Inspection method for detecting defective joining interfaces in a sample substrate and measurement

Abstract

The invention relates to a measuring system (MS) and to an inspection method for detecting defective bonding interfaces in a sample substrate (1) comprising at least one element (3) arranged on a support (2). According to the invention, the method comprises a provision step (S1) of placing the sample substrate (1) in a measurement system (MS), a measurement step (S2) of establishing a tilt map of the exposed surface (1a), an analysis step (S3) of the tilt map for identifying one or more regions of the exposed surface in which the tilt deviates from the reference surface by more than a given threshold, and a decision step (S4) of detecting the presence of a defective joint between the element (3) and the support (2) on the basis of the result of the analysis step (S3).

Description

Technical Field

[0001] The present invention relates to a method for inspecting a sample substrate and for indicating the presence of a defective bonding interface in the sample substrate. Such a bonding interface may exist between at least one element (film, functional device) and a support, the element and the support forming the sample substrate. A defective bond may correspond to a weak bond between the element and the support or a partial delamination between the element and the support. In the context of the present disclosure, "bonding" refers to any stacking technique known in the semiconductor industry for assembling two elements or substrates together, such as direct bonding, thermocompression bonding, or interconnect bonding between bumps and vias. The present invention has particular applications in the field of wafer-level testing of semiconductor substrates (such as silicon-on-insulator substrates) or advanced integrated circuits (such as high-bandwidth memories, system-on-chips, integrated photonics components, etc.). Background Art

[0002] Bonding techniques have many applications in the integrated circuit (IC) industry. For example, 3DIC packaging techniques such as wafer-level packaging (WLP) provide IC components with high-density packaging that is substantially the same size as the chip or die itself. According to these techniques, chips or dies can be stacked and bonded to each other according to a thermocompression process that includes heating two bonding bodies and applying heat and mechanical pressure thereto. Diffusion of the metal results in a metallurgical bond between the two surfaces. As an alternative method, the bond can be achieved by a hybrid bonding process that involves molecular adhesion of a dielectric layer and thermofusion of metal interconnects. Such a technique is used, for example, in the manufacture of high-bandwidth memories (HBM). Hybrid bonding can be used for die-on-die, die-on-wafer, and wafer-on-wafer bonding.

[0003] According to other integration techniques, chips or dies are integrated in a molding compound and connected to solder bumps via a redistribution layer (RDL) as a system-on-chip (SoC). These components can then be stacked in multiple layers by thermocompression of the solder bumps.

[0004] There are also other integration techniques, for example, for manufacturing larger-sized photonics component wafers by bonding tiles of III-V materials initially grown epitaxially on a silicon wafer. This allows such substrates to be used on a larger scale in the manufacturing process.

[0005] In all the cases listed above, the bonding quality is crucial for ensuring the proper operation and reliability of the components. In the case of a poor bond between two elements that are vertically interconnected to allow the flow of current, some defects can be detected by electrical tests. However, these electrical tests do not always allow the detection of weak bonds or delaminations, where an electrical connection is established but the mechanical adhesion is poor. These defective bonding conditions can lead to subsequent failures of the components during operation, so it is important to detect them before integrating the device into the final package and putting it into use.

[0006] Since the bonding interface is buried between the die or film and the support, it cannot be easily and directly inspected. Existing inspection methods provide limited results or lack sensitivity. Such a method can, for example, involve inspecting the surface by obtaining the local height of the surface through bright-field imaging and dark-field imaging or optical and mechanical profilometry. However, a poor bond results in very small height changes that are difficult to detect. In the case of bright-field imaging, the change in optical contrast at the area affected by the defective bond is not strong enough to allow reliable detection. In the case of dark-field imaging, the tilt caused by delamination does not scatter enough light for detection. The limited field of view of the optical profiler and the typical averaging movement and measurement time of the mechanical profiler severely affect the efficiency of the inspection step over the entire wafer, so the inspection cost per unit increases sharply.

[0007] Object of the Invention

[0008] The object of the present invention is to solve the above problems at least in part. More precisely, the object of the present invention is to propose a method for indicating the presence of a defective bond between an element of a sample substrate and a support. The defective bond can correspond to delamination, partial delamination, poor bonding, or weak bonding between the element and the support. Another object of the present invention is to propose an inspection method for indicating the presence of a defective bond, which allows high-throughput and complete inspection of the sample substrate for applications in a high-volume manufacturing environment. Summary of the Invention

[0009] To this end, the present invention relates to an inspection method for detecting a defective bonding interface in a sample substrate, the sample substrate including at least one element disposed on a support, the bonding interface being defined between the at least one element and the main surface of the support, the outer surface of the at least one element being exposed on the front side of the sample substrate and at least partially defining the exposed surface of the sample substrate.

