JP2001004818A - Diffraction optics and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a diffraction optics having high precision by dividing a region having a stepwise shape. SOLUTION: In this manufacturing method, regions A1, A2, A3 of a diffraction optics 1 are divided successively into a circular and two annular regions in this order in the radial direction, and an eight step stair structure is manufactured in the region A1 by repeating patterning and etching processes. Next, a diffraction structure having an eight step stair structure is manufactured by repeating patterning and etching processes in the region A2 in the same way. As this time, since an incident angle used in optimization is largely deviated from a vertical line, etching amount in the region A2 is reduced to a smaller amount than the amount in the region A1 toward the periphery. Then, an eight step stair structure is manufactured by repeating the same work in the region A3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a diffractive optical element suitably used for an optical system having a particularly large angle of view and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, a method of manufacturing a diffractive optical element has been established with the progress of lithography technology, and various optical systems using the diffractive optical element have been proposed. A method of manufacturing such a diffractive optical element is disclosed in Japanese Patent No. 255554600, and a desired diffractive optical element is obtained by repeating a process of patterning a desired diffraction pattern as a whole and removing a material by etching a plurality of times. Obtainable.

A diffractive optical element mainly uses a light diffraction phenomenon, unlike a refractive optical element using a light refraction phenomenon. For this reason, it has an incident angle dependence of the diffraction efficiency, which is an optical characteristic not found in the refractive optical element. What is diffraction efficiency?
It is a relative intensity of light diffracted in a predetermined diffraction direction with respect to the intensity of the incident light beam. It is known that the diffraction efficiency of a general diffractive optical element shows a tendency as shown in FIG. 11 depending on the difference in the incident angle. I have.

That is, when the diffractive optical element is applied to an imaging system, it is often used for point-to-point imaging.
In this case, the grating pitch of the diffractive optical element can be obtained from three factors: the incident angle of each light beam on the diffractive optical element, the wavelength of the incident light beam, and the order. The diffraction efficiency is generally optimized using only the incident angle of the principal ray. In a rotationally symmetric optical system, the incident angle is 0 ° with respect to the optical axis to optimize the diffraction efficiency.

[0005]

However, FIG.
In an optical system having a high NA, that is, a large numerical aperture as shown in FIG. Would.

Further, as shown in FIG. 13, when the diffractive optical element D is used in an imaging system for an object having a finite size, unlike the case of point-to-point imaging, the height of the object is increased with respect to each incident position. A plurality of corresponding light beams will be incident. These rays are incident on the diffractive optical element D at different incident angles, and the angles are generally not 0 °, and the average value is generally not 0 °.

As described above, in an optical system having a general field of view and a numerical aperture as shown in FIGS.
When the diffractive optical element D is used, the diffraction efficiency depends on the incident angle, and the intensity of the diffracted light of an incident light beam whose incident angle is not 0 ° is reduced. Therefore, since the light intensity in the optical system and the relative balance change, there arises a problem that the imaging performance is deteriorated due to a decrease in illuminance or uneven illuminance. Further, when a plurality of diffractive optical elements D are used in the optical system, the effect of the reduction in the diffraction efficiency follows a power law, so that the problem in the entire optical system becomes even more remarkable.

It is an object of the present invention to provide a diffractive optical element which can suppress a decrease in diffraction efficiency even when used in an optical system having a wide field of view and a large numerical aperture.

Another object of the present invention is to provide a method for manufacturing a diffractive optical element having the above-mentioned performance.

[0010]

In order to achieve the above object, a diffractive optical element according to the present invention divides a region on a substrate into a plurality of regions, and within each of these regions, determines the center of gravity and the center of gravity based on the angular distribution of incident light. An incident angle is obtained, and the depth is different for each of the regions so that the diffraction efficiency is maximized at the incident angle.

In the method of manufacturing a diffractive optical element according to the present invention, a region on a substrate is divided into a plurality of regions, and an incident angle which becomes a center of gravity is determined from an angle distribution of incident light in each of the regions.
The patterning and etching steps are independently repeated for each of the regions so that the depth differs for each of the regions so that the diffraction efficiency is maximized at the incident angle, and the amount of etching in each of the etching processes is changed. It is characterized by the following.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the illustrated embodiment. FIG. 1 is a plan view of a diffractive optical element 1 according to a first embodiment. Regions A1, A2, and A3 each represent a circular or toroidal region divided into three in the radial direction, and FIG. 2 shows a cross-sectional view of the element 1. FIG.
Since the structure of the diffractive optical element 1 is extremely fine, an eight-step structure is actually manufactured, but in FIG.
It is shown enlarged to the staircase structure of steps. The one-pitch depths of the diffractive optical element 1 corresponding to the regions A1 and A3 are depths h1 and h3, respectively.

