JP2007294792A - Method of forming exposure object to be used for proximity exposure, proximity exposure method and method of manufacturing element by proximity exposure method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of forming an exposure object to be used for proximity exposure which can execute uniform exposure over an entire mask and form a highly definite micro-pattern, and to provide a proximity exposure method and a method of manufacturing an element using the proximity exposure method. <P>SOLUTION: The method of forming the exposure object is used for proximity exposure in which a light shielding film having micropores smaller than the wavelength size of an exposure light is closely attached and a light is emitted from an exposure light source to transfer a pattern. The method has a step of forming a layer 202 having both functions as a profile buffering layer and a light absorbing layer on a substrate 201 having unevenness, so that the unevenness of the substrate is buried, and planarizing the substrate surface; and a step of forming a photosensitive resist layer 204 on the layer having both the functions as the profile buffering layer and the light absorbing layer. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a method for forming an object to be used for near-field exposure, a near-field exposure method, and a device manufacturing method using the near-field exposure method.
In particular, the present invention relates to a method for forming an object to be used for a lithography technique based on near-field exposure when manufacturing a semiconductor device or an optical device, a near-field exposure method, and an element manufacturing method based on a near-field exposure method.

With the advancement and diversification of lithography techniques, various exposure methods have been proposed as emerging lithography techniques for exploring new possibilities.
Among them, Patent Documents 1 and 2 propose an exposure method using an optical near field as one of exposure methods that enable fine processing beyond the diffraction limit of light.
In such a near-field exposure method, the mask is composed of an elastic body, and the mask is elastically deformed so as to follow the resist surface shape, thereby bringing the entire mask into close contact with the resist surface and using an optical near field. Exposure is performed.
On the other hand, as a fine pattern forming method, a pattern forming method using a three-layer resist method is known (for example, see Patent Document 3).
In this method, for example, when there is a step in the base substrate, a three-layer resist comprising a lower resist layer, an intermediate layer on the lower resist layer, and an upper resist layer on the intermediate layer is formed on the base substrate. By doing so, a fine pattern is formed.
Japanese Patent Laid-Open No. 11-145051 JP-A-11-184094 Japanese Patent Application Laid-Open No. 61-075525

Nowadays, there is an increasing demand for high-definition fine processing, and further improvements in transfer accuracy are required in a method for forming a fine pattern by lithography.
However, when the underlying substrate has irregularities, the above-described conventional near-field exposure method causes uneven exposure, and even if a pattern formation method using a three-layer resist method is applied, there is a need for the above high-definition fine processing. It was difficult to meet.

  In view of the above problems, the present invention provides a method for forming an object to be used for near-field exposure that can perform uniform exposure on the entire mask surface and can form a high-definition fine pattern, and near-field exposure. It is an object of the present invention to provide an element manufacturing method using the method and the near-field exposure method.

In order to solve the above problems, the present invention provides a method for forming an object to be used for near-field exposure configured as follows, a near-field exposure method, and a device manufacturing method using the near-field exposure method.
In the method for forming an object to be exposed according to the present invention, an object to be used for near-field exposure in which a light-shielding film having a minute opening having a wavelength size equal to or smaller than the wavelength of exposure light is closely attached and light is irradiated from an exposure light source to transfer the pattern. A forming method comprising:
Forming a layer having a function as a shape buffer layer and a light absorption layer so as to bury the irregularities of the substrate on a substrate having irregularities, and planarizing the substrate surface;
Forming a photosensitive resist layer on the layer having the function of the shape buffer layer and the light absorption layer.
Further, in the method for forming an object to be exposed according to the present invention, the unevenness of the substrate is an unevenness having a height of 0.05 times or more the wavelength of exposure light in the photosensitive resist layer,
The planarization of the substrate surface is characterized in that the unevenness of the substrate surface is less than 0.05 times the wavelength of the exposure light.
Further, in the method for forming an object to be exposed according to the present invention, an intermediate layer having resistance to oxygen plasma etching is provided between the layer having the function as the shape buffer layer and the light absorption layer and the photosensitive resist layer. It is formed.
In the method for forming an object to be exposed according to the present invention, the photosensitive resist layer is formed of a resist having resistance to oxygen plasma etching.
In the near-field exposure method of the present invention, a light-shielding film having a microscopic aperture of a wavelength size or less is brought into close contact with an object having a photoresist layer formed on a substrate, and light is irradiated from an exposure light source. In the near-field exposure method for transferring the pattern,
As the object to be exposed, an object to be exposed formed by any of the above-described methods for forming an object to be exposed is used.
The element manufacturing method of the present invention is manufactured using the above-mentioned near-field exposure method.

