CN111551488B - Method for testing interlayer adhesion and method for preparing test sample - Google Patents
Method for testing interlayer adhesion and method for preparing test sample Download PDFInfo
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Abstract
The invention discloses a method for testing interlayer adhesion and a method for preparing a test sample wafer, wherein the test sample wafer comprises a silicon wafer substrate strip and a film to be tested attached to the surface of the silicon wafer substrate strip, and the test sample wafer is placed in a corresponding position in a four-point bending tester clamp and used for testing the adhesion of the film, and the method for preparing the test sample wafer comprises the following steps: obtaining a plurality of silicon wafer substrate strips which accord with the target size and contain the film to be detected; selecting a plurality of second-layer substrate structures according to the elastic modulus and the breaking strength of the material; carrying out roughening treatment on one surface of the second-layer substrate structure; and adhering one surface of the silicon wafer substrate strip containing the film to be detected with the roughened surface of the second-layer substrate structure. According to the invention, through improving the substrate material, structure and test method, the test success rate is obviously improved, and the numerical upper limit of the adhesion force in the four-point bending test is improved.
Description
Technical Field
The invention relates to the relevant fields of integrated circuit manufacturing, solar systems, large-scale display circuits and the like, in particular to a method for testing interlayer adhesion and a method for preparing a test sample wafer.
Background
In the fabrication of Si-based products such as integrated circuits, solar systems, and large-scale display circuits, multilayer thin film structures are often employed. With the rapid development of manufacturing technology, the adhesion strength between different films is directly related to the reliability and service life of the whole system structure. In use, problems of film peeling, voids and the like caused by defects are often found at the weakest interface, which seriously affect the yield, so that the stable adhesion quantitative characterization of the multilayer film structure is important.
There are various methods for measuring the adhesion between the multi-layered films, such as a tape method, a nanoindentation method, a four-point bending method, and the like. Compared with other types of adhesion tests, the test result of the four-point bending method is slightly influenced by the residual stress of the film, the adhesion strength between the films can be quantitatively described, and the data show stronger reliability and repeatability.
For a standard four-point bending test, a sample to be tested comprises an upper layer of elastic silicon substrate strip and a lower layer of elastic silicon substrate strip, wherein the <110> crystal orientation of the silicon substrate strip is parallel to the long edge of the substrate. And (3) sticking the silicon substrate strip containing the film to be tested and the silicon substrate strip without the film, wherein the film to be tested is positioned in the middle layer. A pre-breaking groove was prepared in the middle of the back side of the silicon substrate strip containing the film using a cutting tool, followed by loading at a constant speed on a four-point bending tester, and a curve of the indenter load and its travel distance was recorded. At the critical load of the curve, the strain relief energy becomes greater than the crack resistance of the interface, causing the film desorption to extend along the interface. At the stage of uniform-speed desorption of the film, the fracture energy of the film is calculated according to parameters such as critical load and the like, and the calculation formula is as follows:
wherein G is the strain energy release rate and represents the strength of the adhesion force between the films to be tested; upsilon is the Poisson ratio of the lower substrate; e is the elastic modulus of the lower substrate; p is critical load; l is the vertical distance between the inner and outer contact points on the single side of the contact between the pressure head and the test sample in the loading process; b and h are the width and thickness of the monolayer sample strip, respectively.
However, with the advent of new high-adhesion film structures and the reduction in the thickness of the films to be tested, the success rate of testing adhesion by the four-point bending method has decreased, and testing adhesion between multilayer films has become increasingly difficult. However, in the conventional four-point bending test, a silicon substrate is completely used for preparing a test sample, and the silicon substrate is often subjected to brittle fracture in the test process to cause test failure, because silicon belongs to a brittle material at normal temperature and is often fractured under a lower load in the test process, when fracture occurs before the thin film is separated, the test failure is caused, namely the success rate of the four-point bending test is influenced; in factIn the actual test, it is difficult to measure the adhesion to be higher than 40J/m2The above data limit the upper limit of the test value and the application range of the test method.
