WO2010082977A1 - Equi-biaxial flexure test device for thin and ultra-thin semiconductor wafers and other wafers - Google Patents

Equi-biaxial flexure test device for thin and ultra-thin semiconductor wafers and other wafers

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Publication number
WO2010082977A1
WO2010082977A1 PCT/US2009/066074 US2009066074W WO2010082977A1 WO 2010082977 A1 WO2010082977 A1 WO 2010082977A1 US 2009066074 W US2009066074 W US 2009066074W WO 2010082977 A1 WO2010082977 A1 WO 2010082977A1
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WO
Grant status
Application
Patent type
Prior art keywords
test
chamber
wafer
device
specimen
Prior art date
Application number
PCT/US2009/066074
Other languages
French (fr)
Inventor
Sivaraman Guruswamy
Cody A. Pearce
Original Assignee
University Of Utah Research Foundation
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date

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Classifications

    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N3/00Investigating strength properties of solid materials by application of mechanical stress
    • G01N3/20Investigating strength properties of solid materials by application of mechanical stress by applying steady bending forces
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/0014Type of force applied
    • G01N2203/0023Bending
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/02Details not specific for a particular testing method
    • G01N2203/022Environment of the test
    • G01N2203/023Pressure
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/02Details not specific for a particular testing method
    • G01N2203/022Environment of the test
    • G01N2203/0236Other environments
    • G01N2203/0242With circulation of a fluid
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/02Details not specific for a particular testing method
    • G01N2203/025Geometry of the test
    • G01N2203/0254Biaxial, the forces being applied along two normal axes of the specimen
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/02Details not specific for a particular testing method
    • G01N2203/025Geometry of the test
    • G01N2203/0258Non axial, i.e. the forces not being applied along an axis of symmetry of the specimen
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/02Details not specific for a particular testing method
    • G01N2203/026Specifications of the specimen
    • G01N2203/0262Shape of the specimen
    • G01N2203/0278Thin specimens
    • G01N2203/0282Two dimensional, e.g. tapes, webs, sheets, strips, disks or membranes

Abstract

A test device for applying a biaxial load on a test specimen includes a housing having an internal chamber and a support positioned in the internal chamber upon which the test specimen is positioned. The test specimen is engageable with the support to divide the internal chamber into a first chamber portion and a second chamber portion. The test device also includes an inlet through which a pressurized fluid is transferred to the first chamber portion to apply the biaxial load upon the test specimen, a pressure sensor operable to detect the pressure of the pressurized fluid in the first chamber portion, and a displacement sensor operable to detect movement of the test specimen in response to the biaxial load applied by the pressurized fluid. The test device enables determination of biaxial flexural strength and load deflection information for thin/ultra thin wafers of semiconductors and other brittle materials.

Description

EQUI-BIAXIAL FLEXURE TEST DEVICE FOR THIN AND ULTRA-THIN SEMICONDUCTOR WAFERS AND OTHER WAFERS

RELATED APPLICATIONS

[0001] This application claims priority to co-pending U.S. Provisional Patent

Application No. 61/145,160 filed on January 16, 2009, the entire content of which is incorporated herein by reference.

STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH OR

DEVELOPMENT

[0002] This invention was made with government support under Grant

#DMR0241603 awarded by the National Science Foundation and Award #FA9453-04-C- 0205 awarded by the USAF/AFOSR - Air Force Office of Scientific Research. The Government has certain rights in this invention.

FIELD OF THE INVENTION

[0003] The present invention relates to test devices, and more particularly to test devices for measuring a flexural strength of a test specimen.

BACKGROUND OF THE INVENTION

[0004] Germanium is a semi-conducting material utilized in many applications, including in gamma and X-ray detectors, as substrates in high-performance solar cell arrays, and in infrared optics. In order to reduce the costs associated with using germanium, germanium wafers are typically cut ultra-thin. This yields a relatively large width to thickness ratio, often making the germanium wafers susceptible to mechanical stresses during processing. Therefore, knowing the stress criteria for fracture of germanium wafers is important to prevent micro-cracking or total failure of the wafers while being handled during an automated manufacturing process.

