JP2007116016A - Diffractive optical element, pattern forming apparatus, and pattern forming method - Google Patents

Abstract

Pattern formation by stable interference exposure is performed with a simple apparatus.
A substrate includes a laser oscillator 101 and a diffractive optical element 200 that receives a beam oscillated from the laser oscillator 101 and generates a plurality of diffracted beams. The substrate 300 is subjected to interference exposure using the diffracted beams. In the pattern forming apparatus 100 for forming a pattern, the diffractive optical element 200 generates a ± 1st order diffracted beam having the same intensity and a 0th order diffracted beam having a smaller intensity than the ± 1st order diffracted beam. Interference exposure is performed by the interference light intensity distribution formed immediately after the diffractive optical element 200 due to interference of the diffracted beam.
[Selection] Figure 1

Description

  The present invention relates to a diffractive optical element, a pattern forming apparatus using interference exposure, and a pattern forming method.

With the miniaturization of device sizes such as optical elements and semiconductor elements, improvement in processing accuracy of fine patterns is required.
As a method for forming a fine pattern, a method using two-beam interference of a laser beam is known. In this method, for example, two laser beams divided by a beam splitter or the like are crossed on a photosensitive material such as a photoresist formed on a substrate, and the photosensitive material is formed using an interference light intensity distribution generated at this time. Exposure. Thereafter, the substrate is developed to form a pattern on the substrate.
Such a pattern forming method using two-beam interference of a laser beam is disclosed in Patent Document 1, for example.

Japanese Patent Laid-Open No. 5-142979

  In the method as described above, in order to obtain a desired interference light intensity distribution, it is necessary to split the laser beam by a beam splitter or the like and then propagate the two beams in the air for a long distance and then interfere with each other on the substrate. is there. For this reason, each beam is affected by air fluctuations, vibrations of the apparatus, etc., and the interference light intensity distribution is not kept constant on the substrate, making it difficult to perform stable interference exposure. Further, in order to prevent air fluctuations and vibrations of the apparatus, a large-scale facility construction is required, which requires a large amount of cost.

  Therefore, an object of the present invention is to perform pattern formation by stable interference exposure with a simple apparatus.

The diffractive optical element of the present invention has a support substrate, a periodic structure layer having a periodic uneven shape, and a refractive index different from that of the support substrate and the periodic structure layer between the support substrate and the periodic structure layer. Having an intermediate layer.
Preferably, the refractive index of the intermediate layer is larger than the refractive index of the support substrate and the average refractive index of the periodic structure layer.
As a result, ± 1st order diffracted beams having the same intensity can be obtained, and by adjusting the thickness of the intermediate layer, the intensity of the 0th order diffracted beam can be kept small, and a good interference light intensity distribution can be obtained. it can.

A pattern forming apparatus according to the present invention includes a laser oscillator and a diffractive optical element that receives a beam oscillated from the laser oscillator and generates a plurality of diffracted beams, and performs interference exposure using the diffracted beams. A pattern forming apparatus for forming a pattern on a workpiece, wherein the diffractive optical element includes a ± 1st order diffracted beam having the same intensity and a 0th order diffracted beam having a smaller intensity than the ± 1st order diffracted beam. The interference exposure is performed by an interference light intensity distribution formed immediately after the diffractive optical element due to the interference of the ± 1st order diffracted beams.
As a result, the distance that the ± 1st-order diffracted beam propagates in the air becomes very short before it interferes, making it less susceptible to disturbances such as air fluctuations and vibrations of the device. Pattern formation by interference exposure can be performed.

The diffractive optical element has a refractive index different from that of the support substrate and the periodic structure layer between the support substrate, the periodic structure layer having a periodic uneven shape, and the support substrate and the periodic structure layer. A relationship of n> 2λ / P is established among the refractive index n of the intermediate layer, the beam wavelength λ oscillated from the laser oscillator, and the period P of the periodic structure layer.
Further, the thickness of the intermediate layer is adjusted so that the intensity of the 0th-order diffraction beam is minimized.
As a result, ± 1st order diffracted beams having the same intensity can be obtained, the intensity of the 0th order diffracted beam can be kept small, and a good interference light intensity distribution can be obtained.

The pattern forming method of the present invention includes a step of emitting a beam from a laser oscillator, a step of causing the beam to enter a diffractive optical element to generate a plurality of diffracted beams, and performing interference exposure using the diffracted beams. A step of forming a pattern on the workpiece, and in the step of generating the diffracted beam, a ± 1st order diffracted beam having the same intensity and a 0th order diffracted beam having a smaller intensity than the ± 1st order diffracted beam The interference exposure is performed by an interference light intensity distribution formed immediately after the diffractive optical element due to interference of the ± 1st order diffracted beams.
As a result, the distance that the ± 1st-order diffracted beam propagates in the air becomes very short before it interferes, making it less susceptible to disturbances such as air fluctuations and vibrations of the device. Pattern formation by interference exposure can be performed.

