Abstract:
A method and an apparatus for verifying or testing test substrates, i.e. wafers and other electronic semiconductor components, in a prober under defined thermal conditions. Such a verifying apparatus, known to the person skilled in the art as a prober, has a housing having at least two housing sections, in one housing section of which, designated hereinafter as test chamber, the test substrate to be verified is held by a chuck and is set to a defined temperature, and in the other housing section of which, designated hereinafter as probe chamber, probes are held. For verification purposes, the test substrate and the probes are positioned relative to one another by means of at least one positioning device and the probes subsequently make contact with the test substrate.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a U.S. National Stage application of International Patent Application No. PCT/EP2009/059962, filed Jul. 31, 2009, which claims priority to German Patent Application No. DE 10 2008 047 337.5, filed Sep. 15, 2008, and is incorporated by reference herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The invention relates to a method and an apparatus for verifying or testing test substrates, i.e. wafers and other electronic semiconductor components, in a prober under defined thermal conditions. Such a verifying apparatus, known to the person skilled in the art as a prober, has a housing having at least two housing sections, in one housing section of which, designated hereinafter as test chamber, the test substrate to be verified is held by a chuck and is set to a defined temperature, and in the other housing section of which, designated hereinafter as probe chamber, probes are held. For verification purposes, the test substrate and the probes are positioned relative to one another by means of at least one positioning device and the probes subsequently make contact with the test substrate. 
         [0003]    For particular test tasks, in particular for the measurement of very small currents, it is necessary to prevent interfering influences on the measuring arrangement which can corrupt the measurement results. Such an arrangement has for such tests a shielding system that can be used to minimize the electromagnetic influencing (EMI) of the measurement of the test substrates. A prober with electromagnetic shielding is known from DE 298 20 106 U1, which describes that an assembly for receiving the test substrates including the positioning unit thereof and also an assembly for receiving and positioning probes are shielded with a housing from the external electromagnetic influences. The cables to the control and evaluation units constitute the interfaces toward the outside. An optical and an electromagnetic shielding of the measuring equipment are thus obtained. A shielding with respect to low-frequency magnetic fields also proves to be particularly problematic. Such a low-frequency shielding can be obtained by means of thick-walled housings composed of ferromagnetic materials. However, accesses to such walls cannot be realized without significantly weakening the shield. 
         [0004]    The problem of such housings is, however, the accessibility to individual components, in particular to the positioning units of the probes and/or the mount of the test substrate, generally designated as chuck. In U.S. Pat. No. 6,492,822 B2, therefore, parts of both positioning units are lead through the housing wall toward the outside, such that the manipulation thereof is possible from the outside without opening the housing. Such housing entrances prove to be disadvantageous, however, since they constitute an interruption of the shield. 
         [0005]    DE 10 2007 053 862 A1 discloses a prober, the housing of which is subdivided in such a way that both the chuck with its chuck positioning unit and the probe mounts with the positioning units thereof are integrated in the shielding housing. The integration of such or comparable apparatuses and the cables thereof into the electromagnetic shielding system is effected in such a way that mutual influencing of the apparatuses and of the test substrate can be minimized even within the system. Despite the complex and variable shielding system, the individual components to be operated during a measurement cycle, such as e.g. the positioning unit of the chuck and also, if appropriate, of the probes, are accessible and observation of the test substrate during the measurement is possible. By way of example, the probe mounts are accessible by individual housing sections being open, while the housing section that directly surrounds the test substrate remains closed. 
         [0006]    The configuration of the housing with a plurality of housing sections to be opened individually and the thus possible good accessibility of individual components of the prober with minimized interruption of the shield also allows the inclusion of an apparatus for signal conditioning, e.g. for signal preprocessing or for signal processing, into the electromagnetic shielding of the housing. Therefore, e.g. such cables which act as an antenna outside the housing and can corrupt the measurement can also be integrated into the shield of the housing. The prober proposed in DE 10 2007 053 862 A1 also encompasses the possibility of configuring the shielding system for shielding against low-frequency magnetic fields. Such shielding is obtained by means of housings or housing sections composed of thick-walled, ferromagnetic materials. 
