JP2638914B2 - X-ray intensity measurement method for exposure - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Overview] SR in synchrotron radiation (SR) lithography
Regarding the method of measuring the intensity, we propose a method that can easily measure the incident X-ray intensity directly with a semiconductor detector in the exposure apparatus, and aim at realizing high-precision exposure. In the X-ray exposure method using synchrotron radiation, A substrate for measurement formed by sequentially applying a reinforcing film, a phosphor film, and an X-ray absorber film over the entire surface of the original substrate including the opening, on the surface of the original substrate having the through holes. The surface of the substrate receives incident X-rays, and the fluorescent light generated by the incident X-rays transmitted through the absorber film and attenuated by the incident X-rays is transmitted to the opening of the reinforcing film and the silicon substrate and the incident X-rays. The semiconductor light detector is received through a diagonally provided optical path, and the photocurrent flowing through the photodetector is converted into the intensity of the incident X-ray.

The present invention relates to a method for measuring SR intensity in synchrotron radiation (SR) lithography.

In VLSI manufacturing, sub-micron processing technology is required. Therefore, in the lithography process,
SR, which has extraordinarily high intensity and excellent parallelism, has been considered as a light source for transfer.

However, for this to be practical, it is necessary to establish basic techniques such as measurement of SR intensity.

[Conventional technology]

In SR exposure, only a wavelength band (4 to 15 °) necessary for X-ray exposure is extracted from a continuous spectrum from X-rays to visible light using a bandpass filter.

As a bandpass filter, a total reflection mirror is generally used for removing short wavelength components, and a window material such as beryllium (Be) is generally used for removing long wavelength components.

However, when such a bandpass filter is used, the optical system fluctuates with time, and the X-ray intensity fluctuates. For example, a change in the arrangement angle of the total reflection mirror, a change in reflectance due to contamination of the mirror surface, and the like cause problems.

On the other hand, since the electron beam in the electron storage ring attenuates with time, the intensity of X-rays incident on the exposure chamber attenuates accordingly.

For the above reasons, in order to perform X-ray exposure with a constant X-ray irradiation amount, X-ray intensity measurement is required.

Conventionally, in X-ray exposure using SR, X-ray intensity has not been measured at present.

The reason is that a half detector capable of accurately detecting X-rays of normal intensity is readily available, but the maximum count rate of X-ray photons is about 10 ⁴ photons / sec / cm ^-2. This is because the SR intensity emitted from the 2.5 GeV electron storage ring is as large as 10 ¹⁴ photons / sec / cm ^-2 and cannot be directly detected by a semiconductor detector.

As a measuring method of a conventional X-ray irradiation intensity, scintillation counters and using a photoelectron tube, the atmosphere such as Ar or N ₂ is X-ray is ionization chamber or the like for measuring the ionization current when passing through. However, these methods have a large measuring system and are difficult to incorporate into an X-ray exposure apparatus.

[Problems to be solved by the invention]

Therefore, in the case of the SR exposure apparatus, the exposure apparatus and the measuring apparatus have to be separated, and the measurement values are different from those of the actual apparatus, so that there is a problem in accuracy.

SUMMARY OF THE INVENTION The present invention proposes a method for easily measuring the incident X-ray intensity of SR exposure directly in a lithographic apparatus using a semiconductor detector, and aims at realizing high-precision exposure.

[Means for solving the problem]

In order to solve the above-mentioned problem, a chuck provided in an exposure chamber of an X-ray exposure apparatus using synchrotron radiation and for mounting a substrate to be exposed includes an opening on a surface of an original substrate having a through hole. A measurement substrate formed by sequentially applying a reinforcing film, a phosphor film, and an X-ray absorber film to at least the entire surface of the original substrate to which the synchrotron radiation is irradiated is attached, and the surface of the measurement substrate is mounted. Receives the incident X-rays and transmits the fluorescence generated in the phosphor film by the incident X-rays transmitted through the absorber film and attenuated to the reinforcing film and the opening of the original substrate and the chuck to the incident X-rays. This is achieved by a method of measuring the intensity of an exposure X-ray which receives a semiconductor photodetector through an obliquely provided optical path and converts a photocurrent flowing through the photodetector into the intensity of the incident X-ray.

[Action]

 FIG. 1 is a diagram illustrating the principle of the present invention.

In the figure, 1 is a measurement substrate consisting of 11 to 14, 11 is an original substrate having an opening, a silicon (Si) substrate, 12 is a substrate reinforcing film, 13 is a phosphor film, and 14 is an X-ray absorber film. Reference numeral 2 denotes a wafer chuck for sucking a substrate, reference numeral 3 denotes an optical path provided obliquely to incident X-rays in the wafer chuck, reference numeral 4 denotes a semiconductor detector, and reference numeral 5 denotes incident X-rays.