[0005] The relationship of stress versus strain in brittle materials (e.g., brittle ceramics and semiconductors) is typically determined using a test method different than that when testing metals because brittle ceramics and semiconductors (e.g., germanium wafers) are difficult to grip without damaging or fracturing the wafer. A three-point bend test is the most frequently used test for brittle materials. As shown in prior art FIG. 1, the three-point bend test includes supporting the ends of a test specimen (e.g., a germanium wafer 10) with discrete supports 14 (e.g., a straight, metal rod) and applying a load on the wafer 10 with a third straight, metal rod 18 between the discrete supports 14. However, the three-point bend test only imparts uniaxial loading (i.e., loading in the plane of the wafer 10 in only a single direction) on the wafer 10, which does not accurately represent the stress distribution conditions to which the wafer 10 would be exposed during an automated manufacturing process.

[0006] For the test conditions to more accurately represent the actual conditions encountered by the wafer 10 during handling in an automated manufacturing process, the wafer 10 should be subjected to biaxial loading (i.e., loading in two orthogonal directions in the plane of the wafer 10). The current ASTM standard for simulating a biaxial load on a test specimen is the ring-on-ring test, shown in prior art FIG. 2. The ring-on-ring test involves supporting a test specimen (e.g., the germanium wafer 10) by a first circular ring 22 and loading the wafer 10 with a smaller, second circular ring 26 that is concentric with the first ring 22. However, the ring-on-ring test is not a true equi-biaxial test because the wafer 10 is not loaded over its entire surface, and is not suitable when large deflections are involved, which is the case when testing ultra-thin germanium wafers 10.

SUMMARY OF THE INVENTION

[0007] The present invention provides, in one aspect, a test device operable to apply a biaxial load on a test specimen. The test device includes a housing having an internal chamber and a support positioned in the internal chamber upon which the test specimen is positioned. The test specimen is engageable with the support to divide the internal chamber into a first chamber portion and a second chamber portion substantially fluidly isolated from the first chamber portion. The test device also includes an inlet through which a pressurized fluid is transferred to the first chamber portion to apply the biaxial load upon the test specimen, a pressure sensor operable to detect the pressure of the pressurized fluid in the first chamber portion, and a displacement sensor operable to detect movement of the test specimen in response to the biaxial load applied by the pressurized fluid.

[0008] The present invention provides, in another aspect, a method of determining flexural strength of a test specimen. The method includes providing a housing having an internal chamber, supporting the test specimen in the internal chamber, substantially fluidly isolating a first portion of the internal chamber from a second portion of the internal chamber with the test specimen, introducing a pressurized fluid into the first portion of the internal chamber to apply a biaxial load upon the test specimen, measuring the pressure of the pressurized fluid in the first portion of the internal chamber, and measuring the movement of the test specimen in response to the biaxial load applied by the pressurized fluid.

[0009] Other features and aspects of the invention will become apparent by consideration of the following detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 is a schematic illustrating a prior-art three-point bend test device.

[0011] FIG. 2 is a schematic illustrating a prior-art ring-on-ring test device.

[0012] FIG. 3 is a schematic illustrating a test device of the present invention for applying an equi-biaxial load on a test specimen.

[0013] FIG. 4 is a schematic illustrating the test device of the present invention incorporated as a stand-alone unit.

[0014] Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.

DETAILED DESCRIPTION

[0015] FIG. 3 schematically illustrates an equi-biaxial flexure test device 30 operable to apply a biaxial load on a test specimen (e.g., the germanium wafer 10) and calculate the biaxial flexural stress or strength of the wafer 10. Biaxial flexural stress on the wafer 10, in other words, is stress on the wafer 10 in two orthogonal directions in the plane of the wafer 10. The wafers 10 utilized with the test device 30 may be made from germanium, silicon, or other thin or ultra-thin, brittle semi-conducting materials.