         [0007]    In the prober, a test substrate is arranged on the chuck and moved by means of the positioning unit of the chuck, generally also designated as chuck drive, in the working region, such that it is positioned relative to the probes of the prober. The test substrate is generally positioned in the horizontal, i.e. X Y, plane by means of a compound table and also by means of an apparatus for angular orientation and by means of a vertical, i.e. Z, advancing drive, which enables e.g. a feed movement of the test substrate in the direction of the probes arranged above the test substrate. By means of the positioning units of the probes, also designated as probe heads, a plurality of probes can be moved relative to one another or to a preferred direction of the test substrate in the X, Y and Z directions or in a feed movement to the test substrate. In alternative configurations, the probes are fixedly mounted. 
         [0008]    For verification purposes, the probes, having the form of contact-making needles, make contact with the test substrate and verification signals are applied to or tapped off from said test substrate. The probes including the probe heads are generally situated outside the working region on a plate which upwardly delimits the working region and which often also serves for the mounting of the probes and in this case is designated as a probe mounting plate. The tips of the probes make contact with the test substrate through an opening in the plate, in which case, in order to optimize the electromagnetic shielding, the opening itself is made as small as possible or is supplemented by an electromagnetic shield, which is arranged above the test substrate and below the plate and has the necessarily small opening for the probes to reach through. 
         [0009]    In probers, electronic components are verified with regard to their functional reliability preferably under the ambient conditions which correspond to the use conditions of the respective component, wherein the setting of the test substrate to defined temperatures usually in the range up to a few hundred degrees Celsius constitutes a main emphasis. The temperature of the test substrate is set by means of the chuck, which can be heated or cooled by means of suitable apparatuses. 
         [0010]    It has been found however, that, via the plate that upwardly delimits the working region, and in particular via the opening therein and likewise via the contact of the probes with the test substrate, a heat exchange takes place between the working space and the overlying housing section, in which the probe mounts, the probe heads and also, if appropriate, the apparatus for signal conditioning are arranged and which shall be designated hereinafter as probe chamber. 
         [0011]    Particularly in the case of relatively large temperature differences with respect to the ambient temperature, e.g. in the case of measurement temperatures of a few hundred degrees Celsius, all components and apparatuses arranged in the probe chamber are heated to such a temperature, which prevent, or at least make more difficult, exact positioning of the probes or maintenance of the position thereof over a relatively long verification period. This is because heating or cooling of the probe heads and also of the probes leads to drift phenomena on account of thermal expansion in the course of the measurement, these effects being intensified with the length of the verification tips. If the apparatuses for signal conditioning are arranged in a probe chamber, their electrical parameters are also altered and the measurement is corrupted. Furthermore, the housing of a probe chamber can also heat up to such a great extent that combustion can occur upon contact with the housing. 
         [0012]    In order to overcome these problems, a prober is specified in which, in a housing section which lies outside the working region and encompasses at least one probe and the probe mount thereof, a temperature that is independent of the temperature of the test substrate is set by means of a temperature-regulated gas flow that flows through this housing section. The independent temperature setting of test substrate and probes makes it possible, in a manner dependent e.g. on the test temperature, on the thermal properties of the probes and/or on the type of test, to set the probes to such a temperature which either minimally influences the test substrate, maintains the positioning of the probes even for long-term tests, and/or to ensure the constant function of sensitive further components of the prober which are connected to the probes. Thus, e.g. even at very high or low test temperatures, the probes and the surroundings thereof such as e.g. signal conditioning apparatuses in the probe chamber can be set to the ambient temperature of the prober. It is nevertheless possible to maintain the temperature of the test substrate by means of suitable further measures described below. 