Here, the reinforcing film 12 is made of a substance that transmits the fluorescent light emitted from the phosphor film 13 so that the phosphor film 13 and the X-ray absorber film 14 can be formed on the opening of the original substrate. Film.

Also, the Si substrate used as the original substrate has a function of shielding the phosphor except at the openings. Other substrates having the same properties may be used.

The power spectrum P ₀ (λ) on the electron orbital plane of SR is given by the following equation ¹⁾ .

P ₀ (λ) = 3.92 × 10 ⁻³⁰ (γ ³ / R ² ) I · y ⁴ K _2/3 ² (y / 2) [W / Å · mrad ² · mA]. Where λ = wavelength (Å), R = radius of the electron storage ring (m), I = current of the electron storage ring (mA), γ = 1.96 × 10 ³ · E (E is the energy of electrons, GeV), y = λ _c / λ (λ _c = 4πR / 3γ ³ ), K _2/3 = Modified Bessel function of the second kind. It is.

1) Takafumi Oshio, Michio Sasanuma, Characteristics of orbital radiation of the IEEJ electron synchrotron, Applied Physics, Vol. 37, No. II (1968). Here, by integrating P ₀ (λ) with respect to a wavelength from ₀ to 1000 °, the total energy amount of SR can be obtained.

Furthermore, SR is attenuated by a Be window or the like when guided into an exposure chamber in a helium (He) atmosphere.

Therefore, P ₀ (λ) · exp (−Σμ _j (λ) t _j ). Here, μ _j (λ): the linear absorption coefficient for the wavelength of the Be window, t _j : the thickness of the Be window, and j: the number of attenuating substances that pass through the SR. Is integrated over wavelength, the total energy of SR reaching the substrate can be determined.

For example, the acceleration energy of electrons is 2.5 GeV, the storage current is 300 mA,
SR from the electron storage ring with a radius of 8.66 m is 25 μm thick B
After passing through the e-window, it can be calculated to have an intensity of 50 mW / mm ² at a point 30 m away from the light emitting point on the orbital plane.

These power spectra further reach the measurement substrate surface after passing through the mask and the He gas.

The incident X-rays 5 arriving at the substrate in this way are further attenuated by the X-ray absorber film 14 made of Ta, Au or the like on the surface of the measurement substrate. For example, in the case of a Ta film having a thickness of 2 μm, the energy amount arriving at the phosphor film is 4.23 mW / mm ² (wavelength: 1 to 15 °).

In response, the phosphor film 13 emits light, but calcium tungstate, which emits light having a wavelength of 4000 to 8000 mm (peak wavelength 5800 mm) in response to a wavelength of 20 mm or less as a phosphor,
If zinc sulfide or the like is used, the semiconductor detector 4 can be detected by a Si PIN photodiode having a peak sensitivity of 5800 °.

At this time, even if the luminous efficiency of the phosphor is 60%, when the sensitivity of the PIN photodiode is 0.3A / W, 0.7W
Is obtained, it is possible to record as a voltage value by IV conversion.

The X-rays emitted from the phosphor film have attenuated energy but still contain short wavelength components. If this short wavelength component is directly received by the PIN photodiode, it may be destroyed. Therefore, utilizing the fact that the short-wavelength component has straightness, an optical path 3 oblique to the incident direction is provided to prevent destruction. .

〔Example〕

Hereinafter, an embodiment of the present invention will be described by dividing into (1) production of a wafer chuck, (2) production of a measurement substrate, and (3) a measurement method.

(1) Production of wafer chuck FIGS. 2 (1) and 2 (2) are a plan view and a sectional view of a wafer chuck used in one embodiment of the present invention.

In the figure, the wafer chuck 2 has a thickness of 10 mm and a diameter of 125 mm
A vacuum suction groove 21 and a vacuum suction hole 22 for sucking the substrate are provided on the surface of the stainless steel or aluminum disk.

Diameter at the center of the surface with an inclination of 30 ° to the perpendicular of the substrate
An optical path 3 of 5 mmφ is formed.

A holder 4 ′ for the semiconductor detector is formed in accordance with the opening of the optical path 3 opened on the back surface of the wafer chuck 2.

Since the cross section of the SR beam used was 30 mm x 5 mm, the semiconductor detector was placed at a depth of 10 mm from the wafer chuck surface.
There is no worry about being destroyed because it is fixed at a position shifted 5.8mm from the center.