The diffractive optical element has a refractive index different from that of the support substrate and the periodic structure layer between the support substrate, the periodic structure layer having a periodic uneven shape, and the support substrate and the periodic structure layer. The relationship n> 2λ / P is established among the refractive index n of the intermediate layer, the beam wavelength λ emitted from the laser oscillator, and the period P of the periodic structure layer.
The thickness of the intermediate layer is adjusted so that the intensity of the 0th-order diffracted beam is minimized.
As a result, ± 1st order diffracted beams having the same intensity can be obtained, the intensity of the 0th order diffracted beam can be kept small, and a good interference light intensity distribution can be obtained.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
Embodiment 1 FIG.
FIG. 1 is a diagram showing a configuration of a pattern forming apparatus 100 according to the present invention. As shown in the figure, the pattern forming apparatus 100 includes a laser oscillator 101, mirrors 102 and 103, a shutter 104, a lens 105, a spatial filter 106, a diffractive optical element 200, and a stage 107.

FIG. 2 is a diagram showing the structure of the diffractive optical element 200 according to the present invention. As shown in the figure, the diffractive optical element 200 includes a support substrate 201, an intermediate layer 202, and a periodic structure layer 203.
The support substrate 201 and the periodic structure layer 203 are made of, for example, quartz (refractive index 1.501). The intermediate layer 202 is formed between the support substrate 201 and the periodic structure layer 203, and the support substrate 201 and the periodic structure layer 203 are formed of materials having different refractive indexes. For example, LaSF (refractive index 2.087) can be used. In addition, the refractive index quoted here is a value with respect to the light wavelength 266 nm mentioned later.
Further, the average refractive index n _av of the periodic structure layer 203 is given by the following equation.
n _av = 1.0 + f (n−1.0) (1)
Here, f is a fill factor (ratio of convex portions in one period), n is a refractive index of the material of the periodic structure layer 203, and incident light is TE polarized light (linearly polarized light whose polarization direction is orthogonal to the incident surface). For example, if f = 0.4, n _av = 1.200.
Therefore, the refractive index of the intermediate layer 202 is larger than the refractive index of the support substrate 201 and the average refractive index of the periodic structure layer 203.

The periodic structure layer 203 includes a fine structure (period P) having a period formed on the intermediate layer 202. It is designed so that the following relationship is established between the period P and the wavelength λ of the incident laser beam.
λ <P (2)
Thereby, when the laser beam is incident substantially perpendicularly from the support substrate 201 or the periodic structure layer 203 side, ± 1st order diffracted beam and 0th order diffracted beam having the same intensity are generated.

Various laser oscillators can be used as the laser oscillator 101. Here, a solid-state UV laser Nd: YVO ₄ (fourth harmonic: wavelength 266 nm, maximum output 200 mW, CW oscillation) is used as a laser light source. . The emitted beam diameter is about 1 mm here.
The laser beam is preferably in the UV region with a wavelength of 400 nm or less. Further, the beam is linearly polarized light, and TE polarized light whose azimuth is orthogonal to the incident surface.

  The laser beam emitted from the laser oscillator 101 is changed in optical path by the mirrors 102 and 103, passes through the shutter 104, is collected by the lens 105, passes through the spatial filter 106, and enters the diffractive optical element 200.

The shutter 104 has a function of passing or blocking the laser beam.
The lens 105 and the spatial filter 106 constitute a beam expander. The spatial filter 106 has a pinhole, and when the laser beam condensed by the lens 105 enters the pinhole, the beam diameter of the laser beam is expanded. Here, the beam system is expanded to about 200 mm by passing through the beam expander.

  A plane wave can also be used for interference exposure by disposing a collimator lens between the spatial filter 106 and the diffractive optical element 200.

FIG. 3 is a diagram for explaining the interference light generated by the diffractive optical element 200. When the laser beam (B0) is incident on the diffractive optical element 200 substantially perpendicularly, two diffracted beams (B1, B2) having intensities of the + 1st order and the −1st order are generated. Due to the interference between these diffracted beams, an interference light intensity distribution (F) is formed immediately after the diffractive optical element 200. Here, assuming that the wavelength of the incident laser beam (B0) is λ, the crossing angle of the ± 1st-order diffracted beams is θ, and the period of the interference light intensity distribution F (interference fringes) is P ′, the period P ′ is expressed by the following equation. Given.
P ′ = λ / (2 sin θ) (3)

Note that the relationship of the following equation holds between the period P of the periodic structure layer 203 of the diffractive optical element 200 and the period P ′ of the interference light intensity distribution.
P = 2P ′ (4)
Therefore, for example, when it is desired to form an interference fringe with P ′ = 140 nm, the period P of the diffractive optical element 200 may be set to 280 nm.

