JP3483445B2 - Diffractive optical element and method for manufacturing the element - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diffractive optical element used as a lens of an optical system incorporated in an exposure device, a photographing device, a lighting device and the like.

[0002]

2. Description of the Related Art Conventionally, a diffraction grating has been used as a spectroscopic element of a spectroscope, and the cross section of the grating has a sawtooth shape, which is called a blazed type, and there are some diffraction efficiency of 100%. On the other hand, in recent years, a binary optics (BO) element having a stepwise grating cross-sectional shape has been attracting attention as an optical element utilizing diffraction. A BO element in which a ring-shaped grating having a predetermined period is formed is also called a BO lens, and since an achromatic effect and an aspherical effect are expected, there is great expectation for development of a new optical system.

The required specifications for the BO lens greatly exceed the current cutting limit of the blazed type.
High-precision fine processing is enabled to some extent by a lithography method which is a processing method of a semiconductor. When a BO lens is applied to a lens optical system for taking a picture of a general steel camera or the like, it can be manufactured by a plastic and glass molding method by a mold processing using a metal mold material. In order to apply it to a light beam having a short wavelength, finer processing accuracy and higher dimensional accuracy are required. Therefore, for example, an i-line stepper is used for exposure and baking, a parallel plate type RIE device is used for dry etching, and a photolithography technique using ultraviolet rays for semiconductor manufacturing is used, and in the case of a 4-step BO lens, 2 The quartz substrate is directly processed by using three masks, and in the case of an 8-step BO lens, three masks are used.

[0004]

However, the above-mentioned conventional lens materials and processing methods can be applied even if the accuracy is low when the light source used has a long wavelength in the visible light region or infrared light region. However, in order to apply to far-ultraviolet light, beyond the limits of the current exposure and printing apparatus for ultraviolet rays, for example, position accuracy, overlay accuracy, etching accuracy, thickness (step)
Precision such as precision and edge precision (angle, inclination, wall surface) is required. Further, in the method of manufacturing a BO lens, the precision of superposition has a great influence on the edge precision of each element, and it is extremely difficult to make the overlapping side surfaces of 8 steps and 16 steps vertical. Further, since the size of the BO lens, that is, the lens diameter is large, it is necessary to perform the divided exposure to manufacture the BO lens.
This is a fatal problem for the above accuracy.

The object of the present invention is to solve the above problems,
An object of the present invention is to provide a high-performance diffractive optical element that can be accurately formed into a staircase shape and can be used for ultraviolet rays.

Another object of the present invention is to provide a method of manufacturing a high-performance diffractive optical element with high efficiency.

[0007]

A diffractive optical element according to the present invention for achieving the above object uses a translucent etching mask arranged at a position which is the uppermost step of a staircase shape,
A diffractive optical element formed by performing a predetermined number of steps
Therefore, the translucent etching mask is located at the uppermost position.
It is characterized in that a step or a part of the step is formed .

[0008]

Further, in the method for manufacturing a diffractive optical element according to the present invention, when forming a staircase structure, a step of forming an etching mask only at a position which should be the uppermost stage of the staircase structure and the etching mask are used. And a step of forming a staircase structure with a predetermined number of steps.

[0010]

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail with reference to the illustrated embodiments. FIG. 1 is a perspective view of a BO lens 1 having a diffractive element (grating) formed in an annular shape, FIG. 2 is a sectional view, and FIG. 3 is a partially enlarged sectional view. 24 wavelength used by design
Assuming that it is for an 8 nm KrF laser, the number of orbicular zones that are diffraction element units is about 1800, and each orbicular zone has a step-like BO shape with five steps as shown in FIG.
A 0 mm circular BO lens 1 is configured. This BO
The outermost ring of lens 1 has a design value of 0.5 for each step.
6 μm, the height is 0.124 μm, and the width of the ring zone is 2.8 μm and the height is 0.49 as the diffractive element unit of the BO lens.
It is 6 μm.

