Test system for performing high voltage tests

Abstract

A test system (100) for testing a device under test (DUT) is herein described, said test system (100) having a plurality of contact elements (10) which extend along a longitudinal direction (H-H) between a first end (10a), adapted to contact pads (DUTa, DUTb) of the device under test (DUT), and a second and opposite end (10b), at least one guide (20) provided with guide holes (20h) for housing at least a portion of the contact elements (10), a conveying system provided with at least one duct (30c) and configured to convey a gas flow (A) toward the device under test (DUT), and a peripheral structure (40) having a body (40b) with an end face (40f) facing the device under test (DUT), wherein the peripheral structure (40) is structured to define a cabin (C) that is in fluid communication with the conveying system for conveying the gas flow (A) thereinto, the first ends (10a) of the contact elements (10) being protruding from the guide (20) and being housed in said cabin (C), wherein the body (40b) of the peripheral structure (40) has an extension along the longitudinal direction (H-H) such as to form, during the testing operation of the device under test (DUT), a fluid constriction (S) between said device under test (DUT) and its end face (40f), thus causing an overpressure in said cabin (C) when the gas flow (A) is introduced thereinto.

Description

[0001] Title: Test system for performing high voltage tests

[0002] DESCRIPTION

[0003] Field of application

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

[0005] Prior art

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

[0007] The test performed on integrated circuits is particularly useful for detecting and isolating defective circuits as early as in the production phase. Normally, probe heads are thus used for the testing of the circuits integrated on wafers before cutting and assembling 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 equipped with guide holes and are located at a certain distance from each other, so as to leave a free area or air gap for the movement and the possible deformation of the contact probes, which are normally formed by wires of special alloys with good electrical and mechanical properties. 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.

[0009] 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 carefully evaluated and calibrated in the manufacturing step of a probe head, and the good electrical connection between the contact probes and the device under test should always be ensured.

[0010] Furthermore, the need of performing high voltage tests, for instance (but not only) in the automotive field, is increasingly common nowadays. Specifically, in recent years, the demand for power electronic components has increased dramatically due to the production of electric cars, with the need of performing tests at very high voltages, greater than 2000 V (even up to 10000 V), and at high currents, even greater than 3000 A. In these cases, the applied voltages are so high that very damaging phenomena may occur, such as for instance the onset of electric arcs or the emission of molten metal material from the pads of the device under test toward the probe head.

[0011] In order to counteract the onset of electric arcs, in recent years test systems have been proposed that involve conditioning the environment at the areas of the wafer affected by the test. Particularly, pressurized gas at the test area is supplied in order to inhibit the formation of electric arcs, since the higher the pressure, the higher the arc ignition voltage, as described by the Paschen curves.

[0012] For instance, some known solutions use a floating disk that creates an overpressure cabin on the surface of the tested wafer; however, this solution has some drawbacks, mainly due to the difficulty of testing the chips that are at the edge of the wafer.

[0013] The technical problem of the present invention is to devise a test system having such structural and functional features as to allow overcoming the limitations and drawbacks still affecting the known solutions, in particular which allows avoiding the onset of electric arcs during the test and at the same time ensures effective testing of all the chips integrated on the semiconductor wafer.

[0014] Summary of the invention

[0015] The solution idea underlying the present invention is to integrate a vertical probe head (i.e., a probe head having vertical probes) with a series of components (for instance comprising suitable ceramics) to create a static cabin equipped with walls that obstruct the passage of a pressurized gas (for instance air supplied thereinto through suitable ducts) from inside to outside the test system. In this way, a small constriction is formed between the lower face of the cabin and the semiconductor wafer (for instance the constriction being in a range between 50 gm and 150 gm) which creates a resistance to the passage of the gas such as to increase the pressure in the test area, thus reducing the probability of the occurrence of electric arcs in accordance with Paschen ’s law.

[0016] Based on this solution idea, the above technical problem is solved by a test system for testing a device under test, said test system comprising a plurality of contact elements which extend along a longitudinal direction between a first end, adapted to contact pads of the device under test, and a second and opposite end, at least one guide including guide holes for housing at least a portion of the contact elements, a conveying system provided with at least one duct and configured to convey, through said at least one duct, a gas flow toward the device under test, and a peripheral structure (or barrier) comprising a body with an end face facing the device under test, wherein the peripheral structure is structured to define a static cabin (or test area, in particular an area between the guide - which in some examples closes the cabin itself - and the device) in fluid communication with the conveying system for conveying del gas flow thereinto, the first ends of the contact elements being protruding from the guide and being at least partially arranged in said cabin (in particular surrounded by it). According to the invention, the body of the peripheral structure has an extension along the longitudinal direction such as to form, during the test of the device under test, a constriction between said device under test and its end face, thereby causing an overpressure in said cabin when the gas flow is introduced thereinto.

[0017] More particularly, the invention comprises the following additional and optional features, taken individually or in case in combination. Said additional and optional features are defined for instance in dependent claims 2 to 20.