  According to the present invention, a method for forming an object to be used for near-field exposure, a near-field exposure method, and a proximity method capable of performing uniform exposure on the entire mask surface and forming a high-definition fine pattern. An element manufacturing method using the field exposure method can be realized.

With the above configuration, the above-described problem of the present invention can be achieved, which is based on the following knowledge of the present inventors.
As a result of intensive studies by the present inventors, as one of the causes of exposure unevenness due to the unevenness of the substrate and the difference in reflectance in the conventional exposure method, the optical path length of the exposure light from the near-field exposure mask to the substrate surface It was found that the distribution of near-field light changes due to the difference between the two.
For example, when light is incident with a mask attached to a substrate having a resist film thickness as shown in FIG. 7, the distribution of near-field light generated in the resist,
The distribution of the near-field light generated in the resist when the mask is brought into close contact with a substrate having a different resist film thickness as shown in FIG. 8 and incident on the resist. The optical path of the exposure light from the near-field exposure mask to the substrate surface The distribution of the near-field light changes depending on the length.

As an example of such a phenomenon, the result of calculating the distribution of near-field light oozing from the near-field exposure mask will be introduced.
The light intensity distributions shown in FIGS. 7 and 8 are the results of calculation using the finite difference time domain method (FDTD method).
As shown in FIG. 1, the near-field exposure mask has a 500-nm-thick silicon nitride (SiN) film having a refractive index of 1.9 as a mask base material and 50 nm as a light-shielding material that blocks exposure light on the mask base material. It is composed of chromium (Cr) with a thickness.
A fine slit in the order of nm is formed in Cr of the light shielding material.
The calculation result introduced here is an example in which fine slits having a width of 20 nm are periodically arranged at a pitch of 90 nm in the light shielding material Cr.
This mask was in close contact with the photoresist on the silicon substrate. The wavelength of the light source was calculated as i-line of 365 nm in vacuum.
As an example of the calculation result, a near-field exposure mask is brought into close contact with a substrate having a structure in which a photoresist film is formed with a thickness of 160 nm on the surface of a flat silicon substrate, and light having a wavelength of 365 nm is incident from the near-field exposure mask side. The distribution in this case is shown (FIG. 7).
From this calculation result, it can be seen that near-field light exists up to a distance of about 50 nm from the mask surface.

As another example, a near-field exposure mask is closely attached to a substrate having a structure in which a photoresist film is formed with a thickness of 220 nm on the surface of a flat silicon substrate, and light having a wavelength of 365 nm is incident from the near-field exposure mask side. FIG. 8 shows the distribution in the case of the above.
From this calculation result, it can be seen that near-field light exists up to a distance of about 20 nm on the mask surface.
The only difference between the two results is the thickness of the photoresist film formed on the surface of the silicon substrate.
From these results, the thickness of the photoresist film, that is, the distance between the near-field exposure mask surface and the surface of the silicon substrate from which the light is reflected, changes the distance from the mask surface where the near-field light exists. all right.
The comparison can also be made from the contrast of the intensity of light on a surface at a certain distance from the mask.

