JP3408217B2 - Method for producing fine structure and diffractive optical 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 method for forming a fine structure and a diffractive optical element used in various optical instruments.

[0002]

2. Description of the Related Art A diffractive optical element is an optical element that utilizes the diffraction phenomenon of light and is composed of a plurality of diffraction gratings. A diffractive optical element having a stepped cross section is disclosed in Japanese Patent Laid-Open No. 6-
As described in Japanese Patent No. 258510, the resist is patterned after forming the multilayer film substrates which are alternately laminated while sufficiently controlling the film thicknesses of the two kinds of thin films having different reactivities to the etching gas. Next, the type of etching gas is changed after etching a thin film having high reactivity to one etching gas and low reactivity to the other etching gas, and It can be prepared by etching a thin film having low reactivity and high reactivity with the other etching gas.

[0003]

Further, in the diffraction grating in the system of the above-mentioned publication, resist is applied on the surface having a step caused by etching, and the patterning of the next step is performed. The side walls of the resist, especially the side walls of the lower step, are affected by the step walls on the opposite side during exposure, causing a non-negligible inclination of the resist side wall with respect to the lower surface. There is a drawback in that the shape is inclined as if the inclined shape of the resist were copied.

An object of the present invention is to solve the above-mentioned problems and to provide a method for producing a fine structure having a stepwise accurate cross section and a diffractive optical element.

[0005]

[0006]

A method for producing a fine structure according to the present invention for achieving the above object is a method for producing a fine structure in which a plurality of step-like elements are arranged, in which etching gas is applied on a substrate. A plurality of first thin films that react with each other and a plurality of second thin films having an etching rate smaller than that of the first thin films are alternately laminated, the first thin films being a main part of the step-like element, and A first step in which the second thin film is used as a stopper layer when etching the first thin film, and the first thin film is etched leaving a slope on its side surface so that the second thin film is exposed; After the first step, a second step of correcting the side surface of the first thin film by etching the side surface of the first thin film with the second thin film exposed so that the angle of the side surface becomes vertical , Each of the first thin films to the first Unlike tilt amount remaining on the side surface after etching in step with each other, characterized in that the minimum film thickness of the film thickness commensurate with the correction of the tilt of the second thin film.

[0007]

[0008]

[0009]

[0010]

[0011]

[0012]

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail with reference to the illustrated embodiments. The drawings show explanatory views of a process for producing a diffractive optical element having a staircase shape in Examples. First
1 shows a laminated film 1 before etching treatment.
Is formed on a substrate 2 made of a cleaned Si wafer having a diameter of 8 inches, and the substrate 2 is arranged in a sample holder so as to face a target of a sputtering device (not shown). After the chamber is sufficiently evacuated, the substrate 2 is uniformly heated to 300 ° C., equal amounts of oxygen gas and argon gas are introduced into the chamber, and the pressure is set to 2 Pa. Further, by applying a high frequency power of 800 W to an Al target by using an RF power source, an Al ₂ O ₃ film 3a which is an auxiliary film functioning as an etching taper adjusting layer having a film thickness of about 15 nm is uniformly formed on the substrate _2. To do.

Subsequently, the Al target was maintained without opening the vacuum in the chamber.
SiO2₂Change to the target, and with the oxygen gas in the tank
Adjust the mixing ratio of argon gas to be 1:10,
Al ₂O₃A stepwise main part with a film thickness of about 600 nm on the film 3a
Which is the main film forming the ₂The film 4a is formed.

Further, by repeating the above-mentioned process twice, the Al ₂ O ₃ films 3b and 3c having film thicknesses of about 45 μm and 36 μm and the film thicknesses of about 570 nm and 579 nm are sequentially formed from the substrate 2 side.
SiO ₂ films 4b and 4c are alternately laminated. The laminated film 1 thus obtained is taken out from the sputtering apparatus after introducing air into the tank after cooling.

The laminated film 1 taken out from the sputtering apparatus is annealed for about 2 hours in an air atmosphere at 450 ° C. in a heating high temperature furnace, and is further arranged so as to face a chromium evaporation source in a vacuum evaporation apparatus. .
After the chamber of the vacuum vapor deposition apparatus was sufficiently evacuated, the laminated film 1 was uniformly heated to 300 ° C., and chromium was heated using an electron gun to form a mask on the uppermost SiO ₂ film 4c. After depositing a chromium film 5 having a film thickness of about 35 nm, cooling it sufficiently and introducing air into the tank, the laminated film 1 is taken out from the vacuum evaporation apparatus.

Further, in this embodiment, the Al ₂ O ₃ film 3 is used.
Although the chromium film 5 is used as a mask having a different reactivity with the etching gas used to etch the SiO ₂ film 4, other metal thin films, dielectric films, synthetic resins, etc. may be used.

