Patent ID: 12222322

DETAILED DESCRIPTION

In the following detailed description, directional terminology, such as “top”, “bottom”, “left”, “right”, “upper”, “lower” etc., is used with reference to the orientation of the Figure(s) being described. Because components of the disclosure can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration only.

In addition, while a particular feature or aspect of an example may be disclosed with respect to only one of several implementations, such feature or aspect may be combined with one or more other features or aspects of the other implementations as may be desired and advantageous for any given or particular application, unless specifically noted otherwise or unless technically restricted. Furthermore, to the extent that the terms “include”, “have”, “with” or other variants thereof are used in either the detailed description or the claims, such terms are intended to be inclusive in a manner similar to the term “comprise”. The terms “coupled” and “connected”, along with derivatives thereof may be used. It should be understood that these terms may be used to indicate that two elements cooperate or interact with each other regardless whether they are in direct physical or electrical contact, or they are not in direct contact with each other; intervening elements or layers may be provided between the “bonded”, “attached”, or “connected” elements. However, it is also possible that the “bonded”, “attached”, or “connected” elements are in direct contact with each other. Also, the term “exemplary” is merely meant as an example, rather than the best or optimal.

The semiconductor substrate mentioned further below may be manufactured by different technologies and may include for example integrated electrical, electro-optical or electro-mechanical circuits and/or passives, logic integrated circuits, control circuits, microprocessors, memory devices, etc. The semiconductor substrate may have contact pads (or electrodes) which allow electrical contact to be made with the integrated circuits of semiconductor devices included in the semiconductor substrate. The electrodes may be arranged all at only one main side of the semiconductor substrate or at both main sides of the semiconductor substrate. The semiconductor substrate may be manufactured from specific semiconductor material, for example Si, SiC, SiGe, GaAs, GaN, or from any other semiconductor material, and, furthermore, may contain one or more of inorganic and organic materials that are not semiconductors, such as for example insulators, plastics or metals. The semiconductor substrate may e.g. comprise or consist of a semiconductor wafer, a compound wafer, a panel, or a singulated semiconductor die.

FIG.1shows a system100for the acoustic detection of cracks in a semiconductor substrate. The system100comprises a force generating unit110, a detector unit120, and an evaluation unit130.

The force generating unit110is configured to press down onto a semiconductor substrate140(which is not part of system100and is therefore indicated by dashed lines inFIG.1) and thereby apply a force onto the semiconductor substrate140. The force generating unit110may for example be configured to apply a force of 100 mN or more, 200 mN or more, 500 mN or more, 1000 mN or more, or 2000 mN or more.

The detector unit120comprises a resonating indenter121and an acoustic emission sensor122coupled to the resonating indenter121. The acoustic emission sensor122may e.g. be a piezoelectric acoustic emission sensor. The resonating indenter121may e.g. be coupled to a detector surface of the acoustic emission sensor122using a hard glue layer, a soft solder layer, or mechanical fixing means. The resonating indenter121may e.g. be a probe pin. The resonating indenter121may comprise a tapered tip that is configured to contact the semiconductor substrate140. The resonating indenter121may be configured to transmit acoustic signals from the semiconductor substrate140into the acoustic emission sensor122.

The resonating indenter121is configured to contact the semiconductor substrate140at a lateral distance d from the force generating unit110. The lateral distance d may for example be 0.5 cm or more, or 1 cm or more, or 2 cm or more, or 5 cm or more, or 10 cm or more. The lateral distance may e.g. be more than 20% of a width w of the semiconductor substrate140, or more than 30%, or more than 50%, or more than 70%.

The force generating unit110and the resonating indenter121are configured to contact the semiconductor substrate140on the same side. For example, the semiconductor substrate140may comprise a first main side141, an opposing second main side142and lateral sides143connecting the first and second main sides141,142. The force generating unit110and the resonating indenter121may both be configured to contact the first main side141. The semiconductor substrate140may for example be arranged on a temporary carrier (e.g. a wafer chuck or a tape) during acoustic detection of cracks by the system100, wherein the second main side142faces the temporary carrier.