[0010] According to the present invention, the method comprises:

[0011] · a providing step of placing the sample substrate in a measurement system;

[0012] · A measuring step of using a measuring system to establish an inclination map of an exposed surface, the inclination map being composed of a plurality of local inclination measurement values relative to a reference surface;

[0013] · An analysis step of the inclination map, the analysis step identifying one or more regions where the inclination of the exposed surface deviates from the inclination of the reference surface by more than a given threshold, the one or more regions being referred to as "identified regions"; and

[0014] · A decision step of detecting a defective engagement between a component and a support based on the result of the analysis step.

[0015] Additional non-limiting features that can be employed alone or in any technically feasible combination according to this aspect of the present invention:

[0016] - The reference surface corresponds to the main surface of the support;

[0017] - The inspection method further includes a calibration step of the measuring system (MS) before the measuring step, the calibration step defining an inclination map of the main surface of the support;

[0018] - The measuring system includes a holder for receiving a sample substrate during the measuring step, and the calibration step includes a first sub-step of establishing an inclination map of the holder and a second sub-step of defining the reference surface as the inclination map of the holder;

[0019] - The measuring system includes a holder for receiving a sample substrate during the measuring step, and the calibration step includes a first sub-step of placing a dummy substrate on the holder, a second sub-step of establishing an inclination map of the exposed surface of the dummy substrate, and a third sub-step of defining the reference surface as the inclination map of the exposed surface of the dummy substrate;

[0020] - The inspection method further includes an offset step of applying an offset map to the inclination map after the measuring step, the transformation offsetting the local inclination measurement values of the inclination map relative to the main surface of the support;

[0021] - Wherein, the offset step includes a sub-step of calculating a representative value of the local inclination measurement values of the inclination map established by the measuring step;

[0022] - Select the representative value from the group formed by: average value, median value, mode value.

[0023] - The offset step includes:

[0024] o A first sub-step of identifying local inclination measurement values associated with the main surface of the support in the inclination map;

[0026] o A second sub-step of defining the offset map according to the identified local inclination measurement values;

[0027] - The second sub-step includes interpolating the identified local tilt measurements to define each entry of the offset map;

[0028] - The analysis step includes:

[0029] o A first sub-step of providing a positioning map that defines the positions of a plurality of predetermined

[0030] regions of the exposed surface of the sample substrate;

[0031] o A second sub-step of calculating a representative value of the local tilt measurements associated with the predetermined regions;

[0032] - Selecting a representative value of the local tilt measurements associated with the predetermined regions from the group formed by: mean value, median value, mode value;

[0033] - The positioning map includes at least one predetermined region corresponding to the outer surface of at least one element;

[0034] - The first sub-step of providing the positioning map includes: providing an image of the exposed surface (1a) of the sample substrate and applying numerical processing to the image to identify the outer surface of at least one element.

[0035] According to another aspect, the present invention relates to a measurement system for detecting defective bonding interfaces in a sample substrate, the sample substrate including at least one element disposed on a support, the bonding interface being defined between the at least one element and the main surface of the support, the outer surface of the at least one element being exposed on the front side of the sample substrate and at least partially defining the exposed surface of the sample substrate.

[0036] According to the present invention, the measurement system includes a holder for receiving the sample substrate and a processing unit configured to perform an inspection method, the inspection method including:

[0037] · A measurement step of establishing a tilt map of the exposed surface, the tilt map being composed of a plurality of local tilt measurements relative to a reference surface;

[0038] · An analysis step of the tilt map, the analysis step identifying one or more regions where the tilt of the exposed surface deviates from the tilt of the reference surface by more than a given threshold, the one or more regions being referred to as "identified regions"; and

[0039] · A decision step of detecting the presence of a defective bond between the element and the support based on the result of the analysis step.

