JPH10213702A - Method and device for forming diffraction grating, and diffraction garting pattern - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a distribution of diffraction efficiency in a dot uniform by delicately controlling the diffraction grating by using quasi-coherent light, varying the optical path difference between two pieces of luminous flux which is made incident on a photosensitive material, and varying characteristics of a formed diffraction grating. SOLUTION: A laser beam source which emits a beam such as quasi-coherent light is used. A controller controls respective elements (refractive index modulating element, etc.) according to data on coordinates, characteristics, etc., of the diffraction grating on the photosensitive material. The refractive index modulating element can modulate an optical distance by which the laser beam passes and control the optical path difference from the other laser beam. Through the modulation of the refractive index, the optical distance Lopt when the laser beam passes through the refractive index modulating element varies so that Lopt =Lreal ×n. Here Lreal is a distance by which the laser beam travels straight, impinges on, and exits from and (n) is the refractive index. Therefore, the variation in refractive index by the refractive index modulating element becomes the variation of the optical path difference and corresponds to variation in interference fringe density recorded based on the visibility.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an improvement of a method and an apparatus for forming dots formed by a diffraction grating,
The present invention relates to a pattern in which the dots are arranged as desired on a substrate.

[0002]

2. Description of the Related Art A method of forming a diffraction grating by interfering two coherent lights such as a laser beam on a photosensitive material (2).
Light beam interference) is well known, and a method of arranging minute dot-shaped diffraction gratings on a substrate as desired to form a pattern is disclosed in Japanese Patent Application Laid-Open Nos. 59-166913 and 60-1560 by the present applicant.
No. 04, JP-A-2-72319, and the like.

The parameters of the diffraction grating (grating fringes) include the direction of the diffraction grating, the pitch of the diffraction grating, the diffraction efficiency, and the like.
Determines the frequency (the color seen at a fixed point), and determines the brightness of the diffracted light.

In the two-beam interference according to the known prior art, when it is desired to change the brightness of the diffraction grating, the intensity of the incident light or the increase or decrease of the exposure time is adjusted.
The amount of exposure (intensity x time) is changed.

In the above method, it is difficult to delicately control the amount of exposure, and it is difficult to accurately control the brightness of the diffraction grating. In particular, when forming dots with low diffraction efficiency in a short exposure time, it is extremely difficult to precisely adjust the desired diffraction efficiency.

In the case of two-beam interference using laser light, the spatial exposure distribution within a dot also changes depending on the intensity distribution (Gaussian distribution) of the laser light, and a uniform diffraction grating is formed. It is necessarily difficult to do.

[0007]

SUMMARY OF THE INVENTION The present invention provides a method of forming a diffraction grating which enables fine control of the diffraction efficiency and makes the distribution of the diffraction efficiency uniform within a dot.
It is an object of the present invention to provide a device, and to provide a diffraction grating pattern composed of a group of the dots composed of a diffraction grating.

[0008]

According to the present invention, a diffraction grating is formed by two-beam interference using quasi-coherent light. The invention according to claim 1 uses the quasi-coherent light instead of the coherent light, and changes the optical path difference between the two light beams incident on the photosensitive material, so that the visibility (visibility, sharpness) of the interference fringe depending on the optical path difference between the two light beams. Degree) change,
The characteristics of the diffraction grating formed on the photosensitive material are changed.

According to a second aspect of the present invention, the diffraction efficiency (brightness of the diffracted light) is changed by changing the density of the diffraction grating (interference fringe) as a characteristic of the diffraction grating to be changed.

A third aspect of the present invention is a method for forming a diffraction grating, wherein two quasi-coherent lights having different wavelengths are superposed and used.

According to a fourth aspect of the present invention, there is provided a method for forming a diffraction grating, comprising changing a spatial distance as means for changing an optical path difference between two light beams.

A fifth aspect of the present invention is a method for forming a diffraction grating, wherein a refractive index modulation element is used as a means for changing an optical path difference between two light beams.

According to a sixth aspect of the present invention, there is provided a diffraction grating forming apparatus, comprising: a light source for emitting a quasi-coherent beam; and a shutter capable of controlling an exposure time by selecting passage / blocking of the beam. A beam splitter that splits a beam from the shutter into two beams, and an optical path length control unit that can change an optical path length of one of the split beams within a certain range, and via the optical path length control unit. The beam and the other beam are crossed on a photosensitive material, and interference fringes by the two beams are recorded on the photosensitive material, thereby forming a dot-like diffraction grating.

