JPS6037402B2 - How to measure film thickness - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring the thickness of a thin film material such as a deposited film.

Conventional methods for measuring film thickness include methods using various types of microscopes and methods using light interference.

With these methods, it is difficult to measure the thickness of particularly thin films. Another method uses secondary ions and photons emitted from the thin film surface by ion sputtering. These methods are destructive measurement methods, and the sample whose film thickness has been measured cannot be used again. In the present invention, after measuring the film thickness, the film is grown again. The present invention provides a method for non-destructively measuring film thickness, which can be used for thinning and other measurements. First, the principle of film thickness measurement according to the present invention will be explained.

Generally, each substance has a unique light absorption coefficient. Of course, the value differs depending on the wavelength of the light. When a substance is irradiated with light in a constant volume and pressure, a portion of the energy of the light is absorbed by the substance. The absorbed energy turns into heat. This light-to-heat exchange coefficient is determined by the probability of non-radiative transition from the excited state to the ground state of the system to be measured. Initially, the volume inside the measurement container, which is maintained at a certain pressure, is constant, so the pressure increases due to heat radiation from the substance. If the amount of irradiation light is kept constant, the pressure inside the container will change depending on the amount of substance present. Therefore, when there is a thin film formed by vapor deposition on a substrate with a certain thickness, if you irradiate it with light and examine the pressure change inside the container, you will find that the light absorption coefficient at each wavelength of the substrate material and the thin film material is The absorption energy spectrum can be obtained in the form of the sum of .

Therefore, if the thickness of the substrate is kept constant, changes in the thickness of the thin film and changes in the intensity of the absorption spectrum at each wavelength can be observed in correspondence. By creating absorption spectra corresponding to the type and thickness of the substrate material and the type and thickness of the thin film forming substance in advance, it is possible to know the thickness and type of the substrate of the unknown sample and the thin film formed on it. I can do it.

．． Hereinafter, the present invention will be explained by way of examples thereof.

FIG. 1 is a block diagram showing the configuration of a film thickness measuring device.
1 is a light source, and light emitted from the light source is focused by a lens 2 and enters a monochromator 3.

This light is separated into monochromatic colors by a monochromator 3, and then modulated by a chopper 4. The pulsed monochromatic light passes through the lens 5 and enters the sample S in the measurement container 6 . The window material 7 of the measurement container may be replaced depending on the wavelength of the irradiated light (ultraviolet rays, visible light, infrared rays, etc.). Usually, one made of fused silica is used. The measuring container 6 has a constant volume. The pressure inside the container is ~, Ne, Xe, K
Adjust using gas such as r. Reference numeral 8 denotes a pressure sensor such as a microphone that detects changes in pressure within the measurement container, and converts changes in pressure into electrical signals.

This electrical signal is amplified by a preamplifier 9, and extracted by a lock-in amplifier 10 as a signal synchronized with the signal from the chopper 4. Signal processing is performed by using the computer 11 or directly by the recorder 12. Second
The figure shows the intensity of the pressure signal in the measurement container corresponding to the wavelength of the incident light and the absorbed energy. Spectrum a is a spectrum of only the substrate, and spectrum b is a spectrum of the substrate and thin film. In spectra a and b,
The shapes of the spectra are obviously different. When the relationship between film thickness and signal intensity is investigated using light of a wavelength whose spectrum intensity changes significantly with respect to film thickness changes, a proportional relationship shown by the solid line in FIG. 3 is obtained within a certain range. Points c and d in FIG. 3 depend on the substrate material, the type and thickness of the deposited film material, and the performance of the measurement system. Using such a straight line, calculate the number 10
Films with a thickness of 0A or more can be measured. As described above, according to the present invention, non-destructive measurement is possible, and it is possible to measure from thin to thick films.

Furthermore, since average information can be obtained, the method has features such as small errors even in the case of samples with film thickness distribution.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a film thickness measuring device in an embodiment of the present invention, FIG. 2 is a diagram showing the relationship between the wavelength of incident light and the intensity of a pressure signal corresponding to absorbed energy, and FIG. It is a figure showing the relationship between film thickness and intensity of a pressure signal. 1... Light source, 2, 5... Lens, 3... Monochromator, 4... Chopper, 6... Measuring container, 8...
・Pressure sensor, 9...preamplifier, 12...recorder. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1 A film thickness measurement method characterized by determining the thickness of a thin film by irradiating a thin film sample with light in a container with a constant volume and constant pressure, and measuring the absorbed energy as a pressure change inside the container. Measuring method.