JP2012242248A - Adhesion evaluation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an adhesion evaluation method capable of quantitatively evaluating adhesion between a base material and a thin film.SOLUTION: An adhesion evaluation method related to the present invention is the adhesion evaluation method for evaluating adhesion between a base material and a thin film formed thereon, including a peeling process for peeling the thin film from the base material with the use of a cutting blade. The peeled thin film includes a first bending part and a second bending part adjacent to the first bending part. The method also includes: a peeling area calculation process for calculating the peeling area of the thin film to be held between the first bending part and the second bending part; a horizontal force acquisition process for obtaining the horizontal force Fof the cutting blade when peeling the thin film; a peeling energy calculation process for calculating peeling energy to be required in the peeling on the basis of the product of the integrated value of the horizontal force Fand the horizontal velocity V of the cutting blade in a time section ta including the maximum value of the horizontal force F; and a unit peeling energy calculation process for calculating unit peeling energy per unit area by dividing the peeling energy by the peeling area.

Description

  The present invention relates to an adhesion evaluation method for evaluating adhesion between a substrate and a thin film.

  Conventionally, as a thin film adhesion evaluation method, a method in which a tape is attached to a thin film and peeled off, a scratch method in which the surface of the thin film is scratched with an indenter such as diamond, and a tension type in which a tension jig is attached to the surface of the thin film with an adhesive and peeled off. A test method and a peel test in which the thin film itself is chucked and peeled off while maintaining a specific angle have been widely used.

  However, either method can perform qualitative adhesion evaluation, but cannot quantitatively evaluate adhesion. In addition, the sample size required for the test inevitably increases, and the limit on the sample size on the test increases.

  An evaluation method such as a cycus test method has been proposed for the above method (see, for example, Patent Document 1). In this method, the adhesion of the thin film can be evaluated by measuring the horizontal force applied to the cutting edge when the thin film is peeled off from the base using a hard cutting edge with a blade width of several hundreds of micrometers. It is said that a test in a minute region is possible as compared with.

JP 2002-195938 A

  However, in the cycus test method described in Patent Document 1, the physical relationship between the magnitude of the horizontal force and the adhesion during peeling can be determined by graphing the relationship between the horizontal force and the test time. It is only proposed and is not a quantitative adhesion evaluation method.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an adhesion evaluation method capable of quantitatively evaluating the adhesion between a substrate and a thin film.

  The adhesion evaluation method according to the present invention is an adhesion evaluation method for evaluating adhesion between a substrate and a thin film formed thereon, and has a peeling step of peeling the thin film from the substrate with a cutting blade. The peeled thin film has a first bent portion and a second bent portion adjacent to the first bent portion, and is further sandwiched between the first bent portion and the second bent portion. The product of the peel area calculation process for calculating the peel area of the thin film, the horizontal force acquisition process for obtaining the horizontal force of the cutting edge when peeling the thin film, and the integrated value of the horizontal force time and the horizontal speed of the cutting edge A peeling energy calculating step for calculating a peeling energy required for peeling, and a unit peeling energy calculating step for calculating a unit peeling energy per unit area by dividing the peeling energy by a peeling area. And effect.

  In the adhesion evaluation method according to the present invention, the thin film peeled in the peeling step has a first bent portion and a second bent portion adjacent to the first bent portion, and peels while periodically bending. is there.

  In the temporal change of the horizontal force of the cutting blade that peels the thin film in such a peeling mode, a maximum value periodically appears as will be described later. The horizontal force can be measured with a load cell.

  Here, as a result of performing detailed cross-sectional observation during the test, the present inventors started to float while bending each of the peeled portions around the tip, so that the horizontal force is directed from the maximum value (mountain portion) to the valley portion. It was found that peeling was considered to be completed in a very short time near the peak, just before the drop in horizontal force. In addition, since the thin film is difficult to peel off due to the close contact with the base material, the cutting blade that is about to move at a predetermined horizontal speed is prevented from moving and pressed against the thin film. I also found that the climb to the mountain occurred.

  Therefore, peeling of the thin film occurs when the horizontal force reaches the maximum value of the peak, that is, when the critical horizontal force that causes peeling is reached, and the work applied to the cutting blade during the peeling progresses. The present inventors thought that it was consumed as bending / friction of the part.