The contrast here means that the maximum value of the light intensity is Imax and the minimum value is Imin in the X direction on the vertical axis Z in FIGS.
Contrast C = (Imax−Imin) / (Imax + Imin)
It is defined as
FIG. 10 shows a graph in which the contrast is plotted on the horizontal axis and the contrast is plotted on the Y axis. In this graph, the solid line indicates the value at Z = 10 nm, the broken line indicates the value at Z = 20 nm, and the alternate long and short dash line indicates the value at Z = 30 nm.
From this graph, it can be seen that the light intensity distribution changes strongly depending on the thickness of the photoresist film because the contrast changes remarkably as the thickness of the photoresist film changes.

The present inventors have found the following from the calculation results of both of them.
When the substrate on which the photoresist film is formed has unevenness as shown in FIG. 9, the thickness of the photoresist film varies from place to place.
Since the thickness of this photoresist film is different, the reach distance of near-field light is different as described in FIGS. 7 and 8, and when the exposed photoresist film / substrate is developed, the depth and shape of the pattern after development are different. Different.
Since the post-development photoresist pattern is used to perform post-processes such as plating and etching, this phenomenon indicates that it is difficult to use near-field exposure to a substrate having irregularities.

From the above, the present inventors have a layer having a function as a shape buffer layer and a light absorption layer (hereinafter referred to as a shape buffer / light absorption layer) so as to embed the unevenness of the substrate on the substrate having the unevenness. The substrate surface is flattened and a photoresist film is formed thereon.
Thereby, by the shape buffer / light absorption layer, it is possible to suppress the reflection from the unevenness of the substrate, suppress the change in the near-field distribution due to the difference in the thickness of the photoresist film described above depending on the location in the substrate, Uniform exposure with near-field light can be performed on the entire mask surface.

Next, an embodiment of the present invention specifically configured based on these findings will be described with reference to the drawings.
In the near-field exposure photomask shown in FIG. 1, a light-shielding material 102 that shields the light source wavelength is formed on a mask base material 101 that is transparent to the light source wavelength, and the width of the light-shielding material is smaller than the wavelength of the light source. The minute opening pattern 103 is arranged.
In this photomask, the substrate is coated with a photoresist, is exposed to exposure light from the photomask side, and the mask pattern is exposed to the photoresist.
The photoresist used here refers to a material that is exposed to light and forms a pattern by performing some development process.
In particular, this embodiment mode is a method for exposing a substrate 201 having unevenness, and is characterized by a photoresist layer formed on the substrate.
The unevenness of the substrate having unevenness used in this embodiment has a step of 0.05λ (where λ is the effective wavelength of exposure light in the photoresist) or more (FIG. 2). (A)) The material which comprises the level | step difference shows what differs in refractive index from photoresist material.

The surface of the shape buffer / light absorption layer is flattened by forming the shape buffer / light absorption layer 202 made of a material having a good embedding property on the substrate with a thickness greater than the level difference of the unevenness. (FIG. 2 (b)).
The planarization described here indicates that the surface roughness of the shape buffer / light absorption layer is less than 0.05λ.
For the shape buffer / light absorption layer here, a material that absorbs ultraviolet exposure light and fills the unevenness of the substrate with unevenness to form a flat surface is used.
For example, a film made of a coumarin derivative, a benzophenone derivative, a thioxanthone derivative, an anthracene derivative, a carbazole derivative, or a perylene derivative known as a low molecular compound can be used.
Further, an acrylic resin, a styrene resin, an epoxy resin, an amide resin, an amide epoxy resin, an alkyd resin, a phenol resin, or a novolac resin may be added to the above material as a binder.
In addition, a polymer having a main chain having an aromatic ring or a heterocyclic ring, such as polyimide, polybenzoxazole, and aromatic polyamide, which are high molecular compounds, and
Also included are all π-conjugated polymers such as polyacetylene, polydiacetylene, polypyrrole, polyparaphenylene, polyparaphenylene sulfide, polythiophene, and poly (p-phenylene vinylene).
A shape buffer / light absorption layer is formed on a substrate having irregularities by using a film forming means such as a spin coating method, a pulling method, or vapor deposition polymerization of these materials.
Note that the film forming methods and film materials listed here are merely examples, and the present invention is not limited to such film forming methods and materials.