In this embodiment, the BO lens 1 having a diameter of 20 mm is formed on a quartz substrate having a diameter of 100 mm and a thickness of 2 mm by using the lithography method. Using FIG. 4,
A method of manufacturing the BO lens 1 will be described. Note that FIG. 4 shows an enlarged cross-sectional view of a partial region of the BO lens 1 formed similarly to FIG.

First, in the step of FIG. 4 (a), 0.6 μ is formed on a substrate 2 made of a quartz substrate or the like by using a spin coater.
Photoresist 3 is applied to a film thickness of m. Next, FIG.
In the step (b), an i-line stepper is used to expose a pattern for defining the edge of the grating for one period. 3 '
Is a pattern of the exposed exposure area, and a mask for defining an edge of a grating (diffraction element) of one period is formed in the pattern 3 ′ by a process described later.

Then, in the step of FIG. 4C, the photoresist 3 is developed. In this embodiment, since the positive type resist is used, the pattern 3'is removed. continue,
In the step of FIG. 4D, a 0.124 μm-thick alumina (Al ₂ O ₃ ) film 4 is vapor-deposited on the substrate 2 on which the resist pattern is formed, using a sputtering vapor deposition apparatus. Then, in the step of FIG. 4E, the photoresist 3 is removed from the substrate 2 by the lift-off method by an asher or remover process using oxygen plasma. here,
An annular mask 4'for defining the above-mentioned one period of the grating edge is completed.

In the subsequent steps, resist coating,
A series of steps of exposure, development, etching, and resist removal are repeated to form a stepped structure having a predetermined number of steps in a region other than the region where the mask 4'is formed. In the step of FIG. 4F, a two-step staircase structure is formed on the substrate 2 by using the dry etching (RIE) method with the resist having the pattern of the chrome mask 5 exposed as an etching mask. In the process of FIG. 4 (g), the chrome mask 6
The resist having the exposed pattern is used as an etching mask to form a four-step staircase structure on the substrate 2.

Finally, in the step of FIG. 4H, etching is performed using the mask 4'as an etching mask to form a 5-step staircase structure on the substrate 2.

In this embodiment, since the mask 4'for defining the edge of the grating of one period is formed before the step structure is formed on the substrate 2, the grating is formed in the subsequent step for forming the step structure. The BO element can be manufactured with high accuracy without any positional deviation with respect to the edge of the.

In this embodiment, the manufacturing process of the BO lens 1 having five steps has been described. However, the width of the mask 4'is set to a predetermined width, that is, the width of one step to be finally formed, and as shown in FIG. 4) and FIG. 4 (g) are repeated while changing the patterns of the chrome masks 5 and 6, so that BO lenses other than the five-stage can be manufactured. Note that FIG. 4 (f) and FIG.
In the step (g), 2 ² = 4 steps of stair structure are formed by using two chromium masks 5 and 6, that is, 2 ^N steps are formed by using N chromium masks. A method other than this, for example, a method of forming a staircase structure step by step may be used. Also, FIG. 4 (f)-
There is no problem even if the steps of FIG. 4 (h) are performed in the reverse order.

Next, the second embodiment will be described. However, since the manufacturing method shown in FIG. 4 is almost the same as the manufacturing method shown in FIG. The reference numerals used in the description are the same as those used in FIG. In the second embodiment, as in the first embodiment, a quartz substrate 2 having a diameter of 100 mm and a thickness of 2 mm and a chromium (Cr) thin film as an etching mask are used, and an RF for sputtering vapor deposition is formed on the substrate 2. It is possible to form a circular BO lens 1 having a diameter of 20 mm by forming a chromium film with a thickness of about 0.1 μm using a sputtering device.

First, as a pre-processing step, a chromium film is formed on a portion of the ring zone having a step width of 0.56 μm at the edge portion corresponding to the uppermost outermost peripheral region of the grating unit of one cycle of the BO lens 1. In advance, a resist is applied on the substrate 2 to a thickness of about 0.5 μm using a spin coater, and then a chromium film is deposited to a thickness of about 0.1 μm using a vacuum vapor deposition device. Then, the resist is removed by an asher method using oxygen plasma to form a ring-shaped zone pattern of the chromium film by the lift-off effect. At this time, the metal chromium film is converted into a transparent chromium oxide film by excessively performing the plasma asher method.

