Method and apparatus for electron beam testing of electrical connections on a substrate - Patents.com

Abstract

A method is described for testing electrical connections of a substrate having a first surface contact (21) and a first electrical connection (20) extending from the first surface contact (21). The method includes the steps of (a) discharging the first surface contact (21) by focusing and deflecting a first electron beam (111) having a first electron energy on the first surface contact (21), (b) charging the first surface contact (21) by focusing and deflecting a second electron beam (112) having a second electron energy different from the first electron energy on the first surface contact (21), and (c) inspecting the first electrical connection (20) by detecting signal electrons emitted from the substrate. An apparatus for testing electrical connections of a substrate using two electron beams of different electron energies according to the methods described herein is further described.

Description

[Technical field]

[0001] The present disclosure relates to methods and apparatus for testing electrical connections extending through a substrate. More particularly, embodiments described herein relate to non-contact testing of electrical interconnects in a substrate using an electron beam, particularly for identification and characterization of defects such as shorts, opens, and / or leaks via voltage contrast measurements. [Background technology]

[0002] In many applications it is necessary to inspect a substrate to monitor its quality. For example, for the display market, glass substrates are manufactured on which a layer of coating material is deposited. During the processing of the substrate, for example during coating of the substrate, defects can occur, so inspection of the substrate to check for defects and monitor the quality of the display can be beneficial.

[0003] Additionally, semiconductor substrates and printed circuit boards for manufacturing complex microelectronic or micromechanical components are typically tested before, during, and / or after manufacturing to determine defects such as shorts or opens in metal paths and interconnects provided on the substrate. For example, a substrate for manufacturing a complex microelectronic device may include multiple interconnect paths for connecting semiconductor chips mounted on the substrate. The device under test may further include, for example, thin film transistors (TFTs), connection networks, transistors, display pixels, and other components.

[0004] Various methods are known for testing such components, for example by mechanically contacting contact pads of the component under test with contact probes to determine whether the component is defective, however, due to the increasing miniaturization of components, the components and contact pads are becoming smaller and smaller, which may make it difficult to contact the contact pads with the contact probes and may even risk damaging the device under test during testing.

[0005] For example, it is also possible to contactlessly probe the component under test using the electron beam of an electron beam testing column (EBT column). Electron beam testing can be used to monitor electrical connections of a board for defects. In EBT testing, a specific voltage is applied to the component under test and a primary electron beam is used to generate signal electrons that are emitted from the board and from which a conclusion can be made about the integrity of the component. However, traditional electron beam testing methods may not be suitable for testing advanced microelectronic components, considering the ever-increasing number of miniaturized components to be tested in short time intervals on one board while maintaining a high throughput.

[0006] It would therefore be beneficial to provide a test method and apparatus suitable for reliably and quickly testing complex microelectronic devices. Summary of the Invention

[0007] In light of the above, a method and an apparatus for testing electrical connections of a substrate are provided according to the independent claims. Further aspects, advantages and beneficial features are apparent from the dependent claims, the description and the accompanying drawings.

[0008] According to one aspect, a method for testing electrical connections of a substrate is provided, the substrate having a first surface contact and a first electrical connection extending from the first surface contact, the method includes (a) discharging the first surface contact by focusing and deflecting a first electron beam having a first electron energy on the first surface contact, (b) charging the first surface contact by focusing and deflecting a second electron beam having a second electron energy different from the first electron energy on the first surface contact, and (c) inspecting the first electrical connection by detecting signal electrons emitted from the substrate.

[0009] In some embodiments, the substrate is an advanced packaging substrate (AP substrate) or a panel level packaging substrate (PLP substrate).

[0010] In some embodiments, discharging (a) is performed before charging (b). In some embodiments, discharging (a) is additionally or alternatively performed after inspection (c). In some embodiments, discharging (a) is performed before charging (b) and after inspection (c). In other words, discharging (a) of the first surface contact with the first electron beam may be performed before charging (b) of the first surface contact with the second electron beam, so that a substantially uncharged first surface contact having a defined potential can be charged in the charging step (b). Alternatively or additionally, discharging (a) of the first surface contact with the first electron beam may be performed after charging and inspection. Thus, after inspection, discharging (a) of the first surface contact with the first electron beam can return the first surface contact to the defined potential.

[0011] Charging (b) and inspecting (c) can be performed simultaneously, for example by detecting a secondary electron signal emitted by the substrate during charging (b) as a function of time. Alternatively, inspecting (c) can be performed after charging (b), for example by probing the first surface contact and / or by probing one or more further surface contacts with a second electron beam or the first electron beam after charging (c).

[0012] According to another aspect, there is provided an apparatus configured to test electrical connections of a substrate according to any of the methods described herein.

[0013] An apparatus for inspecting electrical connections of a substrate described herein may include a vacuum chamber housing a stage for positioning the substrate, a first electron source configured to generate a first electron beam having a first electron energy, a second electron source configured to generate a second electron beam having a second electron energy different from the first electron energy, and a controller configured to control the apparatus to inspect a first electrical connection connected to the first surface contact by focusing and deflecting the first electron beam on the first surface contact to discharge the first surface contact in a discharging step (a), focusing and deflecting the second electron beam on the first surface contact to charge the first surface contact in a charging step (b), and detecting signal electrons emitted from the substrate with an electron detector during or after the charging step (b).

[0014] According to a further aspect, an apparatus for testing electrical connections of a substrate is provided, the apparatus comprising: a vacuum chamber housing a stage for positioning the substrate; a first electron source configured to generate a first electron beam having a first electron energy; a second electron source configured to generate a second electron beam having a second electron energy different from the first electron energy; a focusing lens device for focusing the first electron beam on the substrate in a discharging phase and for focusing the second electron beam on the substrate in a charging phase; a beam deflection device for deflecting the first electron beam on the first surface contact of the substrate to discharge the first surface contact in the discharging phase and for deflecting the second electron beam on the first surface contact to charge the first surface contact in the charging phase; an electron detector for detecting signal electrons emitted from the substrate; and an analysis unit for inspecting the first electrical connections connected to the first surface contact based on the signal electrons, in particular via a voltage contrast measurement.

[0015] The embodiments are also directed to apparatuses for carrying out the disclosed methods, including apparatus parts for carrying out each method aspect described. These method aspects may be carried out by hardware components, a computer programmed by appropriate software, by any combination of the two, or in any other manner. Furthermore, the embodiments according to the present disclosure are also directed to methods for operating the described apparatuses, as well as methods for manufacturing the apparatuses and devices described herein. The methods for operating the described apparatuses include method aspects for carrying out all the functions of the apparatus.

