second cleaning apparatus is to be provided for the second side. The disclosure of an apparatus which is known from JP-A 03 155 550 and in which a surface of a semiconductor product is inspected by blowing off foreign bodies and then observing the effect does not go any further than the content of disclosure of U.S. Pat. No. 6,055,742. 
     JP-A 04 151 153 has disclosed an apparatus and a corresponding method in which, in a scanning mode, a compressed gas is passed onto a surface of a semiconductor product which is to be checked in order to be able to draw a functional distinction between defects in the semiconductor product and contaminating particles thereon. 
     JP-A 61 087326 has disclosed a method for cleaning X-ray masks in which an oxygen gas which is supplied is converted into atomic oxygen by a plasma, and in this way organic impurities on the surface of the X-ray masks are cleaned off. 
     U.S. Pat. No. 4,677,704 has disclosed a system for cleaning a statically charged surface of a semiconductor wafer in which a gas at which vibrations have been produced is passed onto a surface of a wafer, the static charging being kept to a minimum. 
     JP-A 55 134 851 has disclosed a mask-cleaning apparatus in which a gas which is mixed with ozone is blown at right angles onto a surface of a drying plate, which is held in a drying-plate holder, in order in this way to blow dust off the plate, the dirt-containing gas then being extracted through outlets in the cleaning apparatus. 
     JP-A 06 168 864 has disclosed a cleaning apparatus in which nitrogen is blown onto a surface of a reticle with the aid of a gas spray, dust being removed from the surface and at the same time being discharged by the nitrogen gas. 
     U.S. Pat. No. 4,715,392 has disclosed a washing and cleaning device for semiconductor products in which foreign particles are washed off that surface of the semiconductor product which is to be cleaned using a cleaning liquid, after which the semiconductor product is fed to an inspection device for foreign particles and then, if necessary, is returned to the washing and cleaning device. 
     SUMMARY OF THE EXEMPLARY EMBODIMENTS 
     This is where the exemplary embodiments intervene, being based on the object of providing measures with which the levels of scrap caused by impurities in the fabrication of semiconductor components can be reduced with the minimum possible outlay. One aspect of the exemplary embodiments is to take up the minimum possible footprint, and it is to be possible for the cleaning to be performed efficiently. 
     Therefore, the exemplary embodiments propose a cleaning apparatus for semiconductor component production, which is provided with two feed devices, each of which can be used to guide fluid medium over in each case once surface of an object which is to be cleaned, in particular of a semiconductor production means, so that different sides of the object can be cleaned simultaneously, at least two gas feed devices for introducing a cleaning gas which is under super atmospheric pressure opening out into a cleaning chamber, the gas feed devices each having a means for directing a gas stream onto a surface of the object which is to be cleaned, at least two suction means, by means of which gas which has been introduced into the cleaning chamber can be discharged, leading out of the cleaning chamber, and a support being present for holding the object in the cleaning chamber, in which apparatus the object can be introduced into the cleaning chamber through at least one gap in the cleaning chamber, and gas and particles located in the cleaning chamber can be ionized using at least two ionization means, in each case one ionization means being located between in each case one directing means and one suction device. 
     The first consequence of the measures of the exemplary embodiments is that an object, for example a flat object, used in semiconductor production can simultaneously be cleaned from two sides using a dry fluid or example a gas, so that space and resources are saved. 
     The object is also achieved by a method in which the object which is to be cleaned is introduced into a cleaning chamber of this type, a gaseous medium is passed onto a surface of the object to be cleaned, for example at an angle of less than 90°, and gaseous medium which is deflected by the surface of the object is extracted. 
     According to the exemplary embodiments, unlike in previously known cleaning apparatus and methods from semiconductor production, cleaning is carried out using a gaseous—and therefore dry—fluid. Surprisingly, it has been found that gases can also be used to remove soiling particles with a high level of reliability. With the cleaning apparatus according to the exemplary embodiments it is possible to clean semiconductor production means, in particular reticles. Of course, it is also possible, however, to use the apparatus to clean semiconductor products or intermediate products, such as wafers. 