[0016] The test device 30 includes a housing 34 having a substantially cylindrical hollow vessel 38 having a bottom open end 42 and a top open end 46, and a cover 50 secured to the top open end 46 of the vessel 38. Alternatively, the vessel 38 may be configured in any of a number of different non-cylindrical shapes. The vessel 38 and cover 50 may be made from any of a number of different materials (e.g., metals such as aluminum, etc.). A circular seal 54 (e.g., an O-ring) is provided between the top open end 46 of the vessel 38 and the cover 50 to provide a substantially fluid-tight seal between the vessel 38 and the cover 50. Fasteners 58 (e.g., bolts, cap screws, etc.) are utilized to secure the cover 50 to the vessel 38. Alternatively, one or more quick-release fasteners (e.g., a clasp, etc.) may be utilized to facilitate removal of the cover 50 from the vessel 38. As a further alternative, the housing 34 may be made from more than two interconnected pieces to allow for increased and/or simplified access to the wafer 10 inside the housing 34. The bottom open end 42 of the vessel 38 is supported on a support surface 62 (e.g., a table), such that debris from the fractured wafer 10 may fall onto the support surface 62 for removal and disposal after testing is complete. As is described in detail below, the bottom open end 42 of the vessel 38 need not be sealed to the support surface 62, nor need the housing 34 be secured to the support surface 62 because the weight of the housing 34 is sufficient to hold the housing 34 in place on the support surface 62.

[0017] With continued reference to FIG. 3, a combination of the vessel 38, the cover

50, and the support surface 62 defines an internal chamber 66, and the vessel 38 includes a circular support 70 positioned in the internal chamber 66 upon which the wafer 10 is positioned. In the illustrated construction of the test device 30, the support 70 is positioned on a radially inwardly-extending ledge 72, such that for a gas introduced into the internal chamber 66 at a location above the support 70 (i.e., from the point of view of FIG. 3) to flow to another location in the internal chamber 66 below the support 70, the gas must pass through the space coinciding with the inside diameter of the support 70. The support 70 is substantially continuous such that an interface between the wafer 10 and the support 70 creates a substantially continuous seal between the support 70 and the wafer 10. In the illustrated construction of the test device 30, the support 70 is configured as a substantially continuous O-ring upon which the wafer 10 is positioned. Alternatively, the support 70 may be configured having any of a number of different non-circular shapes, provided the support 70 does not include any distal ends. The wafer 10 is sized having a diameter at least as large as a nominal diameter D of the support 70.

[0018] Also, in the illustrated construction of the test device 30, a low-friction grease

74 is utilized between the wafer 10 and the support 70 to enhance the seal between the wafer 10 and the support 70. The grease 74 is sufficiently tacky to secure the wafer 10 in position on the support 70 without requiring the wafer 10 to be positively clamped to the support 70. Alternatively, other non-mechanical means may be employed to secure the wafer 10 to the support 70 without clamping the wafer 10 to the support 70 (e.g., using releasable adhesives, etc.).

[0019] The seal between the wafer 10 and the support 70 also effectively divides the internal chamber 66 of the housing 34 into a first chamber portion 78 and a second chamber portion 82 substantially fluidly isolated from the first chamber portion 78 because the only path around the support 70, in absence of the wafer 10, is through the interior space coinciding with the inside diameter of the support 70. The first chamber portion 78 is defined by the hollow vessel 38, the cover 50, and the wafer 10, while the second chamber portion 82 is defined by the hollow vessel 38, the wafer 10, and the support surface 62. As is described in detail below, the first chamber portion 78 is pressurized during the testing process. Because the seal between the wafer 10 and the support 70 substantially prevents any pressurized fluid from entering the second chamber portion 82, the bottom open end 42 of the vessel 38 need not be sealed to the support surface 62.