[0016] So that the above-recited features of the present disclosure may be understood in detail, a more particular description of the present disclosure briefly summarized above can be had by reference to embodiments. The accompanying drawings relate to embodiments of the present disclosure and are described below. [Brief description of the drawings]

[0017] [Figure 1]1 is a schematic cross-sectional view of an apparatus for testing electrical connections of a substrate according to embodiments described herein. [Diagram 2] 1 is a schematic cross-sectional view of an apparatus for testing electrical connections of a substrate according to embodiments described herein. [Figure 3A] FIG. 1 is a schematic diagram of a testing method according to an embodiment described herein. [Figure 3B] FIG. 1 is a schematic diagram of a testing method according to an embodiment described herein. [Figure 3C] FIG. 1 is a schematic diagram of a testing method according to an embodiment described herein. [Figure 3D] FIG. 1 is a schematic diagram of a testing method according to an embodiment described herein. [Figure 4] 4 is a flow diagram of a method for testing electrical connections of a substrate according to embodiments described herein. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Reference will now be made in detail to various exemplary embodiments, one or more examples of which are illustrated in the figures. Each example is provided by way of explanation and not meant to be limiting. For example, features illustrated or described as part of one embodiment can be used on or in conjunction with other embodiments to yield still further embodiments. It is intended that the present disclosure include such modifications and variations.

[0019] In the following description of the drawings, the same reference numbers refer to the same components. Only the differences with respect to the individual embodiments are described. The structures shown in the drawings are not necessarily drawn to scale, but rather are to serve to better understand the embodiments.

[0020] In an effort to reduce the space requirements of semiconductor packages, the complexity of packaging substrates has increased over the years. Traditional semiconductor packages are manufactured from semiconductor wafers, then diced and packaged. The semiconductor packages may then be mounted onto a printed circuit board (PCB) along with other microelectronic components.

[0021] To reduce manufacturing costs, advanced packaging technologies such as 2.5D IC, 3D-IC, and Wafer Level Packaging (WLP), e.g., fan-out WLP, have been proposed. In WLP technology, integrated circuits are packaged before dicing but are still part of the wafer. Thus, the resulting package has substantially the same size as the wafer.

[0022] "2.5D integrated circuits" (2.5D ICs) and "3D integrated circuits" (3D ICs) are combinations of multiple dies into a single integrated package. Here, two or more unpackaged dies are disposed on a packaging substrate, e.g., a silicon interposer. In 2.5D ICs, the dies are disposed side-by-side on the packaging substrate, whereas in 3D ICs, at least some of the dies are disposed on top of each other. The assembly can be packaged as a single component, thus reducing cost and size compared to traditional 2D circuit board assemblies. Advanced Packaging (AP) substrates provide inter-device electrical interconnection paths on or within a wafer, such as a silicon wafer. For example, an AP substrate can include through silicon vias (TSVs), e.g., provided in a silicon interposer, or other conductor lines extending through the AP substrate. Panel Level Packaging (PLP) substrates are typically provided from a composite material, e.g., a printed circuit board (PCB) material, or another composite material, e.g., including ceramic and glass materials.

[0023] A packaging substrate typically includes a plurality of inter-device electrical interconnect paths for providing electrical connections between the dies disposed on the packaging substrate. The inter-device electrical interconnect paths may extend vertically (perpendicular to the surface of the packaging substrate) and / or horizontally (parallel to the surface of the packaging substrate) through the body of the packaging substrate in a complex network of connections, with end points (referred to herein as surface contacts) exposed at the substrate surface.

[0024] To further reduce manufacturing costs, panel level substrates are manufactured that are configured to integrate multiple devices (e.g., chips / dies, which may be heterogeneous, e.g., different sizes and configurations) into a single integrated package. The panel level substrate typically provides chip sites on its surface, e.g., on one or both sides thereof, for arranging multiple chips / dies, and multiple inter-device electrical interconnect paths that extend through the body of the packaging substrate. It is noteworthy that the size of the panel level substrate is not limited to the size of the wafer. For example, the panel level substrate may be rectangular or have another shape. Specifically, the panel level substrate may have a surface area larger than that of a typical wafer, e.g., 1000 cm2. 2 For example, the panel level substrate may have a size of 30 cm×30 cm or more, 60 cm×30 cm or more, 60 cm×60 cm or more, or larger.

[0025] Conventional test equipment may not be compatible or suitable for testing advanced packaging substrates due to the geometry and density of the surface contacts and / or due to the size of the packaging substrate, which may differ from the size of a conventional die or printed circuit board. The present disclosure relates to a method and apparatus, respectively, for testing a substrate having a plurality of closely spaced surface contacts and a plurality of electrical connections extending between two or more surface contacts. In particular, the method and apparatus described herein may be suitable for testing a packaging substrate configured to integrate a plurality of devices into one integrated package and including at least one inter-device electrical interconnect path extending between a first surface contact and at least one second surface contact.

[0026] A "surface contact" may be understood as an end point of an electrical interconnection path (also referred to herein as an "electrical connection") exposed on the surface of a substrate such that an electron beam can be directed at the surface contact to contactlessly charge or probe the surface contact. A surface contact may refer to making electrical contact to a chip / die disposed on the surface of the substrate, for example, via soldering. For example, the surface contact may be configured as a solder bump.

[0027] 1 illustrates in schematic cross-sectional view an apparatus 100 for testing microelectronic connections, such as interconnect paths and / or vias, in a substrate 10, according to embodiments described herein. The apparatus 100 includes a vacuum chamber 101, which may be a test chamber specially configured for testing or may be one vacuum chamber of a larger vacuum system, such as a processing chamber of a substrate manufacturing system or substrate processing system. For example, the apparatus may be configured as an in-line inspection apparatus integrated into a substrate processing system.

[0028] As depicted diagrammatically in Fig. 1, the substrate 10 includes a first surface contact 21 and a first electrical connection 20 extending from the first surface contact 21 through the substrate to one or more second surface contacts 22, which may be provided, for example, on the same surface of the substrate as the first surface contact 21. The substrate 10 may include a plurality of surface contacts and a plurality of electrical connections extending from the plurality of surface contacts, for example 1,000 or more electrical connections, in particular 10,000 or more electrical connections, or even 100,000 or more electrical connections. The plurality of electrical connections extending from the plurality of surface contacts may be tested according to the methods described herein.

