JP2014191323A - Photomask for proximity exposure and pattern exposure method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photomask structure and a pattern exposure method capable of stably forming a fine pattern by reducing the influence of variation in exposure gap in a photomask for forming a fine pattern by proximity exposure.SOLUTION: There is provided a photomask for proximity exposure, wherein L/S of a slit pattern specified by a transmitting portion/a semitransmitting portion is 5 μm or less and the semitransmitting portion is a halftone film made of a metal oxide having a function of delaying the phase of incident light by approximately 90°.

Description

  The present invention relates to a photomask used in an exposure process of a photolithography method in manufacturing a semiconductor product, a liquid crystal display device, or the like.

A pattern forming method using a photolithography method has been researched and developed in the past, and is widely used in the manufacture of flat display devices such as semiconductor products and liquid crystal display devices.
In the photolithography method, the surface of a substrate (object to be irradiated) coated with a photoresist, which is a photosensitive resin, is selectively exposed with parallel light through an exposure machine through a photomask, and the exposed portion is exposed. This is a technique for generating a photoresist pattern having an arrangement with an unexposed portion, and a surface treatment is performed on a portion where the photoresist has been removed by development. Alternatively, the photoresist left after development is used as it is, such as a color filter for a liquid crystal display device. There are negative photosensitive resins that leave the exposed parts indevelopable by photocuring, and positive photosensitive resins that make the exposed parts develop soluble by photolysis and are removed in the development process. Depending on the process, the light transmission and non-transmission pattern arrangement of the photomask to be used is selected.

In recent years, the pattern used for semiconductor products and liquid crystal display devices has been miniaturized with the aim of improving the performance of final products, while the processing capability including high-speed processing for increasing the processing speed by the exposure apparatus has been improved. Yes. In particular, in order to improve productivity related to liquid crystals, the size of photomasks for handling large mother substrates is also increasing. In response to this situation, even if it is limited to the exposure process, in order to increase the definition of the photomask pattern on a large substrate used for proximity exposure (proximity exposure) with high throughput, photomask substrate materials and photo Along with improvements in resist material characteristics and exposure apparatus, the overall drawing process technology has been improved.
Further, as shown in Patent Document 1, in proximity exposure in which an exposure gap of several tens to several hundreds of μm is provided between a photomask pattern surface and a processing target substrate surface and exposed with substantially parallel light having a wavelength of 430 nm or less. There has been proposed a method for improving the photomask pattern design in which a double slit pattern is formed as a photomask pattern to obtain a single fine line pattern on the substrate surface to be processed.

  On the other hand, a phase shift mask is used as a technique for stably producing a high-definition pattern with high accuracy, particularly in the manufacture of a semiconductor product by a photolithography method. 1A and 1B are partial schematic views for explaining an example of a conventional phase shift mask, where FIG. 1A is a plan view and FIG. 1B is a cross-sectional view. In a typical example of the phase shift mask 11, the light-transmitting portion 20 is left on one side of the photomask substrate 10, the light-shielding portion 30 such as a metal chromium film, and the semi-transparent phase shift region 4 such as a MoSi film. And a pattern is formed. The phase shift region 4 is not necessarily translucent but may be completely transmissive type (Levenson type), and a phase is formed by depositing a transparent film in the phase shift region or dug the photomask substrate 10 in the corresponding region. It is also possible to provide a shift function. The order of formation of the light-shielding portion 30 and the phase shift region 4 is selected for convenience in the manufacturing process of the phase shift mask regardless of the vertical relationship in the figure.

  FIG. 2 is a schematic cross-sectional view for explaining an example of the pattern exposure method using the conventional phase shift mask shown in FIG. The exposure light 6 from the back surface side of the phase shift mask 11 is substantially parallel light having a wavelength of 430 nm or less, and an exposure gap h indicated by a bidirectional arrow is obtained by stepper exposure from proximity exposure or a reticle type photomask. The photosensitive layer (not shown) on the surface of the substrate 5 to be processed is selectively irradiated. Although the exposure light 6 has a large inclination in the emphasized expression of the drawing, this schematic diagram is applied when the width of the transmission portion 20 is extremely small with respect to the exposure gap h. The exposure light 6 represents light substantially parallel to each other. Of the exposure light 6, what is represented by a solid line arrow is light having a reference phase, and what is represented by a dotted line arrow is light having a phase shift of approximately 180 °, that is, light having a phase opposite to that of the reference phase. The light selectively irradiated onto the surface of the substrate 5 to be processed interferes with each other, thereby obtaining a distribution of the intensity 7 of the irradiation light expressed by the dense vertical line group. As a result, the intensity 7 of the irradiation light acts greatly only on the narrow width region corresponding to the fine pattern appearing in the vicinity of the center in the horizontal direction in the drawing, and effective exposure with high contrast is given.