[0040] Additional non-limiting features according to this aspect of the present invention, taken alone or in any technically feasible combination:

[0041] - The measurement system further includes:

[0042] o An illumination device for providing two coherent light beams directed at the exposed surface of the sample substrate, the two light beams illuminating the exposed surface (1a) of the sample substrate in the displacement region;

[0043] o A detector for collecting the light reflected by the exposed surface of the two light beams, the reflected light

[0044] generating an interference signal on the detector;

[0045] o The processing unit is further configured to analyze the interference signal and generate at least one local

[0046] tilt measurement value of the tilt map;

[0047] - The measurement system further includes:

[0048] o A display screen configured to display a measurement pattern, such as a grid or stripes;

[0049] o A camera disposed in the system relative to the display screen and relative to the sample substrate to image the pattern displayed by the display screen and reflected by the exposed surface of the sample substrate;

[0050] o The processing unit is further configured to analyze the image generated by the camera and generate a tilt map or at least one local tilt measurement value of the tilt map;

[0051] o The processing unit is further configured to analyze the image generated by the camera and generate a tilt map or at least one local tilt measurement value of the tilt map;

[0052] o The processing unit is further configured to analyze the image generated by the camera and generate a tilt map or at least one local tilt measurement value of the tilt map;

[0053] - The measurement system further includes a scanning unit for scanning the exposed surface of the sample substrate to generate a tilt map. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] When considered in conjunction with the accompanying drawings, many other features and advantages of the present invention will become apparent upon reading the following detailed description, in which:

[0055] - Figure 1a and Figure 1b represent different views of a first exemplary sample substrate that can be subjected to the inspection method according to the present invention;

[0056] - Figure 2a and Figure 2b represent different views of a second exemplary sample substrate that can be subjected to the inspection method according to the present invention;

[0057] - Figure 3 represents a preferred embodiment of a measurement system that allows the implementation of the inspection method according to the present invention;

[0058] - Figure 4 Represents another embodiment of a measurement system that allows the implementation of the inspection method according to the present invention;

[0059] - Figure 5 Schematically represents the sequence of steps of the inspection method according to the present invention. Detailed implementation manner

[0060] Generally and as presented in the previous background section, the sample substrate 1 that is the object of the detection method of this specification includes a support 2 and at least one element 3 provided on the support 2. The surface of the support 2 provided with the element 3 defines the front side of the sample substrate 1. The element 3 can correspond to a thin film or a thin substrate (potentially having integrated circuit elements thereon) extending on the main part of the support 2. Alternatively, the element 3 can correspond to a block of material, a die, or a chiplet, potentially having integrated circuit elements thereon. A plurality of such elements 3 can be provided on the support 2 to cover it. In some embodiments, the element 3 and the support 2 include connecting lines, pads, or bumps to be electrically connected together. In all cases, the exposed surface 1a of the sample substrate 1 located on its front side at least partially includes the outer surface 3a of the element 3.

[0061] Since this is conventional in the semiconductor industry, the support 2 can be in the form of a wafer or a disk (whose diameter can be 100 mm, 150 mm, 200 mm, 300 mm, or even 450 mm), and usually has a thickness of several hundred micrometers. The support can be made of a semiconductor material or substrate (such as silicon or silicon carbide) or an insulating material (such as glass or sapphire) or include a semiconductor material or substrate (such as silicon or silicon carbide) or an insulating material (such as glass or sapphire). However, the present invention is not limited to a support having a specific shape, size, or property.

[0062] The support presents a main surface 2a provided with at least one element 3 and a back surface 2b opposite to the main surface. Thus, the outer surface 3a of at least one element 3 is exposed on the front side of the sample substrate 1.

[0063] Figure 1a An example of such a sample substrate 1 is represented in a top view, and Figure 1b In a cross-section along the Figure 1a X-X axis of this exemplary sample substrate 1 is represented. In the example represented in these figures, the sample substrate 1 includes a plurality of elements 3 covering the main surface 2a of the support. Each element 3 is composed of a block of material that may have been processed to form a functional semiconductor die or may not have been processed to form a simple material chiplet.

[0064] In Figure 1a 、 Figure 1bIn an exemplary sample substrate 1, a plurality of elements 3 do not completely cover the main surface 2a of the support 2. Accordingly, the surface of the main surface 2a of the support 2 between two juxtaposed elements 3 is exposed. The exposed surface 1a on the front side of the sample substrate 1 is formed by the outer surface 3a of the element 3 and the exposed surface of the main surface 2a of the support 2.

