WO2017191634A1

WO2017191634A1 - A method and system for determining voids in a bump or similar object

Info

Publication number: WO2017191634A1
Application number: PCT/IL2017/050487
Authority: WO
Inventors: Michael Geffen; Doron REINIS; Colin Smith; Roni PERETZ
Original assignee: Xwinsys Ltd
Priority date: 2016-05-04
Filing date: 2017-05-02
Publication date: 2017-11-09

Abstract

A method and a system for a bump's inspection are disclosed. The inspection is done by comparing the geometrical volume contained in the bump's outside contour and the volume of the solid materials (atomic volume) from which the bump is made and/or analyzing the bump's solid materials ratio. Principally, the inspection is done by preparing an empirical reference table of the emitted energy received from the solid materials, from which a reference bump with a given volume is comprised, using EDXRF (Energy-Dispersive-X-ray-Fluorescence) analysis; obtaining a geometrical volume of the bump using a 3D image-processing method; adapting the reference table according to the difference between the atomic volume and the geometrical volume of the bump; The difference between atomic volume and geometrical volume are used to inspect the bump and to determine the presence and volume of voids within the bump. Similar techniques can also be employed in connection with the determination of, for example, the thickness dimensions of a multi-layered stacked array of metals, the depth dimensions of relevant features, and surface uniformity or irregularity.

Description

A METHOD AND A SYSTEM FOR DETERMINING VOIDS

IN A BUMP OR SIMILAR OBJECT

FIELD OF INVENTION AND BACKGROUND

The present invention relates to the field of wafer inspections, more specifically the present invention relates to a method and a system for inspecting the existence of voids in a bump and calculating the void's volume as well as other critical dimensions thereof. The present invention is an extension of US 9,335, 283 to Geffen et al. The present invention combines a 3D optical component with EDXRF technology in order to be capable of determining additional various parameters of semiconductor components, bumps, and similar objects. Inter alia, measuring critical dimensions of multi-component bumps and other multilayer and multi-component features of semiconductor components.

A "bump" is a half sphere shaped salient, made of solderable material, located on the face of a microelectronic chip. The bump exists in some chips and substitutes as a lead by means of which a component is able to be connected to the printed circuit when the bumps are soldered to the board. The bump shape is like a half ball and a chip can contain a large number of bumps. During the last few years the electronics industry moved from SnPb solders to lead-free solders. To-day the high lead SnPb bumps are exempted from the WEEE and RoHS directives. In the new wafer technologies, use of SnAg bumps can be found instead of SnPb bumps. The typical bump's dimensions are 50-60 μιη in diameter and 20-30 μιη in height. The skullcap is placed on a 50-60 μιη diameter pillar of copper with a height of approximately 50 μιη. The whole structure is placed on a silicon base with a top passivation layer made of a polymer.

During the wafer's production, voids can be created in the soldering layer of the bump and in the case that the volume of the voids passes a threshold, the quality of the product is damaged. Usually, a threshold of 0.01% of volume is used in the wafer's quality inspection.

The present invention uses two well-known and stable technologies to recognize a void or voids in a bump and estimates the total volume of the void or voids inside the bump.

There are several technologies for calculating the volume of an object using 3D imaging techniques, one of these technologies is the first that is used in the present invention.

The second technology, known as EDXRF (Energy-Dispersive-X-Ray- Fluorescence analysis), is a well-established and stable technology used for years in the industry. In the last two years there have been great advances in this technology with the adoption of SD detectors that enable much better resolution and count rate. This gives the ability to go down to lower levels of detection limits in much less time. This technology is a spectroscopy technique that belongs to high energy spectroscopy processing. The technology utilizes an emission of the characteristic lines. When an atom is hit by X-rays, a characteristic energy is emitted from the atom and this energy is analyzed into the materials spectra of qualification and quantification. In a provided diagram, each of the bump's soldering material is presented as a column, the magnitude of the column representing the material volume.

X-ray optics can be used to enhance EDXRF instrumentation. For conventional XRF instrumentation, typical focal spot sizes, at the sample surface, range in diameter from several hundred micrometers up to several millimeters. Polycapillary focusing optics collects X-rays from the divergent X-ray source and direct them to a small focused beam at the sample surface with diameters as small as tens of micrometers. The resulting increased intensity delivered to the sample in a small focal spot allows for enhanced spatial resolution for small feature analysis and enhanced performance for measurement of trace elements for micro EDXRF applications.