According to a seventh aspect of the present invention, there is provided a table on which a photosensitive material is placed, an incident position of two beams associated with movement of the table, an optical path length difference between the two beams associated with control of the optical path length control means, A controller for controlling the opening and closing of the shutter, wherein the characteristics of the diffraction grating are appropriately changed for each dot under the control of the controller.

The invention according to claim 8 is characterized in that a laser light source is used as a light source for emitting a quasi-coherent beam.

A ninth aspect of the present invention is characterized in that a refractive index modulation element is used as the optical path length control means.

According to a tenth aspect of the present invention, as the optical path length control means, a moving stage provided with a mirror for changing a reflection optical path of one beam is used.

According to the eleventh aspect of the present invention, which relates to a diffraction grating pattern produced by using the above-described forming method / forming apparatus, the density and / or the diffraction efficiency of the diffraction grating are uniform within the dot, and the unit of the dot is It is a diffraction grating pattern composed of a plurality of dots that are arbitrarily changed.

According to the second aspect, the "diffraction efficiency" is changed as a characteristic of the diffraction grating. As other characteristics, the polarization characteristic of the diffracted light and the incident angle of the illumination light are controlled by controlling the depth of the diffraction grating. It is also conceivable to change the dependence characteristics and the like.

As means for changing the optical path difference between the two light beams, there are mechanical (changing the distance spatially) and electrical (changing the optical distance by controlling the refractive index modulation element), and precise and accurate control of the characteristics. Is possible. In particular, when controlling electrically, no mechanical operation is required,
It is possible to change the optical path difference at high speed.

Note that the optical path difference is a difference in optical distance, and indicates a difference in distance corresponding to a distance in which light propagates in a vacuum.

<Operation> Even when the exposure time is extremely short,
It is possible to control the characteristics of the diffraction grating without having to increase or decrease the exposure time.

The density of interference fringes due to two-beam interference depends on the visibility of light and the optical path difference between the two beams. That is, 2
Due to the optical path difference between the light beams, a time shift occurs in which the respective light beams reach the photosensitive material, thereby changing the visibility of the interference fringes.

Since the visibility corresponds to the density of interference fringes, it becomes the density of the diffraction grating recorded on the photosensitive material. In the present invention, since the density of the interference fringes changes uniformly in the area on the photosensitive material where light is incident, a uniform diffraction grating is recorded.

Depending on the photosensitive material (kind of diffraction grating), the density of the diffraction grating is either the literal recording density of the diffraction grating (amplitude type diffraction grating) or the depth of the diffraction grating (surface relief type diffraction grating). ), Or recorded as a refractive index modulation degree (phase type diffraction grating).

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the visibility of interference fringes are shown in FIGS. The horizontal axis is the time shift τ of the two light beams (proportional to the optical path difference), and the vertical axis is the visibility.

FIG. 1 shows the visibility characteristics of the completely coherent light. Perfect coherent light beams (even if they do not originate from the same light source) always have a visibility of 1 (= 1) without depending on a time shift τ (optical path difference between two light beams).
00%), a high-contrast lattice fringe is recorded by interference.

Even a laser beam generally used as interference light is not actually completely coherent light, and the visibility varies between 1 and 0 depending on the optical path difference.

The visibility cycle of the laser beam is several meters.
Since the optical path difference of about m is long enough not to cause a problem, interference fringes by two laser beams emitted from the same light source can stably record interference fringes on the photosensitive material.

In the present invention, the visibility cycle is several meters.
Two-beam interference using quasi-coherent light that is affected by an optical path difference of about m is employed. By using two monochromatic lights (laser lights) having different wavelengths in an overlapped manner, it is possible to cause two-beam interference by the above quasi-coherent light.

When two monochromatic lights having different wavelengths are used as the quasi-coherent light, periodic visibility is provided, so that a periodic optical path difference can be handled, the degree of freedom of the optical system is increased, and the realization is easy. Become.

FIGS. 2 and 3 show quasi-coherent visibility characteristics in the present invention. FIG. 4 is an explanatory diagram showing the visibility characteristics of a mercury lamp.