JP 2008-309985 A

  In the above-mentioned Patent Document 1, a thin black matrix pattern having a line width of 4 μm or less of a color filter for a liquid crystal display device can be stably produced by proximity exposure using a photomask provided with a double slit pattern under certain conditions. . That is, it is possible to obtain a fine pattern in which the fluctuation of the line width of the pattern formed on the processing target substrate surface is suppressed to some extent with respect to the fluctuation of the exposure gap in proximity exposure. However, as the size of the mother board increases further, proximity exposure requires a large photomask, and the exposure gap variation in the proximity exposure process will become larger. Even if a photomask provided with a slit pattern is used, fluctuations in the line width of the pattern to be formed cannot be sufficiently suppressed. Similarly, in the pattern exposure using the conventional phase shift mask shown in FIGS. 1 and 2, if the fluctuation of the exposure gap becomes large, the fluctuation of the line width of the formed pattern cannot be sufficiently suppressed. With a conventional phase shift mask, if the exposure gap in proximity exposure is as wide as 50 to 100 μm, the light spreads on the substrate to be exposed, and light cancels out due to the phase difference even near the center of the pattern. It has been confirmed that the result is worse.

  The present invention is proposed in view of the above-mentioned problems, and the problem to be solved by the present invention is to reduce the influence of exposure gap fluctuation in a photomask for forming a fine pattern by proximity exposure. Then, the structure of the photomask which can form a fine pattern more stably is proposed.

As means for solving the above problems,
The photomask according to the present invention comprises:
A proximity exposure photomask capable of modulating the light amount distribution of transmitted light and the resolution of transmitted light intensity on the exposure target substrate according to the distance from the exposure target substrate,
L / S of the slit pattern defined by the transmission part / semi-transmission part is 5 μm or less, and the semi-transmission part is a halftone film made of a metal oxide having a function of delaying the phase of incident light by about 90 ° It is characterized by that.

Also, a proximity exposure photomask that forms an image of transmitted light having a line width of 5 μm or less on the exposure target substrate with a sufficient amount of light and transmitted light intensity,
A half-tone film made of a metal oxide having a function of delaying the phase of incident light by about 90 ° is formed at the boundary between the transmission part and the light-shielding part and the slit line width defined by the transmission part / light-shielding part is 5 μm or less. Thus, the line width of the slit is defined.

The pattern exposure method according to the present invention includes:
Proximity exposure is performed on the photosensitive resin layer formed on the surface of the substrate to be exposed with parallel light having a wavelength of 430 nm or less by appropriately changing the distance from the substrate to be exposed using the photomask. It is characterized by that.

With the photomask of the present invention, it becomes possible to improve the resolution of the exposure pattern (resolution of slit transmitted light intensity) and form a fine pattern with an L / S of 5 μm or less on the exposure target substrate, which can be easily manufactured, A photomask that can be easily applied to a practical pattern exposure method is provided.
Further, when a fine pattern is formed by proximity exposure using the photomask of the present invention, the influence of exposure gap variation can be reduced, and the fine pattern can be formed more stably.