[0065] Figure 2a and Figure 2b Another example of the sample substrate 1 is represented in a top view and a cross-sectional view. In this second example, the sample substrate 1 includes a thin substrate 3 disposed on the main surface 2a of the support 2. The thin substrate 3 extends onto the main surface 2a of the support 2 to completely or almost completely cover it. In Figure 2a and Figure 2b illustrations, an annular portion and a peripheral portion of the main surface 2a of the support are exposed on the front side 1a of the sample substrate 1, but this is not necessary. The thin substrate 3 can be formed by a layer of material or a stack of layers. The thin substrate 3 may or may not have been processed. In this example, the exposed surface 1a on the front side of the sample substrate 1 is substantially formed by the outer surface 3a of the thin substrate 3.

[0066] Regardless of the nature of the elements 3 (die, tile, film or thin substrate), they have been assembled onto the main surface 2a of the support 2 by a bonding technique such as direct bonding, thermocompression bonding or interconnect bonding between bumps and vias. Accordingly, a bonding interface 3b is defined between the element 3 and the main surface 2a of the support 2.

[0067] The inspection method of the present specification is intended to detect defective bonding at this interface 3b. Defective bonding can correspond to weak bonding between the element 3 and the support 2 or partial delamination between the element 3 and the support 2, as Figure 1b and Figure 2b shown. In these figures, a region 4 of the sample substrate 1 is presenting defective bonding between the element 3 and the support 2. The applicant has observed that defective bonding can be revealed by the inclination of the outer surface of the element 3 with respect to its surroundings. In addition, the applicant has realized that this parameter seems to be very sensitive to any type of defect at the origin of defective bonding, such that defective bonding between the element 3 and the support can be determinedly detected by analyzing the inclination measurement values of the exposed surface 1a of the sample substrate 1.

[0068] The present invention makes use of this observation to propose an inspection method for the sample substrate 1 to identify one or more elements whose inclination deviates from the inclination of the underlying support 2. Such a deviation indicates a defective bonding interface.

[0069] To this end and as will be described in more detail in the next chapter of this specification, the inspection method uses a measurement system MS configured to establish and utilize an inclination map of the exposed surface 1a of the sample substrate 1. Preferably, the measurement system is capable of measuring a quantity that directly represents the inclination at a defined point of the exposed surface 1a. That is to say, the inclination is not reconstructed based on an indirect measurement (such as by deriving the height of the exposed surface 1a).

[0070] Figure 3 FIG. 4 shows a preferred embodiment of such a measurement system MS that allows the implementation of the inspection method according to the invention. The measurement system MS includes a holder 5 for receiving the sample substrate 1. The measurement system MS further includes a display screen 6 (such as a TFT screen) configured to display a measurement pattern MP (such as a grid or stripes). The measurement pattern MP can be prepared and sent by a computing device connected to the screen 6. The screen 6 is positioned and oriented in the measurement system MS towards the sample substrate 1 such that the pattern can be reflected by the exposed surface 1a of the sample substrate 1. The measurement system MS further includes a camera 7 arranged relative to the display screen 6 and relative to the sample substrate 1 to image the pattern reflected by the exposed surface 1a of the sample substrate 1. The measurement system MS further includes a processing unit PU connected to the camera 7, the processing unit PU being adapted to receive and analyze the image generated by the camera 7 and to calculate an inclination map by deflectometry. As is well known, for example, from US7812942, the processing unit PU can in particular reconstruct the path of the light reflected by the exposed surface 1a and captured by the camera 7 to establish an inclination map. This method is advantageous because it allows the rapid generation of an inclination map in one measurement step without scanning the main surface 1a by measurement points or lines. However, it is not excluded that the deflectometry system is provided with means for scanning the main surface 1a of the sample substrate, because such a scan may still be useful, for example, if the measurement pattern reflected on the camera 7 does not fully extend across the exposed surface 1a of the sample substrate 1.

[0071] Note that, after at least one element 3 is joined to the support 2, the exposed surface 1a of the sample substrate is prepared, for example by polishing, and this exposed surface exhibits strong specular properties. Thus, the exposed surface 1a is particularly suitable for such deflection measurement techniques. In fact, when the exposed surface 1a is flat and specular, light from the pattern displayed on the screen 6 is reflected by this surface 1a at similar reflection angles at all points. Except for the distortion caused by the geometry of the measurement system and the imaging path (which can be calibrated), the camera 7 images the pattern displayed by the screen without distortion. In the case where there are local deformations or slope changes on the exposed surface 1a, the light is locally reflected at different angles, which results in the imaged pattern being distorted compared to the imaging pattern produced by a perfectly flat surface. This distortion directly resulting from the angular deviation of the specular light due to surface tilt provides information about the tilt with very high sensitivity. By continuously preparing and displaying on the screen 7 several patterns with different orientations, periods, and / or spatial displacements, the local tilt at each point of the surface on which the pattern is imaged can be determined based on the images produced by the camera 7. The sensitivity and resolution of the tilt measurement values as measured by this technique can be made very high.

