JPH1137725A - Method for measuring film thickness distribution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method by which the thickness of a film to be measured, which has different thicknesses in projecting section and recessed section on the base step of a semiconductor substrate, can be measured simultaneously after a CPM step in a semiconductor manufacturing process. SOLUTION: The thickness of a film 6 having different thicknesses on the uneven surface of a semiconductor substrate 5 on projecting sections and recessed sections on the base step of the substrate 5 is simultaneously measured by irradiating the film 6 with light from a multi-wavelength oscillation coherent light source 1 and detecting the intensity spectra of reflected light rays caused by intra-film reflection by separating the spectra for every prescribed plural wavelength, and then, performing spectrum separation on the detected results for every film thickness of the film 6. In the method, the spectrum separation is performed for every film thickness by the method of least squares by using the intensity spectra of reflected light rays with respect to detected wavelength components and the calculated values of intensity spectra of the reflected light rays at a previously deduced wavelength and at every prescribed thickness of the film 6 or the actually measured values of the intensity spectra of the reflected light rays at a prescribed wavelength of a previously prepared standard sample and at every prescribed thickness of the film 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for measuring a film thickness distribution in a method for manufacturing a semiconductor device, and more particularly to a method for simultaneously measuring the thickness of a film to be measured formed on an uneven portion on the surface of a semiconductor substrate.

[0002]

2. Description of the Related Art As a conventional example of a method of measuring the thickness of an insulating film formed on an uneven portion on the surface of a semiconductor substrate, measurement is performed by an interference film thickness meter utilizing light interference. This method monitors interference intensity corresponding to a change in wavelength, and obtains a film thickness from wavelengths at two interference intensity peaks as disclosed in, for example, Japanese Patent Application Laid-Open No. 64-57107.

The above publication discloses a method for measuring a resist film thickness distribution on a patterned wafer by using a method of measuring an interference pattern intensity with respect to wavelength and an interference pattern intensity measured at each sample point. Means for determining the distribution are disclosed.

[0004] The basic principle of measurement is to use the interference between the reflected light of the incident light from the surface of the film to be measured and the light reflected from the interface of the base film of the film to be measured. For example, when the thickness of the film to be measured is d and the refractive index is n, when the wavelength λ of the incident light is changed, the reflected light intensity becomes strong when 4d / (n × λ) is an integer multiple of an even number. , When it is an odd integer multiple. If the wavelengths of adjacent peak values of the reflected light intensity are λ ₁ and λ ₂ , respectively, then (2d / n) (1 / λ ₂ -1 / 1 /
λ ₁ ) = 1 holds.

The film thickness d is obtained from the above relational expression. In actual measurement, the incident light can be narrowed down to only about 10 μm at most, so in consideration of the influence of the edge of the incident light area, a film with a thickness of about 20 to 30 μm is usually provided for film thickness measurement. We are measuring the thickness. Then, the average film thickness of the region prepared for the film thickness measurement is obtained according to the above principle.

[0006]

Since the measurement is performed as described above, according to the conventional film thickness measurement technique, the film thickness as point data or the average of the area having a certain size is used. Only a film thickness was obtained. Regarding the average film thickness in the illumination area of incident light, CMP (Chemical Mechanical
l Polishing) has a strong pattern dependence, and the thickness of the film depends on the size of the pattern. There is also a problem that the result is different between the thickness of the remaining film and the thickness of the actual remaining device pattern.

Further, in a semiconductor device manufacturing process, a film to be measured 6 is formed on the surface of a semiconductor substrate 5 having irregularities as shown in FIG.
When the step pattern obtained by polishing the fine pattern is a fine pattern of the order of μm or less, the diameter of the light to be incident on the semiconductor substrate is much larger than that. a, it was impossible to measure the thickness b of the film to be measured on the concave portion.

[0008] The present invention solves the above problem by using CMP.
It is an object of the present invention to provide a method capable of simultaneously measuring the film thickness of a film to be measured on a convex portion and a concave portion of a semiconductor substrate base stage having different film thicknesses after performing the above.

