JPH0321804A - Method and device for measuring thickness of extremely thin film - Google Patents

Abstract

PURPOSE:To speedily and securely know that light interference occurs while the thickness of the extremely thin film is measured by measuring the quantity of transmitted infrared rays while varying the angle of incidence of infrared rays on the extremely thin film. CONSTITUTION:The extremely thin film F is run laterally to detect the output value of an infrared sensor 40 when infrared rays from a black body 10 pass through a 1st optical path and the output value of the sensor 40 when the infrared rays pass through a 2nd optical path OP2. Then the difference between both the output values is found and when the difference is smaller than a specific reference value, it is judged that the two output values are correct. When the difference is larger than the reference value, on the other hand, the smaller value between the two output values or none of them is used as the measured value of the extremely thin film thickness. Consequently, it is speedily and securely known that the light interference occurs, and the mismeasurement of the thickness due to the interference can be removed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method and apparatus for measuring the thickness of an ultra-thin film. [Prior Art] A conventional device for measuring the thickness of an ultra-thin film (for example, 0.5 to 207 zm) places an ultra-thin film between an infrared ms and an infrared sensor, and measures the infrared rays from an infrared source. An infrared sensor measures the transmitted infrared ml through an ultra-thin film, and the thickness of the film is determined based on this measured value. [Problems to be Solved by the Invention] When the thickness of a film becomes as thin as that of an ultra-thin film, interference occurs when infrared rays pass through the film. For example, when infrared rays are transmitted through a 3 pm thick film and interference occurs,
Only infrared radiation corresponding to a thickness of 4 JLm or 57Lm is transmitted through the film. In other words, interference occurs most when the thickness of the film is equal to half the wavelength of the light that passes through the film, and this interference reduces the amount of infrared light that passes through the film. The measured film thickness is thicker than the actual thickness. The present invention provides a method and apparatus for measuring the thickness of an ultra-thin film that can quickly and reliably determine that the interference has occurred when light interference occurs while measuring the thickness of the ultra-thin film. The purpose is to [Means for Solving the Problems] The present invention allows infrared rays from an infrared source to pass through an ultra-thin film, an infrared sensor measures the amount of infrared rays that has passed through, and based on this measurement value, the ultra-thin film is In this method, the amount of transmitted infrared rays is measured by sequentially changing the incident angle at which infrared rays from the infrared source toward the infrared sensor are incident on the ultrathin film. [Operation 1] The present invention measures the amount of transmitted infrared rays by sequentially changing the angle of incidence of infrared rays transmitted from an infrared source through an ultra-thin film and directed toward an infrared sensor into the ultra-thin film. If light interference occurs during measurement, there will be a difference in the amount of infrared rays received by the infrared sensor, allowing you to quickly and reliably know that interference has occurred. [Example] FIG. 1 is an explanatory diagram of an example of the present invention. In this embodiment, an extremely thin film F runs between a black body 10, which is an infrared source, and an infrared sensor 40, and the thickness of the running film F is instantaneously measured. A disk-shaped chopper 20 is installed between the black body IO and the film F.
The chopper is rotated by a motor 21. FIG. 2 is a plan view of the chopper 20 in the above embodiment. The chopper 20 is divided into six equal parts, each having two of three types of parts: a part with a through hole 24, a part with a shielding part 25, and a part with a total reflection mirror 22. A through hole 23 is provided below the mirror 22. FIG. 3 shows that in the above embodiment, the through hole 24 is located directly above the black body 10, and the infrared rays from the black body 10 directly pass through the film F, pass through the half mirror 33, and reach the infrared sensor 40. FIG. Note that, as shown in Figure 2, when the mirror 22 is positioned directly above the black body 10 in the figure, infrared rays from the black body 10 are reflected by the mirror 22, and this reflected light is reflected by total internal reflection. A mirror 3l is provided, and after the infrared rays reflected by the mirror 3l pass through the ultra-thin film F, it is reflected by the total reflection mirror 32, and this reflected light is reflected by the half mirror 33 and sent to the infrared sensor 40. Further, as shown in FIG. 3, when the through hole 24 of the chopper 20 is directly above the black body 10 in the figure, the infrared rays from the black body 10 are not reflected and are directly irradiated onto the polar FI film F. The light passes through the half mirror 33 and is sent to the infrared sensor 40. Note that the through hole 2 of the chopper 20
4 directly above the black body 10, it passes directly through the film F from the black body 10, passes through the half mirror 33, and heads toward the infrared sensor 40. Among this optical path, the chopper 20
The optical path between the half mirror 33 and the first optical path OPIJ
(indicated by a dashed line in Figure 1). Furthermore, when the mirror 22 is positioned directly above the black body 10 as shown in FIG.
1, 32, and 33, and heads toward the infrared sensor 40. Of this optical path, the optical path between the mirrors 31 and 32 is
