Background Statement for SEMI Draft Document #5691 New Standard: Test Method for Measurement of Chip (Die) Strength by Mean of Cantilever Bending Notice: This background statement is not part of the balloted item. It is provided solely to assist the recipient in reaching an informed decision based on the rationale of the activity that preceded the creation of this Document. Notice: Recipients of this Document are invited to submit, with their comments, notification of any relevant patented technology or copyrighted items of which they are aware and to provide supporting documentation. In this context, patented technology is defined as technology for which a patent has issued or has been applied for. In the latter case, only publicly available information on the contents of the patent application is to be provided. Background Statement Spreading out of 3D Packaging, chip (die) thickness becomes thinner and thinner. Die strength measurement had already been standardized, but it needs special tool for less than 50μm thickness. The current standard is not convenient method. To solve this problem, we propose new bending strength measurement method called Cantilever Bending Method for ultra-thin die. When the die thickness reduces to nearly less than 30μm, it is reported that Si physical characteristics becomes more fragile and easy to warp. The data of Si effective Young s Modulus measured by Nano-Indentation is reduced depend on die thickness. Consequently in the case of 3 points bending method, Si die under evaluation is sliding inside between the supports under measurement. This phenomenon induces wide deviations of measured value. This Cantilever Bending Method can also avoid this issue. From above, it will make easy to prescribe in requirements and specifications among several suppliers and achieve smooth handling through the supply-chain. Ballot will be discussed at Thin Chip (Die) Bending Strength Measurement Task Force and adjudicated at the Japan Packaging committee meetings in SEMI Japan Office, Tokyo, Japan, on May 8, 2014. If you have any questions, please contact to Thin Chip (Die) Bending Strength Measurement Task Force; Haruo Shimamoto, AIST, at haruo.shimamoto@aist.go.jp Shoji Yasunaga, Rohm, at shoji.yasunaga@lsi.rohm.co.jp Morihiro Kada, AIST, at m-kada@aist.go.jp Or contact SEMI Staff, Naoko Tejima at ntejima@semi.org 1
SEMI Draft Document #5691 New Standard: Test Method for Measurement of Chip (Die) Strength by Mean of Cantilever Bending 1 Purpose 1.1 This test method defines a procedure for evaluation of die strength by mean of cantilever bending where 3 point bending is not easy to measure strength in case of wafer thickness less than 50μm. 2 Scope 2.1 This test method applies only for cantilever bending method, and other methods will be defined by separate documents. 2.2 This test method is used to measure die strength for dies from processed wafers. 2.3 Wafer thinning technology becomes popular to meet the demand for thin packages, so the die strength data is critical for the die quality and certification. This standard extends to the region of ultra-thin thickness from 3 point bending measurement method SEMI G86-0303 which describes the Die Strength Evaluation Method, Measurement Data Summary Technique and Data Usage for Test Report. NOTICE: SEMI Standards and Safety Guidelines do not purport to address all safety issues associated with their use. It is the responsibility of the users of the Documents to establish appropriate safety and health practices, and determine the applicability of regulatory or other limitations prior to use. 3 Referenced Standards and Documents 3.1 SEMI Standards and Safety Guidelines SEMI G86 TEST METHOD FOR MEASUREMENT OF CHIP (DIE) STRENGTH BY MEAN OF 3 POINT BENDING 3.2 ISO Standards 1 ISO 468 Surface Roughness Parameters, Their Values and General Rules for Specifying Requirements ISO 6508-1 Metallic Materials Rockwell Hardness Test (scales A,B,C,D,E,F,G,H,K,N,T) Part1: Test Method 3.3 Effective Young s Modulus Data of Si effective Young s Modulus measured by Nano-Indentation is reduced depend on die thickness <50μm. See: Related 1-1 NOTICE: Unless otherwise indicated, all documents cited shall be the latest published versions. 4 Terminology 4.1 Definitions 4.1.1 Deflection L distance over which bottom surface of the test specimen at fixed point deviates from its original position during flexture. NOTE 1: It is expressed in millimeters (mm). 4.1.2 flexural stress σf nominal stress of the our surface of the test specimen at test point. NOTE 2: It is calculated from the relationship given in Section 8, equation(1) in Section 9, and is expressed in megapascals (MPa). 4.1.3 flexural stress at break σfb flexural stress at break of the test specimen. NOTE 3: It is expressed in megapascals (MPa). 4.1.4 loading tool tool to apply the force to test specimen 1 International Organization for Standardization, ISO Central Secretariat, 1 rue de Varembé, Case postale 56, CH-1211 Geneva 20, Switzerland; Telephone: 41.22.749.01.11, Fax: 41.22.733.34.30, http://www.iso.ch. Page 2