[0018] According to an aspect of the present invention, the (fluid) constriction may correspond to the distance between the first end of the contact elements and the end face of the peripheral structure (or analogously, in use, the distance between the end face and the wafer or a pad of the device). Said distance may be measured along said longitudinal direction.

[0019] For instance, said distance may be in a range between 25 gm and 300 gm; this distance is suitable to create the desired overpressure.

[0020] According to an aspect of the present invention, the peripheral structure may be a protrusion projecting toward the device under test

[0021] For example, the peripheral structure, and thus the cabin, may be a protrusion projecting from a support element.

[0022] The support element may be selected from the guide itself or the protective element described below (i.e. a protective element which, during the testing operation, is arranged between the guide and the device under test and comprising a body equipped with holes in which the contact elements are housed, wherein said body is configured as a protective barrier against emissions of molten metal coming from the device under test toward the guide, thus preventing said emissions from reaching said guide; in this case, the protective element comprises protrusions which form the peripheral structure).

[0023] According to an aspect of the present invention, the peripheral structure may be static with respect to the guide.

[0024] In general, the peripheral structure is a static structure (for instance, but not necessarily, a ring) connected to elements of the test system (for instance connected to the guide, or to a shield, or to a housing, projecting therefrom, however without limiting to a specific example, in general connected to a support element) in a peripheral position with respect to the contact probes, so as to surround said contact probes, in particular their ends protruding from the guide holes.

[0025] According to an aspect of the present invention, the body of the peripheral structure may comprise at least one wall which defines a perimeter of the cabin.

[0026] According to an aspect of the present invention, the peripheral structure may be made of a ceramic material.

[0027] According to an aspect of the present invention, the test system may further comprise a stiffener, an interface board connected to the stiffener, and a housing configured to house at least partially the contact elements.

[0028] According to an aspect of the present invention, the conveying system may be formed by at least part of the stiffener, of the interface board and of the housing, said stiffener, said interface board and said housing being shaped to define the ducts (for example ducts passing through them) for the circulation of the gas flow therethrough and toward the cabin.

[0029] According to an aspect of the present invention, the test system may comprise a spacer connected to the body of the peripheral structure, said spacer being removable to vary, by removing it, the entity of said constriction.

[0030] According to an aspect of the present invention, in a particular embodiment, the peripheral structure may be connected, directly or indirectly, with the conveying system (in particular with the lowest component of said conveying system) and represents the terminal portion thereof, thus defining together an external structure which surrounds the contact elements.

[0031] According to an aspect of the present invention, the cabin may be connected with the at least one duct and may be open toward the device under test so that, during the test, the pressurized gas flow is at said device under test.

[0032] According to an aspect of the present invention, the guide may represent the upper portion of the cabin, said upper portion being opposite the device under test (for instance with reference to the longitudinal direction), the peripheral structure being protruding from said guide.

[0033] According to an aspect of the present invention, the test system may also comprise a protective element which, during the test, is arranged between the guide and the device under test, said protective element comprising a body equipped with holes where the contact elements are housed, wherein said body is configured as a protective barrier against emissions of molten metal coming from the device under test toward the guide, thus preventing said emissions from reaching said guide.

[0034] According to an aspect of the present invention, the protective element may be removably connected to the test system.

[0035] According to an aspect of the present invention, the protective element may comprise a peripheral protruding portion and at least one internal protruding portion, both projecting from the body thereof toward the device under test, wherein the peripheral protruding portion forms the peripheral structure, and wherein the protective element represents the upper portion of the cabin, said upper portion being opposite the device under test (for instance with reference to the longitudinal direction) .

[0036] According to an aspect of the present invention, the contact elements may be adapted to move with respect to the protective element, which is a fixed component of the test system.

[0037] According to an aspect of the present invention, the holes of the protective element may have a diameter greater than the diameter of the guide holes of the guide (the term diameter for example meaning a transversal direction) .

[0038] According to an aspect of the present invention, the holes of the protective element may be sized to allow the passage of the gas flow toward the cabin.

[0039] According to an aspect of the present invention, the contact elements may be divided into first contact probes, which are grouped in at least one group and are configured to contact, as a group, a corresponding first pad of the device under test, and in at least one second contact probe configured to contact a corresponding second pad of the device under test which is different from the first pad, wherein the first pad is a source pad of the device under test and the second pad is a gate or drain pad of the device under test.

[0040] According to an aspect of the present invention, the test system may comprise a plurality of groups of first contact probes, each of said groups being configured to contact a respective first pad of a plurality of first pads on a semiconductor wafer, wherein, for each of said groups, the respective first contact probes are configured to contact all together, as a group, said respective first pad, and wherein said groups of first contact probes are alternated to second contact probes, each of said second contact probes being arranged to contact a respective second pad of a plurality of second pads on the semiconductor wafer.

[0041] According to an aspect of the present invention, the test system may comprise a single cabin defined by a single peripheral structure which surrounds all of said groups of contact probes (regardless of the presence of the groups, there may be a single cabin which surrounds all of the contact elements, in particular their ends protruding toward the device under test).