The evaluation unit130is configured to evaluate acoustic signals detected by the detector unit120and it is configured to determine whether a crack has occurred in the semiconductor substrate140based on the detected signals. Such a crack may for example occur due to mechanical stress caused by the force generating unit110.

According to an example, the downward pressure exercised by the force generating unit110is only a byproduct of some process step during semiconductor device fabrication, e.g. electrical testing, wire bonding, dicing, or molding.

For example, the semiconductor substrate140may comprise a plurality of semiconductor devices (e.g. transistor circuits) and during fabrication the electrical functionality of these devices is tested. In this case, the force generating unit110may comprise a probe card of a testing equipment for electrical testing. Such a probe card may comprise testing pins which are brought into contact with contact pads of the semiconductor devices in the semiconductor substrate140. The testing pins may exert a force onto the semiconductor substrate140, which may cause a crack (and therefore damage one or more of the semiconductor devices).

According to another example, the force generating unit110comprises a bondhead of a wire bonding equipment which is used for attaching bond wires to semiconductor devices in the semiconductor substrate140. According to yet another example, the force generating unit110comprises a saw of a dicing equipment which is used for sawing through kerfs in the semiconductor substrate140.

In each of the above-mentioned examples, it may be desirable to detect cracks in the semiconductor substrate140, for example in order to discard damaged semiconductor devices.

The force generating unit110may comprise a contact area111, wherein the contact area111is configured to contact the first main side141of the semiconductor substrate140. The contact area111may for example comprise the tips of testing pins, the bondhead of a wire bonder, or the cutting edge of a saw. The contact area111may have any suitable size, for example a size of 300 μm2or more, or 1 mm2or more, or 1 cm2or more. The contact area111may be configured to cover only a small part of the first main side141of the semiconductor substrate140, e.g. 20% or less, or 10% or less, or 5% or less.

The force generating unit110may be configured to contact only specific parts of the first main side141of the semiconductor substrate. For example, in the case that the force generating unit110comprises a probe card of a testing equipment for electrical testing or a bondhead of a wire bonding equipment, the force generating unit110may be configured to solely touch contact pads on the first main side141but no other part of the first main side141. In the case that the force generating unit110comprises a saw of a dicing equipment, the force generating unit110may be configured to solely touch kerfs on the first main side141but no other part of the first main side141.

The force generating unit110may be configured to exert a pressure onto a given semiconductor substrate140only once or to exert a pressure repeatedly. The force generating unit140may be configured to exert the pressure for any suitable timespan, e.g. a fraction of a second, or one second or more, or several seconds or more.

The detector unit120may comprise a single resonating indenter121and a single acoustic emission sensor122. Alternatively, it may comprise several resonating indenters121and/or several acoustic emission sensors.

According to an example, the resonating indenter121has a first resonance frequency and the acoustic emission sensor122has a second resonance frequency, wherein the first and second resonance frequencies are attuned to one another such that an optimal sensitivity of the detector unit120to cracks in the semiconductor substrate140is ensured. The first and second resonance frequencies may for example be in the range of 100 kHz to 1 MHz, in particular in the range of 100 kHz to 200 kHz. The detector unit120may for example be sensitive to acoustic signals in the range of 50 kHz to 1 MHz. The detector unit120may e.g. be sensitive to acoustic signals with peak amplitudes of 10 dBAE or more, or 20 dBAE or more.

The evaluation unit130may e.g. comprise evaluation electronics configured to evaluate acoustic signals detected by the detector unit120. The evaluation unit130may be configured to inform a user of the fact that a crack was detected in the semiconductor substrate140and/or it may be configured to pass on this information to other automated equipment, e.g. for automatically discarding damaged semiconductor devices.

The evaluation unit130may be coupled to the detector unit120(e.g. to an output of the detector unit120) and it may also be coupled to the force generating unit110. A coupling between the evaluation unit130and the force generating unit110may e.g. be used to inform the evaluation unit130that the force generating unit110is lowered down to touch the semiconductor substrate140or that the force generating unit110is raised back up. This may e.g. be useful for detecting acoustic signals in a time-synchronous manner with a contact force exerted by the force generating unit110.