FIG. 2 shows a photoresist 6a having a desired pattern formed on the chromium film 5. In this embodiment, a pitch 4 is formed on the chromium film 5 by using a spinner.
A photoresist 6a having a film thickness of 1 μm and having a line-and-space structure of μm and an opening of 3 μm is applied. After that, this patterning is formed by exposing and developing it by a known method.

Next, as shown in FIG. 3, the exposed portion of the chromium film 5 is dipped in a chromium removing solution and removed by wet etching, and the laminated film is further etched so that the film formation surface is etched on the electrode of the RIE etching apparatus. 1 is placed and the chamber is evacuated, and then CF ₄ gas and CH are used as etching gas.
F ₃ gas is introduced into the tank, and the pressure is set to 1 Pa. After that, output from the high frequency power supply to the electrode 100W
Is applied and discharged to etch the exposed portion of the SiO ₂ film 4c. In addition, after confirming that the Al ₂ O ₃ film 3c functioning as a taper adjusting layer is confirmed to have been etched by plasma measurement, a predetermined time required for the side wall of the SiO ₂ film 4c to become vertical to the substrate surface. Only etching.

Further, after introducing the atmosphere into the tank, the laminated film 1
Then, the photoresist 6a is peeled off as shown in FIG. Then, as shown in FIG. 5, a spinner was used as in FIG.
Photoresist 6 consisting of μm line and space
b is patterned, exposed and developed. In order to offset the misalignment, the photoresist 6b on the chromium film 5 is patterned so that its end portion reaches the inside of the chromium film 5. However, in this embodiment, the inclination of the side wall portion and the corrugation of the surface which occur in the photoresist 6 are not shown.

Then, as shown in FIG. 6, a SiO ₂ film 4b is formed.
Al ₂ O ₃ to function as an etching mask for
The exposed portion of the film 3c is removed by wet etching.

Further, as shown in FIGS. 7 to 12, the sample is set in the RIE etching apparatus by using the above-mentioned process, and the SiO ₂ film 4 which reacts with the _{second and} subsequent steps of the stairs.
Etching, resist stripping, patterning, Al ₂ O ₃
The wet etching of the film 3 is repeated.

By providing an alternating laminated film in which the film thickness of the Al ₂ O ₃ film 3 which is an auxiliary film is different in each step, even if the inclined portion of the photoresist 6 caused by patterning recedes by etching, the photoresist 6 Since the etching rate of the Al ₂ O ₃ film 3 thereunder is significantly slower than that of the SiO ₂ film 4 and the photoresist 6, it functions as a mask. This is because the patterning inclination amount that changes depending on the step amount and pattern size of each step or the material of the photoresist 6 and the exposure amount, and the time required to etch the SiO ₂ film 4 of each step to a desired depth. , The Al ₂ O ₃ film 3 is minimized, so that the side wall of the SiO ₂ film 4 can be etched perpendicularly to the substrate surface.

Even if the SiO ₂ film 4 is inclined during etching, the etching rate of the Al ₂ O ₃ film 3 therebelow is significantly slower than that of the SiO ₂ film 4 and the photoresist 6, and the taper angle is adjusted. Functions as a layer. To this end, by setting the thickness of the Al ₂ O ₃ film 3 to a minimum in order to correct the etching inclination amount of the SiO ₂ film 4 which differs in each stage, the side wall of the SiO ₂ film 4 with respect to the substrate surface is set. Etch vertically.

The exposure of the desired pattern, an Al ₂ O ₃ film 3 after the development and etching, by means of etching the SiO ₂ film 4 to expose the main surface of the lower, Al ₂ to give the desired patterning O ₃ film 3 underneath SiO ₂ film 4
By reliably using it as a mask for the etching, the side wall of the etching of the lower SiO ₂ film 4 can be etched perpendicularly to the bottom surface.

Further, as shown in FIG. 13, the Al ₂ O ₃ film 3 damaged by etching is removed by wet etching only at the exposed portion to expose the smooth and flat SiO ₂ film 4, and then FIG. As shown in the drawing, the chromium film 5 damaged by etching is removed by wet etching to expose the smooth and flat SiO ₂ film 4, so that the step difference per step becomes uniform, and moreover, the cross-sectional staircase shape, especially The side wall on the side facing the stairs is perpendicular to the bottom surface, and a four-stage diffractive optical element having a rectangular shape can be manufactured.

Although not shown in this embodiment, a reflective diffractive optical element is formed by forming an Al reflective film on the diffraction grating surface of the obtained four-stage diffractive optical element using a vacuum vapor deposition apparatus. You can also do it.