[0020] With continued reference to FIG. 3, the cover 50 includes an inlet 86 through which a pressurized fluid is transferred to the first chamber portion 78 to exert a biaxal load upon the wafer 10 during testing. The inlet 86 may include an inlet coupling or fitting (e.g., a Swagelok fitting, a quick-release fitting, etc.) configured to interconnect with another mating coupling or fitting on a conduit 90 through which the pressurized fluid is transferred. The pressurized fluid may be an inert gas (e.g., argon) or any gas that would not react with the particular material from which the wafer 10 is made (e.g., silicon or germanium).

[0021] The pressurized fluid may be transferred into the first chamber portion 78, via the conduit 90, from a pressurized fluid vessel 94 (e.g., a gas cylinder). A valve 98 may be utilized between the pressurized fluid vessel 94 and the housing 34 to meter the flow of the pressurized fluid into the first chamber portion 78. The valve 98 may be configured as a precision needle valve 98 to provide a controlled opening through which the pressurized fluid may flow. In the illustrated construction of the test device 30, the valve 98 is positioned in the inlet 86 in the cover 50. Alternatively, the valve 98 may be disposed anywhere along the conduit 90 or in the outlet of the pressurized fluid vessel 94. Further, a pump may be utilized to facilitate transfer of the pressurized fluid from the pressurized fluid vessel 94 into the first chamber portion 78.

[0022] With continued reference to FIG. 3, the test device 30 includes a pressure sensor 102 operable to detect the pressure of the pressurized fluid in the first chamber portion 78. In the illustrated construction of the test device 30, the pressure sensor 102 is configured as a pressure transducer operable to output an electrical signal corresponding to the pressure of the pressurized fluid in the first chamber portion 78. Alternatively, the pressure sensor 102 may be configured as a peak-and-hold type sensor having an analog or digital display that is readable by an operator of the test device 30 during and after the test (i.e., after the wafer 10 breaks). Also, in the illustrated construction of the test device 30, the pressure sensor 102 is coupled to the cover 50 and is therefore removable with the cover 50 when the cover 50 is removed from the vessel 38. Alternatively, the pressure sensor 102 may be coupled to the vessel 38, such that the pressure sensor 102 remains in place when the cover 50 is removed from the vessel 38.

[0023] The test device 30 also includes a displacement sensor 106 operable to detect the movement or deflection of the wafer 10 during the testing process in response to the application of the biaxial load by the pressurized fluid. In the illustrated construction of the test device 30, the displacement sensor 106 is configured as a contact-type sensor (e.g., a linear resistance displacement transducer or "LRDT") that is operable to output an electrical signal corresponding to the deflection of the wafer 10. In other words, the sensor 106 includes a tip 110 that is engaged with the wafer 10 and that is movable with the wafer 10 as the wafer deflects due to the biaxial loading. Alternatively, the displacement sensor 106 may be configured as a non-contact type sensor (e.g., an optical sensor; see FIG. 4), such that the sensor 106 need not be engaged with the wafer 10 during testing. Also, in the illustrated construction of the test device 30, the displacement sensor 106 is positioned in the second chamber portion 82 beneath the wafer 10. The vessel 38 may include an access door (not shown) to allow an operator to access the second chamber portion 82 to set up the displacement sensor 106 with respect to the wafer 10 in preparation for testing. Alternatively, the displacement sensor 106 may be positioned in the first chamber portion 78 (i.e., in conjunction with a bracket for supporting the displacement sensor 106) or outside the internal chamber 66 of the housing 34.

[0024] The displacement sensor 106 is also aligned with a location on the wafer 10 exhibiting the most amount of deflection or movement in response to the application of the biaxial load by the pressurized fluid. In the illustrated construction of the test device 30, the displacement sensor 106 is substantially aligned or coaxial with a central axis 114 of the support 70 and the geometrical center of the wafer 10, which corresponds with the location on the wafer 10 that will exhibit the most amount of deflection when subjected to the biaxial loading.