     In this context, a detection device for detecting soiling which has been deposited on the objects which are to be cleaned is accommodated in the same housing as the cleaning apparatus. The overall footprint required for the two functional units can be reduced in size, since they can use common components, such as a device for preparing clean air, a joint electrical power supply unit and computer unit for controlling the functional units, a handling device, etc. The footprint required becomes particularly small if individual functional units of the apparatus are arranged substantially above one another. 
     According to a further aspect of the exemplary embodiments, a cleaning apparatus which can be used to clean the objects is integrated in a stocker (storage device) for objects from semiconductor production, in particular reticles. With a combined cleaning and storage apparatus of this type, it is possible to reduce the size of the footprint required, since in this case two individual functional units are integrated in a common housing. Secondly, it is also possible for these functional units to use common components. Examples of these are once again a facility for generating clean room conditions within the housing, a joint handling device, by means of which the semiconductor production means are fed to the individual functional units and removed from them, or a joint control computer. The control computer is advantageously responsible for both control and management functions which relate to the individual functional units themselves and control functions of coordinating sequences between the functional units. The control computer is intended in particular to be responsible for managing the objects which have been temporarily stored in the storage device and to store information about these objects. 
     On account of the advantages of the cleaning apparatus according to the exemplary embodiments described above, it is expedient for an apparatus of this type also to be provided in a combined cleaning and storage apparatus according to the exemplary embodiments. 
     In a refinement of the storage device according to the exemplary embodiments, a detection device may additionally be integrated in the housing and can be used to detect soiling which is present on a surface of a semiconductor production means. By way of example, a detection device which is marketed by the applicant under the name “Particle Detection System (PDS)”—and is therefore already known—can be used to check reticles. As the light-emitting element, this device has a laser. The two laser beams which it produces are guided substantially in parallel over the top side (glass side) and underside (pellicle side) of the reticles. If there are dirt particles on one of the sides, the laser beam is diverted at this point. The top side and underside of the reticle are guided past in each case one camera, at a distance therefrom, and the camera is used to measure deflected light. The size and position of individual particles can be determined on the basis of the intensity of the diverted light. 
     Further configurations of the exemplary embodiments will emerge from the dependent claims, the drawing and the associated description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained in more detail on the basis of the exemplary embodiments illustrated diagrammatically in the figures, in which: 
         FIG. 1  shows a side view of a storage apparatus according to the invention in which a plurality of functional units are integrated in one housing; 
         FIG. 2  shows an SMIF container with reticles arranged therein; 
         FIG. 3  shows a highly diagrammatic illustration of a detection device; 
         FIG. 4  shows an exemplary embodiment of a cleaning apparatus according to the invention; 
         FIG. 5  shows a gripper of a handling device of the apparatus according to the invention; 
         FIG. 6  shows the storage apparatus from  FIG. 1 , in a simplified illustration of a further side view. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a cleaning and storage apparatus  1  for reticles in accordance with an exemplary embodiment, which has a housing  2  which is substantially rectangular in cross section and which closes off the apparatus  1  on all sides. A plurality of functional units are accommodated in the housing  2  and carry out various functions in connection with the reticles. These include an introduction/discharge device  3 , a handling device  4 , a cleaning device  5  and a detection device  6 . 
     On one side of the housing  2 , the introduction/discharge device  3  has firstly what is known as an SMIF station  7 , by means of which transport containers (not shown), which are known per se, can be opened and reticles arranged therein can be removed. The term SMIF is an abbreviation of “Standard Mechanical Interface” and denotes the standardized transport containers which are customary in the semiconductor sector.  FIG. 2  shows a purely diagrammatic view of a container  8  of this type, in which the reticles  9  are arranged in compartments  10  of a magazine  11  of the container  8 . The magazine  11  stands on a baseplate  12  of the container, which can be closed off in an airtight manner by a container hood  13 , so that in this state the reticles  9  are not exposed to the atmosphere. 
     The SMIF station  7  shown in  FIG. 1  can in principle be of the same design as the same applicant&#39;s station which is described in European patent application EP 0 875 921, in the name of the same applicant. Therefore, the content of disclosure of European patent application EP 0 875 921 is incorporated in its entirety by reference in terms of the design structure of the station described therein. Although the SMIF station described in the abovementioned European patent application is an apparatus for handling SMIF containers for wafers, only slight adaptations are necessary in order to handle cassettes for reticles instead of wafers. 