[0072] Although Figure 3 the deflectometry measurement system MS represents a preferred measurement system for implementing the inspection method according to the present invention, it does not form the only applicable measurement system. For example and alternatively, the measurement system can implement interferometric techniques, such as differential interference contrast (DIC) techniques. In this case, as Figure 4 presented, the measurement system MS can include an illumination device that includes a coherent light source 8, a polarizer 9, and a Nomarski or Wollaston prism 10 for splitting the light of the source so as to form two inspection beams B1, B2 directed towards the exposed surface 1a of the sample substrate 1 positioned on the substrate holder 5 of the system. The measurement system is arranged such that the two beams B1, B2 illuminate the exposed surface of the sample substrate in a region of lateral displacement.

[0073] According to the well-known DIC technique, the spatial separation of the beams can be achieved, for example, by an optical polarizer 9 that polarizes the light of the source 8 such that the light falls on the prism 10 with linear polarization oriented at 45 degrees to the axis of the prism 10. Then, the light is split by the prism 10 into two perpendicularly polarized beams that leave such a prism 10 with corresponding propagation axes in different and crossed directions. Then, these beams are focused by focusing lenses 11 onto the exposed surface 1a of the sample substrate 1 as two laterally displaced beams or spots B1, B2.

[0074] Light reflected from the surface is returned towards a collector or detector 13 via prism 10 and beam splitter 12. Analyzer 14 is positioned in the path of the light towards detector 13 together with detector lens 16. The analyzer forms a polarizer oriented relative to the beam perpendicular to the orientation of polarizer 9.

[0075] Light from two beams B1, B2 falls on the exposed surface 1a at slightly shifted positions. A height change of the surface between these beam positions results in an optical path difference between the two beams B1, B2. As the light returns through prism 10, the optical path difference will result in light components with a polarization different from that of the incident light. Analyzer 14 excludes all light components except those caused by the optical path difference between the two beams B1, B2. These components are combined to interfere on detector 13 and produce an intensity modulation representative of the optical path difference between beams B1, B2. The processing unit PU of the measurement system is configured to analyze the signal produced and deduce the optical path length difference between the two beams B1, B2. Since these beams are projected on shifted areas of surface 1a, this optical path length difference directly represents the local tilt of surface 1a between the illuminated areas.

[0076] In Figure 4 In the arrangement shown, light source 8, spots B1, B2 and detector 13 are optically conjugated via source lens 15, focusing lens 11 and detector lens 16. The light source can be arranged to provide point illumination with two localized spots B1, B2 on the surface. Then, detector 13 can be a point detector, such as a photodiode. In this case, the exposed surface can be scanned by examining the beams (e.g., by moving the sample substrate holder in the x and y directions) to provide a tilt map.

[0077] The illumination device can be configured to provide an inspection field corresponding to multiple pairs of beams, each pair illuminating an area of the exposed surface 1a, and each resulting interference being detected by a separate detector, or by pixels of a matrix detector or a linear array detector. In this case, detector 13 can be a linear array camera or a matrix camera. Scanning may be required if the inspection field does not extend across the entire exposed surface 1a.

[0078] The lighting device can also provide two strip-shaped illumination beams that are parallel to each other and can be large enough to cover the dimensions of the sample substrate only in one main direction (e.g., the diameter if the sample substrate is disc-shaped). The light source 8 can then be arranged to provide linear or strip-shaped illumination. The detector 13 can then be a line array detector, and each pixel of the line array detector collects the interference of the two beams in the area corresponding to the pixel projected on the exposed surface 1a by the imaging system. In this context, preparing the tilt map by the processing unit may require scanning the exposed surface 1a only in a single direction (the main direction perpendicular to the extension of the inspection beam) through interference inspection of the light field. This operation can be repeated in two perpendicular directions on the sample substrate to obtain the tilt map in all directions.

[0079] Regardless of which measurement system is selected and which tilt measurement technique is employed in the measurement system, the processing unit PU of the measurement system is capable of generating a tilt map of the exposed surface 1a of the sample substrate, that is, a plurality of local tilt measurement values, each local tilt being associated with a defined position on the exposed surface 1a. The local tilt measurement value can correspond to the angle existing between the direction tangent to the exposed surface or the normal direction and the reference direction at the defined position.