To improve the success rate of four-point bending tests, Dauskardt et al modified the sample preparation method to use<111>Crystal orientation cut silicon chip instead of traditional one<110>The silicon wafer cut in the crystal orientation is used as a substrate, and the adhesion energy is tested to be 12J/m2The success rate increased to 88% with the following films, but for samples of conventional dimensions (e.g., 50 mm. times.10 mm. times.1.4 mm), the adhesion energy was tested to exceed 40J/m2The load of 60N or more is required, whereas the conventional silicon substrate structure sample is broken when the load reaches 40N or more, and it is difficult to maintain a stable state under the load of 60N or more until the end of the test.
Dauskardt et al also tested an adhesion energy of 35J/m by preparing test specimens of T-type structure2Ultra-thin films with a success rate of about 20% (reference: Birringer R P, Chidester P J, Dauskardt R H. high yield four-point band thin film addition technique [ J ]]Engineering specific mechanisms, 2011,78(12):2390 and 2398). However, the sample preparation process of the structure is complicated, and the cleaning degree of residual glue can seriously affect the test result.
Wang et al partially pretreated the film to be tested with a BOE solution and tested for adhesion energy of less than 20J/m2The test success rate of the film is improved from 0% to more than 60% (reference documents: Wang Y, Yang Y J, Chong M M, et al. four-Point bundling method definition for 40nm technology Cu/Nblk interface addition measure [ C]2015IEEE 22nd International Symposium on the Physical and Failure Analysis of Integrated circuits IEEE 2015 469-. The method has high requirements on sample preparation process, and the adhesion energy is more than 40J/m in test2The film of (3) does not give an ideal test curve.
In addition, researchers improve the film structure through etching, filling, polishing and other processes to improve the success rate of the test, but the method also has the defects that the sample preparation is complex and the method cannot be applied to the test of the ultrahigh-adhesion film.
Therefore, a reliable and relatively convenient method for preparing a test sample is urgently needed, and the success rate of testing a novel high-adhesion film is improved.
Disclosure of Invention
The invention aims to provide a method for testing interlayer adhesion and a method for preparing a test sample wafer.
In order to achieve the purpose, the invention is realized by the following technical scheme:
the invention provides a method for testing interlayer adhesion, which is characterized by comprising the following steps: providing a test sample wafer, and testing the interlayer adhesion by using a four-point bending method; the test sample wafer comprises a silicon wafer substrate strip and a film to be tested attached to the surface of the silicon wafer substrate strip, and the interlayer adhesion comprises one or more of the following: the method comprises the following steps of (1) testing the adhesion between a single-layer film and a silicon wafer substrate strip, the adhesion between any one film layer in a multilayer film and another adjacent film layer, and the adhesion between the film layer in the multilayer film and the silicon wafer substrate strip; the preparation method of the test sample wafer at least comprises the following processes:
obtaining a plurality of silicon wafer substrate strips which accord with the target size and contain the film to be detected;
selecting a plurality of second-layer substrate structures matched with the silicon wafer substrate strips according to the elastic modulus and the breaking strength of the material;
carrying out roughening treatment on one surface of the second-layer substrate structure;
bonding one surface of the silicon wafer substrate strip containing the film to be detected with the roughened surface of the corresponding second-layer substrate structure;
in the test method, the calculation formula of the variable energy release rate G is as follows:
λ＝E'2/E'Si；
wherein, P is critical load; l is the vertical distance between the inner and outer contact points on the single side of the contact between the pressure head and the test sample in the loading process; b is the width of the test sample; e2Representing the modulus of elasticity of the second layer substrate structure; upsilon is2Representing the poisson's ratio of the second-layer substrate structure; eSiRepresenting the elastic modulus of the silicon wafer substrate strip; upsilon isSiRepresenting the Poisson's ratio of the silicon wafer substrate strip; etai＝hi/(h1+h2)，h1And h2Respectively showing the thickness of the silicon wafer substrate strip and the second-layer substrate structure in the test sample wafer.
Preferably, the second layer substrate structure comprises stainless steel.
Preferably, the stainless steel comprises 304 stainless steel, and the second-layer substrate structure is a stainless steel substrate strip.
