JP2861032B2 - Film thickness measurement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] Regarding a method for measuring the film thickness of a local portion of a thin film which is deposited on a substrate of which the material is known and has a film quality that allows an electron beam to be transmitted appropriately, (1) The resist thin film coated on the substrate is scanned with an electron beam probe, and the electrons which have passed through the resist thin film and reached the substrate are used to scan the material constituting the substrate. The generated characteristic X-ray intensity is measured, and the film thickness of the resist thin film is obtained from the previously determined relationship between the film thickness of the resist thin film and the characteristic X-ray intensity.

(2) When the electron beam probe irradiates the resist thin film deposited on the substrate with an electron beam probe, and the electrons that have reached the substrate through the resist thin film start generating characteristic X-rays from a substance constituting the substrate. The electron beam acceleration voltage is measured, and the thickness of the resist thin film is obtained from the relationship between the film thickness of the resist thin film and the acceleration voltage obtained in advance.

[Industrial applications]

The present invention relates to a method for measuring the film thickness of a local portion of a thin film which is deposited on a substrate of which the material is known and has a film quality that allows an electron beam to pass appropriately.

In recent years, along with the high integration of devices, it has become necessary to measure a very thin film thickness and a very fine local region.

Measurement of a very fine area requires a measurement system having a fine probe (measurement needle) of sub-micron or less, but the present invention can be used for such a purpose.

[Conventional technology]

Conventional methods for measuring film thickness include a method of physically scanning a step using a microneedle equipped with a sensor (a method using tally steps) and a method using optical interference, wavelength, deflection, intensity, and the like. .

However, the conventional method has a limitation that the probe size cannot be reduced so much.

[Problems to be solved by the invention]

When trying to measure the film thickness of a resist pattern having a thin line width of about 0.5 μm on a semiconductor device, the measurement could not be performed in the conventional example because the minimum value of the probe size was about several μm.

For example, in the case of a film thickness measuring instrument (ellipsometer) using elliptically polarized light, the minimum value of the probe size is about 20 μm.

An object of the present invention is to provide a method capable of measuring the film thickness of a minute region.

[Means for solving the problem]

To solve the above problems, (1) a resist thin film deposited on a substrate is scanned by an electron beam probe, and electrons are transmitted from the resist thin film and reach the substrate to be generated from a substance constituting the substrate. This is achieved by a film thickness measuring method in which characteristic X-ray intensity is measured, and the thickness of the resist thin film is determined from the relationship between the previously determined thickness of the resist film and the characteristic X-ray intensity. Or (2) when the resist thin film coated on the substrate is irradiated with an electron beam probe, and characteristic X-rays start to be generated from the substance constituting the substrate by the electrons that have passed through the resist thin film and reached the substrate. This is achieved by a film thickness measuring method of measuring the acceleration voltage of the electron thin film and obtaining the film thickness of the resist thin film from the previously determined relationship between the film thickness of the resist thin film and the acceleration voltage.

[Action]

 FIGS. 1 (1) and 1 (2) are the principle diagrams of the first invention.

In FIG. 1A, a thin film 2 to be measured, which is deposited on a substrate 3 and patterned, is scanned by a fine electron beam (EB) probe 1 on a film thickness measuring section, and a characteristic X-ray generated from the substrate is measured. Measure the strength and convert to a film thickness.

FIG. 1 (2) or the relationship of the characteristic X-ray intensity with respect to the scanning distance. The electron dose reaching the underlying substrate is reduced by the absorption of the electron beam in the thin film at the position of the thin film 2 to be measured. The intensity of the characteristic X-rays generated also decreases.

If the relationship between the characteristic X-ray intensity and the film thickness is determined in advance as shown in FIG. 3, the characteristic X-ray intensity is measured by the X-ray detector 4 and the film thickness can be measured from this.

FIG. 3 is a diagram showing the relationship between the characteristic X-ray intensity and the resist film thickness using the acceleration voltage as a parameter.

This relationship is for the case where a resist film is used as the thin film and A1 is used for the substrate.

 The acceleration voltage is higher in (2) than in (1).

 FIGS. 2A and 2B are diagrams illustrating the principle of the second invention.

In FIG. 2A, the EB probe 1 is fixed to a film thickness measuring unit, and the acceleration voltage of the EB probe is gradually increased, and the film thickness is determined from the acceleration voltage at which characteristic X-rays of the substrate are generated.

FIG. 2 (2) is a diagram showing the relationship between the acceleration voltage at which characteristic X-rays of the substrate are generated and the thickness of the thin film. If this relationship is determined in advance for the materials of the thin film and the substrate, the film thickness can be measured from the acceleration voltage at which characteristic X-rays of the substrate are generated.

FIG. 4 shows the relationship between the acceleration energy of electrons and the scattering range in the resin (resist). When a resist film is considered as a thin film, the range R of electrons irradiated on the resist film is expressed by the following equation.

R = 4.6 × 10 ⁻⁶ ρ ⁻¹ E ^1.75 . Here, R is the range of electrons in the resist in cm, E is the acceleration energy in KeV, and ρ is the laser density in g / cm ² .

From this equation, it is possible to estimate the magnitude of the acceleration energy of the electrons for the electrons to pass through the thin film and reach the substrate.

〔Example〕

 FIG. 5 is a sectional view for explaining one embodiment of the present invention.

In the figure, a resist film 2 patterned to a width of 0.5 μm on an Al substrate 3 is scanned by a fine EB probe 1 on a film thickness measuring portion, and the intensity of characteristic X-rays generated from the Al substrate is measured. The amount of change in the characteristic X-ray intensity is converted into a film thickness using a previously prepared calibration curve (the relationship in FIG. 3).

At this time, it is necessary to select an electron accelerating voltage which is equal to or higher than the energy of the characteristic X-ray kα _1,2 1487 eV of Al and an energy which transmits the resist appropriately.

Since the electrons are scattered in the resist and lose energy, the number of electrons reaching the Al substrate is reduced according to the film thickness, and the intensity of characteristic X-rays generated from the Al substrate is also reduced.

Further, by fixing the EB probe at the position to be measured, igniting the accelerating voltage of electrons, the film thickness can be obtained from the accelerating voltage at which characteristic X-rays start to be generated.

In each case, the EB probe is 100 mm to several μm.
Can be narrowed down to spots.

As the X-ray detector, an ordinary Geiger counter or scintillation counter used in an X-ray explanation system is used.

〔The invention's effect〕

As described above, according to the present invention, it is possible to measure the film thickness of a minute region.

For example, the film thickness of a fine resist pattern having a submicron width can be measured, and the cross-sectional structure of the device can be quickly investigated without destruction.

[Brief description of the drawings]

FIGS. 1 (1) and 1 (2) are the principle diagrams of the first invention, FIGS. 2 (1) and 2 (2) are the principle diagrams of the second invention, and FIG. FIG. 4 is a diagram showing the relationship between the characteristic X-ray intensity with respect to the thickness, FIG. 4 is a diagram showing the relationship between the scattering range in the resin and the accelerating voltage of the electrons, and FIG. . In the figure, 1 is an electron beam (EB) probe, 2 is a thin film to be measured (resist), 3 is a substrate, and 4 is an X-ray detector.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01B 15/00-15/08

Claims (2)

(57) [Claims] An electron beam probe scans a resist thin film deposited on a substrate, and a characteristic X-ray intensity generated from a substance constituting the substrate by electrons passing through the resist thin film and reaching the substrate. And measuring the thickness of the resist thin film from the previously determined relationship between the thickness of the resist thin film and the characteristic X-ray intensity. 2. A resist thin film deposited on a substrate is irradiated with an electron beam probe, and a characteristic X-ray is generated from a substance constituting the substrate by electrons which have passed through the resist thin film and reached the substrate. A film thickness measuring method, comprising: measuring an acceleration voltage of an electron beam at the time of starting; and calculating a film thickness of the resist thin film from a relationship between the film thickness of the resist thin film and the acceleration voltage obtained in advance.