         [0013]    The invention will be explained in greater detail below on the basis of an exemplary embodiment. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL DRAWINGS 
         [0014]      FIG. 1  shows a prober with a housing in a frontal sectional illustration, wherein the housing is subdivided into two housing sections by a sample mounting plate, 
           [0015]      FIG. 2  shows a further configuration of housing sections arranged above a probe mounting plate in sectional illustration and 
           [0016]      FIG. 3  shows a detail illustration of a gas outlet in the housing wall. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0017]    An embodiment of a prober as illustrated in  FIG. 1  has a housing having two housing sections. A chuck  5  is arranged in the lower of the two housing sections, a test substrate  7  being placed and held on said chuck. Chuck  5  is generally understood to be a particular holding apparatus for test substrates  7  which is adapted to their particular mechanical, electrical and geometrical requirements and realizes suitable holding mechanisms in accordance with the test substrate  7  and the verification. A chuck  5  regularly comprises a chuck positioning unit  6 , by means of which the chuck  5  can be moved in the X, Y and Z directions and can be rotated about the Z axis in a certain angular range. The chuck  5  including its chuck positioning unit  6  is mounted on a baseplate  1  of the prober and surrounded laterally by a lower housing wall  10 . By means of a coolable or heatable chuck  5 , the test substrate  7  is set to the test temperature and held during the entire test duration. 
         [0018]    Arranged opposite the chuck  5  and at the same time the test substrate  7  is a probe mounting plate  4 , which upwardly terminates the lower housing wall  10  and thus forms the lower housing section. This lower housing section encloses the chuck  5 , the chuck positioning unit  6  and the test substrate  7  and shall therefore be designated hereinafter as test chamber  2 , for the sake of better differentiation. The lower housing wall  10 , the baseplate  1  and the probe mounting plate  4  consist of an electrically conductive material and realize, if appropriate in a manner supplemented by a specific construction of the chuck  5 , the electromagnetic shielding of the test substrate  7 . 
         [0019]    The upper housing section extends above the probe mounting plate  4 , the wall of said upper housing section, for the electromagnetic shielding of the components arranged therein, likewise consisting of electrically conductive material. Consequently, the probe mounting plate  4  subdivides the housing of the prober into a lower housing section and an upper housing section, wherein both housing sections realize electromagnetic shielding with respect to the surroundings and with respect to the other housing section in each case. The individual housing parts and the probe mounting plate are electrically connected to one another via their surface contacts, such that closed shielding is obtained. In a further configuration, the housing does not serve for electromagnetic shielding, but rather only for enclosing the test arrangement, e.g. for setting test conditions that deviate from the ambient conditions. 
         [0020]    A central opening  26  is arranged in the probe mounting plate  4 , through which opening the probes  23  mounted on the probe mounting plate  4  by means of probe heads  21  make electrical contact with the test substrate  7 . Probe heads  21  are generally understood to be mounts which hold the probes  23  either individually or in a manner arranged on so-called probe cards in their defined position with respect to the probe mounting plate  4  and with respect to the further probes  23  and realize the electrical connection to the probes  23 . 
         [0021]    The central opening  26  in the probe mounting plate  4  constitutes an opening in the shielding of the test chamber  2  toward the top and also of the upper housing section toward the bottom. In the embodiment illustrated, this opening is virtually completely closed by a shield  9 , which extends between the probe mounting plate  4  and the test substrate  7  and has an opening only in the region where the probe tips  25  directly make contact with the test substrate  5 . Since the shield  9  supplements the shielding of the two housing sections that adjoin one another here, the shield  9  also consists of an electrically conductive material and is mounted on the probe mounting plate  4  by means of spacers  14 . 
         [0022]    This configuration is only one of many possible configurations. In one alternative configuration, the shielding of the two housing sections with respect to one another can be realized without a shield  9 , by means of a suitable configuration of the probe mounting plate  4  or by means of a very extensive closure of the central opening  26 . In another configuration, the separation of the test chamber  2  from one or more upper housing sections can be effected, instead of by means of the probe mounting plate  4 , by means of a further housing wall, e.g. if the probes  23  are held and arranged in some other way. 
         [0023]    The shielding between the two housing sections simultaneously also realizes the very extensive spatial separation thereof. In other configurations, the spatial separation, which, in accordance with the description below, reduces the influence of the temperature-regulated gas flowing through the probe chamber  3  on the test substrate, can also be effected by other suitable measures. 