It is called the second optical path OP2J (indicated by a solid arrow in Figure 1). Here, the optical path after the infrared rays passing through the first optical path OPI passes through the half mirror 33 is the same as the optical path after the infrared rays passing through the second optical path OP2 reflects the mirrors 32 and 33. The angle of each mirror 22, 3l, 32, 33 is set in advance. Also, when there is no ultra-thin film F between the black body 10 and the infrared sensor 40, the amount of infrared rays after passing through the first optical path OPI and the amount of infrared rays after passing through the half mirror 33, and the amount of infrared rays passing through the second optical path OP2. The reflectance of the mirrors 22, 31, 32, and 33 and the transmittance of the mirror 33 are set in advance so that the amount of infrared rays reflected by the mirrors 32 and 33 is the same. The black body lO, the through hole 24, and the half mirror 33 are an example of a first optical system in which infrared rays directed from an infrared source to an infrared sensor are incident on the ultrathin film at a first incident angle. Also, black body 1
0, the through hole 23, and the mirrors 22, 3l, and 32.32 are a second channel in which the infrared rays directed from the infrared source toward the infrared sensor are incident on the ultrathin film at a second incident angle different from the first incident angle. This is an example of an optical system. Next, the operation of the above embodiment will be explained. First, remove the ultra-thin film F from between the black body 10 and the infrared sensor 40, rotate the motor 21, and set it so that the through hole 24 is located directly above the black body 10 in FIG. Then, the infrared rays from the black body 10 pass through the first optical path OPl and reach the half mirror 33.
The amount of infrared rays after passing through the mirror 2 directly above the black body 10
2 is set, the infrared rays from the black body lO
Confirm that the amount of infrared rays after passing through optical path OP2 and being reflected by mirror 33 is the same. If at this time,
If the above two amounts of infrared rays (output values of the infrared sensor 40) are different, the infrared sensor 4 in either case
It is necessary to correct the output value of 0. Next, as shown in FIG.
The output value of the infrared sensor 40 when the infrared rays pass through the optical path OPI and the output value of the infrared sensor 40 when the infrared rays from the black body 10 pass through the second optical path OP2 are detected. The two output values are usually approximately the same or are the same, and in this case, it is determined that no light interference occurs and the output value of the infrared sensor 40 is correct. Specifically, the output value of the infrared sensor 40 when the infrared rays pass through the first optical path OPI, and the output value of the infrared rays when the infrared rays pass through the second optical path OPI.
The difference between the output value and the output value of the infrared sensor 40 when passing through P2 is determined, and when this difference is smaller than a predetermined reference value, it is determined that the two output values are correct. On the other hand, if the above difference is greater than or equal to the reference value, the smaller of the output values is used as the measurement value for the ultra-thin film thickness, or both output values are used to measure the ultra-thin film thickness. Avoid using it as a measurement value. By doing this, it is possible to quickly and reliably know that light interference is occurring, and also to eliminate erroneous thickness measurements due to the interference. In other words, since the angle of incidence of the first optical path OP1 on the ultra-thin film F and the angle of incidence of the second optical path OP2 on the ultra-thin film F are different, the film thickness value when the infrared rays pass through the first optical path OPI and the angle of incidence of the second optical path OP2 on the ultra-thin film F are different. Although it differs from the film thickness data obtained when passing through two optical paths OP2, the difference is slight. However, if the infrared rays passing through the first optical path OPI or the second optical path OP2 cause optical interference, the thickness value of one of the films becomes extremely large, and the above-mentioned difference becomes large. By detecting this difference, it is possible to know whether interference is occurring. In the above embodiment, the intersection angle (difference in incidence angle) between the first optical path OPI and the second optical path OP2 is approximately 5 to 10', but it may be set to a range other than that. In the above embodiment, only one black body 10 is provided, but in addition to the black body 10 shown in FIG.
Another black body may be provided at the lower left of 1, the mirror 31 may be removed, and the infrared rays from this other black body may be passed through the second optical path OP2. Further, in the above embodiment, only one infrared sensor is provided, but in addition to the infrared sensor 40, another infrared sensor is provided at the upper right of the mirror 32 in FIG. The infrared rays that have passed through the two optical paths OP2 may be received by another infrared sensor. Further, in the above embodiment, the optical path OPI. OP2 no 2
Although only one optical path is set, it is also possible to provide three or more optical paths with different incident angles and measure the thickness of the ultra-thin film F based on the infrared rays that have passed through the three or more optical paths. good. [Effects of the Invention] According to the present invention, when light interference occurs while measuring the thickness of an ultra-thin film, it is possible to quickly and reliably know that the interference has occurred.