[0025] With continued reference to FIG. 3, the test device 30 further includes a data acquisition system 118 operable to receive and record the electrical signals output by the pressure sensor 102 and the displacement sensor 106 corresponding to the pressure of the first chamber portion 78 and the deflection of the wafer 10, respectively, during testing. The data acquisition system 118 is also operable to process the electrical signals received from the sensors 102, 106 into data and perform calculations using the data (using a microprocessor, for example). The test device 30 also includes an input device 122 (e.g., a keyboard, keypad, touch screen, etc.), a data storage device 126 (e.g., a hard drive, etc.), a display 130, and one or more communication ports 134 through which other devices (e.g., a printer, etc.) may interface with the test device 30. The display 130 may be configured to show any of a number of different measurements and/or calculations performed by the data acquisition system 118 (e.g., the flexural stress or strength of the wafer 10, the deflection of the wafer 10, the pressure in the first chamber portion 78, etc.). The input device 122 may be used by the operator of the test device 30 to input data or other information to the data acquisition system 118, while the storage device 126 may be used to store data or other information input to the data acquisition system 118 or calculated by the data acquisition system 118.

[0026] With reference to FIG. 4, the test device 30 may be incorporated as a standalone unit with the housing 34, the pressure sensor 102, the displacement sensor 106, the valve 98, the data acquisition system 118, the display 130, the input device 122, the storage device 126, and the communication port 134. The stand-alone test device 30 may then be supported on the support surface 62 to facilitate removal of debris in a similar manner as described above. Alternatively, the data acquisition system 118, the display 130, the storage device 126, the input device 122, and the communication port 134 may be incorporated in a unit separate from the housing 34 (e.g., a PC or laptop computer). As a further alternative, the data acquisition system 118, the display 130, the storage device 126, the input device 122, and the communication port 134 may be separate components that are electrically connected to each other using cables, etc.

[0027] In preparation for utilizing the test device 30 for measuring the flexural strength of a test specimen (e.g., the germanium wafer 10 shown in FIG. 3), the support 70 is first covered with the low-friction grease 74 and the wafer 10 is then positioned on the greased support 70, thereby dividing the internal chamber 66 into the first chamber portion 78 and the second chamber portion 82. The cover 50 is then positioned over the top open end 46 of the vessel 38 and fastened to the vessel 38 to provide a fluid-tight seal between the cover 50 and the vessel 38. The inlet 86 is then connected to the conduit 90 (with the valve 98 closed), which is already fluidly connected to the pressurized fluid vessel 94. The displacement sensor 106 is then positioned relative to the wafer 10 for measurement of the wafer deflection using the previously-mentioned access door in the vessel 38. Specifically, when using a contact-type displacement sensor 106, such as an LRDT, the tip 110 of the LRDT is aligned with the central axis 114 and positioned to just make contact with the bottom surface of the wafer 10. Alternatively, when using a non contact-type displacement sensor 106, the displacement sensor 106 is positioned or aligned with the central axis 114 of the support 70, which corresponds with the location of maximum deflection of the wafer 10. As a further alternative, the displacement sensor 106 may be positioned in the internal chamber 66 of the housing 34 prior to positioning the wafer 10 on the support 70, should the vessel 38 not include the previously-mentioned access door. Finally, the displacement sensor 106 and the pressure sensor 102 are electrically connected to the data acquisition system 118.

[0028] To initiate the testing process, the data acquisition system 118 is triggered to record the pressure data and the displacement data provided by the pressure sensor 102 and the displacement sensor 106, respectively, in real time for the duration of the test. Then, the flow or transfer of pressurized fluid (e.g., argon gas) is initiated to the first chamber portion 78 by the controlled opening of the precision needle valve 98 in the inlet 86, causing the wafer 10 to slowly deflect as a result of the biaxial load imparted by the pressurized fluid over the entire top surface of the wafer 10. The flow rate of the pressurized fluid entering the first chamber portion 78 may be controlled such that the duration of the test (i.e., from initial pressurization of the first chamber portion 78 to breakage of the wafer 10) is about two minutes or more. The pressurized fluid entering the first chamber portion 78 also provides a controlled and uniform application of a very small biaxial load on the wafer 10, while allowing continuous measurement of the resultant deflection of the wafer 10. The opening of the valve 98 may be controlled by the data acquisition system 118 or other controller in communication with the data acquisition system 118, such that the testing process may be initiated by depressing a single button on the input device 122.