The diffractive optical element 1 in this embodiment has a function of a convex lens in the optical system of a refractive lens. As the angle of incidence on the diffractive optical element 1 approaches the outer peripheral portion of the diffractive optical element 1, the center of gravity of the light beam density has an angle from the vertical, and is about 20 ° at the maximum. Therefore, the distribution of the incident angle is represented by three incident angles, and the etching amount is designed for each region in accordance with the representative incident angle.

First, by repeating the patterning and etching steps in the area A1, 8
Build a staircase structure. Subsequently, by repeating the patterning and etching steps in the same manner for the region A2, an eight-step staircase structure is manufactured. At this time, the incident angle used for optimization deviates greatly from the vertical as it goes toward the periphery, so that the etching amount in the region A2 is smaller than that in the region A1. Subsequently, the same operation is repeated for the region A3 to produce an eight-step staircase structure. In the region A3, since the incident angle to be optimized is designed to be 20 °, the depth is about 94% of the center of the region A1. Since the diffractive optical element 1 is designed using a KrF excimer laser as a light source, the pitch depth at the center is 427 nm. Further, the number of steps of the diffractive optical element 1 and the order of the steps in each region are not related to the effects of the present invention.

In this embodiment, since a series of steps of patterning and etching are repeated for each region, the target value of etching can be changed for each region.
Further, since the process is the same as the normal etching process except that the region is divided, it is possible to perform etching with the original accuracy, thereby changing the etching depth for each region and optimizing the diffraction efficiency. The diffractive optical element 1 can be manufactured stably.

Further, in patterning a large-diameter diffractive optical element, patterning is often performed by joining exposure regions. Particularly, when the division boundary and the region boundary for optimizing the etching amount are matched, the efficiency is particularly high. It is a target.

Further, since the substrate of the diffractive optical element 1 is made of fluorite instead of quartz, the substrate can be used in the ultraviolet region, particularly, in the wavelength λ = 1.
ArF laser light of 93 nm, F of wavelength λ = 157 nm
₍₂ ) A diffractive optical element having high internal transmittance and good characteristics with respect to the wavelength of the laser beam can also be manufactured. When Si is used for the substrate, a diffractive optical element that can be used in the infrared region can be manufactured.

FIG. 3 is a sectional view of the diffractive optical element 11 according to the second embodiment.
3 is formed, and after patterning the entire region of the quartz substrate 12, the Cr film 13 is etched. At this time, the designed pattern of the diffractive optical element 11 is transferred to the Cr film 13. Subsequently, a window for specifying a region having an optimized etching amount is formed by applying the resist 14.

FIG. 4 is a flowchart showing a series of steps in FIG. 3 in detail. First, in step S1, a Cr film 13 is formed on a quartz substrate 12. Subsequently, after patterning the entire region of the quartz substrate 12 in step S2, the Cr film 13 is etched.
Next, in step S3, a resist 14 is applied, and a window for specifying an etching region is formed in the resist 14 in accordance with the region having the optimized etching amount. Further, in step S4, the region formed by the resist 14 is etched to a desired depth using the Cr film 13 as a mask. Subsequently, in step S5, the resist 1
4 to form a window in the next area. Then, similarly, the region formed by the resist 14 is etched to a desired depth using the Cr film 13 as a mask.

If this process is repeated by the number of divisions of the region where the amount of etching is optimized, it is possible to manufacture while optimizing the patterning and etching of one layer for each region.

Therefore, in order to obtain a 2 ⁿ -step structure, it is necessary to pattern and etch the n-layer.
It is necessary to process the layer. In step S6, the Cr film 13 is formed and patterned, and a second layer pattern is formed on the entire surface and transferred to the Cr film 13. Then,
A resist window is formed for each region where the etching amount is optimized, and the etching is repeated while appropriately changing the etching amount. Similarly, by performing the processing of the third layer, an eight-step structure can be obtained.

In patterning a large-diameter diffractive optical element, patterning is often performed by joining exposure regions of a patterning apparatus. In order to improve the number of patterning exposure regions and diffraction efficiency, an optimized etching amount is used. This is effective when the number of regions does not match, or when the dividing boundary of patterning and the boundary of the region with the optimum etching amount cannot match.

When a film of Al, Ti, Ni, Mo, W, TiO ₂ , or ITO is used instead of the Cr film 13 used in this embodiment, a good diffractive optical element can be obtained with good pattern transfer. Can be made.