  Therefore, in the adhesion evaluation method according to the present invention, when calculating the peeling energy required for peeling, for example, using an integrated value of the horizontal force in a predetermined time interval including the maximum value of the horizontal force, the integrated value and the horizontal speed of the cutting edge are used. The peel energy is calculated by the product of Then, by dividing the calculated peeling energy by the peeling area, a unit peeling energy that is a peeling energy per unit area can be calculated. Using this unit peeling energy, it is possible to quantitatively evaluate the adhesion between the base material and the thin film. The horizontal speed of the cutting blade can be obtained from the rotational speed of a motor that is a drive source for moving the cutting blade.

  In the peeling energy calculation step, when the strain energy due to bending of the thin film at the time of peeling and the friction energy between the thin film and the cutting blade are negligibly small with respect to the peeling energy, the strain energy and the above The friction energy need not be subtracted.

  The horizontal force indicates a change in which a maximum value appears periodically. In the peeling area calculation step, the product of the time of one cycle of the maximum value and the horizontal speed of the cutting edge is calculated from the first bent portion to the second time. If the peeling area is calculated by multiplying the peeling length which is the length to the bent part and calculating the peeling area by the product of the peeling length and the peeling width of the thin film, the above peeling area is calculated without actually measuring the peeling length. can do.

  In the peeling area calculation step, the peeling area may be calculated by the product of the length from the first bent portion to the second bent portion measured during or after the test and the peel width of the thin film.

  The integral value in the peeling energy calculation step is preferably a time interval including at least a time during which the horizontal force reaches a maximum value as an integral interval. Since the peeling of the thin film occurs when the horizontal force becomes maximum, it is possible to obtain the peeling energy with high accuracy by integrating in that interval.

  The integration interval preferably does not include a time interval in which the horizontal force becomes a maximum value and becomes less than 80% of the maximum value. Since the energy applied after the horizontal force reaches the maximum value is not used for peeling (cracking), it is possible to accurately obtain the peeling energy by excluding this time interval.

  According to the adhesion evaluation method according to the present invention, it is possible to quantitatively evaluate the adhesion between the base material and the thin film formed thereon using the calculated unit peeling energy.

It is explanatory drawing which shows a mode that a thin film is peeled from a base material in this embodiment. It is explanatory drawing which shows the mode of peeling of a thin film. It is explanatory drawing which shows a time-dependent change of the horizontal force of a cutting blade. (A) is a graph which shows a time-dependent change of the horizontal force of a cutting blade, (b) is an enlarged graph of one area | region of (a).

  Hereinafter, the thin film adhesion evaluation method according to the present embodiment will be described with reference to the drawings.

1. 1. About a base material and a thin film FIG. 1: is explanatory drawing which shows a mode that a thin film is peeled from a base material in this embodiment.

  In the adhesion evaluation method according to this embodiment, as shown in FIG. 1, by calculating the unit peeling energy when the thin film 2 formed on the substrate 1 is peeled by the cutting blade 10, The adhesion with the thin film 2 can be evaluated.

  In FIG. 1, the thin film 2 is peeled from the base material 1 by moving the cutting edge 10 along the direction of the arrow A. In the figure, reference numeral 3 denotes an interface between the substrate 1 and the thin film 2. In addition to the interface between the substrate 1 and the thin film 2 formed thereon, the interface 3 refers to an interface between the first thin film and the second thin film formed on the substrate 1 or a thin film having two or more laminated structures. It shall include the interface between each layer.

  The material of the cutting blade 10 is not particularly limited as long as the material is harder than the material of the base material 1 and the thin film 2, but in order not to cause plastic deformation, a harder material is preferred. For example, it is desirable to use the cutting blade 10 made of diamond, cemented carbide, sintered CBN (cubic boron nitride) material, or the like.

  The substrate 1 is made of metal, ceramics, resin, and the like, and is, for example, a single crystal silicon wafer substrate, a glass substrate, a copper or copper alloy substrate, an aluminum or aluminum alloy substrate, etc. It is not limited.

  The thin film 2 formed on the substrate 1 is a metal film (pure metal, alloy film, amorphous metal film, etc.), a ceramic film (nitride film, carbonized film, diamond-like carbon film, etc.), or a resin film (FEPT film, etc.). And one or more layers are formed on the substrate 1. In the case of a multilayer film of two or more layers, it may be made of the same kind of thin film material or different kind of thin film material, and is not particularly limited.

