JPH07115116A - Thick film measuring method - Google Patents

Abstract

PURPOSE:To provide a method with which the thickness of a conductor thin film can be measured precisely in a semiconductor manufacturing method. CONSTITUTION:A plurality of types of samples of conductive thin films of different thickness are formed covering the region, requiring measurement of film thickness, on a semiconductor substrate in accordance with the requirement of the manufacturing process of a semiconductor device. The sheet resistance R of the conductive thin films is measured by a four-probe measuring method, and the thickness of each conductive thin film is measured in advance. The constants A, B and C are computed by the following formula (T=1000t). R=A+ BT+CT<2>. The sheet resistance of the part, where film thickness is required to recognize, is measured and film thickness is computed from the obtained value R.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a more accurate method for measuring the thickness of a conductive thin film, which requires less time and labor than before.

[0002]

2. Description of the Related Art As a method of nondestructively measuring a sample, a method of measuring a sheet resistance and converting it into a film thickness is widely used as a method of measuring a film thickness of a conductive thin film.

On the other hand, as a direct sample destruction method, there is a method of measuring the film thickness of the conductor thin film by measuring a step with a probe or observing with an electron microscope. In the step measurement, the step of the conductor thin film to be measured is formed on the sample having a smooth surface. That is, first, a conductor thin film to be measured is formed on a sample surface having a smooth surface, and then an etching mask pattern is formed on the conductor thin film to be measured. Next, using the etching mask pattern as a mask, only the conductor thin film to be measured is removed by etching with an appropriate acid or alkali solution, and only the etching mask pattern is removed, and this step difference is measured.
Therefore, in this case, the measured conductor thin film is destroyed. Further, the film thickness measurement requires time for forming a step of the conductor thin film to be measured, and it is impossible to instantaneously measure the film thickness.

Further, in the method based on electron microscope observation, a conductor thin film to be measured is formed on a smooth sample surface, and the sample cross section that has been opened is observed by an electron microscope. Thereby, the thickness of the measured conductor thin film can be measured. However, in this case, it is necessary to precisely calibrate the magnification of the electron microscope image before the measurement. Therefore, even in this case, the measured conductor thin film is destroyed. In addition, it is impossible to measure the film thickness instantaneously.

On the other hand, in the manufacturing process of a semiconductor device, a conductor thin film is usually used for wiring used for connecting elements. In order to confirm during the manufacturing process whether or not the conductor thin film of the intended thickness is formed so that there is no problem with the performance, reliability, and yield of the semiconductor device,
It is necessary to confirm the film thickness of the conductor thin film used for wiring during the manufacturing process of the semiconductor device. If you fail to confirm whether the conductor thin film of the intended thickness is formed,
If the film thickness deviates from the intended film thickness, semiconductor devices continue to be manufactured even if they should be defective. Therefore, manufacturing of semiconductor devices different from enormous designs is continued, resulting in enormous defective products. In the manufacturing process of a semiconductor device, it is important to obtain the film thickness of the conductive thin film formed in each manufacturing process instantly and accurately without delaying the manufacturing time of the semiconductor device.

A method of measuring the film thickness of the conductive thin film, which is generally used in the manufacturing process of semiconductor devices, is a method of measuring the sheet resistance of the conductive thin film and converting it into the film thickness.
The measurement of the sheet resistance of the conductor thin film can be easily realized nondestructively by the four-point probe measurement method. In the 4-probe measurement method, four conductor needles arranged at equal intervals are brought into contact with the surface of the sample to be measured, a constant current is applied to the two needles at both ends, and the voltage is measured with the two needles in the center. It is a method of obtaining resistance. Four
According to the probe measurement method, it is possible to measure the sheet resistance of the conductor to be measured non-destructively, and it is particularly easy and instantaneous to perform measurement without the need to process or devise the sample. it can.

The following relationship generally exists between the sheet resistance and the film thickness of the conductor thin film. If the sheet resistance is R _S , the resistivity (resistivity) of the measured conductor thin film is ρ, and the film thickness of the measured conductor thin film is t, then ρ = R _S × t ………………………… … (1). Therefore, the specific resistance ρ of the conductor thin film to be measured can be calculated in advance from the formula (1) by measuring the sheet resistance and measuring the step difference, which is a direct sample destruction method, and measuring the film thickness of the conductor thin film by electron microscope observation. By obtaining by measurement,
It is possible to easily measure the film thickness of the conductor thin film by measuring the sheet resistance.

