Measuring system for performing high-voltage tests and related apparatus

Abstract

A measuring system (100, 100') for the testing of devices under test (DUT) integrated on a semiconductor wafer (WS) is described, comprising a probe head (101) comprising a plurality of contact elements (1) which extend along a longitudinal direction (H-H) between a first end (la), adapted to contact pads of a device under test (DUT), and a second and opposite end (lb) and a housing (2) configured to house the plurality of contact elements (1). The measuring system (100, 100') further comprises a pressurization structure (4) adapted to abut, in use during the test, on a semiconductor wafer (WS) or on a chuck (3) that houses the semiconductor wafer (WS). The pressurization structure (4) comprises a peripheral wall (5) defining a housing area (A) therein and at least one sealing component (6) arranged inside the housing area (A) and comprising a hole (8) in which the housing (2) is housed, defining a chamber (P) in the housing area (A) and at least one inlet (I) adapted to allow conveying a pressurized gas into the chamber (P), making, in use during the test, said chamber (P) an overpressure area. An apparatus comprising this measuring system is also described.

Description

[0001] Title: Measuring system for performing high-voltage tests and related apparatus

[0002] DESCRIPTION

[0003] Field of application

[0004] The present invention relates to a measuring system for the testing of electronic devices integrated on a semiconductor wafer for performing high-voltage tests. The following description is done with reference to this field of application with the only aim of simplifying the exposition thereof.

[0005] Prior art

[0006] As it is known, a probe head is essentially a device adapted to electrically connect a plurality of contacts pads or pads of a microstructure, particularly an electronic device integrated on a semiconductor wafer, with corresponding channels of a testing apparatus which performs the verification of the functionality thereof.

[0007] The test performed on integrated circuits serves in particular to detect and isolate defective circuits already in the production step. Normally, the probe heads are thus used for testing the circuits integrated on a wafer before cutting and mounting them inside a chip containment package.

[0008] A probe head essentially comprises a plurality of contact probes housed in a pair of supports or guides which are substantially plate-like and parallel to each other. These plate-like supports are provided with suitable guide holes and are located at a distance from each other so as to create a free area or air gap for the movement and the possible deformation of the contact probes, which are usually formed by wires made of special alloys with good electrical and mechanical properties.

[0009] The contact probes generally extend between a first end portion, intended to contact the pads of the device under test, and a second end portion, intended to contact a space transformer or a printed circuit board (PCB) associated with the probe head.

[0010] The correct operation of a probe head is basically linked to two parameters: the vertical movement (or overtravel or overdrive) of the contact probes and the horizontal movement (or scrub) of the contact tips of these probes on the pads during the contact with the device under test. All these features are to be evaluated and calibrated in the manufacturing step of a probe head, the good electrical connection between the contact probes and the device under test should always be ensured.

[0011] Furthermore, the need to perform high-voltage tests is nowadays increasingly common, for example (but not only) in the automotive field, a category which then branches into several type of tests. Specifically, in recent years the demand for electronic power components has dramatically increased due to the production of electric cars, with the need to perform tests at very high voltages. In these cases, the applied voltages are so high that very damaging phenomena may occur, such as for example the occurrence of electric arcs between a device under test with another one under test or with a device not under test.

[0012] High-voltage tests have been often performed on so-called “singulated dies”, which provide the preliminary cutting of the devices under test (DUT) from the semiconductor wafer, the positioning thereof one at a time on a support indicated in the field with chuck and the single test procedure. Hence, in this case, no interference problems between adjacent devices occur, but electric arc formation phenomena between the device and the chuck may however occur.

[0013] This problem is due to the fact that the air dielectric strength can be estimated, as a generally adopted indicative value, at 3KV / mm, and to the fact that the distances for this type of test are very small. In order to solve this problem, it can be envisaged to perform the test in very hard vacuum conditions, but this involves significant operational problems, or it affects the environment in the wafer areas concerned by the test. In particular, it is envisaged to supply pressurized gas at the test area in order to prevent electric arcs from being formed, since the higher the pressure, the higher the electric arc striking voltage, as described by Paschen curves.

[0014] Most of the studies are to date more directed towards this second solution. Therefore, an overpressure test area is created, at about 1-2 atm,

[0015] In the future it would also be desirable to increase this pressure.

[0016] In the above tests on “singulated dies” either solutions providing a contact with the chuck on which the device under test is positioned or contactless solutions are adopted.

[0017] The solutions providing a contact provide the use of a dome with a sealing ring on the bottom, which is larger than the device under test, which rests on the chuck, the pressurization of the so-delimited volume in test conditions, and the depressurization and removal following the test, to proceed then with the following ones. This solution is not very popular since it provides the imposition of a significant force on the chuck.

[0018] The contactless solutions provide, for example the use of a floating disk that creates an overpressure cabin at about 1-2 atm on the surface of the wafer under test with the continuous introduction and exit of gas, generally air or nitrogen, in and from said cabin. The disk is maintained at distances of about dozens of pm and which self-regulate depending on the pressures achieved. This solution is not devoid of drawbacks, both in view of the increase in the pressures involved, and for the air flow that continuously escapes from the formed cabin, with amounts even of 80 1 / min. Moreover, in case nitrogen is used, this tends to saturate the working environment by eliminating oxygen, which creates a safety problem for any operator who is present. Nitrogen can thus be used only in “low leakage” conditions.