Then, using a stepper for i-line of λ = 365 nm, the patterns of the chrome masks 5 and 6 are reduced and baked on the photoresist on the substrate 2, and the developed resist pattern is used as a mask to perform dry etching (RIE). ) Method is used to etch the quartz substrate 2. At this time, the etching gas used is CF ₄ / H ₂ , CH ₂ F ₂
Main gas is used. The above process is performed by using two masks 5,
Repeat twice using 6 and dry etching is performed using an etching mask of chrome film to obtain a step of 0.1
After forming 24 μm, the resist is removed by using an asher method using oxygen plasma, so that the chromium film is converted into a chromium oxide film having sufficiently good light transmittance. In this way, the cross-sectional shape as shown in FIG.
The BO lens 1 of a step is created.

As a third embodiment, a 9-step BO lens 1 having a diameter of 20 mm is prepared by using the same manufacturing method as in the first embodiment. Calcium fluoride (CaF ₂ ) was used as the etching mask 4'instead of alumina, the etching mask was formed into a 0.31 μm wide ring, and three chrome masks were used to perform the photolithography process and dry etching. By the process, the 9-step BO lens 1 having a step difference of 0.62 μm and high diffraction efficiency is prepared.

As a fourth embodiment, after forming an etching mask of metal such as magnesium (Mg) or aluminum (Al) on the quartz substrate 2 as in the second embodiment,
After the photolithography process and the dry etching process, a light-transmissive process is performed by using a fluorine ion irradiation method in the processing and the final process, thereby forming the BO lens 1 having five stages.

As a fifth embodiment, similarly to the second embodiment, a photolithography process and a dry etching process are performed after forming an etching mask of tin (Sn), hafnium (Hf), aluminum or the like on a quartz substrate. After that, an oxidative light-transmitting process using an oxygen plasma asher method is performed in a process in the middle of processing to form a BO lens 1 having five stages.

As a sixth embodiment, a quartz substrate 2 provided with an alumina etching mask as in the first embodiment is used to process a 5-step BO lens 1 through a photolithography process and a dry etching process. And this 5 step BO
An antireflection film is provided on both surfaces of the lens 1. As the antireflection film, magnesium oxide (MgO) and magnesium fluoride (MgF ₂ ) are used by the RF sputtering method.
Laminate to each thickness of 62 nm. When the diffraction efficiency of the laminated substrates 2 is measured using KrF laser light, good results of 80% or more on average are obtained.

The seventh embodiment uses the same quartz substrate 2 having a diameter of 100 mm and a thickness of 2 mm as in the first embodiment. As a pre-processing step, one cycle of the BO lens 1 is used as shown in FIG. A chromium film is formed in the region corresponding to the outermost circumference of the uppermost stage of the lattice unit. In advance, a resist was applied on the substrate 2 by a spin coater to a thickness of about 0.5 μm, and then a chromium film was vapor-deposited to a thickness of 50 nm by using a vacuum vapor deposition device, and the resist was developed by a developer, so that the chromium was lifted off. Form an annular pattern of membranes.

Using a stepper for i-line of λ = 365 nm and two chrome masks 5 and 6 shown in FIG. 4, the pattern is reduced and baked on the photoresist on the quartz substrate 2 and developed resist Using the pattern as a mask, the chromium film 4 on the quartz substrate 2 is etched by using the dry etching (RIE) method. By repeating this step twice, four steps are formed, and in the next step, about 0.1 μm dry etching is performed by one step using the pattern of the chromium film previously provided on the substrate 2 as an etching mask, A total of 5 steps are formed. Finally, an etchant composed of cerium ammonium sulfate and perchloric acid is used to remove the etching mask of the chromium film 3 to form a BO lens 1 having a diameter of 20 mm and having a 5-step BO diffraction grating shown in FIG. Is completed.