Thereafter, a film having resistance to oxygen dry etching is formed as an intermediate layer on the shape buffer / light absorption layer 202.
Examples of the intermediate layer include a metal oxide film formed by spin-on-glass (SOG) or a sol-gel process, and SiOx formed by a vacuum film forming technique.
Other materials having resistance to oxygen dry etching are not limited to these materials.

Next, a film having photosensitivity to exposure light is formed as the upper resist layer 204 to be exposed using near-field exposure.
As this upper resist layer 204, a method of forming a photoresist film used in photolithography by spin coating, or a photoresist having photosensitivity containing silicon atoms as an upper resist is used. It can also serve as a layer.
In addition, here, the pattern is formed by being exposed to exposure light and developed, but the material is not limited to this as long as the property of the material is changed by the exposure light.
For example, as shown in FIG. 3 described in the next embodiment, the upper layer resist may be formed by a three-layer resist method.

  When the plurality of films described above are formed on a substrate having irregularities in this way, reflection from the irregularities of the substrate can be suppressed by the shape buffer / light absorbing layer that absorbs exposure light. By doing so, it is possible to suppress the change in the near-field distribution due to the difference in the thickness of the photoresist film described above depending on the location in the substrate, and perform uniform exposure over the entire mask surface by near-field light.

Examples of the present invention will be described below.
[Example 1]
In the first embodiment, a near-field exposure method to which the present invention is applied will be described.
FIG. 3 is a view for explaining the coating process of the shape buffer / light absorbing layer and the upper layer resist in this embodiment.
In this embodiment, first, a silicon substrate 301 having line and space irregularities with a depth of 50 nm is prepared (FIG. 3A).
Next, a polyimide having a large absorption on the i-line (λ = 365 nm) of the mercury lamp serving as the shape buffer / light absorption layer 302 is applied to the silicon substrate 301 with a thickness of 150 to 200 nm by spin coating. .
Thereafter, this substrate is preferably placed on a hot plate heated to 200 to 400 ° C., more preferably 300 to 350 ° C., to cure the polyimide. Thereby, the unevenness | corrugation which the silicon substrate 301 has is embedded, and the polyimide surface is planarized (FIG.3 (b)).
Next, a SiO ₂ film having a thickness of 20 nm is formed as the intermediate layer 303 by sputtering (FIG. 3C).
Further, as the upper layer resist 304, a chemically amplified positive photoresist having sensitivity to i-line (λ = 365 nm) of a mercury lamp is formed by spin coating to a thickness of 20 nm (FIG. 3D). .

With the above structure, reflection of exposure light from the substrate can be suppressed and a flat photoresist surface can be obtained.
Furthermore, although the near-field light exists only to a distance of about 50 nm from the mask surface, the thickness of the upper resist 304 is 20 nm, which is thinner than this, so that exposure is performed up to the bottom of the upper resist (the interface between the upper resist and the intermediate layer). can do.
At this time, the tolerance with respect to the change of exposure amount is also large.

Next, an exposure procedure for patterning by near-field exposure on a substrate having irregularities coated with a shape buffer / light absorbing layer and an upper layer resist will be described.
FIG. 4 shows a diagram for explaining the exposure procedure.
In FIG. 4, 401 is a near-field exposure photomask.
The front surface (lower side in FIG. 4) of the photomask 401 is disposed outside the pressure adjustment container 404, and the back surface (upper side in FIG. 4) is disposed so as to face the pressure adjustment container 404.
The pressure adjusting container 404 can adjust the internal pressure by the pressure adjusting means 411.
An object to be exposed is obtained by forming the above-described shape buffer / light absorption layer on the surface of the substrate 405 and a resist film 406 having a four-layer structure using a three-layer resist.
The resist film 406 / substrate 405 is mounted on the stage 407, the stage 407 is driven in the xy plane, and relative alignment in the two-dimensional direction in the mask plane of the substrate 405 is performed with respect to the near-field exposure mask 401.