[Brief Description of the Drawings] Figure 1 is an explanatory diagram of one embodiment of the present invention. FIG. 2 is a plan view of the chopper 20 in the above embodiment. FIG. 3 shows that in the above embodiment, the through hole 24 is located directly above the black body 10, and the infrared rays from the black body 10 directly pass through the film F, pass through the half mirror 33, and reach the infrared sensor 40. FIG. 33: n-7 mirror l 10...black body, 20...chopper, 22, 31, 32...total reflection mirror 33.../\-7 mirror 40...infrared sensor, F...・Ultra-thin film.

Claims (5)

[Claims] (1) Infrared rays from an infrared source pass through an ultra-thin film,
In a method in which an infrared sensor measures the amount of transmitted infrared rays, and the thickness of the ultra-thin film is measured based on the measured value, the infrared rays directed from the infrared source to the infrared sensor are incident on the ultra-thin film. A method for measuring the thickness of an ultra-thin film, characterized in that the amount of transmitted infrared rays is measured by changing the angle one after another. (2) Infrared rays from an infrared source pass through an ultra-thin film,
In an ultra-thin film thickness measuring device in which an infrared sensor measures the amount of transmitted infrared rays and measures the thickness of the ultra-thin film based on this measurement value, the infrared rays directed from the infrared source to the infrared sensor are 1
a first optical system that enters the ultra-thin film at an incident angle of; infrared rays directed from the infrared source toward the infrared sensor enter the ultra-thin film at a second incident angle different from the first incident angle; An ultra-thin film thickness measuring device comprising: a second optical system; (3) In claim (2), the infrared source and infrared sensor in the second optical system are common to the infrared source and infrared sensor in the first optical system, and the infrared rays from the infrared source in the first optical system are is intermittently reflected by two mirrors, this reflected light is transmitted through the ultra-thin film, this transmitted light is reflected by another mirror, and is sent to the infrared sensor in the first optical system. Ultra-thin film thickness measuring device. (4) In claim (2), when the ultra-thin film is not present, the amount of light received by the infrared sensor in the first optical system and the amount of light received by the infrared sensor in the second optical system are set to be equal. An ultra-thin film thickness measuring device featuring: (5) In claim (2), when the difference between the amount of light received by the infrared sensor in the first optical system and the amount of light received by the infrared sensor in the second optical system is a predetermined value or more, Ultra-thin film thickness characterized in that the smaller of the received light amounts is used as the measurement value of the ultra-thin film thickness, or both of the above-mentioned received light amounts are not used as the measurement value of the ultra-thin film thickness. measuring device.