[0029] In some embodiments, which may be combined with other embodiments described herein, one or more electrical connections extending between surface contacts on different sides of a substrate are inspected. In yet other embodiments, a first plurality of electrical connections extending between surface contacts on a first side of a substrate, a second plurality of electrical connections extending between surface contacts on a second side of a substrate, and / or a third plurality of electrical connections extending between surface contacts on different sides of a substrate are inspected. For example, one or more electron beam columns may be positioned on both sides of a substrate (not shown) to charge and / or discharge the surface contacts on both sides of a substrate to inspect and test the respective electrical connections.

[0030] Returning to FIG. 1, the apparatus 100 includes a first electron source 121 configured to generate a first electron beam 111 having a first electron energy, and a second electron source 122 configured to generate a second electron beam 112 having a second electron energy different from the first electron energy, in particular higher than the first electron energy.

[0031] The apparatus further includes a controller 161 configured to control the apparatus 100 to: in a discharging phase (a), focus and deflect the first electron beam 111 on the first surface contact 21 to discharge the first surface contact; in a charging phase (b), focus and deflect the second electron beam 112 on the first surface contact 21 to charge the first surface contact; and inspect the first electrical connection 20 extending from the first surface contact 21 by detecting signal electrons emitted from the substrate using the electron detector 180 during or after the charging phase (b).

[0032] The discharging step (a) and the charging step (b) are performed sequentially, using a first electron beam for discharging the first surface contact and a second electron beam for charging the first surface contact. Alternatively, the charging step (b) and the inspection step (c) can be performed simultaneously (i.e. by simultaneously charging and inspecting), in particular by detecting and analyzing a secondary electron signal emitted by the substrate as a function of time during charging (b). It is also possible to perform charging and inspection sequentially, i.e. by first charging the first surface contact with the second electron beam and then inspecting the first electrical connection by probing the first surface contact and / or the further surface contact with the first or second electron beam.

[0033] In some embodiments, which may be combined with other embodiments described herein, the first electron energy of the first electron beam 111 is lower than the second electron energy of the second electron beam 112. The "electron energy" of an electron beam refers to the (average) energy of the electrons of the electron beam propagating towards the substrate. In particular, the first electron energy of the first electron beam 111 may be ≧1 keV and ≦3 keV, in particular about 1.5 keV, and / or the second electron energy of the second electron beam 112 may be ≧5 keV and ≦15 keV, in particular about 10 keV.

[0034] In some implementations, the first electron energy of the first electron beam 111 may be below the neutral charging point and the second electron energy of the second electron beam 112 may be above the neutral charging point. As used herein, "neutral charging point" refers to an electron energy of an electron beam that does not change the charge on an essentially uncharged surface contact when struck by the electron beam, such that the amount of signal electrons ejected from the substrate upon impact substantially corresponds to the amount of electrons transferred to the surface contact by the electron beam. The neutral charging point may correspond to an electron energy of the electron beam of approximately 2 keV.

[0035] When the first electron beam 111 having an electron energy below the neutral charging point (e.g., 1.5 keV) impinges on the surface contact, the amount of signal electrons leaving the substrate is typically greater than the amount of electrons transferred to the substrate by the first electron beam 111, for example because of a high probability that the impinging electrons will generate secondary electrons (SEs) that leave the substrate. Thus, negative charge is removed from the surface contact, allowing the surface contact to be discharged together with the electrical connections extending therefrom. As used herein, "discharge" particularly refers to the removal of negative charge, i.e., electrons, that have accumulated on the surface contact.

[0036] When the second electron beam 112, having an electron energy above the neutral charging point (such as 10 keV), strikes the surface contact, the amount of signal electrons leaving the substrate is typically less than the amount of electrons transferred to the substrate by the second electron beam 112, for example because of the low probability of high energy electrons leaving the substrate or generating secondary electrons leaving the substrate. Thus, a negative charge is applied to the surface contact, thereby charging the surface contact (negatively) together with the electrical connections extending therefrom. As used herein, "charging" particularly relates to applying a negative charge, i.e., electrons, to the surface contact, resulting in a predetermined potential of the surface contact.

[0037] Because the first electron beam 111 and the second electron beam 112 have different electron energies, particularly below and above the neutral charging point, the first electron beam 111 can be used to remove electrons, i.e., to discharge the surface contact, and the second electron beam 112 can be used to apply electrons, i.e., to charge the surface contact to a predetermined potential.

[0038] The electrical connections of the substrate can be inspected by charging the electrical connections, for example by directing an electron beam onto a first surface contact electrically connected to the electrical connections, until the electrical connections are charged to a predefined potential. After charging the electrical connections, if the electrical connections are free of defects, one or more second surface contacts electrically connected to the first surface contact via the electrical connections will be at the same potential as the first surface contact. The potential of the one or more second surface contacts can be probed, for example by directing an electron beam onto the one or more second surface contacts and measuring the electron energy, SE signal yield, and / or signal strength of the emitted signal electrons. For example, the number of emitted signal electrons is higher when the probed surface contact is at a negative potential, i.e. is charged. Such so-called voltage contrast measurements allow probing the surface contacts of the charged electrical connections to determine defects in the electrical connections of the substrate.

[0039] However, the density of surface contacts on a substrate has increased over the years, which can make it difficult to negatively charge a particular surface contact to a predetermined potential using an electron beam. For example, pre-existing charge on a surface contact (e.g., charge originally present on the sample and / or charge applied during a prior measurement of an adjacent surface contact) can adversely affect measurement accuracy, since charging a pre-charged surface contact for a predetermined period of time may not bring the surface contact to the predetermined potential. Furthermore, pre-existing charge on adjacent surface contacts can adversely affect measurement accuracy, since the charge can deflect signal electrons such that only a portion of them reach the electron detector. Pre-existing charge on adjacent surface contacts can also adversely affect the probing electron beam impinging on the surface contact, which can result in inaccurate positioning and inability to test small surface contacts.

[0040] To solve the above mentioned problems, according to the embodiments described herein, a first electron beam 111 with a first electron energy is used to discharge the first surface contact 21 before charging it with the second electron beam 112 and / or after testing. The discharge of the first surface contact 21 in the discharging phase, i.e. the removal of the negative charge that may be present on the first surface contact 21, allows the first surface contact 21 to be in a defined state with a low or zero potential before and / or after testing. By "discharging" it is not necessarily meant that the potential of the respective surface contact is zero with respect to the ground potential. Rather, this potential may be at a defined (low) voltage value, so that a subsequent charging phase can start from the defined potential.

[0041] In some embodiments, discharging the surface contact with the first electron beam (a) may be performed before charging the surface contact with the second electron beam (b), allowing the charging step (b) to start from a defined potential, improving measurement accuracy.