[0019] However, despite these drawbacks, it can be noted that the problems of arc formation in case of tests on “singulated dies” are sufficiently under control.

[0020] The situation is different if, as per the increasingly pressing market demand, it comes to perform tests on the whole wafer, always at high voltage, testing either the entire wafer together or a certain number of separate “Dies” (the so-called “stepping”), but without performing a preliminary division of the various devices.

[0021] In this case, it can also be required to perform a test of the whole wafer without pressurization, thus at atmospheric pressure, for example the so-called “wafer level burn-in” test in which the devices are electrically biased and positioned in hot environments, to test the lifetime strength thereof. In other words, the devices are subject to high temperatures while they are in an electrical stress condition, and the results thereof are evaluated.

[0022] However, this type of test is not in line with the current demand for test voltages of about 1- 1,5 KV, but which are expected to rise to more than 3,5 KV. The currents will increase as well, as mentioned above, with the voltages.

[0023] The need to perform also the tests on the whole wafer in pressurization conditions is felt.

[0024] At present, there are no reliable solutions to this problem, especially if it is necessary to perform the above-mentioned “stepping”.

[0025] Attempts are made to translate the above contactless solutions on a limited number of devices under test, but the problems due to the high flow of outgoing gas remain, and there are additional problems on the wafer boundary, where the overpressure cabin formed is not properly delimited and there are pressure losses. Furthermore, there are drawbacks in the possible enlargement of the cabin to cover a greater number of device arrays (for example the so-called “parallel 4” or “parallel A solution could be to position the whole test machine in a pressurized hyperbaric chamber for example at 4 atm and thus proceed with the test in this overall overpressure condition.

[0026] However, this solution is complex both for the need to have an extremely efficient hyperbaric chamber, which should also have inlet and outlet chambers to balance the pressures, and for the expensiveness of displacing the test machine.

[0027] The technical problem of the present invention is to devise a measuring system having such structural and functional features as to allow the limitations and drawbacks still affecting known solutions to be overcome, which allows in particular to prevent electric arcs from occurring during the test while ensuring an efficient test of all the chips integrated on the semiconductor wafer.

[0028] Specifically, object of the invention is to solve the problem related to the formation of electric arcs for tests on a whole semiconductor wafer both with a single test (“Full Wafer Single Touch”) and in the case of the above “stepping” between several devices, being allowed to move inside the overpressure area.

[0029] Summary of the invention

[0030] The solution idea underlying the present invention is to integrate a vertical probe head with a series of components to create such an area adapted to contain pressurized gases as to reduce the probability that electric arcs occur in accordance with the Paschen law, and to make the configuration of this area preferably variable depending on the test requirements.

[0031] Based on this solution idea, the above technical problem is solved by a measuring system for the testing of devices under test (DUT) integrated on a semiconductor wafer comprising a probe head comprising a plurality of contact elements which extend along a longitudinal direction between a first end, adapted to contact pads of a device under test, and a second and opposite end and a housing configured to house the plurality of contact elements.

[0032] The measuring system further comprises a pressurization structure adapted to abut or connect (in general be associated), in use during the test, on a semiconductor wafer or on a chuck that houses the semiconductor wafer.

[0033] The pressurization structure comprises a peripheral wall defining therein a housing area and at least one sealing component arranged inside the housing area and comprising a hole in which the housing is housed, defining a chamber in the housing area and at least one inlet adapted to allow conveying a pressurized gas in the chamber, making, in use during the test, the chamber an overpressure area.

[0034] Advantageously, the present invention allows to form a pressurized cabin, which can be applied on the semiconductor wafer without imparting a force directly on the surface, it is thus possible to perform the test in the best conditions to prevent electric arcs from being formed and then move the pressurization structure.

[0035] More particularly, the invention comprises the following additional and optional features, taken individually or in combination if necessary. These additional and optional features are defined for example in the dependent claims 2 to 16.

[0036] In a preferred embodiment, the sealing component is movable inside the housing area.

[0037] Advantageously, the sealing component is therefore adaptable in its configuration inside the measuring system.

[0038] Still in a preferred embodiment, the sealing component is ring-shaped and the housing is housed in the ring, preferably at the center of the ring.

[0039] Advantageously, the present solution is well suited to the solutions provided in the prior art with substantially cylindrical probe heads, and advantageously it is also externally devoid of edge points.

[0040] In a more preferred embodiment, the pressurization structure comprises a plurality of sealing components which are movable with respect to each other and provided with holes of different diameter, intended as a measure along a direction that is substantially orthogonal to the longitudinal direction.

[0041] The plurality of sealing components comprise a first sealing component comprising an outer perimeter and adapted to directly connect with the peripheral wall, a second sealing component comprising the hole adapted to receive the housing containing the contact elements and a plurality of intermediate sealing components.

[0042] The first sealing component, the second sealing component and the plurality of intermediate sealing components are cascade-connected in a mutually sliding manner.

[0043] Advantageously, the present solution allows to perform the above- mentioned “stepping” in an appropriate manner, keeping the probe head stationary and sliding below the chuck supporting the semiconductor wafer by modifying the mutual position of the plurality of movable rings.

[0044] This can be done either by depressurizing from time to time the gap comprised between the pressurization structure and the semiconductor wafer, thus detaching the housing containing the contact elements and properly repositioning the chuck supporting the semiconductor wafer on which the pressurization structure is mounted, or by performing this reconfiguration of the movable sealing components of the pressurization structure while the gap comprised between the pressurization structure and the semiconductor wafer is still pressurized.

