JP2002131036A - Method and apparatus for measuring film thickness - Google Patents

Abstract

PROBLEM TO BE SOLVED: To highly precisely and quickly measure and control the film thickness of a specimen in film production due to deposition by a device in which a structure around the specimen is simple. SOLUTION: The film thickness measuring device comprises a board 11, an electron gun 12 for primary electron irradiation, a deposition device 13 for specimen deposition and a secondary electron detector 14. The electron gun 12 has a function capable of setting primary energy from 10 eV to 30 keV.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for measuring the thickness of a deposited film, and more particularly to a method and an apparatus suitable for dynamically measuring the deposited film thickness at an atomic layer level.

[0002]

2. Description of the Related Art When a thin film made of a material different from that of a substrate is formed on a sample surface serving as a substrate by a vacuum evaporation method, Auger signal intensity is used as a method of measuring the thickness of the deposited film at an atomic layer level. It is known to use the phenomenon of kink per atomic layer as a function of the deposited film thickness, for example, Thin Solid Films
Vol. 188 (1990), pp. 109-122. The method of measuring the film thickness of the sample based on the Auger signal intensity can be explained by the following principle.

[0003] Considering the case where a thin film having a thickness of one atomic layer d is present on a substrate, the signal intensity Is of Auger electrons from the substrate decreases when passing through the thin film, and Is =
Is0exp (-d / As). On the other hand, the signal intensity Id of Auger electrons from the thin film is Id = Id0 (1-e
xp (-d / Ad)). Here, Is0 is the value of Is when d is 0, Id0 is the value of Id when d is infinite, and As and Ad are the average escape depths of Auger electrons.

The signal intensity of Auger electrons emitted from the inside of a sample attenuates when passing through the upper layer. Therefore, the signal intensity of Auger electrons from the substrate and the thin film when the layered thin film whose n-th layer coverage is r is present on the substrate can be expressed by Equations 1 and 2, respectively. Here, Is1 and Id1 are the signal intensities of Auger electrons from the substrate and the thin film when the thin film is a single atomic layer.

[0005]

[Equation 1] Isn (r) = Is0 ((Is1 / Is0) ^ (n−1)) (1+ (Is1 / Is0−1) r)... (1)

[0006]

[Expression 2] Idn (r) = Id0 (1 − ((Id1 / Id0) ^ (n−1)) (1− (Id1 / Id0) r))... (2) During the deposition of a thin film sample on a substrate, the signal intensity of Auger electrons changes linearly during the formation of each layer, but at the completion of the formation of each layer, the gradient changes discontinuously, resulting in a kink. It is observed as Therefore, it is possible to measure the film thickness at the atomic level by measuring the discontinuous change of the gradient, that is, the position of the kink.

[0007]

However, in the above-mentioned prior art, only minute Auger electrons must be selected and collected from all the electrons emitted from the vicinity of the sample surface. A dedicated electron optical system (energy analyzer) with resolution had to be prepared. In addition, the energy analyzer for selecting the Auger electrons has a complicated structure, is expensive, and detects the Auger electrons having a weak signal intensity. Therefore, it takes time to measure the signal, and the deposition rate cannot be increased. And so on.

In addition, the energy analyzer for detecting Auger electrons must be installed sufficiently close to the sample surface, and therefore, a special sample stage for preventing the deposition material from being impeded on the substrate surface. Not only is required,
This complicates the configuration around the sample, and also causes a problem that handling of the device becomes difficult.

It is an object of the present invention to provide a method and an apparatus for measuring a film thickness in which an energy analyzer can be installed at a certain distance from the surface of a sample, thereby eliminating the need for a special sample stage. It is another object of the present invention to provide a method and an apparatus for measuring a film thickness, in which it is not necessary to select only minute Auger electrons from all the electrons emitted from a sample.

Still another object of the present invention is to provide a method and an apparatus for measuring the thickness of a film, in which the structure around the sample is simple and the handling of the apparatus is easy. Still another object of the present invention is to provide a method and an apparatus for measuring the thickness of a film, which can increase the deposition rate of a sample as compared with the case of measuring the film thickness using Auger electrons.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to reduce the phenomenon that the intensity of secondary electrons emitted from the surface of a sample during vacuum deposition causes a kink per atomic layer thickness as a function of the film thickness of the sample. It is solved by using.