4.1.5 speed of testing v rate of loading tool movement. NOTE 4: It is expressed in millimeters per minute (mm/min). 4.1.6 supports to support the test specimen during flexural test. 4.1.7 loading height H distance from supports to loading tool. 4.1.8 effective loading height H* add the corner edge radius R of Tool and Support to H. 4.1.9 processed wafer finished by wafer process or assembly process including TSV fabrication and so on. 5 Summary of Test Method 5.1 This test method is based on cantilever bending test and calculating flexural stress at break 6 Apparatus 6.1 Test machine 6.1.1 The machine shall be capable of maintaining the test speed (speed of the loading tool) with the tolerance of ±0.05mm/min. 6.1.2 The machine shall be capable of measuring and recording the test force in newtons (N). 6.1.3 The error in the indicated force shall not exceed 0.5% of the actual value. 6.2 Supports and Loading Tool 6.2.1 Supports and loading tool shall be arranged as shown in Figure 1 to Figure 2. Datum Plane X and Datum Plane Z are perpendicular each other. Figure 1 Position of the Specimen at the Start of a Measurement (Side view) Page 3
Figure 2 Front view from right side of Figure 1 6.2.2 The corner edge radius R of the supports and the loading tool shall be 0.1mm ± 0.05mm 6.2.3 The width B1 of supports and the width B2 of the loading tool shall be longer than the width b of test specimen. 6.2.4 Two supports to the loading tool shall be parallel to Y direction within ±2 degree. And two supports shall be parallel to Y direction within ± 0.05mm, Z direction within ± 0.02mm.(see Figure 3) Figure 3 Top view of Tool Setting 6.2.5 The tip of the supports and loading tool shall be hardened more than HRc60 specified in ISO/DIS6508-1. 6.2.6 The tip of the supports and loading tool shall have the roughness less than 1.6μmRa specified in ISO468. 6.2.7 Two supports hold specimen with minimum loading where specimen stays and with maximum loading where sample will not damage. Page 4
7 Test Specimens 7.1 The shape and dimensions of the test specimens shall be agreed between the interested parties. 7.2 Test specimen shall be Silicon processed die. If applied to the other materials, adequate test conditions shall be considered such as test speed, tool height and so on. 7.3 At least 25 test specimens shall be pulled from a wafer. 8 Procedure 8.1 Measure the thickness h, width b, and length w. The accuracy of h and b shall be within ± 5%. 8.2 Adjust the loading height H in accordance with the following conditions described in Figure 4. 8.2.1 Setting Procedure For a test specimen, measurement for a relation between Displacement and Applied Force is performed with a test height H. If an appearance of an inflection point is observed, set a minimum test height H with the inflection point as minimun test height Hmin. The measurement of die strength shall be performed in a range of test height H more than Hmin. 8.2.2 Interpretation of measurement result With reference to Figure 4, in the Case 1 the result curve shows a Break Point without an inflection point, and the measurement shall be considered as a fail. The measurement height H is considered to be low. If a Break Point is appeared before an appearance of an inflection point in the result curve with increasing the test height H, it is considered that the strength is decreased by not a bulk character but a certain factor such as crack. If no inflection points are observed according to a factor such as TSV formation, it is considered that the strength is decreased by some factor especially in the case of composite materials. In the Case 2 of Figure 4, the result curve shows both a Break Point and an inflection point, and the measurement shall be considered as a success. In the Case 3 of Figure 4, the result curve does not show a Break Point, and the measurement shall be considered as a fail. It is considered that the test tool start to slip on die, because the test height H is too high. H ( Case 1 ) < H ( Case 2 ) < H ( Case 3 ) Figure 4 Concept of Measurement Height H and measured curve NOTE 5: Minimum test height Hmin varies with a friction coefficient between the test specimen and loading tool. 8.3 Decide the speed of testing v from Figure 5. Otherwise use 5mm/min can be optional. Page 5
Figure 5 Typical value of correlation between loading height and speed of testing 8.4 Place the test specimen on the two supports within ± 2 degree of deviation from datum plane (See Figure 3). The evaluated surface shall be applied the tensile force (that is face to loading tool). 8.5 Set the test speed less than 5mm/min in order to avoid the damage on test specimen and apply force at loading height H. Set the adequate number considering correlation between loading height and test speed (See Figure5). 8.6 Record the force of the specimen at the break. 9 Calculations 9.1 Flexural Stress Calculate the flexural stress parameters defined in Section 4 using the following equation: σfb=6pbh*/bh2 (1) Where: σfb is the flexural stress at break in question (MPa); PB is the applied force at break (N) H* is the effective loading height (mm) (=H+2R) b is the width in millimeters (mm) of the test specimen h is the thickness, in millimeters (mm), of the test specimen NOTE 1: Equation (1) can only be used for test specimens with linear stress/strain behavior. 10 Report 10.1 The test report shall include the following information: the directions major axes of the specimens if test specimen has a direction dependency the evaluated surface side (equal to loading side) the dimensions of the test specimens (thickness h, width b, length w) test height (H,H*) sample size the speed of testing (v) the individual test results, the flexural stress at break the date of the test Page 6