[0042] Alternatively or additionally, discharging the surface contacts with the first electron beam (a) may be performed after inspection (c), allowing the surface contacts to be returned to a defined (low) potential after being charged and inspected, so that subsequent measurements at adjacent surface contacts are not adversely affected by charges that may remain on the surface contacts after inspection.

[0043] In some embodiments, which may be combined with other embodiments described herein, discharge (a) is performed on the first surface contact before charging (b), and discharge (a) is performed again on the first surface contact after testing (c). Measurement accuracy can be improved for both the testing of the first electrical connection and the subsequent testing of adjacent electrical connections. In other words, discharge (a), charging (b), and testing (c) may be performed in the following order: (a), (b)+(c), and (a) again, where the order is used for testing each electrical connection of the plurality of electrical connections, and "(b)+(c)" indicates that (b) and (c) can be performed sequentially or simultaneously.

[0044] In some embodiments, which may be combined with other embodiments described herein, a substrate includes a plurality of surface contacts and a plurality of electrical connections extending from the plurality of surface contacts, e.g., 1,000 or more electrical connections or 10,000 or more electrical connections to be tested. To inspect the plurality of electrical connections extending from the plurality of surface contacts, discharging (a), charging (b), inspecting (c), and optionally discharging (a) again can be performed on each surface contact of the plurality of surface contacts.

[0045] For example, after inspection of the first electrical connection 20, the second electrical connection 24 extending from the third surface contact 23 of the substrate can be tested as follows: the third surface contact 23 is discharged by focusing and deflecting the first electron beam 111 on the third surface contact 23, the third surface contact 23 is charged by focusing and deflecting the second electron beam 112 on the third surface contact 23, and the second electrical connection 24 is inspected by detecting signal electrons emitted from the substrate during and / or after charging. The discharging of the third surface contact 23 by focusing and deflecting the first electron beam 111 on the third surface contact 23 may be performed before charging and / or after inspection. The method can then proceed by similarly testing other electrical connections in succession, in particular 1,000 or more electrical connections, by deflecting and focusing the first and second electron beams on respective surface contacts extending from the plurality of electrical connections.

[0046] According to the embodiments described herein, the first electron beam 111 and the second electron beam 112 are then focused on the first surface contact, in particular by the focusing lens arrangement 140. In particular, the focusing lens arrangement 140 may be configured to focus a selected one of the first and second electron beams on the substrate. For example, the spot diameter of the first electron beam 111 and / or the second electron beam 112 focused on the substrate may be 10 μm or less, in particular 1 μm or less. Thus, unlike UV light sources or electron flood guns typically used to remove charge from substrates in other applications, the first electron beam 111 is focused on the substrate to specifically target and discharge the predetermined surface contact. Targeted removal of charge from only the area of ​​interest, for example from the specific surface contact currently being tested, is enabled. Repeated discharge of large substrate areas using unfocused beams such as flood guns takes a significant amount of time. The present disclosure allows for rapid targeted removal of charge from specific surface contacts under test, facilitating testing and improving measurement accuracy.

[0047] According to the embodiments described herein, the first electron beam 111 and the second electron beam 112 are deflected on the first surface contact, in particular by the beam deflection device 130. For example, the beam deflection device 130 can be configured to deflect a selected one of the first and second electron beams to a predefined position on the substrate, such as the first surface contact or another surface contact. The beam deflection device 130 can be an electrostatic and / or magnetic beam deflection device configured to deflect the first electron beam 111 or the second electron beam 112 to a predefined position on the substrate surface, the substrate surface being provided in an xy-plane. The beam deflection device 130 can enable beam deflection in two directions, i.e., in the x-direction and the y-direction, so that the first and second electron beams can be deflected to any predefined position in the xy-plane in which the multiple surface contacts are distributed.

[0048] In some embodiments, the deflection area provided by the beam deflection device 130 is at least 9 cm above the substrate surface for the first electron beam 111 and the second electron beam 112. 2 In particular, the beam deflection device 130 may be positioned at least 9 cm above the substrate surface with respect to the first electron beam 111 and the second electron beam 112. 2 In other words, the deflection device 130 can be used to deflect the first electron beam and the second electron beam by at least 9 cm without moving the stage. 2 In some embodiments, the overlapping deflection regions may be at least 16 cm apart. 2 , especially at least 100 cm 2 , or at least 225 cm 2For example, the beam deflection device 130 may provide an overlapping deflection region for the first electron beam 111 and the second electron beam 112, the overlapping deflection region having a dimension D1 in the xy plane of the substrate of at least 3 cm×3 cm, in particular at least 4 cm×4 cm, more particularly at least 10 cm×10 cm, or even at least 15 cm×15 cm.

[0049] In particular, the beam deflection device 130 can deflect the first electron beam to any position within a deflection area of ​​at least 5 cm×5 cm on the substrate surface, and the deflection device 130 can deflect the second electron beam to any position within the same deflection area of ​​at least 5 cm×5 cm on the substrate surface, in particular within the same deflection area of ​​at least 10 cm×10 cm. The deflection areas provided for the first and second electron beams can partially or totally overlap, so that by appropriately controlling the beam deflection device 130, the first and second electron beams can be deflected to the same surface contact of the substrate without moving the substrate. By deflecting the first and second electron beams to respective surface contacts that may be distributed over a substrate area of ​​at least 10 cm×10 cm without moving the stage 105 (i.e. while the substrate remains stationary), large sub-areas of the substrate surface or even the entire substrate can be inspected.

[0050] Using the beam deflection device 130 to deflect the first electron beam 111 and / or the second electron beam 112 onto one or more surface contacts to be tested is beneficial compared to the use of one or more stationary electron beams. In particular, moving the stage 105 relative to one or more stationary electron beams is time-consuming and less precise compared to beam deflection. Furthermore, the first electron beam can be quickly deflected several times onto the surface contacts for discharging, e.g., before and after charging and probing, without requiring time-consuming reciprocating motion of the stage. Furthermore, multiple surface contacts can be tested in succession quickly and conveniently using the first electron beam 111 deflected onto each surface contact for discharging and then the second electron beam 112 deflected onto each surface contact for charging and / or probing.

[0051] According to the embodiments described herein, a fast and reliable way of accurately testing multiple electrical connections is provided. Specifically, in a discharging step (a), the first electron beam 111 is deflected by the beam deflection device 130 so that the first electron beam 111 is focused on the first surface contact. In a charging step (b), the second electron beam 112 is deflected by the beam deflection device 130 so that the second electron beam 112 is focused on the first surface contact for charging. To test the first electrical connections, signal electrons emitted from the substrate are detected by the electron detector 180 when the second electron beam 112 is used to probe a specific surface contact of the substrate, particularly during or after the charging step. Focusing and deflecting the electron beam on different surface contacts increases the test speed and ensures that adjacent areas of the substrate are less affected by the electron beam, improving the measurement accuracy. A discharging step before and / or after charging and testing brings each surface contact to a defined potential before and after testing. A large number of densely packed surface contacts and their respective electrical connections can be tested quickly and reliably.