         [0024]    In the embodiment illustrated in  FIG. 1 , the probe chamber  3  is subdivided into two partial sections by an observation region  40  by virtue of the observation region  40  extending centrally and over the entire depth (viewed perpendicularly to the plane of the drawing) of the upper housing section and is lowered relative to the upper housing wall  30  to close to the probe mounting plate  4 . The lowered observation region  40  is delimited toward the probe mounting plate  4  by the lowered part of the upper housing wall  30 , which runs approximately parallel to and at such a distance from the probe mounting plate  4  that the probes  23  can extend in this distance without touching the probe mounting plate  4  or said lowered part. The objective of a microscope  43  projects into this central section, such that the production of the contact between probe tips  25  and test substrate  7  and the maintenance thereof during the test can be observed by means of the microscope  43 . This central region is a constituent part of the probe chamber  3 , but shall be designated hereinafter as objective chamber  41  for the sake of better differentiation. 
         [0025]    Both partial sections of the probe chamber  3  each comprise a group of probe heads  21 . Each probe head  21  receives a probe  23  and comprises a probe positioning unit  22 , micrometer screw gauges in the present case, by means of which each probe  23  can be finely positioned individually in X, Y and Z directions. In alternative configurations of the prober, instead of the micrometer screw gauges, other, including electrically driven means for positioning the probes  23  can be arranged or the probes  23  are themselves not movable, such that contact is made with the test substrate  7  by the probes  23  by means of a feed movement performed by the chuck positioning unit  6  or by a movement of the entire probe mounting plate  4 . 
         [0026]    Directly alongside each group of probe heads  26  and thus within the probe chamber  3 , an apparatus for signal conditioning  28  is in each case arranged on the probe mounting plate  4 , such as e.g. a signal processing unit. Each apparatus for signal conditioning  28  is connected via a connector  29  to measuring arrangements or evaluation devices that are arranged outside the housing and not illustrated in more specific detail. 
         [0027]    In order to produce a gas flow, the probe chamber  3  has, in each of its sections, gas inlets  12  distributed in the upper region and gas outlets  13  distributed in the lower region. Openings in the upper housing wall  30  and also a non-gas-tight connection of the upper housing wall  30  to the probe mounting plate  4  are possible as gas outlets  13 , depending on the gas volumetric flow rate required for the temperature regulation of the probe chambers  3 . 
         [0028]    In one configuration, a gas flow  11  through the probe chamber  3  is already produced by the position and the distribution of the gas inlets  12  and gas outlets  13  on account of the thermal conditions. In another configuration, the flow direction can be supported by an extraction by suction at the gas outlets  13 , such that the gas flow  11  does not penetrate into the test chamber  2  or a negligible proportion of said gas flow penetrates into said test chamber. Other suitable measures are also possible for this purpose, e.g. the production of a counterflow from the test chamber  2  into the probe chamber  3  or the minimization of passages between the two chambers, as described above. 
         [0029]    The gas flow  11 , before it is introduced into the probe chamber  3 , is set to the required temperature, in which case both a heating of the gas and a cooling, e.g. by means of a Peltier cooler, can be effected. If the verification in the prober takes place at high temperatures, a cooling of the probes can also already be effected with a gas flow  11  at room temperature. For the gas flow  11  it is possible to use air, which can be dried, in order to avoid condensate in the probe chamber  3  or, if appropriate, on the test substrate  7  or the test chamber. Flushing with nitrogen can also be used, e.g. in order to prevent oxidation processes or in order to utilize the favorable heat transfer properties of nitrogen. Other gases can likewise be used taking account of the test conditions and the construction of the prober. 
         [0030]    The gas flow  11  running through the probe chamber  3  from top to bottom in the embodiment according to  FIG. 1  flows around and regulates the temperature of the probe heads  21  and also the apparatuses for signal conditioning  28 . In this way, it is possible, for example, even at relatively high test temperatures of a few hundred degrees, to set the temperature of electronic components arranged in the probe chamber virtually to room temperature or to 25° C.±5 degrees, at which the functional parameters of said components are ensured. 