[0009]

According to the present invention, there is provided a method for measuring a film thickness distribution, comprising irradiating a film to be measured formed on an uneven surface on a semiconductor substrate with light from a multi-wavelength oscillation coherent light source. The reflected light intensity spectrum generated by the internal interference is detected separately for each of a plurality of predetermined wavelengths, and the reflected light intensity spectrum related to the detected wavelength component is the wavelength of the incident light by the multi-wavelength oscillation coherent light source, Based on the theoretical relationship between the refractive index and the thickness of the film to be measured, the spectrum is separated for each of the different film thicknesses of the film to be measured, and the film thickness of the film to be measured on the convex portions and the concave portions of the semiconductor substrate base stage is simultaneously measured. I do.

In the spectrum separating method, the reflected light intensity spectrum relating to the detected wavelength component is obtained by calculating a reflected light intensity spectrum for each of a predetermined wavelength and a predetermined thickness of a film to be measured, Alternatively, the spectrum is separated for each film thickness by the least square method using a predetermined wavelength prepared by a standard sample of the film to be measured and an actually measured value of the reflected light intensity spectrum for each predetermined film thickness of the film to be measured.

[0011]

According to the method of measuring the film thickness distribution of the present invention, the reflected light spectrum dependent on the wavelength obtained by irradiating the light on the actual device is converted into the wavelength λ _{k of the} incident light, the refractive index n and the thickness of the film to be measured. Based on the theoretical relationship of d _p , (2d _p / n) (1 / λ _{k + 1}
-1 / λ _k ) = 1 to separate the spectrum corresponding to the film thickness on the semiconductor substrate unevenness by spectrum separation, and to derive the film thickness on the semiconductor substrate unevenness using this spectrum. Will be able to

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be specifically described below with reference to the drawings. 1 and 2 show schematic configuration diagrams of a measurement system according to an embodiment of the present invention. As shown in FIG. 1, the measuring system of the present embodiment is configured such that polychromatic light from a multi-wavelength oscillation coherent light source 1 is incident on a semiconductor substrate 5 and reflected light interfered by a film to be measured 6 is converted by a monochromator 3. Spectroscopy,
The reflected light intensity for each wavelength is detected by the photomultiplier tube 4.

Alternatively, as shown in FIG. 2, the measuring system disperses the polychromatic light emitted from the multi-wavelength oscillation coherent light source 1 by the monochromator 3 and then makes it incident on the semiconductor substrate 5 to be measured. The intensity of the reflected light that has been interfered by 6 may be detected by the photomultiplier 4. The light incident on the semiconductor substrate 5 is focused to about 20 μmφ by a lens system (not shown in FIGS. 1 and 2).

As shown in FIG. 6, a measurement sample is formed by forming a film 6 to be measured on the surface of a semiconductor substrate 5 having irregularities,
The film to be measured 6 is polished by the P method. this is,
This is a state in the middle of a process usually performed in a semiconductor device manufacturing process, and a step pattern is a fine pattern of μm order or less.

In this embodiment, silicon is used as the semiconductor substrate 5 and a silicon oxide film having a refractive index of 1.47 is used as the film 6 to be measured. The step pattern is a line and space of about 1 μm, and the height of the step is 900 nm.

When the measurement sample shown in FIG. 6 is measured using the measurement system shown in FIG. 1 or 2 and the wavelength is scanned by the monochromator 3, the wavelength spectrum shown in FIG. 3 is obtained. This is a combination of the reflected light from the film thickness a on the convex portion and the reflected light from the film thickness b on the concave portion in FIG.