  The method for forming the thin film 2 is not particularly limited. For example, a vacuum deposition method (physical vapor deposition method (sputtering method, arc ion plating method, molecular beam epitaxy (MBE) method, vapor deposition method, etc.), chemical vapor deposition, etc. Method (thermal CVD method, plasma CVD method, etc.), a formation method applied by a spin coater, thermal spraying, a dipping (plating, etc.) method and the like.

  The thin film 2 that is an object to which the adhesion evaluation method according to the present embodiment is applied exhibits peeling behavior while the peeling portion is periodically bent at the time of the test. Specifically, as shown in FIG. Peeling is performed so as to form a plurality of linear peeling portions 20 (peeling portions 20a, 20b, 20c,...) So that 20 draws a substantially circle. In the figure, 21 (21a, 21b, 21c,...) Denotes a bent portion at the end of the peeling portion 20. In addition, let the length of one peeling part 20 (peeling part 20a, 20b, 20c, ...) be peeling length lc (peeling length lca, lcb, lcc, ...).

  Examples of the thin film 2 exhibiting such peeling behavior include a metal film having a film thickness of about 2 μm or less, particularly an Al film and a Cu film. The thin film may be peeled off at the interface between the base material and the thin film, or may be caused by cohesive failure due to the progress of cracks in one of the vicinity of the interface between the base material and the thin film. . The adhesion evaluation method according to the present embodiment can be applied to both cases of peeling. The peeling width may be longer or shorter than the cutting edge width L, and is not particularly limited. However, the peeling width is preferably less than the cutting edge width. More preferably, the peeling width is the same as the cutting edge width.

2. About the quantitative adhesion evaluation method in this embodiment In this embodiment, the unit peeling area required for peeling (cohesive failure) using the relationship between the horizontal force F _H of the cutting edge 10 during the peeling progress and the test time t. Hit energy (hereinafter referred to as unit peeling energy) Ga is calculated. Hereinafter, the calculation method will be described in detail.

  First, the work U performed by the cutting blade 10 is calculated by the following formula (1). V is the horizontal speed of the cutting edge 10, and ta is the peeling progress time (predetermined time interval).

  Further, the relationship of the following formula (2) is established for the work U described above, and the work U is not only the peeling energy Ua required for peeling (cohesive failure), but also the strain energy Ub due to bending of the peeling portion and the cutting edge rake face. Is consumed as the frictional energy Uf between the contact point and the peeled portion, and the unit peel energy Ga is calculated by the following equation (3).

  However, when Ub and Uf are negligibly small with respect to Ua, the following equations (4) and (5) are established. In this case, U = Ua.

  From the above formula (5), the unit peeling energy Ga (the peeling energy Ua divided by the peeling area (peeling length lc × peeling width L)) can be calculated.

  Therefore, based on the obtained unit peeling energy Ga, the adhesiveness between the substrate and the thin film can be quantitatively evaluated. In addition, about the peeling width of the peeling area (peeling length lc x peeling width) used when calculating the unit peeling energy Ga, the value of the cutting edge width L is assumed that the peeling width and the cutting edge width L are the same. Is used. When the peel width is smaller than the cutting edge width L, the value of the sample width is used as the peel width.

Figure 3 is an explanatory view showing the change over time KH of the horizontal force F _H of the cutting edge.

When showing the behavior of the thin film 2 is peeled off while folded periodically (see FIG. 2), as shown in FIG. 3, the crest in temporal change KH of the horizontal force F _H of the cutting edge (maximum value) and valleys And appear periodically.

When the cross-section of the thin film after the test is observed, the peel length (also referred to as a crack length) lc of the peeled portion 20 peeled at once is the length of the portion of the peeled portion 20 that is substantially linear. believed to be (see FIG. 2), the present inventors found that in temporal change KH of the horizontal force F _H, peel length lc of the once peeled peeling section 20 corresponds to one period of the crest test It has been found that it almost coincides with the product of the time t1 and the horizontal speed V of the cutting edge.

As for the test time t1 corresponding to one cycle of the crest described above, any time may be adopted as long as it corresponds to the region in which the cutting blade moves without rubbing the substrate surface. It is not limited. However, since the horizontal force F _H also changes when the period changes, it is not preferable in terms of quantitative evaluation to calculate the peeling length lc of the peeling part 20 using a value obtained by averaging a plurality of periods.