Preferably, the preparation method of the test sample wafer comprises one or more of the following processes:
cutting a silicon wafer containing a film to be detected to obtain a plurality of silicon wafer substrate strips containing the film to be detected, wherein the silicon wafer substrate strips conform to the target size;
cutting a 304 stainless steel plate to obtain a plurality of 304 stainless steel substrate strips, wherein the thickness of the 304 stainless steel substrate strips is the same as that of the silicon wafer substrate strips, or the thickness of the 304 stainless steel substrate strips is different from that of the silicon wafer substrate strips;
bonding the silicon wafer substrate strip with the corresponding 304 stainless steel substrate strip by using glue, and curing the glue after bonding;
and cutting the back center of the silicon wafer substrate strip perpendicular to the long edge of the substrate to form a pre-breaking groove to obtain a test sample to be tested, or forming a scratch with a certain depth on the back of the silicon wafer substrate strip to obtain the test sample to be tested.
Preferably, after a silicon wafer containing a film to be measured is cut to obtain a silicon wafer substrate strip containing the film to be measured, the silicon wafer substrate strip is cleaned, wherein the silicon wafer is cut along the <110> crystal direction of the silicon wafer; and/or cutting the 304 stainless steel plate to obtain a 304 stainless steel substrate strip, and cleaning the substrate strip.
Preferably, the 304 stainless steel substrate strip is the same length and/or width as the silicon wafer substrate strip.
Preferably, the roughening treatment method is: the stainless steel surface of the 304 stainless steel substrate strip is textured by mechanical abrasion using a corrosive reagent or using sandpaper.
Preferably, the bonding strength between the glue and the silicon wafer substrate strip or the 304 stainless steel substrate strip is higher than that between the film to be tested and the silicon wafer substrate strip; the glue is quick-drying glue, the curing temperature range of the glue during curing is 25-150 ℃, and the curing time of the glue is 1-30 minutes.
The invention also provides a preparation method of the test sample for testing the film adhesion by the four-point bending method, which adopts the preparation method of the test sample.
The invention also provides a test sample wafer for testing the film adhesion by a four-point bending method, which is the test sample wafer, and the test sample wafer comprises a silicon wafer substrate strip and a film to be tested attached to one side surface of the silicon wafer substrate strip.
Compared with the prior art, the invention has the beneficial effects that: the invention provides a preparation method of a test piece for detecting the interlayer adhesion of a thin film, which remarkably improves the success rate of testing and the upper limit of the numerical value of the adhesion of a four-point bending method by improving the material and the structure of a substrate; compared with a standard sample preparation method, the method can test the film with higher adhesive performance by using the test result of the invention, and the test success rate is improved from 10% to more than 70%.
Drawings
FIG. 1 is a flow chart of the novel sample preparation method of the present invention;
FIG. 2 is a schematic diagram of a thin film structure to be tested according to a first embodiment of the present invention;
FIG. 3 is a silicon substrate strip without a thin film used in a conventional standard sample preparation method;
FIG. 4 is a graph of the adhesion test of the film obtained using the conventional standard sample preparation method in example one;
FIG. 5 shows SUS304 and a surface treatment method used in the present invention;
FIG. 6 is a schematic diagram of a sample to be tested and stainless steel which are adhered by quick-drying glue in the sample preparation method of the invention;
FIG. 7 is a graph of the adhesion test of the film obtained by the sample preparation method of the present invention in the first example;
FIG. 8 is a schematic diagram of a film structure to be tested according to a second embodiment of the present invention;
FIG. 9 is a graph showing the adhesion test curve of the film obtained by the sample preparation method of the present invention in example II;
FIG. 10 is a schematic diagram of a thin film structure to be tested according to a third embodiment of the present invention;
FIG. 11 is a graph of the adhesion test of the film obtained using the standard sampling method in example III;
FIG. 12 is a film adhesion test curve obtained by the sample preparation method of the present invention in example III.
Detailed Description
The technical solution of the present invention is fully described below with reference to the accompanying drawings, and it is apparent that the focus of this invention and the examples described below apply to thin films deposited on silicon substrates, but the principles can be applied to any type of flexible substrate containing a thin film to be measured. All other examples, which can be obtained by a person skilled in the art without making any creative effort based on the examples in the present invention, belong to the protection scope of the present invention.
As shown in fig. 1, the present invention provides a method for preparing a test piece for testing the adhesiveness of a thin film by a four-point bending method, comprising the steps of:
step S1, cutting the silicon wafer A containing the film to be tested (usually along the crystal orientation favorable for cutting, such as <110> crystal orientation) to the required size of the device (such as 50mm x 10mm), and obtaining a plurality of silicon wafer substrate strips A1 containing the film to be tested.