A substrate 300 is placed on a stage 107 disposed immediately after the diffractive optical element 200, and a photoresist layer adjusted to the wavelength of the incident beam is formed on the surface of the substrate 300.
This photoresist is exposed by interference light formed immediately after the diffractive optical element 200.

  Thereafter, the exposed substrate 300 is developed to form a pattern corresponding to the interference light intensity distribution by the developed photoresist layer. Further, the resist pattern is transferred to the substrate 300 by performing etching using the photoresist layer as a mask.

In order to form a resist pattern having a high aspect and a good shape, it is essential to sufficiently increase the contrast of interference fringes. The contrast C of the interference fringes is given by the following equation, where Δx is the displacement of the interference fringes. FIG. 4 is a diagram (graph) showing the relationship of this equation.
C = sin (Δx) / (Δx) (5)

  As can be seen from the graph of FIG. 4, in order to increase the contrast of the interference fringes, the displacement of the interference fringes during exposure must be suppressed to almost zero. In order to realize this, it is necessary to eliminate air fluctuations and vibrations of the apparatus.

  In the pattern forming apparatus 100, since the beam incident on the diffractive optical element 200 forms an interference fringe immediately after the diffractive optical element 200, the distance between the diffractive optical element 200 and the substrate 300 can be set to 1 mm or less, for example. . For this reason, it is possible to make the influence of the fluctuation of the air, the vibration of the apparatus, etc. received while the beam propagates between them very small.

  As described above, the diffractive optical element 200 is designed to generate ± first-order beams of equal intensity when the laser beam is incident substantially perpendicularly. At this time, a zero-order diffracted beam is also generated. When the intensity of the zero-order beam exceeds a certain level, the interference light intensity distribution necessary for pattern formation cannot be obtained.

  FIG. 5 shows the intensities of the zero-order and ± first-order beams and the depth of the periodic structure layer 203 of the diffractive optical element 200 when a diffractive optical element having no intermediate layer is used between the support substrate and the periodic structure layer. It is a figure (graph) which shows the example of the relationship with length H. The graph shows values when the period P of the diffractive optical element 200 is 280 nm, the polarization of the incident beam is TE, and the fill factor of the periodic structure layer 203 is 0.4. FIG. 5A shows the result when the beam is incident from the support substrate 201 side, and FIG. 5B shows the result when the beam is incident from the periodic structure layer 203 side. From the figure, it can be seen that the intensity of the 0th-order diffracted beam does not drop below a certain level.

  FIGS. 6 and 7 are diagrams (graphs) showing an example of the relationship between the zero-order and ± first-order beam intensities and the thickness of the intermediate layer 202 when the diffractive optical element 200 according to the present invention is used. . FIG. 6 shows the result when the beam is incident from the support substrate 201 side, and FIG. 7 shows the result when the beam is incident from the periodic structure layer 203 side. Here, the refractive index n of the intermediate layer 202 is 2.05.

  When the thickness of the intermediate layer 202 is changed from 0 nm to 500 nm, the intensity of the 0th-order and ± 1st-order beams also changes, and a phenomenon in which the intensity of the 0th-order diffracted beam is significantly reduced at a specific thickness is observed. The reason why the intensity of the 0th-order diffracted beam is small is that the refractive index of the intermediate layer 202 is different from the refractive indexes of the support substrate 201 and the periodic structure layer 203, so that the boundary condition between the layers changes, and the resonance region This is because a kind of anomaly (singularity) occurs. FIG. 6B and FIG. 7B are enlarged views of a graph around a thickness of 114.5 nm where an anomaly is observed.

  As can be seen from FIGS. 6 and 7, the tolerance of the thickness of the intermediate layer 202 that causes the anomaly is not large. For example, by adjusting the angle of the incident beam, the thickness error can be corrected to generate the anomaly. Is possible.

In order to generate anomalies, the following relationship must be established between the refractive index n of the intermediate layer 202, the incident beam wavelength λ, and the period P of the diffractive optical element 200.
n> 2λ / P (6)
As the value of n increases, anomalies occur under more conditions (thickness of the intermediate layer 202).

  In the examples shown in FIGS. 6 and 7, n = 2.05, which satisfies Expression (6), but anomalies occur under the condition of n ≦ 2λ / P = 2 · 266/280 = 1.90. I did not.

  Further, it is desirable that the values of the period P and the wavelength λ of the incident laser beam are not far apart from each other in terms of generating anomalies.

  As described above, according to the pattern forming apparatus 100 of the present invention, each beam forming the interference light intensity distribution is not easily affected by disturbances such as air fluctuations and vibrations of the apparatus. Exposure can be performed.