[0052] In some embodiments, the inspection (c) includes performing a voltage contrast measurement based on signal electrons detected upon impingement of the second electron beam 112 on the substrate. In particular, the second electron beam 112 can be used to both charge the first surface contact and to probe further surface contacts that should be electrically connected to the first surface contact or electrically isolated from the first surface contact. Alternatively, the first electron beam 111 can be used to both discharge and probe the surface contacts that have been charged by the second electron beam 112.

[0053] In particular, the inspection (c) may include charging the first surface contact 21 with the second electron beam 112, and then probing any one or more of the following surface contacts with the second electron beam 112: the first surface contact 21, one or more second surface contacts 22 that should be electrically connected to the first surface contact 21 via the first electrical connection portion 20, and one or more third surface contacts 23 that should be electrically isolated from the first surface contact 21.

[0054] The first surface contact 21 may be probed after or during charging to determine the charge state of the first electrical connection 20. For example, an unexpectedly high potential on the first surface contact 21 after charging (or already during charging) may indicate a defect (open) in the first electrical connection, since the applied charge cannot flow into the substrate from the first surface contact 21 towards the one or more second surface contacts 22.

[0055] One or more second surface contacts 22 that should be electrically connected to the first surface contact 21 via the first electrical connection 20 can be probed to determine whether the first electrical connection 20 actually extends between the first surface contact 21 and the one or more second surface contacts 22. If the one or more second surface contacts 22 do not charge after charging the first surface contact 21, then the first electrical connection may be defective (open).

[0056] One or more third surface contacts 23, which should be electrically isolated from the first surface contact 21, can be probed to determine whether the first electrical connection 20 is shorted to an adjacent electrical connection. Specifically, if one or more third surface contacts 23 are charged after the first surface contact 21 is charged, the first electrical connection is likely shorted to another electrical connection.

[0057] In some embodiments, which may be combined with other embodiments described herein, the apparatus 100 includes a two-beam column 110 that provides a common electron beam path 115 for the first electron beam 111 and the second electron beam 112. In particular, in a discharging phase (a), the first electron beam 111 can propagate along the common electron beam path 115 through the two-beam column 110 while the second electron beam is deselected, and in a charging phase (b), the second electron beam 112 can propagate along the common electron beam path 115 through the two-beam column 110 while the first electron beam is deselected.

[0058] 1 shows an apparatus 100 having a dual beam column 110. The dual beam column 110 may include a beam selector 150 for selecting one of a first electron beam 111 and a second electron beam 112 propagating through the dual beam column towards a substrate. For example, the beam selector 150 may include a beam blanker and / or a beam dump configured to block a deselected one of the first and second electron beams and allow a selected one of the first and second electron beams to pass along a common electron beam path 115.

[0059] A number of beam optics for affecting a selected one of the first electron beam 111 and the second electron beam 112 may be provided along the common electron beam path 115. In particular, a focusing lens arrangement 140 and / or a beam deflection arrangement 130 may be centrally located with respect to the common electron beam path 115, as depicted diagrammatically in FIG.

[0060] The beam deflection device 130 may be configured to deflect a selected one of the first and second electron beams to a predetermined location on the substrate. In particular, the beam deflection device 130 may be configured to deflect the first and second electron beams 111, 112 to a position at least 9 cm above the substrate. 2 overlapping deflection regions can be provided.

[0061] The controller 161 may be configured to control the beam selector 150, the beam deflection device 130 and / or the focusing lens device 140 such that a selected one of the first and second electron beams is focused and deflected to a predetermined location on the substrate surface, such as the first surface contact or another surface contact. The controller 161 may further be configured to control the beam selector 150 to select the first electron beam 111 for discharging (a) and the second electron beam 112 for charging (b). The first electron beam 111 or the second electron beam 112 may be selected to probe one or more surface contacts to inspect the respective electrical connections.

[0062] Providing two beam columns 110 with a common electron beam path 115 for the first electron beam 111 and the second electron beam 112 may be beneficial since the beam deflection device 130 for both beams is centrally located with respect to the common electron beam path 115 (see FIG. 1 ) and thus provides a large overlapping deflection area that is possible with one common beam deflection device. For example, a large deflection area with a dimension D1 of 3 cm or more, in particular 5 cm or more, or even 10 cm or more in the x- and / or y-direction can be provided. Large sub-areas of the substrate or the entire substrate can be inspected without time-consuming stage movements. In particular, the beam deflection device 130 can provide an overlapping deflection area of ​​at least 3 cm×3 cm, in particular at least 5 cm×5 cm on the substrate surface.

[0063] The beam deflection device 130 may be configured to electrostatically and / or electrically deflect the first electron beam for discharging and the second electron beam for charging onto predetermined surface contacts.

[0064] In some embodiments, which may be combined with other embodiments described herein, the first electron beam 111 is generated by a first electron source 121 having a first emitting tip and a first extraction electrode, and / or the second electron beam 112 is generated by a second electron source 122 having a second emitting tip and a second extraction electrode. The first and second electron sources may be, for example, thermal field emitters (TFEs).

[0065] The electron energy of the first electron beam 111 can be suitably set by applying a first potential to the first emitting tip, and the electron energy of the second electron beam 112 can be suitably set by applying a second potential to the second emitting tip. The second potential can be set such that the second electron beam has a higher electron energy than the first electron beam, in particular a second electron energy of 5 keV or more and 15 keV or less.

[0066] In some embodiments, which may be combined with other embodiments described herein, the apparatus 100 includes an electron detector 180 for detecting signal electrons emitted from the substrate, particularly upon impingement of the second electron beam 112 on the substrate. The signal electrons may include secondary electrons (SE) and / or backscattered electrons (BSE).

[0067] In some embodiments, the electron detector 180 includes an Everhard-Thornley detector, which may be positioned downstream of the focusing lens arrangement 140 and downstream of the beam deflection arrangement 130 in the propagation direction of the first and second electron beams, as shown diagrammatically in Figure 1, to improve detection efficiency.

[0068] An energy filter for the signal electrons 113 may be placed before the electron detector 180, in particular before the Everhard-Thornley detector. The energy filter may include a grid electrode configured to be set to a predetermined potential. The energy filter may be able to suppress low energy signal electrons. The energy filter may be set for optimal voltage contrast detection. Thus, the signal current detected by the electron detector 180 may depend on the energy of the signal electrons, which indicates whether the probed surface contact point is provided at a predetermined potential.