In FIGS. 2 to 4, the visibility changes between 1 and 0 according to the optical path difference. Therefore, by appropriately setting the optical path difference, the visibility of the interference fringes due to the light can be arbitrarily controlled.

The visibility of interference fringes due to two-beam interference indicates the density of the interference fringes in a region where the two beams intersect. In the present invention, an interference fringe is recorded on a photosensitive material at a position where two light beams intersect, so that an interference fringe having an arbitrary density can be recorded.

Since the density of the recorded interference fringes is the density of the diffraction grating, it is generally proportional to the diffraction efficiency of the diffraction grating. From the above, it is clear that the characteristics of the formed diffraction grating can be changed by controlling the optical path difference.

For example, when two beams interfere with each other so as to eliminate the optical path difference (see FIG. 5A), visibility = 1, interference fringes are recorded with the highest contrast, and the diffraction efficiency of the diffraction grating is obtained. Will be higher. On the other hand, when the interference fringes are recorded by changing the optical path difference so that the visibility becomes 0.5 (see FIG. 5B), interference fringes having half the contrast are recorded, and the diffraction efficiency is reduced.

Actually, in the case of a surface relief type or phase type diffraction grating, the diffraction efficiency is determined by the depth or phase modulation degree of the interference fringes, so that visibility = 1 is not always the maximum diffraction efficiency. That is, diffraction efficiency and visibility are
This is because it does not similarly vary between 0% and 100% depending on the depth of the diffraction grating. The explanation in FIGS. 5 (a) and 5 (b)
This is an example in which the exposure amount is set so that the maximum diffraction efficiency is obtained when visibility = 1.

FIG. 6 is an explanatory view showing one embodiment of the diffraction grating forming apparatus. The apparatus includes a laser light source that emits a quasi-coherent beam, a shutter that selects transmission / shielding of the laser beam from the light source, and a half mirror that functions as a beam splitter that divides the laser beam transmitted through the shutter into two beams. A refractive index modulation element that changes the optical path difference of one laser beam passing through a half mirror, and a laser beam that passes through the refractive index modulation element and the other laser beam interfere with each other to form a diffraction grating (interference fringe). Photosensitive material for recording dots, an XZ stage for moving the photosensitive material two-dimensionally to form a diffraction grating at an arbitrary position, a stage for forming a plurality of diffraction gratings (dots), and a refractor. And a controller for controlling the shutter.

The controller controls each element (stage, refractive index modulation element, shutter) in accordance with (prepared) data such as coordinates of the diffraction grating to be formed on the photosensitive material and characteristics (brightness).

Since the refractive index modulation element can modulate the optical distance through which the laser beam passes, the optical path difference from the other laser beam can be controlled. Due to the modulation of the refractive index, the optical distance Lopt when the laser beam passes through the refractive index modulation element changes as follows. L _opt = L _real × n L _real is a distance (thickness of the refractive index modulation element) where the laser beam goes straight from the incidence to the refractive index modulation element and exits, and n is a refractive index.

Therefore, a change in the refractive index by the refractive index modulation element becomes a change in the optical path difference, and corresponds to a change in the density of interference fringes recorded based on visibility.

The refractive index modulation element includes an acousto-optic modulation element (AOM), a liquid crystal element, and the like. In the latter, a homogeneous alignment element is preferable. Since they can be electrically controlled, it is possible to control the refractive index change at high speed, which is effective in reducing the time required for manufacturing a diffraction grating. In addition, since the number of movable parts in the optical system can be reduced, vibrations and the like do not occur, and a stable diffraction grating can be formed.

FIG. 7 is an explanatory view showing another embodiment of the diffraction grating forming apparatus. The above device employs means for mechanically changing the spatial distance of two light beams, instead of the refractive index modulation element in the device of FIG. That is, a mirror is placed on a moving stage (in the figure, both are collectively referred to as a moving mirror), and by changing the position of the moving mirror up and down, the optical path difference can be arbitrarily controlled. ing.

In the case of FIG. 7, the condition of the optical path difference = 0 cannot be realized (since the optical path lengths of the two light beams are necessarily different regardless of the position of the moving mirror), but if the periodicity of the visibility is used. It is possible to change the characteristics of the diffraction grating. Also, by making some changes to the device of FIG. 7,
It is also possible to use an optical system that realizes an optical path difference including zero.