[0080] Reference Figure 5 , the inspection method for detecting a defective bonding interface 3b between components 3 provided on a support 2 of a sample substrate 1 includes a providing step S1 of placing the sample substrate 1 in a measurement system. Generally, the sample substrate 1 is positioned on a holder 5 of the measurement system MS manually or by an articulated arm such that the exposed surface 1a of the substrate 1 is exposed for inspection. As is well known in the art, the sample substrate can be clamped to the holder by an electrostatic device or by suction.

[0081] In a subsequent measurement step S2, a tilt map of the exposed surface 1a is established by the measurement system MS, as detailed in the foregoing paragraphs of this specification. The tilt map is composed of a plurality of local tilt measurement values relative to a reference surface of the measurement system MS. The local tilt measurement values are prepared by the processing unit PU of the measurement system MS, and preferably a complete tilt map is prepared.

[0082] The original local tilt measurement values provided by the measurement system MS are relative to a reference surface that needs to be properly defined inside the measurement system. To conform to the principles of the present invention (that is, to identify the component 3 where the tilt of the sample substrate deviates from the tilt of the underlying support 2), it is advantageous to define the reference surface as the main surface 2a of the support 2.

[0083] To this end and according to one embodiment, the inspection method may include a calibration step S0 of the measurement system, which is performed before the provision step S1 of placing the sample substrate 1 in the measurement system MS. The calibration step S0 includes a first sub-step of establishing an inclination map of the holder 5 and a second sub-step of defining a reference surface as the inclination map of the holder. The method assumes that the support 2 of the sample substrate 1 is flat and has a very uniform thickness, such that the inclination map of the holder represents the inclination map of the main surface 2a of the support 2. The method is particularly applicable when the sample substrate 1 is, for example, maintained against the holder by an electrostatic device or suction so as to eliminate any deformation (bending or warping) of the sample substrate. In a variant, the calibration step S0 may include a first sub-step of placing a virtual substrate that is shape-representative of the support 2 on the holder 5 of the measurement system MS, a second sub-step of establishing an inclination map of the virtual substrate, and a third sub-step of defining a reference surface as the inclination map of the virtual substrate. This variant may not require clamping the sample substrate 1 on the holder 5.

[0084] Regardless of which variant is selected, the inclination map provided in the subsequent measurement step S2 of the inspection method will refer to the main surface 2a of the support 2.

[0085] Alternatively or in addition to the calibration method applied before the measurement step S2, the inspection method may include an offset step S2' of applying a transformation to the inclination map of the main surface 1a of the sample substrate 1 after the measurement step S2. The transformation applies the offset value of the offset map to the local raw inclination measurement values provided by the measurement system MS in the measurement step S2, for example, by addition or subtraction.

[0086] The offset map may be stored in a library of the processing unit and may be selected from a set of offset maps in the library to correspond to the support 2 of the sample substrate 1. In a variant, the offset map is established according to the virtual substrate during the calibration step S0, as already explained above.

[0087] In an implementation variant of the offset step S2', the offset map may be established by numerical processing of the inclination map of the main surface 1a itself. For example, the method may include a first sub-step of calculating a representative value (e.g., the average value, median value, or mode value (i.e., the most frequent value)) of the raw local inclination measurement values of the inclination map. The offset map is constructed according to the representative value by setting each entry of the map to the representative value.

[0088] In another implementation variant of the offset step S2', the offset map is constructed by a first sub-step of identifying in the inclination map the local inclination measurement values associated with the main surface 2a of the support 2. These local inclination measurement values may, for example, correspond to the visible part of the main surface 2a between two juxtaposed elements 3 (as Figure 1aas shown), or a circular portion corresponding to the front side 1a of the sample substrate 1 (such as Figure 2a as shown). The positions of these local tilt measurements on the exposed surface 1a of the sample substrate 1 can be known in advance, and thus can be selected among all the tilt measurements in the tilt map. This variant of the offset step S2' also includes a second sub-step of defining an offset map based on the identified local tilt measurements. This second sub-step may include interpolating the identified local tilt measurements to define each entry of the offset map.

[0089] When the inspection method involves the calibration step S0 and / or the offset step S2', a tilt map composed of a plurality of local tilt measurements with respect to the main surface 2a of the support 2 is available.

