JPH11260694A - Method for measuring proximity effect parameter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately measure, without depending on fluctuations of a beam diameter of electron beams and unrequire measurement each developing condition. SOLUTION: A tungsten film 12 is formed on an upper face of a silicon substrate 10, and a positive type of electron beam resist film 16 is formed on the upper face. A plurality of line pattern regions 18, which are arranged in parallel to each other at an equal interval and have a same line width, are defined on this film. Different dose amounts of electron beams are irradiated on each line pattern region 18, respectively. An electron beam resist film on which electron beams are irradiated is developed, and a resist line pattern 16a of a pattern corresponding to the line pattern region 18 is obtained. A resist space 22 is formed in a resist removal part. The linewidth of this resist space is measured, whereby an electron width dose amount dependence of the linewidth of the resist line pattern is obtained. The electron width dose amount dependence of the linewidth of the resist line pattern obtained by the measurement is compared with the electron width dose amount dependence of the linewidth of the resist line pattern, and proximity effect parameters are obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a method for measuring proximity effect parameters in electron beam lithography.

[0002]

2. Description of the Related Art An electron beam drawing method is effective for producing a semiconductor device having a fine pattern of 0.1 μm level. However, since the electron beam is scattered in the resist film and largely reflected from the underlying substrate, the effective electron beam absorption energy distribution in the resist film becomes larger than the incident electron beam profile. For this reason, the resolution of the electron beam drawing method is reduced, and a pattern as designed cannot be formed. This phenomenon is called the proximity effect. In order to suppress the proximity effect, it is common practice to control the dose of the incident electron beam for each pattern so that the effective electron beam absorption energy distribution in the resist film has a constant value. I have. For this purpose, it is necessary to accurately know the effective electron beam absorption energy distribution in the resist film.

[0003] Reference 1 "Jpn. J. Appl.
s. , Vol. 35 (1996), pp 1929-19
36, the electron beam absorbed energy distribution in the resist film is approximated by a double Gaussian.
Proximity effect parameters (forward scattering parameter α in the resist film, backscattering parameter β from the substrate, and reflection parameter η as a ratio of α and β) which are the coefficients of the double Gaussian are the resist material, the base substrate material, Since these parameters depend on the resist film thickness, electron beam acceleration voltage, development time, and temperature, it is necessary to measure these parameters for each drawing condition. According to Document 1, an electron beam spot is incident on a resist film, the resist spot diameter after development is measured, and the proximity effect parameter is estimated from the electron beam dose dependence.

[0004]

However, in the method disclosed in the above-mentioned document 1, the diameter of the resist spot varies due to the fluctuation of the beam diameter of the electron beam. For this reason, it has been difficult to obtain an accurate value of the proximity effect parameter.

[0005] Since the resist spot diameter also depends on the developing conditions, the proximity effect parameter depends on the developing conditions. Therefore, it was necessary to repeat the measurement each time the development conditions were changed.

Therefore, there has been a demand for a new proximity effect parameter measurement method which can accurately measure without depending on the fluctuation of the beam diameter of the electron beam and does not require measurement for each development condition.

[0007]

Therefore, according to the method for measuring proximity effect parameters of the present invention, a step of forming an electron beam resist film on a base, and a step of forming an electron beam resist film on the formed electron beam resist film at regular intervals. Defining a plurality of line pattern regions having the same line width arranged in parallel with each other, irradiating each defined line pattern region with an electron beam having a different dose, and irradiating the electron beam. Developing the electron beam resist film to obtain a resist line pattern of a pattern corresponding to the line pattern area, and measuring the line width of the resist line pattern so that the line width of the resist line pattern depends on the electron beam dose. The electron beam absorption energy distribution approximated by double Gaussian to the electron beam dose amount dependence of the line width of the resist line pattern. By comparing the results of the simulation obtained using the conditions, characterized in that it comprises the steps of obtaining a proximity effect parameters are the coefficients of a double Gaussian.

As described above, an isolated line is drawn by changing the dose of the electron beam, and the line width of the resist line pattern created as a result is measured. Therefore, the fluctuation of the beam diameter of the electron beam is averaged over the line, so that the statistical error caused by the fluctuation is reduced.

Further, in order to compare the dependence of the line width of the resist line pattern obtained by the measurement on the electron beam dose with a simulation result including a development process, it is necessary to determine how much the proximity effect parameter depends on the development conditions. Can be estimated. Therefore, by optimizing the development conditions, it is possible to obtain a proximity effect parameter having an optimal value for forming a desired resist pattern.