     The SMIF station  7  is surrounded by part  2 ′ of the housing  2  which is close to the base. On a top side of the housing part  2 ′ there is a stationary frame  16 , in which there is a receiving plate  18  which can be displaced vertically downward from a position at the level of the frame  16  by means of a lift device  17  and vice versa. The frame is provided with means (not shown) for fixing the baseplate  12  of the SMIF container  8 . Moreover, the hood  13  can be detached from the baseplate  12  by means of a mechanism arranged in the receiving plate  18 , and the two elements can be secured to the frame  16  and the receiving plate  18 , respectively. In this way, the magazine  11  of an SMIF container  8  which is standing on the baseplate  12  can be automatically removed therefrom as a result of the receiving plate  18  being displaced vertically downward. The reticles  9  arranged in the magazine  11  are in this way introduced into the housing  2  of the apparatus toward a loading and unloading position. In the process, the magazine  11  is guided past a scanning device  19 , for example a CCD camera and/or a light barrier sensor, which determined in which compartment a reticle  9  is arranged. If appropriate, the scanning device  19  can also be used to read an identification means, for example a bar code, arranged on each reticle. 
     On the same side of the housing  2  as the SMIF station  7  and above the latter, there is, as a further component of the introduction/discharge device  3 , a cassette station  20 , by means of which individual reticles arranged in commercially available cassettes (not shown) can be moved into and out of the housing  2  via a lock. Numerous cassette stations of this type are known per se. 
     With respect to a vertical direction, the detection device  6 , which is provided with its own housing and the basic structure of which is illustrated in more detail in  FIG. 3 , is present between the SMIF station and the cassette station  20  above a central electrical power supply unit  21  of the apparatus according to an exemplary embodiment. A reticle  9  is arranged between two arms  22 ,  23  of a support, on a carriage which is not shown-in more detail and can be displaced in a horizontal X-Y plane. The glass side  26  of the reticle faces upward, and the pellicle side  27  of the reticle faces downward. A high-resolution CCD line-scan camera  28 ,  29  is arranged on each arm  22 ,  23 . 
     Moreover, the reticle  9  is located in the beam path of two laser beams  30 ,  31 , which are directed in such a way that one laser beam impinges on the glass side  26  and the other laser beam impinges on the pellicle side  27  of the reticle  9 . Both laser beams  30 ,  31  run with only a slight angle of inclination, and therefore virtually parallel, to and directly above the associated surfaces. Therefore, dirt particles  32 ,  33  on the surfaces  26 ,  27  are located in the beam path of the laser beams and deflect the laser beams  30 ,  31 . The corresponding CCD camera  28 ,  29  detects the deflected light  36  and—should this be of interest—can determine the size of the dirt particles  32 ,  33  and their position on the reticle  9  as a function of the measured light. 
       FIG. 1  shows that the cleaning device  5  is arranged above the detection device  6  and is likewise provided with its own housing. The cleaning device  5  has a connection  38 , which leads from the outside through the housing  2  of the apparatus  1 , for gas which is under super atmospheric pressure, for example pure nitrogen, from a gas feed device  39 . The connection leads into two feed pipes  40 ,  41  which are connected to a cleaning chamber  42 . Moreover, the cleaning chamber  42  can be connected to a suction means in a manner which is not illustrated in more detail. Moreover, the cleaning device  5  is provided with a carriage  43  which can be displaced along an X-axis (i.e. horizontally in the plane of the drawing shown in  FIG. 1 ). The carriage has, as support for reticles, a gripper  47 , by means of which a horizontally oriented reticle  9  can be gripped at one of its ends. 