[0029] Data acquisition is stopped upon breakage of the wafer 10, as indicated by a sudden pressure drop measured by the pressure sensor 102 and a loud noise associated with the breakage of the wafer 10 and the sudden expansion of the pressurized fluid into the remainder of the interior chamber 66 (i.e., into the second chamber portion 82). After the wafer 10 breaks or fractures, the wafer shards fall onto the support surface 62. At the conclusion of the testing process, the wafer shards may be removed from the support surface 62 by lifting the housing 34 and sweeping the wafer shards off the support surface 62 and into a debris container. Alternatively, data acquisition may be stopped prior to breakage of the wafer 10 at some user-determined pressure value (e.g., a minimum pressure value corresponding with some design requirement).

[0030] The measured pressure versus deflection data is then plotted or displayed the on the display 130, and the flexural stress or strength of the wafer 10 is calculated using the following equations, which account for diaphragm stresses:1

where "q" denotes the measured pressure in the first chamber portion 78, "a" denotes the nominal diameter of the support 70 or O-ring (also denoted as letter "D" in FIG. 3), "y" denotes the deflection of the wafer 10, "t" denotes the thickness of the wafer 10, "E" denotes the Young's modulus of the material from which the wafer 10 is made, and "σ" is the flexural stress or strength at the center of the wafer 10. K1, K2, K 3j and K4 are constants that are dependent upon the given nature of the test setup's edge support conditions and the test specimen material's elastic properties. As described above, the outer edge of the wafer 10 is simply supported (i.e., neither fixed nor held) and the wafer 10 is exposed to a uniform pressure over its entire surface. For simply-supported (i.e., neither fixed nor held) circular plates under (i) a distributed load of uniform pressure "q" over the entire plate and (ii) producing large deflections, the values for Ki through K4 in Roark's formulas for stress and strain are Ki =1.016/(l-υ), K2 = 0.376, K3 = 1.238/(l-υ), and K4 = 0.29418. The value for Poisson's ratio ("υ") is determined in accordance with the method below. Equation (A) is used to solve for "y" and this value can be used in Equation (B) to solve for the flexural stress or strength at the center of the wafer 10. The flexural stress or strength of the wafer 10 may then be shown on the display 130 immediately after breakage of the wafer 10.

[0031] The nominal diameter D of the support 70 is sized as large as practically possible, and the wafer overhang on the support 70 is not included in the flexural stress calculation. According to calculations carried out using a ball-on-ring test in Shetty et al.2, the overhang error is approximately equal to 0.25%.

[0032] In the case of single crystal wafers, the variation of Young's modulus "E" and Poisson's ratio "υ" in different directions in the plane of the wafer 10 is expected to result in a deviation from a circularly uniform strain distribution. The calculations of the stress and strain distribution should consider this anisotropy in mechanical behavior. An appropriate choice of Young's modulus "E" and Poisson's ratio "υ" in Equation (B) would be plane averaged values. For (100) germanium and silicon wafers, the fracture of the wafer 10 is expected to occur by cleavage along the [110] direction in the {110} and {111} planes. An appropriate choice of Young's modulus "E" and Poisson's ratio "υ" in Equation (B) for (100) germanium wafers would be (lOO)-plane averaged values of 120 GPa for "E" and 0.13 for

"υ"3'4.