[0008]

The problems of the method for measuring the film thickness of the conductor thin film based on the conventional technique will be described. In the conventional method for measuring the film thickness of the conductive thin film by the formula (1), the specific resistance ρ of the measured conductive thin film is treated as a constant. However, although the specific resistance ρ originally has a value peculiar to the substance, in the case of a thin film, the specific resistance changes with respect to the film thickness of the conductive thin film according to the following equation (2).

Ρ = ρ _B + ρ _i + ρ _G + ρ _SURF (2) where ρ _B is the specific resistivity of the substance (bulk), and ρ _i is the impurity scattering in the thin film. Resistivity, ρ _G is the resistivity due to grain boundary scattering of the thin film, and ρ _SURF is the resistivity due to surface scattering of the thin film. Among them, the crystal grain boundary scattering becomes remarkable when the grain size of the crystal grains forming the thin film becomes smaller than the mean free path of electrons, thereby increasing the specific resistance. Further, surface scattering becomes remarkable when the film thickness of the thin film becomes thinner than the mean free path of electrons, and the specific resistance is increased. Therefore, it can be seen that the specific resistance of the conductor thin film changes depending on the growth state of crystal grains, the mixing state of impurities, and the film thickness depending on the forming conditions. That is, the specific resistance of the conductor thin film increases as the film thickness decreases, and does not take a constant value. As described above, it is understood that an error occurs when P in equation (1) is treated as a constant.

Generally, in the process of manufacturing a semiconductor device,
A conductor thin film is used for wiring for connecting the elements, and the film thickness of the conductor thin film is usually several tens nm to 1 nm.
Used around μm. For example, when a conductor thin film having a film thickness of 1 μm is used, in the manufacturing process of a semiconductor device,
It is controlled by whether or not the conductor thin film is formed in the range of the film thickness (1 ± 0.1) μm. In such a case, when it is attempted to measure the film thickness of the conductor thin film based on the equation (1), the specific resistance when the film thickness of the conductor thin film is exactly 1 μm is used to calculate the film thickness from the sheet resistance. Use the method of converting to. That is, the film thickness of the conductor thin film is 0.9 to 1.1 μm.
Assuming that the specific resistance does not change within the range, the film thickness is obtained from the sheet resistance. However, since the specific resistance of the conductor thin film changes sequentially depending on the film thickness of the conductor thin film, there is no problem if the thickness of the formed conductor thin film is 1 μm as desired, but from 1 μm If there is a slight deviation, the specific resistance is also changing, so an accurate film thickness cannot be obtained. In addition, although the film thickness can be accurately measured by using the specific resistance corresponding to the actual film thickness of the formed conductor thin film, the purpose is to measure the unknown film thickness of the formed conductor thin film. Therefore, it is impossible to predict and set the specific resistance corresponding to the actual film thickness of the formed conductor thin film in advance.

In the manufacturing process of a semiconductor device, a conductor thin film is used for the wiring used for connecting the elements. Usually, a conductor thin film is formed according to each step in the manufacturing process of the semiconductor device. Even if they are the same, the film thickness may be changed intentionally. For example, when a multilayer wiring is formed for connecting elements in a semiconductor device, the first layer wiring and the second layer wiring having different thicknesses are used. Generally, the film thickness of the first layer wiring is made smaller than the film thickness of the second layer wiring in order to reduce the step difference of the multilayer wiring. That is, in the manufacturing process of a semiconductor device, it is necessary to measure the film thickness of two or more different film thicknesses even for the same conductive thin film.

In the manufacturing process, for example, five kinds of film thickness t₁，
t₂, T₃, T_Four, T_FiveTaking the case of using the conductor thin film of
Then, for five types of film thickness, the film thickness t₃Resistivity at₃only
Then, from the measurement of the sheet resistance, it is converted into the film thickness by the equation (1).
Then, as shown in FIG. ₁, T₂, T_Four, T_FiveSo wrong
It can be seen that there is a difference and accurate film thickness measurement cannot be performed. here
The black dots in Fig. 2 are the sheet resistance measured by the 4-probe method.
Measurement result R₁, R₂, R ₃, R_Four, R_FiveAnd those who destroy the sample
However, it is a direct method of film thickness measurement
The thickness t of the conductive thin film₁, T₂, T₃, T_Four, T_FiveTo measure
The horizontal axis shows the film thickness of the conductor thin film, and the vertical axis shows the sheet resistance.
Is plotted as. Also, the black measurement points
The curve that connects the
From the measured resistance, the specific resistance ρ₃(= R₃× t₃)
Then, when converted to the film thickness of the conductor thin film by the formula (1),
The result.