In the eighth embodiment, a titanium thin film is used for the etching mask, and the diameter is 20 as in the seventh embodiment.
A circular BO lens 1 having a size of mm is prepared. Diameter 100m
A quartz crystal substrate 2 having a thickness of 2 mm and a thickness of 2 mm is used, and as a pre-stage of the processing of the BO lens 1, it corresponds to a region corresponding to the uppermost stage of the lattice unit of one period of the BO lens 1 on the substrate 2, that is, an edge portion. A resist is applied in advance to a region of about 0.5 μm using a spin coater, and then a titanium film is deposited to a thickness of 60 nm using a sputtering vapor deposition device. Furthermore,
By removing the resist using an acetone solution,
An annular pattern of the titanium film 3 is obtained by the lift-off effect.

Using a stepper for i-line of λ = 365 nm, the patterns of the chrome masks 5 and 6 are reduced and baked on the photoresist on the BO substrate, and the developed resist pattern is used as a mask to perform dry etching (RIE). The quartz substrate 2 is used for etching. At this time, a gas mainly containing CF ₄ / H ₂ and CH ₂ F ₂ is used as an etching gas. This step is repeated twice for the masks 5 and 6 to form a staircase having four steps, and further dry etching is performed using an etching mask of a titanium film to form one step. Finally, the titanium film is removed with a nitric acid-based etchant to complete the five-stage BO lens 1 having good edge accuracy. With respect to the diffraction efficiency of this BO lens 1, good results of 70% or more on average have been obtained.

As a ninth embodiment, a 9-step BO lens 1 having a diameter of 20 mm is prepared by using the same manufacturing method as in the seventh embodiment. By using tungsten (W) instead of chromium as an etching mask material, a photolithography process and a dry etching process, and finally using a fluorine-nitric acid-based etchant to remove the tungsten film, a high diffraction efficiency of 9 is obtained. A stepped BO lens 1 can be created.

As a tenth embodiment, as in the seventh embodiment, tin (Sn), tantalum (Ta),
After forming an etching mask of aluminum (Al) or the like, a 5-step BO lens 1 is formed through a photolithography process and a dry etching process. When the diffraction efficiency of this BO lens 1 was measured using a KrF laser beam, a good result of 70% or more was similarly confirmed.

As an eleventh embodiment, a quartz substrate 2 provided with an etching mask of chromium is used as in the seventh embodiment, and a BO lens 1 having five stages is processed through a photolithography process and a dry etching process. After doing this BO
An antireflection film is provided on both surfaces of the lens 1. As the antireflection film, magnesium oxide and alumina are placed on the lateral layers each having a thickness of 62 nm by using the RF sputtering method. When the diffraction efficiency of this BO lens 1 was measured using a KrF laser beam, a good result of 80% on average was obtained.

As a twelfth embodiment, Cr ₂ O which is an oxide of chromium, tin, tungsten, tantalum (Ta), aluminum or the like is formed on the fluorite substrate 2 as in the seventh embodiment.
After depositing an etching mask of ₃ , SnO ₂ , WO ₃ , Ta ₂ O ₅ , Al ₂ O _3, etc., a photolithography process, a dry etching process, and an etching mask peeling process are performed, and then the five-stage BO lens 1 is formed. To create. This B
When the diffraction efficiency of the O lens 1 was measured using KrF laser light, good results were obtained.

As described above, before the step processing of the BO element for improving the overlay accuracy is started, an etching mask for dry etching resistance is provided in advance at the uppermost position of the step so that the side surface Since the edge accuracy can be determined independently of the overlay and alignment accuracy, it is possible to specify the edge overlay accuracy at a high level, and always increase the step by one step to obtain 2 ^N for the step ^N.
The number of steps can be set to +1 and the BO optical element having a higher diffraction efficiency, that is, the BO lens 1 can be manufactured.