[0069] An analysis unit 181 may be provided for inspecting the first electrical connection 20 connected to the first surface contact 21 based on the signal electrons detected by the electron detector 180. For example, the analysis unit 181 may provide an output indicative of a status of the plurality of electrical connections, e.g., "defective" or "not defective" for each of the plurality of electrical connections. Optionally, a type of defect (such as an "open" defect or a "short" defect) may be determined by the analysis unit 181 based on the electronic signal detected upon probing of a particular surface contact.

[0070] In some embodiments, one or more further beam optical components 171 for influencing the first electron beam and / or the second electron beam, such as a condenser lens arrangement and / or an aberration correction arrangement, such as an astigmatism correction arrangement, a chromatic aberration correction arrangement and / or another aberration correction arrangement, may be provided in the common electron beam path 115.

[0071] In some embodiments, the substrate 10 is a packaging substrate configured to provide multi-device intra-package interconnects, and the first electrical connection 20 is an inter-device electrical interconnect path. In particular, the substrate 10 may be an advanced packaging (AP) substrate, a panel level packaging (PLP) substrate, a wafer level packaging (WLP) substrate, or a micro LED substrate.

[0072] 2 shows a schematic cross-sectional view of an apparatus 200 for testing electrical connections of a substrate 10 according to an embodiment described herein. The apparatus 200 may be similar to the apparatus 100 shown in FIG. 1 and may include corresponding features, so reference can be made to the above description, which will not be repeated here. The differences will be described below.

[0073] The apparatus 200 includes a vacuum chamber 101 housing a stage 105 for placing a substrate 10 thereon, a first electron source 121 for generating a first electron beam 111 having a first electron energy, and a second electron source 122 for generating a second electron beam 112 having a second electron energy. The apparatus 200 further includes a focusing lens device 140 for focusing a selected one of the first electron beam 111 and the second electron beam 112 on the substrate, and a beam deflection device 130 for deflecting a selected one of the first electron beam 111 and the second electron beam 112 on the first surface contact 21. Specifically, the first electron beam 111 can be deflected on the first surface contact 21 to discharge the first surface contact 21 in a discharging step (a), and the second electron beam 112 can be deflected on the first surface contact 21 to charge the first surface contact 21 in a charging step (b). Please refer to the above explanation, which will not be repeated here.

[0074] The apparatus 200 further includes an electron detector 180 for detecting signal electrons emitted from the substrate upon impact of the second electron beam 112, which can be used to probe the surface contact, particularly after charging, and an analysis unit 181 for inspecting the first electrical connection 20 extending from the first surface contact 21 based on the detected signal electrons.

[0075] In some embodiments, which may be combined with other embodiments described herein, the apparatus 200 includes a first beam column 201 for the first electron beam 111 and a second beam column 202 for the second electron beam 112 arranged next to the first beam column 201. Each of the first and second beam columns may provide a respective beam path for the respective electron beam, such that the first and second electron beams propagate along different beam paths through the respective beam column before being focused and deflected successively on the first surface contact and / or the further surface contact.

[0076] The beam deflection device 130 may include a first beam deflector 231 provided in or below the first beam column 201 to deflect the first electron beam 111 to a predetermined position on the substrate surface, and a second beam deflector 232 provided in or below the second beam column 202 to deflect the second electron beam 112 to a predetermined position on the substrate surface. The first beam deflector 231 and / or the second beam deflector 232 may be electrostatic and / or magnetic beam deflectors capable of deflecting the respective electron beams in two directions, i.e., in the x-direction and the y-direction that define the substrate plane. The first electron beam 111 and the second electron beam 112 can be deflected to the same position in the deflection region without moving the stage. In particular, the first beam column 201 and the second beam column 202 may be positioned close to each other, such that the first beam deflector 231 and the second beam deflector 232 provide an at least partially overlapping deflection area of ​​at least 3 cm x 3 cm, in particular at least 4 cm x 4 cm, more particularly at least 10 cm x 10 cm, or even at least 15 cm x 15 cm, within which the first and second electron beams can be deflected to any surface contact.

[0077] In some embodiments, the first beam column 201 and the second beam column 202 may be disposed adjacent to each other and tilted toward each other (see FIG. 2). For example, the first electron beam path defined by the first beam column 201 and the second electron beam path defined by the second beam column 202 may be at an angle of 5° or more and 45° or less with respect to each other, as depicted diagrammatically in FIG. 2. By tilting the first and second beam columns toward each other, the overlapping deflection area provided by the beam deflection device 130 including the first beam deflector 231 and the second beam deflector 232 may be increased, even if the first and second beam deflectors are disposed at a distance from each other in two adjacent beam columns.

[0078] The focusing lens arrangement 140 may include a first focusing lens 241 provided in or below the first beam column 201 for focusing the first electron beam 111 propagating along a first electron beam path defined by the first beam column 201, and a second focusing lens 242 provided in or below the second beam column 202 for focusing the second electron beam 112 propagating along a second electron beam path defined by the second beam column 202. The first focusing lens 241 and / or the second focusing lens 242 may be magnetic and / or electrostatic objective lenses, respectively. For example, the first focusing lens 241 and / or the second focusing lens 242 may include magnetic and / or electrostatic lens components. In other embodiments, purely magnetic or purely electrostatic objective lenses, each including one or more electrodes, may be provided for focusing the electron beam on the substrate surface.

[0079] In some embodiments, the first focusing lens 241 may include a first main focusing lens and a first refocusing lens, e.g., an auxiliary focusing coil. The first refocusing lens may be configured to ensure that the first electron beam 111 is focused on the surface of the substrate even when a large deflection angle is applied by the first deflector 231. For example, the first refocusing lens may apply a focus correction that is dependent on the deflection angle applied by the first deflector 231, and may reduce or prevent a deflection-dependent spot size or spot shape. Alternatively or additionally, the second focusing lens 242 may include a second main focusing lens and a second refocusing lens, e.g., an auxiliary focusing coil. The second refocusing lens may be configured to ensure that the second electron beam 112 is focused on the surface of the substrate even when a large deflection angle is applied by the second deflector 232.

[0080] The controller 161 may be configured to control the apparatus 200 to focus and deflect, in a discharging phase (a), the first electron beam 111, in particular by the first focusing lens 241 and the first beam deflector 231, onto the first surface contact to discharge the first surface contact 21. The second electron beam 112 may be deselected, e.g. blanked, blocked or interrupted, in the discharging phase (a).