Since the specific resistance ρ, the film thickness t, and the sheet resistance R _s cannot all be treated as constants in the equation (1), the accurate film thickness t is obtained only for the specific resistance ρ ₃ and the sheet resistance R ₃ in FIG. _{Although 3} can be obtained, other than that, accurate film thickness measurement cannot be performed by the conventional film thickness measurement method for a conductor thin film. In order to further improve the accuracy, the film thicknesses t ₁ , t ₂ , t ₃ ,
Even if specific resistances ρ ₁ , ρ ₂ , ρ ₃ , ρ ₄ , and ρ ₅ are derived for t ₄ and t ₅ and converted from the measured sheet resistance value to the film thickness using the equation (1), As shown in FIG. 6, although the error is smaller than that in FIG. 5, it can be seen that the conductive film having a film thickness other than the film thicknesses t ₁ , t ₂ , t ₃ , t ₄ , and t ₅ cannot be accurately measured. .

An object of the present invention is to derive a relational expression (approximate equation) between the sheet resistance and the film thickness in the method for measuring the film thickness of a conductor thin film by measuring the film resistance and to use the relational expression. It is to convert the sheet resistance to the film thickness.
Further, by deriving the relational expression between the sheet resistance and the film thickness, the film thickness error due to the change in the specific resistance depending on the film thickness of the conductor thin film is prevented. further,
An object of the present invention is to provide a more accurate method for measuring a film thickness of a conductive thin film, which has less error than the conventional technique in measuring the film thickness of the conductive thin film in the manufacturing process of a semiconductor device.

[0015]

Means for Solving the Problems A step of measuring a sheet resistance R _n of a conductor thin film having n kinds of film thicknesses, a step of measuring a film thickness t _{n of a} conductor thin film, and a sheet resistance R _n Film thickness t _n to 3
The method includes a step of deriving the constants A, B, C of the types, and the measured value R of the sheet resistance of the conductor thin film and the constants A, B, 3 of the three types.
A method for measuring the thickness of a conductor thin film, which comprises deriving the film thickness of the conductor thin film from C.

[0016]

In the method for measuring the thickness of the conductor thin film of the present invention,
Three types of constants A, B, C based on the conductor thin film formed by the conductor thin film manufacturing apparatus used in the semiconductor device manufacturing process.
Therefore, it is possible to calibrate according to the usage conditions, and it is possible to reduce the error in film thickness measurement.

Further, since the sheet resistance of the conductor thin film is approximated by a quadratic expression which is the reciprocal of the film thickness of the conductor thin film, very accurate approximation can be performed and error can be reduced. Therefore, the film thickness of the conductor thin film can be accurately measured by measuring the sheet resistance of the conductor thin film.

[0018]

EXAMPLE FIG. 1 is a conceptual diagram showing a method for measuring the film thickness of a conductive thin film, which measures the film thickness from the measurement of the sheet resistance in the example of the present invention. A method for measuring a film thickness of a conductor thin film according to an embodiment of the present invention includes a step of measuring a sheet resistance R _s ,
A step of deriving the three constants A, B, C, a step of deriving the film thickness t from the sheet resistance measurement result R _s and the constants A, B, C, and a step of outputting the film thickness t and the sheet resistance R _s. Equipped with.

The individual steps of the embodiment of the present invention will be described below with reference to the drawings. In the examples, a titanium thin film is used as an example of the conductor thin film, and a method for converting the sheet resistance measurement result by the 4-probe measurement method or the like into the film thickness will be described. In the present embodiment, the relationship between the film thickness and the sheet resistance is changed by the function of the sheet resistance of t = F (R _s ) ... (3) instead of the conventional equation (1). Derive the formula.

First, a method of deriving the three constants A, B and C will be described. Samples of titanium thin films having different film thicknesses at several points are prepared so as to cover the film thickness range where film thickness measurement is required. Here, the titanium thin film is formed by a DC magnetron sputtering method on a semiconductor substrate having a smooth surface with an insulator formed on the surface. The samples were made into 5 kinds of film thickness, and those film thicknesses were obtained in the DC magnetron sputtering method by making the gas pressure and the input power constant and making the sputtering time different to 5 kinds.

Here, the titanium thin film is manufactured according to the manufacturing process of a semiconductor device which requires film thickness measurement. An apparatus for forming a conductive thin film by forming a titanium thin film by a conductive thin film manufacturing apparatus that is actually used in a semiconductor manufacturing process,
It is possible to derive the three constants A, B, and C according to the forming conditions. That is, when measuring the film thickness from the sheet resistance, the measurement accuracy can be improved.