In the proximity effect parameter of the present invention,
Preferably, the result of the above simulation is to obtain an in-plane distribution of the electron beam energy absorbed by the electron beam resist film by integrating the electron beam absorption energy distribution approximated by double Gaussian over the line width of the line pattern region. Calculating the cross-sectional shape of the developed electron beam resist film from the in-plane distribution and the sensitivity curve of the electron beam resist film to the amount of electron beam irradiation, and calculating the line width of the resist line pattern. It is good to do.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. It should be noted that the drawings merely schematically show the configuration, arrangement, and size to the extent that the present invention can be understood. The conditions such as numerical values and materials described below are merely examples. Therefore, the present invention is not limited to this embodiment.

A method of measuring the proximity effect parameter according to this embodiment will be described with reference to FIGS.
FIG. 1 is a diagram for explaining a method of measuring a proximity effect parameter. FIG. 1A is a sectional view, and FIGS.
(D) is a plan view. FIG. 2 is a cross-sectional view showing a sample on which a resist pattern for proximity effect parameter measurement has been prepared.

First, a tungsten film 12 is formed on the upper surface of a silicon substrate 10 by a sputtering method. The thickness of the formed tungsten film 12 is 0.5 μm. The laminated structure of the silicon substrate 10 and the tungsten film 12 serves as a base 14 for depositing an electron beam resist film. Subsequently, a positive electron beam resist film 16 is formed on the upper surface of the underlayer 14, that is, the upper surface of the tungsten film 12 by a spin coating method (FIG. 1A). The thickness of the formed electron beam resist film 16 is 0.2 μm. In this embodiment,
ZEP manufactured by Zeon Corporation as the electron beam resist film 16
(Trademark).

Next, on the formed electron beam resist film 16, a plurality of line pattern regions 18 having the same line width and being arranged in parallel at equal intervals are defined (FIG. 1B). Each line pattern region 18 is an isolated line having a line width of 0.1 μm. In this example, 30 isolated lines are 100 μm
Are arranged at a line interval of.

Next, the defined line pattern regions 18 are irradiated with electron beams having different doses. In this example, for each line pattern area 18, 20 μC / c
^{m 2, 40μC / cm 2,} 60μC / cm 2, 80μC
/ Cm ² , 200 μC / cm ² , 400 μC / cm ² ,
600 μC / cm ² , 800 μC / cm ² , 2000 μ
C / cm ² , 4000 μC / cm ² , 6000 μC / c
m ² , 8000 μC / cm ² , 20,000 μC / cm ²
The dose of the electron beam to be irradiated is changed.
As a result, a latent image 20 of a line pattern is formed at the position of the electron beam resist film 16 irradiated with the electron beam.
(C)).

Next, the electron beam resist film 16 irradiated with the electron beam is developed to obtain a resist line pattern 16a having a pattern corresponding to the line pattern region 18 (FIG. 1).
(D)). In this example, xylene was used as the developer,
The development time is 2 minutes, isopropyl alcohol is used as a rinse solution, and the rinse time is 2 minutes. As a result of the development, the portion of the latent image 20 of the line pattern, that is, the portion irradiated with the electron beam is removed, and the resist line pattern 16a having a linear pattern remains. In the following description, the portion where the resist is removed is referred to as a resist space 22.

Next, the line width of the resist line pattern 16a is measured to obtain the electron beam dose dependency of the line width of the resist line pattern 16a. In this example, the line width of the resist space 22 is measured as the line width of the resist line pattern 16a. The measurement of the line width is performed using a scanning electron microscope.

FIG. 2 shows a cross section of the cut surface taken along the line II in FIG. 1 (D). As shown in FIG.
The line width of the resist space 22 formed in the portion where the electron beam dose is small is relatively small. If the electron beam dose is equal to or less than the resist sensitivity of the electron beam resist film 16, the resist remains without being removed after development, and the surface of the tungsten film 12 of the underlayer 14 is not exposed. In this case, the remaining electron beam resist film, that is, the resist line pattern 16
The line width of the resist space 22 is measured at the position on the surface a. That is, the line width is measured as the length indicated by the symbol a in FIG.

On the other hand, the line width of the resist space 22 formed in a portion where the electron beam dose is large is relatively large. In this case, the electron beam dose is equal to or higher than the resist sensitivity of the electron beam resist film 16. Therefore, the resist is completely removed after the development, and the tungsten film 1
2 Surface is exposed. In this case, the line width of the resist space 22 is measured at the position of the exposed surface of the tungsten film 12. That is, the line width is measured as a length as shown by symbols b and c in FIG.

Next, a simulation is performed using the electron beam absorbed energy distribution approximated by double Gaussian and the developing conditions. In this simulation, first, the electron beam absorption energy distribution approximated by double Gaussian is integrated over the line width of the line pattern region 18. It is known that when one point on a resist film is irradiated with an electron beam, the in-plane distribution of energy absorbed by the resist film is approximated by a double Gaussian (Reference 1). Therefore, in this example, 0.
Since the line pattern region 18 having a width of 1 μm is irradiated (drawn) with an electron beam, the in-plane distribution of the electron beam energy absorbed by the electron beam resist film 16 is 0.1 μm of double Gaussian.
It is obtained by integrating over m widths. As a result, an in-plane distribution of the electron beam energy absorbed by the electron beam resist film 16 is obtained.