Hereinafter, a method of analyzing the film thickness according to the first embodiment of the present invention will be described. In general, the reflected light intensity I from the film thickness d is represented by the following formula: I = COS ² (4 · π · d / n · λ) (1)

Therefore, the intensity Ia of reflected light from the film thickness a on the convex portion is expressed by the following formula: Ia = COS ² (4 · π · a / n · λ) (2)

The intensity Ib of reflected light from the film thickness b on the concave portion
Is expressed as Ib = COS ² (4 · π · b / n · λ)... (3) As a result, the spectrum Is detected by the photomultiplier tube is Is = Ia + Ib = X · COS ² (4 · π · a / n · λ) + Y · COS ² (4 · π · b / n · λ) ... (4)

Here, n is the refractive index of the film to be measured, and is 1.47 in this embodiment. Λ indicates a wavelength.
X and Y are coefficients depending on the area of the convex and concave portions of the step of the semiconductor substrate 5. The region of the incident light incident on the semiconductor substrate 5 includes a large number of uneven portions, and depends on the ratio of the area corresponding to the uneven portions. Here, since the purpose is to obtain the values of the film thickness a and the film thickness b, the following calculation is performed.

First, reflected light spectra for various film thicknesses are obtained numerically in advance by the above equation (1).
Here, k + 1 types of film thickness are obtained. That is, the film thickness d
Divides the value from 0 to L into k equal parts, and obtains the wavelength spectrum when d is d _p = Lp / k (p is a natural number from 0 to k) (5). As the value of L (maximum thickness), the value of the film to be measured formed before polishing by CMP is input.

Here, a numerical calculation is performed for each value obtained by equally dividing the wavelength λ between 350 and 800 (nm), for example, every 2 nm. That is, the film thickness is _{d p (= L · p /} k), when the wavelength is lambda _l,
The reflected light intensity and I (p, λ _l). I (p, 350), I (p,
352), I (p, 354),…, I (p, λ _l ),…, I (p, 79
6), a data set of I (p, 798) and I (p, 800) is set as one set, and k + 1 sets in which p is 0 to k are registered. Next, the measured reflected light intensity spectrum in the case of lambda is lambda _l
Is, I (350), I (352), I (354),…, I (λ _l ),…, I (7
96), I (798), and I (800).

Then, P (X, Y, p, q) = (I (350) − (X · I (p, 350) + Y · I (q, 350))) ² + (I (352) − (X · I (p, 352 ) + Y · I (q, 352))) 2 + (I (354) - (X · I (p, 354) + Y · I (q, 3 54))) 2 + …… + (I (λl)-(X II (p, λl) + Y II (q, λl))) ² + …… + (I (800)-(X II (p, 800) + Y · I (q, 800))) ² …… (6)

Here, p and q are repeatedly calculated for each combination of 0 to k in equation (5) of the preset database. For X and Y, X is a value obtained by dividing a value from 0 to 1 into x values, and Y is a value obtained by repeatedly dividing a value from 0 to 1 into y values.
That is, the value of P (X, Y, p, q) in equation (6) is (x + 1)
(y + 1) ・ (k + 1) ^Two are obtained.

The smallest P (X, Y, p,
In the combination of X, Y, p, and q, q), p and q indicate the thicknesses of the films to be measured on the convex portions and the concave portions, respectively, of the measurement sample.

Putting the obtained p and q into the equation (5),
The respective film thicknesses a and b are obtained, and the above-mentioned a and b are further expressed as (2)
In the equations (3), the spectra shown in FIGS. 4 and 5 are obtained. FIGS. 4 and 5 show reflected light intensity spectra obtained by separating the actually measured reflected light intensity spectra for each film thickness of the film to be measured on the concave and convex portions of the semiconductor substrate.

These show the reflection spectra from the convex portions and the concave portions in FIG. 6, respectively. FIG. 4 shows a reflected light intensity spectrum corresponding to the film thickness of the film to be measured on the convex portion of the semiconductor substrate, and FIG. 5 shows a reflected light intensity spectrum corresponding to the film thickness of the film to be measured on the concave portion of the semiconductor substrate. In addition,
The spectra in FIGS. 4 and 5 show that the cycle of the peak caused by the difference in the film thickness is different, and the shorter the film thickness, the shorter the cycle.

Next, a second embodiment of the present invention will be specifically described with reference to the drawings. The measurement system used in this embodiment is the same as that shown in FIG. 1 or FIG. 2 used in the first embodiment of the present invention.
Use the same as above. Here, as in the first embodiment, the calculation is performed by previously measuring a large number of flat standard samples having different film thicknesses from a set of k + 1 data previously calculated from the equation (1). It is prepared without using.