In general, a conductive thin film is formed by a forming method and forming conditions, that is, a forming method such as a vacuum deposition method, a sputtering method, a plating method, a vacuum degree of a forming apparatus, a thin film forming speed, a substrate temperature at the time of forming a thin film, a thin film. It changes depending on various conditions such as the impurity concentration of the forming material, the cleanliness of the forming apparatus, the cleanliness of the substrate on which the thin film is formed, the state of materials, and the like. That is, the specific resistance of the conductor thin film formed by these conditions is determined,
This is because the impurity concentration in the thin film, the size of crystal grains, and the like change. In order to measure the film thickness of a titanium thin film formed by the sputtering method in the manufacturing process of a semiconductor device, for example, even if a titanium thin film formed by the vacuum deposition method is used here, the accurate film thickness of the titanium thin film formed by the sputtering method It is not possible to make measurements.

Five kinds of titanium thin films are obtained by the four-point probe measuring method or the like.
Sheet resistance R₁, R₂, R ₃, R_Four, R_FiveMeasure
To do. Continued accurate film thickness t of 5 kinds of titanium thin film₁，
t₂, T₃, T_Four, T_FiveTo measure. Step measurement for film thickness measurement
As accurate as possible using standard methods and electron microscopy.
Measure the film thickness. With the above
And accurate relationship between film thickness and sheet resistance (R₁, T₁),
(R₂, T₂), (R₃, T₃), (R_Four, T_Four), (R_Five，
t_Five) Is obtained. In the titanium thin film in this embodiment,
It will be the lower value.

(R ₁ , t ₁ ) = (69.5 Ω, 15.3 nm) (R ₂ , t ₂ ) = (39.5 Ω, 23.1 nm) (R ₃ , t ₃ ) = (26.8 Ω, (30.8 nm) (R ₄ , t ₄ ) = (21.1 Ω, 38.5 nm) (R ₅ , t ₅ ) = (16.7 Ω, 46.2 nm) The film thickness of the five titanium thin films obtained above. And the sheet resistance, the following relational expression is obtained. That is, the sheet resistance of the titanium thin film is approximated by a quadratic equation that is the inverse of the film thickness. The sheet resistance of the conductor thin film can be accurately approximated by a quadratic equation that is the reciprocal of the film thickness of the conductor thin film.

R _s = A + BT + CT ² …………………… (4) However, T = 1000 / t A, B, and C are constants The three constants A, B, and C can be derived from the above. In the titanium thin film of this embodiment, the constants A, B and C have the following numbers.

A = 0.764 B = 5.556 C = 1.058 Theoretically, the sheet resistance of a thin film can be expressed by the following relational expression.

R _s = BT + CT ² (5) However, T = 1 / t That is, when the film thickness is 0 nm, the sheet resistance becomes infinite, and thus theoretically a constant. A is 0. However, in this embodiment, the constant term A is added. The addition of the constant term A enables approximation with less error.

Subsequently, from the measured value R _s of the sheet resistance of the conductive thin film and the three constants A, B and C, the film thickness t of the conductive thin film is obtained.
The derivation method of will be described. The following relational expression is obtained from the expression (5).

T = {− B + [B ² −4A (C−R _s )] ^−1/2 } / 2A (6) From the above, the relational expression between the film thickness and the sheet resistance is calculated by the function of the sheet resistance. Can be derived. That is, thereafter, it becomes possible to convert the measured value of the sheet resistance by the 4-probe measurement method or the like into the film thickness by the equation (6).

Subsequently, the film thickness t and the sheet resistance R _s are displayed by using a liquid crystal display device or an LED display device.

The results of applying the embodiment of the present invention to a titanium thin film are shown in FIG. The black dots in FIG. 2 are the sheet resistance measurement results R ₁ of the titanium thin film by the 4-probe measurement method,
_{R 2, R 3, R 4} , and R _5, the result of measurement of the titanium film thickness of the thin film _{t 1, t 2, t 3} , t 4, t 5 by step measurement, the horizontal axis of the titanium thin film thickness, The vertical axis is plotted as the sheet resistance. The curve connecting the black measurement points is the result when the sheet resistance is measured by the 4-probe measurement method according to the embodiment of the present invention and converted to the film thickness of the titanium thin film by the formula (6).