Next, the stage 407 is driven in the normal direction of the mask surface to bring the photomask 401 close to the resist film 406 on the substrate 405.
Thereafter, the pressure in the pressure adjusting container 404 is adjusted by the pressure adjusting means 411 so that the distance between the front surface of the near-field exposure mask 401 and the resist film 406 on the substrate 405 is 100 nm or less over the entire surface. Adhere.
Thereafter, the exposure light EL emitted from the exposure light source 408 is collimated by the collimator lens 409, and then introduced into the pressure adjusting container 404 through the glass window 410, and the back surface ( Irradiation is from the upper side in FIG.
By such illumination, the resist film 406 is exposed in the near field generated near the minute opening on the front surface of the near field exposure mask 401.

Next, a procedure for transferring a pattern to the resist film exposed as described above will be described. FIG. 5 is a diagram for explaining the above procedure.
In FIG. 5, reference numeral 501 denotes an upper resist layer that has been subjected to near-field exposure according to the above procedure (FIG. 5A).
The exposed upper resist layer 501 is dip developed with a 2.38% aqueous solution of TMAH to form a pattern (FIG. 5B).
Using this upper layer resist as an etching mask, dry etching is performed with a mixed gas of SF ₆ and CHF ₃ to transfer the pattern to the SiO ₂ layer of the intermediate layer 502 (FIG. 5C).
Further, using the intermediate layer 502 as an etching mask, the polyimide as the shape buffer / light absorption layer 503 is etched by a mixed gas of oxygen and argon to transfer the pattern (FIG. 5D).

By performing the above steps, the pattern of the near-field exposure mask can be uniformly formed on the entire surface of the substrate having unevenness.
By transferring the resist pattern thus prepared to substrates of various materials, it is possible to form structures of various shapes having a size of 100 nm or less.
Such a manufacturing technique of a structure having a size of 100 nm or less can be applied to specific element manufacturing such as the following (1) to (5).
(1) A quantum dot laser device by using a GaAs quantum dot having a size of 50 nm arranged in a two-dimensional structure at intervals of 50 nm.
(2) A sub-wavelength device (SWS) structure having a light reflection preventing function by using a 50 nm sized conical SiO ₂ structure on a SiO ₂ substrate two-dimensionally arranged at 50 nm intervals.
(3) A photonic crystal optical device or a plasmon optical device by using a structure of 100 nm size made of GaN or metal in a two-dimensional periodic arrangement at 100 nm intervals.
(4) Biosensors and micrototal analysis using localized plasmon resonance (LPR) and surface-enhanced Raman spectroscopy (SERS) by using 50 nm-sized Au fine particles in a two-dimensional arrangement on a plastic substrate at 50 nm intervals System (μTAS).
(5) Nanoelectromechanical systems (NEMS) such as SPM probes by using them for manufacturing sharp structures with a size of 50 nm or less used in scanning probe microscopes (SPM) such as tunnel microscopes, atomic force microscopes, and near-field optical microscopes )element.

[Example 2]
In Example 2, a configuration example using a material that performs the function of the upper layer resist and the function of the intermediate layer in one layer will be described.
FIG. 6 is a diagram for explaining a configuration example of this embodiment.

First, a polythiophene having a large absorption in the i-line (λ = 365 nm) of a mercury lamp as a shape buffer layer / light absorption layer 602 on a silicon substrate 601 having a line-and-space unevenness with a depth of 50 nm in a chloroform solvent. Melt. Then, a film having a thickness of 200 nm is formed by spin coating.
Next, a positive photoresist containing silicon atoms as an upper resist / intermediate layer 603 having both functions of an upper resist and an intermediate layer is formed on the thiophene layer, which is a shape buffer / light absorption layer, by spin coating to a thickness of 20 nm. A photoresist film is formed with a thickness (FIG. 6A).
The substrate with the resist film thus configured is subjected to near-field exposure in the same manner as in Example 1 and developed with a 2.38% aqueous solution of TMAH, and a pattern is formed on the silicon atom-containing positive photoresist as the upper layer resist / intermediate layer 603. It forms (FIG.6 (b)).
Thereafter, the shape buffer / light absorption layer is dry-etched with a mixed gas of oxygen and argon to transfer the pattern (FIG. 6C).

