CN104677738A - Bubbling method for measuring mechanical property of film - Google Patents

Abstract

The invention discloses a bubbling method for measuring the mechanical property of a film by utilizing the vacuum operating environment and the high-resolution microscopic feature of a scanning electron microscope. A lamination hollow specimen is put into the scanning electron microscope, so that the film of the lamination material is deformed so as to form bubbling, and the displacement field in plane of the surface of the film is obtained via a DIC algorithm by utilizing the speckle images of the film; the stress in plane of bubbling and the out-of-plane height of the surface of the film are obtained by utilizing the displacement field in plane, and further the biaxial modulus of the film and the initial residual stress of the film are obtained. According to the invention, the problems of complex loading device and high cost of a traditional bubbling method are overcome, and the biaxial modulus and the residual stress can be measured at the same time only by once loading.

Description

A kind of bubbling method for measuring thin film mechanics characteristic

Technical field

The invention belongs to optical measurement mechanics and material property detection technique field, particularly a kind of bubbling method measuring thin film mechanics characteristic.

Background technology

In micro-nano, the technical field such as microelectronics and material, the application of film is very extensive.Film refers to that the yardstick of its thickness direction is far smaller than the material structure of other direction yardsticks.The film of same material has power, electricity, magnetic, heat, light and chemical property not available for its bulk sample usually, the microelectric technique of based thin film structure has played irreplaceable vital role in national defense construction and economic development, therefore causes the extensive concern of researcher and engineering staff and greatly payes attention to.And the measurement of thin film mechanical performance and characterization technique ensure that membrane structure is effectively on active service, realizing the important technology guarantee to membrane structure optimal design, is the key areas of current thin film study.

In view of the design feature of film, the method for the block material mechanical performance of conventional measurement is no longer applicable to the mechanical property measuring film.At present the experimental technique of general thin performance test and sign is mainly contained to Bubbling method, Using Nanoindentation, uniaxial direct tensile method, peels off mensuration and 4 beam deflection methods etc.Wherein, Bubbling method because of its principle simple, measuring accuracy is high, and numerous mechanics parameter such as elastic modulus, Poisson ratio, unrelieved stress, yield limit that can realize film carries out measuring etc. advantage simultaneously, developed rapidly in recent years, become a kind of method of important measurement thin film mechanical performance.

In prior art, a typical Bubbling method device mainly comprises three parts: hydraulic pressure or air pressure loading device and control system, bubbling deflection measuring apparatus, bubbling clamping device.When film is arranged on after on bubbling clamping device, apply uniformly distributed load by hydraulic pressure or air pressure loading device in the side of film, film can be heaved to correspondingly opposite side normal direction.The amount of deflection that bubbling sample heaves can be measured by bubbling deflection measuring apparatus.The amount of deflection of record corresponding to different loads, can obtain the load-deflection curve of film, finally can obtain elastic modulus and the unrelieved stress of film.

US Patent No. 6772642B2 discloses a kind of device of efficient application Bubbling method test material mechanical property, its maximum feature is to load multiple film simultaneously, sample bench is made up of multiple pipeline, pipeline is made up of the indeformable hard material of pressurized, sample is placed on sample bench, pressurizeed to sample by pipeline, deformation of thin membrane is recorded by displacement transducer.This device adopts displacement transducer, therefore there is the problem of sample location of the core difficulty, if location is inaccurate, resultant error will be very large.

Chinese patent CN201163222Y discloses a kind of ganoine thin film residual stress test instrument, He-Ne laser instrument is adopted to produce incident beam, once arrive optical flame detector via the transmission of semi-permeable mirror and the reflection of strip, by amplifying the radius-of-curvature measuring test piece the increase of light path.Measure the distance of semi-permeable mirror center line and strip and silicon photocell moving line, thus obtain the radius-of-curvature of test piece.According to relevant theoretical model, and then obtain the unrelieved stress of film.

In the above-mentioned prior art enumerated, Bubbling method device must be made up of three front parts.Any part lacked wherein all cannot realize Bubbling method and measure.Its deficiency is: bubbling deflection measuring apparatus is measured by displacement transducer or laser interference device usually, and its measurement sensistivity is restricted; Bubbling deflection measuring apparatus is only measured from face amount of deflection, cannot measuring surface internal strain, and thus this effective information of opposite internal strain cannot perception; Charger integrated complex and cost intensive; In continuous loading procedure, the Nonlinear creep of film can affect measuring accuracy etc.