[0042] According to another aspect of the present invention, the test system may comprise a plurality of cabins, wherein there is a cabin for one or more respective groups of said plurality of groups, said cabins being defined by a plurality of respective local peripheral structures arranged around the contact probes of said one or more respective groups.

[0043] The features and advantages of the test 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.

[0044] Brief description of the drawings

[0045] In these drawings:

[0046] - figure 1 schematically shows a test system according to the present invention;

[0047] - figure 2 schematically shows a test system according to an embodiment of the present invention;

[0048] - figure 3 shows a detail of the test system of figure 2; - figure 4 shows a further detail of the test system of figure 2; and

[0049] - figure 5 shows a bottom schematic view of a portion of the test system according to an embodiment of the present invention.

[0050] Detailed description

[0051] With reference to these figures, reference number 100 globally and schematically indicates a test or measurement system (or apparatus) according to the present invention for testing devices under test (herein indicated with DUT - acronym for “Device Under Test”) integrated on a semiconductor wafer.

[0052] It should be noted that the figures represent schematic views and are not drawn to scale, but they are instead drawn, so as to emphasize the important features of the invention. Furthermore, in the figures, the different elements are represented schematically, and their shape can vary depending on the desired application. Moreover, it should be noted that, in the figures, identical reference numbers refer to elements which are identical in shape or function. Finally, particular expedients described in relation to an embodiment illustrated in a figure can also be used for the other embodiments illustrated in the other figures.

[0053] Moreover, it is noted that, unless expressly stated, described process steps can also be reversed if necessary.

[0054] Further, in the context of the present invention, the term “test system” is used to indicate a contact structure with pads (for instance pads of the device under test DUT) without being limited by the presence or not of particular components. In general, said term thus indicates a set of components associable with further components (for instance a test apparatus) for testing devices integrated on a semiconductor wafer, and thus in general it indicates an apparatus for testing electronic devices. Said test system may also be indicated with the term “probe card” or “contact system”.

[0055] The test system 100 is thus adapted to connect with an apparatus (not illustrated in the figures) to perform the test of devices under test DUT integrated on a semiconductor wafer (indicated with reference number 23), for instance to perform high voltage tests.

[0056] As illustrated in figure 1, the test system 100 comprises a plurality of contact elements or contact probes 10 which are slidingly housed therein and intended to connect the device under test DUT integrated on the semiconductor wafer 23 with the test apparatus.

[0057] In order to house the contact probes 10, the test system 100 comprises at least one guide 20 comprising guide holes 20h within which the contact probes 10 can slide. The guide holes 20h are thus suitably configured to house at least a portion of the contact probes 10 and to guide said contact probes 10 in their overtravel and scrub movement during the test. The guide 20 comprises a first face FA facing, during the test, the device under test DUT (said 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 (said face FB thus being an upper face according to the reference of the figures) .

[0058] In the embodiment illustrated in the figures, the guide 20 is a lower guide (i.e. it is the closest guide to the device under test DUT) and the test system 100 also comprises an upper guide 90, which comprises corresponding guide holes 90h and is separated from the lower guide by an air zone or gap G, even if the present invention is not limited to this specific configuration and the upper guide 90 may not be present or there may also be one or more intermediate guides (not illustrated in the figures), depending on the needs and / or circumstances.

[0059] As known, the assembly formed by the contact probes 10 and by the guide / s is indicated as “probe head”.

[0060] Furthermore, the test system 100 may comprise a housing 70 adapted to contain at least part of the contact probe body, wherein the lower guide 20 and the upper guide 90 are separated by said housing 70, which also acts as a protection.

[0061] Each contact probe 10 comprises a body lOp which extends along a longitudinal axis (or direction) H-H between a first end 10a and a second and opposite end 10b, which are adapted to contact respective contact pads (herein simply indicated as “pads”). By way of example, the first end 10a (also called contact tip) is adapted to contact pads of the device under test DUT integrated on the semiconductor wafer 23, whereas the second end 10b (also called contact head) is adapted to contact pads of a space transformer or of a printed circuit board (PCB), said component being generically identified with reference number 60 and being generally defined herein as “interface board 60”. It is noted that the ends 10a and 10b may be of any shape suitable to the needs and / or circumstances, and thus they are not necessarily pointed in shape.

[0062] The contact probes 10 are thus vertical contact probes which extend along the longitudinal axis H-H between the two opposite ends, for instance probes of the buckling beam type. The test system 100 further comprises a stiffener 50, which the above mentioned interface board 60 is connected to. The stiffener 50 is adapted to keep the components of the test system 100 in position and to solve flatness problems. As illustrated in figure 1, even the housing 70 is connected to the stiffener 50, in particular it is connected to a lower face of said stiffener 50 (i.e. its closest face to the device under test).