     As can be seen from  FIG. 4 , the cleaning chamber  42  of the cleaning device  5  is formed symmetrically with respect to a substantially horizontally running X-Y plane, in which the reticle also moves in the directions indicated by the double arrow  48 . The cleaning chamber  42  is therefore composed of two mirror-symmetrically identical upper and lower halves  42   a ,  42   b , which each have an approximately concavely curved chamber wall  49 . In the region of an end of each chamber wall  49 , a gas feed has a feed outlet or nozzle  50  of the gas feed device  39  that opens out into the cleaning chamber  42 . Next to each nozzle  50  there is an ionization means  51 , the electrodes  52  of which project into the chamber. The electrodes  52  are occupied by titanium emitters which extend over the entire width of the chamber and emit positive and negative ions into the chamber. The ions are generated by a generator which is not shown in more detail and is connected to the electrodes  52 . 
     At the other end of the chamber  42 , a suction device  53  is arranged in each of the two chamber halves  42   a ,  42   b  and is connected, in a manner which is not illustrated in more detail, to the suction means for generating a subatmospheric pressure. Between the two chamber halves  42   a ,  42   b , there is a gap  56  at both the front and rear ends of the chamber, through which a reticle  9  can be passed through the chamber  42 . Both a width of the chamber  42  (dimension orthogonally to the plane of the drawing in  FIG. 4 ) and a height of the gap  56  (vertical direction in  FIG. 4 , i.e. parallel to the thickness of the reticle  9 ) are only insignificantly larger than a reticle  9  itself. A diffuser  57  of each suction device  53  is located at the narrowest point of the gap  56 , i.e. the location at which the gap  56  is at the shortest distance from the reticle. By way of example, a height of the gap could amount to at most the thickness of the reticle  9  plus at most 22 mm, preferably plus at most 0.5 mm to 1 mm. 
     With the aid of the carriage  43  and its gripper  47  ( FIG. 1 ), the reticle  9  in question can be guided through the chamber  42 , so that the gas streams  58  emerging from the nozzles  50  can be directed onto any point on the top side and underside of the reticle ( FIG. 4 ). The gas streams  58  can each impinge on the corresponding reticle surface at an angle of incidence of approximately 30° to 60°, preferably of approx. 45°. The two gas streams  58  are reflected by the top side or underside of the reticle at a reflection angle which substantially corresponds to the angle of incidence. In this context, it is preferable if a flow component of the emerging gas which is parallel to the reticle  9  is directed oppositely to the direction of movement of the reticle  9  in the chamber  42  during the cleaning process. Soiling, in particular particles, which has been deposited on the top side or underside of the surfaces is detached and entrained by the corresponding gas stream  58 . 
     To prevent the particles in the gas stream  58  or the cleaning chamber from being statically charged and deposited on the reticle  9  or the cleaning device, the ionization means performs an active ionization. This is to be understood as meaning that statically charged particles are neutralized by the generation of positive and negative ions. 
     The gas streams  58  then move in an approximately wavy form toward the diffusers  57  of the suction device and the gap  56 . Both the kinetic energy of the gas streams  58  and the subatmospheric pressure generated by the suction devices contribute to this movement. The gas is then sucked out of the chamber through the diffusers  57 . 
     A further functional unit of the apparatus according to the invention which is shown in  FIG. 1  may be a storage device for a multiplicity of reticles  9 . A storage device of this type may include compartments, which are arranged in rows and columns, for receiving and temporarily storing reticles. The receptacles may substantially be slots into which the reticles are pushed. In the illustration shown in  FIG. 1 , the receptacles may be located in front of and behind the Z axis. 
     As can be seen from  FIG. 1 , the handling device  4  of the apparatus  1  is arranged between the SMIF station  7  and the cassette station  20 , on the one hand, and detection device  6  and the cleaning device  5 , on the other hand. The handling device  4  has a vertically oriented linear Z axis  62 , on which a carriage  63 , which can be displaced in the Z direction and is only indicated in  FIG. 1 , is arranged. The carriage is illustrated in more detail in  FIGS. 5 and 6 . It can be used to transfer reticles to transfer locations  65  which are in each case installed in a fixed position in front of the individual functional units and to pick them up from the transfer locations  65 . 