The system100may further comprise an amplifier for amplifying signals detected by the detector unit120. The amplifier may for example be comprised in the detector unit120or in the evaluation unit130. The system100may comprise a convertor for converting an analog signal into a digital signal for evaluation.

FIG.2shows the detector unit120according to an example. In the example ofFIG.2, the resonating indenter121comprises a tip121_1, a shaft121_2and a base121_3, wherein the base121_3has a larger diameter than the shaft121_2. According to an example, an adhesive layer123may be used to attach the resonating indenter121to the acoustic emission sensor122.

The resonating indenter121may comprise or consist of any suitable material, e.g. Cu, Rh, W, or steel. The resonating indenter121may essentially be rigid. The tip121_1may e.g. comprise or consist of diamond. The tip121_1may e.g. have an essentially rounded shape or a tapered shape. The tip121_1may e.g. have a diameter of 10 μm or more, or 20 μm or more. The resonating indenter121may have a length measured between the tip121_1and the adhesive layer123of less than 10 mm, or 10 mm or more, or 20 mm or more. The shaft121_2may have any suitable diameter, e.g. a diameter in the range of 0.8 mm to 1.5 mm.

The adhesive layer123may be a “hard” layer, meaning that it is dimensionally stable and inelastic. Due to these properties, the adhesive layer123may be a good transmitter for acoustic signals. According to an example, the adhesive layer123comprises or consists of cyanoacrylate.

FIG.3shows the semiconductor substrate140according to an example. As shown inFIG.3, the semiconductor substrate140may comprise a layer stack. The layer stack may e.g. comprise one or more of a first metal layer310, an oxide layer320, a second metal layer330, and another isolating layer or gate oxide layer340.

The first metal layer310may e.g. comprise or consist of Al and/or Cu. The first metal layer310may comprise contact pads of semiconductor devices comprises in the semiconductor substrate140.

The oxide layer320may e.g. comprise a silicon oxide. The oxide layer320may be arranged under the first metal layer310.

The second metal layer330may e.g. comprise or consist of Cu. The second metal layer330may e.g. be an electrical redistribution layer and it may be electrically coupled to the first metal layer310. The second metal layer330may be arranged under the oxide layer320or embedded within the oxide layer320.

The isolating layer340may e.g. comprise an oxide material. Another isolating layer or gate oxide layer340may be arranged under the second metal layer330or the second metal layer330may be embedded within the isolating layer340.

As shown inFIG.3, the contact area111of the force generating unit110may be brought into contact with the semiconductor substrate140, e.g. with the first metal layer310. The force generating unit110may exert a pressure onto the semiconductor substrate140which may cause a plastic deformation350and/or a crack360in the semiconductor substrate140. A plastic deformation350and/or a crack360may for example occur if the force generating unit110was lowered down onto the semiconductor substrate140with too much force.

The plastic deformation350may for example occur in the first metal layer310. The first metal layer310may be at least somewhat malleable and may therefore not be prone to crack. The crack360may for example occur in the oxide layer320(as shown inFIG.3), or in the dielectric layer340. The oxide layer320and/or the dielectric layer340may be brittle and may therefore be prone to crack when the force generating unit110exerts too much force onto the semiconductor substrate140. A crack360may for example have a size of about 1 μm or less up to about 10 μm.

The crack360may reduce the ability of the oxide layer320to act as an electrical insulator and may therefore cause an electrical failure. The crack360may occur directly under the contact area111as shown inFIG.3or it may occur somewhere else within the semiconductor substrate140. Generally speaking, cracks and plastic deformations in the semiconductor substrate140may cause damage to insulating layers. Such damage may cause electrical failures during operation, for example leakage currents and/or electrical shorts.

The plastic deformation350may cause an acoustic signal with a comparatively small peak amplitude. The plastic deformation350may in particular cause an acoustic signal which is not readily transmitted across the semiconductor substrate140, e.g. due to attenuation within the semiconductor substrate140. For example, after having traversed the distance d between the force generating unit110(i.e. the site of the plastic deformation350) and the detector unit120, an acoustic signal caused by the plastic deformation350may be attenuated to such a degree that the detector unit120is unable to detect it. On the other hand, an acoustic signal caused by the crack360may have a comparatively large peak amplitude and may in particular be readily transmitted across the semiconductor substrate140. After traversing the distance d, an acoustic signal caused by the crack360may therefore be readily detectable by the detector unit120.