[0063] In many high power applications, for instance in the automotive field, the device under test DUT comprises a first type of pads (hereinafter called “first pads” and indicated with reference “DUTa”), which are characterised by very high voltages and are generally large in size (for instance with sides or diameters of a few millimeters), and a second type of pads (hereinafter called “second pads” and indicated with reference “DUTb”), which are used for lower voltages and are thus different from the first pads DUTa. Generally, in light of the very high voltages of the first pads DUTa, many contact probes are used to contact said first pads DUTa, in order to distribute the current on several probes during the test. Said pads are contacted by the first end 10a of the contact probes 10, as previously described.

[0064] Particularly, according to an embodiment of the present invention, the contact probes 10 are divided into first contact probes, herein identified with reference number 10’, and into second contact probes, herein identified with reference number 10”. More particularly, the first contact probes 10’ are grouped in at least one group (identified with reference number 10g) and are configured to contact, as a group, a corresponding first pad DUTa of the device under test DUT. In this way, the first contact probes 10’, grouped in the group 10g, are all adapted to simultaneously contact a same pad of the device under test DUT, in particular a power pad (i.e. they are arranged to contact, all together in said group 10g, a same first pad DUTa). As above indicated, the device under test DUT also comprises at least one second pad DUTb, which is contacted by at least one second contact probe 10” configured to perform said contact, which second contact probe 10” is generally arranged alternately with the first contact probes 10’, said second pad DUTb being different from the first pad DUTa.

[0065] By way of example, as above mentioned, the first pad DUTa may be a source pad of the device under test DUT, whereas the second pad DUTb may be a gate pad (or a drain pad) .

[0066] Furthermore, since the voltage on the first pad DUTa is very high, there is a high number of probes which contact said first pad DUTa, a number which may vary from 50 to 350, however without being limited by a particular number; in this way, there are multiple contact probes in contact with the first power pad DUTa, so as to easily allow the high voltage signal passage.

[0067] It is noted that in the figures, for simplicity, an example is illustrated with a limited number of contact probes on the pad of a device under test DUT (in this case comprising the two pads DUTa and DUTb), although it should be understood that the figures are only provided by way of non-limiting example of the present invention and any number, even if high, may be provided for.

[0068] As above indicated, in high voltage tests, unwanted phenomena may occur, such as for instance the formation of electric arcs between the pads of the device under test DUT. In order to inhibit the formation of said electric arcs, the environment in the areas of the wafer affected by the test is conditioned, in particular by supplying pressurized gas at the test area, taking into account the fact that the higher the pressure, the higher the arc ignition voltage, as described by Paschen’s curves.

[0069] Particularly, the test system 100 comprises a conveying system comprising at least one duct (indicated with reference number 30c) and configured to convey, through said at least one duct 30c, a gas flow toward the device under test DUT (for instance air, said flow being indicated with reference A and being represented in the figures by an arrow) .

[0070] In an embodiment of the present invention, the conveying system is formed by (comprises) at least part of the stiffener 50, of the interface board 60 and of the housing 70, which are suitably shaped to define the above duct 30c (in particular a plurality of ducts 30c) for the circulation of the gas flow A through them toward the test area. In other words, the stiffener 50, the interface board 60 and the housing 70 are shaped so as to define the various ducts 30c therein, which thus separate different portions of the above components from each other.

[0071] Advantageously according to the present invention, the probe head (i.e., the assembly comprising the guides and the contact probes) is associated with the above components and further elements to create a static cabin into which the gas flow A that circulates in the ducts 30c is conveyed.

[0072] More particularly, the test system 100 comprises a peripheral structure (also indicated as “peripheral barrier”, reference number 40) having a body 40b with an end face 40f facing the device under test DUT. This peripheral structure 40 is suitably structured to define a cabin C (or chamber) which is in fluid communication with the above conveying system for supplying the gas flow A thereinto.

[0073] The term “cabin C” thus indicates a specific area of the test system 100 at the device under test DUT into which pressurized gas is inserted. More particularly, the cabin C is arranged, during the test, at the device under test DUT, in particular in an area between the guide 20 and said device under test DUT.

[0074] In the embodiment illustrated in the figures, the first ends 10a of the contact probes 10 protrude from the guide 20 and are housed in said cabin C.

[0075] The cabin C is a static cabin, i.e. it does not move with respect to the remaining components of the test system (in particular with respect to the guide 20, which, in an embodiment, is its upper wall).

[0076] The body 40b of the peripheral structure 40, which defines the cabin C, comprises at least one wall 40w that forms the perimeter of said cabin C.

[0077] The peripheral structure 40 is not limited by a specific shape, for instance the defined profile may be circular, as well as it may be squared-shaped or rectangular, without any limitation, said peripheral structure 40 surrounding the contact probes 10 at least partially, in particular the lower portion of said contact probes 10 (and it does not house contact probes in its own body). In general, the peripheral structure 40 surrounds the contact probes, in particular their end protruding from the guide toward the device under test DUT. Suitably, the body 40b of the peripheral structure 40 which defines the cabin C has an extension along the longitudinal direction H- H such as to form, during the test of the device under test DUT, a fluid constriction (indicated with reference S) between said device under test DUT (in particular between the surface of the semiconductor wafer 23 or the pads of the DUT itself) and its end face 40f. In this way, an overpressure is created in the cabin C when the gas flow A is introduced thereinto, since the constriction S creates a resistance to the passage of the gas flow A exiting from the cabin C, such as to increase the pressure in the test area, thus reducing the probability of occurrence of electric arcs according to the Paschen law.