Next, the sectional shape of the developed electron beam resist film 16 is calculated from the calculated in-plane distribution and the sensitivity curve of the used electron beam resist film 16 to the amount of electron beam irradiation. The sensitivity curve is a curve showing the relationship between the reduced film thickness of the resist due to development and the amount of electron beam irradiation. The above-described values are used as the development conditions. As a result, the line width of the resist line pattern 16a, that is, the line width of the resist space 22 is calculated. By performing the simulation as described above, the dependence of the line width of the resist line pattern 16a on the electron beam dose can be obtained by calculation.

Then, the dependency of the line width of the resist line pattern 16a obtained by the measurement on the electron beam dose and the dependency of the line width of the resist line pattern 16a obtained by the simulation on the electron beam dose are compared. That is, the graph curve and the double Gaussian curve of the dependence of the line width of the resist space 22 on the electron beam dose obtained by the measurement are fitted. The resulting fitting parameters are the proximity effect parameters (α, β, η)
It is.

FIG. 3 is a graph showing the measured electron beam dose dependence of the line width of the resist space 22 and a double Gaussian curve. The horizontal axis represents the line width of the resist space 22 in units of μm, and the range from 0 μm to 2 μm is 0.2
The scale is shown every 5 μm. The vertical axis indicates the electron beam dose in an arbitrary unit, and shows a range of 0.001 to 1 in logarithmic representation. A plot (black point) in the graph indicates a measured value, and a curve a in the graph indicates double Gaussian, that is, a calculated value.

As shown in FIG. 3, as a result of the fitting, the proximity effect parameters are respectively set to α = 0.07 μm.
m, β = 0.6 μm, and η = 1.3. Also,
As a result of performing a predetermined proximity effect correction using the proximity effect parameter obtained in this way and drawing a pattern, a resist pattern substantially equal to the design dimensions was obtained. Therefore, by using the value of the proximity effect parameter obtained by the method of this embodiment, it is possible to accurately predict the electron beam absorption energy distribution determined from the used resist material, base substrate material, electron beam acceleration voltage, and development conditions. Is possible.

[0025]

According to the method for measuring the proximity effect parameter of the present invention, an isolated line is drawn by changing the dose of the electron beam, and the line width of the resist line pattern created as a result is measured. Therefore, the fluctuation of the beam diameter of the electron beam is averaged over the line, so that the statistical error caused by the fluctuation is reduced.

In order to compare the dependence of the line width of the resist line pattern obtained by the measurement on the electron beam dose with the simulation result including the development process, the degree to which the proximity effect parameter depends on the development condition is determined. Can be estimated. Therefore, by optimizing the development conditions, it is possible to obtain a proximity effect parameter having an optimal value for forming a desired resist pattern.

[Brief description of the drawings]

FIG. 1 is a diagram provided for describing a method of measuring a proximity effect parameter.

FIG. 2 is a diagram showing a sample on which a resist pattern for proximity effect parameter measurement has been prepared.

FIG. 3 is a view showing the electron beam dose amount dependence of the line width of a resist space.

[Explanation of symbols]

 10: Silicon substrate 12: Tungsten film 14: Underlayer 16: Electron beam resist film 18: Line pattern area 20: Latent image of line pattern 22: Resist space 16a: Resist line pattern

Claims (2)

[Claims] 1. A step of forming an electron beam resist film on a base, and defining a plurality of line pattern regions having the same line width arranged at equal intervals in parallel with each other on the formed electron beam resist film. Irradiating each defined line pattern region with an electron beam of a different dose amount, and developing the electron beam resist film irradiated with the electron beam to correspond to the line pattern region. Obtaining a resist line pattern of the obtained pattern, obtaining the electron beam dose dependence of the line width of the resist line pattern by measuring the line width of the resist line pattern, and measuring the line width of the resist line pattern. The simulation results obtained by using the electron beam absorption energy distribution approximated by double Gaussian and the development conditions were used to determine the electron beam dose dependence. By compare, the measurement method of the proximity effect parameters, characterized in that it comprises the steps of obtaining a proximity effect parameters are coefficients of the double Gaussian. 2. The proximity effect parameter measuring method according to claim 1, wherein the simulation result is obtained by integrating an electron beam absorbed energy distribution approximated by a double Gaussian over a line width of the line pattern region. Obtaining an in-plane distribution of the electron beam energy absorbed by the electron beam resist film; and a sectional shape of the developed electron beam resist film from the in-plane distribution and a sensitivity curve of the electron beam resist film with respect to the amount of electron beam irradiation. And calculating the line width of the resist line pattern.