For this reason, it may be possible to distinguish a crack from a plastic deformation using the system100. By properly setting the distance d and/or a sensitivity of the detector unit120, the system100only detects acoustic signals caused by cracks. A proper value for the distance d for this purpose may for example be about 1 cm or more, or 5 cm or more, or 8 cm or more, or 10 cm or more, depending on the specific semiconductor substrate140and/or the sensitivity of the detector unit120.

FIGS.4A and4Bshow a further system400for the acoustic detection of cracks in a semiconductor substrate. The system400may be similar to or identical with the system100, except that it comprises several detector units120instead of a single one.FIG.4Ashows a side view andFIG.4Bshows a top-down view.

The system400may be configured to determine the location at which a crack has occurred in the semiconductor substrate140. The location of a crack may for example be determined by analyzing the times at which an acoustic signal is detected by individual detector units120that are arranged at a distance to one another. Thereby, the distances between the individual detector units120and the crack may be determined. The system400may for example comprise at least three detector units120in order to precisely locate cracks in the semiconductor substrate140. The individual detector units120may be coupled to a common evaluation unit130.

The individual detector units120may for example be arranged around the force generating unit110, as shown inFIG.4B. However, the individual detector units120may e.g. also be arranged on one side of the force generating unit110. The individual detector units120may be arranged in any pattern suitable for the localization of cracks.

According to another example, the system400does not comprise more than one detector unit120, but instead the single detector unit120comprises several acoustic emission sensors122and several resonating indenters121, wherein each resonating indenter121is coupled to a different acoustic emission sensor122.

FIGS.5A to5Cshow different examples for the force generating unit110which may be used in the systems100and400.

FIG.5Ashows the force generating unit110to comprise a probe card510of a testing equipment for electrical testing. The probe card510comprises a plurality of testing pins511for electrically contacting semiconductor devices in the semiconductor substrate140. The tips of the testing pins511form the contact area111.

FIG.5Bshows the force generating unit110to comprise a bondhead520of a wire bonding equipment. The contact area111may e.g. be formed by the tip of the bondhead520, by bond wire521, or by cutting edge522.

FIG.5Cshows the force generating unit110to comprise a saw530of a dicing equipment. The contact area111may be formed by the edge of the saw530.

FIG.6is a flow chart of a method600for the acoustic detection of cracks in a semiconductor substrate. The method600may for example be performed using the system100or400.

The method600comprises at601an act of pressing down onto a semiconductor substrate with a force generating unit and thereby applying a force onto the semiconductor substrate, at602an act of contacting the semiconductor substrate with a resonating indenter of a detector unit, the detector unit further comprising a acoustic emission sensor coupled to the resonating indenter, and at603an act of evaluating with an evaluation unit acoustic signals detected by the detector unit and determining, whether a crack has occurred based on the detected signals, wherein the resonating indenter is configured to contact the semiconductor substrate at a lateral distance from the force generating unit, and wherein the force generating unit and the resonating indenter are configured to contact the semiconductor substrate on the same side.

According to an example, the method600is performed during electrical testing of the semiconductor substrate (i.e. electrical testing of e.g. transistor circuits in the semiconductor substrate), or during wire bonding, or during dicing. According to an example, the method600further comprises an act of determining the location of a crack in the semiconductor substrate by using more than one detector units, wherein the more than one detector units contact the semiconductor substrate at different locations. Furthermore, the method600may comprise determining in which semiconductor device of a plurality of semiconductor devices comprised in the semiconductor substrate the crack occurred.

EXAMPLES

In the following, the system and method for the acoustic detection of cracks in a semiconductor substrate are further explained using specific examples.