The phenomenon that the intensity of secondary electrons shows a kink for each atomic layer can be explained by the following principle. Now, consider a case where a sample having a thickness of one atomic layer T is vacuum-deposited on a substrate. When a sample is irradiated with primary electrons, the yield of secondary electrons emitted from the sample surface changes depending on the type of the sample. Therefore, the secondary electron yield for the substance A constituting the substrate is IA, and that for the vapor deposition sample B is IB. When the sample B is deposited on the substrate surface, the intensity of the secondary electrons gradually changes as a function of the thickness of the deposited sample. Assuming that one atomic layer of the sample B is deposited on the substrate by the vacuum deposition, the intensity of secondary electrons emitted from the surface of the sample is quantitatively expressed as follows.

First, the intensity at which secondary electrons generated inside the substrate are emitted into a vacuum is approximately IAexp based on empirical rules.
(−T / LB). Here, LB is an amount called the escape depth of the secondary electrons from the vapor deposition sample B, and the ratio of the secondary electrons generated inside the substrate due to the vapor deposition of the sample B onto the substrate and jumping out into the vacuum is 1 / e. Is given as the thickness of the deposited sample. On the other hand, secondary electrons are also emitted from the sample deposited on the substrate surface, but the yield is IB (1
-Exp (-T / LB)).

Therefore, the total secondary electron intensity emitted from the sample surface is the sum of the two, and is given by Equation 3.

[0015]

IAexp (−T / LB) + IB (1−exp (−T / LB)) (3) Therefore, a thin film composed of the (m−1) layer of the sample B exists on the substrate, When the coverage of the m-th layer, which is the uppermost layer, is q, the intensity I (q) of all the secondary electrons emitted from the sample surface is given by Expression 4.

[0016]

I (q) = (1−q) (IAexp (− (m−1) T / LB) + IB (1−exp (− (m−1) T / LB))) + q (IAexp (− (m) T / LB) + IB (1−exp (− (m) T / LB))) (4) Since this equation is a linear function of q, it is a secondary function during actual vacuum deposition. The intensity of the electrons changes linearly during the formation of each layer, and the gradient changes discontinuously when the formation of each layer is completed. As described above, the phenomenon in which the intensity of the secondary electrons shows a kink for each atomic layer can be explained. This makes it possible to know the thickness of the sample during vacuum deposition with an accuracy of one atomic layer or less, as in the case of the film thickness measurement method using Auger electron signal intensity.

According to the present invention, since the yield of the secondary electron intensity is much higher than that of the Auger electron signal intensity,
When a sample is formed by a vacuum evaporation method, highly accurate film thickness measurement can be performed even at a higher evaporation rate.

Further, in the present invention, since it is not necessary to select only weak Auger electrons, a high-sensitivity and high-resolution energy analyzer, which is indispensable for measuring the Auger electron signal strength, is not required. Further, in the present invention, since there is no need to dispose the energy analyzer in close proximity to the sample surface, a special sample stage as in the prior art is not required, and handling such as operation or maintenance of the apparatus becomes easy.

Here, the energy of the primary electrons may be larger than about 10 eV, which is the minimum energy at which the secondary electrons can be excited from the substrate and the deposited film. In order to see the kink more clearly, the substrate sample A and the vapor deposition
The energy at which the difference in the secondary electron yield increases may be appropriately selected and used.

Further, the energy of the primary electrons at which the kink of the secondary electron intensity appears most remarkably may vary depending on the plane orientation and crystallinity of the sample. Therefore, by changing the energy of the primary electrons according to the plane orientation and the crystallinity of the sample, the present method may be used under the optimum condition where the kink of the intensity of the secondary electrons appears most remarkably.

[0021]

FIG. 1 is a diagram showing a first basic configuration of an embodiment of a film thickness measuring method and apparatus according to the present invention.
In this configuration, a substrate 11, an electron gun 12 for irradiating the substrate 11 with primary electrons, a vapor deposition device 13 for vapor-depositing a sample on the substrate 11, and 2
It comprises a secondary electron detector 14 for measuring the intensity of secondary electrons. Here, the electron gun 12 converts the energy of the primary electrons to 10 e
It has a function that can be freely set from V to 30 keV.

In this configuration, the vapor deposition device 13
While the sample is being deposited using
Irradiate primary electrons having an energy of 000 eV. At this time, the intensity of secondary electrons emitted from the sample surface is measured by the secondary electron detector 14. The measured intensity of the secondary electrons monotonically decreases or increases as a function of the thickness of the sample formed on the substrate 11. At this time, as described above, the intensity of the secondary electrons during the vacuum deposition changes linearly during the formation of each layer, but the gradient changes discontinuously at the completion of the formation of each layer. And kink occurs at the film thickness.

FIG. 2 shows how the secondary electron intensity increases when iron is used as the substrate 11 and gold is used as the sample. When the energy of the primary electrons is 2000 eV, the secondary electron yield for gold is larger than that for iron, so that the total secondary electron intensity increases as the deposition amount of gold increases. Therefore, as shown in FIG. 2, the secondary electron intensity exhibits a behavior that gradually increases as a function of the thickness of the gold deposition film.

As described above, the kink appearing in FIG. 2 is equal to the thickness of one atomic layer of gold. Therefore, by calibrating the gold film on the horizontal axis using the position of the kink, an accurate gold thin film can be formed. You can see the thickness. Therefore, by using this phenomenon, it is possible to measure the film thickness with high accuracy in one atomic layer or less.

Further, as described above, the energy of primary electrons where the kink of the intensity of secondary electrons appears most remarkably may vary depending on the type of sample, plane orientation, and crystallinity. In this embodiment, as an example, the energy of primary electrons is set to 2000 eV.
But depending on the sample type, plane orientation, and crystallinity,
By changing the energy of the secondary electrons, the present method may be used under the optimum condition where the kink of the secondary electron intensity appears most remarkably.

FIG. 3 is a diagram showing a second basic configuration of an embodiment of the film thickness measuring method and apparatus according to the present invention. This configuration includes a substrate 11, an electron gun 12 for irradiating the substrate 11 with primary electrons, and a vapor deposition apparatus 1 for vapor-depositing a sample on the substrate 11.
3, a secondary electron detector 14 for measuring the intensity of the secondary electrons hit by the primary electrons, and a computer 31 for controlling these devices, collecting data, and displaying images. Here, it is assumed that the electron gun 12 has a function of freely setting the energy of primary electrons from 10 eV to 30 keV.

In this configuration, the vapor deposition device 13
While the sample is being deposited using
Irradiate primary electrons having an energy of 000 eV. At this time, the intensity of secondary electrons emitted from the sample surface is measured by the secondary electron detector 14.

Here, by performing the following primary electron irradiation method, it is possible to monitor the film thickness at an arbitrary position in the visual field while monitoring the sample surface image. That is,
The sample surface image is generally the same as a method for obtaining a scanning electron microscope image. When primary electrons are scanned in the sample plane, the intensity of secondary electrons emitted from the irradiation point of the primary electrons is determined by the brightness of the point. The signal is obtained by forming an image on the monitor of the computer 31 in synchronization with the scanning signal of the primary electron.
In obtaining the sample surface image, all the device control and the imaging process may be performed using the computer 31.

When obtaining an image of the sample surface, if an arbitrary point within the scanning range of the primary electrons is defined as the X point, the change with time of the intensity of the secondary electrons emitted when the primary electrons irradiate the X point is obtained. , 2
The measurement is performed using the secondary electron detector 14. The intensity of the secondary electrons measured in this way monotonically attenuates or increases as a function of the thickness of the sample formed on the substrate 11, as in the first embodiment.

At this time, as described above, the intensity of the secondary electrons during the vacuum deposition changes linearly during the formation of each layer, but the gradient becomes discontinuous when the formation of each layer is completed. And a kink occurs in the film thickness. Since this kink is equal to the thickness of one atomic layer of the deposition material, highly accurate thin film measurement at one atomic layer or less can be performed by using the position of this kink. Because the film thickness can be measured,
The film thickness can be measured at an arbitrary position in the sample surface image while monitoring the sample surface image. Further, by monitoring the kink position of the above-mentioned change in the secondary electron intensity by the computer 31, the film thickness measurement is automated.

Further, as described above, the energy of the primary electron where the kink of the intensity of the secondary electron appears most remarkably may vary depending on the type, plane orientation, and crystallinity of the sample. In the present embodiment, the energy of the primary electrons is set to about 2000 eV as an example. However, by changing the energy of the primary electrons according to the type, plane orientation, and crystallinity of the sample, the kink of the intensity of the secondary electrons is most remarkable. The method may be used under the optimal conditions appearing in the above. At this time, the kink measurement of the change in the secondary electron intensity and the control of the electron gun 12 are performed by the computer 31, thereby enabling automation.

Further, in this embodiment, the control of the vapor deposition rate can be automated by monitoring the film thickness with respect to the vapor deposition time by the computer 31 and controlling the vapor deposition apparatus 13 so that the vapor deposition rate becomes an arbitrary rate.

Further, in this embodiment, the film thickness with respect to the vapor deposition time is monitored by the computer 31, and when the target film thickness is obtained, the vapor deposition is automatically stopped by the computer 31, so that a sample having an arbitrary film thickness can be produced. Can be automated. At this time, the information on the target film thickness may be input to the computer 31 in advance.

[0034]

According to the present invention, since it is not necessary to select and collect only minute Auger electrons from all the electrons emitted from the vicinity of the sample surface, it is necessary to bring the electron optical system sufficiently close to the substrate surface. There is an effect that it is possible to provide a method and an apparatus for measuring a film thickness that does not occur. Further, according to the present invention, there is an effect that a special sample stage that does not prevent the deposition material from being incident on the substrate becomes unnecessary.

Further, according to the present invention, it is not necessary to select only minute Auger electrons from all the electrons emitted from the sample, so that an electron optical system having sufficient brightness and high energy resolution is not required. . Further, according to the present invention, there is an effect that the configuration around the sample is simplified, thereby facilitating the handling of the apparatus. Further, according to the present invention, there is an effect that the vapor deposition rate of the sample in the vacuum vapor deposition method can be higher than in the case of using Auger electrons. The application of these effects to academic fields, and their industrial value, is very high.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first basic configuration of the present invention.

FIG. 2 is a diagram showing a kink of a secondary electron intensity change obtained by the present invention.

FIG. 3 is a diagram showing a second basic configuration of the present invention.

[Explanation of symbols]

11 ... substrate, 12 ... electron gun, 13 ... vapor deposition device, 14 ... 2
Next electron detector, 31 ... computer.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2F067 AA27 BB18 EE10 HH06 JJ05 KK04 QQ01 SS15 2G001 AA03 AA09 BA07 CA03 GA01 HA01 JA02 KA11 LA02 MA05 NA10 NA12 NA17 RA08 5C033 RR08

Claims (6)

[Claims] 1. During the preparation of a thin film sample by vacuum deposition, a change in the intensity of secondary electrons emitted by irradiating the sample surface with primary electrons is kinked at every atomic layer thickness as a function of the film thickness of the sample. A film thickness measuring method characterized by utilizing a phenomenon that causes the film thickness. 2. The method according to claim 1, wherein the use of an electron gun having a function of setting the primary electron energy to an arbitrary value allows the kink of the secondary electron intensity change to appear most clearly.
A film thickness measuring method characterized by selecting and using energy of a secondary electron. 3. A means for forming a vapor-deposited film on the surface of a sample by vacuum vapor deposition, means for irradiating the surface of the sample with primary electrons for forming the vapor-deposited film, and emission from the surface of the sample by irradiation of the primary electrons. Means for measuring the intensity of secondary electrons;
A film thickness measuring device comprising means for detecting a kink portion of a change in intensity of a next electron. 4. A film thickness measuring apparatus according to claim 3, wherein said means for irradiating said primary electrons is provided with a function capable of setting the energy of said primary electrons to an arbitrary value. 5. An electron gun for irradiating a sample with primary electrons, a vapor deposition device for vapor-depositing a substance on the sample,
A secondary electron detector for measuring the intensity of the secondary electron hit by the secondary electron, and for setting the energy of the primary electron emitted from the electron gun to a desired value from 10 eV to 30 keV. 5. The method and apparatus for measuring a film thickness according to claim 3, wherein: 6. An electron gun for irradiating a sample with primary electrons, a vapor deposition apparatus for vapor-depositing a substance on the sample, and a secondary device for measuring the intensity of secondary electrons hit by the primary electrons. An electron detector, means for scanning a finely focused primary electron beam emitted from the electron gun on the surface of the sample, and an intensity of secondary electrons emitted from the surface of the sample by the primary electron by a scanning electron microscope. 6. A film thickness measuring apparatus according to claim 3, further comprising means for observing the progress of deposition of the sample in real time by using a luminance signal of a monitor by a method.