[0090] Return reference Figure 5 and a general description of the inspection method, which includes an analysis step S3 after the measurement step S2. During the analysis step S3, the tilt map is analyzed to identify one or more regions of the exposed surface 1a, the tilt of such regions deviates from the tilt of the reference surface by more than a given threshold, and advantageously deviates from the tilt of the support 2 by more than a given threshold. For the sake of simplicity of expression, one or more regions identified in the tilt map will be referred to as "identified regions" in the rest of this specification. This step may be performed by the processing unit PU of the measurement system MS, or by an additional processing unit connected to the measurement system MS.

[0091] Different methods can implement the analysis step S3. In some instances, the analysis step relies on a positioning map that defines the positions and shapes of a plurality of predetermined regions on the exposed surface 1a of the sample substrate 2. The predetermined regions can be defined by laying an arbitrary grid of regular or irregular basic surfaces on the exposed surface 1a. More advantageously, the predetermined regions of the positioning map correspond to the outer surfaces 3a of the elements 3 provided on the support 2. In this case, the predetermined regions on the outer surfaces of the elements 3 may not cover some parts of the main surface 2a of the support 2. For example, an image of the exposed surface can be provided and processed according to conventional computer vision techniques to identify the outer surface 3a on the support 2 in the image and automatically construct the positioning map. The image can be provided by a camera (e.g., Figure 3 the camera 7 of the deflectometry system) provided in the measurement system MS.

[0092] In all cases, the analysis step S3 includes a first sub-step of providing the positioning map. Then, in the second sub-step of the analysis step S3, a representative value of the local tilt measurements associated with each predetermined region is calculated. The representative value can be selected from the group formed by: the average value, the median value, and the mode value of the local tilt measurements associated with each predetermined region.

[0093] Thus, for each region, the representative tilt value is compared with a predetermined threshold. If the representative tilt value of a predetermined region exceeds the threshold, it forms an identified region, i.e., a region including an element 3 defectively joined to the support 2. The analysis step S3 establishes and provides a list of such identified regions.

[0094] Finally and after the analysis step S3, the inspection method includes a decision step S4 of detecting the presence of a defective join between the element 3 and the support 2 based on the result of the analysis step S3. For example, if the previous analysis step S3 fails to identify a predetermined region with an orientation deviation exceeding a given threshold, no defective join is detected in the sample substrate 1, and the decision step S4 provides a "pass" signal or data to indicate that the sample substrate is defect-free. Conversely, and in the most simplified form of the decision step S4, if the analysis step S3 provides at least one identified region with an orientation deviation exceeding a given threshold, a defective join is detected in the sample substrate 1, and the decision step provides a "fail" signal or data to indicate that the sample substrate is defective.

[0095] The decision step can provide more information than just a "pass or fail" signal. It can provide information related to the identified region (the location of the identified region on the sample substrate or the serial number allowing the location of the identified region, the representative tilt value of the predetermined region). The decision step S4 can, for example, provide an image of the main surface 1a of the sample substrate 1 (in which the identified region is highlighted and / or the representative tilt value of the predetermined region is shown) to further assist in characterizing the sample substrate 1.

[0096] By studying the drawings, the disclosure and the appended claims, those skilled in the art can understand and implement other variants of the disclosed embodiments when practicing the claimed invention.

Claims

1. An inspection method for detecting defective bonding interfaces in a sample substrate (1), the sample substrate including at least one element (3) disposed on a support (2), a bonding interface (3b) being defined between the at least one element (3) and a main surface (2a) of the support (2), an outer surface (3a) of the at least one element (3) being exposed on a front side of the sample substrate (1) and at least partially defining an exposed surface (1a) of the sample substrate (1), the method comprising: · A providing step (S1) of placing the sample substrate (1) in a measurement system (MS); · A measuring step (S2) of using the measurement system (MS) to establish an inclination map of the exposed surface (1a), the inclination map being composed of a plurality of local inclination measurement values with respect to a reference surface; · An analyzing step (S3) of the inclination map, the analyzing step identifying one or more regions where the inclination of the exposed surface deviates from the inclination of the reference surface by more than a given threshold, the one or more regions being referred to as "identified regions"; And · A decision-making step (S4) of detecting a defective bond between the element (3) and the support (2) according to the result of the analyzing step (S3).

2. The inspection method according to claim 1, wherein, The reference surface corresponds to the main surface (2a) of the support (2).