[0045] This generally depends on the desired pressure conditions and size of the semiconductor wafer, but clearly these conditions will also vary in the future with the technological and material developments. According to an aspect of the invention, the plurality of movable sealing components are slidingly connected to each other so that a lower surface of at least one sealing component is sliding on an upper surface of an adjacent sealing component.

[0046] Advantageously, the present solution allows a rapid and accurate mutual reconfiguration between the movable sealing components, only moving those required to accurately move on the device under test.

[0047] Preferably, the first sealing component is, in use, the furthest one from the semiconductor wafer, is fixed and is the one having the greatest diameter, the diameters progressively decreasing in the passage from the first sealing component to the second sealing component which, in use, is the closest one to the semiconductor wafer.

[0048] Advantageously, this solution is the most practical in the arrangement and mutual reconfiguration of the movable sealing components.

[0049] According to an aspect of the invention, each of the plurality of movable sealing components is connected to the adjacent one by interposing at least one sliding element.

[0050] Advantageously, the present solution facilitates the mutual sliding between the movable sealing components especially in a use providing to keep a pressurization condition in the gap comprised between the pressurization structure and the semiconductor wafer during the reconfiguration of the movable sealing components of the pressurization structure.

[0051] Preferably the at least one sliding element is a bearing.

[0052] Nothing prevents to provide different solutions, for example disk-like elements made of suitable materials.

[0053] According to a further aspect of the invention, the measuring system further comprises at least one seal element between the hole of the at least one sealing component and the housing.

[0054] Advantageously, the present solution allows to ensure a certain independence of movement between the housing and the pressurization structure, in particular for movements of alignment and small relative rotation of the semiconductor wafer with respect to the contact elements.

[0055] According to an embodiment of the invention, the measuring system further comprises at least one adaptor element between the hole of the at least one sealing component and the housing.

[0056] Advantageously, the present solution allows to adopt a same pressurization structure with different dimensions of the housing with respect to the hole.

[0057] Nothing prevents to provide different solutions, such as replacing the seal element interposed between the housing and the hole, according to the above-mentioned embodiment, or simply providing different housings.

[0058] According to a further aspect of the invention the at least one sealing component is made of metal material, preferably steel, or of composite material, preferably carbon fiber.

[0059] Advantageously, the metal solution is productively simple and provides to use different thicknesses depending on the adopted pressurization level.

[0060] Alternatively, advantageously, the composite solution allows a greater lightness of the whole pressurization structure while keeping an appropriate stiffness.

[0061] According to another aspect of the invention, the pressurization structure comprises a bayonet system configured to connect it to the chuck by means of a bayonet system.

[0062] Advantageously, the present solution allows a simple and prompt coupling and uncoupling of the pressurization structure on the chuck. Nothing prevents to provide different coupling solutions depending on the contingent production and operational requirements.

[0063] According to an aspect of the present invention, the system may further comprise an upper cover and at least one bearing, for example made of an elastomeric material, connected to said at least one sealing component and abutting on said upper cover.

[0064] In an embodiment, each movable sealing component is provided with its own bearing (while it may not be provided for the fixed ring) .

[0065] Advantageously, this solution allows to counter the swelling effect of the at least one sealing component and of the chuck when they are subject to pressure.

[0066] The present invention also relates to an apparatus for the testing of devices under test integrated on a semiconductor wafer.

[0067] This apparatus comprises a system as described above, a chuck adapted to house the semiconductor wafer and a conveying system including at least one duct in fluid connection with the inlet of the system for conveying the pressurized gas into the seal chamber.

[0068] Preferably, the at least one duct of the conveying system is formed by at least one of a duct made in the chuck, a duct made in the peripheral wall, a duct passing through the housing.

[0069] Advantageously, the duct in the chuck allows to make the probe head completely independent from the chuck and from the pressurization structure.

[0070] Advantageously, the duct in the peripheral wall allows instead a customization depending on the system in which it is implemented.

[0071] Finally, advantageously, the duct passing through the housing allows to exploit the fact that the latter, which contains the contact elements, must be pressurized during operation to prevent electric arcs from being formed.

[0072] According to an aspect of the present invention, in particular if the above upper cover is present, the apparatus also comprises at least one movable support (in particular a sliding one) adapted to move said chuck that is contained inside the pressurization structure. As mentioned above, this allows to counter the swelling effect of the at least one sealing component and of the chuck when they are subject to pressure.

[0073] According to a preferred embodiment, the gas flow provides a gas with a high dielectric strength which is greater than that of air.

[0074] Advantageously, the use of this type of gas contributes to the missing formation of electric arcs.

[0075] Preferably, the high dielectric strength gas is sulfur hexafluoride.

[0076] Advantageously, this is an inert gas (thus non-toxic for an operator) which is historically used for high-voltage applications, such as transformers or high-voltage sealed switches.

[0077] In fact, this gas has a dielectric strength which is 4-5 times higher than that of air, thus requiring a pressurization which is 4-5 times lower to have the same result in terms of missing formation of electric arcs. For example, a similar condition can be achieved by adopting air at 4-5 atm or sulfur hexafluoride at 1 atm, with subsequent production and operational advantages.

