CN111351702B

CN111351702B - Method for determining fracture strain of flexible substrate metal film

Info

Publication number: CN111351702B
Application number: CN202010194407.8A
Authority: CN
Inventors: 罗雪梅; 吴绪苹; 张广平; 宋竹满
Original assignee: Institute of Metal Research of CAS
Current assignee: Institute of Metal Research of CAS
Priority date: 2020-03-19
Filing date: 2020-03-19
Publication date: 2021-10-15
Anticipated expiration: 2040-03-19
Also published as: CN111351702A

Abstract

The invention discloses a method for determining fracture strain of a flexible substrate metal film, and belongs to the technical field of metal film mechanical property tests. The method comprises four steps: preparing a flexible base metal film into a tensile sample, performing a tensile test on the flexible base metal film, measuring the film resistance in situ, and using a formula delta R/R₀＝(1+ε)^m-1 initial phase of fitting the relative resistance change-strain curve, determining the strain at break of the film corresponding to a deviation of 5% of the experimental curve from the theoretical curve obtained by fitting. The invention can simply and effectively determine the fracture strain of the flexible substrate metal film. The method for determining the fracture strain of the flexible substrate metal film provided by the invention has a wide application range, and provides a new idea for evaluating the tensile property of the flexible substrate metal film.

Description

Method for determining fracture strain of flexible substrate metal film

Technical Field

The invention relates to the technical field of metal film mechanical property tests, in particular to a method for determining fracture strain of a flexible substrate metal film.

Background

Metal thin films are widely used as interconnects of microelectronic devices, and particularly in recent years, the rise of flexible electronic devices has led to the widespread attention on the electrical and mechanical properties of metal thin films on flexible substrates. Tensile properties are an important index for evaluating thin metal film interconnects. Therefore, it is important to determine the fracture strain of the flexible base metal thin film. The widely used method at present is to obtain a relative resistance change-tensile curve through a tensile test, and then deviate the experimental curve based on a formula delta R/R₀＝ε²The strain at 5% of the theoretical curve of +2 epsilon is determined as the breaking strain of the film. In some cases, however, the above theoretical formula does not reflect the resistance variation with strain during the stretching of the film very well, so that it is necessary to provide a more widely applicable method for determining the breaking strain of the metal film on the flexible substrate.

Disclosure of Invention

Aiming at the problem of how to determine the fracture strain of various flexible base metal films, the invention aims to provide a method for determining the fracture strain of the flexible base metal film, which has better universality compared with the existing method and provides a new technical means for evaluating the tensile property of the flexible base metal film.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

a method of determining the fracture strain of a flexible base metal film, the method comprising the steps of:

(1) preparing a metal film of a flexible substrate into a tensile sample;

(2) performing a tensile test on the tensile sample prepared in the step (1), measuring the resistance value of the metal film in the tensile process, and obtaining a relative resistance change-strain curve of the film in the tensile process, namely an experimental curve;

(3) using the formula Δ R/R₀＝(1+ε)^m-1 fitting experimental data points on the experimental curve at lower strain, the resulting fitted curve being referred to as a theoretical curve;

(4) the strain corresponding to a 5% deviation of the experimental curve from the theoretical curve was determined as the strain at break of the film.

In the step (1), the preparation process of the tensile sample comprises the following steps: firstly, preparing a metal film on a flexible substrate, and then cutting the flexible substrate with the metal film into a rectangular tensile sample.

In the step (2), the resistance measurement lead is fixed at the clamping end of the tensile sample (the lead is fixed on the metal film) by using the conductive adhesive tape, the resistance of the film is measured in situ by using a four-wire method, and a relative resistance change-strain curve is obtained.

In the step (3), the fitting process specifically includes: selecting any m value to preliminarily draw a formula delta R/R₀＝(1+ε)^m1, adjusting the value of m to make the plotted curve substantially coincide with the experimental curve obtained in the step (2) when the strain is small (the strain in the initial stage of the experimental curve is small); then selecting experimental data points on the experimental curve which are basically consistent with the drawn curve, and further using a formula delta R/R₀＝(1+ε)^m-1 fitting these data points accurately to obtain a theoretical curve.

In the above step (3), the formula Δ R/R₀＝(1+ε)^mIn-1, m is pseudoSum of parameters, Δ R/R₀ε is the strain for the relative resistance change.

The invention has the following advantages:

1. the invention provides a method for determining the breaking strain of a flexible substrate metal film, and perfects an evaluation method for the tensile property of the flexible substrate metal film. The method uses the formula Δ R/R₀＝(1+ε)^m-1 fitting the initial phase of the curve of relative resistance change versus strain when the film is stretched, determining the strain at break of the film corresponding to a deviation of the experimental curve by 5% from the theoretical curve obtained by the fitting.

2. The method for determining the fracture strain of the flexible substrate metal film is simple to operate, the obtained fracture strain result can accurately and effectively reflect the fracture of the flexible substrate metal film in the stretching process, and practice proves that: the strain at break obtained by this method corresponds to the strain at which a considerable amount of microcracks are generated when the film is stretched.