In the step S1, the <110> crystal orientation is a natural cleavage crystal orientation for most silicon wafers, and it is generally cut along this direction, and it is easy to obtain a sample with regular size, and the <110> crystal orientation is preferably a cutting direction in the present invention, but the present invention is not limited to this direction and is applicable to a sample cut in any direction. In addition, in order to avoid interference of chips, pollutants and the like generated in the cutting process, a cleaning agent can be adopted to clean the silicon wafer substrate strip, so that the interference result is prevented.
Step S2, a 304 stainless steel plate B (hereinafter referred to as SUS304) is selected and cut to obtain a plurality of stainless steel substrate strips B2, which are cleaned with a cleaning agent and then ready for use.
Preferably, the selected 304 stainless steel plate can be the same thickness as the silicon wafer to be tested, but the invention is not limited thereto, and the invention is also applicable to stainless steel plates with non-uniform thickness. Illustratively, the stainless steel substrate strip B2 is the same size (length and width) as the silicon wafer substrate strip A1. The cleaning agent can be an organic solvent or other reagents capable of cleaning the sample, and can prevent chips, pollutants and the like generated in the cutting process from interfering the result.
In the step S2, a 304 stainless steel plate is selected to have strong toughness, similar elastic modulus to silicon, and low cost, whereas the conventional sample preparation method uses a silicon wafer as a substrate and can be broken under a low load, but the stainless steel used in the invention does not break even if a large load is applied, so that the test is performed smoothly, i.e., the success rate is increased. It should be noted that the present invention is not limited to the 304 stainless steel substrate, and other substrates, such as other materials that do not deform during loading, may be selected, as long as the test can be performed smoothly without breaking easily under a large load.
Step S3, the stainless steel surface of the stainless steel substrate strip B2 is roughened, and the roughened surface is formed in the step, so that the surface area of the micro stainless steel substrate strip B2 is increased, and the attachment capability of the glue is improved in the following steps. Optionally, in step S3, the stainless steel surface of the substrate strip B2 is textured and roughened by mechanical grinding using a corrosive reagent or sand paper, and meanwhile, the stainless steel surface of the substrate strip B2 is dried after cleaning the stainless steel surface debris by ultrasonic cleaning or the like.
And step S4, adhering the side of the silicon wafer substrate strip A1 containing the film to be tested to the roughened side of the stainless steel substrate strip B2 by using an adhesive. Illustratively, the adhesive is glue, the glue is high-strength glue, and the bonding strength between the high-strength glue and the silicon wafer substrate strip A1 or the stainless steel substrate strip B2 is higher than that between the film to be tested and the silicon wafer substrate strip A1.
And step S5, completely curing the glue, wherein the curing temperature is in the range of room temperature to 150 ℃ (for example, 25 ℃ to 150 ℃). If the curing temperature is too high, the silicon wafer is easily warped, and if the curing temperature is low, a long time may be required. Therefore, it is important to select proper glue. Preferably, the glue is low-temperature quick-drying glue and is placed at 25-35 ℃ for 30 minutes.
S6, cutting the silicon wafer substrate strip A1 back center perpendicular to the long side direction of the substrate by using a high-speed cutting grinding wheel or a laser cutting machine to form a pre-breaking groove and obtain a sample sheet to be tested; the depth of the groove is about 2/3 of the thickness of the silicon wafer substrate strip, so that the test sample wafer is preferentially broken at the pre-breaking groove in the subsequent test process; alternatively, the thickness of the silicon wafer substrate strip is about 700 μm, which corresponds to the model of the silicon wafer, and the thickness of the silicon wafer substrate strip is not limited by the present invention. It should be noted that the invention is not limited to the formation of the pre-breaking groove, but also can form a scratch on the back surface of the silicon wafer substrate strip, and also can realize that the test sample wafer is preferentially broken at the scratch in the test process, and the depth of the scratch can be designed according to the practical application situation.