[0078] The features and advantages of the measuring system according to the invention will be apparent from the following description of an exemplary embodiment thereof given by way of non-limiting example with reference to the attached drawings.

[0079] Brief description of the drawings

[0080] In the drawings: - figure 1 schematically shows a probe head adopted in a measuring system according to the present invention;

[0081] - figure 2 schematically shows an apparatus comprising a measuring system according to the invention comprising a first configuration of a pressurization structure;

[0082] - figure 3 schematically shows the apparatus comprising the measuring system of figure 2 comprising a second configuration of the pressurization structure;

[0083] - figure 4 schematically shows the apparatus comprising the measuring system of figure 2 comprising a third configuration of the pressurization structure; and

[0084] - figure 5 shows an alternative embodiment of the present invention.

[0085] Detailed description

[0086] With reference to the figures, a measuring (or testing) system (or apparatus) according to the present invention for the testing of devices under test (herein indicated with the abbreviation DUT - acronym for “Device Under Test”) integrated on a semiconductor wafer WS is globally and schematically indicated with 100 or 100’ and the related apparatus which this measuring system 100 can be associated with is indicated with 1000.

[0087] It should be noted that the figures are schematic views and are not drawn to scale, but they are instead drawn so as to emphasize the important features the invention. Furthermore, in the figures, the different elements are schematically depicted, the shape thereof being changeable depending on the desired application. Furthermore, it should be noted that, in the figures, identical reference numbers refer to identical elements in terms of shape or function. Finally, special arrangements described in relation to an embodiment illustrated in a figure can also be used for the other embodiments illustrated in the other figures. It is noted that, unless it is expressly stated to the contrary, described process steps can also be inverted if necessary.

[0088] Furthermore, it is noted that, in the context of the present invention, the term “measuring system” is used to indicate a structure for contacting pads (for example pads of the device under test DUT) without being limited by the presence or absence of particular components, in addition to what is defined by the attached claims. In general, this term thus indicates a set of components which can be associated with further components (for example a testing apparatus) for testing devices integrated on a semiconductor wafer WS, and thus it generally indicates an apparatus for measuring electronic devices. This measuring system can also be indicated with the term “probe card” or “contact system”.

[0089] The measuring system 100 is thus adapted to connect with the related apparatus 1000 to perform the test of devices under test DUT integrated on a semiconductor wafer (indicated with the reference WS), for example to perform high-voltage tests.

[0090] As illustrated in figure 1, the measuring system 100 comprises a probe head 101 comprising a plurality of contact elements or contact probes 1 slidingly housed in a housing 2, which also acts as a protective element, and intended to connect the device under test DUT integrated on the semiconductor wafer WS with the testing apparatus.

[0091] In order to keep the contact probes 1 in place, the probe head 101 generally comprises at least one guide 102 provided with guide holes 102h through which the contact probes 1 are able to slide. The guide holes 102h are thus suitably configured to house at least one portion of the contact probes 1 and to guide said contact probes 1 in the overtravel and scrub movement thereof during the test. The guide 102 comprises a first face FA facing, during the test, the device under test DUT (this first face FA being thus a lower face according to the reference of the figures) and a second face FB opposite the first face FA (this face FB being thus an upper face according to the reference of the figures) . In the embodiment illustrated in the figures, the guide 102 is a lower guide (i.e. it is the guide which is closest to the device under test DUT) and the measuring system 100 also comprises an upper guide 103, which is provided with corresponding guide holes 103h and is separated from the lower guide by an air area or gap G, although the present invention is not limited to this specific configuration and the upper guide 103 may not be present or an intermediate guide may also be present (not illustrated in the figures), depending on the requirements and / or circumstances.

[0092] The set formed by the contact probes 1 and by the guide / s is, as mentioned, indicated with “probe head” 101.

[0093] Each contact probe 1 comprises a body lp which extends along a longitudinal axis (or direction) H-H between a first end la and a second and opposite end lb, which are adapted to contact respective contact pads (commonly also indicated in the field as “pads”). By way of example, the first end la (also called contact tip) is adapted to contact pads of the device under test DUT integrated on the semiconductor wafer WS, while the second end lb (also called contact head) is adapted to contact pads of a space transformer or of a printed circuit board (PCB), this component being generically identified with the numeral reference 105 and being generally called in the present description “interface board 105”. It is noted that the ends la and lb can have any shape which is suited to the requirements and / or circumstances, and thus they have not necessarily a pointed shape.

[0094] In a non-limiting embodiment, the contact elements 1 are thus vertical contact probes which extend along the longitudinal axis H-H between the two opposite ends, for example of the buckling beam type.

[0095] The measuring system 100 can further comprise a stiffener 106 to which the above interface board 105 is connected. The stiffener 106 aims at keeping the components of the measuring system 100 in place and to solve planarity problems. The housing 2 can also be connected to the stiffener 106, and is generally connected to a lower face of the stiffener 106 (i.e. the face thereof which is closest to the device under test).

[0096] It is noted that an example with a limited number of contact probes 1 on pads of a device under test DUT is illustrated for simplicity in the figures, even if it should be understood that the figures are provided only by way of non-limiting example of the present invention and any number, even a high one, can be envisaged.

[0097] As indicated above, in high-voltage tests, undesirable phenomena may occur such as, for example, the formation of electric arcs between the pads of the device under test DUT.