According to this embodiment, the film thickness is directly measured, and the sheet resistance of the titanium thin film can be measured by the four-point probe measurement method or the like without depending on the film thickness measurement of the titanium thin film by the step measurement, which takes time to prepare the sample. From the measurement results, it can be seen that the conversion to the film thickness of the titanium thin film can be performed without a large error.

FIG. 3 shows the results of applying the embodiment of the present invention to an aluminum alloy thin film. The black dots in FIG. 3 represent the sheet resistance measurement results R ₁ , R ₂ , R ₃ , R ₄ , R ₅ of the aluminum alloy thin film by the 4-probe measurement method and the film thickness of the aluminum alloy thin film by the step measurement. t ₁ , t ₂ , t
_The results of measuring ₃ , t ₄ , and t ₅ are plotted by plotting the horizontal axis as the film thickness of the aluminum alloy thin film and the vertical axis as the sheet resistance. The curve connecting the black measurement points is the result when the sheet resistance is measured by the 4-probe measurement method according to the embodiment of the present invention and converted into the film thickness of the aluminum alloy thin film by the formula (6).

According to this embodiment, the film thickness is directly measured, and the sheet resistance of the four-point probe measurement method or the like can be used even if the film thickness of the aluminum thin film is not measured by measuring the step, which takes time to prepare the sample. From the measurement results, it can be seen that the conversion into the film thickness of the aluminum alloy thin film can be performed without a large error.

FIG. 4 shows the result when the embodiment of the present invention is applied to the titanium nitride thin film. The black dots in FIG. 4 represent the sheet resistance measurement results R ₁ , R ₂ , R ₃ , R ₄ , R ₅ of the titanium nitride thin film by the four-point probe measurement method and the titanium nitride thin film Film thickness t ₁ , t ₂ , t ₃ , t ₄ , t ₅
Is a plot of the measurement results of the film thickness of the titanium nitride thin film on the horizontal axis and the sheet resistance on the vertical axis. Also,
The curve connecting the blackened measurement points is 4 according to the embodiment of the present invention.
It is the result of converting the sheet resistance by the probe measurement method to the film thickness of the titanium nitride thin film by the formula (6).

According to the present embodiment, the film thickness is measured directly, and the sheet is measured by the four-point probe measurement method or the like without depending on the film thickness measurement of the titanium nitride thin film by the step measurement which takes time to prepare the sample. From the measurement result of the resistance, it can be seen that the conversion into the film thickness of the titanium nitride thin film can be performed without a large error.

As described above, according to the embodiment of the present invention, it can be applied even if the kind of the conductive thin film is changed, and the film thickness of the conductive thin film can be accurately obtained by measuring the sheet resistance of the conductive thin film. be able to.

[0038]

According to the present invention, the sheet resistance is formed by a quadratic equation of the reciprocal of the film thickness by using the conductor thin film formed by the conductor thin film forming apparatus actually used in the manufacturing process of the semiconductor device. By approximating the above, the film thickness of the conductor thin film can be approximated by a function of the sheet resistance of the conductor thin film without a large error. By using the film thickness of the conductor thin film as a function of the sheet resistance of the conductor thin film, the conductor thin film forming apparatus actually used in the manufacturing process of the semiconductor device, the sheet resistance From the measurement, it is possible to accurately measure the sheet resistance of the conductor thin film. Further, in the manufacturing process of the semiconductor device, the film thickness of the conductor thin film can be instantaneously measured accurately, and it is possible to manufacture the designed semiconductor device with high precision without causing defects.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a film thickness measuring method of a conductor thin film of the present invention.

FIG. 2 is a diagram showing a first embodiment of the method for measuring the thickness of a conductor thin film of the present invention.

FIG. 3 is a diagram showing a second embodiment of the method for measuring the thickness of a conductor thin film of the present invention.

FIG. 4 is a diagram showing a third embodiment of the method for measuring the thickness of a conductor thin film of the present invention.

FIG. 5 is a diagram showing a problem to be solved by a conventional method for measuring a film thickness of a conductor thin film.

FIG. 6 is a diagram showing a problem to be solved by a conventional method for measuring a film thickness of a conductor thin film.

Claims (1)

[Claims] 1. A sheet resistance R of a conductor thin film having n kinds of film thickness.
a step of measuring _n , a step of measuring the film thickness t _{n of the} conductor thin film, and a step of deriving constants A, B and C satisfying R _n = A + BT + CT ² from the sheet resistance R _n and the film thickness t _n ( However, T =
1000 / t _n ) and deriving the film thickness of the conductive thin film from the measured value R of the sheet resistance of the conductive thin film.