As a second embodiment, the SiO ₂ film which is the main film is directly formed on the substrate 2 without forming the Al ₂ O ₃ film 3a which is the auxiliary film on the substrate 2 in the first embodiment. 4 may be formed into a film. At this time, the number of laminated SiO ₂ films 4 is increased from 3 layers to 7 layers, and the film thicknesses of the SiO ₂ films 4 are sequentially changed from the substrate 2 side to 263 nm, 233 nm, 239 nm, 243 nm, 2 layers.
44 nm, 246 nm and 246 nm. Also, Si
The film thickness of the Al ₂ O ₃ film 3 formed on the O ₂ film 4 is 30 nm, 24 nm, 20 nm, 1 in this order from the SiO ₂ side of the bottom layer.
9 nm, 17 nm, and 17 nm.

Further, the Al ₂ O ₃ film 3 of each layer is not wet-etched, but is dry-etched in the same manner as the SiO ₂ film 4 in the RIE etching apparatus while performing plasma measurement using CCl ₄ etching gas. The other steps are the same as those in the first embodiment.

SiO ₂ on a substrate 2 consisting of a Si wafer
Even if the film 4 is directly formed, since Si has different reactivity with the etching gas of the SiO ₂ film 4, it functions sufficiently as a taper angle adjusting layer.

The diffractive optical element produced in this way is
As in the case of the first embodiment, a stepwise stepped diffractive optical element having a uniform step and a stepped sectional shape, in particular, a side wall opposite to the step is perpendicular to the bottom surface and has a rectangular shape with eight steps is provided. realizable.

By omitting one Al ₂ O ₃ film 3, the total stress of the laminated film 1 can be relaxed, and the substrate 2
On the other hand, it is possible to form an eight-layered alternating laminated film having high adhesion, and it is possible to obtain a diffractive optical element having high diffraction efficiency.

Further, the SiO ₂ film 4, the Al ₂ O ₃ film 3 and the chromium film 5 can obtain the same effect except for the combination of the materials mentioned above. For example, as in the present embodiment, a SiO ₂ film and a chromium film may be used for the main film and the mask, and the same Si as the substrate 2 may be used for the auxiliary film. In this case,
CF ₄ gas was used for etching the auxiliary film, and Si of SiO ₂ was used.
A similar diffractive optical element can be obtained by increasing the etching selection ratio with respect to and removing by etching.

As a third embodiment, an Al film is used in place of the SiO ₂ film 4 in the first embodiment, a Cu film is used in place of the Al ₂ O ₃ film 3, a Mo film is used in place of the chromium film 5, and a substrate is used. A laminated film is formed on 2. The Al film can be dry-etched with a CCl ₄ etching gas, and the Cu film and the Mo film can be removed by wet etching using the respective etching solutions.

The laminated film 1 in this case is excellent in productivity because all the materials forming the film are metal films having a high film formation rate.

As a fourth embodiment, a quartz substrate is used instead of the substrate 2 made of the Si wafer used in the first embodiment, and an Al reflection film is used on the diffraction grating surface of the obtained diffractive optical element. By forming the antireflection film using a vacuum vapor deposition device, a transmission type diffractive optical element having excellent diffraction characteristics can be obtained. Also, a transparent optical base material other than the quartz substrate may be used.

Further, instead of the Al ₂ O ₃ film 3, a Si ₃ N ₄ film is used, and the film thicknesses are 15 nm, 600 nm, 3 from the substrate 2 side in this order.
5 nm, 580 nm, 25 nm, 590 nm, and Si
An alternating laminated film of ₃ N ₄ film and SiO ₂ film 4 is formed, and CF ₃ Br
A good diffractive optical element can be obtained even by adding oxygen gas as an additional gas to the etching gas and performing etching while performing plasma measurement.

As a fifth embodiment, A is formed on the diffraction grating surface in the four-stage diffractive optical element prepared in the first embodiment.
The obtained diffractive optical element can be used as a mold without forming a 1-reflecting film. UV-curing resin is dropped on this diffractive optical element, and optical glass is stuck on it,
A replica-transferred diffractive optical element can be obtained by irradiating ultraviolet rays from the back surface or front surface side of the diffractive optical element to cure and then peeling it off. Further, by forming an Al reflection film on the diffraction grating surface of the replica-transferred diffractive optical element, a reflective diffractive optical element can be formed.

The reflective diffractive optical element thus prepared has a uniform step difference per step as in the first embodiment, and the reflective diffractive optical element can be manufactured with good reproducibility and at low cost. . Of course, the method of using the mold may be other than that described in the present embodiment.

As a sixth embodiment, the mold prepared in the fifth embodiment is attached to an injection molding machine, and a transparent thermoplastic resin is used to mold the substrate 2 and the diffractive optical element into an integral shape. By depositing an antireflection film on the surface of the diffractive optical element and the back surface of the substrate 2, a transmissive diffractive optical element integrated with the substrate 2 can be obtained.