[0081] The controller 161 may be configured to control the apparatus 200 to focus and deflect the second electron beam 112, in particular by the second focusing lens 242 and the second beam deflector 232, on the first surface contact in a charging step (b) to charge the first surface contact 21. The charging may bring the first surface contact to a predetermined potential. The first electron beam 111 may be deselected, for example blanked, blocked or interrupted, in the charging step (b).

[0082] The controller 161 may be further configured to control the apparatus 200 to inspect the first electrical connection after or during the charging step (b) by detecting signal electrons emitted from the substrate with the electron detector 180. For example, the signal electrons may be detected while probing the first surface contact 21, the one or more second surface contacts 22, and / or the one or more third surface contacts 23 with the second electron beam 112.

[0083] Providing two separate beam columns, one for the first electron beam and one for the second electron beam, may be beneficial because the control of beam selection, beam deflection and beam focusing may be less complicated and faster compared to one two-beam column adapted to deflect and focus both electron beams successively to a predetermined surface contact. If the first beam column 201 and the second beam column 202 are arranged close to each other, a large overlapping deflection area may also be possible. For example, the first and second electron beam paths defined by the first and second beam columns may be at a distance of 5 cm or less from each other, in particular 3 cm or less. Furthermore, the first and second beam columns may be tilted towards each other to further increase the overlapping deflection area. For example, the first and second beam columns may be tilted towards each other to further increase the overlapping deflection area. For example, the first and second beam columns may be tilted towards each other to further increase the overlapping deflection area. 2 More than 100cm 2 More than that, even 225cm 2 Larger overlapping deflection regions are possible.

[0084] In some embodiments, one or two additional electron beam columns (e.g., configured to generate discharging and charging electron beams) may be positioned on the other side of the substrate so that surface contacts on the first and second surfaces of the substrate may be discharged and / or charged, e.g., electrical connections connecting surface contacts on different sides of the substrate may be inspected.

[0085] 3A-3D are schematic diagrams illustrating a testing method according to an embodiment described herein. The illustrated testing method can be performed using any of the devices described herein.

[0086] 3A, a discharge step (a) is shown: To remove negative charges that may be present on the first surface contact 21 and on the first electrical connection 20 extending therefrom, a first electron beam 111 having an electron energy suitable for removing the negative charges is focused and deflected on the first surface contact 21.

[0087] In FIG. 3B, the charging step (b) is shown. The first electrical connection 20 is set to a predefined potential, and a second electron beam 112 with an appropriate electron energy is focused and deflected on the first surface contact 21 to apply a negative charge so that a voltage contrast measurement can then be performed. Since the first surface contact 21 has been previously discharged in the discharging step (a), an amount of negative charge can be applied by the second electron beam 112 that corresponds exactly to the predefined potential. Since the second electron beam 112 is focused and deflected on the first surface contact, charging of the surrounding substrate area can be reduced or avoided. Optionally, the signal electrons 113 can already be detected during the charging step (b) to check and / or monitor whether the secondary electron signal during charging behaves as expected. In particular, the secondary electron signal during charging may already indicate a defect. In particular, if the first surface contact 21 charges faster than expected, an "open" defect may be identified, and if the first surface contact 21 charges slower than expected, a "short" defect may be identified.

[0088] In Fig. 3C, an inspection stage (c) is shown. The second electron beam 112 probes any one or more of the following surface contacts: the first surface contact 21, one or more second surface contacts 22 which should be electrically connected to the first surface contact 21, and / or one or more third surface contacts 23 which should be electrically isolated from the first surface contact 21, especially of nearby electrical connections. Signal electrons 113 are detected during the probe.

[0089] An "open" defect 31 in the first electrical connection 20 is identified when the second surface contact 22 is not charged and can be detected by probing the second surface contact 22. A "short" defect 32 between the first electrical connection 20 and the second electrical connection 24 is identified when the third surface contact 23 is charged and can be detected by probing the third surface contact 23. In particular, multiple surface contacts can be probed to identify whether the charged state of each of the multiple surface contacts is correct and expected.

[0090] After the inspection, in Fig. 3D another discharge step (a) is shown. A first electron beam 111 having a first electron energy suitable for removing the negative charge is focused and (again) deflected on the first surface contact 21 in order to remove the previously applied negative charge from the first surface contact 21. The adverse effect of the previously applied charge on subsequent measurements can be reduced or avoided. The removal of the charge from the first surface contact 21 after the inspection allows the testing of the first electrical connection 20 to be completed.

[0091] Thereafter, the second electrical connection 24 extending from the second surface contact 22 may be similarly inspected.

[0092] A number of additional electrical connections extending from the number of surface contacts can then be similarly inspected, particularly 1,000 or more, or even 1,000,000 or more electrical connections can be tested in series.

[0093] Because the beam deflection device 130 provides a large overlapping deflection area for the first and second electron beams, multiple electrical connections may be inspected without moving the substrate by simply deflecting the first and second electron beams in succession over multiple surface contacts, improving test speed and accuracy over other methods that may rely on substrate movement and / or electron flood guns for charging.

[0094] FIG. 4 illustrates a flow diagram of a method for testing electrical connections of a substrate according to embodiments described herein.

[0095] In box 410, a substrate having a plurality of surface contacts and a plurality of electrical connections extending therefrom is placed on a stage within a vacuum chamber. The substrate may be an advanced packaging substrate or a panel level packaging substrate.

[0096] In box 420, negative charge is removed from a first surface contact of the substrate by focusing and deflecting a first electron beam having a first electron energy onto the first surface contact.

[0097] In box 430, a negative charge is applied to the first surface contact by focusing and deflecting a second electron beam having a second electron energy onto the first surface contact. The first surface contact and the first electrical connection extending therefrom are set to a predetermined potential by focusing and deflecting the second electron beam onto the first surface contact for a predetermined time.

[0098] In box 440, the first electrical connection is inspected, particularly by detecting signal electrons emitted from the substrate upon impact with the second electron beam during or after charging. As noted above, boxes 430 and 440 may be performed simultaneously or subsequently.

[0099] In box 450, the previously applied negative charge is removed from the first surface contact by a first electron beam.

[0100] It should be noted that in some embodiments described herein, one of the discharging steps (i.e., box 420 or box 450) may be omitted. For example, in some embodiments, it may be sufficient to discharge the first surface contact after testing.

[0101] In box 460, a number of additional electrical connections can be similarly inspected by successively deflecting the first and second electron beams over the surface contacts through which the additional electrical connections extend.