The present invention combines these technologies and provides a method and a system for inspecting bumps. Continuing further, with the advent of complex 3D structures within the semiconductor industry, inspection and metrology face a challenge to effectively adapt to such 3D structures and to be able to simultaneously monitor both the geometries and elemental compositions of the various semiconductor components. Not only is it desirable to know the chemical compositions of the various semicon- ductor components, but also their volumes, thickness dimensions, height dimensions, width dimensions, and surface characteristics, for manufacturing tolerances and adherence to manufacturing specifications. The present invention effectively combines a 3D optical component with EDXRF technology so as to be capable of determining these various parameters of the semiconductor components, bumps, and/or similar objects.

SUMMARY OF THE INVENTION

The present invention is a method and a system for bumps inspection by comparing the geometrical volume contained in the bumps outside contour and the volume of the solid materials from which the bump is made and/or analyzing the bumps solid materials ratio.

According to one preferred embodiment of the present invention, there is provided a method for a bump's inspection by comparing the geometrical volume contained in the bump's external contour and the volume of the solid materials from which the bump is made and/or analyzing the bump's solid materials ratio. The geometrical volume is calculated by using three dimensional image processing.

According to another preferred embodiment the method is provided, wherein the solid material volume is calculated by EDXRF (Energy-Dispersive-X- ray-Fluorescence analysis) analysis. According to another preferred embodiment, the method is used for recognizing one or more voids in a bump and calculating the volume of the void of voids, if the void or voids exist within the bump, and this method comprises the steps of preparing an empirical reference table of the emitted energy received from the solid materials from which a reference bump with a predetermined volume is comprised using EDXRF (Energy-Dispersive-X-Ray-Fluorescence) analysis to analyze energy emissions; obtaining a geometrical volume contained in the external contour of the bump using a 3D image-processing technique; adapting the reference table according to the difference between the atomic volume and the geometrical volume of the bump; The recognition of a void or voids within the bump and the calculation of the void volume is done in accordance with the following functions: if the geometrical volume and the atomic volume are equal, the bump does not contain any voids. If there is a difference between the geometrical volume and the atomic volume, wherein the geometrical volume is larger than the atomic volume, the difference in the volumes represents the volume of the void or voids within the bump; and if the volume of the void or voids is larger than a

predetermined threshold , the bump should be disqualified.

According to another preferred embodiment, the method uses poly- capillary focusing optics to collect the X-rays from the tube into a small focused narrow beam. According to another preferred embodiment the method is provided, the method is used for analyzing the bump's solid materials ratio in order to inspect whether the bump's material combination matches the combination criteria.

According to another aspect of the present invention, there is provid- ed a system for a bump's inspection, wherein the system comprises an optical means for aiming the system to the inspected bump and capturing a 3D image of the inspected bump; an X-ray tube to project X-rays onto the inspected bump; an X-ray detector for detecting fluorescent radiation reflected from the inspected bump as a result of the projection of the X-rays onto the bump; and a computing system.

The computing system is operative for storing an empirical reference table of the emitted energy received from the solid materials, from a reference bump with a predetermined volume obtained from EDXRF analysis; optical means for aiming the system toward the inspected bump and onto a spot position for the X-ray tube and X-ray detector; calculating the external contour volume of the inspected bump using a captured 3D image; adapting the reference table according to the volume difference between the reference bump and the external contour volume; using the reflected fluorescent radiation and EDXRF analysis to obtain the volume of each one of the solid materials from which the inspected bump is made; comparing the total volume of the solid materials with the calculated external contour volume of the inspected bump; and reporting the volume of each solid material contained within the inspected bump, the total volume of all solid materials of the inspected bump, the calculated volume of the external contour of the inspected bump, and the result of the volume comparison.

According to another preferred embodiment, the system further in- eludes polycapillary focusing optics in order to collect the X-rays from the X-ray tube into a small focused narrow beam. According to another preferred embodiment the system is provided wherein the geometrical position of the X-ray tube, the geometrical position of the X-ray detector, and the geometrical position of the optical means is fixed.

According to another preferred embodiment the system is provided wherein the spot size of the X-ray tube is within the range of 1-1000 μιη.

Lastly, the present invention comprises the use of 3D and EDXRF analysis and techniques to determine volumetric and various dimensional and surface irregularity characteristics of semiconductor components and bumps or similar objects.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice:

Figure 1 illustrates a bump for inspection;

Figure 2 illustrates a setup of the system for determining the external volume of the bump and any voids present within the bump, according to the pre- sent invention;

Figure 3 illustrates the setup of the EDXRF;

Figure 4 illustrates the results of the EDXRF analysis;

Figure 5 is a schematic drawing illustrating the use of the new and improved 3D and EDXRF components to measure, for example, thickness dimensions of semiconductor components; and

Figure 6 is a schematic drawing illustrating the use of the new and improved 3D and EDXRF components, as illustrated within Figure 5, to measure thickness dimensions, cavity dimensions, and surface uniformity or irregularity properties of a semiconductor component.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is a method and a system for bumps inspection by comparing the volume contained in the bumps outside contour and the volume of the solid materials from which the bump is made and/or analyzing the bumps solid materials ratio. In addition, the present invention teaches the use of 3D and EDXRF analysis and techniques to determine volumetric and various dimensional and surface irregularity characteristics of semiconductor components and bumps or other relevant objects.

The principles and operation of the methods and systems according to the present invention may be better understood with reference to the drawing figures and the accompanying description. Figure 1 illustrates a bump for inspection. The bump 11 is located on copper 13 and one of the typical defects that should be inspected is a missing material that creates void or voids 12 inside the bump 11. If the total volume of the voids 12 is larger from a given threshold, the bump is indicated as defective bump. Figure 2 illustrates a setup of the system according to the present invention. The inspected bump 11 is located on the wafer 14. The system uses the optical means 15 to navigate the setup - including the X-ray tube 16 and the X-ray detector 17 - to the correct spot position. The optical means 15 captures a 3D image of the bump and a computing system, not shown, calculates the volume of the bump 11 according the external outline of its contour. X-rays are projected onto the bump 1 1 from the X-ray tube 16, and fluorescent energy is emitted from the material of the bump 11 so as to be detected by means of the X-ray detector 17.

Figure 3 illustrates EDXRF's setup. In order to analyze the solid materials that comprise the bump 11 using EDXRF technology, the X-ray tube 16 pro- jects high X-ray energy 18 onto the bump 11 to be inspected. Fluorescent energy 19 is emitted from the solid materials of the bump 11 and is detected by the X-ray detector 17. From the detected energy, the volume of each solid material of the bump 11 can be obtained as illustrated in Figure 4. In the illustrated case there is a void 12 in the bump. Therefore, the sum of the material volumes that comprise the bump 11 is less than the bump's volume that was calculated by using the 3D imaging technique. The volume difference therefore represents the volume of the void.

Figure 4 illustrates the results of the EDXRF analysis. The EDXRF technology analyzes the solid materials from which the fluorescent energy was reflected or emitted. Energy transmissions will result in emitted photons and are mea- sured. A spectragraph that represents qualification and quantification analysis is presented. Each of the soldering material is illustrated by a column 20 and the magnitude of the column represents the material volume. The sum of the volumes is the overall volume of the solid materials comprising the bump. With reference now being made to Figure 5, there is schematically shown a new and improved system 100 for simultaneously determining the volumes of semiconductor components, the presence of voids within the semiconductor components, as well as various critical dimensions of the semiconductor components, such as, for example, the height or thickness dimensions thereof. It is to be noted that the system 100 illustrated within Figure 5 is similar to the system illustrated within Figures 2 and 3, and therefore those components of system 100 which correspond to similar components utilized within the system illustrated within Figures 2 and 3 will be designated by similar reference characters except that they will be denoted by reference characters within the 100 series.

More particularly, it is seen, for example, that the system 100 comprises an optical means 115 which comprises a 3D imaging system 122 which is to be used in connection with the imaging and analyzing of a bump or multi-layered stacked array 124 of metal components 126,128,130 which are disposed atop a substrate 132. The 3D imaging system 122, which comprises, for example, a con- focal microscope, effectively captures a 3D image of the multi-layered stacked array 124 which, through means of its computer, not shown, is capable of calculating the external volume of the multi-layered stacked array 124 as well as the height or thickness dimension at each XY coordinate of the three dimensional object being scanned. In conjunction with the 3D imaging system 122, there is also provided an X-ray tube or X-ray emitter 116 and an X-ray detector 117. As was the case with the system illustrated within Figures 2 and 3, the X-rays or energy emitted from the X-ray tube or emitter 116 impinge upon the multi-layered stacked array 124, and the reflected or energy emitted from the different materials or metals 126,128,130 comprising the multi-layered stacked array 124 are detected by means of the X-ray detector 117. The EDXRF technology is then used to compute or calculate the volumes of the different materials or metals 126,128,130 comprising the multi-layered stacked array 124 in a manner similar to that illustrated within Figure 4. However, it is to be noted that the EDXRF cannot be used to measure the thickness of a plate or layer of material which has a thickness dimension that is greater than the saturation limit of the EDXRF, which is typically tens of microns. In this case, for example, the EDXRF cannot be used to determine the thickness of the first or lowermost layer 126 of the multi-layered stacked array 124. Accordingly, a "reverse" measuring process must be employed, however, the disclosed system can in fact readily perform such process and achieve the required measurement. Since the 3D imaging system 122 will initially provide a 3D volumetric and height or thickness measurement of the entire or overall multilayered stacked array 124 comprising the three different metal materials 126,128,130, and since the EDXRF can provide the volu- metric or height measurements of the individual layers 128,130 of the multi-layered stacked array 124, that is H2 and H3, and since the overall height dimension HO of the multi-layered stacked array 124 is already known from the 3D imaging system 122, then subtracting the height dimensions H2 and H3 of the second and third metal materials 128,130 from the overall height dimension HO of the multi-layered stacked array 124, the height dimension H1 of the first or lowermost metal material 126 of the multi-layered stacked array 124 can be readily derived.