As described above, instead of obtaining the peel length lc of the peeled portion 20 by the product of the test time t1 and the horizontal speed V, as another method, a cross-sectional observation of the peeled thin film material is performed during or after the test. Thus, the peeling length lc of the peeling portion 20 may be measured. At this time, peel length lc of the actually measured peeling section 20, it is preferable to ensure that they correspond to t1 in time course KH of the horizontal force F _H used to obtain the release energy.

  As a method for observing the cross section, for example, a cross section of the sample after the test is prepared and observed using an optical microscope, a scanning electron microscope (SEM) or the like, or a sample capable of observing the cross section during the test is prepared. Although there is a method of attaching an appropriate observation device such as a CCD camera, an optical microscope, or a scanning electron microscope (SEM) so that the cross section of the sample can be observed, there is no particular limitation.

Subsequently, FIG. 4 (a) is a graph showing the change over time KH of the horizontal force F _H of the cutting blade is an enlarged graph of the region E1 of (b) is (a).

In FIG. 4A, the reason why the horizontal force F _H in the region E2 is large is that the thin film is cut from the upper surface to the lower surface before the thin film is peeled off from the substrate (FIG. 4). 1). Therefore, the horizontal force F _H in the region E2 is not considered when calculating the peeling energy.

As shown in FIG. 4 (b), peaks and valleys in the variation with time KH of the horizontal force F _H of the cutting edge appears periodically. In addition, in FIG.4 (b), the two peak parts 30 and 31 are shown.

As a result of performing detailed cross-sectional observation during the test, the present inventors have started to float while bending each of the peeled portions around the tip, so that the horizontal force F _H is directed from the peak portions 30 and 31 toward the valley portions. It has been found that the peeling is considered to be completed in a very short time near the peak, which is just before the horizontal force F _H is lowered.

Further, in order to thin hardly peeled by adhesion to the base material, because the cutting edge to be moved in a horizontal velocity V is pressed against the thin film are prevented from moving, the mountain portions from the valley portion of the horizontal force F _H It was also found that the rise of.

Therefore, peeling of the thin film occurs when the horizontal force F _H reaches the maximum value of the peaks 30 and 31, that is, when the critical horizontal force that causes peeling is reached, and the work U loaded on the cutting blade during the peeling progress. However, the present inventors considered that it is consumed as the peeling progresses and the bending / friction of the peeling portion.

  In view of the above, the peeling of the thin film is a section including the maximum value in the vicinity of the peak portion, and is less than 80% of the maximum value after the horizontal force reaches the maximum value. Considering that the travel proceeds in a section not including the time section, the time corresponding to this section is defined as the above-described peeling progress time ta as a predetermined time section. In order to improve the calculation accuracy of the unit peeling energy Ga, the peeling progress time measured by capturing the progress of peeling by observing the cross section during the test may be used.

In the above embodiment, the horizontal force F _H is used in the temporal change KH. However, the horizontal force F _H / the cutting edge width L or the horizontal force F _H / the sample width may be used. Alternatively, the product of the test time t and the horizontal speed V of the cutting edge may be used instead.

  The present invention is not limited by the above-described embodiments, and can be implemented with appropriate modifications within a range that can be adapted to the gist of the present invention, all of which are within the technical scope of the present invention. Is included.

  Hereinafter, the present invention will be described more specifically with reference to examples. The present invention is not limited by the following examples, and can of course be implemented with appropriate modifications within a range that can be adapted to the above-described gist. Included in the range.

  In this example, for Al (1 μm) / Corning # 1737 glass, processing conditions 1 (no substrate ion bombardment before film formation) and processing conditions 2 (substrate ion bombardment before film formation) are used as substrate processing conditions before film formation. Two samples were prepared by performing the treatment for 180 seconds.

When calculating the peel area in the peel area calculating step, the product of the time of one cycle of the maximum value of the horizontal force F _H and the horizontal speed V of the cutting edge is the peel length, which is the length between adjacent bent parts. The peeling area was calculated by the product of the peeling length and the peeling width of the thin film.

In the peeling energy calculation step, the horizontal speed V of the cutting edge used for calculating the peeling energy is 1.0 μm / second, the sampling rate (dt) is 0.2 seconds, and the predetermined time interval ta is 0.2. Seconds (one sampling period in which the horizontal force F _H is maximized). Note that the strain energy due to bending of the thin film at the time of peeling and the friction energy between the thin film and the cutting edge were ignored, assuming that the peeled part would lift after the peeling was completed, so these were subtracted from the calculated peeling energy. Absent.