Example 1 is a system for the acoustic detection of cracks in a semiconductor substrate, the system comprising: a force generating unit configured to press down onto a semiconductor substrate and thereby apply a force onto the semiconductor substrate, a detector unit comprising a resonating indenter and an acoustic emission sensor coupled to the resonating indenter, and an evaluation unit configured to evaluate acoustic signals detected by the detector unit and configured to determine, whether a crack has occurred based on the detected signals, wherein the resonating indenter is configured to contact the semiconductor substrate at a lateral distance from the force generating unit, and wherein the force generating unit and the resonating indenter are configured to contact the semiconductor substrate on the same side.

Example 2 is the system of example 1, wherein the force generating unit comprises a probe card of a testing equipment for electrical testing, or a bondhead of a wire bonding equipment, or a saw of a dicing equipment.

Example 3 is the system of example 1 or 2, further comprising: one or more additional detector units, wherein the resonating indenters of the detector units are configured to contact the semiconductor substrate at locations that are spaced apart from one another, and wherein the evaluation unit is configured to determine the location at which a crack occurred based on the signals detected by the detector units.

Example 4 is the system of one of the preceding examples, wherein the resonance frequencies of the resonating indenter and the acoustic emission sensor are attuned to one another.

Example 5 is the system of example 4, wherein the resonance frequencies are in the range of 100 kHz to 1 MHz.

Example 6 is the system of one of the preceding examples, wherein the resonating indenter comprises a tip and wherein the tip has a diameter of 20 μm or less.

Example 7 is the system of example 6, wherein the tip comprises diamond.

Example 8 is the system of one of the preceding examples, wherein the resonating indenter has a length of 10 mm or more.

Example 9 is the system of one of the preceding examples, wherein the lateral distance is 1 cm or more.

Example 10 is the system of one of the preceding examples, wherein due to the lateral distance the system is configured to differentiate an acoustic signal generated by a crack in the semiconductor substrate from an acoustic signal generated by a plastic deformation in the semiconductor substrate.

Example 11 is the system of one of the preceding examples, wherein the force generating unit and/or the detector unit are moveable across a plane parallel to the semiconductor substrate.

Example 12 is the system of one of the preceding examples, wherein the detector unit is configured to press the probe tip onto the semiconductor substrate with a force of 1000 mN or less.

Example 13 is a method for the acoustic detection of cracks in a semiconductor substrate, the method comprising: pressing down onto a semiconductor substrate with a force generating unit and thereby applying a force onto the semiconductor substrate, contacting the semiconductor substrate with a resonating indenter of a detector unit, the detector unit further comprising an acoustic emission sensor coupled to the resonating indenter, and evaluating with an evaluation unit acoustic signals detected by the detector unit and determining, whether a crack has occurred based on the detected signals, wherein the resonating indenter is configured to contact the semiconductor substrate at a lateral distance from the force generating unit, and wherein the force generating unit and the resonating indenter are configured to contact the semiconductor substrate on the same side.

Example 14 is the method of example 13, wherein the method is performed during electrical testing of the semiconductor substrate, or during wire bonding, or during dicing.

Example 15 is the method of example 13 or 14, further comprising: determining the location of a crack in the semiconductor substrate by using more than one detector units, wherein the more than one detector units contact the semiconductor substrate at different locations.

Example 16 is the method of example 15, further comprising: determining in which semiconductor device of a plurality of semiconductor devices comprised in the semiconductor substrate the crack occurred.

Example 17 is the method of one of examples 13 to 16, wherein due to the size of the lateral distance, the detector unit is sensitive to acoustic signals of cracks but not to acoustic signals of plastic deformations caused by the force generating unit in the semiconductor substrate.

Example 18 is the method of one of examples 13 to 17, wherein the lateral distance is 1 cm or more.

Example 19 is an apparatus comprising means for performing the method of one of examples 13 to 18.

While the disclosure has been illustrated and described with respect to one or more implementations, alterations and/or modifications may be made to the illustrated examples without departing from the spirit and scope of the appended claims. In particular regard to the various functions performed by the above described components or structures (assemblies, devices, circuits, systems, etc.), the terms (including a reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component or structure which performs the specified function of the described component (e.g., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary implementations of the disclosure.