It is a partial schematic diagram for demonstrating an example of the conventional phase shift mask, Comprising: (a) is a top view, (b) shows sectional drawing. FIG. 6 is a schematic cross-sectional view for explaining an example of a pattern exposure method using a conventional phase shift mask. Cross-sectional explanatory drawing which shows an example of the exposure state using the photomask for proximity exposure by this invention. Cross-sectional explanatory drawing which shows the other example of the exposure state using the photomask for proximity exposure by this invention. Explanatory drawing which shows the design information of the mask made into the object of simulation evaluation. Explanatory drawing which shows the design information of the mask made into the object of simulation evaluation. Explanatory drawing which shows the design information of the mask made into the object of simulation evaluation. Explanatory drawing which shows the simulation result about intensity distribution (image formation state of a light ray). Explanatory drawing which shows the simulation result about intensity distribution (image formation state of a light ray). The simulation result which compares and compares the exposure intensity (upper waveform of the figure) with the exposure object board | substrate, and the image formation state (lower side of the figure) of a light ray. The simulation result which compares and compares the exposure intensity (upper waveform of the figure) with the exposure object board | substrate, and the image formation state (lower side of the figure) of a light ray.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
<Embodiment 1>
FIG. 3 is an explanatory cross-sectional view showing an example of a proximity exposure photomask that forms an image of transmitted light having a line width of 5 μm or less on the exposure target substrate with a sufficient amount of light and transmitted light intensity.
A half-tone film made of a metal oxide having a function of delaying the phase of incident light by about 90 ° is formed at the boundary between the transmission part and the light-shielding part and the slit line width defined by the transmission part / light-shielding part is 5 μm or less. It is the structure which was made.
The transmission part 20 consists of a portion where the glass substrate 10 is exposed, and is formed by patterning a layer of chromium or the like constituting the light shielding part 30.
A halftone film (semi-transmissive part) 21 made of a metal oxide having a function of delaying the phase of incident light by about 90 ° is formed on both sides of the transmissive part 20, and the line width of the transmissive part 20 is defined. As the material of the halftone film 21, indium tin oxide and molybdenum oxynitride silicide are typical.

The optical characteristics of the transmission part, the semi-transmission part, and the light-shielding part are defined as follows for the sake of convenience, and are shared in the following description.
Transmitting part: transmittance 100%, phase difference 0
Semi-transmissive part: transmittance 20%, phase difference 90 °
Shading part: 0% transmittance

The optical path during pattern exposure is conceptually shown in FIG.
When the light incident on the photomask from the upper side of the figure passes through the transmissive part 20 and the semi-transmissive part 21 and is transmitted and emitted as slit light to the lower side of the figure, the semi-transmissive part 21 changes the phase of the incident light by about 90. As shown in the figure, the delayed transmitted light (transmittance 20%) is generated, thereby acting to reduce the optical interference effect in the same phase at the boundary illuminated adjacently on the exposure target substrate. In this way, the light is emitted as if it is condensed with high intensity directly below the transmission part 20.

<Embodiment 2>
FIG. 4 is a cross-sectional explanatory view showing another example of a proximity exposure photomask that forms an image of transmitted light having a line width of 5 μm or less on the exposure target substrate with a sufficient amount of light and transmitted light intensity.
The difference from FIG. 3 is that the L / S (line and space) of the slit pattern defined by the transmission part / semi-transmission part is 5 μm or less, and the semi-transmission part is within the wide opening defined by the light shielding part 30. 21 is a slit pattern in which a plurality of transmitting portions 20 each having an opening width of 5 μm or less are arranged adjacent to each other as shown in the figure.

The optical path during pattern exposure is conceptually shown in FIG.
Similarly to FIG. 3, when the light incident on the photomask from the upper side of the figure passes through the transmissive part 20 and the semi-transmissive part 21 and is emitted as three slit lights on the lower side of the figure, the semi-transmissive part 21 Generates transmitted light (transmittance 20%) that delays the phase of incident light by about 90 °, so that the light interference effect in the same phase is reduced at the boundary illuminated adjacently on the exposure target substrate. In order to act, as shown in the figure, the light is emitted as if it is condensed with high intensity directly below each of the three transmitting portions 20.

In order to manufacture a photomask, first, a photomask substrate 10 is prepared.
The photomask substrate 10 has a high transmittance with respect to short-wavelength light having a wavelength of 430 nm or less, a low coefficient of thermal expansion that affects the dimensional stability with respect to a temperature change, excellent physical and chemical resistance in the pattern formation process, and smoothness. Synthetic quartz that can be processed with good properties and has few internal optical defects is a preferable material.

Next, a light shielding portion and a halftone portion (phase shift region) are pattern-formed on one side of the photomask substrate.
In the configuration of FIG. 1, the case where the layers constituting the phase shift region 4 are formed first is shown, but the order of forming the light shielding portions is not limited, and the reverse order is also possible due to the suitability of alignment in the exposure process. .
A metal chrome film can be used as the material constituting the light shielding portion, and a MoSi halftone film can be used as the material constituting the halftone portion (phase shift region).
Each of the above layers can be formed by sputtering, and a desired pattern can be formed by pattern formation of a resist layer by photolithography or electron beam lithography and dry or wet etching of the opening. Further, if necessary, other types of metal films or the like can be used as the etching resist.