         [0031]    On account of the gas inlets  12  distributed over the entire width of the probe chamber  3 , there is a flow through the entire probe chamber  3  and the temperature thereof is regulated before the gas emerges from the probe chamber  3  through the lower gas outlets  13 . In this case, that proportion of the gas flow  11  which flows through the central part of the probe chamber  3 , which part serves as the objective chamber  41  and has a smaller height in the exemplary embodiment, brings about the temperature regulation of the probe arms  24 . The latter are relatively long in the exemplary embodiment, such that a temperature drift, on account of the associated change in thermal expansion, would have a distinct effect in a drift of the position of the probe tips  25  on the test substrate  7 . Such a drift can be avoided by the temperature regulation of the probes  23  by means of the gas flow  11  since the temperature regulation supports the maintenance of a thermal equilibrium—set before the measurement—in the entire system. This equilibrium temperature can be determined computationally or experimentally and can be used as a basis for the temperature regulation of the probes  23 . 
         [0032]    If, in a further configuration, instead of the needle-like probes  23 , probe cards having a multiplicity of short probes are used, the probe card, which would be arranged parallel to the test substrate  7  in the central opening  26  in the probe mounting plate  4 , can also be temperature-regulated by the gas flow  11  flowing past. 
         [0033]    Furthermore, the gas flow  11  in the objective chamber  41  can also regulate the temperature of the objective, e.g. in order to prevent the slow adaptation thereof to the temperature of the test substrate  7  lying directly below the objective, and thus to ensure the continuous observation of the test. 
         [0034]    In a further configuration, the test chamber  2  and/or the chuck positioning unit  6  can supplementarily also be temperature-regulated in order to avoid changes in the position of the test substrate  7  or the electrical properties thereof as a result of a temperature drift. 
         [0035]      FIG. 2  shows a further configuration of the probe chamber  3  of the prober. The essential construction of the illustrated part of the prober corresponds to that in  FIG. 1 , for which reason reference is made to the explanations in respect thereof. The same components of the prober have been identified by the same reference symbols. For the sake of better clarity, no observation device is illustrated. However, there is freedom to enable the probe tips  25  to be observed during the verification in another suitable manner. The configuration in accordance with  FIG. 2  furthermore differs from that illustrated in  FIG. 1  in that no shield  9  is arranged below the probe mounting plate  4 . In order nevertheless to reduce the thermal influence of the test substrate  7  and of the chuck  5  on the probe chamber  3 , the central opening  26  in the probe mounting plate  4  has been reduced to the minimum dimension required for the positioning of the probe tips. 
         [0036]    In the configuration in accordance with  FIG. 2 , a central partial section of the probe chamber  3 , in which section the probe arms  24  extend, is thermally shielded from the lateral partial sections, in which the probe heads  21  are arranged, by thermal diaphragms  31 . The probes  23  held by the probe heads  21  extend through the diaphragms  31  right into the central region of the probe chamber  3 . The diaphragms  31  are thermally insulating but permeable to a gas flow  11 , which is produced separately by means of gas channels  32  in each partial section. In each partial section of the probe chamber  3 , there is arranged in the upper region a tubular gas channel  32  having, along a generatrix, openings serving as gas inlet  12 . This configuration of the gas inlet  12  permits a directed flow, e.g. with respect to the mounts of the probes  23  and the diaphragms  31 . The gas channel  32  in the central partial section of the probe chamber  3  is configured in such a way that the gas flow  11  flows in the direction of the probes  23  but not into the central opening  26  since the temperature of the gas flow  11  can deviate significantly from that of the test substrate  7  and thermal stresses and displacements in the test substrate  7  and the probe tips  25  are thus avoided. 
         [0037]    The direction of the gas flow  11  can furthermore be set and altered by means of a rotatable gas channel  32  and/or by means of directed, nozzle-like openings in the gas channel  32 . The use of a directed gas flow  11  which flows through the probe chamber  3  permits the target temperature regulation also of individual components with minimal influence on the temperature of the working region and of the test substrate  7  arranged there. 
         [0038]    Provided that the temperature in the test chamber  2  is significantly above that in the probe chamber, the air flowing from the test chamber  2  additionally prevents the cooler gas flow  11  from penetrating into the test chamber  2 . The gas flows  11  mixing in the central partial section of the probe chamber  3  escape through the diaphragms  31  into the lateral partial sections, are cooled further there and escape through the gas outlets  13  distributed at the base point of the upper housing wall  30 , if appropriate in a manner supported by extraction by suction. If a measurement is carried out at 200 to 300° C., for example, the probe chamber  3  can be cooled by an air flow at room temperature and, with appropriate dimensioning of the amount of air flowing through the probe chamber  3 , a temperature of approximately 25° C. can be maintained in the probe chamber  3  throughout the verification. 