  Table 1 shows the unit peel energy Ga obtained by dividing the calculated peel energy by the calculated peel area, and the result of the tensile load when peeled by the StudPull (pull type) test. Each value in Table 1 is an average value.

  The StudPull (tension type) test is a simple method in which a tensile jig is attached to a thin film to be peeled with an adhesive, and the adhesion is qualitatively determined based on the tensile load when the thin jig is peeled off. In addition, since the unit peeling energy Ga showed a negative value when considering the bending of the peeling part at the time of peeling progress, and the friction between the peeling part and the cutting edge, the peeling part is considered to be lifted after peeling, Strain energy Ub and friction energy Uf due to bending were ignored. Further, the above-described peeling progress time ta was adopted as the peeling progress time.

In the processing condition 1, the width of the unit peeling energy Ga is 6.5 to 9.0 J / m ² , and in the processing condition 2, the width of the unit peeling energy Ga is 1.2 to 2.0 J / m ² , The treatment condition 1 resulted in higher adhesion than the treatment condition 2.

  Further, even when the tensile load was measured by the StudPull (tensile type) test for the same sample, the substrate with the thin film subjected to the processing condition 1 was larger than that of the processing condition 2, so that the unit peeling energy Ga The result which supports the magnitude relation of the above-mentioned calculation result was able to be obtained.

Furthermore, for example, the agglomeration / breaking energy per unit peeling area for various thin film materials and substrates described in the literature (Yu Kiyono: Material Testing Technology Vol. 54 No. 4 P8-14 (2009)) is 4 According to the result obtained by the point bending method, since the order of the energy value is several to several tens of J / m ² , it was confirmed that the value of the calculated unit peeling energy Ga is appropriate. Note that the substrate ion bombardment treatment before film formation is usually a pretreatment for improving the adhesion, but the detailed cause of the decrease in the adhesion due to this treatment is unknown, but the cleaning of the substrate is not necessary in the first place. It is estimated that there was a high possibility that it was sufficient.

DESCRIPTION OF SYMBOLS 1 Base material 2 Thin film 3 Interface 10 Cutting blade 20 Peeling part 21 Bending part F _H Horizontal force Ga Unit peeling energy KH Horizontal force temporal change lc Peeling length ta Peeling progress time V Cutting blade horizontal speed

Claims (6)

An adhesion evaluation method for evaluating adhesion between a substrate and a thin film formed thereon,
Having a peeling step of peeling the thin film from the substrate by a cutting blade;
The peeled thin film has a first bent portion and a second bent portion adjacent to the first bent portion,
Further, a peeling area calculating step for calculating a peeling area of the thin film sandwiched between the first bent part and the second bent part,
A horizontal force acquisition step of obtaining a horizontal force of the cutting blade when peeling the thin film;
A peeling energy calculation step for calculating a peeling energy required for the peeling by a product of an integral value with respect to the time of the horizontal force and a horizontal speed of the cutting edge;
A unit peel energy calculating step for calculating a unit peel energy per unit area by dividing the peel energy by the peel area;
An adhesion evaluation method characterized by comprising:   The said peeling energy calculation process WHEREIN: The distortion energy by the bending of the said thin film at the time of the said peeling and the friction energy of the said thin film and the said cutting blade are subtracted from the calculated said peeling energy. Adhesion evaluation method. The horizontal force indicates a change in which a local maximum appears periodically,
In the peeling area calculation step, the product of the time of one period of the maximum value and the horizontal speed of the cutting edge is a peeling length that is a length from the first bent portion to the second bent portion. The adhesion evaluation method according to claim 1, wherein the peel area is calculated by calculating a product of the peel length and the peel width of the thin film.   2. The peeling area calculation step calculates the peeling area by a product of a length from the first bent portion to the second bent portion measured during or after the test and a peel width of the thin film. Or the adhesion evaluation method according to 2.   5. The adhesion evaluation method according to claim 1, wherein the integral value in the peeling energy calculation step is a time interval including at least a time during which the horizontal force reaches a maximum value as an integral interval. The adhesion evaluation method according to claim 5, wherein the integration interval does not include a time interval in which the horizontal force becomes a maximum value and becomes less than 80% of the maximum value.

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