In the testing process, the sample sheet obtained in step S6 is placed in a corresponding position in a four-point bending tester fixture, and testing parameters (for example, a constant loading speed is set, which is usually a value between 0.05 μm/S and 0.30 μm/S) are set through software, so as to perform testing, for example, testing the adhesion between a single-layer film and a silicon wafer substrate strip, or testing the adhesion between any one film layer and another adjacent film layer in a multi-layer film, or testing the adhesion between a film layer and a silicon wafer substrate strip in a multi-layer film. In most of the apparatuses, two pairs of indenters with different pitches are in contact with both sides of the sample, and the length of the sample piece is generally required to be larger than the pitch of any pair of indenters.
In addition, in the test process, the calculation formula of the variable energy release rate G is corrected as follows:
λ＝E'2/E'Si (5)
wherein, P is critical load; l is the vertical distance between the inner and outer contact points on the single side of the contact between the pressure head and the test sample in the loading process; b is the width of the test sample; eSUS304Representing the modulus of elasticity of the underlying 304 stainless steel substrate strip, typically 193-200 GPa; upsilon isSUS 304Represents a poisson's ratio of 0.29 for a 304 stainless steel substrate strip; eSiRepresenting the elastic modulus of the silicon wafer substrate strip; upsilon isSiRepresenting the Poisson's ratio of the silicon substrate; etai＝hi/(h1+h2) In the present invention, h1And h2Respectively testing the thickness of the silicon substrate strip and the stainless steel substrate strip in the sample wafer, and when h is1＝h2Eta is theni＝0.5。
In addition, the invention uses the stainless steel material, after the test is finished, the glue on the surface of the stainless steel can be removed by grinding and the like, and the glue is used for preparing the test sample again, so that the test cost is reduced.
In summary, the present invention provides a method for preparing a test strip for detecting the adhesion between layers of a thin film. Compared with a standard sample preparation method, the method can test the film with higher adhesive performance by using the test result of the invention, and the test success rate is improved from 10% to more than 70%.
The first embodiment is as follows:
FIG. 2 is a schematic diagram of a thin film structure to be tested, wherein 100 is a silicon substrate strip with a thickness of about 700 μm, according to an embodiment of the present invention; 101 is a dielectric material SiO2About 20nm thick; 102 is a Ru film of a diffusion impervious layer material, and the thickness of the Ru film is about 5 nm; 103 is an interconnect copper film with a thickness of about 500 nm. The silicon wafer containing the film to be tested is cleaved into a strip-shaped silicon substrate 100, namely, the silicon wafer substrate strips A1, the specific size of which is determined according to the equipment requirement, in the embodiment, the silicon wafer substrate strips A1 have the size of 50mm multiplied by 10mm and are used for cleaning and backup.
FIG. 3 shows a silicon substrate strip without a thin film used in a conventional standard sample preparation method. In the prior art, when a traditional standard sample preparation method is used, a silicon-optical wafer is cleaved into a strip-shaped substrate with the same size as a sample to be detected, namely 50mm multiplied by 10mm, so that adhesion data obtained by the method disclosed by the invention and the traditional sample preparation method are compared conveniently; in the traditional standard sample preparation, a silicon wafer containing a film to be detected is respectively adhered to a silicon substrate without the film by preparing epoxy resin adhesive, and in the traditional standard sample preparation, the adhered sample is placed in a high-temperature drying oven at 150 ℃ and taken out after 1 hour; and finally, loading the to-be-tested piece on a four-point bending tester, setting the loading speed to be a constant value (such as 0.05 mu m/s), recording the critical load value, and combining the relevant parameters of the equipment and using a formula (1) to obtain the adhesion energy data of the film. FIG. 4 is a pressure-displacement plot of the average adhesion calculated according to equation (1) from four-point bend test specimens prepared by conventional standard methods using the film shown in FIG. 2Can be 2.9J/m2。
FIG. 5 is a schematic view showing a 304 stainless steel (SUS304) used in the method of the present invention, wherein the numeral 500 indicates that SUS304 having a thickness equal to that of the silicon wafer substrate strip is used, i.e., SUS304 having a thickness of 700 μm is used, which can reduce errors in the calculation results caused by replacement of the substrate material; in this example, a 304 stainless steel plate is formed into a plurality of substrate strips by a wire-cut processing method, i.e., the plurality of stainless steel substrate strips B2 described above. The specific dimensions of the substrate strip B2 are required according to the requirements of the test equipment, in this case the dimensions of the substrate strip B2 are 50mm x 10mm x 0.7 mm.