[0098] The present invention precisely matches with this need to prevent these electric arcs from occurring, and it is envisaged to affect the environment in the areas of the semiconductor wafer WS concerned by the test, providing pressurized gas at the testing area, taking into account the fact that the higher the pressure the higher the striking voltage of the electric arc, as described by Paschen curves.

[0099] Specifically, the present invention aims to solve this need for the tests on the whole semiconductor wafer WS both with a single test (test called “Full Wafer Single Touch” in the field) and by adopting the so-called “stepping” between several devices, thus moving the probe head between specific DUTs under test on the semiconductor wafer.

[0100] The apparatus 1000 with which the measuring system 100 may be associated further comprises a support for the semiconductor wafer, called “chuck” 3 in the field.

[0101] As can be seen in figures 2-4, in the illustrated embodiment the system 100 provides a pressurization structure 4 adapted to be connected on the chuck 3 or to the wafer, comprising a peripheral wall 5 or outer wall.

[0102] In an embodiment, this peripheral wall 5 connects on the chuck 3, preferably transversely with respect to the chuck 3. In the present embodiment this connection is made by means of a bayonet system.

[0103] Therefore, the peripheral wall 5 provides at least one coupling projection (not shown), which can be inserted into a related recess of the chuck 3, a coupling projection which can be, for example, locked in position by means of a rotational movement, and unlocked by means of a reverse movement, due to a related recess machining.

[0104] This also allows to insert the pressurization structure 4 only when required for the specific high-voltage tests.

[0105] The peripheral wall 5 defines a housing area A therein.

[0106] The pressurization structure 4 then provides at least one sealing component 6 comprising a central hole 8 adapted to receive the housing 2, said sealing component 6 being arranged inside the housing area A.

[0107] Preferably, the sealing component 6 is ring-shaped, a solution che adapts to the solutions provided in the prior art with substantially cylindrical probe heads, and advantageously it is also externally devoid of edge points.

[0108] Therefore, in the embodiments provided below, reference will be made to this configuration, and specifically sealing rings 6 will be dealt with, but it is well understood how different shapes, particularly for specific requirements, may be adopted and fall within the scope of the attached claims.

[0109] The at least one sealing component 6, corresponding as mentioned in this case to a sealing ring 6, is preferably parallel to the semiconductor wafer WS and transverse with respect to the peripheral wall 5.

[0110] A configuration with a single sealing ring 6 is provided if only the type of test of the whole semiconductor wafer WS simultaneously (“Full Wafer Single Touch”) is to be performed. In this case, the single sealing ring 6 is suitably sized forming a single sealed overpressure area P, and is connected to the peripheral wall 5 at an outer perimeter 7 thereof.

[0111] In other words, by means of the peripheral wall 5 and the pressurization structure 4 a bell is substantially formed above the semiconductor wafer WS, by abutting on the chuck 3 on which it is placed, and providing an opening, corresponding to the hole 8 of the sealing ring 6, sized to allow the passage and the coupling with the probe head 101, specifically with the housing 2, which reaches the semiconductor wafer WS under test by means of the contact heads 1 contained therein.

[0112] Below the bell, i.e. in the so-formed housing area A, a gas flow G which generates the overpressure area P is inserted.

[0113] At the hole 8 at least one seal element 14 is further provided for coupling with the housing 2 and thus to form a sealed chamber (reference P), defined by the sealing ring 6, by the housing and by the peripheral wall, said chamber P closing on the chuck during the test.

[0114] This also allows, in addition to the seal in the related coupling portion, a certain independence of movement of the probe head 101 through slight alignment and rotation movements with respect to the semiconductor wafer WS.

[0115] Furthermore, in a variant not shown, if the same pressurization structure 4 is always to be used, without providing specific sizing for each dimension of the housing 2, at least one adaptor element between the hole 8 of the sealing ring 6 and the housing 2 may be provided.

[0116] Alternatively, nothing prevents also to size in a different manner various seal elements 14, which thereby also perform the dimensional adaptation function.

[0117] In the apparatus 1000, the gas flow G is inserted below the system 100 by means of a conveying system 9 including at least one duct 10 just configured to convey the gas flow G on the semiconductor wafer WS. To this purpose, the measuring system 100 comprises at least one inlet I adapted to allow conveying the pressurized gas flow G into the chamber P, making as mentioned, in use during the test, the chamber P an overpressure area (always indicated with the reference P) .

[0118] In the embodiment shown, the at least one duct 10 is made in the chuck 3.

[0119] This allows to make the probe head completely independent from the chuck 3 and from the pressurization structure 4.

[0120] Alternatively, the at least one duct of the conveying system can be made in the peripheral wall 5, so as to be able to customize a pressurization structure 4 depending on the system in which it is implemented.

[0121] Still alternatively it is possible to provide the at least one duct 10 coinciding with the housing.

[0122] In fact, even the housing 2 containing the contact elements 1 must be pressurized during the operation to prevent electric arcs from being formed, and it is thus possible to optimize the compactness of the apparatus 1000 comprising the measuring system 100 by adopting the housing 2 also as a supply of the gas flow G.

[0123] The gas flow G is withdrawn from an external supply line (which is part of means outside the measuring system 100).

[0124] As a gas A, a preferable condition compared to the use of air would be to use gases having a high dielectric strength, which is greater than air, which contribute to the missing formation of electric arcs.

[0125] Among them, an ideal solution provides the use of sulfur hexafluoride, which is an inert gas (thus non-toxic for an operator) and which is historically used for high-voltage applications, such as the transformers or the high-voltage sealed switches. In fact, this gas has a dielectric strength which is 4-5 times higher than that of air, thus requiring a pressurization which is 4-5 times lower to have the same result in terms of missing formation of electric arcs. For example, a similar condition can be achieved by adopting air at 4-5 atm or sulfur hexafluoride at 1 atm, with subsequent production and operational advantages.

[0126] However, depending on the contingent requirements nothing prevents to provide the use of air, or nitrogen according to the prior art, or other gases which are useful for specific requirements of the applications of interest.

[0127] The evaluation can also be performed in connection with the material of the at least one sealing ring 6.

[0128] Preferably, the at least one sealing ring 6 is made of metal material, more preferably steel, a solution which is productively simple and provides to use different thicknesses depending on the adopted pressurization level.

[0129] Alternatively, the at least one sealing ring 6 can be made of composite material, preferably carbon fiber, which ensures a greater lightness of the whole pressurization structure 4 while keeping an appropriate stiffness.

[0130] However, nothing prevents to provide the use of different materials depending on the specific intended application.

[0131] Up to now the example of a single ring has been illustrated, although, in most applications, in order to perform the test of the whole wafer, a plurality of rings is provided for a step test which will be discussed below (where the above-described features will also be applied in this case with the necessary precautions).

[0132] In particular, in the embodiment represented in figures 2-4, a pressurization structure 4 is provided, comprising a plurality of sealing rings 6 which are movable with respect to each other and with a variable configuration i.e. whose relative position can be varied during the test. This plurality of sealing rings 6 comprise a first sealing component 6a, here represented by a first peripheral ring 6a comprising the outer perimeter 7 directly connected with the peripheral wall 5, a second sealing component, here represented by a second central ring 6b comprising the hole 8 adapted to receive the housing 2 and a plurality of intermediate sealing components 6c, here represented by intermediate rings 6c.

[0133] The second ring 6b is the one with a lower diameter and is the one comprising the hole 8 in which the housing is inserted, said hole having, in an embodiment, a size which is substantially identical to that of the housing, although this is not necessary and as seen above a suitable adaptor can be provided, which allows to use a same pressurization structure 4 with various probe heads. The intermediate rings 6c have gradually increasing dimensions up to the first one 6a which is the one having the greatest diameter.

[0134] More specifically, as mentioned above, the sealing rings 6, which are movable with respect to each other, are provided with holes of different diameter, intended as a measure along a direction that is substantially orthogonal to the longitudinal direction H-H, the first peripheral ring 6a, in use the furthest one from the semiconductor wafer WS and fixed, is the one having the greatest diameter, and the diameters progressively decrease in the passage from this first peripheral ring 6a to the second ring 6b which, in use, is the closest one to the semiconductor wafer WS.

[0135] The first ring 6a, the second ring 6b and the plurality of intermediate rings 6c are cascade-connected in a mutually sliding manner.

[0136] Specifically, in the shown embodiment, this cascade connection is made by slidingly connecting to each other a lower surface 11 of a sealing ring on an upper surface 12 of an adjacent sealing ring.

[0137] In the present embodiment of the apparatus 100 the chuck 3, the semiconductor wafer WS under test positioned on the chuck 3, the measuring system 100 comprising the pressurization structure 4 connected through its own peripheral surface 5 to the chuck 3, and a series of sealing rings 6 which are movable parallel to the semiconductor wafer WS, the probe head 101 passing in the hole 8 of the central ring 6b are therefore provided.

[0138] During the test, the internal pressure in the overpressure area P helps to transversely seal the plurality of sealing rings 6 against each other, increasing the overall seal.

[0139] However, an absolute seal of the measuring system 100 is not essential, but small leakages are allowed. If they are minimal nitrogen can also be used as a gas A, without incurring the above-disclosed drawbacks.

[0140] If there are leakages, recirculation systems could also be used, which are useful both to prevent, if nitrogen is used, that it spreads in the working environment, and to recover a useful gas like sulfur hexafluoride and reuse it.

[0141] This solution is very useful in case of a test which provides the “stepping” between various DUTs or various pads, keeping the probe head 101 in place and reconfiguring the various movable sealing rings 6 and the related shape of the bell defined by them, depending on the position of the DUT under test.

[0142] This reconfiguration of the mutual position of the plurality of sealing rings 6 can be appreciated by looking at the different positions of the latter in figures 2-4.

[0143] Figure 2 shows a configuration in which all the sealing rings 6 are all slid so that all the corresponding outer circumference portions are aligned and stacked at a boundary of the chuck 3 to have the probe head 101 at a boundary of the semiconductor wafer WS.

[0144] In figure 3, the sealing rings 6 are instead coaxial with respect to each other, so that the probe head 101 is substantially on a centreline of the semiconductor wafer WS.

[0145] Finally, in figure 4 there is a situation which mirrors that of figure 2, the sealing rings 6 being all slid so that all the outer circumference portions opposite those of figure 2 are aligned and stacked at an opposite boundary of the chuck 3 to have the probe head 101 at the opposite boundary of the semiconductor wafer WS.