FIG. 5 is a sectional view of the diffractive optical element 21 according to the third embodiment. The diffractive optical element 21 in this embodiment divides the substrate 22 into two in the radial direction, divides the region for optimizing the etching amount into two, and forms each region separately on the front and back surfaces of the diffractive optical element 21. . This makes it possible to easily separate the etching process for each region. In this case, there is no problem even if the region where the staircase structure is not formed is etched at the same time as the non-etched region by the resist or the like.

The light ray L incident on the medium from the air is
It is known that the angle of refraction becomes smaller than the angle of incidence according to Snell's law. Therefore, it is preferable to mount the diffractive optical element in the optical system such that the staircase structure is directed to the light-emitting side at the periphery of the diffractive optical element having a large incident angle. In FIG. 5, this corresponds to the incidence of a light beam from the upper side of the diffractive optical element 21. Of course, the distance between the front and back surfaces is taken into consideration when designing.

FIG. 6 is a sectional view of a diffractive optical element 31 according to the fourth embodiment. In the present embodiment, the region for optimizing the etching amount is divided into two parts in consideration of the incident angle of the light beam, and stepped shapes A1 and A2 are formed on different substrates 32 and 33, respectively. By directly joining and integrating the surfaces having the stair structure so as to face each other, the diffractive optical element 31 in which the optimized region is divided into two can be manufactured.

As a joining method, a direct joining method called an optical contact is used, and as shown in FIG. 7A, quartz and water, water and fluorite are interposed via water or the like adsorbed on the surface of the optical member. The optical member is directly joined by hydrogen bonding with water or the like or by Van der Waals force as shown in FIG. In these direct bonding methods, optical members such as glass and quartz can be bonded to each other without using an adhesive or the like.However, in order to obtain sufficient bonding strength, the surface roughness of the bonding surface is determined by the square root mean square. To 5 nm or less and a water content of 10 ¹³
It is desirable to control it to be at least molecule / cm ² .

Normally, the surface of the joining portion has a fine gap h as shown in FIG. 8, but assuming a radius r, a surface energy γ, an elastic modulus E, and a thickness t, the following equation (1) It is known that direct joining is possible within a range satisfying ()). h / r ² <(r / E / t ³ ) ^1/2 (1)

Equation (1) shows a case where the gap h exists at one place, but the gap h exists innumerably in the whole substrate having a diameter of several hundred mm. From formula (1), it is necessary to consider the gap h and the surface energy γ in order to perform direct bonding, and it can be seen that the surface roughness measured by AFM or the like and the moisture content measured by APIMS or the like serve as references. Therefore, in order to ensure the surface roughness of the diffractive optical element, before processing the diffractive optical element in a semiconductor process, polishing or the like is performed to secure the surface roughness of the substrate, and further during and after processing. Careful consideration must be given to the surface roughness.

Regarding the surface energy γ, a normal quartz substrate can secure a water content of 10 ¹³ molecules / cm ² , so that a sufficient surface energy γ can be obtained, but the substrate is contaminated. Causes a shortage of surface energy γ. In the case of a hydrophilic material such as quartz,
Although it is possible to recover the water content by washing with ultraviolet rays, ozone, or the like, it is necessary to secure the water content of a hydrophobic material by spraying water after the cleaning or treating with a hydrophilic chemical solution.

In the present embodiment, the etching process is performed separately according to each optimized etching amount. In addition, by separating the work into two substrates and then joining the step structure opposite to each other, the etching process can be separated for each region and the two diffractive optical element structures can be spatially close to each other.

Further, since the diffractive optical element 31 has the stair structure opposing to each other, dust and the like do not adhere to the diffractive optical surface. Even if dust or the like is attached, the diffractive optical element 31 in the present embodiment has a smooth surface and can be easily cleaned.

FIG. 9 is a sectional view of a diffractive optical element 41 according to the fifth embodiment. The diffractive optical element 41 according to the present embodiment has stepped shapes A 1, A 2, and A 4 optimized for substrates 41, 42, and 43, respectively. By forming A3 and joining using optical contacts as in the fourth embodiment, it is possible to manufacture the diffractive optical element 41 in which the optimized region is divided into three.

FIG. 10 shows a diffractive optical element 51 according to a sixth embodiment, in which a substrate 52 having a region A3 formed with a region A1 and a substrate 53 having a region A2 formed therein are integrated.

In the same manner as in the second embodiment, C
The pattern of the entire surface is transferred to the r film 13, and thereafter, the entire surface is etched to the depth of the region having the least amount of etching,
Subsequently, after the first etching is completed, a resist 14 is applied, and patterning is performed so that only the outermost region A3 is covered with the resist 14. Further, in the regions A1 and A2 through the windows of the resist 14, the shortage of the first etching is performed with the etching amount of the region A2 having the second smallest etching amount. Hereinafter, the same process is used to cover the area other than the area A1 with the resist 14 and to process the shortage of the etching amount, thereby obtaining a diffractive optical element processed with the optimum etching amount to maximize the diffraction efficiency for each area. Obtainable.