With reference lastly being made to Figure 6, the use of the new and improved 3D and EDXRF components, as illustrated within Figure 5, will now be discussed in connection with the measurement of thickness dimensions, cavity dimensions, and surface uniformity or irregularity properties of a semiconductor component. It is again to be noted that components of this embodiment system of the present invention which correspond to components disclosed within the previously described embodiment systems as illustrated, for example, within Figures 2-4, will be designated by similar reference characters except that they will be within the 200 series. More particularly, a confocal microscope, an X-ray tube/emitter, and X- ray detector, similar to those used and illustrated within FIGURES 3 and 5, will likewise be used, although for brevity, they have not been shown in FIGURE 6. As can be seen, however, within FIGURE 6, there is disclosed a substrate 232 upon which are disposed a pair of dual-layer semiconductor components 224 and 224'. Both semiconductor components comprise first lower layers 226,226' comprised of, for example, nickel, and second upper layers 228,228' comprised of, for example, gold. The lower layers 226,226' each have a thickness dimension T1 , while the upper layers 228,228' each have a thickness dimension T2, and therefore the overall thickness of the semiconductor components are T1 + T2, or TV + T2', or TO and TO'. It is also seen that each one of the semiconductor components 224,224' has a cavity 234,234' respectively formed within the upper surface portions thereof, and the height or depth of each one of the cavities 234,234' is denoted as H1 , HI. In addition, it will also be noted that a suitable polysilicon material 236, which acts as an insulator, is inter-posed between each semiconductor component 224,224'. It is therefore desirable, for example, for various manufacturing production tolerance, uniformity, and qualitative conditions, that the various dimensions T1 ,T2,T3, and H1 be capable of being ascertained, the height or thickness dimension T3 being the distance between the upper surface or limit of the polysilicon material 236 and the top or upper limit of the lowermost material 226 or the bottom or lower limit of the upper material 228. It is desirable to know such dimension so as to ensure quality control procedures and to adhere to required manufacturing tolerances.

Accordingly, it can be readily appreciated that the overall volume and height dimension TO of the two layers 226,228 comprising, for example, the dual- layer semiconductor component 224 can be determined by means of the 3D con- focal microscope 122 as has been described hereinbefore. Subsequently, using the EDXRF technology, the height or thickness dimension T2 of the upper layer 228 can be determined, and then subtracting the height or thickness T2 of the upper layer 228 from the overall height or thickness dimension TO of the semiconductor component 224, the height or thickness dimension T1 of the lower layer 226 can be determined. In a similar manner, the 3D microscope 122 can likewise be used to determine the height or thickness dimension T4 which is the height or thickness dimension of the polysilicon material 236, and if one then subtracts the height or thickness dimension T4 of the polysilicon material 236 from the height or thickness dimension T1 of the lower layer or material 226, the height or thickness dimension T3 can be derived. Now, knowing the height or thickness dimension T3, as well as the height of thickness dimension T2, the combined height or thickness dimension T2 + T3 can be known. Lastly, using the 3D confocal microscope 122, when focus- ed upon the cavity 234, the height or depth dimension of the cavity 234 can be readily obtained. Still yet further, the 3D confocal microscope can be utilized to readily obtain height or depth dimensions of various surface portions of the semiconductor components and thereby provide information concerning surface uniformity, surface irregularities, and the like. Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications, and variations that fall within the spirit and broad scope of the appended claims.

Claims

CLAIMS:

1. A system for the determination of thickness dimensions of a component part comprising solid material and at least two different material layers, comprising: means for determining the overall height dimension of said component part; means for determining the height dimension of a first one of said at least two different material layers of said component part wherein the height dimension of a second one of said at least two different material layers is not able to be determined by said means for determining the height dimension of said first one of said at least two different material layers; and

means for subtracting said height dimension of said first one of said at least two different material layers of said component part from said overall height dimension of said component part such that the height dimension of said second one of said at least two different materials layers can in fact be determined.

2. The system as set forth in Claim 1 , wherein:

said means for determining the overall height dimension of said component part comprises optical means for capturing a three-dimensional image of said component part and computing means for calculating the height dimension of said component part.

3. The system as set forth in Claim 1 , wherein:

said means for determining said overall height dimension of said component part comprises a confocal microscope.

4. The system as set forth in Claim 1 , wherein:

said means for determining the height dimension of said first one of said at least two material layers of said component part comprises an X-ray emitter for projecting X-ray energy onto said component part, and an X-ray detector for receiving fluorescent energy emitted from said solid materials comprising said component part after said X-ray energy is projected onto said component part.

5. The system as set forth in Claim 4, wherein:

said means for determining the height dimension of said first one of said at least two material layers of said component part comprises energy-dispersive X-ray fluorescence analysis means.

6. The system as set forth in Claim 1 , wherein:

said at least two material layers of said component part comprises three material layers wherein the height dimension of one of said three material layers cannot be determined by said means for determining the height dimension of said first one of said material layers of said component part.

7. The system as set forth in Claim 6, wherein:

said means for determining the height dimension of said first one of said material layers of said component part can determine the height dimensions of second and third layers of said three material layers of said component part where-by the height dimension of said one of said three material layers, that could not be determined by said means for determining the height dimension of said first one of said material layers of said component part, can be determined by subtracting the height dimensions of said second and third layers from the overall height dimension of said component part.

8. The system as set forth in Claim 1 , wherein:

said means for determining the height dimension of said first one of said material layers of said component part can also determine the depth dimension of a cavity within said component part.

9. The system as set forth in Claim 1 , wherein:

said component part comprises a semiconductor.

10. The system as set forth in Claim 9, wherein:

said first one of said at least two different material layers of said semiconductor comprises gold.

1 1. The system as set forth in Claim 9, wherein:

said second one of said at least two different material layers of said semiconductor comprises nickel.

12. A method for the determination of thickness dimensions of a component part comprising solid material and at least two different material layers, comprising: determining the overall height dimension of said component part;

determining the height dimension of a first one of said at least two different material layers of said component part wherein the height dimension of a second one of said at least two different material layers is not able to be determined; and subtracting said height dimension of said first one of said at least two different material layers of said component part from said overall height dimension of said component part such that the height dimension of said second one of said at least two different materials layers can in fact be determined.

13. The method as set forth in Claim 12, wherein:

said step for determining the overall height dimension of said component part comprises the use of optical apparatus for capturing a three-dimensional image of said component part and calculating the height dimension of said component part.

14. The method as set forth in Claim 12, wherein:

said determination of said overall height dimension of said component part comprises the use of a confocal microscope.

15. The method as set forth in Claim 12, wherein:

said determination of the height dimension of said first one of said at least two material layers of said component part comprises the use of an X-ray emitter for projecting X-ray energy onto said component part, and the use of an X-ray detector for receiving fluorescent energy emitted from said solid materials comprising said component part after said X-ray energy is projected onto said component part.

16. The method as set forth in Claim 15, wherein:

said determination of the height dimension of said first one of said at least two material layers of said component part comprises energy-dispersive X-ray fluorescence analysis.

17. The method as set forth in Claim 12, wherein:

said at least two material layers of said component part comprises three material layers wherein the height dimension of one of said three material layers cannot be determined.

18. The method as set forth in Claim 17, wherein:

the height dimension of second and third layers of said three material layers of said component can be determined whereby the height dimension of said one of said three material layers, that could not be originally determined, can be determined by subtracting the height dimensions of said second and third layers of said components from the overall height dimension of said component part.

19. The method as set forth in Claim 12, further comprising the step of:

determining the height dimension of a cavity within said component part.

20. The method as set forth in Claim 12, wherein:

said component part comprises a semiconductor.

21. The method as set forth in Claim 20, wherein:

22. The method as set forth in Claim 20, wherein: