This article introduces the resistance method to measure the thickness of the metal film, and compares the results with the optical interference method, which fully meets the requirements of the experimental teaching. The resistance method is used to measure the thickness of the metal film. The instrument used is cheap and easy to operate. This method can be widely used by students. Coating experiment film thickness measurement.
Vacuum coating technology has been continuously improved, and metal films have been widely used in optical thin film technology and semiconductor devices. 7 Vacuum coating technology is one of the basic experiments in modern physics experiment teaching. Due to limited conditions, the measurement of metal film thickness has not been widely carried out. , the following introduces a simple and applicable method for measuring the thickness of metal films
Experimental principle
Experiments have shown that the resistance of a conductor is related to the geometry and temperature of its material. For a conductor with a uniform cross-section made of a certain material, its resistance is determined by the following formula:
R=l/S
Where l is the length of the conductor, ) is the cross-sectional area of the conductor, and s is the resistivity determined by the material and temperature of the conductor . When the temperature is not too low and the temperature range is small, there is approximately the following linear relationship between the resistivity of pure metals and the temperature
ρ= ρ 0 (1+ αt )
Among them, ρ and ρ 0 represent the resistivity at t°C and 0°C, and α is the temperature coefficient of resistance. This α depends on the type of material, and ρ 0 and α can be obtained by looking up the table.
As shown in the figure above, let the length, width, and thickness of the aluminum-plated metal film be L, W, and H respectively, and the resistance of the aluminum metal film can be calculated by the above formula:
R= ρ(L/W×H）
And the thickness of aluminum metal is:
H= ρ(L/W×R)
In this way, knowing the length L, width W, resistance R and resistivity ρ of the aluminum film, the thickness H of the aluminum film can be calculated according to the above formula.
experimental method
For the convenience of measurement, the aluminum film is plated on the rectangular glass, the length L and width W of the aluminum film are measured with a vernier caliper, and the resistance R of the aluminum metal film at room temperature is measured with a QJ42 portable DC double-arm bridge. Look up the table and get ρ 0 =2.5×10 -8 Ωm, α=4.7×10 -3 ℃ -1 of metal aluminum , calculate the value of ρ at room temperature through the formula , put L, W, R and ρ into (3 ) formula, the thickness H of the aluminum metal film at room temperature can be calculated.
The key to measuring the thickness of the metal film by resistance is to accurately measure the resistance of the metal film, so the contact resistance is required to be small enough during the measurement process, which can be ignored compared with the resistance of the metal film.
On the rectangular glass sheet that has been coated with aluminum film, protect the part of the aluminum film to be tested with metal foil, and then plate a thicker copper film on the unprotected aluminum film as the measuring electrode, install the lead wire, and remove the protective cover. Metal foil can be used for resistance measurement.
Experimental results
Interference microscopy is often used to measure the thickness of the film. In order to illustrate the reliability of the resistance method to measure the thickness of the metal film, we used the optical interference method and the resistance method to measure the thickness of the same coated film. The measurement results are as follows:
In the table, h c and h 0 represent the film thickness measured by resistance method and light interferometry, respectively. The measurement results show that the measurement of metal film thickness by resistance method and the measurement of metal film thickness by interferometry have obtained the same satisfactory results. The measurement of film thickness by resistance method can fully meet the measurement requirements of metal film thickness in modern physics experiment teaching ∋ In order to reduce the system error , the resistance method needs to be coated twice to measure the thickness of metal film ∋ The first aluminum coating is to be tested, and the second copper coating The film is used as an electrode, and the thickness of the metal film is measured with an interference microscope. In order to observe the interference fringes produced by the thickness of the aluminum film to be measured , it is also necessary to perform two coatings . The two measurement methods are compared . The film thickness of the resistance method uses QJ42 portable DC dual The arm bridge is a general-purpose instrument in the laboratory . It is easy to operate, easy to adjust , convenient to read , and low in price . It is only one-thirteenth of the value of the interference microscope. Therefore , the resistance method to measure the thickness of metal films can be vigorously used in relevant colleges and universities. promote .
Author: Fang Zhiyuan, Department of Physics, Central CHINA Normal University
Source: "Physical Experiments", Volume 8, Issue 5