(2) Production of Measurement Substrate FIGS. 3 (1) to (4) are cross-sectional views illustrating a method of forming a measurement substrate used in one embodiment of the present invention.

In FIG. 3A, a film such as boron nitride (BN), indium tin oxide (ITO), silicon dioxide (SiO ₂ ) or the like is deposited as a reinforcing film 12 on a Si substrate 11.

In FIG. 3 (2), a through hole of 100 to 500 μm square is opened from the back surface at the center of the Si substrate 11 using ordinary lithography.

In FIG. 3 (3), calcium tungstate or zinc sulfide is used as a fluorescent substance,
The phosphor film 13 is formed by applying a thickness of about 500 μm.

In FIG. 3 (4), Ta or Au is used as an X-ray absorbing substance.
Sputtered to a thickness of 0.5 to 3 μm and deposited on the fluorescent film body 13,
An X-ray absorber film 14 is formed.

As described above, the Si substrate 11 with the opening, the reinforcing film 12, the phosphor film
13, A measurement substrate including the X-ray absorber film 14 is manufactured.

(3) Measurement method The measurement substrate is set on a carrier for transporting the substrate in the same manner as a normal substrate. After the setting, the position is determined on the exposure apparatus side, and the wafer is mounted on the wafer chuck of the fine movement stage with an accuracy of ± 10 μm. Therefore, the opening at the center of the substrate can be reliably aligned with the hole of the wafer chuck.

Next, open the beam shutter.
By irradiating an SR of mm × 5 mm onto the substrate, moving the stage in the X and Y directions with the substrate aperture diameter as the minimum resolution step, and measuring the intensity with respect to the coordinates, the intensity distribution can be obtained.

Here, the intensity (energy) _Em (W / mm ² ) is obtained by converting the measured voltage value by the following equation.

E _m = (V / R) · K _W · K _L · K _P. Here, V: measured voltage value, R: resistance value during IV conversion, K _W : unit conversion coefficient of A → W , K _L : reciprocal of the conversion efficiency coefficient of the fluorescent substance, K _P : reciprocal of the absorption efficiency of the X-ray absorber, (for the measurement wavelength band). It is.

FIG. 4 is a diagram showing an example of an intensity distribution in the X (Y) direction with respect to the SR.

According to the embodiment as described above, the intensity distribution on the substrate can be obtained with high accuracy only by coefficient conversion.

By changing the wavelength sensitivity of the fluorescent substance on the measurement substrate, the intensity can be measured at an arbitrary wavelength.

The optical path oblique to the incident direction can prevent damage to the semiconductor detector due to the short wavelength component of X-rays.

Since the X-ray absorber film is formed on the surface of the measurement substrate, it can be measured even in the atmosphere.

 The intensity distribution can be measured by moving the stage.

Etc. become possible.

〔The invention's effect〕

As described above, according to the present invention, the incident X
The line intensity can be easily measured by a semiconductor detector directly in the exposure apparatus, contributing to the realization of high-precision exposure.

[Brief description of the drawings]

1 is a principle view of the present invention, FIGS. 2 (1) and 2 (2) are a plan view and a sectional view of a wafer chuck used in one embodiment of the present invention, and FIGS. 3 (1) to (4) are FIG. 4 is a cross-sectional view for explaining a method of forming a measurement substrate used in one embodiment of the present invention. FIG. 4 is a view showing an example of an intensity distribution in the X (Y) direction with respect to the SR. In the figure, 1 is a measurement substrate consisting of 11 to 14, 11 is an original substrate having an opening, a Si substrate, 12 is a reinforcing film of the substrate, 13 is a phosphor film, 14 is an X-ray absorber film, and 2 is an X-ray absorber film. A wafer chuck for sucking the substrate, 3 is an optical path provided obliquely to the incident X-ray, 4 is a semiconductor detector, and 5 is an incident X-ray. It is.

Claims (1)

(57) [Claims] 1. A chuck provided in an exposure chamber of an X-ray exposure apparatus utilizing synchrotron radiation and for mounting a substrate to be exposed, comprising: Attach a measurement substrate formed by sequentially applying a reinforcing film, a phosphor film, and an X-ray absorber film to at least the entire surface to be irradiated with the synchrotron radiation, and irradiate the surface of the measurement substrate. X-rays are received, and the fluorescent light generated on the phosphor film by the incident X-rays transmitted through the absorber film and attenuated is obliquely incident on the reinforcing film, the opening of the original substrate and the chuck with respect to the incident X-rays. A method for measuring the intensity of X-rays for exposure, wherein the intensity is received by a semiconductor photodetector through an optical path provided in the photodetector, and the photocurrent flowing through the photodetector is converted into the intensity of the incident X-ray.