The pattern forming apparatus 100 of the present invention can be used for manufacturing an optical thin film device such as an inorganic polarizing element.
For example, extending the life of a liquid crystal projector for home use has become a problem, but in order to solve this problem, it is essential to improve the light resistance of a polarizing element used in the liquid crystal projector. In this respect, the inorganic polarizing element is superior in light resistance as compared with a polarizing element formed of a polymer.

  In the inorganic polarizing element, an aluminum film is first formed on a substrate 300 (glass substrate) by means such as sputtering or vacuum deposition, an antireflection layer is formed thereon by spin coating, and a resist is formed thereon by spin coating. Form a layer. When the resist is baked and developed after the interference exposure, a desired resist pattern can be formed on the aluminum film. The resist pattern can be transferred onto the aluminum film by dry etching the formed resist pattern by a method such as ICP or ECR. Further, by forming the resist antireflection layer, it is possible to prevent an interference standing wave due to reflection on the back surface and to form a good pattern.

  The resist pattern can be transferred to, for example, quartz or silicon other than the above aluminum film.

It is a figure which shows the structure of the pattern formation apparatus of this invention. It is a figure which shows the structure of the diffractive optical element of this invention. It is a figure explaining the interference light generated by a diffractive optical element. It is the figure which showed the relationship between the contrast of an interference fringe, and the displacement of an interference fringe. It is a figure which shows the relationship between the 0th-order and +/- 1st-order beam intensity at the time of using the diffractive optical element which does not have an intermediate | middle layer, and the depth of the periodic structure layer of a diffractive optical element. It is a figure which shows the relationship between the 0th-order and +/- 1st-order beam intensity at the time of using the diffractive optical element by this invention, and the intermediate | middle layer thickness of a diffractive optical element. It is a figure which shows the relationship between the 0th-order and +/- 1st-order beam intensity at the time of using the diffractive optical element by this invention, and the intermediate | middle layer thickness of a diffractive optical element.

Explanation of symbols

100 pattern forming apparatus, 101 laser oscillator, 102, 103 mirror, 104 shutter, 105 lens, 106 spatial filter, 107 stage, 200 diffractive optical element, 201 support substrate, 202 intermediate layer, 203 periodic structure layer, 300 substrate

Claims (8)

A support substrate;
A periodic structure layer having a periodic uneven shape;
A diffractive optical element comprising an intermediate layer having a refractive index different from that of the support substrate and the periodic structure layer between the support substrate and the periodic structure layer. The diffractive optical element according to claim 1, wherein a refractive index of the intermediate layer is larger than a refractive index of the support substrate and an average refractive index of the periodic structure layer. A laser oscillator;
A pattern forming apparatus that includes a diffractive optical element that receives a beam oscillated from the laser oscillator and generates a plurality of diffracted beams, and forms a pattern on a workpiece by performing interference exposure using the diffracted beams Because
The diffractive optical element generates a ± 1st order diffracted beam having the same intensity and a 0th order diffracted beam having a lower intensity than the ± 1st order diffracted beam, and the ± 1st order diffracted beam interferes to cause the interference. The pattern forming apparatus, wherein the interference exposure is performed by an interference light intensity distribution formed immediately after the diffractive optical element. The diffractive optical element includes a support substrate, a periodic structure layer having a periodic concavo-convex shape, and an intermediate having a refractive index different from that of the support substrate and the periodic structure layer between the support substrate and the periodic structure layer. With layers,
Between the refractive index n of the intermediate layer, the beam wavelength λ oscillated from the laser oscillator, and the period P of the periodic structure layer,
n> 2λ / P
The pattern forming apparatus according to claim 3, wherein: 5. The pattern forming apparatus according to claim 3, wherein a thickness of the intermediate layer is adjusted so that an intensity of the 0th-order diffraction beam is minimized. Emitting a beam from a laser oscillator;
Incident the beam on a diffractive optical element to generate a plurality of diffracted beams;
Forming a pattern on the workpiece by performing interference exposure using the diffracted beam,
In the step of generating the diffracted beam, a ± 1st order diffracted beam having the same intensity and a 0th order diffracted beam having a smaller intensity than the ± 1st order diffracted beam are generated,
The pattern forming method, wherein the interference exposure is performed by an interference light intensity distribution formed immediately after the diffractive optical element due to interference of the ± first-order diffracted beams. The diffractive optical element includes a support substrate, a periodic structure layer having a periodic concavo-convex shape, and an intermediate having a refractive index different from that of the support substrate and the periodic structure layer between the support substrate and the periodic structure layer. With layers,
Between the refractive index n of the intermediate layer, the beam wavelength λ emitted from the laser oscillator, and the period P of the periodic structure layer,
n> 2λ / P
The pattern forming method according to claim 6, wherein: 8. The pattern forming method according to claim 6, wherein the thickness of the intermediate layer is adjusted so that the intensity of the 0th-order diffraction beam is minimized.

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