[0078] Specifically, the constriction S corresponds to the distance (identified with reference D) that is created during the test between the first end 10a of the contact probes 10 and the end face 40f of the peripheral structure 40. This distance D is thus less than the distance between the first end 10a of the contact probes 10 and the face FA of the guide 40, thus creating the above constriction S (or also less than the distance between the first end 10a and a lower face of a protective element that will be described hereinafter, more generally a face of a lower support).

[0079] By way of example, the distance D may be in a range between 25 gm and 300 gm, preferably between 50 gm and 150 gm, and thus such as to create a constriction for the gas flow A exiting from the cabin C, with the formation of a local overpressure area at the power pad whereon the test is executed.

[0080] In the example of figure 1, the guide 20 is the upper portion of the cabin C (i.e. the portion opposite the device under test DUT with respect to the longitudinal direction H-H), whereas the peripheral structure 40 defines its side walls by protruding below from said guide 20; said peripheral structure 40 may be formed integrally with the guide 20 or it can be connected thereto at a later time, without limiting the scope of the present invention. In any case, other configurations are possible, as it will be illustrated hereinafter in the present description.

[0081] In other words, in general, the peripheral structure 40 is a protrusion (in particular a local protrusion) projecting from a support element (for instance the guide 20 or a protective element having the features described below, or still from any other support element) toward the device under test DUT; it may be static with respect to said guide.

[0082] In general, the peripheral structure 40 may be a local structure formed at the periphery of the guide 20 and may protrude below therefrom as described above, thus forming the chamber C that surrounds the area under test, or it may be a structure arranged externally, for instance directly in contact with the outermost portions of the housing, without limiting the scope of the present invention.

[0083] In the context of the present invention the term “peripheral structure” indicates a structure that is in a peripheral position with respect to the contact probes, which are contained in the active area of the probe head (in general in the active zone of the test system 100), i.e. in the perforated part of the guide 20 that houses the contact probes 10, and that protrudes below toward the device under test DUT to create the above constriction S.

[0084] In an embodiment of the present invention (as illustrated in figure 1), the peripheral structure 40 is connected with the conveying system (for instance connected thereto indirectly through the outermost portion of the guide 20) and represents its terminal portion, thus defining with it an external structure that surrounds the contact probes 10. More particularly, in this example, the peripheral structure 40 is associated with the peripheral part of the guide 20, which is connected with peripheral portions of the housing 70 (in particular its upper face is connected to the housing), even if the present invention is not limited to this configuration and other embodiments are possible, as it will be illustrated hereinafter.

[0085] In any case, the cabin C is connected above with the ducts 30c of the conveying system and is open below toward the device under test DUT, so that, during the test, the pressurized gas flow A is supplied at said device under test DUT.

[0086] In order to ensure an effective supply of the gas flow A, sealing means 30t, such as for instance suitable O-rings, are provided at the connections between a component and the other, such as for instance between the stiffener 50 and the housing 70.

[0087] Summing up, according to the present invention, the gas flow A is channeled toward the surface of the semiconductor wafer 23 by means of openings inside the test system 100, working for instance on housing and ceramics. Still more particularly, the conveying system illustrated in the exemplifying figures comprises the stiffener 50 perforated on top, so as to have an inlet 50in for the gas flow A, said inlet 50in being in fluid communication with an external supply line (being part of means external to the test system 100) adapted to supply the gas flow A that is conveyed into the cabin C. In this way, the conveying system is in fluid communication with the external supply line and comprises components joined to each other, thus allowing the gas flow A to also circulate inside the probe head where the contact probes 10 are housed, which probe head is in fluid communication with the cabin C.

[0088] The ducts 30c are thus formed through a suitable conformation (shaping) of the walls of the housing 70, stiffener 50, and interface board 60, as well as through the use of suitable ceramics, and in this way one or more suitable openings are present to allow conveying the pressurized gas flow A into the cabin C (and thus toward said semiconductor wafer 23).

[0089] The gas exiting from the cabin C through the constriction S is then conveyed outside through suitable discharge channels.

[0090] In an embodiment, the peripheral structure 40 is made of ceramic material, even if the present invention is in no way limited by the used materials.

[0091] Now, with reference to figure 2, in an embodiment of the present invention, in order to effectively protect the test system 100 from molten metal emissions coming from the device under test, it also comprises a protective element 80 (also called “shield”) associated with the guide 20.

[0092] In the context of the present invention, the term “associated” indicates that the protective element 80 is arranged close to the guide 20 and form, together with said guide 20, a set of elements, for instance substantially parallel to each other and suitably spaced apart.