[0102] While the forgoing is directed to certain embodiments, other and further embodiments may be devised without departing from the basic scope thereof, which is determined by the claims that follow.

Claims

1. 1. A method for testing electrical connections of a substrate having a first surface contact (21) and a first electrical connection (20) extending from the first surface contact, comprising: (a) discharging the first surface contact (21) by focusing and deflecting a first electron beam (111) having a first electron energy on the first surface contact (21); (b) charging the first surface contact (21) by focusing and deflecting a second electron beam (112) having a second electron energy different from the first electron energy on the first surface contact (21); (c) inspecting the first electrical connection (20) by detecting signal electrons emitted from the substrate; A method comprising:

2. 2. The method of claim 1, wherein (a) is performed before (b) and (a) is performed again after (c).

3. 3. The method of claim 1 or 2, wherein for each surface contact of a plurality of surface contacts of the substrate, (a), (b)+(c), and optionally (a) again are performed in that order to inspect a plurality of electrical connections connected to the plurality of surface contacts.

4. Multiple surface contacts at least 9 cm 2 4. The method of claim 1, wherein the first and second electron beams are successively deflected on the plurality of surface contacts using a beam deflection device without movement of a stage (105).

5. 5. The method according to claim 1, wherein the first electron energy is lower than the second electron energy, in particular the first electron energy is between 1 keV and 3 keV and the second electron energy is between 5 keV and 15 keV.

6. 6. The method of claim 1, wherein (c) comprises performing a voltage contrast measurement based on the signal electrons detected upon impingement of the second electron beam (112) or the first electron beam (111) on the substrate.

7. (c) after said charging of said first surface contact by said second electron beam (112), charging the following surface contacts by said second electron beam (112) or by said first electron beam (111): The first surface contact (21), one or more second surface contacts (22) to be electrically connected to the first surface contacts (21) via the first electrical connection portion (20); and one or more third surface contacts (23) to be electrically isolated from said first surface contacts (21); The method of any one of claims 1 to 6, comprising probing any one or more of:

8. In (a), the first electron beam (111) propagates along a common electron beam path (115) through two beam columns (110) while the second electron beam is deselected; (b), while the first electron beam is deselected, the second electron beam (112) propagates through the two beam columns (110) along the common electron beam path (115). The method according to any one of claims 1 to 7.

9. In (a), the first electron beam (111) propagates through a first beam column (201), is focused by a first focusing lens (241) of the first beam column, and is deflected onto the first surface contact by a first beam deflector (231) of the first beam column; In (b), the second electron beam (112) propagates through a second beam column (202), is focused by a second focusing lens (242) of the second beam column, and is deflected onto the first surface contact by a second beam deflector (232) of the second beam column. The method according to any one of claims 1 to 7.

10. 10. The method of claim 9, wherein the first beam column (201) and the second beam column (202) are disposed adjacent to each other and are inclined toward each other.

11. 11. The method according to claim 1, wherein the first electron beam is generated by a first electron source (121) having a first emitting tip set to a first potential and the second electron beam is generated by a second electron source (122) having a second emitting tip set to a second potential.

12. The method according to any one of claims 1 to 11, wherein the substrate (10) is a packaging substrate configured to provide a multi-device intra-package interconnection and the first electrical connection (20) is an inter-device electrical interconnection path, in particular the substrate (10) is an Advanced Packaging (AP) substrate, a Panel Level Packaging (PLP) substrate, a Wafer Level Packaging (WLP) substrate, or a Micro LED substrate.

13. An apparatus (100, 200) for testing electrical connections of a substrate, comprising: A vacuum chamber (101) that houses a stage (105) for placing a substrate; a first electron source (121) configured to generate a first electron beam (111) having a first electron energy; a second electron source (122) configured to generate a second electron beam (112) having a second electron energy different from the first electron energy; Controlling the device In a discharging step (a), the first electron beam (111) is focused and deflected on a first surface contact (21) to discharge the first surface contact; In a charging step (b), the second electron beam (112) is focused and deflected onto the first surface contact (21) to charge the first surface contact; A first electrical connection (20) connected to the first surface contact (21) is inspected by detecting signal electrons emitted by the substrate by an electron detector (180) during or after the charging step (b). A controller (161) configured as follows: An apparatus (100, 200).

14. 14. The apparatus of claim 13, comprising a dual beam column (110) providing a common electron beam path (115) for the first electron beam and the second electron beam, the dual beam column comprising a beam selector (150) for selecting one of the first electron beam and the second electron beam to propagate through the dual beam column (110) towards the substrate.

15. 14. The apparatus of claim 13, comprising a first beam column (201) having a first focusing lens (241) and a first beam deflector (231) for focusing and deflecting the first electron beam (111), and a second beam column (202) having a second focusing lens (242) and a second beam deflector (232) for focusing and deflecting the second electron beam (112), the first beam column and the second beam column being disposed adjacent to each other.

16. The apparatus of any one of claims 13 to 15, comprising a beam deflection device (130) configured to deflect a selected one of the first and second electron beams to a predetermined position on the substrate, and / or a focusing lens device (140) configured to focus the selected one of the first and second electron beams on the substrate.

17. The beam deflection device (130) is at least 9 cm above the substrate with respect to the first electron beam (111) and the second electron beam (112). 2 , in particular at least 100 cm 2 , more particularly at least 225 cm 2 17. The apparatus of claim 16, providing overlapping deflection regions.

18. The apparatus according to any one of claims 13 to 17, wherein the second electron beam (112) is focused and deflected on at least one of the first surface contact (21), one or more second surface contacts (22) to be electrically connected to the first surface contact, and one or more third surface contacts (23) to be electrically isolated from the first surface contact, in order to inspect the first electrical connection (20), and the signal electrons emitted by the substrate are each detected by the electron detector (180) to perform a voltage contrast measurement.

19. 1. An apparatus for testing electrical connections on a substrate, comprising: a vacuum chamber that houses a stage for placing a substrate; a first electron source configured to generate a first electron beam having a first electron energy; a second electron source configured to generate a second electron beam having a second electron energy different from the first electron energy; a focusing lens arrangement (140) configured to focus the first electron beam onto the substrate during a discharging phase and to focus the second electron beam onto the substrate during a charging phase; a beam deflection device (130) configured to deflect the first electron beam onto a first surface contact of the substrate in the discharging step to discharge the first surface contact, and to deflect the second electron beam onto the first surface contact in the charging step to charge the first surface contact; an electron detector (180) for detecting signal electrons emitted from the substrate; an analysis unit (181) for inspecting a first electrical connection (20) extending from the first surface contact (21) based on the signal electrons; An apparatus comprising:

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