As a means for changing the optical distance, it is very easy to change the distance spatially, and it is also possible to freely set the variable range of the distance, and to design an optical system in accordance with the characteristics of the quasi-coherent light. Not only is it possible, but it is easy to control the accuracy as needed.

In the diffraction grating forming apparatus according to the above two embodiments, the visibility due to the interference of two light beams can be easily and accurately controlled by the optical path difference. Can be manufactured.

The visibility depending on the optical path difference is as follows.
Since the interference fringes change uniformly, the visibility of the interference fringes is uniform, and a diffraction grating having a uniform diffraction efficiency within the dot can be manufactured.

Further, even when the exposure time is extremely short,
There is no need to strictly control the opening and closing time of the shutter.
High-precision control is possible only by controlling the optical path difference of the light beam.

[0049]

According to the present invention, there is provided a method and apparatus for forming a diffraction grating capable of finely controlling the diffraction efficiency and making the distribution of the diffraction efficiency uniform within a dot when the dot is a constituent unit. And a diffraction grating pattern comprising a group of the dots comprising the diffraction grating is provided.

[0050]

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing visibility characteristics of complete coherent light.

FIG. 2 is an explanatory diagram showing quasi-coherent visibility characteristics.

FIG. 3 is an explanatory diagram showing quasi-coherent visibility characteristics.

FIG. 4 is an explanatory diagram showing visibility characteristics of a mercury lamp.

5A and 5B show states in which interference fringes are recorded by changing visibility, wherein FIG. 5A shows visibility = 1, and FIG.
FIG.

FIG. 6 is an explanatory view showing one embodiment of a diffraction grating forming apparatus.

FIG. 7 is an explanatory view showing another embodiment of the diffraction grating forming apparatus.

Claims (11)

[Claims] 1. A method of forming a diffraction grating by recording interference fringes on a photosensitive material by two-beam interference of coherent light, wherein a quasi-coherent light is used instead of the coherent light, and an optical path of two light beams incident on the photosensitive material. A method of forming a diffraction grating, comprising: changing a difference to change characteristics of a diffraction grating formed on a photosensitive material based on a change in visibility of interference fringes depending on an optical path difference between two light beams. 2. The method according to claim 1, wherein the diffraction efficiency is changed as a characteristic of the diffraction grating. 3. The quasi-coherent light having two wavelengths different from each other.
2. The method according to claim 1, wherein two monochromatic lights are used in an overlapping manner.
Or the method for forming a diffraction grating according to 2. 4. The method of forming a diffraction grating according to claim 1, wherein a spatial distance is changed as a means for changing an optical path difference between the two light beams. 5. The method for forming a diffraction grating according to claim 1, wherein a refractive index modulation element is used as means for changing the optical path difference between the two light beams. 6. A light source for emitting a quasi-coherent beam, a shutter capable of controlling an exposure time by selecting passage / blocking of the beam, and splitting a beam from the shutter into two beams. A beam splitter, and an optical path length control unit capable of changing an optical path length of one of the branched beams within a certain range, wherein the beam passing through the optical path length control unit and the other beam are formed on a photosensitive material. A diffraction grating forming apparatus for forming a dot-like diffraction grating by recording interference fringes of two beams on the photosensitive material. 7. A table on which a photosensitive material is placed, an incident position of two beams associated with movement of the table, an optical path length difference between the two beams associated with control of the optical path length control means, opening and closing of the shutter, 7. The diffraction grating forming apparatus according to claim 6, further comprising: a controller for controlling the characteristics of the diffraction grating for each dot under the control of the controller. 8. A laser light source as a light source for emitting a quasi-coherent beam.
Or the apparatus for forming a diffraction grating according to 7. 9. The diffraction grating forming apparatus according to claim 6, wherein a refractive index modulation element is used as the optical path length control means. 10. A diffraction grating forming apparatus according to claim 6, wherein a moving stage provided with a mirror for changing a reflection optical path of one beam is used as the optical path length control means. . 11. A diffraction grating pattern produced by using the diffraction grating forming method according to any one of claims 1 to 5 and the diffraction grating forming apparatus according to any one of claims 6 to 10. A diffraction grating pattern composed of a plurality of dots in which the density and / or diffraction efficiency of the diffraction grating is uniform within the dots and arbitrarily changed in dot units.