with/without TSV (see related R1-4) with/without Bump TSV layout and measurement point Die description and structure Break mode after measurement Page 7
RELATED INFORMATION 1 ADDITIONAL INFORMATION FOR TEST NOTICE: This Related Information is not an official part of SEMI [designation number] and was derived from the work of the global [committee name] Technical Committee. This Related Information was approved for publication by full letter ballot procedures on [A&R approval date]. R1-1 Related Documents R1-1.1 Mechanical Characteristics of Thin Dies/Wafers in Three-Dimensional Large-Scale Integrated systems M. Murugesan, T. Fukushima, J.C. Bea, K.W. Lee, T. Tanaka and M. Koyanagi, IEEE Advanced Semiconductor Manufacturing Conference, p.66, 2013 R1-1.2 Minimizing the Local Deformation Induced around Cu-TSVs and CuSn/InAu-Microbumps in High-Density 3D-LSIs. M. Murugesan, H. Kobayashi, H. Shimamoto, F. Yamada,T. Fukushima, J.C. Bea, K.W. Lee,T. Tanaka, and M. Koyanagi, IEEE International Electron Devices Meeting, p. 657, 2012. R1-1.3 Locally Induced Stress in Stacked Ultrathin Si wafers: XPS and u-raman study M. Murugesan, H. Nohira, H. Kobayashi, T. Fukushima, T. Tanaka and M. Koyanagi, IEEE Electronic Components and Technology Conference, p. 625, 2012. R1-2 Concept of loading height and die bending Figure R1-1 shows a typical example of bending strength measurement results. Figure R1-1 concept of loading height and die bending NOTE 2:. Tool moving distance L=v t Friction Co-efficiency μ fixed by the material of Tool & Specimen Page 8
Bending Angle Θ Angle between F and Fx Maximum Friction Co-efficiency us the value when the tool slip on Si Specimen Maximum Bending angle λ the value when the tool slip on Si Specimen λ= arctan(us), u=l/h, Θ=arctan(u) R1-3 Guideline to use the cantilever bending method and the 3 point bending method R1-3.1 In an overlapping area of the die thickness, either bending method can be selected in consideration of existing databases and continuity with the existing databases. Figure R1-2 relation between Die Thickness and measurement method R1-4 Typical Case example of bending strength measurement results with die including TSV R1-4.1 Measurement should be performed by clarifying the following conditions: Tool and Supports location on a die with TSV. Direction of configuration of TSV (see Figure R1-3) Dashed Line 1,2 : along or across the TSV configuration Dashed Line 3 : between the TSV configuration Page 9
Figure R1-3 Example of Wide IO die with TSV Lay-out R1-5 Test Machine R1-5.1 When the measurement of deflection is based on the movement of loading tool, the frame compliance of the test machine should be more than 40 kn/mm. R1-5.2 The interval of data sampling, such as test force and movement of the loading tool, should be more than 1000 times per second when the test machine records the data in digital format. R1-6 Test Specimens R1-6.1 The number of test specimen is 0.25 of Acceptance Quality Level, specified in ISO/DIS 2859-1.2, Sampling Procedures for Inspection by Attributes Part 1: Sampling Schemes Indexed by Acceptable Quality Level (AQL) for Lot-by-Lot Inspection. R1-6.2 Test specimens should be pulled from a wafer in every direction without leaning. R1-6.3 When test results are compared, same test conditions such as loading height H(H*), the speed of testing v and specimens dimension (width b) should be used. R1-6.4 When excessive film is attached to test specimens, equation (1) in 9.1 is not applied for stress on a silicon material. R1-7 Recording the Force R1-7.1 Not only the force at the break points but also test force of the specimen under the test should be recorded. It is recommended that an automatic recording system is used. R1-8 Test Report R1-8.1 Test report should include the failure characteristics of the failed specimens. R1-8.2 When possible, the test report should include failures which occur at any notable defect on the die. Page 10
NOTICE: Semiconductor Equipment and Materials International (SEMI) makes no warranties or representations as to the suitability of the Standards and Safety Guidelines set forth herein for any particular application. The determination of the suitability of the Standard or Safety Guideline is solely the responsibility of the user. Users are cautioned to refer to manufacturer s instructions, product labels, product data sheets, and other relevant literature, respecting any materials or equipment mentioned herein. Standards and Safety Guidelines are subject to change without notice. By publication of this Standard or Safety Guideline, SEMI takes no position respecting the validity of any patent rights or copyrights asserted in connection with any items mentioned in this Standard or Safety Guideline. Users of this Standard or Safety Guideline are expressly advised that determination of any such patent rights or copyrights, and the risk of infringement of such rights are entirely their own responsibility. Page 11