3. The inspection method according to claim 2, wherein the inspection method further comprises: A calibration step (S0) of the measurement system (MS) before the measuring step (S2), the calibration step (S0) defining an inclination map of the main surface (2a) of the support.

4. The inspection method according to claim 3, wherein, The measurement system (MS) includes a holder (5) for receiving the sample substrate (1) during the measuring step (S2), and the calibration step includes a first sub-step of establishing an inclination map of the holder (5), and a second sub-step of defining the reference surface as the inclination map of the holder (5).

5. The inspection method according to claim 3, wherein, The measurement system (MS) includes a holder (5) for receiving the sample substrate (1) during the measuring step (S2), and the calibration step includes a first sub-step of placing a virtual substrate on the holder (5), a second sub-step of establishing an inclination map of an exposed surface of the virtual substrate, and a third sub-step of defining the reference surface as the inclination map of the exposed surface of the virtual substrate.

6. The inspection method according to claim 2, the method further comprising: An offset step (S2') of applying an offset map to the inclination map after the measuring step (S2), the transformation causing the local inclination measurement values of the inclination map to be offset with respect to the main surface (2a) of the support (2).

7. The inspection method according to claim 6, wherein, The offset step (S2') includes a sub-step of calculating a representative value of the local inclination measurement values of the inclination map established by the measuring step (S2).

8. The inspection method according to claim 6, wherein, The offset step (S2') includes: · A first sub-step of identifying local inclination measurement values associated with the main surface (2a) of the support (2) in the inclination map; · A second sub-step of defining the offset map according to the identified local inclination measurement values.

9. The inspection method according to any one of claims 1 to 8, wherein The analyzing step (S3) includes: · A first sub-step of providing a positioning map that defines the positions of a plurality of predetermined regions of the exposed surface (1a) of the sample substrate (1); · A second sub-step of calculating a representative value of the local tilt measurement associated with the predetermined region.

10. The method according to claim 9, wherein, The positioning map includes at least one predetermined region corresponding to the outer surface (3a) of the at least one element (3).

11. The method according to claim 9 or 10, wherein, The first sub-step of providing the positioning map includes: providing an image of the exposed surface (1a) of the sample substrate (1), and applying numerical processing to the image to identify the outer surface (3a) of the at least one element (3).

12. A measurement system (MS) for detecting defective bonding interfaces in a sample substrate (1), the sample substrate including at least one element (3) disposed on a support (2), the bonding interface (3b) being defined between the at least one element (3) and the main surface (2a) of the support (2), the outer surface (3a) of the at least one element (3) being exposed on the front side of the sample substrate (1) and at least partially defining the exposed surface (1a) of the sample substrate (1), the measurement system (MS) including a holder (5) for receiving the sample substrate (1) and a processing unit (PU) configured to perform an inspection method, the inspection method including: · A measurement step (S2) of establishing a tilt map of the exposed surface (1a), the tilt map being composed of a plurality of local tilt measurements relative to a reference surface; · An analysis step (S3) of the tilt map, the analysis step identifying one or more regions where the tilt of the exposed surface deviates from the tilt of the reference surface by more than a given threshold, the one or more regions being referred to as "identified regions"; And · A decision step (S4) of detecting the presence of a defective bond between the element (3) and the support (2) based on the result of the analysis step (S3).

13. The measurement system (MS) according to claim 12, the measurement system further including: · An illumination device for providing two coherent light beams directed at the exposed surface (1a) of the sample substrate (1), the two light beams illuminating the exposed surface (1a) of the sample substrate (1) in a shift region; · A detector (13) for collecting the light reflected from the exposed surface (1a) of the two light beams, the reflected light generating an interference signal on the detector; · The processing unit (PU) is further configured to analyze the interference signal and generate at least one local tilt measurement value of the tilt map.

14. The measurement system (MS) according to claim 12, the measurement system further including: · A display screen (6) configured to display a measurement pattern, such as a grid or stripes; · A camera (7) which is arranged in the system relative to the display screen (6) and relative to the sample substrate (1) to image the pattern displayed by the display screen (6) and reflected by the exposed surface (1a) of the sample substrate (1); · The processing unit (PU) is further configured to analyze the image generated by the camera (7) and generate the tilt map or at least one local tilt measurement value of the tilt map.

15. The measurement system (MS) according to claim 13 or 14, the measurement system further comprising a scanning unit for scanning the exposed surface (1a) of the sample substrate (1) to generate the tilt map.

Images