3. The method for determining the fracture strain of the flexible base metal film has wide applicability, can be used for the fracture strain of various flexible base metal films with different microstructures, expands the original method into a more universal application range by introducing the fitting parameter m, and is proved by practice that: the value of m is capable of reflecting the microstructure of the metal thin film to some extent.

Drawings

FIG. 1 is a schematic representation of a stretched sample prepared in example 1.

FIG. 2 is a schematic diagram of in-situ resistance measurement.

FIG. 3 is a graph showing the relative resistance change-strain curve and the equation Δ R/R for Ti films with different thicknesses on polyimide substrates in example 1₀＝(1+ε)^m-1 of a fitted curve.

FIG. 4 shows the breaking strain of Ti films with different thicknesses of polyimide substrates in example 1.

FIG. 5 is a graph showing the relative resistance change-strain curves and the equation Δ R/R for Cu-5 at% Al thin films with different thicknesses for the polyimide substrate in example 2₀＝(1+ε)^m-1 of a fitted curve.

FIG. 6 shows the fracture strain of Cu-5 at% Al films of different thicknesses of the polyimide substrate in example 2.

Detailed Description

The invention is described in detail below with reference to the figures and examples.

Example 1

In this embodiment, to determine the fracture strain of the magnetron sputtering Ti thin film with the thickness of 50nm, 100nm, and 300nm, the flexible substrate is polyimide with a thickness of 125 μm, the specific steps are as follows:

step 1: ti films of different thicknesses were all prepared into tensile test specimens of 3mm width and 10mm gauge length (FIG. 1).

Step 2: tensile tests were performed on tensile test specimens of Ti films and the sheet resistance was measured in situ using a four-wire method (fig. 2), and the resulting relative resistance change-strain curve is shown in fig. 3.

And step 3: selecting m-2 to draw the formula delta R/R preliminarily₀＝(1+ε)^m-1, adjusting the value of m to make the plotted curve substantially coincide with the experimental curve when the strain is small; then selecting experimental data points on the experimental curve which are basically consistent with the preliminarily drawn curve, and further using a formula delta R/R₀＝(1+ε)^m1, determining the value of m at that time, and fitting a curve (theoretical curve) as shown in FIG. 3, the values of the fitting parameter m also being indicated in the figure.

And 4, step 4: the strain corresponding to the deviation of the experimental curve from the theoretical curve by 5% was determined as the breaking strain of the film, and the breaking strain results are shown in fig. 4.

Example 2

In this example, to determine the fracture strain of magnetron sputtering Cu-5 at% Al thin films with thicknesses of 10nm, 200nm, and 1000nm, respectively, a flexible substrate is polyimide with a thickness of 125 μm, the specific steps are as follows:

step 1: cu-5 at% Al films with different thicknesses are prepared into tensile samples with the width of 6mm and the gauge length of 10 mm.

Step 2: tensile tests were performed on Cu-5 at% Al films and the film resistance was measured in situ, and the resulting relative resistance change-strain curve is shown in fig. 5.

And step 3: selecting m-2 to draw a formula delta R/R₀＝(1+ε)^m-1, adjusting the value of m to make the plotted curve substantially coincide with the experimental curve when the strain is small, then selecting the experimental data points on the experimental curve that substantially coincide with the plotted curve, and further using the formula Δ R/R₀＝(1+ε)^m1, determining the value of m at that time, and fitting a curve as shown in FIG. 5, wherein the values of the fitting parameter m are also indicated.

And 4, step 4: the strain corresponding to the deviation of the experimental curve from the theoretical curve by 5% was determined as the strain at break of the film, and the strain at break results are shown in fig. 6.

Claims

1. A method of determining the fracture strain of a flexible base metal film, characterized by: the method comprises the following steps:

(1) preparing a metal film of a flexible substrate into a tensile sample;

(3) using the formula Δ R/R₀＝(1+ε)^m-1 fitting experimental data points on the experimental curve at lower strain, the resulting fitted curve being referred to as a theoretical curve; the fitting process specifically comprises the following steps: selecting any m value to preliminarily draw a formula delta R/R₀＝(1+ε)^m1, adjusting the value of m to make the plotted curve substantially coincide with the experimental curve obtained in step (2) when the strain is small; then selecting experimental data points on the experimental curve which are basically consistent with the drawn curve, and further using a formula delta R/R₀＝(1+ε)^m-1 performing a precise fit on the data points to obtain a theoretical curve; the formula Δ R/R₀＝(1+ε)^mIn-1, m is a fitting parameter,. DELTA.R/R₀Is the relative resistance change, and epsilon is the strain;

2. The method of determining the breaking strain of a flexible base metal film of claim 1, wherein: in the step (1), the preparation process of the tensile sample comprises the following steps: firstly, preparing a metal film on a flexible substrate, and then cutting the flexible substrate with the metal film into a rectangular tensile sample.

3. The method of determining the breaking strain of a flexible base metal film of claim 1, wherein: in the step (2), a resistance measurement lead is fixed at the clamping end of the tensile sample by using a conductive adhesive tape, the resistance of the film is measured in situ by using a four-wire method, and a relative resistance change-strain curve is obtained.