     The carriage  63  is illustrated in more detail in  FIG. 5 . It has a support arm  66 , on which a pneumatically driven gripper  67  for handling individual reticles  9  is arranged. Moreover, the support arm  66  can be pivoted through at least 180° about the Z axis, so that the gripper  67  can transfer or remove reticles to or from all the functional units of the apparatus according to the invention. Moreover, the support arm  66  can be displaced in the X direction along its longitudinal axis. For this purpose, it is mounted on a guide shaft  68  by means of ball sleeves and is driven to carry out this movement by a pneumatic cylinder  69 . The gripper  67  can therefore be arranged at different distances from the Z axis. The gripper  67  has in each case two pairs of clamping fingers  70 , between which in each case one reticle  9  can be gripped by side faces. Therefore, the handling device  4  is used to convey the reticles between the individual functional units and to transfer them to these units. 
     Finally, as shown in  FIG. 1 , a device  71  for providing the clean air, which flows from the top downward in the housing, and for generating the direction of flow of the clean air is provided above the Z axis  62 . The air can emerge through slots (not shown) which are present in the base of the housing  2 . Numerous devices  71  of this type are known per se and are used primarily to discharge any particles which are present in the housing  2  before they can be deposited. 
     The individual functional units of the apparatus according to an exemplary embodiment are controlled and coordinated by a central computer unit (not shown in the drawing). By way of example, a functional sequence of the apparatus can begin by a reticle being removed from its cassette in the cassette station  20 , the bar code of the reticle  9  being read and this information identifying the reticle being stored in a memory of the computer unit. Then, the reticle  9  is picked up at the cassette station  20  by the gripper  67 , transferred to the detection device  6  and given over to the latter. In the detection device  6 , the reticle is inspected for soiling. The number, size and location of the particles on the glass side and the pellicle side are measured, and the measured values are stored in the memory as further information relating to the corresponding reticle  9 . 
     If the examination shows that cleaning is necessary, the gripper  67  moves the reticle  9  from the detection device  6  to the cleaning device  5 , in which the reticle is cleaned in the manner described above. Before the reticle is then either placed back into a cassette in the cassette station or placed into a compartment of the storage device, it may optionally be moved back to the detection device  6 . The effect of cleaning can be monitored or checked by examining the reticle again after the cleaning operation. Alternating cleaning and checking of the reticle can be repeated automatically until there is no longer any soiling larger than a defined particle size. It is also possible for the reticle to be cleaned before a first inspection and only then for an inspection to be carried out in the detection device. If the reticle satisfies the predefined cleanness requirements and is to be placed into the storage device for temporary storage, the gripper  67  moves it to in front of a receptacle which has been predetermined by the computer unit and the reticle is placed into this receptacle. As soon as this operation has ended, information identifying the corresponding receptacle is also added to the stored information about the reticle in question, so that the reticle can easily be found again. If the reticle is to be taken out at a later time, the corresponding reticle can be requested via an input device (not shown), whereupon the gripper  67  moves to the corresponding receptacle, removes the reticle, takes it to the introduction/discharge device and transfers it to this device, after which the reticle is discharged. In the process, the reticle once again moves past one of the scanning devices, which read the bar code of the reticle and record this reticle in the computer unit as having been discharged. 
     With regard to the arrangement of the individual functional units in the apparatus according to the exemplary embodiments, it will be obvious that numerous variations are possible. It is also possible for some of the functional units shown in  FIG. 1  to be omitted if their functions are not required. For example, it is also possible for the apparatus to have only one or two transfer stations (SMIF station  7  and/or cassette station  20 ) of an introduction/discharge device and a detection device  6  in the housing. It is optionally also possible for a storage device to be present in this housing. In this case, the reticles can be cleaned outside the housing in a separate cleaning device. 
     In a refinement of the latter exemplary embodiment, a cleaning device may additionally be added to the introduction/discharge station and the detection device. Apart from the storage device, this exemplary embodiment may correspond to the apparatus illustrated in  FIG. 1 . Finally, it may also be advantageous if, in the apparatus according to the exemplary embodiment, all the functional units are arranged at substantially the same height. For this purpose, the apparatus may, for example, be circular in cross section and the functional units, apart form the handling device, may be distributed substantially uniformly over the circumference of the cross section. The handling device may be arranged in the center, so that it has access to all the functional units. In another exemplary embodiment, the cross section may be rectangular and the functional units may be distributed uniformly over the two longitudinal sides.