[0033] The following publications, referenced above in superscript, are incorporated herein by reference:

1W. C. Young and R. G. Budynas, "Flat Plates"; pp. 427-524 in Roark's Formulas for Stress and Strain, 7th edition, Edited by L. Hager. McGraw-Hill, New York, 2002.

2D. K. Shetty, A. R. Rosenfield, P. McGuire, G. K. Bansal, and W. H. Duckworth, "Biaxial Flexure Tests for Ceramics," J. Ceram. Bull, 59, 1193-7 (1980). 3J. J. Wortman and R. A. Evans, "Young's Modulus, Shear Modulus, and Poisson's Ratio in Silicon and Germanium," J. Appl. Phys., 36 [1] 153-6 (1965).

4"Mechanical Properties, Elastic Constants, Lattice Vibrations of Germanium (Ge)," http ://www.ioffe.rssi.ru/S VA/NSM/Semicond/Ge/mechanic.html, (2005).

[0034] Various features of the invention are set forth in the following claims.

Claims

CLAIMSWhat is claimed is:
1. A test device operable to apply a biaxial load on a test specimen, the test device comprising: a housing having an internal chamber; a support positioned in the internal chamber upon which the test specimen is positioned, the test specimen engageable with the support to divide the internal chamber into a first chamber portion and a second chamber portion substantially fluidly isolated from the first chamber portion; an inlet through which a pressurized fluid is transferred to the first chamber portion to apply the biaxial load upon the test specimen; a pressure sensor operable to detect the pressure of the pressurized fluid in the first chamber portion; and a displacement sensor operable to detect movement of the test specimen in response to the biaxial load applied by the pressurized fluid.
2. The test device of claim 1 , wherein the housing includes a hollow vessel having a bottom open end and a top open end, and a cover secured to the top open end of the vessel, and wherein the bottom open end is supported on a support surface.
3. The test device of claim 2, wherein the first chamber portion is at least partially defined by the hollow vessel, the cover, and the test specimen.
4. The test device of claim 2, wherein the second chamber portion is at least partially defined by the hollow vessel, the test specimen, and the support surface.
5. The test device of claim 1, wherein the support is substantially continuous, and wherein an interface between the test specimen and the support is configured to create a substantially continuous seal to maintain the pressurized fluid in the first chamber portion.
6. The test device of claim 5, further comprising a low-friction grease between the test specimen and the support to provide the seal between the test specimen and the support.
7. The test device of claim 1, wherein the support is configured as a substantially continuous O-ring upon which the test specimen is positioned.
8. The test device of claim 1, wherein the pressure sensor is configured as a pressure transducer operable to output an electrical signal corresponding to the pressure of the pressurized fluid in the first chamber portion.
9. The test device of claim 8, further comprising a data acquisition system operable to receive and record the electrical signal from the pressure transducer.
10. The test device of claim 1, wherein the displacement sensor is configured as a displacement transducer operable to output an electrical signal corresponding to the movement of the test specimen.
11. The test device of claim 10, further comprising a data acquisition system operable to receive and record the electrical signal from the displacement transducer.
12. The test device of claim 10, wherein the displacement transducer is engageable with the test specimen to detect the movement of the test specimen.
13. The test device of claim 10, wherein the displacement transducer is configured as a non-contacting displacement transducer.
14. The test device of claim 1 , wherein the displacement sensor is positioned in one of the first chamber portion and the second chamber portion.
15. The test device of claim 14, wherein the displacement sensor is positioned in the second chamber portion.
16. The test device of claim 14, wherein the support is substantially continuous and defines a central axis, and wherein the displacement sensor is substantially aligned with the central axis.
17. The test device of claim 1, further comprising: a data acquisition system operable to receive and record electrical signals from the pressure sensor and the displacement sensor corresponding to the pressure of the pressurized fluid in the first chamber portion and the movement of the test specimen, respectively; a display operable to output information processed by the data acquisition system; and an input device utilized by an operator of the test device to input information into the data acquisition system.
18. The test device of claim 17, further comprising a data storage device operable to record the electrical signals from the pressure sensor and the displacement sensor.