[0146] Evidently, the present configurations are merely exemplary and the sealing rings 6 can be moved along all the directions defined by the radii thereof to allow a suitable and specific reconfiguration along the plane defined by axes X and Y in figures 2-4. What matters is that the ring system allows the passage of the probe head and the substantial chamber sealing in each configuration.

[0147] Obviously, keeping all the sealing rings 6 in a single position nothing prevents to use the same solution even in the case of testing the whole semiconductor wafer WS simultaneously (“Full Wafer Single Touch”).

[0148] Depending on the pressurization conditions, which, as mentioned above, also depend on the type of gas A adopted, on the materials, on the dimensions of the semiconductor wafer WS, etc., at the end of a test, the pressurization structure 4 can be depressurized, thus allowing the uncoupling from the probe head 101, the reconfiguration of the sealing rings 6, the coupling and pressurization and a new test, or a reconfiguration of the sealing rings 6 can be provided while keeping the overpressure area P.

[0149] For example, a semiconductor wafer WS of 12 inches (i.e. 30 cm in diameter) and a pressure brought to 1 atm, there is a resulting force in the overpressure area P of about 600 kg. In these conditions it is difficult to slide the movable rings while maintaining the overpressure.

[0150] In this case, by adopting a plurality of steel sealing rings 6 with a thickness of about 2 mm, they would be subject to an upward bending of 3-4 mm. A different result can be obtained with different materials or by increasing the thickness of the movable rings.

[0151] A resulting force is clearly different in the case of a semiconductor wafer WS of 6-8 inches with a pressure brought always of 1-2 atm.

[0152] In the case of an internal pressure in the overpressure area P, it is possible to provide at least one sliding element 13 at the sliding points between each of the plurality of sealing rings 6 and the adjacent ones, for example bearings. Nothing prevents to provide different sliding elements 13, for example disk-like elements, or different elements.

[0153] In this regard, an alternative embodiment of an apparatus 1000’ and of a measuring system 100’, as shown in Figure 5 is also provided.

[0154] In this case an upper cover 107 of the overpressure area P is provided, which acts as a feedback to the force exerted by the pressure on the movable rings 6.

[0155] The movable rings 6 can thereby be made with a more reduced thickness.

[0156] Furthermore, a plurality of bearings 15 are provided, which are fixed to the movable rings 6 and incident on the upper cover 107, which allows the mutual sliding of the movable rings 6 with respect to each other and with respect to the upper cover 107, which, as mentioned, acts as a feedback to the force generated by the pressure in the overpressure area P.

[0157] In particular, in an exemplary embodiment, a bearing 15 is provided, made for example of an elastomeric material, for each movable ring, just as it is possible to provide one or more bearings associated with the pressurization structure 4, in particular with the upper portion thereof in contact with the above upper cover 107.

[0158] Furthermore, it is possible to provide a movement of the chuck 3 and to this purpose the apparatus 1000’ further comprises one or more movable supports 16 (in particular sliding ones), preferably of small diameter, which move the chuck 3 in lifting and lowering inside the overpressure area P. The chuck 3 does not thereby counter all the force exerted by the internal pressure during the lifting and lowering thereof.

[0159] Figure 5 also represents the perimetral connection 108 (or docking) towards the test machine.

[0160] In other words, in the present embodiment of figure 5, the drawback of the force exerted by the internal pressure that is discharged on the chuck 3 and on the movable rings 6, tending to deform and bend them, is also addressed.

[0161] In the embodiment of Figure 5, the chuck 3 and the housing are thus inserted into the structure 4 (in particular inserted into the structure delimited above by the upper cover 107) but are not subject to all the force caused by the internal pressure of the overpressure area P itself. Suitably, the upper cover 107 for force feedback and the bearings 15 abutting thereon allow the movable rings 6 to slide without swelling upwards when the overpressure area P is in fact pressurized.

[0162] In this embodiment, the structure 4 is thus closed at the bottom not by the chuck 3 or by the semiconductor wafer WS but by a lower wall 110.

[0163] In the example shown in the figures, the PCB 105 is arranged outside the structure 4, and thus above the upper cover 107, which is suitably shaped to house said component and also the housing.

[0164] In general, from what has been said above it is possible to provide, depending on the intended pressure in the overpressure area P: for more reduced overpressures and semiconductor wafers WS of smaller dimensions, the movement of the plurality of sealing rings 6 without depressurizing the overpressure area P each time; for higher overpressures but within a limit set by the materials and by the other above-mentioned features, the use of at least one sliding element 13, such as for example a bearing, to facilitate the mutual sliding thereof;

[0165] - for even higher overpressures, a depressurization and a displacement, with different packing of the plurality of sealing rings 6, from time to time.

[0166] In any case, even providing a depressurization from time to time, given that there is a generally very lowered configuration, and thus with elements which are very close to each other, the loss of gas A upon detachment of the probe head 101 would be minimum, for example of about 1-2 1.

[0167] In conclusion, summarizing the above, the present invention thus allows to overcome the technical problem, providing the above measuring system and solving in a simple manner all the drawbacks of the prior art, due to the possibility to create a pressurized bell for conditioning the testing area, or, due to the shown embodiment, to reconfigure the pressurization structure 4 depending on the specific testing requirements, in particular in the presence of “stepping” needs.

[0168] Therefore, the problem of the formation of electric arcs for tests on a whole semiconductor wafer WS is solved both with single test (“Full Wafer Single Touch”) and in the case of the above “stepping” between several devices, being allowed to move inside the overpressure area P.