In the pattern exposure method using the photomask manufactured as described above, h-ray (wavelength 405 nm), i-line (wavelength 365 nm) of a high-pressure mercury lamp and various laser light sources are used as parallel light having a wavelength of 430 nm or less as an exposure light source. Can do.
As an exposure method, proximity exposure in which the exposure gap h between the surface of the photomask 1 and the surface of the substrate 5 to be processed is set to several tens to several hundreds of micrometers, preferably about 90 μm can be used.
Here, the phase shift region using the above-described MoSi halftone film can be controlled to have a transmittance of 20% and a phase difference of about 90 ° with respect to short wavelength light in the wavelength range of 430 nm or less to the near ultraviolet region, for example.

  Hereinafter, based on the simulation results, the exposure gap is obtained when proximity exposure is performed with parallel light having a wavelength of 430 nm or less using a photomask according to the present invention and a conventional structure while appropriately changing the distance from the exposure target substrate. Consider the effect of fluctuations on line width fluctuations.

<Simulation conditions>
Simulator: Layout Lab (GenISys)
Exposure beam λ: (365nm: 313nm) = (100: 35)
Collimation angle: 2.0 °
Exposure gap (separation distance): 30-120μm (changes in 10μm increments)

<Mask used>
(1) No halftone film (2) Halftone film (phase shift amount = 180 °)
(3) With halftone film (phase shift amount = 90 °)
(1) For each of the conventional structure of (2) and the structure of the present invention of (3), there is one 3.5 μm wide transmission slit, and three L / S = 3.5 μm 3.5 μm wide transmission slits. Masks were evaluated. 5 to 7 show design information of each mask.

<Figure 5>
(1) -1: The boundary of one transmission part slit is defined by a light shielding part (2) -1: The boundary of one transmission part slit is defined by a halftone film (phase difference 180 °) (3) -1: The boundary of one transmission slit is defined by a halftone film (phase difference 90 °) <Fig. 6>
(1) -2: The boundary of the three transmission part slits is defined by the light shielding part (2) -2: The boundary of the three transmission part slits is defined by the halftone film (phase difference 180 °) (3) -2: The boundary of the three transmission slits is defined by a halftone film (phase difference 90 °) <Fig. 7>
(3) -3: The boundary between the two transmission slits in the center is defined by a halftone film (phase difference 90 °), and the boundary between the two transmission slits at both ends is a halftone film (phase difference 90 °). ) And the structure defined by the light-shielding part (3) -4: The boundary of the four transmission part slits is defined by the halftone film (phase difference 90 °)

  FIG. 8 shows the relationship between the exposure target substrate and the photosensitive resin layer formed on the surface of the substrate to be exposed based on the above simulation conditions for three types of masks having one transmission part slit having a width of 3.5 μm. It is explanatory drawing which shows the simulation result about the intensity distribution (image formation state of a light ray) on an exposure object board | substrate at the time of changing proximity distance by 30 micrometers in steps of 10 micrometers, and performing proximity exposure.

According to the figure, in the case of the (1) -1 type mask in which the opening (slit with 100% transmittance) is defined by the light shielding portion (transmittance 0%) around the periphery, when the separation distance becomes 80 μm, The image formation state becomes unclear and no image formation is confirmed from 90 μm or more.
In the case of the (1) -2 type mask in which the opening (slit with a transmittance of 100%) is defined by a halftone film (phase difference of 180 °) consisting of a semi-transmissive portion (transmittance of 20%) around the periphery, 80 μm From the above, imaging is not confirmed.
In the case of the (1) -3 type mask in which the opening (slit with a transmittance of 100%) is defined by a halftone film (phase difference of 90 °) consisting of a semi-transmissive portion (transmittance of 20%) around the periphery Up to a distance of 90 μm, a clear light beam imaging state (hereinafter also referred to as a bright line) is maintained.

  FIG. 9 shows a photosensitive resin layer formed on the surface of a substrate to be exposed, based on the above simulation conditions, for three types of masks having L / S = 3.5 μm and three adjacent transmission slits. Explanation showing the simulation result of the intensity distribution (light beam imaging state) on the exposure target substrate when proximity exposure is performed by changing the separation distance from the exposure target substrate in increments of 10 μm from 30 to 120 μm FIG.