19. The test device of claim 17, further comprising at least one communication port configured to interface the test device with another device.
20. A method of determining flexural strength of a test specimen, the method comprising: providing a housing having an internal chamber; supporting the test specimen in the internal chamber; substantially fluidly isolating a first portion of the internal chamber from a second portion of the internal chamber with the test specimen; introducing a pressurized fluid into the first portion of the internal chamber to apply a biaxial load upon the test specimen; measuring the pressure of the pressurized fluid in the first portion of the internal chamber; and measuring the movement of the test specimen in response to the biaxial load applied by the pressurized fluid.
21. The method of claim 20, wherein supporting the test specimen in the internal chamber includes supporting the test specimen on a substantially continuous support.
22. The method of claim 21 , wherein supporting the test specimen in the internal chamber further includes covering the continuous support with a low-friction grease, and placing the test specimen on the greased support, thereby dividing the internal chamber into the first portion and the second portion.
23. The method of claim 21 , wherein supporting the test specimen includes supporting the test specimen on the support without clamping the test specimen to the support.
24. The method of claim 20, wherein providing the housing includes providing a hollow vessel having a bottom open end and a top open end, and a cover secured to the top open end of the vessel, wherein the bottom open end is supported on a support surface.
25. The method of claim 24, wherein providing the hollow vessel and the cover includes fastening the cover to the vessel after the test specimen is supported in the internal chamber.
26. The method of claim 20, wherein measuring the movement of the test specimen includes positioning a displacement sensor relative to the test specimen.
27. The method of claim 26, wherein positioning the displacement sensor includes substantially aligning the displacement sensor with a central axis of a support upon which the test specimen is positioned.
28. The method of claim 26, wherein positioning the displacement sensor includes contacting a tip of the displacement sensor with a surface of the test specimen.
29. The method of claim 26, wherein measuring the pressure of the pressurized fluid in the first portion of the internal chamber includes detecting the pressure of the pressurized fluid with a pressure sensor.
30. The method of claim 29, further comprising connecting the displacement sensor and the pressure sensor to a data acquisition system.
31. The method of claim 30, further comprising initiating the data acquisition system to record pressure data and displacement data provided by the pressure sensor and the displacement sensor, respectively.
32. The method of claim 31 , further comprising stopping data acquisition in response to at least one of breakage of the test specimen as indicated by a sudden pressure drop in the first portion of the internal chamber, and a user-determined pressure value prior to breakage of the test specimen.
33. The method of claim 20, wherein measuring the pressure of the pressurized fluid in the first portion of the internal chamber includes detecting the pressure of the pressurized fluid with a pressure sensor.
34. The method of claim 20, wherein introducing the pressurized fluid into the first portion of the internal chamber includes introducing the pressurized fluid through a controlled opening of a precision needle valve.
35. The method of claim 20, further comprising displaying data relating to the measured pressure and movement of the test specimen on a display.
36. The method of claim 20, further comprising calculating the flexural strength of the test specimen using the following equations:
wherein "q" denotes the measured pressure in the first portion of the internal chamber corresponding with breakage of the test specimen, "a" denotes a diameter of a support upon which the test specimen is positioned, "y" denotes the measured movement of the test specimen, "t" denotes a thickness of the test specimen, "E" denotes the Young's modulus of the material of the test specimen, and "σ" is the flexural strength at the center of the test specimen, wherein Ki =1.016/(l-υ), K2 = 0.376, K3 = 1.238/(l-υ), and K4 = 0.29418 in which "υ" denotes the Poisson's ratio of the material of the test specimen, and wherein Equation (A) is used to solve for "y" which, in turn, is used in Equation (B) to solve for the flexural strength at the center of the test specimen.
PCT/US2009/066074 2009-01-16 2009-11-30 Equi-biaxial flexure test device for thin and ultra-thin semiconductor wafers and other wafers WO2010082977A1 (en)

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