  As described above, the material having both functions of the intermediate layer and the upper layer resist is used for the upper layer of the shape buffer / light absorption layer, so that one film forming process of the intermediate layer and the upper layer resist is added in addition to the effect of the first embodiment. It is possible to reduce the dry etching process by one.

The figure which shows the structure of the mask for near field exposure used for embodiment of this invention. The figure for demonstrating the application | coating process of the shape buffer / light absorption layer and upper layer resist in embodiment of this invention. The figure for demonstrating the application | coating process of the shape buffer / light absorption layer and upper layer resist in Example 1 of this invention. The figure for demonstrating the exposure procedure which patterns by near field exposure in Example 1 of this invention. The figure for demonstrating the process of transferring a pattern to the resist film by which the near field exposure in Example 1 of this invention was carried out. The figure for demonstrating the structural example using the material which performs the function of the upper resist in Example 2 of this invention, and the function of an intermediate | middle layer by 1 layer. It is the calculation result of the light intensity distribution which arises when light injects into a near field exposure mask produced when the thickness of a photoresist film is 160 nm. It is a calculation result of the light intensity distribution generated when light is incident on the near-field exposure mask, which occurs when the thickness of the photoresist film is 220 nm. The conceptual diagram of thickness distribution at the time of apply | coating a photoresist film to the board | substrate which has an unevenness | corrugation. The graph of the contrast of light intensity distribution at the time of forming a slit with a 90 nm pitch.

Explanation of symbols

101: mask base material 102: light shielding material 103: minute opening pattern 201: substrate 202: shape buffer / light absorption layer 203: intermediate layer 204: upper resist layer 301: silicon substrate 302: shape buffer / light absorption layer 303: intermediate layer 304: Upper resist layer 401: Photomask for near-field exposure 402: Mask base material 403: Mask pattern 404: Pressure adjustment container 405: Substrate 406: Resist film 407: Stage 408: Exposure light source 409: Collimator lens 410: Glass window 411 : Pressure adjusting means 501: exposed upper resist layer 502: intermediate layer 503: shape buffer / light absorbing layer 601: silicon substrate 602: shape buffer layer / light absorbing layer 603: upper resist / intermediate layer

Claims (6)

A method of forming an object to be exposed used for near-field exposure in which a light-shielding film having a microscopic aperture having a wavelength size equal to or smaller than the wavelength of exposure light is adhered and light is irradiated from an exposure light source to transfer the pattern,
Forming a layer having a function as a shape buffer layer and a light absorption layer so as to bury the irregularities of the substrate on a substrate having irregularities, and planarizing the substrate surface;
Forming a photosensitive resist layer on the layer having the function as the shape buffer layer and the light absorption layer;
A method for forming an object to be exposed, comprising: The unevenness of the substrate is an unevenness having a height of 0.05 times or more the wavelength of exposure light in the photosensitive resist layer,
2. The method of forming an object to be exposed according to claim 1, wherein the flattening of the substrate surface is to make the unevenness of the substrate surface less than 0.05 times the wavelength of the exposure light.   The intermediate layer having resistance to oxygen plasma etching is formed between the layer having the function of the shape buffer layer and the light absorption layer and the photosensitive resist layer. Item 3. A method for forming an object to be exposed according to Item 2.   The method for forming an object to be exposed according to claim 1, wherein the photosensitive resist layer is formed of a resist having resistance to oxygen plasma etching. In a near-field exposure method in which a light-shielding film having a microscopic aperture of a wavelength size or less is adhered to an exposure object having a photoresist layer formed on a substrate, and a pattern is transferred by irradiating light from an exposure light source.
The near field exposure method characterized by using the to-be-exposed object formed by the to-be-exposed object forming method in any one of Claims 1 thru | or 4 as said to-be-exposed object.   A device manufacturing method, comprising manufacturing a device using the near-field exposure method according to claim 5.

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