         [0039]    This is also supported the thermal separation by means of the diaphragms  31 , which are removable in one configuration of a prober for flexible application. The use of diaphragms  31  depends firstly on the temperature difference and secondly on the size of the opening between the two chambers. 
         [0040]    Both the gas flow  11  in the objective chamber  41  and that in the partial sections of the probe chamber  3  which lie laterally with respect thereto bring about a temperature regulation of the probe mounting plate  4 , which has a stabilizing effect on the thermal equilibrium of the test system. In the above-described case of a high temperature difference between probe chamber  3  and test substrate  7 , the probe mounting plate  4  can have a thermal insulation  27 . In the exemplary embodiment, said thermal insulation is arranged at the underside of the probe mounting plate  4  owing to the mounting of the probes  23  and the probe heads  21  on said probe mounting plate. Alternatively, that is also possible above said plate. 
         [0041]    In a further configuration, the housing of a prober, besides the function as EMI shielding, can also be embodied in light-tight fashion, e.g. for the verification of optoelectronic test substrates  7 .  FIG. 3  shows a possible gas outlet  13  that fulfills both functions. For this purpose, a profile  34  is inserted in an opening in the upper housing wall  30 , which profile, by virtue of mutually overlapping webs, precludes direct visual contact through the opening but, by virtue of sufficiently large distances between the webs, allows a gas flow through the profile  34 . For a maximum absorption of incident light, the profile  34  is produced from matt black material. The electromagnetic shielding in the region of the opening is realized by an EMI shielding substance  35 , which is in electrical contact with the probe mounting plate  4  and the upper housing wall  30 . Alternatively, the gas outlet  13  can also fulfill only one of the functions and, consequently, only have either the profile  34  or the electromagnetic shielding. 
         [0042]    For the verification, which, in the exemplary embodiment, is intended to be carried out at temperatures above 200° C., a test substrate  7  is arranged on a chuck  5  and coarsely positioned in the working region within the test chamber  2  and thus below the central opening  26 . Afterward, the test substrate  7  bearing on the chuck  5  in planar fashion is heated to the test temperature by means of a chuck heating system (not illustrated). At this point in time, three separate gas flows  11  composed of dried air at room temperature flow through the probe chamber  3 , which is subdivided into three partial sections with a central objective chamber  41 . Severe heating of the probes  23  and, via the thermal contact thereof, also of the probe heads  21  is prevented in this way. A thermal equilibrium is established in which the test substrate  7  has assumed the test temperature and a temperature of approximately 25° C. is set for the probes  23 , the probe heads  21  and signal preprocessing units within the lateral partial sections of the probe chamber  3 . 
         [0043]    After the setting of the thermal equilibrium, the contact of the probes  23  with the test substrate is produced by fine positioning by means of chuck positioning unit  6  and probe heads  21  and the subsequent feed between the probes  23  and the test substrate  7 . On account of the maintenance of the temperature of the probes  23  by means of the gas flows  11 , the thermal expansion of the probes does not change, such that even long-term measurements and, in particular, also with long probe arms  24  are possible without losing the contact between the probes and the test substrate during verification. 
         [0044]    The terms and expressions which have been employed in the foregoing specification are used therein as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow. 
       LIST OF REFERENCE SYMBOLS 
       [0000]    
       
         
           
               1  Baseplate 
               2  Test chamber 
               3  Probe chamber 
               4  Probe mounting plate 
               5  Chuck 
               6  Chuck positioning unit 
               7  Test substrate 
               8  Objective chamber 
               9  Shield 
               10  Lower housing wall 
               11  Gas flow 
               12  Gas inlet 
               13  Gas outlet 
               21  Probe head 
               23  Probe 
               24  Probe arm 
               25  Probe tip 
               26  Central opening 
               27  Thermal insulation 
               28  Apparatus for signal conditioning 
               29  Connector 
               30  Upper housing wall 
               31  Diaphragm 
               32  Gas channels 
               34  Profile 
               35  EMI shielding substance 
               40  Observation region 
               41  Objective chamber 
               43  Microscope