Metals, metal oxides, and metal fluorides can be used as the material of the etching mask. That is, Cr, Ti, Zn, Sn, Al, Hf, Si, N
Metals such as d, W, Mo and Ta and oxides thereof, or metals such as Al, Ca, Mg, Li, Ba, Na, Nd and La and fluorides thereof can be used. A compound may be used as the metal oxide or fluoride from the beginning, or a metal thin film may be provided on the substrate in advance and the compound may be produced by reacting oxygen gas or fluorine gas later. Good.

FIG. 5 is a block diagram of the optical system of the exposure apparatus.
A light source 11 such as a lamp or a laser from above, and this light source 11
An illumination optical system 12 for uniformly illuminating the reticle R with light from the reticle R, a reticle R, a projection optical system 13 for projecting a projection pattern formed on the reticle R onto the wafer W,
Wafers W are arranged in sequence.

The BO lens used in this exposure apparatus has been subjected to the steps of the above-described embodiment and then divided into 9 by stepper exposure.
The steps are made to have a diameter of 200 mm. By incorporating this BO lens in the illumination optical system 12 and the photographing optical system 13 and mounting this optical system in the exposure apparatus, semiconductor manufacturing can be performed with high accuracy for reduction printing on the wafer W using the stepper for KrF laser light. It can be a device.

As described above, by using the BO lens manufactured with high precision in the optical system of the exposure apparatus, it is possible to improve the optical performance of the exposure apparatus as a whole. Also,
With this exposure apparatus, semiconductor elements such as ICs and LSIs, liquid crystal elements, image pickup elements such as CCDs, magnetic elements such as magnetic heads, and optical elements such as BOEs can be accurately manufactured.

[0039]

As described above, in the diffractive optical element according to the present invention, a transparent etching mask is provided in advance at the uppermost position of the step shape, and this etching mask is the highest.
By forming a step in the step position or a part of that step,
By performing the step processing of a predetermined number of steps, it is possible to solve the problem of the processing accuracy of the edge that comes from the alignment and overlay accuracy, not only visible light, infrared light, ultraviolet light region, far ultraviolet light, It can also be applied to the vacuum ultraviolet region. Furthermore, if the lens is incorporated into the optical system, the performance of the optical device can be improved.

[0040]

Further, in the method of manufacturing a diffractive optical element according to the present invention, when forming a staircase structure, a step of forming an etching mask only at a position which should be the uppermost stage of the staircase structure,
It has a step of forming a staircase structure with a predetermined number of steps using an etching mask, and can improve the deterioration of performance due to a change in the processing steps, not only visible light, infrared light, and ultraviolet light regions, but also far ultraviolet light, A high-performance diffractive optical element used in the vacuum ultraviolet region can be efficiently manufactured.

[0042]

[Brief description of drawings]

FIG. 1 is a perspective view of a BO lens.

FIG. 2 is a cross-sectional view of a BO lens.

FIG. 3 is a partially enlarged cross-sectional view of a BO lens.

FIG. 4 is an explanatory diagram of a method of manufacturing a BO lens.

FIG. 5 is a configuration diagram of an optical system of the exposure apparatus.

[Explanation of symbols]

1 BO lens 2 substrates 3 photoresist 4 membranes 5, 6 chrome mask 11 light source 12 Illumination optical system 13 Photographic optical system

Claims (5)

(57) [Claims] 1. Arranged at the uppermost position of the staircase shape
A diffractive optical element formed by performing a predetermined number of steps using a translucent etching mask , wherein the translucent
The etching mask is the step at the uppermost position or a part of the step.
A diffractive optical element, characterized in that it is formed . 2. An optical system equipped with the diffractive optical element according to claim 1 . 3. An exposure printing apparatus having the optical system according to claim 2 . 4. A semiconductor manufacturing apparatus incorporating the exposure printing apparatus according to claim 3 . 5. When forming a staircase structure, a step of forming an etching mask only at a position which should be the uppermost stage of the staircase structure, and a step of forming a predetermined number of steps of staircase structure using the etching mask. A method of manufacturing a diffractive optical element, comprising: