JPH0749943B2 - Film thickness measurement method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention measures the film thickness of a sample by irradiating the sample with an electron beam at various accelerating voltages and measuring the accelerating voltage at which the characteristics of the reflected electron intensity from the sample change. Regarding the method.

[0002]

2. Description of the Related Art Conventionally, in measuring the thickness of a thin film, a stylus is brought into contact with the surface of the film, and this is scanned to measure the film thickness from the vertical movement of the stylus due to the unevenness of the film. For
It is necessary to read from the difference in the height of the stylus between the non-deposited surface and the deposited surface, but in order to do this, it is necessary to create an undeposited area on the same substrate. If the substrate itself has irregularities, accurate film thickness measurement cannot be performed.

[0003]

According to the present invention, it is not necessary to form a region not formed on a substrate, and the thickness of a thin film can be measured nondestructively and highly accurately regardless of the unevenness of the substrate itself. An object of the present invention is to provide a film thickness measuring method capable of performing the above.

[0004]

In order to achieve the above object, according to the present invention, electrons reflected by the thin film are irradiated by irradiating the thin film in the vacuum atmosphere with an electron beam whose acceleration voltage is changed vertically. Measure the intensity, detect the accelerating voltage whose characteristics change, and determine the film thickness at the electron beam irradiation position based on the relationship between the film thickness of the thin film substance prepared in advance and the accelerating voltage at which the characteristics of the reflected electron intensity change. It is characterized by measuring.

[0005]

In the method of the present invention, the relationship between the film thickness and the accelerating voltage at which the characteristics of the backscattered electron intensity change is obtained for the thin film forming substance to be measured in advance, and the information is input to, for example, a computer. Every other time, at the time of measurement, the electron beam irradiating device capable of accelerating the measurement point of the thin film irradiates the electron beam accelerated to the extent that the electron beam penetrates more than the thickness of the thin film,
The backscattered electrons generated by the irradiated electron beam detect the acceleration voltage that shows the characteristics from the underlayer of the thin film, and the detected value is loaded into the computer, etc., and the relationship between the film thickness and the acceleration voltage that has been input in advance is detected. Based on this, the film thickness for the detected value is calculated and measured.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 shows a schematic diagram of an apparatus for carrying out the present invention. The digital accelerating voltage signal generated by the computer 12 is controlled by the DA converter 8 in order to control the accelerating voltage.
It is converted and input to the electron gun 1. An electron beam emitted from an electron gun 1 arranged on the upper part of the apparatus passes through a focusing lens 2, a scanning coil 3 and an objective lens 4 to irradiate a sample 6.

In the middle of the objective lens 4 and the sample 6, two pieces are provided symmetrically with respect to the center axis on each of two orthogonal axes having an origin at an intersection with the center axis on a plane orthogonal to the center axis of the objective lens 4. A total of four backscattered electron detection elements 5 are arranged, and the backscattered electrons from the sample 6 are captured and converted into a backscattered electron signal. The four channels of backscattered electron signals from the backscattered electron detectors 5 arranged in axial symmetry are sequentially amplified through the amplifiers 9 and 10 for each channel and led to the AD converter 11.
The 12-bit digital signal is processed by the computer 12 in the process as described in detail below, and the data concerning the film thickness of the sample 6 is displayed on the display 13. In the scanning of the electron beam, the digital scanning signal generated by the computer 12 is supplied to the scanning coils 3 in both the horizontal and vertical directions via the DA converter 8, and the electron beam is deflected to perform surface scanning. This enabled the measurement of the film thickness distribution.

The relationship between the film thickness and the accelerating voltage at which the characteristic of the reflected electron intensity changes by the above measuring apparatus will be described in detail with reference to a sample in which gold is formed on a polystyrene substrate as an example.

FIG. 2 shows the result of measuring the backscattered electron signal from the sample by irradiating the sample with various film thicknesses with the electron beam vertically while changing the accelerating voltage. As the backscattered electron signal, the average value of the signals from the four detectors was used, and the influence of the shape of the sample on the signal was suppressed. The output signal increases almost in proportion to the increase of the acceleration voltage, but there is a break point where the slope changes at a certain acceleration voltage. FIG. 3 shows the relationship between the accelerating voltage value that causes a break and each film thickness. It is possible to measure this characteristic curve in advance, store the result in a computer, and measure the film thickness of a sample having a thin film of the same material based on this.

[0010]

According to the present invention, since the film thickness can be measured in a vacuum atmosphere, the film thickness distribution can be measured in the process of forming a thin film, which can be used for forming a high quality thin film. Further, the film thickness of the thin film can be measured nondestructively and highly accurately regardless of the unevenness of the substrate.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an apparatus for carrying out a film thickness measuring method of the present invention.

FIG. 2 is a diagram showing a relationship between an acceleration voltage and a backscattered electron signal in each film thickness using the above-described apparatus.

FIG. 3 is a relationship diagram between a film thickness and an acceleration voltage value that causes a break point.

[Explanation of symbols]

 1 Electron gun 2 Focusing lens 3 Scanning coil 4 Objective lens 5 Reflection electron detector 6 Sample 7 Exhaust pump 8 D-A converter 9 Signal amplifier 10 Signal amplifier 11 A-D converter 12 Computer 13 Display

Continuation of the front page (56) References JP-A-63-9807 (JP, A) Japanese Patent Publication 2-11842 (JP, B2)

Claims (1)

[Claims] 1. When the thin film is irradiated with electron beams accelerated by various acceleration voltages, the intensity of reflected electrons from the sample is measured,
By measuring the acceleration voltage whose characteristic changes linearly with the acceleration voltage at which the electron beam reaches the underlayer of the thin film, and based on the relationship between the film thickness of the thin film substance prepared in advance and the acceleration voltage whose characteristic changes linearly A method for measuring film thickness, which comprises measuring the film thickness at a position irradiated with a line.