In the first embodiment of the present invention, a 600-mesh sand paper was used and grains were formed on the surface of stainless steel by mechanical grinding, so that the surface was rough. In this example, the stainless steel surface is polished to form a grid pattern 501. The surface texture is not limited to the pattern of grid texture 501 of figure 5. Any method for polishing the surface to generate grains, such as a cross grid, a square grid, a long grid, unequal-distance grains and the like, so that the surface roughness is protected by the invention.
FIG. 6 is a schematic diagram of the invention after a silicon wafer substrate strip A1 containing a film to be tested and a stainless steel substrate strip B2 are adhered by using a quick-drying adhesive. The sample formed by the sticking is then placed in a vacuum oven at a drying temperature of 30-50 deg.C (one preferred temperature is 30 deg.C) for 30 minutes. In particular, epoxy glues are commonly used in the prior art, which generally require high temperature drying for achieving the highest strength, at drying parameters of 150 ℃ for 1 hour; the invention selects another quick-drying glue different from epoxy resin, which has different requirements on the highest strength from epoxy resin glue, the glue can be quickly dried at normal temperature, and in order to completely dry the glue in the sample, the glue is determined to be dried at a proper temperature (for example, 30 ℃) and finally reaches a certain strength.
When the above steps are completed, a pre-breaking groove is prepared, as shown in fig. 6, in this example, a laser cutting machine is used to prepare a pre-breaking groove 600, the depth of which is in the range of 300-500 μm (preferably, about 400 μm); wherein 601 is a silicon wafer substrate strip containing a film to be detected; 602 is quick-drying glue between two side substrates (namely between a silicon wafer substrate strip A1 and a stainless steel substrate strip B2), and the thickness is less than 2 μm; 603 is a stainless steel substrate strip used in this example.
In the present invention, a sample sheet to be tested is loaded on a four-point bending tester, the loading speed is set to a constant value (for example, 0.05 μm/s), the critical load value is recorded, and the adhesion energy data of the film can be obtained by using the formulas (2) to (4) in combination with the relevant parameters. FIG. 7 is a load-displacement curve of the film shown in FIG. 2, which is calculated according to the modified equations (equations 2 to 5) to have an average adhesion energy of 2.8J/m2。
In general, data from systems with poor adhesion are readily obtained using the four-point bending method. Ruthenium (Ru) on SiO2The adhesion on the substrate is substantially in the range of 2.8 to 3.0J/m in the literature2The results obtained with the conventional method used and the method employed in the example of the present invention are consistent with those reported in the literature. As can be seen by comparison, the data obtained by the method of the invention and the traditional preparation method are similar, and the error is within 3 percent, so the method has higher reliability.
Example two:
the second embodiment relates to the use of the method of the present invention to measure the typical barrier layer materials TaN and SiO currently used in the integrated circuit interconnection2The adhesive property therebetween. FIG. 8 is a schematic diagram of a thin film structure to be tested used in the second embodiment, wherein 800 is a silicon substrate with a thickness of about 700 μm; 801 dielectric material SiO2About 300nm thick; 802 is a TaN film of a diffusion barrier layer material, and the thickness is about 2 nm; 803 is a Ta metal film of the material of the adhesion layer, the thickness of which is about 2 nm; 804 is an interconnect copper film with a thickness of about 800 nm. The silicon wafer containing the film to be tested is cleaved into a strip-shaped silicon substrate, namely the silicon wafer substrate strips A1, the specific size of which is determined according to the equipment requirement, in the example, the silicon wafer substrate strips A1 are 50mm multiplied by 10mm, and the silicon wafer substrate strips are used for cleaning and backup.
First, a test sample is prepared using a conventional standard sample preparation method, and a photo silicon wafer is cleaved into a strip-shaped substrate having the same size as that of a sample to be tested, i.e., 50mm × 10 mm. Similar to the conventional standard sample preparation method described in example one, the preparation process finally loads the test piece onto a four-point bending tester, sets the loading speed to a constant value (for example, 0.05 μm/s), records the critical load value, and uses the formula (1) to obtain the adhesion energy data of the film by combining the relevant parameters of the equipment itself. Since the adhesion of the thin film structure is good, the silicon substrate is broken before stable data is not obtained during the test, so that the test fails completely, and adhesion data is not obtained.