[0093] The protective element 80, during the test, is between the guide 20 and the device under test DUT and comprises a body 80b comprising holes 80h where the contact probes are housed. In this way, the protective element 80 is configured as a protection barrier against the molten metal emissions coming from the device under test DUT toward the guide 20, thus preventing said emissions from reaching said guide 20. In other words, the molten metal emissions coming from the device under test DUT during the test at high voltage are blocked by the protective element 80, which is arranged and shaped so as to intercept the emitted metal before it reaches the guide, said metal impacting on its lower face.

[0094] In the absence of the protective element 80, portions of molten metal coming from the device under test DUT would hit the guide 20, thus blocking the probes in the guide holes 20h and causing a short circuit between the first pad DUTa and the second pad DUTb (for instance a short circuit between source and gate of the device). Thanks to the protective element 80 of the present invention, the molten metal emissions are blocked by it, and said protective element 80 is arranged and shaped so as to intercept the metal portions before they reach the guide 20, thus avoiding a jamming of the contact probes 10 and keeping the suitable separation between source and gate.

[0095] In an embodiment, the protective element 80 is removably connected to the test system 100. The fact that the protective element 80 is removable is advantageous since in this way it is possible to replace it after a certain accumulation of metal.

[0096] In this embodiment, it is possible to use the protective element 80 for forming the cabin C, for instance by using said protective element 80 as upper portion of said cabin C and making the peripheral structure 40 protrude from it toward the device under test DUT for the formation of the constriction S.

[0097] Particularly, as detailed in figures 3 and 4, the protective element 80 comprises protruding portions projecting from the body 80b thereof toward the device under test DUT, in particular it comprises a peripheral protruding portion 80p’ and internal protruding portions 80p” (i.e., arranged internally, in particular surrounded by said peripheral protruding portion 80pj. In an embodiment, the peripheral protruding portion 80p’ forms the peripheral structure 40. The internal protruding portions 80p” instead ensure a suitable separation between different types of contact probes (for instance between source and gate), so that the emitted molten metal portions do not cause a short circuit between the different pads DUTa and DUTb of the device under test DUT. In an embodiment, the peripheral protruding portion 80p’ surrounds the contact probes and creates the cabin C, whereas the internal protruding portions 80p” do not surround the probes, as illustrated in figure 5, which shows a schematic sectional bottom view (or top view, whereas the previous figures are front sectional views).

[0098] Obviously, this is only an example and other configurations may be implemented. For instance, the peripheral structure 40 may be a component independent from the protective element 80 (and thus a component external thereto which does not protrude therefrom); in other embodiments, the internal protruding portions of 80p” (which in the above embodiment only act as barriers) could be exploited to also create a second chamber adjacent to the first chamber.

[0099] The protective element 80 may be made of a ceramic material (as the guide 20), even if the present invention is not limited by the materials used.

[0100] In an embodiment, the protective element 80 is a static shield and the contact probes 10 are adapted to move with respect thereto (which is thus a fixed component of the test system 100). In this case, the holes 80h of the protective element 80 have a diameter greater than the diameter of the guide holes 20h of the guide 20, and in general a diameter greater than that of the contact probes 10.

[0101] In the context of the present invention, the term “diameter” indicates a dimension measured in a direction that is substantially orthogonal to the longitudinal axis H-H of the contact probes 10 (and thus in a direction substantially transversal).

[0102] In other words, in this embodiment, the protective element 80 is connected and integral to the guide 20 and may be easily removed and changed (for instance through connection elements such as screws between said guide and said shield) when the metal accumulation starts compromising the holes 80h (which, as seen above, are wider than the contact probes) for the passage of the contact probes 10. In general, it is noted that it is the guide 20 that has the function of guiding the contact probes 10, whereas the protective element 80 is not configured to perform this task, but it is still important that in this embodiment there is not an excessive accumulation of metal in the holes in order to prevent the probes from getting stuck.

[0103] Still more particularly, in this embodiment, the holes 80h of the protective element 80 are sized so as to allow the passage of the gas flow A introduced from the ducts 30c in the probe head toward the cabin C. In other words, the gas flow is conveyed through the holes 80h in order to create a flow which, in addition to inhibiting the phenomenon of electric arcs generation, further protects from the above phenomenon of emission of molten metal from the device under test DUT, ensuring a greater cleaning of said holes 80h.

[0104] As above discussed, the protective element 80 thus contributes forming the cabin C, i.e. it is itself a portion of said cabin C (it represents in particular the upper wall, with suitable openings for the passage of the pressurized gas, and possibly with the peripheral protruding portion 80p’ which is the peripheral structure 40 of the system) .

[0105] Furthermore, in an embodiment of the present invention, a spacer 90 connected to the body 40b of the peripheral structure 40 is provided (a schematic example is shown in figures 3 and 4), said spacer 90 being removable to vary, by removing the same, the entity of the constriction S, in particular the distance D between the first end 10a of the contact probes 10 and the end face 40f of the peripheral structure 40, for instance following the consumption of the contact probes 10.

[0106] Finally, in an embodiment of the present invention, the contact probes 10 may be arranged in the guide 20 in such a way that there is a plurality of groups 10g of first contact probes 10’ (i.e. the probes intended to contact the source pads). Each of the above groups 10g is thus intended to contact a specific first pad DUTa of a plurality of first pads on the semiconductor wafer 23 (there can be multiple devices under test and more generally multiple first pads DUTa on the semiconductor wafer 23). In this way, for each of the above groups 10g, the first contact probes 10’ are adapted to contact altogether a respective first pad DUTa. These groups 10g of first contact probes 10’ are alternated with second contact probes 10”, which are arranged to contact respective second pads DUTb (as seen above, there may be multiple devices under test and thus multiple second pads DUTb on the semiconductor wafer 23). Figure 5 is an example of this feature.

[0107] The various pads may be pads of a same device under test DUT or may be the respective pads of different devices on the semiconductor wafer 23, without any limitation for the scope of the present invention.

[0108] It is thus possible to test multiple dices in parallel, thanks to the possibility of dividing the contact probes into groups as above discussed and of arranging the various groups at the chips or dices under test (for instance 4 dices), preferably with the presence of a single cabin C defined by a single peripheral structure 40 that surrounds the entire active area where the contact probes 10 are present (as represented in figure 5). In this case, the peripheral structure 40 (which may be substantially a ceramic ring that protrudes below and that surrounds the probes) is extended and spaced apart from the probes, so that, during the test, it is at the single dices which are adjacent to the dices under test and which, as a whole, surround them (taking into account that the dices under test are generally arranged at a distance of one or more dices from the wafer edge) .

[0109] In any case, less preferred embodiments are not excluded, which provide for the formation of various static cabins C delimited by the own local peripheral structures which protrude toward the device under test DUT surrounding the various test areas.

[0110] In the example of the figures, each group 10g may be further divided into subgroups of first probes 10’ (for instance a subgroup of four probes), but said probes are anyway in contact with the same first pad DUTa (for instance, the division into subgroups may help the routing of the signal on the PCB), even if obviously this is in no way limiting for the scope of the present invention.

[0111] In conclusion, summarizing the above, the present invention thus allows brilliantly overcoming the technical problem, by providing the above test system and solving all of the prior art drawbacks in a simple manner, thanks to the formation of the overpressure static cabin.

[0112] Advantageously according to the present invention, components for the formation of the above cabin are associated with a probe head, thus creating a static overpressure system integrated in the probe head. For instance, this integration allows creating the cabin by means of ceramic walls which close the passage of pressurized gas (for example, compressed air) from inside to outside the test system. The small air gap which is created between the surface of the peripheral structure and the semiconductor wafer (for instance between 50 gm and 150 gm) creates such a resistance as to increase the pressure at the centre in the test area, with the formation of overpressure areas delimited by the peripheral constrictions on the tested area (in general the peripheral structure that defines the chamber is a protrusion from a lower support projecting toward the device under test, even more generally a structure, for instance a ring, which surrounds the probes), thus reducing the probability of occurrence of electric arcs, according to the Paschen law.

[0113] Thanks to the adopted solution, moreover, it is possible to use vertical probes, with all of the advantages that said technology involves.

[0114] It is also possible to run tests with high parallelism, with multiple dice tested simultaneously.

[0115] Finally, it should be noted that, advantageously, the proposed solution does not have problems in the test at the edge of the wafer, since even in the most extreme (outermost) chips it is always possible to ensure the formation of overpressure areas thanks to the shape of the cabin, with the formation of the static peripheral structure around the tested area (which peripheral structure is substantially a static ring that surrounds the probes): the peripheral structure may directly rest on the board dies (precisely the last ones, generally not working), to test the adjacent dies, and there are no complex floating mechanical structures which extend beyond the edge and which cause problems for maintaining cabin pressure.

[0116] It is possible, by grouping the probes, to test dices in parallel, while solving the problem of wafer-edge testing.

[0117] Obviously, in order to meet contingent and specific requirements, a person skilled in the art can bring to the above-described test system several modifications and variants, all falling within the scope of protection of the invention as defined by the following claims.

Claims

CLAIMS1. A test system (100) for testing a device under test (DUT), said test system (100) comprising:- a plurality of contact elements (10) which extend along a longitudinal direction (H-H) between a first end (10a), which is adapted to contact pads (DUTa, DUTb) of the device under test (DUT), and a second and opposite end (10b);- at least one guide (20) comprising guide holes (20h) for housing at least a portion of the contact elements (10);- a conveying system including at least one duct (30c) and configured to convey a gas flow (A) toward the device under test (DUT); and- a peripheral structure (40) comprising a body (40b) having an end face (40f) facing the device under test (DUT), wherein the peripheral structure (40) is structured to define a cabin (C) in fluid communication with the conveying system for conveying the gas flow (A) thereinto, the first ends (10a) of the contact elements (10) being protruding from the guide (20) and being at least partially located in said cabin (C), wherein the body (40b) of the peripheral structure (40) has an extension along the longitudinal direction (H-H) such as to form, during the testing operation of the device under test (DUT), a fluid constriction (S) between said device under test (DUT) and its end face (40f), thus causing an overpressure in said cabin (C) when the gas flow (A) is introduced thereinto.