The diffractive optical element produced in this way is 1
It is possible to produce a transmissive diffractive optical element having uniform steps and excellent productivity with low reproducibility and at low cost. The diffractive optical element can be used as a color separation filter in an image reading device and a liquid crystal projector, and can be used as a diffractive lens in a photographing optical system and a projection optical system.

The Al ₂ O ₃ films 3a, 3b, and 3c are not the optimum film thickness for each layer, and the diffractive optical element formed by unifying the layers to the thickest film of 45 nm is The adhesion was weak, and some surface deformation was observed due to film lifting in the surface. Further, since the Al ₂ O ₃ films 3a, 3b, and 3c are removed three times by wet etching, the upper Al ₂ O ₃ film 3 is removed.
A lateral constriction is observed at the end of c, a highly precise stepped diffractive optical element having a rectangular shape cannot be obtained, and further, the film formation time becomes very long and the productivity is poor. Moreover, the diffraction spectral characteristic of the obtained diffractive optical element has a low reflectance, and the desired spectral characteristic cannot be obtained.

In the first embodiment, the SiO ₂ film 4 is used.
After the etching, the Al ₂ O ₃ film 3 is not removed by patterning with the photoresist 6 and the process is changed to the patterning with the photoresist 6, so that the diffractive optical element is produced while the SiO ₂ film 4 is being etched. Since the end of the photoresist 6 recedes due to etching,
_In some cases, the side wall of the film 4 has an inclination similar to that of the photoresist 6 with respect to the bottom surface, so that a step diffraction grating having a desired rectangular shape may not be obtained.

[0044]

As described above, in the method of forming a fine structure according to the present invention, even if the inclination amount of resist patterning of each step changes or the step amount or depth of each step changes, it faces the steps. The side sidewalls can be perpendicular to the bottom surface. Even if the main film is etched under the etching condition having a slight inclination, the side wall can be corrected so as to be perpendicular to the bottom surface, that is, the substrate surface.

Further, even if the inclination amount of the resist patterning of each step changes or the step amount, that is, the depth of each step changes, the side wall facing the stairs can be accurately vertical to the bottom surface. Therefore, the width of each step can be controlled accurately.

In addition, the step width of each step maintains a desired pattern dimension with high precision, and etching is performed, so that the etched surface is less rough and both surfaces are smooth and flat, and the diffraction characteristics are excellent. A diffractive optical element is obtained.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a manufacturing process of a diffractive optical element.

FIG. 2 is an explanatory diagram of a manufacturing process of a diffractive optical element.

FIG. 3 is an explanatory diagram of a manufacturing process of a diffractive optical element.

FIG. 4 is an explanatory diagram of a manufacturing process of a diffractive optical element.

FIG. 5 is an explanatory diagram of a manufacturing process of the diffractive optical element.

FIG. 6 is an explanatory diagram of a manufacturing process of the diffractive optical element.

FIG. 7 is an explanatory diagram of a manufacturing process of the diffractive optical element.

FIG. 8 is an explanatory diagram of a manufacturing process of the diffractive optical element.

FIG. 9 is an explanatory diagram of a manufacturing process of the diffractive optical element.

FIG. 10 is an explanatory diagram of a manufacturing process of the diffractive optical element.

FIG. 11 is an explanatory diagram of a manufacturing process of the diffractive optical element.

FIG. 12 is an explanatory diagram of a manufacturing process of the diffractive optical element.

FIG. 13 is an explanatory diagram of a manufacturing process of the diffractive optical element.

FIG. 14 is an explanatory diagram of a manufacturing process of the diffractive optical element.

[Explanation of symbols]

1 Multilayer Film 2 Substrate 3 Al ₂ O ₃ Film 4 SiO ₂ Film 5 Chrome Film 6 Photoresist

Claims (2)

(57) [Claims] 1. A method of forming a microstructure in which a plurality of step-like elements are arranged side by side, which is responsive to an etching gas on a substrate.
A plurality of first thin films and the first thin film having an etching rate
Alternately stacking a plurality of second thin films smaller than the film,
The first thin film serves as a main part of the stepped element, and the second thin film
Stopper for etching the first thin film
The first thin film as a layer so that the second thin film is exposed.
First step of etching the film leaving a slope on its side surface
And a state in which the second thin film is exposed after the first step.
By etching the side surface of the first thin film
Second step of correcting the angle of the side surface to be vertical
And each of the first thin film in the first step
The amount of tilt remaining on the side surface after etching with
And the film thickness of each of the second thin films is
A method for producing a fine structure, characterized in that the film thickness is set to a minimum value commensurate with the correction . 2. Diffracted light produced by the method according to claim 1.
Science element .