When the method of the present invention is used to prepare a test sample, the SUS304 shown in fig. 5 is used, and the preparation process is similar to the method described in the first embodiment, and the steps of cutting, surface polishing, pasting, drying, preparation of a pre-fracture groove, etc. are sequentially completed, which are not described herein again; and then loading the to-be-tested piece on a four-point bending tester, setting the loading speed to be a constant value (for example, 0.05 mu m/s), recording the critical load value, and combining related parameters to obtain the adhesion energy data of the film by using formulas (2) to (5). FIG. 9 is a load-displacement curve calculated from the modified equations (2) to (5) for the sample shown in FIG. 8, and the average adhesion energy is 39.5J/m2。
For a typical TaN/Ta structural film, since it is in SiO2Adhesion on substrates is good and therefore, testing by the traditional four-point bending method is difficult to succeed, and very few documents report adhesion data before. By using the novel sample preparation method, not only is the accurate value of the adhesion obtained, 10 samples are tested, but also the success rate in the test is about 70%.
Example three:
the third embodiment relates to a method for testing a high-adhesion thin film used in an integrated circuit, which is used for measuring the high-adhesion thin film and SiO-containing thin film2Adhesion between Si substrates of the dielectric layers. FIG. 10 is a schematic diagram of a thin film structure to be tested used in the present embodiment, wherein 1000 is a silicon substrate with a thickness of about 700 μm; 1001 dielectric material SiO2About 20nm thick; 1002 is a novel RuZn alloy prepared by a sputtering method, having a thickness of about 5 nm; 1003 is an interconnect copper film with a thickness of about 300 nm. Cleaving the wafer containing the film to be measured into strip-shaped silicon substrates, i.e. the above-mentioned silicon chip substratesThe specific dimensions of the bottom strip A1 are determined according to the equipment requirements, and the dimensions of the silicon substrate strip A1 in the example are 50mm 10mm for cleaning and backup.
First, a test sample is prepared using a conventional standard sample preparation method, and a photo silicon wafer is cleaved into a strip-shaped substrate having the same size as that of a sample to be tested, i.e., 50mm × 10 mm. Similar to the conventional standard sample preparation method described in example one, the preparation process finally loads the test piece onto a four-point bending tester, sets the loading speed to a constant value (for example, 0.05 μm/s), records the critical load value, and uses the formula (1) to obtain the adhesion energy data of the film by combining the relevant parameters of the equipment itself. FIG. 11 is a load-displacement curve plot prepared by a standard method using the film sample of FIG. 10, and having an average adhesion energy of 44.1J/m calculated according to equation (1)220 samples were tested with a success rate of about 10%.
When the test sample is prepared by using the method of the present invention, the SUS304 shown in fig. 5 is used, and the preparation process is similar to the method described in the first embodiment, and the steps of cutting, surface polishing, pasting, drying, preparation of the pre-fracture groove, and the like are sequentially completed, which is not described herein again. And then loading the to-be-tested piece on a four-point bending tester, setting the loading speed to be a constant value (for example, 0.05 mu m/s), recording the critical load value, and combining related parameters to obtain the adhesion energy data of the film by using formulas (2) to (5). FIG. 12 is a load-displacement curve calculated from the modified equations (2) to (5) for the film samples shown in FIG. 10, and having an average adhesion energy of 44.3J/m2. By adopting the method, 4 samples are tested, the testing success rate is improved to 75%, and the data obtained by the novel sample preparation method has higher repeatability.
The results of the four-point bending test and the success rate of the conventional standard method and the method of the present invention in the above examples were compared in a comprehensive manner, and are shown in table 1:
table 1 is a comparative list of results and success rates for four-point bend tests of the conventional standard method and the inventive method
In conclusion, the SUS304 is adopted as the lower-layer substrate, and the surface of the substrate is pretreated to prepare the four-point bending test sample, so that the test success rate is obviously improved, and the test cost is saved; meanwhile, the upper substrate and the lower substrate are adhered by using novel glue, so that the drying time is shortened, the processing temperature is reduced, and the testing efficiency is improved; the comparison of the data obtained by the standard sample preparation method shows that the novel sample preparation method can obtain the test result similar to that before the improvement, and can obviously improve the test success rate in the test of the high-adhesion film.