The actual measuring method and calculation method are basically the same as those of the first embodiment, but differ in the following two points. That is, the first difference is that the number of d _p which is a parameter of data set in advance is k + 1 set in calculation in the first embodiment.
_{While p} is discretely constant, in the present embodiment, the number of d _{p is} the number of samples prepared in advance as standard samples, and d _p is a point that is irregularly discrete.

The second difference is that, when calculating the equation (6), p and p correspond to the data set of the first point.
The set number of q is the same as the number of standard samples. That is, assuming that the number of standard samples is z, the type of P (X, Y, p, q) calculated by equation (6) is (x + 1) × (y +
1) ・ z becomes ² . In the second embodiment, since the local refractive index and the reflectance of the film to be measured can be considered as compared with the first embodiment, more accurate thickness unevenness distribution and average thickness can be obtained. it can. Needless to say, it is clear that the greater the number of types of film thickness of the standard sample prepared in advance, the higher the measurement accuracy.

[0031]

As described above, according to the present invention,
It is possible to measure the thickness of the film to be measured on the uneven portion of the semiconductor substrate even when the step pattern of the semiconductor substrate is a fine pattern of the order of μm or less, which has been difficult in the past. After the process, the film thickness of the film to be measured on the convex portion and the concave portion of the semiconductor substrate underlayer having different film thicknesses can be simultaneously measured.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a measurement system according to an embodiment of the present invention.

FIG. 2 is a diagram showing a schematic configuration of a measurement system according to an embodiment of the present invention.

FIG. 3 is a diagram showing a measured reflected light intensity spectrum with respect to a wavelength according to the embodiment of the present invention.

FIG. 4 is a diagram showing a reflected light intensity spectrum corresponding to the film thickness of a film to be measured on a convex portion of a semiconductor substrate obtained by separating an actually measured reflected light intensity spectrum according to the present invention.

FIG. 5 is a diagram showing a reflected light intensity spectrum corresponding to the thickness of a film to be measured on a semiconductor substrate recess obtained by separating an actually measured reflected light intensity spectrum according to the present invention.

FIG. 6 is a schematic diagram showing the thickness of a film to be measured on a semiconductor substrate according to an example of the present invention.

[Explanation of symbols]

 1 Light source 2 Half mirror 3 Monometer 4 Photomultiplier tube 5 Semiconductor substrate 6 Film to be measured a Thickness of film to be measured on convex portion of semiconductor substrate b Thickness of film to be measured on concave portion of semiconductor substrate

Claims (5)

[Claims] 1. A method of irradiating a film to be measured formed on an uneven surface on a semiconductor substrate with light from a multi-wavelength oscillation coherent light source,
The reflected light intensity spectrum generated by the in-film interference is separated and detected for each of a plurality of predetermined wavelengths, and the reflected light intensity spectrum related to the detected wavelength component is the wavelength of the incident light by the multi-wavelength oscillation coherent light source, Based on the theoretical relationship between the refractive index and the film thickness of the film to be measured, the spectrum is separated for each different film thickness of the film to be measured, and A film thickness distribution measuring method characterized by simultaneously measuring the film thickness. 2. The spectrum separating method according to claim 1, wherein the reflected light intensity spectrum relating to the detected wavelength component is obtained by calculating a reflected light intensity spectrum for each of a predetermined wavelength and a predetermined thickness of the film to be measured. 2. The method according to claim 1, wherein a spectrum is separated for each film thickness by a least square method using the calculated values. 3. The method according to claim 1, wherein the reflected light intensity spectrum relating to the detected wavelength component is reflected by a standard sample of a film to be measured prepared at a predetermined wavelength and a predetermined thickness of the film to be measured. 2. The method according to claim 1, wherein a spectrum is separated for each film thickness by a least square method using an actually measured value of the light intensity spectrum. 4. The wavelength region of the reflected light intensity spectrum is
4. The method according to claim 1, wherein the thickness is in the range of 350 nm to 800 nm. 5. The film thickness distribution measuring method according to claim 1, wherein a wavelength interval for detecting the reflected light intensity spectrum is 2 nm.