It should be noted that the diffraction optical element manufactured according to the first to sixth embodiments is used, and the optical system constituted by K is mounted.
Using a stepper for rF laser, a high-performance semiconductor device can be manufactured by reduction baking on a silicon substrate and a series of semiconductor manufacturing steps.

[0037]

As described above, the diffractive optical element according to the present invention divides the area of the diffractive optical element in the radial direction,
By etching, optimization can be performed for each region, and diffraction efficiency can be improved.

The method for manufacturing a diffractive optical element according to the present invention can easily manufacture a diffractive optical element having good diffraction efficiency.

[Brief description of the drawings]

FIG. 1 is a plan view of an optical element according to a first embodiment.

FIG. 2 is a cross-sectional view of the optical element according to the first embodiment.

FIG. 3 is a sectional view of an optical element according to a second embodiment.

FIG. 4 is a flowchart of a second embodiment.

FIG. 5 is a sectional view of an optical element according to a third embodiment.

FIG. 6 is a sectional view of an optical element according to a fourth embodiment.

FIG. 7 is an explanatory diagram of a reaction process.

FIG. 8 is a sectional view of a microstructure.

FIG. 9 is a sectional view of an optical element according to a fifth embodiment.

FIG. 10 is a sectional view of an optical element according to a sixth embodiment.

FIG. 11 is a diffraction efficiency distribution diagram of the diffractive optical element.

FIG. 12 is an explanatory diagram of an optical system using a diffractive optical element.

FIG. 13 is an explanatory diagram of an optical system using a diffractive optical element.

[Explanation of symbols]

1, 11, 21, 31, 41, 51 Diffractive optical elements 2, 12, 22, 32, 33, 42, 43, 44, 5,
2,53 substrate 13 Cr film 14 resist

Claims (13)

[Claims] 1. An area on a substrate is divided into a plurality of areas, and in each of these areas, an incident angle serving as a center of gravity is determined from an angular distribution of incident light. A diffractive optical element wherein the depth is different for each region. 2. An area on a substrate is divided into a plurality of areas, and in each of these areas, an incident angle serving as a center of gravity is determined from an angular distribution of incident light, and the respective angles are set so that the diffraction efficiency is maximized at the incident angle. The steps of patterning and etching are repeated independently for each region so that the depth differs for each region,
A method of manufacturing a diffractive optical element, wherein an etching amount in each of the etching steps is changed. 3. The patterning is performed by repeatedly joining some of the patterns, and the etching amount is optimized in accordance with the boundary of the joining of the patterns in the radial direction and the incident angle which is the center of gravity of the incident angle distribution. 3. The method for manufacturing a diffractive optical element according to claim 2, wherein the boundary of the converted region coincides with the boundary. 4. The pattern is transferred to the second material by performing the patterning on the entire surface and etching a second material having an etching selectivity with respect to the base material, and excluding a region to be sequentially etched from the base material. 4. The method of manufacturing a diffractive optical element according to claim 2, wherein the material is covered with a third material having an etching selectivity with respect to the material, and is sequentially etched with the different etching amount. 5. The method according to claim 1, wherein the second material is Cr, Al, Ti, N.
5. The method according to claim 4, wherein the third material is a resist made of any one of i, Mo, W, TiO ₂ , and ITO.
Method for manufacturing diffractive optical element according to 6. The region where the amount of etching is changed is 2
4. The method according to claim 2, wherein each of these regions is formed on the front and back surfaces of the substrate. 7. The method of manufacturing a diffractive optical element according to claim 6, wherein the region having a large incident angle used for optimizing the etching amount is a light emission side. 8. The diffraction according to claim 2, wherein at least one of the regions in which the etching amount is optimized or another region is formed on another substrate and integrated by direct bonding. A method for manufacturing an optical element. 9. The method for manufacturing a diffractive optical element according to claim 8, wherein at least one set of diffractive optical element structures among the diffractive optical element structures manufactured on the another substrate is bonded to face each other. . 10. The method of manufacturing a diffractive optical element according to claim 2, wherein the material of the substrate is any one of quartz, fluorite, and silicon. 11. An optical system using a diffractive optical element produced by the method according to claim 2. 12. An exposure printing apparatus for manufacturing a semiconductor using the optical system according to claim 11. 13. A semiconductor device manufactured using the exposure printing apparatus for manufacturing a semiconductor according to claim 12.