While the present invention has been described in detail with reference to the preferred embodiments, it should be understood that the above description should not be taken as limiting the invention. Various modifications and alterations to this invention will become apparent to those skilled in the art upon reading the foregoing description. Accordingly, the scope of the invention should be determined from the following claims.
Claims (8)
1. A method for testing interlayer adhesion, the method comprising: providing a test sample wafer, and testing the interlayer adhesion by using a four-point bending method; the test sample wafer comprises a silicon wafer substrate strip and a film to be tested attached to the surface of the silicon wafer substrate strip, and the interlayer adhesion comprises one or more of the following: the adhesive force between the single-layer film and the silicon wafer substrate strip, the adhesive force between any one film layer in the multilayer film and the other adjacent film layer, and the adhesive force between the film layer in the multilayer film and the silicon wafer substrate strip; the preparation method of the test sample wafer at least comprises the following processes:
obtaining a plurality of silicon wafer substrate strips which accord with the target size and contain the film to be detected;
selecting a plurality of second-layer substrate structures matched with the silicon wafer substrate strips according to the elastic modulus and the breaking strength of the material;
carrying out roughening treatment on one surface of the second-layer substrate structure;
bonding one surface of the silicon wafer substrate strip containing the film to be detected with the roughened surface of the corresponding second-layer substrate structure;
in the test method, the calculation formula of the variable energy release rate G is as follows:
λ＝E'2/E'Si；
wherein, P is critical load; l is the vertical distance between the inner and outer contact points on the single side of the contact between the pressure head and the test sample in the loading process; b is the width of the test sample; e2Representing the modulus of elasticity of the second layer substrate structure; upsilon is2Representing the poisson's ratio of the second-layer substrate structure; eSiRepresenting the elastic modulus of the silicon wafer substrate strip; v. ofSiRepresenting the Poisson's ratio of the silicon wafer substrate strip; etai＝hi/(h1+h2)，h1And h2Respectively showing the thickness of the silicon wafer substrate strip and the second-layer substrate structure in the test sample wafer.
2. The method of claim 1,
the second layer substrate structure comprises stainless steel.
3. The method of claim 2,
the stainless steel comprises 304 stainless steel, and the second-layer substrate structure is a stainless steel substrate strip.
4. The method of claim 3,
the preparation method of the test sample wafer comprises one or more of the following processes:
cutting a silicon wafer containing a film to be detected to obtain a plurality of silicon wafer substrate strips containing the film to be detected, wherein the silicon wafer substrate strips conform to the target size;
cutting a 304 stainless steel plate to obtain a plurality of 304 stainless steel substrate strips, wherein the thickness of the 304 stainless steel substrate strips is the same as that of the silicon wafer substrate strips, or the thickness of the 304 stainless steel substrate strips is different from that of the silicon wafer substrate strips;
bonding the silicon wafer substrate strip with the corresponding 304 stainless steel substrate strip by using glue, and curing the glue after bonding;
and cutting the back of the silicon wafer substrate strip perpendicular to the long edge of the substrate to form a pre-breaking groove to obtain a test sample to be tested, or forming a scratch with a certain depth on the back of the silicon wafer substrate strip to obtain the test sample to be tested.
5. The method of claim 4,
cutting a silicon wafer containing a film to be detected to obtain a silicon wafer substrate strip containing the film to be detected, and cleaning the silicon wafer substrate strip, wherein the silicon wafer substrate strip is cut along the <110> crystal direction of the silicon wafer;
and/or cutting the 304 stainless steel plate to obtain a 304 stainless steel substrate strip, and cleaning the substrate strip.
6. The method of claim 4,
the 304 stainless steel substrate strip is the same length and/or width as the silicon wafer substrate strip.
7. The method of claim 1,
the roughening treatment method comprises the following steps: the stainless steel surface of the 304 stainless steel substrate strip is textured by mechanical abrasion using a corrosive reagent or using sandpaper.
8. The method of claim 4,
the bonding strength between the glue and the silicon wafer substrate strip or the 304 stainless steel substrate strip is higher than that between the film to be tested and the silicon wafer substrate strip;
the glue is quick-drying glue, the curing temperature range of the glue during curing is 25-150 ℃, and the curing time of the glue is 1-30 minutes.
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