According to the figure, the (1) -2 type of the configuration in which three openings (slits with a transmittance of 100%) are defined adjacent to the light shielding portion (transmittance of 0%) with L / S = 3.5 μm. In the mask, when the separation distance is 50 μm, the image formation state of the light becomes unclear, and the image formation is not confirmed from 60 μm or more.
A halftone film (phase difference 180 °) consisting of a semi-transmission part with a transmittance of 20% at L / S = 3.5 μm / transmission of 100% in an opening defined by a light-shielding part (transmission 0%) In the case of the (2) -2 type mask in which slits are alternately arranged and three openings (slits having a transmittance of 100%) are defined by a halftone film around the periphery, when the separation distance becomes 60 μm, The image formation state becomes unclear, 70 μm has 2 bright lines, 80 μm has 2 bright lines outside the 2 bright lines, and 90 μm and 100 μm has 2 unsharp lines, 110 μm or more. No image formation is confirmed.
A halftone film (phase difference 90 °) consisting of a semi-transmission part with a transmittance of 20% at L / S = 3.5 μm / transmission of 100% within an opening defined by a light-shielding part (transmission 0%) In the case of the (3) -2 type mask in which slits are alternately arranged and three openings (slits with a transmittance of 100%) are defined by a halftone film around the periphery, three bright lines up to 100 μm However, two unclear lines are confirmed at 110 μm and 120 μm.

  FIG. 10 shows the simulation results for the (1) -2 type mask (prior art), the exposure intensity on the exposure target substrate (waveform on the upper side in the figure) and the imaging state of the light beam (the lower side in the figure). FIG. 6 is an explanatory view showing a comparison in the case where the separation distance is changed in increments of 10 μm from 30 to 120 μm. (Corresponding to FIG. 9)

  FIG. 11 shows the simulation results for the (3) -3 type and (3) -4 type masks (present invention), the exposure intensity on the exposure target substrate (waveform on the upper side of the figure), and the imaging state of the light beam. It is explanatory drawing which contrasts and shows about the case where a separation distance is changed by 30 micrometer from 10 to 30 micrometer (lower side of the figure).

In FIG. 10, three bright lines are imaged only in the case of exposure at a separation distance of 30 and 40 μm, but in FIG. 11, as many as seven lines are imaged at a separation distance of 30 μm.
In the (3) -3 type and (3) -4 type masks, it can be considered that there are four slits with a transmittance of 100% and three slits with a transmittance of 20% in total, with seven slits in between. When close to the exposure target substrate, the image is formed with all seven lines, but when the separation distance is 50 μm or more, the image is formed as three bright lines up to approximately 100 μm. .

From the above simulation results, when a slit pattern having an L / S of 5 μm or less is to be stably exposed and imaged as a bright line by proximity exposure, the slit pattern defined by the transmission part / light-shielding part → transmission part / Slit pattern defined by semi-transmission part (phase difference 180 °) → slit pattern defined by transmission part / semi-transmission part (phase difference 90 °), and without variation due to the separation distance between the mask and the exposure target substrate It can be seen that the conditions for reliably imaging are increasing.
Therefore, when proximity exposure of a fine pattern is performed using a large photomask, it is effective in obtaining stable reproducibility of a high-definition pattern.

4 ... Phase shift region (halftone film)
6 ... exposure light 7 ... irradiation light intensity 10 ... photomask substrate (glass)
11 ... Phase shift mask 20 ... Transmission part 21 ... Semi-transmission part (halftone film)
30 ... Light-shielding part

Claims (3)

A proximity exposure photomask capable of modulating the light amount distribution of transmitted light and the resolution of transmitted light intensity on the exposure target substrate according to the distance from the exposure target substrate,
L / S of the slit pattern defined by the transmission part / semi-transmission part is 5 μm or less, and the semi-transmission part is a halftone film made of a metal oxide having a function of delaying the phase of incident light by about 90 ° Proximity exposure photomask characterized by the above. A half-tone film made of a metal oxide having a function of delaying the phase of incident light by about 90 ° is formed at the boundary between the transmission part and the light-shielding part and the slit line width defined by the transmission part / light-shielding part is 5 μm or less. And a photomask for proximity exposure, characterized in that the line width of the slit is defined. Parallel light having a wavelength of 430 nm or less is obtained by appropriately changing the distance from the exposure target substrate with respect to the photosensitive resin layer formed on the exposure target substrate surface using the photomask according to claim 1 or 2. A pattern exposure method characterized in that proximity exposure is performed.

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