2. The test system (100) according to claim 1, wherein said fluid constriction (S) corresponds to the distance (D) between the first end (10a)of the contact elements (10) and the end face (40f) of the peripheral structure (40).

3. The test system (100) according to claim 2, wherein said distance (D) is in a range between 25 gm and 300 gm.

4. The test system (100) according to any one of the preceding claims, wherein the peripheral structure (40) is a protrusion projecting toward the device under test (DUT) and is static with respect to the guide (20).

5. The test system (100) according to any one of the preceding claims, wherein the body (40b) of the peripheral structure (40) comprises at least one wall (40w) which defines a perimeter of the cabin (C) .

6. The test system (100) according to any one of the preceding claims, wherein the peripheral structure (40) is made of ceramic material.

7. The test system (100) according to any one of the preceding claims, further comprising:- a stiffener (50);- an interface board (60) connected to the stiffener (50); and- a housing (70) configured to house at least partially the contact elements (10).

8. The test system (100) according to claim 7, wherein the conveying system is formed by at least part of the stiffener (50), the interface board (60) and the housing (70), said stiffener (50), said interface board (60) and said housing (70) being shaped to define the at least one duct (30c) for the circulation of the gas flow (A) through them and toward the cabin (C).

9. The test system (100) according to any one of the precedingclaims, comprising a spacer (90) connected to the body (40b) of the peripheral structure (40), said spacer (90) being removable to vary, by removing it, the extent of said fluid constriction (S) .

10. The test system (100) according to any one of the preceding claims, wherein the peripheral structure (40) is connected, directly or indirectly, with the conveying system and represents the terminal portion thereof, defining together with said conveying system an external structure which surrounds the contact elements (10), said cabin (C) being connected with the at least one duct (30c) and being open toward the device under test (DUT) so that, during the testing operation, the pressurized gas flow (A) is at said device under test (DUT) .

11. The test system (100) according to any one of the preceding claims, wherein the guide (20) is the upper portion of the cabin (C), said upper portion being opposite the device under test (DUT), the peripheral structure (40) being protruding from said guide (20).

12. The test system (100) according to any one of the claims from 1 to 10, further comprising a protective element (80) which, during the testing operation, is arranged between the guide (20) and the device under test (DUT), said protective element (80) comprising a body (80b) equipped with holes (80h) in which the contact elements (10) are housed, wherein said body (80b) is configured as a protective barrier against emissions of molten metal coming from the device under test (DUT) toward the guide (20), thus preventing said emissions from reaching said guide (20).

13. The test system (100) according to claim 12, wherein the protective element (80) is removably connected to said test system (100).

14. The test system (100) according to claim 12 or 13, wherein the protective element (80) comprises a peripheral protruding portion (80p’) and at least one internal protruding portion (80p”) projecting from the body (80b) thereof toward the device under test (DUT), wherein the peripheral protruding portion (80pj forms the peripheral structure (40), and wherein the protective element (80) is the upper portion of the cabin (C), said upper portion being opposite the device under test (DUT).

15. The test system (100) according to any one of the claims from 12 to 14, wherein the contact elements (10) are adapted to move with respect to the protective element (80), which is a fixed component of said measuring test system (100), and wherein the holes (80h) of said protective element (80) have a diameter that is greater than a diameter of the guide holes (20h) of the guide (20).

16. The test system (100) according to any one of the claims from 12 to 15, wherein the holes (80h) of the protective element (80) are sized to allow the passage of the gas flow (A) toward the cabin (C) .

17. The test system (100) according to any one of the preceding claims, wherein the contact elements (10) are divided into first contact probes (10’), which are grouped in at least one group (10g) and are configured to contact, as a group, a corresponding first pad (DUTa) of the device under test (DUT), and into at least one second contact probe (10”) configured to contact a corresponding second pad (DUTb) of the device under test (DUT) which is different from the first pad (DUTa), wherein the first pad (DUTa) is a source pad of the device under test (DUT) and the second pad (DUTb) is a gate or drain pad of the device under test (DUT).

18. The test system (100) according to claim 17, comprising aplurality of groups (10g) of first contact probes (10’), each of said groups (10g) being configured to contact a respective first pad (DUTa) of a plurality of first pads on a semiconductor wafer (23), wherein, for each of said groups (10g), the respective first contact probes (10’) are configured to contact all together said respective first pad (DUTa), and wherein said groups (10g) of first contact probes (10”) are alternated with second contact probes (10”), each of said second contact probes (10”) being arranged to contact a respective second pad (DUTb) of a plurality of second pads on the semiconductor wafer (23).

19. The test system (100) according to claim 18, comprising a single cabin (C) defined by a single peripheral structure (40) surrounding all groups of contact probes (10).

20. The test system (100) according to claim 18, comprising a plurality of cabins (C), wherein there is a cabin for one or more respective groups of said plurality of groups, said cabins (C) being defined by a plurality of respective local peripheral structures (40) arranged around the contact probes (10) of said one or more respective groups.

Images