The people such as Li Chuanwei proposed a kind of quick Bubbling method based on scanning electron microscope in its paper Novel scanning electron microscope bulge test technique integrated with loading function in 2014, measured by the elastic modulus of the method to Kapton.The method is integrated with described Bubbling method charger and bubbling deflection measuring apparatus, reduces measurement cost.But the method weak point is: the unrelieved stress of acquiescence film is zero, simplifies measurement, introduce excessive error although do so simultaneously.

In sum, we have invented a kind of bubbling method measuring thin film mechanics characteristic.By carrying out necessary amendment to the classical governing equation of Bubbling method, we can be implemented in the twin shaft modulus and unrelieved stress of measuring film in scanning electron microscope simultaneously.

Summary of the invention

The present invention proposes a kind of bubbling method for measuring thin film mechanics characteristic, comprising the following steps:

A. metallic film is prepared at the upper surface of the substrate with manhole, and prepare speckle pattern at the upper surface of this film, at the lower surface coating epoxy glue of substrate, metallic film and epoxy glue cover upper surface and the lower surface of substrate respectively, make through hole become airtight cavity, and metallic film, substrate, epoxy glue three are combined together to form laminated hollow sample regularly;

B. this laminated hollow sample is placed on scanning electron microscope sample bench, open the Low-vacuum mode of scanning electron microscope, the operating distance of adjustment scanning electron microscope and enlargement factor are to obtain the picture rich in detail of laminated hollow sample upper surface, take the scanning electron microscope image of the now central area of laminated hollow sample upper surface, the field range of shooting is 1/10 ~ 1/3 of the manhole diameter of substrate;

C. the high vacuum pattern of scanning electron microscope is opened, keep the operating distance of now scanning electron microscope identical with step b with enlargement factor, after laminated hollow specimen surface produces bubbling and blister shape no longer changes, take the scanning electron microscope image of the now central area of laminated hollow sample, the field range of shooting and the field range in step b keep identical;

D. utilize digital picture related algorithm to carry out correlation computations to the two width images obtained in step b and step c, obtain the face internal strain ε of film;

E. keep the high vacuum pattern of scanning electron microscope and operating distance constant, the enlargement factor of scanning electron microscope be adjusted to 1/3 ~ 1/8 in step b and again focus, to obtain clear scanning electron microscope image and shooting image now, the field range of shooting is 1.5 ~ 4 times of the manhole diameter of substrate;

F. by the sample bench tilt angle alpha of scanning electron microscope, after inclination, necessary three-dimensional position adjustment is done to sample bench, make laminated hollow sample still in visual field, keep scanning electron to show the enlargement factor of emblem mirror and the image taken now identical with step e with operating distance after tilting, the field range of shooting is identical with step e;

G. digital picture related algorithm is again utilized to carry out digital picture correlation computations to two width images captured in step e and f, obtain this film inclination sample bench forward and backward its in the horizontal plane perpendicular to the displacement variable Δ y of the projection of sample bench rotor shaft direction, and utilize formula try to achieve film from face height ω ₀, and then utilize following formula to try to achieve twin shaft modulus M and the unrelieved stress σ of film ₀, wherein, a is the radius of the manhole of substrate, and P is 1 atmospheric pressure, and h is the thickness of film.

$M,{\mathrm{\σ}}_0(\mathrm{\ϵ},{\mathrm{\ω}}_0)=\left\{\begin{array}{c}{\mathrm{\σ}}_0\left(\frac{{6a}^2\mathrm{\ϵ}-{4\mathrm{\ω}}_0^2}{{6a}^2\mathrm{\ϵ}-{\mathrm{\ω}}_0^2}\right)\frac{{\mathrm{Pa}}^2}{{4\mathrm{h\ω}}_0}\\ M=\frac{{6a}^{2}P}{{4\mathrm{h\ω}}_0({6a}^2\mathrm{\ϵ}-{\mathrm{\ω}}_0^2)}\end{array}\right.$

The present invention has following remarkable advantage and high-lighting effect:

1) present invention utilizes vacuum working environment and the micro-characteristic of its high resolving power of scanning electron microscope, integrated loading and measurement function, overcome traditional Bubbling method charger complexity and the problem of cost intensive;

2) present invention utilizes this actual parameter of face internal strain, twin shaft modulus and these two mechanical parameters of unrelieved stress can be measured by once loading simultaneously;

3) base material of the present invention has manhole structure, and this structure is easy to processing and obtains, and the concentration phenomenon that can eliminate stress, in addition, the advantages such as it is high that the present invention also has measuring accuracy, easy and simple to handle.

Accompanying drawing explanation

Fig. 1 shows the structural representation of laminated hollow sample, and wherein, the upper surface preparation of metallic film has speckle pattern, and containing air in cylindrical enclosure cavity, the pressure in this airtight cavity is 1 atmospheric pressure;

Fig. 2 shows the electron scanning micrograph of central area under Low-vacuum mode of laminated hollow sample upper surface, and in figure, scale is the width of scanning electron microscope visual field, and enlargement factor is now 2500 times;

Fig. 3 shows the electron scanning micrograph of central area under high vacuum pattern of laminated hollow sample upper surface, and in figure, scale is the width of scanning electron microscope visual field, and enlargement factor is now 2500 times;

The scanning electron microscope image of Fig. 4 laminated hollow sample under showing high vacuum pattern, enlargement factor is now 300 times, and figure acceptance of the bid footage number illustrates the diameter of substrate via, i.e. the diameter of border circular areas shown in dotted line in figure;

Fig. 5 is the scanning electron microscope image of laminated hollow sample in inclination 6 ° of rear center regions under showing high vacuum pattern, and enlargement factor is now 300 times, and figure acceptance of the bid footage number illustrates the diameter of substrate via, i.e. the diameter of border circular areas shown in dotted line in figure.

Embodiment

Below in conjunction with accompanying drawing to the initial residual stress σ of the present invention at measurement metallic aluminium film ₀enforcement ten thousand formula in applying with twin shaft modulus M.

The radius that has being 400 μm at thickness is that the upper surface of the silicon base of the manhole of 300 μm prepares the metallic aluminium film that thickness is 2 μm, and prepare speckle pattern at the upper surface of metallic aluminium film, at the lower surface coating epoxy glue of silicon base, make metallic aluminium film, silicon base, epoxy glue three is combined together to form laminated hollow sample regularly, the through hole making metallic aluminium film and epoxy glue cover substrate makes it form cylindrical enclosure cavity, and the radius of the cylindrical enclosure cavity of described formation is 300 μm.It should be noted that the thickness of substrate also can between 200 μm ~ 600 μm preferably, within the scope of this, its variation in thickness can not have influence on the result of experiment; The radius of described manhole also can between 200 μm ~ 600 μm preferably; Described substrate also can adopt other nonmetallic materials such as silicon dioxide; Described film also can be made up of metal materials such as nickel, chromium, copper, and the method such as magnetron sputtering, transfer printing can be adopted to prepare metallic film at the upper surface of substrate.In addition, the pressure in the cylindrical enclosure cavity in laminated hollow sample is now 1 atmospheric pressure.

This laminated hollow sample is placed on the field emission scanning electron microscope sample bench that model is FEI QUANTA 450, open the Low-vacuum mode of scanning electron microscope, electron microscope device ready to be scanned is after 5 ~ 10 minutes, take the electron scanning micrograph of the now central area of laminated hollow sample upper surface, as shown in Figure 2, enlargement factor is now 2500 times, operating distance is 11.6mm, 100 μm, the scale occurred in Fig. 2 is the width of now scanning electron microscope visual field, namely the peak width now taking sample is 100 μm, in view of the pressure differential inside and outside the cavity of laminated hollow sample is lower, now the change of shape of metallic aluminium film is very little, therefore the change of shape of now metallic aluminium film can be ignored, the now photo of the metallic aluminium film surface of the near central regions of through hole has been shown in Fig. 2.It should be noted that and can adjust the field range of now taking, the field range of shooting should be 1/10 ~ 1/3 of the diameter of the manhole of substrate.