[0169] It should be further observed that, advantageously, the suggested solution does not have problems concerning the test at the boundary of the semiconductor wafer WS, since even in the most extreme chips it is always possible to ensure the formation of overpressure areas due to the shape of the pressurization structure 4 connected to the chuck 3, externally with respect to said boundary of the semiconductor wafer WS.

[0170] Obviously, in order to meet contingent and specific requirements, a person skilled in the art will be allowed to bring several modifications and variants to the above-described measuring system, all falling within the scope of protection of the invention as defined by the following claims.

Claims

CLAIMS1. A measuring system (100, 100’) for the testing of devices under test (DUT) integrated on a semiconductor wafer (WS), comprising:- a probe head (101) comprising:• a plurality of contact elements (1) which extend along a longitudinal direction (H-H) between a first end (la), adapted to contact pads of a device under test (DUT), and a second and opposite end (lb);• a housing (2) configured to house said plurality of contact elements (i);- a pressurization structure (4) adapted to be associated, during the test, with a semiconductor wafer (WS) or with a chuck (3) that houses said semiconductor wafer (WS), and comprising:• a peripheral wall (5) defining a housing area (A) therein;• at least one sealing component (6) arranged inside said housing area (A) and comprising a hole (8) in which the housing (2) is housed, defining a chamber (P) in said housing area (A); and- at least one inlet (I) adapted to allow conveying a pressurized gas into said chamber (P), making, during the test, said chamber (P) an overpressure area.

2. The measuring system (100, 100’) according to claim 1, wherein the sealing component (6) is movable inside the housing area (A).

3. The measuring system (100, 100’) according to claim 1 or 2, wherein the sealing component (6) is ring-shaped and the housing (2) is housed in said ring, preferably at the center of said ring.

4. The measuring system (100, 100’) according to any one of the preceding claims, wherein the pressurization structure (4) comprises aplurality of sealing components (6) which are movable with respect to each other and provided with holes of different diameter, intended as a measure along a direction that is substantially orthogonal to said longitudinal direction (H-H), said plurality of sealing components (6) comprising:- a first sealing component (6a) comprising an outer perimeter (7) and adapted to directly connect with said peripheral wall (5);- a second sealing component (6b) comprising said central hole (8) adapted to receive said housing (2); and- a plurality of intermediate sealing components (6c) between said first sealing component (6a) and second sealing component (6b), said first sealing component (6a), said second sealing component (6b) and said plurality of intermediate sealing components (6c) being cascade- connected in a mutually sliding manner.

5. The measuring system (100, 100’) according to claim 4, wherein said movable sealing components (6a, 6b, 6c) are slidingly connected to each other so that a lower surface (11) of at least one sealing component is sliding on an upper surface (12) of an adjacent sealing component.

6. The measuring system (100, 100 j according to claim 4 or 5, wherein the first sealing component (6a) is, in use, the furthest one from the semiconductor wafer (WS), is fixed and is the one having the greatest diameter, said diameters progressively decreasing in the passage from said first sealing component (6a) to said second sealing component (6b) which, in use, is the closest one to the semiconductor wafer (WS).

7. The measuring system (100, 100 j according to any one of claims 4 to 6, wherein each of said plurality of movable sealing components (6) is connected to the adjacent one by interposing at least one sliding element8. The measuring system (100, 100’) according to claim 7, wherein said at least one sliding element (13) is a bearing.

9. The measuring system (100, 100’) according to any one of the preceding claims, further comprising at least one seal element (14) between said hole (8) of said at least one sealing component (6) and said housing (2).

10. The measuring system (100, 100’) according to any one of the preceding claims, further comprising at least one adaptor element between said hole (8) of said at least one sealing component (6) and said housing (2).

11. The measuring system (100, 100’) according to any one of the preceding claims, wherein said at least one sealing component (6) is made of a metal material, preferably steel, or of a composite material, preferably carbon fiber.

12. The measuring system (100, 100’) according to any one of the preceding claims, wherein said pressurization structure (4) comprises a bayonet system configured to connect it to the chuck (3).

13. The measuring system (100’) according to any one of the preceding claims, further comprising an upper cover (107) and at least one bearing (15) connected to said at least one sealing component (6) and abutting on said upper cover (107).

14. An apparatus (1000, 1000’) for the testing of devices under test (DUT) integrated on a semiconductor wafer (WS), comprising:- a measuring system (100) according to any one of the preceding claims;- a chuck (3) adapted to house the semiconductor wafer (WS); and- a conveying system (9) including at least one duct (10) in fluid connection with the inlet (I) of the system (100) for conveying the pressurized gas into the seal chamber (P).

15. The apparatus (1000, 1000’) according to claim 14, wherein the at least one duct (10) of said conveying system (9) is formed by at least one of:- a duct made in said chuck (3); - a duct made in said peripheral wall (5);- a duct passing through the housing (2).

16. The apparatus (1000’) according to claim 14 or 15, comprising at least one movable support (16) adapted to move said chuck (3) that is contained inside the pressurization structure (4).

17. The apparatus (1000, 1000’) according to any one of claims 14 to 16, wherein said gas flow (G) provides a gas with a high dielectric strength which is greater than that of air.

18. The apparatus (1000, 1000’) according to claim 17, wherein said high dielectric strength gas is sulfur hexafluoride.

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