Then, open the high vacuum pattern of scanning electron microscope, enlargement factor is now kept to be still 2500 times, operating distance is still 11.6mm, electron microscope device ready to be scanned, laminated hollow specimen surface produces bubbling and after blister shape no longer changes, takes the electron scanning micrograph of the circle centre position of now sample central area, as shown in Figure 3.100 μm, the scale occurred in Fig. 3 is the width of scanning electron microscope visual field, and the peak width namely now taking sample is 100 μm.Because now laminated hollow sample is in high vacuum environment, therefore the upper surface pressure of metallic aluminium film is 0 atmospheric pressure, and its lower surface is 1 atmospheric pressure, under the pressure difference effect on upper and lower surface, metallic aluminium film raises up, thus forms circular blister.But because current shooting visual field width is 100 μm, and the diameter of substrate via is 600 μm, simultaneously, in view of the electron scanning micrograph provided in Fig. 3 is only the metallic aluminium film photo of substrate via near central regions, so time laminated hollow specimen surface define circular blister, but the circular blister of formation cannot be found out from Fig. 3.

Utilize digital picture related algorithm (DIC, Digital Image Correlation) correlation computations is carried out to Fig. 2 and Fig. 3, the face internal strain ε of metallic aluminium film can be obtained, specifically, by VIC-2D ver 1.0 software, Fig. 2 and Fig. 3 can be carried out the face internal strain ε that digital picture correlation computations obtains metallic aluminium film.

Subsequently, keep the operating distance of the high vacuum pattern of scanning electron microscope and 11.6mm constant, the enlargement factor of scanning electron microscope is adjusted to 300 times, to obtain picture rich in detail and shooting image now, as shown in Figure 4, the field range of now taking is 1000 μm, it should be noted that, the enlargement factor of scanning electron microscope also between 1.5 ~ 4 of the diameter of the manhole of substrate times preferably, also can be adjusted to 1/3 ~ 1/8 of original enlargement factor and again focus by the field range of now taking.

600 μm, the scale occurred in Fig. 4 indicates the diameter of substrate via, i.e. the diameter of border circular areas shown in dotted line in figure.Because shooting visual field is now greater than the diameter of substrate via, again because now laminated hollow sample is in high vacuum environment, thus the region as can be seen from Figure 4 shown by dotted line is exactly the circular blister region that laminated hollow specimen surface is formed, as can be seen from Figure 4 wherein the gray scale in region shown in dotted line and other regions and brightness all variant, this caused because this region film forms bubbling.After shooting Fig. 4, tilted by the sample bench of scanning electron microscope 6 °, do necessary three-dimensional position adjustment to sample bench after inclination, and keep enlargement factor to be 300 times, maintenance operating distance is 11.6mm, and shooting image now, as shown in Figure 5.

According to Such analysis, from Fig. 5, also can find out the circular blister of formation.600 μm, the scale occurred in Fig. 5 indicates the diameter of substrate via, i.e. the diameter of border circular areas shown in dotted line in figure.Again utilize above-mentioned digital picture related algorithm DIC, digital picture correlation computations is carried out to Fig. 4 and Fig. 5, obtain this film before and after inclination sample bench its in the horizontal plane perpendicular to the displacement variable Δ y of the projection of sample bench rotor shaft direction, and utilize formula (1) can obtain tested film from face height ω ₀, wherein, α is the angle that the sample bench of scanning electron microscope tilts.Also the sample bench of scanning electron microscope can be tilted 3 ° ~ 10 °, it should be noted that and need to do necessary three-dimensional position adjustment to it after sample bench tilts, laminated hollow sample is still in visual field after tilting.

${\mathrm{\ω}}_0=\frac{\mathrm{\Δy}}{2\sin \mathrm{\α}}---\left(1\right)$

By the face internal strain ε that tries to achieve with from face height ω ₀with in substitution formula (2), thus try to achieve twin shaft modulus and the unrelieved stress of film.

$M,{\mathrm{\σ}}_0(\mathrm{\ϵ},{\mathrm{\ω}}_0)=\left\{\begin{array}{c}{\mathrm{\σ}}_0\left(\frac{{6a}^2\mathrm{\ϵ}-{4\mathrm{\ω}}_0^2}{{6a}^2\mathrm{\ϵ}-{\mathrm{\ω}}_0^2}\right)\frac{{\mathrm{Pa}}^2}{{4\mathrm{h\ω}}_0}\\ M=\frac{{6a}^{2}P}{{4\mathrm{h\ω}}_0({6a}^2\mathrm{\ϵ}-{\mathrm{\ω}}_0^2)}\end{array}\right.---\left(2\right)$

Finally, can determine that the twin shaft modulus M of the aluminium film in the present embodiment is about 85GPa, initial residual stress σ ₀be about 125MPa.

Claims (10)

1. the present invention proposes a kind of bubbling method for measuring thin film mechanics characteristic, comprising the following steps:

A. metallic film is prepared at the upper surface of the substrate with manhole, and prepare speckle pattern at the upper surface of this film, at the lower surface coating epoxy glue of substrate, metallic film and epoxy glue cover upper surface and the lower surface of substrate respectively, make through hole become airtight cavity, and metallic film, substrate, epoxy glue three are combined together to form laminated hollow sample regularly;

B. this laminated hollow sample is placed on scanning electron microscope sample bench, open the Low-vacuum mode of scanning electron microscope, the operating distance of adjustment scanning electron microscope and enlargement factor are to obtain the picture rich in detail of laminated hollow sample upper surface, take the scanning electron microscope image of the now central area of laminated hollow sample upper surface, the field range of shooting is 1/10 ~ 1/3 of the diameter of the manhole of substrate;

C. the high vacuum pattern of scanning electron microscope is opened, keep the operating distance of now scanning electron microscope identical with step b with enlargement factor, after laminated hollow specimen surface produces bubbling and blister shape no longer changes, take the scanning electron microscope image of the now central area of laminated hollow sample, the field range of shooting is identical with the field range in step b;

D. utilize digital picture related algorithm to carry out correlation computations to the two width images obtained in step b and step c, obtain the face internal strain ε of film;

E. keep the high vacuum pattern of scanning electron microscope and operating distance constant, the enlargement factor of scanning electron microscope be adjusted to 1/3 ~ 1/8 in step b and again focus, to obtain clear scanning electron microscope image and shooting image now, the field range of shooting is 1.5 ~ 4 times of the diameter of the manhole of substrate;

F. by the sample bench tilt angle alpha of scanning electron microscope, after inclination, necessary three-dimensional position adjustment is done to sample bench, laminated hollow sample is still in visual field after tilting and keeps the enlargement factor of scanning electron microscope identical with step e with operating distance and the image taken now, the field range of shooting is identical with step e;

G. digital picture related algorithm is utilized to carry out digital picture correlation computations to two width images captured in step e and f, obtain this film inclination sample bench forward and backward its in the horizontal plane perpendicular to the displacement variable Δ y of the projection of sample bench rotor shaft direction, and try to achieve film from face height ω ₀, and then try to achieve twin shaft modulus M and the unrelieved stress σ of film ₀.

2. bubbling method as claimed in claim 1, is characterized in that, can utilize formula try to achieve film from face height ω ₀, wherein, α is the sample bench angle of inclination of scanning electron microscope.

3. bubbling method as claimed in claim 1, is characterized in that, following formula can be utilized to try to achieve twin shaft modulus M and the unrelieved stress σ of film ₀,

$M,{\mathrm{\σ}}_0(\mathrm{\ϵ},{\mathrm{\ω}}_0)=\left\{\begin{array}{c}{\mathrm{\σ}}_0=\left(\frac{{6a}^2\mathrm{\ϵ}-{4\mathrm{\ω}}_0^2}{{6a}^2\mathrm{\ϵ}-{\mathrm{\ω}}_0^2}\right)\frac{{\mathrm{Pa}}^2}{4h{\mathrm{\ω}}_0}\\ M=\frac{{6a}^{4}P}{4h{\mathrm{\ω}}_0({6a}^2\mathrm{\ϵ}-{\mathrm{\ω}}_0^2)}\end{array}\right.$

Wherein, a is the radius of the manhole of substrate, and P is 1 atmospheric pressure, and h is the thickness of film.

4. bubbling method as claimed in claim 1, it is characterized in that, described base silicon or silicon dioxide are made.

5. bubbling method as claimed in claim 1, it is characterized in that, described film can be made up of any one metal in aluminium, nickel, chromium, copper.

6. bubbling method as claimed in claim 1, is characterized in that, magnetically controlled sputter method can be adopted to prepare metallic film at the upper surface of substrate.

7. bubbling method as claimed in claim 1, is characterized in that, printing transferring method can be adopted to prepare metallic film at the upper surface of substrate.

8. bubbling method as claimed in claim 1, it is characterized in that, the thickness of described substrate is 200 μm ~ 600 μm.

9. bubbling method as claimed in claim 1, it is characterized in that, the radius of described manhole is 200-600 μm.

10. bubbling method as claimed in claim 1, it is characterized in that, the tilt angle alpha of the sample bench of scanning electron microscope is 3 ° ~ 10 °.